Effects of Fe and Zn alone and combined treatment on Triticum aestivum L. seed germination

Seed germination represents a pivotal phase in crop production, exhibiting pronounced sensitivity to abiotic stresses. In this study, wheat seeds of the 'Ningchun 4' variety were subjected to treatments involving zinc (Zn) chloride and iron (Fe) chloride, both individually and in combination. The impacts of these treatments on Fe and Zn accumulation, starch mobilization, antioxidant responses, and nitric oxide (NO) metabolism during seed germination were thoroughly examined. Individual application of Fe or Zn significantly inhibited and delayed wheat seed germination, which was accompanied by elevated levels of starch, sucrose, and soluble sugars, as well as increased reactive oxygen species and malondialdehyde concentrations. Concurrently, total amylase and α-amylase activities were downregulated, while antioxidant enzyme activities and the expression of TaCAT, TaAPX, and TaGR were upregulated. Seeds treated solely with Fe exhibited excessive Fe accumulation, heightened Fe²⁺ content, and diminished Zn content. Conversely, these trends were reversed in seeds treated with Zn alone. Furthermore, reduced NO levels were associated with downregulated nitrate reductase and nitric oxide synthase activities, alongside decreased expression of their corresponding genes in response to Fe exposure. Notably, the above effects induced by Zn alone were less severe compared to those induced by Fe stress. Importantly, the addition of Zn (100 µM or 250 µM) significantly alleviated the detrimental effects of Fe on several parameters in germinating seeds. The results from NO fluorescent probe staining corroborated the quantitative NO measurements across different treatments. In conclusion, an appropriate concentration of Zn effectively promoted the germination of Fe-stressed wheat seeds by mitigating Fe accumulation, attenuating oxidative damage, and enhancing starch mobilization during seed germination.