Estimation and Analysis of Cucumber (Cucumis sativus L.) Leaf Cellular Heat Sensitivity

Triphenyl tetrazolium chloride (TTC) reduction by cucumber (Cucumis sativus L. cv Poinsett 76 and cv Ashley) leaf discs was used as a viability assay to examine the effect of temperature pretreatment on the tissue response to acute hyperthermia. Semi-logarithmic plots of TTC reduction as a function of incubation time at different temperatures from 40 to 60[deg]C resembled the heat survival curves of animal cells. Heat inactivation rates were obtained and subjected to "quasi" Arrhenius analyses by analytical methods derived from the animal studies. The Arrhenius plots of TTC reduction rates for cv Ashley leaf discs preincubated at 25 or 37[deg]C and for cv Poinsett 76 preincubated at 37[deg]C were linear with the same activation energy (Ea) of about 80 kcal mol-1. The Arrhenius plot of cv Poinsett 76 preincubated at 25[deg]C was nonlinear with an Ea of about 80 kcal mol-1 at temperatures below 46[deg]C and an Ea of about 27.5 kcal mol-1 at temperatures above 47[deg]C. The significance of these differences is discussed in terms of the role of protein denaturation in the thermal sensitivity of cucumber disc reduction of TTC and the applicability of these methods to the analysis of plant cellular heat sensitivity.     

紫外光B辐射增强对水稻叶片内IAA和ABA含量的影响

 两个水稻品种CK46和Dular生长在人工气候箱的条件下,在0.0和13.0kJm-2 day-1(模拟臭氧浓度下降20％的UVB强度)的紫外光B(UV-B 280 nm-320 nm)下进行4周的照射处理,研究UV-B对水稻体内内源IAA和ABA含量的影响。结果表明：随着UV—B处理时间的延长,CK46和Dular叶片内的IAA含量下降。相反,UV-B辐射增强使两个品种叶片内的ABA含量上升。     

CO(2) Enhancement of Growth and Photosynthesis in Rice (Oryza sativa) : Modification by Increased Ultraviolet-B Radiation

Two cultivars of rice (Oryza sativa L.) IR-36 and Fujiyama-5 were grown at ambient (360 microbars) and elevated CO₂ (660 microbars) from germination through reproduction in unshaded greenhouses at the Duke University Phytotron. Growth at elevated CO₂ resulted in significant decreases in nighttime respiration and increases in photosynthesis, total biomass, and yield for both cultivars. However, in plants exposed to simultaneous increases in CO₂ and ultraviolet-B (UV-B) radiation, CO₂ enhancement effects on respiration, photosynthesis, and biomass were eliminated in IR-36 and significantly reduced in Fujiyama-5. UV-B radiation simulated a 25% depletion in stratospheric ozone at Durham, North Carolina. Analysis of the response of CO₂ uptake to internal CO₂ concentration at light saturation suggested that, for IR-36, the predominant limitation to photosynthesis with increased UV-B radiation was the capacity for regeneration of ribulose bisphosphate (RuBP), whereas for Fujiyama-5 the primary photosynthetic decrease appeared to be related to a decline in apparent carboxylation efficiency. Changes in the RuBP regeneration limitation in IR-36 were consistent with damage to the photochemical efficiency of photosystem II as estimated from the ratio of variable to maximum chlorophyll fluorescence. Little change in RuBP regeneration and photochemistry was evident in cultivar Fujiyama-5, however. The degree of sensitivity of photochemical reactions with increased UV-B radiation appeared to be related to leaf production of UV-B-absorbing compounds. Fujiyama-5 had a higher concentration of these compounds than IR-36 in all environments, and the production of these compounds in Fujiyama-5 was stimulated by UV-B fluence. Results from this study suggest that in rice alterations in growth or photosynthesis as a result of enhanced CO₂ may be eliminated or reduced if UV-B radiation continues to increase.     

