Metabolic Responses to Lead of Metallicolous and Nonmetallicolous Populations of Armeria maritima

Metabolic responses to Pb(NO₃)₂ (Pb) ions of excised leaves of metallicolous (MPs) and nonmetallicolous populations (NMPs) of Armeria maritima, cultivated on normal soil, were examined. Detached leaves were exposure to Pb for 24 h, and metabolic parameters were investigated. Pb decreased the photosynthesis (Pn) rate and photosystem II (PSII) activity, whereas the photochemical efficiency of PSII remained unchanged. In both populations, Pb ions caused increase in O₂ uptake of dark-treated leaves; however, respiration after Pn was not affected. Pb increased superoxide dismutase activity in MP leaves and malondialdehyde content in NMP leaves. Other metabolites after Pb treatment were increased (proline or H₂O₂) or decreased (malate). Ascorbate peroxidase activity and adenosine triphosphate content decreased more in MP than in NMP leaves. Our results indicate that A. maritima is well adapted to heavy metal-contaminated soils, and we discuss potential causes of the stimulation of respiration by Pb ions and possible reasons for the tolerance to oxidative stress of plants growing in a metal-rich habitat.