UV effects on stoichiometry and PUFAs of Selenastrum capricornutum and their consequences for the grazer Daphnia magna

1. The effect of ultraviolet (UV) radiation (280–400 nm) on fatty acid composition and elemental ratios of carbon (C), nitrogen (N) and phosphorus (P) of a unialgal culture of the chlorophyte Selenastrum capricornutum was investigated. Algae were cultured in the presence or absence of UV radiation and were subsequently fed to Daphnia magna to assess potential effects of UV on zooplankton fatty acid composition, growth and reproduction. 2. Algal growth rate was substantially reduced by UV radiation, probably because of a severe inhibition of photosynthetic efficiency (measured as optimal quantum yield). 3. Algae exposed to UV radiation had a significantly reduced content of 18 : 1 n‐9, while C18 polyunsaturated fatty acids (PUFAs) were higher under UV radiation. These observations point at an increased demand for and synthesis of PUFAs under UV stress. 4. The C : P and N : P ratios showed a remarkable decrease in UV‐exposed cells primarily owing to an increased uptake of P. The nutritional quality in terms of both fatty acid composition and stoichiometry was therefore higher in the UV treatment relative to the control. 5. Despite the UV‐induced changes in nutritional quality of S. capricornutum, no significant effects on D. magna growth or reproduction were detected. The fatty acid composition of Daphnia fed on UV irradiated algae showed a significantly lower content of 18 : 1 n‐9, but no changes in the essential PUFAs.     

Reduced digestibility of UV-B stressed and nutrient-limited algae by Daphnia magna

Daphnia magna was fed the green alga Selenastrum capricornutum, cultured under four different growth conditions: (1) phosphorus limitation, (2) nitrogen limitation, (3) UV-B irradiation, and (4) no nutrient limitation, no UV-B irradiation. Contrary to non-limited algal cells, nutrient-limited cells were not efficiently assimilated. Especially, P-limited cells passed through the gut mostly intact, while N-limited cells were partly assimilated. Also, algae exposed to moderate doses of UV-B radiation (0.3 mW cm^–2 of UV₃₁₂) were less efficiently assimilated after being grazed. Digestibility of the algae decreased with increased UV-B exposure time. Nutrient-limited and UV-B stressed algal cells increased in volume and became granular in appearance. These changes in the algal cells, combined with changed cell wall properties, most probably reduced their digestibility.     

The Response of Bean Plants to UV-B Radiation Under Different Irradiances of Background Visible Light

Plants of Phaseolus vulgaris L. (cv. Stella) were grown in controlledconditions under three different irradiances of visible lightwith or without UV-B (280–320nm) radiation. The biologicallyeffective UV-B radiation (UV-B_BE) was 6.17 kJ m^–2 d^–1,and simulated a c. 5% decrease in stratospheric ozone at 55.7?N,13.4?E. The photon flux densities of the photosyntheticallyactive radiation (PAR, 400–700 nm) were either 700 µmolm^–2–1 (HL), 500, µmol m^–2 s^–1(ML) or 230 µmol m^–2 s^–1 PAR (LL). Under highlight (HL) conditions plus UV-B radiation, bean plants appearedmost resistant to the enhanced levels of UV-B radiation, andresponded only by increasing leaf thickness by c. 18%. A smallincrease in UV screening pigments was also observed. Both thelower irradiances (ML and LL) increased the sensitivity of theplants to UV-B radiation. Changes in leaf structure were alsoobserved. Photosystem II was inhibited under ML and LL togetherwith UV-B radiation, as determined by Chi fluorescence inductionand calculation of the fluorescence half-rise times. Leaf reflectivitymeasurements showed that the amount of PAR able to penetrateleaves of UV-B treated plants was reduced, and that a possiblecorrelation may exist between the reduced PAR levels, loss ofChi and lowered photosynthetic activity, especially for LL +UV-Bgrown plants, where surface reflection from leaves was highest.Changes in leaf chlorophyll content were mostly confined toplants grown under LL + UV-B, where a decrease of c. 20% wasfound. With regard to protective pigments (the carotenoids andUV screening pigments) plants subjected to different visiblelight conditions responded differently. Among the growth parametersmeasured, there was a substantial decrease in leaf area, particularlyunder LL + UV-B (c. 47% relative to controls), where leaf dryweight was also reduced by c. 25%. Key words: Chlorophyll fluorescence induction, bean, flavonoids, Phaseolus vulgaris, reflectance, UV-B radiation     

