Effects of UV radiation of different wavebands on pigmentation, 15N-ammonium uptake, amino acid pools and adenylate contents of marine diatoms

Three marine diatoms Lauderia annulata Cleve, Odontella sinensis (Greville) Grunow and Thalassiosira rotula Meunier were exposed to ultraviolet (UV) radiation of different wavebands under controlled laboratory conditions (0.035 vol% CO₂, 18 °C). Several changes in the patterns of pigments in these organisms were seen depending on the waveband of UV radiation and species examined. UV-B and UV-B plus UV-A radiation led to a reduction in the overall pigment content of all three diatoms. The uptake of ¹⁵N-ammonium was less affected by 5-h UV-A (WG 320) but significantly reduced after UV-B and UV-B plus UV-A exposure. The pattern of free amino acid pools varied depending on the applied UV wavebands and the tested diatom. The main protein-bound amino acids of T. rotula decreased after 5-h UV irradiance except leucine. Contents of adenosine 5′-mono-, di-, and triphosphate (AMP, ADP and ATP) were affected differently by UV radiation; ATP values increased at the end of UV-B and UV-B plus UV-A exposure. These results have been discussed with reference to the impact of the different UV sources and the influence on the nitrogen metabolism in connection to pigments and supply with energy. Received: 13 May 1997 / Accepted: 11 October 1997     

Growth and DNA damage in young Laminaria sporophytes exposed to ultraviolet radiation: implication for depth zonation of kelps on Helgoland (North Sea)

Growth as an integrative parameter of all physiological processes was measured in young sporophytes of temperate Laminaria digitata, Laminaria saccharina and Laminaria hyperborea exposed in the laboratory to irradiance consisting of either only photosynthetically active radiation (PAR) or to a spectrum including ultraviolet radiation (UVR) (PAR+UVA+UVB) by use of cut-off glass filters. Size increment was measured every 10 min over a period of 18–21 days using growth chambers with on-line video measuring technique. In the chamber, plants were grown at 10±2°C and 16:8 h light–dark cycles with 6 h additional UVR exposure in the middle of the light period. Tissue morphology and absorption spectra were measured in untreated young sporophytes while chlorophyll a content and DNA damage were measured in treated thalli at the end of the experiment. Sensitivity of growth under UVR was found to be related to the observed upper depth distribution limit of the upper sublittoral L. digitata, upper to mid sublittoral L. saccharina and lower sublittoral L. hyperborea. Tissue DNA damage is, however, dependent on thallus thickness which minimizes UVR effect where outer cell layers shade inner cells and provide longer pathlength for UVR. Exposure to UVR causes cellular, enzymatic and molecular damage. Presence of UV-absorbing compounds further reduces effective UVR from reaching physiological targets. The cost of producing higher amount of UV-absorbing compounds and effective DNA repair mechanism can, however, divert photosynthate at the expense of growth. Tissue chlorophyll a content was not significantly different between treatments suggesting a capacity for acclimation to moderate UVR fluence. Growth acclimation to repeated UVR exposure was observed within a period of 12 days while growth inhibition was observed after a longer UVR exposure period of 21 days. The results give further insight into the effects of UVR on the cellular level and show how ecological parameters such as the upper depth distribution limit are dependent on cellular processes.     

连续两年紫外线-B辐射增强对玉米种子发芽及幼苗生长的影响

研究了在紫外线 (UV -B)辐射增强条件下与自然光下生长的玉米种子的发芽和幼苗生长特性以及对UV -B反应的变化。结果表明 :与自然光下生长的玉米种子相比 ,UV -B辐射增强条件下生长的玉米种子的发芽率和幼苗生长指标有不同程度的下降 ,但在连续两年UV -B强度增加条件下 ,其种子发芽和幼苗生长指标受高强度UV -B影响的程度显著下降。在连续两年UV -B辐射增强条件下生长的玉米种子萌发的幼苗叶片类黄酮含量显著高于在自然光下生长的玉米种子萌发的幼苗 ,这可能是在UV -B辐射增强条件下生长的玉米对UV -B辐射增强产生适应性的重要原因之一。     

