Far‐red light inhibits growth but promotes carotenoid accumulation in the green microalga Dunaliella bardawil

Abstract

It has been demonstrated that far‐red light reduces growth of marine phytoplankton and that light quality controls growth and photosynthetic metabolism in algae. The green halotolerant microalga, Dunaliella bardawil, accumulates high amounts of β‐carotene (up to 10% of its dry weight) under conditions of high light or nutrient limitation. The influence of increasing irradiance and of far‐red light in D. bardawil was studied. Continuous irradiance was provided by white fluorescent lamps alone (WL) or supplemented with far‐red Linestra lamps (WL+FR). For both types of light, cultures were acclimatized at increasing irradiances (50‐300 µmol m−2 s−1), and cell density, photosynthetic activity and pigment content were determined. Cell density increased with the photon irradiance, and was higher in WL than in WL+FR under the same irradiance, but the reverse occurred in respect of cell volume. Growth rate was higher under WL+FR. Far‐red light induced faster growth but reduced the maximal cell density of the cultures. Chlorophyll a concentration was higher in white light, but total carotenoid content increased dramatically in both far‐red light treatments (about 50% on a per cell basis) and with the increase of irradiance. Our results show that far‐red light has a significant influence on growth and photosynthesis of D. bardawil, inducing a decrease in cell density, photosynthetic activity and chlorophyll concentration, and an increase in growth rate, cell volume and carotenoid content.