Cadmium induces senescence symptoms in leaf peroxisomes of pea plants

The effect of growing pea (Pisum sativum L.) plants with a toxic CdCl2 conc entration (50 muM) on the metabolism and proteolytic activity of leaf perox isomes was studied : In peroxisomes purified from plants treated with cadmi um, an increase in the total protein concentration and in the activity and protein level of the photorespiratory enzyme glycolate oxidase was found. T he glyoxylate cycle enzymes, malate synthase and isocitrate lyase, whose ac tivity is normally very low in leaf peroxisomes, were enhanced by Cd treatm ent. The activity of the endogenous proteases of leaf peroxisomes was deter mined. Two leucine-aminopeptidase isozymes (AP1-AP2) were detected, and the ir activity was slightly higher in Cd-treated plants. Five endopeptidases ( EP1-EP5) were present in pea leaf peroxisomes, and in plants grown with Cd the activity of isozymes EP1-EP4 was increased. The ultrastructural analysi s of pea leaves showed that Cd produced a disorganization of the chloroplas t structure, with an increase in the number of plastoglobuli, and the forma tion of vesicles in the vacuoles. Taken together, these results indicate th at Cd induces senescence symptoms in leaf peroxisomes, and probably a metab olic transition of leaf peroxisomes into glyoxysomes, and suggest that the peroxisomal proteases could participate in the metabolic changes produced b y Cd.