IMPACT4SOIL OpenAire Flore (Florence Research Repository) Archivio della Ricerca - Università di Pisa IRIS Cnr Crossref Microsoft Academic Graph Archivio Istituzionale della Ricerca dell'Università degli Studi di Milano CNR ExploRA Europe PubMed Central Journal of Plant Physiology Restricted 2012-04-24 2024-02-16 2017-07-12 2015-04-28 The experiment was conducted using Fraxinus ornus plants grown outside under full sunlight irradiance, and supplied with 100% (well-watered, WW), 40% (mild drought, MD), or 20% (severe drought, SD) of the daily evapotranspiration demand, with the main objective of exploring the effect of excess light stress on the activity of antioxidant enzymes and phenylpropanoid biosynthesis. Net CO₂ assimilation rate at saturating light and daily assimilated CO₂ were significantly smaller in SD than in WW and MD plants. Xanthophyll-cycle pigments supported nonphotochemical quenching to a significantly greater extent in SD than in MD and WW leaves. As a consequence, the actual efficiency of PSII (Φ(PSII)) was smaller, while the excess excitation-energy in the photosynthetic apparatus was greater in SD than in WW or MD plants. The concentrations of violaxanthin-cycle pigments relative to total chlorophyll (Chl(tot)) exceeded 200 mmol mol⁻¹ Chl(tot) in SD leaves at the end of the experiment. This leads to hypothesize for zeaxanthin a role not only as nonphotochemical quencher, but also as chloroplast antioxidant. Reductions in ascorbate peroxidase and catalase activities, as drought-stress progressed, were paralleled by greater accumulations of esculetin and quercetin 3-O-glycosides, both phenylpropanoids having effective capacity to scavenge H₂O₂. The drought-induced accumulation of esculetin and quercetin 3-O-glycosides in the vacuoles of mesophyll cells is consistent with their putative functions as reducing agents for H₂O₂ in excess light-stressed leaves. Nonetheless, the concentration of H₂O₂ and the lipid peroxidation were significantly greater in SD than in MD and WW leaves. It is speculated that vacuolar phenylpropanoids may constitute a secondary antioxidant system, even on a temporal basis, activated upon the depletion of primary antioxidant defences, and aimed at keeping whole-cell H₂O₂ within a sub-lethal concentration range. 0301 basic medicine Analysis of Variance Principal Component Analysis 0303 health sciences Time Factors Light Propanols Antioxidant enzymes Drought stress Phenylpropanoids Water relations Violaxanthin-cycle pigments Hydrogen Peroxide Pigments, Biological Carbon Dioxide 15. Life on land Antioxidants 6. Clean water Antioxidant enzymes; Drought stress; Phenylpropanoids; Violaxanthin-cycle pigments; Water relations; Analysis of Variance; Antioxidants; Carbon Dioxide; Fraxinus; Hydrogen Peroxide; Malondialdehyde; Mesophyll Cells; Microscopy, Fluorescence; Photosynthesis; Pigments, Biological; Plant Leaves; Principal Component Analysis; Propanols; Stress, Physiological; Time Factors; Droughts; Light; Plant Science; Physiology; Agronomy and Crop Science Droughts Plant Leaves 03 medical and health sciences Fraxinus Microscopy, Fluorescence Stress, Physiological Antioxidant enzymes; drought stress; flavonoids Malondialdehyde Photosynthesis Mesophyll Cells FINI, ALESSIO, L. Guidi, FERRINI, FRANCESCO, BRUNETTI, CECILIA, M. D. Ferdinando, BIRICOLTI, STEFANO, S. Pollastri, CALAMAI, LUCA, M. Tattini, 2012-07-01 journalpaper The experiment was conducted using Fraxinus ornus plants grown outside under full sunlight irradiance, and supplied with 100% (well-watered, WW), 40% (mild drought, MD), or 20% (severe drought, SD) of the daily evapotranspiration demand, with the main objective of exploring the effect of excess light stress on the activity of antioxidant enzymes and phenylpropanoid biosynthesis. Net CO₂ assimilation rate at saturating light and daily assimilated CO₂ were significantly smaller in SD than in WW and MD plants. Xanthophyll-cycle pigments supported nonphotochemical quenching to a significantly greater extent in SD than in MD and WW leaves. As a consequence, the actual efficiency of PSII (Φ(PSII)) was smaller, while the excess excitation-energy in the photosynthetic apparatus was greater in SD than in WW or MD plants. The concentrations of violaxanthin-cycle pigments relative to total chlorophyll (Chl(tot)) exceeded 200 mmol mol⁻¹ Chl(tot) in SD leaves at the end of the experiment. This leads to hypothesize for zeaxanthin a role not only as nonphotochemical quencher, but also as chloroplast antioxidant. Reductions in ascorbate peroxidase and catalase activities, as drought-stress progressed, were paralleled by greater accumulations of esculetin and quercetin 3-O-glycosides, both phenylpropanoids having effective capacity to scavenge H₂O₂. The drought-induced accumulation of esculetin and quercetin 3-O-glycosides in the vacuoles of mesophyll cells is consistent with their putative functions as reducing agents for H₂O₂ in excess light-stressed leaves. Nonetheless, the concentration of H₂O₂ and the lipid peroxidation were significantly greater in SD than in MD and WW leaves. It is speculated that vacuolar phenylpropanoids may constitute a secondary antioxidant system, even on a temporal basis, activated upon the depletion of primary antioxidant defences, and aimed at keeping whole-cell H₂O₂ within a sub-lethal concentration range. Drought Stress Has Contrasting Effects On Antioxidant Enzymes Activity And Phenylpropanoid Biosynthesis In Fraxinus Ornus Leaves: An Excess Light Stress Affair? 10.1016/j.jplph.2012.02.014 https://doi.org/10.1016/j.jplph.2012.02.014