Integrative role of plant mitochondria facing oxidative stress: The case of ozone.

Ozone is a secondary air pollutant, which causes oxidative stress in plants by producing reactive oxygen species (ROS) starting by an external attack of leaf apoplast. ROS have a dual role, acting as signaling molecules, regulating different physiological processes and response to stress, but also inducing oxidative damage. The production of ROS in plant cells is compartmented and regulated by scavengers and specific enzyme pathways.

Ozone exposure and flux-based response functions for photosynthetic traits in wheat, maize and poplar.

Ozone exposure- and dose-response relationships based on photosynthetic leaf traits (CO2 assimilation, chlorophyll content, Rubisco and PEPc activities) were established for wheat, maize and poplar plants grown in identical controlled conditions, providing a comparison between crop and tree species, as well as between C3 and C4 plants. Intra-specific variability was addressed by comparing two wheat cultivars with contrasting ozone tolerance. Depending on plant models and ozone levels, first-order, second-order and segmented linear regression models were used to derive ozone response functions.

Ozone affects ascorbate and glutathione biosynthesis as well as amino acid contents in three Euramerican poplar genotypes.

Ozone is an air pollutant that causes oxidative stress by generation of reactive oxygen species (ROS) within the leaf. The capacity to detoxify ROS and repair ROS-induced damage may contribute to ozone tolerance. Ascorbate and glutathione are known to be key players in detoxification.

Distinct responses to ozone of abaxial and adaxial stomata in three Euramerican poplar genotypes.

Ozone induces stomatal sluggishness, which impacts photosynthesis and transpiration. Stomatal responses to variation of environmental parameters are slowed and reduced by ozone and may be linked to difference of ozone sensitivity. Here we determine the ozone effects on stomatal conductance of each leaf surface.

A physiological and proteomic study of poplar leaves during ozone exposure combined with mild drought.

The occurrence of high-ozone concentrations during drought episodes is common considering that they are partially caused by the same meteorological phenomena. It was suggested that mild drought could protect plants against ozone-induced damage by causing the closure of stomata and preventing the entry of ozone into the leaves. The present experiment attempts to create an overview of the changes in cellular processes in response to ozone, mild drought and a combined treatment based on the use of 2D-DiGE to compare the involved proteins, and a number of supporting analyses.

Analysis of cytosolic isocitrate dehydrogenase and glutathione reductase 1 in photoperiod-influenced responses to ozone using Arabidopsis knockout mutants.

Oxidative stress caused by ozone (O3 ) affects plant development, but the roles of specific redox-homeostatic enzymes in O3 responses are still unclear. While growth day length may affect oxidative stress outcomes, the potential influence of day length context on equal-time exposures to O3 is not known. In Arabidopsis Col-0, day length affected the outcome of O3 exposure.

Effects of ozone on stomatal responses to environmental parameters (blue light, red light, CO2 and vapour pressure deficit) in three Populus deltoides × Populus nigra genotypes.

The effect of ozone (O(3)) on stomatal regulation was studied in three Euramerican poplar genotypes (Populus deltoides × Populus nigra: Carpaccio, Cima and Robusta). The impact of O(3) on stomatal conductance responses to variations in blue light, red light, CO(2) concentration and vapour pressure deficit (VPD) was studied. Upon O(3) exposure, a sluggish response of stomatal movements was observed, characterized by slower reactions to increases in blue light intensity, CO(2) concentration and VPD, and lower amplitude of the response to variations in light intensity.

Capacity for NADPH regeneration in the leaves of two poplar genotypes differing in ozone sensitivity.

Cell capacity for cytosolic NADPH regeneration by NADP-dehydrogenases was investigated in the leaves of two hybrid poplar (Populus deltoides × Populus nigra) genotypes in response to ozone (O3 ) treatment (120 ppb for 17 days). Two genotypes with differential O3 sensitivity were selected, based on visual symptoms and fallen leaves: Robusta (sensitive) and Carpaccio (tolerant). The estimated O3 flux (POD0 ), that entered the leaves, was similar for the two genotypes throughout the treatment.

Elevated CO2 and/or ozone modify lignification in the wood of poplars (Populus tremula x alba).

Trees will have to cope with increasing levels of CO(2) and ozone in the atmosphere. The purpose of this work was to assess whether the lignification process could be altered in the wood of poplars under elevated CO(2) and/or ozone. Young poplars were exposed either to charcoal-filtered air (control), to elevated CO(2) (800 μl l(-1)), to ozone (200 nl l(-1)) or to a combination of elevated CO(2) and ozone in controlled chambers.

The response to daylight or continuous ozone of phenylpropanoid and lignin biosynthesis pathways in poplar differs between leaves and wood.

Ozone induces a stimulation of the phenylpropanoid and lignin biosynthesis pathways in leaves but the response of wood, the main lignin-producing tissue, is not well documented. The purpose of this study was to compare the responses of phenylpropanoid and lignin pathways in leaves and stem wood by a simultaneous analysis of both organs. Young poplars (Populus tremula×alba) were subjected either to daylight ozone (200 nL L(-1) during light period) or continuous ozone (200 nL L(-1) during light and dark periods) in controlled chambers.

A difference gel electrophoresis study on thylakoids isolated from poplar leaves reveals a negative impact of ozone exposure on membrane proteins.

Populus tremula L. x P. alba L.

Cellulose and lignin biosynthesis is altered by ozone in wood of hybrid poplar (Populus tremula × alba).

