Effect of salinity on seed germination, seedling growth, and inorganic and organic solutes accumulation in sunflower (Helianthus annuus L.)

To investigate the effects of saline stress on seed germination, ion distribution, and organic solutes changes of sunflower (Helianthus annuus L.), in the present study, seeds and 3-week-old seedlings were subjected to a series of external NaCl concentrations (5-200 mmol). The results showed that high salinity (200 mmol) remarkably inhibited the germination of seed and delayed germination time in sunflower. It was found that 25-200 mmol NaCl significantly reduced both stem and leaf dry weight. Concentrations of 100 and 200 mmol also caused a clear reduction in tissues water content. With the increase of NaCl concentration, Na+ concentrations both in root and stem showed the increasing trend, whereas to a lesser degree in root than in stem. In leaf, Na+ concentration remained unchanged when the external concentrations of NaCl were below 100 mmol, while significantly increased by 41-fold when plants were exposed to 200 mmol. By contrast, K+ concentration in root displayed the decreasing trend with the increase of NaCl concentrations. Neither lower (5 and 10 mmol) nor higher (100 and 200 mmol) salinity significantly affected K+ concentration both in stem and leaf, while moderate levels (25 and 50 mmol) significantly enhanced K+ accumulation. High salinity significantly enhanced soluble sugar concentration in stem by 28% and proline in leaf by 166%. It was proposed that sunflower plants adapt to saline stress to some extent through regulating distribution of Na+ and K+, maintaining higher selective absorption capacity for K+ over Na+, and accumulating more osmoprotectants, such as soluble sugar and proline.