Copper Stress Alters Physiology and Deteriorates Seed Quality of Rapeseed

Abstract

ABSTRACT To observe the effects of deficiency and excess of copper (Cu) on rapeseed (Brassica napus L. cv ‘T44’), plants were raised in refined sand at variable levels of Cu (as copper sulfate): 0.01, 0.1, 0.5, 1, 10, 100, and 200 μM, representing a range from acute deficiency to excess. In rapeseed, excess Cu (200 μM) induced chlorosis on young leaves similar to iron (Fe) deficiency symptoms and appeared earlier (day 30) than symtoms of Cu deficiency (day 40). Foliar symptoms of Cu deficiency (0.01 μM) were initiated on young leaves as interveinal chlorosis, later leading to necrosis. The margins of the affected leaves curled inward and leaves hung down due to loss of turgor. The deficiency (< 1 μM Cu) and excess (100 and 200 μM Cu) of Cu lowered the biomass, pod, and seed yield, concentration of chlorophylls (a and b), Hill reaction activity, activity of catalase and polyphenol oxidase, and increased the activity of ribonuclease and acid phosphatase in leaves. The activity of peroxidase decreased and the concentration of copper in leaves (young and old) and seeds increased with an increase in Cu from low to excess. The accumulation of Cu was greater in old than in young leaves. The seed quality of rapeseed was poor both in deficiency (< 1 μM) and excess (> 1 μM) of Cu, which was reflected in reduction in size and number of pods and seeds, oil content, concentration of protein, carbohydrate fractions (sugars and starch), protein nitrogen (N), and methionine, and increased concentration of phenols and non-protein N in seeds. The values of Cu deficiency, threshold of deficiency, threshold of toxicity, and toxicity were, respectively, 3.8, 6.6, 32, and 54 μg Cu g−1 dry matter in young leaves and 2.2, 5.8, 20, and 28 μg Cu g−1 dry weight in seeds of rapeseed.