The mechanism(s) involved in the photoprotection of PSII at elevated CO₂ in nodulated alfalfa plants
2008
Aranjuelo, Iker | Erice, Gorka | Nogués, Salvador | Morales, Fermín | Irigoyen, Juan J. | Sánchez Díaz, Manuel
In a previous study, we found that enhanced CO₂ subjected to nodulated alfalfa plants grown at different temperatures (ambient and ambient+4°C) and water availability regimes could protect PSII from photodamage. The main objective of this study was to determine the mechanism(s) involved in the photoprotection of PSII at elevated CO₂ levels in this plant. Elevated CO₂ reduced carboxylation capacity-induced photosynthetic acclimation and reduced enzymatic and/or nonenzymatic antioxidant activities, suggesting that changes in electron flow did not cause any photooxidative damage (which was also confirmed by H₂O₂ and lipid peroxidation analyses). Enhanced nonphotochemical quenching and xanthophyll cycle pigments revealed that plants grown at 700μmolmol⁻¹ CO₂ compensated for the reduction in energy sink with a larger capacity for nonphotochemical dissipation of excitation energy as heat, i.e., modulating the status of the VAZ components. Elevated CO₂ induced the de-epoxidation of violaxanthin to zeaxanthin, facilitating thermal dissipation and protecting the photosynthetic apparatus against the deleterious effect of excess excitation energy.
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