Response of seed germination and physiological mechanism of Vigna angularis and Dolichos lablab to salt stress

Soil salinization has an important effect on seed germination of plants; however, little attention has given to the effect of salt stress on the seed germination of legumes. The Vigna angularis variety 'Yuhongdou 2' and traditional Dolichos lablab variety were used to determine the germination percentage, germination potential, germination index, vigor index, radicle length, embryo length, and fresh weight, malondialdehyde (MDA) content, and superoxide dismutase (SOD) and peroxidase (POD) activity under different NaCl concentrations (0 mmol·L^-1, 20 mmol·L^-1, 40 mmol·L^-1, 60 mmol·L^-1, 80 mmol·L^-1, 100 mmol·L^-1) in an artificial climate chest. The goal of this study was to investigate the relationship between osmotic regulators, stress resistance enzymes, and salt tolerance of leguminous plants under NaCl stress. The results were as follows:1) salinity stress inhibited the germination index of V. angularis. Then germination percentage, germination potential, germination index, and vigor index of V. angularis decreased with increasing NaCl stress and was significantly higher than that of D. lablab. 2) The relative salt damage rate of V. angularis and D. lablab increased with the increase in NaCl concentration. When the NaCl concentration was 80 mmol·L^-1 and 100 mmol·L^-1, the relative salt damage rate of D. lablab was 96.58% and 96.67%, whereas the relative salt damage rate of V. angularis was 47.05% and 83.18%, indicating that the salt damage to V. angularis was less intense. 3) The radicle length, embryo length, and fresh weight of V. angularis and D. lablab seedlings decreased with the increase of NaCl concentration. When NaCl concentration was 100 mmol·L^-1, the radicle length of D. lablab was 0, and that of V. angularis was 0.23 cm. 4) With the increase of NaCl concentration, the content of MDA in the leaves of V. angularis and D. lablab increased, resulting in a gradual increase in cell membrane permeability, but the accumulation of MDA in V. angularis seedlings was lower than that in D. lablab, which indicated that the cell membrane of V. angularis leaves was less damaged. 5) Under NaCl stress, SOD activity of V. angularis and D. lablab increased significantly, but SOD activity of V. angularis was significantly higher than that of D. lablab. Under NaCl stress, POD activity of V. angularis increased significantly, but the POD activity of D. lablab decreased significantly. It was found that V. angularis could reduce the oxidative damage of the cell membrane and the accumulation of MDA by increasing SOD and POD activities, thus improving the germination ability of seeds. V. angularis was higher in salt tolerance than D. lablab under the same concentration of NaCl stress and can better adapt to a salt stress environment.