Research note: Irradiance of photosynthetically active radiation determines ultraviolet-susceptibility of photosynthesis in Ulva lactuca L.(Chlorophyta)

The respective ratio of photosynthetically active to ultraviolet radiation is of crucial importance to results obtained in ultraviolet (UV)‐research on photoautotrophic organisms. Specimens of the green macroalga Ulva lactuca L. were exposed to a constant irradiance of UV‐radiation at increasing irradiances of photosynthetically active radiation (PAR). The effects of experimental irradiance and spectral composition on photoinhibition of photosynthesis and its recovery were monitored by chlorophyll fluorescence measurements and the activity of the xanthophyll cycle was assessed by high performance liquid chromatography‐(HPLC) based pigment analysis. Results indicate a UV‐induced delay in recovery from PAR‐induced photoinhibition and a deceleration of violaxanthin conversion within the xanthophyll cycle due to the presence of UV‐radiation. Also the concentration of the protective pigment lutein increased considerably and could be indicative of the existence of an additional light‐protective mechanism, as, for example, the lutein‐epoxid cycle in Ulva. In total, results clearly show that the extent of UV‐induced inhibition of photosynthesis to be found in UV‐exposure experiments is highly dependent on the irradiance of background photosynthetically active radiation: with increasing irradiance of PAR the UV‐effects were diminished. Exemplified by the green algae Ulva lactuca this study demonstrates the crucial importance of the ratios of PAR:UV applied in UV‐research, particularly when conducting laboratory experiments in an ecological context.     

Field relationships between scytonemin density,growth, and irradiance in cyanobacteria occurring in low illumination regimes

In situ measurements of ultraviolet (UV) irradiance, carbon fixation, and scytonemin pigmentation were made on Scytonema populations from contrasting localities in England. Significant negative correlations were obtained between the following variate pairs: pigmentation and UV irradiance; pigmentation and carbon fixation rate. A significant positive correlation was found between pigmentation and sheath thickness.The negative correlation between pigmentation and UV irradiance was unexpected and appeared contrary to the results of previous studies, which indicated a positive correlation between the variates and the recognition of scytonemin as a radiation shield. However, by considering how radiation damage is related to cell division and the water relations of the sites investigated, it was shown that scytonemin is still functioning as a radiation shield, even in shaded sites. Rivularia colonies produced scytonemin only upon their upper, sun-exposed surfaces and were positively correlated with UV irradiance. This paper also describes the successful use of some new and inexpensive techniques to measure pigments in cyanobacterium sheaths, and integrated in situ UV-irradiance.     

Bleaching in coral reef anthozoans: effects of irradiance,ultraviolet radiation,and temperature on the activities of protective enzymes against active oxygen

Recent widespread bleaching of coral reef anthozoans has been observed on the Great Barrier Reef, the Pacific coast of Panama, and in the Caribbean Sea. Bleaching events have been correlated with anomalously high sea surface temperatures which are presumed to cause the expulsion of zooxanthellae from their hosts. Our experimental results show that increases in temperature significantly reduce the total number of zooxanthellae per polyp. At the same time temperature, irradiance (photosynthetically active radiation=PAR), and ultraviolet radiation (UV) independently increase the activities of the enzymes superoxide dismutase, catalase, and ascorbate peroxidase within the zooxanthellae of the zoanthid Palythoa caribaeorum. Enzyme activities within the host are only suggestive of similar changes. These enzymes are responsible for detoxifying active forms of oxygen, and their elevated activities indirectly indicate an increase in the production of active oxygen species by increases in these environmental factors. Historically, bleaching has been attributed to changes in temperature, salinity, and UV. Increases in temperature or highly energetic UV radiation can increase the flux of active forms of oxygen, particularly at the elevated oxygen concentrations that prevail in the tissues during photosynthesis, with oxygen toxicity potentially mediating the bleaching event. Additionally, the concentration of UV absorbing compounds within the symbiosis is inversely related to temperature, potentially increasing exposure of the host and zooxanthellae to the direct effects of UV.     

