Ultraviolet radiation causes leaf warming due to partial stomatal closure.

Variation in solar ultraviolet radiation induces a wide-range of plant responses from the cellular to whole-plant scale. We demonstrate here for the first time that partial stomatal closure caused by ultraviolet radiation exposure results in significant increases in leaf temperature. Significant leaf warming in response to ultraviolet radiation was consistent in tomato (Solanum lycopersicum L.) across different experimental approaches. In field experiments where solar ultraviolet radiation was attenuated using filters, exposure to ultraviolet radiation significantly decreased stomatal conductance and increased leaf temperature by up to 1.5°C. Using fluorescent lamps to provide ultraviolet radiation treatments, smaller but significant increases in leaf temperature due to decreases in stomatal conductance occurred in both multi-day controlled environment growth room experiments and short-term (< 2 hours) climate cabinet irradiance response experiments. We show that leaf warming due to partial stomatal closure is independent of any direct warming effects of ultraviolet radiation manipulations. We discuss the implications of ultraviolet radiation-induced warming both for horticultural crop production and understanding broader plant responses to ultraviolet radiation.

The Montreal Protocol protects the terrestrial carbon sink.

The control of the production of ozone-depleting substances through the Montreal Protocol means that the stratospheric ozone layer is recovering1 and that consequent increases in harmful surface ultraviolet radiation are being avoided2,3. The Montreal Protocol has co-benefits for climate change mitigation, because ozone-depleting substances are potent greenhouse gases4-7. The avoided ultraviolet radiation and climate change also have co-benefits for plants and their capacity to store carbon through photosynthesis8, but this has not previously been investigated. Here, using a modelling framework that couples ozone depletion, climate change, damage to plants by ultraviolet radiation and the carbon cycle, we explore the benefits of avoided increases in ultraviolet radiation and changes in climate on the terrestrial biosphere and its capacity as a carbon sink. Considering a range of strengths for the effect of ultraviolet radiation on plant growth8-12, we estimate that there could have been 325-690 billion tonnes less carbon held in plants and soils by the end of this century (2080-2099) without the Montreal Protocol (as compared to climate projections with controls on ozone-depleting substances). This change could have resulted in an additional 115-235 parts per million of atmospheric carbon dioxide, which might have led to additional warming of global-mean surface temperature by 0.50-1.0 degrees. Our findings suggest that the Montreal Protocol may also be helping to mitigate climate change through avoided decreases in the land carbon sink.

New understanding of the direct effects of spectral balance on behaviour in Myzus persicae.

The study of insect responses to colour has mainly focused on flying species and morphs, however colour cues are likely to be important for insect positioning within the canopy. We examine the role of illumination colour in canopy positioning of apterous Myzus persicae (Sulzer) using both a field experiment, utilising various UV-manipulating optical filters, and a laboratory experiment using video tracking of individuals illuminated by a variable intensity UVA-Blue-Green LED-array. In the field experiment, approximately twice as many aphids were located on exposed leaf surfaces under UV-deficient environments compared to UV-rich environments. The lab experiment showed all three M. persicae photoreceptors were involved in a visually-mediated feeding/avoidance behaviour. Highly UV-rich, green-deficient environments were up to 3 times as likely to trigger an avoidance behaviour compared to UV-absent, green-rich environments such as those found below the leaf surface. We show that apterous M. persicae use this, in addition to other cues, in order to locate feeding positions that minimise exposure to direct sunlight. This has relevance to both the fundamental understanding of photoprotective behaviour in Hemiptera as well as to applied research of crop production environments that disrupt pest behaviour.

Increased occurrence of pesticide residues on crops grown in protected environments compared to crops grown in open field conditions.

