Mohammad Modarresi

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 algae. One of the objectives of this study was to investigate the effect of gibberellic acid treatment on growth, photosynthetic pigments, dry biomass, endogenous gibberellic acid level, and total lipid content in N. salina cultivated in f/2 medium. Experimental treatments included concentrations of 0 (control), 0.5, 5, 10, and 20 mg/L of gibberellic acid. This experiment was conducted using a completely randomized design (CRD) with three replications in the year during 2021-2022 at the Persian Gulf Science and Technology Park in Bushehr, Iran. The measured traits encompassed growth rate, doubling time, chlorophyll a and b content, total chlorophyll and carotenoid, dry biomass, endogenous gibberellic acid levels, and total lipid content. The analysis of variance (ANOVA) showed that gibberellic acid treatment has a significant effect on examined traits at a significant level of (p < 0.01). Exogenous application of gibberellic acid treatment increased the growth rate, chlorophyll-b content, dry biomass, and total lipid content 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 GA treatment, respectively. This was while the highest growth rate was obtained at the concentration of 0.5 mg/L gibberellic acid (GA3). It 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 microalgae under an f/2 medium.