Growth and nitrogen utilization in seedlings of mountain birch (Betula pubescens ssp. tortuosa ) as affected by ultraviolet radiation (UV-A and UV-B) under laboratory and outdoor conditions

 Growth patterns and nitrogen economy were studied in pot-grown seedlings of mountain birch subjected to different ultraviolet radiation under both laboratory and outdoor conditions at Abisko in northern Sweden. In the laboratory, nutrient supply, temperature, humidity, ultraviolet radiation-A (UV-A, 320–400 nm) and B (UV-B, 280–320 nm) were controlled, while photosynthetically active radiation (PAR, 400–700 nm) and photoperiod varied naturally. Under outdoor conditions nutrient supply was controlled, and the irradiation treatments were ambient and above-ambient UV-B using additional fluorescent lamps. Mountain birch nitrogen economy was affected by increased ultraviolet radiation, as reflected by a changed relationship between plant growth and plant nitrogen both in the laboratory and outdoors. In the laboratory enhanced UV-A decreased leaf area per unit plant biomass (leaf area ratio) but increased biomass productivity, both per unit leaf area (leaf area productivity) and per unit leaf nitrogen (leaf nitrogen productivity). Low levels of UV-B affected growth patterns and nitrogen economy in a similar way to enhanced UV-A. High levels of UV-B clearly decreased relative growth rate and nitrogen productivity, as leaf area ratio, leaf area productivity and leaf nitrogen productivity were all decreased. Under outdoor conditions above-ambient levels of UV-B did not alter growth or biomass allocation traits of the seedlings, whilst nitrogen productivity was increased. Mountain birch seedlings originating from different mother trees varied significantly in their responses to different ultraviolet radiation. Received: 10 April 1997 / Accepted: 19 September 1997     

Growth enhancement of soybean (Glycine max) upon exclusion of UV-B and UV-B/A components of solar radiation: characterization of photosynthetic parameters in leaves

Exclusion of UV (280–380 nm) radiation from the solar spectrum can be an important tool to assess the impact of ambient UV radiation on plant growth and performance of crop plants. The effect of exclusion of UV-B and UV-A from solar radiation on the growth and photosynthetic components in soybean (Glycine max) leaves were investigated. Exclusion of solar UV-B and UV-B/A radiation, enhanced the fresh weight, dry weight, leaf area as well as induced a dramatic increase in plant height, which reflected a net increase in biomass. Dry weight increase per unit leaf area was quite significant upon both UV-B and UV-B/A exclusion from the solar spectrum. However, no changes in chlorophyll a and b contents were observed by exclusion of solar UV radiation but the content of carotenoids was significantly (34–46%) lowered. Analysis of chlorophyll (Chl) fluorescence transient parameters of leaf segments suggested no change in the F _v/F _m value due to UV-B or UV-B/A exclusion. Only a small reduction in photo-oxidized signal I (P700⁺)/unit Chl was noted. Interestingly the total soluble protein content per unit leaf area increased by 18% in UV-B/A and 40% in UV-B excluded samples, suggesting a unique upregulation of biosynthesis and accumulation of biomass. Solar UV radiation thus seems to primarily affect the photomorphogenic regulatory system that leads to an enhanced growth of leaves and an enhanced rate of net photosynthesis in soybean, a crop plant of economic importance. The presence of ultra-violet components in sunlight seems to arrest carbon sequestration in plants. An erratum to this article can be found at     

Enhanced UV-B radiation under field conditions increases anthocyanin and reduces the risk of photoinhibition but does not affect growth in the carnivorous plant Pinguicula vulgaris

