Objectives The effects of exogenous Zn supply on root development, photosynthesis, metal ion homeostasis, and the expression of Zn homeostasis-related genes (TaZIPs) in wheat seedlings were investigated in this study. The objective was to provide insight into the mechanism of wheat seedling adaption to Zn deficiency.
Methods Wheat (Triticum aestivum L.cv. Bainong 207) was grown in a chelator-buffered nutrient solution, with Zn levels at 0, 0.05, 0.25, 1.0, and 2.5 mg/L, respectively. The plant height, root length, dry matter weight, root morphology, photosynthetic parameters, metal ion concentrations, and gene expression in wheat seedlings were measured three weeks after treatment.
Results Normal Zn supply (0.05, 0.25 mg/L) (P<0.05) promoted the growth and development of wheat seedlings. Wheat seedlings’ highest growth and dry matter weight were recorded under Zn0.05. The root morphology (root surface area, root volume, root diameter), photosynthetic parameters, and Zn transport capacity of the seedlings were the highest under Zn0.25. In contrast to Zn0, wheat seedlings’ biomass, root morphology, and photosynthetic parameters under normal Zn levels (0.05, 0.25 mg/L) increased by 16.66%–35.91%, 0.30%–27.0%, and 3.55%–58.11%, respectively, which effectively promoted the normal growth and development of the seedlings. With the increase in Zn supply level, Zn concentration and accumulation in the roots and shoots of wheat seedlings (P<0.05) increased, while Mn, Fe, and Cu concentrations decreased. Compared with normal Zn treatments (Zn0.05, Zn0.25), the growth of wheat seedlings was (P<0.05) inhibited under Zn deficiency (Zn0) and excess Zn supply (Zn1.0, Zn2.5). Further, wheat seedling biomass decreased by 25.6%–31.6%, compared to Zn0.05, root morphology decreased by 1.3%–21.2% compared to Zn0.25, and photosynthetic parameters decreased by 5.00%–16.69% compared to Zn0.25. This resulted in growth inhibition, metal ion imbalance, and disruption of wheat photosynthetic system. The expression levels of TaZIP3, TaZIP5, TaZIP7, and TaZIP13 in roots decreased with increasing Zn supply, suggesting that Zn-deficiency induced the expression of these genes, thereby promoting Zn absorption and maintaining seedling growth through higher expression under Zn deficiency. The TaZIP6 gene showed a constitutive expression in roots, and its expression was almost independent of Zn supply levels. In contrast, the expression of TaZIP6 in shoots increased with increasing Zn supply, indicating that TaZIP6 might be involved in the Zn transport process.
Conclusions The growth and development of wheat seedlings are inhibited by insufficient and excessive Zn supply. Wheat seedlings adapted to Zn deficiency and excess in different paths. At Zn deficiency, wheat up-regulates the expression of Zn-related genes to improve the absorption, utilization, and transport of Zn ions. Excessive Zn reduces the absorption of Fe, Mn, Cu elements, maintains the balance of ions inside and outside the cell membrane of wheat, and down-regulates the expression levels of Zn-related genes, alleviating the Zn toxicity.
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