Abstract: To investigate the effects of K⁺ on the growth and relevant physiological parameters in sainfoin (Onobrychis viciaefoia) under high-salt stress, in this study, 4-week-old seedlings, with or without 100 mmol·L^-1 NaCl (high-salt stress), were subjected to various concentrations (5, 10, 25 and 50 mmol·L^-1) of KCl for 7 days, in this study. It was found that high-salt stress significantly inhibited the growth of sainfoin seedlings compared to the control. However, the addition of different concentrations of KCl clearly ameliorated the inhibition of high-salt stress on growth of seedlings. Under high-salt stress, with increasing KCl concentration, fresh weight, dry weight, tissue water and total chlorophyll contents showed a trend of gradual increase, reaching their greatest values when KCl concentration was 25 mmol·L^-1, while Na⁺ concentrations in both shoots and roots displayed a gradual reduction, but K⁺ concentrations and K⁺/Na⁺ ratios, remarkably, displayed an increasing trend. Proline, soluble sugar and soluble protein contents also reached their peak values when concentration of KCl was 25 mmol·L^-1, and were a little lower at 50 mmol·L^-1 KCl concentration. Malondialdehyde content, and cell wall, cytoplasmic and vacuolar invertase activities exhibited clearly decreasing trends, while superoxide dismutase, catalase, ascorbate peroxidase, sucrose synthase and sucrose phosphate synthase activities, together with sucrose and glucose contents, showed gradually increasing trends. Taken together, our results suggested that the addition of K⁺ alleviates high-salt toxicity to sainfoin seedlings by maintaining K⁺ and Na⁺ homeostasis, enhancing antioxidant enzyme activities, and improving sucrose synthesis and accumulation in shoots.

Key words: salt stress, K⁺/Na⁺, soluble sugars, antioxidant enzymes, malondialdehyde