Effects Of Salt And Alkali Stresses On Photosynthesis And Saccharometabolism Of Chloris Virgata Seedlings

The soil salinization has become a serious ecological environment problems and an important factor in limiting agricultural production. In fact, soil salinization and alkalization frequently co-occur, and this caused severe problems in many areas. A large number of experimental evidence indicates that alkali-stress is more severe than salt-stress on plant growth and ecological environmental damage. Chloris virgata, an alkali resistant halophyte, was chosen as the experimental material. The seedings of C. virgata were treated with varying salinities (0, 50, 100, 150mM) salt-stress(NaCl:NaSO4=1:1) and alkali-stress(NaHCO3:Na2CO3=1:1). To research the physical adjustment of photosynthesis and carbohydrate metabolism of C. virgata under salt and alkali stresses and summarize the physiological characteristics of enzymes related to the saccharometabolism under salt and alkali stress, photosynthesis, chlorophyll fluorescence, starch, sucrose, reducing sugar was determined. The activities of saccharometabolic enzymes, invertase, sucrose phosphate synthase, sucrose synthase and ADP-Glucose pyrophoshorglase, were also explored.The results showed that photosynthesis and photosystemⅡof C. virgata under alkali-stress was restrained and destruct; chlorophyll contents and the net photosynthetic rates decreased, which caused the photosynthesis product such as starch and sucrose reduced, but under salt-stress, these indexes did not change significantly. The activities of acid invertase and neutral invertase under salt and alkali stress both increased, and that was correlated with the reduce of sucrose content and the increases of reducing sugars. The increase of acid invertase activity under salt-stress was higher than that under alkali-stress, on the contrary, the increase of neutral invertase under salt-stress was lower than that under alkali-stress. According to the different effects of salt and alkali stress on sucrose and reducing sugar contents, we can infer that the role of neutral invertase is more important under alkali-stress. Sucrose phosphate synthase and sucrose synthase activities both reduced under salt and alkali stresses, and the decrease under alkali-stress was more than that under salt-stress. Alkali-stress caused the inhibitory of sucrose synthesis and result in the sucrose reduce. Under salt and alkali stresses, ADP-Glucose pyrophoshorglase activity advanced in order to promote the starch synthesis, but that did not change the decline trend of starch under the high salinity and high pH. Stress induced starch degradation, that may also caused the starch decline, and that need further studying.In conclusion, results of the study showed that alkali-stress induced starch and sucrose degradation and accumulation of sugars in C. virgata seedings with a concomitant increase in the activity of invertase and decrease in the activity of sucrose phosphate synthase. The resusts also showed that the effects of alkali-stress on plants are more severe than saltt-stress.