Sensitivity of rice to ultraviolet-B radiation

Variation in ultraviolet-B (UV-B)-induced DNA damage repair mechanisms in plants and humans: an avenue for developing protection against skin photoaging

PURPOSE

The increasing amounts of ultraviolet-B (UV-B) light in our surroundings have sparked worries about the possible effects on humans and plants. The detrimental effects of heightened UV-B exposure on these two vital elements of terrestrial life are different due to their unique and concurrent nature. Understanding common vulnerabilities and distinctive adaptations of UV-B radiation by exploring the physiological and biochemical responses of plants and the effects on human health is of huge importance. The comparative effects of UV-B radiation on plants and animals, however, are poorly studied. This review sheds light on the sophisticated web of UV-B radiation effects by navigating the complex interaction between botanical and medical perspectives, drawing upon current findings.

CONCLUSION

By providing a comprehensive understanding of the complex effects of heightened UV-B radiation on plants and humans, this study summarizes relevant adaptation strategies to the heightened UV-B radiation stress, which offer new approaches for improving human cellular resilience to environmental stressors.

The optimized Maxent model reveals the pattern of distribution and changes in the suitable cultivation areas for Reaumuria songarica being driven by climate change

Reaumuria songarica, a drought-resistant shrub, is widely distributed and plays a crucial role in the northern deserts of China. It is a key species for desert rehabilitation and afforestation efforts. Using the Maxent model to predict suitable planting areas for R. songarica is an important strategy for combating desertification. With 184 occurrence points of R. songarica and 13 environmental variables, the optimized Maxent model has identified the main limiting factors for its distribution. Distribution patterns and variation trends of R. songarica were projected for current and future climates (2030s, 2050s, 2070s, and 2090s) and different scenarios (ssp_126, ssp_370, and ssp_585). Results show that setting parameters to RM (regulation multiplier) = 4 and FC (feature combination) = LQHPT yields a model with good accuracy and high reliability. Currently, R. songarica is primarily suitable for desert control in eight provinces and autonomous regions, including Inner Mongolia, Xinjiang, Qinghai, and Ningxia. The total suitable planting area is 148.80 × 104 km2, representing 15.45% of China's land area. Precipitation (Precipitation of the wettest month, Precipitation of the warmest quarter, and Annual precipitation) and Ultraviolet-B seasonality are the primary environmental factors limiting the growth and distribution of R. songarica. Mean temperature of the warmest quarter is the primary factor driving changes in the distribution of suitable areas for R. songarica under future climate scenarios. In future climate scenarios, the suitable planting area of R. songarica will shrink, and the distribution center will shift towards higher latitude, potentially indicate further desertification. The area of highly suitable habitat has increased, while moderately and less suitable habitat areas have decreased. Increased precipitation within R. songarica's water tolerance range is favorable for its growth and reproduction. With changes in the suitable cultivation area for R. songarica, priority should be given to exploring and utilizing its germplasm resources. Introduction and cultivation can be conducted in expanding regions, while scientifically effective measures should be implemented to protect germplasm resources in contracting regions. The findings of this study provide a theoretical basis for addressing desertification resulting from climate change and offer practical insights for the development, utilization, introduction, and cultivation of R. songarica germplasm resources.

The recent possible strategies for breeding ultraviolet-B-resistant crops

The sensitivity of crops to ultraviolet B (UVB, 280-315 nm) radiation varies significantly. Plants' sensitivity to UVB is heavily influenced by the activity of the enzyme cyclobutane pyrimidine dimer (CPD) photolyase, which fixes UVB-induced CPDs. Crops grown in tropical areas with high level of UVB radiation, like O. glaberrima from Africa and O. sativa ssp. indica rice from Bengal, are more sensitive to UVB radiation and could suffer more as a result of rising UVB levels on the earth's surface. Therefore, creating crops that can withstand high UVB is crucial in tropical regions. There is, however, little information on current techniques for breeding UVB-resistant plants. The most recent techniques for producing UVB-resistant crops are presented in this review. The use of DNA methylation, boosting the antioxidant system, regulating the expression of micro-RNA396, and overexpressing CPD photolyase in transgenic plants are some of the methods that are discussed. CPD photolyase overexpression in transgenic plants is the most popular technique for producing UVB-resistant rice. The study also offers several strategies for creating UVB-resistant plants using gene editing techniques. To feed the world's rapidly expanding population, researchers can use the information from this study to improve food production.

