Abstract
Sugar cane (Saccharum officinarum L.) cv. CoS 767 was grown in refined; sand at graded levels of zinc, ranging from acute deficiency to excess supply. Growth depression was observed at low (0.00065 to 0.013 mg L-1) and high (1.3 and 6.5 mg L-1) zinc supply. The visible symptoms of zinc deficiency were marked on middle leaves of plants receiving <0.065 mg Zn L-1. The number of millable canes, fresh weight, and sucrose concentration in cane juice were maximum at a level 10 times higher (0.65 mg Zn L-1) than the adequate zinc supply. Both acute deficiency (<0.013 mg Zn L-1) and toxicity (1.3 and 6.5 mg Zn L-1) of zinc reduced the yield of millable canes and sucrose concentration of cane juice. The activity of acid phosphate and peroxidase increased in zinc-deficient leaves. The carbonic anhydrase activity increased with increase in zinc concentration in leaves and appears to be a good biological indicator of the zinc status of sugar cane. The threshold values of deficiency, sufficiency, and toxicity of zinc were found to be 14.8, 21.2, and 44 ?g Zn g-1 dry matter, corresponding to 30, 45, and 76.5 EU carbonic anhydrase mg-1 protein, respectively, in sugar cane.
