Impact of novel coronavirus disease (COVID-19) lockdown on ambient air quality of Saudi Arabia

The outbreak of COVID-19 has spread globally affecting human activities but with improvement in ambient air quality. The first case of the virus in the Kingdom of Saudi Arabia was on the 2nd of March 2020. The impact of COVID-19 lockdown on the ambient air quality of the Kingdom of Saudi Arabia for the first time using data from nine cities was determined in this study. Hourly air quality data, based on concentrations of carbon monoxide (CO), particulate matter (PM₁₀), sulfur dioxide (SO₂), nitrogen dioxide (NO₂) and ozone (O₃), and meteorological conditions (atmospheric temperature, relative humidity, and wind speed) of the nine cities studied were obtained from Saudi Arabian General Authority of Meteorology and Environmental Protection (GAMEP), for the period between January 2019 to May 2020. Significant variation (p < 0.05) was recorded for the five atmospheric pollutants across the cities before and during the lockdown, with lower concentrations during the lockdown except for the concentration of O₃ in Tabuk, Al Qasim, and Haql. This can be a result of NO and O₃ reaction, causing the inability of effective O₃ depletion. The percentage changes in concentrations of CO (33.60%) and SO₂ (44.16%) were higher in Jeddah; PM₁₀ (91.12%) in Riyadh, while NO₂ (44.35%) and O₃ (18.98%) were highest in Makkah. However, even though there was a decrease in pollutants concentrations during the lockdown, the concentrations for CO, PM₁₀, SO₂, NO_2, and O₃ were still above WHO 24 h and annual mean limit levels. The COVID-19 lockdown in the Kingdom of Saudi Arabia revealed the possibility of significant atmospheric pollutant reduction by controlling traffic, activities by industries, and environmentally friendly transportation programs such as green commuting programs.     

Ozone effects on soluble protein content of Acer negundo, Quercus robur and Platanus spp. pollen

In this study, the effect of three different ozone (O₃) levels on soluble protein content of Acer negundo, Quercus robur and Platanus spp. pollen was investigated. Pollen was directly collected from each plant and exposed to O₃ values below, equal and four times the limit for human health protection in an environmental chamber system. With this chamber, it was possible to control and reproduce the O₃ levels between different experiments. Total protein content was determined colorimetrically with Coomassie protein assay reagent (Pierce) by the Bradford method. Results showed that O₃ has significant effects on pollen causing a decrease in soluble proteins that seem to be dependent on species and gas concentration. Also, the existence of reproducibility in the effects of O₃, within the same concentration, on the protein content of pollen was verified.     

Pollen analysis of honeys of Melipona (Michmelia) seminigra merrillae and Melipona (Melikerria) interrupta (Hymenoptera: Apidae) bred in Central Amazon,Brazil

The pollen present in honey in colonies of Melipona seminigra merrillae and Melipona interrupta bred in Manaus was analysed. Between August and October 2012, honey samples were collected from the Sucupira meliponary, located in Manaus, Amazonas, Brazil. We identified a total of 70 pollen types belonging to 35 botanical families. In the samples from Melipona seminigra merrillae, the most represented pollen types were: Miconia-type (Melastomataceae) was the dominant pollen (DP) in August (51.19%), September (76.83%) and October (58.33%); Triplaris-type (Polygonaceae) was an accessory pollen (AP) in August (20.5%); and the remaining pollen types were classified as isolated pollen (IP), with Talisia macrophylla (Sapindaceae) exhibiting the highest percentage in August (12.92%). For Melipona interrupta, the most frequent pollen types were as follows: Miconia-type was the DP in August (59.33%) and October (61.33%) and an AP in September (37.5%); and Triplaris-type was an AP in August (35.83%), September (34.16%) and October (23.33%). The diversity of pollen types was not significantly different between the bees in the months evaluated. However, there was a large significant niche overlap in the months studied, August (O_ik = 0.95), October (O_ik = 0.89) and September (O_ik = 0.69), revealing that of the 70 pollen types found in the samples, 22 were shared by the two bee species in large proportions, 28 were exploited exclusively by Melipona seminigra merrillae and 20 were collected only by Melipona interrupta.     

