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Papers by Dr. K. Riazunnisa YVU

Indian journal of biochemistry & biophysics

Intact and metabolically very active mesophyll protoplasts were isolated rapidly from pea (Pisum ... more Intact and metabolically very active mesophyll protoplasts were isolated rapidly from pea (Pisum sativum) leaves. The functional performance of protoplasts at various stages of their isolation was analyzed by using fast Chl αfluorescence OJIP transients and compared with that of intact leaves. The results demonstrated that the OJIP transients could successfully be used to monitor the quality of mesophyll protoplasts at different isolation steps. The protoplasts maintained their integrity and photosynthetic status very well, and their performance was very similar to that of the intact leaves.

Photosynthesis. Energy from the Sun, 2008

ABSTRACT The biochemical basis of interactions between chloroplasts and mitochondria to optimize ... more ABSTRACT The biochemical basis of interactions between chloroplasts and mitochondria to optimize photosynthesis is examined using pea or Arabidopsis. Mesophyll protoplasts of pea required much less CO2 for maximal photosynthesis, than their chloroplasts. Such low requirement for CO2 could be due to an internal carbon source and/or a CO2 concentrating mechanism in mesophyll protoplasts. The suppression of protoplast photosynthesis by photorespiratory inhibitors (aminooxyacetate, AOA or glycine hydroxamate, GHA) indicated that photorespiration could be a significant source of CO2 for photosynthesis by mesophyll protoplasts at limiting CO2 and atmospheric oxygen. Photosynthesis in Asc-deficient vtc1 mutant of Arabidopsis decreased strongly at high light and was quite sensitive to SHAM. We suggest that recycling of photorespiratory CO2 and ascorbate can be additional factors involved in the beneficial interactions of mitochondria and chloroplasts.

Physiologia Plantarum, 2007

A simple and quick method is described for rapid isolation of metabolically active mesophyll prot... more A simple and quick method is described for rapid isolation of metabolically active mesophyll protoplasts from leaves of Arabidopsis thaliana. The optimal composition of the digestion medium, period of digestion and stability of protoplast preparation were examined. A large number of protoplasts could be prepared within an hour. The isolated protoplasts were intact, stable and metabolically very active, as indicated by their high rates of photosynthetic oxygen evolution. The important factors during the preparation of protoplasts are short time of digestion, composition of medium, use of nylon nets for filtration, centrifugation at low speed and use of pH 7.0 for storage. The highest rate of photosynthesis obtained in these experiments was 130 AE 4 mmol O 2 evolved mg 21 Chl h 21 , at 1 mM sodium bicarbonate and at a light intensity of 600 mE m 22 s 21 . The present technique of isolation can be very useful for making Arabidopsis protoplasts for studies on not only metabolic processes, such as photosynthesis, but also metabolomics, proteomics and genomics.

Physiologia Plantarum, 2006

Mesophyll protoplasts of pea required only 74.1 mM CO 2 for maximal photosynthesis, unlike chloro... more Mesophyll protoplasts of pea required only 74.1 mM CO 2 for maximal photosynthesis, unlike chloroplasts, which required up to 588 mM CO 2 . Such a markedly low requirement for CO 2 could be because of an internal carbon source and/or a CO 2 concentrating mechanism in mesophyll protoplasts. Ethoxyzolamide (EZA), an inhibitor of internal carbonic anhydrase (CA) suppressed photosynthesis by mesophyll protoplasts at low CO 2 (7.41 mM) but had no significant effect at high CO 2 (741 mM). However, acetazolamide, another inhibitor of CA, did not exert as much dramatic effect as EZA. Three photorespiratory inhibitors, aminoacetonitrile or glycine hydroxamate (GHA) or aminooxyacetate inhibited markedly photosynthesis at low CO 2 but not at high CO 2 . Inhibitors of glycolysis or tricarboxylic acid cycle (NaF, sodium malonate) or phosphoenolpyruvate carboxylase (3,3-dichloro-2-dihydroxy phosphinoyl-methyl-2-propenoate) had no significant effect on photosynthesis. The CO 2 requirement of protoplast photosynthesis and the sensitivity of photosynthesis to EZA were much higher at low oxygen (65 nmol ml 21 ) than that at normal oxygen (212 nmol ml 21 ). In contrast, the inhibitory effect of photorespiratory inhibitors on protoplast photosynthesis was similar in both normal and low oxygen medium. The marked elevation of glycine/serine ratio at low O 2 or in presence of GHA confirmed the suppression of photorespiratory decarboxylation by GHA. While demonstrating interesting difference between the response of protoplasts and chloroplasts to CO 2 , we suggest that photorespiration could be a significant source of CO 2 for photosynthesis in mesophyll protoplasts at limiting CO 2 and at atmospheric levels of oxygen. Obviously, carbonic anhydrase is essential to concentrate or retain CO 2 in mesophyll cells.

