Influence of Magnesium Deficiency on Induction of Activity of Antioxidative Enzymes and Increased Tolerance to Active Oxygen-Generating Herbicides in Cucumber and Kidney Bean Plants.

Abstract

The influence of a deficient (7μM) or sufficient (1000μM) supply of magnesium (Mg2+) on the content of Mg2+, chlorophyll and protein, and the activity of superoxide dismutase (SOD), ascorbate peroxidase (AP) and glutathione reductase (GR) were studied in cucumber (Cucumis sativus L.) and kidney bean (Phaseolus vulgaris L.) plants over an 11-day period. Tolerance of kidney bean to paraquat and oxyfluorfen dependent injury were also determined with intact primary leaves. Mg2+ content in the primary leaves of cucumber and kidney bean plants grown in nutrient solution with sufficient Mg2+ supply was increased, while that in the leaves of plants grown with insufficient Mg2+ was very low. Mg2+ deficiency caused more severe chlorosis and protein reduction in cucumber than in kidney bean. The activities of AP, GR and SOD of Mg2+-deficient cucumber leaves were greatly enhanced compared to those of Mg2+-sufficient leaves. In Mg2+-deficient kidney bean leaves, AP and SOD activities were enhanced, but GR activity was decreased. The results suggested that Mg2+ deficiency enhances the antioxidative enzymes in plants. Foliar application of paraquat and oxyfluorfen, active oxygen-generating herbicides, to kidney bean plants caused herbicidal damage. However, the chlorosis and water loss of kidney bean by the herbicides were much lower in Mg2+-deficient leaves than in Mg2+-sufficient ones. The data demonstrated that Mg2+-deficient kidney bean plants became highly tolerant to paraquat and oxyfluorfen injury.