Forecasting airborne Platanus pollen in the Madrid region

This study analyses the atmospheric concentration of Platanus pollen in four stations in the Madrid region over a period of 10 years (1994–2003). Various statistical analyses (regression analysis and decision tree) were used to prepare a forecasting model for possible application as a preventive measure in pollinosis. The data comes from the PALINOCAM network and the samplers used were Hirst type (Burkard pollen trap). Platanus pollen is present in the atmosphere during a short period of time in spring, and the maximum concentrations are detected during the last two weeks of March and the first week of April. Regression analysis shows that the pollen concentration of the two previous days is the best predictive variable. The models obtained for the four stations analysed account for between 37 and 61% of the variation in pollen levels in the air. The decision trees show how the introduction of meteorological variables improves prediction for this pollen type.     

Mesoscale Transport of Corylus Pollen Grains in Winter Atmosphere

Measurements of atmospheric pollen concentration were made at different sites of the Po Valley, Italy, during the winter of 1978. The concentration was determined with volumetric samplers both near the ground and at different heights up to 500 m. Only Corylus and Alnus pollen grains were found during the experimental period. Due to the large quantity of grains released and the detailed information available about the source areas, the Corylus pollen was used to investigate the features of atmospheric transport. It was found that the three-dimensional patterns of pollen concentration are strongly influenced by meteorological conditions. Moreover, it appears that pollen is present in the atmosphere for a longer time with respect to the emission period, due to the relevant effect of the resuspension of the deposited pollen grains. This effect is detectable at all the sampling points, and not only near the sources.     

Response of in vitro pollen germination and pollen tube growth of groundnut (Arachis hypogaea L.) genotypes to temperature

Air temperatures of greater than 35 °C are frequently encountered in groundnut‐growing regions, especially in the semi‐arid tropics. Such extreme temperatures are likely to increase in frequency under future predicted climates. High air temperatures result in failure of peg and pod set due to lower pollen viability. The response of pollen germination and pollen tube growth to temperature was quantified in order to identify differences in pollen tolerance to temperature among 21 groundnut genotypes. Plants were grown from sowing to harvest in a poly‐tunnel under an optimum temperature of 28/22 °C (day/night). Pollen was collected at anther dehiscence and was exposed to temperatures from 10° to 47·5 °C at 2·5 °C intervals. The results showed that a modified bilinear model most accurately described the response to temperature of percentage pollen germination and maximum pollen tube length. Genotypes were found to range from most tolerant to most susceptible based on both pollen characters and membrane thermostability. Mean cardinal temperatures (T_min, T_opt and T_max) averaged over 21 genotypes were 14·1, 30·1 and 43·0 °C for percentage pollen germination and 14·6, 34·4 and 43·4 °C for maximum pollen tube length. The genotypes 55‐437, ICG 1236, TMV 2 and ICGS 11 can be grouped as tolerant to high temperature and genotypes Kadiri 3, ICGV 92116 and ICGV 92118 as susceptible genotypes, based on the cardinal temperatures. The principal component analysis identified maximum percentage pollen germination and pollen tube length of the genotypes, and T_max for the two processes as the most important pollen parameters in describing a genotypic tolerance to high temperature. The T_min and T_opt for pollen germination and tube growth, rate of pollen tube growth were less predictive in discriminating genotypes for high temperature tolerance. Genotypic differences in heat tolerance‐based on pollen response were poorly related (R² = 0·334, P = 0·006) to relative injury as determined by membrane thermostability.     