Journal of Biosciences, 2011

<>Ascorbic acid mediates mitochondria-chloroplasts interactions <> The p... more <>Ascorbic acid mediates mitochondria-chloroplasts interactions <> The possible role of L-ascorbate (AsA) as a biochemical signal during the interactions between photosynthesis and respiration was examined in leaf discs of Arabidopsis thaliana. AsA content was either decreased as in AsA-deficient vtc1 mutants or increased by treatment with L-galactono-1, 4-lactone (L-GalL, a precursor of AsA; EC 1.3.2.3). In mutants, photosynthesis was extremely sensitive to both antimycin A (inhibitor of the cytochrome c oxidase pathway [COX pathway]) and salicylhydroxamic acid (SHAM, inhibitor of the alternative pathway [AOX pathway]), particularly at high light conditions. Mitochondrial inhibitors lowered the ratio of reduced AsA to total AsA, at high light, indicating oxidative stress in leaf discs. Elevation of AsA by L-GalL decreased the sensitivity of photosynthesis at high light to antimycin A or SHAM, sustained photosynthesis at supraoptimal light and relieved the extent of photoinhibition. High ratios of reduced AsA to total AsA in L-GalL-treated leaf discs suggests that L-GalL lowers oxidative stress. The protection by L-GalL of photosynthesis against the mitochondrial inhibitors and photoinhibition was quite pronounced in vtc1 mutants. Our results suggest that the levels and redox state of AsA modify the pattern of modulation of photosynthesis by mitochondrial metabolism. The extent of the AOX pathway as a percentage of the total respiration in Arabidopsis mesophyll protoplasts was much higher in vtc1 than in wild type. We suggest that the role of AsA becomes pronounced at high light and/or when the AOX pathway is inhibited. While acknowledging the importance of the COX pathway, we hypothesize that AsA and the AOX pathway may complement each other to protect photosynthesis against photoinhibition.

Salinity is one of the major environmental aspects, which affects on plant growth, development an... more Salinity is one of the major environmental aspects, which affects on plant growth, development and productivity of the agricultural crops worldwide. The aim of this study was to evaluate germination, initial growth parameters, antioxidant enzyme (CAT, APX and GR) activities and proline accumulation, Na + / K + content in seedlings of four onion cultivars Agrifound Rose, Bellary, Prema-178 and Nasik Red exposed to salt stress with different concentrations of NaCl (0, 50, 100, 150 and 200 mM). In all cultivars, morphological parameters and relative water content decreased with increasing NaCl concentrations, whereas antioxidant enzyme activities, proline accumulation and Na + / K + content increased. Bellary cultivar showed highest salt tolerance than the Agrifound Rose, Prema-178 and Nasik Red. Decrease in RWC was least in Bellary as compared to other cultivars. The results suggest that high NaCl concentrations have a negative effect on the physiological quality of onion seedlings, resulting in lower seedling growth rates and increased antioxidant enzyme activity and among four cultivars Bellary was found more tolerant to salt stress.

