Jenny Shen - Academia.edu (original) (raw)

Papers by Jenny Shen

Proceedings of The National Academy of Sciences, 2005

We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potenti... more We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potential role in the insulin-signaling pathway. BVR is both a substrate for insulin receptor (IR) tyrosine kinase (IRK) activity and a kinase for serine phosphorylation of IR substrate 1 (IRS-1). Our previous studies have revealed serine͞ threonine kinase activity of BVR. Y 198 , in the YMKM motif found in the C-terminal domain of BVR, is shown to be a substrate for insulin-activated IRK. This motif in IRS proteins provides a docking site for proteins that contain a Src homology 2 domain. Additionally, Y 228 in the YLSF sequence and Y 291 are IRK substrates; the former sequence provides optimum recognition motif in the tyrosine phosphatase, SHP-1, and for SHC (Src homology 2 domain containing transfroming protein 1). BVR autophosphorylates Nterminal tyrosines Y 72 and Y 83 . Serine residues in IRS-1 are targets for BVR phosphorylation, and point mutation of serine residues in the kinase domain of the reductase inhibits phosphotransferase activity.

Proceedings of The National Academy of Sciences

We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potenti... more We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potential role in the insulin-signaling pathway. BVR is both a substrate for insulin receptor (IR) tyrosine kinase (IRK) activity and a kinase for serine phosphorylation of IR substrate 1 (IRS-1). Our previous studies have revealed serine͞ threonine kinase activity of BVR. Y 198 , in the YMKM motif found in the C-terminal domain of BVR, is shown to be a substrate for insulin-activated IRK. This motif in IRS proteins provides a docking site for proteins that contain a Src homology 2 domain. Additionally, Y 228 in the YLSF sequence and Y 291 are IRK substrates; the former sequence provides optimum recognition motif in the tyrosine phosphatase, SHP-1, and for SHC (Src homology 2 domain containing transfroming protein 1). BVR autophosphorylates Nterminal tyrosines Y 72 and Y 83 . Serine residues in IRS-1 are targets for BVR phosphorylation, and point mutation of serine residues in the kinase domain of the reductase inhibits phosphotransferase activity.

Pump Industry Analyst, 2000

Arrays of coupled oscillators have been proposed as signal sources for beam-steered array antenna... more Arrays of coupled oscillators have been proposed as signal sources for beam-steered array antennas by York et al., (1993, 1997, 1999), and their coworkers. The engineering considerations for designing an array based on coupled oscillators is discussed herein and performance features are compared with those of conventional phased arrays wherever possible. It is shown that there is a direct relationship between departure of the free-running frequencies of individual oscillators and phase errors in the signal produced by the oscillator. Considerations for minimizing the sensitivity to frequency errors and the achievability of reproducible free running frequencies are discussed. The correspondence between the phase of an individual oscillator in an array in phase-shifted state and the phase setting of a phase shifter is discussed

Plant and Soil, 2004

White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled condit... more White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled conditions at 20/12 °C (12/12 h) for 76 d to investigate the effect of phosphorus (P) deficiency on root-induced acidification and excess cation uptake by N2-fixing plants. Phosphorus was added in each column as FePO4 at a level of 10 (limited P) or 200 μg P g−1 (adequate P). Supply of 10 μg P g−1 restricted plant growth from 58 d after sowing (DAS) and decreased P concentrations significantly in shoots from 49 DAS and in roots from 40 DAS compared with plants supplied with 200 μg P g−1. Phosphorus concentrations in shoots of plants receiving 10 μg P g−1 decreased steadily from 2.1 to 1.1 mg P g−1 dry weight from 40 to 76 DAS, but P concentrations in roots were constant with time. Total P uptake increased with time irrespective of P supply, and the P uptake by plants at 10 μg P g−1 was only 35–75% of that at 200 μg P g−1. Plants fed with 10 μg P g−1 had higher Ca and Mg concentrations but lower S concentration in shoots than the plants fed with 200 μg P g−1. The concentrations of excess cations in plants were higher at 10 μg P g−1 than 200 μg P g−1 after 49 DAS. Phosphorus deficiency decreased the pH of root exudate solution due to the enhanced release of protons (H+) from roots. The pH of root exudate solution decreased rapidly with time and dropped to the lowest (4.28) at 58 DAS in the 10 μg P g−1 treatment. The decreased pH of root exudate solution was correlated with the increased concentrations of excess cations in plants. The pH of root exudate solution showed a different pattern of change with time compared with citrate exudation, suggesting that exudation of citrate anions contributes only a part of total acidification, but excess cation uptake dominantly contributes net proton release from roots of plants grown in P-deficient soil. Plant tissue had a significant accumulation of citrate in the treatment of 10 μg P g−1 compared with 200 μg P g−1 after 67 DAS. The results suggest that P deficiency enhances the excess cation uptake and concomitant proton release, and non-synchronous processes are involved in tissue accumulation and root exudation of organic anions under P deficiency.

Plant and Soil, 2006

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxyla... more The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P1, deficient) and 50 µM P (P50, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P1, but at P50 shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P50 treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P1, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P1 than in P50 treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 µmol g−1 root DW h−1 at P1, but was under the detection limit at P50; at pH 7.8, it was 2.4-fold higher in P1 than in P50 plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P1 and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.