Evaluation of chlorophyll fluorescence, in vivo spectrophotometric pigment absorption and ion leakage as biomarkers of UV-B exposure in marine macroalgae

The photosynthetic fluorescence ratio F_v:F_m, in vivo absorption spectra and ion leakage were evaluated as biomarkers of ambient and elevated UV-B (280 to 320 nm) exposure of the intertidal alga Enteromorpha intestinalis (Chlorophyta) and the sublittoral alga Palmaria palmata (Rhodophyta). Measurements of thallus growth were also used to assess adverse biological effects. Ambient and elevated UV-B significantly inhibited photosynthesis in both species. It was shown that the F_v:F_m ratio is a sensitive, non-specific general biomarker of UV-B exposure in both species. Moreover, the in vivo absorption of what was tentatively identified as chlorophylls a and b as well as phycoerythrin and/or carotenoids, phycoerythrobilin and phycocyanin decreased in a dose-response dependent manner and was associated with a decrease in growth rate in P. palmata. The intertidal alga E. intestinalis showed a greater degree of tolerance to UV-B exposure. These results indicate that changes in the F_v:F_m ratio together with reductions in in vivo pigment absorption could provide an early quantitative warning of the detrimental effects of UV-B in marine macroalgae. Received: 16 May 1997 / Accepted: 16 July 1997     

Sensitivity and acclimation to UV radiation of zoospores from five species of Laminariales from the Arctic

Spores of five Laminariales from Arctic Spitsbergen were exposed in the laboratory to photosynthetically active radiation (PAR; 400–700 nm), PAR+UVA radiation (UVAR; 320–400 nm) and PAR+UVAR+UVB radiation (UVBR; 280–320 nm). Subsequently, germination was monitored over periods of 3, 6 and 9 days. The investigated species were the upper sublittoral Saccorhiza dermatodea, the upper to mid-sublittoral Alaria esculenta and Laminaria digitata, the mid-sublittoral L. saccharina and the lower sublittoral L. solidungula. The germination capacity decreased sharply after 16 h exposure to PAR+UVAR+UVBR in all species. However, S. dermatodea was able to recover from the damaging effects of UVBR. There was also a small increase in percentage germination of A. esculenta 6–9 days after the treatment. No recovery was evident in the other species. After 8 h exposure to PAR+UVA+UVB, L. digitata recovered completely, and L. saccharina and L. solidungula, partially. The only species susceptible to PAR+UVAR was L. solidungula. One prominent cytological feature of UVR-exposed spores was the enlargement of phenolic vesicles (physodes) (particularly seen in S. dermatodea and A. esculenta), which may have a protective function against UVR. Pilot experiments under natural irradiance conditions indicate that the PAR component of solar radiation exerts an additional stress. Overall the data show that zoospores of the species from the upper sublittoral are less sensitive to UVR or have the capacity to recover from UV stress in contrast to species from deeper waters, probably due to their UV protective and repair capabilities.Communicated by O. Kinne, Oldendorf/Luhe     

UV-radiation versus grazing pressure: long-term floating of kelp rafts (<Emphasis Type="Italic">Macrocystis pyrifera</Emphasis>) is facilitated by efficient photoacclimation but undermined by grazing losses

Large quantities of floating macroalgae are traveling in coastal waters of the SE Pacific and in other temperate climate zones. While afloat, these algae are potentially exposed to full solar radiation, including UVA and UVB, which can have profound effects on their physiological and growth performance. Latitudinal variations in UV-radiation (UVR) are hypothesized to affect floating algae differently with higher impacts at low latitudes than at high latitudes. In addition, UVR together with grazing might accelerate the demise of floating kelps. This hypothesis was tested with outdoor laboratory experiments in which sporophytes of the giant kelp Macrocystis pyrifera (L.) C. Agardh were exposed to a combination of different UVR regimes (PAR only, PAR + UV) and grazing at three sites along the Chilean coast (20°S, 30°S, and 40°S). A latitudinal trend in irradiance was detected with increasing values from 40°S to 20°S. Surprisingly, floating M. pyrifera responded with a high acclimation potential within this latitudinal UVR gradient. At 20°S, floating kelps were slightly sensitive to UVR, which was reflected in reduced blade growth. At 30°S, physiological responses were hardly affected by the prevailing irradiance but sporophyte growth and thus persistence mainly depended on the presence or absence of amphipod grazers. At high latitudes, grazing had only minor impacts on algal biomass and blade growth, and kelps thrived well under all tested environmental conditions. Overall, our results reveal that floating M. pyrifera was only slightly affected by UVR and that sporophytes can efficiently acclimate over a latitudinal UVR gradient that spans from 20°S to 40°S. Given this high acclimation potential, we suggest that these (and possibly other) positively buoyant algae are important dispersal agents over a wide range of temperate latitude conditions.     

