Abstract
The metabolic links between S and Fe nutrition are well documented in Strategy II plants (e.g. barley and maize). Recent evidence that S deprivation can impair Fe-deficiency response and that S re-supply to deficient plants can allow the restoration of their capacity to cope with Fe shortage (Astolfi et al., 2010), led us to investigate whether increasing sulphate supply in nutrient solution could improve plant efficiency to take up and accumulate Fe. Durum wheat (Triticum durum L cv. Svevo) plants were grown for 14 days in nutrient solution under three different sulphate supplies (0, 1.2 and 2.5 mM, deficient, adequate and high, respectively) and two Fe-III-EDTA levels (10 and 80 mu M). High S supply increased the concentration of Fe in the shoots; concentrations of Fe and S in the leaves were significantly correlated, irrespective of Fe availability in nutrient solution. The effect of S nutrition on Fe accumulation can be explained by an increased production of phytosiderophores and nicotianamine possibly due to increased methionine level. Actually, we found higher rates of both synthesis and release of phytosiderophores and higher levels of enzymes (ATPS and OASTL) involved in the S assimilation pathway. In particular, PSs release rate increased with increasing S supply in wheat plants under Fe-limiting condition and it reached its highest value (approximately 30% higher than the S-deficient control) under high-S condition. It is worth to note that S-containing compounds are involved also in Zn acquisition and transport. However, no significant correlation was evidenced between leaf S and Zn concentrations, which underlines that S-induced effect was specific for Fe. Results indicate that providing S above adequate concentrations may result in the improvement of Fe use efficiency in wheat plants. It is also interesting to note that this S nutritional effect seems to be especially advantageous for plants grown under severe Fe limitation. (C) 2011 Elsevier B.V. All rights reserved.