| Abstrakt: |
Sunflower (Helianthus annuus L.) cv. Jwala Mukhi was grown until maturity in refined sand at variable levels of zinc ranging from acute deficiency to excess (0.00065 to 65 mg L[SUP1]). Both low (<0.065 mgL[SUP-1]) and high (>0.065 mg L[SUP1]) zinc depressed the growth of sunflower. Foliar symptoms of zinc deficiency appeared on mature middle and old leaves of plants at 0.00065 and 0.0065 mg Zn L[SUP-1] as interveinal chlorosis and fading of green color from margins and apices. Later, leaf apices of the affected leaves turned necrotic and dry. Biomass, capitulum size, seed number, seed weight, concentration of chlorophylls a and b, and soluble proteins were maximum at 0.065 mg Zn L[SUP-1] (adequate), and were lowered significantly in both deficiency and excess of zinc. The effect of excess zinc (65mg ZnL[SUP-1]) on these parameters was more pronounced. An increase in zinc from low (0.00065 mg L[SUP-l]) to high (65 mg Zn L[SUP-l]) increased the activity of carbonic anhydrase (up to 6.5 mg Zn L[SUP-l]) and decreased that of acid phosphatase in sunflower leaves. Zinc deficiency lowered the concentration of zinc and increased that of phosphorus in leaves. In sunflower seeds, the oil content was highest (23.4%) at 0.65 mg ZnL[SUP-1] and was reduced more by Zn excess than deficiency. In leaves, tissue Zn concentrations associated with deficiency, threshold of deficiency, threshold of toxicity and toxicity were 20, 30, 190, and 240 μgg[SUP-1] on a dry matter basis, respectively. [ABSTRACT FROM AUTHOR] |
