Climate change and health with an emphasis on interactions with ultraviolet radiation: a review

Climate change is increasingly recognized as a major risk to human health, and health concerns are assuming more importance in international debates on mitigation and adaptation strategies. Health consequences of climate change will occur through direct and indirect routes, and as a result of interactions with other environmental exposures. Heatwaves will become more common and are associated with higher mortality particularly in the elderly and those with pre‐existing cardiovascular and respiratory illnesses. Warmer ambient temperatures will result in more dehydration episodes and increased risks of renal disease and, through effects on pollen seasons, there may be an increase in allergic disease such as asthma and hayfever. Other adverse effects including on air quality, food safety and security and an expanding distribution of some infectious diseases, including vector‐borne diseases, are postulated. A related but separate environmental exposure is that of ultraviolet radiation (UVR). Interactions between climate change and stratospheric ozone (and the causes of ozone depletion) will cause changes to levels of ambient UVR in the future and warmer temperatures are likely to change sun exposure behaviour. Co‐occurring effects on aquatic and terrestrial ecosystems have potential consequences for food safety, quality and supply. Climate change‐related exposures are likely to affect the incidence and distribution of diseases usually considered as caused by UVR exposure; and changes in UVR exposure will modulate the climate change effects on human health. For example, in some regions warmer temperatures due to climate change will encourage more outdoor behaviour, with likely consequences for increasing skin cancer incidence. Although many of the health outcomes of both climate change and the interaction of climate change and UVR exposure are somewhat speculative, there are risks to over‐ or under‐estimations of health risks if synergistic and antagonistic effects of co‐occurring environmental changes are not considered.     

Grazing rates of Calanus finmarchicus on Thalassiosira weissflogii cultured under different levels of ultraviolet radiation

UVB alters photosynthetic rate, fatty acid profiles and morphological characteristics of phytoplankton. Copepods, important grazers of primary production, select algal cells based upon their size, morphological traits, nutritional status, and motility. We investigated the grazing rates of the copepod Calanus finmarchicus on the diatom Thalassiosira weissflogii cultured under 3 levels of ultraviolet radiation (UVR): photosynthetically active radiation (PAR) only (4 kJ-m(-2)/day), and PAR supplemented with UVR radiation at two intensities (24 kJ-m(-2)/day and 48 kJ-m(-2)/day). There was no significant difference in grazing rates between the PAR only treatment and the lower UVR treatment. However, grazing rates were significantly (～66%) higher for copepods feeding on cells treated with the higher level of UVR. These results suggest that a short-term increase in UVR exposure results in a significant increase in the grazing rate of copepods and, thereby, potentially alters the flow rate of organic matter through this component of the ecosystem.     

An examination of the potential effects of food limitation on the ultraviolet radiation (UVR) tolerance of Diaptomus minutus

• 1 A series of field and laboratory experiments was performed to test the possible influence of food limitation on UVR tolerance in the calanoid copepod Diaptomusminutus.
• 2 Food‐limited animals incubated at 0.5 m in a clear‐water lake for over three days showed no evidence for increased mortality compared to food‐replete animals when exposed to UVR.
• 3 Animals exposed to artificial UVR in the laboratory showed high mortality. There was no evidence that feeding improved UVR tolerance.
• 4 The results of these experiments show that UVR tolerance is not affected by a short‐term lack of energy or a lack of essential nutrients. However, effects of non‐nutritive dietary components such as carotenoids and mycosporine‐like amino acids cannot be excluded.

     

Carryover effects from environmental change in early life: An overlooked driver of the amphibian extinction crisis?

Ecological carryover effects, or delayed effects of the environment on an organism's phenotype, are central predictors of individual fitness and a key issue in conservation biology. Climate change imposes increasingly variable environmental conditions that may be challenging to early life-history stages in animals with complex life histories, leading to detrimental physiological and fitness effects in later life. Yet, the latent nature of carryover effects, combined with the long temporal scales over which they can manifest, means that this phenomenon remains understudied and is often overlooked in short-term studies limited to single life-history stages. Herein, we review evidence for the physiological carryover effects induced by elevated ultraviolet radiation (UVR; 280–400 nm) as a potential contributor to recent amphibian population declines. UVR exposure causes a suite of molecular, cellular and physiological consequences known to underpin carryover effects in other taxa, but there is a lack of research linking embryonic and larval UVR exposures to fitness consequences post-metamorphosis in amphibians. We propose that the key impacts of UVR on disease-related amphibian declines are facilitated through carryover effects that bridge embryonic and larval UVR exposure with potential increased disease susceptibility post-metamorphosis. We conclude by identifying a practical direction for the study of ecological carryover effects in amphibians that could guide future ecological research in the broader field of conservation physiology. Only by addressing carryover effects can many of the mechanistic links between environmental change and population declines be elucidated.     

