Sulfhydryl groups in root‐cell plasma membranes of wheat genotypes differing in Zn efficiency

Sulfhydryl groups were quantified in root‐cell plasma membranes of two genotypes of wheat (Triticum aestivum cv. Warigal and T. turgidum conv. durum cv. Durati) differing in Zn efficiency. Smaller amounts of 5,5′‐dithio‐bis(2‐nitrobenzoic acid)‐reactive sulfhydryl groups were found in Zn‐deficient than in Zn‐sufficient roots; and also in Zn‐inefficient genotype Durati compared to Zn‐efficient Warigal, regardless of Zn supply. Upon transfer of 15‐day‐old Zn‐deficient plants into solutions containing various Zn²⁺ activities, a Zn‐dependent increase in the amount of reactive sulfhydryl groups was evident in roots of both genotypes, but occurred only in Warigal when 20‐day‐old plants were used, indicating irreversible physiological damage in Durati plants due to prolonged Zn deficiency. Upon transfer into solutions of increasing Zn²⁺ activities, the increase in total Zn concentration in roots was about an order of magnitude smaller than the increase in amounts of reactive sulfhydryl groups in the roots of both genotypes, suggesting that, in wheat roots, a relatively small amount of Zn is required for preventing oxidation of sulfhydryl groups into disulfides. The amount of reactive sulfhydryl groups in the roots is positively related to Zn efficiency of wheat genotypes and may be one of the mechanisms that, under conditions of Zn deficiency, allow better growth and productivity of Zn‐efficient genotypes in comparison to Zninefficient ones.