Zinc stress disturbed the physiology of French bean

Zinc stress was induced in french bean cv. Anupama in refined sand at variable levels of zinc from deficient (0.00065 mg/l) to excess (13.0 mg/l) supply. After 35 days, depression in growth followed by initiation of chlorosis at margins of middle leaves was observed under zinc deficiency. At later stage with continuous low supply, zinc deficient plants were very retarded and stunted in growth with dense small leaves. At excess Zn (13 mg/l) level, interveinal chlorosis appeared on young leaves started from the base of the lamina and spread towards the centre. Zinc stress (both deficiency and excess) caused reduction in biomass and economic yield. The concentrations of reducing sugar, starch, protein nitrogen, soluble protein and specific activity of carbonic anhydrase were decreased and stimulation in specific activities of acid phosphatase and ribonuclease in leaves and pods of french bean was observed under zinc stress. The concentration of Zn in dry matter increased with an increase in zinc supply. It appears that the zinc concentration values at deficiency, threshold of deficiency, threshold of toxicity and toxicity in leaves were 18, 32, 117 and 138 μg Zn/g dry matter respectively.