The effects of salicylic acid on pigment contents in ultraviolet radiation stressed pepper plants

Pepper (Capsicum annuum L.) plants were sprayed with salicylic acid (SA) and treated with ultraviolet radiation UV-A (320–390 nm), UV-B (312 nm), and UV-C (254 nm) of 6.1, 5.8, and 5.7 W m⁻², respectively. UV significantly reduced contents of chlorophyll (Chl) a and b, and carotenoids (Car). SA treatment moderated Chl and Car reduction in plants treated with UV-B and UV-C. The quantity of antocyanins, flavonoids, rutin, and UV-absorbing compounds in plants that were treated with UV-B, UV-C, and SA were significantly increased. Foliar spray of SA counteracted the UV effects on pepper.     

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.     

Changes in leaf protein and pigment contents and photosynthetic activities during senescence of detached maize leaves: influence of different ultraviolet radiations

Senescence induced loss in pigments and proteins of detached maize (Zea mays L. cv. Col) leaves was significantly enhanced on the exposure of leaves to different ranges of ultraviolet (UV) radiation. Compared to UV-A (320-400 nm) and UV-B (280-320 nm), the UV-C (200-320 nm) was the most damaging for the pigments and macromolecules. A severe decline in photosystem (PS) 2 mediated photoreduction during senescence of detached leaves exposed to UV irradiation suggested a damage of the system. The PS1 mediated photoreduction of methylviologen with 2,6-dichlorophenol indophenol as electron donor was stimulated by UV-A and UV-B radiations, suggesting a reorganisation of the PS1 complex. These results were fortified by the values of fast and slow kinetics of chlorophyll (Chl) a fluorescence transients.     

Changes in leaf protein and pigment contents and photosynthetic activities during senescence of detached maize leaves: influence of different ultraviolet radiations

Senescence induced loss in pigments and proteins of detached maize (Zea mays L. cv. Col) leaves was significantly enhanced on the exposure of leaves to different ranges of ultraviolet (UV) radiation. Compared to UV-A (320-400 nm) and UV-B (280-320 nm), the UV-C (200-320 nm) was the most damaging for the pigments and macromolecules. A severe decline in photosystem (PS) 2 mediated photoreduction during senescence of detached leaves exposed to UV irradiation suggested a damage of the system. The PS1 mediated photoreduction of methylviologen with 2,6-dichlorophenol indophenol as electron donor was stimulated by UV-A and UV-B radiations, suggesting a reorganisation of the PS1 complex. These results were fortified by the values of fast and slow kinetics of chlorophyll (Chl) a fluorescence transients. This revised version was published online in June 2006 with corrections to the Cover Date.     

Differential Responses of Growth and Photosynthesis in Cyamopsis Tetragonoloba L. Grown under Ultraviolet-B and supplemental long-wavelength radiations

Cyamopsis tetragonoloba L. seedlings were subjected to continuous ultraviolet (UV)-B radiation for 18 h and post-irradiated with "white light" (WL) and UV-A enhanced fluorescent radiations. UV-B treatment alone reduced plant growth, pigment content, and photosynthetic activities. Supplementation of UV-A promoted the overall seedling growth and enhanced the synthesis of chlorophyll and carotenoids with a relatively high photosystem 1 activity. Post UV-B irradiation under WL failed to photoreactive the UV-B damage whereas a positive photoregulatory effect of UV-A was noticed in electron transport rates and low temperature fluorescence emission spectra.     

UV tolerance in the two-spotted spider mite, Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae was exposed to UV-C (250 nm), UV-B (300 nm), and UV-A (350 nm). In non-diapausing females, the median effective doses for 50% mortality plus escape incidence (ED₅₀) were 21 (UV-C) and 104 kJ m⁻² (UV-B); those for 50% oviposition rate in continuous darkness-treated mites were 6.2 (UV-C) and 41 kJ m⁻² (UV-B). No significant effects of UV-A on mortality and oviposition rate were observed. The ED₅₀ values for UV-B were similar to the natural UV-B observed for 2-5 days in summer when T. urticae inhabits the undersides of leaves. Therefore, T. urticae possibly uses leaves as a filter to avoid the deleterious effects of UV-B. In diapausing females, low mortality was observed even at high doses of UV radiation, but more than half escaped even at low doses. The orange body color of diapausing females results from accumulation of carotenoids, a scavenger for UV-induced reactive oxygen species; this may explain the low mortality of diapausing females. Diapausing females may overcome the deleterious effects of UV-B during winter in the absence of leaves by emigrating to UV-free environments and by accumulating carotenoids.     

UV-B-induced synthesis of photoprotective pigments and extracellular polysaccharides in the terrestrial cyanobacterium Nostoc commune.

