A cosegregation analysis of zinc (Zn) accumulation and Zn tolerance in the Zn hyperaccumulator Thlaspi caerulescens.

• To analyse the relation between zinc (Zn) accumulation and Zn tolerance in the Zn hyperaccumulator, Thlaspi caerulescens, a cross was made between a plant from a nonmetallicolous population (LE: high accumulation, low tolerance) and one from a calamine population (LC: low accumulation, high tolerance). • More or less homogeneous F3 lines with contrasting extreme accumulation phenotypes were selected and phenotyped for tolerance, using the threshold exposure level for chlorosis as a tolerance measure. Zn accumulation and tolerance segregated largely independently, although there was a significant degree of association between low accumulation and high tolerance. • Plants from an F2 family were phenotyped for Zn tolerance and their Zn accumulation rates were compared. The plants with low Zn tolerance exhibited significantly higher Zn accumulation than did the more tolerant plants. • The results suggest that the superior Zn tolerance in LC plants compared with LE plants results from a superior plant-internal Zn sequestration capacity and, although to a lower degree, a reduced rate of Zn accumulation. It is argued that the relatively low Zn accumulation capacity levels found in LC and several other calamine T. caerulescens populations might represent an adaptive response to Zn-toxic soil.

Enhanced ATP-dependent copper efflux across the root cell plasma membrane in copper-tolerant Silene vulgaris.

We studied copper uptake in inside-out plasma membrane vesicles derived from roots of copper-sensitive, moderately copper-tolerant and highly copper-tolerant populations of Silene vulgaris (Amsterdam, Marsberg and Imsbach, respectively). Plasma membrane vesicles were isolated using the two-phase partitioning method and copper efflux was measured using direct filtration experiments. Vesicles derived from Imsbach plants accumulated two and three times more copper than those derived from Marsberg and Amsterdam plants, respectively. This accumulation was ATP-dependent. Also, 9-amino-6-chloro-2-methoxyacridine fluorescence quenching rates upon copper addition decreased in the order Imsbach>Marsberg>Amsterdam. Our results support the hypothesis that efflux of copper across the root plasma membrane plays a role in the copper tolerance mechanism in S. vulgaris.