Ozone-exposed Plants Research Articles

Effects of ozone stress on flowering phenology, plant-pollinator interactions and plant reproductive success.

Tropospheric ozone is a highly oxidative pollutant with the potential to alter plant metabolism. The direct effects of ozone on plant phenotype may alter interactions with other organisms, such as pollinators, and, consequently, affect plant reproductive success. In a set of greenhouse experiments, we tested whether exposure of plants to a high level of ozone affected their phenological development, their attractiveness to four different pollinators (mason bees, honeybees, hoverflies and bumblebees) and, ultimately, their reproductive success. Exposure of plants to ozone accelerated flowering, particularly on plants that were growing in autumn, when light and temperature cues, that commonly promote flowering, were weaker. Simultaneously, there was a tendency for ozone-exposed plants to disinvest in vegetative growth. Plant exposure to ozone did not substantially affect pollinator preference, but bumblebees had a tendency to visit more flowers on ozone-exposed plants, an effect that was driven by the fact that these plants tended to have more open flowers, meaning a stronger attraction signal. Honeybees spent more time per flower on ozone-exposed plants than on control plants. Acceleration of flower production and the behavioural responses of pollinators to ozone-exposed plants resulted in retained reproductive fitness of plants pollinated by bumblebees, honeybees and mason bees, despite the negative effects of ozone on plant growth. Plants that were pollinated by hoverflies had a reduction in reproductive fitness in response to ozone. In a natural setting, acceleration of flowering by ozone might foster desynchronization between plant and pollinator activities. This can have a strong impact on plants with short flowering periods and on plants that, unlike wild mustard, lack compensatory mechanisms to cope with the absence of pollinator activity in the beginning of flowering.

Micro-morphological and anatomical response of groundnut (Arachis hypogaea L.) cultivars to ground-level ozone

Tropospheric ozone is a phytotoxic gaseous pollutant with global warming potential that disrupts the plants growth and development directly or through climate change. Ozone enters into a plant???s body through stomatal pores and develops oxidative stress, which results in injury to foliage and modifies leaf micro-morphology and anatomy. A field study was conducted to assess the morphological, micro-morphological, and anatomical response of groundnut cultivars (Arachis hypogaea L.) to enhance the level of ozone. This study observed ozone-like visible injury symptoms on all groundnut cultivars. Visible injury was maximum in cultivar Dh-86 and minimum in cultivar TPG-41. Micro-morphological characteristics, such as increase in stomata, epidermal cells number, and its index, were also increased under enhanced ozone-exposed plants. The highest stomatal index was found in cultivar TPG-41 and lowest were noted in cultivar GG-20. Cultivars TAG-24 > TG-37A > and Dh-86 show moderate modification in the morphological and micro-morphological characteristics of plants. Elevated ozone also affected the stomatal movement and leaf internal tissue. Most of the stomata of all the groundnut cultivars were observed as closed during the enhanced ozone exposure, suggesting a protective mechanism from ozone stress. The study concluded that the micro-morphological and anatomical characteristics are important aspects to determine the effect of ozone on plants and to influence plants sensitivity to ozone. On the basis of these characteristics, cultivar TPG-41 was found to be less sensitivity, while cultivar Dh-86 was found to be highly sensitive to ozone pollution.

Plant-mediated effects of ozone on herbivores depend on exposure duration and temperature

Abiotic stress by elevated tropospheric ozone and temperature can alter plants’ metabolism, growth, and nutritional value and modify the life cycle of their herbivores. We investigated how the duration of exposure of Sinapis arvensis plants to high ozone and temperature levels affect the life cycle of the large cabbage white, Pieris brassicae. Plants were exposed to ozone-clean (control) or ozone-enriched conditions (120 ppb) for either 1 or 5 days and were afterwards kept in a greenhouse with variable temperature conditions. When given the choice, P. brassicae butterflies laid 49% fewer eggs on ozone-exposed than on control plants when the exposure lasted for 5 days, but showed no preference when exposure lasted for 1 day. The caterpillars took longer to hatch on ozone-exposed plants and at lower ambient temperatures. The ozone treatment had a positive effect on the survival of the eggs. Ozone decreased the growth of caterpillars reared at higher temperatures on plants exposed for 5 days, but not on plants exposed for 1 day. Overall, longer exposure of the plants to ozone and higher temperatures affected the life cycle of the herbivore more strongly. With global warming, the indirect impacts of ozone on herbivores are likely to become more common.

