A major photoprotective mechanism that plants employ against excess light
involves interplay between the xanthophyll cycle and the accumulation of
protons. Using mutants in the xanthophyll cycle, the roles of violaxanthin,
antheraxanthin and zeaxanthin have already been well established. In this
paper, we present data on intact leaves of a mutant [coupling factor
quick recovery mutant (cfq); atpC1:E244K] of
Arabidopsis thaliana that we expected, based on 515-nm
absorbance changes (Gabrys et al. 1994,
Plant Physiology 104,
769–776), to have differences in light-induced ΔpH. The
significance of this paper is: (i) it is the first study of the
photoprotective energy dissipation involving a mutant of the pH gradient; it
establishes that protons play an important role in the pattern of
non-photochemical quenching (NPQ) of chlorophyll (Chl) a
fluorescence; and (ii) differences between the cfq and the wild type (wt) are
observed only under subsaturating light intensities, and are strongest in the
initial few minutes of the induction period. Our results on light-intensity
dependent Chl* a fluorescence transients (the
Kautsky effect), and on NPQ of Chl a fluorescence, at
50–250 μmol photons m–2
s–1 demonstrate: (i) the
‘P-to-S’ (or
‘T’) decay, known to be related to
[H+] (Briantais
et al. 1979,
Biochimica et Biophysica Acta 548,
128–138), is slowed in the mutant; and (ii) the pattern of NPQ kinetics
is different in the initial 100 s — in the wt leaves, there is a marked
rise and decline, and in the cfq mutant, there is a slowed rise. These
differences are absent at 750 μmol photons m–2
s–1. Pre-illumination and nigericin (an uncoupler
that dissipates the proton gradient) treatment of the cfq mutant, which has
lower ΔpH relative to wild type, confirm the conclusion that protons
play an important role in the quenching of Chl a
fluorescence.
Dissecting and modeling zeaxanthin- and lutein-dependent nonphotochemical quenching in Arabidopsis thaliana
