Analysis of limitations to CO2 assimilation on exposure of leaves of two Brassica napus cultivars to UV-B

Apex and Bristol cultivars of oilseed rape (Brassica napus) were irradiated with 0.63 W m^?2 of UV-B over 5 d. Analyses of the response of net leaf carbon assimilation to intercellular CO₂ concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bis-phosphate on leaf photosynthesis. Simultaneous measurements of chlorophyll fluorescence were used to estimate the maximum quantum efficiency of photosystem II (PSII) photochemistry, the quantum efficiency of linear electron transport at steady-state photosynthesis, and the light and CO₂-saturated rate of linear electron transport. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) content and activities were assayed in vitro. In both cultivars the UV-B treatment resulted in decreases in the light-saturated rate of CO₂ assimilation, which were accompanied by decreases in carboxylation velocity and Rubisco content and activity. No major effects of UV-B were observed on end-product inhibition and stomatal limitation of photosynthesis or the rate of photorespiration relative to CO₂ assimilation. In the Bristol cultivar, photoinhibition of PSII and loss of linear electron transport activity were observed when CO₂ assimilation was severely inhibited. However, the Apex cultivar exhibited no major inhibition of PSII photochemistry or linear electron transport as the rate of CO₂ assimilation decreased. It is concluded that loss of Rubisco is a primary factor in UV-B inhibition of CO₂ assimilation.     

Ultraviolet-B radiation causes shade-type ultrastructural changes in Brassica napus

Cell and chloroplast structural changes in palisade cells from mature leaves of Brassica napus L. cv. Paroll were quantified following exposure of plants to enhanced ultraviolet-B (280–320 nm; 13 kJ m^?2 day^?1 biologically effective UV-B) radiation at two different levels of photosynthetically active radiation (PAR, 400–700 nm; 200 and 700 μmol m^?2 s^?1). Short-term changes in leaf ultrastructure after 30 min and longer term changes after one day and one week were analyzed using stereological techniques incorporating light and electron microscopy and mathematical reconstruction of a mean cell for each sample. Ultraviolet-B together with either relatively high or low PAR resulted in cell structural changes resembling those typical of plants under shade conditions, with the most marked response occurring after 30 min of UV-B radiation. The ultrastructural changes at the cellular level were generally similar in both the relatively high and low PAR plus UV-B radiation treatments. The surface areas of all three thylakoid types, the appressed, non-appressed and margin thylakoids increased in the palisade tissue under supplemental UV-B irradiation. Although the appressed and non-appressed thylakoids increased in surface area, they did not increase equally, leaving open the possibility that the two thylakoid types have independent regulatory systems or different sensitivity to UV-B radiation. Increased thylakoid packing (mm² thylakoid membrane per mm² leaf surface) in UV-B-exposed plants may increase the statistical probability of photon interception. An increased level of UV-absorbing pigments after one week of supplemental UV-B radiation did not prevent or significantly ameliorate UV effects. Our data supported the assumption that UV-B radiation may have a regulatory role besides damaging effects and that an increased UV-B environment will likely increase this regulatory influence of UV-B radiation.     

Effect of enhanced UV-B radiation on pollen quantity,quality, and seed yield in Brassica rapa (Brassicaceae)

