Effects Of Photorespiration Research Articles

Modelling 18O2 and 16O2 unidirectional fluxes in plants. IV: Role of conductance and laws of its regulation in C3 plants

Numerous studies focus on the measurement of conductances for CO2 transfer in plants and especially on their regulatory effects on photosynthesis. Measurement accuracy is strongly dependent on the model used and on the knowledge of the flow of photochemical energy generated by light in chloroplasts. The only accurate and precise method to quantify the linear electron flux (responsible for the production of reductive energy) is the direct measurement of O2 evolution, by 18O2 labelling and mass spectrometry. The sharing of this energy between the carboxylation (P) and the oxygenation of photorespiration (PR) depends on the plant specificity factor (Sp) and on the corresponding atmospheric concentrations of CO2 and O2 (André, 2013). The concept of plant specificity factor simplifies the equations of the model. It gives a new expression of the effect of the conductance (g) between atmosphere and chloroplasts. Its quantitative effect on photosynthesis is easy to understand because it intervenes in the ratio of the plant specificity factor (Sp) to the specificity of Rubisco (Sr). Using this ‘simple’ model with the data of 18O2 experiments, the calculation of conductance variations in response to CO2 and light was carried out.The good fitting of experimental data of O2 and CO2 exchanges confirms the validity of the simple model. The calculation of conductance variation during the increase of external CO2 concentration reveals a linear law of regulation between external and internal CO2 concentrations. During CO2 variations, the effects of g regulation tend to maintain a higher level of oxygenation (PR) in expense of a better carboxylation (P). Contrary to CO2, the variation of O2 creates a negative feedback effect compatible with a stabilization of atmospheric O2. The regulation of g amplifies this result. The effect of light in combination with CO2 is more complex. Below 800μmolquantam–2s–1 the ratio PR/P is maintained unchangeable in expense of carboxylation efficiency. Above that irradiance value, PR/P increases dramatically. It appears that the saturation curves of photosynthesis under high light could be simply due to the regulation by the conductance g and not by any biochemical or biophysical limitation. In conclusion, the regulatory effect of conductance operates in a way that it preserves the rate of photorespiration. This confirms a positive and protective role of photorespiration at the biochemical, whole plant and atmosphere levels. Since the effects of photorespiration are linked to the properties of Rubisco, they add new arguments for a co-evolution of plant and atmosphere, including the evolution of CO2 conductance.

Ecological effect of photorespiration of plants under environmental stress

Photorespiration is an important metabolic process in C3 plants.This article analyzes the effects of human and economic development like increased CO2 emission,ultraviolet radiation,temperature,light,etc.,which influence photorespiration such as directly or indirectly changing photorespiration rate that can lead to secondary effects on plant physiological and ecological development.When C3 plants are under environmental stress,photorespiration corresponds to metabolism which eludes the stress,especially when the environmental stress is severe.Hence photorespiration of C3 plants under environmental stress leads to a new direction of research in environmental ecology and photorespiration.

Carbon isotope fractionation during photorespiration and carboxylation in Senecio.

The magnitude of fractionation during photorespiration and the effect on net photosynthetic (13)C discrimination (Delta) were investigated for three Senecio species, S. squalidus, S. cineraria, and S. greyii. We determined the contributions of different processes during photosynthesis to Delta by comparing observations (Delta(obs)) with discrimination predicted from gas-exchange measurements (Delta(pred)). Photorespiration rates were manipulated by altering the O(2) partial pressure (pO(2)) in the air surrounding the leaves. Contributions from (13)C-depleted photorespiratory CO(2) were largest at high pO(2). The parameters for photorespiratory fractionation (f), net fractionation during carboxylation by Rubisco and phosphoenolpyruvate carboxylase (b), and mesophyll conductance (g(i)) were determined simultaneously for all measurements. Instead of using Delta(obs) data to obtain g(i) and f successively, which requires that b is known, we treated b, f, and g(i) as unknowns. We propose this as an alternative approach to analyze measurements under field conditions when b and g(i) are not known or cannot be determined in separate experiments. Good agreement between modeled and observed Delta was achieved with f = 11.6 per thousand +/- 1.5 per thousand, b = 26.0 per thousand +/- 0.3 per thousand, and g(i) of 0.27 +/- 0.01, 0.25 +/- 0.01, and 0.22 +/- 0.01 mol m(-2) s(-1) for S. squalidus, S. cineraria, and S. greyii, respectively. We estimate that photorespiratory fractionation decreases Delta by about 1.2 per thousand on average under field conditions. In addition, diurnal changes in Delta are likely to reflect variations in photorespiration even at the canopy level. Our results emphasize that the effects of photorespiration must be taken into account when partitioning net CO(2) exchange of ecosystems into gross fluxes of photosynthesis and respiration.