UV-B增加与酸雨复合处理对大豆种子萌发和幼苗生长的影响

研究了UV-B辐射增加与酸雨的复合处理对大豆种子萌发和幼苗生长的影响。结果表明：UV-B辐射增加对大豆种子的萌发没有影响，酸雨处理降低了大豆种子的发芽率。UV-B辐射增加与酸雨的复合处理，降低了幼苗的株高、绿叶数、叶面积、干质量、叶绿素和蒸腾速率，复合胁迫的下降幅度明显高于单一因子胁迫，并且下降幅度受UV-B辐射强度与酸雨pH的影响。UV-B辐射增加与酸雨处理在抑制幼苗生长上具有协同作用。     

UV-absorbing substances in zooxanthellate and azooxanthellate clams

The effects of UV-A and UV-B radiation on photosynthesis of zooxanthellae within the siphonal mantle of the giant clam, Tridacna crocea, and in isolation were studied. While UV-B irradiation (2.4 W m⁻², 20 min) completely suppressed photosynthesis of the isolated zooxanthellae, it had little effect on their photosynthetic ability if they were irradiated while within the siphonal mantle of the host tissue. Chemical analysis of the siphonal mantle of T. crocea showed the presence of significant amounts of mycosporine-like amino acids (MAAs), which absorb UV-A and -B light. However, no MAA was detected in the isolated zooxanthellae. MAAs were concentrated in the siphonal mantle and kidney tissues in comparison with other tissues. In the siphonal mantle, MAA concentrations were the highest in the outermost surface layer where most of the zooxanthella cells resided. This indicates that the zooxanthellae are protected from UV radiation by a screen of concentrated MAAs in the host clam. Aside from T. crocea, significant amounts of MAAs were found not only in other zooxanthellate clams, such as T. derasa, Hippopus hippopus, Colculum cardissa and Fragum unedo, but also in a closely related azooxanthellate clam, Vasticardium subrugosum. On the other hand, no MAA was detected in any of the zooxanthellae from these zooxanthellate clams. No MAA was detected in the tissues of a deep-sea bivalve, Calyptogena soyoae. Although MAAs seem to block strong UV radiation in the shallow-water clam, they are probably not essential for the clam's life in the dark. MAAs in shallow-water clams may be derived from food and accumulated in their tissues, especially in the siphonal mantle and kidney. Received: 29 November 1996 / Accepted: 13 January 1997     

Effects of ultraviolet radiation and water motion on the reef coral Porites compressa Dana: a flume experiment

The effects of water flow and ultraviolet radiation (UVR, 280–400 nm) on the reef coral Porites compressa Dana were explored in a manipulative flume experiment. The aim of this study was to determine whether this coral responds to changes in the UVR environment by adjusting the tissue concentration of UV-absorbing compounds (mycosporine-like amino acids, MAAs), and to see whether such an acclimation is affected by water flow. Also, calcification rate and chlorophyll-a concentration were measured during the experiment to estimate the potential costs (in the form of slowed growth and/or reduced photosynthetic capacity) to the coral–alga symbiosis of being exposed to UVR and producing MAAs. Branches of P. compressa from a single male colony were exposed to high or low flow (15 cm s⁻¹ and 3 cm s⁻¹, respectively) and ambient or no UVR in an outdoor, continuous-flow seawater system. Chlorophyll-a and MAA concentrations were determined after zero, 3 and 6 weeks of exposure to the experimental conditions. Increase in buoyant weight during the two 3-week periods was used to calculate calcification rate. The presence of UVR had a significant positive effect on total MAA concentration in the P. compressa colonies; however, there were significant interactions present. In colonies exposed to UVR, MAA concentration increased and then decreased to initial levels in high water flow, and increased steadily in low water flow. In colonies receiving no UVR, MAA concentration decreased steadily, declining 23% in 6 weeks. The absence of UVR did not result in higher chlorophyll-a concentrations, but the calcification rate was slightly affected by UVR. This study supports the putative photoprotective role of MAAs in P. compressa, and suggests that the costs of mitigating the effects of ambient UVR are detectable, but they are very small. Received: 29 February 2000 / Accepted: 20 September 2000     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Effects of ultraviolet radiation on different life cycle stages of the south Pacific kelps, Lessonia nigrescens and Lessonia trabeculata (Laminariales, Phaeophyceae)

