Translocation and function of zinc in roots

Abstract

Wheat seedlings were grown with entire or split root systems in nutrient solutions with variable levels of Zn.

Entire root systems with 1 μM Zn progressively lowered solution pH for 16 days (D16); roots without Zn lowered pH identically until D13 after which it increased. Shoot growth of seedlings without Zn was depressed from D14.

Split root systems had each half root in a separate solution (A and B) with either the same Zn concentration (nil or 1 μM = Zn₀₀ or Zn₊₊) or 0.05, 0.1, or 1 μM Zn in A and none in B (Zn₊₀). To solution A, ⁴⁵Ca was added on D7 and ⁶⁵Zn on D23; no Ca was found in solution B at any time. On D24, Zn₀₀ plants were Zn deficient with dry matter (DM) depressed in shoots and enhanced in roots; Zn concentrations in the youngest emerged leaf blade (YEB) and root B were low (13 and 12 μg/g DM). Zn₊₀ plants had the same DM as ZN₊₊ plants; their Zn concentrations in YEB and root B were relatively high (more than 19 and 21 μg/g DM). From ⁶⁵Zn levels in root B, the rate of Zn translocation in Zn₊₀ plants with 1 μGmm Zn in solution A was 0.7 ng Zn/g DM root B/day. All solutions with Zn (A and B of Zn++ and A of Zn₊₀) were more acidic than those without (A and B of Zn₀₀ and B of Zn₊₀).

The present results suggest that Zn‐adequate wheat plants may translocate sufficient Zn in their phloem to maintain growth of parts of their root systems in environments lacking Zn. In such environments, the absence of Zn may have a direct effect on rhizosphere pH, possibly through an effect on membrane activity.

Key words:

• Zinc translocation
• root growth
• root function