Plant and Soil, 2008

The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosp... more The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosphere of durum wheat (Triticum turgidum durum L.) and common bean (Phaseolus vulgaris L.) grown in monocropping and intercropping systems with nitrate supply. Wheat and common bean were grown either alone or in association in a cropping device with a thin (1 mm) soil layer sandwiched between large root mats. Wheat intercropped with common bean exhibited a 33% increase in shoot biomass and a 22% increased root biomass, without significantly affecting common bean growth. After 12 days of culture, rhizosphere pH decreased by 1.66 and 1.13 units in monocropping system of common bean and intercropping system, respectively. Wheat increased intercropped common bean proton release by 36% compared with monocropped beans. Common bean and wheat exhibited different behaviors in rhizosphere P dynamics. Monocropped wheat decreased Resin-P, NaHCO3-P and NaOH-P in its rhizosphere by 24, 96 and 10%, respectively. However, NaHCO3-P and NaOH-P were increased by 61 and 10% in the rhizosphere of intercropping. Almost all values about P fraction in intercropping system were between those in monocropped common bean and monocropped wheat. Through taping different P fraction, different plants species possibly can alleviate competition for phosphorus in intercropping system.

Plant and Soil, 2004

Rhizosphere processes of individual plants have been widely investigated since 1904 when the term... more Rhizosphere processes of individual plants have been widely investigated since 1904 when the term “rhizosphere” was first put forward. However, little attention has been paid to rhizosphere effects at an agro-ecosystem level. This paper presents recent research on the rhizosphere processes in relation to plant nutrition in main cropping systems in China. In the peanut (Arachis hypogaea L.)/maize (Zea mays L.) intercropping system, maize was found to improve the Fe nutrition of peanut through influencing its rhizosphere processes, suggesting an important role of phytosiderophores released from Fe-deficient maize. Intercropping between maize and faba bean (Vicia faba L.) was found to improve nitrogen and phosphorus uptake in the two crops compared with corresponding sole crop. There was a higher land equivalent ratio (LER) in the intercropping system of maize and faba bean than the treatment of no root interactions between the two crops. The increased yield of maize intercropped with faba bean resulted from an interspecific facilitation in nutrient uptake, depending on interspecific root interactions of the two crops. In the rotation system of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) crops, Mn deficiency in wheat was caused by excessive Mn uptake by rice and Mn leaching from topsoil to subsoil due to periodic cycles of flooding and drying. However, wheat genotypes tolerant to Mn deficiency tended to distribute more roots to deeper soil layer and thus expand their rhizosphere zones in the Mn-deficient soils and utilize Mn from the subsoil. Deep ploughing also helped root penetration into subsoil and was propitious to correcting Mn deficiency in wheat rotated with rice. In comparison, oilseed rape (Brassica napus L.) took up more Mn than wheat through mobilizing sparingly soluble soil Mn due to acidification and reduction processes in the rhizosphere. Thus, oilseed rape was tolerant to the Mn-deficient conditions in the rice-oilseed rape rotation. Oxidation reactions on root surface of rice also resulted in the formation of Fe plaque in the rice rhizosphere. Large amounts of Zn were accumulated on the Fe plaque. Zinc uptake by rice plants increased as Fe plaque formed, but decreased at high amounts of Fe plaque. It is suggested that to fine-tune cropping patterns and optimize nutrient management based on a better understanding of rhizosphere processes at an agro-ecosystem level is crucial for increasing nutrient use efficiency and developing sustainable agriculture in China.

Plant and Soil, 2003

The present study examined the effect of phosphorus (P) limitation on cluster root formation and ... more The present study examined the effect of phosphorus (P) limitation on cluster root formation and exudation of carboxylates by N2-fixing white lupin (Lupinus albus L. cv. Kiev) grown in a P-deficient sandy soil. Plants received 10 (limited P) or 200 μg P g−1 soil as FePO4 (adequate P) and were grown in a phytotron at 20/12 °C (12/12 h) for 76 days in soil columns. Cluster root formation was assessed and root exudates were collected at 9-day intervals. Shoot and root dry weights were higher in plants grown in the adequate-P compared to the limited-P treatment for 67 days. No clear difference in the total root length was observed between two P treatments before day 58. However, the specific root length increased rapidly from 17 m g−1 DW at day 40 to 28 m g−1 at day 49 in the P-limited plants, but decreased in the P-adequate plants. The effect of P limitation on enhancement of cluster root formation was observed from day 40 and reached the maximum at day 58. The number of cluster roots was negatively correlated with the P concentration in both roots and shoots. Phosphorus limitation increased exudation of citrate from day 40. The exudation of citrate displayed a cyclic pattern throughout the experiment, and appeared related to internal P concentration in plants, particularly P concentration in shoots. The sorption of exogenously added citrate in the soil was also examined. The amount of extractable citrate remained unchanged for 2 h, but decreased thereafter, suggesting that the soil had a low capacity to sorb citrate, and the rate of its decomposition by microorganisms was slow. Collecting solution leached through a soil column is a simple and reliable method to acquire root exudates from white lupin grown in soil. The results suggest that formation of cluster roots and exudation of citrate in white lupin are regulated by P concentration in shoots.