SHORT‐TERM AND LONG‐TERM EFFECTS OF TEMPERATURE ON PHOTOSYNTHESIS IN THE DIATOM THALASSIOSIRA PSEUDONANA UNDER UVR EXPOSURES1

Temperature is expected to modify the effects of ultraviolet radiation (UVR) on photosynthesis by affecting the rate of repair. We studied the effect of short‐term (1 h) and long‐term (days) acclimation to temperature on UVR photoinhibition in the diatom Thalassiosira pseudonana Hasle et Heimdal. Photosynthesis was measured during 1 h exposures to varying irradiances of PAR and UVR + PAR at 15, 20, and 25°C, the latter corresponding to the upper temperature limit for optimal growth in T. pseudonana. The exposures allowed the estimation of photosynthesis–irradiance (P–E) curves and biological weighting functions (BWFs) for photoinhibition. For the growth conditions used, temperature did not affect photosynthesis under PAR. However, photoinhibition by UVR was highly affected by temperature. For cultures preacclimated to 20°C, the extent of UVR photoinhibition increased with decreasing temperature, from 63% inhibition of PAR‐only photosynthesis at 25°C to 71% at 20°C and 85% at 15°C. These effects were slightly modified after several days of acclimation: UVR photoinhibition increased from 63% to 75% at 25°C and decreased from 85% to 80% at 15°C. Time courses of photochemical efficiency (Φ_PSII) under UVR + PAR were also fitted to a model of UVR photoinhibition, allowing the estimation of the rates of damage (k) and repair (r). The r/k values obtained for each temperature treatment verified the responses observed with the BWF (R² = 0.94). The results demonstrated the relevance of temperature in determining primary productivity under UVR exposures. However, the results suggested that temperature and UVR interact mainly over short (hours) rather than long (days) timescales.     

Ultraviolet radiation directly induces pigment production by cultured human melanocytes

In humans the major stimulus for cutaneous pigmentation is ultraviolet radiation (UVR). Little is known about the mechanism underlying this response, in part because of the complexity of interactions in whole epidermis. Using a recently developed culture system, human melanocytes were exposed daily to a physiologic range of UVR doses from a solar simulator. Responses were determined 24 hours after the last exposure. There was a dose-related increase in melanin content per cell and uptake of 14C-DOPA, accompanied by growth inhibition. Cells from donors of different racial origin gave proportionately similar increases in melanin, although there were approximately tenfold differences in basal values. Light and electron microscopy revealed UVR-stimulated increases in dendricity as well as melanosome number and degree of melanization, analogous to the well-recognized melanocyte changes following sun exposure of intact skin. Similar responses were seen with Cloudman S91 melanoma cells, although this murine cell line required lower UVR dosages and fewer exposures for maximal stimulation. These data establish that UVR is capable of directly stimulating melanogenesis. Because cyclic AMP elevation has been associated in some settings with increased pigment production by cultured melanocytes, preliminary experiments were conducted to see if the effects of UVR were mediated by cAMP. Both alpha-MSH and isobutylmethylxanthine (IBMX), as positive controls, caused a fourfold increase in cAMP level in human melanocytes and/or S91 cells, but following a dose of UVR sufficient to stimulate pigment production there was no change in cAMP level up to 4 hours after exposure. Thus it appears that the UVR-induced melanogenesis is mediated by cAMP-independent mechanisms.     