We conducted three experiments to examine the influence of ultraviolet-B radiation (UV-B; 280–320 nm) exposure on reproduction in Brassica rapa (Brassicaceae). Plants were grown in a greenhouse under three biologically effective UV-B levels that simulated either an ambient stratospheric ozone level (control), 16% (“low enhanced”), or 32% (“high enhanced”) ozone depletion levels at Morgantown, WV, USA in mid-March. In the first experiment, we examined whether UV-B level during plant growth influenced in vivo pollen production and viability, and flower production. Pollen production and viability per flower were reduced by ≈50% under both enhanced UV-B levels relative to ambient controls. While plants under high-enhanced UV-B produced over 40% more flowers than plants under the two lower UV-B treatments, whole-plant production of viable pollen was reduced under high-enhanced UV-B to 17% of that of ambient controls. Whole-plant production of viable pollen was reduced under low-enhanced UV-B to 34% of ambient controls. In the second experiment, we collected pollen from plants under the three UV-B levels and examined whether source-plant UV-B exposure influenced in vitro pollen germination and viability. Pollen from plants under both enhanced-UV-B treatments had initially lower germination and viability than pollen from the ambient level. After in vitro exposure to the high-enhanced UV-B levels for 6 h, viability of the pollen from plants grown under ambient UV-B was reduced from 65 to 18%. In contrast, viability of the pollen from plants grown under both enhanced UV-B treatments was reduced to a much lesser extent: only from ≈43 to 22%. Thus, ambient source-plant pollen was more sensitive to enhanced UV-B exposure. In the third experiment, we used pollen collected from source plants under the three UV-B levels to fertilize plants growing under ambient-UV-B levels, and assessed subsequent seed production and germination. Seed abortion rates were higher in plants pollinated with pollen from the enhanced UV-B treatments, than from ambient UV-B. Despite this, seed yield (number and mass) per plant was similar, regardless of the UV-B exposure of their pollen source. Our findings demonstrate that enhanced UV-B levels associated with springtime ozone depletion events have the capacity to substantially reduce viable pollen production, and could ultimately reduce reproductive success of B. rapa.     

Variation in the glucosinolate content of oilseed rape (Brassica napus L.) leaves

The glucosinolate content of oilseed rape {Brassica napus) leaves was monitored over the growth period 30–70 days after planting, and a comparison made between a single-low cultivar (low in erucic acid), Bienvenu, and a double-low cultivar (low in erucic acid and glucosinolate), Cobra. In older, fully-expanded leaves the glucosinolate concentration was very low (< 0.3 μmol/ml tissue water) and did not alter during the course of the experiment. In developing sixth leaves glucosinolate content increased rapidly and reached a maximum concentration (4–5 μmol/ml tissue water) 40 days after planting (6 days after leaf emergence). The concentration then declined, to about 1 μmol/ml after 60 days although the total glucosinolate content in leaves continued to increase until 50 days; much of the reduction in concentration was simply a result of leaf expansion. No major differences were seen between the two varieties in total glucosinolate content or in the individual compounds present. Cv. Cobra developed more quickly than cv. Bienvenu so direct comparison between leaves of the two cultivars was complex. When comparing the glucosinolate content of oilseed rape leaves, between cultivars or between treatments, it is vital to ensure that carefully matched leaves of comparable developmental age are selected.     

UV-B辐射对蚕豆叶膜脂过氧化的影响及其机制

温室种植的吞豆在0（CK）,8．82kJ/m2(T1)和12．6kJ/m2(T2)3种剂量的紫外线B（UV－B）辐射引起膜脂变化及其机制的研究结果表明,UV0B处理后,蚕豆叶片中丙二醛（MDA）和H2O2含量升高,膜脂肪酸不饱和度指数（IUFA）降低,脂氧合酶（LOX）活性升高,超氧歧化酶（SOD）活性稍有波动,而3种多胺－腐胺（Put)精胺（Spd)和尸胺（Spn)在照射7天后均有积累,但在处理后期（21d)有所回落,推测由LOX主导的酶促膜过氧化作用和氧自由基引起的非酶促过作用在膜结构的破坏中起重要作用,SOD活性和多胺含量的变化蚕豆对UV－B胁迫的一种适应性生理反应。     

陆生植物体内酶系统对UV-B辐射增强的响应

臭氧层减薄导致地表中波紫外线UV-B(280～320 nm)辐射的增强,UV-B辐射能量远高于可见光,且能被植物体内蛋白质和核酸等生物大分子吸收.酶是植物体内起催化作用的一类蛋白质,酶的数量和活性对UV-B辐射增强有强烈的响应.本文将近年来增强UV-B辐射对植物体内酶影响的研究工作进行了综述.主要包括抗氧化酶、核酮糖-1,5-二磷酸羧化酶、硝酸还原酶和谷氨酰胺合成酶.并就今后该方面的研究提出建议.     

