Changes in chlorophyll fluorescence quenching and pigment composition in the green alga Chlorococcum sp., grown under nitrogen deficiency and salinity stress

Changes in the in vivo chlorophyll fluorescence quenching, photosynthesis and pigment composition were followed in the green alga Chlorococcum sp. during exposure of the culture to nitrogen deficiency and salinity stress with the aims to study the interrelations between changes in physiological and photochemical parameters and xanthophyll-cycle pigments content during adaptation to stress, and to evaluate the capacity of this green alga to produce secondary carotenoids in tubular photobioreactors. Exposure of Chlorococcum to nitrogen deficiency, 0.2 M NaCl and high irradiance outdoors caused a strong depression of the photosynthetic activity and of photochemical quantum yield of PSII (Fv/Fm). These changes were accompanied by an increase of the non-photochemical quenching coefficient (NPQ), of the amount of xanthophyll-cycle pigments and of the carotenoid/chlorophyll ratio. As a result of exposure to stress conditions, cell division completely stopped, although an increase in the biomass dry weight could be detected due to an increase in the cell size. These processes were followed, with a certain delay (15-20 h), by massive appearance of secondary carotenoids that reached the maximum (about 50% total carotenoids) after 2-3 days of cultivation. The results show that despite of the lower carotenoid content (2 mg g-1dry wt) as compared with Haematococcus, Chlorococcum can be a potentially interesting strain for secondary carotenoid production because of its higher growth rate.