ultraviolet-B Tolerance Research Articles

Induced heat shock protein 70 confers biological tolerance in UV-B stress–adapted Myzus persicae (Hemiptera)

As an environmental stress factor, ultraviolet-B (UV-B) radiation directly affects insect growth, development, and reproduction. Heat shock protein 70s kDa (Hsp70s) plays an important role in the environmental adaptation of insects. To determine the role of MpHsp70s in the UV-B tolerance of Myzus persicae (Sulzer), we identified the complete complementary DNA sequences of seven MpHsp70s. They were found to be ubiquitously expressed during different developmental stages and were highly expressed in second-instar nymphs and wingless adults. The expression levels of the MpHsp70s were significantly upregulated when exposed to different durations of UV-B stress. Nanocarrier-mediated dsMpHsp70 suppressed the expression of the MpHsp70s and reduced the body length, weight, survival rate, and fecundity of M. persicae under UV-B exposure. When the combinational RNAi approach was adopted, the effects on the survival rate and fecundity were greater under UV-B stress, except for MpHsc70-4. These results suggest that MpHsp70s are essential for the resistance of M. persicae to UV-B stress.

OsRLCK160 contributes to flavonoid accumulation and UV-B tolerance by regulating OsbZIP48 in rice.

Plants produce specialized metabolites to adapt to the ever-changing environments. Flavonoids are antioxidants essential for growth, development, and breeding with increased stress resistance in crops. However, the mechanism of the involvement of flavonoids in ultraviolet-B (UV-B) stress in rice (Oryza sativa) is largely unknown. In this study, we cloned and functionally identified a receptor-like kinase (OsRLCK160) and a bZIP transcription factor (OsbZIP48) positively regulating flavonoid accumulation through metabolite-based genome-wide association study of the flavonoid content in rice. Meanwhile, OsRLCK160 interacted with and phosphorylated OsbZIP48 to regulate the flavonoid accumulation and participate in UV-B tolerance in rice. Our study indicates the importance of applying OsRLCK160 and OsbZIP48 to advance the fundamental understanding of stable rice production and breed UV-B-tolerant rice varieties, which may contribute to breeding high-yield rice varieties.

Exogenous Stilbenes Improved Tolerance of Arabidopsis thaliana to a Shock of Ultraviolet B Radiation.

Excessive ultraviolet B (UV-B) irradiation is one of the most serious threats leading to severe crop production losses. It is known that secondary metabolite biosynthesis plays an important role in plant defense and forms a protective shield against excessive UV-B irradiation. The contents of stilbenes and other plant phenolics are known to sharply increase after UV-B irradiation, but there is little direct evidence for the involvement of stilbenes and other plant phenolics in plant UV-B protection. This study showed that foliar application of trans-resveratrol (1 and 5 mM) and trans-piceid (5 mM) considerably increased tolerance to a shock of UV-B (10 min at 1800 µW cm−2 of irradiation intensity) of four-week-old Arabidopsis thaliana plants that are naturally incapable of stilbene production. Application of trans-resveratrol and trans-piceid increased the leaf survival rates by 1–2%. This stilbene-induced improvement in UV-B tolerance was higher than after foliar application of the stilbene precursors, p-coumaric and trans-cinnamic acids (only 1–3%), but less than that after treatment with octocrylene (19–24%), a widely used UV-B absorber. Plant treatment with trans-resveratrol increased expression of antioxidant and stress-inducible genes in A. thaliana plants and decreased expression of DNA repair genes. This study directly demonstrates an important positive role of stilbenes in plant tolerance to excessive UV-B irradiation, and offers a new approach for plant UV-B protection.

Hormonal Regulation in Different Varieties of Chenopodium quinoa Willd. Exposed to Short Acute UV-B Irradiation.

