Spores potentially dispersed to longer distances are more tolerant to ultraviolet radiation: A case study in the moss genus Orthotrichum

PREMISE OF THE STUDY

Ultraviolet (UV) radiation influences the viability of algal spores and seed-plant pollen depending on the species, the dose, and the wavelength. In bryophytes, one of the dominant groups of plants in many habitats, UV radiation could determine their spore dispersal strategy, and such data are critical for reconstructing the ancestral state in plants and for determining the distribution range and persistence of bryophyte species.

METHODS

Spores of four bryophyte species of the moss genus Orthotrichum that were either hygrochastic or xerochastic (spores dispersed under wet or dry conditions, respectively) were exposed to realistic doses of UV radiation under laboratory conditions. Spore viability was evaluated through germination experiments and, for the first time in bryophytes, ultrastructural observations. Given that the UV-B doses used were relatively higher than the UV-A doses, the UV effect was probably due more to UV-B than UV-A wavelengths.

KEY RESULTS

All four species reduced their spore germination capacity in a UV dose-dependent manner, concomitantly increasing spore ultrastructural damage (cytoplasmic and plastid alterations). Most spores eventually died when exposed to the highest UV dose. Interestingly, spores of hygrochastic species were much more UV-sensitive than those of xerochastic species.

CONCLUSIONS

UV tolerance determines moss spore viability, as indicated by germination capacity and ultrastructural damage, and differs between spores of species with different dispersal strategies. Specifically, the higher UV tolerance of xerochastic spores may enable them to be dispersed to longer distances than hygrochastic spores, thus extending more efficiently the distribution range of the corresponding species.

A Plant Cryptochrome Controls Key Features of the Chlamydomonas Circadian Clock and Its Life Cycle

Cryptochromes are flavin-binding proteins that act as blue light receptors in bacteria, fungi, plants, and insects and are components of the circadian oscillator in mammals. Animal and plant cryptochromes are evolutionarily divergent, although the unicellular alga Chlamydomonas reinhardtii (Chlamydomonas throughout) has both an animal-like cryptochrome and a plant cryptochrome (pCRY; formerly designated CPH1). Here, we show that the pCRY protein accumulates at night as part of a complex. Functional characterization of pCRY was performed based on an insertional mutant that expresses only 11% of the wild-type pCRY level. The pcry mutant is defective for central properties of the circadian clock. In the mutant, the period is lengthened significantly, ultimately resulting in arrhythmicity, while blue light-based phase shifts show large deviations from what is observed in wild-type cells. We also show that pCRY is involved in gametogenesis in Chlamydomonas pCRY is down-regulated in pregametes and gametes, and in the pcry mutant, there is altered transcript accumulation under blue light of the strictly light-dependent, gamete-specific gene GAS28 pCRY acts as a negative regulator for the induction of mating ability in the light and for the loss of mating ability in the dark. Moreover, pCRY is necessary for light-dependent germination, during which the zygote undergoes meiosis that gives rise to four vegetative cells. In sum, our data demonstrate that pCRY is a key blue light receptor in Chlamydomonas that is involved in both circadian timing and life cycle progression.

The decision to germinate is regulated by divergent molecular networks in spores and seeds

Dispersal is a key step in land plant life cycles, usually via formation of spores or seeds. Regulation of spore- or seed-germination allows control over the timing of transition from one generation to the next, enabling plant dispersal. A combination of environmental and genetic factors determines when seed germination occurs. Endogenous hormones mediate this decision in response to the environment. Less is known about how spore germination is controlled in earlier-evolving nonseed plants. Here, we present an in-depth analysis of the environmental and hormonal regulation of spore germination in the model bryophyte Physcomitrella patens (Aphanoregma patens). Our data suggest that the environmental signals regulating germination are conserved, but also that downstream hormone integration pathways mediating these responses in seeds were acquired after the evolution of the bryophyte lineage. Moreover, the role of abscisic acid and diterpenes (gibberellins) in germination assumed much greater importance as land plant evolution progressed. We conclude that the endogenous hormone signalling networks mediating germination in response to the environment may have evolved independently in spores and seeds. This paves the way for future research about how the mechanisms of plant dispersal on land evolved.

Spectroscopy and viability of Bacillus subtilis spores after ultraviolet irradiation: implications for the detection of potential bacterial life on Europa

One of the most habitable environments in the Solar System outside of Earth may exist underneath the ice on Europa. In the near future, our best chance to look for chemical signatures of a habitable environment (or life itself) will likely be at the inhospitable icy surface. Therefore, it is important to understand the ability of organic signatures of life and life itself to persist under simulated europan surface conditions. Toward that end, this work examined the UV photolysis of Bacillus subtilis spores and their chemical marker dipicolinic acid (DPA) at temperatures and pressures relevant to Europa. In addition, inactivation curves for the spores at 100 K, 100 K covered in one micron of ice, and 298 K were measured to determine the probability for spore survival at the surface. Fourier transform infrared spectra of irradiated DPA showed a loss of carboxyl groups to CO2 as expected but unexpectedly showed significant opening of the heterocyclic ring, even for wavelengths>200 nm. Both DPA and B. subtilis spores showed identical unknown spectral bands of photoproducts after irradiation, further highlighting the importance of DPA in the photochemistry of spores. Spore survival was enhanced at 100 K by ∼5× relative to 298 K, but 99.9% of spores were still inactivated after the equivalent of ∼25 h of exposure on the europan surface.