The effect of elevated ozone on floral chemistry of Brassicaceae species

Tropospheric ozone is a major atmospheric pollutant; it is phytotoxic and has a strong effect on phytochemicals, which are constitutively present in plant tissues, but also produced de novo in response to stress. It has been shown that ozone exposure can modify volatile phytochemical emissions from leaves, which could disturb interactions between plants and other organisms. However, there is a lack of knowledge on the effects of ozone on floral chemistry. The aim of this study was to determine the effects of two elevated ozone exposure scenarios (80 and 120 ppb during daylight hours for 5 consecutive days) on the floral volatile emissions and floral chemical (molecular size range C6–C20) content of four Brassicaceae species: Sinapis alba, Sinapis arvensis, Brassica napus and Brassica nigra. The results showed that the emissions of individual compounds and their relative contributions to volatile blends are both affected by ozone exposure. In addition, for all four species studied, three diterpenes (neophytadiene, cis-phytol and trans-phytol) were present in significantly lower amounts and a fourth diterpene (hexahydrofarnesyl acetone) in significantly greater amounts in ozone-exposed plants. Consistent effects of ozone exposure on volatile emissions and terpene content were observed for each of the four species studied with no significant effect of exposure level. It appeared that B. napus is the most ozone-sensitive species, whereas B. nigra is the most ozone-tolerant. Since earlier studies have indicated that ratios of phytochemicals can have substantial effects on the efficacy of chemical use by pollinators, these changes may have ecological and biological relevance that should be the focus of further elucidation.

Role of Phytohormones in Ozone-exposed Plants

Role of Phytohormones in Ozone-exposed Plants

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. (Populus x canescens (Aiton) Smith), clone INRA 717-1-B4, saplings were subjected to 120 ppb ozone exposure for 28 days. Chloroplasts were isolated, and the membrane proteins, solubilized using the detergent 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC), were analyzed in a difference gel electrophoresis (DiGE) experiment comparing control versus ozone-exposed plants. Extrinsic photosystem (PS) proteins and adenosine triphosphatase (ATPase) subunits were detected to vary in abundance. The general trend was a decrease in abundance, except for ferredoxin-NADP(+) oxidoreductase (FNR), which increased after the first 7 days of exposure. The up-regulation of FNR would increase NAPDH production for reducing power and detoxification inside and outside of the chloroplast. Later on, FNR and a number of PS and ATPase subunits decrease in abundance. This could be the result of oxidative processes on chloroplast proteins but could also be a way to down-regulate photochemical reactions in response to an inhibition in Calvin cycle activity.

Calcium/calmodulin and cAMP/protein kinase-A pathways function in sperm motility regulation in the stallion

Tropospheric ozone is a major atmospheric pollutant; it is phytotoxic and has a strong effect on phytochemicals, which are constitutively present in plant tissues, but also produced de novo in response to stress. It has been shown that ozone exposure can modify volatile phytochemical emissions from leaves, which could disturb interactions between plants and other organisms. However, there is a lack of knowledge on the effects of ozone on floral chemistry. The aim of this study was to determine the effects of two elevated ozone exposure scenarios (80 and 120 ppb during daylight hours for 5 consecutive days) on the floral volatile emissions and floral chemical (molecular size range C6–C20) content of four Brassicaceae species: Sinapis alba, Sinapis arvensis, Brassica napus and Brassica nigra. The results showed that the emissions of individual compounds and their relative contributions to volatile blends are both affected by ozone exposure. In addition, for all four species studied, three diterpenes (neophytadiene, cis-phytol and trans-phytol) were present in significantly lower amounts and a fourth diterpene (hexahydrofarnesyl acetone) in significantly greater amounts in ozone-exposed plants. Consistent effects of ozone exposure on volatile emissions and terpene content were observed for each of the four species studied with no significant effect of exposure level. It appeared that B. napus is the most ozone-sensitive species, whereas B. nigra is the most ozone-tolerant. Since earlier studies have indicated that ratios of phytochemicals can have substantial effects on the efficacy of chemical use by pollinators, these changes may have ecological and biological relevance that should be the focus of further elucidation.

