Responses of Castor Bean (Ricinus communis L.) to Lead Stress

Abstract

Castor bean (Ricinus communis L.) plantlets were exposed to lead to study the detoxification mechanism. The results showed that castor bean could survive in soils spiked with 800 mg/kg dry weight Pb for 30 days and grew normally without suffering phytotoxicity. Lead is accumulated mostly in the roots while a small quantity is translocated to the leaves. Changes were detected in both pattern and intensity of Ascorbate peroxidase isoenzyme, while, in case of Guiacol peroxidase, Superoxide dismutase and Glutathione reductase isoenzyme changes were detected only in the intensity. The band intensity of all the isoenzymes increased with the increase of extraneous lead. Increased amount of Malondialdehyde was indicative of lipid peroxidation and free radical generation under lead stress while increased level of proline pointed to the occurrence of mechanism of scavenging free radicals. A decline in chlorophyll content was observed under lead stress. In contrast, carotenoid content was increased in the treated plants. Semi-quantitative reverse transcriptase-PCR was performed to study the expression of an ATP binding casette transporter under lead stress. The expression of the ATP binding casette transporter was recorded only in roots and not in the leaves. The expression was maximum in 800 mg/kg dry weight lead treated plants. These results show that R. communis has a high tolerance and low avoidance to lead.