Comparison of the physiological factors in ion accumulation and photosynthetic electron transport between legumes Medicago truncatula and Medicago sativa under salt stress

Purpose Aimed to identify the differences in ion accumulation and photosynthetic electron transport between Medicago truncatula and Medicago sativa during NaCl stress, and reveal their different physiological mechanism of salt resistance.Methods The plants were cultivated in nutrient solutions with and without 300 mM NaCl. We then measured the plant growth, leaf ion contents, prompt and delayed chlorophyll a fluorescence (PF and DF), and modulated 820 nm reflection (MR/MRO) values of the leaves on the 0 d, 10 d, 20 d, 30 d, and 40 d of NaCl stress.Results The lower dry weight reduction and leaf wilting were found in M. sativa compared with M. truncatula under NaCl stress, and M. sativa appeared to have lower leaf Na+/K+, Na+/Ca2+, Na+/Mg2+ ratios than M. truncatula. With the NaCl treatment, the PF intensity at P-step (F-P) values in the prompt chlorophyll a fluorescence transient (OJIP) curves for both species decreased gradually as the duration of exposure increased. However, the F-P value of M. truncatula suggested a faster decline than that of M. sativa. Compared with M. truncatula, the DF amplitude in M. sativa exhibited a decrease that was slower and lower in response to the NaCl treatments, NaCl stress also made the lowest points of the MR/MRO appear later in M. truncatula, but not in M. sativa.Conclusion Our results indicated that M. sativa was more effective in inhibiting Na+ and Cl- accumulation and regulating nutrient ion balance in leaves than M. truncatula during NaCl stress. Moreover, M. sativa had a strong ability to maintain stable electron transport under NaCl stress, so it is suitable for cultivation in saline soil.