Photoinhibition
[2] The visible-light part of the action spectrum was found to have a peak in the red-light region, suggesting that chlorophylls act as photoreceptors of photoinhibition.
In the 1980s, photoinhibition became a popular topic in photosynthesis research, and the concept of a damaging reaction counteracted by a repair process was re-invented.
[8] Many details of the repair cycle, including the finding that the FtsH protease plays an important role in the degradation of the D1 protein, have been discovered since.
[10] The following year, laser pulse photoinhibition experiments done by Itzhak Ohad's group led to the suggestion that charge recombination reactions may be damaging because they can lead to production of singlet oxygen.
[4][19] It has been suggested that even in a healthy leaf, the oxygen-evolving complex does not always function in all PSII centers, and those ones are prone to rapid irreversible photoinhibition.
[12] Inhibition of PSII is caused by singlet oxygen produced either by weakly coupled chlorophyll molecules[22] or by cytochromes or iron–sulfur centers.
Data from the group of W. S. Chow indicate that in leaves of pepper (Capsicum annuum), the first-order pattern is replaced by a pseudo-equilibrium even if the repair reaction is blocked.
[27] In photoinhibition studies, repair is often stopped by applying an antibiotic (lincomycin or chloramphenicol) to plants or cyanobacteria, which blocks protein synthesis in the chloroplast.
It is also apparent that turning or folding of leaves, as occurs, e.g., in Oxalis species in response to exposure to high light, protects against photoinhibition.
Because there are a limited number of photosystems in the electron transport chain, organisms that are photosynthetic must find a way to combat excess light and prevent photo-oxidative stress, and likewise, photoinhibition, at all costs.
Elicited by a relatively low luminal pH, plants have developed a rapid response to excess energy by which it is given off as heat and damage is reduced.
The studies of Tibiletti et al. (2016) found that PsBs is the main protein involved in sensing the changes in the pH and can therefore rapidly accumulate in the presence of high light.
Additionally, studies conducted by Glowacka et al. (2018) show that a higher concentration of PsBs is directly correlated to inhibiting stomatal aperture.
Thus, when PsBs was overexpressed in a plant, water uptake efficiency was seen to significantly improve, resulting in new methods for prompting higher, more productive crop yields.
These recent discoveries tie together two of the largest mechanisms in phytobiology; these are the influences that the light reactions have upon stomatal aperture via the Calvin Benson Cycle.
This in turn results in an activation of the redox state of Quinone A and there is no change in the concentration of carbon dioxide in the intracellular airspaces of the leaf; ultimately increasing stomatal conductance.
[16] This ratio can be used as a proxy of photoinhibition because more energy is emitted as fluorescence from Chlorophyll a when many excited electrons from PSII are not captured by the acceptor and decay back to their ground state.
[11] This dependence has been interpreted to indicate that the flashes cause photoinhibition by inducing recombination reactions in PSII, with subsequent production of singlet oxygen.
[12] Some researchers prefer to define the term “photoinhibition” so that it contains all reactions that lower the quantum yield of photosynthesis when a plant is exposed to light.
