Shimon Gepstein | Technion Israel Institute of Technology (original) (raw)

Papers by Shimon Gepstein

telem-pub.openu.ac.il, 2010

Phytopathogenic fungi penetrate plants by breaking down the cuticular barrier with cutinase. Cuti... more Phytopathogenic fungi penetrate plants by breaking down the cuticular barrier with cutinase. Cutinases are extracellular hydrolytic enzymes that degrade cutin, a polyester composed of hydroxy and epoxy fatty acids. Until now, cutinase has been recognized by its ability to release labeled cutin monomers or by a non-specific esterase assay based on the hydrolysis of p-nitrophenyl esters of short fatty acids. In this work, an insoluble p-nitrophenyl derivative was synthesized and purified, and its structure was determined to be 4-nitrophenyl (16-methyl sulfone ester) hexadecanoate (pNMSEH) by nuclear magnetic resonance (H+ NMR) analysis. pNMSEH was tested as a new cutinase substrate with Pseudomonas mandocino cutinase and porcine liver esterase. While a linear release over time of p-nitrophenol (pNP) was recorded in the presence of cutinase, no response was obtained with the esterase. The calculated kinetic parameters of pNMSEH hydrolysis by cutinase revealed a high specificity (Km = 1.8 mM), albeit a low catalytic rate (Vmax = 10.5 μmol min−l l−1). This new synthetic substrate may be helpful for detecting and assaying cutinase activity in mixed solutions, such as crude fungal extracellular extracts.

During senescence of primary bean leaves (Phaseolus vulgaris), there are differential changes in ... more During senescence of primary bean leaves (Phaseolus vulgaris), there are differential changes in the rates at which thylakoid proteins are synthesized. In particular, synthesis of the 32 kD herbicide-binding protein continues throughout senescence, whereas formation of the a and 3 subunits of ATPase, the 68 kD photosystem I reaction center polypeptide, cytochrome f, cytochrome b 6 and the structural apoprotein of the lightharvesting chlorophyll protein complex (LHCP) declines. Pulse-chase experiments with intact leaves indicated rapid degradation of the 32 kD protein, which is consistent with its known rapid rate of turnover. This degradation was light-dependent and inhibited by DCMU, and the kinetics of degradation were similar for young and senescent membranes. In Coomassie-stained gels, the 68 kD reaction center polypeptide of photosystem I, the oL and 3 subunits of ATPase and the LHCP were the dominant proteins for all ages of membranes. Western blot analysis indicated that cytochrome f and cytochrome b 6 are selectively depleted during senescence. The data have been interpreted as indicating that translational disruptions in both the cytoplasmic and chloroplastic compartments may contribute to the decline in photosynthetic electron transport in the senescing leaf.

Proceedings of the National Academy of Sciences

Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senesce... more Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senescence, leading to a decrease in canopy size, loss in photosynthesis and reduced yields. On the basis of the assumption that senescence is a type of cell death program that could be inappropriately activated during drought, we hypothesized that it may be possible to enhance drought tolerance by delaying drought-induced leaf senescence. We generated transgenic plants expressing an isopentenyltransferase gene driven by a stress- and maturation-induced promoter. Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth after a long drought period that killed the control plants. The transgenic plants maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought. Moreover, the transgenic plants displayed minimal yield loss when watered with only ...

Instruction in large higher education introductory courses is usually based on lectures which dis... more Instruction in large higher education introductory courses is usually based on lectures which discourage students from taking responsibility of their own learning. We developed an instructional model that harnesses technology to support students in assuming such responsibility, and gradually implemented it in a large introductory biology course. We examined how the gradual shift of responsibility from the instructor to the students affected their self regulation and self-efficacy. Verbal analysis of students' utterances revealed that students felt a sense of confidence when all course contents were provided to them in the lectures and the tutorial, which encouraged them to take responsibility of their own learning. However, when students were required to self-learn some of the course materials which were not covered in lectures, they became reluctant from taking that responsibility. We conclude that it's imperative to provide supports that will induce students' confidence, and encourage them to assume responsibility.

