PHYTOCHELATINS AND GLUCOSINOLATES ACCUMULATION IN SEEDLINGS OF BRASSICA-NAPUS TREATED WITH CADMIUM CHLORIDE

Thirty days old seedlings of Brassica napus var. oleifera were submitt ed to short term treatments with CdCl2 in order to investigate the eff ect of this heavy metal on sulfur channelling for both phytochelatins (PC) and glucosinolates (GLS) synthesis and accumulation. PC peptides, from the roots, containing 2 to 5 gamma-glutamyl-cysteinyl units were characterized and their individual content determined in relation to both treatment durations and CdCl2 concentrations. PC synthesis was de tectable 1 hour after the onset of the treatment, being then maintaine d at a constant rate until reaching a level related to CdCl, concentra tion in the external medium. A maximum PC level of 1.28 mumol SH g fre sh weight-1 was obtained after a 48 h treatment with 150 muM CdCl2. Th e relative levels of various PCs remained constant except for low conc entrations (below 10 muM) and in treatments shorter than 15 h. In thes e cases, the relative abundance of PC2 and PC3 are increased. PC accum ulation in rapeseed was prevented when CdCl2 and buthionine sulfoximin e were applied together. This inhibitory effect was abolished with the glutathione addition. Thus, it is concluded that the processes involv ed in PC synthesis and accumulation by rapeseed roots are quite simila r to that occurring in a number of other species. Preliminary results obtained for GLS stored in vegetative parts of young rape plants treat ed with CdCl2 suggest that sulfur consumption for PC synthesis did not occur at the expense of the sulfur available for GLS synthesis since the effects induced by Cd were not significant.