Department of Plant Sciences

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    A screening of the dicotyledonous weed flora for the occurrence of C < inf > 4 < /inf > dicarboxylic acid pathway of photosynthesis
    ( 1973-03-01) Das, V. S.Rama ; Raghavendra, A. S.
    Using the criteria of leaf anatomy, carbon dioxide compensation point and photosynthetic rate under reduced oxygen tension, a number of the local herbaceous and dicotyledonous weeds were screened for the occurrence of the C4 pathway of photosynthesis. Of the thirty-two species, belonging to nine families seventeen species revealed the characteristics of the C4 plants. All of the plants surveyed here were hitherto not tested and therefore the present results extend the number of plants already known to possess the Hatch-Slack pathway of photosynthesis. Another noteworthy feature of the investigation was the finding of interspecific differences within the genera Heliotropium, Alternanthera, Mollugo and Euphorbia in the presence or absence of the C4 pathway. © 1973 Indian Academy of Sciences.
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    Malonate-inhibition of allosteric phosphoenolpyruvate carboxylase from Setaria italica
    ( 1975-09-02) Raghavendra, A. S. ; Das, V. S.R.
    Malonate inhibited phosphoenolpyruvate carboxylase activity in crude extracts of Setaria italica Beauv. and Pennisetum typhoides S & H leaves. Kinetic studies revealed the competetive inhibition of partially purified phosphoenolpyruvate carboxylase preparation from Setaria italica. Glucose-6-phosphate activated the enzyme. Oxalacetate also competetively inhibited the enzyme and malate in a noncompetetive manner. Results clearly indicated the allosteric nature of phosphoenolpyruvate carboxylase from Setaria italica. © 1975 Academic Press, Inc.
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    Characterisation of abscisic acid inhibition of stomatal opening in isolated epidermal strips
    ( 1976-01-01) Raghavendra, A. S. ; Rao, I. M. ; Das, V. S.R.
    Abscisic acid (ABA) inhibited the light-induced opening of stomata in isolated epidermal strips of Commelina benghalensis. It did not alter stomatal closure in the dark. The ABA-induced inhibition in light was released under conditions conducive for cyclic photophosphorylation and remarkably reversed by ATP in the presence of pyruvate. Cyclic photophosphorylation rates of isolated guard cell chloroplasts were significantly reduced by ABA. It is proposed that the direct effect of ABA on stomatal opening was mediated in two ways: (1) by inhibition of cyclic photophosphorylation activities of guard cell chloroplasts and (2) by blocking organic acid formation in guard cells. © 1976.
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    Adenosine triphosphatase in epidermal tissue of Commelina benghalensis: Possible involvement of isozymes in stomatal movement
    ( 1976-01-01) Raghavendra, A. S. ; Rao, I. M. ; Das, V. S.R.
    Lower epidermal extracts of Commelina benghalensis possessed high ATPase activity. The presence of two isoenzymes of ATPase was indicated by their pH response and their preferential activation by K+ or Ca2+. One of the two isozymes of ATPase was with an optimal pH of 5.5 (ATPase 5.5), activated by Ca2+ and the other with an optimal pH of 7.5 (ATPase 7.5) was stimulated by K+. The response of these two isozymes to various inhibitors was in close agreement with their effect on stomatal movement. Activity of ATPase 5.5 was maximal in night and minimal during the day. On the other hand ATPase 7.5 was active during the day and was at a low level at night. Thus the optimal pH, inhibitor response and their diurnal rhythm suggested the existence of two isozymes of ATPase in the lower epidermis: ATPase 7.5 associated with stomatal opening and ATPase 5.5 with stomatal closure. © 1976.
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    Suppression of the stomatal opening by morphactins in isolated epidermal strips
    ( 1976-01-01) Das, V. S.R. ; Rao, I. M. ; Swamy, P. M. ; Raghavendra, A. S.
    The effects of three morphactins, chlorflurenol, flurenol and EMD 7301 W, were examined on the stomatal aperture using isolated epidermal strips of Commelina benghalensis. Morphactins produced, a striking decrease in the stomatal opening in light but had no effect on stomatal closure in darkness. Various catalysts and inhibitors of photophosphorylation had no influence on the morphactin-induced stomatal closure. The stimulatory effects of ATP, pyruvate and KC1 on stomatal opening were suppressed by the morphactins. The cytokinin, benzyladenine stimulated the stomatal opening even in the presence of a morphactin. The influence of morphactins on the stomatal aperture closely resembled the effect of abscisic acid. © 1976 Oxford University Press.
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    Inhibition of chloroplast photochemical reactions with 2-chloromercuri 4,6-dinitrophenol
    ( 1976-01-01) Raghavendra, A. S. ; Das, V. S.R.
    2-Chloromercuri 4,6-dinitrophenol inhibited photosystem I mediated photochemical reactions of Euphorbia hirta chloroplasts. The compound inhibited cyclic photophosphorylation and NADP reduction (in the presence of dichlorophenol indophenol and ascorbate couple) at concentrations as low as 10-6 m. At higher concentrations (above 10-4 m), however, it affected all NADP reductions but still showed negligible effect on ferricyanide reduction or noncyclic photophosphorylation. The compound may be used as an inhibitor of cyclic photophosphorylation. © 1976.