The recent relationship between ultraviolet-B radiation and biotic resistance in plants: a novel non-chemical strategy for managing biotic stresses

Ultraviolet-B radiation (UVB; 280-315 nm) is a significant environmental factor that alters plant development, changes interactions between species, and reduces the prevalence of pests and diseases. While UVB radiation has negative effects on plant growth and performance at higher doses, at lower and ambient doses, UVB radiation acts as a non-chemical method for managing biotic stresses by having positive effects on disease resistance and genes that protect plants from pests. Understanding the recent relationship between UVB radiation and plants' biotic stresses is crucial for the development of crops that are resistant to UVB and biotic stresses. However, little is known about the recent interactions between UVB radiation and biotic stresses in plants. This review discusses the most recent connections between UVB radiation and biotic stresses in crops, including how UVB radiation affects a plant's resistance to disease and pests. The interaction of UVB radiation with pathogens and herbivores has been the subject of the most extensive research of these. This review also discusses additional potential strategies for conferring multiple UVB-biotic stress resistance in crop plants, such as controlling growth inhibition, miRNA 396 and 398 modulations, and MAP kinase. This study provides crucial knowledge and methods for scientists looking to develop multiple resistant crops that will improve global food security.

Ultraviolet-B radiation in relation to agriculture in the context of climate change: a review

Over the past few decades, the amount of ultraviolet-B radiation (UV-B) reaching the earth's surface has been altered due to climate change and stratospheric ozone dynamics. This narrow but highly biologically active spectrum of light (280-320 nm) can affect plant growth and development. Depletion of ozone and climate change are interlinked in a very complicated manner, i.e., significantly contributing to each other. The interaction of climate change, ozone depletion, and changes in UV-B radiation negatively affects the growth, development, and yield of plants. Furthermore, this interaction will become more complex in the coming years. The ozone layer reduction is paving a path for UV-B radiation to impact the surface of the earth and interfere with the plant's normal life by negatively affecting the plant's morphology and physiology. The nature and degree of the future response of the agricultural ecosystem to the decreasing or increasing UV-B radiation in the background of climate change and ozone dynamics are still unclear. In this regard, this review aims to elucidate the effects of enhanced UV-B radiation reaching the earth's surface due to the depletion of the ozone layer on plants' physiology and the performance of major cereals.

High ultraviolet-B sensitivity due to lower CPD photolyase activity is needed for biotic stress response to the rice blast fungus, Magnaporthe oryzae

Sensitivity to ultraviolet-B (UVB, 280-315 nm) radiation varies widely among rice (Oryza sativa) cultivars due to differences in the activity of cyclobutane pyrimidines dimer (CPD) photolyase. Interestingly, cultivars with high UVB sensitivity and low CPD photolyase activity have been domesticated in tropical areas with high UVB radiation. Here, we investigated how differences in CPD photolyase activity affect plant resistance to the rice blast fungus, Magnaporthe oryzae, which is one of the other major stresses. We used Asian and African rice cultivars and transgenic lines with different CPD photolyase activities to evaluate the interaction effects of CPD photolyase activity on resistance to M. oryzae. In UVB-resistant rice plants overexpressing CPD photolyase, 12 h of low-dose UVB (0.4 W m^-2) pretreatment enhanced sensitivity to M. oryzae. In contrast, UVB-sensitive rice (transgenic rice with antisense CPD photolyase, A-S; and rice cultivars with low CPD photolyase activity) showed resistance to M. oryzae. Several defense-related genes were upregulated in UVB-sensitive rice compared to UVB-resistant rice. UVB-pretreated A-S plants showed decreased multicellular infection and robust accumulation of reactive oxygen species. High UVB-induced CPD accumulation promoted defense responses and cross-protection mechanisms against rice blast disease. This may indicate a trade-off between high UVB sensitivity and biotic stress tolerance in tropical rice cultivars.

Intraspecific variation in photosynthetic efficiency in soybean (Glycine max L.) varieties towards solar ultraviolet radiations

In the current study, we used four soybean varieties PK-1029, PK-472, NRC-7, and Hardee to examine the effect of exclusion of solar UV radiation on photosynthetic efficiency and to test possible variety-dependent sensitivity to ambient UV (280-400 nm). Plants that were grown under UV exclusion filters had higher chlorophyll a and b, efficiencies of PSII and more active reaction centers indicated that PSII were substantially affected by solar UV radiation. The significant increase in net photosynthesis was linked to increased stomatal conductance and lower intercellular concentration of CO2 in UV-excluded plants. The exclusion of solar UV increased seed mass per plant in all soybean varieties as compared to the control; this indicates that ambient UV exclusions boost photosynthetic efficiency and improve soybean yield. The overall cumulative stress response index of four varieties implies that Hardee and PK-472 were more sensitive whereas NRC-7 and PK-1029 were resistant to ambient UV radiations.

β-Sitosterol differentially regulates key metabolites for growth improvement and stress tolerance in rice plants during prolonged UV-B stress

BACKGROUND

Elevated ultraviolet-B (UV-B) radiation is potentially deleterious to many organisms specifically crop plants and has become a global challenge. Rice is an exceptionally important staple food which is grown worldwide, and many efforts have been done recently to improve rice varieties against UV-B stress. This current study aims to investigate the effects of exogenous application of β-sitosterol (βSito) on growth improvement and tolerance level of rice plants against prolonged UV-B stress. The physiological and metabolic responses were evaluated in rice plants not supplemented with βSito (Nβ) and those supplemented with βSito (Sβ).