Plant and Soil, 2004

White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled condit... more White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled conditions at 20/12 °C (12/12 h) for 76 d to investigate the effect of phosphorus (P) deficiency on root-induced acidification and excess cation uptake by N2-fixing plants. Phosphorus was added in each column as FePO4 at a level of 10 (limited P) or 200 μg P g−1 (adequate P). Supply of 10 μg P g−1 restricted plant growth from 58 d after sowing (DAS) and decreased P concentrations significantly in shoots from 49 DAS and in roots from 40 DAS compared with plants supplied with 200 μg P g−1. Phosphorus concentrations in shoots of plants receiving 10 μg P g−1 decreased steadily from 2.1 to 1.1 mg P g−1 dry weight from 40 to 76 DAS, but P concentrations in roots were constant with time. Total P uptake increased with time irrespective of P supply, and the P uptake by plants at 10 μg P g−1 was only 35–75% of that at 200 μg P g−1. Plants fed with 10 μg P g−1 had higher Ca and Mg concentrations but lower S concentration in shoots than the plants fed with 200 μg P g−1. The concentrations of excess cations in plants were higher at 10 μg P g−1 than 200 μg P g−1 after 49 DAS. Phosphorus deficiency decreased the pH of root exudate solution due to the enhanced release of protons (H+) from roots. The pH of root exudate solution decreased rapidly with time and dropped to the lowest (4.28) at 58 DAS in the 10 μg P g−1 treatment. The decreased pH of root exudate solution was correlated with the increased concentrations of excess cations in plants. The pH of root exudate solution showed a different pattern of change with time compared with citrate exudation, suggesting that exudation of citrate anions contributes only a part of total acidification, but excess cation uptake dominantly contributes net proton release from roots of plants grown in P-deficient soil. Plant tissue had a significant accumulation of citrate in the treatment of 10 μg P g−1 compared with 200 μg P g−1 after 67 DAS. The results suggest that P deficiency enhances the excess cation uptake and concomitant proton release, and non-synchronous processes are involved in tissue accumulation and root exudation of organic anions under P deficiency.

Plant and Soil, 2006

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxyla... more The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P1, deficient) and 50 µM P (P50, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P1, but at P50 shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P50 treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P1, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P1 than in P50 treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 µmol g−1 root DW h−1 at P1, but was under the detection limit at P50; at pH 7.8, it was 2.4-fold higher in P1 than in P50 plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P1 and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.

Plant and Soil, 2008

The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosp... more The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosphere of durum wheat (Triticum turgidum durum L.) and common bean (Phaseolus vulgaris L.) grown in monocropping and intercropping systems with nitrate supply. Wheat and common bean were grown either alone or in association in a cropping device with a thin (1 mm) soil layer sandwiched between large root mats. Wheat intercropped with common bean exhibited a 33% increase in shoot biomass and a 22% increased root biomass, without significantly affecting common bean growth. After 12 days of culture, rhizosphere pH decreased by 1.66 and 1.13 units in monocropping system of common bean and intercropping system, respectively. Wheat increased intercropped common bean proton release by 36% compared with monocropped beans. Common bean and wheat exhibited different behaviors in rhizosphere P dynamics. Monocropped wheat decreased Resin-P, NaHCO3-P and NaOH-P in its rhizosphere by 24, 96 and 10%, respectively. However, NaHCO3-P and NaOH-P were increased by 61 and 10% in the rhizosphere of intercropping. Almost all values about P fraction in intercropping system were between those in monocropped common bean and monocropped wheat. Through taping different P fraction, different plants species possibly can alleviate competition for phosphorus in intercropping system.

Plant and Soil, 2004

Rhizosphere processes of individual plants have been widely investigated since 1904 when the term... more Rhizosphere processes of individual plants have been widely investigated since 1904 when the term “rhizosphere” was first put forward. However, little attention has been paid to rhizosphere effects at an agro-ecosystem level. This paper presents recent research on the rhizosphere processes in relation to plant nutrition in main cropping systems in China. In the peanut (Arachis hypogaea L.)/maize (Zea mays L.) intercropping system, maize was found to improve the Fe nutrition of peanut through influencing its rhizosphere processes, suggesting an important role of phytosiderophores released from Fe-deficient maize. Intercropping between maize and faba bean (Vicia faba L.) was found to improve nitrogen and phosphorus uptake in the two crops compared with corresponding sole crop. There was a higher land equivalent ratio (LER) in the intercropping system of maize and faba bean than the treatment of no root interactions between the two crops. The increased yield of maize intercropped with faba bean resulted from an interspecific facilitation in nutrient uptake, depending on interspecific root interactions of the two crops. In the rotation system of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) crops, Mn deficiency in wheat was caused by excessive Mn uptake by rice and Mn leaching from topsoil to subsoil due to periodic cycles of flooding and drying. However, wheat genotypes tolerant to Mn deficiency tended to distribute more roots to deeper soil layer and thus expand their rhizosphere zones in the Mn-deficient soils and utilize Mn from the subsoil. Deep ploughing also helped root penetration into subsoil and was propitious to correcting Mn deficiency in wheat rotated with rice. In comparison, oilseed rape (Brassica napus L.) took up more Mn than wheat through mobilizing sparingly soluble soil Mn due to acidification and reduction processes in the rhizosphere. Thus, oilseed rape was tolerant to the Mn-deficient conditions in the rice-oilseed rape rotation. Oxidation reactions on root surface of rice also resulted in the formation of Fe plaque in the rice rhizosphere. Large amounts of Zn were accumulated on the Fe plaque. Zinc uptake by rice plants increased as Fe plaque formed, but decreased at high amounts of Fe plaque. It is suggested that to fine-tune cropping patterns and optimize nutrient management based on a better understanding of rhizosphere processes at an agro-ecosystem level is crucial for increasing nutrient use efficiency and developing sustainable agriculture in China.