UVR defense mechanisms in eurytopic and invasive Gracilaria vermiculophylla (Gracilariales, Rhodophyta)

The invasive success of Gracilaria vermiculophylla has been attributed to its wide tolerance range to different abiotic factors, but its response to ultraviolet radiation (UVR) is yet to be investigated. In the laboratory, carpospores and vegetative thalli of an Atlantic population were exposed to different radiation treatments consisting of high PAR (photosynthetically active radiation) only (P), PAR+UV-A (PA) and PAR+UV-A+UV-B (PAB). Photosynthesis of carpospores was photoinhibited under different radiation treatments but photosystem II (PSII) function was restored after 12 h under dim white light. Growth of vegetative thalli was significantly higher under radiation supplemented with UVR. Decrease in chlorophyll a (Chl a) under daily continuous 16-h exposure to 300 µmol photons m(-2) s(-1) of PAR suggests preventive accumulation of excited chlorophyll molecules within the antennae to minimize the generation of dangerous reactive oxygen species. Moreover, an increase in total carotenoids and xanthophyll cycle pigments (i.e. violaxanthin, antheraxanthin and zeaxanthin) further suggests effective photoprotection under UVR. The presence of the ketocarotenoid β-cryptoxanthin also indicates protection against UVR and oxidative stress. The initial concentration of total mycosporine-like amino acids (MAAs) in freshly-released spores increased approximately four times after 8-h laboratory radiation treatments. On the other hand, initial specific MAAs in vegetative thalli changed in composition after 7-day exposure to laboratory radiation conditions without affecting the total concentration. The above responses suggest that G. vermiculophylla have multiple UVR defense mechanisms to cope with the dynamic variation in light quantity and quality encountered in its habitat. Beside being eurytopic, the UVR photoprotective mechanisms likely contribute to the current invasive success of the species in shallow lagoons and estuaries exposed to high solar radiation.

Recruitment potential of a green alga Ulva flexuosa Wulfen dark preserved zoospore and its development

The recruitment potential and the ability of Ulva flexuosa Wulfen zoospores to survive darkness were tested under different conditions in the present study. The dark preserved zoospore was cultured under a two-factor experimental design to test the effect of salinity and nitrate, effect of salinity and phosphate, effect of light and salinity, and effect of light and phosphate. The recruitment (germination and growth) of zoospores was significantly affected by light and salinity. The nitrate concentration of 20 µmol.l(-1) was found to initiate the process of germination and its subsequent growth and, its effect appeared greatest under 25 psu condition. While nitrate enhances the growth of biomass more than phosphate, both show a positive interactive effect on biomass increase when crossed with salinity. The combined effect of 25 psu salinity and 8 µmol.l(-1) phosphate exhibited higher biomass growth. There was a significant effect of light and salinity on the biomass of zoospore, though there was no significant interaction between the two factors. There was an increase in biomass of growing zoospores to increase in light intensity and 80 µmol.m(-2).s(-1) of light intensity was considered optimal. Similarly, high light intensity condition favored higher biomass growth and there was significant interaction between light (80 µmol. m(-2). s(-1)) and phosphate (4 µmol. l(-1)) in high salinity (35 psu) condition. The result of this study showed that dark preserved zoospores of U. flexuosa have the potential for recruitment and it gives us an understanding how different factors play a role in the process of recruitment.

Moist-heat resistance, spore aging, and superdormancy in Clostridium difficile

Clostridium difficile spores can survive extended heating at 71°C (160°F), a minimum temperature commonly recommended for adequate cooking of meats. To determine the extent to which higher temperatures would be more effective at killing C. difficile, we quantified (D values) the effect of moist heat at 85°C (145°F, for 0 to 30 min) on C. difficile spores and compared it to the effects at 71 and 63°C. Fresh (1-week-old) and aged (≥20-week-old) C. difficile spores from food and food animals were tested in multiple experiments. Heating at 85°C markedly reduced spore recovery in all experiments (5 to 6 log(10) within 15 min of heating; P < 0.001), regardless of spore age. In ground beef, the inhibitory effect of 85°C was also reproducible (P < 0.001), but heating at 96°C reduced 6 log(10) within 1 to 2 min. Mechanistically, optical density and enumeration experiments indicated that 85°C inhibits cell division but not germination, but the inhibitory effect was reversible in some spores. Heating at 63°C reduced counts for fresh spores (1 log(10), 30 min; P < 0.04) but increased counts of 20-week-old spores by 30% (15 min; P < 0.02), indicating that sublethal heat treatment reactivates superdormant spores. Superdormancy is an increasingly recognized characteristic in Bacillus spp., and it is likely to occur in C. difficile as spores age. The potential for reactivation of (super)dormant spores with sublethal temperatures may be a food safety concern, but it also has potential diagnostic value. Ensuring that food is heated to >85°C would be a simple and important intervention to reduce the risk of inadvertent ingestion of C. difficile spores.

The molecular and physiological responses of Physcomitrella patens to ultraviolet-B radiation

Ultraviolet-B (UV-B) radiation present in sunlight is an important trigger of photomorphogenic acclimation and stress responses in sessile land plants. Although numerous moss species grow in unshaded habitats, our understanding of their UV-B responses is very limited. The genome of the model moss Physcomitrella patens, which grows in sun-exposed open areas, encodes signaling and metabolic components that are implicated in the UV-B response in flowering plants. In this study, we describe the response of P. patens to UV-B radiation at the morphological and molecular levels. We find that P. patens is more capable of surviving UV-B stress than Arabidopsis (Arabidopsis thaliana) and describe the differential expression of approximately 400 moss genes in response to UV-B radiation. A comparative analysis of the UV-B response in P. patens and Arabidopsis reveals both distinct and conserved pathways.

Ca2+ influx and phosphoinositide signalling are essential for the establishment and maintenance of cell polarity in monospores from the red alga Porphyra yezoensis

The asymmetrical distribution of F-actin directed by cell polarity has been observed during the migration of monospores from the red alga Porphyra yezoensis. The significance of Ca2+ influx and phosphoinositide signalling during the formation of cell polarity in migrating monospores was analysed pharmacologically. The results indicate that the inhibition of the establishment of cell polarity, as judged by the ability of F-actin to localize asymmetrically, cell wall synthesis, and development into germlings, occurred when monospores were treated with inhibitors of the Ca2+ permeable channel, phospholipase C (PLC), diacylglycerol kinase, and inositol-1,4,5-trisphosphate receptor. Moreover, it was also found that light triggered the establishment of cell polarity via photosynthetic activity but not its direction, indicating that the Ca2+ influx and PLC activation required for the establishment of cell polarity are light dependent. By contrast, inhibition of phospholipase D (PLD) prevented the migration of monospores but not the asymmetrical localization of F-actin. Taken together, these findings suggest that there is functional diversity between the PLC and PLD signalling systems in terms of the formation of cell polarity; the former being critical for the light-dependent establishment of cell polarity and the latter playing a role in the maintenance of established cell polarity.