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    DISTRIBUTION OF THE C < inf > 4 < /inf > DICARBOXYLIC ACID PATHWAY OF PHOTOSYNTHESIS IN LOCAL MONOCOTYLEDONOUS PLANTS AND ITS TAXONOMIC SIGNIFICANCE
    ( 1976-01-01) RAGHAVENDRA, A. S. ; DAS, V. S.R.
    The photosynthetic characteristics of fifty‐six monocotyledonous plants belonging to seventeen families were examined. As many as twenty‐three plants, hitherto unreported, showed C4 pathway characteristics. C4 species were recorded in ten new genera. The C4 plants were confined to the families, Cyperaceae and Gramineae. The findings confirm the highly evolved nature of the tribes Andropogoneae and Paniceae in contrast to the primitive features of Agrosteae and Festuceae. On the basis of photosynthetic characteristics, it is suggested that Aristida should be included in a separate tribe, Aristideae, whereas Eragrostis resembles more panicoid grasses rather than the members of Festuceae. The importance of the C4 syndrome in relation to the evolution of grasses is stressed. Copyright © 1976, Wiley Blackwell. All rights reserved
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    REVERSAL OF ABSCISIC ACID INDUCED STOMATAL CLOSURE BY BENZYL ADENINE
    ( 1976-01-01) DAS, V. S.R. ; RAO, I. M. ; RAGHAVENDRA, A. S.
    Benzyl adenine enhanced stomatal opening in isolated epidermal strips of Commelina benghalensis and Tridax procumbens. The stimulation was maximum at a concentration of 5 × 10‐5 M BA. But kinetin had no remarkable effect on stomatal opening. The activity of benzyl adenine was observed over a narrow range of concentrations, from 10‐5 M to 10‐4 M. The increase in stomatal aperture was more pronounced in Commelina than in Tridax. Presence of benzyl adenine in the medium prevented the stomatal closure expected from abscisic acid and could reverse considerably the stomatal closure induced earlier by abscisic acid. It is felt that the balance between abscisic acid and cytokinins can possibly control the stomatal aperture effectively. Copyright © 1976, Wiley Blackwell. All rights reserved
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    Phytochrome regulation of peroxidase activity in maize
    ( 1976-01-01) Sharma, Rameshwar ; Sopory, Sudhir K. ; Guha-Mukherjee, Sipra
    Phytochrome (Pfr) regulates peroxidase activity in maize in a manner characteristic of photomodulation. The increase in peroxidase activity under continuous far-red (FR) light is sensitive to puromycin but not to chloramphenicol and actinomycin D. Cycloheximide (CHI) enhanced the peroxidase activity, both in dark-grown and FR-irradiated seedlings. However, the kinetics of enhancement of peroxidase activity by continuous FR light and CHI is different. © 1976.
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    C < inf > 4 < /inf > photosynthesis and a unique type of Kranz anatomy in Glossocordia boswallaea (Asteraceae)
    ( 1976-07-01) Das, V. S.Rama ; Raghavendra, A. S.
    A special form of Kranz anatomy, a single chlorenchymatous bundle sheath around a central ground tissue embedding the vascular bundles, was observed to be associated with the C4 pathway of photosynthesis in Glossocordia boswallaea, a member of Asteraceae. The chloroplasts were centripetally located in the sheath cells. During short term carbon fixation, C4 acids, aspartate and malate were predominantly labelled. Radioactivity was transferred from aspartate to sugar phosphates, sucrose and starch via phosphoglyceric acid. Enzyme activities in the leaves revealed that the plant is an aspartate forming NAD malic enzyme type. The activities of both photosystems I and II were detected in mesophyll as well as the bundle sheath chloroplasts. The findings are discussed in relation to its tropical habitat. © 1976 Indian Academy of Sciences.
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    ASPARTATE‐DEPENDENT ALANINE PRODUCTION BY LEAF DISCS OF AMARANTHUS PANICULATUS, AN ASPARTATE UTILIZING NAD‐MALIC ENZYME TYPE C < inf > 4 < /inf > PLANT
    ( 1977-01-01) RAGHAVENDRA, A. S. ; DAS, V. S.R.
    Illuminated leaf discs of Amaranthus paniculatus formed alanine rapidly after infiltration with aspartate. a‐oxoglutarate and glutamate accelerated aspartate‐dependent alanine production. Alanine was also formed by A. paniculatus leaf discs infiltrated with oxalacetate; this production was stimulated only by glutamate. Our results confirm that alanine can be formed rapidly from aspartate in C4 plants. Aspartate‐dependent alanine production was stimulated greatly by light. The stimulatory effect of light could almost be replaced by ATP in presence of sodium ions. These findings are discussed in relation to a possible light‐dependent active transport of amino acids into the bundle sheath, mediated by Na+‐dependent ATPase activity. Copyright © 1977, Wiley Blackwell. All rights reserved
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    SHIFTS IN PHOTOSYNTHETIC CARBON LABELLING PATTERN BY ETIOLATED RICE (ORYZA SATIVA L.) SEEDLINGS DURING GREENING
    ( 1977-01-01) RAGHAVENDRA, A. S. ; DAS, V. S.R.