Plant and Soil, 2003

The present study examined the effect of phosphorus (P) limitation on cluster root formation and ... more The present study examined the effect of phosphorus (P) limitation on cluster root formation and exudation of carboxylates by N2-fixing white lupin (Lupinus albus L. cv. Kiev) grown in a P-deficient sandy soil. Plants received 10 (limited P) or 200 μg P g−1 soil as FePO4 (adequate P) and were grown in a phytotron at 20/12 °C (12/12 h) for 76 days in soil columns. Cluster root formation was assessed and root exudates were collected at 9-day intervals. Shoot and root dry weights were higher in plants grown in the adequate-P compared to the limited-P treatment for 67 days. No clear difference in the total root length was observed between two P treatments before day 58. However, the specific root length increased rapidly from 17 m g−1 DW at day 40 to 28 m g−1 at day 49 in the P-limited plants, but decreased in the P-adequate plants. The effect of P limitation on enhancement of cluster root formation was observed from day 40 and reached the maximum at day 58. The number of cluster roots was negatively correlated with the P concentration in both roots and shoots. Phosphorus limitation increased exudation of citrate from day 40. The exudation of citrate displayed a cyclic pattern throughout the experiment, and appeared related to internal P concentration in plants, particularly P concentration in shoots. The sorption of exogenously added citrate in the soil was also examined. The amount of extractable citrate remained unchanged for 2 h, but decreased thereafter, suggesting that the soil had a low capacity to sorb citrate, and the rate of its decomposition by microorganisms was slow. Collecting solution leached through a soil column is a simple and reliable method to acquire root exudates from white lupin grown in soil. The results suggest that formation of cluster roots and exudation of citrate in white lupin are regulated by P concentration in shoots.

Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protei... more Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protein kinases constitute control circuits to regulate pre-mRNA splicing and coordinate splicing with transcription in mammalian cells. We present here the finding that similar SR networks exist in Schizosaccharomyces pombe. We previously showed that Dsk1 protein, originally described as a mitotic regulator, displays high activity in phosphorylating S. pombe Prp2 protein (spU2AF59), a homologue of human U2AF65. We now demonstrate that Dsk1 also phosphorylates two recently identified fission yeast proteins with RS repeats, Srp1 and Srp2, in vitro. The phosphorylated proteins bear the same phosphoepitope found in mammalian SR proteins. Consistent with its substrate specificity, Dsk1 forms kinase-competent complexes with those proteins. Furthermore, dsk1 ؉ gene determines the phenotype of prp2 ؉ overexpression, providing in vivo evidence that Prp2 is a target for Dsk1. The dsk1-null mutant strain became severely sick with the additional deletion of a related kinase gene. Significantly, human SR protein-specific kinase 1 (SRPK1) complements the growth defect of the doubledeletion mutant. In conjunction with the resemblance of dsk1 ؉ and SRPK1 in sequence homology, biochemical properties, and overexpression phenotypes, the complementation result indicates that SRPK1 is a functional homologue of Dsk1. Collectively, our studies illustrate the conserved SR networks in S. pombe consisting of RS domain-containing proteins and SR protein-specific kinases and thus establish the importance of the networks in eucaryotic organisms.

Molecular and Cellular Biology, 2000

Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protei... more Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protein kinases constitute control circuits to regulate pre-mRNA splicing and coordinate splicing with transcription in mammalian cells. We present here the finding that similar SR networks exist in Schizosaccharomyces pombe. We previously showed that Dsk1 protein, originally described as a mitotic regulator, displays high activity in phosphorylating S. pombe Prp2 protein (spU2AF59), a homologue of human U2AF65. We now demonstrate that Dsk1 also phosphorylates two recently identified fission yeast proteins with RS repeats, Srp1 and Srp2, in vitro. The phosphorylated proteins bear the same phosphoepitope found in mammalian SR proteins. Consistent with its substrate specificity, Dsk1 forms kinase-competent complexes with those proteins. Furthermore, dsk1 ؉ gene determines the phenotype of prp2 ؉ overexpression, providing in vivo evidence that Prp2 is a target for Dsk1. The dsk1-null mutant strain became severely sick with the additional deletion of a related kinase gene. Significantly, human SR protein-specific kinase 1 (SRPK1) complements the growth defect of the doubledeletion mutant. In conjunction with the resemblance of dsk1 ؉ and SRPK1 in sequence homology, biochemical properties, and overexpression phenotypes, the complementation result indicates that SRPK1 is a functional homologue of Dsk1. Collectively, our studies illustrate the conserved SR networks in S. pombe consisting of RS domain-containing proteins and SR protein-specific kinases and thus establish the importance of the networks in eucaryotic organisms.

Proceedings of The National Academy of Sciences, 2005

We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potenti... more We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potential role in the insulin-signaling pathway. BVR is both a substrate for insulin receptor (IR) tyrosine kinase (IRK) activity and a kinase for serine phosphorylation of IR substrate 1 (IRS-1). Our previous studies have revealed serine͞ threonine kinase activity of BVR. Y 198 , in the YMKM motif found in the C-terminal domain of BVR, is shown to be a substrate for insulin-activated IRK. This motif in IRS proteins provides a docking site for proteins that contain a Src homology 2 domain. Additionally, Y 228 in the YLSF sequence and Y 291 are IRK substrates; the former sequence provides optimum recognition motif in the tyrosine phosphatase, SHP-1, and for SHC (Src homology 2 domain containing transfroming protein 1). BVR autophosphorylates Nterminal tyrosines Y 72 and Y 83 . Serine residues in IRS-1 are targets for BVR phosphorylation, and point mutation of serine residues in the kinase domain of the reductase inhibits phosphotransferase activity.

