High specificity in response of pea mutant SGECdt to toxic metals: Growth and element composition

The present report aimed to better understand the mechanisms of plant co-tolerance to various toxic metals, and relationships between metal tolerance and metal accumulation. The pea (Pisum sativum L.) line SGE and its mutant SGECd(t), having increased tolerance to and accumulation of Cd, but decreased tolerance to and accumulation of Hg, were cultivated in hydroponics at a range of toxic concentrations of heavy metals (Cd, Co, Cr, Hg, La, Ni, Pb and Zn), as well as Al, Fe, Mn, NaCI and H+ ions. The SGECd(t) mutant showed increased tolerance to Co (increased root biomass at 12 and 25 mu M Co and shoot biomass at 25, 50 and 100 mu M Co), but similar root and shoot Co contents as SGE. No significant differences between SGE and SGECd(t) in biomass response to other metals and low pH were detected. However at particular metal concentrations, SGECd(t) tended to (Student's t test, P < 0.05) have increased: (i) shoot biomass (34%) in the presence of 400 mu MZn; (ii) root and shoot biomass (32%) in the presence of 100 mu M Fe; (iii) root Mn or Zn contents (65% or 8%, respectively) in the presence 400 mu M Mn or Zn, compared to SGE plants. No genotypic differences in the content of other toxic metals were observed, except for the previously reported increased Cd content and decreased Hg content in SGECd(t). Generally, metal toxicity decreased macro-and micro-element (nutrient) concentrations in plants, however opposite effects were also observed particularly on Hg-treated plants. SGECd(t) had increased root Ca, Fe, Mg, Mn and S content and shoot B, Ca, Mg, Mn, Na and Zn content in Cd-treated plants. In the presence of toxic Hg the mutant contained less root and shoot Ca, K, Mg and S, but had increased root Co, Cr and Cu contents. Genotypic differences in individual nutrient elements were also observed following Ag, Al, La, Mn, Ni or Zn treatment. Taken together, the results indicate high specificity in phenotypic responses of SGECd(t) exposed to toxic metals and that the mutation might affect some regulatory genes, which could modulate nutrient (particularly Ca) homeostasis and regulation of ion transporters. (C) 2016 Elsevier B.V. All rights reserved.