The Efficacy of Different Concentrations of Gibberellic Acid on Growth Rate, Dry Biomass, Endogenous Gibberellic Acid, Lipid Content, and Some Photosynthetic Pigments of Nannochloropsis salina Microalgae in Guillard (f/2) Medium

Nannochloropsis salina is a promising candidate for lipid and biomass production used in aquaculture and biofuel production. On the other hand, phytohormones have different effects on the metabolism of single-celled microalgae species. One of the objectives of this study was to investigate the impact of different gibberellic acid (GA) treatments on growth, some photosynthetic pigments, dry biomass, endogenous GA level, and total lipid content in N.salina microalgae in a Guillard (F/2) medium. The experimental treatments included 0 (control), 0.5, 5, 10, and 20 mg L-1 of GA concentrations. This experiment was conducted in a completely randomized design (CRD) with three replications during 2021-2022 in the Persian Gulf Microalgae Development Laboratory at Persian Gulf Science and Technology Park, Bushehr, Iran. The measured traits included growth rate, doubling time, chlorophyll a and b content, total carotenoid, dry biomass, endogenous GA level, and total lipid content. The analysis of variance (ANOVA) showed that GA treatments had a significant effect on all studied traits at the level of (p 0.01). The exogenous application of GA treatment increased the growth rate and the rate doubled to 0.085 per day and 8.2 days respectively, with the content of chlorophyll b with an average of 2.07 µg/g DW, total chlorophyll to the amount of 72 4.0 µg/g DW in N. salina microalgae, and the highest amount of total lipid and dry biomass with 24.69% and 0.79 g/L were observed in 20 mg/L treatment, respectively. While the highest growth rate was obtained at the concentration of 0.5 mg/L GA. It is suggested that a concentration of 20 mg/L GA be used in the exponential growth phase to increase biomass production and total lipid content in N. salina under Guillard (f/2) medium.