基于人体健康的3种城市森林夏季林内紫外线辐射环境特征比较研究

以中波紫外线为主的紫外辐射对人体健康具有多种生物学影响,城市森林能够为居民提供温和的紫外辐射环境。为了解林下紫外线辐射环境特征是否存在树种间差异,对北京市3种常见遮荫树种的夏季林下紫外辐射(UV)强度、林内与林外UV辐射的比值(SR)、UV-B在总UV辐射中占比(UV-B/UV),以及VD合成和红斑效应两种人体作用有效辐射强度(UV_VD、UV_er)进行了测算。结果表明：(1)三种林分林内紫外辐射总量是林外的3%—10%,不同林分的林内UV强度具有显著差异,元宝枫林对UV屏蔽能力最强,其次是栾树林和国槐林;(2)三种林分林冠对不同波长上紫外辐射能量的屏蔽能力具有明显的一致性,林冠对UV-B的屏蔽能力没有在UVA波段强和稳定,林内UV-B/UV普遍高于林外,其中元宝枫林最高,其次为栾树林,国槐林最低;(3)林冠明显改变了日光UV_VD和UV_er两种人体作用光谱曲线的形态,三种林分内的人体作用光谱曲线形态相似,强度上,林内外UV_VD/UV_er值均接近1,不同林分间...     

Insect perception of ambient ultraviolet-B radiation

Solar ultraviolet‐B radiation (UV‐B, 290–315 nm) has a strong influence on the interactions between plants and animal consumers. Field studies in various ecosystems have shown that the intensity of insect herbivory increases when the UV‐B spectral band of solar radiation is experimentally attenuated using filters. This effect of UV‐B on insect herbivory has been attributed to UV‐B‐induced changes in the characteristics of plant tissues, and to direct damaging effects of UV‐B photons on the animals. We tested for effects of UV‐B radiation on insect behaviour using field experiments with the thrips Caliothrips phaseoli. When placed in a ‘choice’ tunnel under natural daylight, these insects showed a clear preference for low‐UV‐B environments, and this preference could not be accounted for by differences between environments in total irradiance. These results provide the first evidence of ambient UV‐B photoperception in an insect, challenging the idea that animals are unable to detect variations in the narrow UV‐B component of solar radiation.     

Influence of solar ultraviolet radiation on photosynthesis and motility of marine phytoplankton

Abstract: The effects of solar ultraviolet radiation (UV) on carbon uptake, oxygen evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west coast of Sweden (58° 30'N, 11° 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400–700 nm) 1670 μmol m⁻² s⁻¹; ultraviolet-A radiation (UV-A, 320–400 nm) 35.9 W m⁻² and ultraviolet-B radiation (UV-B, 280–320 nm) 1.7 W m⁻². UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greater than 100–150 cm. Inhibition of carbon uptake by UV-A and UV-B in natural phytoplankton populations was greatest at 50 cm depth and the effects of UV-B were greater than those of UV-A. At depths greater than 50 cm there was almost no effect of ultraviolet radiation on carbon uptake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagellate Prorocentrum minimum . Inhibition of oxygen evolution was greater after 4 h than 2 h but it was not possible to distinguish the negative effects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phytoplankton to different light regimes before being exposed to natural solar radiation is discussed.     