Wood formation in trees is a dynamic process that is strongly affected by environmental factors. However, the impact of ozone on wood is poorly documented. The objective of this study was to assess the effects of ozone on wood formation by focusing on the two major wood components, cellulose and lignin, and analysing any anatomical modifications.

Source-sink imbalance increases with growth temperature in the spring geophyte Erythronium americanum.

Spring geophytes produce larger storage organs and present delayed leaf senescence under lower growth temperature. Bulb and leaf carbon metabolism were investigated in Erythronium americanum to identify some of the mechanisms that permit this improved growth at low temperature. Plants were grown under three day/night temperature regimes: 18/14 °C, 12/8 °C, and 8/6 °C.

Differential impact of chronic ozone exposure on expanding and fully expanded poplar leaves.

Populus tremula L. × Populus alba L. (Populus ×c anescens (Aiton) Smith) - clone INRA 717-1-B4 saplings (50 cm apex to base and carrying 19 leaves on average) - were followed for 28 days.

The alternative respiratory pathway allows sink to cope with changes in carbon availability in the sink-limited plant Erythronium americanum.

Mechanisms that allow plants to cope with a recurrent surplus of carbon in conditions of imbalance between source and sink activity has not received much attention. The response of sink growth and metabolism to the modulation of source activity was investigated using elevated CO(2) and elevated O(3) growth conditions in Erythronium americanum. Sink activity was monitored via slice and mitochondrial respiratory rates, sucrose hydrolysis activity, carbohydrates, and biomass accumulation throughout the growth season, while source activity was monitored via gas exchanges, rubisco and phosphoenolpyruvate carboxylase activities, carbohydrates, and respiratory rates.

The impact of atmospheric composition on plants: a case study of ozone and poplar.

Tropospheric ozone is the main atmospheric pollutant that causes damages to trees. The estimation of the threshold for ozone risk assessment depends on the evaluation of the means that this pollutant impacts the plant and, especially, the foliar organs. The available results show that, before any visible symptom appears, carbon assimilation and the underlying metabolic processes are decreased under chronic ozone exposure.

Ozone-induced changes in photosynthesis and photorespiration of hybrid poplar in relation to the developmental stage of the leaves.

Young poplar trees (Populus tremula Michx. x Populus alba L. clone INRA 717-1B4) were subjected to 120 ppb of ozone for 35 days in phytotronic chambers.

Ozone risk assessment for plants: central role of metabolism-dependent changes in reducing power.

The combination of stomatal-dependent ozone flux and total ascorbate level is currently presented as a correct indicator for determining the degree of sensitivity of plants to ozone. However, the large changes in carbon metabolism could play a central role in the strategy of the foliar cells in response to chronic ozone exposure, participating in the supply of reducing power and carbon skeletons for repair and detoxification, and modifying the stomatal mode of functioning. To reinforce the accuracy of the definition of the threshold for ozone risk assessment, it is proposed to also consider the redox pool (NAD(P)H), the ratio between carboxylases and the water use efficiency as indicators of the differential ozone tolerance of plants.

The different fates of mitochondria and chloroplasts during dark-induced senescence in Arabidopsis leaves.

Senescence is an active process allowing the reallocation of valuable nutrients from the senescing organ towards storage and/or growing tissues. Using Arabidopsis thaliana leaves from both whole darkened plants (DPs) and individually darkened leaves (IDLs), we investigated the fate of mitochondria and chloroplasts during dark-induced leaf senescence. Combining in vivo visualization of fates of the two organelles by three-dimensional reconstructions of abaxial parts of leaves with functional measurements of photosynthesis and respiration, we showed that the two experimental systems displayed major differences during 6 d of dark treatment.

A DIGE analysis of developing poplar leaves subjected to ozone reveals major changes in carbon metabolism.

Tropospheric ozone pollution is described as having major negative effects on plants, compromising plant survival. Carbon metabolism is especially affected. In the present work, the effects of chronic ozone exposure were evaluated at the proteomic level in developing leaves of young poplar plants exposed to 120 ppb of ozone for 35 days.

Foliar CO2 fixation in bean (Phaseolus vulgaris L.) submitted to elevated ozone: distinct changes in Rubisco and PEPc activities in relation to pigment content.

Using open-top chambers, the impact of ozone (O(3)) on foliar carboxylases of bean (Phaseolus vulgaris L.) was investigated. From sowing, beans were exposed to non-filtered air (NF) and NF supplied with 40 (+40) and 80 (+80) nL L(-1) O(3).

Alternative oxidase regulation in roots of Vigna unguiculata cultivars differing in drought/salt tolerance.

The alternative oxidase (Aox) was studied at different levels (transcript, protein and capacity) in response to an osmotic shock applied to roots of cowpea (Vigna unguiculata). Two cultivars of V. unguiculata were used, Vita 3 and Vita 5, tolerant and sensitive to drought/saline stress respectively.

In vivo and in situ rhizosphere respiration in Acer saccharum and Betula alleghaniensis seedlings grown in contrasting light regimes.

A perfusive method combined with an open-system carbon dioxide measurement system was used to assess rhizosphere respiration of Acer saccharum Marsh. (sugar maple) and Betula alleghaniensis Britton (yellow birch) seedlings grown in 8-l pots filled with coarse sand. We compared in vivo and in situ rhizosphere respiration between species, among light regimes (40, 17 and 6% of full daylight) and at different times during the day.