Variable fluorescence of chlorophyll a in Dunaliella bardawil with different B-carotene content.
M.P. Sánchez Saavedra, C. Jiménez and F.L. Figueroa
In vivo chlorophyll a fluorescence varies according to phytoplankton species and physiological state of the cells. The halotolerant flagellate Dunaliella bardawil was grown under white light(WL) of different irradiance and under white light supplemented with far-redlight (WL+FR). Far-red light highly increased the β-carotene cellcontent of D. bardawil, whereas the photosynthetic efficiency (α)and maximal photosynthetic rate (Pmax) decreased. The ratio of the variable to maximal fluorescence (Fv/Fm) and effective quantum yield (DF/Fm´)decreased with increasing photon fluence rates in both cultures. Photochemical(qP) and non-photochemical quenching (qN) of photosystem II(PSII) were higher in WL+FR cultures indicating that the increase of the carotenoid concentration at high irradiance and under FR light is related to a decrease in Fv/Fm and DF/Fm´ and to an increase in qP and qN, which constitutes an acclimation mechanism against excessive irradiance. A linear correlation was found between the effective quantum yield and maximal photosynthetic rate in both WL and WL+FR cultures, suggesting that the fluorescence parameters can be used instead of the photosynthetic parameters to determine the physiological status of the algal cells.