The sequence of change within the photosynthetic apparatus of wheat following short-term exposure to ozone

• Published in: Plant physiology (Bethesda) Vol. 95; no. 2; pp. 529 - 535
• Main Authors: Farage, P.K. (University of Essex, Essex, UK), Long, S.P, Lechner, E.G, Baker, N.R
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.02.1991
• Subjects: 551000 - Physiological Systems; 560300 - Chemicals Metabolism & Toxicology; BASIC BIOLOGICAL SCIENCES; Biological and medical sciences; CARBON COMPOUNDS; CARBON DIOXIDE; CARBON OXIDES; Carboxylation; CEREALS; CHALCOGENIDES; CHEMICAL REACTIONS; Chloroplasts; DIOXIDO DE CARBONO; DIOXYDE DE CARBONE; ECHANGE GAZEUX; effects on; FITOTOXICIDAD; Fluorescence; FOTOSINTESIS; Fumigation; Fundamental and applied biological sciences. Psychology; GRAMINEAE; INHIBICION; INHIBITION; INTERCAMBIO DE GASES; LEAVES; LILIOPSIDA; LUMIERE; LUZ; MAGNOLIOPHYTA; Metabolism; OXIDES; OXIGENO; Oxygen; OXYGEN COMPOUNDS; OXYGENE; OZONE; OZONO; PHOTOCHEMICAL REACTIONS; PHOTOSYNTHESE; PHOTOSYNTHESIS; Photosynthesis, respiration. Anabolism, catabolism; PHOTOSYNTHETIC REACTION CENTERS; PHYTOTOXICITE; Plant physiology and development; PLANTS; RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT; REACCIONES QUIMICAS; REACTION CHIMIQUE; Stomatal conductance; SYNTHESIS; TOXICITY; TRITICUM AESTIVUM; UPTAKE; WHEAT; Chlorophyll; Light effect; Monocotyledones; Oxygen; Fumigation; Carbon dioxide; Stomatal conductance; Fluorescence; Ozone; Cereal crop; Absorption; Gramineae; Angiospermae; Evolution; Air pollution; Spermatophyta; Gas exchange; Photosynthesis; Triticum aestivum
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.95.2.529

The basis of inhibition of photosynthesis by single acute exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O3 for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO2 uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO2 uptake and the internal CO2 concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O3; no significant increase occurred for any of the other treatments. Analysis of the response of CO2 uptake to the internal CO2 concentration implied that the predominant factor responsible for the reduction in light-saturated uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O3, respectively. At saturating concentrations of CO2, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O3. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO2 uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O3, requiring 8 hours at 400 nanomoles per mole O3 before a significant reduction occurred. The photochemical efficiency of photosystem if estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO2 uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthes is in vivo following acute O3 fumigation