Influence of Cadmium on Growth and Nitrogen Metabolism ofAnabaena cylindricaLemm

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Abstract
A study was made of the effects of cadmium on the Cyanobacterium (blue-green alga) Anabaena cylindrica Lemm. as part of the paddy-field ecosystem. A simple culture vessel has been designed, which allows periodical measurement of growth (optical density) and nitrogenase activity (C2H2-C2H4 method). The influence of medium renewal was checked: the renewal of the medium maintained a higher growth rate and higher nitrogen fixation ability. The cadmium effects were studied using six concentration levels ranging from 0 (control) to 2 parts 10−6 with renewed media (10% every day). No significant differences could be seen up to 1 part 10−6 for nitrogenase activity and relative percentage of heterocysts (decreasing as a function of time from ±4% to ±1.5%). Inhibition of growth (OD and dry weight) was weak at 1 part 10−6 but important at 2 parts 10−6; at this concentration cadmium induced morphological and physiological effects: chlorosis, cellular malformations and destruction, and increase in heterocyst frequency (up to 7.72% ±0.19). The cadmium concentration factors were much lower than those reported for other plants like Chlorella and water pests