Statistical analysis and biological interpretation of the flow cytometric heterogeneity observed in bacterial axenic cultures

Histogram comparison and meaningful statistics in flow cytometry is probably the most widely encountered mathematical problem in flow cytometry. Ideally, a test for determining the statistical equality or difference of flow cytometric distributions will identify the significant differences or similarities of the obtained histograms. This situation is of particular interest when flow cytometry is used to study the heterogeneity of axenic bacterial populations. We have statistically measured the heterogeneity of successive cytometric measures, the modifications produced after 20 transfers from the same culture, and the differences between 20 subcultures of identical origin. The heterogeneity of the bacterial populations and the similarity of the obtained 360 histograms were analysed by standard statistical methods. We have studied bacterial axenic cultures in order to detect, quantify and interpret their cytometric heterogeneity, and to assess intrinsic differences and differences produced by laboratory manipulations. We concluded that the standard axenic cultures have a considerable intrinsic cellular and molecular heterogeneity. We suggest that the heterogeneity we have detected basically has two origins: cell size diversity and cell cycle variations.     

Acclimation of brown algal photosynthesis to ultraviolet radiation in Arctic coastal waters (Spitsbergen, Norway)

In field studies conducted at the Kongsfjord (Spitsbergen) changes of the irradiance in the atmosphere and the sublittoral zone were monitored from the beginning of June until the end of August 1997, to register the minimum and maximum fluxes of ultraviolet and photosynthetically active radiation and to characterise the underwater light climate. Measurements of photosynthesis in three abundant brown algal species (Alaria esculenta, Laminaria saccharina, Saccorhiza dermatodea) were conducted to test whether their photosynthetic performance reflects changing light climate in accordance with depth. Plants sampled at various depths were exposed to controlled fluence rates of photosynthetically active radiation (400–700 nm), UV-A (320–400 nm) and UV-B (280–320 nm). Changes in photosynthetic performance during the treatments were monitored by measuring variable chlorophyll fluorescence of photosystem II. In each species, the degree of inhibition of photosynthesis was related to the original collection depth, i.e. shallow-water isolates were more resistant than plants from deeper waters. The results show that macroalgae acclimate effectively to increasing irradiance levels for both photosynthetically active and ultraviolet radiation. However, the kinetics of acclimation are different within the different species. It is shown that one important strategy to cope with higher irradiance levels in shallow waters is the capability for a faster recovery from high light stress compared to isolates from deeper waters. Received: 13 March 1998 / Accepted: 16 May 1998     

Refinement of the dichlorofluorescein assay for flow cytometric measurement of reactive oxygen species in irradiated and bystander cell populations

Reactive oxygen species (ROS) have been implicated in many ionizing radiation-related phenomena, including bystander effects. The oxidation of 2'7'-dichlorofluorescin (DCFH) to fluorescent 2'7'-dichlorofluorescein (DCF) is commonly used for the detection of radiation-induced ROS. The DCF assay was adapted for efficient, systematic flow cytometry quantification of low-linear energy transfer (LET) gamma-radiation-induced ROS in vitro in Chinese hamster ovary (CHO) cells. This method is optimized for increased sensitivity to radiation-induced ROS and to discriminate against measurement of extracellular ROS. This method can detect a significant increase in ROS in cells exposed to gamma radiation at doses as low as 10 cGy. The antioxidants N-acetyl-cysteine and ascorbic acid (vitamin C) significantly reduced the amount of ROS measured in cells exposed to 5 Gy ionizing radiation. This method was used to measure the intracellular ROS in unirradiated CHO bystander cells co-cultured with low-LET-irradiated cells. No increase in ROS was measured in bystander cell populations co-cultured with the irradiated cells beginning 9 s after radiation exposure.     

ULTRAVIOLET SUNSCREENS IN GYMNODINIUM SANGUINEUM (DINOPHYCEAE): MYCOSPORINE-LIKE AMINO ACIDS PROTECT AGAINST INHIBITION OF PHOTOSYNTHESIS