Chloroplasts do not have a polarity for light-induced accumulation movement

Chloroplast photorelocation movement in green plants is generally mediated by blue light. However, in cryptogam plants, including ferns, mosses, and algae, both red light and blue light are effective. Although the photoreceptors required for this phenomenon have been identified, the mechanisms underlying this movement response are not yet known. In order to analyze this response in more detail, chloroplast movement was induced in dark-adapted Adiantum capillus-veneris gametophyte cells by partial cell irradiation with a microbeam of red and/or blue light. In each case, chloroplasts were found to move toward the microbeam-irradiated area. A second microbeam was also applied to the cell at a separate location before the chloroplasts had reached the destination of the first microbeam. Under these conditions, chloroplasts were found to change their direction of movement without turning and move toward the second microbeam-irradiated area after a lag time of a few minutes. These findings indicate that chloroplasts can move in any direction and do not exhibit a polarity for chloroplast accumulation movement. This phenomenon was analyzed in detail in Adiantum and subsequently confirmed in Arabidopsis thaliana palisade cells. Interestingly, the lag time for direction change toward the second microbeam in Adiantum was longer in the red light than in the blue light. However, the reason for this discrepancy is not yet understood.

Efficiency of Artemia cysts removal as a model invasive spore using a continuous microwave system with heat recovery

A continuous microwave system to treat ballast water inoculated with Artemia salina cysts as a model invasive spore was tested for its efficacy in inactivating the cysts present. The system was tested at two different flow rates (1 and 2 L x min(-1)) and two different power levels (2.5 and 4.5 kW). Temperature profiles indicate that the system could deliver heating loads in excess of 100 degrees C in a uniform and near-instantaneous manner when using a heat recovery system. Except for a power and flow rate combination of 2.5 kW and 2 L x min(-1), complete inactivation of the cysts was observed at all combinations at holding times below 100 s. The microwave treatment was better or equal to the control treatment in inactivating the cysts. Use of heat exchangers increased the power conversion efficiency and the overall efficiency of the treatment system. Cost economics analysis indicates that in the present form of development microwave treatment costs are higher than the existing ballast water treatment methods. Overall, tests results indicated that microwave treatment of ballast water is a promising method that can be used in conjunction with other methods to form an efficient treatment system that can prevent introduction of potentially invasive spore forming species in non-native waters.

Effects of freezing, drying, ultraviolet irradiation, chlorine, and quaternary ammonium treatments on the infectivity of myxospores of Myxobolus cerebralis for Tubifex tubifex

The effects of freezing, drying, ultraviolet irradiation (UV), chlorine, and a quaternary ammonium compound on the infectivity of the myxospore stage of Myxobolus cerebralis (the causative agent of whirling disease) for Tubifex tubifex were examined in a series of laboratory trials. Freezing at either -20 degrees C or -80 degrees C for a period of 7 d or 2 months eliminated infectivity as assessed by the absence of production of the actinospore stage (triactinomyxons [TAMs]) from T. tubifex cultures inoculated with treated myxospores over a 4-5-month period. Myxospores retained infectivity when held in well water at 5 degrees C or 22 degrees C for 7 d and when held at 4 degrees C or 10 degrees C d for 2 months. In contrast, no TAMs were produced from T. tubifex cultures inoculated with myxospores held at 20 degrees C for 2 months. Drying of myxospores eliminated any evidence of infectivity for T. tubifex. Doses of UV from 40 to 480 mJ/cm2 were all effective for inactivating myxospores of M. cerebralis, although a few TAMs were detected in one replicate T. tubifex culture at 240 mJ/cm2 and in one replicate culture at 480 mJ/cm2. Treatments of myxospores with chlorine bleach at active concentrations of at least 500 mg/L for 15 min largely inactivated myxospore infectivity for T. tubifex. Likewise, there was no evidence of TAMs produced by T. tubifex inoculated with myxospores treated with alkyl dimethyl benzyl ammonium chloride (ADBAC) at 1,500 mg/L for 10 min. Treatments of myxospores with 1,000-mg/L ADBAC for 10 min reduced TAM production in T. tubifex cultures sevenfold relative to that in cultures inoculated with an equal number of untreated myxospores. These results indicate that myxospores of M. cerebralis demonstrate a selective rather than broad resistance to selected physical and chemical treatments, and this selective resistance is consistent with conditions that myxospores are likely to experience in nature.

Effects of ultraviolet radiation and temperature on the ultrastructure of zoospores of the brown macroalga Laminaria hyperborea

The interactive effects of an 8 h exposure to UV radiation and altered temperatures on the ultrastructure and germination of zoospores of the sublittoral brown alga Laminaria hyperborea (Gunn.) Foslie were investigated for the first time. Spores were exposed to four temperatures (2, 7, 12 and 17 degrees C) and three light regimes (PAR, PAR + UV-A, PAR + UV-A+UV-B). Freshly-released spores of L. hyperborea lack a cell wall and contain a nucleus with fine granular nucleoplasm and a nucleolus, one chloroplast, several mitochondria, dictyosomes and an endoplasmatic reticulum. Further, several kinds of so-called adhesive vesicles, lipid globuli and physodes containing UV-absorbing phlorotannins are embedded in the cytoplasm. No eye-spot is present. Physodes were found but they were rare and small. After an 8 h exposure to UV-B, the nucleoplasm had a mottled structure, chloroplasts contained plastoglobuli, the structure of the mitochondria changed from crista- to sacculus-type and germination was strongly inhibited at all temperatures. UV-A only had an impact on the ultrastructure at the highest temperature tested. The strongest effects were found at 17 degrees C, where germination was reduced to 35%, 32% and 9% after exposure to PAR, PAR+UV-A and PAR + UV-A + UV-B, respectively. This study indicates that UV-B radiation has strong damaging effects on the physiology and ultrastructure of zoospores of L. hyperborea. The results are important for developing scenarios for the effect of enhanced UV radiation and increasing temperatures caused by global climate changes.