Shoot Dry Weight, Chlorophyll and UV-B-absorbing Compounds as Indicators of a Plant's Sensitivity to UV-B Radiation

When studying the effects of ultraviolet-B (UV-B) radiationon plants, a good measure of UV-B sensitivity is a decreasein dry weight, since this reflects the cumulative effect ofmany small disruptions in plant function. Measurements of chlorophyllconcentration and the level of UV-absorbing compounds are alsoused to gauge plant health during and after UV-B exposure. Whena variety of vegetable crop plants were screened for UV-tolerance,it was found that the levels of chlorophyll and UV-absorbingcompounds did not correlate with sensitivity. Biomass accumulationwas, however, correlated with UV-sensitivity; plants that accumulatedmore biomass over a 2-week period were more likely to be UV-Bsensitive. This suggests that a rapid growth rate renders plantsmore sensitive to the injurious effects of UV-B radiation. Copyright2000 Annals of Botany Company UV-B radiation, UV-absorbing compounds, chlorophyll, biomass production, UV-B sensitivity, Capsicum frutescens,Cucurbita pepo , Chicorium endivia, Lactuca sativa, Phaseolus vulgaris, Solanum melongena, Spinacia oleracea, Sinapis alba     

Photosynthesis, Growth, and Ultraviolet Irradiance Absorbance of Cucurbita pepo L. Leaves Exposed to Ultraviolet-B Radiation (280-315 nm)

Net photosynthesis, growth, and ultraviolet (UV) radiation absorbance were determined for the first leaf of Cucurbita pepo L. exposed to two levels of UV-B irradiation and a UV-B radiation-free control treatment. Absorbance by extracted flavonoid pigments and other UV-B radiation-absorbing compounds from the first leaves increased with time and level of UV-B radiation impinging on leaf surfaces. Although absorbance of UV-B radiation by extracted pigments increased substantially, UV-B radiation attenuation apparently was insufficient to protect completely the photosynthetic apparatus or leaf growth processes. Leaf expansion was repressed by daily exposure to 1365 Joules per meter per day of biologically effective UV-B radiation but not by exposure to 660 Joules per meter per day. Photosynthesis measured through ontogenesis of the first leaf was depressed by both UV-B radiation treatments. Repression of photosynthesis by UV-B radiation was especially evident during the ontogenetic period of maximum photosynthetic activity.     

The effect of ultraviolet radiation on photosynthesis and ultraviolet-absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta)

In field studies conducted at the Kongsfjord (Spitsbergen), the effect of filtered natural radiation conditions (solar without ulraviolet [UV]-A+UV-B, solar without UV-B, solar) on photosynthesis and the metabolism of UV-absorbing mycosporine-like amino acids (MAAs) in the marine red alga Devaleraea ramentacea have been studied. While solar treatment without UV-A+UV-B did not affect photosynthesis during the course of a day, solar without UV-B and the full solar spectrum led to a strong inhibition. However, after offset of the various radiation conditions, all algae fully recovered. Isolates collected from different depths were exposed in the laboratory to artificial fluence rates of photosynthetic active radiation (PAR), PAR+UV-A, and PAR+UV-A+UV-B. The photosynthetic capacity was affected in accordance with the original sampling depth, i.e. shallow-water isolates were more resistant than algae from deeper waters, indicating that D. ramentacea is able to acclimate to changes in irradiance. Seven different UV-absorbing MAAs were detected in this alga, namely mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol, and palythene. The total amount of MAAs continuously decreased with increasing collecting depth when sampled in mid June, and algae taken in late August from the same depths contained on average 30–45% higher MAA concentrations, indicating a seasonal effect as well. The presence of increasing MAA contents with decreasing depth correlated with a more insensitive photosynthetic capacity under both UV-A and UV-B treatments. Populations of D. ramentacea collected from 1 m depth, with one fully exposed to solar radiation and the other growing protected as understorey vegetation underneath the kelp Laminaria saccharina, exhibited quantitatively different MAA compositions in the apices. The exposed seaweeds contained 2.5-fold higher MAA values compared with the more shaded algae. Moreover, the exposed isolates showed a strong tissue gradient in MAAs, pigments, and proteins. The green apices contained 5-fold higher MAA contents than the red bases. Transplantation of D. ramentacea from 2 m depth to the surface induced the formation and accumulation of MAAs after 1 week exposure to the full solar spectrum. Control samples which were treated with the solar spectrum without UV-A+B or with solar without UV-B showed unchanged MAA contents, indicating a strong UV-B effect on MAA metabolism. All data well supported the suggested physiological function of MAAs as natural UV sunscreens in macroalgae.     