Marine phytoplankton are sensitive to inhibition of photosynthesis by solar ultraviolet (UV) radiation, although sensitivity varies, depending on the growth environment. A mechanism suggested to increase resistance to UV inhibition is the accumulation of UV-absorbing compounds, such as the mycosporine-like amino acids (MAAs) found in many marine organisms. However, the effectiveness of these compounds as direct optical screens in microorganisms has remained unclear. The red-tide dinoflagellate Gymnodinium sanguineum Hirasaka accumulates about 14-fold more MAAs (per unit of chlorophyll) in high (76 W·m⁻²) than in low (15 W·m⁻²) growth irradiance. Biological weighting functions were estimated for UV inhibition of photosynthesis and showed that the high-light-grown cultures have lower sensitivity to UV radiation at wavelengths strongly absorbed by the MAAs. The time course of photosynthesis during exposure to UV radiation was measured using pulsed amplitude modulated (PAM) fluorometry and displayed a steady-state level after 15 min of exposure, indicating active repair of damage to the photosynthetic apparatus. Repair was blocked in the presence of the antibiotic streptomycin, yet high-light G. sanguineum remained less sensitive to UV radiation than did low-light cultures. These experiments show that MAAs act as spectrally specific UV sunscreens in phytoplankton.     

MICROENVIRONMENTAL CONTROL OF PHOTOSYNTHESIS AND PHOTOSYNTHESIS-COUPLED RESPIRATION IN AN EPILITHIC CYANOBACTERIAL BIOFILM1

The photosynthetic performance of an epilithic cyano-bacterial biofilm was studied in relation to the in situ light field by the use of combined microsensor measurements of O₂, photosynthesis, and spectral scalar irradiance. The high density of the dominant filamentous cyanobacteria (Oscillatoria sp.) embedded in a matrix of exopolymers and bacteria resulted in a photic zone of < 0.7 mm. At the biofilm surface, the prevailing irradiance and spectral composition were significantly different from the incident light. Multiple scattering led to an intensity maximum for photic light (400–700 nm) of ca. 120% of incident quantum irradiance at the biofilm surface. At the bottom of the euphotic zone in the biofilm, light was attenuated strongly to < 5–10% of the incident surface irradiance. Strong spectral signals from chlorophyll a (440 and 675 nm) and phycobilins (phycoerythrin 540–570 nm, phycocyanin 615–625 nm) were observed as distinct maxima in the scalar irradiance attenuation spectra in the upper 0.0–0.5 mm of the biofilm. The action spectrum for photosynthesis in the cyanobacterial layer revealed peak photosynthetic activity at absorption wavelengths of phycobilins, whereas only low photosynthesis rates were induced by light absorption of carotenoids (450–550 nm). Respiration rates in light- and dark-incubated biofilms were determined using simple flux calculations on measured O₂ concentration profiles and photosynthetic rates. A significantly higher areal O₂ consumption was found in illuminated biofilms than in dark-incubated biofilms. Although photorespiration accounted for part of the increase, the enhanced areal O₂ consumption of illuminated biofilms could also be ascribed to a deeper oxygen penetration in light as well as an enhanced volumetric O₂ respiration in and below the photic zone. Gross photosynthesis was largely unaffected by increasing flow velocities, whereas the O₂ flux out of the photic zone, that is, net photosynthesis, increased with flow velocity. Consequently, the amount of produced O₂ consumed within the biofilm decreased with increasing flow velocity. Our data indicated a close coupling of photosynthesis and respiration in biofilms, where the dissolved inorganic carbon requirement of the photo-synthetic population may largely be covered by the respiration of closely associated populations of heterotrophic bacteria consuming a significant part of the photosynthetically produced oxygen and organic carbon.     

Ultraviolet Radiation Absorbance by Coral Reef Fish Mucus: photo-protection and Visual Communication

Tropical reef fishes are exposed to high levels of damaging ultraviolet radiation. Here we report the widespread distribution of both UVA- and UVB-absorbing compounds in the epithelial mucus of these fishes. Mucus from 137 reef fish species was examined by spectrophotometry and 90% were found to have strong absorbance peaks between 290 and 400nm. Most fish species (78%) had more than one peak, that suggests a broad-band ultraviolet screening function for their mucus. Thalassoma duperrey, a tropical wrasse, was able to alter the absorbance of its epithelial mucus in response to both naturally and experimentally manipulated UV regimes. Visual modeling suggests that a fish with UV vision, such as Dascyllus albisella, could detect the changes in mucus spectra of T. duperrey that occurred in these experiments.     