The effects of enhanced UV-B radiation were investigated in the carnivorous plant Pinguicula vulgaris in a field experiment performed in Abisko, North Sweden (68° 21' N, 18° 49' E, 380 m above sea level). Potted plants were exposed to either ambient or ambient plus supplemental UV-B radiation, simulating a 15% ozone depletion. No effect was observed on either the epicuticular (external) or cellular (internal) UV absorbing capacity of the leaves. However, the anthocyanin content was more than doubled by supplemental UV-B radiation. In laboratory experiments, the anthocyanin rich, UV-B treated leaves were less susceptible to a low temperature/high light photoinhibitory treatment, as judged by in vivo chlorophyll fluorescence measurements. Yet, this potential benefit did not considerably affect the growth of the plant in the field (leaf area and dry mass, reproductive dry mass, flowering frequency, senescence rates, dry mass of winter buds). However, there was a marginally significant increase in root dry mass and in the root to shoot ratio, which may underlie the significant increase in the nitrogen content of the leaves. We suggest that P. vulgaris is resistant against UV-B radiation damage and that the possible negative effects of additional UV-B radiation on the growth of these plants may have been effectively counterbalanced by the lower risk of photoinhibition, due to the concomitant increase in anthocyanins.     

Responses to ultraviolet-B radiation (280–315 nm) of pea (Pisum sativum) lines differing in leaf surface wax

To test the hypothesis that leaf surface wax influences plant responses to UV-B, 6 lines of cultivated pea (Pisum sativum L.), selected as having more or less wax, were grown at 0 or 6.5 kJ m^-2 day^-1 plant-weighted UV-B against a background of 850–950 μmol m^-2 s^-1 photosynthetically active radiation. In the 4 lines with least leaf surface wax the amount of wax on adaxial and abaxial leaf surfaces was increased following exposure to 6.5 kJ m^-2 day^-1 UV-B, but UV-B decreased surface wax in Scout, which had the greatest wax deposits. On the adaxial leaf surface, UV-B radiation caused a shift in wax composition from alcohols to esters and hydrocarbons and the ratio of short to long chain length alkyl ester homologues was increased. There was no evidence of a shortening in carbon chain length of hydrocarbons, primary alcohols or fatty acids due to UV-B and no significant correlation between wax amount and UV reflectance from leaves. UV-B induced significant increases in UV-absorbing compounds in the expanded leaves and buds of most lines. UV-B reduced the growth of all lines. Foliage area (leaves plus stipules) declined by 5–30%, plant dry weight by 12–30%, and plant height by 24–38%. Reductions in growth occurred in the absence of any changes in chlorophyll fluorescence or photosynthetic rate. UV-B also had no major effect on carbon allocation patterns. The effects of UV-B on growth appeared to be due to changes in tissue extension and expansion. Indeed, many of the responses to UV-B observed in this study of pea appear more consistent with indirect effects being expressed in developing tissues rather than through the direct action of UV-B on mature tissues. There was no evidence that wax amount or biochemistry was associated with the sensitivity of the lines to UV-B radiation. Furthermore, induction of pigments was not correlated with changes in growth. However, lines with the greatest constitutive amounts of pigments in unexpanded bud tissues were most tolerant of elevated UV-B.     

Response of 19 cultivars of soybeans to ultraviolet-B irradiance

Nineteen soybean cultivars were grown for four weeks in controlled environmental chambers with artificial daylight supplemented by five UV-B irradiance regimes to determine the range of growth and development responses of seedlings. Data from nine plant characteristics were assessed: leaf area, dry weight of leaves, stems and roots, total plant dry weight, height, ratio of roots to shoots and leaf area to weight and rating of leaves for damage. Significant differences were observed in the responses noted. Stunting, leaf chlorosis and loss of apical dominance were three general symptoms apparent on all cultivars which received UV-B irradiance. Varying degrees of reduced leaf area and dry weight of the plants and altered ratios of weights of leaves per unit area and weight of roots to shoots were also found. It was concluded that different soybean cultivars demonstrate a marked difference in sensitivity to UV-B radiation under the artificial conditions of controlled environmental growth chambers and this may indicate a genetic basis for variability in sensitivity of soybean cultivars to this waveband. However, the sensitivity to UV-B radiation was increased by the lower than normal photon fluence of photosynthetically active radiation (225 μE m⁻² s⁻¹).     

