Researches On The Morphological And Physiological Adaptations Of S. Portulacastrum Under Ions Treatments

Soil salinity is a major abiotic stress in plant agriculture worldwide, the detrimental effects of high salinity on plants was attributed to osmotic stress and interfering ionic equilibrium. Many halophytes can be adapted to the saline environment and showed good growth in the moderate salt concentration. Some studies suggest that halophytes and glycophytes have the same mechanism of salt tolerance. Sesuvium portulacastrum is a perennial halophyte, Mainly distributed in tropical and subtropical sand, is an associated plant of mangrove. Sesuvium portulacastrum has a variety of research value, it has the role of fixing sand dunes, stabilizing the saline soil, desalinating of seawater ect.In this study, The Sesuvium portulacastrum was treated in different concentrations of NaCl and different ions. Optical microscope, mercury-bromophenol blue slice, atomic absorption spectroscopy, transmission electron microscopy and scanning electron microscopy, X-Ray-spectroscopy combined with elements of micro-analysis technology etc, were used to analyse the morphology and physiological changes of the Sesuvium portulacastrum. On the morphology, after0-400mM concentration of salt stress, the diameter of the epidermal cells, the degree of stem and leaf succulent increased, and there also had a corresponding increase in biomass and water content, and200mM NaCl is the optimum growth concentration. When the concentration of NaCl reached600mM the growth of the S. portulacastrum became inhibited. Flame emission and SEM-X-ray microanalysis suggested that NaCl treated S. portulacastrum accumulated high content of Na+but low content of K+,600mM NaCl treated plants, about140and40mg/g DW of Na+accumulation was observed in leaves roots, respectively. But the Na+/K+ratio in both leaf and stem of S. portulacastrum was increased dramatically with the increasing concentration of NaCl.The transmission electron microscopy analysis showed that the chloroplast shrinked and the lipid ball and starch grains accumulated in a large number to reduce the osmotic stress. TEM-X-ray microanalysis of Na+element demonstrated that Most of Na+accumulation in the vacuole, followed by the apoplast, and then thecytoplasm, and finally the cell wall. compartmentalized into vacuoles of palisade tissues in leaves. These results suggest that Sesuvium portulacastrum could alleviate the poison of the salt ions by succulenting stems and leaves, enlargement of cells and compartmentalized the Na+ions to survive in the salt environment.In the study of effects of different ions on the growth and development of S. portulacastrum, we found that the sodium ion is more effective than other ions in promoting the succulence and enlargement of cell. Other ions usually have inhibitory action to the growth of S. portulacastrum. It suggest that sodium may be a more important macronutrient than other ions for S. portulacastrum.These results suggest that the Sesuvium Portulacastrum not only could succulent stems and leaves but also has a salt ions compartmentalization mechanism to relieve excessive salt ions in cells or tissues to adapt to the high salt environment.