Increased ultraviolet-B (UV-B) due to global change can affect plant development and metabolism. Quinoa tolerates extreme conditions including high UV levels. However, the physiological mechanisms behind its abiotic stress tolerance are unclear, especially those related to UV-B. We previously demonstrated that 9.12 kJ m−2 d−1 may induce UV-B-specific signaling while 18.24 kJ m−2 d−1 promotes a UV-B-independent response. Here, we explored the effects of these UV-B doses on hormonal regulation linked to plant morphology and defense among diverse varieties. Changes in fluorescence parameters of photosystem II, flavonoids and hormones (indoleacetic acid (IAA), jasmonic acid (JA), abscisic acid (ABA) and salicylic acid (SA)) were surveyed under controlled conditions. Here, we showed that the sensitivity to short acute UV-B doses in varieties from different habitats is influenced by their parental lines and breeding time. UV-B sensitivity does not necessarily correlate with quinoa’s geographical distribution. The role of flavonoids in the UV-B response seems to be different depending on varieties. Moreover, we found that the extent of changes in JA and SA correlate with UV-B tolerance, while the increase of ABA was mainly related to UV-B stress.

UV-B promotes flavonoid synthesis in Ginkgo biloba leaves

Ultraviolet-B (UV-B) radiation is a natural source of environmental stress for plants. Notably, plants have evolved various protective mechanisms to combat the detrimental effects of UV-B exposure, including the production of UV-absorbing flavonoid compounds. Flavonoids are pharmaceutical active substances in Ginkgo biloba extracts. To clarify the molecular mechanisms underlying UV-B tolerance in G. biloba, we determined the flavonol composition and transcriptomic profile of G. biloba leaves after long-term UV-B exposure. Using high performance liquid chromatography and mass spectroscopy, we observed significant accumulation of flavonols in G. biloba leaves after UV-B exposure. In particular, isorhamnetin increased more than 16-fold. Combined transcriptome data with quantitative real-time polymerase chain reaction, structural genes involved in flavonoid synthesis were identified to be up-regulated expression after UV-B exposure. Particularly, the expression of FLS (Gb_22751) and F3’H (Gb_19792, Gb_04545, and Gb_11520) increased significantly, indicating their important roles in flavonoid synthesis response to long-term UV-B radiation. In addition, we found bZIP transcription factor (TF) Gb_12012 (encoding elongated hypocotyl-5, HY5) and MYB TFs (Gb_38090) were up-regulated, while MYB TFs (Gb_18153, Gb_40629, and Gb_05115) were down-regulated. We further identified two UV-B signalling molecules, including UVR8 (Gb_14008) and constitutive photomorphogenic-1 (COP1, Gb_15627) in G. biloba. These results suggest that the enhanced long-term UV-B radiation could promote flavonoid biosynthesis and metabolism, which is beneficial for the accumulation of medically active ingredients in G. biloba leaves.

Physiological function of photoreceptor UVR8 in UV-B tolerance in the liverwort Marchantia polymorpha.

The physiological importance of MpUVR8 in UV-B resistance and translocation in a UV-B-dependent manner from the cytosol into the nucleus is characterized in Marchantia polymorpha. UV RESISTANCE LOCUS 8 (UVR8) is an ultraviolet-B (UV-B) light receptor functioning for UV-B sensing and tolerance in Arabidopsis thaliana and other species. It is unclear whether UVR8 physiologically functions in UV-B-induced defense responses in Marchantia polymorpha, which belongs to the earliest diverging group of embryophyte lineages. Here, we demonstrate that UVR8 has a physiological function in UV-B tolerance and that there is a UVR8-dependent pathway involved. In addition, a UVR8-independent pathway is revealed. We examine the tissue-specific expression pattern of M. polymorpha UVR8 (MpUVR8), showing that it is highly expressed in the apical notch in thalli and gametangiophores, as well as in antheridial and archegonial heads. Furthermore, Mpuvr8KO plant transformants, in which the MpUVR8 locus was disrupted, were produced and analyzed to understand the physiological and molecular function of MpUVR8. Analysis using these plants indicates the important roles of MpUVR8 and MpUVR8-regulated genes, and of MpUVR8-independent pathways in UV-B tolerance. Subcellular localization of Citrine-fused MpUVR8 in M. polymorpha cells was also investigated. It was found to translocate from the cytosol into the nucleus in response to UV-B irradiation. Our findings indicate strong conservation of the physiological function of UVR8 and the molecular mechanisms for UVR8-dependent signal transduction through regulation of gene expression in embryophytes.