Modern Biopharmaceuticals, 2005

... Shimon Gepstein, Anil Grover, and Eduardo Blumwald ... These variables are, in fact, advantag... more ... Shimon Gepstein, Anil Grover, and Eduardo Blumwald ... These variables are, in fact, advantageous to plants, and plants have selected these as decisive factors in controlling their various physiological attri-butes such as timing of seed germination, length of the period of ...

Methods in molecular biology (Clifton, N.J.), 2007

Molecular and cellular processes related to the senescence syndrome are determined by programs of... more Molecular and cellular processes related to the senescence syndrome are determined by programs of differential gene expression. Subtractive cDNA hybridization is a powerful approach to identify and isolate differentially expressed genes in various systems. A highly effective method, termed suppression subtractive hybridization (SSH), has been applied for the generation of subtracted cDNA library of senescing leaves. The method consists of two main stages, the normalization step that equalizes the abundance of cDNAs within the target population and the subtraction step that eliminates the common sequences between the target and the driver populations. The successful generation of library containing high numbered of rare and abundant cDNA clones in senescing plant cells proves the applicability of this method for global identification of differentially expressed genes during cellular senescence.

Plant molecular biology, 2013

The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant response... more The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant responses to abiotic stresses. Both processes have an enormous negative global agro-economic impact and endanger food security worldwide. Premature plant senescence is the main cause of losses in grain filling and biomass yield due to leaf yellowing and deteriorated photosynthesis, and is also responsible for the losses resulting from the short shelf life of many vegetables and fruits. Under abiotic stress conditions the yield losses are often even greater. The primary challenge in agricultural sciences today is to develop technologies that will increase food production and sustainability of agriculture especially under environmentally limiting conditions. In this chapter, some of the mechanisms involved in abiotic stress-induced plant senescence are discussed. Recent studies have shown that crop yield and nutritional values can be altered as well as plant stress tolerance through manipulating t...

Transgenic Research, 2005

Parasitic plants present some of the most intractable weed problems for agriculture in much of th... more Parasitic plants present some of the most intractable weed problems for agriculture in much of the world. Species of root parasites such as Orobanche can cause enormous yield losses, yet few control measures are effective and affordable. An ideal solution to this problem is the development of parasite-resistant crops, but this goal has been elusive for most susceptible crops. Here we report a mechanism for resistance to the parasitic angiosperm Orobanche based on expression of sarcotoxin IA in transgenic tobacco. Sarcotoxin IA is a 40-residue peptide with antibiotic activity, originally isolated from the fly, Sarcophaga peregrina. The sarcotoxin IA gene was fused to an Orobanche-inducible promoter, HMG2, which is induced locally in the host root at the point of contact with the parasite, and used to transform tobacco. The resulting transgenic plants accumulated more biomass than non-transformed plants in the presence of parasites. Furthermore, plants expressing sarcotoxin IA showed enhanced resistance to O. aegyptiaca as evidenced by abnormal parasite development and higher parasite mortality after attachment as compared to non-transformed plants. The transgenic plants were similar in appearance to non-transformed plants suggesting that sarcotoxin IA is not detrimental to the host.

The Plant Journal, 2003

Leaf senescence is a form of programmed cell death, and is believed to involve preferential expre... more Leaf senescence is a form of programmed cell death, and is believed to involve preferential expression of a speci®c set of`senescence-associated genes' (SAGs). To decipher the molecular mechanisms and the predicted complex network of regulatory pathways involved in the senescence program, we have carried out a large-scale gene identi®cation study in a reference plant, Arabidopsis thaliana. Using suppression subtractive hybridization, we isolated approximately 800 cDNA clones representing SAGs expressed in senescing leaves. Differential expression was con®rmed by Northern blot analysis for 130 non-redundant genes. Over 70 of the identi®ed genes have not previously been shown to participate in the senescence process. SAGencoded proteins are likely to participate in macromolecule degradation, detoxi®cation of oxidative metabolites, induction of defense mechanisms, and signaling and regulatory events. Temporal expression pro-®les of selected genes displayed several distinct patterns, from expression at a very early stage, to the terminal phase of the senescence syndrome. Expression of some of the novel SAGs, in response to age, leaf detachment, darkness, and ethylene and cytokinin treatment was compared. The large repertoire of SAGs identi®ed here provides global insights about regulatory, biochemical and cellular events occurring during leaf senescence.