Proceedings of The National Academy of Sciences

We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potenti... more We describe here the tyrosine kinase activity of human biliverdin reductase (BVR) and its potential role in the insulin-signaling pathway. BVR is both a substrate for insulin receptor (IR) tyrosine kinase (IRK) activity and a kinase for serine phosphorylation of IR substrate 1 (IRS-1). Our previous studies have revealed serine͞ threonine kinase activity of BVR. Y 198 , in the YMKM motif found in the C-terminal domain of BVR, is shown to be a substrate for insulin-activated IRK. This motif in IRS proteins provides a docking site for proteins that contain a Src homology 2 domain. Additionally, Y 228 in the YLSF sequence and Y 291 are IRK substrates; the former sequence provides optimum recognition motif in the tyrosine phosphatase, SHP-1, and for SHC (Src homology 2 domain containing transfroming protein 1). BVR autophosphorylates Nterminal tyrosines Y 72 and Y 83 . Serine residues in IRS-1 are targets for BVR phosphorylation, and point mutation of serine residues in the kinase domain of the reductase inhibits phosphotransferase activity.

Pump Industry Analyst, 2000

Arrays of coupled oscillators have been proposed as signal sources for beam-steered array antenna... more Arrays of coupled oscillators have been proposed as signal sources for beam-steered array antennas by York et al., (1993, 1997, 1999), and their coworkers. The engineering considerations for designing an array based on coupled oscillators is discussed herein and performance features are compared with those of conventional phased arrays wherever possible. It is shown that there is a direct relationship between departure of the free-running frequencies of individual oscillators and phase errors in the signal produced by the oscillator. Considerations for minimizing the sensitivity to frequency errors and the achievability of reproducible free running frequencies are discussed. The correspondence between the phase of an individual oscillator in an array in phase-shifted state and the phase setting of a phase shifter is discussed

Plant and Soil, 2004

White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled condit... more White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled conditions at 20/12 °C (12/12 h) for 76 d to investigate the effect of phosphorus (P) deficiency on root-induced acidification and excess cation uptake by N2-fixing plants. Phosphorus was added in each column as FePO4 at a level of 10 (limited P) or 200 μg P g−1 (adequate P). Supply of 10 μg P g−1 restricted plant growth from 58 d after sowing (DAS) and decreased P concentrations significantly in shoots from 49 DAS and in roots from 40 DAS compared with plants supplied with 200 μg P g−1. Phosphorus concentrations in shoots of plants receiving 10 μg P g−1 decreased steadily from 2.1 to 1.1 mg P g−1 dry weight from 40 to 76 DAS, but P concentrations in roots were constant with time. Total P uptake increased with time irrespective of P supply, and the P uptake by plants at 10 μg P g−1 was only 35–75% of that at 200 μg P g−1. Plants fed with 10 μg P g−1 had higher Ca and Mg concentrations but lower S concentration in shoots than the plants fed with 200 μg P g−1. The concentrations of excess cations in plants were higher at 10 μg P g−1 than 200 μg P g−1 after 49 DAS. Phosphorus deficiency decreased the pH of root exudate solution due to the enhanced release of protons (H+) from roots. The pH of root exudate solution decreased rapidly with time and dropped to the lowest (4.28) at 58 DAS in the 10 μg P g−1 treatment. The decreased pH of root exudate solution was correlated with the increased concentrations of excess cations in plants. The pH of root exudate solution showed a different pattern of change with time compared with citrate exudation, suggesting that exudation of citrate anions contributes only a part of total acidification, but excess cation uptake dominantly contributes net proton release from roots of plants grown in P-deficient soil. Plant tissue had a significant accumulation of citrate in the treatment of 10 μg P g−1 compared with 200 μg P g−1 after 67 DAS. The results suggest that P deficiency enhances the excess cation uptake and concomitant proton release, and non-synchronous processes are involved in tissue accumulation and root exudation of organic anions under P deficiency.

Plant and Soil, 2006

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxyla... more The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P1, deficient) and 50 µM P (P50, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P1, but at P50 shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P50 treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P1, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P1 than in P50 treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 µmol g−1 root DW h−1 at P1, but was under the detection limit at P50; at pH 7.8, it was 2.4-fold higher in P1 than in P50 plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P1 and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.

Plant and Soil, 2008

The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosp... more The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosphere of durum wheat (Triticum turgidum durum L.) and common bean (Phaseolus vulgaris L.) grown in monocropping and intercropping systems with nitrate supply. Wheat and common bean were grown either alone or in association in a cropping device with a thin (1 mm) soil layer sandwiched between large root mats. Wheat intercropped with common bean exhibited a 33% increase in shoot biomass and a 22% increased root biomass, without significantly affecting common bean growth. After 12 days of culture, rhizosphere pH decreased by 1.66 and 1.13 units in monocropping system of common bean and intercropping system, respectively. Wheat increased intercropped common bean proton release by 36% compared with monocropped beans. Common bean and wheat exhibited different behaviors in rhizosphere P dynamics. Monocropped wheat decreased Resin-P, NaHCO3-P and NaOH-P in its rhizosphere by 24, 96 and 10%, respectively. However, NaHCO3-P and NaOH-P were increased by 61 and 10% in the rhizosphere of intercropping. Almost all values about P fraction in intercropping system were between those in monocropped common bean and monocropped wheat. Through taping different P fraction, different plants species possibly can alleviate competition for phosphorus in intercropping system.

