A Review of the Effects of Major Atmospheric Pollutants on Pollen Grains, Pollen Content, and Allergenicity.

This review summarizes the available data related to the effects of air pollution on pollen grains from different plant species. Several studies carried out either on in situ harvested pollen or on pollen exposed in different places more or less polluted are presented and discussed. The different experimental procedures used to monitor the impact of pollution on pollen grains and on various produced external or internal subparticles are listed. Physicochemical and biological effects of artificial pollution (gaseous and particulate) on pollen from different plants, in different laboratory conditions, are considered. The effects of polluted pollen grains, subparticles, and derived aeroallergens in animal models, in in vitro cell culture, on healthy human and allergic patients are described. Combined effects of atmospheric pollutants and pollen grains-derived biological material on allergic population are specifically discussed. Within the notion of "polluen," some methodological biases are underlined and research tracks in this field are proposed.

The promoters of 3 celery salt-induced phloem-specific genes as new tools for monitoring salt stress responses.

Genes induced by a progressive 3 week salt stress (final NaCl concentration 300 mM) were identified in the phloem of celery (Apium graveolens L., cv Vert d'Elne). A subtractive library was constructed and screened for salt-induced, phloem-specific genes. Work was focused on phloem due to its central role in inter-organ exchanges. Three genes were studied in more details, 2 coding for metallothioneins (AgMT2 and AgMT3) and one for a new mannitol transporter (AgMaT3). Expression of a reporter gene in transgenic Arabidopsis under control of promoter of each gene was located in the phloem. pAgMT2 has a typical phloem pattern with slight induction by salt stress. pAgMT3 and pAgMaT3 expression was induced by salt stress, except in minor veins. pAgMaT3 was highly active in stressed roots. The promoters described here could be regarded as new tools for engineering salt-resistant plants.

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). Twenty days after emergence, primary and first trifoliate leaves were sampled. Biochemical characteristics of leaves from +40 were quite similar to those from NF. Conversely, +80 induced distinct biochemical effects in primary and first trifoliate leaves. Regarding primary leaves, +80 reduced ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity by 33% whereas it stimulated phosphoenolpyruvate carboxylase (PEPc) activity by 376%. The reduction in Rubisco activity was accompanied by a decrease in both Rubisco subunit amounts and a consistent oxidative modification of the Rubisco small subunit (SSU). These changes came with a drastic loss in pigmentation. Regarding first trifoliate leaves, +80 stimulated Rubisco activity by 33% while it disturbed neither PEPc activity nor pigmentation. Surprisingly, the enhanced Rubisco activity was associated with a slight decrease in Rubisco protein quantity, which was not coupled with the formation of carbonyl groups in Rubisco-SSU.

Changes in PEP carboxylase, rubisco and rubisco activase mRNA levels from maize (Zea mays) exposed to a chronic ozone stress.

We quantified the ozone impact on levels of Zea mays L. cv. Chambord mRNAs encoding C4-phosphoenolpyruvate carboxylase (C4-PEPc), ribulose-l,5-bisphosphate carboxylase/oxygenase small and large subunits (Rubisco-SSU and Rubisco-LSU, respectively) and Rubisco activase (RCA) using real-time RT-PCR. Foliar pigment content, PEPc and Rubisco protein amounts were simultaneously determined. Two experiments were performed to study the ozone response of the 5th and the 10th leaf. For each experiment, three ozone concentrations were tested in open-top chambers: non-filtered air (NF, control) and non-filtered air containing 40 (+40) and 80 nL L-1 (+80) ozone. Regarding the 5th leaf, +40 atmosphere induced a loss in pigmentation, PEPc and Rubisco activase mRNAs. However, it was unable to notably depress carboxylase protein amounts and mRNAs encoding Rubisco. Except for Rubisco mRNAs, all other measured parameters from 5th leaf were depressed by +80 atmosphere. Regarding the 10th leaf, +40 atmosphere increased photosynthetic pigments and transcripts encoding Rubisco and Rubisco activase. Rubisco and PEPc protein amounts were not drastically changed, even if they tended to be increased. Level of C4-PEPc mRNA remained almost stable. In response to +80 atmosphere, pigments and transcripts encoding PEPc were notably decreased. Rubisco and PEPc protein amounts also declined to a lesser extent. Conversely, the level of transcripts encoding both Rubisco subunits and Rubisco activase that were not consistently disturbed tended to be slightly augmented. So, the present study suggests that maize leaves can respond differentially to a similar ozone stress.

Ozone-induced oxidation of Rubisco: from an ELISA quantification of carbonyls to putative pathways leading to oxidizing mechanisms.