Indian journal of biochemistry & biophysics

Intact and metabolically very active mesophyll protoplasts were isolated rapidly from pea (Pisum ... more Intact and metabolically very active mesophyll protoplasts were isolated rapidly from pea (Pisum sativum) leaves. The functional performance of protoplasts at various stages of their isolation was analyzed by using fast Chl αfluorescence OJIP transients and compared with that of intact leaves. The results demonstrated that the OJIP transients could successfully be used to monitor the quality of mesophyll protoplasts at different isolation steps. The protoplasts maintained their integrity and photosynthetic status very well, and their performance was very similar to that of the intact leaves.

Photosynthesis. Energy from the Sun, 2008

ABSTRACT The biochemical basis of interactions between chloroplasts and mitochondria to optimize ... more ABSTRACT The biochemical basis of interactions between chloroplasts and mitochondria to optimize photosynthesis is examined using pea or Arabidopsis. Mesophyll protoplasts of pea required much less CO2 for maximal photosynthesis, than their chloroplasts. Such low requirement for CO2 could be due to an internal carbon source and/or a CO2 concentrating mechanism in mesophyll protoplasts. The suppression of protoplast photosynthesis by photorespiratory inhibitors (aminooxyacetate, AOA or glycine hydroxamate, GHA) indicated that photorespiration could be a significant source of CO2 for photosynthesis by mesophyll protoplasts at limiting CO2 and atmospheric oxygen. Photosynthesis in Asc-deficient vtc1 mutant of Arabidopsis decreased strongly at high light and was quite sensitive to SHAM. We suggest that recycling of photorespiratory CO2 and ascorbate can be additional factors involved in the beneficial interactions of mitochondria and chloroplasts.

Physiologia Plantarum, 2007

A simple and quick method is described for rapid isolation of metabolically active mesophyll prot... more A simple and quick method is described for rapid isolation of metabolically active mesophyll protoplasts from leaves of Arabidopsis thaliana. The optimal composition of the digestion medium, period of digestion and stability of protoplast preparation were examined. A large number of protoplasts could be prepared within an hour. The isolated protoplasts were intact, stable and metabolically very active, as indicated by their high rates of photosynthetic oxygen evolution. The important factors during the preparation of protoplasts are short time of digestion, composition of medium, use of nylon nets for filtration, centrifugation at low speed and use of pH 7.0 for storage. The highest rate of photosynthesis obtained in these experiments was 130 AE 4 mmol O 2 evolved mg 21 Chl h 21 , at 1 mM sodium bicarbonate and at a light intensity of 600 mE m 22 s 21 . The present technique of isolation can be very useful for making Arabidopsis protoplasts for studies on not only metabolic processes, such as photosynthesis, but also metabolomics, proteomics and genomics.

Physiologia Plantarum, 2006

Mesophyll protoplasts of pea required only 74.1 mM CO 2 for maximal photosynthesis, unlike chloro... more Mesophyll protoplasts of pea required only 74.1 mM CO 2 for maximal photosynthesis, unlike chloroplasts, which required up to 588 mM CO 2 . Such a markedly low requirement for CO 2 could be because of an internal carbon source and/or a CO 2 concentrating mechanism in mesophyll protoplasts. Ethoxyzolamide (EZA), an inhibitor of internal carbonic anhydrase (CA) suppressed photosynthesis by mesophyll protoplasts at low CO 2 (7.41 mM) but had no significant effect at high CO 2 (741 mM). However, acetazolamide, another inhibitor of CA, did not exert as much dramatic effect as EZA. Three photorespiratory inhibitors, aminoacetonitrile or glycine hydroxamate (GHA) or aminooxyacetate inhibited markedly photosynthesis at low CO 2 but not at high CO 2 . Inhibitors of glycolysis or tricarboxylic acid cycle (NaF, sodium malonate) or phosphoenolpyruvate carboxylase (3,3-dichloro-2-dihydroxy phosphinoyl-methyl-2-propenoate) had no significant effect on photosynthesis. The CO 2 requirement of protoplast photosynthesis and the sensitivity of photosynthesis to EZA were much higher at low oxygen (65 nmol ml 21 ) than that at normal oxygen (212 nmol ml 21 ). In contrast, the inhibitory effect of photorespiratory inhibitors on protoplast photosynthesis was similar in both normal and low oxygen medium. The marked elevation of glycine/serine ratio at low O 2 or in presence of GHA confirmed the suppression of photorespiratory decarboxylation by GHA. While demonstrating interesting difference between the response of protoplasts and chloroplasts to CO 2 , we suggest that photorespiration could be a significant source of CO 2 for photosynthesis in mesophyll protoplasts at limiting CO 2 and at atmospheric levels of oxygen. Obviously, carbonic anhydrase is essential to concentrate or retain CO 2 in mesophyll cells.

