Properties of enhanced tonoplast zinc transport in naturally selected zinc-tolerant Silene vulgaris

It was demonstrated recently that isolated tonoplast vesicles derived from plants of a Zn-tolerant ecotype of Silene vulgaris accumulate more Zn than vesicles derived from a Zn-sensitive ecotype. We have now characterized the tonoplast-transport system that causes this uptake difference and demonstr ated its genetic correlation to Zn tolerance using plant crosses. We conclu de that the tonoplast Zn uptake system of the tolerant ecotype differs grea tly in its characteristics from that of the sensitive one, with the most pr ominent differences being its insensitivity to protonophores and ortho-vana date and its stimulation by Mg-CTP. These differences in characteristics ar e most likely due to the fact that Zn can be taken up by two or more parall el pathways, which are not present in the same proportions in both ecotypes . In both ecotypes, Zn is actively transported across the tonoplast (temper ature coefficient > 1.6), most likely as a free ion, since citrate does not accumulate in vesicles. Most importantly, the uptake difference found usin g the ecotypes was also found between homozygous Zn-tolerant and Zn-sensiti ve F-3 plants, proving the genetic correlation between increased tonoplast Zn transport and naturally selected Zn tolerance in S. vulgaris.