Relationship of leaf ultrastructure of mangrove Kandelia candel (L.) Druce to salt tolerance

Abstract

The leaf ultrastructure of mangrove Kandelia candel (L.) Druce planted in pots under different salinity conditions was compared under a transmission electron microscope (TEM). The results showed that the plasmalemma in plants grown in salinity conditions of 0‰ treatment (control) and 25‰ treatment was tightly combined, while in plants with salinity of 50‰ treatment, the plasmalemma crimpled remarkably and plasmolysis occurred. The nucleus and its two-layer membranes were obvious in control plants. In the case of 25‰ treatment, the membrane breakdown was observed, nucleoplasm dispersed in cytoplasm, and the electron density of cells was lower than that in control plants. In plants treated with 50‰ salinity the nucleus collapsed and no structure of the nucleus could be observed. As far as chloroplasts in control plants were concerned, they were oblong with a typical arrangement of grana and stroma thylakoids and one or two grains of starch. However, the chloroplasts in plants treated with 25‰ salinity were swelling and usually contained more grains of starch and few plastoglobuli. Most chloroplasts had a reduced number of grana, particularly of thylakoids in grana as compared with control plants. The chloroplasts of plants treated with 50‰ salinity had a considerably reduced system of grana and stroma thylakoids, and sometimes they were even deformed morphologically. They were mixed-up and contained more grains of starch and plastoglobuli. The indistinct structure of mitochondrial cristae was observed only in plants treated with 50‰ salinity. These showed that mitochondria are cell organs less sensitive to hypersaline conditions than chloroplasts and nucleus, and it was deduced that respiration was more conservative to an environment change than photosynthesis.