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    Phonons in disordered Si-Ge alloys
    ( 1973-01-01) Srivastava, Vipin ; Joshi, S. K.
    The coherent-potential approximation for phonons in disordered binary alloys has been used to interpret the observed Raman spectra of the substitutionally disordered Si-Ge alloys. The spectral density function is calculated for the q→=0 optical phonons. © 1973 The American Physical Society.
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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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    Cluster effects in disordered alloys
    ( 1973-12-01) Srivastava, V. ; Joshi, S. K.
    Cluster effects are dealt with self-consistently in disordered alloys within the multiple scattering framework. Pairs are handled explicitly. The results are also shown to be compatible with the findings of the diagrammatic analysis and the mean field approach.
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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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    Polarized Optical Absorption Studies on Copper and Silver Diethyldithiocarbamates
    ( 1976-11-01) Rajasekharan, M. V. ; Sethulakshmi, C. N. ; Mancharan, P. T. ; Gudel, Hans
    Polarized optical absorption measurements are reported for bis(N,N-diethyldithiocarbamato)copper(II) and -silver(II) diluted in the corresponding zinc complex. The measurements have been made at room, liquid nitrogen, and helium temperatures. The results for the copper complex are at variance with those reported earlier by Reddy and Srinivasan. The electronic transition energies are used in conjunction with the previously reported spin-Hamiltonian parameters to derive the molecular orbital coefficients for the two complexes. © 1976, American Chemical Society. All rights reserved.
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    Short range order in disordered alloys
    ( 1977-01-01) Srivastava, V. ; Kumar, D. ; Joshi, S. K.
    Effect of short range order on the electronic density of states and localization in disordered alloys has been studied. Self-consistent pair-calculations have been performed on disordered binary alloys possessing cubic structure and short range order has been introduced in the averaging procedure. Promising agreement has been found with the qualitative arguments given by Lifshitz. © 1977.
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    NEW NUMERICAL RESULTS FOR ANDERSON LOCALISATION.
    ( 1977-01-01) Weaire, D. ; Srivastava, V.
    Calculations of the average inverse participation ratio by the method of Weaire and Williams have produced a number of new results. These include a revision of the critical value of diagonal disorder in three dimensions, and the first numerical results for localisation in the presence of off-diagonal disorder, and for localisation in lattices of dimension d greater than 3.
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    Numerical results for Anderson localisation in the presence of off-diagonal disorder
    ( 1977-01-01) Weaire, D. ; Srivastava, V.
    Numerical calculations of the inverse participation ratio have been performed for the diamond cubic lattice with nearest neighbour interactions, and both diagonal and off-diagonal disorder. We confirm the prediction of Economou and Antoniou that off-diagonal disorder cannot, per se, produce an Anderson transition, although it reduces the amount of diagonal disorder necessary for the transition. In the presence of off-diagonal disorder alone we do not detect any substantial localisation even in the wings of the band. © 1977.
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    On a recent theory for localisation in random lattices
    ( 1977-01-01) Srivastava, Vipin ; Kumar, Deepak ; Joshi, S. K.
    An attempt has been reported which avoids an approximation used in a method proposed by Licciardello and Economou to study the problem of localisation in random lattices. Contrary to expectation, our improved approximation leads to physically unreasonable results for percolation concentration. © 1977.
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