RESULTS

The Nβ and Sβ plants were grown under non-stress (ns) and under prolonged UV-B stress (uvs) conditions and termed as Nβ^ns, Sβ^ns and Nβ^uvs, Sβ^uvs, respectively. The application of βSito contributes positively under non-stress and specifically to UV-B stress in terms of improving numerous physiological parameters associated with growth and development such as shoot and root length, RWC, whole plant biomass, chlorophyll pigments, and photosynthetic-related parameters (Pn, Gs, Tr, WUEi, Fv/Fm, and NPQ) in Sβ compared with Nβ plants. Moreover, enhanced oxidative stress tolerance of Sβ^uvs vs. Nβ^uvs plants under stress was attributed to low levels of ROS and substantial trigger in activities of antioxidant enzymes (SOD, POD, CAT, and APX). Metabolic analysis was performed using GC-TOFMS, which revealed higher accumulation of several key metabolites including organic acids, sugars, amino acids, and others in Sβ^uvs vs. Nβ^uvs plants, which were mainly reduced in Nβ plants under stress vs. non-stress conditions.

CONCLUSION

These results provide useful data regarding the important role of βSito on growth maintenance and modulation of several metabolites associated with osmotic and redox adjustments during UV-B stress tolerance in rice plants. Importantly, βSito-regulated plasticity could further be explored specifically in relation to different environmental stresses in other economically useful crop plants.

UV-B signalling in rice: Response identification, gene expression profiling and mutant isolation

Responses of rice seedlings to UV-B radiation (UV-B) were investigated, aiming to establish rice as a model plant for UV-B signalling studies. The growth of japonica rice coleoptiles, grown under red light, was inhibited by brief irradiation with UV-B, but not with blue light. The effective UV-B fluences (10^-1 -10³ μmol m^-2 ) were much lower than those reported in Arabidopsis. The response was much less in indica rice cultivars and its extent varied among Oryza species. We next identified UV-B-specific anthocyanin accumulation in the first leaf of purple rice and used this visible phenotype to isolate mutants. Some isolated mutants were further characterized, and one was found to have a defect in the growth response. Using microarrays, we identified a number of genes that are regulated by low-fluence-rate UV-B in japonica coleoptiles. Some up-regulated genes were analysed by real-time PCR for UV-B specificity and the difference between japonica and indica. More than 70% of UV-B-regulated rice genes had no homologs in UV-B-regulated Arabidopsis genes. Many UV-B-regulated rice genes are related to plant hormones and especially to jasmonate biosynthetic and responsive genes in apparent agreement with the growth response. Possible involvement of two rice homologs of UVR8, a UV-B photoreceptor, is discussed.

Transgenic rice Oryza glaberrima with higher CPD photolyase activity alleviates UVB-caused growth inhibition

The ultraviolet B (UVB) sensitivity of rice cultivated in Asia and Africa varies greatly, with African rice cultivars (Oryza glaberrima Steud. and O. barthii A. Chev.) being more sensitive to UVB because of their low cyclobutane pyrimidine dimer (CPD) photolyase activity, which is a CPD repair enzyme, relative to Asian rice cultivars (O. sativa L.). Hence, the production of UVB-resistant African rice with augmented CPD photolyase activity is of great importance, although difficulty in transforming the African rice cultivars to this end has been reported. Here, we successfully produced overexpressing transgenic African rice with higher CPD photolyase activity by modifying media conditions for callus induction and regeneration using the parental line (PL), UVB-sensitive African rice TOG12380 (O. glaberrima). The overexpressing transgenic African rice carried a single copy of the CPD photolyase enzyme, with a 4.4-fold higher level of CPD photolyase transcripts and 2.6-fold higher activity than its PL counterpart. When the plants were grown for 21 days in a growth chamber under visible radiation or with supplementary various UVB radiation, the overexpressing transgenic plants have a significantly increased UVB resistance index compared to PL plants. These results strongly suggest that CPD photolyase remains an essential factor for tolerating UVB radiation stress in African rice. As a result, African rice cultivars with overexpressed CPD photolyase may survive better in tropical areas more prone to UVB radiation stress, including Africa. Collectively, our results provide strong evidence that CPD photolyase is a useful biotechnological tool for reducing UVB-induced growth inhibition in African rice crops of O. glaberrima.

