Foliar spray with sodium hydrosulfide and calcium chloride advances dynamic of critical elements and efficiency of nitrogen metabolism in Cucurbita pepo L. under nickel stress

The current study sought to explore the effects of leaf spray with sodium hydrosulfide (NaHS) and calcium chloride (CaCl2) on the growth, the content of essential elements, and nitrogen metabolism in zucchini plants under normal and nickel (Ni) stress conditions. The 10-day old zucchini plants were exposed to Ni concentrations (0, 50, and 100 mg L−1) for 15 days. The results showed that both Ni levels reduced the fresh and dry weights of roots and shoots, leaf area, leaf water content and decreased the content of photosynthetic pigments due to the Ni accumulation and depletion of essential elements in tissues. Moreover, Ni stress increased electrolyte leakage (EL) and decreased the total protein content, the activities of catalase (CAT) and nitrate reductase (NR) in the leaves of the zucchini plant. Foliar spray with NaHS (100 μM) and CaCl2 (15 mM) alone or combined improved growth parameters and the content of chlorophyll a, b and carotenoids under non-stress and Ni stress conditions. Leaf spray with NaHS and CaCl2 and especially their combined application reduced the accumulation of Ni in the roots and shoots, lessened Ni uptake and the translocation factor values in plants, lowered EL and increased CAT activity in leaves. Foliar spray with NaHS and/or CaCl2 improved the homeostasis of macro- and micro-nutrients (N, P, K, Ca, Mg, Fe, and Cu) in the roots and shoots, increased the total protein content and enhanced the NR activity in leaves of zucchini plants under Ni stress. These novel results indicated that the interactive effect of H2S and Ca2+ not only alleviates oxidative stress but also contributes to maintaining nutrient homeostasis and efficiency of N metabolism in plants.