Quantitative proteomics identifies oxidant-induced, AtMPK6-dependent changes in Arabidopsis thaliana protein profiles

In Arabidopsis thaliana, oxidant-induced signalling has been shown to utilize the mitogen-activated protein kinase (MAPK), AtMPK6. To identify proteins whose accumulation is altered by ozone in a MPK6-dependent manner we employed isotope-coded affinity tagging (ICAT) technology to investigate the impact of AtMPK6-suppression on the protein profiles in Arabidopsis both before (air control) and during continuous ozone (O3) fumigation (500 nL L-1 for 8 h). Among the 150 proteins positively identified and quantified in the O3-treated plants, we identified thirteen proteins whose abundance was greater in the AtMPK6-suppressed genotype than in wild-type (WT). These include the antioxidant proteins, monodehydroascorbate reductase, peroxiredoxin Q, and glutathione reductase. A further eighteen proteins were identified whose abundance was lower in the ozone-treated AtMPK6-suppressed line relative to ozone-exposed WT plants. These predominantly comprised proteins involved in carbohydrate-, energy-, and amino acid metabolism, and tetrapyrrole biosynthesis. In control plants, five proteins increased, and nine proteins decreased in abundance in the AtMPK6-suppressed genotype compared to that of the WT, reflecting changes in the protein composition of plants that have AtMPK6 constitutively suppressed. Since a number of these proteins are part of the redox response pathway, and loss of AtMPK6 renders Arabidopsis more susceptible to oxidative stress, we propose that AtMPK6 plays a key role in the plant’s overall ability to manage oxidative stress.

Chlorophyll a fluorescence, antioxidant enzymes and lipid peroxidation in tomato in response to ozone and benomyl

Ozone is a widely distributed phytotoxic air pollutant and is known to reduce the yield of several important agricultural crops in Spain. However, benomyl has been found to lessen the adverse impact of ozone on plants. We studied the effects of ozone and benomyl on chlorophyll a fluorescence, antioxidant enzymes, and lipid peroxidation in tomato ( Lycopersicon esculentum Mill. cv. Tiny Tim) grown in open-top chambers in the field. Our results indicate that benomyl prevented the peroxidation of membrane lipids and increased protection of PSII from ozone. There was also a significant reduction in the activity of the antioxidant enzyme superoxide dismutase in ozone-exposed plants that had not been treated with benomyl. Comparing plants treated with benomyl to untreated plants we found that, on exposure to ozone, a greater fraction of light absorption energy was cycled through the photosynthetic system in benomyl-treated plants, as shown by the higher PSII-mediated electron flow and the higher fraction of open PSII reaction centers. The values analyzed in the fluorescence parameters and lipid peroxidation were similar for plants without benomyl grown in a charcoal-filtered environment and benomyl-treated plants exposed to ozone.

Effects of long-term open-field ozone exposure on leaf phenolics of European silver birch (Betula pendula Roth).

The response of phenolic compounds as a result of long-term low open-field ozone exposure was studied in ozone-sensitive and ozone-tolerant clones of European silver birch (Betula pendula Roth). The saplings were exposed to 1.5-1.6 times the ambient (elevated) ozone and ambient air (as control) over three growing seasons from May 1996 until August 1998. Quantification by modified Folin-Ciocalteau assay showed a 16.2% increase in total phenolics in elevated ozone plants as compared to that in controls and a corresponding 9.9% increase of 10 phenolic compounds quantified by HPLC. Five nonflavonoids and five flavonoids showed 8.4% and 11.4% increases, respectively. The phenolic results indicated slightly higher ozone sensitivity of clone 5 as compared to clone 2. The most ozone-responsive phenolic compounds in clone 2 and clone 5 were (+)-catechin (CT), chlorogenic acid (CGA), 5-p-coumaroylquinic acid (5CQA), 3-p-coumaroylquinic acid (3CQA), myricetin galactopyranoside (MG), quercetin-3-O-glucuronopyranoside (QGR), and quercetin-3-O-arabinofuranoside (QA). Increased phenolic content in ozone-exposed plants was related to impaired growth and accelerated leaf senescence, indicated by enhanced autumn leaf yellowing and lower chlorophyll and Mg content. The change in carbon allocation towards defensive phenolics at the expense of growth was greater in the ozone-sensitive clone as compared to tolerant clone.

