Pigment composition,optical properties,and resistance to photodamage of the microalga Haematococcus pluvialis cultivated under high light

The relationships between changes in cell suspension absorbance, pigment composition, and resistance to photodamage were investigated in the microalga Haematococcus pluvialis Flotow em. Wille (Chlorophyta) IPPAS H-239 cultivated under high level of photosynthetically active radiation (PAR, 50 W/m²). When the green flagellated cells of H. pluvialis lacking astaxanthin (Ast) and possessing low (<0.5) carotenoid/chlorophyll ratio were irradiated by intense light (2500 W/m² PAR), rapid and synchronous photobleaching of 70–80% of chlorophyll (Chl) and carotenoids (Car) was observed. By contrast, the rate of pigment photobleaching in cells with Car/Chl > 1, which retained high Chl content (> 0.6 fmol/cell) and accumulated significant amounts of Ast, was two times lower than in the green cells. Red aplanospores, with Car/Chl > 10, containing high amounts of Ast and low amounts of Chl (> 0.8 and < 0.1 fmol/cell, respectively) were resistant to photodestruction. The extent of cell resistance to photobleaching correlated closely with an increase in contribution of Car to light absorption by H. pluvialis cell suspensions. The build up of Ast during acclimation to high light was accompanied by a gradual increase in the optical density ratio OD₄₈₀/OD₆₇₈, whereas synchronous (OD₄₈₀/OD₆₇₈ ≈ const; r ² > 0.99) and profound (>20%) bleaching of Car and Chl absorption bands was characteristic of photodamage. The spectral features of photoacclimation and photodamage revealed in this work can be used for nondestructive diagnostics of photodamage in H. pluvialis cultures and for on-line assessment of cell resistance to photooxidative death. The results are discussed with respect to the nondestructive monitoring of laboratory and production cultures of H. pluvialis and their protection from photooxidative death.