Radiobiological investigations of soft X-rays near carbon, nitrogen, oxygen K-shell edges on Aspergillus oryzae spores

Soft X-rays at carbon, nitrogen, oxygen K-shell edges have special radiobiological effects. Using Aspergillus oryzae spores as sample, the radiation effects of soft X-rays near the K-shell edges of C, N and O elements from synchrotron radiation were investigated. Also the dose depositions of different X-ray energies in spore were discussed. At the same time, the spores were irradiated by gamma rays from 60Co and relative biological effects were compared with those produced by soft X-rays. The results showed that soft X-rays near K-shell edges of O element had higher ability of radiation damage than that of X-rays near K-shell edges of C and N elements as compared with one another. But they all had higher killing abilities per unit dose than that of gamma rays from 60Co. The relative biological effects (RBEs), the comparison of dose to gamma rays at 10% survival level, of the three soft X-rays were 1.65, 1.73 and 1.91, respectively.

UV effects on photosynthesis and DNA in propagules of three Antarctic seaweeds (Adenocystis utricularis, Monostroma hariotii and Porphyra endiviifolium)

Ozone depletion is highest during spring and summer in Antarctica, coinciding with the seasonal reproduction of most macroalgae. Propagules are the life-stage of an alga most susceptible to environmental perturbations therefore, reproductive cells of three intertidal macroalgal species Adenocystis utricularis (Bory) Skottsberg, Monostroma hariotii Gain, and Porphyra endiviifolium (A and E Gepp) Chamberlain were exposed to photosynthetically active radiation (PAR), PAR + UV-A and PAR + UV-A + UV-B radiation in the laboratory. During 1, 2, 4, and 8 h of exposure and after 48 h of recovery, photosynthetic efficiency, and DNA damage were determined. Saturation irradiance of freshly released propagules varied between 33 and 83 mumol photons m(-2) s(-1) with lowest values in P. endiviifolium and highest values in M. hariotii. Exposure to 22 mumol photons m(-2) s(-1 )PAR significantly reduced photosynthetic efficiency in P. endiviifolium and M. hariotii, but not in A. utricularis. UV radiation (UVR) further decreased the photosynthetic efficiency in all species but all propagules recovered completely after 48 h. DNA damage was minimal or not existing. Repeated exposure of A. utricularis spores to 4 h of UVR daily did not show any acclimation of photosynthesis to UVR but fully recovered after 20 h. UVR effects on photosynthesis are shown to be species-specific. Among the tested species, A. utricularis propagules were the most light adapted. Propagules obviously possess good repair and protective mechanisms. Our study indicates that the applied UV dose has no long-lasting negative effects on the propagules, a precondition for the ecological success of macroalgal species in the intertidal.

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.

Negative phototropic response of rhizoid cells in the fern Adiantum capillus-veneris

In general, phototropic responses in land plants are induced by blue light and mediated by blue light receptor phototropins. In many cryptogam plants including the fern Adiantum capillus-veneris, however, red as well as blue light effectively induces a positive phototropic response in protonemal cells. In A. capillus-veneris, the red light effect on the tropistic response is mediated by phytochrome 3 (phy3), a chimeric photoreceptor of phytochrome and full-length phototropin. Here, we report red and blue light-induced negative phototropism in A. capillus-veneris rhizoid cells. Mutants deficient for phy3 lacked red light-induced negative phototropism, indicating that under red light, phy3 mediates negative phototropism in rhizoid cells, contrasting with its role in regulating positive phototropism in protonemal cells. Mutants for phy3 were also partially deficient in rhizoid blue light-induced negative phototropism, suggesting that phy3, in conjunction with phototropins, redundantly mediates the blue light response.

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 micromol 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.

Acyl-homoserine lactones modulate the settlement rate of zoospores of the marine alga Ulva intestinalis via a novel chemokinetic mechanism

Bacteria utilize quorum sensing to regulate the expression of cell density-dependant phenotypes such as biofilm formation and virulence. Zoospores of the marine alga Ulva intestinalis exploit the acyl-homoserine lactone (AHL) quorum sensing system to identify bacterial biofilms for preferential settlement. Here, we demonstrate that AHLs act as strong chemoattractants for Ulva zoospores. Chemoattraction does not involve a chemotactic orientation towards the AHL source. Instead, it occurs through a chemokinesis in which zoospore swimming speed is rapidly decreased in the presence of AHLs. The chemoresponse to AHLs was dependant on the nature of the acyl side chain, with N-(3-oxododecanoyl)-homoserine lactone (30-C12-HSL) being the most effective signal molecule. Mean zoospore swimming speed decreased more rapidly over wild-type biofilms of the marine bacteria Vibrio anguillarum relative to biofilms of the vanM mutant, in which AHL synthesis is disrupted. These data implicate a role for AHL-mediated chemokinesis in the location and preferential settlement of Ulva zoospores on marine bacterial assemblages. Exposure to AHLs did not inhibit the negative phototaxis of Ulva zoospores, indicating that chemoattraction to bacterial biofilms does not preclude the response to a light stimulus in substrate location.

Neutron flow exposure as a test for survival of Artemia salina spores

Live and heat-inactivated Artemia salina spores (samples with the same mass and filling density) were exposed to a flow of thermal neutrons from a (252)Cf radioactive source at an equivalent dose power of about 1 microSv/h. Irradiation led to a 4-fold acceleration of nauplius development and to modification of the element profiles of live spores. The difference between absorption/diffusion of thermal neutrons by live and dead spores was revealed.

