Response and the detoxification strategies of green alga Acutodesmus obliquus (Chlorophyceae) under lead stress

The responses of Acutodesmus obliquus (Chlorophyceae) cells to the presence of lead (Pb2+) at the range of concentrations 0.01-500 μM during 7 days of culture were studied. The growth rate was clearly reduced and the changes in the level of low molecular weight metabolites, particularly involved in heavy metal chelation and glutathione synthesis pathway under Pb2+ stress, were observed. External metal induced the accumulation of phytochelatins (PC) precursors (cysteine, glutathione) and stimulated the activity of phytochelatins synthase leading directly to enhanced production of PC2-5 responsible for binding and detoxification of Pb2+. The enhancement of xanthophyll cycle indicates its significant role in algal adaptation to adverse environmental conditions. Another defense mechanisms against metal stress is the disturbances in hormonal homeostasis, as indicated by the increase in the level of abscisic acid with simultaneous decreases in the contents of indole-3-acetic acid and trans-zeatin, representatives of auxins and cytokinins, respectively. Results suggest that the green alga A. obliquus has evolved a complex network to maintain toxic concentrations of Pb2+ within physiological limits and to minimize the harmful effects of this nonessential metal.