Cadmium tolerance and accumulation in the noxious weed Zygophyllum fabago

Zygophyllum fabago L. is an invasive weed able to proliferate in coarse mineral substrates contaminated with heavy metals. To quantify its Cd tolerance, seedlings from seeds collected from a heavy metal contaminated area in Southeast Spain were exposed for 4 weeks to a nutrient solution containing 10 mu mol center dot L-1 CdCl2. Although Cd inhibited axillary bud development, it did not reduce plant survival or dry mass. Most of the absorbed Cd remained in the roots, but the shoots were able to accumulate up to 156 mg center dot kg(-1) dry mass of Cd. Zygophyllum fabago was able to regulate Cd translocation from roots to shoots, where it accumulated preferentially in the older leaves. Accumulation of Cd reduced the water content and water potential in shoots, as well as osmotic potential and leaf stomatal conductance in young leaves, although the plants were able to partly adapt to reestablish a more favourable water balance after 4 weeks of stress exposure. The population displayed considerable heterogeneity, and it may be possible to select individual plants combining high biomass production and a high rate of Cd accumulation. The use of Z. fabago as a Cd-tolerant species for phytoremediation is discussed.