响应面法优化麻疯树花粉离体萌发培养基的研究

麻疯树因其种子含油率较高,种子油提炼的生物柴油可部分替代汽油,而成为一种极具潜能的能源作物,但由于产量低,麻疯树在热带、亚热带的发展受到极大限制。杂交育种是提高产量的重要手段,杂交亲本花粉生活力的高低直接影响到育种的成效。因此,寻求麻疯树离体花粉萌发的最适培养基配方,探明花粉萌发培养基中各主要培养基成分间的交互作用对生产上麻疯树杂交结实率和种子产量的提高具有重要意义。该研究以麻疯树开花初期雄花上花药刚散粉时的成熟花粉粒为材料,采用Box-Behnken设计(Box-Behnken design,BBD)的响应面法,对麻疯树花粉离体萌发培养基中各主要培养基成分的浓度配比及各主要培养基成分的交互作用进行了研究。以花粉萌发率为响应指标,建立了4种营养成分(蔗糖、硼酸、硝酸钙、硝酸钾)与花粉萌发率的响应面模型,并对各主要培养基成分的浓度配比进行了优化。通过R软件进行响应面分析的结果表明:4因素对花粉萌发率的影响顺序为蔗糖硼酸硝酸钙硝酸钾;蔗糖与硼酸、蔗糖与硝酸钙、蔗糖与硝酸钾之间的交互作用显著。响应面建模优化后的最佳培养基为13.77%蔗糖+32.14 mg·L~(-1)硼酸+22.21 mg·L~(-1)硝酸钙+19.95 mg·L~(-1)硝酸钾+200 mg·L~(-1)硫酸镁,在此条件下的理论萌发率为99.73%。采用此培养基成分配比得到麻疯树花粉离体试验萌发率为98.97%,与理论响应值相吻合,同时也表明利用BBD设计的响应面模型进行麻疯树花粉离体萌发培养条件优化方法的有效性。     

Seasonal distribution of pollen in the atmosphere of Darwin,tropical Australia: Preliminary results

Pollen loads in the atmosphere of Darwin, a city located in the wet‐dry tropics of Australia, have been monitored for the period March 2004 to November 2005 as part of a large research program looking at atmospheric particles and human health. Seven pollen types dominate the pollen spectrum, the herbaceous families of Poaceae (grasses) and Cyperaceae (sedges), as well as several native tree and shrub taxa, Acacia, Callitris, Casuarina, Arecaceae and Myrtaceae. The pollen loads were found to have a strong seasonal component associated with the alternating wet (November to March) and dry (April to October) seasons of the region. Seventy percent of the yearly pollen load is captured during the dry season, with the peak pollen period occurring at the onset of the dry season (April–May) when most grasses are in flower. The daily pollen concentration decreases as the dry season progresses, accompanied by a change in composition; fewer herbaceous but increasing woody taxa. Preliminary health outcomes reveal a positive association between hay fever, Poaceae and Acacia pollen, as well as a significant association between total fungal spore concentrations and asthma. The Darwin record contrasts significantly with surveys conducted in the subtropical and temperate cities of Australia where temperature as opposed to rainfall and the prevalence of northern hemisphere exotic tree species have a greater influence over the seasonality and composition of the pollen loads.     

Analysis of protein content in pollen loads produced in north-west Spain

An analysis was made of the protein content of pollen loads produced by the bees in a hive situated in Viana do Bolo (Ourense, north-west Spain), to establish whether or not the relative quantity of protein in the pollen of each plant species influences the preference made by the bee of the flowers that supply pollen to the hive. This analysis was performed on all types of pollen that formed more than 5% of the pollen spectrum. Pollen load samples were collected directly from the hive from March to September. Pollen loads were separated by colour, and their specific homogeneity was confirmed microscopically. The Bradford method has been used for protein extraction and spectrophotometry was used for the determination of protein content. The results show that the different pollen loads have high protein content. Pollen of the plant species that reached relatively higher percentages in the pollen spectrum are also those that have the highest protein content. These were Cytisus scoparius type, uncultivated Poaceae, Quercus robur type, Sanguisorba minor, Salix fragilis and Spergularia rubra type. The pollen of the systematic units, which had pollen loads that could be identified at the level of species, maintained a constant value of protein content independently of the date the samples were obtained. The pollen of the systematic units, which had pollen loads that could be identified at the level of pollen type, has varied in protein content in the analyses performed on samples obtained on different dates. This result is due to the fact that the different species that integrate the pollen type flower on different dates, and thus have a pollenkitt with different characteristics.     

