The influence of photoperiod and light intensity on the growth and photosynthesis of Dunaliella salina (chlorophyta) CCAP 19/30

The green microalga Dunaliella salina survives in a wide range of salinities via mechanisms involving glycerol synthesis and degradation and is exploited for large amounts of nutraceutical carotenoids produced under stressed conditions. In this study, D. salina CCAP 19/30 was cultured in varying photoperiods and light intensities to study the relationship of light with different growth measurement parameters, with cellular contents of glycerol, starch and carotenoids, and with photosynthesis and respiration. Results show CCAP 19/30 regulated cell volume when growing under light/dark cycles: cell volume increased in the light and decreased in the dark, and these changes corresponded to changes in cellular glycerol content. The decrease in cell volume in the dark was independent of cell division and biological clock and was regulated by the photoperiod of the light/dark cycle. When the light intensity was increased to above 1000 μmol photons m−2 s−1, cells displayed evidence of photodamage. However, these cells also maintained the maximum level of photosynthesis efficiency and respiration possible, and the growth rate increased as light intensity increased. Significantly, the intracellular glycerol content also increased, >2-fold compared to the content in light intensity of 500 μmol photons m−2 s−1, but there was no commensurate increase in the pool size of carotenoids. These data suggest that in CCAP 19/30 glycerol stabilized the photosynthetic apparatus for maximum performance in high light intensities, a role normally attributed to carotenoids.