| Evaluation of solar-ultraviolet radiation effects upon DNA molecule |
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André Passaglia Schuch Department of Microbiology, Universidade de São Paulo, Sao Paulo, SP, Brazil. |
To better understand the impact of solar UV radiation upon DNA molecule, we developed a biological system based on the exposure of plasmid DNA to artificial and natural UV sources. The quantification of DNA lesions was performed using specific DNA repair enzymes and antibodies. Complementing these analyses, the biological effects of sunlight as well as artificial UV-radiation were evaluated through the determination of the DNA inactivation rate and mutagenesis frequency of supF gene after replication of pCMUT vector in E.coli MBL50 strain. As expected, a significant number of CPDs and 6-4PPs were observed when the DNA-dosimeter system was exposed to increasing doses of UVB radiation. Moreover, CPDs could also be clearly detected in plasmid DNA when this system was exposed to either UVA or directly to sunlight. Interestingly, although less abundant, 6-4PPs and oxidative DNA damage were also generated after exposure to both UVA and sunlight. Surprisingly, the profiles of DNA damages induced by sunlight at different latitudes varied especially according to the induction of oxidative DNA damages and 6-4PPs, thus reflecting the incidence of UVA and UVB doses in the specific latitude. In addition, our data clearly indicate that the induction of DNA inactivation and mutagenesis is related to the presence of photoproducts in UV-exposed DNA samples, and suggest that oxidative damages are not related to these biological processes. Therefore, a very suitable system was developed capable of providing a wide comprehension of the biological effects of solar-UV radiation upon the DNA molecule. |
| Does UV radiation drive methane emissions from plant foliage? |
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Andy R. McLeod Centre for the Study of Environmental Change and Sustainability, University of Edinburgh, Edinburgh, Scotland, UK. |
The production of volatile organic compounds by vegetation is well known, but several recent studies have reported an in situ methane emission from plant foliage. Methane is the second most important greenhouse gas after carbon dioxide and was thought to originate mostly from anaerobic microbial processes in soils, industrial emissions and biomass burning. However, it was recently suggested that there is an unknown aerobic process generating methane in plant leaves. This presentation will describe experiments, which demonstrate that the ultraviolet radiation component of sunlight can cause emission of methane and other trace gases from plant leaves and from pectin, a major plant cell wall polysaccharide, and has a role for reactive oxygen species (ROS) in this process. It will also describe how satellite data have been used to estimate the contribution of UV-driven plant emissions from the major plant biomes and agricultural crops and their contribution to the global methane budget. |
| UV exposure: effects on hydrophobicity and microbial composition of fired forest soils. |
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Anne J. Anderson, Biology Department, Utah State University, Logan, Utah, USA |
Soil hydrophobicity present problems in agriculture and forestry. Fire events in forests promote the development of a hydrophobic sublayer that can lead to water run off and mud slides on inclines. Hydrophobicity is attributed to deposition of aromatic compounds onto soil particles resulting from condensation of volatiles from the incomplete combustion of organic materials. Soils were studied from two fire sites, one, a revegetated three year-old montane site and a second, a high desert pinyon pine-juniper area that was not revegetated one year after the fire. The hydrophobicity of both soils decreased upon 5 and 8 days exposure of thin soil layers to intense sunlight during the normal diurnal cycle. This change could be attributed to photocatalytic degradation of the aromatics contributing to hydrophobicity. FTIR analysis of the soils pre and post sunlight exposure showed changes in spectra associated with phenolic residues. The microbial content of the soil also was modified by sunlight exposure. However, surviving culturable isolates included those that produced surfactants and cells that grew as mixed communities on the polycyclic aromatic hydrocarbon pyrene used as a model of aromatics