Biology Reference
In-Depth Information
description of the experiments dealing with the discovery of this mecha-
nism and its first characterization, see
Karapetyan (2007)
,
Kirilovsky (2007)
and
Bailey and Grossman (2008)
. For more recent reviews, see
Kirilovsky
(2010)
and
Kirilovsky and Kerfeld (2012)
.
2.2. The OCP Induces a Decrease of the Effective Antenna Size
The OCP-mediated fluorescence quenching correlates with a decrease of
the effective size of the antenna and in the amount of energy arriving at
the reaction centres (
Gorbunov, Kuzminov, et al., 2011
;
Rakhimberdieva,
Elanskaya, et al., 2010
;
Wilson, Ajlani, et al., 2006
). Measurements of oxygen
evolving activity at different light intensities showed that PSII activity satu-
rates at higher light intensities in 'quenched' cells than in 'non-quenched'
cells (
Wilson, Ajlani, et al., 2006
). Using
Synechocystis
mutants lacking
the PSII or PSI and measuring PSI (or PSII) activities,
Rakhimberdieva,
Elanskaya, et al. (2010)
demonstrated that only 60-70 % of the energy
absorbed by the phycobilisome arrives at the reaction centres. In
Synecho-
cystis
and
Synechococcus
sp. CCMP 1379 cells grown at high light intensities
(600 µmol photons), strong blue light can induce about 63% of fluores-
cence quenching that was correlated to a decrease of the functional cross-
section of PSII by 53% (
Gorbunov, Kuzminov, et al., 2011
). Under low-light
growth conditions, the magnitude of fluorescence quenching was minimal
(
Gorbunov, Kuzminov, et al., 2011
).The amplitude of fluorescence quenching
depends on the concentration of the OCP. In wild-type (WT)
Synechocystis
cells (grown at 60 µmol photons), which contain one OCP per 2-3 phyco-
bilisomes, a maximum fluorescence quenching of 35% is observed, whereas
in a mutant strain containing about 8 times more OCP (3-4 OCP per phy-
cobilisome), 65-70% of fluorescence quenching is observed (
Kirilovsky &
Kerfeld, 2012
;
Wilson, Punginelli, et al., 2008
). The expression of the OCP
also increases under different stress conditions (high light (
Hihara, Kamei,
et al., 2001
), salt stress (
Fulda, Mikkat, et al., 2006
), iron starvation (
Wil-
son, Boulay, et al., 2007
)) and oxidative stress (
Blot, Daniella Mella-Flores,
et al., 2011
). Under iron starvation and high-light growth conditions, a larger
fluorescence quenching correlating with a greater OCP concentration was
observed (
Boulay, Abasova, et al., 2008
;
Gorbunov, Kuzminov, et al., 2011
;
Wilson, Boulay, et al., 2007
). Thus, since the maximum amplitude of fluores-
cence quenching and the extent of the decrease of the effective functional
antenna size depends on the amount of the OCP in the cell, different ampli-
tudes of fluorescence quenching could be observed under different growth
conditions. These results suggested that the OCP-related photoprotection
