Ultraviolet Tolerance Research Articles

The copepod Tigriopus brevicornis (O. F. Müller, 1776) gains UV protection by feeding on UV-acclimated algae

Primary producers exposed to ultraviolet (UV) radiation accumulate a range of metabolites as part of their UV-acclimation response. These metabolites play an important role in plant and algal UV protection. We investigated whether UV protection is transferred to consumers that feed on UV-acclimated algal biomass and showed that the copepod Tigriopus brevicornis (O. F. Muller, 1776) displays increased UV tolerance when fed on UV-acclimated Enteromorpha sp. (Clorophyta). We conclude that dietary transfer of metabolites produced in UV-acclimated biomass underlies the increased UV protection of the copepods. The data emphasise the complexity of the effects of UV radiation on the rock pool ecosystem.

Effects of increased seawater temperature on UV tolerance of Antarctic marine macroalgae

Cold-adapted Antarctic marine macroalgae have different physiological strategies to tolerate the ultra- violet (UV) radiation at low seawater temperatures around 0 °C. The warming of Antarctica's coasts driven by global climate change may alter the physiology such to influence their UV tolerance. This study examined the interactive effects of different seawater temperatures (2 vs. 7 °C) and UV radiation on the physiological performance (primary photochemistry: F v /F m , soluble and insoluble phlorotan- nins, radical scavenging capacity) of seven macroalgae, which are dominant in Antarctic coastal ecosystems. Four brown and three red macroalgae, collected from Fildes Bay (King George Island, South Shetland Islands) in January/ February, were exposed to 6 h of UV/temperature stress, followed by a 16-h recovery. The brown macroalgae Des- marestia menziesii and Ascoseira mirabilis showed the highest UV tolerance at 2 °C, followed by Desmarestia anceps, and the rhodophytes Iridaea cordata, Tremato- carpus antarcticus, and Palmaria decipiens. Himanto- thallus grandifolius (Phaeophyceae) was sensitive to UV radiation at 2 °C. At 7 °C, UV tolerance was improved in UV-sensitive macroalgae probably due to a more efficient damage repair of the photosynthetic apparatus. Tempera- ture, however, did not modulate UV tolerance in D. anceps,

Interactions between Arabidopsis DNA repair genes UVH6, DDB1A, and DDB2 during abiotic stress tolerance and floral development

Plants must protect themselves from a spectrum of abiotic stresses. For example, the sun is a source of heat, intense light, and DNA-damaging ultraviolet (UV) rays. Damaged DNA binding protein 1A (DDB1A), DDB2, and UV hypersensitive 6 (UVH6)/XPD are all involved in the repair of UV-damaged DNA – DDB1A and DDB2 in the initial damage recognition stage, while the UVH6/XPD helicase unwinds the damaged strand. We find that, as predicted, Arabidopsis ddb1a and ddb2 mutants do not affect uvh6/xpd UV tolerance. In addition, uvh6 is heat sensitive, and ddb1a and ddb2 weakly enhance this trait. The uvh6 ddb1a and uvh6 ddb2 double mutants also exhibit sensitivity to oxidative stress, suggesting a role for DDB1 complexes in heat and oxidative stress tolerance. Finally, we describe a new uvh6 phenotype, the low penetrance production of flowers with five petals and five sepals. ddb1a and ddb2 suppress this phenotype in uvh6 mutants. Interestingly, heat treatment also induces five-petalled flowers in the ddb1a and ddb2 single mutants. Thus UVH6, DDB1A, and DDB2 all contribute to UV tolerance, heat tolerance and floral patterning.