Lower levels of UV-B light trigger the adaptive responses by inducing plant antioxidant metabolism and flavonoid biosynthesis in Medicago sativa seedlings

Ultraviolet-B (UV-B) light, as an intrinsic part of sunlight, has more significant effects on plant growth and photomorphogenesis than other organisms due to plant's sessile growth pattern. In our studies, we have observed that alfalfa (Medicago sativa L.) seedlings are very sensitive to UV-B performance. Seedlings have grown better at lower levels of UV-B light (UV-B irradiation dosage <17.35 μW cm-2 day-1), and have higher UV-resistance. However, the higher levels of UV-B light (UV-B irradiation dosage >17.35 μW cm-2 day-1) has caused severe stress injuries to alfalfa seedlings, and seriously inhibited its growth and development. Chlorophyll biosynthesis and chlorophyll fluorescence have been suppressed under all different dosage of UV-B light conditions. Plant antioxidant enzymes were induced by lower levels of UV-B, but greatly inhibited under higher levels of UV-B light. The contents of flavonoid compounds significantly increased under UV-B light compared with controls, and that was more significant under lower levels of UV-B than higher levels of UV-B. Therefore, we have assumed that the significant induction of plant antioxidant capacity and flavonoid excessive accumulation play a central role in alfalfa UV-B tolerance to lower levels of UV-B irradiation.

Effects of Low Temperature on Spider Mite Control by Intermittent Ultraviolet-B Irradiation for Practical Use in Greenhouse Strawberries.

The application of ultraviolet-B (UVB) radiation to control spider mites is challenging as a key technology for integrated pest management (IPM) in greenhouse strawberries in Japan. To address this, concurrent use of phytoseiid mites and reduced UVB irradiance is desirable to ensure control effects in areas shaded from UVB radiation and to minimize the sunscald in winter, respectively. We designed experiments reproducing the UVB dose on the lower leaf surfaces in strawberry and evaluated the effects of intermittent UVB irradiation at midnight for practical application in the greenhouse and low temperature on the survival of the spider mite Tetranychus urticae Koch (Acari: Tetranychidae) and damage to the phytoseiid mite Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). The midnight intermittent UVB irradiation effectively suppressed egg hatching and development of larvae of T. urticae, and the control effect was reinforced at 20°C (no eggs hatched at 0.13 kJ m-2 d-1) rather than, at 25°C (70.8% eggs hatched). In contrast, the hatchability of N. californicus eggs was unaffected by intermittent UVB irradiation at 0.27 kJ m-2 d-1 at 25°C and 20°C. However, residual effects of UVB irradiation to N. californicus eggs on survival of hatched larvae were seen, so that reducing the UVB dose is also advantageous for this phytoseiid mite. N. californicus showed a photoreactivation capacity, whereas their UVB tolerance was improved by prey species, suggesting the possibility of the improvement of phytoseiid mites by diet. The reduction of UVB dose and concurrent use of phytoseiid mites increase reliability of the UVB method in IPM strategies in strawberry greenhouse.

Isolation of a novel UVB-tolerant rice mutant obtained by exposure to carbon-ion beams

UVB radiation suppresses photosynthesis and protein biosynthesis in plants, which in turn decreases growth and productivity. Here, an ultraviolet-B (UVB)-tolerant rice mutant, utr319 (UV Tolerant Rice 319), was isolated from a mutagenized population derived from 2500 M1 seeds (of the UVB-resistant cultivar ‘Sasanishiki’) that were exposed to carbon ions. The utr319 mutant was more tolerant to UVB than the wild type. Neither the levels of UVB-induced cyclobutane pyrimidine dimers (CPDs) or (6-4) pyrimidine-pyrimidone photodimers [(6-4) photoproducts], nor the repair of CPDs or (6-4) photoproducts, was altered in the utr319 mutant. Thus, the utr319 mutant may be impaired in the production of a previously unidentified factor that confers UVB tolerance. To identify the mutated region in the utr319 mutant, microarray-based comparative genomic hybridization analysis was performed. Two adjacent genes on chromosome 7, Os07g0264900 and Os07g0265100, were predicted to represent the mutant allele. Sequence analysis of the chromosome region in utr319 revealed a deletion of 45 419 bp. RNAi analysis indicated that Os07g0265100 is most likely the mutated gene. Database analysis indicated that the Os07g0265100 gene, UTR319, encodes a putative protein with unknown characteristics or function. In addition, the homologs of UTR319 are conserved only among land plants. Therefore, utr319 is a novel UVB-tolerant rice mutant and UTR319 may be crucial for the determination of UVB sensitivity in rice, although the function of UTR319 has not yet been determined.

