Investigation of the differential response of near-isogenic lines of durum wheat (Triticum turgidum var. durum) to cadmium (II)

This study was performed to elucidate the mechanisms of tolerance and accumulation of Cd2+ in Triticum turgidum var. durum (durum wheat) using near-isogenic lines that differ in accumulation and translocation of Cd2+. Two pairs of isolines (8982-SF and 8982-TL) with each pair consisting of a low- and a high-accumulating isoline were extensively analyzed. Variables were investigated to determine what factors relate to differential accumulation of Cd2+ in the near-isogenic lines of durum wheat under conditions of acute exposure at the seedling stage. The hypothesis that differential Cd2+-accumulation is correlated with differential physiological responses was tested. Analyses were conducted to determine possible physiological mechanisms responsible for the differential concentration of Cd2+ in mature grain.; The effect of acute exposure to CdCl2 on durum wheat was assessed using conventional biomass indices, measurement of Cd2+ concentration using ICP-AES, chlorophyll content, parameters of chlorophyll fluorescence, variation in organic acids using HPLC, and malate dehydrogenase (MDH) activity assays. Both pairs of isolines showed some symptoms of Cd2+-toxicity; biomass and concentration of chlorophylls a and b declined with increasing Cd2+ in solution, and the concentration of Cd2+ in plant tissue increased with CdCl2-treatment. Fluorescence parameters Fo, Fm and Fv/Fm did not vary with acute exposure to CdCl2 despite the reduced chlorophyll content. The concentrations of Cd2+ in shoots of both high-accumulating isolines were double those of the corresponding low-accumulating isolines, when grown in low doses of Cd2+ in solution. The hypothesis that organic acids play a role in differential response to Cd2+ was not resolved and other mechanisms may be involved. In vitro CdCl2 treatment of crude protein extract suggests that NAD-MDH is susceptible to Cd2+-toxicity; however, in vivo analysis indicates a positive relationship between Cd2+ and MDH activity in seedlings of the SF pair and in mature plants of the TL pair but a negative relationship in the short term. A difference in accumulation of Cd2+ after acute exposure (between high- and low accumulating isolines and with the TL pair having more Cd2+ than the SF pair) existed in the absence of a change in stress response. The current study has demonstrated differences between the pairs of isolines (8982-SF and 8982-TL) that are independent of the high and low patterns of Cd2+-accumulation and translocation.