[Effects of salt stress on cucumber seedlings root growth and polyamine metabolism].

By the method of water culture, this paper studied the effects of NaCl stress on the seedlings root growth and polyamine metabolism of two cucumber cultivars 'Changchun mici' and 'Jin-chun No. 2'. The results showed that under NaCl stress, root growth was inhibited, and lipid peroxidation and electrolyte leakage increased. These changes were more obvious in salt-sensitive 'Jin-chun No. 2' than in salt-tolerant 'Changchun mici'. NaCl stress caused an increase of arginine decarboxylase (ADC), ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC) activities in cucumber roots, which was much greater in 'Changchun mici' than in 'Jinchun No. 2'. At the highest value, ADC, ODC and SAMDC activities increased by 149.3%, 60.1% and 69.4% in 'Changchun mici' and 118.6%, 56.2% and 50.6% in 'Jinchun No. 2', respectively, in comparison with the control. Diamine oxidase activity increased in 'Changchun mici' but not in 'Jinchun No. 2', and the increment of polyamine oxidase activity in 'Changchun mici' was smaller than that in 'Jinchun No. 2'. As a result, the contents of free spermidine and spermine and of conjugated and bound polyamines in 'Changchun mici' increased significantly, while that of free putrescine had a significant increase in 'Jinchun No. 2'. It could be concluded that higher levels of free spermidine and spermine and of conjugated and bound polyamines and lower level of free putrescine in roots could improve the adaptability of cucumber seedlings to salt stress.