An in vitro method for increasing UV-tolerance in a strain of Helicoverpa armigera (Lepidoptera: Noctuidae) nucleopolyhedrovirus

A method for increasing tolerance to ultraviolet (UV) radiation in a strain of nucleopolyhedrovirus of cotton bollworm, Helicoverpa armigera (Hübner) (HearNPV) using a solar simulator is described. The Coimbatore isolate (CBE I) of HearNPV was subjected to a five-step sequence of selection to increase its UV tolerance. Each step consisted of irradiation of wet deposits of the virus to near UV (at energy level of 300W/m2), bioassay against second instar H. armigera larvae and propagation in early fifth instar larvae. Selection steps carried out at 15, 30, 60 and 90 minutes of exposure revealed that the continuous exposure of HearNPV-CBE I at low doses of UV irradiation (270–540 KJ/m2) did not significantly affect the virus activity as measured by its biological activity against second instar larvae. Selection at higher doses (1620 KJ/m2) led to loss of viral activity in the first two exposure cycles; however, there was retention of virulence coupled with increased tolerance to UV doses from third cycle onwards. Further, studies on the persistence of UV tolerant strain of HearNPV-CBE I in comparison with original strain showed that the tolerant strain had more persistence even after 7 days of weathering both under exposed (18% original activity remaining) and shaded (26% original activity remaining) condition on potted cotton plant.

Genetic Interactions Between ArabidopsisDET1andUVH6During Development and Abiotic Stress Response

Plants must adapt to a variety of abiotic inputs, including visible light, ultraviolet (UV) light, and heat. In Arabidopsis thaliana, DE-ETIOLATED 1 (DET1) plays a role in visible light signaling, UV tolerance, and development. UV-HYPERSENSITIVE 6 (UVH6) mutants are UV and heat sensitive, as well as dwarf and pale, like det1. In this study, we examine the genetic interactions between these two genes. In dark-grown seedlings, uvh6 exhibits a weak de-etiolated phenotype but does not affect the stronger de-etiolated phenotype of det1. In the light, det1 is epistatic to uvh6 with regard to chlorophyll level, but their effect on all size parameters is additive and therefore independent. With regard to UV tolerance, det1 UV resistance is epistatic to uvh6 UV sensitivity. In heat stress experiments, det1 enhances heat-induced tissue damage in the uvh6 background but suppresses heat-induced growth inhibition. Thus, det1 acts epistatically to uvh6 with respect to de-etiolation, chlorophyll level, UV tolerance, and heat-induced growth inhibition, whereas det1 and uvh6 act additively to regulate plant size and heat-induced cell death. These data provide insight into interplay between light and heat signaling.

Comparison of UV-B tolerance between wild and hatchery-reared juveniles of red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli)

The amount of ultraviolet (UV)-B radiation reaching the sea surface has increased due to ozone depletion. Several laboratory studies have highlighted the negative impacts of UV radiation on fish using hatchery-reared specimens. However, potential differences in UV tolerance between wild and hatchery-reared fish have been given little consideration. Wild and reared juveniles of red sea bream and black sea bream were exposed to one of four different UV-B radiation levels (1.8; 1.1; 0.4; 0 W/m2) for 4 h. Survival rate was measured every 2 h for a period of 24 h (red sea bream) or 48 h (black sea bream) following exposure. Wild and reared juvenile red sea bream were characterized by similar survival rate, with survival declining to almost 0 % 24 h after exposure at the 1.1 and 1.8 W/m2 levels. In black sea bream, wild individuals showed significantly higher survival than reared fish in levels 1.1 and 1.8 W/m2. Melanophore density was also measured since melanin absorbs UV radiation. Wild black sea bream showed higher melanophore density compared to reared individuals, while no such difference was observed in red sea bream. We conclude that wild black sea bream juveniles acquire higher UV tolerance partly by increasing melanophore density through exposure to UV radiation. Our results indicate that the predicted impacts of UV radiation on fish populations solely based on experimentation with hatchery-reared specimens may be overestimated for some species.