Very high sensitivity of African rice to artificial ultraviolet-B radiation caused by genotype and quantity of cyclobutane pyrimidine dimer photolyase

Ultraviolet-B (UVB) radiation damages plants and decreases their growth and productivity. We previously demonstrated that UVB sensitivity varies widely among Asian rice (Oryza sativa L.) cultivars and that the activity of cyclobutane pyrimidine dimer (CPD) photolyase, which repairs UVB-induced CPDs, determines UVB sensitivity. Unlike Asian rice, African rice (Oryza glaberrima Steud. and Oryza barthii A. Chev.) has mechanisms to adapt to African climates and to protect itself against biotic and abiotic stresses. However, information about the UVB sensitivity of African rice species is largely absent. We showed that most of the African rice cultivars examined in this study were UVB-hypersensitive or even UVB-super-hypersensitive in comparison with the UVB sensitivity of Asian O. sativa cultivars. The difference in UVB resistance correlated with the total CPD photolyase activity, which was determined by its activity and its cellular content. The UVB-super-hypersensitive cultivars had low enzyme activity caused by newly identified polymorphisms and low cellular CPD photolyase contents. The new polymorphisms were only found in cultivars from West Africa, particularly in those from countries believed to be centres of O. glaberrima domestication. This study provides new tools for improving both Asian and African rice productivity.

Intraspecific variation in sensitivity of high yielding rice varieties towards UV-B radiation

Effective screening of thirteen commonly cultivated rice (Oryza sativa L.) varieties was carried out to evaluate the varietal-specific differences in morphological, physiological and biochemical responses to various doses of UV-B irradiation (7, 14, 21 and 28 kJ m-2d-1). Determination of UV-B tolerant rice varieties would be helpful in selecting a suitable variety for the areas experiencing higher influx of UV-B radiation. Based on the initial screening of thirteen rice varieties, carried out by analyzing shoot length, fresh weight, photosynthetic pigments and the rate of lipid peroxidation under various doses of UV-B, it was found that Mangalamahsuri, Aathira, Kanchana, Jyothi and Annapoorna were tolerant lines and Neeraja, Swetha, Swarnaprabha and Aiswarya were the sensitive ones. Further screening of these nine varieties was done by analyzing primary metabolites (total protein, soluble sugar and proline content) and non enzymatic antioxidants (ascorbate and glutathione) involved in free radical scavenging mechanism to mitigate the negative effects of UV-B irradiation. Based on the cumulative stress response index (CSRI), the sum of relative individual component responses (total protein, soluble sugar, proline, ascorbate and glutathione content) at each UV-B treatment and total stress response index (TSRI), the sum of CSRI of all the four UV-B treatments for each variety, nine rice varieties selected after primary screening were classified as tolerant (Mangalamahsuri, Aathira and Kanchana), intermediate (Jyothi, Annapoorna, Neeraja and Swetha) and sensitive (Swarnaprabha and Aiswarya).

Beyond Arabidopsis: Differential UV-B Response Mediated by UVR8 in Diverse Species

Ultraviolet-B radiation (UV-B, 280-315 nm) is an important environmental signal that regulates growth and development in plants. Two dose-dependent UV-B response pathways were described in plants: a specific one, mediated by UVR8 (the specific UV-B receptor) and an unspecific one, activated by the oxidative damage produced by radiation. The constitutively expressed receptor appears inactive as a dimer, with the two monomers dissociating upon UV-B irradiation. The monomer then interacts with COP1, an ubiquitin ligase, hindering its ability to poly-ubiquitinate transcriptional factor HY5, thus averting its degradation and activating the photomorphogenic response. HY5 induces the synthesis of proteins RUP1 and RUP2, which interact with UVR8, releasing COP1, and inducing the re-dimerization of UVR8. This mechanism has been thoroughly characterized in Arabidopsis, where studies have demonstrated that the UVR8 receptor is key in UV-B response. Although Arabidopsis importance as a model plant many mechanisms described in this specie differ in other plants. In this paper, we review the latest information regarding UV-B response mediated by UVR8 in different species, focusing on the differences reported compared to Arabidopsis. For instance, UVR8 is not only induced by UV-B but also by other agents that are expressed differentially in diverse tissues. Also, in some of the species analyzed, proteins with low homology to RUP1 and RUP2 were detected. We also discuss how UVR8 is involved in other developmental and stress processes unrelated to UV-B. We conclude that the receptor is highly versatile, showing differences among species.

Efficient removal of cyclobutane pyrimidine dimers in barley: differential contribution of light-dependent and dark DNA repair pathways

Barley stress response to ultraviolet radiation (UV) has been intensively studied at both the physiological and morphological level. However, the ability of barley genome to repair UV-induced lesions at the DNA level is far less characterized. In this study, we have investigated the relative contribution of light-dependent and dark DNA repair pathways for the efficient elimination of cyclobutane pyrimidine dimers (CPDs) from the genomic DNA of barley leaf seedlings. The transcriptional activity of barley CPD photolyase gene in respect to the light-growth conditions and UV-C irradiation of the plants has also been analyzed. Our results show that CPDs induced in the primary barley leaf at frequencies potentially damaging DNA at the single-gene level are removed efficiently and exclusively by photorepair pathway, whereas dark repair is hardly detectable, even at higher CPD frequency. A decrease of initially induced CPDs under dark is observed but only after prolonged incubation, suggesting the activation of light-independent DNA damage repair and/or tolerance mechanisms. The green barley seedlings possess greater capacity for CPD photorepair than the etiolated ones, with efficiency of CPD removal dependent on the intensity and quality of recovering light. The higher repair rate of CPDs measured in the green leaves correlates with the higher transcriptional activity of barley CPD photolyase gene. Visible light and UV-C radiation affect differentially the expression of CPD photolyase gene particularly in the etiolated leaves. We propose that the CPD repair potential of barley young seedlings may influence their response to UV-stress.

