UPTAKE OF ZINC FROM CHELATE-BUFFERED NUTRIENT SOLUTIONS BY WHEAT GENOTYPES DIFFERING IN ZINC EFFICIENCY

Zinc-efficient Triticum aestivum (cv. Warigal) and Zn-efficient Tritic um turgidum conv. durum (cv. Durati) were grown in chelate-buffered, c omplete nutrient solutions providing either deficient or sufficient Zn supply. When transferred to fresh chelate-buffered nutrient solutions containing a wide range of Zn supplies (0-1.28 mu mol m(-3) Zn2+ acti vity) for 24-48 h, both genotypes increased net Zn uptake linearly wit h an increase in solution Zn2+ activities, Zinc-efficient Warigal accu mulated Zn at a greater rate than Zn-inefficient Durati, The greater r ate of net Zn uptake was observed by plants of both genotypes when pre treated at deficient Zn supply, Net loss of Zn to the solution was hig her in plants pretreated with sufficient Zn and was inversely related to Zn2+ activity in the external solution. When continuously supplied with 40 nmol m(-3) Zn2+, net Zn by Zn-efficient uptake Warigal was sig nificantly greater than that of Zn-inefficient Durati, but the differe nce diminished with plant age, Shoot concentrations of Fe, Mn and Cu w ere higher when plants were grown at deficient than at sufficient Zn s upply, The Zn-efficient genotype transported less Zn and Fe to shoots and had higher Fe concentrations in roots than the Zn-inefficient geno type, supporting the hypothesis that Zn efficiency may be connected wi th inefficient transport of Fe from roots to shoots and thus initiatio n of the Fe-deficiency response resulting in increased release of Zn- and Fe-binding phytosiderophores, It is concluded that differential Zn efficiency of wheat genotypes is at least partly due to a greater abi lity of efficient genotypes to accumulate Zn.