Effects of ultraviolet radiation on productivity and nitrogen fixation in the Cyanobacterium, Anabaena sp. (Newton’s strain)

The biological effects of ultraviolet radiation (UVR; 290–400 nm), especially the UV-B (320–400 nm) component of the spectrum, include both direct and indirect effects on many cellular processes. In cyanobacteria both photosynthesis and nitrogen fixation can be affected directly by UVR, and indirectly by UVR through the production of reactive oxygen species (ROS). For the heterocystous cyanobacterium, Anabaena sp. (Newton’s strain), exposure to UVR causes a significant decline in the quantum yields of photosystem II (PSII) fluorescence and maximum productivity despite an increase in UVR absorbing compounds, mycosporine-like amino acids (MAAs), in those cells exposed to UVR. Concurrent with these observations are significant increases in the activities of superoxide dismutase indicative of an increase in the level of oxidative stress in cells exposed to UVR. Additionally, measurements of nitrogenase activity (acetylene reduction) show a significant decrease in cyanobacteria exposed to UVR, which manifests itself as a decrease in cellular nitrogen and an increase in C:N ratios. These results show that these nitrogen-fixing cyanobacteria are particularly sensitive to UVR, both its direct and indirect effects. The effects of UVR reported here add to the increasing evidence that UVR effects on this important group of prokaryotes could affect the input of new nitrogen, and the biogeochemical cycling of this essential macronutrient in terrestrial, marine, and freshwater habitats. Handling editor: L. Naselli-Flores An erratum to this article can be found at     

Biological weighting function for xanthophyll de-epoxidation induced by ultraviolet radiation

The light-induced de-epoxidation of xanthophylls is an important photoprotective mechanism in plants and algae. Exposure to ultraviolet radiation (UVR, 280–400 nm) can change the extent of xanthophyll de-epoxidation, but different types of responses have been reported. The de-epoxidation of violaxanthin (V) to zeaxanthin (Z), via the intermediate antheraxanthin, during exposure to UVR and photosynthetically active radiation (PAR, 400–700 nm) was studied in the marine picoplankter Nannochloropsis gaditana (Eustigmatophyceae) Lubián. Exposures used a filtered xenon lamp, which gives PAR and UVR similar to natural proportions. Exposure to UVR plus PAR increased de-epoxidation compared with under PAR alone. In addition, de-epoxidation increased with the irradiance and with the inclusion of shorter wavelengths in the spectrum. The spectral dependence of light-induced de-epoxidation under UVR and PAR exposure was well described by a model of epoxidation state (EPS) employing a biological weighting function (BWF). This model fit measured EPS in eight spectral treatments using Schott long pass filters, with six intensities for each filter, with a R² = 0.90. The model predicts that 56% of violaxanthin is de-epoxidated, of which UVR can induce as much as 24%. The BWF for EPS was similar in shape to the BWF for UVR inhibition of photosynthetic carbon assimilation in N. gaditana but with about 22-fold lower effectiveness. These results demonstrate a connection between the presence of de-epoxidated Z and the inhibition under UVR exposures in N. gaditana . Nevertheless, they also indicate that de-epoxidation is insufficient to prevent UVR inhibition in this species.     

Positive effects of UV radiation on a calanoid copepod in a transparent lake: do competition, predation or food availability play a role?

Zooplankton tolerant to ultraviolet radiation (UVR) could beindirectly affected by UVR through interactions with UV-sensitivespecies in the same ecosystem. In Lake Giles, Pennsylvania,USA, the calanoid copepod Leptodiaptomus minutus is more UVRtolerant than the cohabiting species Daphnia catawba and Cyclopsscutifer. We asked whether L. minutus is affected by UV-inducedmortality of a food competitor (D. catawba) or a predator ofits nauplii (C. scutifer). We conducted two in situ enclosureexperiments with six treatments: L. minutus alone, L . minutus+ Daphnia and L. minutus + Cyclops in the presence and absenceof UVR. There were few differences in survival among treatmentsin Experiment 1, which had enhanced food and a cumulative UVR(320 nm) dose of 9.3 kJ m^–2. In Experiment 2, which hadambient food and a UVR (320 nm) dose of 20.0 kJ m^–2, L.minutus survival and reproduction were higher in the +UVR comparedto –UVR, regardless of competitors or predators. Chlorophylla (Chl a) in Experiment 2 was higher in the +UVR than –UVR.While interactions between zooplankton species of differingUVR tolerances are potentially important, these results insteaddemonstrate that the beneficial UVR effect on L. minutus isindependent of concurrent detrimental UVR effects on competitorsand predators. Further research on the phytoplankton communityis necessary to determine whether UVR alleviates bacterial competition,increases nutrient availability or affects phytoplankton byother mechanisms.     

