Cadmium-induced Ethylene Production in Bean Plants

Abstract

Studies were conducted to (1) compare stress ethylene production from roots and shoots; (2) determine the association between stress ethylene production and tissue Cd levels; and (3) investigate the time course of stress ethylene production following the rhizosphere application of cadmium chloride solutions. The shoots and/or roots of bush bean plants (Phaseolus vulgaris L. cv. Bush Blue Lake 290) were encapsulated at specific time intervals following CdCl2-application and kept in the dark for 2 h prior to determining ethylene production. Cadmium accumulated more in the roots than in the shoots and ethylene production was likewise higher in the roots. Cadmium chloride (10 mM)-induced stress ethylene production increased rapidly, peaked within 5 to 10 h and declined to 0 h levels within 24 h after treatment. A subsequent application of 10 mM CdCl2 at 24 h elicited a similar ethylene response, indicating that the plants retained functional ethylene metabolism. Consecutive, daily applications (12 days) of CdCl2 (0.1 or 0.5 mM) induced only small increases in ethylene production. In all studies, however, tissues accumulated large amounts of Cd. Significant increases in ethylene production after a single CdCl2 application were associated with Cd concentrations of ≧ 6 μ-gg-1 dry shoot tissue. The association between stress ethylene production and tissue Cd levels was lost as stress ethylene production declined and also in the consecutive application study. The decline in stress ethylene production was attributed to Cd-sequestering which removed the Cd stress.