Plant and Soil, 2004

Rhizosphere processes of individual plants have been widely investigated since 1904 when the term... more Rhizosphere processes of individual plants have been widely investigated since 1904 when the term “rhizosphere” was first put forward. However, little attention has been paid to rhizosphere effects at an agro-ecosystem level. This paper presents recent research on the rhizosphere processes in relation to plant nutrition in main cropping systems in China. In the peanut (Arachis hypogaea L.)/maize (Zea mays L.) intercropping system, maize was found to improve the Fe nutrition of peanut through influencing its rhizosphere processes, suggesting an important role of phytosiderophores released from Fe-deficient maize. Intercropping between maize and faba bean (Vicia faba L.) was found to improve nitrogen and phosphorus uptake in the two crops compared with corresponding sole crop. There was a higher land equivalent ratio (LER) in the intercropping system of maize and faba bean than the treatment of no root interactions between the two crops. The increased yield of maize intercropped with faba bean resulted from an interspecific facilitation in nutrient uptake, depending on interspecific root interactions of the two crops. In the rotation system of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) crops, Mn deficiency in wheat was caused by excessive Mn uptake by rice and Mn leaching from topsoil to subsoil due to periodic cycles of flooding and drying. However, wheat genotypes tolerant to Mn deficiency tended to distribute more roots to deeper soil layer and thus expand their rhizosphere zones in the Mn-deficient soils and utilize Mn from the subsoil. Deep ploughing also helped root penetration into subsoil and was propitious to correcting Mn deficiency in wheat rotated with rice. In comparison, oilseed rape (Brassica napus L.) took up more Mn than wheat through mobilizing sparingly soluble soil Mn due to acidification and reduction processes in the rhizosphere. Thus, oilseed rape was tolerant to the Mn-deficient conditions in the rice-oilseed rape rotation. Oxidation reactions on root surface of rice also resulted in the formation of Fe plaque in the rice rhizosphere. Large amounts of Zn were accumulated on the Fe plaque. Zinc uptake by rice plants increased as Fe plaque formed, but decreased at high amounts of Fe plaque. It is suggested that to fine-tune cropping patterns and optimize nutrient management based on a better understanding of rhizosphere processes at an agro-ecosystem level is crucial for increasing nutrient use efficiency and developing sustainable agriculture in China.

Plant and Soil, 2003

The present study examined the effect of phosphorus (P) limitation on cluster root formation and ... more The present study examined the effect of phosphorus (P) limitation on cluster root formation and exudation of carboxylates by N2-fixing white lupin (Lupinus albus L. cv. Kiev) grown in a P-deficient sandy soil. Plants received 10 (limited P) or 200 μg P g−1 soil as FePO4 (adequate P) and were grown in a phytotron at 20/12 °C (12/12 h) for 76 days in soil columns. Cluster root formation was assessed and root exudates were collected at 9-day intervals. Shoot and root dry weights were higher in plants grown in the adequate-P compared to the limited-P treatment for 67 days. No clear difference in the total root length was observed between two P treatments before day 58. However, the specific root length increased rapidly from 17 m g−1 DW at day 40 to 28 m g−1 at day 49 in the P-limited plants, but decreased in the P-adequate plants. The effect of P limitation on enhancement of cluster root formation was observed from day 40 and reached the maximum at day 58. The number of cluster roots was negatively correlated with the P concentration in both roots and shoots. Phosphorus limitation increased exudation of citrate from day 40. The exudation of citrate displayed a cyclic pattern throughout the experiment, and appeared related to internal P concentration in plants, particularly P concentration in shoots. The sorption of exogenously added citrate in the soil was also examined. The amount of extractable citrate remained unchanged for 2 h, but decreased thereafter, suggesting that the soil had a low capacity to sorb citrate, and the rate of its decomposition by microorganisms was slow. Collecting solution leached through a soil column is a simple and reliable method to acquire root exudates from white lupin grown in soil. The results suggest that formation of cluster roots and exudation of citrate in white lupin are regulated by P concentration in shoots.

Plant and Soil, 2004

White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled condit... more White lupin plants (Lupinus albus L. cv. Kiev) were grown in soil columns under controlled conditions at 20/12 °C (12/12 h) for 76 d to investigate the effect of phosphorus (P) deficiency on root-induced acidification and excess cation uptake by N2-fixing plants. Phosphorus was added in each column as FePO4 at a level of 10 (limited P) or 200 μg P g−1 (adequate P). Supply of 10 μg P g−1 restricted plant growth from 58 d after sowing (DAS) and decreased P concentrations significantly in shoots from 49 DAS and in roots from 40 DAS compared with plants supplied with 200 μg P g−1. Phosphorus concentrations in shoots of plants receiving 10 μg P g−1 decreased steadily from 2.1 to 1.1 mg P g−1 dry weight from 40 to 76 DAS, but P concentrations in roots were constant with time. Total P uptake increased with time irrespective of P supply, and the P uptake by plants at 10 μg P g−1 was only 35–75% of that at 200 μg P g−1. Plants fed with 10 μg P g−1 had higher Ca and Mg concentrations but lower S concentration in shoots than the plants fed with 200 μg P g−1. The concentrations of excess cations in plants were higher at 10 μg P g−1 than 200 μg P g−1 after 49 DAS. Phosphorus deficiency decreased the pH of root exudate solution due to the enhanced release of protons (H+) from roots. The pH of root exudate solution decreased rapidly with time and dropped to the lowest (4.28) at 58 DAS in the 10 μg P g−1 treatment. The decreased pH of root exudate solution was correlated with the increased concentrations of excess cations in plants. The pH of root exudate solution showed a different pattern of change with time compared with citrate exudation, suggesting that exudation of citrate anions contributes only a part of total acidification, but excess cation uptake dominantly contributes net proton release from roots of plants grown in P-deficient soil. Plant tissue had a significant accumulation of citrate in the treatment of 10 μg P g−1 compared with 200 μg P g−1 after 67 DAS. The results suggest that P deficiency enhances the excess cation uptake and concomitant proton release, and non-synchronous processes are involved in tissue accumulation and root exudation of organic anions under P deficiency.