Exposure to ultraviolet radiation (290-400 nm) causes oxidative stress, DNA damage, and expression of p53/p73 in laboratory experiments on embryos of the spotted salamander, Ambystoma maculatum

Developing embryos of the spotted salamander, Ambystoma maculatum, exposed to ultraviolet radiation (UVR; 290-400 nm) in the laboratory show a significant sensitivity to UVB (290-320 nm) radiation. Embryos in laboratory experiments exhibited significant DNA damage during exposures to UVR despite a significant increase in the production of the protective pigment melanin in response to UVR exposure. DNA damage occurs as a result of both the direct effects of exposure to UVR, and the indirect effects are mediated by the production of reduced oxygen intermediates. The production of reactive oxygen species initiates the expression of p53/p73 that leads to either DNA repair or apoptosis. When similar experiments are conducted on salamander embryos exposed to solar UVR in vernal pools, the embryos show significantly less sensitivity and higher survivorship. The differences between laboratory and field experiments are a result of the attenuation of UVR caused by the accumulation of dissolved organic carbon within the pools of these wooded areas. These findings suggest that northeastern populations of spotted salamanders are sensitive to UVR but are not significantly affected by present-day irradiances of UVR in the field. These results do suggest that continued decreases in stratospheric ozone over temperate latitudes have the potential to affect spotted salamanders in their natural habitats.     

Response of oxidative stress parameters and sunscreening compounds in Arctic amphipods during experimental exposure to maximal natural UVB radiation

The paper investigates tolerance to UV radiation (UVR) in 3 amphipod species from the Arctic Kongsfjord, Spitsbergen: the herbivore Gammarellus homari (0- to 5-m water depth), the strictly carnivore scavenger Anonyx nugax (2- to 5-m water depth) and the detritivore/carnivore Onisimus edwardsi (2- to 5-m water depth). In previous radiation exposure experiments, both carnivore species displayed elevated mortality rates already at moderate UVR levels. Therefore, the concentrations of sunscreening compounds (mycosporine-like amino acids, MAAs, and carotenoids) and two antioxidant enzymes (superoxide dismutase, catalase) were studied in the animals under control conditions and following moderate as well as high UVR exposure.In both carnivore amphipods elevated sensitivity to experimental UVR exposure went along with a degradation of the tissue carotenoid and MAAs and a decrease of the enzymatic antioxidant defence, which resulted in increased lipid peroxidation in exposed animals. In contrast, the herbivore G. homari seems well protected by high concentrations of MAAs absorbed from its algal diet, and no oxidative stress occurred under experimental UVR. The species-specific degree of UV tolerance correlates well with the animals' typical vertical distribution in the water column.     

Disruption of planktonic phosphorus cycling by ultraviolet radiation

Ultraviolet radiation (UVR) may alter phosphorous (P) cycling by plankton through changes in the acquisition and/or regeneration of dissolved P. However, to date an effect of UVR on the uptake of P has not been observed at ambient phosphate (PO₄ ³⁻) concentrations. This has lead to the conclusion that the uptake of P by plankton may be insensitive to UVR. Past research has been limited to a few individual systems, prolonged incubations in bags, or lab cultures. We suspect that experimentation with natural plankton assemblages across broader environmental and/or chemical gradients is required to appreciably understand how UVR may alter P kinetics. Therefore, our study aimed to determine the effect of UVR on the turnover time of the dissolved PO₄ ³⁻ pool, the regeneration of dissolved P, the turnover rate of particulate P, and on PO₄ ³⁻ concentrations in natural plankton assemblages across broad environmental and chemical gradients. Second we aimed to assess how UVR may alter phosphatase activity and, determine if a change in phosphatase activity under UVR irradiance is correlated with a change in P uptake as proposed in the literature. Studies were conducted on 18 thermally stratified or polymictic lakes located in Ontario and Saskatchewan, Canada. Lake water samples were exposed to one of three experimental treatments: control, photosynthetically active radiation (PAR), or photosynthetically active radiation plus ultraviolet radiation (PAR + UVR). Our study is the first to demonstrate that UVR exposure has the potential to alter P cycling at ambient (picomolar) PO₄ ³⁻ concentrations. We have demonstrated that the turnover time of the PO₄ ³⁻ pool increases under UVR irradiance (i.e., P uptake decreases), while the regeneration rate of dissolved P and turnover rate of planktonic P are generally not affected; with the net effect being an increase in steady state PO₄ ³⁻ concentration (ssPO₄ ³⁻). Alkaline phosphatase activity (APA) in the dissolved and particulate fractions was significantly reduced in PAR + UVR treatments, but unrelated to changes in P uptake. In summary, we have demonstrated that the cycling of P may be disrupted by UVR, with a decrease in the uptake of P and the accumulation of PO₄ ³⁻ in the dissolved pool. This, in turn may exacerbate planktonic P limitation, alter the nutrient stoichiometry of plankton and/or indirectly alter rates of primary production in limnetic systems.     

