Biosynthesis of a 34-kDa Polypeptide in the Root-cell Plasma Membrane of a Zn-efficient Wheat Genotype Increases upon Zn Deficiency

Zinc-efficient wheat (Triticum aestivum L. cv. Warigal) has a greater rate of net Zn uptake than the Zn-inefficient cv. Durati (T. turgidum conv. durum (Desf.) MacKey). In both genotypes Zn uptake is partly repressed at sufficient Zn supply. In contrast, after prolonged Zn deficiency, the rates of net Zn uptake increased in Zn-efficient Warigal and decreased in Zn-inefficient Durati. Intact plants of these two genotypes grown at four Zn nutrition regimes were labelled with S-35; th, analysis of translation products by SDS-PAGE indicated increased abundance of a 34-kDa polypeptide iii the root-cell plasma membrane fraction of Warigal grown under prolonged Zn deficiency only. Soluble (cytosolic) and microsomal (organelle) fractions did not contain 34-kDa polypeptide in any of the eight treatments. Silver-stained PAGE showed that the 34-kDa polypeptide was present in the plasma membrane of Zn-efficient Warigal regardless of Zn nutrition, indicating that de novo biosynthesis of that polypeptide in 18-day-old plants was regulated by Zn deficiency. The pi of the 34-kDa polypeptide was around pH 5.5 as shown by 2-D PAGE. The 34-kDa polypeptide is the first reported root-cell plasma membrane polypeptide specifically induced under Zn deficiency. Since it is accumulated only in the Zn-efficient wheat genotype, the 34-kDa polypeptide may be connected with the capacity of that genotype to sustain prolonged Zn deficiency.