Plant and Soil, 2006

The study examined the interactive effect of pH and P supply on cluster-root formation, carboxyla... more The study examined the interactive effect of pH and P supply on cluster-root formation, carboxylate exudation and proton release by an alkaline-tolerant lupin species (Lupinus pilosus Murr.) in nutrient solution. The plants were exposed to 1 (P1, deficient) and 50 µM P (P50, adequate) for 34 days in nutrient solution at either pH 5.6 or 7.8. Plant biomass was not influenced by pH at P1, but at P50 shoot and root dry weights were 23 and 18% higher, respectively, at pH 7.8 than at pH 5.6. There was no significant difference in plant biomass between two P treatments regardless of medium pH. Phosphorus deficiency increased significantly the number of the second-order lateral roots compared with the P50 treatment. Both total root length and specific root length of plants grown at pH 5.6 were higher than those at pH 7.8 regardless of P supply. Cluster roots were formed at P1, but cluster-root number was 2-fold higher at pH 7.8 than pH 5.6. Roots released 16 and 31% more protons at pH 5.6 and 7.8, respectively, in P1 than in P50 treatments, and the rate of proton release followed the similar pattern. At pH 5.6, citrate exudation rate was 0.39 µmol g−1 root DW h−1 at P1, but was under the detection limit at P50; at pH 7.8, it was 2.4-fold higher in P1 than in P50 plants. High pH significantly increased citrate exudation rate in comparison to pH 5.6. The uptake of anions P and S was inhibited at P1 and high pH increased cations Na, Mg and Ca uptake. The results suggested that enhanced cluster-root formation, proton release and citrate exudation may account for the mechanism of efficient P acquisition by alkaline-tolerant L. pilosus well adapted to calcareous soils. Cluster-root formation and citrate exudation in L. pilosus can be altered by medium pH and P deficiency. Phosphorus deficiency-induced proton release may be associated with the reduced anion uptake, but high pH-induced proton release may be partly attributed to increased cation uptake.

Plant and Soil, 2008

The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosp... more The main objective of the present study was to investigate phosphorus (P) dynamics in the rhizosphere of durum wheat (Triticum turgidum durum L.) and common bean (Phaseolus vulgaris L.) grown in monocropping and intercropping systems with nitrate supply. Wheat and common bean were grown either alone or in association in a cropping device with a thin (1 mm) soil layer sandwiched between large root mats. Wheat intercropped with common bean exhibited a 33% increase in shoot biomass and a 22% increased root biomass, without significantly affecting common bean growth. After 12 days of culture, rhizosphere pH decreased by 1.66 and 1.13 units in monocropping system of common bean and intercropping system, respectively. Wheat increased intercropped common bean proton release by 36% compared with monocropped beans. Common bean and wheat exhibited different behaviors in rhizosphere P dynamics. Monocropped wheat decreased Resin-P, NaHCO3-P and NaOH-P in its rhizosphere by 24, 96 and 10%, respectively. However, NaHCO3-P and NaOH-P were increased by 61 and 10% in the rhizosphere of intercropping. Almost all values about P fraction in intercropping system were between those in monocropped common bean and monocropped wheat. Through taping different P fraction, different plants species possibly can alleviate competition for phosphorus in intercropping system.

Plant and Soil, 2004

Rhizosphere processes of individual plants have been widely investigated since 1904 when the term... more Rhizosphere processes of individual plants have been widely investigated since 1904 when the term “rhizosphere” was first put forward. However, little attention has been paid to rhizosphere effects at an agro-ecosystem level. This paper presents recent research on the rhizosphere processes in relation to plant nutrition in main cropping systems in China. In the peanut (Arachis hypogaea L.)/maize (Zea mays L.) intercropping system, maize was found to improve the Fe nutrition of peanut through influencing its rhizosphere processes, suggesting an important role of phytosiderophores released from Fe-deficient maize. Intercropping between maize and faba bean (Vicia faba L.) was found to improve nitrogen and phosphorus uptake in the two crops compared with corresponding sole crop. There was a higher land equivalent ratio (LER) in the intercropping system of maize and faba bean than the treatment of no root interactions between the two crops. The increased yield of maize intercropped with faba bean resulted from an interspecific facilitation in nutrient uptake, depending on interspecific root interactions of the two crops. In the rotation system of rice (Oryza sativa L.)-wheat (Triticum aestivum L.) crops, Mn deficiency in wheat was caused by excessive Mn uptake by rice and Mn leaching from topsoil to subsoil due to periodic cycles of flooding and drying. However, wheat genotypes tolerant to Mn deficiency tended to distribute more roots to deeper soil layer and thus expand their rhizosphere zones in the Mn-deficient soils and utilize Mn from the subsoil. Deep ploughing also helped root penetration into subsoil and was propitious to correcting Mn deficiency in wheat rotated with rice. In comparison, oilseed rape (Brassica napus L.) took up more Mn than wheat through mobilizing sparingly soluble soil Mn due to acidification and reduction processes in the rhizosphere. Thus, oilseed rape was tolerant to the Mn-deficient conditions in the rice-oilseed rape rotation. Oxidation reactions on root surface of rice also resulted in the formation of Fe plaque in the rice rhizosphere. Large amounts of Zn were accumulated on the Fe plaque. Zinc uptake by rice plants increased as Fe plaque formed, but decreased at high amounts of Fe plaque. It is suggested that to fine-tune cropping patterns and optimize nutrient management based on a better understanding of rhizosphere processes at an agro-ecosystem level is crucial for increasing nutrient use efficiency and developing sustainable agriculture in China.

