<Emphasis Type="Italic">Sunflower Chlorotic Mottle Virus</Emphasis> in Compatible Interactions with Sunflower: ROS Generation and Antioxidant Response

Sunflower chlorotic mottle virus (SuCMoV) is a recently described potyvirus that causes systemic infections in sunflower plants leading to chlorotic mottling and important growth reductions and yield losses. Oxidative damage is expressed after symptom development in this host-pathogen combination. The involvement of antioxidant enzyme activities in disease susceptibility was studied in two sunflower lines differing in the intensity and rate of development of SuCMoV infections: L2 is more susceptible than L33. A transient superoxide production peak was detected in leaves of both lines before symptom development. H₂O₂ accumulation increased before symptom expression in infected plants of L33 but in L2 such increase was registered only after symptoms became evident. In healthy plants of both lines, superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) showed similar activity levels. In inoculated plants of line L2, but not in L33, SOD and CAT activities increased significantly before the appearance of symptoms, and APX increases were detected later. A 1 mM SA treatment effectively decreased SuCMoV accumulation in plants of L2 but it did not affect it in L33. This treatment increased H₂O₂ accumulation and prevented the increase in antioxidant enzyme activities in infected plants of L2. It is suggested that increases in antioxidant enzyme activities interrupted the signals generated by the increase in ROS, which may have otherwise triggered defence reactions in the host and thus, resulted in a compatible interaction.     

Mechanisms of Phosphate-induced Disease Resistance in Cucumber

Certain phosphate salts are known inducers of systemic acquired resistance (SAR). In the present study, a local spray application of dipotassium hydrogenphosphate (K₂HPO₄) was effective in inducing a high level of systemic protection in cucumber plants against anthracnose caused by Colletotrichum lagenarium. Resistance induction by K₂HPO₄ was associated with localized cell death in cucumber leaves treated with the phosphate salt. The cell death observed, subsequently resulted in the appearance of macroscopically visible, necrotic spots. Appearing lesions resembled those provoked by tobacco necrosis virus (TNV) during a hypersensitive response (HR) that leads to pathogen-induced activation of SAR. Phosphate-mediated cell death was preceeded by a rapid generation of superoxide and hydrogen peroxide. As a further consequence of phosphate application, a local and systemic increase in free and conjugated salicylic acid (SA) levels was detected. The phosphate-induced responses were also identified with a similar time range in cucumber leaves that had been pre-inoculated with TNV. In contrast, none of these responses was triggered by application of the commercial plant activator benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester (BTH), which nevertheless was highly effective in inducing SAR in cucumber against anthracnose. In conclusion, the chemical SAR inducer K₂HPO₄ and the biological inducer TNV share some common early steps in signal transduction leading to SAR in cucumber, which differ from those involved in BTH-mediated SAR.     

Production of hydrogen peroxide and expression of ROS‐generating genes in peach flower petals in response to host and non‐host fungal pathogens

Reactive oxygen species (ROS) play dual roles in plant–microbe interactions in that they can either stimulate host resistance or enhance pathogen virulence. Innate resistance in peach (Prunus persica) to the brown rot fungal pathogen Monilinia fructicola is very limited, and knowledge of the mechanism of virulence is rudimentary. In this study, production of hydrogen peroxide, a major component of ROS, was determined in peach flower petals in response to M. fructicola (a host pathogen) and Penicillium digitatum (a non‐host pathogen). Monilinia fructicola was able to infect flower petals while P. digitatum was not. During the host‐specific interaction, M. fructicola induced hydrogen peroxide accumulation in flower petals. Application of exogenous antioxidants significantly reduced hydrogen peroxide accumulation as well as the incidence of brown rot disease. Application of M. fructicola spores to the surface of intact flower petals induced gene expression and increased enzyme activity of NADPH oxidase and cell wall peroxidase in host tissues, resulting in the production of hydrogen peroxide. Petals inoculated with M. fructicola exhibited high levels of protein carbonylation and lipid peroxidation. No significant response in gene expression, enzyme activity or hydrogen peroxide levels was observed in peach flower petals treated with P. digitatum. These results suggest that M. fructicola, as with other necrotrophic fungi, uses the strong oxidative response as part of a virulence mechanism.     