derived from the fire events. Surfactant production could increase the bioavailability of the aromatic compounds and promote their motility. The microbes with the potential to degrade pyrene could be involved in the remediation of the chemicals accounting for soil hydrophobicity. Identification of the microbes by 16S rRNA sequencing showed the UV-tolerant recovered microbes were pseudomonads. Phylogenetic analysis revealed clustering of the gene sequences with the source of the isolates. Prior to sunlight exposure additional genera of both Gram positive and Gram negative bacteria were identified thus the stress of UV from sunlight imposed a selective pressure on the microbes. The outstanding survival potential of the pseudomonads was not predicted. |
| Photo-elicitation of bioactive secondary metabolite accumulation in plants by UV radiation |
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Arthur G. Fett-Neto Universidade Federal do Rio Grande do Sul, Instituto de Biociências, Departamento de Botânica, Porto Alegre, RS, Brazil. |
Plants produce a large array of secondary metabolites related to defense against pathogens and herbivores, signaling to pollinators and dispersers, as well as tolerance against abiotic stresses. Because of their innumerous biochemical properties, a significant portion of the chemicals that make up the human therapeutic arsenal is composed of plant secondary metabolites. Among the various classes of secondary metabolites, flavonoids are regarded as key players in plant tolerance to UV-B. Evidence to support this notion comes from UV tolerance studies, gene expression profiles, flavonoid-deficient mutant analyses, and transgenic plants. However, a closer evaluation of plant responses to UV in relation to their phytochemical composition and metabolite profile reveals that this role is also played by other classes of secondary metabolites, both induced and constitutive. Significant UV-induced changes in pools of bioactive leaf alkaloids of woody species have been observed. An oxidative stress-related path in these responses is likely, considering the chemical properties of the metabolites, their induction kinetics, and the UV-tolerance profile of the species accumulating them. Purified monoterpene indole alkaloids of Psychotria species were able to rescue yeast mutants defective in antioxidant defense genes exposed to oxidative stress, revealing both antioxidant and antimutagenic properties for these plant metabolites. Experiments involving the addition of purified monoterpene indole alkaloids of Psychotria to UV-sensitive alkaloid-free related plant species (“gain-of-function”) clearly showed positive effects in various UV-B tolerance biochemical and photosynthetic antenna parameters. The identification of transcripts corresponding to putative genes of alkaloid biosynthesis in suppressive subtractive hybridization experiments with leaves of alkaloidaccumulating P. brachyceras has shown that UV-B induced changes in alkaloid metabolism of P. brachyceras, which affects the steady-state of biosynthesis-related mRNAs. Taken together, these data point to a putative role of monoterpene indole alkaloids of Psychotria in UV-B protection, and provide a practical means to enhance the yield of valuable bioactive phytochemicals for pharmacological purposes. The possibility of manipulating this UV tolerance - enhancing pathways in crop species is a potential long-term goal. |
| Global change and the effects of solar UV radiation on terrestrial ecosystems |
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Carlos L. Ballaré Facultad de Agronomía, CONICET y Universidad de Buenos Aires, Argentina. |
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UV radiation (280-400 nm) is a minor component of the solar spectrum reaching the ground surface; yet, it has important effects on organisms and biogeochemical cycles. Many research efforts during the past two decades have thoroughly characterized the effects of the UV-B (280-315 nm) component. In this talk, I will summarize the lessons from this previous work, and highlight some of the important knowledge gaps in connection with the effects of climate change. I will address the following points. A) The effects of UV-B radiation on the growth (biomass accumulation) of terrestrial plants are relatively small. B) On the other hand, UV radiation affects plant secondary chemistry and the activities of canopy arthropods and phyllosphere microorganisms. Therefore, trophic interactions