Plant Nuclei Move to Escape Ultraviolet-Induced DNA Damage and Cell Death

A striking feature of plant nuclei is their light-dependent movement. In Arabidopsis (Arabidopsis thaliana) leaf mesophyll cells, the nuclei move to the side walls of cells within 1 to 3 h after blue-light reception, although the reason is unknown. Here, we show that the nuclear movement is a rapid and effective strategy to avoid ultraviolet B (UVB)-induced damages. Mesophyll nuclei were positioned on the cell bottom in the dark, but sudden exposure of these cells to UVB caused severe DNA damage and cell death. The damage was remarkably reduced in both blue-light-treated leaves and mutant leaves defective in the actin cytoskeleton. Intriguingly, in plants grown under high-light conditions, the mesophyll nuclei remained on the side walls even in the dark. These results suggest that plants have two strategies for reducing UVB exposure: rapid nuclear movement against acute exposure and nuclear anchoring against chronic exposure.

The role of calcium in improving photosynthesis and related physiological and biochemical attributes of spring wheat subjected to simulated acid rain

The response of photosynthesis parameters, catalase, superoxide dismutase and peroxidase activity, malondialdehyde, proline, chlorophyll, yield and yield components to foliar application of calcium and simulated acid rain in wheat were investigated. Foliar treatment of calcium led to significant increases in the photosynthesis rate, transpiration rate, stomatal conductance, proline, chlorophyll, yield and yield components in plants subjected to acid rain. Antioxidant enzyme activity and lipid peroxidation in the wheat leaves decreased because of calcium foliar application. Calcium hindered degradation of the rubisco subunits under acid rain treatment compared with water-treated plants. Results suggest that acid rain induces the production of free radicals resulting in lipid peroxidation of the cell membrane so that significant increase in antioxidant enzyme activity was observed. In addition, photosynthetic parameters i.e. photosynthesis rate, transpiration rate and stomatal conductance were drastically suppressed by acid rain. The cellular damage caused by free radicals might be reduced or prevented by a protective metabolism including antioxidative enzymes and calcium. We report that foliar application of calcium before acid rain may ameliorate the adverse effects of acid rain in wheat plants.

Intraspecific variations in growth, yield and photosynthesis of sorghum varieties to ambient UV (280-400 nm) radiation

A field study was conducted to investigate the impact of ambient solar UV on the various growth, physiological and yield parameters of four sorghum (Sorghum bicolor L.) varieties-Indore-12, Indore-26, CSV-23 and Indore-27 by excluding either UV-B (<315 nm) or UV-A/B (<400 nm) components of solar spectrum. Exclusion of UV significantly enhanced plant height, area and specific leaf weight of flag leaf, biomass accumulation, yield parameters and harvest index in all the sorghum varieties. Chlorophyll b was significantly enhanced and chlorophyll a increased to a lesser extent, UV-B absorbing substances and chlorophyll a/b ratio were significantly decreased by the exclusion of solar UV. The enhancement in the vegetative growth and yield by UV exclusion might be linked to the remarkable increase in rate of photosynthesis in sorghum varieties. The magnitude of the response was high in I-26 and I-27 as compared to CSV-23 and I-12 after exclusion of solar UV. All the varieties of sorghum had a negative cumulative stress response index (CSRI), the sensitivity of the sorghum varieties was in the following sequence I-12>CSV-23>I-26>I-27. Thus I-27 was the most sensitive and I-12 the least sensitive variety to present level of solar UV radiation. The differences in UV sensitivity identified among sorghum varieties might be useful in breeding programs for increased tolerance to UV-B radiation.

Augmentation of CPD photolyase activity in japonica and indica rice increases their UVB resistance but still leaves the difference in their sensitivities

Rice cultivars vary widely in their sensitivity to ultraviolet B (UVB, 280-320 nm). Specifically, many indica rice cultivars from tropical regions, where UVB radiation is higher, are hypersensitive to UVB. Photoreactivation mediated by the photolyase enzyme is the major pathway for repairing UVB-induced cyclobutane pyrimidine dimers (CPDs) in plants. Still, these UVB-sensitive cultivars are less able to repair CPDs through photoreactivation than UVB-resistant cultivars. Here, we produced CPD photolyase-overexpressing transgenic rice plants with higher CPD photolyase activity using UVB-sensitive rice Norin 1 (japonica) and UVB-hypersensitive rice Surjamkhi (indica) as parental line (PL) plants. The results show that these transgenic rice plants were much more resistant to UVB-induced growth inhibition than were PL cultivars. The present findings strongly indicate that UVB-resistance, caused by an increase in CPD photolyase activity, can be achieved in various rice cultivars. However, there was a difference in the level of reduction of UVB-induced growth inhibition among rice cultivars; the level of reduction of growth inhibition in transgenic rice plants generated from the indica strain was lower than that of transgenic rice plants generated from japonica strains. These results indicate that the growth of the UVB-hypersensitive indica strain was strongly inhibited by other factors in addition to CPD levels.