Zoosporangia survival, dehiscence and zoospore formation, and motility in the green alga Rhizoclonium hieroglyphicum as affected by different factors

Urea at 200 ppm (probably serving as a nitrogen source), liquid Bold's basal medium at pH 7.5, temperature of about 22 degrees C and light intensity of about 40 micromol m(-2) s(-1) for 16 h a day induced rapid and/or abundant zoospores formation and zoosporangia dehiscence and favored zoospore liberation, speed and motility time period in the green alga Rhizoclonium hieroglyphicum. However, factors such as water stress (2 and 4 % agarized media, liquid media with 0.2-0.4 mol/L NaCl, 5-60 min blot-dryness of filaments), pH extremes of liquid media (at < or =6.5 and > or =9.5), temperature shock in liquid media (5 and 35 degrees C for > or =5 min), UV exposure (0.96-3.84 kJ/m2), lack of all nutrients from liquid medium (double distilled water), darkness, and presence of "heavy" metals (1-25 ppm Cu, Fe, Zn, Hg, Ni, Co) or organic substances (200-600 ppm captan or DDT, 800 and 1000 ppm 2,4-D, 50 and 400 ppm indole-3-acetic acid (3-IAA), 1000 and 2000 ppm urea, 100 and 200 ppm thiourea) in liquid media decreased and/or delayed at various levels either zoosporangia survival, zoospore formation or zoosporangia dehiscence and/or the rate of zoospore liberation from zoosporangia, zoospore speed and time period of motility in the media or totally inhibited all these processes. 3-IAA at 50 and 400 ppm induced zoosporangial papilla to grow into a tube-like projection of about 30-120 microm in length. Zoosporangial dehiscence rather than zoospore formation or zoosporangia survival, and zoospore motility period rather than zoospore speed are probably more sensitive to various adverse environmental factors. The rate of zoospores liberation from zoosporangium (possibly related directly to some extent on the zoospore number inside) is probably independent of zoospore speed in the medium.

An integrated control of Pythium root rot of greenhouse tomato

Pythium root rot caused by Pythium aphanidermatum is one of the most important diseases of greenhouse tomatoes. Hydroponic culture exacerbates the problem. Both nutrient film technique (NFT) and recirculating growing systems pose a challenge in the control of this disease, because the pathogen, especially the zoospores, can spread easily in the recirculating solution to the whole growing system. Fortunately, hydroponically grown plants are easier to manipulate than soil grown plants, proper manipulation of root environments can lead to excellent disease control. This paper reports the development of an effective integrated control measure for pythium root rot of tomato by integrating pH, bioagent, and ultra-violet irradiation in a specific manner. This integrated control consists of three operations: a) before transplanting, the UV system is connected to sterilize the recirculating solution using 100 mJcm-2; b) after transplanting, the nutrient solution is delivered at pH 5.0 regime for five weeks followed by adjusting pH to 5.8 to 6.2 regime for one week; and c) bacterial bioagent, such as Pseudomonas is introduced into the root zone at 100 mL per plant at 10(8) bacteria mL-1 or added to the nutrient solution to arrive at 10(6) bacteria mL-1 in the solution. This report also discusses the advantages and limitations of this measure in the control of pythium root rot.

[Reactive oxygen forms and luminescence of intact microspore cells]

The participation of reactive oxygen species (ROS) in luminescence (chemiluminescence and autofluorescence induced by ultraviolet light of 360-380 nm) was analyzed. Microspores, the pollen (male gametophyte) of Hippeastrum hybridum, Philadelphus grandiflorus, and Betula verrucosa and vegetative microspores of the spore-breeding plant Equisetum arvense served as models. It was found that the addition of the chemiluminescent probe lucigenin, which luminesces in the presence of superoxide anionradicals, leads to intensive chemiluminescence of microspores. No emission was observed in the absence of lucigenin and in the presence of the dye luminol as a chemiluminescent probe. The emission decreased significantly if superoxide dismutase, an enzyme of the superoxide anionradical dismutation during which this radical disappeared, was added before the dye addition. The autofluorescence intensity of microspores decreased in the presence of both superoxide dismutase and peroxidase, an enzyme destroying hydrogen peroxide and organic peroxides. The most significant effect was noted after the addition of peroxidase, which indicates a greater contribution of peroxides to this type of emission. The fumigation with ozone, which increases the amount of ROS on the cell surface, enhanced the intensity of the chemiluminescence of microspores with lucigenin, but decreased the intensity of the autofluorescence of microspores. Exogenous peroxides (hydrogen peroxide and tert-butylhydroperoxide) stimulated the autofluorescence of pollen and vegetative spores in a concentration-dependent manner. It was shown that the formation of ROS contributes to the luminescence of plant microspores, which reflects their functional state.

The results of biological studies made on board the Voskhod and Voskhod 2 spaceships