    The carbon assimilation pattern in light by dark‐grown rice Oryza sativa seedlings was studied during greening. After exposure of etiolated seedlings to light their capacity to synthesize the C4‐acids, malate and aspartate, increased for 12 h. The labelling of 3‐phospho‐glycerate, sugar phosphates, sucrose and insolubles, did not increase until after 12 h. Thereafter a continuous steep increase in synthesis of Calvin cycle intermediates, but not of C4‐acids, recurred. The levels of carboxylating enzymes (phosphoenolpyruvate and ribulose diphosphate carboxylases) in the seedlings correlated positively with the appearance of label in C4 acids and in Calvin cycle compounds. We suggest that a β‐carboxylation mechanism was activated immediately on illumination but was persistent for only 12 h. After an 8‐h lag period following illumination, the Calvin cycle began to operate and continued during further growth of seedlings in light. Copyright © 1977, Wiley Blackwell. All rights reserved
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    Antitranspirant activity of inhibitors of cyclic photophosphorylation
    ( 1977-04-01) Raghavendra, A. S. ; Das, V. S.R.
    The antitranspirant activity of three inhibitors of cyclic photophosphorylation (2,4-dinitro-phenol, 2-chloromercuri-4,6-dinitrophenol, and salicylaldoxime) on 6-week-old plants of Datura arborea was examined. The test compounds reduced transpiration and the effect persisted for 12 d. The dry matter production by the plants was not affected. The reduction in water loss was caused by stomatal closure. Inhibitors of cyclic photophosphorylation, by virtue of their prolonged action associated with a small effect on dry matter accumulation, may be useful as antitranspirants. © 1977 Oxford University Press.
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    Effects of light quality on photosynthetic carbon metabolism in C < inf > 4 < /inf > and C < inf > 3 < /inf > plants: Rapid movements of photosynthetic intermediates between mesophyll and bundle sheath cells
    ( 1977-10-01) Raghavendra, A. S. ; Das, V. S.R.
    The influence of varying light intensity and quality on the carbon labelling patterns in Rumex vesicarius (a C3 plant), Setaria italica (a malate-formingC4 plant), and Amaranthus paniculatus (an aspartate-forming C4 plant) was studied. In A. paniculatus and B. vesicarius blue light decreased the transfer of radioactivity to sugars and starch but in S. italica only slightly decreased radioactivity in sugar phosphates, sucrose, and insolubles. Negligible transfer was observed from the C4 acids to sugar phosphates, sucrose, and starch under dim blue-green and blue-yellow lights in S. italica and A. paniculatus. Blue light favoured the formation of malate, aspartate, and alanine in all three plants. The differential effect of blue and red light suggested a variation in the mechanisms of C4-photosynthesis in Setaria and Amaranthus.Leaves of S. italica and A. paniculatus were allowed to photosynthesize in 14CO2 for 5 s and then the distribution of the labelled products between the mesophyll and the bundle sheath cells was determined during subsequent photosynthesis in 12CO2. Malate and aspartate which appeared initially in the mesophyll layer moved rapidly into the bundle sheath cells. Phosphoglyceric acid originating in the bundle sheath moved swiftly to the mesophyll layer. Sugar phosphates were recovered from both the mesophyll and the bundle sheath cells. Most of the starch was found in the bundle sheath cells while sucrose and alanine were localized in the mesophyll cells. © 1977 Oxford University Press.
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    Mechanism of stomatal movement
    ( 1977-12-01) Das, V. S.R. ; Rao, I. M. ; Raghavendra, A. S.
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    Development of photochemical activities in mesophyll and bundle sheath chloroplasts of C < inf > 4 < /inf > and C < inf > 3 < /inf > plants during seedling growth
    ( 1978-01-01) Raghavendra, A. S. ; Das, V. S.R.
    The photochemical activities of mesophyll and bundle sheath chloroplasts from Setaria italica, a NADP malic enzyme type C4 plant, were examined during seedling growth and were compared with the pattern of mesophyll chloroplasts from Oryza sativa, a C3 plant. The sheath chloroplasts of S. italica possessed remarkable activities of photosystem (PS) II mediated reactions (non-cyclic photophosphorylation, ferricyanide and NADP reductions) at early stages. They lost much of their PS II but retained PS I activity (cyclic photophosphorylation, NADP reduction with dichlorophenol indophenol-ascorbate) during seedling growth. Mesophll chloroplasts of S. italica developed both PS I and PS II. However the mesophyll chloroplasts of both S. italica and O. sativa were similar in that PS I activity was greater in younger leaves while older leaves possessed more PS II. © 1978.