CADMIUM-INDUCED PROTEIN-PHOSPHORYLATION CHANGES IN RICE (ORYZA-SATIVAL) SEEDLINGS

The effect of cadmium on protein phosphorylation in Oryza sativa L. (r ice) was studied. Cd-treatment induced several proteins in rice. One o f the Cd-inducible proteins (70 kDa) was identified as hsc70 (hsp70 co gnate). Two major changes were observed in protein phosphorylation upo n Cd-treatment. A 68-kDa protein (p68) was specifically phosphorylated in Cd-treated rice. p68 was also phosphorylated when Cd was added in vitro (to kinase assay). Cd-induced phosphorylation of p68 was observe d in two Indian cultivars of rice (viz. hamsa and akashi). It was not observed in maize (Zea mays L.) or Acacia auriculiformis callus and se ems to be specific to rice. Cd-treatment increased hsc70 synthesis, wh ich is also a phosphoprotein. Despite an increase in its amount, its l evel of phosphorylation was decreased in Cd-treated rice. Phosphoamino -acid analysis showed that tyrosine phosphorylation was inhibited in C d-induced hsc70. These changes in hsc70 phosphorylation may have a rol e in its function.