Copper stress affects grain filling in rice

Rice (Oryza sativa L.) cv. Jaya was grown in refined sand at graded levels of copper (Cu) viz. 0.00065, 0.0065, 0.013, 0.065, 0.13, 0.65, and 6.5 mg L -1 In acute Cu deficiency (0.0065, 0.00065 mg L-1), the visible foliar symp toms appeared on young leaves as chlorosis changing to necrosis, later affe cted leaves appeared papery and withered. The biomass and grain yield were highest at 0.065 mg L-1 and compared to this, the decrease in both paramete rs was significant at low and high Cu supply. The concentration of Cu in gr ains increased from 0.4 in acute deficiency to 47.4 ppm at excess Cu. In ri ce leaves, concentration of sugars and activities of polyphenol oxidase and ascorbic acid oxidase were decreased both by low and excess Cu. Both low a nd high Cu also retarded the grain formation as well as their quality by de creasing the grain yield and the concentration of starch, sugars and protei ns in grains and activities of amylase, invertase and starch phosphorylase at the time of grain filling in seeds. In young leaves, 3.9, 6.8, 32, and 4 8 mu g Cu g(-1) dry weight were indicative of deficiency, threshold of defi ciency, threshold of toxicity, and toxicity values of Cu, respectively, in rice.