Crops grown under plastic-clad structures or in greenhouses may be prone to an increased frequency of pesticide residue detections and higher concentrations of pesticides relative to equivalent crops grown in the open field. To test this we examined pesticide data for crops selected from the quarterly reports (2004-2009) of the UK's Pesticide Residue Committee. Five comparison crop pairs were identified whereby one crop of each pair was assumed to have been grown primarily under some form of physical protection ('protected') and the other grown primarily in open field conditions ('open'). For each pair, the number of detectable pesticide residues and the proportion of crop samples containing pesticides were statistically compared (n=100 s samples for each crop). The mean concentrations of selected photolabile pesticides were also compared. For the crop pairings of cabbage ('open') vs. lettuce ('protected') and 'berries' ('open') vs. strawberries ('protected') there was a significantly higher number of pesticides and proportion of samples with multiple residues for the protected crops. Statistically higher concentrations of pesticides, including cypermethrin, cyprodinil, fenhexamid, boscalid and iprodione were also found in the protected crops compared to the open crops. The evidence here demonstrates that, in general, the protected crops possess a higher number of detectable pesticides compared to analogous crops grown in the open. This may be due to different pesticide-use regimes, but also due to slower rates of pesticide removal in protected systems. The findings of this study raise implications for pesticide management in protected-crop systems.

Endopolyploidy as a potential alternative adaptive strategy for Arabidopsis leaf size variation in response to UV-B.

The extent of endoreduplication in leaf growth is group- or even species-specific, and its adaptive role is still unclear. A survey of Arabidopsis accessions for variation at the level of endopolyploidy, cell number, and cell size in leaves revealed extensive genetic variation in endopolyploidy level. High endopolyploidy is associated with increased leaf size, both in natural and in genetically unstructured (mapping) populations. The underlying genes were identified as quantitative trait loci that control endopolyploidy in nature by modulating the progression of successive endocycles during organ development. This complex genetic architecture indicates an adaptive mechanism that allows differential organ growth over a broad geographic range and under stressful environmental conditions. UV-B radiation was identified as a significant positive climatic predictor for high endopolyploidy. Arabidopsis accessions carrying the increasing alleles for endopolyploidy also have enhanced tolerance to UV-B radiation. UV-absorbing secondary metabolites provide an additional protective strategy in accessions that display low endopolyploidy. Taken together, these results demonstrate that high constitutive endopolyploidy is a significant predictor for organ size in natural populations and is likely to contribute to sustaining plant growth under high incident UV radiation. Endopolyploidy may therefore form part of the range of UV-B tolerance mechanisms that exist in natural populations.

Reduction of photosynthetic sensitivity in response to abiotic stress in tomato is mediated by a new generation plant activator.

BACKGROUND: Yield losses as a result of abiotic stress factors present a significant challenge for the future of global food production. While breeding technologies provide potential to combat negative stress-mediated outcomes over time, interventions which act to prime plant tolerance to stress, via the use of phytohormone-based elicitors for example, could act as a valuable tool for crop protection. However, the translation of fundamental biology into functioning solution is often constrained by knowledge-gaps. RESULTS: Photosynthetic and transcriptomic responses were characterised in young tomato (Solanum lycopersicum L.) seedlings in response to pre-treatment with a new plant health activator technology, 'Alethea', followed by a subsequent 100 mM salinity stress. Alethea is a novel proprietary technology composed of three key constituent compounds; the hitherto unexplored compound potassium dihydrojasmonate, an analogue of jasmonic acid; sodium benzoate, a carboxylic acid precursor to salicylic acid, and the α-amino acid L-arginine. Salinity treatment led to a maximal 47% reduction in net photosynthetic rate 8 d following NaCl treatment, yet in Alethea pre-treated seedlings, sensitivity to salinity stress was markedly reduced during the experimental period. Microarray analysis of leaf transcriptional responses showed that while salinity stress and Alethea individually impacted on largely non-overlapping, distinct groups of genes, Alethea pre-treatment substantially modified the response to salinity. Alethea affected the expression of genes related to biotic stress, ethylene signalling, cell wall synthesis, redox signalling and photosynthetic processes. Since Alethea had clear effects on photosynthesis/chloroplastic function at the physiological and molecular levels, we also investigated the ability of Alethea to protect various crop species against methyl viologen, a potent generator of oxidative stress in chloroplasts. Alethea pre-treatment produced dramatic reductions in visible foliar necrosis caused by methyl viologen compared with non-primed controls. CONCLUSIONS: 'Alethea' technology mediates positive recovery of abiotic stress-induced photosynthetic and foliar loss of performance, which is accompanied by altered transcriptional responses to stress.