The biological effects of flight and outer space factors were studied on biological specimens of various organization, viz. spiderwort microspores, dry seeds of the pine tree, wheat, onion and of other higher plants as well as on lysogenic bacteria and wine flies. Furthermore, lysogenic bacteria were studied for the effectiveness of a number of well known ray-proof substances (such as mercaptopropylamine, 5-methoxytriptamine, etc.). The specimens were secured in special containers both on board the spaceships and in the hip pockets of the astronaut Leonov's spacesuit. Biological effectiveness of the factors was evaluated by means of cytogenic, genetic and microbiological procedures. The analysis of the data obtained has shown that under the impact of the complex of flight and outer space factors, including ionizing radiation, both qualitative and quantitative changes occurred in the hereditary structures of some of the specimens, viz.: wheat seeds, spiderwort microspores and lysogenic bacteria. These changes were similar to the effects recorded in the flights of Vostok-2, 3, 6. As compared to the controls, an enlargement was found in the cells of wheat sprout radicles, accompanied by chromosome rearrangements (N. L. Deloney et al.). Increased phage production by lysogenic bacteria (N. N. Zhukov-Verezhnikov, N. I. Rybakov et al.) and impairment of the mitosis mechanism in the spiderwort macrospores were demonstrated (N. L. Deloney, etc.). Higher frequency of dominant lethals and more frequent than normal chromosome indivergence in the wine flies were recorded. Quantitatively, the recorded drifts were insignificant (as was the case with the 'Vostok' spaceships' flights). Of interest are the results of the experiments on spiderwort microspores carried out with B. B. Yegorov's participation. The data obtained show that 1) during the mitosis stage spiderwort microspores show differing sensitivity to the space flight factors, and that 2) the mitosis stages support the previous hypothesis that impairment of the mitosis mechanism is due to the state of weightlessness, while chromosome rearrangements are chiefly induced by the effects of the complex of factors related to the take-off and touch-down stages of the flight. (N. L. Deloney et al.). The analysis of beta-mercaptopropylamine and 5-methoxytriptamine tests indicates that these substances significantly reduce the phage producing activities of the lysogenic bacteria not only blocking the induced phage production but reducing the amount of spontaneous phage production as well (N. N. Zhukov-Verezhnikov, N. I. Rybakov et al.). Thus, the results of biological experiments on various specimens with differing degrees of radiosensitivity agree well among themselves and are consistent with the data on the dosage of space radiation.

Differentiation of Dictyostelium discoideum vegetative cells into spores during Earth orbit in space

We reported previously that emerged amoebae of Dictyostelium (D.) discoideum grew, aggregated and differentiated to fruiting bodies with normal morphology in space. Here, we investigated the effects of space radiation and/or microgravity on the number, viability, kinetics of germination, growth rate and mutation frequency of spores formed in space in a radiation-sensitive strain, gamma s13, and the parental strain, NC4. In gamma s13, there were hardly spores in the fruiting bodies formed in space. In NC4, we found a decrease in the number of spores, a delay in germination of the spores and delayed start of cell growth of the spores formed in space when compared to the ground control. However, the mutation frequency of the NC4 spores formed in space was similar to that of the ground control. We conclude that the depression of spore formation might be induced by microgravity and/or space radiation through the depression of some stage(s) of DNA repair during cell differentiation in the slime mold.

A data analysis of the irradiation parameter D10 for bacteria and spores under various conditions

This paper provides approximate estimates for the irradiation parameter D10 to globally predict the effectiveness of any irradiation process. D10 is often reported to depend on many specific factors, implying that D10 cannot be estimated without exact knowledge of all factors involved. For specific questions these data can of course be useful but only if the conditions reported exactly match the specific question. Alternatively, this study determined the most relevant factors influencing D10, by quantitatively analyzing data from many references. The best first step appeared to be a classification of the data into vegetative bacteria and spores. As expected, spores were found to have significantly higher D10 values (average 2.48 kGy) than vegetative bacteria (average 0.762 kGy). Further analyses of the vegetative bacteria confirmed the expected extreme irradiation resistance of nonpathogenic Deinococcus radiodurans (average 10.4 kGy). Furthermore the analysis identified Enterococcus faecium, Alcaligenes spp., and several members of the Moraxella-Acinetobacter group as having very high resistance at very low temperatures (average 3.65 kGy). After exclusion of high- and low-resistance spores and some specific conditions showing relevant high or low D10 values, the average for spores was estimated to be 2.11 kGy. For vegetative bacteria this average was estimated to be 0.420 kGy. These approximate estimates are not definite, as they depend on the data used in the analyses. It is expected that inclusion of more data will not change the estimates to a great extent. The approximate estimates are therefore useful tools in designing and evaluating irradiation processes.

Monitoring of solar-UV exposure among schoolchildren in five Japanese cities using spore dosimeter and UV-coloring labels

To monitor personal exposure to biologically effective solar-UV radiation, Bacillus subtilis spores on a membrane filter and UV-coloring labels were incorporated into a monitoring badge. The samples were covered with one of three types of filter sheet, dependent on the season, to reduce the amounts of exposure to measurable levels. Five fifth- or sixth-grade classes of primary schools, each consisting of 30-40 children, were chosen in northern (Sapporo), central (Tsukuba and Tokyo), and southern (Miyazaki and Naha) cities in Japan. In all four season, each child wore a badge on an upper arm for the entire waking hours, changing it daily, for a week. Upon collection of the badges, the survival of spores and the extent of coloration of the label were determined. The results were used to estimate the amount of daily exposure to biologically effective UV radiation, expressed as the value of spore inactivation dose. Unexpectedly, the average amounts of exposure were not directly correlated with the outdoor UV irradiance: in the two southern cities, despite high outdoor irradiance from spring to autumn, the average amounts of exposure were less than 3.1% of the average irradiance. Highly concentrated exposures occurred in two central cities on three days when extensive outdoor exercise took place. These results contradict the simple notion that children's exposure is in proportion to the outdoor UV irradiance, and support the view that the extent of solar-UV exposure is primarily determined by life-style rather than living location.

Effect of gamma irradiation on unsporulated and sporulated Toxoplasma gondii oocysts

The effect of 137Cs irradiation on unsporulated and sporulated Toxoplasma gondii oocysts was investigated as a model system for sterilisation of fruit contaminated with other coccidia such as Cyclospora or Cryptosporidium. Unsporulated oocysts irradiated at > or = 0.4 to 0.8 kGy sporulated but were not infective to mice. Sporulated oocysts irradiated at > or = 0.4 kGy were able to excyst, and sporozoites were infective but not capable of inducing a viable infection in mice. Toxoplasma gondii was detected in histologic sections of mice up to 5 days but not at 7 days after feeding oocysts irradiated at 0.5 kGy. Transmission electron microscopy revealed that sporozoites from irradiated oocysts penetrated enterocytes and all cells in the lamina propria except for red blood cells. Sporozoites appeared normal ultrastructurally and formed a typical parasitophorous vacuole containing a well-developed tubulovesicular membrane network. Raspberries inoculated with sporulated T. gondii oocysts were rendered innocuous after irradiation at 0.4 kGy. Results indicate that irradiation at 0.5 kGy is effective in "killing" coccidian oocysts on fruits and vegetables.

