CADMIUM SUPPRESSES PHOSPHATE LEVEL AND INHIBITS THE ACTIVITY OF PHOSPHATASES IN GROWING RICE SEEDLINGS

The effect of increasing concentration of Cd in situ on the metabolic status of total phosphate and the activity of its metabolizing enzymes acid phosphatase, alkaline phosphatase and inorganic pyrophosphatases were examined in growing rice (Oryza sativa L.) seedlings. Some 500 m u M Cd in the medium caused 68-77% decline in phosphate content in sho ots and 56-66% decline in roots in 20-day-old seedlings of the two ric e cultivars Ratna and Jaya. In situ Cd levels of 100 mu M and 500 mu M led to a significant decline in the activities of the three phosphoro lytic enzymes studied. Inhibition in the acid phosphatase activity was greater in roots than in shoots. With 500 mu M Cd 62-88% inhibition i n acid phosphatase activity was observed in roots. A similar Cd level caused 28-31% inhibition in shoots in 20-day-old seedlings, whereas in organic pyrophosphatase activity was inhibited by 27-53% in roots and nearly 50% in shoots. Under in vitro conditions more than 200 mu M Cd( NO3)(2) in the reaction medium significantly inhibited the activities of the phosphorolytic enzymes. Alkaline phosphatase appeared to be mor e tolerant than acid phosphatase at lower (20-100 mu M) concentrations whereas the activity of inorganic pyrophosphatase was completely lost with 2 mM Cd. Isoenzymic studies revealed three acid phosphatase isoe nzymes with R-F values of 0.18, 0.24 and 0.40 in both roots and shoots . The band intensities decreased under Cd treatments. The results indi cate suppression of the activities of phosphatases due to Cd in growin g seedlings.