The effects of exposure to ultraviolet radiation (UVR), 280–400 nm, in different life histories and development stages of the kelps, Lessonia nigrescens and L. trabeculata, collected in the south-east Pacific coast (30°S) were evaluated in the laboratory. Germination and viability (motile zoospores, settled spores), diameter of the primary cell of the gametophytes, percentage of female gametophytes, fertility and sporophytes production were measured after exposure to three radiation treatments (PAR; PAR + UVA; PAR + UVA + UVB). The effects of UVR in young sporophytes (diploid stage) were evaluated as changes in maximal quantum yield of chlorophyll fluorescence of photosystem II (PSII) (F _v/F _m). A significant decrease in all variables was observed for the treatment that included UVB (PAR + UVA + UVB) after 2 and 4 h of exposure, in relation to the control. The motile spores were more sensitive to UVR exposure compared to settled spores and gametophytes, suggesting that along with an increase in ontogenetic development; there is an increase in the tolerance to UVR. In addition, it was observed that early stages of the intertidal L. nigrescens were more tolerant to UVR compared to the subtidal L. trabeculata. These results allow initially to infer that UVR may be regarded as an important environmental factor influencing the upper limit of distribution of these species, mainly through its detrimental effects on the early stages of the life cycle.     

Effects of ultraviolet-B enhancement on marine trophic levels in a stratified coastal system

We examined the effects of enhanced UV-B radiation (relative to ambient) on marine trophic levels inhabiting a stratified coastal ecosystem, using living models (13 000 liter marine enclosures) of a temperate estuarine water column. The experiment was carried out in June and July 1994 on a plankton community drawn from lower Narragansett Bay, Rhode Island, USA. The effects of altered UV-B radiation (elevated 50% over ambient, tenfold DNA-weighted) on three trophic strata: the primary producers (photosynthetic algae), primary herbivores (copepods), and fish eggs and larvae (Anchoa mitchilli Cuvier and Valenciennes) were examined. The goal was to determine if UV-B–induced alterations at the base of the food chain had impacts on other elements of the trophic web. Phytoplankton abundance (P=0.02) and biomass (P=0.007) were significantly reduced in UV-B–enhanced treatments, above but not below the thermocline (2.25 m), during the second week of the study. Copepod nauplii were significantly less abundant in UV-B–enhanced mesocosms than in control treatments during the third and fourth weeks of the study (P=0.01). A portion of the impact on nauplii may be a result of alterations at the base of the food web. The greater mortality of nauplii in UV-B–enhanced systems did not translate to reduced abundance of copepodite (P=0.83) or adult (P=0.29) copepods. No significant effects were observed for microzooplankton (P=0.15). Neither the mortality rates nor the growth rates of larval anchovy were significantly affected by the experimental increase in UV-B (P>0.05). Despite the tenfold increase in biologically damaging UV-B, effects were not seen at higher trophic levels, most likely because of the rapid extinction of UV-B in the highly colored coastal water. Received: 13 November 1996 / Accepted: 18 July 1997     

Photosynthesis and growth of red and green morphotypes of Kappaphycus alvarezii (Rhodophyta) from the Philippines