Inhibition of photosynthesis ofPopulus euramericana andHelianthus annuus by SO2, NO2 and O3

Populus euramericana cv. I-214 andHelianthus annuus L. cv. Russian Mammoth were exposed to various concentrations of O₃ SO₂ or NO₂ for 2 h in a cylindrical assimilation chamber. The threshold concentrations of air pollutants for inhibition of net photosynthesis differed between the two species and also between the pollutants tested. Furthermore, the lethal concentrations where the net photosynthetic rates were completely inhibited, also differed between species and between pollutants. For SO₂ and NO₂,P. euramericana was more tolerant photosynthetically thanH. annuus when related to the concentration of pollutants used during the experiment. However, when related to the cumulative uptake rate of each pollutant, the photosynthetic tolerance of the two species was similar. In contrast to the effects of SO₂ or NO₂, the influence of O₃ on net photosynthesis was quite different. The relative rates of net photosynthesis in both species showed the same linear relationship with O₃ concentration. However, the relationship between the relative rate of net photosynthesis and the cumulative uptake rate of O₃ differed between the two species, although it was linear in both cases.     

Reliability of pollen ratios for environmental reconstructions on the Tibetan Plateau

Aim Pollen ratios are widely used to gain palaeovegetation and palaeoclimatic information from fossil pollen spectra, although their applicability has seldom been tested with modern pollen data. I used a data set of 113 lake‐surface sediments from the eastern Tibetan Plateau to test the reliability of several pollen ratios. Location The lake‐surface pollen spectra cover a wide range of vegetation types (temperate desert, temperate steppe, alpine desert, alpine steppe, high‐alpine meadow, sub‐alpine shrub, coniferous and mixed forest) and climatic conditions (mean July temperature, T_July: 4.0–17.4°C; mean annual precipitation, P_ann: 104–670 mm). Methods Lake‐surface sediments were analysed palynologically, and several pollen ratios were calculated. These ratios were interpreted with respect to vegetation and climatic conditions. Results The arboreal pollen sum (AP) was highest in samples from forested areas and was significantly correlated with P_ann (r² = 0.44). In non‐forested areas, samples from large lakes and from lakes surrounded by sparse vegetation had increased AP values, suggesting that AP is a useful vegetation density indicator. Artemisia/Chenopodiaceae (A/C) ratios were lowest in desert areas and were positively correlated with P_ann (r² = 0.25). The aridity pollen index was inappropriate for inferring (palaeo‐)climatic information from samples on the eastern Tibetan Plateau as it had no significant correlation with the environmental factors. Artemisia/Cyperaceae (A/Cy) ratios had a significant correlation with T_July (r² = 0.23), but only a weak correlation with P_ann, which indicates that the A/Cy ratio is applicable as a temperature indicator. Furthermore, it is a valuable tool for the differentiation of high‐alpine meadow from steppe vegetation. Main conclusions AP sum, A/C ratio and A/Cy ratio are useful tools for qualitative and semi‐quantitative palaeoenvironmental reconstruction on the Tibetan Plateau; however, the results obtained should not be interpreted quantitatively.     

