Probing the effects of high-light stress on pigment and lipid metabolism in nitrogen-starving microalgae by measuring chlorophyll fluorescence transients: Studies with a Δ5 desaturase mutant of Parietochloris incisa (Chlorophyta, Trebouxiophyceae)

a r t i c l e i n f o Keywords: Chlorophyll fluorescence transient Dihomo-γ-linolenic acid Nitrogen deficiency OJIP On-line monitoring Parietochloris incisa We investigated effects of irradiance on the relationships between chlorophyll fluorescence transients (OJIP), carotenoid-to-chlorophyll ratio, and fatty acids in a nitrogen-deprived Parietochloris incisa (Chlorophyta, Trebouxiophyceae) Δ5 desaturase mutant accumulating valuable LC-PUFA dihomo-γ-linolenic acid (DGLA). High light (270 μE·m −2 ·s −1 PAR) and nitrogen starvation brought about a decrease in maximum quantum yield of photosystem II (Φ P0) and electron transport (Φ E0) but enhanced the quantum yield of thermal dissipa-tion (Φ D0) and induced non-photochemical quenching (NPQ) in an irradiance-dependent manner. Under high irradiance a decline in the rate of total fatty acid accumulation and DGLA percentage in comparison with the cultures grown under 130 μE·m −2 ·s −1 PAR was recorded. Increasing irradiance from 130 to 270 μE·m −2 ·s −1 enhanced total fatty acid accumulation only within the first week of nitrogen starvation and negatively affected DGLA production. Regardless of irradiance, Φ P0 , Φ E0 , and Φ D0 exhibited tight (r 2 =0.8–0.9) relationships with the stress-induced changes of total fatty acid and DGLA content and the carotenoid-to-chlorophyll ratio. The applicability and limitations of OJIP and its derived parameters for on-line monitoring of physiological condition and accumulation of value-added products in microalgal cultures grown in photobioreactors are discussed. In various groups of microalgae environmental stresses such as high PAR irradiance and/or nitrogen deficiency bring about profound changes in photosynthetic apparatus (PSA) structure and function as well as in lipid and pigment metabolism [1]. In many cases a build-up of storage triacylglycerols (TAG) coordinated with a decline in chlorophylls (Chl) and accumulation of secondary carotenoids (Car) takes place [2,3]. These phenomena have important biotechnological implications since Car and fatty acids (FA) accumulated by certain microalgae under the stress condition are high-value nutraceuticals and antioxidants; neutral lipids are considered as a promising feedstock for biodiesel [4,5]. The highlight acclimation of microalgal cells involves engagement of photoprotective mechanisms decreasing the absorption of light by the PSA and enhancing thermal dissipation of the absorbed light energy within PSA [1]. In mass culture of microalgae, understanding the relationships of the adaptive rearrangements of the PSA with lipid metabolism is essential for the estimation of stress intensity of oleaginous species. It is also important for timely adjustment of cultivation conditions enabling the organism to cope with the …