High- and Low-Affinity Zinc Transport Systems and Their Possible Role in Zinc Efficiency in Bread Wheat

Abstract

There is considerable variability among wheat (Triticum aestivum L.) cultivars in their ability to grow and yield well in soils that contain very low levels of available Zn. The physiological basis for this tolerance, termed Zn efficiency, is unknown. We investigated the possible role of Zn 2ϩ influx across the root cell plasma membrane in conferring Zn efficiency by measuring short-term 65 Zn 2ϩ uptake in two contrasting wheat cultivars, Zn-efficient cv Dagdas and Zn-inefficient cv BDME-10. Plants were grown hydroponically under sufficient and deficient Zn levels, and uptake of 65 Zn 2ϩ was measured over a wide range of Zn activities (0.1 nm-80 m). Under low-Zn conditions, cv BDME-10 displayed more severe Zn deficiency symptoms than cv Dagdas. Uptake experiments revealed the presence of two separate Zn transport systems mediating high-and low-affinity Zn influx. The low-affinity system showed apparent K m values similar to those previously reported for wheat (2-5 m). Using chelate buffered solutions to quantify Zn 2ϩ influx in the nanomolar activity range, we uncovered the existence of a second, high-affinity Zn transport system with apparent K m values in the range of 0.6 to 2 nm. Because it functions in the range of the low available Zn levels found in most soils, this novel high-affinity uptake system is likely to be the predominant Zn 2ϩ uptake system. Zn 2ϩ uptake was similar for cv Dagdas and cv BDME-10 over both the high-and low-affinity Zn 2ϩ activity ranges, indicating that root Zn 2ϩ influx does not play a significant role in Zn efficiency.

Effects of zinc activity in nutrient solution on uptake, translocation, and root export of cadmium and zinc in three wheat genotypes with different zinc efficiencies

“…Cd0 and Cd1 present free Cd 2þ activities 10 À11.21 and 10 À10.2 mM, respectively. Cadmium concentration in the shoot was less than 0.02 mg kg In line with our results, Hacisalihoglu et al (2001) reported that the uptake of Zn by roots was similar among the wheat genotypes differing in Zn efficiency and concluded that Zn uptake has no relationship with Zn efficiency in wheat. An important point is that in most studies, the sum of apoplasmic and symplasmic Zn has been measured as the root metal uptake while this is actually pseudo root uptake.…”

“…Accordingly, the apoplasmic Zn was greater in ''Arya'' in comparison with two other wheat genotypes (data not shown). Alternatively, Zn efficiency mechanisms might be related to the mobility and distribution of Zn within the shoot (Hacisalihoglu et al 2001). The results of the present study indicated that at the low Zn level (Zn 2þ ¼ 10 À11.11 mM), shoot Zn concentration in the Zn-inefficient ''Arya'' was lower than that in the Zn-efficient ''Cross'' and ''Rushan.''…”

“…This suggests a different transport system for Cd and Zn in this genotype, or the inability of Zn at such concentrations to compete with Cd for the carriers. It is interesting that while the affinity of the Zn/Cd carrier is quite high for Cd 2þ , relatively high Zn 2þ activities may be required to inhibit Cd 2þ uptake (Hacisalihoglu et al 2001;Hart et al 2002). Further research is necessary to elucidate the transport systems of Cd and Zn in different Zn efficiency wheat genotypes.…”

Tolerance to Zinc Deficiency in Rice Correlates with Zinc Uptake and Translocation

“…Our study does not distinguish between rhizosphere effects and uptake kinetics. The latter did not explain variation in ZE among wheat cultivars (Hacisalihoglu et al, 2001). If this is also true for rice, then rhizosphere effects could play a major role in Zn uptake.…”

Respuesta de los frutos cítricos a las bajas temperaturas: estudio mediante micromatrices

“…Es posible que este transportador sea necesario para facilitar el transporte de ese micronutriente ante las bajas temperaturas y que por tanto la piel de F quedaría deficitaria en el mismo, contribuyendo a su deterioro. En ese sentido, el transporte de zinc sería menos eficiente a bajas temperaturas y genes codificantes de transportadores de este tipo se inducen ante situaciones deficitarias del nutriente (Grotz et al, 1998;Hacisalihoglu et al, 2001).…”