The combined influence of 24‑epibrassinolide and 3‑indoleacetic acid on growth and accumulation of pigments and fatty acids in the microalgae Scenedesmus quadricauda (CPCC-158)

Interest in the use of wastewaters of different origins for the industrial production of microalgal biomass for biofuels and bioproducts has stimulated studies on the influence of a variety of compounds in wastewaters on algal physiology. Following the previously published work on the impact of four single phytohormones on the physiology of the microalga Scenedesmus quadricauda (CPCC-158), we investigated the combined effect of the 24‑epibrassinolide (EBL) and 3‑indoleacetic acid (IAA) on S. quadricauda biosynthesis and biomass production. Synergistic increases in S. quadricauda biomass production, chlorophyll-a accumulation, total carotenoid accumulation, as well as total and major neutral lipid (triacylglyceride) accumulation were observed for most of the mixed hormone trials. Mixed hormones had stimulatory effects on growth and biosynthesis of S. quadricauda, but the influence of mixed hormones on algae growth (maximum 1.6-times greater) was less than their influence on algal biosynthesis (maximum 1.7-, 2.7-, and 3.3-fold for chlorophyll-a, total carotenoids, and fatty acids, respectively) compared with single hormone treatments. The mechanism of EBL and IAA cross-talk is likely specific to targeted biosynthetic pathways. The type of relationship between two mixed phytohormones was assessed with Ting-Chao Chou Test. Our results highlight the need for further research on the combined influence of phytohormones on algae physiology.