Proceedings of the National Academy of Sciences, 2007

Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senesce... more Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senescence, leading to a decrease in canopy size, loss in photosynthesis and reduced yields. On the basis of the assumption that senescence is a type of cell death program that could be inappropriately activated during drought, we hypothesized that it may be possible to enhance drought tolerance by delaying droughtinduced leaf senescence. We generated transgenic plants expressing an isopentenyltransferase gene driven by a stress-and maturationinduced promoter. Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth after a long drought period that killed the control plants. The transgenic plants maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought. Moreover, the transgenic plants displayed minimal yield loss when watered with only 30% of the amount of water used under control conditions.

Planta, 2001

To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv.... more To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv. SR1) mRNA that is up-regulated during senescence was isolated by the cDNA-amplified restriction fragment polymorphism method and the cDNA was cloned. The mRNA coded for the early light-induced protein (ELIP), a member of the chlorophyll a/b-binding protein family that has been implicated in assembly or repair of the photosynthetic machinery during early chloroplast development and abiotic stress. A protein antigenically recognized by antibodies to ELIP appeared during senescence with kinetics similar to those of its mRNA. The mRNA, designated ELIP-TOB, was detected earlier when senescence was enhanced by leaf detachment and treatment with 1-amino-cyclopropane-1-carboxylic acid, and was detected later when senescence was retarded by benzyladenine. However, no ELIP-TOB mRNA was seen in the dark even though senescence was accelerated under these conditions. Furthermore, water stress and anaerobiosis stimulated the appearance of ELIP-TOB mRNA before losses of chlorophyll could be detected. We discuss the conditions that may lead to the up-regulation of ELIP-TOB during senescence and speculate as to the role of the gene product in this terminal phase of leaf development.

PLANT PHYSIOLOGY, 2006

Water deficit caused by addition of polyethylene glycol 6000 at 20.5 MPa water potential to well-... more Water deficit caused by addition of polyethylene glycol 6000 at 20.5 MPa water potential to well-aerated nutrient solution for 48 h inhibited the elongation of maize (Zea mays) seedling primary roots. Segmental growth rates in the root elongation zone were maintained 0 to 3 mm behind the tip, but in comparison with well-watered control roots, progressive growth inhibition was initiated by water deficit as expanding cells crossed the region 3 to 9 mm behind the tip. The mechanical extensibility of the cell walls was also progressively inhibited. We investigated the possible involvement in root growth inhibition by water deficit of alterations in metabolism and accumulation of wall-linked phenolic substances. Water deficit increased expression in the root elongation zone of transcripts of two genes involved in lignin biosynthesis, cinnamoyl-CoA reductase 1 and 2, after only 1 h, i.e. before decreases in wall extensibility. Further increases in transcript expression and increased lignin staining were detected after 48 h. Progressive stress-induced increases in wall-linked phenolics at 3 to 6 and 6 to 9 mm behind the root tip were detected by comparing Fourier transform infrared spectra and UV-fluorescence images of isolated cell walls from water deficit and control roots. Increased UV fluorescence and lignin staining colocated to vascular tissues in the stele. Longitudinal bisection of the elongation zone resulted in inward curvature, suggesting that inner, stelar tissues were also rate limiting for root growth. We suggest that spatially localized changes in wall-phenolic metabolism are involved in the progressive inhibition of wall extensibility and root growth and may facilitate root acclimation to drying environments.

PLANT PHYSIOLOGY, 2001

The aromas of fruits, vegetables, and flowers are mixtures of volatile metabolites, often present... more The aromas of fruits, vegetables, and flowers are mixtures of volatile metabolites, often present in parts per billion levels or less. We show here that tomato (Lycopersicon esculentum Mill.) plants transgenic for a heterologous Clarkia breweri S-linalool synthase (LIS) gene, under the control of the tomato late-ripening-specific E8 promoter, synthesize and accumulate S-linalool and 8-hydroxylinalool in ripening fruits. Apart from the difference in volatiles, no other phenotypic alterations were noted, including the levels of other terpenoids such as ␥and ␣-tocopherols, lycopene, ␤-carotene, and lutein. Our studies indicate that it is possible to enhance the levels of monoterpenes in ripening fruits by metabolic engineering. ; fax 972-4 -983-6936.