The UV-B photoreceptor UVR8 promotes photosynthetic efficiency in Arabidopsis thaliana exposed to elevated levels of UV-B.

The UV-B photoreceptor UVR8 regulates expression of genes in response to UV-B, some encoding chloroplast proteins, but the importance of UVR8 in maintaining photosynthetic competence is unknown. The maximum quantum yield of PSII (F (v)/F(m)) and the operating efficiency of PSII (Φ(PSII)) were measured in wild-type and uvr8 mutant Arabidopsis thaliana. The importance of specific UVR8-regulated genes in maintaining photosynthetic competence was examined using mutants. Both F (v)/F(m) and Φ(PSII) decreased when plants were exposed to elevated UV-B, in general more so in uvr8 mutant plants than wild-type. UV-B increased the level of psbD-BLRP (blue light responsive promoter) transcripts, encoding the PSII D2 protein. This increase was mediated by the UVR8-regulated chloroplast RNA polymerase sigma factor SIG5, but SIG5 was not required to maintain photosynthetic efficiency at elevated UV-B. Levels of the D1 protein of PSII decreased markedly when plants were exposed to elevated UV-B, but there was no significant difference between wild-type and uvr8 under conditions where the mutant showed increased photoinhibition. The results show that UVR8 promotes photosynthetic efficiency at elevated levels of UV-B. Loss of the DI polypeptide is probably important in causing photoinhibition, but does not entirely explain the reduced photosynthetic efficiency of the uvr8 mutant compared to wild-type.

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2011.

The parties to the Montreal Protocol are informed by three panels of experts. One of these is the Environmental Effects Assessment Panel (EEAP), which deals with two focal issues. The first focus is the effects of increased UV radiation on human health, animals, plants, biogeochemistry, air quality, and materials. The second focus is on interactions between UV radiation and global climate change and how these may affect humans and the environment. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than believed previously. As a result of this, human health and environmental problems will be longer-lasting and more regionally variable. Like the other panels, the EEAP produces a detailed report every four years; the most recent was published in 2010 (Photochem. Photobiol. Sci., 2011, 10, 173-300). In the years in between, the EEAP produces less detailed and shorter progress reports, which highlight and assess the significance of developments in key areas of importance to the parties. The next full quadrennial report will be published in 2014-2015.

Ecological responses to UV radiation: interactions between the biological effects of UV on plants and on associated organisms.

Solar ultraviolet (UV)-B radiation (280-315 nm) has a wide range of effects on terrestrial ecosystems, yet our understanding of how UV-B influences the complex interactions of plants with pest, pathogen and related microorganisms remains limited. Here, we report the results of a series of experiments in Lactuca sativa which aimed to characterize not only key plant responses to UV radiation in a field environment but also consequential effects for plant interactions with a sap-feeding insect, two model plant pathogens and phylloplane microorganism populations. Three spectrally modifying filters with contrasting UV transmissions were used to filter ambient sunlight, and when compared with our UV-inclusive filter, L. sativa plants grown in a zero UV-B environment showed significantly increased shoot fresh weight, reduced foliar pigment concentrations and suppressed population growth of green peach aphid (Myzus persicae). Plants grown under a filter which allowed partial transmission of UV-A radiation and negligible UV-B transmission showed increased density of leaf surface phylloplane microbes compared with the UV-inclusive treatment. Effects of UV treatment on the severity of two plant pathogens, Bremia lactucae and Botrytis cinerea, were complex as both the UV-inclusive and zero UV-B filters reduced the severity of pathogen persistence. These results are discussed with reference to known spectral responses of plants, insects and microorganisms, and contrasted with established fundamental responses of plants and other organisms to solar UV radiation, with particular emphasis on the need for future integration between different experimental approaches when investigating the effects of solar UV radiation.

