Characterization of zinc uptake in seedlings of wheat cultivars differing in Zn-deficiency tolerance as affected by histidine

Knowledge of the characteristics of zinc (Zn) uptake by plant roots may help in understanding the reasons for variations in the Zn deficiency tolerance of plant cultivars. We investigated the apoplastic and symplastic Zn uptake and proton secretion by roots of three bread wheat genotypes (Triticum aestivum cvs. Rushan, Kavir, and Falat) and a durum wheat genotype (Triticum durum cv. Yavarus) under influence of histidine addition in a nutrient solution. Seedlings of wheat genotypes were planted in a nutrient solution containing 10 mu M Zn with or without added 50 mM histidine (His). A control with no added Zn or histidine was also used. A significant variation was found among wheat genotypes in shoot Zn content and the characteristics of Zn uptake by roots. The addition of Zn enhanced shoot Zn content compared to the control while the effect of His was genotype-dependent. His addition in combination with Zn enhanced shoot Zn content in Rushan and Falat but not in Kavir and Yavarus compared with the only Zn supply treatment. For all wheat genotypes, the addition of Zn enhanced the total, apoplastic, and symplastic root Zn concentration compared to the control. The highest and lowest amounts of proton (H+) were secreted from the roots of Rushan and Yavarus genotypes, respectively. In all wheat genotypes except Falat, the combined addition of zinc and histidine enhanced root H+ secretion compared with the only supply of Zn. Higher plant Zn uptake was associated with a higher ability to secretion of H+ from roots and higher proportion of symplastic to apoplastic Zn.