PLANT PHYSIOLOGY, 1991

Two distinct ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU) popula... more Two distinct ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU) populations were observed in Pteris vittata gametophytes grown under different illumination conditions. Exposure of the fem gametophytes to continuous red light (R) resulted in Rubisco SSUs that were not recognized by polyclonal antibodies raised against SSUs from spinach. Unlike the R-induced SSUs, blue light (B) induced SSUs were well recognized. This difference in SSU composition also reflected in Rubisco activity. In vitro, B-induced Rubisco exhibits a significantly higher carboxylation activity as compared to the R-induced

Plant Molecular Biology, 2004

Growth in the apical elongation zone of plant roots is central to the development of functional r... more Growth in the apical elongation zone of plant roots is central to the development of functional root systems. Rates of root segmental elongation change from accelerating to decelerating as cell development proceeds from newly formed to fully elongated status. One of the primary variables regulating these changes in elongation rates is the extensibility of the elongating cell walls. To help decipher the complex molecular mechanisms involved in spatially variable root growth, we performed a gene identification study along primary root tips of maize (Zea mays) seedlings using suppression subtractive hybridization (SSH) and candidate gene approaches. Using SSH we isolated 150 non-redundant cDNA clones representing root growth-related genes (RGGs) that were preferentially expressed in the elongation zone. Differential expression patterns were revealed by Northern blot analysis for 41 of the identified genes and several candidate genes. Many of the genes have not been previously reported to be involved in root growth processes in maize. Genes were classified into groups based on the predicted function of the encoded proteins: cell wall metabolism, cytoskeleton, general metabolism, signaling and unknown. In-situ hybridization performed for two selected genes, confirmed the spatial distribution of expression shown by Northern blots and revealed subtle differences in tissue localization. Interestingly, spatial profiles of expression for some cell wall related genes appeared to correlate with the profile of accelerating root elongation and changed appropriately under growth-inhibitory water deficit.

Plant Molecular Biology, 2008

A combined chemical, biochemical and molecular study was conducted to understand the differential... more A combined chemical, biochemical and molecular study was conducted to understand the differential accumulation of volatile sesquiterpenes in melon fruits. Sesquiterpenes were present mainly in the rinds of climacteric varieties, and a great diversity in their composition was found among varieties. Sesquiterpenes were generally absent in non-climacteric varieties. Two climacteric melon varieties, the green-fleshed 'Noy Yizre'el', and the orange-fleshed 'Dulce' were further examined. In 'Noy Yizre'el' the main sesquiterpenes accumulated are d-cadinene, c-cadinene and a-copaene, while a-farnesene is the main sesquiterpene in 'Dulce'. Sesquiterpene synthase activities, mainly restricted to rinds of mature fruits, were shown to generate different sesquiterpenes in each variety according to the compositions found in rinds. EST melon database mining yielded two novel cDNAs coding for members of the Tps gene family termed CmTpsNY and CmTpsDul respectively, that are 43.2% similar. Heterologous expression in E. coli of CmTpsNY produced mainly d-copaene, a-copaene, b-caryophyllene, germacrene D, a-muurolene, c-cadinene, d-cadinene, and a-cadinene, while CmTpsDul produced a-farnesene only. CmTpsNY was mostly expressed in 'Noy Yizre'el' rind while CmTpsDul expression was specific to 'Dulce' rind. None of these genes was expressed in rinds of the non-climacteric 'Tam Dew' cultivar. Our results indicate that different sesquiterpene synthases encoded by different members of the Tps gene family are active in melon varieties and this specificity modulates the accumulation of sesquiterpenes. The genes are differentially transcriptionally regulated during fruit development and according to variety and are likely to be associated with chemical differences responsible for the unique aromas of melon varieties.

