Preferential allocation of sulphur into y‐glutamylcysteinyl peptides in wheat plants grown at low sulphur nutrition in the presence of cadmium

Abstract

Plants respond to Cd by synthesising phytochelatins (PC) and similar S‐rich peptides which are important in alleviating Cd toxicity. The hypothesis that S nutrition influences the sensitivity of plants to Cd was examined by measuring the growth, PC and Cd content of wheat plants (Triticum aestivum cv. Condor) grown at 10–1000 µM S with and without 30 µM Cd. In the absence of Cd, 100 µM S was marginally S‐limiting. Cd severely inhibited root growth at 100 µM S but the concentrations of PC, Cd–PC complexes and Cd in the root were similar to those of plants grown at 1000 µM S which exhibited no evidence of Cd toxicity. Plants grown at low S (10 and 30 µM) contained lower concentrations of Cd. However, they produced very low amounts of PC and were very sensitive to Cd. At 10–300 µM S (but not at 1000 µM), Cd enhanced the concentration of S in the root. The data are consistent with a model in which plants preferentially allocate S to PC synthesis. When S was marginally limiting (100 µM), the S supply was sufficient for PC synthesis but not root growth, effectively causing Cd‐induced S deficiency. This did not occur at high S (1000 µM). Conversely, at low S (10 and 30 µM), the synthesis of PC2–PC4 was decreased by 87 and 66%, respectively, thereby resulting in decreased Cd uptake while also making the plants especially sensitive to Cd.