Investigation of the Effects of Foliar Amino Acid, Melatonin and Potassium Applications on Spinach Cultivar under Water Stress

The main objective of this study is to explore the potential benefits of exogenous supplements of asparagine (Asn), phenylalanine (Phe), melatonin (Mel), and potassium (KNO3) in mitigating the effects of drought stress (WD) on spinach. The improvement effects of four chemicals on drought-stressed seedlings were assessed by comparing growth rate traits, chlorophyll, secondary metabolites, nitrogenous compounds, mineral contents and variations in antioxidant enzyme activity. According to the results, the growth rate traits of seedlings were reduced with WD application, but the exogenous supplements of Asn, Phe, Melatonin, and KNO3 alleviated the suppressing effect of drought on growth parameters. Supplements of four stimulants led to a marked boost in the content of chlorophyll, lutein, anthocyanin, phenolic compounds, flavonoids, proline, and GB in the WD-treated seedlings compared to the control. Moreover, these substances suppressed the generation of MDA and H2O2 in seedlings under WD stress but caused a significant enhancement in PPO, APX, CAT, POD and SOD activities. The WD treatment reduced the accumulation of Mg, Ca, Mn, and Fe in seedlings, but induced the accumulation of K, P, S, Ni, Cu, and Zn. Supplementation of four substances to drought-exposed seedlings generally increased Mg, S, K, Ca, Mn, Fe, and Cu levels. Considering all data, it can be said that an exogenous supply of Asn, Phe, Mel and KNO3 to the Acosta spinach variety exposed to drought stress made a significant contribution to increasing yield and nutritional quality by preventing oxidative stress and strengthening enzymatic and non-enzymatic defences.