Volatile emissions and phenolic compound concentrations along a vertical profile of Populus nigra leaves exposed to realistic ozone concentrations (original) (raw)
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Response of Photosynthesis and Cellular Antioxidants to Ozone in Populus Leaves
Plant Physiology, 1991
Atmospheric ozone causes formation of various highly reactive intermediates (e.g. peroxyl and superoxide radicals, H202, etc.) in plant tissues. A plant's productivity in environments with ozone may be related to its ability to scavenge the free radicals formed. The effects of ozone on photosynthesis and some free radical scavengers were measured in the fifth emergent leaf of poplars. Clonal poplars (Populus deltoides x Populus cv caudina) were fumigated with 180 parts per billion ozone for 3 hours. Photosynthesis was measured before, during, and after fumigation. During the first 90 minutes of ozone exposure, photosynthetic rates were unaffected but glutathione levels and superoxide dismutase activity increased. After 90 minutes of ozone exposure, photosynthetic rates began to decline while glutathione and superoxide dismutase continued to increase. Total glutathione (reduced plus oxidized) increased in fumigated leaves throughout the exposure period. The ratio of GSH/GSSG also decreased from 12.8 to 1.2 in ozone exposed trees. Superoxide dismutase levels increased twofold in fumigated plants. After 4 hours of ozone exposure, the photosynthetic rate was approximately half that of controls while glutathione levels and superoxide dismutase activity remained above that of the controls. The elevated antioxidant levels were maintained 21 hours after ozone exposure while photosynthetic rates recovered to about 75% of that of controls. Electron transport and NADPH levels remained unaffected by the treatment. Hence, elevated antioxidant metabolism may protect the photosynthetic apparatus during exposure to ozone. All organisms that have evolved in aerobic environments have a variety of enzymatic and nonenzymatic mechanisms to prevent oxidation of cellular components. It is quite probable that existing mechanisms for detoxifying oxyradicals are invoked in response to ozone since it causes the formation of some highly reactive oxyradicals in aqueous solutions, a major product being the superoxide anion (I1). The superoxide anion can be metabolized by several isozymes of superoxide dismutase found in plants (14). The hydrogen peroxide formed by this reaction is toxic. It can inactivate-SH containing enzymes (5, 13) or react with superoxide to form the hydroxyl radical, which can attack many macromolecular Supported by Environmental Protection Agency grant No. R814197-01-0 to Boyce Thompson Institute, Ithaca, NY, subcontract (BTI 88 No. 1) to R.
Response of photosynthesis and the cellular antioxidant system to ozone in populus leaves
Plant Physiology, Supplement; (USA), 1989
Atmospheric ozone causes formation of various highly reactive intermediates (e.g. peroxyl and superoxide radicals, H202, etc.) in plant tissues. A plant's productivity in environments with ozone may be related to its ability to scavenge the free radicals formed. The effects of ozone on photosynthesis and some free radical scavengers were measured in the fifth emergent leaf of poplars. Clonal poplars (Populus deltoides x Populus cv caudina) were fumigated with 180 parts per billion ozone for 3 hours. Photosynthesis was measured before, during, and after fumigation. During the first 90 minutes of ozone exposure, photosynthetic rates were unaffected but glutathione levels and superoxide dismutase activity increased. After 90 minutes of ozone exposure, photosynthetic rates began to decline while glutathione and superoxide dismutase continued to increase. Total glutathione (reduced plus oxidized) increased in fumigated leaves throughout the exposure period. The ratio of GSH/GSSG also decreased from 12.8 to 1.2 in ozone exposed trees. Superoxide dismutase levels increased twofold in fumigated plants. After 4 hours of ozone exposure, the photosynthetic rate was approximately half that of controls while glutathione levels and superoxide dismutase activity remained above that of the controls. The elevated antioxidant levels were maintained 21 hours after ozone exposure while photosynthetic rates recovered to about 75% of that of controls. Electron transport and NADPH levels remained unaffected by the treatment. Hence, elevated antioxidant metabolism may protect the photosynthetic apparatus during exposure to ozone. All organisms that have evolved in aerobic environments have a variety of enzymatic and nonenzymatic mechanisms to prevent oxidation of cellular components. It is quite probable that existing mechanisms for detoxifying oxyradicals are invoked in response to ozone since it causes the formation of some highly reactive oxyradicals in aqueous solutions, a major product being the superoxide anion (I1). The superoxide anion can be metabolized by several isozymes of superoxide dismutase found in plants (14). The hydrogen peroxide formed by this reaction is toxic. It can inactivate-SH containing enzymes (5, 13) or react with superoxide to form the hydroxyl radical, which can attack many macromolecular Supported by Environmental Protection Agency grant No. R814197-01-0 to Boyce Thompson Institute, Ithaca, NY, subcontract (BTI 88 No. 1) to R.
