Comparative Study On Leaf Antioxidant System Of Green And Red-violet Phenotype Suaeda Salsa

Suaeda salsa L. is a succulent halophyte. S. salsa plants are red-violet (red-violet phenotype) when they grow in tideland and those are green (green phenotype) when they grows in saline soil far from the tideland. Red-violet phenotype Suaeda salsa grows under the stresses of salinity, hypoxia and low temperature, the green one grows under the stresses of salinity and aridity. The different environment induces different phenotype. Under the different stresses, enzymatic and non-enzymatic antioxidant mechaniams could also be different in the two phenotypes to adapt to environmental stresses.In the present study, the mature leaves of two phenotypes S. salsa plants grown under natural environment (in the Yellow Delta) were used to study enzymatic and non-enzymatic antioxidants. On the one hand, water content, osmotic potential, ion content, the contents of soluble sugar,Pro,GSH,AsA were determined to gain insight into the responses of two phenotypes to different environments. On the other hand, the activity of SOD,APX,CAT and POD were measured, and the bands of isozyme of SOD,APX,CAT,POD were also analysed to examine whether there is any difference between two phenotypes. The main results of this study are as follows:1. The comparison of the physiological parameters of the mature leaves of two phenotypes S. salsaThe leaf water content of red-violet phenotype S. salsa was 98.6% and the green one was 96.6%. The degree of leaf succulence of red-violet phenotype S. salsa was much higher than that of green one. Na~+/K~+ ratio of red-violet phenotype S. salsa was much higher than that of green one. Soluble sugar and proline can reduce osmotic potential of leaf and alleviate the stresses. The content of soluble sugar of red-violet phenotype S. salsa(829.6μg/g FW)was much higher than that of green one (630.8μg/g FW). Proline can also protect the membrane. Proline content of red-violet phenotype S. salsa was much higher than that of green one. Red-violet phenotype S. salsa accumulated more ion and soluble solutes than the green one, which is the reason for that osmotic potential (-4.18MPa) of red-violet phenotype was much lower than that of green one (-3.44MPa). It was in favor of absorbing the water under stress environment.2. The comparison of leaf pigment of two phenotypes S. salsaBetacyanin is a kind of soluble pigment in vacuole. It is possiblely involved in reducing the osmotic potential. Recent studies also show that betacyanin is a kind of antioxidants. Betacyanin content of red-violet phenotype S. salsa (61.4μmol/g FW)was much higher than that of green one (26.3μmol/g FW). However, the contents of chlorophyll a and chlorophyll b of green phenotype S. sals were higher than those of the red-violet one. Interestingly, chlorophyll a /chlorophyll b of red-violet phenotype S. sals was higher than that of green one. Chlorophyll a /chlorophyll b ratio indicates the degree of the thylakoids.The higher the ratio, the more powerful photoprotect of the thylakoids. These results suggest that red-violet phenotype S. salsa plants formed in the flooding, low temperature and high salinity possess more efficient antioxidant mechanism than the green one formed only in high salinity.3. The comparison of leaf non-enzymatic antioxidants of two phenotypes S. salsaThe GSH and AsA are two kinds of non-enzymatic antioxidants.The content of GSH and AsA of red-violet phenotype S. salsa was much higher than that of the green one. Meanwhile, AsA is necessary for APX to decompose the H2O2.4. The comparison of leaf enzymatic antioxidants of two phenotypes S. salsaThe activities of SOD and APX in red-violet phenotype leaves were much higher than those in the green ones, meanwhile the activities of POD and CAT of red-violet phenotype leaves were significantly lower than those of the green ones.The bands of isozyme of SOD,APX,CAT,POD were different. It affirmed the difference of activity and quantity of enzymatic antioxidant.The relative activities of SOD and APX in red-violet phenotype leaves were 1.65 times and 1.56 times higher than those in the green ones, respectively. In contrast, relative activities of CAT and POD in green phenotype leaves were 5.2 times and 1.45 times higher than those in the red-violet ones. It showed that two phenotypes S. salsa remove the reactive oxygen species by different enzymatic antioxidants.These results suggest that red-violet phenotype S. salsa plants are able to adapt to integrative stresses of salinity, hypoxia and low temperature possibly via increasing non-enzymatic antixidants such as GSH, AsA contents and activities of key enzymatic antioxidant such as SOD and APX.