Verticillium lecanii Spore Formulation Using UV Protectant and Wetting Agent and the Biocontrol of Cotton Aphids

Verticillium lecanii spores (10⁸ spores ml⁻¹) suspended in 1% (w/v) montmorillonite SCPX-1374 and 1% (w/v) of the wetting agent, EM-APW#2, which is a polyoxyethylene, had approx. 80% survival after exposure to UV-C for 30 min and about 93% after exposure to UV-B for 6 h. In greenhouse testing, cotton aphid densities increased 14-fold over their initial density in 15 d without spore application. However, initial cotton aphid densities were decreased by 60% of the initial level when plants were treated with the spore formulation.     

Artificial and Solar UV Radiation Induces Strand Breaks and Cyclobutane Pyrimidine Dimers in Bacillus subtilis Spore DNA

The loss of stratospheric ozone and the accompanying increase in solar UV flux have led to concerns regarding decreases in global microbial productivity. Central to understanding this process is determining the types and amounts of DNA damage in microbes caused by solar UV irradiation. While UV irradiation of dormant Bacillus subtilis endospores results mainly in formation of the “spore photoproduct” 5-thyminyl-5,6-dihydrothymine, genetic evidence indicates that an additional DNA photoproduct(s) may be formed in spores exposed to solar UV-B and UV-A radiation (Y. Xue and W. L. Nicholson, Appl. Environ. Microbiol. 62:2221–2227, 1996). We examined the occurrence of double-strand breaks, single-strand breaks, cyclobutane pyrimidine dimers, and apurinic-apyrimidinic sites in spore DNA under several UV irradiation conditions by using enzymatic probes and neutral or alkaline agarose gel electrophoresis. DNA from spores irradiated with artificial 254-nm UV-C radiation accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, while DNA from spores exposed to artificial UV-B radiation (wavelengths, 290 to 310 nm) accumulated only cyclobutane pyrimidine dimers. DNA from spores exposed to full-spectrum sunlight (UV-B and UV-A radiation) accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, whereas DNA from spores exposed to sunlight from which the UV-B component had been removed with a filter (“UV-A sunlight”) accumulated only single-strand breaks and double-strand breaks. Apurinic-apyrimidinic sites were not detected in spore DNA under any of the irradiation conditions used. Our data indicate that there is a complex spectrum of UV photoproducts in DNA of bacterial spores exposed to solar UV irradiation in the environment.     

Artificial and solar UV radiation induces strand breaks and cyclobutane pyrimidine dimers in Bacillus subtilis spore DNA

The loss of stratospheric ozone and the accompanying increase in solar UV flux have led to concerns regarding decreases in global microbial productivity. Central to understanding this process is determining the types and amounts of DNA damage in microbes caused by solar UV irradiation. While UV irradiation of dormant Bacillus subtilis endospores results mainly in formation of the "spore photoproduct" 5-thyminyl-5,6-dihydrothymine, genetic evidence indicates that an additional DNA photoproduct(s) may be formed in spores exposed to solar UV-B and UV-A radiation (Y. Xue and W. L. Nicholson, Appl. Environ. Microbiol. 62:2221-2227, 1996). We examined the occurrence of double-strand breaks, single-strand breaks, cyclobutane pyrimidine dimers, and apurinic-apyrimidinic sites in spore DNA under several UV irradiation conditions by using enzymatic probes and neutral or alkaline agarose gel electrophoresis. DNA from spores irradiated with artificial 254-nm UV-C radiation accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, while DNA from spores exposed to artificial UV-B radiation (wavelengths, 290 to 310 nm) accumulated only cyclobutane pyrimidine dimers. DNA from spores exposed to full-spectrum sunlight (UV-B and UV-A radiation) accumulated single-strand breaks, double-strand breaks, and cyclobutane pyrimidine dimers, whereas DNA from spores exposed to sunlight from which the UV-B component had been removed with a filter ("UV-A sunlight") accumulated only single-strand breaks and double-strand breaks. Apurinic-apyrimidinic sites were not detected in spore DNA under any of the irradiation conditions used. Our data indicate that there is a complex spectrum of UV photoproducts in DNA of bacterial spores exposed to solar UV irradiation in the environment.     