Response of photosynthesis and cellular antioxidants to ozone in Populus leaves
Plant Physiology, 1991
Atmospheric ozone causes formation of various highly reactive intermediates (e.g. peroxyl and superoxide radicals, H202, etc.) in plant tissues. A plant's productivity in environments with ozone may be related to its ability to scavenge the free radicals formed. The effects of ozone on photosynthesis and some free radical scavengers were measured in the fifth emergent leaf of poplars. Clonal poplars (Populus deltoides x Populus cv caudina) were fumigated with 180 parts per billion ozone for 3 hours. Photosynthesis was measured before, during, and after fumigation. During the first 90 minutes of ozone exposure, photosynthetic rates were unaffected but glutathione levels and superoxide dismutase activity increased. After 90 minutes of ozone exposure, photosynthetic rates began to decline while glutathione and superoxide dismutase continued to increase. Total glutathione (reduced plus oxidized) increased in fumigated leaves throughout the exposure period. The ratio of GSH/GSSG also decreased from 12.8 to 1.2 in ozone exposed trees. Superoxide dismutase levels increased twofold in fumigated plants. After 4 hours of ozone exposure, the photosynthetic rate was approximately half that of controls while glutathione levels and superoxide dismutase activity remained above that of the controls. The elevated antioxidant levels were maintained 21 hours after ozone exposure while photosynthetic rates recovered to about 75% of that of controls. Electron transport and NADPH levels remained unaffected by the treatment. Hence, elevated antioxidant metabolism may protect the photosynthetic apparatus during exposure to ozone.
Environmental and Experimental Botany, 2006
Physiological and biochemical responses to acute ozone exposure for 29 plants belonging to natural and semi-natural european ecosystems were characterised and used to reveal common features among species. Plants were grown in controlled conditions and exposed to acute ozone fumigation at 150 ppb for 3 h. Parameters of chlorophyll a fluorescence, pigments content and antioxidant enzyme activity were measured in control and ozone-treated plants and the data obtained from these analyses was used to perform multivariate statistics. The results indicated that the treatment with ozone and the species diversity, as well as the interaction between the two factors, were able to significantly affect the variables as a whole. Ozone treatment affected plant metabolism to different extents for the different species, even if the statistical analyses performed proved that most of them could be grouped in two main clusters. The first cluster is mainly affected in the photosynthetic performance, as indicated by the decrease in the F v /F m ratio and the increase in the de-epoxidation index, while the second one grouped species characterised by strong reductions in leaf pigment content and by increases in peroxidase activity. The observation that most of the parameters analysed were differently affected by the treatment in the natural and semi-natural species investigated pointed out that the different constitutive metabolic behaviour could account for a different susceptibility to the pollutant and, as a consequence, for a different performance of some of the species in heavily polluted environments.
Ozone effects on trees, where uptake and detoxification meet
2002
Ozone is the most important air pollutant and its concentration in ambient air is still rising. Ozone concentrations measured at reference height (50 m is EMEP ozone modelling height), do not reflect the real concentration at the top of the vegetative canopy and do not provide sufficient information about the ozone flux entering the leaves. Modelling stomatal conductance is leading to estimations of cumulative ozone uptake and enables much better to evaluate the impact of ozone on trees. The negative impact of ozone exposure has a measurable effect on physiological processes such as stomatal conductance, photosynthesis and respiration. Disturbance of the basic physiological processes is leading to growth and wood production losses. There have been several attempts to establish critical levels (CL) for ozone effects on forest trees. Average concentrations and cumulative exposure indices are satisfactory to some extent, but do not fully describe the potential impact of ozone exposure. Much more promising is an evaluation based on the effective ozone flux, which is a function of the absorbed ozone flux and the defensive response. Ozone uptake takes place primarily through the stomata and reactions of ozone with hydrocarbons released by the plant cells and transformations of dissolved ozone in the apoplastic fluid create many reactive oxygen species of which free radicals are able to initiate membrane lipid peroxidation and destruction of cell membranes. The defence of a plant against absorbed ozone starts in the apoplastic fluid. Ascorbate is believed to be a very important radical scavenger avoiding detrimental effects of reactive oxygen species to the membranes. Other important antioxidants are phenolics. The defensive response can be linked to the abundance of ascorbate or the ability of the plants to regenerate (reduce) ascorbate from monodehydroascorbate and dehydroascorbate. The reduction of dehydroascorbate takes place in the symplast where ascorbate can be transported back through the plasma membrane into the apoplast. Ozone exposure also causes oxidative stress of the plant cell interior by the formation of reactive oxygen species. Plants can cope with those toxic substances in the symplast by using antioxidants such as ascorbate,-tocopherol, glutathione and carotenoids and enzymes such as superoxide dismutases, catalases and several peroxidases. The complexity of the apoplastic and symplastic antioxidative capacity with different turnover rates and transport of antioxidants makes it difficult to determine the total antioxidative power.
