Effects of polyamines on K+, Na+ and Cl− content and distribution in different organs of cucumber (Cucumis sativus L.) seedlings under NaCl stress

Abstract

Seedlings from the salt-sensitive cucumber cultivar Jinchun No. 2 and the salt-tolerant cucumber cultivar Changchun Mici were exposed for 8 days to 50 mmol/L NaCl in the absence or in the presence of exogenous foliar spraying PAs [putrescine (Put), spermidine (Spd), and spermine (Spm) 1 mmol/L] to compare the effects of different kinds of polyamines (PAs) on plant tolerance to salinity. This paper studied the effects of exogenous PAs on K+, Na+ and Cl− in different organs of cucumber seedlings. The results showed that K+ content as well as the ratios of K/Na and Cl/Na decreased, while Na+ and Cl− concentrations increased in salt-treated cucumber seedlings. The differences in K+, Na+ and Cl− content and the K/Na and Cl/Na ratios were greater for the salt sensitive cultivar Jinchun No. 2 than for the salt-tolerant cultivar Changchun Mici. Cucumber seedlings treated with exogenous polyamines and combined with salinity exhibited a higher level of K+ accumulation and lower levels of Na+ and Cl− accumulation compared with the seedlings treated only with salt stress. Among the three kinds of polyamines, Spd and Spm were more effective in inhibiting the accumulation of Na+ and reduction of K+. However, Put was more effective in reducing Cl− accumulation. Furthermore, all of the three kinds of exogenous polyamines could increase the ratio of K/Na, improving the absorption and transport selectivities of K+ and Na+ from stems to leaves for both cultivars. In conclusion, exogenous polyamines could alleviate salt damage to some extent and enhance the accumulation of biomass. Among the three kinds of polyamines, spermidine was most effective. Exogenous polyamines could improve tolerance of cucumber seedlings under salt stress by regulating the absorption and distribution of ions in different organs.