in terrestrial ecosystems are likely to be significantly affected by future variations in UV irradiance. C) Changes in UV resulting from climate change (e.g., variations in cloud cover) may have more important consequences on terrestrial ecosystems than those derived from ozone depletion. This is because the resulting variations in UV may affect a greater range of ecosystems, and will not be restricted solely to the UV-B component. D) Several processes that are not particularly sensitive to UV-B can be strongly affected by UV-A radiation. One example is the physical degradation of plant litter. UV-induced changes in photodegradation may have direct and indirect effects on carbon sequestration in terrestrial ecosystems. |
| Sensitivity of wheat to UV-B radiation throughout the crop cycle |
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Daniel F. Calderini Instituto de Produccion y Sanidad Vegetal, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile. |
Ozone layer depletion increases the level of ultraviolet radiation reaching the earth’s surface, especially in the Southern Hemisphere, affecting both natural and agricultural ecosystems. Considering the harmful effects UV-B radiation has on plant growth, the future productivity of crops could be challenged by both (i) the forthcoming level of UV-B increase and (ii) the sensitivity of wheat to higher UV-B radiation. The assessment of the effect of increased UV-B radiation at different phenophases has not been widely investigated in wheat and other crops. To evaluate the sensitivity of different wheat phases to increased UV-B radiation, an experiment consisting in controls, increased UV-B radiation at specific phenophases (from 3 leaf stage to booting and from booting to maturity), and increased UV-B radiation for the majority of the crop cycle (from 3 leaf stage to maturity) was carried out in Southern Chile. UV-B radiation was increased by Q panel UV-313 lamps set in plastic framed structures. Plants of the controls were grown either without frames or below the same framed structures as those which received increased UV-B treatments. Phenology, above-ground biomass, grain yield, components, grain protein concentration, leaf area index (LAI), Fv/Fm, and pigments were measured at booting and/or at harvest. Above-ground biomass and yield decreased by 11-19% and 12-20% when UV-B radiation was increased at the 3L-Bo phase, while no effect was observed with irradiating later in the crop cycle (Bo-PM). No additional UV-B effects to those observed at booting were detected in plants irradiated during the majority of the crop cycle (3L-PM). Flour protein was not affected by UV-B increase at any phenophase evaluated in this study. In both experiments, leaf green area and weight were negatively affected by increased UV-B radiation. Flavonoid concentration was increased only at plant level (exp 1) and UV-B radiation had no effect on specific leaf area (SLA) in this study. On the other hand, lower Fv/Fm, clorophylls, carotenoids concentration, and carotenoid:clorophyll ratio were found at crop level (exp 2) under higher UV-B in the 3L-Bo and 3L-PM treatments. |
| The implications of increased UV-B radiation on microbial control of insects |
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Donald W. Roberts Department of Biology, Utah State University, Logan, Utah, USA. |
Although not universally accepted in the popular press, there is a very large body of scientific and anecdotal evidence that supports the concept that atmospheric changes on earth have occurred in recent years, and that their negative effects are increasing over time. In addition to precise documentations by scientific teams, global warming is evidenced by obvious diminution of polar and high-altitude ice; and by somewhat erratic but significant rises in ocean and land surface temperatures. Concurrently, and of great importance to our meeting on the effects of UV on agriculture; UV-B irradiance also has increased, due in large measure to ozone-layer depletion. Satellite measurements since 1978 document significant (up to 14%) increases in surface UV-B at latitudes greater than 40 degrees. Percent increase depends on wavelength, with the biologically, more active shorter wavelengths showing a larger percent increase. Regulations of CFC release worldwide has stabilized ozone layer depletion, but warming of earth and ocean surfaces from CO2 methane, etc., is expected to increase another greenhouse gas, viz., water vapor. This