Compound-specific isotope analysis of cyanobacterial pure cultures and microbial mats: Effects of photorespiration?

Microbial mats are considered modern homologs of Precambrian stromatolites. The carbon isotopic compositions of organic matter and biomarker lipids provide clues to the depositional environments of ancient mat ecosystems. As the source of primary carbon fixation for over two billion years, an understanding of cyanobacterial lipid biosynthesis, associated isotopic discriminations, and the influence of physiological factors on growth and isotope expression is essential to help us compare modern microbial ecosystems to their ancient counterparts. Here, we report on the effects of photorespiration (PR) on the isotopic composition of cyanobacteria and biomarker lipids, and on potential PR effects associated with the composition of various microbial mats. The high light, high O2 and limiting CO2 conditions often present at the surface of microbial mats are known to support PR in cyanobacteria. The oxygenase function of ribulose bisphosphate carboxylase/oxygenase can result in photoexcretion of glycolate and subsequent degration by heterotrophic bacteria. We have found evidence which supports an isotopic depletion (increased apparent E) scaled to O2 level associated with growth of Phormidium luridum at low CO2 concentrations (less than 0.04%). Similar to previous studies, isotopic differences between biomass and lipid biomarkers, and between lipid classes were positively correlated with overall fractionation, and should provide a means of estimating the influence of PR on overall isotopic composition of microbial mats. Several examples of microbial mats growing in the hydrothermal waters of Yellowstone National Park and the hypersaline marine evaporation ponds at Guerrero Negro, Baja Sur Mexico will be compared with a view to PR as a possible explanation of the relatively heavy C-isotope composition of hypersaline mats.

Effects of photorespiration, the cytochrome pathway, and the alternative pathway on the triple isotopic composition of atmospheric O2

The triple isotopic composition of atmospheric O2 is a new tracer used to estimate changes in global productivity. To estimate such changes, knowledge of the relationship between the discrimination against 17O and the discrimination against 18O is needed. This relationship is presented as θ = ln(17α)/ln(18α). Here, the value of theta was evaluated for the most important processes that affect the isotopic composition of oxygen. Similar values were found for dark respiration through the cytochrome pathway (0.516 ± 0.001) and the alternative pathway (0.514 ± 0.001), and slightly higher value was found for diffusion in air (0.521 ± 0.001). The combined effect of diffusion and respiration on the atmosphere was shown to be close to that of dark respiration. The value we found for photorespiration (0.506 ± 0.005) is considerably lower than that of dark respiration. Our results clearly show that the triple isotopic composition of the atmosphere is affected by the relative rates of photorespiration and dark respiration. Also, we show that closing the current global isotopic balance will enable the estimation of the current global rate of photorespiration. Using the Last Glacial Maximum as a case study, we show that variations in global rate of photorespiration affected the triple isotopic composition in the past. Strong fractionations measured in illuminated plants indicated that the alternative pathway is activated in the same conditions that favor high rate of photorespiration. This activation suggests that the global rate of the alternative pathway is higher than believed thus far, and may help to close the gap between the calculated and measured Dole Effect.

The Influence of Light and Oxygen on Nitrogenase Activity in the Lichen Stereocaulon paschale

AbstractThalli of the lichen Slereocaulon paschale (L.) Fr. were prctreated in the light (light activated) or in the dark (dark starved). In short‐time experiments with both light activated arid dark starved thalli, the nitrogenasc activity was higher in the light than in the dark, Light activated thalli had a very much higher rale of C2H2 reduction than dark starved thalli, both in the light and in the dark. The dark starved lhalli showed increasing nilrogenase activity when incubated in the light.Either light or oxygen was necessary for nitrogenase activity in light activated thalli. and up to about 10kPa oxygen they showed additive effects. Both in the light and in the dark the nitrogenase activity decreased when the oxygen partial pressure was lower than in normal air. The experimental data thus showed a short‐term effect of light on nilrogenase activity by provision of ATP and reductant, and a long term effect probably by build up of reserves that were later utilized. Any immediate effect of photorespiration on nitrogenase activity could not be found in light activated thalli.