Abstract: By adopting vermiculite culture, this paper studied the malondialdehyde (MDA) content and polyamines (PAs) metabolism in the seeds of two vegetable soybean cultivars with different salt tolerance under the stress of 100 mmol NaCl·L^-1. NaCl stress increased the MDA contents in the seeds of the two cultivars significantly, but the increment was lower for salt-resistant cultivar ‘Lülingtezao’ (LL) than for salt-sensitive cultivar ‘Lixianggaochan 95-1’ (LX). In the whole period of NaCl stress, LL seeds had higher contents of free spermine (Spm), conjugated Spm, conjugated spermidine (Spd),  bound Spd and bound putrescine (Put), higher values of (Spd+Spm)/Put and (cPAs+bPAs)/fPAs, and lower value of Put/PAs, and had higher content of free Spd in the mid and late period (9-15 d) of NaCl stress, as compared with LX seeds. In a longer term (6-15 d) of the stress, LL seeds maintained a higher activity of arginine decarboxylase (ADC) and a lower activity of polyamine oxidase (PAO). All the results suggested that LL seeds had stronger capabilities for polyamines synthesis and for the transformation of Put to Spd and Spm and of free polyamine to conjugated and bound polyamines, which effectively inhibited the membrane lipid peroxidation, possibly being one of the important reasons for the stronger salt tolerance of LL.

Key words: NaCl stress, vegetable soybean, free polyamine, conjugated polyamine, bound polyamine