Effects of DCMU on chlorophyll fluorescence ratio F685/F735 in marine red, brown and green algae

Abstract

The chlorophyll fluorescence ratio F685/F735 in vivo can be a useful indicator for stress detection in higher plants and seaweeds. DCMU [3−(3,4−dichlorophenyl)−1, 1−dimethylurea] treatment influences this ratio. The effets of DCMU on F685/F735 of marine red, brown and green algae under excitation light of different wavelengths were investigated. In the brown algae,Laminaria japonica andUndaria pinnatifida, DCMU did not increase this ratio under blue light excitation but increased the ratio slightly under excitation by green light. For the red algae,Halymenia sinensis, DCMU increased the ratio markedly under both blue and green light excitation. The percentage increase could reach 50% (under green light excitation) and was due to unequal enhancement at the two emission maxima by DCMU. A fraction of chlorophyll which contributed to fluorescence in the 735 nm region was less sensitive to DCMU and was likely from photosystem I of red algae. In the green alga,Ulva pertusa, DCMU caused a slight increase in F685/F735 value under blue, green and red light. Green light excitation during DCMU treatment increased the ratio most (16%) but induced the lowest ratio in the control (without DCMU). It is proposed that a considerable fraction of fluorescence from the 735 nm region at room temperature may be emitted by the chlorophyll of photosystem I in red algae.