Treating seeds with activators of plant defence generates long-lasting priming of resistance to pests and pathogens.

• Priming of defence is a strategy employed by plants exposed to stress to enhance resistance against future stress episodes with minimal associated costs on growth. Here, we test the hypothesis that application of priming agents to seeds can result in plants with primed defences. • We measured resistance to arthropod herbivores and disease in tomato (Solanum lycopersicum) plants grown from seed treated with jasmonic acid (JA) and/or ß-aminobutryric acid (BABA). • Plants grown from JA-treated seed showed increased resistance against herbivory by spider mites, caterpillars and aphids, and against the necrotrophic fungal pathogen, Botrytis cinerea. BABA seed treatment provided primed defence against powdery mildew disease caused by the biotrophic fungal pathogen, Oidium neolycopersici. Priming responses were long-lasting, with significant increases in resistance sustained in plants grown from treated seed for at least 8 wk, and were associated with enhanced defence gene expression during pathogen attack. There was no significant antagonism between different forms of defence in plants grown from seeds treated with a combination of JA and BABA. • Long-term defence priming by seed treatments was not accompanied by reductions in growth, and may therefore be suitable for commercial exploitation.

Increased exposure to UV-B radiation during early development leads to enhanced photoprotection and improved long-term performance in Lactuca sativa.

Plant responses to solar UV radiation are numerous and have often been considered from a perspective of negative outcomes for plant productivity. In this study, we used two experimental approaches consisting of: (1) field-based spectrally modifying filters in addition to (2) controlled indoor exposure to UV-B, to examine the effects of UV radiation on growth and photosynthetic performance of lettuce (Lactuca sativa L.) seedlings. Various aspects of growth were affected in plants grown under a UV-inclusive environment compared to a UV-depleted environment, including reductions in leaf expansion, increases in leaf thickness and the rate of net photosynthesis. After transplantation to a uniform field environment, lettuce plants initially propagated under the UV-inclusive environment exhibited higher harvestable yields than those from a UV-depleted environment. In controlled conditions, photosynthetic rates were higher in plants grown in the presence of UV-B radiation, and relative growth of plants pre-acclimatized to UV-B was also increased, in addition to higher maximum photochemical efficiency of photosystem II (PSII) (F(v) /F(m) ) following subsequent exposure to high photosynthetically active radiation (PAR) and temperature stress. Our findings are discussed within the context of sustainability in agriculture and the paradigm shift in photobiology which such beneficial responses to UV radiation could represent.

Biogenic volatile organic compounds in the Earth system.

Biogenic volatile organic compounds produced by plants are involved in plant growth, development, reproduction and defence. They also function as communication media within plant communities, between plants and between plants and insects. Because of the high chemical reactivity of many of these compounds, coupled with their large mass emission rates from vegetation into the atmosphere, they have significant effects on the chemical composition and physical characteristics of the atmosphere. Hence, biogenic volatile organic compounds mediate the relationship between the biosphere and the atmosphere. Alteration of this relationship by anthropogenically driven changes to the environment, including global climate change, may perturb these interactions and may lead to adverse and hard-to-predict consequences for the Earth system.

UVR8 in Arabidopsis thaliana regulates multiple aspects of cellular differentiation during leaf development in response to ultraviolet B radiation.

