PLANT PHYSIOLOGY , Vol 101, Issue 3 907-913, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Rapid, Blue-Light-Induced Acidifications at the Surface of Ectocarpus and Other Marine Macroalgae
R. Schmid and M. J. Dring
School of Biology and Biochemistry, The Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland
In most brown algae, photosynthesis saturated with red light can be
stimulated by continuous blue light. Pulses of blue light lead to transient
increases in photosynthetic rate. When a CO2-sensitive electrode was used,
occasionally blue light was observed to cause an apparent increase of CO2
instead of the expected decrease. This was changed by buffering the
seawater medium and, under these conditions, blue light caused stimulation
of CO2 consumption. These results led to investigations of
blue-light-dependent pH changes at the outer surface of the plants. Shifts
of the pH were recorded in the presence of the photosynthetic inhibitor
3-(3,4-dichlorophenyl)-1,1-dimethylurea. In all brown algae tested and in
the green algae Ulva and Enteromorpha, blue-light pulses caused transient
acidification of 0.03 to 0.18 pH units, depending on the species. The
kinetics showed lag phases of a few seconds and the minimum was reached
after 5 to 9 min. Fluence response relationships indicated that the
sensitivity (threshold) to blue light was very similar in all species. The
responses in Ectocarpus changed with time, and about 5 h after the
beginning of red light or darkness, a second component became evident,
which peaked 20 min after the blue-light pulse. The refractory period of
the whole system was about 3 h in Ectocarpus. The blue-light-dependent pH
changes show striking similarities to those of higher plant guard cells,
and it is possible that similar responses may occur in other tissues of
higher plants. In red algae, however, no blue-light-dependent
acidifications could be detected. The possible role of the observed pH
shifts in a mechanism of CO2 acquisition is discussed.