Effects of quercetin and enhanced UV-B radiation on the soybean (Glycine max) leaves

The possible ameliorative effects of quercetin on soybean [Glycine max (L.) Merr.] leaves exposed to UV-B radiation were conducted in greenhouse. The symmetrical leaves supplied with quercetin solution (0.2%, 1%) were exposed to UV-B radiation (0, 3.5, 6.5 kJ m⁻² d⁻¹). 0.2% quercetin ameliorated leaf photosynthesis, improved leaf water content (LWC), and decreased lipid oxidation. The unfavorable effect on photosynthetic parameter was displayed in 1% quercetin treatment. The effect of quercetin on phenylalanine ammonia lyase (PAL) activity varied with the quercetin concentration, UV-B radiation intensity and leaf development. In the later development polyphenol oxidase (PPO) activity was increased significantly by quercetin treatments. We suggested that quercetin with suitable concentration could serve as UV-B protective agent partly due to its antioxidant capacity.     

Alterations in photosynthesis and pigment distributions in pea leaves following UV-B exposure

We compared photosynthetic and UV-B-absorbing pigment concentrations, gas-exchange rates and photosystem II (PSII) electron transport rates in leaves of pea (Pisum sativum mutant Argenteum) grown without UV-B or under an enhanced UV-B treatment (18 kJ m^?2 biologically effective daily dose) in a greenhouse. We also compared the distribution of chlorophyll by depth within leaves of each treatment by using image analysis of chlorophyll autofluorescence. Ultraviolet-B treatment elicited putative protective responses such as an 80% increase in UV-B-absorbing compound concentrations (leaf-area basis), and a slight increase in mesophyll thickness (178 in controls compared to 191 μm in UV-B-treated leaves). However, photosynthetic rates of UV-B-treated leaves were only 80% of those of controls. This was paralleled by reductions in leaf conductance to water vapor (50% of controls) and intercellular CO₂ concentrations, suggesting that stomatal limitations were at least partly responsible for lower photosynthetic rates under the UV-B treatment. Total chlorophyll concentrations (leaf-area basis) in UV-B-treated leaves were only 70% of controls, and there was a shift in the relative distribution of chlorophyll with depth in UV-B-treated leaves. In control leaves chlorophyll concentrations were highest near the adaxial surface of the upper palisade, dropped with depth and then increased slightly in the bottom of the spongy mesophyll nearest the abaxial surface. In contrast, in UV-B-treated leaves chlorophyll concentrations were lowest at the adaxial surface of the upper palisade and increased with depth through the leaf. The most notable treatment difference in chlorophyll concentrations was in the upper palisade near the adaxial surface of leaves, where we estimate that chlorophyll concentrations in each 1-μm-thick paradermal layer were about 50% lower in UV-B-treated leaves than in controls. We found reduced electron transport capacity in UV-B-treated leaves, based on lower maximum fluorescence (F_m), variable to maximum fluorescence ratios (F,/F_m) and quantum yield of PSII electron transport (Y). However, the above were assessed from fluorometer measurements on the adaxial leaf surface and may reflect the markedly lower chlorophyll concentrations in the upper palisade of UV-B-treated leaves.     

UV-B辐射增强对马铃薯叶片结构及光合参数的影响

叶片作为植物进行光合作用的主要器官,在长期进化过程中形成了对不同光照环境条件的形态可塑性和相应的适应机制,以保证植物能在变化的、非适宜环境下的生存与繁衍。随着大气臭氧层衰减引起地表UV-B辐射增强,其对植物叶片结构和光合作用的影响显著,但这种气候变化趋势对马铃薯叶片形态结构、光合作用的影响尚不明确。设置增强UV-B辐射2.5 kJm~(-2)d~(-1)(T1)、5.0 kJm~(-2)d~(-1)(T2)、自然光(CK)3个处理,以6个马铃薯品种(系)为材料,研究增强辐射对不同基因型马铃薯叶片结构和光合参数的影响。结果表明:增强的UV-B辐射使马铃薯叶片解剖结构不同程度增厚,叶片厚度增加;叶片气孔和非腺毛的密度增加明显,腺毛有增多倾向。扫描电镜显示处理后的近轴面叶片角质层厚度增加,蜡质晶体增多,但表皮细胞变小且失水萎缩,细胞轮廓模糊;气孔、腺毛及非腺毛附属结构受胁迫影响呈萎缩状态。透射电镜显示处理后的叶肉细胞中基粒类囊体肿胀,结构层次紊乱,胁迫引起细胞质壁分离,细胞壁扭曲并有较多的沉淀物;部分品种过氧化物酶体可见清晰的过氧化氢酶晶体。叶片缩小增厚、腺毛增多、角质层和蜡质增厚、胞内积累过氧化氢酶的形态适应和生理响应并未能有效减少UV-B辐射对光合参数和光合效率的影响,合作88、丽薯6号、师大6号的净光合速率、气孔导度等参数均受到抑制,光能利用效率明显降低,属于UV-B辐射敏感型品种;剑川红21-3、21-1和转心乌3个品种(系)的相关光合特性几乎不受影响,显示云南地方品种具有较强的UV-B辐射耐受性,有待于进一步从生理生化和分子水平探究更多的适应机制。     

