PLANT PHYSIOLOGY , Vol 111, Issue 4 1293-1298, Copyright © 1996 by American Society of Plant Biologists
Predicting Light Acclimation in Cyanobacteria from Nonphotochemical Quenching of Photosystem II Fluorescence, Which Reflects State Transitions in These Organisms
D. Campbell and G. Oquist
Department of Plant Physiology, University of Umea, S901-87 Umea, Sweden
An important factor in photosynthetic ecophysiology is the light regime
that a photobiont is acclimated to exploit. In a wide range of
cyanobacteria and cyano-lichens, the easily measured fluorescence
parameters, coefficient of nonphotochemical quenching of photosystem II
variable fluorescence (qN) and nonphotochemical quenching, decline to a
minimum near the acclimated growth light intensity. This characteristic
pattern predicts the integrated light regime to which populations are
acclimated, information that is particularly useful for cyanobacteria or
cyano-lichens from habitats with highly variable light intensities. qN
reflects processes that compete with photosystem II photochemistry for
absorbed excitation energy. In cyanobacteria, we find no evidence for
energy-dependent quenching mechanisms, which are the predominant components
of qN in higher plants. Instead, in cyanobacteria, qN correlates closely
with the excitation flow from the phycobilisome to photosystem I,
indicating that qN reflects the state transition mechanism for
equilibration of excitation from the phycobilisome to the two photosystems.
