Perspectives on photoinhibition and photorespiration in the field: quintessential inefficiencies of the light and dark reactions of photosynthesis?

Abstract

Taking the long-held view that photoinhibition embraces several processes leading to a reduction in the efficiency of light utilization in photosynthesis, and that photorespiration embraces several processes associated with O2 uptake in the light, photoinhibition and photorespiration now can be considered as inevitable, but essential inefficiencies of photosynthesis which help preserve photosynthetic competence in bright light. Photorespiratory O2 uptake via Rubisco, and O2 uptake via the Mehler reaction, both promote non-assimilatory electron transport, and stimulate photon utilization during CO2-limited photosynthesis in bright light. Although fluorescence studies show that the proportion of total photon use via oxygenase photorespiration in air may decline to only about 10% in full sunlight, mass spectrometer studies show that O2 uptake in Mehler reaction photorespiration in C3 and CAM plants can still account for up to 50% of electron flow in saturating CO2 and light. The Mehler-ascorbate peroxidase reaction has an additional role in sustaining membrane energization which promotes dynamic photoinhibition and photon protection (rapidly reversible decrease in PSII efficiency involving dissipation of the energy of excess photons in the antennae). Net CO2 and O2 exchange studies evidently underestimate the extent of total electron transport, and hence overestimate the extent of photon excess in bright light, leading to overestimates of the role of energy-dependent photon dissipation through dynamic photo-inhibition. Nevertheless, in C3 plants in air all of these processes help to mitigate chronic photoinhibition and photon damage (slowly reversible decrease in PSII efficiency involving loss of reaction centre function). The possibility remains that residual electron transport to O2 from intermediates in the vicinity of PSII may also lead to reactive O2 species that potentiate this photon damage.

Comprehensive Dissection of Spatiotemporal Metabolic Shifts in Primary, Secondary, and Lipid Metabolism during Developmental Senescence in Arabidopsis

“…A high Gly/Ser ratio was also observed at T3, where photosynthesis activity is low due to senescence in the single leaf. It is conceivable that this might be caused by some stress response such as water loss in leaves during the senescence process, since photorespiration has been reported to play a beneficial role during stresses such as heat and drought (Osmond and Grace, 1995;Wingler et al, 2000;Foyer and Noctor, 2009). However, a direct support for this hypothesis in the context of our results is currently lacking.…”

Tansley Review No. 112

“…This implies that, even if it occurs at the high rates that have been suggested (Osmond & Grace, 1995), O # reduction is constrained by the proton gradient, as discussed in the previous section.…”

“…However, the oxygenation of RuBP does significantly increase the energy required per molecule of CO # fixed. This fact has led to the concept that the physiological significance of photorespiration lies in its wastefulness (Osmond & Bjo$ rkman, 1972 ;Heber & Krause, 1980 ;Osmond & Grace, 1995). According to this view, the processes initiated by oxygenation can be considered, in metabolic terms, to be a futile cycle that uses ATP and reductant to avert potentially deleterious excitation energy densities in the photosynthetic apparatus.…”

Effect of salt on ROS homeostasis, lipid peroxidation and antioxidant mechanisms in Pinus pinaster suspension cells

“…The association between salt and oxidative stresses has been previously confirmed: salt decreases water availability and disrupts the homeostasis of water potential and ion distribution, a process which is the basis for oxidative stress generation (Zhu, 2001). At plant level, over-reduction of the photosynthetic apparatus constitutes a major source of ROS (Osmond and Grace, 1995), but salt-associated oxidative stress can also be mediated by superoxide and hydrogen peroxide radicals at the levels of mitochondria and peroxisomes, respectively Hernandez et al, 1993). Furthermore, a novel role has been established for ROS as signalling intermediates during abiotic stress resistance (reviewed by Mittler et al, 2004), and the importance of non-photosynthetic ROS generation during abiotic stress responses has been recently substantiated (reviewed by Van Breusegem et al, 2008).…”