Department of Biological Sciences
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Item Impact of heavy metals on glutamine synthetase and nitrogenase activity in Nostoc calcicola.(J-Stage, 1987) Verma, Sanjay KumarItem Heavy metal Uptake in the Cynobacterium Nostoc calcicola.(IBS, 1988) Verma, Sanjay KumarThe literature on the inhibitory effect of copper on growth (Les &Walker, 1984), photosynthesis (Shiol et al, 1978) and nitrogen fixation (Rai & Raizada, 1985) in algae and higher plants is impressive. Heavy metals inhibit the uptake and assimilation of nutrients (Singh & Yadava, 1983, 1984). Mechanisms governing the metal uptake process in microorganisms (Bhattacharjee, 1986) and in cyanobacteria (Singh & Yadava, 1985) are investigated. The possibility of involvement of carrier (s) and energy in the metal transport across the cell membranes has been suggested (Veltrup, 1977). The toxicity of heavy metal to algae (Hargreaves & Whitton, 1976 a,b; Singh & were diluted to S hli with triple glass distilled water. A furher Pandey 1981) is influenced by environmental factors like pH, light and complexans. However, there have been only a few studies on the effect of environmental factors on copper uptake in cyanobacteria. The present investigation reports on the copper uptake kinetics and the role of various factors on Nostoc calcicola.Item Copper uptake by free and immobilized cyanobacterium(OUP, 1989) Verma, Sanjay KumarCopper uptake in free and immobilized cells of the cyanobacterium Nostoc calcicola has been examined. The immobilized cells invariably maintained a higher profile of Cu intake rate (12.7 nmol mg−1 protein min−1) over the free cells (6.0 nmol mg−1 protein min−1). The total Cu uptake in immobilized cells was almost two and a half-times more than their free cell counterpart under identical experimental conditions. Also, the immobilized cells showed a stronger positive correlation between Cu adsorption and uptake. The results have been discussed in terms of improved metabolic efficiency of immobilized cells.Item Factors regulating copper uptake in a cyanobacterium(Springer, 1990) Verma, Sanjay KumarCopper uptake in the diazotrophic cyanobacteriumNostoc calcicola was found to be typically biphasic, comprising rapid binding of the cations to the cell wall (during the first 10 min) followed by the subsequent metabolism-dependent intracellular uptake for at least 1 h, with a curvilinear kinetics saturating at 40 µM (Km 25.0 µM, Vmax 3.0 nmol Cu mg−1 protein min−1). The cellular Cu uptake was light- and ATP-dependent, and the addition of 3(3,4-dichlorophenyl)-1,1-dimethylurea or exogenous ATP proved that the energy to drive Cu transport was derived mainly through PS II reactions. The application of metabolic inhibitors and uncouplers like carbonylcyanidep-nitrofluoromethoxylphenyl hydrazone, N,N′-dicyclohexycarbodiimide, azide, and p-chloromercuribenzoate revealed that -SH group(s), proton gradient across the cell membrane, and ATP hydrolysis were involved in the transmembrane movement of Cu inN. calcicola. While monothiol (2-mercaptoethanol) caused a twofold reduction in Cu uptake rate, dithiol (dithiothreitol) contributed towards a further drop in the cation uptake rate.Item Genetic transformation of glutamine auxotrophy to prototrophy in the cyanobacterium Nostoc muscorum(Springer, 1990) Verma, Sanjay KumarItem Evidence for energy-dependent copper efflux as a mechanism of Cu2+ resistance in the cyanobacterium Nostoc calcicola(OUP, 1991) Verma, Sanjay KumarWild-type Nostoc calcicola carried out oxygenic photosynthesis extremely sensitive to copper. A Cu(2+)-resistant mutant (Cu-R1) of the cyanobacterium grew normally at high concentrations of Cu2+. Its ability to grow under such conditions was found to be due to mutational acquisition of an energy-dependent efficient system of Cu(2+)-efflux, which rendered Cu(2+)-inhibited oxygenic photosynthesis fully reversible.Item pH regulation of growth, photosynthesis, glutamine synthetase activity and micronutrient transport in the cyanobacterium Hapalosiphon welwitschii(OUP, 1992) Verma, Sanjay KumarOptima for growth, oxygenic photosynthesis and glutamine synthetase activity occurred at pH 10, thus suggesting that the cyanobacterium Hapalosiphon welwitschii is an alkalophile. It produced a Cu-Zn efflux system at pH 9 or 10, but not at pH 7 or 8, to relieve photosynthesis from Cu or Zn inhibition. This finding has a bearing on the ecophysiological competence of the cyanobacterium under natural conditions.Item Glutamate inhibition of aerobic N2-fixation and its regulation by nitrate and ammonium in cyanobacterium Nostoc muscorum(NISCAIR, 1992) Verma, Sanjay KumarItem Inhibition of mitochondrial electron transport is the prime cause behind proline accumulation during mineral deficiency in Oryza sativa(Springer, 1993) Bhagavatula, VaniThe concentration of proline in shoots of rice (Oryza sativa) seedlings raised in distilled water was about 3.3 times higher than in the seedlings raised in modified B5 medium. The shoots of seedlings raised in B5 medium which was depleted of calcium, iron, magnesium or potassium had a higher concentration of proline than those grown in standard B5 medium. The shoots of seedlings raised in distilled water with iron had a lower level of proline than those in distilled water. These results suggest that iron deficiency leads to high proline accumulation.Item Copper toxicity and phosphate utilization in the cyanobacterium Nostoc calcicola(Springer, 1993) Verma, Sanjay KumarItem Multiple metal resistance in the cyanobacterium Nostoc