Effect of flue gas components on succinate production and CO2 fixation by metabolically engineered Escherichia coli

Escherichia coli pfl ldhA ptsG (AFP111) was studied for succinate production in defined medium using trace gases typically found in flue gas; i.e. oxygen (O₂), nitrogen dioxide (NO₂), sulfur dioxide (SO₂) and carbon monoxide (CO). Following aerobic cell growth, cells were exposed to 50% CO₂ and 3–10% O₂, or 50–300 ppm NO₂, SO₂ or CO during the succinate production phase. Although 3% O₂ did not significantly affect succinate formation, 10% O₂ reduced the final succinate concentration from 33 to 17 g/L, specific productivity from 1.90 to 1.13 mmol/g h and yield from 1.15 to 0.81 mol/mol glucose. The effect of O₂ correlated with the culture redox potential (ORP) with more reducing conditions favoring succinate production. The trace gases NO₂ and SO₂ also reduced the rate of succinate formation by as much as 50%, and led to a greater than twofold increase in pyruvate formation. Similar concentrations of CO showed no effect on succinate production rate or yield. Using synthetic flue gas AFP111 generated 12 g/L succinate with a specific productivity of 0.73 mmol/g h and a yield of 0.65 mol/mol.     

Growth of coniferous trees exposed to SO2 and O3 using an open-air fumigation system

Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and Sitka spruce (Picea sitchensis Bong. Carr.) were planted as 2-year-old seedlings in an open-air fumigation facility at Liphook in southern England in March 1985. The soil was a humoferric podzol of pH 4. SO₂ fumigation began in May 1987 and continued until December 1990. Long-term mean SO₂ concentrations were 4,13 and 22 nmol mo^?1. Three plots, one at each SO₂ level, were also exposed to O₃ at an average of 1–3.times the ambient level. O₃ fumigation ran from March to December 1988, May to December 1989 and February to December 1990. Each species reacted differently to treatment. Scots pine showed no growth response to either pollutant, although other work on the site demonstrated a number of deleterious effects of SO₂ on this species, including increased leaf loss and foliar injury. Stem basal diameter growth of Norway spruce was depressed in SO₂-treated plots. In contrast, extension growth of shoots of Sitka spruce increased in SO₂-treated plots, in apparent response to codeposition of NH₃-N. However, diameter growth of Sitka spruce main stems did not increase. No effects of O₃ on growth were recorded for any species.     

Reactive oxygen species are involved in regulation of pollen wall cytomechanics

Production and scavenging of reactive oxygen species (ROS) in somatic plant cells is developmentally regulated and plays an important role in the modification of cell wall mechanical properties. Here we show that H₂O₂ and the hydroxyl radical (^?OH) can regulate germination of tobacco pollen by modifying the mechanical properties of the pollen intine (inner layer of the pollen wall). Pollen germination was affected by addition of exogenous H₂O₂, ^?OH, and by antioxidants scavenging endogenous ROS: superoxide dismutase, superoxide dismutase/catalase mimic Mn‐5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)21H, 23H‐porphin, or a spin‐trap α‐(4‐pyridyl‐1‐oxide)‐N‐tert‐butylnitrone, which eliminates ^?OH. The inhibiting concentrations of exogenous H₂O₂ and ^?OH did not decrease pollen viability, but influenced the mechanical properties of the wall. The latter were estimated by studying the resistance of pollen to hypo‐osmotic shock. ^?OH caused excess loosening of the intine all over the surface of the pollen grain, disrupting polar growth induction. In contrast, H₂O₂, as well as partial removal of endogenous ^?OH, over‐tightened the wall, impeding pollen tube emergence. Feruloyl esterase (FAE) was used as a tool to examine whether H₂O₂‐inducible inter‐polymer cross‐linking is involved in the intine tightening. FAE treatment caused loosening of the intine and stimulated pollen germination and pollen tube growth, revealing ferulate cross‐links in the intine. Taken together, the data suggest that pollen intine properties can be regulated differentially by ROS. ^?OH is involved in local loosening of the intine in the germination pore region, while H₂O₂ is necessary for intine strengthening in the rest of the wall through oxidative coupling of feruloyl polysaccharides.     