Liquid cultures of the terrestrial cyanobacterium Nostoc commune derived from field material were treated with artificial UV-B and UV-A irradiation. We studied the induction of various pigments which are though to provide protection against damaging UV-B irradiation. First, UV-B irradiation induced an increase in carotenoids, especially echinenone and myxoxanthophyll, but did not influence production of chlorophyll a. Second, an increase of an extracellular, water-soluble UV-A/B-absorbing mycosporine occurred, which was associated with extracellular glycan synthesis. Finally, synthesis of scytonemin, a lipid-soluble, extracellular pigment known to function as a UV-A sunscreen, was observed. After long-time exposure, the UV-B effect on carotenoid and scytonemin synthesis ceased whereas the mycosporine content remained constantly high. The UV-B sunscreen mycosporine is exclusively induced by UV-B (< 315 nm). The UV-A sunscreen scytonemin is induced only slightly by UV-B (< 315 nm), very strongly by near UV-A (350 to 400 nm), and not at all by far UV-A (320 to 350 nm). These results may indicate that the syntheses of these UV sunscreens are triggered by different UV photoreceptors.     

Photosynthetic responses to solar UV-A and UV-B radiation in low-and high-altitude populations of <Emphasis Type="Italic">Hippophae rhamnoides</Emphasis>

Two contrasting sea buckthorn (Hippophae rhamnoides L.) populations from the low (LA) and high (HA) altitudinal regions were employed to evaluate the plant physiological responses to solar UV-A radiation and near-ambient UV-B radiation (UV-B+A) under the sheltered frames with different solar ultraviolet radiation transmittance. LA-population was more responsive to solar UV-A. Some modification caused by UV-A only existed in LA-population, such as significant reduction of leaf size, relative water content, and chlorophyll (Chl) b content as well as δ¹³C elevation, coupled with larger increase of contents of total carotenoids (Cars). This higher responsiveness might be an effective pre-acclimation strategy adapting for concomitant solar UV-B stress. Near-ambient UV-B+A radiation caused significant reduction of leaf size and Chl content as well as slight down-regulation of photosystem 2 activity that paralleled with higher heat dissipation, while photosynthetic rate was modestly but significantly increased. The higher photosynthesis under near-ambient UV-B+A radiation could be related to pronounced increase of leaf thickness and effective physiological modification, like the increase of leaf protective pigments (Cars and UV-absorbing compound), constant high photochemical capacity, and improved water economy.     

Role of salicylic acid in regulating ultraviolet radiation-induced oxidative stress in pepper leaves

The effect of salicylic acid (SA) counteracting the UV-A, UV-B, and UV-C-induced action on pepper (Capsicum annuum L.) plants was studied. For this purpose, the activities of antioxidant enzymes (peroxidase, polyphenol oxidase, ascorbate peroxidase, catalase, and glutathione reductase) were measured. Plants were sprayed with SA and treated with UV-A (320–390 nm), UV-B (312 nm), and UV-C (254 nm) radiation with a density of 6.1, 5.8, and 5.7 W/m². The activities of antioxidant enzymes were enhanced in leaves in response to UV-B and UV-C radiation. SA treatment moderated an increase in the activities of some antioxidant enzymes (peroxidase, ascorbate peroxidase, catalase, and glutathione reductase) in plants that were treated with UV radiation. The activity of antioxidant enzyme polyphenol oxidase in plants that were treated with UV-B, UV-C, and SA was significantly increased. The aim of the present study was to investigate the possible protective effect of SA treatment on UV-A, UV-B, and UV-C stress.     

Growth and physiochemical responses of <Emphasis Type="Italic">Camelina sativa</Emphasis> L. under UV-C stress

A study was conducted to estimate the effect of UV-C (200–280 nm) radiation stress on growth and physiochemical responses of Camelina sativa L. cv. Calina (EC643910; a potential bio-fuel crop) for its possible mass multiplication at high-altitude under high radiations. The germination percentage in terms of radicle protrusion and opening of cotyledonary leaves significantly decreased 13.98 and 27.8 %, respectively, as compared to control. However, no significant change was observed in growth parameters including root and shoot lengths and fresh biomass. The relative membrane leakage rate and lipid peroxidation as a malondialdehyde contents significantly increased with the value of ~99 % and 0.17 mM g^?1 FW, respectively, under UV-C stress. Also, the proline, glycine betaine and total soluble sugars contents increased by ~330, ~440, ~144 %, respectively, as compared to control. Among non-enzymatic antioxidants, the ascorbic acid and total phenol contents significantly increased by ~284 and ~537 %, respectively, as compared to control. Likewise, the activity of antioxidant enzyme, ascorbate peroxidase, guaiacol peroxidase and catalase increased under UV-C stress with the value of 1.03, 0.05 and 0.06 µmol mg protein^?1 min^?1, respectively. In addition, the chlorophyll a, b and total (a + b) contents decreased by ~180, ~151 and ~147 %, respectively, as compared to control. In contrast, the total carotenoids and anthocyanin contents increased by ~160 and ~184 %, respectively. Our findings suggest the adaptive growth and physiochemical responses of C. sativa under UV-C stress. Therefore, it may be recommended for large-scale cultivation at high-altitude under intense natural radiations for future bio-fuel production.     

