SUGARCANE RESPONSE TO COPPER IN REFINED SAND

Sugar cane was grown in refined sand at different levels of Cu supply. Visible symptoms of Cu deficiency were observed at concentrations les s than or equal to 0.0065 mg Cu litre(-1) and Cu toxicity at 6.5 mg Cu litre(-1). The fresh weight of millable canes and the concentration o f sucrose in cane juice were highest at 0.65 mg Cu litre(-1). Acute de ficiency (0.00065 mg Cu litre(-1)) and toxicity (6.5 mg Cu litre(-1)) reduced the concentration of chlorophyll a and b, DNA, RNA, non-reduci ng sugars, and the activities of ascorbic acid oxidase, polyphenol oxi dase, and cytochrome oxidase. The concentration of starch was reduced by acute deficiency and was increased by a toxic supply of copper. Ver y low supplies of Cu (less than or equal to 0.0065 mg Cu litre(-1)) an d excess supplies (6.5 mg Cu litre(-1)) increased the concentration of phosphorus, phenols, and activities of peroxidase, acid phosphatase, and ribonuclease. With an increase in Cu supply, the concentration of Cu in leaves and cane juice increased. Threshold of Cu deficiency coul d be indicated by the activities of ascorbic acid oxidase and cytochro me oxidase; the latter could also indicate the threshold of toxicity. Deficiency, threshold of deficiency, and toxicity values of Cu in youn g leaves at 35 weeks after sowing were, respectively, 4, 8.2, 19 mu g g(-1) dry matter.