Mutation frequency of Dictyostelium discoideum spores exposed to the space environment

Two strains of cellular slime mold Dictyostelium discoideum, a radiosensitive mutant and the parental wild-type strain, were used to investigate the effects of cosmic radiation on viability and mutation frequency at the spore stage for about 9 days in Space Shuttle of NASA. We measured little effect of space environment on viability and cell growth in the both strains as compared to ground controls. The mutation frequency of the flown spores were similar to that of ground control. These results suggest that there could be no effect of cosmic radiation, containing high linear energy transfer radiation at about 0.9 mSv/day as detected by real-time radiation monitoring device on the induction of mutation at the spore stage.

Caffeine-resistance in S. pombe: mutations in three novel caf genes increase caffeine tolerance and affect radiation sensitivity, fertility, and cell cycle

Caffeine is a well known base analogue and is cytotoxic to both animal and yeast cells. There are two possible mechanisms by which yeast cells tolerate caffeine concentrations higher than normal, by mutation or by physiological adaptation. We have isolated novel caffeine-resistant mutants of S. pombe which define three distinct genes caf2, caf3 and caf4. These mutants achieved a level of caffeine resistance which is presumed to represent the upper limit attainable by mutation. The caf2-caf4 mutations, as well as the previously identified caf1 mutation, confer UV-sensitivity, caffeine-resistant UV repair, impaired fertility and sporulation, as well as a lengthened cell cycle. They are partially dominant for caffeine resistance and recessive for UV sensitivity. Some auxotrophic caf3-89 double mutants show drastically decreased caffeine resistance. The caf4 mutant is more resistant to gamma-radiation than wild-type cells and shows pH-sensitive growth. As each caf mutation can, individually, confer maximum caffeine resistance to the cells, all four genes are expected to operate in the same pathway. This pathway might also be responsible for the physiological adaptation since adaptation is lost in caf1-caf4 mutants.

[The results of the cytogenetic monitoring of the species of angiosperm plants growing in the area of the radionuclide contamination after the accident at the Chernobyl Atomic Electric Power Station]

Results of investigations of meiosis in microsporogenesis, sporads and pollen grains as well as mitosis in root meristematic cells in 94 species of angiosperms (from 28 families) growing in different ecological conditions in the zone with higher radionuclide pollution after the Ch.NPS accident are present. The low percentage (0.5-2.0%) of anomalies on investigating parameters has been revealed in the majority of species, only in certain species (8-10%) the correlation between an increase of the number of anomalies and an increase of the gamma-radiation level was shown. The data obtained make evident the resistance of the seed reproduction system in higher plants to chronic irradiation by the low doses of ionising radiation.

Microdosimetric considerations of effects of heavy ions on E. coli K-12 mutants

The inactivation cross sections of E. coli K-12 recombination-deficient mutants, JC1553 (recA) and AB2470 (recB), for several MeV/u alpha-particles and N ions have been successfully analyzed by Katz's target theory in which radiosensitivity parameter E0 is assumed to be LET independent and equal to D37 for gamma-rays. For E. coli K-12 wild type, AB1157 (rec+, uvr+), however, it is impossible to interpret the inactivation cross section data by an LET-independent E0-value. In the latter case, as in the case of B. subtilis spore, it is necessary to assume that the radiosensitivity of the target for the core of a heavy ion is higher than that for delta-electrons. As well as Waligorski, Hamm and Katz's dose, the dose around the trajectory of an ion based on Tabata and Ito's energy deposition algorithm for electrons has been used in the course of analysis.

The effect of ultraviolet radiation on the germination of Nosema algerae Vávra and Undeen (Microsporida: Nosematidae) spores

Spores of Nosema algerae Vávra and Undeen were subjected to various dosages of 254 nm ultraviolet radiation (UV). Very high dosages of UV were required to block germination. Germination was normal immediately after UV dosages of 0.2 to 1.0 J/cm2, followed by a delayed effect in which both percentage germination and the intrasporal concentration of trehalose decreased with time after UV exposure. Although a few spores were germinated, most of them were inactivated (rendered temporarily unable to germinate) by exposure to UV of 1.1 J/cm2. Ultraviolet radiation between 1.1 and 3.4 J/cm2 stimulated spores to germinate. However, spores were completely unable to germinate immediately after exposure to dosages above 3.8 J/cm2. Ammonia had little effect on stimulation by UV but was inhibitory to germination after stimulation had occurred. These results demonstrate that UV behaves like a germination stimulus and are discussed in terms of the hypothesis that germination is initiated by the breakdown of barriers between trehalose and trehalase.

Calcium requirement of phytochrome-mediated fern-spore germination: no direct phytochrome-calcium interaction in the phytochrome-initiated transduction chain

Phytochrome-mediated germination of fern spores of Dryopteris paleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h of imbibition. For its realization external Ca2+ was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10(-4) M. At concentrations > or = 10(-1) M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La3+, an antagonist of Ca2+. From these results it is concluded that Ca2+ influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca2+ the R-stimulated system remained capable of responding to Ca2+, added as late as 40 h after R. Moreover, Ca2+ was effective even if added after the active form of phytochrome, Pfr, had been abolished by far-red (FR) 24 h after R. Thus, the primary effect of Pfr, that initiates the transduction chain, does not require calcium. "Coupling" of Pfr to subsequent dark reactions has been investigated by R-FR irradiations with various dark intervals. The resulting "escape kinetics" were characterized by a lag phase (6 h) and half-maximal escape from FR reversibility (19 h). These kinetics were not significantly changed by the presence or absence of calcium. Thus, direct interaction of Pfr and calcium is not a step in the transduction chain initiated by the active form of phytochrome.