Suppression and overexpression of Lsi1 induce differential gene expression in rice under ultraviolet radiation

Low silicon rice gene 1 (Lsi1) belongs to a member of Nod26-like major intrinsic protein (NIP) subfamily and is thought to control silicon (Si) accumulation in rice. In order to further elucidate its regulatory mechanisms in the defense of rice plants to enhanced ultraviolet-B (UV-B) radiation stress, Lsi1 was subjected to suppressed and overexpressed treatments in a UV-B tolerance rice accession Lemont as well as to overexpressed treatment in a UV-B sensitive rice accession Dular. The results showed that transcript levels of Lsi1 increased in Lsi1-overexpressed transgenic lines of rice accessions Lemont and Dular, but down-regulated in Lsi1-RNAi transgenic line of Lemont in comparison with their wild types (WT). A similar tendency was found in the root Si uptake and the Si concentrations in leaves. Further, the different transgenic rice lines and their WT were exposed to enhance UV-B radiation, study by suppression subtractive hybridization (SSH) found that Lsi1 not only could regulate the expression of phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL) and photolyase (PL), but also could induce other signal transduction-, detoxification-, resistance-, and photosynthesis-related genes. The findings suggested that the regulation of silicon nutrient by enhancing/inhibiting expression of Lsi1 could effectively induce the transcription of the mRNAs relative to tolerance in rice.

Variations in constitutive and inducible UV-B tolerance; dissecting photosystem II protection in Arabidopsis thaliana accessions

The rise in ultraviolet-B (UV-B) (280-315 nm) radiation levels, that is a consequence of stratospheric ozone layer depletion, has triggered extensive research on the effects of UV-B on plants. Plants raised under natural sunlight conditions are generally well protected from the potentially harmful effects of UV-B radiation. However, it is mostly unknown to which extent UV protection is constitutive and/or induced. In this study, we have analysed the role of constitutive and inducible protection responses in avoiding UV-B damage to photosystem II of photosynthesis. We have assayed the UV susceptibility of photosystem II in 224 Arabidopsis thaliana accessions from across the Northern hemisphere, and found a continuum of constitutive UV-protection levels, with some accessions being UV sensitive and others UV tolerant. Statistical analysis showed only very weak associations between constitutive UV tolerance and the geographic origin of accessions. Instead, most of the variance in constitutive UV-B protection of photosynthesis is present at the level of local Arabidopsis populations originating in the same geographic and climatic area. The variance in constitutive UV protection is, however, small compared to the amplitude of environmentally induced changes in UV protection. Thus, our data emphasise the importance of inducible responses for the protection of photosystem II against UV-B. Remarkably, the conditions that induce UV-protective responses vary; accessions from lower latitudes were found to switch-on UV defences more readily than those of higher latitudes. Such altered regulation of induction may comprise a suitable adaptation response when levels of a stressor are fluctuating in the short term, but predictable over longer periods.

Interaction of COP1 and UVR8 regulates UV-B-induced photomorphogenesis and stress acclimation in Arabidopsis

The ultraviolet-B (UV-B) portion of the solar radiation functions as an environmental signal for which plants have evolved specific and sensitive UV-B perception systems. The UV-B-specific UV RESPONSE LOCUS 8 (UVR8) and the multifunctional E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) are key regulators of the UV-B response. We show here that uvr8-null mutants are deficient in UV-B-induced photomorphogenesis and hypersensitive to UV-B stress, whereas overexpression of UVR8 results in enhanced UV-B photomorphogenesis, acclimation and tolerance to UV-B stress. By using sun simulators, we provide evidence at the physiological level that UV-B acclimation mediated by the UV-B-specific photoregulatory pathway is indeed required for survival in sunlight. At the molecular level, we demonstrate that the wild type but not the mutant UVR8 and COP1 proteins directly interact in a UV-B-dependent, rapid manner in planta. These data collectively suggest that UV-B-specific interaction of COP1 and UVR8 in the nucleus is a very early step in signalling and responsible for the plant's coordinated response to UV-B ensuring UV-B acclimation and protection in the natural environment.

