Abstract
Stimulation and inhibition of photosynthesis inHydrilla verticillata Presl. with quinine sulphate and quinine alkaloid with concentrations ranging between 0·001 and 100 ppm was observed. Quantitative measurements of photosynthesis were done by a microburette (Audus 1940) and qualitative estimations by the modified apparatus byZutshi (1965a). Maximum inhibition of 50% and 34% is obtained with 100 ppm of quinine sulphate and quinine alkaloid respectively. The inhibition is due to the adverse effect on the pigment system particularly on carotene (Zutshi 1963). Forty percent stimulation of photosynthesis is obtained with 0·01 ppm quinine sulphate and 12·5% with 0·001 ppm quinine alkaloid. Difference in the biological activity of these two alkaloids is due to their different chemical structure and purity.
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