增强紫外B辐射对植物及生态系统影响研究的发展趋势

介绍了一些有关紫外B辐射增强对植物及生态系统影响研究的新进展：1．许多研究已深入到分子水平;2．注意到对植物生长调控的研究;3．更加重视对植物防御、修复的研究;4．有关信号传导的研究日渐增多;5．对植物群体及生态系统影响的研究在不断扩大与加深;6．复合效应研究正在升温。推断今后在一段时间内,有关UV－B辐射对植物和生态系统影响的研究不但不会削弱,可能还会加强,特别分子水平的研究会大大增加,今后对群体和生态系统的研究会重视野外和长期效应的观测。我国在这一领域的研究起步晚,但近些年发展得较快,有部分研究已赶上国际研究进展的步伐。     

UV－B辐射增强对长白山五种藓类植物生长的影响

对生长在中国长白山的5种藓类植物——垂枝藓、拟垂枝藓、塔藓、星塔藓和高山金发藓分别以辐射强度为0.2(自然光照,对照)、3.0(紫外线中等辐射强度)和6.0kJ.m-2.d-1(高剂量辐射强度)的UV-B照射40d后,测定其株高、生物量及叶绿素含量.结果表明:中等和高强度的UV-B辐射使拟垂枝藓和塔藓的株高、生物量和叶绿素含量分别下降了32.3%、62.4%、81.3%和21.4%、59.4%、62.8%,其相对生长速率均为负值;高剂量UV-B辐射处理下垂枝藓的生物量稍有上升,而高山金发藓地下部分的生物量增加1倍,但叶绿素含量变化不明显.高山金发藓和垂枝藓抵抗UV-B辐射的能力较强,拟垂枝藓和塔藓对UV-B辐射较敏感.     

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.     

UV-B辐射增强对NaCl胁迫下小麦幼苗生理生态的影响

研究了0.4w·m-2的紫外线-B(UV-B)辐射对0.8%NaCl胁迫下冬小麦"小偃926"(TriticumaestivumL.xiaoyan-926)幼苗的生长、光合作用、水分状况、黄酮含量和膜脂过氧化等几方面的影响。结果表明,UV-B辐射和NaCl胁迫单独或复合处理下小麦幼苗的株高、生物量、含水量、净光合速率、蒸腾速率、气孔导度和光合色素含量均显著降低,膜脂过氧化产物丙二醛含量和叶片相对电导率则升高,但NaCl胁迫条件下增加UV-B辐射(复合处理)与单独NaCl胁迫相比,上述指标多数均无显著差异(除复合处理下类胡萝卜素含量显著降低外)。两胁迫因子单独或复合处理均明显提高了小麦幼苗黄酮含量及三种抗氧化酶(SOD、POD和CAT)活性,且复合处理的促进效应最大。脯氨酸含量在单独UV-B辐射下明显降低,在单独NaCl胁迫和复合处理下显著升高,且复合处理下增幅最大。结果说明UV-B辐射不会明显加剧NaCl胁迫下小麦幼苗的伤害,这可能与NaCl胁迫提高了小麦幼苗黄酮含量、脯氨酸含量和抗氧化酶活性有关。     

紫外线-B辐射对植物DNA及蛋白质的影响

大气平流层中的臭氧衰减,导致太阳辐射中的紫外辐射量有明显的增加,其中UV-B辐射对植物会产生不同程度的影响。分子生态学理论认为,UV-B辐射对植物造成的损伤,首先伤害植物的生物大分子,即进行光化学修饰。本文就臭氧衰减对生态环境和植物的影响途径进行了讨论,重点论述了UV-B辐射对植物蛋白质合成的抑制和DNA的损伤修复途径。并应用分子生物学技术研究植物对UV-B辐射的抗性机理和DNA修复技术的前景进行了展望。     