Adaptation to the UV-induced suppression of phagocytic activity in murine peritoneal macrophages following chronic exposure to solar simulated radiation.

Exposure of certain strains of mice to ultraviolet radiation (UVR) is known to suppress both local and systemic immune responses, including a reduction in the phagocytic activity of peritoneal macrophages. However, in many instances, the immunological effects have been observed following a single or a limited number of doses of UVR from sources containing a higher proportion of UVB than that emitted by the sun. The first aim of the present study was to establish whether a single exposure of C3H/HeN mice to solar simulated radiation (SSR) suppressed the ability of the peritoneal macrophages to phagocytose opsonised sheep red blood cells. The mice were irradiated with SSR from Cleo Natural lamps and a single dose of 31.9 J cm(-2) was found to be the minimal dose for significant suppression of macrophage phagocytic activity. Such a dose did not modulate the surface expression of I-A(k), CD11b, CD86 or FcgammaRII/III (CD32/16) on the macrophages. The second aim was to assess whether repeated SSR exposures with a dose below the minimal immunosuppressive dose affected macrophage activity and, if so, to test for photoadaptation by repeated exposures followed by a single, normally immunosuppressive dose of SSR, and then assaying the macrophage activity. Groups of mice were irradiated on each of 2, 10 and 30 days with 14.9 J cm(-2) SSR, followed in some instances by a single additional exposure of 31.9 J cm(-2) on the same day as the last irradiation. The phagocytic activity of the peritoneal macrophages was tested 24 h later. It was reduced by 32%, 18% and 4% respectively after 2, 10 and 30 repeated exposures to SSR, and by 39%, 21% and 7% respectively after 2, 10 and 30 repeated exposures plus the additional higher dose at the end. Thus, although the macrophage activity was initially suppressed by the SSR, photoadaptation of this immune parameter occurred following repeated exposures.     

The effects of short-term exposures to ultraviolet radiation in the Hawaiian Coral Montipora verrucosa

Exposure to ultraviolet radiation (UVR, 290–400 nm) is an important abiotic factor that tropical marine organisms have been exposed to over evolutionary time. Additionally, UVR is known to cause coral bleaching independently and is an important synergistic factor in bleaching caused by thermal stress. Corals can avoid some of the damage associated with exposure to UVR by producing UVR-absorbing compounds such as mycosporine-like amino acids (MAAs). To examine the role of MAAs in the UVR photobiology of corals we conducted experiments on the Hawaiian coral Montipora verrucosa. M. verrucosa colonies were collected from 1, 5 and 10 m and exposed to three different UVR treatments for 3 days under constant visible irradiances equivalent to a depth of 0.15 m depth in Kane'ohe Bay. In addition to quantifying the MAA concentration of these corals several types of UVR-induced damage were measured to assess whether MAAs were providing protection. Quantum yields of photosystem II (PSII) fluorescence and excitation pressure on PSII were measured for each coral, and the formation of direct UVR damage to DNA was measured as cyclobutane pyrimidine dimers (CPDs) and (6-4) pyrimidine–pyrimidone photoproducts for the holobiont. All corals exhibited midday depressions in quantum yields, developed DNA photoproducts, and increased their MAA concentrations significantly as a result of UVR exposures. CPD accumulation in M. verrucosa was highest in corals from 1 m, which had the lowest MAA concentrations at the end of the experiment. Corals originally from 10 m showed the highest MAA concentration and lowest DNA damage in response to exposure to UVR. While corals from all collection depths displayed some sensitivity to increased irradiances of UVR, their respective levels of tolerance were clearly dependant on their previous light history.     

