24-Epibrassinolide promoted growth and organic compounds accumulation in Dunaliella parva by enhancing photosynthesis

As a commonly used type of the sixth class of phytohormones brassinosteroids (BRs), 24-epibrassinolide (EBL) plays the important roles in plant growth and development. Dunaliella parva (D. parva) is an important lipid-producing microalga, and its growth and accumulation of organic compounds need to be further improved for higher application value. However, the effects of EBL on D. parva are still unclear now. In this study, D. parva was treated with different concentrations of 24-epibrassinolide (EBL) to evaluate its influence. Cell density of 0.5 mg/L EBL treated group was 1.28-fold of control at 18 d. The contents of chlorophyll, carotenoid, carbohydrate, starch, protein of 0.5 mg/L EBL treated group were 1.31-, 1.18-, 1.49-, 1.35-, and 1.54-fold of control. The highest mRNA levels of rbcS, rbcL, RuPE, PRK, TPI, FBPA, FBPase, SBPase, DpME, CA in EBL treated group were 1.94-, 2.43-, 2.14-, 1.76-, 1.97-, 2.21-, 1.48-, 1.96-, 2.06-, and 1.89-fold of control. The highest enzymatic activities of ME, CA and RuBisCO in EBL-treated group were 1.27-, 1.23-, and 1.37-fold of control. Lipid content of 0.4 mg/L EBL treated group was 1.44-fold of control. This study demonstrated the great potential of EBL to obtain higher biomass and organic compounds accumulation. Our study indicates that EBL treatment is valuable for the subsequent commercial production of biofuel and other high-value metabolites using microalgal biomass as raw material.