Emission of Volatile Organic Compounds from Ozone-Exposed Plants

Plants produce a number of volatile organic compounds (VOCs), and this release plays a significant role in atmospheric chemistry. Although certain factors controlling the emission rates of VOCs from plants are reasonably well understood, the influence of abiotic stress, such as elevated ozone concentrations, is unknown. Therefore, the emission of VOCs from tobacco plants (Nicotiana tabacum L. cv. Bel B and Bel W3) and Scots pine (Pinus sylvestris L.) were studied in continuously stirred tank reactors under ozone exposure. A pulse treatment (5 h) with 120–170 nmol/mol ozone induced visible damages in the ozone-sensitive tobacco cv. Bel W3, while the more tolerant cv. Bel B seemed to be unaffected. The total amount and dynamics of the emission were studied. Both cultivars emitted methyl salicylate and a series of sesquiterpenes after the ozone treatment, but the response was less pronounced for Bel B plants. C6-volatiles that are thought to be derived from the lipoxygenase pathway were emitted only from Bel W3 plants. The results give further support to the hypothesis that the ozone-induced reactions of the ozone-sensitive Bel W3 plants resemble the hypersensitive response found after pathogen attack. Long-term ozone treatment (50 nmol/mol, 8 h/d) of pine led to 40% increased emissions of monoterpenes, while no damage was visible on the needles. Since VOCs are precursors of ozone, an increased VOC emission as a consequence of elevated ozone concentrations in the troposphere may lead to feedback mechanisms in photooxidant formation.

Inhibition of flowering and reproductive success in spreading dogbane ( Apocynum androsaemifolium) by exposure to ambient ozone

Ground-level ozone continues to be a cause for concern in terrestrial ecosystems in the northeastern United States and Canada. Spreading dogbane ( Apocynum androsaemifolium L.) is one of many indigenous herbaceous plant species exhibiting foliar injury that are commonly monitored in ecosystem assessment programs. Details about possible effects of ambient ozone on reproductive components of these species are lacking. For 103 days, from 31 May to 10 September, A. androsaemifolium plants were grown in open-top chambers in either carbon-filtered air (CF), non-filtered air (NF) (approximately 1×ambient), or chamberless ambient air plots (AA). Aspects of sexual reproduction were measured to determine whether impairment occurs in polluted air. Additionally, the ozone protectant chemical ethylenediurea (EDU) was applied to foliage to determine its effect on foliar injury. By the end of the experiment visible foliar injury was absent in CF air and nominal in the NF and AA treatments. Plants grown in CF-chamber air produced significantly more flowers and fruits than those grown in either NF-chamber air or AA plots. Flowers produced by plants grown in CF air also survived to mature fruits at a rate 1.7× greater than plants in NF air and 1.5× greater than plants in AA plots. We were unable to conclude whether EDU protected plants from foliar ozone injury due to the general lack of foliar injury in ozone-exposed plants. The results demonstrate that foliar injury is not necessarily required to elicit negative effects on sexual reproduction in A. androsaemifolium. Implications for the population biology of A. androsaemifolium related to adverse effects of chronic ozone exposure on sexual reproduction are discussed.

Induction of genes for the stress proteins PR-10 and PAL in relation to growth, visible injuries and stomatal conductance in birch (Betula pendula) clones exposed to ozone and/or drought.

Well watered (WW) or drought-stressed (DS) saplings of ozone-sensitive and ozone-tolerant (less sensitive) birch (Betula pendula Roth) clones were exposed for 43 d to 0 nl l-1 or 100 nl l-1 ozone. Relative growth rates of leaves, stem, and roots, leaf discolouration, stomatal conductance and induction of genes encoding stress-related proteins PR-10, PAL and a LEA-group protein BP8 were determined. In general, both ozone and drought stress, singly and in combination, increased transcript levels of PR-10 in both clones. This was related to lower induction of PAL (except in older leaves of the tolerant clone), and increased proportions of visibly injured and yellowed leaves in ozone-exposed plants. The clones differed in their stomatal conductance and growth responses. In the less sensitive clone 2, ozone did not affect growth rates, but high stomatal conductance was observed in WW ozone-exposed plants. The more sensitive clone 5 showed, on the contrary, reduced growth rates and low stomatal conductance in WW ozone plants. Interestingly, clone 2 was sensitive to drought stress alone, whereas clone 5 was highly sensitive to ozone and drought stress experienced together. The results show that appearance of visible injuries (necrotic flecks) and enhanced yellowing of leaves coincided with the induction of genes for stress proteins PR-10 and PAL. The short-term growth responses, however, seemed to be separate processes. Additionally, stomatal conductance was related to leaf injuries and growth rates in a complicated manner, emphasizing the complex nature of ozone sensitivity/tolerance mechanisms in birch.