Plant and Soil, 2003

The present study examined the effect of phosphorus (P) limitation on cluster root formation and ... more The present study examined the effect of phosphorus (P) limitation on cluster root formation and exudation of carboxylates by N2-fixing white lupin (Lupinus albus L. cv. Kiev) grown in a P-deficient sandy soil. Plants received 10 (limited P) or 200 μg P g−1 soil as FePO4 (adequate P) and were grown in a phytotron at 20/12 °C (12/12 h) for 76 days in soil columns. Cluster root formation was assessed and root exudates were collected at 9-day intervals. Shoot and root dry weights were higher in plants grown in the adequate-P compared to the limited-P treatment for 67 days. No clear difference in the total root length was observed between two P treatments before day 58. However, the specific root length increased rapidly from 17 m g−1 DW at day 40 to 28 m g−1 at day 49 in the P-limited plants, but decreased in the P-adequate plants. The effect of P limitation on enhancement of cluster root formation was observed from day 40 and reached the maximum at day 58. The number of cluster roots was negatively correlated with the P concentration in both roots and shoots. Phosphorus limitation increased exudation of citrate from day 40. The exudation of citrate displayed a cyclic pattern throughout the experiment, and appeared related to internal P concentration in plants, particularly P concentration in shoots. The sorption of exogenously added citrate in the soil was also examined. The amount of extractable citrate remained unchanged for 2 h, but decreased thereafter, suggesting that the soil had a low capacity to sorb citrate, and the rate of its decomposition by microorganisms was slow. Collecting solution leached through a soil column is a simple and reliable method to acquire root exudates from white lupin grown in soil. The results suggest that formation of cluster roots and exudation of citrate in white lupin are regulated by P concentration in shoots.

Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protei... more Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protein kinases constitute control circuits to regulate pre-mRNA splicing and coordinate splicing with transcription in mammalian cells. We present here the finding that similar SR networks exist in Schizosaccharomyces pombe. We previously showed that Dsk1 protein, originally described as a mitotic regulator, displays high activity in phosphorylating S. pombe Prp2 protein (spU2AF59), a homologue of human U2AF65. We now demonstrate that Dsk1 also phosphorylates two recently identified fission yeast proteins with RS repeats, Srp1 and Srp2, in vitro. The phosphorylated proteins bear the same phosphoepitope found in mammalian SR proteins. Consistent with its substrate specificity, Dsk1 forms kinase-competent complexes with those proteins. Furthermore, dsk1 ؉ gene determines the phenotype of prp2 ؉ overexpression, providing in vivo evidence that Prp2 is a target for Dsk1. The dsk1-null mutant strain became severely sick with the additional deletion of a related kinase gene. Significantly, human SR protein-specific kinase 1 (SRPK1) complements the growth defect of the doubledeletion mutant. In conjunction with the resemblance of dsk1 ؉ and SRPK1 in sequence homology, biochemical properties, and overexpression phenotypes, the complementation result indicates that SRPK1 is a functional homologue of Dsk1. Collectively, our studies illustrate the conserved SR networks in S. pombe consisting of RS domain-containing proteins and SR protein-specific kinases and thus establish the importance of the networks in eucaryotic organisms.

Molecular and Cellular Biology, 2000

Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protei... more Arginine/serine-rich (RS) domain-containing proteins and their phosphorylation by specific protein kinases constitute control circuits to regulate pre-mRNA splicing and coordinate splicing with transcription in mammalian cells. We present here the finding that similar SR networks exist in Schizosaccharomyces pombe. We previously showed that Dsk1 protein, originally described as a mitotic regulator, displays high activity in phosphorylating S. pombe Prp2 protein (spU2AF59), a homologue of human U2AF65. We now demonstrate that Dsk1 also phosphorylates two recently identified fission yeast proteins with RS repeats, Srp1 and Srp2, in vitro. The phosphorylated proteins bear the same phosphoepitope found in mammalian SR proteins. Consistent with its substrate specificity, Dsk1 forms kinase-competent complexes with those proteins. Furthermore, dsk1 ؉ gene determines the phenotype of prp2 ؉ overexpression, providing in vivo evidence that Prp2 is a target for Dsk1. The dsk1-null mutant strain became severely sick with the additional deletion of a related kinase gene. Significantly, human SR protein-specific kinase 1 (SRPK1) complements the growth defect of the doubledeletion mutant. In conjunction with the resemblance of dsk1 ؉ and SRPK1 in sequence homology, biochemical properties, and overexpression phenotypes, the complementation result indicates that SRPK1 is a functional homologue of Dsk1. Collectively, our studies illustrate the conserved SR networks in S. pombe consisting of RS domain-containing proteins and SR protein-specific kinases and thus establish the importance of the networks in eucaryotic organisms.