ADAPTATION OF A PSYCHROPHILIC FRESHWATER DINOFLAGELLATE TO ULTRAVIOLET RADIATION1

Little is known about the UV photobiology of psychrophilic dinoflagellates, particularly in freshwater systems. We addressed the life strategies of Borghiella dodgei Moestrup, Gert. Hansen et Daugbjerg to cope with ambient levels of ultraviolet radiation (UVR) under cold conditions. Several physiological parameters related to growth, metabolism, and UVR protection were determined for 4 d in UVR‐exposed and control cells by applying stable isotope analysis, spectrophotometry, and liquid chromatography–mass spectrometry (LC/MS). In UVR‐exposed cells, assimilation of ¹⁵N and ¹³C and content of chl a and carotenoids, specifically diatoxanthin with respect to dinoxanthin and diadinoxanthin, were increased; furthermore, catalase activity showed a cyclic pattern with a strong increase after UVR exposure but a rapid return to preexposure levels. Both in UVR‐exposed and control cells, no lipid peroxidation of galactolipids was observed. However, in UVR‐exposed cells, content of galactolipids was higher and linked to an increase in monogalactosyldiacylglycerols (MGDGs). We concluded that Borghiella's adaptation to UVR depended on a general metabolic enhancement and efficient scavenging of oxygen radicals to mitigate and counteract damage. While Borghiella seemed to be well adapted to ambient UVR, the interactive effects of higher temperature and UVR on psychrophilic species in front of climate change merit further investigation.     

Acute Erythemal Ultraviolet Radiation Causes Systemic Immunosuppression in the Absence of Increased 25-Hydroxyvitamin D3 Levels in Male Mice

Vitamin D is synthesised by ultraviolet (UV) irradiation of skin and is hypothesized to be a direct mediator of the immunosuppression that occurs following UV radiation (UVR) exposure. Both UVR and vitamin D drive immune responses towards tolerance by ultimately increasing the suppressive activities of regulatory T cells. To examine a role for UVR-induced vitamin D, vitamin D₃-deficient mice were established by dietary vitamin D₃ restriction. In comparison to vitamin D₃-replete mice, vitamin D₃-deficient mice had significantly reduced serum levels of 25-hydroxyvitamin D₃ (25(OH)D₃, <20 nmol.L⁻¹) and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃, <20 pmol.L⁻¹). Following either acute erythemal UVR, or chronic sub-erythemal UVR (8 exposures over 4 weeks) treatment, serum 25(OH)D₃ levels significantly increased in vitamin D₃-deficient female but not male mice. To determine if UVR-induced vitamin D was a mediator of UVR-induced systemic immunosuppression, responses were measured in mice that were able (female) or unable (male) to increase systemic levels of 25(OH)D₃ after UVR. Erythemal UVR (≥4 kJ/m²) suppressed contact hypersensitivity responses (T helper type-1 or -17), aspects of allergic airway disease (T helper type-2) and also the in vivo priming capacity of bone marrow-derived dendritic cells to a similar degree in female and male vitamin D₃-deficient mice. Thus, in male mice, UVR-induced 25(OH)D₃ is not essential for mediating the immunosuppressive effects of erythemal UVR.     

