Chlorophyll fluorescence ratio F685/F735 in brown algae and its variation under excitation by two types of light and dehydration

Abstract

Calculation and comparative study of the chlorophyll fluorescence ratio F685/F735 in brown alage (Laminaria japonica, Underia pinnatifida andPadina crassa) excited by blue and green light showed that the fluorescence ratios were higher when the algae were excited by blue light (440 nm), but reduced obviously under green light (540 nm) excitation. The values also reduced under dehydration but could recover during rehydration if the stress was not serious. The variation of the fluorescence ratio under dehydration was mainly because changes in fluorescence emission at 735 nm were always sharper than those at 685 nm. The ratio was sensitive to stress and has potential as a stress indicator in phycological research. Measurement of the fluorescence excitation spectra showed that the only peak at 540 nm changed apparently during dehydration. It meant that the function of the Ch1 a/Fucoxanthin protein complex for energy transfer was easily inhibited by water stress. However, no variation of the ratio was found in green algaUlva pertusa under dehydration. So it seemed to be something special for brown algae. The mechanism of this phenomenon is still unclear but may be related to the photosynthetic pigments and structural characteristics of brown algae.