Soil organic carbon fractions as affected by land use in the Sourthern Guinea Savanna ecosystem of Adamawa State, Nigeria

Abstract

Although Cd 2+ is a more effective inducer of phytochelatin (PC) synthesis than Zn 2+ in higher plants, we have observed greater induction of PC synthesis by Zn 2+ than Cd 2+ in the marine green alga, Dunaliella tertiolecta. To elucidate this unique regulation of PC synthesis by Zn 2+ , we investigated the effects of Zn 2+ and Cd 2+ on the activities of both phytochelatin synthase (PC synthase) and enzymes in the GSH biosynthetic pathway. PC synthase was more strongly activated by Cd 2+ than by Zn 2+ , but the difference was not very big. On the other hand, γ-glutamylcysteine synthetase (γ-ECS) and glutathione synthetase (GS) were activated by both heavy metals, but their activities were higher in Zn-treated cells than in Cd-treated cells. Dose-dependent stimulation of intracellular reactive oxygen species (ROS) production was observed with Zn 2+ , but not Cd 2+ treatment. These results suggest that Zn 2+ strongly promotes the synthesis of GSH through indirect activation of γ-ECS and GS by stimulating ROS generation. This acceleration of the flux rate for GSH synthesis might mainly contribute to high level PC synthesis. © 2003 Elsevier Science Ltd. All rights reserved.