A mutation in the uvi4 gene promotes progression of endo‐reduplication and confers increased tolerance towards ultraviolet B light

We have isolated and characterized a new ultraviolet B (UV-B)-resistant mutant, uvi4 (UV-B-insensitive 4), of Arabidopsis. The fresh weight (FW) of uvi4 plants grown under supplemental UV-B light was more than twice that of the wild-type. No significant difference was found in their ability to repair the UV-B-induced cyclobutane pyrimidine dimers, or in the amount of UV-B absorptive compounds, both of which are well-known factors that contribute to UV sensitivity. Positional cloning revealed that the UVI4 gene encodes a novel basic protein of unknown function. We found that the hypocotyl cells in uvi4 undergo one extra round of endo-reduplication. The uvi4 mutation also promoted the progression of endo-reduplication during leaf development. The UVI4 gene is expressed mainly in actively dividing cells. In the leaves of P(UVI4)::GUS plants, the GUS signal disappeared in basipetal fashion as the leaf developed. The total leaf blade area was not different between uvi4 and the wild-type through leaf development, while the average cell area in the adaxial epidermis was considerably larger in uvi4, suggesting that the uvi4 leaves have fewer but larger epidermal cells. These results suggest that UVI4 is necessary for the maintenance of the mitotic state, and the loss of UVI4 function stimulated endo-reduplication. Tetraploid Arabidopsis was hyper-resistant to UV-B compared to diploid Arabidopsis, suggesting that the enhanced polyploidization is responsible for the increased UV-B tolerance of the uvi4 mutant.

Induction of the 72-kilodalton heat shock protein and protection from ultraviolet B–induced cell death in human keratinocytes by repetitive exposure to heat shock or 15-deoxy-Δ12,14-prostaglandin J2

It has been demonstrated that hyperthermia protects keratinocytes from ultraviolet B (UVB)-induced cell death in culture and in vivo. This effect is mediated by the antiapoptotic effect of heat shock proteins that are transiently induced after exposure to heat at sublethal temperatures. Consequently, induction of Hsp has been proposed as a novel means of photoprotection. However, in the face of daily UVB exposure of human skin in vivo, this approach would not be useful if keratinocytes become less sensitive to Hsp induction with repeated exposure to the inducing agent. The aim of this study was to investigate whether repeated exposure to hyperthermia or to the stress protein activating cyclopentenone prostaglandin 15-deoxy-delta(12,14)-prostaglandin J2 (15dPGJ2) leads to adaptation of the cells, attenuation of the heat shock response, and abrogation of the protective effect. Normal human epidermal keratinocytes (NHEK) and the carcinoma-derived cell line A431 were exposed to either 42 degrees C or to 15dPGJ2 for 4 hours at 24-hour intervals for 4 consecutive days. The intracellular level of the 72-kDa heat shock protein (Hsp72) was determined by enzyme-linked immunosorbent assay (ELISA). Cells were exposed to UVB from a metal halide source after the last heat or 15dPGJ2 treatment, and survival was determined 24 hours after exposure by a MTT assay. Our results demonstrate that (1) heat shock and 15dPGJ2 are potent inducers of Hsp72 expression and lead to increased resistance to UVB-induced cell death in human keratinocytes; (2) re-exposure to heat shock leads to a superinduction without attenuation of the absolute increase in Hsp72 and of its UVB-protective effect; (3) the UVB tolerance induced by 15dPGJ2 is enhanced by repeated exposure without a further increase of Hsp72; (4) repeated heat shock and 15dPGJ2 up to a concentration of 1 microg/mL have no influence on cell growth over a period of 4 days. We conclude that through repeated exposure to Hsp-inducing factors, stress tolerance can be maintained without additional toxicity in human keratinocytes. These results provide a basis for the development of nontoxic Hsp inducers that can be repeatedly applied without loss of effect.