Supplemental ultraviolet-B and ozone: impact on antioxidants, proteome and genome of linseed (Linum usitatissimum L. cv. Padmini)

The present investigation used Linum usitatissimum L. cv. Padmini (linseed), under field conditions in open-top chambers, to evaluate the interactive effects of supplemental ultraviolet-B (sUV-B; ambient +7.2 kJ · m(-2) · d(-1)) and ozone (O(3); ambient +10 ppb). Treatment of plants with sUV-B and O(3) , individually or in combination, caused several changes in enzymatic and non-enzymatic components of the antioxidant defence system. Photo-oxidative damage caused by sUV-B and O(3) , included lipid peroxidation, changed protein profiles and caused DNA strand breakage. One-dimensional gel electrophoresis revealed that proteins of 222.24 and 50.5 kDa are specific and appear after sUV-B and O(3) exposure, and could be used as indicator proteins. Effects of sUV-B and O(3) given separately are more detrimental as compared to combined treatment. Mutational and structural alterations in linseed DNA after these stresses were also examined using RAPD with ten different primers. The study concluded that both stresses, i.e. sUV-B and O(3) , are phytotoxic, causing significant changes in metabolites, antioxidants, the leaf proteome and the genome of linseed, but their interactive effect was always less than additive.

Effects of UV-B radiation in morpho-genetic characters of Gnaphalium luteo-album

Genetic analyses of Gnaphalium's DNA showed a high degree of polymorphism in UV-B irradiated plants when compared to controls. Among the five tested primers the four ISSR primers selected for this analysis generated a total of 189 fragments. A high proportion of polymorphic bands ranging from 70% to 28% were found using these ISSR markers. Nei and Li similarity indexes [1] were used to evaluate genetic divergence among plants. The dendrograms obtained using these markers efficiently separate plants from different treatments. A linear relationship was observed between UV-B dose and percentage of dissimilarity which may be related to DNA damage caused by the different UV-B treatments.

Reviewing the technical designs for experiments with ultraviolet-B radiation and impact on photosynthesis, DNA and secondary metabolism

The ultraviolet-B (UV-B) portion of sunlight has received much attention in the last three decades, because radiation from this spectral region increases due to the stratospheric ozone depletion, which results from increases of chlorofluorocarbons in the atmosphere. Plant responses to UV-B exposure vary greatly and the interpretation of and comparison between studies is hindered, mainly by the contrasting experimental conditions used and interactive factors such as low light levels and possible artifacts due to the artificial experimental conditions. It seems likely that increases in solar UV-B radiation of the magnitude anticipated under current stratospheric ozone projections will not significantly inhibit photosynthesis and cause DNA damage in plants. This is in part due to the well-evolved protection mechanisms present in most plant species. One of the significant plant responses to UV-B is changes in foliar secondary chemistry, which could be translated into significant effects at higher trophic levels through plant-herbivore interactions and decomposition. Enhanced UV-B radiation due to stratospheric ozone depletion could also cause morphological changes that would affect competitive interactions, especially if contrasting UV-B sensitivity exists among the competitors.

Continuous UV-B irradiation induces endoreduplication and peroxidase activity in epidermal cells surrounding trichomes on cucumber cotyledons

Most trichomes on the surface of cucumber (Cucumis sativus L.) cotyledons consist of three cells. We previously showed that continuous UV-B (290-320 nm) irradiation induces rapid cellular expansion and the accumulation of polyphenolic compounds, possibly stress lignin, in epidermal cells around these trichomes.(1)) To examine the mechanism of the UV-B-induced cellular expansion and to determine which step is stimulated by UV-B irradiation in the lignin synthesis pathway, we investigated relative DNA contents in epidermal cells, including trichomes, and enzyme activity and gene expression in the phenylpropanoid pathway. UV-B irradiation increased the ploidy level over 15 days, specifically in the epidermal cells surrounding trichomes, but not in the other epidermal cells or trichomes. In epidermal cells surrounding trichomes, UV-B irradiation induced peroxidase (POX) activity from days 7 to 15. In cotyledons, UV-B exposure induced CS-POX1 and CS-POX3 gene expression within 2 days, and it also induced two other enzymes in the phenylpropanoid pathway, sinapyl alcohol dehydrogenase and coniferyl alcohol dehydrogenase, from days 9 to 11. Thus, exposure to UV-B induces expansion, endoreduplication, POX activity, and the accumulation of polyphenolic compounds in epidermal cells surrounding the trichomes of cucumber cotyledons. Because polyphenolic compounds such as lignin absorb UV-B, our data indicate a physiological protective mechanism against UV-B irradiation in cucumber.