will reduce stratosphere temperature and thereby allow further ozone layer depletion with its associated increase in UV-B irradiation of the earth (and fungi). Brazil is the world leader in biological control of insects using entomopathogenic fungi and viruses. Between 1979 and 1980, Brazilian sugarcane plantations controlled spittlebugs (Cercopidae: Homoptera) with the fungi Metarhizium anisopliae in 250 thousand hectares, which was the world largest biological control project at that time (Roberts and Humber, 1980; Roberts et al., 1981). In 2001, the treated area was 500 thousand hectares (Roberts and St. Leger, 2004), and by 2008 this had doubled (Li et al., 2010). Naturally occurring epizootics of entomopathogenic fungi can be very devastating to insect populations; but, in some cases, mortalities are insufficient to afford plant protection. There are a number of research areas that need to be explored before the promising potential entomopathogenic fungi for microbial control is realized. Among these are studies on the effect of environment on (a) viability, (b) disease induction, and (c) discovery of formulation additives that preserve viability and enhance virulence in the field. Ultraviolet radiation and the heat from the sun are the two main factors that reduce fungal viability in the field. Most species of entomopathogenic fungal species are very susceptible to UV radiation. With the exception of Metarhizium acridum, a species found in the deserts areas of Africa, Australia, and Mexico controls grasshoppers; and is very tolerant of UV-B radiation (Braga et al., 2001; Fargues et al., 1997; Rangel et al., 2005), other fungal species, e.g., M. anisopliae, Beauveria bassiana, Verticillium lecanii, Aphanocladium album, and Isaria fumosorosea, have poor survival rates after 4 h under artificial UV irradiation (Braga et al., 2002; Fargues et al., 1997; Fernandes et al., 2007; Rangel et al., 2004). A nucleopolyhedrosis virus (NPV) is widely used in Brazilian soybean to control Anticarsia gemmatalis caterpillars, with one million or more hectares treated annually for the past 20 years. Despite their virions being embedded polyhedron protein, the NPVs are somewhat susceptible to UV-B irradiation; and, therefore, strength of UV-B in the environment is an important consideration in formulation and use of insect viruses. Worldwide, governmental efforts to block release by humans of CFC’s have been only partially effective. These chlorine containing compounds are known to deplete the stratospheric ozone layer that impeded most of the solar UV-B radiation from reaching the earth’s surface. The fact that significant levels of UV-B radiation will be present on Earth for at least the next several decades and impair insect biological control with entomopathogens. Therefore, there is a serious need to study how to improve pathogen UV tolerance for effective field use in the future. References Braga, G.U.L., Flint, S.D., Miller, C.D., Anderson, A.J., Roberts, D.W., 2001. Variability in response to UV-B among species and strains of Metarhizium anisopliae isolates from sites at latitudes from 61°N to 54°S. J. Invertebr. Pathol. 78, 98-108. Braga, G.U.L., Rangel, D.E.N., Flint, S.D., Miller, C.D., Anderson, A.J., Roberts, D.W., 2002. Damage and recovery from UV-B exposure in conidia of the entomopathogens Verticillium lecanii and Aphanocladium album. Mycologia 94, 912-920. Fargues, J., Rougier, M., Goujet, R., Smits, N., Coustere, C., Itier, B., 1997. Inactivation of conidia of Paecilomyces fumosoroseus by near-ultraviolet (UVB and UVA) and visible radiation. J. Invertebr. Pathol. 69, 70-78. Fernandes, E.K., Rangel, D.E., Moraes, A.M., Bittencourt, V.R., Roberts, D.W., 2007. Variability in tolerance to UV-B radiation among Beauveria spp. isolates. J Invertebr Pathol 96, 237-243. Li, Z., Alves, S.B., Roberts, D.W., Fan, M., Delalibera Jr, I., Tang, J., Lopes, R.B., Faria, M., Rangel, D.E.N., 2010. Biological control of insects in Brazil and China: history, current programs and reasons for their successes using entomopathogenic fungi. Biocontrol Sci. Tech. 20, 117-136. Rangel, D.E.N., Braga, G.U.L., Anderson, A.J., Roberts, D.W., 2005. Influence of growth environment on tolerance to UV-B radiation, germination speed, and morphology of Metarhizium anisopliae var. acridum conidia. J Invertebr Pathol 90, 55-58. Rangel, D.E.N., Braga, G.U.L., Flint, S.D., Anderson, A.J., Roberts, D.W., 2004. Variations in UV-B tolerance and germination speed of Metarhizium anisopliae conidia produced on artificial and natural substrates. J Invertebr Pathol 87, 77-83. Roberts, D.W., Humber, R.A., 1980. Entomogenous Fungi. In: Cole, G.T., Kendrick, B., Eds.), Biology of Conidial Fungi. Academic Press, New York, pp. 201-236. Roberts, D.W., LeBrun, R.A., Semel, M., 1981. Control of the Colorado Potato Beetle with Fungi. In: Casagrande, R.a.J.L., (Ed.), Advances in Potato Pest Management. Hutchinson and Ross Publ. Co., Stroudsberg, PA., pp. 119-137. Roberts, D.W., St. Leger, R.J., 2004. Metarhizium spp., cosmopolitan insect-pathogenic fungi: mycological aspects. Adv. Appl. Microbiol. 54, 1-70. |