增强UV-B辐射对彩色马铃薯叶片中相关保护酶活性的影响

以种植于大田中的马铃薯品种'云南转心乌'(块茎紫皮紫环,以下简称'转心乌')和 '大西洋'(块茎白皮白肉)为材料,分别采用自然太阳光照(0～10 W/m2)、2 W/m2和4 W/m2 UV-B辐射进行20～80 d的照射处理,测定了马铃薯叶片内过氧化氢酶(CAT)、过氧化物酶(POD)、超氧化物歧化酶(SOD)、苯丙氨酸解氨酶(PAL)活性以及总叶绿素和丙二醛含量的变化.结果表明:随着UV-B处理时间的延长,'转心乌'和'大西洋'叶片中CAT、POD、SOD、PAL活性均表现出先升后降的趋势,而总叶绿素含量持续降低,丙二醛含量逐渐增加;在增强UV-B辐射条件下,上述指标在处理时间和剂量间大多差异显著,且'转心乌'叶片的各保护酶活性和总叶绿素含量显著高于'大西洋',丙二醛含量则显著低于‘大西洋'.可见,长时间大剂量的UV-B辐射对马铃薯叶片的叶绿素合成代谢和保护酶活性具有一定的抑制作用,从而影响作物正常的生长发育;马铃薯对于紫外线辐射的响应具有品种间差异,'转心乌'较'大西洋'更耐UV-B辐射,其更适合种植在UV-B辐照较强的高海拔地区.     

补充UV-B辐射对浙贝母生长和光合作用的影响

通过模拟西安地区自然光中U V2B辐射,增大辐射剂量对浙贝母生长和光合作用的影响进行研究.3个增强的U V2B辐射2.54、4.25及5.31k J·m-2处理导致浙贝母株高、叶面积、单株干重、叶绿素含量降低,而茎粗增加.在3个U V2B处理中,生物效应以5.31k J·m-2处理为最大,2.54k J·m-2处理影响最小.同时增加的U V2B还使浙贝母的光合速率、蒸腾速率、水分利用率下降,作用效果与辐射强度呈正相关.分析认为,浙贝母对U V2B辐射具有一定的敏感性.     

Field Study of the Interaction between Solar Ultraviolet-B Radiation and Drought on Photosynthesis and Growth in Soybean

Soybean, Glycine max (L.) Merr. cv Essex, plants were grown in the field in a 2 × 2 factorial design, under ambient and supplemental levels of ultraviolet-B (UV-B) radiation (supplemental daily dose of 5.1 effective kilojoules per square meter) and were either well-watered or subjected to drought. Soil water potentials were reduced to −2.0 megapascals by the exclusion of natural precipitation in the drought plots and were maintained at approximately −0.5 megapascal by supplemental irrigation in well-watered plots. Plant growth and gas exchange characteristics were affected under both drought and supplemental UV-B radiation. Whole-leaf gas exchange analysis indicated that stomatal limitations on photosynthesis were only significantly affected by the combination of UV-B radiation and drought but substrate (ribulose bisphosphate) regeneration limitations were observed under either stress. The combined effect of both drought and UV-B radiation on photosynthetic gas exchange was a reduction in apparent quantum efficiency and the rapid appearance of biochemical limitations to photosynthesis concomitant with reduced diffusional limitations. However, the combination of stresses did not result in additive effects on total plant growth or seed yield compared to reductions under either stress independently.     

Behavioral Avoidance of Ultraviolet-B Radiation by Two Species of Neotropical Poison-Dart Frogs

Many animals, plants, and microorganisms are harmed by ultraviolet-B radiation. In particular, several members of class amphibia are negatively affected by exposure to ultraviolet-B radiation. Exposure to ultraviolet-B radiation can cause death or various types of sublethal damage in amphibians. One mechanism to lessen the effect of harmful ultraviolet-B radiation is to limit exposure to sunlight behaviorally. Few studies have examined the behavioral sensitivity of adult amphibians to ultraviolet-B radiation. Using both field experiments and field observations, we found that two species of diurnal poison-dart frogs in Costa Rica ( Dendrobates pumilio, D. auratus ) consistently preferred areas in the field and within experimental testing chambers that offered low levels of ultraviolet-B radiation. In field observations, vocalizing D. pumilio were found at locations with significantly lower levels of ambient ultraviolet-B compared to random locations throughout their natural habitat. Ultraviolet-B avoidance behavior may be an important behavioral response for tropical frogs in light of recent evidence suggesting a significant increase in the levels of ambient ultraviolet-B radiation in the tropics over the past decade.     