Role of dipicolinic acid in survival of Bacillus subtilis spores exposed to artificial and solar UV radiation

Pyridine-2,6-dicarboxylic acid (dipicolinic acid [DPA]) constitutes approximately 10% of Bacillus subtilis spore dry weight and has been shown to play a significant role in the survival of B. subtilis spores exposed to wet heat and to 254-nm UV radiation in the laboratory. However, to date, no work has addressed the importance of DPA in the survival of spores exposed to environmentally relevant solar UV radiation. Air-dried films of spores containing DPA or lacking DPA due to a null mutation in the DPA synthetase operon dpaAB were assayed for their resistance to UV-C (254 nm), UV-B (290 to 320 nm), full-spectrum sunlight (290 to 400 nm), and sunlight from which the UV-B portion was filtered (325 to 400 nm). In all cases, air-dried DPA-less spores were significantly more UV sensitive than their isogenic DPA-containing counterparts. However, the degree of difference in UV resistance between the two strains was wavelength dependent, being greatest in response to radiation in the UV-B portion of the spectrum. In addition, the inactivation responses of DPA-containing and DPA-less spores also depended strongly upon whether spores were exposed to UV as air-dried films or in aqueous suspension. Spores lacking the gerA, gerB, and gerK nutrient germination pathways, and which therefore rely on chemical triggering of germination by the calcium chelate of DPA (Ca-DPA), were also more UV sensitive than wild-type spores to all wavelengths tested, suggesting that the Ca-DPA-mediated spore germination pathway may consist of a UV-sensitive component or components.     

Role of Dipicolinic Acid in Survival of Bacillus subtilis Spores Exposed to Artificial and Solar UV Radiation

Pyridine-2,6-dicarboxylic acid (dipicolinic acid [DPA]) constitutes approximately 10% of Bacillus subtilis spore dry weight and has been shown to play a significant role in the survival of B. subtilis spores exposed to wet heat and to 254-nm UV radiation in the laboratory. However, to date, no work has addressed the importance of DPA in the survival of spores exposed to environmentally relevant solar UV radiation. Air-dried films of spores containing DPA or lacking DPA due to a null mutation in the DPA synthetase operon dpaAB were assayed for their resistance to UV-C (254 nm), UV-B (290 to 320 nm), full-spectrum sunlight (290 to 400 nm), and sunlight from which the UV-B portion was filtered (325 to 400 nm). In all cases, air-dried DPA-less spores were significantly more UV sensitive than their isogenic DPA-containing counterparts. However, the degree of difference in UV resistance between the two strains was wavelength dependent, being greatest in response to radiation in the UV-B portion of the spectrum. In addition, the inactivation responses of DPA-containing and DPA-less spores also depended strongly upon whether spores were exposed to UV as air-dried films or in aqueous suspension. Spores lacking the gerA, gerB, and gerK nutrient germination pathways, and which therefore rely on chemical triggering of germination by the calcium chelate of DPA (Ca-DPA), were also more UV sensitive than wild-type spores to all wavelengths tested, suggesting that the Ca-DPA-mediated spore germination pathway may consist of a UV-sensitive component or components.     