Physiologia Plantarum, 1991

S. 1991. In vitro evidence for the involvement of activated oxygen in light-induced aggregation o... more S. 1991. In vitro evidence for the involvement of activated oxygen in light-induced aggregation of thyiakoid proteins. -Physiol. Plant. 82: 389-396.

telem-pub.openu.ac.il, 2010

Phytopathogenic fungi penetrate plants by breaking down the cuticular barrier with cutinase. Cuti... more Phytopathogenic fungi penetrate plants by breaking down the cuticular barrier with cutinase. Cutinases are extracellular hydrolytic enzymes that degrade cutin, a polyester composed of hydroxy and epoxy fatty acids. Until now, cutinase has been recognized by its ability to release labeled cutin monomers or by a non-specific esterase assay based on the hydrolysis of p-nitrophenyl esters of short fatty acids. In this work, an insoluble p-nitrophenyl derivative was synthesized and purified, and its structure was determined to be 4-nitrophenyl (16-methyl sulfone ester) hexadecanoate (pNMSEH) by nuclear magnetic resonance (H+ NMR) analysis. pNMSEH was tested as a new cutinase substrate with Pseudomonas mandocino cutinase and porcine liver esterase. While a linear release over time of p-nitrophenol (pNP) was recorded in the presence of cutinase, no response was obtained with the esterase. The calculated kinetic parameters of pNMSEH hydrolysis by cutinase revealed a high specificity (Km = 1.8 mM), albeit a low catalytic rate (Vmax = 10.5 μmol min−l l−1). This new synthetic substrate may be helpful for detecting and assaying cutinase activity in mixed solutions, such as crude fungal extracellular extracts.

During senescence of primary bean leaves (Phaseolus vulgaris), there are differential changes in ... more During senescence of primary bean leaves (Phaseolus vulgaris), there are differential changes in the rates at which thylakoid proteins are synthesized. In particular, synthesis of the 32 kD herbicide-binding protein continues throughout senescence, whereas formation of the a and 3 subunits of ATPase, the 68 kD photosystem I reaction center polypeptide, cytochrome f, cytochrome b 6 and the structural apoprotein of the lightharvesting chlorophyll protein complex (LHCP) declines. Pulse-chase experiments with intact leaves indicated rapid degradation of the 32 kD protein, which is consistent with its known rapid rate of turnover. This degradation was light-dependent and inhibited by DCMU, and the kinetics of degradation were similar for young and senescent membranes. In Coomassie-stained gels, the 68 kD reaction center polypeptide of photosystem I, the oL and 3 subunits of ATPase and the LHCP were the dominant proteins for all ages of membranes. Western blot analysis indicated that cytochrome f and cytochrome b 6 are selectively depleted during senescence. The data have been interpreted as indicating that translational disruptions in both the cytoplasmic and chloroplastic compartments may contribute to the decline in photosynthetic electron transport in the senescing leaf.

Proceedings of the National Academy of Sciences

Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senesce... more Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senescence, leading to a decrease in canopy size, loss in photosynthesis and reduced yields. On the basis of the assumption that senescence is a type of cell death program that could be inappropriately activated during drought, we hypothesized that it may be possible to enhance drought tolerance by delaying drought-induced leaf senescence. We generated transgenic plants expressing an isopentenyltransferase gene driven by a stress- and maturation-induced promoter. Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth after a long drought period that killed the control plants. The transgenic plants maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought. Moreover, the transgenic plants displayed minimal yield loss when watered with only ...

Instruction in large higher education introductory courses is usually based on lectures which dis... more Instruction in large higher education introductory courses is usually based on lectures which discourage students from taking responsibility of their own learning. We developed an instructional model that harnesses technology to support students in assuming such responsibility, and gradually implemented it in a large introductory biology course. We examined how the gradual shift of responsibility from the instructor to the students affected their self regulation and self-efficacy. Verbal analysis of students' utterances revealed that students felt a sense of confidence when all course contents were provided to them in the lectures and the tutorial, which encouraged them to take responsibility of their own learning. However, when students were required to self-learn some of the course materials which were not covered in lectures, they became reluctant from taking that responsibility. We conclude that it's imperative to provide supports that will induce students' confidence, and encourage them to assume responsibility.

Modern Biopharmaceuticals, 2005

... Shimon Gepstein, Anil Grover, and Eduardo Blumwald ... These variables are, in fact, advantag... more ... Shimon Gepstein, Anil Grover, and Eduardo Blumwald ... These variables are, in fact, advantageous to plants, and plants have selected these as decisive factors in controlling their various physiological attri-butes such as timing of seed germination, length of the period of ...