Photosynthetic and biochemical characterization of pigments and UV-absorbing compounds in <Emphasis Type="Italic">Phormidium tenue</Emphasis> due to UV-B radiation

We report the effect of UV-B radiation (0.8 ± 0.1 mW cm⁻²) and UV-B radiation supplemented with low-intensity PAR (∼80 μmol photons m⁻² s⁻¹) on the photosynthesis, photosynthetic pigments, phosphoglycolipids, oxidative damage, enzymatic antioxidants, and UV-absorbing compounds in Phormidium tenue, a marine cyanobacterium. UV-B radiation resulted in a decline in photosynthesis and photosynthetic pigments leading to lower biomass. P. tenue synthesized UV-absorbing compounds like mycosporine-like amino acids (MAAs) and scytonemin in response to UV-B radiation. Quantity of MAAs and scytonemin was higher when UV-B was supplemented with low-level PAR. UV-B treatment also resulted in quantitative changes in phosphoglycolipids of the membrane. The UV-B treatment resulted in a slight increase in the level of peroxidation of cell membrane and very little increase in the activity of superoxide dismutase (SOD). Results indicate that UV-B affected photosynthesis and that the main protective system was the synthesis of MAAs and scytonemin-like compounds rather than antioxidant enzymes such as SOD.     

增强UV-B辐射和氮对谷子叶光合色素及非酶促保护物质的影响

以谷子(Setaria italica(L)Beauv.)为对象,从拔节期开始持续给予低氮(1.875 mmol/L)和高氮(15 mmol/L)两种氮供应条件并从抽穗期开始进行26 d两种强度(4.29、7.12 kJ·m-2·d-1)的增强UV-B辐射处理,研究了谷子叶中光合色素含量、类黄酮含量和苯丙氨酸解氨酶(PAL)活性的变化.结果表明:与高氮供应条件相比,低氮供应条件明显降低了谷子叶中光合色素含量但提高了类胡萝卜素/叶绿素含量比值;在开花期中段和灌浆期中段,高氮供应条件下谷子叶中光合色素含量对增强UV-B辐射比低氮供应条件下的谷子更敏感.从灌浆期开始到处理结束,两种影响因子对谷子叶中类黄酮含量均有显著影响,增强UV-B辐射导致谷子叶中类黄酮含量逐渐升高,且相同增强UV-B辐射强度下低氮供应条件下的谷子叶中类黄酮含量明显高于高氮供应条件下的谷子.谷子叶中PAL活性对两种影响因子的响应较类黄酮含量更加敏感,低氮供应条件使谷子叶中PAL活性明显提高.结合上述指标的相关性分析结果可知,低氮供应条件加强了处于繁殖期主要阶段的谷子叶中类黄酮的积累,并使谷子叶中的类胡萝卜素/叶绿素含量比值明显提高,进而有助于维持谷子叶中光合色素含量在增强UV-B辐射条件下的相对稳定性,对植株抵抗UV-B辐射伤害有利.     

Combined effects of CO2 concentration and enhanced UV-B radiation on faba bean

Due to anthropogenic influences, both solar UV-B irradiance at the earth's surface and atmospheric [CO₂] are increasing. To determine whether effects of CO₂ enrichment on faba bean (cv. Minica) growth are modified by UV-B radiation, the effects of enhanced [CO₂] on growth and photosynthetic characteristics, were studied at four UV-B levels. Faba bean was sensitive to enhanced UV-B radiation as indicated by decreases in total biomass production. Growth stimulation by CO₂ enrichment was greatly reduced at the highest UV-B level. [CO₂] by UV-B interactions on biomass accumulation were related to loss of apical dominance. Both [CO₂] and UV-B radiation affected biomass partitioning, UV-B effects being most pronounced. Effects of [CO₂] and UV-B on faba bean growth were time-dependent, indicating differential sensitivity of developmental stages. [CO₂] and UV-B effects on photosynthetic characteristics were rather small and restricted to the third week of treatment. CO₂ enrichment induced photosynthetic acclimation, while UV-B radiation decreased light-saturated photosynthetic rate. It is concluded that the reduction in biomass production cannot be explained by UV-B-induced effects on photosynthesis.     

