Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2003
Publication Date: 2/1/2003
Citation: HACISALIHOGLU, G., HART, J.J., WANG, Y., CAKMAK, I., KOCHIAN, L.V. ZINC EFFICIENCY IS CORRELATED WITH ENHANCED EXPRESSION AND ACTIVITY OF ZN-REQUIRING ENZYMES IN WHEAT. PLANT PHYSIOLOGY. 2003. v. 131. p. 595-602 Interpretive Summary: Crop yields are often limited by low soil levels of mineral micronutrients such as zinc (Zn). It has been estimated that 30% of the world's arable soils are Zn deficient. There is significant genetic variation both within and between plant species in their ability to maintain significant growth and yield under Zn deficiency conditions; this has been termed Zn efficiency (ZE). In recent years, there has been considerable interest in elucidating the physiological mechanisms that confer ZE, as an understanding of these mechanisms is necessary to help develop crops with improved ZE. We previously had shown that root Zn uptake does not play a role in differential ZE. In the present study, we employed several different experimental approaches with Zn efficient and inefficient wheat genotypes to investigate other possible mechanisms of ZE. As it is possible that more efficient Zn transport to the shoot under low Zn conditions could be involved in ZE, this was one of the processes studied. Second, as ZE could involve altered cellular Zn compartmentation in the leaf such that Zn efficient cultivars could maintain higher cytoplasmic Zn levels under low Zn conditions, this was also studied. Finally, the role of biochemical Zn utilization was examined by studying the expression and activity of Zn requiring enzymes. The findings presented here indicated that in wheat, ZE is not associated with altered Zn transport to the shoot or cellular Zn compartmentation. However, we found that the ability of Zn efficient genotypes to maintain higher activity of Zn requiring enzymes in the face of Zn deficiency correlated closely with Zn efficiency. Therefore, it is likely that biochemical Zn utilization plays a role in ZE and this will be the focus of future investigations.
Technical Abstract: Zinc (Zn) is an essential micronutrient for plants. The ability of plants to maintain significant yields under low Zn is termed zinc efficiency (ZE) and its genetic and mechanistic basis is still not well understood. Previously, we showed that root Zn uptake did not play a role in ZE. In the current study, Zn efficient and inefficient wheat (Triticum aestivum L.) genotypes were grown for 13 days in chelate buffer nutrient solutions at low (0.1 pM), sufficient (150 pM) and high (1 mM) Zn2+ activities and analyzed for root-to-shoot translocation of Zn, sub-cellular leaf Zn distribution, and activity and expression of the Zn requiring enzymes in leaves. No correlation between ZE and Zn translocation to the shoot was found. Furthermore, total and water-soluble concentrations of leaf Zn were not associated with ZE, and no differences in subcellular Zn compartmentation were found between Zn efficient and inefficient genotypes. However, the expression and activity of the Zn requiring enzymes Cu/Zn superoxide dismutase (SOD) and carbonic anhydrase (CA) did correlate with differences in ZE. Northern analysis suggested that Cu/ZnSOD gene expression was up-regulated in the Zn-efficient genotype, Kirgiz, but not in inefficient BDME. Under Zn deficiency stress, the very Zn-efficient genotype Kirgiz and moderately zinc efficient Dagdas exhibited an increased activity of Cu/ZnSOD and CA when compared to Zn-inefficient BDME. These results suggest that Zn efficient genotypes may be able to maintain the functioning of Zn requiring enzymes under low Zn conditions, and thus biochemical Zn utilization may be an important component of ZE in wheat.