| The influence of fungal nutrition on conidial tolerance to UV-B radiation |
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Drauzio Eduardo Naretto Rangel Universidade do Vale do Paraíba, Instituto de Pesquisa e Desenvolvimento, São José dos Campos, SP, Brazil. |
| The conidial tolerance of the insect pathogenic fungus Metarhizium robertsii to UV-B
radiation is greatly influenced by the nutritional, physical, chemical growth environment.
High phenotypical plasticity in UV-B tolerance was found in M. robertsii, conidia produced
on insect cadavers, on potato dextrose agar supplemented with yeast extract (PDAY) medium,
and on minimal medium (MM) without any carbon sources had low, medium, and high
tolerance to UV-B radiation, respectively. In addition, mycelial growth on MM with nonpreferred
carbon sources (i.e. arabinose, fructose, galactose, inositol, and lactose) produced
conidia with high UV-B tolerances. Conidia produced under osmotic stress (PDAY medium
with 0.6, 0.8, and 1.0 M NaCl or KCl) also had high conidial tolerance to UV-B radiation. The
conidial tolerance increased as salt concentration increased, whereas conidia produced on 1.0
M have the highest tolerance comparable to conidia produced on MM. Conidia produced on
alkali medium (pH 8 or 9,5) also improved high conidial tolerance. However, Comparisons
between stress tolerance and conidial production particularly with conidia produced under
osmotic and nutritive stress demonstrate that the benefits of producing very tolerant conidia
are outweighed enormous cost of low conidial production. Growth under some physical conditions also could improve conidial tolerance to UVB radiation. This was true when M. robertsii was grown under light. Conidia produced under light were two folds more tolerant than conidia from PDAY in the dark. Conidial yield under light or in the dark was similar, therefore, culture on rich media under light is proposed as the most promising approach to produce conidia with improved UV-B radiation tolerance for biological control of insects in agriculture. |
| Effects of UV radiation on conidia used for control of veterinary ectoparasites, particularly Beauveria spp. versus cattle ticks |
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Éverton Kort Kamp Fernandes Utah State University, Department of Biology, Logan, UT, USA 84322-5305. |
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Laboratory studies have reported that the entomopathogenic fungus Beauveria bassiana has good potential to control arthropod ectoparasites of veterinary importance, including flies (Diptera), fleas (Siphonaptera), and ticks (Acari). Billions of dollars are lost every year in Brazil due to ectoparasites, including damage and control. In general, parasite control is based on the use of chemical products. The use of entomopathogenic fungi to control parasites has been studied as an alternative or supplement to using chemical pesticides; among other reasons because biocontrol normally causes much less food and environmental contamination. Depending on the target arthropod, conidia of EF may be applied directly on the animal host; or on the animal’s environment (e.g., pasture plants), where parasites spend at least part of their life cycles. Solar radiation, particularly the UV-B component, negatively affects the survival of conidia of entomopathogenic fungi in the field. In an effort to identify in the laboratory Beauveria spp. isolates with promise for use in settings with high insolation, we examined UV-B tolerance of 53 Beauveria bassiana isolates, 7 isolates of 4 other Beauveria spp. and Engyodontium albus (=Beauveria alba). A dosage of 2h of weighted UV-B irradiance at 978 mW m−2 (total dose = 7.04 kJ m−2) revealed high variability in UV-B tolerance of the fungal isolates, which allowed their separation into categories of low, medium, or high UV-B