BIOSYNTHESIS OF A 34-KDA POLYPEPTIDE IN THE ROOT-CELL PLASMA-MEMBRANEOF 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 rep ressed at sufficient Zn supply. In contrast, after prolonged Zn defici ency, the rates of net Zn uptake increased in Zn-efficient Warigal and decreased in Zn-inefficient Durati. Intact plants of these two genoty pes grown at four Zn nutrition regimes were labelled with S-35; th, an alysis of translation products by SDS-PAGE indicated increased abundan ce of a 34-kDa polypeptide iii the root-cell plasma membrane fraction of Warigal grown under prolonged Zn deficiency only. Soluble (cytosoli c) and microsomal (organelle) fractions did not contain 34-kDa polypep tide in any of the eight treatments. Silver-stained PAGE showed that t he 34-kDa polypeptide was present in the plasma membrane of Zn-efficie nt Warigal regardless of Zn nutrition, indicating that de novo biosynt hesis of that polypeptide in 18-day-old plants was regulated by Zn def iciency. The pi of the 34-kDa polypeptide was around pH 5.5 as shown b y 2-D PAGE. The 34-kDa polypeptide is the first reported root-cell pla sma membrane polypeptide specifically induced under Zn deficiency. Sin ce it is accumulated only in the Zn-efficient wheat genotype, the 34-k Da polypeptide may be connected with the capacity of that genotype to sustain prolonged Zn deficiency.