增强紫外—B对反枝苋形态、生理及异速生长的影响

在田间条件下,模拟西安地区21.6%的臭氧层减薄,研究增强紫外-B辐射 280～320nm,3.18kJ·m-2·d-1 对双子叶阔叶杂草反枝苋 Amaranthusretroflexus 生理、形态及异速生长的影响.结果表明: 1 与对照相比,处理组的叶绿素、类胡萝卜素含量降低,但叶片紫外吸收物质的含量增加; 2 处理组的株高、叶数及单株重有明显降低; 3 株高与单株重的线性关系有较大的偏离,表现在同等株高下处理组的生物量低于对照.这些表明在补充的紫外-B条件下,反枝苋的形态有较大的可塑性,并进一步会影响该植物在群落中的竞争能力.     

UV-B辐射对雨生红球藻生长和类胡萝卜素含量的影响

以BG11培养基,对雨生红球藻进行了室内培养,研究了增强UV-B辐射对雨生红球藻生长速率和虾青素含量的影响.室内培养的条件是UV-B辐射强度为0.1J·m-2·S-1,0.2J·m-2·S-1, 0.3J·m-2·S-1, 光照强度为60 μmoL·m-2·S-1(昼夜比为12 h:12 h),温度为20～26℃.测定了培养液细胞数目、叶绿素a、类胡萝卜素的含鼍,并对雨生红球藻进行了显微结构观察.结果显示在室内培养雨生红球藻增加UV-B辐射,能够提高其细胞内虾青素的含量,其显微结构显示类胡萝卜素颗粒明显增加的现象.本研究目的是在室内培养雨生红球藻提高虾青素产量的方法.     

增强UV-B辐射与不同水平氮素对谷子（Setaria italica (L.) Beauv.） 叶片保护物质及保护酶的影响

研究了生长在1.875 mmol·L-1和15 mmol·L-1硝态氮素水平条件下的谷子(Setaria italica(L.)Beauv.)开花期间在进行强度为7.12 kJ·m-2.d-1增强UV.B辐射处理时叶片类黄酮含量、苯丙氨酸解氨酶(PAL)和保护酶活性变化差异.主要结果表明在开花期无论是否进行增强UV-B辐射处理,较低水平氮素均比较高水平氮素更有利于提高谷子叶片PAL活性;叶片类黄酮含量除在进行增强UV-B处理时较低氮素条件下生长的谷子在开花末期显著高于较高氮素条件下生长的谷子外,受氮素水平影响不甚明显.而在开花期不进行与进行增强UV-B辐射处理,氮素水平对叶片保护酶的影响有所差异:不进行增强UV-B辐射处理,整个开花期氮素水平对谷子叶片SOD活性有显著影响而对ASP活性无显著影响,对CAT和POD活性则在开花期部分阶段有显著影响.进行增强UV-B辐射处理,整个开花期氮素水平对谷子叶片SOD与CAT活性有显著影响而对ASP、POD活性影响不显著.     

增强UV—B辐射和CO2复合作用对蚕豆幼苗生长和光合作用的影响

在4.52 kJ*m-2*d-1 UV-BBE的UV-B辐射和700 μmol*mol-1的CO2浓度人工模拟复合处理下,研究了对蚕豆(Vicia faba L.)幼苗的生长和光合作用的影响.结果表明,UV-B辐射单因子明显降低蚕豆幼苗的株高、叶面积和生物量,CO2单因子的作用正好相反,二者的作用程度随着处理时间的延长而增大.UV-B辐射和CO2复合作用对蚕豆幼苗的生长影响不明显.同时,增强的UV-B辐射单因子还使蚕豆幼苗的光合速率、气孔导度和水分利用率下降,CO2单因子的作用也相反,且CO2单因子的促进程度大于UV-B辐射单因子的抑制程度.而在UV-B辐射和CO2复合作用下,蚕豆幼苗的光合作用参数基本与对照同步.分析认为,UV-B辐射和CO2复合作用对蚕豆幼苗的影响是一种拮抗作用.