Responses specific to ultraviolet B (UV-B) wavelengths are still poorly understood, both in terms of initial signalling and effects on morphogenesis. Arabidopsis thaliana UV RESISTANCE LOCUS8 (UVR8) is the only known UV-B specific signalling component, but the role of UVR8 in leaf morphogenesis is unknown. The regulatory effects of UVR8 on leaf morphogenesis at a range of supplementary UV-B doses were characterized, revealing both UVR8-dependent and independent responses to UV irradiation. Inhibition of epidermal cell division in response to UV-B is largely independent of UVR8. However, overall leaf growth under UV-B irradiation in wild-type plants is enhanced compared with a uvr8 mutant because of a UVR8-dependent compensatory increase of cell area in wild-type plants. UVR8 was also required for the regulation of endopolyploidy in response to UV-B, and the uvr8 mutant also has a lower density of stomata than the wild type in the presence of UV-B, indicating that UVR8 has a regulatory role in other developmental events. Our findings show that, in addition to regulating UV-protective gene expression responses, UVR8 is involved in controlling aspects of leaf growth and morphogenesis. This work extends our understanding of how UV-B response is orchestrated at the whole-plant level.

A comparative study on the aqueous photodegradation of two organophosphorus pesticides under simulated and natural sunlight.

Aqueous solutions of fenitrothion and methyl parathion were photochemically degraded in an Atlas Suntest solar simulator (500 W m(-2)) as well as under ambient sunlight at Lancaster University (June & August 2007, 54 degrees N) and the degradation kinetics and disappearance quantum yields are reported. Fenitrothion degradation confirmed to first order kinetics (r(2) = 0.90-0.99) with a half-life range of 4.9 h-5.3 h, shorter than previously reported studies. In contrast, methyl parathion did not show significant degradation over the duration of these experiments. Light irradiances were monitored with a spectroradiometer during the Suntest simulator and outdoor experiments. The filtered-xenon arc lamp of the Suntest yielded spectral irradiances comparable to natural sunlight in the UVB and UVA wavelength range (280-400 nm), but with higher irradiances in the visible region (400-750 nm). Nonetheless, as both compounds have light absorption spectra at wavelengths < 400 nm, then the half-lives and disappearance quantum yields were similar between the Suntest and natural sunlight, and demonstrated that the Suntest is suitable for environmentally-relevant photochemical degradation experiments.

The aqueous photodegradation of fenitrothion under various agricultural plastics: implications for pesticide longevity in agricultural 'micro-environments'.

Plastic cladding is increasingly used in agriculture to create micro-environments to improve crop yield/growth. Many of these plastics can alter the solar light spectrum by inhibiting or reducing the transmittance of certain parts of the solar spectrum. In this study, we investigated the aqueous photolysis of fenitrothion, under a selection of different plastic films commonly used in agriculture. Three different grades of polyethylene film were used: 'standard', 'transparent' and 'opaque'. The transmittance of light wavelengths in the UV region (290-400 nm), measured with a spectroradiometer, was found to decrease in the order of transparent>standard>opaque. Fenitrothion, an organophosphorothioate insecticide possesses molar absorptivity in the solar wavelength range of 290-400 nm. Aqueous first order degradation rate constants for fenitrothion determined over a 12 h period were found to be considerably less for those experiments conducted under the standard and opaque plastic films, compared to the transparent film and no-film control. The experiments were conducted in an Atlas Suntest solar simulator using a UV-filtered Xenon arc lamp to simulate sunlight. The first order half-life for fenitrothion was 100 and 250 h under the standard and opaque films, respectively, compared to approximately 10 h for the transparent film and no-film experiments. Our results suggest that pesticide longevity could be greatly extended within these plastic micro-environments, especially for those chemicals which may degrade/transform via photolytic or photochemical pathways.

Ultraviolet radiation as a limiting factor in leaf expansion and development.

Reductions in leaf growth are a commonly observed response to ultraviolet radiation, but the underlying mechanisms remain poorly defined. This study examined the response of leaves exposed to a UV environment across a range of organizational scales, including leaf expansion rate, epidermal cell size and number, biomechanical properties, leaf-water relations and activity of cell-wall peroxidases. Two experimental approaches were used; Lettuce (Lactuca sativa L.) plants were propagated under (a) supplementary UV-B (9 kJ m(-2) day(-1)) in controlled environment (CE) conditions, and (b) field conditions, where plants were placed under three horticultural films with differing UV transmissions. In both experiments, UV-B caused the greatest reductions in leaf expansion and final leaf size, with some reductions attributable to UV-A wavelengths. In supplementary UV-B conditions, adaxial cell size was reduced, while in field plants, both cell size and cell number were lower in an increased UV environment, as was the case with abaxial cells in CE plants. Although leaf turgor and leaf extensibility were not affected by UV wavelengths, breaking strain of leaf tissue was decreased under supplementary UV-B. Cell-wall peroxidase activity was increased in both supplementary UV conditions and in the field, where only a zero UV environment showed no upregulation of cell-wall peroxidase.