Effects of enhanced ultraviolet-B radiation on plant nutrients and decomposition of spring wheat under field conditions

Spring wheat (Triticum aestivum) was grown in the field under ambient and supplemental levels of ultraviolet-B (UV-B, 280–315 nm) radiation to determine the potential for alteration in plant nutrients, decomposition, leaf quality and dry matter yield. Supplemental UV-B radiation simulating a 12, 20 and 25% stratospheric ozone depletion significantly decreased dry matter yield, but had no significant impact on harvest index. UV-B radiation resulted in an increase of the concentrations of N and K in all plant parts; changes of the concentrations of P, Mg, Fe and Zn varied in a tissue-dependent manner, as the decrease of P in leaves and stems, and its increase in spikes and grains. The mass of N, P, K, Mg, Fe and Zn in various plant parts and whole plant was generally decreased except leaf N mass was increased by enhanced UV-B radiation. Enhanced UV-B radiation decreased the concentrations of soluble carbohydrates in leaves and increased that of holocellulose and soluble proteins. After 60 and 100 days of decomposition of leaves and stems in the field, enhanced UV-B radiation stimulated the loss of organic C. As a consequence, the nutrient content of soils might be less diminished under enhanced UV-B radiation.     

Ultraviolet-B radiation effects on the Mediterranean ruderal Dittrichia viscosa

Young seedlings of Dittrichia viscosa L. (syn. Inula viscosa (L.) Aiton) (Asteraceae) were extensively treated with artificial rain in order to remove the water soluble component of their epicuticular UV-B absorbing compounds. As a result, 75% of the epicuticular absorbing capacity at 300 nm was lost. The seedlings were subsequently grown in a naturaly lit glasshouse for 80 days under 0.06, 6.41 and 10.14 kJ m^-2 day ^-1 biologicaly effective UV-B radiation doses. The initial, pre-rain values of the water soluble, epicuticular UV-B absorbing potential was restored in about three weeks. During this transient period the plants were exposed to the enhanced UV-B radiation doses with part of their UV-B radiation screen removed. Although a trend for increased accumulation of epicuticular UV-B absorbing capacity was observed with increasing UV-B radiation doses, the allelopathic potential of the epicuticular material remained unchanged. Internal (cellular) UV-B absorbing compounds and chlorophylls were unaffected, but total carotenoids were increased, indicating a possible protective role against UV-B radiation damage. Leaf, stem and root dry mass were the same under all treatments but UV-B radiation caused a reduction in the dry mass invested per unit leaf area with a concomitant increase in leaf area. The importance of this UV-B radiation induced selective allocation of photosynthate to the production of assimilative surfaces is discussed.     

Stratospheric Ozone Depletion: High Arctic Tundra Plant Growth on Svalbard is not Affected by Enhanced UV-B after 7 years of UV-B Supplementation in the Field

The response of tundra plants to enhanced UV-B radiation simulating 15 and 30% ozone depletion was studied at two high arctic sites (Isdammen and Adventdalen, 78° N, Svalbard).The set-up of the UV-B supplementation systems is described, consisting of large and small UV lamp arrays, installed in 1996 and 2002. After 7 years of exposure to enhanced UV-B radiation, plant cover, density, morphological (leaf fresh and dry weight, leaf thickness, leaf area, reproductive and ecophysiological parameters leaf UV-B absorbance, leaf phenolic content, leaf water content) were not affected by enhanced UV-B radiation. DNA damage in the leaves was not increased with enhanced UV-B in Salix polaris and Cassiope tetragona. DNA damage in Salix polaris leaves was higher than in leaves of C. tetragona. The length of male gametophyte moss plants of Polytrichum hyperboreum was reduced with elevated UV-B as well as the number of Pedicularis hirsuta plants per plot, but the inflorescence length of Bistorta vivipara was not significantly affected. We discuss the possible causes of tolerance of tundra plants to UV-B (absence of response to enhanced UV-B) in terms of methodology (supplementation versus exclusion), ecophysiological adaptations to UV-B and the biogeographical history of polar plants     