海南岛西北沿岸海域浮游桡足类的分布及群落特征

为了解昌江沿岸海域生态系统的现状, 探讨海域环境因素对浮游动物的生存环境造成的影响。本文根据2008年11月至2009年7月在海南西部昌江沿岸水域21个测站、4个季度月调查所获的浮游桡足类样品数据, 对该海域浮游桡足类群落结构、分布、季节变化及影响因素进行了分析。本调查共鉴定出桡足类44种, 隶属4目17科24属, 其中秋季25种, 冬季23种, 春季22种, 夏季23种。本次调查共发现优势种6种, 分别是微刺哲水蚤(Canthocalanus pauper)、亚强次真哲水蚤(Subeucalanus subcrassus)、锥形宽水蚤(Temora turbinata)、刺尾纺锤水蚤(Acartia spinicauda)、椭形长足水蚤(Calanopia elliptica)和精致真刺水蚤(Euchaeta concinna), 优势种以近岸暖水种居多。浮游桡足类丰度季节变化明显: 冬季最高, 达409 ind./m³; 秋季次之, 为144 ind./m³, 春季为55 ind./m³, 夏季最低仅为17 ind./m³。其丰度的平面分布显示: 秋、冬季节分别在海区中部和南部形成明显密集区, 春、夏季节则大致呈现由外海向近岸逐渐递减的趋势。浮游桡足类的多样性指数(H')表现为夏季>春季>秋季>冬季, 春、夏季的均匀度指数(J')明显高于秋、冬季。本调查反映出该海区的桡足类群落具有热带—亚热带区系特征, 种类组成季节更替明显, 桡足类种群受海域水温和硅藻的影响明显, 受盐度影响不明显。     

In Vivo Function of Tryptophans in the Arabidopsis UV-B Photoreceptor UVR8

Arabidopsis thaliana UV RESISTANCE LOCUS8 (UVR8) is a photoreceptor specifically for UV-B light that initiates photomorphogenic responses in plants. UV-B exposure causes rapid conversion of UVR8 from dimer to monomer, accumulation in the nucleus, and interaction with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1), which functions with UVR8 in UV-B responses. Studies in yeast and with purified UVR8 implicate several tryptophan amino acids in UV-B photoreception. However, their roles in UV-B responses in plants, and the functional significance of all 14 UVR8 tryptophans, are not known. Here we report the functions of the UVR8 tryptophans in vivo. Three tryptophans in the β-propeller core are important in maintaining structural stability and function of UVR8. However, mutation of three other core tryptophans and four at the dimeric interface has no apparent effect on function in vivo. Mutation of three tryptophans implicated in UV-B photoreception, W233, W285, and W337, impairs photomorphogenic responses to different extents. W285 is essential for UVR8 function in plants, whereas W233 is important but not essential for function, and W337 has a lesser role. Ala mutants of these tryptophans appear monomeric and constitutively bind COP1 in plants, but their responses indicate that monomer formation and COP1 binding are not sufficient for UVR8 function.     

Photoactivated UVR8-COP1 Module Determines Photomorphogenic UV-B Signaling Output in Arabidopsis

In Arabidopsis, ultraviolet (UV)-B-induced photomorphogenesis is initiated by a unique photoreceptor UV RESISTANCE LOCUS 8 (UVR8) which utilizes its tryptophan residues as internal chromophore to sense UV-B. As a result of UV-B light perception, the UVR8 homodimer shaped by its arginine residues undergoes a conformational switch of monomerization. Then UVR8 associates with the CONSTITUTIVELY PHOTOMORPHOGENIC 1-SUPPRESSOR OF PHYA (COP1-SPA) core complex(es) that is released from the CULLIN 4-DAMAGED DNA BINDING PROTEIN 1 (CUL4-DDB1) E3 apparatus. This association, in turn, causes COP1 to convert from a repressor to a promoter of photomorphogenesis. It is not fully understood, however, regarding the biological significance of light-absorbing and dimer-stabilizing residues for UVR8 activity in photomorphogenic UV-B signaling. Here, we take advantage of transgenic UVR8 variants to demonstrate that two light-absorbing tryptophans, W233 and W285, and two dimer-stabilizing arginines, R286 and R338, play pivotal roles in UV-B-induced photomorphogenesis. Mutation of each residue results in alterations in UV-B light perception, UVR8 monomerization and UVR8-COP1 association in response to photomorphogenic UV-B. We also identify and functionally characterize two constitutively active UVR8 variants, UVR8^W285A and UVR8^R338A, whose photobiological activities are enhanced by the repression of CUL4, a negative regulator in this pathway. Based on our molecular and biochemical evidence, we propose that the UVR8-COP1 affinity in plants critically determines the photomorphogenic UV-B signal transduction coupling with UVR8-mediated UV-B light perception.