Discrimination of plant volatile signatures by an electronic nose: aA potential technology for plant pest and disease monitoring.

The volatile organic compounds (VOCs) profile emitted from plants often changes in response to environmental factors, and monitoring the change of such profiles could provide a nondestructive means of plant health measurement An electronic nose (e-nose) was used to discriminate among VOC bouquets emitted by cucumber, pepper, and tomato leaves subjected to mechanical damage or pest and disease attacks compared with undamaged control leaves. Principle component analysis, discriminant function analysis, and cluster analysis were applied to evaluate the data. The results indicate that the e-nose can discriminate among VOCs from undamaged leaves of the three tested species. It can also discriminate undamaged and artificially damaged leaves of the same plant species. In cucumber, the e-nose can discriminate among VOCs emitted from control, artificially damaged, and spider-mite-infested leaves. It could also discriminate among VOCs emitted from control, artificially damaged, hornworm-damaged, and powdery-mildew-infected tomato leaves. The relationships between the changes in volatile signatures detected by the e-nose to changes in the underlying chemistry of plant VOC signatures in response to applied stresses were quantified by gas chromatography mass spectrometry. We conclude that the e-nose had genuine responses to changes in plant VOC signatures and can successfully discriminate them. These studies demonstrate the potential use of such e-nose technology as a real time pest and disease monitoring system in agricultural and horticultural settings.

Isoprene emissions influence herbivore feeding decisions.

Isoprene (C(5)H(8), 2-methyl 1,3-butadiene) is synthesized and emitted by many, but not all, plants. Unlike other related volatile organic compounds (monoterpenes and sesquiterpenes), isoprene has not been shown to mediate plant-herbivore interactions. Here, for the first time, we show, in feeding choice tests using isoprene-emitting transgenic tobacco plants (Nicotiana tabacum cv. Samsun) and non-emitting azygous control plants, that isoprene deters Manduca sexta caterpillars from feeding. This avoidance behaviour was confirmed using an artificial (isoprene-emitting and non-emitting control) diet. Both in vivo and in vitro experiments showed that isoprene can activate feeding avoidance behaviour in this system with a dose-response effect on caterpillar behaviour and an isoprene emission threshold level of <6 nmol m(-2) s(-1).

The dose rate of UVA treatment influences the cellular response of HaCaT keratinocytes.

The contribution of UV exposure to the etiology of skin cancer and photoaging is undisputed. However, the effect of altering the intensity or dose rate of UV, which varies considerably with geographical location, the time of day or year, and the use of sunscreens, is not understood. In this study, the effect of altering the dose rate of UVA was investigated in the immortalized human keratinocyte cell line, HaCaT. Lowering the dose rate of UVA resulted in increased cytotoxicity, which correlated with increases in both lipid peroxidation and DNA damage. Furthermore, exposure at low dose rate did not appear to reduce the ability of UVA to induce the phenomenon of persistent genomic instability. Pretreatment with the antioxidant vitamin E significantly protected against UVA dose-rate effects observed with respect to lipid peroxidation and survival. Additionally, cell populations irradiated at low dose rate exhibited a shift towards a more pro-oxidant state. Taken together, these observations suggest an oxidative stress mechanism is underlying the UVA dose-rate effect. This study demonstrates that dose rates must be included as a key factor when evaluating the biological effects of UVA, especially considering the concerns, which exist regarding the efficacy and photostability of sunscreens to UVA.