Response of cotton and sorghum to several levels of subambient solar UV-B radiation: a test of the saturation hypothesis

Some have proposed that plant responses to above-ambient or supplemented levels of solar ultraviolet-B radiation (UV-B; 280–315 nm) are typically subtle because targets or receptors in plants become saturated. If true, in solar UV-B filter exclusion experiments we would expect that plant responses would level off or 'saturate' as doses approached ambient levels. To test this so-called 'saturation hypothesis' we examined the response of Gossypium hirsutum (cotton) and Sorghum bicolor (sorghum) to filter exclusions that provided five levels of biologically effective UV-B, ranging from 36 to 91% of ambient solar levels in Arizona, USA. UV-B dose had no effect on biomass production of either species. As UV-B dose increased or approached ambient, individual leaves of S. bicolor were smaller, but plants produced more tillers and leaves. In G. hirsutum , individual leaves as well as total plant leaf area were smaller, but plants produced more branches. Bulk concentrations of soluble UV-B absorbing compounds increased with UV-B dose in both species. Leaf epidermal UV-B transmittance, assessed with the chlorophyll fluorescence technique, declined with increasing UV-B dose, and was well correlated with bulk concentrations of soluble UV-B screening compounds. Bulk concentrations of insoluble or wall-bound UV-B absorbing compounds were not affected by UV-B dose. The intensity of UV-induced blue fluorescence from leaf surfaces was strongly correlated with bulk concentrations of wall-bound UV-B absorbing compounds, and this signal has the potential to provide a rapid, non-invasive method to estimate concentrations of these compounds, which are time-consuming to extract. While both species were responsive to solar UV-B, responses did not appear to become saturated as doses approached ambient levels. Rather, responses required a threshold dose of >70% of solar ambient UV-B levels before they became apparent.     

The effect of solar UV radiation on four plant species occurring in a coastal grassland vegetation in The Netherlands

During the summer of 1992, growth and some physiological parameters of four native plant species occurring in a coastal grassland in The Netherlands, were studied after reduction of solar UV irradiance using different cut-off filters. Biomass production, morphology and photosynthesis of all species tested were unaffected by the different treatments. Litter production of Plantago lanceolata was increased in the absence of the total UV waveband, indicating a possible role for this waveband in plant senescence. Depletion of the total UV waveband from sunlight resulted in alterations in biomass allocation in Calamagrostis epigeios and Urtica dioica while no changes were observed in P. Ianceolata and Verbascum thapsus. In C. epigeios an increase in the specific leaf area was observed, whereas in U. dioica root weight per total plant weight was decreased resulting in an increase in the shoot/root ratio. Both photosynthetic and UV-absorbing pigment concentrations were altered by the different filter applications. When compared to control plants receiving full sunlight, depletion of UV-B resulted in a significant increase in chlorophyll concentration in U. dioica leaves, this however did not affect photosynthetic rate. The presence of UV-B radiation enhanced the UV-absorbance of leaf extracts of all species except P. lanceolata. Optical characteristics of the leaves were also changed. Both the quantity ( P. lanceolata and U. dioica ) and the quality (all species) of radiation transmitted by the leaves was affected by the different treatments.     

