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)

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) Delta 5 desaturase mutant accumulating valuable LC-PUFA dihomo-gamma-linolenic acid (DGLA). High light (270 mu E . m(-2) . s(-1) PAR) and nitrogen starvation brought about a decrease in maximum quantum yield of photosystem II (Phi(P0)) and electron transport (Phi(E0)) but enhanced the quantum yield of thermal dissipation (Phi(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 mu E . m(-2) . s(-1) PAR was recorded. Increasing irradiance from 130 to 270 mu E . 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, Phi(P0), Phi(E0), and Phi(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. (C) 2013 Elsevier B. V. All rights reserved.