Effect of fertilization on ozone-induced changes in the metabolism of birch (Betula pendula) leaves.

Cloned cuttings of Betula pendula Roth were grown in field fumigation chambers at Birmensdorf throughout one growing season in filtered air with either < 3 (control) or 90/40 nl l-1 O3 (day/night; ozone generated from pure oxygen). Each ozone regime was split into high and low soil nutrient regimes by watering plants with either a 0.05 % or a 0.005% solution of a fertilizer which contained macronutrients and micronutrients. Fertilization had a strong effect on plant growth, enzyme activities and the expression of ozone-induced effects at the biochemical level. The activities of PEPC and Rubisco were enhanced about threefold in the plants with high fertilization (HF). Significant effects of ozone were in most cases found only in the older leaves of the plants with low fertilization (LF), There, sucrose, glucose and fructose levels were enhanced. In both fertilization treatments, the number of starch granules along the minor veins was increased. These ozone effects point to a decreased or inhibited phloem loading. The increased PEPC activity and the enhanced malate levels in the ozone-exposed plants might be the result of a redirection of carbon flow from sucrose synthesis and translocation towards anapleurotic processes, which can feed detoxification and repair of ozone injury as indicated by enhanced respiration. These findings agree well with the observed effects of ozone in lowering the root: shoot biomass ratio. Although there was a marked reduction in the O3 /LF plants, O3 /HF plants showed no significant response. Inositol was decreased under ozone exposure in both fertilizer treatments, contrasting with the pattern for carbohydrates. These results demonstrate the role of fertilization as an important modifier of ozone-induced effects at the plant biochemical level. Well fertilized plants appear to cope better with the impact of ozone on metabolism.

Ageing-related Anatomical and Ultrastructural Changes in Leaves of Birch ( Betula pendula Roth.) Clones as Affected by Low Ozone Exposure

Effects of ozone on the leaf anatomy and ultrastructure of five birch ( Betula pendula Roth.) clones were studied during one growing season in open-field conditions. Cumulative ozone exposure was 1·5 times higher than ambient. Ozone exposure decreased total leaf thickness in one, ozone sensitive, clone. The effect on palisade spongy mesophyll thickness was clone-specific, while the amount of palisade intercellular space was reduced in all clones. A second effect was a change in the relative amounts of adaxial and abaxial epidermis. In palisade and spongy parenchyma cells of all clones, ozone increased the number of irregular and spherical shaped chloroplasts, the electron density of chloroplast stroma, swelling and curling of thylakoids, translucency of the mitochondrial matrix and also the amount of cytoplasmic lipids. In the sensitive clone shorter chloroplasts and reduced amount of starch were observed in ozone-exposed plants, whilst, in the tolerant clone, the size of chloroplasts and the amount of starch were unaffected. Ozone effects on number, size and electron density of plastoglobuli and vacuolar tannin were clone-dependent. At the ultrastructural level, the normal leaf ageing process progressed at different rates in the birch clones. Ozone accelerated senescence-related structural changes, in accordance with earlier observations of deciduous species.

Increased 8-Hydroxyguanine Content of Chloroplast DNA from Ozone-Treated Plants

The mechanism of ozone-mediated plant injury is not known but has been postulated to involve oxygen free radicals. Hydroxyl free radicals react with DNA causing formation of many products, one of which is 8-hydroxyguanine. By using high performance liquid chromatography with electrochemical detection, the 8-hydroxy-2'-deoxyguanosine (8-OHdG) content of a DNA enzymatic digest can be sensitively quantitated. Beans (Phaseolus vulgaris L.) and peas (Pisum sativum L.) were treated with an ozone regime that caused acute injury. Chloroplast DNA was obtained from plants harvested either immediately after ozone treatment or 24 hours later. Ozone-exposed plants in general had nearly two-fold higher levels of 8-OHdG as compared to control plants. In vitro treatment of DNA in buffer solution with ozone did not cause formation of 8-OHdG in DNA, even though ozone did react directly with the macromolecule per se. Exposure of isolated, illuminated chloroplasts to ozone caused nearly a seven-fold increase in the amount of 8-OHdG in the chloroplast DNA as compared to none-ozone-exposed chloroplasts. These results suggest that ozone exposure to plants causes formation of enhanced levels of oxygen free radicals, thus mediating formation of 8-OHdG in chloroplast DNA. The reaction of ozone with DNA per se did not cause formation of 8-OHdG. Therefore, it is the interaction of ozone with plant cells and isolated chloroplasts which mediates oxygen free radical formation.

