UPTAKE OF ZINC AND IRON BY WHEAT GENOTYPES DIFFERING IN TOLERANCE TO ZINC-DEFICIENCY

The effect of zinc nutrition on release of phytosiderophores (PS) and uptake and transport to shoots of Zn-65 and Fe-59 was studied in two g enotypes of wheat (Triticum aestivum cv. Warigal and T. turgidum conv. durum cv. Durati) differing in tolerance to Zn deficiency, There was little difference in root and shoot concentrations of Zn in the two ge notypes pre-grown under different Zn supply. In contrast, Zn deficienc y decreased shoot growth of 18-day-old plants of Zn-deficiency-sensiti ve Durati more than those of Zn-deficiency tolerant Warigal. Compared to Zn-sufficient roots, Zn-deficient roots of Durati released five tim es and those of Warigal 37 times more PS. Zn-deficient roots of Wariga l released three times more PS than Zn-deficient Durati roots. Rates o f Zn-65 uptake followed a similar pattern of differences among the tre atments as did PS release. With an increase in severity of the Zn-defi ciency stress between 14 and 18 days of growth at 0 Zn, uptake of Zn-6 5 increased by 170 % in Zn-deficiency-tolerant Warigal but remained un changed in Zn-deficiency-sensitive Durati. Zn-deficient Warigal plants transported amounts of Zn-65 to shoots than plants in any other treat ment. When plants were pre-grown at 0 Zn uptake was increased in Warig al, but decreased with severity of Zn deficiency in Durati. Transport of Fe-59 to shoots was inversely related to rates of Fe-59 uptake in W arigal. It is concluded that increased tolerance to Zn deficiency of W arigal plants is due to increased PS release under Zn deficiency, poss ibly as a consequence of decreased Fe transport to shoot. The regulati on of Zn uptake is different from that of Fe, even though PS may be in volved in both processes.