Combined effects of 24-epibrassinolide and salinity on the growth and physiological perfor-mance of Ulva prolifera

Abstract

In order to study the combined effects of brassinosteroids and salinity on the growth and physiological performance of Ulva prolifera under low temperature condition, we investigated the growth, chlorophyll content, chlorophyll fluorescence parameters, soluble protein and carbohydrate contents in this algae, which was grown under three salinity in the presence or absence of 24-epibrassinolide. The results showed that, compared to control salinity (25) treatment, the growth rate of U. prolifera was enhanced by 45.9% under the moderate hyposaline condition (10), but decreased under low salinity (5) treatment, which showed high contents of chlorophyll and soluble protein. However, the presence of EBR (0.2 mg·L-1) significantly reduced the growth of U. prolifera, especially under the control salinity (25) treatment, under which the fresh mass decreased and more spores were released. Additionally, the effective quantum yield (Fv'/Fm'), the activity of SOD and the content of soluble carbohydrate also decreased, but the soluble protein content increased under the control salinity treatment in the presence of EBR. In conclusion, moderatehypo-saline condition could be used to enhance the growth of U. prolifera at 15 ℃, and under normal salinity (25), the EBR could be used to promote the release of spores and produce more materials for mass production of U. prolifera.