Different physiological responses of two aquatic bryophytes to enhanced ultraviolet-B radiation

Two aquatic bryophytes, the moss Fontinalis antipyretica Hedw. and the foliose liverwort Jungermannia exsertifolia Steph. subsp. cordifolia (Dumort.) Váña were analysed with regard to their ultraviolet-B (UV-B) tolerance. The plants were cultivated in the laboratory for 36 days under three different radiation regimes which were set up using appropriate lamps and filters: P (PAR alone, control), PA (PAR + UV-A) and PAB (PAR + UV-A + UV-B). The two bryophytes responded differently to the enhancement in UV-B radiation, while UV-A radiation had only a slight biological effect. The samples of the moss which were irradiated with UV-B showed, with respect to the control, decreases in the chlorophyll and carotenoids concentration, the chlorophyll a/b quotient, the chlorophylls/phaeopigments ratios, the net photosynthesis rates, the light saturation point, the maximum quantum yield of photosystem II (Fv/Fm) and the apparent electron transport rate (ETR). They also showed increases in the sclerophylly index and the dark respiration rates. The majority of these changes are indicative of plant stress and some of them had been found previously in bryophytes exposed to enhanced UV-B radiation. However, the UV-B-irradiated samples of the liverwort only showed a decrease in Fv/Fm, which might be the most sensitive physiological variable to UV-B, together with an increase in the concentration of UV-absorbing compounds. This defence mechanism, rarely described in bryophytes, would enable the liverwort to have a higher tolerance than the moss against UV-B radiation, at least under the specific experimental conditions used in this study. Also, the increment of UV-absorbing compounds in the liverwort, which seems to be a specific response to the enhancement in UV-B radiation, might be a useful ecophysiological tool in the bioindication of this phenomenon; long-term field research is needed to confirm this usefulness. The different UV-B tolerances of the species studied may be related, to a certain extent, with their different distribution and ecology. Given that UV-B tolerance depends on the species, bryophytes should not be grouped as a single functional type in the prediction of the consequences of a hypothetic enhancement in UV-B radiation.

White clover sensitivity to UV-B radiation - biochemical relationships and interaction with drought

During summertime in New Zealand, white clover experiences high levels of ultraviolet-B (UV-B) radiation. This frequently coincides with periods of summer drought. We investigated responses to UV-B and to the combination of UV-B and drought in various white clover populations, including New Zealand cultivars and ecotypes as well as overseas germplasm. The results were obtained under controlled environmental conditions in three independent trials. Overall, white clover growth was reduced by UV-B. The population comparisons indicated that low growth rate and adaptation to other forms of stress may be related to UV-B tolerance under well-watered conditions, but not during extended periods of drought. Flavonoid pigments that are involved in stress protection were strongly increased under UV-B and were further enhanced in the combination of UV-B and drought. The responses among these flavonoids were highly specific, with more pronounced UV-B-induced increases in quercetin glycosides, compared to their closely related kaempferol counterparts. UV-B toler ance of the less productive white clover populations was linked to the accumulation of quercetin compounds. In conclusion, these studies suggest (i) that slow-growing white clover ecotypes adapted to other stresses have higher capacity for biochemical acclimation to UV-B under well-watered conditions and (ii) that these biochemical attributes may also contribute to decreased UV-B sensitivity across white clover populations under drought. The findings alert plant breeders to potential benefits of selecting productive germplasm for high levels of specific flavonoids to balance trade-offs between plant productivity and stress tolerance. Keywords: Drought, flavonoids, genetic variation, HPLC, kaempferol, quercetin, str ess, Trifolium repens L., ultraviolet-B, white clover

Amphibian defenses against ultraviolet-B radiation.

As part of an overall decline in biodiversity, amphibian populations throughout the world are disappearing. There are a number of potential causes for these declines, including those related to environmental changes such as increasing ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion. UV-B radiation can kill amphibian embryos or can cause sublethal effects that can harm amphibians in later life stages. However, amphibians have defenses against UV-B damage that can limit damage or repair it after exposure to UV-B radiation. These include behavioral, physiological, and molecular defenses. These defenses differ interspecifically, with some species more able to cope with exposure to UV-B than others. Unfortunately, the defense mechanisms of many species may not be effective against increasing persistent levels of UV-B radiation that have only been present for the past several decades due to human-induced environmental damage. Moreover, we predict that persistent UV-B-induced mortality and sublethal damage in species without adequate defenses could lead to changes in community structure. In this article we review the effects of UV-B radiation on amphibians and the defenses they use to avoid solar radiation and make some predictions regarding community structure in light of interspecific differences in UV-B tolerance.

Effects of ultraviolet-B radiation on common frog Rana temporaria embryos from along a latitudinal gradient.

