Studys On The Antioxidant Function Of Betacyanin Accumulating In Suaeda Salsa L.

Betacyanin is synthesized in vegetative and reproductive organs of some plants. In vegetative organs, its accumulation is highly affected by enviromental condition, but in reproductive organs such as petals, stamens, seeds and fruits, betacyanin is mainly controlled by developmental stages. Previous studies were mainly focused on the factors, which influenced the accumulation of betacyanin, e.g. plant growth regulators, light quality (e.g. red light, far-red light and blue light), light quantity, temperature and nutrition elements (e.g. K+,NO3+,PO43-,sucrose and Cu2+).The Chenopodiaceae Suaeda salsa L., a C3 plant, is a succulent euhalophyte. Shoots of S. salsa are violet-red throughout the whole growth period under hypoxia, high salt and low temperature conditions in the intertidal zone, but green on saline inland far from the seaside. Nowadays, the pigment in plants has been identified as betacyanin in S. salsa which occurs in the intertidal zone. In our previous investigations, when seeds of S. salsa from either violet-red phenotype plants grown in the intertidal zone or green phenotype plants grown in saline inland were sown in sand and cultivated in a greenhouse, their phenotype were green regardless of their mother plants. The result demonstrates that the accumulation of betacyanin is mostly regulated by enviromental factors. As a halophyte, physiological and molecular responses of Suaeda salsa to salinity stress have been extensively studied. But nothing is known about the antioxidant function of betacyanin accumulating in S. salsa.In the present study, firstly, the effects of hypoxia, salt and low temperature on the betacyanin accumulation of S. salsa were investigated. The results indicated that the betacyanin contents were the highest in both stems and leaves of S. salsa plants treated with flooding for 2 h daily for 60 d. Different salts in a certain range of concentrations led to different betacyanin accumulation, e.g. 15 mmol/L MgSO4, 20 mmol/L KCl, 20 mmol/L CaCl2, 150 mmol/L MgCl2 and 150 mmol/L KNO3 gave rise to the higher betacyanin content, compared with control. Surprisingly, NaCl had an inhibitory effect on the betacyanin accumulation. Under the 4 h/d of low temperature (4±2℃) treatment for 60 d, the betacyanin of S. salsa was the hightest among the all treatments. Nevertheless, the effects of various treatments on the betacyanin content were different in different organs of S. salsa, e.g. the betacyanin content in stems was significantly higher than that in leaves. These results suggested that the accumulation of betacyanin in S. salsa is comprehensively influenced by different factors such as hypoxia, salts and low temperature, and hypoxia and low temperature is the main factor.Under comprehensive consitions (15 mmol/L MgSO4, 150 mmol/L MgCl2, 20 mmol/L KCl, 150 mmol/L KNO3, 20 mmol/L CaCl2, hypoxia treatment for 2 h/d and low temperature treatment for 4 h/d), the H2O2 content of stem was significantly higher than that of leaf. The DAB staining of stem and leaf showed that the H2O2 induction for betacyanin was not only related to the content of H2O2, but also related to the H2O2 transport through vascular or its distribution. The result indicated that H2O2 may be acted as a signal molecule. At the morphological top of stem, the betacyanin content was lower, but the H2O2 content was higher. The biosynthesis of betacyanin or its molecular structure may have an activity of eliminating H2O2. Both under the treatment of the tyrosinase inhibitor, arbutin, and the comparision of stem and leaf treated with comprehensive condition, the betacyanin contents were significantly different from the control. But the existence of betacyanin had different effects on the antioxidant enzymes activities. The APX activity was increased, the SOD activity was increased or decreased, and the CAT activity was not affected. These results suggested that the betacyanin may have an activity of eliminating O2˙. In the present study, the leaves of red-violet phenotype and green phenotype S.salsa grown in the same intertidal zone were used to comparatively study the activity of antioxidant enzymes (SOD, APX and CAT) and the content of H2O2, and to examine the correlation between the exogenous H2O2 concentration and betacyanin content of red-violet phenotype using detached leaves. The results showed that the H2O2 content of green phenotype S.salsa leaves was significantly higher than that of red-violet phenotype leaves, while no significant differences in the activity of antioxidant enzymes (SOD, APX and CAT) were detected between the two phenotypes of S. salsa. Correlative analysis showed that the exogenous H2O2 concentration was significantly negative correlated to betacyanin content of the detached leaves of violet-red phenotype S. salsa.These results suggest that betacyanin possibly plays an important role as a non-enzymatic antioxidant in regulating the level of H2O2, sequentially alleviating the oxidative damage caused by oxidative stress.