Early quantitative method for measuring germination in non-green spores of Dryopteris paleacea using an epifluorescence-microscope technique

A method is described to determine germination by blue-light excited red fluorescence in the positively photoblastic spores of Dryopteris paleacea Sw. This fluorescence is due to chlorophyll as evidenced from 1) a fluorescence-emission spectrum in vivo, where a bright fluorescence around 675 nm is obtained only in red light (R)-irradiated spores and 2) in vitro measurements with acetone extracts prepared from homogenized spores. Significant amounts of chlorophyll can be found only in R-treated spores; this chlorophyll exhibits an emission band around 668 nm, when irradiated with 430 nm light at 21 degrees C. Compared to other criteria for germination, such as swelling of the cell, coat splitting, greening, and rhizoid formation, which require longer periods after induction for their expression, chlorophyll fluorescence can be used to quantify germination after two days. This result is confirmed by fluence-response curves for R-induced spore germination; the same relationship between applied R and germination is obtained by the evaluation with the epifluorescence method 2 days after the light treatment as compared with the evaluation with bright-field microscopy 5 days after the inducing R. Using this technique we show for the first time that Ca2+ contributes to the signal-transduction chain in phytochrome-mediated chlorophyll synthesis in spores of Dryopteris paleacea.

Breaking survival curves and oxygen removal times in irradiated bacterial spores

Although there are ambiguities about these results and their interpretations, this unambiguous experimental observation was made: the two kinds of experiments designed to measure deoxygenation times did not give the same answer, for a given N2 flushing rate, unless t-butanol was present. The addition of t-butanol caused large changes in the positions of the survival curve breakpoints, but only small changes in the 'times to anoxia' in the pre-irradiation glushing experiments. Although careful additional work is needed, these initial results suggest that in the spore, the survival curve breakpoint probably does not represent the dose at which anoxia is reached unless t-butanol is present.

Sterilization of bacteria by means of microwave heating

Despite the simplicity and convenience of microwave heating, descriptions in the current literature of attempts to provide a thorough sterilization process have not been encouraging nor has any manufacturer of sterilization equipment introduced such a device to the market. Trials conducted at Providence Hospital using a commercial microwave oven operating at 2450 MHz resulted in a satisfactory sterilization process, that is, the destruction of heat-resisting spore forms (B. stearothermophilus), provided that the materials undergoing sterilization were placed in sealed containers with sufficient water present to provide steam during the heating process. Suggestions are made for further investigation involving the microwave spectrum of the molecule of dipicolinic acid as well as the possibilities of practical applications which could result in reducing hospital costs.

The effects of heat and cobalt-60 gamma-radiation on excystation of the rat coccidium, Eimeria nieschulzi Dieben, 1924

Sporulated oocysts of Eimeria nieschulzi Dieben, a rat coccidium, were exposed for 1 hr to Cobalt-60 gamma-radiation (15, 30, or 60k-rads), to heat (35, 40, or 45 C) , or to both concurrently (15, 30, OR 60 K-RADS AT 35 C) to compared the excystation capabilities of treated vs nontreated parasites. Intact treated oocysts appeared structurally unaltered when viewed with the light microscope. Excystation of sporozoites occured in all treated groups when their sporocysts were exposed to a trypsin-sodium taurocholate (TST) fluid, but after 150 min in TST the excystation rate was significantly lower than in nontreated sporocysts. Sporozoites which excysted from treated sporocysts were abnormal both in the excystation process and in their form and movement once outside the sporocysts.

Photoreactivation of UV-irradiated blue-green algae and algal virus LPP-1

Ultraviolet (UV) sensitivity and photoreactivation of blue-green algae Cylindrospermum sp., Plectonema boryanum, spores of Fischerella muscicola and algal virus (cyanophage) LPP-1 were studied. The survival value after UV irradiation of filaments of Cylindrospermum sp. and Virus LPP-1 showed exponential trend and these were comparatively sensitive towards UV than F.muscicola and P.boryanum. Photoreactivation of UV-induced damage occurred in black, blue, green, yellow, red and white light in Cylindrospermum sp., however only black, blue and white light were capable of photorepair of UV-induced damage in P.boryanum, spores of F.muscicola and virus LPP-1 in infected host alga. Pre-exposure to yellow and black light did not show photoprotection. The non-heterocystous and nitrogen fixation-less mutants of Cylindrospermum sp. were not induced by UV and their spontaneous mutation frequency was not affected after photoreactivation. The short trichome mutants of P.boryanum were more resistant towards UV. The occurrence of photoreactivation of UV-induced killing wide range of light in Cylindrospermum sp. is the first report in organisms.

Chromosomes and cellular radiosensitivity. IV. A new radiotaxon represented by the ferns

Survival curves were constructed and D0 values determined after X-irradiation of single-celled germinating spores of 14 species of ferns, which had a wide variation in interphase chromosome and nuclear volumes and in DNA content per chromosome and per nucleus. A good fit to a line of slope equal to -1 is given on a log-log plot relating D0 to interphase chromosome volume. In a previous publication (Sparrow, Underbrink and Sparrow 1967), ferns fell into radiotaxon VIII, but the new data suggest that they should be assigned to a new group (VIIa) falling midway between radiotaxa VII and VIII. The calculated energy absorption per chromosome at D0 for VIIa is also intermediate between those for VII and VIII. If the value of this parameter is set at 1 for radiotaxon V, that for VIIa is approximately 32 times greater and the radiotaxa V, VI, VII and VIIa form a series 1 : 4 : 14 : 32. The new results indicate that radiotaxon VIII may have to be abandoned unless some other radiobiologically unexplored group (e.g. algae) fills the gap.

Effects of ionizing radiation on dried spores of Osmunda regalis III. 35 GHz e.s.r. study

The use of 35 GHz microwave frequency has greatly simplified the separation of overlapping signals in dried irradiated fern spores. While in general confirming the conclusions previously drawn from X-band spectra, the use of Q-band has clarified several assignments of radical groups and allowed the recognition of additional radical groups or sub-groups.