Methods in molecular biology (Clifton, N.J.), 2007

Molecular and cellular processes related to the senescence syndrome are determined by programs of... more Molecular and cellular processes related to the senescence syndrome are determined by programs of differential gene expression. Subtractive cDNA hybridization is a powerful approach to identify and isolate differentially expressed genes in various systems. A highly effective method, termed suppression subtractive hybridization (SSH), has been applied for the generation of subtracted cDNA library of senescing leaves. The method consists of two main stages, the normalization step that equalizes the abundance of cDNAs within the target population and the subtraction step that eliminates the common sequences between the target and the driver populations. The successful generation of library containing high numbered of rare and abundant cDNA clones in senescing plant cells proves the applicability of this method for global identification of differentially expressed genes during cellular senescence.

Plant molecular biology, 2013

The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant response... more The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant responses to abiotic stresses. Both processes have an enormous negative global agro-economic impact and endanger food security worldwide. Premature plant senescence is the main cause of losses in grain filling and biomass yield due to leaf yellowing and deteriorated photosynthesis, and is also responsible for the losses resulting from the short shelf life of many vegetables and fruits. Under abiotic stress conditions the yield losses are often even greater. The primary challenge in agricultural sciences today is to develop technologies that will increase food production and sustainability of agriculture especially under environmentally limiting conditions. In this chapter, some of the mechanisms involved in abiotic stress-induced plant senescence are discussed. Recent studies have shown that crop yield and nutritional values can be altered as well as plant stress tolerance through manipulating t...

Transgenic Research, 2005

Parasitic plants present some of the most intractable weed problems for agriculture in much of th... more Parasitic plants present some of the most intractable weed problems for agriculture in much of the world. Species of root parasites such as Orobanche can cause enormous yield losses, yet few control measures are effective and affordable. An ideal solution to this problem is the development of parasite-resistant crops, but this goal has been elusive for most susceptible crops. Here we report a mechanism for resistance to the parasitic angiosperm Orobanche based on expression of sarcotoxin IA in transgenic tobacco. Sarcotoxin IA is a 40-residue peptide with antibiotic activity, originally isolated from the fly, Sarcophaga peregrina. The sarcotoxin IA gene was fused to an Orobanche-inducible promoter, HMG2, which is induced locally in the host root at the point of contact with the parasite, and used to transform tobacco. The resulting transgenic plants accumulated more biomass than non-transformed plants in the presence of parasites. Furthermore, plants expressing sarcotoxin IA showed enhanced resistance to O. aegyptiaca as evidenced by abnormal parasite development and higher parasite mortality after attachment as compared to non-transformed plants. The transgenic plants were similar in appearance to non-transformed plants suggesting that sarcotoxin IA is not detrimental to the host.

The Plant Journal, 2003

Leaf senescence is a form of programmed cell death, and is believed to involve preferential expre... more Leaf senescence is a form of programmed cell death, and is believed to involve preferential expression of a speci®c set of`senescence-associated genes' (SAGs). To decipher the molecular mechanisms and the predicted complex network of regulatory pathways involved in the senescence program, we have carried out a large-scale gene identi®cation study in a reference plant, Arabidopsis thaliana. Using suppression subtractive hybridization, we isolated approximately 800 cDNA clones representing SAGs expressed in senescing leaves. Differential expression was con®rmed by Northern blot analysis for 130 non-redundant genes. Over 70 of the identi®ed genes have not previously been shown to participate in the senescence process. SAGencoded proteins are likely to participate in macromolecule degradation, detoxi®cation of oxidative metabolites, induction of defense mechanisms, and signaling and regulatory events. Temporal expression pro-®les of selected genes displayed several distinct patterns, from expression at a very early stage, to the terminal phase of the senescence syndrome. Expression of some of the novel SAGs, in response to age, leaf detachment, darkness, and ethylene and cytokinin treatment was compared. The large repertoire of SAGs identi®ed here provides global insights about regulatory, biochemical and cellular events occurring during leaf senescence.