Biochemical changes associated with in vivo RbcL fragmentation by reactive oxygen species under chilling-light conditions

During physiological stress, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) degradation is accelerated, which is considered to be one of the key factors responsible for photosynthetic decline. A recent study has shown that the large subunit (RbcL) of Rubisco is directly fragmented by hydroxyl radicals in Cucumis sativus leaves under chilling-light conditions. In the present study, we investigated biochemical aspects associated with this in vivo RbcL fragmentation by reactive oxygen species. RbcL fragmentation was observed in C. sativus and Phaseolus vulgaris, but not in Solanum lycopersicum, Glycine max, Oryza sativa, Triticum aestivum, Spinacia oleracea or Arabidopsis thaliana. In C. sativus and P. vulgaris, RbcL fragmentation followed the fragmentation of PsaB, while in the other species, PsaB fragmentation did not occur. In C. sativus and P. vulgaris, the activities of antioxidant enzymes decreased dramatically under chilling-light conditions, and the proportion of uncarbamylated Rubisco increased. These data suggest that in vivo RbcL fragmentation under chilling-light conditions is associated with a combination of events, namely, inactivation of antioxidant enzymes, destruction of photosystem I and an increase of uncarbamylated Rubisco, which can produce hydroxyl radicals via the Fenton reaction at the catalytic site of RbcL.

Signal Transduction in Responses to UV-B Radiation

UV-B radiation is a key environmental signal that initiates diverse responses in plants that affect metabolism, development, and viability. Many effects of UV-B involve the differential regulation of gene expression. The response to UV-B depends on the nature of the UV-B treatment, the extent of adaptation and acclimation to UV-B, and interaction with other environmental factors. Responses to UV-B are mediated by both nonspecific signaling pathways, involving DNA damage, reactive oxygen species, and wound/defense signaling molecules, and UV-B-specific pathways that mediate photomorphogenic responses to low levels of UV-B. Importantly, photomorphogenic signaling stimulates the expression of genes involved in UV-protection and hence promotes plant survival in UV-B. Photomorphogenic UV-B signaling is mediated by the UV-B-specific component UV RESISTANCE LOCUS8 (UVR8). Both UVR8 and CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1) are required for UV-B-induced expression of the ELONGATED HYPOCOTYL5 (HY5) transcription factor, which plays a central role in the regulation of genes involved in photomorphogenic UV-B responses.

UVB sensitivity and cyclobutane pyrimidine dimer (CPD) photolyase genotypes in cultivated and wild rice species

We investigated the UVB-sensitivity in 12 rice strains belonging to two cultivated species (O. sativa and O. glaberrima) and three wild species (O. barthii, O. meridionalis and O. rufipogon) of rice possessing the AA genome, while focusing on the CPD photolyase activity and the genotypes of CPD photolyase. Although the UVB sensitivity, CPD photolyase activity, and CPD photolyase genotype varied widely among these rice species, the sensitivity to UVB radiation depended on the activity of the CPD photolyase, regardless of grass shape, habitat, or species. The rice strains examined here clearly divided into three groups based on the CPD photolyase activity, and the activity of the strains greatly depended on amino acid residues at positions 126 and 296, with the exception of the W1299 strain (O. meridionalis). The amino acid residues 126 and 296 of CPD photolyase in Sasanishiki strain (O. sativa), which showed higher enzymatic activity and more resistance to UVB, were glutamine (Gln) and Gln, respectively. An amino acid change at position 126 from Gln to arginine ("Nori"-type) in the photolyase led to a reduction of enzymatic activity. Additionally, an amino acid change at position 296 from Gln to histidine led to a further reduction in activity. The activity of the W1299 strain, which possesses a "Nori"-type CPD photolyase, was the highest among the strains examined here, and was similar to that of the Sasanishiki. The CPD photolyase of the W1299 contains ten amino acid substitutions, compared to Sasanishiki. The alterations in amino acid residues in the W1299 CPD photolyase compensated for the reduction in activity caused by the amino acid substitutions at positions 126. Knowledge of the activity of different CPD photolyase genotypes will be useful in developing improved rice cultivars.

From crop domestication to super-domestication

Research related to crop domestication has been transformed by technologies and discoveries in the genome sciences as well as information-related sciences that are providing new tools for bioinformatics and systems' biology. Rapid progress in archaeobotany and ethnobotany are also contributing new knowledge to understanding crop domestication. This sense of rapid progress is encapsulated in this Special Issue, which contains 18 papers by scientists in botanical, crop sciences and related disciplines on the topic of crop domestication. One paper focuses on current themes in the genetics of crop domestication across crops, whereas other papers have a crop or geographic focus. One feature of progress in the sciences related to crop domestication is the availability of well-characterized germplasm resources in the global network of genetic resources centres (genebanks). Germplasm in genebanks is providing research materials for understanding domestication as well as for plant breeding. In this review, we highlight current genetic themes related to crop domestication. Impressive progress in this field in recent years is transforming plant breeding into crop engineering to meet the human need for increased crop yield with the minimum environmental impact - we consider this to be 'super-domestication'. While the time scale of domestication of 10 000 years or less is a very short evolutionary time span, the details emerging of what has happened and what is happening provide a window to see where domestication might - and can - advance in the future.