Interspecific variation in ultraviolet-B (UV-B) radiation tolerance in amphibians is well established, but little is known about the possible intraspecific variation in UV-B radiation tolerance within any species. We studied the effects of UV-B radiation on common frog Rana temporaria embryos originating from eight populations spanning a 1,200km latitudinal gradient across Sweden. Newly fertilised eggs were exposed to three different UV-B treatments [absent (no UV-B), normal (1.254kJ m-2) and enhanced (1.584kJ m-2, 26% above normal) levels] in a laboratory, and effects on survival, frequency of developmental anomalies, developmental rate and hatchling size were documented. UV-B radiation treatments did not have main factor effects on embryonic mortality or frequency of developmental anomalies. Survival to hatching was lower at higher latitudes, but it was independent of UV-B treatments. High UV-B treatment prolonged development time in five populations, whereas in one population development time was longest in the absence of UV-B. Even though the northernmost populations had the shortest development times, the interaction between latitude and development time was not significant. There was a significant population×UV-B interaction in hatchling size, indicating that hatchling size was negatively affected by the UV-B treatments in some of the populations. Hatchling size increased until mid-latitudes and was again somewhat smaller at the northernmost latitudes, but this was independent of UV-B treatments. These results suggest that although R. temporaria embryos are rather tolerant of UV-B radiation, and there is no clear latitudinal pattern to UV-B tolerance in this species, the sublethal effects of UV-B on embryonic development may differ among different populations.

Inheritance of UV-B tolerance in seven ecotypes of Arabidopsis thaliana L. Heynh. and their F1 hybrids.

We used a partial diallel mating design to examine morphologic response to supplementary ultraviolet-B (UV-B) radiation of seven ecotypes of Arabidopsis thaliana L. Heynh. from several geographic locations in Europe. We were particularly interested in the inheritance of UV-B tolerance by the F1 generation. Morphologic traits included plant height, rosette diameter, number of shoots (lateral branches from the rosette) and branches (lateral branches above the rosette), and reproductive and vegetative dry mass. To effect a large difference in UV treatments, plants under treatment received 11 kJ/m2/day of biologically effective UV-B radiation while control plants received no UV-B radiation. Genotype effects were observed for all traits (P < .0001), but a significant treatment effect and genotype x treatment interactions were detected only for plant height (P = .0001), rosette diameter (P = .0229), and vegetative (P = .0260) and reproductive dry mass (P = .0900). General combining ability was significant for plant height (P < .0001) and vegetative mass (P = .0563), whereas specific combining ability was significant for rosette diameter (P = .0220) and vegetative mass (P = .0506). These results suggest that both pure lines and hybrids of Arabidopsis can be developed for greater tolerance of UV-B radiation. Similar findings for crop species might lead to the development of UV tolerant varieties.

Potential Effect of Soybean Heliotropism on Ultraviolet‐B Irradiance and Dose

Assessing the potential for decreases in crop yield due to stratospheric ozone loss and concomitant increases in ultraviolet‐B (UVB) radiation requires knowledge of the characteristics of UVB irradiance above and within crops and the sensitivity of crops to the detrimental effects of the irradiance. Evaluations of the tolerance of many crops to increases in UVB irradiance have been made. The tolerance or intolerance of a crop to UVB irradiance is in part a result of physical characteristics of the plant. This study evaluated both the distribution of irradiance and the effects of plant leaf heliotropic movement of soybean [Glycine max (L.) Merr.] cultivars on the irradiance received on the leaf surface. Measurements of the above‐canopy UVB irradiance on planes having a wide range of slope and aspect were made under cloud‐free skies in a soybean field during the summer of 1990. Results showed that the relative irradiance was strongly dependent on the leaf inclination angle and could be modeled by a simple function having a relative irradiance accuracy of 0.14 (root mean square error); with greater model error at small incidence angles to the sun than at large incidence angles. The developed model was then used to evaluate the influence of heliotropy on the UVB dose received on the terminal leaflet. These results suggest that heliotropy in the leaflet acts to reduce irradiance. Since the more tolerant soybean cultivars appear to orient leaflets away from the sun, results suggest that the classification of UVB tolerance may be due in part to the capacity for paraheliotropic response reducing the UVB radiation received.