Effect of low doses of UV-A and UV-B radiation on photosynthetic activities in<Emphasis Type="Italic">Phaseolus mungo</Emphasis> L.

The effect of low doses of UV-A (320–400 nm) and UV-B (280–320 nm) radiation on photosynthetic activities inPhaseolus mungo L. was investigated under field condition. Supplementation of UV-A enhanced the synthesis of chlorophyll and carotenoids than the UV-B supplemented plants. Significant increase was seen in the concentration of UV-B absorbing compounds of UV-B treated plants. Increase of PS 2 activity in UV-A treated plants was seen. Changes in photosynthetic activity were measured in terms of PS 2 mediated O₂ evolution and Chl a fluorescence.     

Responses in the physiology and biochemistry of Korean pine (Pinus koraiensis) under supplementary UV-B radiation

The effect of supplementary UV-B radiation on Korean pine (Pinus koraiensis Sieb. et Zucc) was investigated. Compared with the control, the T1, T2, and T3 UV-B treatments increased by 1.40, 2.81, and 4.22 kJ m^?2 d^?1, respectively. Gas-exchange parameters, photosynthetic pigment concentrations, contents of secondary metabolites, epicuticular wax, free radical, malondialdehyde (MDA), and the activities of antioxidant enzymes were determined after 40 d of exposure. The concentrations of chlorophyll (Chl) a, Chl b, total Chl, carotenoid (Car), and the ratio Chl a/b in the pine needles were in the following order: T1 > T2 > T3. Compared with the control, the contents of flavonoids and epicuticular wax significantly decreased in all levels of supplementary UV-B radiations (p<0.05). Moreover, the contents of hydrogen peroxide (H₂O₂) and MDA significantly increased with the enhanced UV-B radiations (p<0.05). Korean pine can increase the catalase, ascorbate peroxidase, and superoxide dismutase activities to prevent oxidative stress by supplementary UV-B radiation. However, its defence mechanism is not efficient enough to prevent UV-Binduced damage.     

The effect of UV-B and UV-C radiation on Hibiscus leaves determined by ultraweak luminescence and fluorescence induction

The effects of UV-C (254 nm) and UV-B (280-320 nm) on chlorophyll fluorescence induction and ultraweak luminescence (UL) in detached leaves of Hibiscus rosa-sinensis L. were investigated. UL from leaves exposed to UV-B and UV-C radiation reached a maximum 72 h after irradiation. In both cases most of the light was of a wavelength over 600 nm. An increase in the percentage of long wavelength light with time was detected. UV radiation increased peroxidase activity, which also reached a maximum 72 h after irradiation. UV-B and UV-C both reduced variable chlorophyll fluorescence. No effect on the amount of chlorophyll or UV screening pigments was observed with the short-term irradiation used in this investigation.     

Effect of UV radiation on pigments of the Antarctic macroalga Leptosomia simplex L.

Impact of UV-A and UV-B radiation on pattern of pigments of the Antarctic macroalga Leptosomia simplex L. was studied during the Polarstern cruise (ANT XII/2) 1994/95 under controlled laboratory conditions. An 8 h exposure to UV-A of 17.6 W m-2 led usually to an increase of carotenoid contents, but to a decrease in contents of chlorophyllide (Chlide) a and chlorophyll (Chl) a. UV-B irradiation (300-320 nm) caused a decrease in contents of Chlide a, lutein, and zeaxanthin, but an increase in contents of Chl a and carotenes. Enhancement of carotenoid contents was attributed to a protection of the photosynthetic apparatus. UV effects on the 15N-ammonium uptake were correlated with the changes in pigment contents.     

UV-B induces biomass production and nonenzymatic antioxidant compounds in three cyanobacteria

In the present study, the impact of low fluence rate of UV-B (0.045 W.m^?2) on biomass production, photosynthetic pigments (chlorophyll a, carotenoids, and phycobiliproteins), chlorophyll fluorescence, nonenzymatic antioxidants: proline, ascorbate, cysteine, and nonprotein thiols, total phenolic contents, and antioxidant potential (radical scavenging activity) was investigated in three cyanobacteria, viz. Nostoc muscorum, Phormidium foveolarum, and Arthrospira platensis. Selected fluence rate of UV-B caused enhancing effect on these parameters; however, the increased values of these attributes were greater in A. platensis followed by P. foveolarum and N. muscorum. Results indicate that UV-B (at selected fluence rate) could be used as technique that may modify cyanobacterial system for efficient and economic production of natural food supplements and/or natural pharmaceuticals.     

