Cadmium Toxicity in Leaf Peroxisomes from Pea Plants: Effect on the Activated Oxygen Metabolism Protrelytic Activity

Abstract

In this work the effect of growing pea (Pisum sativum L.) plants with a toxic CdC1₂ concentration on the activated oxygen metabolism of leaf peroxisomes was studied. Pea plants were grown in the greenhouse under optimum conditions for 14 days, and then media were supplemented with 50 µM CdC1₂ and grown for 21 days. Peroxisomes were purified from pea leaves and in the peroxisomal fractions from control and Cd-treated plants the activity of endogenous proteases and different enzymes of the activated oxygen metabolism was determined. The H₂O₂ content of leaf peroxisomes increased in plants grown with Cd. Likewise, the proteolytic activity of peroxisomes (aminopeptidase and endopeptidase activity) was enhanced in Cd-treated plants. The increased activity in response to Cd of some enzymes of the ascorbateglutathione cycle (ascorbate peroxidase and glutathione reductase) as well as three NADP-dehydrogenases (glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and isocitrate dehydrogenase), suggests that these peroxisomal enzymatic systems could be important in the defence of cells against Cd-derived oxidative stress. The increased activity of the glyoxylate cycle enzymes, malate synthase and isocitrate lyase, and proteases, indicate that Cd induces senescence symptoms in leaf peroxisomes. The antioxidative enzymes of peroxisomes appear to be a good choice to design molecular strategies directed to improve the tolerance of plants to heavy-metals.