Nitric Oxide Alleviates Oxidative Damage Induced by Enhanced Ultraviolet-B Radiation in Cyanobacterium

To study the role of nitric oxide (NO) on enhanced ultraviolet-B (UV-B) radiation (280–320 nm)-induced damage of Cyanobacterium, the growth, pigment content, and antioxidative activity of Spirulina platensis-794 cells were investigated under enhanced UV-B radiation and under different chemical treatments with or without UV-B radiation for 6 h. The changes in chlorophyll-a, malondialdehyde content, and biomass confirmed that 0.5 mM sodium nitroprusside (SNP), a donor of nitric oxide (NO), could markedly alleviate the damage caused by enhanced UV-B. Specifically, the biomass and the chlorophyll-a content in S. platensis-794 cells decreased 40% and 42%, respectively under enhanced UV-B stress alone, but they only decreased 10% and 18% in the cells treated with UV-B irradiation and 0.5 mM SNP. Further experiments suggested that NO treatment significantly increased the activities of superoxide dismutase (SOD) and catalase (CAT), and decreased the accumulation of O ₂ ⁻ in enhanced UV-B-irradiated cells. SOD and CAT activity increased 0.95- and 6.73-fold, respectively. The accumulation of reduced glutathione (GSH) increased during treatment with 0.5 mM SNP in normal S. platensis cells, but SNP treatment could inhibit the increase of GSH in enhanced UV-B-stressed S. platensis cells. Thus, these results suggest that NO can strongly alleviate oxidative damage caused by UV-B stress by increasing the activities of SOD, peroxidase, CAT, and the accumulation of GSH, and by eliminating O ₂ ⁻ in S. platensis-794 cells. In addition, the difference of NO origin between plants and cyanobacteria are discussed.     

Decreased Ultraviolet-B Radiation Alters the Vertical Biomass Distribution in Cocksfoot

A greenhouse experiment was conducted to investigate whether small differences in UV-B irradiance would lead to changes in competition between cocksfoot (Dactylis glomerata L. cv. Athos) and white clover (Trifolium repens L. cv. Mervi). Plants were grown in greenhouses covered with different thicknesses of UV-transmittant plexi (3 and 5 mm) resulting in 82 % and 88 % of ambient UV-B radiation. Aboveground biomass was harvested at 4-week intervals and the vertical distribution of biomass, leaf thickness and specific leaf area were determined. Tillering, stubble and root biomass and crop height were also measured. There was only one significant effect: at 88 % of ambient UV-B radiation a larger fraction of the biomass was present in the lower layers and a smaller fraction was present in the upper layers.     

Alleviation of Ultraviolet-B Radiation-Induced Growth Inhibition of Green Gram by Triadimefon

Supplementary UV-B (12.2 kJ m⁻² d⁻¹ UV-B_BE) provided to Vigna radiata for 2 h d⁻¹ suppressed the length of root, shoot and whole plants, number of leaves, total leaf area, leaf area index, specific leaf mass, fresh and dry mass of leaves and shoot, relative growth rate and net productivity. In unstressed green gram plants (10 kJ m⁻² d⁻¹ UV-B_BE), triadimefon (TRIAD) (20 mg dm⁻³) enhanced growth in all parameters over control. The growth promoting effect of TRIAD enabled the UV-B impacted plants to overcome the growth inhibitions to varying degrees indicating its protective potential against UV-B stress. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inactivation of Cyanobacterial Nitrogenase After Exposure to Ultraviolet-B Radiation

