Zinc sulfate biofortification enhances physio-biochemical attributes and oxidative stress tolerance in rice varieties grown in zinc deficient alkaline soil

Zinc (Zn) is a crucial trace mineral with diverse roles in plants; its deficiency in edible plant parts results in micronutrient malnutrition, leading to stunted growth. Zinc deficiency in the soil is a significant factor leading to poor rice quality. This research aimed to reveal the impact of Zn biofortification on rice productivity and to introduce rice cultivars with enriched nutrients. The effects of various zinc sulfate (ZnSO4) rates viz. 100, 200, 300, 400 and 500 mM (designated as T1, T2, T3, T4 and T5, respectively) on the germination process, chlorophyll pigments, biochemical activities, and the mitigation of oxidative damage in four different rice (Oryza sativa L.) cultivars (KSK-133, Basmati-198, Basmati-515, and PK-386) grown in alkaline Zn-deficient soil were evaluated. A control without Zn application (T0) was kept for comparison. Results demonstrated that Zn treatments significantly affected the germination rates, vegetative growth, photosynthetic attributes, and enzymatic and non-enzymatic activities of all tested cultivars. Zn application significantly ameliorated the oxidative stress by increasing antioxidant enzyme activities such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), 2,2-diphenyl-1-picrylhydrazyl (DPPH), glutathione peroxidase, and non-enzymatic compounds (such as flavonoids, proline, phenolics, reducing sugar and non-reducing sugar, total carbohydrates, and free amino acid) in all tested cultivars. Among the application rates, ZnSO4 application at 400 mM depicted the highest values of the above-mentioned traits. Furthermore, recorded data also revealed that ZnSO4 had a significant impact on flavonoids, total carbohydrates, and phenolic contents where its application at 400 mM depicted significantly higher values than other treatments. Among the tested cultivars, Basmati-198 exhibited the highest values of flavonoids, total carbohydrates, and phenolic contents showing an increase of 134.53%, 103.57%, and 265.34%, respectively, over the average of other cultivars. In sum, ZnSO4 application at 400 mM significantly improved rice performance under alkaline conditions whereas its application at 500 mM onsets toxic effect on all tested cultivars. However, to gain a comprehensive understanding of the underlying mechanisms, further research is needed to conduct long-term field studies at the molecular level.