自然条件下滤减UV-B辐射对烤烟光合色素含量的影响

在自然环境中,以烟草栽培品种K326为材料,通过覆盖不同透明薄膜滤减UV—B辐射,研究100％（CK）、75％（T1）、50％（T2）、35％（T3）UV—B辐射透过率处理下,不同强度UV—B辐射对烟草光合色素含量的影响。结果表明：烤烟三类光合色素对UV—B辐射有不同响应。类胡萝卜素对UV—B辐射响应较敏感。成熟初期,类胡萝卜素含量与UV—B辐射强度变化具有较好的正相关性,而chl a和chl b含量基本与UV—B辐射强度呈反向变化关系。成熟后期,由于UV—B辐射累积效应,光合色素含量变化没有明显规律。现蕾期至成熟采烤烟初期,chl a：chl b与UV—B辐射的反向变化关系较明显,后期则无明显规律,其含量的下降与UV—B辐射的累积效应有关。     

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.     

UV Effects on Pigments and Assimilation of 15N-Ammonium and 15N-Nitrate by Natural Marine Phytoplankton of the North Sea

Effects of ambient solar UV radiation in the field and of artifical UV irradiation under controlled laboratory conditions were studied with natural phytoplankton populations from Helgoland, German Bight, North Sea. The pattern of pigments varied after UV-A or UV-B plus a low dose of UV-A radiation: UV-A usually induced a stimulation of pigment biosynthesis; whereas UV-B plus UV-A led to a reduction of the contents of chlorophyll a, diadinoxanthin, fucoxanthin, peridinin and an unknown carotenoid; content of diatoxanthin was significantly enhanced. The damaging effect on nitrogen assimilation by UV was more pronounced after artificial UV-B plus UV-A irradiance compared to the influence of ambient solar UV under field conditions. The uptake of inorganic nitrogen was dependent on the dose and exposure time of UV radiation as well as on the species composition. The uptake of ¹⁵N-nitrate by natural phytoplankton collected in spring was more sensitive to UV irradiation than the assimilation of ¹⁵N-ammonium. UV-A radiation with a small part of shorter wavelengths at 315 nm (Philips-lamps in conjunction with the cut-off filter WG 320) caused a reduction of up to 12% whereas a stimulation of the ¹⁵NH₄⁺ uptake was observed after exposure to UV-A without any UV-B (Philips lamps TL 60W/09N). Pattern of ¹⁵N-incorporation into free amino acids and pool sizes varied in dependence on the applied nitrogen compound and on the irradiation conditions. The impact of UV radiation on the pattern of ¹⁵N-Iabelled free amino acids and the pool sizes was different. ¹⁵N enrichment into all the tested amino acids was reduced after 5 h UV-B plus UV-A exposure and after application of ¹⁵NH₄⁺. A depression of the glutamate and glutamine pools was observed after addition of ¹⁵N-nitrate alone. Pools of all main amino acids from phytoplankton in summer 1993/94 were inhibited by UV irradiance. Results are discussed with reference to the UV target (e.g. enzymes, pigments) and the adaptation to the environmental conditions.     

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.     

Effects of solar ultraviolet radiation on the potential efficiency of photosystem II in leaves of tropical plants

The effects of solar ultraviolet (UV)-B and UV-A radiation on the potential efficiency of photosystem II (PSII) in leaves of tropical plants were investigated in Panama (9°N). Shade-grown tree seedlings or detached sun leaves from the outer crown of mature trees were exposed for short periods (up to 75 min) to direct sunlight filtered through plastic or glass filters that absorbed either UV-B or UV-A+B radiation, or transmitted the complete solar spectrum. Persistent changes in potential PSII efficiency were monitored by means of the dark-adapted ratio of variable to maximum chlorophyll a fluorescence. In leaves of shade-grown tree seedlings, exposure to the complete solar spectrum resulted in a strong decrease in potential PSII efficiency, probably involving protein damage. A substantially smaller decline in the dark-adapted ratio of variable to maximum chlorophyll a fluorescence was observed when UV-B irradiation was excluded. The loss in PSII efficiency was further reduced by excluding both UV-B and UV-A light. The photoinactivation of PSII was reversible under shade conditions, but restoration of nearly full activity required at least 10 d. Repeated exposure to direct sunlight induced an increase in the pool size of xanthophyll cycle pigments and in the content of UV-absorbing vacuolar compounds. In sun leaves of mature trees, which contained high levels of UV-absorbing compounds, effects of UV-B on PSII efficiency were observed in several cases and varied with developmental age and acclimation state of the leaves. The results show that natural UV-B and UV-A radiation in the tropics may significantly contribute to photoinhibition of PSII during sun exposure in situ, particularly in shade leaves exposed to full sunlight.