Alterations in Pigment Content in Leaves of Pisum sativum After Exposure to Supplementary UV-B

Pea plants were either illuminated with visible light supplementedwith ultraviolet-B (UV-B) radiation for five days, or transferredback to control light after short exposures (hours) to UV-B.Spectra of NaOH-extracted pigments from UV-B-exposed plantsshowed a decrease in absorption in the visible region and anincrease in the UV region: the former a consequence of the lossof chlorophyll, the latter probably due to induced synthesisof protective pigments. The decrease in chlorophyll absorptionwas an earlier event than the increase in UV absorption. Inextracts from plants which had recovered, the increase in UVabsorption was greater than in leaves subjected to three daysof UV-B. This stresses the importance of recovery from UV-Bfor extensive synthesis of protective pigments. Analysis oftetrapyrrolic pigments showed that UV-B treatment caused noallomerization of chlorophylls. Formation of chlorophyllidesa and b was greatly enhanced during the degradation of chlorophylls;however, the concentrations of chlorophyllides were three ordersof magnitude lower than those of the chlorophylls and did notincrease greatly as chlorophyll degradation progressed. No protoporphyrinIX, uro- or copro-porphyrins III were detected, which suggeststhat early steps in chlorophyll synthesis are not affected byUV-B light. (Received May 15, 1992; Accepted August 6, 1992)     

Effects of Microscale Water Level Fluctuations and Altered Ultraviolet Radiation on Periphytic Microbiota

Abstract Microscale fluctuations in water level (1–20 mm) are common on a diurnal basis in shallow (<5–10 cm) wetlands, coupled to evapotranspiration losses during the daytime in excess of groundwater resupply. These depth variations alter the intensity of UV irradiance reaching attached periphytic algal and bacterial microbial communities. Effects of alterations of UV irradiance by micro-changes in water level on periphytic microbiota were examined experimentally. Attached microbial communities, grown on glass fiber filters in situ in a natural wetland, were exposed experimentally to near-natural levels of UV irradiance of differing spectral quality. UV intensity was altered by varying the distance of the communities from the light source, changes in UV-attenuating natural dissolved organic matter (DOM), and small changes in water level (2 or 4 mm). Algal productivity and photosynthetic oxygen production were significantly reduced by small enhancements of UV-B radiation, by decreased water levels of only 2 mm, and by reductions in concentrations of DOM. UV-B had only small short-term effects on chlorophyll a, although small increases in water depth and DOM concentration reduced pigment damage. Experimental removal of UV-B during in situ growth indicated that algae could adapt to UV radiation during growth in natural environments. Microbial oxygen consumption and bacterial productivity and biomass were also lowered significantly by UV-B exposure, and damage decreased with small (2 mm) increases in water depth or in DOM concentration. Selective inhibitors of algal photosynthesis and production of released extracellular organic substrates caused a concomitant reduction in bacterial productivity and a significant increase in magnitude of UV-B damage to bacterial biomass. These effects suggested that metabolic interactions between the periphytic autotrophs and heterotrophs altered community responses to UV-B radiation. Microscale water level reductions, common on a diurnal basis in shallow wetlands, and associated increased UV intensity can result in rapid alterations in periphytic metabolism. Received: 27 January 1999; Accepted: 18 May 1999     

Selection in vitro for UV-tolerant sugar beet (Beta vulgaris) somaclones

With a reduced stratospheric ozone concentration, the generation of UV-tolerant plants may be of particular importance. Among different crop plants there is large variation in sensitivity to UV-B radiation. This study was undertaken to investigate the possibilities of using somaclonal variation and selection in vitro for improving UV-B tolerance in sugar beet (Beta vulgaris L.). Sugar beet callus was exposed to UV radiation (280–320 nm, 0.863–5.28 kJ m^-2 day^-1, unweighted) and resultant shoots were selected from surviving cells. After establishment of the plants, they were grown under either visible radiation (114 μmol m^-2 s^-1 PAR) or with the addition of UV radiation (6.3 kJ m^-2 day^-1 biologically effective UV-B). Screening of regenerants in vivo for tolerance to UV radiation was undertaken 10 months after termination of the UV selection pressure. Screening was done visually and by using a number of physiological parameters, including chlorophyll fluorescence induction, ultraweak luminescence, pigment analysis and total content of UV-screening pigments. A clear difference between the unselected and the UV-selected somaclones was observed when visually studying the UV damage and other leaf injury. The observations were supported by the ultraweak luminescence measurements. Unselected plants showed significantly greater damage when subjected to subsequent UV radiation as compared to the selected plants. The clones subjected to UV selection pressure displayed a significantly higher concentration of UV-screening pigments under subsequent UV radiation. The unselected plants under subsequent UV treatment showed a lower carotenoid concentration when compared to selected plants. However, no significant difference between treatments was found for chlorophyll a/b, or F/F_max, a measure of photosynthetic quantum yield.     