The effect of photosynthetic available radiation (PAR) levels, light quality, ultraviolet (UV) radiation, and temperature on photosynthesis, growth, and chlorophyll fluorescence was evaluated in red and green morphotypes of the rhodophyte Kappaphycus alvarezii (Doty) Doty under controlled conditions. Chlorophyll a and phycoerythrin (PE) levels were similar in the red and green morphotypes cultured under the same conditions, but phycocyanin (PC) and allophycocyanin (APC) levels were 2-fold greater in the green than in the red morphotype. Pigment characterization indicated that the overexpression of PC and APC masked the red pigmentation in the green morphotype. Maximum photosynthesis and photosynthetic efficiency were similar between the two morphotypes assayed at a wide temperature range, which was reflected in the similar growth rates observed in outdoor culture systems. In the green morphotype, photosynthetic efficiency increased 2-fold relative to the red morphotype when assayed with red light (λ > 600 nm), indicating that photosynthetic characteristics are modified as a result of pigment variation in these morphotypes. Such increase in photosynthetic efficiency in the green morphotype, however, did not result in greater growth rates when cultured under white light. Short exposure to high levels of solar radiation (UV-A + UV-B + PAR), and filtered solar radiation (UV-A + PAR or PAR) decreased effective quantum yield (ΔF/F _m′) in both morphotypes. The reduction of ΔF/F _m′ values in the red and green morphotypes was accounted for by high levels of PAR and not by the UV-A + UV-B + PAR and UV-A + PAR treatments. Photoinhibition caused by UV-A, UV-B, or PAR was completely reversed within 30 h after incubations. Recovery rates from photoinhibition, however, were significantly reduced in the green morphotype when incubated with UV-B radiation. The results here suggest that the overexpression of pigments do not necessarily increase photosynthesis and growth in these morphotypes. Received: 19 June 2000 / Accepted: 28 November 2000     

UVR-induced photoinhibition of summer marine phytoplankton communities from Patagonia

During austral summer 2006, experiments were carried out to evaluate the effects of ultraviolet radiation (UVR, 280–400 nm) on carbon fixation of natural phytoplankton assemblages from Patagonia (Argentina). Surface water samples were collected (ca. 100 m offshore) at mid morning using an acid-cleaned (1 N HCl) dark container. The short-term impact of UVR (measured as radiocarbon incorporation) was immediately assessed by exposing samples to three artificial illumination treatments: PAR (400–700 nm), PAR + UV-A (320–700 nm), and PAR + UV-A + UV-B (280–700 nm). Pico-nanoplankton characterized the assemblages, and taxon-specific pigment fingerprinting combined with CHEMTAX and supplemented with microscopic observations showed varied proportions of diatoms, chlorophytes, and cyanobacteria throughout January–February 2006. Photosynthetic efficiency, as assessed through assimilation numbers, was high [between 4.4 and 10.4 μg C (μg chl-a)⁻¹ h⁻¹], and it was probably favored by the supply of inorganic nutrients from the Chubut River. UVR-induced photoinhibition appeared to be related to the taxonomic composition: in general, higher photoinhibition was observed when diatoms dominated, whereas this was lower when samples were dominated by chlorophytes. Our data suggest that xanthophyll pigments might have provided only limited protection in these already highlighted acclimated assemblages.     

Inhibition of photosynthesis by ultraviolet radiation as a function of dose and dosage rate: Results for a marine diatom

The effects of ultraviolet radiation on phytoplankton are usually described as a function of dose (J m^–2, weighted appropriately). Experiments conducted in 1988 and 1989 on a marine diatom,Thalassiosira pseudonana (Clone 3H), demonstrate that during lightlimited photosynthesis in visible radiation, the inhibition of photosynthesis by supplemental ultraviolet radiation (principally UV-B: 280 to 320 nm) is a function of irradiance (W m^–2) as well as of dose: for equal doses of UV-B, a relatively short exposure to high UV-B irradiance is more damaging to photosynthesis than a longer exposure to lower irradiance. In fact, photoinhibition by UV-B is well described as a monotonic, nonlinear function of irradiance for time scales of 0.5 to 4 h. A nitrate-limited culture was about nine times more sensitive to UV-B than was a nutrient-replete culture, but the kinetics of photoinhibition were similar. These results have some bearing on efforts to describe the effects of ultraviolet radiation on marine primary productivity. Action spectra of photoinhibition by UV can be constructed, but they should only be used to describe photoinhibition for specified time scales. Vertical profiles of relative photoinhibition must be interpreted cautiously because photoinhibition by UV-B is likely to be a function of incubation time and results must therefore be interpreted in the context of vertical mixing.     

