Abstract
In soybean seedlings, Cd2+ affected growth and inhibited photosynthesis. Both the length and fresh mass decreased more in roots than in shoots. Cd2+ stress caused an increase in ratio of chlorophyll (Chl) (a+b)/b by 1.3 fold and ratio of total xanthophylls/beta-carotene by 3 fold compared to the control. A reduced activity of photosystem 2 by about 85% measured in Cd2+-treated chloroplasts was associated with a dramatic quenching of fluorescence emission intensity, with a band shift of 4 mm. A major suppression of absorption was accompanied with shift in peaks in the visible region of the spectrum. In Cd2+-treated chloroplasts a selective decline in linolenic acid (18:3), the most unsaturated fatty acid of chloroplasts, paralleled with the ten fold enhancement in ethylene production. A three fold increase in peroxidase activity was found in chloroplasts treated with Cd2+ compared to the control. Addition of 1 mM glutathione (GSH) counteracted all the retardation effects in soybean seedling growth induced by Cd2+. Thus GSH may control the Cd2+ growth inhibition as it detoxifies Cd2+ by reducing its concentration in the cytoplasm and removing hydrogen peroxide generated in chloroplasts.