Glutathione counteracts the inhibitory effect induced by cadmium on photosynthetic process in soybean

In soybean seedlings, Cd2+ affected growth and inhibited photosynthesis. Bo th the length and fresh mass decreased more in roots than in shoots. Cd2+ s tress 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 con trol. A reduced activity of photosystem 2 by about 85% measured in Cd2+-tre ated chloroplasts was associated with a dramatic quenching of fluorescence emission intensity, with a band shift of 4 mm. A major suppression of absor ption was accompanied with shift in peaks in the visible region of the spec trum. In Cd2+-treated chloroplasts a selective decline in linolenic acid (1 8:3), the most unsaturated fatty acid of chloroplasts, paralleled with the ten fold enhancement in ethylene production. A three fold increase in perox idase activity was found in chloroplasts treated with Cd2+ compared to the control. Addition of 1 mM glutathione (GSH) counteracted all the retardatio n effects in soybean seedling growth induced by Cd2+. Thus GSH may control the Cd2+ growth inhibition as it detoxifies Cd2+ by reducing its concentrat ion in the cytoplasm and removing hydrogen peroxide generated in chloroplas ts.