Exposure of the N₂-fixing cyanobacterium Anabaena BT2 to ultraviolet-B radiation (2.5 W m⁻²) for 30 min resulted in complete loss of nitrogenase activity but 100% cell killing occurred only after a 90-min exposure. Inactivation of nitrogenase activity was not specific to Anabaena BT2; other species also showed a similar effect. The time required for 100% killing and inactivation of nitrogenase activity differed in various species, and this difference may be ascribed to the presence of different levels of UV-B protection mechanisms in individual species. Inhibition of nitrogenase activity was immediate, since exposure of cultures to UV-B for as little as 5 min elicited some inhibition of activity. The activity of UV-B-inhibited nitrogenase did not recover upon transfer of exposed cells to fluorescent light, suggesting that the inhibition may be due to specific inactivation of the enzyme. By employment of inhibitors of protein synthesis and PS-II activity, it was demonstrated that restoration of nitrogenase activity in a UV-B-treated culture occurred by fresh synthesis of nitrogenase polypeptide. Our findings suggest that estimation of nitrogenase activity in diazotrophic species may be used as a marker enzyme for assessing the impact of UV-B radiation. Received: 13 June 2002 / Accepted: 22 July 2002     

Influence of UV-B Supplemental Radiation on Growth and Pigment Content in Suaeda Maritima L.

In a field experiment with a mangrove species Suaeda maritima L. grown under ambient and supplementary UV-B radiation corresponding to 20 % ozone depletion, changes in growth and contents of photosynthetic and UV-absorbing pigments were determined. Supplemental UV-B irradiation for 9 d significantly reduced the growth and concentration of photosynthetic pigments. However, anthocyanin and flavonoid contents were significantly increased in UV-treated plants and which could be reduce the UV-B penetration and damage to the underlying tissues.     

Protection of Photosynthesis against Ultraviolet-B Radiation by Carotenoids in Transformants of the Cyanobacterium Synechococcus PCC7942

The cyanobacterium Synechococcus PCC7942 was transformed with various carotenogenic genes, and the resulting transformants either accumulated higher amounts of β-carotene and zeaxanthin or showed a shift in the carotenoid pattern toward the formation of zeaxanthin. These transformants were exposed to ultraviolet-B (UV-B) radiation, and the degradation of phycobilins, the inactivation of photosynthetic oxygen evolution, and the activity of photosystem II were determined. In the genetically modified cells, the influence on destruction of phycobilins was negligible. However, protection of photosynthetic reactions against UV-B damage was observed and was dependent on the carotenoid concentrations in the different transformants. Furthermore, it was shown that endogenous zeaxanthin is more effective than β-carotene. Our results suggest that carotenoids exert their protective function as antioxidants to inactivate UV-B-induced radicals in the photosynthetic membrane.     

Flux Imbalance Analysis and the Sensitivity of Cellular Growth to Changes in Metabolite Pools

Stoichiometric models of metabolism, such as flux balance analysis (FBA), are classically applied to predicting steady state rates - or fluxes - of metabolic reactions in genome-scale metabolic networks. Here we revisit the central assumption of FBA, i.e. that intracellular metabolites are at steady state, and show that deviations from flux balance (i.e. flux imbalances) are informative of some features of in vivo metabolite concentrations. Mathematically, the sensitivity of FBA to these flux imbalances is captured by a native feature of linear optimization, the dual problem, and its corresponding variables, known as shadow prices. First, using recently published data on chemostat growth of Saccharomyces cerevisae under different nutrient limitations, we show that shadow prices anticorrelate with experimentally measured degrees of growth limitation of intracellular metabolites. We next hypothesize that metabolites which are limiting for growth (and thus have very negative shadow price) cannot vary dramatically in an uncontrolled way, and must respond rapidly to perturbations. Using a collection of published datasets monitoring the time-dependent metabolomic response of Escherichia coli to carbon and nitrogen perturbations, we test this hypothesis and find that metabolites with negative shadow price indeed show lower temporal variation following a perturbation than metabolites with zero shadow price. Finally, we illustrate the broader applicability of flux imbalance analysis to other constraint-based methods. In particular, we explore the biological significance of shadow prices in a constraint-based method for integrating gene expression data with a stoichiometric model. In this case, shadow prices point to metabolites that should rise or drop in concentration in order to increase consistency between flux predictions and gene expression data. In general, these results suggest that the sensitivity of metabolic optima to violations of the steady state constraints carries biologically significant information on the processes that control intracellular metabolites in the cell.     

