The relationship between the antioxidant system and phycocyanin production in Spirulina maxima with respect to nitrate concentration

The relationship among antioxidant enzyme activities, such as iron-superoxide dismutase (FeSOD) and ascorbate-dependent peroxidase (AsA-POD), and phycocyanin, chlorophyll, total carotenoid, ascorbate contents, and lipid peroxidation (LPO) levels were investigated in Spirulina maxima SAG 84.79 in nitrate limited (10 mM), control (30 mM), and supplemented (50 mM) conditions. In the present study, extracellular nitrate and intracellular iron, magnesium, and copper levels were also investigated. The highest FeSOD and AsA-POD activities and chlorophyll content and the lowest LPO levels were found in control conditions on day 13: 21.9 +/- 1.5, 5.7 +/- 0.3 IU mg(-1), 16.2 +/- 0.5 mg g(-1), and 0.322 +/- 0.01 nmol malondialdehyde g(-1) wet weight, respectively. The highest phycocyanin content was determined in nitrate supplemented conditions on day 13, at 190.68 +/- 9.3 mg g(-1). The similar LPO levels observed in supplemented (50 mM nitrate) and control (30 mM) conditions showed that phycocyanin demonstrated effective protection of S. maxima membranes. The data revealed that its response against nitrate exposure was related to the antioxidant enzymes and compounds in the antioxidant defence system of S. maxima.