In an attempt to detect a possible relationship between protein oxidation and ozone (O3) atmospheric concentration, we used a sensitive enzyme-linked immunosorbent assay (ELISA) method for measuring carbonyl formation in amino acid residues that constitute Rubisco (EC 4.1.1.39) small subunit (Rubisco-SSU). Using open-top chamber technology, bean plants (Phaseolus vulgaris L. cv. Bergamo) were exposed for 21 d (from emergence) to four different atmospheres characterized by average daylight O3 concentrations of 12, 70, 89 and 109nL L-1. Rubisco-SSU extracted from primary leaves was fixed specifically on wells coated with anti-SSU antibodies. Aldehydes and ketones, previously derivatized with 2,4-dinitrophenylhydrazine (DNP), were quantified with anti-DNP antibodies conjugated with alkaline phosphatase. A significant positive O3 effect on carbonyl formation was detected, and the number of carbonyls was found to be linearly increased (r2=0.82) when plotted against increasing external O3 dose expressed as accumulated exposure over a threshold of 40 nL L-1 h (AOT40). Furthermore, these O3-induced oxidative modifications were connected with a significant reduction in the amount of native SSU that linearly decreased (r2=0.95) as AOT40 increased from 0 to about 8295 nL L-1 h. A possible pathway leading to oxidation of Rubisco is proposed, with special reference to O3 reactivity.

The response of vacuolar phenolic content of common bean (Phaseolus vulgaris cv. Bergamo) to a chronic ozone exposure: questions and hypotheses.

Using open-top chamber technology, we investigated the foliar phenolic response of common bean (Phaseolus vulgaris L. cv. Bergamo) to a chronic, moderate ozone stress. Three atmospheric concentrations of ozone were tested: non-filtered air (NF) prevailing at the experimental site, and non-filtered air supplied with 40 (NF+40) and 60 nL L-1 ozone (NF+60), respectively. Both constitutive and ozone-induced non-polymerized phenolics were considered with regards to pollutant concentration, exposure time, leaf type (primary or trifoliate), and leaf growth. The biomass of primary leaves was unaffected by the tested ozone concentrations, whereas dry mass of first and second trifoliate leaves significantly decreased as atmospheric ozone increased. Characteristic symptoms were observed on the upper surface of leaves from the two ozone-supplied treatments. Their severity reflected both leaf exposure time and ozone concentration. As a whole, the total content of foliar soluble constitutive phenolics remained unchanged as the ozone increased, even for leaves almost totally covered with dark-brown discolourations. Nonetheless, among the three main detected phenolics, the accumulation of the kaempferol derivative could be significantly stimulated by ozone. Also, six ozone-induced phenolics could be synthesized by leaves exposed to the two pollutant-enriched atmospheres, and their elicitation and amount were closely connected with both exposure time and ozone concentration.

Describing and modelling ozone-dependent variation in flavonoid content of bean (Phaseolus vulgaris cv. Bergamo) leaves: a particular dose-response relationship analysis.

We investigated the ozone-dependent variation in the amount of a flavonoid accumulated by bean leaves (Phaseolus vulgaris L. cv. Bergamo). The phenolic response was modelled with special regard to different ozone exposure indexes. Using open-top chamber technology, six atmospheres of increasing ozone concentration were tested. Four successive harvests were carried out during a 33-d experiment. Primary and first trifoliate leaves were collected. Visible foliar injuries were recorded and the quantification of an ozone-responsive flavonoid was achieved by HPLC. Ozone significantly increased the amount of kaempferol glucuronide, which normally decreased with leaf ageing. Depending on the leaf type, this increase occurred either before or after the appearance of visible foliar damage. A linear regression could account for the ozone dose-phenolic response relationship. However, with respect to leaf type, the agreement between the model and observed values was influenced by the way in which ozone dose was calculated. Among the ozone exposure indexes tested, only the index with the highest threshold (AOT60) was appropriate to make the phenolic response linear in the case of primary leaves while in the case of first trifoliate leaves, this index always displayed the poorest adjustment compared with SUM00, SUM60, and AOT40 indexes. The study of the relationship suggests that sensitivity to ozone could be dependent on leaf type.

Changes in PEP Carboxylase, Rubisco and Rubisco activase mRNA levels from maize (Zea mays) exposed to a chronic ozone stress

We quantified the ozone impact on levels of Zea mays L. cv. Chambord mRNAs encoding C4-phosphoenolpyruvate carboxylase (C4-PEPc), ribulose-l,5-bisphosphate carboxylase/oxygenase small and large subunits (Rubisco-SSU and Rubisco-LSU, respectively) and Rubisco activase (RCA) using real-time RT-PCR. Foliar pigment content, PEPc and Rubisco protein amounts were simultaneously determined. Two experiments were performed to study the ozone response of the 5th and the 10th leaf. For each experiment, three ozone concentrations were tested in open-top chambers: non-filtered air (NF, control) and non-filtered air containing 40 (+40) and 80 nL L-1 (+80) ozone. Regarding the 5th leaf, +40 atmosphere induced a loss in pigmentation, PEPc and Rubisco activase mRNAs. However, it was unable to notably depress carboxylase protein amounts and mRNAs encoding Rubisco. Except for Rubisco mRNAs, all other measured parameters from 5th leaf were depressed by +80 atmosphere. Regarding the 10th leaf, +40 atmosphere increased photosynthetic pigments and transcripts encoding Rubisco and Rubisco activase. Rubisco and PEPc protein amounts were not drastically changed, even if they tended to be increased. Level of C4-PEPc mRNA remained almost stable. In response to +80 atmosphere, pigments and transcripts encoding PEPc were notably decreased. Rubisco and PEPc protein amounts also declined to a lesser extent. Conversely, the level of transcripts encoding both Rubisco subunits and Rubisco activase that were not consistently disturbed tended to be slightly augmented. So, the present study suggests that maize leaves can respond differentially to a similar ozone stress.