Changes in metabolism, root quality and nutritive characters of carrot under copper stress

Carrot was grown in refined sand at 4 levels of copper - 0.01, 0.1 (deficient), 1.0 (adequate) and 100 (μM Cu (excess) as CuSO₄ to monitor the changes in metabolism and quality of carrot caused by Cu-deficiency or Cuexcess. In addition to depression in growth, young leaves of plants supplied with deficient Cu (0.01 μM) showed chlorosis and necrosis along apices and margins with reduced leaf size. In carrot visible effects of Cu excess were prominent than its deficiency. Copper excess (100 μM Cu) in plants induced interveinal chlorosis on upper leaflets similar to that of iron deficiency. Emerging leaves of these plants were chlorotic even before expansion. Carrot plants exposed to Cu-deficiency/Cu-excess showed morphological changes and poor development of root. Root length, volume and girth of carrot were significantly reduced and dull red in colour in acute Cu-deficiency (0.01 μM) as well as in Cu-excess (100 μM). Root fresh weight was reduced to 59% in Cu-deficiency and 36% in Cu-excess. Exposure of carrot plant to copper stress (< 1.0 μM >) declined biomass, root fresh weight, chlorophyll content, Hill reaction activity and induced changes in the activity of antioxidant enzymes - catalase, peroxidase and polyphenol oxidase (PPG). Both deficiency and excess of copper reduced carrot yield and deteriorated its quality, nutritive values by reducing the concentration of sugars, starch, protein, protein nitrogen, carotene and increasing the non-protein nitrogen and phenols in carrot root.