The effect of solar UV-B radiation on terpenes and biomass production in Grindelia chiloensis (Asteraceae), a woody perennial of Patagonia,Argentina

UV-B radiation is absorbed effectively by nucleic acids and other sensitive targets, potentially causing harmful photochemical effects. Protection against UV-B radiation may be afforded by flavonoids and other phenolics, which absorb strongly in the UV region, but little is known about the role played by other compounds, such as terpenes. Grindelia chiloensis, native of Patagonia (Argentina), can accumulate as much as 25% resin (terpenes) in its leaves. The present investigation was carried out to test the effect of solar UV-B radiation on the allocation of photoassimilates to biomass and terpenes. Exposure to UV-B radiation reduced whole plant biomass, plant height and leaf area, and increased leaf thickness and resin accumulation in Grindelia chiloensis. Higher absorbance was found for refined resin in the UV-B waveband from plants grown under solar UV-B radiation than plants without UV-B radiation. These chemical and structural changes could protect the plant from UV radiation, and may help elucidate the importance of epicuticular resins for a species as G. chiloensis native to an environment with maximum daily integrated values of solar UV-B irradiance.     

增强UV-B辐射和氮素互作对植物生长代谢影响的研究进展

不同氮源条件下,UV-B辐射增强能改变植株对氮的吸收利用以及植株叶片的碳氢比和碳氮比,增加氨基酸的生物合成.缺氮条件下, UV-B辐射增强使植物叶片中SOD、POD活性增强,MDA含量增加;氮素过量时,UV-B辐射增强会降低植物对UV-B辐射的耐性.UV-B辐射增强和氮缺乏相互作用会降低叶片的光合速率、叶绿素含量、可溶性糖及淀粉含量,从而抑制植物的生长,降低生物量.该文对近年来国内外有关UV-B辐射增强与氮素相互作用对植物抗氧化系统、氮代谢、光合作用、生物量和形态结构的影响进行综述.     

短期增强UV-B辐射对青榨槭幼苗生理特性的影响

在中国科学院茂县生态站选择2年生青榨槭幼苗进行室外盆栽实验,以人工增强0.27 W·m^-2(7.7kJ·m^-2·d^-1)的UV-B辐射剂量,研究模拟当地平流层臭氧削减1%时近地面太阳UV-B的增强对木本植物幼苗生理生态适应性的影响.处理0 d后,移除UV-B处理装置,就地测定气体交换参数和叶绿素荧光参数,并取样测定叶绿素及UV吸收物质含量.结果表明,增强UV-B辐射显著降低了青榨槭幼苗叶片最大净光合速率P_max(对照为6.214,处理为4.42),显著增加叶片暗呼吸速率Rd(对照为0.413,处理为1.29)和光补偿点LCP(对照为21.629,处理为9.861),但对表观量子速率a(对照为0.021,处理为0.032)影响不明显;它降低青榨槭幼苗每日净光合速率和水分利用效率,以及原初光化学效率(F_v/F_m)和实际光化学量子产量(ΦPS∏).此外,增强UV-B辐射使叶片叶绿素a、b含量降低(对照为16.23,.39,处理为13.17,4.93),但对叶绿素b含量影响未达显著水平.增强UV-B处理降低了青榨槭幼苗UV吸收物质含量(对照为0.87,处理为0.79).光合指标、叶绿素荧光指标和叶绿素含量的变化有较好的一致性,表明增强UV-B对青榨槭幼苗的光合作用可能有一定的抑制作用.     

Changes in growth and pigment concentrations with leaf age in pea under modulated UV-B radiation field treatments