Continuous UV-B irradiation induces morphological changes and the accumulation of polyphenolic compounds on the surface of cucumber cotyledons

Sharp-headed and globular-headed trichomes are found on the surface of cucumber (Cucumis sativus L.) cotyledons. Most sharp-headed trichomes consist of three cells. Toluidine blue O stains sharp-headed but not globular-headed trichomes. The effect of continuous ultraviolet-B (UV-B; 290-320 nm) irradiation on the surface of cucumber cotyledons was examined with respect to the two trichome types. Continuous UV-B irradiation induced cell division at or under the basal part of sharp-headed trichomes, resulting in an increase in the number of cell layers from three to six. In parallel, the area stained by toluidine blue O expanded to include epidermal cells surrounding sharp-headed trichomes. Regions of alkali-induced fluorescence due to the presence of polyphenolic compounds coincided with areas stained by toluidine blue O. In contrast, continuous UV-B irradiation did not cause morphological changes in globular-headed trichomes. Thus, continuous UV-B irradiation causes the accumulation of polyphenolic compounds in cucumber cotyledons and induces specific morphological changes in or around sharp-headed trichomes. UV-B exposure also increases lignin content in this tissue. Therefore, continuous UV-B irradiation may induce the specific accumulation of polyphenolic compounds, especially stress lignins, in and near sharp-headed trichomes.

Two alternatively spliced transcripts generated from OsMUS81, a rice homolog of yeast MUS81, are up-regulated by DNA-damaging treatments

OsMUS81, a rice homolog of the yeast MUS81 endonuclease gene, produced two alternative transcripts, OsMUS81alpha and OsMUS81beta. OsMus81alpha contained a Helix-hairpin-Helix (HhH) motif at the N- and C-termini, and a conserved XPF-like motif in the center, while the OsMus81beta isoform lacked the second HhH motif by alternative splicing of a cryptic intron generating a truncated protein. The two transcripts were induced after DNA-damaging treatments such as high intensity light, UV-C and gamma-radiation. The yeast two-hybrid assay detected a strong interaction between OsMus81 and OsRad54 recombinational repair proteins. These findings suggest that OsMus81 functions in maintaining genome integrity through homologous recombination.

Multiple functions of DNA polymerases

The primary role of DNA polymerases is to accurately and efficiently replicate the genome in order to ensure the maintenance of the genetic information and its faithful transmission through generations. This is not a simple task considering the size of the genome and its constant exposure to endogenous and environmental DNA damaging agents. Thus, a number of DNA repair pathways operate in cells to protect the integrity of the genome. In addition to their role in replication, DNA polymerases play a central role in most of these pathways. Given the multitude and the complexity of DNA transactions that depend on DNA polymerase activity, it is not surprising that cells in all organisms contain multiple highly specialized DNA polymerases, the majority of which have only recently been discovered. Five DNA polymerases are now recognized in Escherichia coli, 8 in Saccharomyces cerevisiae, and at least 15 in humans. While polymerases in bacteria, yeast and mammalian cells have been extensively studied much less is known about their counterparts in plants. For example, the plant model organism Arabidopsis thaliana is thought to contain 12 DNA polymerases, whose functions are mostly unknown. Here we review the properties and functions of DNA polymerases focusing on yeast and mammalian cells but paying special attention to the plant enzymes and the special circumstances of replication and repair in plant cells.

Identification and expression of the gene product encoding a CPD photolyase from Dunaliella salina

Ultraviolet light induces photoproducts, cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts (6-4PPs), in cellular DNA, which cause cytotoxic and genotoxic effects on the cells. Cells have several DNA repair mechanisms to repair the damage and to maintain genetic information of the cells. Photoreactivation is one of the DNA repair mechanism to remove UV-induced DNA damage from cellular DNA catalyzed by photolyase under visible light. Two types of photolyase, CPD photolyase and (6-4) photolyase, are specific for CPDs and for (6-4)PPs. We have isolated a gene product encoding CPD photolyase, named PHR2, from Dunaliella salina which is a kind of unicellular alga. Sequence analysis showed that PHR2 encodes a protein that has 529 amino acids and is similar to other Class II CPD photolyase. The complementation assay of the photoreactivation deficiency of the Escherichia coli SY2 by PHR2 cDNA showed a significant increase in survival rate when cells were irradiated with UV-C. Real-time PCR analysis indicated that the transcription of PHR2 was induced by UV-C, white light, high salinity, and H(2)O(2).