Screening capacity of UV-absorbing compounds in spores of Arctic Laminariales

The functional significance of phlorotannins as ultraviolet radiation screens in brown algae is presented. Spectral analysis of zoospore suspensions of the three Arctic Laminariales Saccorhiza dermatodea, Alaria esculenta and Laminaria digitata showed strong absorption in the UV waveband, characteristic of phlorotannins. An induction in the synthesis of the UV-absorbing compound in zoospore suspensions of S. dermatodea and A. esculenta was observed as an increase in absorbance in the UV region after 8 h exposure to the whole light spectrum. Transmission of UVR was also negatively correlated with zoospore density in both these species but not in L. digitata. ‘Biofilters’ constructed from UV-transparent acrylic sheet, containing zoospore suspensions or solutions of phloroglucinol showed varying capacity to protect zoospore cultures from the lethal effects of ultraviolet radiation. Phloroglucinol protects the zoospores from damage by screening out the much harmful shorter UV-B spectra (280-290 nm). Cultured spores of A. esculenta and L. digitata after exposure to the whole light spectrum covered by filters containing phloroglucinol showed high rates of germination, unlike controls covered by seawater-only filters that showed 100% mortality. Biofilters containing zoospore suspensions act as buffers and showed variable UV-protection properties on the germination of its conspecies. At highest zoospore density (∼ 4 × 10⁶ spores ml^− 1), zoospores were observed to screen UV radiation maintaining viability among shielded spores in all species investigated. The protective function of zoospore film is, however, density-dependent in L. digitata. At lower spore density, UV-screening function in S. dermatodea and A. esculenta is attributed to their capacity to accumulate and release UV-absorbing compounds into the medium. Ultraviolet radiation transmission by zoospore suspensions of Saccorhiza and Alaria decreased during exposure to the whole light spectrum which is consistent with the earlier observation of enlarged phenolic vesicles following UVR exposure. The increase in vesicle size and the corresponding increase in UV-absorbing capacity may contribute to greater tolerance of UVR exposure in both species.     

Role of the spore coat layers in Bacillus subtilis spore resistance to hydrogen peroxide, artificial UV-C, UV-B, and solar UV radiation

Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective mutants of B. subtilis (containing the gerE36 and/or cotE::cat mutation) were used to study the relative contributions of spore coat layers to spore resistance to hydrogen peroxide (H(2)O(2)) and various artificial and solar UV treatments. Spores of strains carrying mutations in gerE and/or cotE were very sensitive to lysozyme and to 5% H(2)O(2), as were chemically decoated spores of the wild-type parental strain. Spores of all coat-defective strains were as resistant to 254-nm UV-C radiation as wild-type spores were. Spores possessing the gerE36 mutation were significantly more sensitive to artificial UV-B and solar UV radiation than wild-type spores were. In contrast, spores of strains possessing the cotE::cat mutation were significantly more resistant to all of the UV treatments used than wild-type spores were. Spores of strains carrying both the gerE36 and cotE::cat mutations behaved like gerE36 mutant spores. Our results indicate that the spore coat, particularly the inner coat layer, plays a role in spore resistance to environmentally relevant UV wavelengths.     

Bacterial endospores and their significance in stress resistance

In terms of resistance to extreme environmental stresses, the bacterial spore represents a pinnacle of evolution. Spores are highly resistant to a wide variety of physical stresses such as: wet and dry heat, UV and gamma radiation, oxidizing agents, chemicals, and extremes of both vacuum and ultrahigh hydrostatic pressure. Some of the molecular mechanisms underlying spore resistance properties have been elucidated in the laboratory, and involve both: (i) protection of vital spore macromolecules during dormancy, and (ii) repair of damaged macromolecules during germination. Our group has recently become interested in testing if the laboratory model of spore UV resistance is relevant to spore persistence in the environment. We have constructed a number of Bacillus subtilis strains which are defective in various DNA repair systems and spore structural components. Using spores of these strains, we have been exploring: (i) the types of damage induced in DNA by the UV-B and UV-A components of sunlight; (ii) the relative contribution of the major spore DNA repair systems to spore solar radiation resistance; and (iii) the role of spore structural components such as the spore coats and dipicolinic acid (DPA) in attenuation of the lethal and mutagenic effects of solar UV. The current data are reviewed with the ultimate goal of obtaining a complete model describing spore persistence and longevity in the terrestrial solar UV radiation environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparative Sensitivity to UV-B Radiation of Two Bacillus thuringiensis Subspecies and Other Bacillus sp.

