Influence of High Light Intensity and Nitrate Deprivation on Growth and Biochemical Composition of the Marine Microalgae Isochrysis galbana

Abstract Isochrysis galbana is a brown microalgae widely used as a feed for marine organism in aquaculture. The aim of present study is to investigate the growth, biochemical composition, fatty acid profile, photosynthetic parameters and antioxidant activity (radical scavenging activity) of Isochrysis galbana cells cultivated under different levels (sub-optimum; 50 ± 1.5,optimum; 125 ± 2.5 and supra-optimum; 325 ± 3.5 µmol photons m-2 s -1) of photosynthetic active radiation (PAR), and subsequently treated with different concentration of nitrate deprivation (8mM, 2mM and 0.5mM). The experiment was carried out under controlled conditions utilizing a factorial design 3x3 (light intensity and nitrate concentration). The result depicts that PAR positively influences the growth of Isochrysis galbana which is maximum under supra-optimum PAR. Nitrate deprivation (2mM & 0.5mM) induced decline in growth in terms of dry weight is observed as 60.1% & 61.9% in suboptimum and 26.5% and 34.9% in supra-optimum respectively over the values recorded in their respective controls. Supra-optimum PAR decreased primary photosynthetic pigment Chl a and Chl c by 15.7% and 8.5%, whereas carotenoid content increased by 45.9% in supra-optimum PAR which displays potential interest as antioxidant agent in addition to total phenolic content and radical scavenging activity. The results suggest that combined stress of high light and nitrogen deprivation shifts the metabolic physiology from protein synthesis to energy reserve (carbohydrate and lipid) and accumulation of saturated fatty acid on expense of unsaturated fatty acid except docosahexaenoic acid. These valuable compounds exhibit potential applications in mariculture, nutraceutical and biofuel industry.

Inhibitory Effect of Growth-inhibitor on Isochrysis galbana and Inhibition of Antioxidants on Growth-inhibitor Damage to Its Cells / 生物化学与生物物理进展

The inhibitory effects of growth-inhibitor on the growth of Isochrysis galbana, malondialdehyde (MDA) content and activities of antioxidant enzymes (superoxide dismutase and peroxidase) were studied. And the inhibition effects of 4 species of antioxidants on this damage to its cells were also investigated. The results showed that 0.10 mg/L of GI marked decreased cell densities, activities of superoxide dismutase (SOD) and peroxidase (POD), and MDA content increased. With increase of GI concentrations, cell densities and activities of SOD and POD decreased sharply, and MDA content increased obviously. When concentration of GI was 0.30 mg/L, the cell densities, activities of SOD and POD decreased to 0.05, 0.56 and 0.59 folds of the control, respectively, and MDA content increased to as higher as 2.2 folds of that of the control set. L-Ascorbic acid, citrazinic acid, lenediamiaetetraacetic acid disodium salt (Na2EDTA) and 3-tert-butyl-4-hydroxyanisole could decrease MDA content obviously, and marked increased cell densities and activities of SOD and POD. When 4 species of antioxidants were added to the medium, the cell densities, and activities of SOD and POD increased to as high as 1.38～1.90, 1.49～2.12 and 1.55～2.13 folds of that of the control set, respectively, and MDA content decreased by 57.7%～87.9%. It was indicated that the excess active oxygens were produced under growth-inhibitor stress and active oxygen participated in the damage of growth-inhibitor to Isochrysis galbana; the L-ascorbic acid, citrazinic acid, lenediamiaetetraacetic acid disodium salt and 3-tert-butyl-4-hydroxyanisole could effectively inhibit membrane lipid peroxidation and further alleviated algal damage.