The results showed that K+ content decreased while Na+ and Cl- contents increased in salt-treated cucumber seedlings, so the ratios of K/Na and Cl/Na all decreased. The difference in K+, Na+ and Cl- contents and the K/Na and Cl/Na ratios was greater for the salt susceptible cv. ‘Jinchun No.2’ than for the salt tolerant cv. ‘Changchun Mici’. Sodium ion content increased significantly in all of organs. Furthermore, Na+ accumulated primarily in lower leaves, root-stem transition zone and stem. The chloride ion accumulated mainly in the stem and root-stem transition zone. So cucumber seedlings may compartmentlize the deleterious ions at the organ level, which was one of their major salt-tolerance mechanisms. The accumulation of Na+ in the leaves and roots relative to the control was greater than that for Cl- indicating that Na+ might be the major toxic ion.
Cucumber seedlings treated with exogenous polyamines combined with salinity showed higher levels of K+ accumulation and lower levels of Na+ and Cl- accumulation compared with the seedlings treated with salt stress only. 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, improve the absorbing selectivity of K+ to Na+. Exogenous polyamines improved the transporting selectivity of K+ to Na+ from stem to leaves for both cultivars. In addition, exogenous polyamines enhanced the transporting selectivity of K+ to Na+ from root to stem of ‘Changchun Mici’. Exogenous polyamines had no significant effect on the transporting selectivity of Cl- to Na+ from stem to leaves, however, they improved the transporting selectivity of Cl- to Na+ from root to stem.
In conclusion, exogenous polyamines could alleviate salt damage to some extent, and enhance the accumulation of biomass. Among the three kinds of polyamines, Spd was the more effective. Exogenous polyamines could improve tolerance of cucumber seedlings to salt stress by regulating the uptake and distribution of ions in different organs.