Susceptibility of Bacillus thuringiensis spores and toxins to the UV-B range (280–330 nm) of the solar spectrum reaching Earth's surface may be responsible for its inactivation and low persistence in nature. Spores of the mosquito larvicidal B. thuringiensis subsp. israelensis were significantly more resistant to UV-B than spores of the lepidopteran-active subsp. kurstaki. Spores of subsp. israelensis were as resistant to UV-B as spores of B. subtilis and more resistant than spores of the closely related B. cereus and another mosquito larvicidal species B. sphaericus. Sensitivity of B. thuringiensis subsp. israelensis spores to UV-B radiation depended upon their culture age; 24-h cultures, approaching maximal larvicidal activity, were still sensitive. Maximal resistance to UV-B was achieved only at 48 h. Received: 13 December 2000/Accepted: 19 January 2001     

Role of the Spore Coat Layers in Bacillus subtilis Spore Resistance to Hydrogen Peroxide, Artificial UV-C, UV-B, and Solar UV Radiation

Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective mutants of B. subtilis (containing the gerE36 and/or cotE::cat mutation) were used to study the relative contributions of spore coat layers to spore resistance to hydrogen peroxide (H₂O₂) and various artificial and solar UV treatments. Spores of strains carrying mutations in gerE and/or cotE were very sensitive to lysozyme and to 5% H₂O₂, as were chemically decoated spores of the wild-type parental strain. Spores of all coat-defective strains were as resistant to 254-nm UV-C radiation as wild-type spores were. Spores possessing the gerE36 mutation were significantly more sensitive to artificial UV-B and solar UV radiation than wild-type spores were. In contrast, spores of strains possessing the cotE::cat mutation were significantly more resistant to all of the UV treatments used than wild-type spores were. Spores of strains carrying both the gerE36 and cotE::cat mutations behaved like gerE36 mutant spores. Our results indicate that the spore coat, particularly the inner coat layer, plays a role in spore resistance to environmentally relevant UV wavelengths.     

The impact of nutrition on spore yields for various fungal entomopathogens in liquid culture

Spore yields were measured for various fungal entomopathogens grown in six nutritionally different liquid media with low and high carbon concentrations (8 and 36 g l^–1, respectively) at carbon-to-nitrogen (C:N) ratios of 10:1, 30:1 and 50:1. Six fungi were tested: two Beauveria bassiana strains, three Paecilomyces fumosoroseus strains and one Metarhizium anisopliae strain. Spore yields were examined after 2, 4 or 7 days growth. In general, highest spore yields were obtained in media containing 36 g/l and a C:N ratio of 10:1. After 4 days growth, highest spore yields were measured in the three Paecilomyces isolates (6.9–9.7 × 10⁸ spores ml^–1). Spore production by the B. bassiana isolates was variable with one isolate producing high spore yields (12.2 × 10⁸ spores ml^–1) after 7 days growth. The M. anisopliae isolate produced low spore concentrations under all conditions tested. Using a commercial production protocol, a comparison of spore yields for the coffee berry borer P. fumosoroseus and a commercial B. bassiana isolate showed that highest spore concentrations (7.2 × 10⁸ spores ml^–1) were obtained with the P. fumosoroseus isolate 2-days post-inoculation. The ability of the P. fumosoroseus strain isolated from the coffee berry borer to rapidly produce high concentrations of spores prompted further testing to determine the desiccation tolerance of these spores. Desiccation studies showed that ca. 80% of the liquid culture produced P. fumosoroseus spores survived the air-drying process. The virulence of freshly produced, air-dried and freeze-dried coffee berry borer P. fumosoroseus blastospores preparations were tested against silverleaf whiteflies (Bemisia argentifolii). While all preparations infected and killed B. argentifolii, fresh and air-dried preparations were significantly more effective. These results suggest that screening potential fungal biopesticides for amenability to liquid culture spore production can aid in the identification of commercially viable isolates. In this study, P. fumosoroseus was shown to possess the production and stabilization attributes required for commercial development.     

