Microalgae have many commercial applications including biofuel production, use in human and animal nutrition, as pharmaceuticals and therapeutic compounds, in beauty-related products and as biofertilizers in the agricultural sector. However, more research needs to be directed to reducing production costs in an environmentally friendly way before their commercial potential can be fully realized. This review discusses the current knowledge on the occurrence and physiological roles of phytohormones in microalgae and explores the potential of phytohormone treatments to improve cultivation practices, including increasing lipid content and productivity for biofuel production. Microalgae synthesize a wide array of phytohormones and are able to regulate the levels of active phytohormones. Biosynthetic and conversion pathways share some key components but are more rudimentary compared to vascular plants and are likely to have some unidentified conjugation mechanisms. Phytohormones have a dual function in microalgae. Specific phytohormones are involved in the regulation of the cell cycle and other metabolic processes, influencing biomass and primary metabolite accumulation. They are also involved in responses to abiotic stresses, allowing microalgae to adapt to the prevailing conditions. Phytohormones provide a promising strategy to improve mass culture biotechnology due to their intrinsic role in microalgal growth and survival, increasing lipid productivity and improving their tolerance to more extreme environmental changes. This makes them less susceptible to environmental fluctuations. This improves the productivity of the cultures for biofuel production and would be beneficial in a biorefinery approach. Overall, phytohormones provide an exciting and promising avenue of research to improve microalgae cultivation, taking it a step closer to successful commercialization.
Keywords: Biosynthesis; Growth; Homeostasis; Lipid productivity; Primary metabolites; Secondary metabolites; Stress tolerance.
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