Copper stress affects grain filling in rice

Abstract

Rice (Oryza sattva 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 symptoms appeared on young leaves as chlorosis changing to necrosis, later affected 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 parameters was significant at low and high Cu supply. The concentration of Cu in grains increased from 0.4 in acute deficiency to 47.4 ppm at excess Cu. In rice leaves, concentration of sugars and activities of polyphenol oxidase and ascorbic acid oxidase were decreased both by low and excess Cu. Both low and high Cu also retarded the grain formation as well as their quality by decreasing the grain yield and the concentration of starch, sugars and proteins 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 48 μg Cu g^‐1dry weight were indicative of deficiency, threshold of deficiency, threshold of toxicity, and toxicity values of Cu, respectively, in rice.