Effect of UV radiation on photoinhibition of marine macrophytes in culture systems

The present study examined the effect of UV andphotosynthetically active radiation (PAR) onphotoinhibition and recovery in the Phaeophyte Macrocystis pyrifera, the Rhodophyte Chondruscrispus and the Chlorophyte Ulva lactuca underoutdoor culture conditions. There was an increase inphotoinhibition as a consequence of high exposure toUV-B radiation in M. pyrifera, however, highlevels of PAR accounted for most of thephotoinhibition in C. crispus and U.lactuca. Photodamage by UV-A, UV-B and PAR wascompletely repaired within 5 h and effective quantumyield reached pretreatment values in the three speciesstudied. Species were less susceptible tophotoinhibition after being incubated for 5 d underhigh exposures of natural irradiance suggesting aphotoadaptive process. The recovery of the effectivequantum yield was impaired by long exposure to highlevels of UV-B in C. crispus and UV-A, UV-B andPAR in M. pyrifera. This suggests a differentkind of damage by UV-A and PAR radiation, one to thephotosynthetic apparatus and another which affects therepair mechanism of some species. There was anincrease in UV-absorption ( 330 nm) in M. pyrifera and C. crispus within four days ofthe initiation of the experiment suggesting that thesespecies photoprotect their photosynthetic system whenexposed to elevated UV and PAR levels.     

Insecticidal activities of leaf essential oils from Cinnamomum osmophloeum against three mosquito species

The larvicidal activities of leaf essential oils and their constituents from six chemotypes of indigenous cinnamon (Cinnamomum osmophloeum Kaneh.) trees were evaluated against three mosquito species. Results of larvicidal tests demonstrated that the leaf essential oils of cinnamaldehyde type and cinnamaldehyde/cinnamyl acetate type had an excellent inhibitory effect against Aedes albopictus larvae, and their LC(50) values in 24h were 40.8 microg/ml (LC(90)=81.7 microg/ml) and 46.5 microg/ml (LC(90)=83.3 microg/ml), respectively. Results of the 24-h mosquito larvicidal assays also showed that the effective constituents in leaf essential oils were trans-cinnamaldehyde and benzaldehyde and that the LC(50) values of these constituents against A. albopictus larvae were below 50 mug/ml. In addition, cinnamaldehyde type leaf essential oil and trans-cinnamaldehyde have also exhibited great larvicidal performance against Culex quinquefasciatus and Armigeres subalbatus larvae. Comparisons of mosquito larvicidal activity of trans-cinnamaldehyde congeners revealed that alpha-methyl cinnamaldehyde, benzaldehyde, and trans-cinnamaldehyde exhibited strong mosquito larvicidal activity.     

Response of the estuarine cyanobacterium <Emphasis Type="Italic">Lyngbya aestuarii</Emphasis> to UV-B radiation

Growth response and changes in the spectral properties of methanolic extract of an estuarine cyanobacterium, Lyngbya aestuarii Agardh, to UV-B radiation were studied. Increase in growth accompanied by increase in chlorophyll a, protein and carbohydrate content was observed up to 12 h of UV-B irradiation followed by a decline with further increase in the duration of UV exposure. Carotenoid content progressively increased with the UV-B dose. The organism synthesized, to a significant extent, mycosporine amino acid-like substances (MAAs) upon UV-B exposure. The cells in the trichome became coiled followed by formation of small bundles as a response to UV-B radiation. SDS protein profile of the UV irradiated cells showed repression of 20 and 22 kDa proteins. However, irradiation with UV-B for 6–24 h led to overproduction of 84, 73, 60, 46, 40, 37 KDa proteins, possibly conferring protection to the organism from UV-B. UV irradiated cells cultured in florescent light for up to 7 days showed revival from UV damage of the pigments and macromolecular contents, suggesting existence of a repair mechanism in the organism.     

Below-ambient levels of UV induce chloroplast structural change and alter starch metabolism