Effects of ozone or sulfur dioxide on growth and yield of rice

Three cultivars of rice, Oryza sativa, M7, M9 and S201 were exposed in open-top field chambers to ozone and sulfur dioxide to determine the effects of these important air pollutants on field-grown plants. Exposures were for 15 weeks with ozone at 0, 98, 196, 294 or 392 μg m −3 for 5 h day −1, 5 days week −1, and sulfur dioxide at 131, 262, 393 or 524 μg m −3 for 24 h day −1, 5 days week −1. Three harvests of rice were made after 27 and 68 days and at the end of the exposures. At the first harvest following early plant growth, ozone at the highest concentrations resulted in reductions in growth whereas sulfur dioxide resulted in increased growth. At the second harvest, ozone-exposed plants continued to show reduced growth, whereas sulfur dioxide resulted only in reduced plant height. At the final and major harvest, ozone at 392 μg m −3 reduced total seed weight 12, 29 and 21% in cultivars M7, M9 and S201, respectively. Weight of 100 seeds and straw weight were reduced in M9 and S201 and percent seed sterility in panicles was increased. Ozone reduced height of all cultivars and increased the number of panicles. Sulfur dioxide at 524 μg m −3 reduced total seed weight of M9 and S201 by 22 and 14%, respectively, and weight per hundred seed by 11 and 10%, respectively. The results showed that ozone is much more injurious to rice per unit of pollutant than sulfur dioxide and that reduced yield due to both pollutants was caused mostly by reduced seed size. Increased seed sterility was partially offset by ozone exposure of the plants which produced more panicles. Cultivar M7 was more resistant to ozone or sulfur dioxide than M9 and S201.

Effects of ozone exposure on mycorrhiza formation and growth of Festuca arundinacea

Exposure of mycorrhizal Festuca arundinacea to 0.1 ppm ozone for 3 months reduced root weights and intensity of mycorrhiza formation as compared to plants in filtered air. This response may be a result of reduced photosynthesis by ozone-exposed plants. Nonmycorrhizal plants grew so poorly that ozone exposure was irrelevant in comparison to mycorrhiza treatment.

Effect of Ozone Injury and Light Stress on Response of Tomato to Infection by the Vesicular-arbuscular Mycorrhizal Fungus, Glomus fasciculatus1

Abstract Tomato seedlings (Lycopersicon esculentum Mill. ‘Heinz 1350’) were inoculated with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatus (Thaxter) Gerd. &amp; Trappe and either exposed to 30 pphm (589 μg/m3) ozone or to filtered air for 3 hours once weekly, beginning 3 weeks after inoculation, under long photoperiods (12–13.5 hr). Root infection by G. fasciculatus in ozone-exposed plants was retarded from week 3 to 5 compared to controls but recovered by week 7. Growth rates of mycorrhizal control plants were significantly greater than ozone-exposed mycorrhizal plants, but there were no differences in growth rates of nonmycorrhizal controls, mycorrhizal ozone-exposed plants, and nonmycorrhizal ozone-exposed plants. Under short photoperiods (less than 12 hr), growth rates of mycorrhizal controls were less than nonmycorrhizal controls and ozone did not significantly affect growth rates of nonmycorrhizal plants relative to controls. Leaf chlorophyll levels were similar whether plants were mycorrhizal, nonmycorrhizal, or exposed to ozone.

Impact of ozone on quantity and quality of greenhouse-grown potato plants

The impact of ozone on quality and quantity of greenhouse-grown potatoes was considered. In two experiments conducted in 1977 and 1978, 'Norland' and 'Kennebec' potato plants were grown in a conventional greenhouse. Once every 2 weeks, 10 plants of each cultivar were exposed to 387 ..mu..g/m/sup 3/ (0.20 ppm) ozone for 3 h in a controlled environment chamber. At 120 and 140 days, for 'Norland' and 'Kennebec', respectively, vines were killed and tubers were harvested. The number and weight of tubers harvested from ozonized plants decreased significantly in both cultivars. Significant decreases in total solids and increases in reducing sugars of tubers from ozone-exposed plants were identified.