基于海藻糖的生物节水抗逆农业研究进展

生物节水农业主要包括新品种选育、外源有益物质和激素的添加及高效节水栽培措施的建立三个方向。海藻糖是国际上开发的主要低聚糖之一,常被作为外源有益物质应用于农业生产。在综合国内外相关研究文献的基础上,对海藻糖的性质及其提高植物抗逆性的机理、海藻糖与气孔免疫的关系等方面进行分析,发现外源性的海藻糖具有良好的非特异性保护作用,它能有效提高植物的抗逆性以及抗病虫害的能力。其次,海藻糖能通过调节气孔发育和气孔运动进一步增强农作物的抗旱性。本文认为海藻糖在生物节水农业方面有广阔的应用前景,是提高农作物水分利用效率的重要途径。     

Activation of Defense Pathways: Synergism between Reactive Oxygen Species and Salicylic Acid and Consideration of Field Applicability

Treatment of tobacco with a mixture containing reactive oxygen species (ROS) and salicylic acid (SA) provided greater protection of tobacco against infection by Pseudomonas syringae pv. tabaci than either treatment alone. Synergism in expression from the promoter of the defense gene PR-1a was also observed. Although the ROS hydrogen peroxide and peracetic acid were poor inducers alone, they enhanced the level of -glucuronidase (GUS) activity expressed from the PR-1a promoter when applied with SA to a transgenic plant bearing a PR-1a::GUS fusion. PR-1a expression was not correlated with increased cell death as determined by Evans blue staining. There was no effect on the timing at which expression was increased by the mixture compared with the separate treatments. The mixture of hydrogen peroxide and SA partially mimicked the effect of a commercial product Oxycom that has field efficacy in improving plant performance. Repetitive applications of Oxycom enhanced expression from the PR-1a promoter and the production of the PR-1 protein. Enhanced activity occurred systemically both from aerial applications to single leaves and from root drenches. Root application strongly promoted veinal expression for the PR-1a promoter compared with confluent production in leaves of sprayed seedlings. Application methods and timing may aid in the success of activators of systemic acquired resistance in field conditions.     

干旱胁迫下桑树活性氧信号传导及转录组分析

对干旱胁迫处理后的桑树幼苗(‘湖桑32’和‘德果1号’)进行ROS信号组织定位和叶的转录组测序,旨在从细胞和分子角度探究干旱胁迫后ROS信号在桑树组织细胞中的分布规律及与之相关的代谢通路和基因调控表达变化。结果表明:在正常情况下桑叶组织细胞中会产生少量的■,而干旱胁迫处理后桑叶组织细胞中ROS积累增多,推测ROS作为一种动态信号分子,会向毗邻细胞或远端细胞进行信号转导,进而与多种信号组分共同完成系统响应表达以调控桑树的生长发育及抗逆性。转录组数据表明:重度干旱胁迫处理后‘湖桑32’有5677个差异表达基因显著多于‘德果1号’(5575),且差异显著基因(DEGs)主要富集在半乳糖代谢、淀粉和蔗糖代谢、果糖和甘露糖代谢、碳代谢等通路中,推测‘湖桑32’的抗旱性与渗透调节物质的合成有关。同时,挑选11个基因进行qRT-PCR验证,其中11个DEGs的表达趋势与对应的RNA-Seq数据一致。研究也发现调控MKK4/5和WRKY22表达的相关基因LOC21384958和LOC21396104,在弱抗旱桑‘德果1号’中分别上调表达0.72(P<0.05)和2.16(P<0.05),而...     

