Physiological responses to lead and PEG-simulated drought stress in metallicolous and non-metallicolous Matthiola (Brassicaceae) species from Iran

Aims: Plants growing on quarry tailings at the Irankouh Pb/Zn mine encounter both drought stress and high levels of Pb. To better understand role of drought and Pb in plant adaptation to Pb/Zn quarry tailings, we compared effects of drought stress (simulated by polyethylene glycol - PEG) and Pb, individually and in concert, to determine how these stressors affected two plant species: the metallicolous species Matthiola flavida and the non-metallicolous M. incana . Methods Plants were exposed to Pb (Pb(NO 3 ) 2 ) and three levels of PEG (0, -0.5, and − 0.75 MPa) in a complete factorial design. Results Lead had non-significant effects on growth and oxidative stress but enhanced levels of osmoprotectants and phenol compounds in the metallicolous M. flavida , whereas in the non-metallicolous M. incana Pb had non-significant or toxic effects on the same variables (except for the osmoprotectants proline and glycine betaine, and anthocyanins). In contrast to M. incana , the metallicolous species was hypertolerant of Pb, showing strongly reduced root-to-shoot translocation and enhanced Pb accumulation in the root, especially when under drought stress. Conclusion We conclude that enhanced Pb accumulation in the root and reduced translocation to the shoot, particularly when under high PEG exposure in the metallicolous species, reduced toxic effects of Pb in the shoot. This was aided by the accumulation of reducing sugars and phenolic compounds as well as greater catalase activity.