Role of rice shoot vacuoles in copper toxicity regulation

Rice (Oryza sativa L. cv. Safari) plants were grown over a 30-day period in nutrient solutions containing 0.002-1.25 mg l(-1) Cu concentrations. It was found that increasing Cu concentrations led to increasing Cu contents in the plant's shoot and to an inhibition of its growth. Transmission electron microscopy showed no obvious ultrastructural changes in the shoot tissues, except for electron-dense deposits adherent to the tonoplast, appearing from the 0.25 mg l(-1) Cu treatment onwards. On a protein basis, Cu and SH groups concentrations in isolated shoot vacuoles increased by 41% and 120%, respectively, from the 0.01 to the 1.25 mg l(-1) Cu treatments. In spite of increased vacuolar Cu contents, the activities of NADH-cytochrome c reductase and acid phosphatase were not inhibited, apparently because of metal binding to sulphydryl groups contained in the vacuole. (C) 1998 Published by Elsevier Science B.V. All rights reserved.