Light absorption and pigment content in natural populations and cultures of a non-gas vacuolate cyanobacterium OsciUatoria bourrellyi (=Tychomema bourrellyi)

Vertical profiles of temperature, the flux density and spectralcomposition of irradiance and the vertical distribution of Oscillatoriabourrellyi were measured in the North and South Basins of Windermerein the English Lake District At the population maximum (8–14m) the photon flux was 0.3–14 µmol m^–2 s^–1with the waveband 512–580 nm contributing 54–60%of the photosyn-thetically active irradiance. Samples of O.bourrcllyitaken concurrently from 0 and 12 m were analysed to determinethe absorption properties of the populations and the phycoerythrin-relatedfluorescence of individual filaments. The 12 m populations weredistinguished from the surface populations by higher beam absorptioncoefficients at all wavelengths throughout the visible spectrum.These differences were accentuated when the absorption characteristicswere calculated using in situ irradiance profiles. The deeperpopulations consistently absorbed a greater fraction of theavailable irradiance than the shallow populations. This wasdue to an overall increase in the total pigment per cell ratherthan the differential synthesis of phycobiliprotein pigments.These observations were confirmed by both laboratory and fieldexperiments using cultures of O. bourrellyi In these experimentslow white light was sufficient to induce the synthesis of bothphycoerythnn and phycocyanin as well as chlorophyll Mean individualfilament fluorescence also distinguished populations from differentdepths These measurements further demonstrated that filamentswithin a population located at a discrete depth have a widerange of fluorescence. This variation increased with decreasinglight intensity and suggests that phycoerythrin could be usedas a cellular marker to determine the provenance of individualfilaments The benefits of photo-adaptation in O.bourreUyi areanalysed in relation to the variable underwater light climateof Windermere, UK Their ecological significance for this algaduring periods of intense but intermittent stratification ina nutrient-limited environment are discussed. The ecologicalimplications of both intra- and inter-specific variations inthe absorption properties of phytoplankton are discussed inrelation to the use of simple community or populations meansas the data entry points for models of photosynthetic production.     

Spectral properties of plant leaves pertaining to urban landscape design of broad-spectrum solar ultraviolet radiation reduction

Human exposure to harmful ultraviolet (UV) radiation has important public health implications. Actual human exposure to solar UV radiation depends on ambient UV irradiance, and the latter is influenced by ground reflection. In urban areas with higher reflectivity, UV exposure occurs routinely. To discover the solar UV radiation regulation mechanism of vegetation, the spectral reflectance and transmittance of plant leaves were measured with a spectrophotometer. Typically, higher plants have low leaf reflectance (around 5%) and essentially zero transmittance throughout the UV region regardless of plant species and seasonal change. Accordingly, incident UV radiation decreases to 5% by being reflected and is reduced to zero by passing through a leaf. Therefore, stratified structures of vegetation are working as another terminator of UV rays, protecting whole terrestrial ecosystems, while vegetation at waterfronts contributes to protect aquatic ecosystems. It is possible to protect the human population from harmful UV radiation by urban landscape design of tree shade and the botanical environment. Even thin but uniformly distributed canopy is effective in attenuating UV radiation. To intercept diffuse radiation, UV screening by vertical structures such as hedges should be considered. Reflectivity of vegetation is around 2%, as foliage surfaces reduce incident UV radiation via reflection, while also eliminating it by transmittance. Accordingly, vegetation reduces incident UV radiation to around 2% by reflection. Vegetation influence on ambient UV radiation is broad-spectrum throughout the UV region. Only trees provide cool UV protective shade. Urban landscapes aimed at abating urban heat islands integrated with a reduction of human UV over-exposure would contribute to mitigation of climate change.     