We assessed whether growth of garden pea (Pisum sativum mutant Argenteum) was reduced under ecologically relevant enhancements of ultraviolet-B radiation (UV-B, 280–320 nm) by employing modulated field lampbanks which simulated 0, 16 or 24% ozone depiction. In addition, we determined whether enhanced UV-B altered the concentration and distribution of chlorophyll and UV-B-absorbing compounds in leaves, and whether this was dependent on leaf age. There were no significant UV-B effects on the four whole-plant parameters we examined (height, above-ground biomass, total leaflet area or average leaflet area). Of the 12 leaf-level parameters we examined, UV-B had a significant effect (P < 0.05) on only one parameter: the ratio of UV-B-absorbing compounds to chlorophyll, which was greatest at the highest UV-B level. Total chlorophyll concentrations tended to be lower under enhanced UV-B (P= 0.11), while the proportion of UV-B-absorbing compounds in the adaxial epidermis tended to be higher (P= 0.11). Total leaf concentrations of UV-B-absorbing compounds were unaffected by UV-B level. Cooler, suboptimal growing conditions during this late summer/early autumn experiment may have masked some potential UV-B effects. In contrast to the UV-B effects, we found strong leaf-age effects on nearly all parameters that we assessed. On an area basis, concentrations of total chlorophyll and UV-B-absorbing compounds increased with leaf age, while Chlorophyll a/b) ratios decreased. One of the few parameters unaffected by leaf age was the ratio of UV-B-absorbing compounds to total chlorophyll, which remained constant within a given UV-B treatment. Pea was much less sensitive to enhanced UV-B than in previous growth-chamber and greenhouse studies, and in nearly all cases UV-B treatment effects were overshadowed by leaf-age effects. In view of the large effect leaf age had on concentrations of UV-B-absorbing compounds, as well as their distribution within leaves, researchers may need to consider leaf age in UV-B experimental designs.     

Changes of epicuticular wax induced by enhanced UV-B radiation impact on gas exchange in Brassica napus

The epicuticular wax covering on plant surface plays important roles in protecting plants against UV radiation. However, the role of epicuticular wax in affecting leaf gas exchange under enhanced ultraviolet-B (UV-B) radiation remains obscure. In the present study, different aged leaves of Brassica napus were used to analyze the responses of crystal structure and chemical constituents of epicuticular wax to UV-B radiation and the effects of such responses on gas exchange indices. Enhanced UV-B radiation significantly decreased the amount of esters in all leaves except the first leaf, amount of secondary alcohols in the second, third and fourth leaves, and amount of primary alcohols in the second and third leaves, while increased the amounts of ketones and aldehydes in the first leaf. Enhanced UV-B level had no significant effect on the amounts of alkanes and total wax in all leaves. Exposure to UV-B radiation resulted in wax fusion on adaxial leaf and stomata opening on abaxial leaf. Fusions of plates and rods on adaxial leaf surface covered most of the stomata, thereby influencing the photosynthesis in the upper mesophyll of leaves. Enhanced UV-B level significantly reduced the net photosynthesis rate (P _N) but increased the stomata conductance (g _s), concentrations of intercellular CO₂ (C _i ), and transpiration rate (E) in all leaves. Both UV-B radiation and the wax fusion induced by enhanced UV-B radiation resulted in different stomata status on abaxial and adaxial leaf surface, causing decrease of P _N, and increase of g _s, C _i and E in leaves.     

Effects of ultraviolet-B radiation on the growth and yield of crop plants

This paper reviews growth chamber, greenhouse, and field studies on the effects of ultraviolet-B (UV-B. between 280 and 320 nm) radiation on agricultural crop plants. Our understanding of the physiological effects of UV-B radiation comes primarily from growth chamber studies, where UV-B is artificially supplied via filtered lamps. Both photosystems I and II, as well as carboxylating enzymes, are sensitive to UV-B radiation. Ultraviolet-B radiation also affects stomatal resistance, chlorophyll concentration, soluble leaf proteins, lipids, and carbohydrate pools. In general, the effects of UV-B radiation are accentuated by the low levels of visible radiation typically found inside growth chambers. Ultraviolet-B radiation has also been shown to affect anatomical and morphological plant characteristics. Commonly observed UV-B induced changes include plant stunting, reductions in leaf area and total biomass, and alterations in the pattern of biomass partitioning into various plant organs. In sensitive plants, evidence of cell and tissue damage often appears on the upper leaf epidermis as bronzing, glazing, and chlorosis. Epidermal transmission in the UV region decreases in irradiated leaves. This decrease is primarily associated with a stimulation in flavonoid biosynthesis and is thought to be a protective, screening response to the deleterious effects of UV-B. A considerable degree of variability exists in sensitivity to UV-B radiation between different species. Approximately 30% of the species tested were resistant, another 20% were extremely sensitive, and the remainder were of intermediate sensitivity, in terms of reductions in total dry weight. In addition to this sizable interspecific variability, there appears to be a similarly wide intraspecific variability in UV-B response. The effects of UV-B radiation on crop yield have only been examined in a limited number of field studies, with ambient levels of UV-B radiation being supplemented with fluorescent sun lamps. Due to various deficiencies, all these field experiments to date have only limited utility for assessing the potential impact of enhanced levels of UV-B on crop productivity.     