Biochemical and Ultrastructural Changes in Pollen ofZea maysL. Grown Under Enhanced UV-B Radiation

The influence of ultraviolet-B (UV-B) radiation on the developmentof the male gametophyte was studied inZea maysL. cv. LG12 grownin a growth chamber under PAR light supplemented with UV-B radiationand compared with a second set of plants grown under PAR light.Pollen samples collected from both groups of plants were culturedon germination medium and it was found that UV-B had no effecton pollen germination. Total pollen protein content was notaffected but UV-B absorbing pigments increased. Some ultrastructuralalterations were observed in pollen and pollen tubes, in particularlarge amounts of electron dense deposits were seen throughoutthe cytoplasm and in association with the pollen wall. In maturespikes of UV-B treated plants, anthers retained numerous pollengrains in their loculi while anthers of control plants werealmost empty. UV-B treatment delayed flowering by 2–3d. These results show that UV-B treatment of maize plants interfereswith flowering, pollen ultrastructure and anther maturationeven though pollen germination is unaffected. The significantincrease of UV-B absorbing pigments in pollen grains could representa defence mechanism that enables plants to complete their reproductivecycle.Copyright 1998 Annals of Botany Company Zea maysL., maize, UV-B radiation, pollen.     

UV-B-induced damage and photoreactivation in three species of Boeckella (Copepoda, Calanoida)

Solar ultraviolet (UV) radiation poses a threat to most livingorganisms. Aquatic organisms have evolved three basic mechanismsto cope with harmful levels of radiation. Two mechanisms, avoidance(e.g. vertical migration) and photoprotection (e.g. productionof photoprotective compounds that act as filters, antioxidants,etc.), serve to minimize the dose of UV radiation that reachesthe organism's vital structures (DNA, membranes, etc.). Thethird mechanism, repair (e.g. dark repair mechanisms, such asnucleotide excision repair; or photoreactivation mechanisms,such as photoenzymatic repair), serves to repair the damagefollowing UV exposure. Here, we compare the vulnerability toUV-B radiation of three copepod species (Boeckella brevicaudata,Boeckella gibbosa, and Boeckella gracilipes) that occur in lakesthat differ in UV-B penetration and depth. Our aim was to gaininsight into the significance of each of the three mechanismsin different UV-B environments. Results from a 3-day ‘insitu’ incubation in ultra-oligotrophic Lake Toncek showedthat B.gracilipes is highly vulnerable to UV-B and UV-A radiation.In contrast, virtually no mortality was observed in B.gibbosaand B.brevicaudata during the same period. In order to discriminatethe contribution of photoprotection and photoreactivation, thethree species were subsequently exposed in the laboratory toan artificial source of UV-B radiation, both in the presenceand absence of visible radiation (recovery radiation). The photoprotectionpotential (i.e. resistance to UV-B in the absence of recoveryradiation) of B.gracilipes and B.gibbosa was lower than thatof B.brevicaudata. On the other hand, photoreactivation (higherresistance to UV-B in the presence of recovery radiation) wasobserved in B.brevicaudata and B.gibbosa, but not in B.gracilipes.To cope with damaging UV-B levels in nature, B.gracilipes dependsexclusively on the attenuation by the external media (i.e. avoidance).Although B.gibbosa tends to avoid the surface waters of lakes,it also occurs in shallow transparent pools. Most likely itsability to survive in these shallow, high UV environments isdue to its photoreactivation potential. Finally, despite itsoccurrence in highly turbid lakes, B.brevicaudata seems extremelywell suited to cope with UV-B radiation thanks to a combinationof photoreactivation and photoprotection.     

青藏高原强UV-B辐射对美丽风毛菊光合作用和色素含量的影响

以青藏高原矮嵩草草甸的主要伴随种美丽风毛菊为材料,通过滤除太阳辐射光谱中UV-B成分的模拟试验,研究了强太阳UV-B辐射对高山植物光合作用、光合色素和紫外吸收物质的影响.结果表明：与对照相比,弱UV-B处理能促使美丽风毛菊叶片净光合速率增加和提高稳态PSⅡ光化学效率;对照中叶片厚度的相对增加能弥补单位叶面积光合色素的光氧化损失,是高山植物对强UV B辐射的一种适应方式.短期滤除UV-B辐射处理时紫外吸收物质含量几乎没有变化,说明高山植物叶表皮层中该类物质受环境波动的影响较小.强UV-B环境下光合色素的相对增加是一种表象,而青藏高原强太阳UV-B辐射对高山植物美丽风毛菊的光合生理过程仍具有潜在的负影响.     

