Abstract:

Aims Betalains are an important class of water-soluble pigments that comprise the red-violet betacyanins and the yellow betaxanthins and accumulate in most families of the Caryophyllales and some higher fungi. However, little is known about the regulation of betalain bio-synthesis by environmental factors in higher plants. Our objective is to explore the mechanism and the biological role of betacyanin accumulation induced by dark in leaves of the C₃ halophyte Suaeda salsa.
Methods Seeds of S. salsa were cultured in 24 h dark and 14 h light/10 h dark, and watered with 0, 0.2% and 1.0% H₂O₂ nutrient solution. Seedlings were harvested three days later and assayed for betacyanin content, H₂O₂ content, activity of catalase (CAT) and superoxide dismutase (SOD) in leaves.
Important findings Darkness significantly enhanced H₂O₂ content, betacyanin content, activity of SOD and CAT in S. salsa leaves. Application of different concentrations of H₂O₂ to the culture solution increased H₂O₂ content, betacyanin content, activity of SOD and CAT compared to the dark treatment. Betacyanin content and H₂O₂ content in S. salsa leaves were closely related. Moreover, the scavenging superoxide ($\mathop{{O}}_{2}^{{\mathop{}-{\ •}^{-}}}$) ability of the betacyanins from S. salsa leaves in vitro was lower than that of vitamin C, while the scavenging hydroxyl radical (·OH) ability of the betacyains was much higher than that of vitamin C. These results suggest that betacyanin accumulation in S. salsa leaves grown in dark is possibly induced via reactive oxygen species (ROS) such as H₂O₂ and that betacyanin is involved in alleviating damage caused by oxidative stress due to its high ROS scavenging ability.

Key words: betacyanins, catalase, hydrogen peroxide, hydroxyl radicals, superoxide dismutase, superoxide, Suaeda salsa