Specific features of source-sink relations in alloplasmic hybrid of winter wheat with alien cytoplasm of goatgrass with emphasis on resistance to low temperature stress

We studied the influence of alien cytoplasm of spring goatgrass Aegilops ovata L. on some physiological parameters in winter wheat (Triticum aestivum L.), Mironovskaya 808, under normal conditions and in the case of modified source-sink relations. Measurements of relative rates of plant dry matter growth and its distribution among organs, CO₂ exchange (photosynthesis upon light saturation and dark respiration), content of sugars (sucrose + glucose + fructose) and their ratio in leaves, frost hardiness, and indices of membrane stability and damage of leaves by frost have shown that, on average, alloplasmic hybrid differed from the initial cultivar by almost all parameters. Reduced frost hardiness, increased index of leaf damage by frost, lowered leaf content of sugars, and reduced sucrose/(glucose + fructose) ratio in the alloplasmic hybrid were combined with higher roots/leaves ratio, relative rate of dry matter growth, and photosynthesis and respiration rates. The alloplasmic hybrid was more tolerant to decreased source strength in source-sink relations as compared to the initial cultivar.     

芒果老叶在增强UV-B辐射处理下的损伤和保护反应

以‘台衣一号’芒果盆栽苗离体老叶为试材,研究增强UV—B辐射条件下芒果老叶的损伤和保护反应。结果表明：UV—B辐射处理使芒果叶片MDA含量和相对电导率升高、叶绿素含量和叶绿素a／b降低,表明叶片受到损伤,且随处理时间延长叶片损伤加重。UV—B辐射处理叶片可溶性蛋白含量、抗氧化酶（SOD、CAT、POD）活性、保护色素（类胡萝卜素、类黄酮）和还原型GSH含量显著高于对照叶片,UV—B辐射处理叶片维生素C含量显著低于对照叶片,表明增强UV—B辐射可诱导叶片细胞通过提高活性氧清除能力和积累保护色素而直接吸收部分UV—B辐射来提高抗增强UV—B辐射损伤的能力。     

Intraspecific differences in Cucumis sativus sensitivity to ultraviolet-B radiation

Cucumber ( Cucumis sativus L.) cultivars Marketmore, Lama, XPH 1187, XPH 1484 and Sprint 440 (N) were grown in a greenhouse under two levels of biologically effective ultraviolet-B ( UV -B) radiation (daily dose: 0 and 11.6 kJ m⁻² UV-B_BE) for 31 days. Significant intraspecific differences were observed in plant height, number of leaves, leaf area and total dry weight. Based upon total biomass accumulation, Marketmore was found to be the most tolerant, and XPH 1484 the most sensitive to UV-B radiation. The dose response of accumulation of UV absorbing compounds (measured as absorbance of methanolic extracts) in leaf tissues showed an increase in UV absorbing compounds with UV-B dose in Marketmore, Sprint 440 (N) and XPH 1187. In Lama and XPH 1484, however, doses below 8.7 kJ m⁻² UV-B_BE produced no change in UV absorbing compounds. This study suggests that intraspecific differences in UV-B radiation sensitivity in cucumber may be related to inherent differences in the accumulation of UV absorbing compounds in leaves.     

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.