tolerance. In addition, surviving B. bassiana conidia demonstrated delayed germination; and this is an important finding in that fungal virulence to arthropods has been reported to be negatively influenced by slow germination. Among B. bassiana isolates originating from 0° to 22° latitudes, those from the lower latitudes demonstrated UV-B tolerances significantly greater than isolates from higher latitudes. These same fungal isolates also were investigated as to their thermotolerance, and virulence to the cattle tick, Rhipicephalus microplus. Out of 60 isolates, five B. bassiana isolates had 50% or greater germination after heat treatment (45°C, 2 h). These five isolates also were highly virulent (LC50’s between 107 and 108 conidia ml-1) to R. microplus larvae. Based on the laboratory findings, these five isolates are considered the most promising of the 60 Beauveria spp. isolates tested for further development as biological control agents for controlling veterinary ectoparasites under field conditions. Widening the screen to new and novel fungal isolates is proposed, since this may identify isolates with even greater promise. |
| Effects of Solar UV Radiation on Fungal Conidia |
| Gilberto U. L. Braga Departamento de Análises Clínicas, Toxicológicas e Bromatológicas, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil |
| Conidia are asexual specialized structures of filamentous fungi that are frequently
involved in reproduction, dispersal, and environmental persistence of these microorganisms.
In pathogenic species, conidia are also involved in host recognition and infection. The
conidium is the fungal stage normally used as the field inoculum in biological control
programs. In contrast to vegetative mycelium, which has high metabolic activity, the conidia
of most fungi are dormant or quiescent structures with low metabolic activity. Processes such
as transcription and protein synthesis normally do not occur in the conidia, which limits their
physiological adaptation and response to environmental stresses. We have established conidial
and mycelial proteome reference maps for the entomopathogenic fungus Metarhizium
acridum using two-dimensional gel electrophoresis and matrix-assisted laser desorption
ionization mass spectrometry. Comparison of the two protein-expression profiles reveled that
only 35% of the protein spots were common to both developmental stages. One of the main environmental factors that can kill and/or damage conidia is solar UV radiation [UVA (320-400 nm) and UVB (290-320 nm)]. Solar radiation can limit the survival and dispersal of important plant and animal pathogenic fungi, and its deleterious effects represent a serious impediment to the use of entomopathogenic fungi as bioinsecticides. Direct exposure to solar radiation for a few hours can kill conidia. In addition to killing the conidia, exposure to sublethal doses of solar UV radiation can cause other adverse effects on the conidia. Surviving conidia usually have reduced germination rate and virulence. Cyclobutane pyrimidine dimers (CPDs) are the major DNA photoproducts induced by solar UVB. We examined the occurrence of CPDs in DNA of both wild-type and albino conidia exposed to sublethal doses of UVB radiation. Conidia of M. acridum, Aspergillus nidulans, and A. fumigatus were exposed to 1000 mW m-2 UV irradiance for 15, 30, 60, and 90 min. Total Quaite-weighted doses were 0.9, 1.8, 3.6, and 5.4 kJ m-2, respectively. The frequencies of dimers were linear and directly proportional to the doses, with 0.215, 0.455, 0.803, and 1.628 CPDs/10 kb detected at the doses of 0.9, 1.8, 3.6, and 5.4 kJ m-2 in A. fumigatus, 0.037, 0.077, 0.142, and 0.202 CPDs/10 kb in A. nidulans, and 0.041, 0.085, 0.155, and 0.255 CPDs/10 kb in M. acridum. The frequency of dimers in the M. anisopliae albino mutant DWR 180 (0.552/10 kb) was approximately ten times higher than of the green wild-type ARSEF 23 strain (0.057/10 kb) after exposure to doses of 1.8 kJ m-2. The deleterious effects of UV radiation have led the cells to develop a series of defense systems involving (1) pigments localized on the surface, which can block the entry of radiation into the cell; (2) proteins and enzymes, capable of protecting the macromolecules and the cell components from the harmful effects of radiation; (3) complex enzymatic systems, capable of repairing the damage induced by radiation; (4) enzymes that can inactivate the toxic substances induced by radiation, and (5) small cellular metabolites that