Pollinosis in trentino (Northern Italy). Aerobiological and clinical research

Summary A study to evaluate and define the atmospheric pollen concentration in Trentino was carried out through the aerobiologic sampling in three localities chosen according to their different climatic conditions.1375 patients with pollinosis living in Trentino were studied retrospectively over the period ranging from 1986 to 1988 and selected according to the area they came from.Results have proved that the most allergenic pollen types are the following: Poaceae, Urticaceae (Parietaria), Compositae (Artemisia) and the tree pollen of Betulaceae and Corylaceae (Alnus, Betula, Corylus), and that pollinosis caused by such pollen, types has different features and frequencies according to the different localities.As far as symptoms are concerned, our data shows that rhinoconjuntivitis is more frequent in those patients who are allergic toParietaria while asthma results being more frequent in patients who are allergic to tree pollen.     

Air and surface soil samples – two different pairs of shoes? Comparing the pollen spectrum on different days of the pollen season

The pollen spectra of air and surface soil samples from a rooftop (at 14 m) and from ground level (at 1.6 m) in the suburbs of Vienna (Austria) were compared. Two soil samples and two air samples were taken on four different days to account for possible differences: in winter when no pollination occurred (reference day), in spring during the main flowering of Betula (birch day), in spring/summer during the main flowering of Poaceae (grass day), and in autumn during the main flowering of Ambrosia (ragweed day). Thirty-five different pollen types were used to describe the pollen spectra. Frequencies of certain pollen types reflect a seasonal impact on both the surface soil and air samples and show a similarity between air and soil samples on most of the days. However, the seasonal impact is higher in the air samples and shows a high consistency for ground and rooftop level. Kendall’s tau correlation coefficients further substantiate the similarities of the samples especially for the pollen season days. Exceptions include the winter day when pollination was low and the air samples recorded nearly no pollen at all, and the ragweed day when Ambrosia pollen was abundant in three of four samples but not in the ground surface soil sample. Thus, (1) air and surface pollen samples record similar signals during the pollen season but not during the ragweed and winter season and (2) air and surface pollen samples show the impact of local vegetation also in pollen traps located at different heights.     

Pollen concentrations inside private cars during the Poaceae and Artemisia spp. pollen season – a case study

A growing number of studies are researching indoor air concentrations of pollen in buildings, but to our knowledge no studies have dealt with the precise concentration of pollen inside private cars. The aim of this study was to assess the risk of exposure to pollen in private cars throughout the Poaceae and Artemisia spp. pollen season.

The study was conducted in the town of Lappeenranta and along Highway 6 in south‐east Finland between July 14 and August 17, 2003. The pollen concentrations were measured inside two moving and parked cars using rotorod‐type samplers. Surface and ambient Burkard samples were also collected.

Both Poaceae and Artemisia spp. pollen were recorded only on one day and in low concentrations (<10 pollen grains per cubic meter, pg/m³) inside moving and parked cars, whereas the concentrations of Betula spp. (0–15 vs. 0–12?pg/m³) and Pinus (0–41 vs. 0–80?pg/m³) ranged from low to moderate, respectively. The number of pollen grains on the inside surfaces of cars ranged from zero to 72?pg/cm² during the measurement periods.

The concentrations of Poaceae and Artemisia spp. pollen in the indoor air of the car during the flowering period were low, therefore, likely to cause reactions only in the most sensitive people. By contrast, even after the main flowering period the concentrations of Betula spp. pollen were on a level high enough to cause reactions in individuals with allergies.     

Fusicoccin and Air Pollutant Injury to Plants : Evidence for Enhancement of SO(2) but Not O(3) Injury