muscorum(Springer, 1995) Verma, Sanjay KumarItem Effect of short-term heat treatment of rice seedlings on sensitivity of thylakoid membranes to photoinhibition(Springer, 1996) Bhagavatula, VaniThe after-effects of 24 h high temperature (35 or 45 ~ treatment on the photochemical activities and photooxidative lipid peroxidation, subsequent to their irradiation were studied in 7-d-old etiolated rice (Oryza sativa) seedlings. Photosystem (PS) 1 and PS 2 mediated photoreactions of thylakoids isolated from the seedlings exposed to high temperature did not differ significantly from the thylakoids isolated from control seedlings (25 ~ Hence, all kinds of tested thylakoids were equally efficient in capturing and utilizing radiant energy. The high irradiance induced loss in PS 2 activity and lipid peroxidation measured in terms of malondialdehyde production was more rapid in thylakoids isolated from stressed seedlings as compared to that of control seedlings. Thus the thylakoids isolated from the stressed seedlings were more prone to photodamage than those from the control seedlings.Item Alteration in NAD+/NADH ratio regulates salt stress induced proline accumulation in Vigna radiata.(NAS, 1996) Bhagavatula, VaniFive-day-old vigna radiata seedlings exposed to NaCI stress induced a significant enhancement in proline levels accompanied by reduction in growthItem Effect of elevated temperature on natural killer cell and antibody-dependent cellular eytoboxieity(HALOCYNTHIA ASSOCIATION, 1998) Dubey, Uma S.Several studies have shown a direct correlation between temperature and immune response. The effect of elevated temperature on cytotoxic effector functions is not well known. In the present study we have investigated the effect of elevated temperatures (38.5 and 40 °C) on cytotoxicity of lymphokine-activated killer cells (LAK), monocyte cytotoxicity, cytotoxic T lymphocytes (CTL) and tumor necrosis factor (TNF)-mediated cytotoxicity, and compared them with results at 37°C. LAK cell cytotoxicity was inhibited significantly at 40°C (p < 0.01) and there was no marked difference at 38.5°C (p = 0.17) as compared to 37 °C when natural killer (NK)-sensitive K562 cells were used as target. When NK-resistant Raji cells were used as a target, cytotoxicity was inhibited at 40°C (p = 0.33). Monocyte cytotoxicity was enhanced at 40°C (p= 0.19) as well as at 38.5°C (p = 0.38) as compared to 37°C but differencesItem Structure-function correlation during the etioplast-chloroplast transition in cucumber cotyledonary leaves(IJPR, 1998) Bhagavatula, VaniWe studied the development of chloroplasts from etioplasts in the cotyledonary leaves of 4-d-old dark-grown cucumber (Cucumis sativus) seedlings after irradiation (20 μmol m-2 s-1). Upon irradiation, the triggering of chlorophyll (Chl) synthesis and accumulation showed a relatively short lag phase. The irradiation of etiolated seedlings initiated the synthesis of apoproteins of pigment-protein complexes. While Chl-protein 2 (CP2) was detected at 6 h after irradiation, CP1 only after 29 h. The appearance and accumulation of some of the apoproteins were monitored by Western-blotting. LHC2 apoprotein was detected after a 6 h-irradiation. The amounts of D1 protein of photosystem (PS) 2 and PsaA/B protein of PS1 were quantitated by ELISA. Further, the thylakoid membrane function during this time period in terms of PS1- and PS2-mediated electron transfer activity and intersystem electron pool size were analyzed. While PS1 activity was detected after 4 h, PS2-mediated O2 evolution was detected only after a 17 h-irradiation. Fv/Fm value of Chl a fluorescence measurements indicated that the photochemical efficiency of these leaves reached its maximum after 29 h of irradiation. The intersystem pool size of cotyledonary leaves was equivalent to that of the control cotyledonary leaves grown for 25 h under continuous irradiation. Thus etioplasts develop into fully functional chloroplasts after approximately 25 h when 4 d-dark grown cucumber seedlings are continuously moderately irradiated. The development of photosynthetic electron transport chain seems to be limited in time at the level of PS2, possibly at the donor side.Item Heat stress on rice leaves probed by the fluorescence transient OKJIP.(Springer, 1999) Bhagavatula, VaniItem Exploring the Structural Repertoire of Guanine-Rich DNA Sequences: Computer Modelling Studies(Elsiever, 1999) Chowdhury, ShibasishItem Molecular Databases(EMI, 2001) Verma, Sanjay KumarItem Alteration in chloroplast structure and thylakoid membrane composition due to in vivo heat treatment of rice seedlings: correlation with the functional changes(Elsiever, 2001) Bhagavatula, VaniExposure of 25 °C-grown, seven-day-old rice seedlings to mild heat stress of 40 °C for 24 h in dark did not cause any change in protein or pigment content of the thylakoids, but produced major disorganization of chloroplast ultrastructure. This heat induced disorganization of thylakoid structure/organization caused significant (∼65 percnt;) loss in PSII activity, slight loss in PSI activity, and brought about a decrease in relative quantum efficiency of PSII. The herbicide 14C atrazine binding assay revealed a decreased number of binding sites of the herbicide and altered the herbicide dissociation constant, suggesting that the heat induced disorganization of the thylakoids affects the acceptor side of PSII. Cation induced Chla fluorescence analyses at room temperature and low temperature indicated thatin vivo heat exposure of rice seedlings altered the extent of energy transfer in favor of PSI