Effect of phytohormones on growth and accumulation of pigments and fatty acids in the microalgae Scenedesmus quadricauda

The phytohormones abscisic acid (ABA), 24-epibrassinolide (EBL), brassinolide (BL), and 3-indoleacetic acid (IAA), at concentrations relevant to that in hydroponic wastewater, were investigated for their physiological effects on the microalga Scenedesmus quadricauda. All phytohormones tested had positive stimulatory effects on S. quadricauda cell growth, biomass production, as well as on intracellular concentrations of chlorophyll-a, carotenoid, and lipids biosynthesis. The most powerful inducers of chlorophyll-a and carotenoid biosynthesis were EBL and IAA, while the phytohormone effect on fatty acids biosynthesis followed the order: IAA ≥ ABA > EBL > BL. Both the quantities of fatty acids and their profiles depended on the phytohormone type and the specific concentrations tested. All tested phytohormones altered S. quadricauda cell size and positive or negative effects were dose-dependent. To our knowledge, this is the first report that systematically compares the influence of four phytohormones, including two types of brassinosteroids, on a broad-range of S. quadricauda physiological parameters.