Effect of NaCl stress on ultrastructure of mesophyll cells of five tree species introduced from North America.

In order to definite the salt tolerance of five tree species introduced from North America,such as Fraxinus americana L.,Acer ginnala Maxim.,Alnus rubra Bong.,Nyssa aquatica L.and Gleditsia triacanthos L.,using water culture method,the ultrastructure of mesophyll cells of one-year-old seedlings of them after treated with 0(CK),4 and 8 g·L-1NaCl was observed and compared by TEM technique.The observation results show that under normal condition(0 g·L-1NaCl),mesophyll cell of five tree species has slight difference in chloroplast morphology and osmiophilic granule number,and so on,but no occurrence of plasmolysis.Generally,chloroplasts and cell nuclei of mesophyll cells of five tree species are injured at different degrees after stressed by NaCl,it is presented as disappearance of chloroplast membrane,swelling of thylakoid lamella structure,chloroplast degradation,osmiophilic granule increase or bigger,disappearance of cell nuclear membrane,nuclear chromatin condensation.And with rising of NaCl concentration,the injure degrees of chloroplasts and cell nuclei are gradually severe.Under 4 and 8 g·L-1NaCl stress condition,the plasmolysis appears in mesophyll cells of G.triacanthos,A.ginnala and N.aquatica,while the annulate lamellae appear in mesophyll cells of A.rubra,F.americana and N.aquatica.According to the observation results,it is conjectured that the tolerance to NaCl stress of A.rubra and F.americana is stronger while that of N.aquatica is the weakest,and G.triacanthos and A.ginnala also possess a certain tolerance to NaCl stress.