UV induces reactive oxygen species,damages sperm,and impairs fertilisation in the sea urchin <Emphasis Type="Italic">Anthocidaris crassispina</Emphasis>

We demonstrated that environmentally relevant levels of UVA and UVB can reduce sperm motility (UVA: by 38–58%; UVB: by 42–85%; P < 0.05) and subsequently fertilisation success (UVA: by 38–72%; UVB: by 91–98%; P < 0.05) of urchins (Anthocidaris crassispina) in a dose-dependent manner, implicating that recruitment of urchin populations might be reduced by UVR (ultraviolet radiation) prevailing in their natural habitats. Concomitantly, reactive oxygen species (ROS) production was enhanced by UVA and UVB in a dose-dependent manner (UVA: by 1.3-fold; UVB: by 6.6–7.3-fold; P < 0.05), and the increase in ROS resulted in an increase in lipid peroxidation (LPO) in urchin sperm (UVA: by 4.2–7.2-fold; UVB: by 2.3–2.7-fold; P < 0.05). This study demonstrated that ROS production and oxidative damages enhanced by UVR may account for the observed declines in sperm motility and fertilisation, and suggests that levels of UVR prevailing in the environment may pose a significant threat to the reproductive success of natural populations of urchins spawning in shallow waters.     

UVR-induced toxicity of sludge and polycyclic aromatic hydrocarbons on seed germination and seedling growth of Triticum aestivum L.

The depletion of the ozone layer and enhancement of solar radiation may exert an adverse influence on the ecosystem. Phototoxicity of sludge and polycyclic aromatic hydrocarbons (PAHs) under ultraviolet radiation (UVR) to seedling was studied. Seeds of wheat (Triticum aestivum) were planted in sludge and PAHs (anthracene (An), benzo(a)pyrene (BaP) and pyrene (Py)) with and without UVR. Toxicity of sludge increased in the presence of UVR in wheat. UVB radiation was found to be more hazardous than UVA radiation. Results demonstrated that An, BaP and Py induced phototoxicity at various concentrations (1–10?µg/mL) under UVA (1.5?mW/cm²) or UVB (1.08?J/cm²) exposure. The pattern of phototoxicity was An?>?Py?>?BaP to shoot length, root length, and fresh weight; chlorophyll, protein content, enzyme activity of catalase and α-amylase were reduced while the activity of superoxide dismutase and starch was enhanced. Reduction in seedling growth and biochemical parameters may be related to less photosynthesis, less nutritional uptake, and distortion of root cap. Thus, the synergistic effect may be due to alterations in photosynthesis, phytohormones, or nutritional uptake.     

Growth patterns of Codium fragile ssp. tomentosoides in response to temperature,irradiance, salinity,and nitrogen source

Seasonal patterns of growth, reproduction, and productivity of Codium fragile spp. tomentosoides (van Goor) Silva were monitored at 3 locations in Rhode Island. Maximal growth occurred during the summer and was more significantly correlated with temperature than any other factor measured in this study. Multiple correlation models suggested an interaction between temperature, irradiance, and available nitrogen. Maximal reproduction occurred in late summer and early fall. The maximal productivity, based on harvested quadrats, was 2. 10 g dry weight m^-2 day^-1. A large amount (up to 87.3%) of the annual production entered the detrital food chain during the winter by fragmentation of the thallus. Culture studies examined the effects of temperature (6° to 30°C), irradiance (7 to 140 E m^-2 sec^-1), daylength (8 h light: 16 h dark to 24 h light: O h dark) and salinity (6 to 48) on growth. Differentiated thalli grew over a broad range of experimental conditions, with maximal growth at 24°C, 24 to 30 S, a minimal irradiance of 28 E m^-2 sec^-1, and 16 h daylength. The effect of increasing daylength was due to increased total daily irradiance rather than to a true photoperiodic effect. Undifferentiated sporelings survived and grew in a narrower range of environmental conditions than thalli. c. fragile spp. tomentosoides grew equally well with nitrate, nitrite, ammonium, and urea as a nitrogen source. The addition of NaHCO₃ stimulated growth at levels of 2.4 to 4.8 mM, suggesting an inorganic carbon limitation in static cultures. This study supports the hypothesis that the in situ seasonal growth pattern of c. fragile spp. tomentosoides is primarily due to the interaction of temperature and irradiance.     