A Rice Cytochrome P450OsCYP84AThat May Interact with the UV Tolerance Pathway

Cytochrome P450s are widespread in the plant kingdom. The functions of plant P450s are dispersed through many aspects of plant metabolisms, which are involved in the biosynthesis of defense compounds and protectants against ultraviolet rays, as well as metabolic pathways for the biosynthesis and/or degradation of fatty acids, hormones, and signaling molecules. We found a gene for rice P450, OsCYP84A, which was classified into CYP84A in the CYP71 clan. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that this gene was ubiquitously expressed without any temporal and spatial specificity under normal growth conditions, but its expression was inducibly and significantly increased by ultraviolet (UV)-B and UV-C irradiation. Rice transformants in which OsCYP84A expression was suppressed by the antisense gene showed apparent growth retardation with obvious symptoms of damage on the plant bodies under UV-B irradiation, although no phenotypic alteration occurred under normal growth conditions. These results suggest the existence of a novel UV-tolerance system involving OsCYP84A.

Protective and reactivating effect of the protein exometabolite on yeast cells inactivated by the ultraviolet irradiation

It has been shown that Saccharomyces cerevisiae, Kluyveromyces lactis, and Candida utilis strains produce the protein exometabolites, which has a protective and reactivating effect on the ultraviolet irradiated yeast cells. The protective effect of the preliminary ultraviolet irradiated (activated) protein exometabolite of all strains increased 2-3 times, though its reactivating activity did not change. Yarrowia lipolytica yeast cells, isolated from the areas with the high daily irradiation, and Endomyces magnusii, the obligate fungi parasites, were characterized by the highest ultraviolet tolerance in comparison with the other strains. However, they did not produce the exometabolites with the antistress effect. Luteococcus casei reactivating factor demonstrated protective and reactivating cross-action in relation to the ultraviolet irradiated S. cerevisiae, K. lactis, and C. utilis cells and were inactive in relation to Y. lipolytica and E. magnusii. Using killer and nonkiller S. cerevisiae strain, it has been shown that the peptide exometabolite accumulation was not associated with toxin production.

Cell wall‐bound ultraviolet‐screening compounds explain the high ultraviolet tolerance of the Antarctic moss, Ceratodon purpureus

* Studies of ultraviolet (UV) light-induced DNA damage in three Antarctic moss species have shown Ceratodon purpureus to be the most UV tolerant, despite containing lower concentrations of methanol-soluble UV-screening compounds than the co-occurring Bryum pseudotriquetrum. * In this study, alkali extraction of cell wall-bound phenolics, combined with methanol extraction of soluble phenolics, was used to determine whether cell wall-bound UV screens explain the greater UV tolerance of C. purpureus. * The combined pool of UV screens was similar in B. pseudotriquetrum and C. purpureus, but whilst B. pseudotriquetrum had almost equal concentrations of MeOH-soluble and alkali-extractable cell wall-bound UV-screening compounds, in C. purpureus the concentration of cell wall-bound screening compounds was six times higher than the concentration of MeOH-soluble UV screens. The Antarctic endemic Schistidium antarctici possessed half the combined pool of UV screens of the other species but, as in C. purpureus, these were predominantly cell wall bound. Confocal microscopy confirmed the localization of UV screens in each species. * Greater investment in cell wall-bound UV screens offers C. purpureus a more spatially uniform, and potentially more effective, UV screen. Schistidium antarctici has the lowest UV-screening potential, indicating that this species may be disadvantaged under continuing springtime ozone depletion. Cell wall compounds have not previously been quantified in bryophytes but may be an important component of the UV defences of lower plants.

62-kb Plasmids Harboring rulAB Homologues Confer UV-tolerance and Epiphytic Fitness to Pseudomonas syringae pv. syringae Mango Isolates

The presence of genetic determinants homologous to rulAB genes for ultraviolet (UV) radiation resistance was determined in a collection of Pseudomonas syringae pv. syringae strains isolated from mango. The potential role of these plasmids in UV tolerance and ecological fitness in the mango phyllosphere was also evaluated. Nearly all of the 62-kb plasmids present in the P. syringae pv. syringae strains hybridized with a rulAB probe, but these 62-kb plasmids showed differences in restriction patterns. In vitro assays of tolerance to UV radiation of P. syringae pv. syringae strains showed a higher survival of the strains harboring the 62-kb plasmids compared to strains lacking plasmids when exposed to UVC or UVA+B fractions. Similar results were observed when transconjugants harboring the 62-kb plasmid were tested. Survival assays were carried out under field conditions, and a higher survival of P. syringae pv. syringae strains harboring 62-kb plasmids under direct solar radiation on the adaxial surface of leaves was also observed. When the assays were carried out in shady areas or on the abaxial surface of leaves, survival time was comparable for all the assayed strains, whether or not they contained a 62-kb plasmid hybridizing to rulAB. Our results indicate that P. syringae pv. syringae strains harboring 62-kb plasmids show an increase in ecological fitness when colonizing the mango phyllosphere.