Short term exposure with ultraviolet radiations: A strategy to improve resistance against root-infecting fungi in Luffa cylindrica (L.) Roem

Ultraviolet (UV) radiation is a component of the solar radiations that alter various physiological and biochemical processes in plants. There have been interests in UV-C and UV-B radiations because of their effects on plant physiology. In this study, we investigated the effect of short term UV irradiance on both biochemical parameters and pathogenicity of several root-infecting fungi in Luffa cylindrica. Plant seedlings were exposed once to UV-B and UV-C radiation for 0, 1, 2, 3, 4, and 5 h. After exposure, plant seedlings were transferred to a potting soil that contained natural populations of root-infecting fungi for 30 days. Initially, the plant height and weight enhanced with the increase of exposure time but then plants showed slower growth at the highest time (5 h) of exposure. Colonization of Macrophomina phaseolina, Rhizoctonia solani, and Fusarium species was reduced when plants were exposed to UV radiation at various time intervals. We also found increased levels of chlorophyll ´a`, chlorophyll ‘b’, and carotenoids in plants exposed to radiation. An increase in protein content was also recorded under UV-B and UV-C exposure. Enhanced catalase (CAT) activity was noted after maximum time exposure with UV-C irradiance. Ascorbate peroxidase (APX) activity was increased with the exposure time to UV radiation. We conclude that short time UV irradiation causes alteration in photosynthetic pigments and stress enzymes activities in L. cylindrica that play a major role in the improvement of resistance against root-infecting fungi.     

Effects of UV-B radiation on near-surface zooplankton of puget sound

Summary An increase in incident solar ultraviolet irradiation, resulting from possible deterioration of the stratospheric ozone layer, would have important biological effects. Though the oceans are relatively opaque to UV radiation, compared to visible light, increases in incident UV may affect organisms living within the first few meters of the sea surface.Shrimp larvae, crab larvae, and euphausids were exposed to various low levels of simulated solar UV radiation (UV-B, 290–315 nm) under laboratory conditions. Comparisons between solar and artificial spectra were based on spectroradiometric measurements converted to erythemally effective irradiance. These zooplankton tolerated UV-B irradiance levels up to threshold levels with no significant reduction in survival or developmental rates compared to control organisms. Beyond the threshold levels, activity, development, and survival rapidly declined. The apparent UV thresholds are near present incident UV levels.Observed survival threshold levels for each experimental group were superimposed on seasonal solar incident UV levels at the experimental site. These threshold levels appeared to be exceeded by median ambient UV levels late in the season of surface occurrence of each species. UV increases resulting from ozone depletion may significantly shorten this season. Although the apparent impact would be lessened by the decrease in UV with depth, irreversible detrimental effects would probably occur before reported survival thresholds were exceeded.Contribution No. 1107 from the Department of Oceanography, University of Washington, Seattle, WA 98195, USA     

Role of mitochondria in ultraviolet-induced oxidative stress

The biological effects of ultraviolet radiation (UV), such as DNA damage, mutagenesis, cellular aging, and carcinogenesis, are in part mediated by reactive oxygen species (ROS). The major intracellular ROS intermediate is hydrogen peroxide, which is synthesized from superoxide anion ((*)O(2)(-)) and further metabolized into the highly reactive hydroxyl radical. In this study, we examined the involvement of mitochondria in the UV-induced H(2)O(2) accumulation in a keratinocyte cell line HaCaT. Respiratory chain blockers (cyanide-p-trifluoromethoxy-phenylhydrazone and oligomycin) and the complex II inhibitor (theonyltrifluoroacetone) prevented H(2)O(2) accumulation after UV. Antimycin A that inhibits electron flow from mitochondrial complex III to complex IV increased the UV-induced H(2)O(2) synthesis. The same effect was seen after incubation with rotenone, which blocks electron flow from NADH-reductase (complex I) to ubiquinone. UV irradiation did not affect mitochondrial transmembrane potential (DeltaPsi(m)). These data indicate that UV-induced ROS are produced at complex III via complex II (succinate-Q-reductase).     