Plant susceptibility to ozone: A tower of Babel?
Science of The Total Environment, 2019
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The effects of tropospheric ozone on plant species: New perspectives
Acta Brasiliensis
The effect of tropospheric ozone on the physiology of plants has been well established using physicochemical analysis and visual assessment. One of the main metabolic processes, in plants that is affected by ozone, is photosynthesis. This in turn affects a number of secondary processes required for the survival of plants. This study focused on two main aspects; the qualitative determination of damage through visual assessment and the quantification of damage through the determination of the content of chlorophyll and other quality parameters using spectrophotometric techniques in a number of plant species. Three distinct setups were considered, mainly rural, urban and semiurban, representing the topography of the islands of Malta and Gozo. It was observed that chlorosis was not the sole factor contributing to the yellowing of the leaves. Another important finding was the correlation between ozone levels (50.18-69.35 ppb) and the anthocyanin content (2.57-28.99 mg/kg) of leaves. From...
Physiologia Plantarum, 2008
Young poplar trees (Populus tremula Michx. Â Populus alba L. clone INRA 717-1B4) were subjected to 120 ppb of ozone for 35 days in phytotronic chambers. Treated trees displayed precocious leaf senescence and visible symptoms of injury (dark brown/black upper surface stippling) exclusively observed on fully expanded leaves. In these leaves, ozone reduced parameters related to photochemistry (Chl content and maximum rate of photosynthetic electron transport) and photosynthetic CO 2 fixation [net CO 2 assimilation, Rubisco (ribulose-1,5-bisphosphate carboxylase oxygenase) activity and maximum velocity of Rubisco for carboxylation]. In fully expanded leaves, the rate of photorespiration as estimated from Chl fluorescence was markedly impaired by the ozone treatment together with the activity of photorespiratory enzymes (Rubisco and glycolate oxidase). Immunoblot analysis revealed a decrease in the content of serine hydroxymethyltransferase in treated mature leaves, while the content of the H subunit of the glycine decarboxylase complex was not modified. Leaves in the early period of expansion were exempt from visible symptoms of injury and remained unaffected as regards all measured parameters. Leaves reaching full expansion under ozone exposure showed potential responses of protection (stimulation of mitochondrial respiration and transitory stomatal closure). Our data underline the major role of leaf phenology in ozone sensitivity of photosynthetic processes and reveal a marked ozone-induced inhibition of photorespiration.
Mechanisms of Impairment of the Photosynthetic Apparatus in Intact Leaves by Ozone
Zeitschrift für Naturforschung C, 1999
Tropospheric ozone has been recognised as a limiting factor for plant growth since late fifties of our century. The decrease in the rate of light saturated net photosynthesis (Asat) was shown to be the major effect of ozone in leaves with negative consequences for plant growth and the development of plant communities. The reasons for the ozone-induced decrease in Asat are still under investigation. Possible mechanisms are an increasing stomatal limitation, an increase in mesophyll limitation including a reduction of the CO2 fixation in the Calvin cycle and an impairment of the photochemical reactions in the grana membranes of chloroplasts. We conclude from the reviewed literature and from our own experiments that a decrease in carboxylation efficiency (CE) seems to be an early event caused by ozone leading to a decrease in Asat. The loss in current photochemical capacity (Fv/Fm) appears with a lag phase of many days and therefore the loss is thought to be a secondary effect due to a...