Nickel and zinc hyperaccumulation by Alyssum murale and Thlaspi caerulescens (Brassicaceae) do not enhance survival and whole-plant growth under drought stress
Nickel and Zn hyperaccumulation by Alyssum murale and Thlaspi caerulescens bear substantial energetic costs and should confer benefits to the plant. This research determined whether metal hyperaccumulation can increase osmotic adjustment and resistance to water stress (drought). Alyssum murale and Thlaspi caerulescens treated with low or high concentrations of Ni or Zn were exposed to moderate (−0·4 MPa) and severe (−1·0 MPa) water stresses using aqueous polyethylene glycol. In the absence of metals both water deficits inhibited shoot growth. Nickel and Zn hyperaccumulation did not ameliorate growth inhibition by either level of water stress. The water stress did not induce major changes in shoot metal concentrations of these constitutive hyperaccumulators. Moreover, metal hyperaccumulation had minimal effects on the osmolality of leaf-sap extracts, relative water content of the shoots, or rate of evapotranspiration. It is concluded that Ni or Zn hyperaccumulation does not augment whole-plant capacity for drought resistance in A. murale and T. caerulescens.