In the present study we have investigated that 4.0gL -1 NaNO 3 concentration is toxic to the growth of wild type Spirulina platensis and its Li + R and Na + R mutant strains. Highest level of extracellular nitrite release was shown by Na + R strain, when grown in 4.0gL -1 NaNO 3 concentration followed by Li + R and wild type strain of S. platensis whereas Li + R strain uptake nitrate more rapidly followed by Na + R and wild type strain of S. platensis, when estimated after 8d of incubation.

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... ures assimilate nitrate more rapidly in light than in darkness which suggests that nitrate uptake process depend on photosynthetically generated light energy. The nitrate uptake pattern consisted of two distinct phase : initial rapid phase followed by the slower second phase. There is no lag in the initial uptake of nitrate in either of the culture suggesting that rapid phase is not dependent on reduction of nitrate whereas slower phase seemed to be dependent on metabolism. Among these three strains of S. platensis Li + R strain assimilate nitrate more rapidly and fix it into ammonia by sequential action of nitrate reductase and nitrite reductase.