Proceedings of the National Academy of Sciences, 2007

Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senesce... more Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senescence, leading to a decrease in canopy size, loss in photosynthesis and reduced yields. On the basis of the assumption that senescence is a type of cell death program that could be inappropriately activated during drought, we hypothesized that it may be possible to enhance drought tolerance by delaying droughtinduced leaf senescence. We generated transgenic plants expressing an isopentenyltransferase gene driven by a stress-and maturationinduced promoter. Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth after a long drought period that killed the control plants. The transgenic plants maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought. Moreover, the transgenic plants displayed minimal yield loss when watered with only 30% of the amount of water used under control conditions.

Planta, 2001

To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv.... more To better understand the genetic controls of leaf senescence, a tobacco (Nicotiana tabacum L. cv. SR1) mRNA that is up-regulated during senescence was isolated by the cDNA-amplified restriction fragment polymorphism method and the cDNA was cloned. The mRNA coded for the early light-induced protein (ELIP), a member of the chlorophyll a/b-binding protein family that has been implicated in assembly or repair of the photosynthetic machinery during early chloroplast development and abiotic stress. A protein antigenically recognized by antibodies to ELIP appeared during senescence with kinetics similar to those of its mRNA. The mRNA, designated ELIP-TOB, was detected earlier when senescence was enhanced by leaf detachment and treatment with 1-amino-cyclopropane-1-carboxylic acid, and was detected later when senescence was retarded by benzyladenine. However, no ELIP-TOB mRNA was seen in the dark even though senescence was accelerated under these conditions. Furthermore, water stress and anaerobiosis stimulated the appearance of ELIP-TOB mRNA before losses of chlorophyll could be detected. We discuss the conditions that may lead to the up-regulation of ELIP-TOB during senescence and speculate as to the role of the gene product in this terminal phase of leaf development.

PLANT PHYSIOLOGY, 2006

Water deficit caused by addition of polyethylene glycol 6000 at 20.5 MPa water potential to well-... more Water deficit caused by addition of polyethylene glycol 6000 at 20.5 MPa water potential to well-aerated nutrient solution for 48 h inhibited the elongation of maize (Zea mays) seedling primary roots. Segmental growth rates in the root elongation zone were maintained 0 to 3 mm behind the tip, but in comparison with well-watered control roots, progressive growth inhibition was initiated by water deficit as expanding cells crossed the region 3 to 9 mm behind the tip. The mechanical extensibility of the cell walls was also progressively inhibited. We investigated the possible involvement in root growth inhibition by water deficit of alterations in metabolism and accumulation of wall-linked phenolic substances. Water deficit increased expression in the root elongation zone of transcripts of two genes involved in lignin biosynthesis, cinnamoyl-CoA reductase 1 and 2, after only 1 h, i.e. before decreases in wall extensibility. Further increases in transcript expression and increased lignin staining were detected after 48 h. Progressive stress-induced increases in wall-linked phenolics at 3 to 6 and 6 to 9 mm behind the root tip were detected by comparing Fourier transform infrared spectra and UV-fluorescence images of isolated cell walls from water deficit and control roots. Increased UV fluorescence and lignin staining colocated to vascular tissues in the stele. Longitudinal bisection of the elongation zone resulted in inward curvature, suggesting that inner, stelar tissues were also rate limiting for root growth. We suggest that spatially localized changes in wall-phenolic metabolism are involved in the progressive inhibition of wall extensibility and root growth and may facilitate root acclimation to drying environments.

PLANT PHYSIOLOGY, 2001

The aromas of fruits, vegetables, and flowers are mixtures of volatile metabolites, often present... more The aromas of fruits, vegetables, and flowers are mixtures of volatile metabolites, often present in parts per billion levels or less. We show here that tomato (Lycopersicon esculentum Mill.) plants transgenic for a heterologous Clarkia breweri S-linalool synthase (LIS) gene, under the control of the tomato late-ripening-specific E8 promoter, synthesize and accumulate S-linalool and 8-hydroxylinalool in ripening fruits. Apart from the difference in volatiles, no other phenotypic alterations were noted, including the levels of other terpenoids such as ␥and ␣-tocopherols, lycopene, ␤-carotene, and lutein. Our studies indicate that it is possible to enhance the levels of monoterpenes in ripening fruits by metabolic engineering. ; fax 972-4 -983-6936.

