UPTAKE AND TRANSPORT OF ZINC IN ZINC-SENSITIVE AND ZINC-TOLERANT SILENE-VULGARIS

The uptake and transport of zinc in zinc-sensitive and zinc-tolerant Silene vulgaris were compared in a short-term experiment. Although the roots of tolerant plants contained more CaCl2-exchangeable zinc, tolerance can not result from exclusion through binding of zinc to the cell wall, because the total uptake of zinc was not significantly different between the populations. Compared at equal levels of zinc injury, measured by root-length growth inhibition, the uptake of zinc was much higher in the tolerant plants. Up to the NOEC for root-length growth of sensitive plants, an equal zinc concentration of the roots was found in sensitive and tolerant plants, but at a higher supply the zinc concentration of the roots was higher in tolerant plants. In sensitive plants the zinc concentration of the shoot was higher than in tolerant ones, except after 3 and 7 days at the highest zinc supply, and the percentage of zinc allocated to the shoot was higher at all external zinc concentrations. The results of a split-root experiment clearly show that zinc has a direct inhibitory effect on root growth. Zinc tolerance seems to result from an efficient sequestration of zinc inside the root cells. This probably causes a lower transport of zinc to the shoot.