mitigate the effects of the stress. Several metabolites present in fungal conidia, such as pigments, sugars, and polyols have been associated with stress tolerance. The discovery of new secondary metabolites present in fungal conidia will contribute to the better understanding of the biology of this specialized structure, including molecular aspects of its environmental persistence, germination, and pathogenicity. We examined extracts of Metarhizium anisopliae conidia by 1H and 13C nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry for the presence of novel secondary metabolites. A novel UV absorbing compound consisting of betaine conjugated with tyrosine was detected and structurally identified as 2-{[1-carboxy-2-(4-hydroxyphenyl)ethyl]amino}-N,N,N-trimethyl-2- oxoethanammonium. Its natural occurrence was previously undescribed. The fungal tyrosine betaine was detected also in conidial extracts of three other M. anisopliae and three M. acridum isolates, but it was not detected in A. nidulans conidial extract. |
| From Ozone Depletion to Agriculture: Understanding the Role of UV Radiation in Sustainable Crop Production |
| Dr. Jason Wargent Institute of Natural Resources, Massey University, New Zealand |
Plant responses to ultraviolet (UV) radiation are numerous, resulting in rapid and often permanent alteration to numerous aspects of plant form, physiology and biochemistry. Such responses to UV radiation, and UV-B radiation in particular, have been previously studied largely due to concerns regarding stratospheric ozone depletion, but a recent re-focus towards the effects of environmentally relevant UV-B doses suggests that key plant responses to UV-B radiation over a range of organisational scales may be exploitable in the context of a significant sustainable contribution towards the strengthening of global crop production. Our work to date has examined the knock-on effects of manipulating the UV environment for plant pathogen incidence, pest attack, and the mechanistic basis for positive changes in crop quality and yield, in addition to determinations of the consequences of spectral manipulation for agrochemical persistence. These topics will be discussed with a focus on considerations of the linkages between fundamental plant biology, ecology, and crop-level outcomes as can be applied to plant UV-B response. |
| Effects of UV radiation on CO2 exchange and volatile organic compound emissions at ecosystem level |
| Riikka Rinnan Terrestrial Ecology Section, Department of Biology, University of Copenhagen, Copenhagen, Denmark. |
Exchange of gases between the ecosystem and the atmosphere involves both plants and microorganisms above and below ground. The green aboveground plant parts take up CO2 in photosynthesis, and all tissues release CO2 in respiration. Soil microbial communities contribute to a significant part of the ecosystem respiration. Results from field experiments conducted using modulated UV enhancement suggest that photosynthesis is little affected by UV radiation. However, it appears that plant-mediated effects possibly via root exudation influence soil microbial communities even though they are not exposed to direct UV radiation. There is evidence showing that these UV-effects that were observed in the belowground part of the ecosystem may be detected as altered ecosystem respiration. Emission of volatile organic compounds (VOCs) from natural sources far exceeds the global anthropogenic VOC emissions. The reactive VOCs can influence climate change as they take part in the formation of tropospheric ozone and secondary organic aerosols, and affect the lifetime of greenhouse gases. In biological perspective, VOCs function e.g. in plant protection against oxidative stress and communication between plants and insects. As UV radiation is known to increase the amount of secondary metabolites in plants, it could be expected that emission of VOCs would also be affected. The few pieces of evidence that exist suggest that UV has limited effects on VOC emissions from vegetation. However, it appears that under heat stress the emission of the most emitted individual compound, isoprene, may increase. In this presentation I review the current state of knowledge on UV effects on exchange of CO2 and VOCs between ecosystems and the atmosphere. |
| Subtle effects of small differences in photosynthetically active radiation:
implications for UV radiation experiments. |
| Stephan D. Flint Department of Rangeland Ecology and Management, University of Idaho, Moscow, Idaho, USA.. |