Temperature‐dependent ultraviolet responses in zooplankton: Implications of climate change

Climate warming and stratospheric ozone depletion increase temperature and ultraviolet (UV) in mid‐ to highlatitude ecosystems; however, little is known about the interactive effects of temperature and UV on organisms. We exposed Daphnia catawba, Leptodiaptomus minutus, and Asplanchna girodi to UV‐B at four different temperatures: 10, 15, 20, and 25°C. Elevated temperatures increased UV tolerance in D. catawba and L. minutus, species that depend heavily on photoenzymatic repair (PER), but decreased UV tolerance in A. girodi, a species that has less PER. Also, body size in Daphnia decreased with increasing UV dose. These results demonstrate that climate change can alter responses to UV through temperature‐mediated effects in aquatic ecosystems, and these effects can be species‐specific and dependent on PER ability.

Dauer juvenile longevity and stress tolerance in natural populations of entomopathogenic nematodes: is there a relationship?

Qualitative and quantitative genetic analysis of life span in experimental adult animals predicts that resistance to stress and longevity are positively correlated, but such studies on field populations of animals are rare. We tested this hypothesis using dauer juveniles of 15 natural populations of the entomopathogenic nematode, Heterorhabditis bacteriophora, collected from diverse localities. Dauer juvenile longevity at 25 °C in autoclaved tap water and tolerance to major environmental stresses including heat (survival at 40 °C for 2 h), ultraviolet (UV) radiation (original virulence remaining after exposure to 302 nm UV for 5 min), hypoxia (survival at approximately 0% dissolved O 2 at 25 °C for 96 h), and desiccation (survival in 25% glycerol at 25 °C for 72 h) differed significantly among populations. Intrinsic dauer juvenile longevity, defined as the number of weeks to 90% mortality (LT 90) estimated using probit analysis of nematode survival data at 25 °C varied between 6 and 16 weeks among populations. Longevity was most strongly correlated with heat followed by UV and hypoxia tolerance, respectively, but showed no correlation with desiccation tolerance. The strong positive correlation of longevity with heat tolerance was further confirmed through principal components analysis which showed almost identical variance for heat and longevity. Among the stress factors, only UV tolerance was positively correlated with heat and hypoxia tolerance. Differences in longevity and stress tolerance in nematode populations isolated from a single 200 m 2 grassland locality further support another hypothesis that population structure of heterorhabditid nematodes is highly fragmented, thus suggesting the existence of metapopulation dynamics.

Selection of a UV-tolerant Strain of the Gypsy Moth, Lymantria dispar (L.) (Lepidoptera: Lymantriidae) Nucleopolyhedrosis Virus 1

Gypsy moth nucleopolyhedrosis (NPV) was exposed to ultraviolet (UV) radiation for periods of 0 to 240 min. During the first five UV exposures (and passages) little change in UV tolerance occurred, as measured by biological activity of UV-exposed and nonexposed virus or by viral inactivation time. During the first five UV selection steps (UV no. 1–5), 22% of original viral activity remained after a 60-min exposure period. At the sixth exposure, however, 56% of original viral activity remained, i.e., a 2.5-fold increase in viral persistence. During the succeeding UV exposures, viral persistence remained stable. Although an increase in UV tolerance occurred during the sixth UV exposure (60 min), little change in activity of the selected virus occurred. Although no change in UV tolerance occurred during the 240-min UV exposures, activity increased during the sixth UV treatment, but was still 2.4-fold less than that of the nonirradiated, control NPV.