• V N R Rao

      Articles written in Proceedings – Plant Sciences

    • Studies onCyclotella meneghiniana kütz. IV. Progressive diminution in cell size

      V N R Rao

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      Cyclotella meneghiniana, when grown under different salinity regimes, shows varying rates of size reduction which is directly proportional to the salinity of the medium and is always greater for large than for small cells. The differential flexibility of the girdle band is responsible for differences in size reduction. Cells of dia 7·5–3·0μ are elongated on the pervalvar axis. The elongation is maximum in Reimann medium and decreased with increasing salinities and is brought about by the formation of new intercalary bandsC. meneghiniana maintains an internal osmotic pressure in excess of the surrounding medium and this ability helps in its survival in an environment of fluctuating salinities.

    • Effect of some antialgal chemicals on growth ofStigeoclonium tenue Kütz. in laboratory cultures

      V N R Rao P Jerome Manohar

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      Stigeoclonium tenue Kütz., a chief inhabitant of metal polluted waters, was studied in culture to understand its tolerance towards certain metals such as copper, manganese, mercury, silver and zinc. This study was carried out also with two other chemicals DDT and CaOCl2. The alga was inhibited by very low concentrations of HgCl2, AgNO3 and DDT while it tolerated high levels of other metals and CaOCl2.

    • Relative concentrations of Na, Ca and Mg for growth of some diatoms

      V N R Rao V Kannan A Duraisamy

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      The two types of waters, i.e., freshwater and seawater differ in their total solids (salinity), ratio of monovalent to divalent cations, the amount of the predominant cations or anions, and the Ca/Mg ratio. The growth behaviour of four diatoms isolated from these habitats was studied in different concentrations of Na, Ca and Mg which were varied taking into account the salient features of both water types. Results indicate that the growth response of these diatoms show little relationship to the composition of either fresh or seawater. It is evident that the ecological category of a species cannot be determined merely on the basis of presence or absence of its growth in certain concentrations and ratios of major ions.

    • Uptake and assimilation of nitrogen by marine diatoms—I. Kinetics of nitrogen uptake

      V Sivasubramanian V N R Rao

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      Axenic cultures of marine diatoms,Achnanthes hauckiana Grun.,Amphora coffeaeformis (Agardh) Kütz.,Fragilaria pinnata Ehr.,Synedra tabulata (Agardh) Kütz.,Thalassiosira weissflogii (Grun.) Fryxell et Hasle (=Thalassiosira fluviatilis Hustedt) andTriceratium dubium Brightwell isolated from tropical waters were used for a comparative study of kinetics of NO3, NO2 and NH4+ uptake. Nitrogen uptake by diatoms in this study followed the classical kinetics reported by previous workers. Diatoms which showed highK3 for NO3 uptake had highK3 for NH4+ and NO2 uptake. But no correlation could be obtained between cell size andK3 for nutrient uptake and an inverse relationship between specific growth rate andK3 was also not obtained. However, there was good correlation between the observedK3 and nutrient status of the habitats from which the diatoms were isolated. Studies on the interactions between NO3, NO2 and NH4+ revealed that NH4+ inhibited both NO2 and NO3 uptake non-competitively whereas NO3 of NO2 inhibited each other in a competitive manner. Inhibition by NO3 of NO2 uptake was greater than the reverse situation.

    • Uptake and assimilation of nitrogen by marine diatoms—II. Kinetics of nitrogen assimilation

      V Sivasubramanian V N R Rao

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      A comparison ofKM values for nitrate and nitrite reductases with uptake capacities of 6 marine diatoms indicated that intracellular accumulation of NO3 and NO2 is necessary for efficient functioning of the enzymes.Amphora coffeaeformis, Thalassiosira weissflogii andSynedra tabulata accumulated very little NO3 whereasTriceratium dubium, Achnanthes hauckiana andFragilaria pinnata accumulated 0·02 to 1· 5mM NO2. Studies with inhibitors of nitrate and nitrite reductase indicated that nitrite reductase could be located i in a different compartment such as chromatophores as in higher plants. NH4+ was also accumulated by the diatoms. Studies on the kinetics of glutamine synthetase and glutamate dehydrogenase indicated that the primary enzyme involved in NH4+ assimilation could be glutamate dehydrogenase, because of its lowKMNH4+ and relatively greater activity than glutamine synthetase. Intracellular analysis of NH4+ revealed that its concentration was well below theKMNH4+ for glutamine synthetase.


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