Garden peas (Pisum sativum L. cv Alsweet) and a tomato mutant (Lycopersicon esculentum Mill. var flacca) were sprayed with fusicoccin, a fungal toxin affecting membrane transport properties, before exposure to SO₂ or O₃. Tomatoes treated with 10 micromolar fusicoccin and exposed to SO₂ (0.6 microliter per liter for 2 hours) exhibited twice as much foliar necrosis as untreated plants exposed to SO₂. Peas treated with fusicoccin and exposed to SO₂ (0.7 to 1.0 microliter per liter for 2 hours) exhibited 2 to 6 times more injury than untreated plants exposed to SO₂. Peas treated with fusicoccin and exposed to O₃ had less injury than untreated plants exposed to O₃ (0.1 to 0.3 microliter per liter for 2 hours). Several lines of evidence suggested that the fusicoccin enhancement of SO₂ injury is not the result of increased gas exchange, i.e. the tomato mutant has permanently open stomata under all conditions, and in peas fusicoccin had no effect on SO₂ or H₂O flux in plants exposed to 0.12 microliter per liter SO₂. However, a 21% greater leaf conductance in fusicoccin treated versus untreated plants indicated the possibility of some differences in gas exchange for peas exposed to 1.0 microliter per liter SO₂.     

A study of variation in the pollen spectra of honeys sampled from the Baixa Limia‐Serra do Xurés Nature Reserve in north‐west Spain

The pollen content of eleven honey samples from ten different apiaries in the Baixa Limia – Serra do Xurés Nature Reserve and other honey commercialised by the cooperative as “Mel do Xurés” (north‐west Spain) was subjected to quantitative and qualitative melissopalynological analysis. The quantitative analysis found that ten samples belonged to Maurizio's Class III and one to Class IV. According to the qualitative analysis, four samples were classified as unifloral honey with Erica, four samples as multifloral honey with Erica pollen as the principal component and three samples as multifloral honey with Cytisus‐type pollen and Erica as the principal component pollen. The pollen spectra differ between the diverse honeys analysed, with a common denominator being Erica and Cytisus‐type pollen being abundant in all. For the rest of the samples, the pollen spectra were mainly the same, but with different relative percentages among secondary elements. Thus, either as a secondary or an important element, 91% of the honeys contained Quercus, 82% Castanea sativa Miller, 45% Rubus, 36% Cistus and 27% Lithodora prostrate (Loisel) Griseb,. In particular, we record for the first time the presence of Ribes and Ilex aquifolium L. pollen in Spanish honeys as an important minor or minor pollen component.     

Metabolic Basis for Injury to Plants from Combinations of O(3) and SO(2): Studies with Modifiers of Pollutant Toxicity

Pisum sativum L. cv Alsweet (garden pea) and Lycopersicon esculentum Mill. flacca (mutant tomato) were chosen to evaluate the metabolic basis for plant injury from combinations of O₃ + SO₂. The plants were exposed under conditions reported to specifically alter O₃ or SO₂ toxicity; light versus dark exposures, and treatment with the fungal metabolite fusicoccin (FC), the O₃ injury inhibitor N-[2-(2-oxo-1-imidazolidiny) ethyl]-N′-phenylurea (EDU), and the SO₂ injury stimulator diethyldithiocarbamate (DDTC). Plants were grown in controlled environment chambers and exposed to combinations of O₃ (0.05-0.2 microliters per liter) and SO₂ (0.1-0.3 microliters per liter) for 2 hours. Peas treated with FC had the same or greater injury (quantified by visual rating) with O₃ + SO₂ exposures compared to plants not treated with FC. For plants with open stomata in the dark as well as light, i.e. FC-treated peas and tomatoes, there was no change or an increase in foliar necrosis with O₃ + SO₂ exposures in the dark versus light. Peas treated with EDU had an almost complete absence of O₃ injury, no change in SO₂ injury, and moderate decreases in injury from combinations of O₃ + SO₂ compared to plants not treated with EDU. Tomatoes treated with DDTC showed the same or less injury compared to plants not treated with DDTC and exposed to O₃ or SO₂. The plant responses to the experimental treatments and O₃ + SO₂ resembled O₃ responses more than SO₂ responses. The evidence for O₃-like responses are: no change or increase in injury in the light versus dark, and EDU-induced decreases in injury. Evidences for SO₂-like responses are: incomplete protection from injury with EDU, and no change or increased injury to FC-treated versus untreated plants. Thus, a metabolic mechanism affected by both pollutants may be associated with the combination injury, e.g. effects the plasma membrane.