PHOTOSYNTHETIC CHARACTERIZATION OF A MUTANT OF NANNOCHLOROPSIS DEFICIENT IN THE SYNTHESIS OF EICOSAPENTAENOIC ACID

Photosynthetic performance of an eicosapentaenoic acid (EPA; 20:5 omeg a 3) deficient mutant of the eustigmatophyte Nannochloropsis sp. was c ompared to the wild type (Wt) strain in order to evaluate the effect o f fatty acid composition on the function of the photosynthetic apparat us. Cellular photosynthetic capacity and the cellular pool of pigments and of reaction centers were reduced in the mutant concomitant with a reduction in the amount of thylakoid membranes and their volume-speci fic density. Despite the changes observed in photosynthetic activity, the fluorescence properties of the mutant were virtually the same as t hose of the wild type, although the phase transition of thylakoid memb rane was recorded at higher temperature in the mutant than in the Wt. The results suggest that the change in one double bond in a very long chain fatty acid of the thylakoid lipids plays a minor role in regulat ing photosynthetic electron transport, but that the mutation modified the ability of the mutant to acclimate to low-irradiance conditions.