PHYSIOLOGICAL AND BIOCHEMICAL-STUDIES ON AN ACID-TOLERANT CHLORELLA-VULGARIS UNDER COPPER STRESS

This study compared the growth, photosynthesis, electron transport, AT P content, NO3- and NH4+ uptake, Na+ and K+ loss, nitrate reductase an d ATPase activities of an acid-tolerant strain and a wild-type strain of Chlorella vulgaris exposed to Cu at varied pHs (pH 6.8, 5.0, 4.0 an d 3.5). A general reduction in growth, NH4+ uptake, photosynthesis and nitrate reductase activity of both the strains was noticed at decreas ing pH. In contrast, the acid-tolerant strain depicted an increased NO 3- uptake, insignificant Na+, K+ loss and superactive ATPase at decrea sing pH. Both pH and Cu produced a non-competitive inhibition of NO3- uptake. An increase in V-max of ATPase of acid-tolerant Chlorella and inhibition of the V-max of its wild-type strain at decreasing pH was n oticed. Though the magnitude of Cu toxicity was significantly low in t olerant strain, a significant negative correlation (r=-0.99, p<0.01) o f Cu uptake with acid pH was noticed. The acid-tolerant Chlorella was less sensitive to Cu and physiologically more efficient than the wild type. Presence of a superactive ATPase and change in membrane permeabi lity are considered responsible for acid tolerance in Chlorella.