Journal of Biosciences, 2011

<>Ascorbic acid mediates mitochondria-chloroplasts interactions <> The p... more <>Ascorbic acid mediates mitochondria-chloroplasts interactions <> The possible role of L-ascorbate (AsA) as a biochemical signal during the interactions between photosynthesis and respiration was examined in leaf discs of Arabidopsis thaliana. AsA content was either decreased as in AsA-deficient vtc1 mutants or increased by treatment with L-galactono-1, 4-lactone (L-GalL, a precursor of AsA; EC 1.3.2.3). In mutants, photosynthesis was extremely sensitive to both antimycin A (inhibitor of the cytochrome c oxidase pathway [COX pathway]) and salicylhydroxamic acid (SHAM, inhibitor of the alternative pathway [AOX pathway]), particularly at high light conditions. Mitochondrial inhibitors lowered the ratio of reduced AsA to total AsA, at high light, indicating oxidative stress in leaf discs. Elevation of AsA by L-GalL decreased the sensitivity of photosynthesis at high light to antimycin A or SHAM, sustained photosynthesis at supraoptimal light and relieved the extent of photoinhibition. High ratios of reduced AsA to total AsA in L-GalL-treated leaf discs suggests that L-GalL lowers oxidative stress. The protection by L-GalL of photosynthesis against the mitochondrial inhibitors and photoinhibition was quite pronounced in vtc1 mutants. Our results suggest that the levels and redox state of AsA modify the pattern of modulation of photosynthesis by mitochondrial metabolism. The extent of the AOX pathway as a percentage of the total respiration in Arabidopsis mesophyll protoplasts was much higher in vtc1 than in wild type. We suggest that the role of AsA becomes pronounced at high light and/or when the AOX pathway is inhibited. While acknowledging the importance of the COX pathway, we hypothesize that AsA and the AOX pathway may complement each other to protect photosynthesis against photoinhibition.

Salinity is one of the major environmental aspects, which affects on plant growth, development an... more Salinity is one of the major environmental aspects, which affects on plant growth, development and productivity of the agricultural crops worldwide. The aim of this study was to evaluate germination, initial growth parameters, antioxidant enzyme (CAT, APX and GR) activities and proline accumulation, Na + / K + content in seedlings of four onion cultivars Agrifound Rose, Bellary, Prema-178 and Nasik Red exposed to salt stress with different concentrations of NaCl (0, 50, 100, 150 and 200 mM). In all cultivars, morphological parameters and relative water content decreased with increasing NaCl concentrations, whereas antioxidant enzyme activities, proline accumulation and Na + / K + content increased. Bellary cultivar showed highest salt tolerance than the Agrifound Rose, Prema-178 and Nasik Red. Decrease in RWC was least in Bellary as compared to other cultivars. The results suggest that high NaCl concentrations have a negative effect on the physiological quality of onion seedlings, resulting in lower seedling growth rates and increased antioxidant enzyme activity and among four cultivars Bellary was found more tolerant to salt stress.