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

• Pea mutant SGECdt was characterized by the response to 14 toxic metals.
• SGECdt shows increased Cd- and Co-tolerance, but decreased Hg-tolerance.
• Metal toxicity causes disturbance in the uptake of nutrient elements in plants.
• Plant tolerance to Cd and Hg is related to nutrient homeostasis, particularly Ca.
• The mutated gene of SGECdt may be involved in regulation of ion transporters.

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 SGECdt, 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, NaCl and H+ ions. The SGECdt mutant showed increased tolerance to Co (increased root biomass at 12 and 25 μM Co and shoot biomass at 25, 50 and 100 μM Co), but similar root and shoot Co contents as SGE. No significant differences between SGE and SGECdt in biomass response to other metals and low pH were detected. However at particular metal concentrations, SGECdt tended to (Student's t test, P < 0.05) have increased: (i) shoot biomass (34%) in the presence of 400 μM Zn; (ii) root and shoot biomass (32%) in the presence of 100 μM Fe; (iii) root Mn or Zn contents (65% or 8%, respectively) in the presence 400 μM 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 SGECdt. Generally, metal toxicity decreased macro- and micro-element (nutrient) concentrations in plants, however opposite effects were also observed particularly on Hg-treated plants. SGECdt 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 SGECdt 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.