Changes in non protein thiols, some antioxidant enzymes activity and ultrastructural alteration in radish plant (Raphanus sativus L.) grown under lead toxicity.

Abstract

Forty days old radish plants (Raphanus sativus L.) were exposed to different regimes of lead stress as Pb(NO3)2 at the following concentrations 0, 25, 50, 100, 150, 250 and 500 ppm. The possible generation of oxidative stress, antioxidant metabolism and changes in the chloroplast and cell membrane ultrastructure were investigated. Greater loss of the photosynthetic pigments (Chl. a, Chl. b and total carotenoids) were observed especially under 500 ppm lead (Pb). The accumulation of lead in roots and leaves of plant were measured and the results showed that lead accumulation increased with increasing of the metal treatment concentration. An increasing trend was observed in levels of ascorbate and decreasing trend in glutathione. Also, the antioxidant enzymes, viz., guaiacol peroxidase (GPX) ascorbate peroxidase (APX), catalase (CAT) and glutathione S-transferase (GST) showed significant variation with the increase in lead stress compared to control (untreated) plants. The rapid inducibility of some of these enzymes is useful early and sensitive indicators of heavy metal toxicity. Native polyacrylamide gel electrophoresis revealed an increase in the isoenzymes profile of CAT in both leaves and roots. While POD isoenzymes bands prominently increased in leaves and slightly decreased in roots at the higher Pb concentration in the growth media. The ultrastructural studies at selected concentrations; 100 and 500 ppm of Pb showed distortion of the structure and cell membranes in roots. Therefore, the changes in the levels of some antioxidants may play an important role against oxidative injury.