Summary. Electromagnetic radiation (EMR) in the 400–700 nm bandwidth of photosynthetically active radiation (PAR) has been established as an important source of energy for photosynthesis and environmental signals regulating many aspects of green-plant life. Above-ambient levels of UV-B radiation (290–320 nm) under high-PAR conditions have been shown to elicit responses in chloroplasts of Brassica napus similar to those of chloroplasts at low-PAR exposure (W. Fagerberg and J. Bornman, Physiol. Plant. 101: 833–844, 1997). The question arises as to whether UV at normal levels can also evoke similar responses. Here we provide evidence that even below-ambient levels of UV-B (1/28 ambient; Durham, N.H., U.S.A., 1200 hours, March) were capable of inducing an increase in thylakoid surface area relative to the chloroplast volume typical of a low-PAR response (shade response) in sunflowers. This response occurred even though leaves were concurrently exposed to PAR levels that normally induce a “sun” or high-PAR response in the absence of UV-B. Subambient levels of UV-B were also associated with a decrease in chloroplast and starch volume. Exposure to levels of UV-A 1/10 of ambient appeared to enhance the high-PAR response of the chloroplast, characterized by an increase in the amounts of stored starch, an increase in chloroplast volume density ratio values, and a decrease in thylakoid surface area density ratios relative to the high-light controls. These effects were opposite to those seen in UV-B-exposed tissue. In a general sense, subambient levels of UV-B evoked a response similar to that elicited by low-PAR irradiance, while subambient UV-A elicited responses similar to those typical of high-PAR irradiance. The fact that below-ambient levels of UV altered a normal chloroplast structural response to PAR provides evidence that UV may be an important environmental signal for plants. Correspondence and reprints: Department of Plant Biology, University of New Hampshire, Durham, NH 03824, U.S.A. This is Scientific Contribution number 2292 from the New Hampshire Agricultural Experiment Station.     

Stratospheric Ozone Depletion: High Arctic Tundra Plant Growth on Svalbard is not Affected by Enhanced UV-B after 7 years of UV-B Supplementation in the Field

The response of tundra plants to enhanced UV-B radiation simulating 15 and 30% ozone depletion was studied at two high arctic sites (Isdammen and Adventdalen, 78° N, Svalbard).The set-up of the UV-B supplementation systems is described, consisting of large and small UV lamp arrays, installed in 1996 and 2002. After 7 years of exposure to enhanced UV-B radiation, plant cover, density, morphological (leaf fresh and dry weight, leaf thickness, leaf area, reproductive and ecophysiological parameters leaf UV-B absorbance, leaf phenolic content, leaf water content) were not affected by enhanced UV-B radiation. DNA damage in the leaves was not increased with enhanced UV-B in Salix polaris and Cassiope tetragona. DNA damage in Salix polaris leaves was higher than in leaves of C. tetragona. The length of male gametophyte moss plants of Polytrichum hyperboreum was reduced with elevated UV-B as well as the number of Pedicularis hirsuta plants per plot, but the inflorescence length of Bistorta vivipara was not significantly affected. We discuss the possible causes of tolerance of tundra plants to UV-B (absence of response to enhanced UV-B) in terms of methodology (supplementation versus exclusion), ecophysiological adaptations to UV-B and the biogeographical history of polar plants     

<Emphasis Type="Italic">Isatis indigotica</Emphasis> seedlings derived from laser stimulated seeds showed improved resistance to elevated UV-B

Sterilized seeds of Isatis indigotica (Brassicacae) were divided into four groups based on irradiation pretreatments. These control groups (C) were non irradiated, He–Ne laser treated seeds (L), UV-B treated seeds (B) and He–Ne laser followed by UV-B radiation treated seeds (LB). Laser radiation was provided by He–Ne laser, UV-B radiation was provided by filtered Qin brand 30 W fluorescent sun lamps. Malondialdehyde (MDA), proline, UV-B absorbing compounds and ascorbic acid (AsA) concentrations, as well as, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were measured in the cotyledons of seedlings from all the four irradiation treatments. The result indicate that UV-B radiation enhanced the concentration of MDA while decreasing the activities of SOD, CAT, POD and the concentration of AsA in the seedlings compared with the controls. The concentration of MDA decreased, while the activities of SOD, CAT, POD and the concentration of AsA increased in seedling treated with He–Ne laser and UV-B compared to UV-B alone. The concentration of proline and UV absorbing compounds increased progressively with treatments i.e. UV-B irradiation, He–Ne laser irradiation, and He–Ne laser irradiation followed by UV-B irradiation compared to the controls. The present data suggest that Isatis indigotica seedlings derived from laser stimulated seeds showed improved resistance to elevated UV-B.     