Leaf expansion and development of PHOTOSYNTHETIC CAPACITY AND PIGMENTS IN Liquidambar styraciflua (Hamamelidaceae)—EFFECTS OF UV-B RADIATION

In order to perform their functions as photosynthetic organs, leaves must cope with excess heat and potentially damaging ultraviolet radiation. Possible increases in the UV-B portion of the solar spectrum may place an additional burden on leaves, and this could be particularly important for young expanding leaves with poorly developed UV-B defense mechanisms. We evaluated the effects of supplemental UV-B radiation on leaf expansion and the development of photosynthetic capacity and pigments in sweetgum (Liquidambar styraciflua L.) seedlings. Seedlings were grown in the field under either ambient or ambient plus 3 or 5.0 kJ of biologically effective supplemental UV-B radiation. Although final leaf size was unaffected, the rate of leaf elongation and accumulation of leaf area was slower in leaves exposed to the lower supplemental UV-B irradiance. In contrast, chlorophyll accumulation and the development of photosynthetic capacity was more rapid in plants exposed to the higher, compared to the lower supplemental UV-B irradiance. The accumulation of anthocyanins and other putative flavonoids or UV-absorbing compounds was scarcely affected by exposure to supplemental UV-B radiation. These results suggest that the UV-B portion of the solar spectrum may, in the absence of gross affects on biomass, exert subtle influences on leaf ontogeny and the development of photosynthetic pigments and capacity in sweetgum.     

Spectral balance and UV-B sensitivity of soybean: a field experiment

Soybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV-B radiation (280–320 nm) under different combinations of UV-A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV-B and UV-A lamps electronically modulated to track ambient radiation. Significant UV-B-caused decreases in total aboveground production and growth were seen only when PFD and UV-A were reduced to less than half their flux in sunlight. When PFD was low, UV-A appeared to be particularly effective in mitigating UV-B damage. However, when PFD was high, substantial UV-A did not appear to be required for UV-B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV-B, leaves in all experiments exhibited increased UV-absorbing pigments and decreased whole-leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV-B experiments conducted in glasshouse or growth cabinet conditions to plant UV-B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.     

Solar ultraviolet radiation affects the activity of ribulose-1,5-bisphosphate carboxylase-oxygenase and the composition of photosynthetic and xanthophyll cycle pigments in the intertidal green alga Ulva lactuca L

The effect of solar UV radiation on the physiology of the intertidal green macroalga Ulva lactuca L. was investigated. A natural Ulva community at the shore of Helgoland was covered with screening foils, excluding UV-B or UV-B + UV-A from the solar spectrum. In the sampled material, changes in the activity and concentration of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco), and the concentration of photosynthetic and xanthophyll cycle pigments were determined. Exclusion of UV radiation from the natural solar spectrum resulted in an elevated overall activity of Rubisco, related to an increase in its cellular concentration. Among the photosynthetic pigments, lutein concentration was substantially elevated under UV exclusion. In addition, marked UV effects on the xanthophyll cycle were found: exclusion of solar UV radiation (and particularly UV-B) resulted in an increased ratio of zeaxanthin concentration to the total xanthophyll content, indicating adverse effects of UV-B on the efficiency of photoprotection under high irradiances of photosynthetically active radiation. The results confirm a marked impact of present UV-B levels on macroalgal physiology under field conditions.     

外源NO对增补UV-B辐射下兴安落叶松幼苗叶片光合色素和叶绿素荧光特性的影响

在增强UV-B辐射下,以3年生兴安落叶松幼苗为实验材料,研究了外源NO供体硝普钠(Sodium nitroprusside,SNP)对幼苗的光合色素（Chla、Chlb和Car）和叶绿素荧光参数的影响。方差分析结果表明0.5 mmol·L^-1的SNP对增补UV B胁迫下的兴安落叶松幼苗产生显著影响。0.5 mmol·L^-1的SNP能够显著抑制增补UV-B辐射后光合色素、F_v/F_m、Φ_PSⅡ、F_v′/F_m′和qP的明显下降以及Chla /Chlb、F_o和NPQ的升高。表明了外源NO能够减轻UV-B辐射胁迫下兴安落叶松幼苗光合反应中心的生理损伤,从而增强兴安落叶松幼苗对增补UV-B辐射胁迫环境的适应能力。