The effects of ultraviolet-B radiation on plant growth in field experiments are often fairly subtle. Thus it is critical that the experimental treatments only provide different UV-B radiation regimes and do not differentially attenuate other wavebands. This is important both in studies that filter solar UV and in studies that supplement UV-B with lamps. For studies filtering sunlight, canopy photosynthesis models indicated that even small differences in PAR transmittance of filters could, under many circumstances, have significant effects on plant carbon gain. In studies with UV-B lamps, sometimes multiple levels of UV-B radiation have been achieved by suspending lamps at different heights above the plants. Using two common heights of lamp racks, we calculated the sequence of shade intervals and showed the patterns and durations of shade which the plants received is distributed differently over the course of the day for different heights of the lamp racks. We also conducted a greenhouse experiment with plants (canola, sunflower, and maize) grown under lamp racks suspended at the same two heights above the canopy. Even though the lamps were not turned on, growth characteristics differed in unpredictable ways between plants grown under the two heights of lamp racks. In both the filter and lamp examples described here, these small differences in photosynthetically active radiation could either enhance or obscure potential UV-B effects. In addition, differences in leaf mass per unit foliage area caused by variations in shading could contribute to differences in plant UV-B sensitivity. |
| Spectral weighting functions and other issues determining the realism of
field UV experiments. |
| Stephan D. Flint Department of Rangeland Ecology and Management, University of Idaho, Moscow, Idaho, USA. |
Common UV lamp/filter systems do not perfectly simulate either current solar UV radiation or the solar spectrum that would occur with ozone depletion. To deal with this problem, spectral irradiance at each wavelength is multiplied by a dimensionless biological spectral weighting function (BSWF), which represents the effectiveness of each wavelength in bringing about a biological response. A significant problem is that there are a number of different BSWF, which characterize responses for a variety of plant performance characteristics. There is uncertainty about which BSWF to select for plant growth experiments. Recent tests show that BSWF that extend to varying degrees into the UV-A waveband are the most appropriate, yet most past experiments have used a BSWF which is confined to the UV-B waveband. For field experiments, the most serious problem is that, at longer wavelengths, the solar UV is decreased by shading from the lamp array. Lamp supplementation at these longer wavelengths is minimal. Thus, the magnitude of the biologically effective UV under the lamps at these longer wavelengths is decreased to some degree relative to unobstructed sunlight, and the ozone depletion levels simulated are less than intended. Careful spectral irradiance measurements of different field irradiation systems are needed to determine the extent of this problem. |
| UV resistance mechanisms of bacterial spores: implications for agriculture |
| Wayne L. Nicholson Department of Microbiology and Cell Science, University of Florida, Space Life Sciences Laboratory, Kennedy Space Center, FL, USA |
Bacterial spores have in recent years become increasingly important to agriculture, both as beneficial agents to combat pathogens, and as pathogens themselves. A key factor in the persistence of spores in the agricultural environment is their resistance to solar ultraviolet radiation (UV), of which UV-B (290-320 nm) and UV-A (320-400 nm) penetrate to the Earth’s surface. Basic research in our laboratory and others has concentrated on the molecular mechanisms by which bacterial spores resist the lethal effects of UV. Spore DNA is the primary cellular target of UV, and spores utilize a number of mechanisms to: (i) shield DNA; (ii) alter the UV photochemistry of DNA; and (iii) repair UV damage during spore germination. Most of these mechanisms have been elucidated by studying spores in the laboratory with monochromatic 254-nm UV-C, conditions that in large part do not reflect the environmental situation. This seminar will discuss recent attempts to relate the laboratory model of spore UV resistance with practical field applications in agriculture. |