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 fluorescencequenching, photosynthesis and pigment composition werefollowed in the green alga Chlorococcum sp.during exposure of the culture to nitrogen deficiencyand salinity stress with the aims to study theinterrelations between changes in physiological andphotochemical parameters and xanthophyll-cyclepigments content during adaptation to stress, and toevaluate the capacity of this green alga to producesecondary carotenoids in tubular photobioreactors.Exposure of Chlorococcum to nitrogendeficiency, 0.2 M NaCl and high irradiance outdoorscaused a strong depression of the photosyntheticactivity and of photochemical quantum yield ofPSII (F_v/F_m). These changes wereaccompanied by an increase of the non-photochemicalquenching coefficient (NPQ), of the amount ofxanthophyll-cycle pigments and of thecarotenoid/chlorophyll ratio. As a result of exposureto stress conditions, cell division completelystopped, although an increase in the biomass dryweight could be detected due to an increase in thecell size. These processes were followed, with acertain delay (15–20 h), by massive appearance ofsecondary carotenoids that reached the maximum (about50% total carotenoids) after 2–3 days of cultivation.The results show that despite of the lower carotenoidcontent (2 mg g^-1 dry wt) as compared with Haematococcus, Chlorococcum can be apotentially interesting strain for secondarycarotenoid production because of its higher growthrate.