Exposure to ultraviolet radiation delays photosynthetic recovery in Arctic kelp zoospores

Seasonal reproduction in some Arctic Laminariales coincides with increased UV-B radiation due to stratospheric ozone depletion and relatively high water temperatures during polar spring. To find out the capacity to cope with different spectral irradiance, the kinetics of photosynthetic recovery was investigated in zoospores of four Arctic species of the order Laminariales, the kelps Saccorhiza dermatodea, Alaria esculenta, Laminaria digitata, and Laminaria saccharina. The physiology of light harvesting, changes in photosynthetic efficiency and kinetics of photosynthetic recovery were measured by in vivo fluorescence changes of Photosystem II (PSII). Saturation irradiance of freshly released spores showed minimal I _k values (photon fluence rate where initial slope intersects horizontal asymptote of the curve) values ranging from 13 to 18 μmol photons m⁻² s⁻¹ among species collected at different depths, confirming that spores are low-light adapted. Exposure to different radiation spectra consisting of photosynthetically active radiation (PAR; 400–700 nm), PAR+UV-A radiation (UV-A; 320–400 nm), and PAR+ UV-A+UV-B radiation (UV-B; 280–320 nm) showed that the cumulative effects of increasing PAR fluence and the additional effect of UV-A and UV-B radiations on photoinhibition of photosynthesis are species specific. After long exposures, Laminaria saccharina was more sensitive to the different light treatments than the other three species investigated. Kinetics of recovery in zoospores showed a fast phase in S. dermatodea, which indicates a reduction of the photoprotective process while a slow phase in L. saccharina indicates recovery from severe photodamage. This first attempt to study photoinhibition and kinetics of recovery in zoospores showed that zoospores are the stage in the life history of seaweeds most susceptible to light stress and that ultraviolet radiation (UVR) effectively delays photosynthetic recovery. The viability of spores is important on the recruitment of the gametophytic and sporophytic life stages. The impact of UVR on the zoospores is related to the vertical depth distribution of the large sporophytes in the field.     

Effects of UV on the spores of the fungal species Arthrobotrys oligospora and A. ferox

. The effects of UV irradiation (at 5>380 nm and 5>265 nm) on spore suspensions of a European strain of Arthrobotrys oligospora (hyphomycete) have been investigated and compared with those on a strain of the Antarctic species, A. ferox. Emission and excitation spectra of control and irradiated spore suspensions of both strains suggest a higher vulnerability of A. oligospora, which would be consistent with changes in membrane permeability and a lower amount of UV-protecting substances. Germination tests on UV-B irradiated spores confirm the higher resistance of A. ferox, which seems better adapted to the high UV radiation levels characterizing Antarctic environments.     

Rapid determination of spore chemistry using thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy.

Spore chemistry is at the centre of investigations aimed at producing a proxy record of harmful ultraviolet radiation (UV-B) through time. A biochemical proxy is essential owing to an absence of long-term (century or more) instrumental records. Spore cell material contains UV-B absorbing compounds that appear to be synthesised in variable amounts dependent on the ambient UV-B flux. To facilitate these investigations we have developed a rapid method for detecting variations in spore chemistry using combined thermochemolysis gas chromatography-mass spectrometry and micro-Fourier transform infrared spectroscopy. Our method was tested using spores obtained from five populations of the tropical lycopsid Lycopodium cernuum growing across an altitudinal gradient (650-1981 m a.s.l.) in S.E. Asia with the assumption that they experienced a range of UV-B radiation doses. Thermochemolysis and subsequent pyrolysis liberated UV-B pigments (ferulic and para-coumaric acid) from the spores. All of the aromatic compounds liberated from spores by thermochemolysis and pyrolysis were active in UV-B protection. The various functional groups associated with UV-B protecting pigments were rapidly detected by micro-FTIR and included the aromatic C[double bond, length as m-dash]C absorption band which was exclusive to the pigments. We show increases in micro-FTIR aromatic absorption (1510 cm(-1)) with altitude that may reflect a chemical response to higher UV-B flux. Our results indicate that rapid chemical analyses of historical spore samples could provide a record ideally suited to investigations of a proxy for stratospheric O3 layer variability and UV-B flux over historical (century to millennia) timescales.