PLANT PHYSIOLOGY, 1991

Two distinct ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU) popula... more Two distinct ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit (SSU) populations were observed in Pteris vittata gametophytes grown under different illumination conditions. Exposure of the fem gametophytes to continuous red light (R) resulted in Rubisco SSUs that were not recognized by polyclonal antibodies raised against SSUs from spinach. Unlike the R-induced SSUs, blue light (B) induced SSUs were well recognized. This difference in SSU composition also reflected in Rubisco activity. In vitro, B-induced Rubisco exhibits a significantly higher carboxylation activity as compared to the R-induced

Plant Molecular Biology, 2004

Growth in the apical elongation zone of plant roots is central to the development of functional r... more Growth in the apical elongation zone of plant roots is central to the development of functional root systems. Rates of root segmental elongation change from accelerating to decelerating as cell development proceeds from newly formed to fully elongated status. One of the primary variables regulating these changes in elongation rates is the extensibility of the elongating cell walls. To help decipher the complex molecular mechanisms involved in spatially variable root growth, we performed a gene identification study along primary root tips of maize (Zea mays) seedlings using suppression subtractive hybridization (SSH) and candidate gene approaches. Using SSH we isolated 150 non-redundant cDNA clones representing root growth-related genes (RGGs) that were preferentially expressed in the elongation zone. Differential expression patterns were revealed by Northern blot analysis for 41 of the identified genes and several candidate genes. Many of the genes have not been previously reported to be involved in root growth processes in maize. Genes were classified into groups based on the predicted function of the encoded proteins: cell wall metabolism, cytoskeleton, general metabolism, signaling and unknown. In-situ hybridization performed for two selected genes, confirmed the spatial distribution of expression shown by Northern blots and revealed subtle differences in tissue localization. Interestingly, spatial profiles of expression for some cell wall related genes appeared to correlate with the profile of accelerating root elongation and changed appropriately under growth-inhibitory water deficit.

Plant Molecular Biology, 2008

A combined chemical, biochemical and molecular study was conducted to understand the differential... more A combined chemical, biochemical and molecular study was conducted to understand the differential accumulation of volatile sesquiterpenes in melon fruits. Sesquiterpenes were present mainly in the rinds of climacteric varieties, and a great diversity in their composition was found among varieties. Sesquiterpenes were generally absent in non-climacteric varieties. Two climacteric melon varieties, the green-fleshed 'Noy Yizre'el', and the orange-fleshed 'Dulce' were further examined. In 'Noy Yizre'el' the main sesquiterpenes accumulated are d-cadinene, c-cadinene and a-copaene, while a-farnesene is the main sesquiterpene in 'Dulce'. Sesquiterpene synthase activities, mainly restricted to rinds of mature fruits, were shown to generate different sesquiterpenes in each variety according to the compositions found in rinds. EST melon database mining yielded two novel cDNAs coding for members of the Tps gene family termed CmTpsNY and CmTpsDul respectively, that are 43.2% similar. Heterologous expression in E. coli of CmTpsNY produced mainly d-copaene, a-copaene, b-caryophyllene, germacrene D, a-muurolene, c-cadinene, d-cadinene, and a-cadinene, while CmTpsDul produced a-farnesene only. CmTpsNY was mostly expressed in 'Noy Yizre'el' rind while CmTpsDul expression was specific to 'Dulce' rind. None of these genes was expressed in rinds of the non-climacteric 'Tam Dew' cultivar. Our results indicate that different sesquiterpene synthases encoded by different members of the Tps gene family are active in melon varieties and this specificity modulates the accumulation of sesquiterpenes. The genes are differentially transcriptionally regulated during fruit development and according to variety and are likely to be associated with chemical differences responsible for the unique aromas of melon varieties.

Physiologia Plantarum, 1991

S. 1991. In vitro evidence for the involvement of activated oxygen in light-induced aggregation o... more S. 1991. In vitro evidence for the involvement of activated oxygen in light-induced aggregation of thyiakoid proteins. -Physiol. Plant. 82: 389-396.