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 35S; the analysis of translation products
by SDS-PAGE indicated increased abundance of a 34-kDa polypeptide in 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.
Calculated activity of Mn2+ at the outer surface of the root cell plasma membrane governs Mn nutrition of cowpea seedlings