Biological weighting of ultraviolet (280–400 nm) induced mortality in marine zooplankton and fish. II. Calanus finmarchicus (Copepoda) eggs

The copepod Calanus finmarchicus Gunnerus is a key component of the planktonic food web in the Gulf of St. Lawrence, Canada. In this region, productivity-determining biophysical interactions occur in the upper 0 to 30 m of the water column. The eggs and nauplii of C. finmarchicus are found in this layer. Measurements of the diffuse attenuation coefficients for solar ultraviolet-B radiation (280 to 320 nm, UV-B) at various locations in this region indicated maximum 10% depths (the depth to which 10% of the surface energy penetrates) of 3 to 4 m at a wavelength of 310 nm. This represents a significant percentage of the summer mixed-layer water column: organisms residing in this layer are exposed to UV-B radiation. Laboratory experiments using a Xenon-arc-lamp based solar simulator revealed that C. finmarchicus embryos exposed to UV-B exhibited high wavelength-dependent mortality. The strongest effects occurred under exposures to wavelengths below 312 nm. A significant percentage of nauplii hatched from eggs exposed to these wavelengths exhibited malformations indicative of errors in pattern formation during embryogenesis. At the shorter wavelengths (<305 nm), UV-B-induced mortality was strongly dependent on cumulative exposure. The biological weighting function (BWF) derived for UV-B-induced mortality in C. finmarchicus eggs is similar to that reported for naked DNA. This suggests that the UV-B-induced mortality effect on C. finmarchicus embryos is a direct result of DNA damage. There was no evidence of a detrimental effect of ultraviolet-A radiation (320 to 400 nm). Calculations based upon the BWF indicate that, under current noon surface irradiance, 50% of C. finmarchicus eggs located at or very near (within 10 cm) the ocean surface will be dead after 2.5 h of exposure. Under solar spectral irradiance simulating a 20% decrease in ozone layer thickness, this time drops to 2.2 h. These are first-order estimates based upon irradiance taken at a time of day during which the values would be maximal. Nonetheless, they illustrate the relative changes in UV-B effects that will result from ozone layer depletions expected over the coming decades. It is also important to point out that variability in cloud cover, water quality, and vertical distribution and displacement within the mixed layer, can all have a greater effect on the flux of UV-B radiation to which C. finmarchicus eggs are exposed than will ozone layer depletion at these latitudes. Received: 2 March 1998 / Accepted: 18 December 1998     

水稻对UV-B辐射响应的敏感性差异

综述了UV-B辐射对水稻（Oryza sativa L.）的影响和水稻对UV-B辐射的抗性机制。UV-B辐射对水稻生长、叶片形态、生物量、产量、光合系统、病害等产生一定的影响。水稻对UV-B辐射的敏感性因子主要有CPD光解酶、UV-B吸收物质、抗氧化酶等。UV-B辐射使水稻叶片中产生了ROS,导致Rubisco酶降解,光合色素含量变化,抑制了光合作用,最终影响水稻籽粒形成和产量。水稻对UV-B辐射响应存在着品种差异,CPD光解酶编码基因的自然突变会引起水稻UV-B敏感性的差异,CPD光解酶活性是水稻对UV-B敏感性的关键因素。通过建立响应指数公式,对水稻UV-B响应敏感性的品种差异进行评估,存在品种差异的原因主要是基因、生长、生理、生育期和环境背景的差异。最后对UV-B辐射对水稻的影响、水稻对UV-B响应的差异及机理有待深入研究的方向进行了展望。