Physiological and biochemical responses in the leaves of two mangrove plant seedlings ( Kandelia candel and Bruguiera gymnorrhiza) exposed to multiple heavy metals

Abstract

The accumulation of heavy metals and their effect on photosynthetic pigments, proline, glutathione (GSH) and phytochelatins (PCs-SH) were studied in the leaves of two mangrove plants seedlings ( Kandelia candel and Bruguiera gymnorrhiza) grown for 30 days in the nutrient solution containing four different concentrations of Cd 2+, Pb 2+ and Hg 2+ ( T 1, T 2, T 3 and T 4). An increase in Cd, Pb and Hg content was found in the leaves of both species exposed to multiple heavy metal stress, whereas higher heavy metal levels (> T 1) led to a remarkable breakdown of chlorophyll in the leaves of both species. The content of proline, GSH and PCs-SH in the leaves of both species exhibited a significant increase in response to heavy metal stress, at least under most of experimental conditions. Increased contents of proline, GSH and PCs-SH in metal-treated plants suggest that metal tolerance in both K. candel and B. gymnorrhiza might be associated to the efficiency of these antioxidants. Moreover, proline, GSH and PCs-SH in K. candel may play more important role in ameliorating the effect of heavy metal toxicity than those in B. gymnorrhiza.