The Response Mechanism Of Chloroplasts In Tetraploid Black Locust Under Salt Stress

Tetraploid black locust was formed by chromosome doubling, belongs to the new polyploidy varieties. Many studies have shown that tetraploid black locust has many excellent characteristics in physiology and biochemistry, is a pioneer species of Chinese’s afforestation. In this study, we used diploid and tetraploid black locust as test materials. The uniform grows of plants were treated by250mM and500mM salt stress for seven days, then sampling respectively. We determined the changes of physiological indicators and observed the differences in morphological structure of chloroplast. Further proteomic technology analysis on chloroplast protein, so as to explore the mechanism of salt tolerance. Hope to provide useful theoretical basis for later research on salt tolerance mechanism of woody plants.Salt stress injury symptoms of tetraploid black locust chloroplasts were less significant than that in diploid. Before salt treatment, we found that the ultramicrostructure of chloroplasts on two kinds of black locust were showed full appearance and complete construction. Chloroplasts were distributed at the edge of the cell wall evenly. After salt treatment, the structure of chloroplast on diploid black locust appeared loose and departed the cell wall, showing a random distribution. The shape of grana lamellae became ambiguity, so much as thylakoids disintegrated. Nevertheless, changes were not obvious in tetraploid black locust chloroplast. The above results indicated that the chloroplast of tetraploid black locust had ultramicrostructure characteristics which shown more salt resistance.These antioxidant enzymes (SOD, APX, GR, DHAR, MDHAR and GST) activity in tetraploid black locust chloroplast were generally higher than that of diploid chloroplast, which can detoxify reactive oxygen species more quickly and effectively that generated during salt stress in the chloroplast, in order to protect the integrity of chloroplast membrane structure, ensuring better photosynthesis of plants. Meanwhile, there were some antioxidants (MDA, ascorbate, glutathione and so on) also played an important role in AsA-GSH circulatory system, and the relative content in chloroplast of tetraploid black locust were higher than diploid. These results further indicated that tetraploid black locust was less sensitive to salt environment.We detected the chloroplast protein changes of diploid and tetraploid black locust by two-dimensional electrophoresis technology. In tetraploid black locust chloroplast, we have found that43protein spots were down-regulated,28protein spots were up-regulated,3protein spots were no significantly changed,4protein spots were not detected and9protein spots were newly detected. In diploid black locust chloroplast, we have detected that34protein spots were down-regulated,13protein spots were up-regulated,4protein spots were no significantly changed,21protein spots were not detected and9protein spots were newly detected. In addition, there were obvious differences between tetraploid and diploid chloroplast protein. The analysis indicated that these chloroplast protein can be divided into photosynthesis calvin cycle protein, photosynthesis electron transfer protein, regulation/defense protein, chaperone, energy metabolism protein, redox homeostasis protein and some protein with unknown function.