UV-B Radiation Suppresses the Growth and Antioxidant Systems of Two Marine Microalgae, Platymonas subcordiformis （Wille） Hazen and Nitzschia closterium （Ehrenb.） W. Sm

This study investigated whether increased solar UV-B radiation (280-315nm) could suppress the growth of marine microalgae through effects on their antioxidant systems. Two marine microalgae species, Platymonas subcordiformis (Wille) Hazen and Nitzschia closterium (Ehrenb.) W. Sm, were exposed to a range of UV-B radiation and both showed reductions in their growth rates, and the chlorophyll a(Chl a) and carotenoid (Car) contents when UV-B radiation dose increased. Superoxide anion radical (O2^ )production and the concentration of hydrogen peroxide (H2O2) and malodiadehyde (MDA) also increased with the increasing of UV-B radiation. Antioxidant systems, non-enzymic components (Car and glutathione content) and enzymic components (superoxide dismutase (SOD) and catalase (CAT) activity), decreased as a result of enhanced UV-B radiation. When the exogenous glutathione (GSH) was added, the effects of UV-B radiation on the growth of the two species were alleviated. These results suggest that enhanced UV-B radiation suppressed the antioxidant systems and caused some active oxygen species to accumulate, which in turns retarded the development of the marine microalgae.     

光活化杀虫剂α-三噻吩的电子自旋共振分析及其对库蚊保护酶系统活性的影响

以淡色库蚊Culex pipiens pallens为试材,初步进行了典型光活化杀虫剂α-三噻吩（α-T）的电子自旋共振（ESR）分析,并研究其对昆虫保护酶系统的影响。ESR分析表明,近紫外光和药剂α-T均可促进活性氧自由基浓度升高,且两者具有协同关系,近紫外光能显著促进α-T增加自由基的作用,处理3 h时试虫自由基总浓度增加了99.6%。近紫外光和药剂α-T对保护酶系统的影响随酶的种类而有所不同,但在近紫外光存在的条件下,α-T对超氧物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活体活性均有抑制作用,且光照3 h时,抑制作用最强。     

Genetic study of resistance to inhibitory effects of UV radiation in rice (Oryza sativa)

Genetic analysis of resistance to the inhibitory effects of UV radiation on growth of rice ( Oryza sativa L.) cultivars was carried out. Some experimental plants were grown in visible radiation supplemented with UV radiation containing a large amount of UV-B and a small amount of UV-C in a phytotron, while others were grown without UV radiation. The degree of resistance to UV radiation was estimated in terms of the degree of reduction caused by supplemental UV radiation in the fresh weight of the aboveground plant parts and the chlorophyll content per unit fresh weight. Fresh weight and chlorophyll content in F₂ plants generated by reciprocally crossing cv. Sasanishiki, a cultivar more resistant to UV radiation, and Norin 1, a cultivar less resistant to such radiation exhibited a normal frequency distribution. The heritabilities of these two properties in F₂ plants were low under conditions of non-supplemental UV radiation. Under elevated UV radiation, the F₂ population shifted to the lower range of fresh weight and chlorophyll content, and the means were close to those of Norin 1. The heritabilities of these two properties were the same in the reciprocal crosses, indicating that maternal inheritance was not involved. Inheritance of chlorophyll content per unit fresh weight was further determined in F₃ lines generated by self-fertilizing F₂ plants of Sasanishiki and Norin 1. The results showed that the F₃ population was segregated into three genotypes, namely, resistant homozygotes, segregated heterozygotes and sensitive homozygotes, with a ratio of 1:65:16.
It was thus evident that the resistance to the inhibitory effect of elevated UV radiation in these rice plants was controlled by recessive polygenes.