Subcellular Localisation of Copper and Partial Isolation of Copper Proteins in Roots From Rice Plants Exposed to Excess Copper

Abstract

Rice (Oryza sativa L.) plants were grown over a 30 day period in nutrient solution containing concentrations of Cu varying from 0.002 to 6.25 mg/L. Electron microscopy of root tissues showed large amounts of electron-dense Cu-containing deposits inside the root cell vacuoles in concentrations higher than 0.05 mg/L. Cu-binding proteins, 30 and 8.5 kDa in size, were partially isolated from plants grown in Cu concentrations between 0.002 and 1.25 mg/L. Two additional Cu-binding protein peaks corresponding to sizes of 11 and 2 kDa were observed in the 6.25 mg/L Cu treatment. A positive correlation between Cu concentrations and both histidine and methionine was observed in all protein fractions. These amino acids decreased in the 30 kDa protein fractions and increased in the 8.5 kDa protein fractions, in parallel with increasing Cu concentrations. The existence of a specific subcellular localisation of Cu in rice is presented. Furthermore, Cu proteins in rice roots which appear to be related to Cu accumulation were partially isolated.