植物对增强UV-B辐射的防御机制研究进展

由于大气同温层的臭氧层逐渐被破坏变薄,增加了太阳UV-B辐射抵达地球表面的强度,对植物产生不同程度的影响.本文综述了近年来有关植物对增强UV-B辐射的防御机制,包括植物在生长、繁育与次生代谢过程中存在的防御机制、植物体内生物大分子对于UV-B辐射增强的防御和不同植物对于UV-B辐射增强的防御能力的差异,以及如何有效地利用该机制;同时提出了今后研究的方向和重点.     

Influence of Ultraviolet-B Radiation on Peroxidase Activity of Allium schoenoprasum Leaves

An approximately 7 % difference in biologically effective ultraviolet-B (UV-B) radiation did not significantly influence leaf length or leaf peroxidase activity of chives (Allium schoenoprasum L.). However, correlation and regression analyses with different climatic parameters revealed that increased UV-B radiation enhanced ascorbate peroxidase activity in chive leaves whereas guaiacol peroxidase was inhibited. This revised version was published online in July 2006 with corrections to the Cover Date.     

Protective Effect of Rare Earth Against Oxidative Stress Under Ultraviolet-B Radiation

The effects of lanthanum (III) (La(III)) in protecting soybean leaves against oxidative stress induced by ultraviolet-B (UV-B) radiation were investigated. The increase in contents of hydrogen peroxide (H₂O₂) and superoxide () due to UV-B radiation suggested oxidative stress. The increase in the content of malondialdehyde (MDA) and the decrease in the index of unsaturated fatty acid (IUFA) indicated oxidative damage on cell membrane induced by UV-B radiation. La(III) partially reversed UV-B-radiation-induced damage of plant growth. The reduction in the contents of H₂O₂, , and MDA and increase in the content of IUFA, compared with UV-B treatment, also indicated that La(III) alleviated the oxidative damage induced by UV-B radiation. The increase in the activities of superoxide dismutase and peroxidase and the contents of ascorbate, carotinoids, and flavonoids were observed in soybean leaves with La(III) + UV-B treatment, compared with UV-B treatment. Our data suggested that La(III) could protect soybean plants from UV-B-radiation-induced oxidative stress by reacting with reactive oxygen species directly or by improving the defense system of plants.     

Lysozyme Modification by the Fenton Reaction and Gamma Radiation

A comparative study was performed on lysozyme modification after exposure to Fenton reagent (Fe(II)/H 2 O 2 ) or hydroxyl radicals produced by &#110 radiation. The conditions were adjusted to obtain, with both systems, a 50% loss of activity of the modified ensemble. &#110 radiation modified almost all types of amino acid residues in the enzyme, with little specificity. The modification order was Tyr > Met=Cys > Lys > Ile+Leu > Gly > Pro=Phe>Thr+Ala>Trp=Ser>Arg>Asp+Glu, with 42 mol of modified residues per initial mole of native enzyme. In contrast, when the enzyme was exposed to the Fenton reaction, only some types of amino acids were modified. Furthermore, a smaller number of residues (13.5) were damaged per initial mole of enzyme. The order of the modified residues was Tyr > Cys > Trp > Met >His > Ile+Leu > Val > Arg. These results demonstrate that the modifications elicited by these two free radical sources follow different mechanisms. An intramolecular free radical chain reaction is proposed to play a dominant role in the oxidative modification of the protein promoted by &#110 radiation.