Ca2+-Priming Improves Tolerance to Osmotic Stress in Early Growth Stage of Quinoa (Chenopodium quinoa Willd.) by Ameliorating the Capacity of Seed Protective Mechanism

Quinoa as halophytic plant species often cultivates in arid environments, where seed germination and seedling growth are markedly influenced. Therefore, this study aimed to investigate the efficacy of CaCl2 priming in alleviating the adverse effects of osmotic stress on seed germination, seedling growth, and underlying biochemical mechanisms. Seed priming was performed with different concentrations of CaCl2 (5, 10, and 15 mM) at priming temperatures of 5, 10, and 15 degrees C for different durations. Thus, treated seeds with the optimized priming protocol and non-primed (control) seed germinated in different osmotic potentials of PEG (0, -4, -8, -12, and -16 bar). The findings showed that primed seeds with 15 mM CaCl2 for 30 h at 5 degrees C recorded the highest osmotic tolerance in seeds. The osmotic stress caused an increment in the accumulation of H2O2 and thereby increased the process of lipid peroxidation (MDA), leading to a reduction in germination performance and seedling development. However, the improvement of Ca2+-primed seed vigor against osmotic stress was accompanied by an increase in the activities of antioxidant enzymes (SOD, CAT, APX, PPO, and GPX) and higher accumulation of antioxidant metabolites (total antioxidant activity, phenolic, and flavonoids) in seeds during priming as well as in early seedling growth. Furthermore, the tolerance of primed seeds to osmotic stress also was developed by increasing the content of proline, glycine betaine, and soluble sugar in seeds, resulting in an improvement in germination and seedling growth. Therefore, induction of stress memory in quinoa seeds by CaCl2 priming could be an effective method to improve the tolerance mechanism against osmotic stress in germinating seeds of quinoa, especially in arid ecosystems.