Fungal endophyte protects Atractylodes lancea from root rot caused by Fusarium oxysporum

Endophytic fungi, which stimulate a variety of defence reactions in host plants without causing visible disease symptoms, have been isolated from almost every plant. However, beneficial interactions between fungal endophytes and pathogens from the same habitat remain largely unknown. An inoculation of Atractylodes lancea plantlets with Gilmaniella sp. AL12 (AL12) prior to infection with Fusarium oxysporum prevented the necrotization of root tissues and plant growth retardation commonly associated with fusarium root rot. Quantification of F. oxysporum infections using real‐time PCR revealed a correlation between root rot symptoms and the relative amount of fungal DNA. Pretreatment with AL12 reduced the accumulation of reactive oxygen species stimulated by F. oxysporum. An in vitro analysis of their interactions under axenic culture conditions showed AL12 could inhibit F. oxysporum growth. Additionally, F. oxysporum infections were shown to decrease salicylic acid (SA) production compared with control plantlets. SA biosynthesis inhibitors, 2‐aminoindan‐2‐phosphonic acid and paclobutrazol, abolished the inhibition of F. oxysporum growth in A. lancea even after inoculation with AL12. The results indicated that the fungal endophyte protected A. lancea not only by direct antibiosis, but also by reversing the F. oxysporum‐mediated suppression of SA production.     

稻曲病菌侵染对水稻小穗发育的影响及H_2O_2的变化趋势

稻曲病是由稻绿核菌(Ustilaginoidea virens)侵染引起的水稻穗部病害,在全世界不同稻作区均有发生,并在近年呈加重趋势。本研究通过水稻穗期接种后的显微观察及H_2O_2检测,分析了稻曲病菌侵染引起的小穗结构变化及侵染过程中H_2O_2变化趋势。结果表明,稻曲病菌侵染会导致水稻花粉粒畸形、雌蕊发育受抑制、小穗无法正常扬花授粉,抑制谷粒的正常形成,造成稻曲球及白色秕粒的产生。受侵染小穗的H_2O_2含量显著高于对照,其中处于突破颖壳期的受侵染小穗H_2O_2含量是对照的7倍;形成白色秕粒的小穗H_2O_2含量是对照的11倍;二氨基联苯胺染色结果显示,形成稻曲球的小穗中,在受侵染小穗的花药基部、花药顶端、浆片等部位颜色变深,形成H_2O_2富集区;形成白色秕粒的小穗中,H_2O_2富集的特征更为明显,富集区域与病菌在小穗内的侵染途径密切相关。     

外源NO对渗透胁迫下黑麦草种子萌发及活性氧代谢的影响

以黑麦草为试材,研究了一氧化氮(NO)供体硝普钠(SNP)对聚乙二醇6000渗透胁迫下种子萌发、幼苗叶片活性氧代谢和渗透溶质积累的影响,探讨外源NO对渗透胁迫下牧草生理响应的调节作用.结果表明:100μmol/L SNP显著提高了渗透胁迫下黑麦草种子的发芽率、发芽指数和活力指数,缓解了植株鲜重和干重的下降幅度,提高了幼苗叶片SOD、POD、APX、质膜H+-ATPase活性及谷胱甘肽、可溶性糖、游离氨基酸、脯氨酸、K+、Na+含量和植株含水量,降低了O2-.产生速率及H2O2、丙二醛和可溶性蛋白含量.表明外源NO能够促进渗透胁迫下黑麦草种子的萌发,对渗透胁迫引起的黑麦草幼苗膜脂过氧化具有缓解作用.     

增强UV-B辐射对立枯丝核菌抗氧化酶及细胞壁降解酶活性影响研究

作为太阳光谱的一部分,到达地球表面的UV-B辐射有逐渐增加的趋势,影响地球生态系统.为揭示增强UV-B辐射对立枯丝核菌的影响,本文采用UV-B灯辐照处理病菌菌丝,并对菌丝生长、菌核形成,活性氧稳态和细胞壁降解酶进行分析.结果表明,增强UV-B辐射可导致供试菌株菌丝生长抑制、刺激菌核提早形成.处理菌株O2和H2O2的含量...     

苄嘧磺隆对谷子叶绿素荧光特性和活性氧清除系统的影响

为从光系统Ⅱ(photosystem Ⅱ,PSⅡ)活性和活性氧清除代谢的角度阐明苄嘧磺隆对谷子的安全性以及谷子对该除草剂的生理响应,通过盆栽试验测定不同剂量苄嘧磺隆处理7 d和30 d后谷子幼苗倒2叶的叶绿素荧光参数、抗氧化酶活性和抗氧化物质含量。结果表明,剂量≤300 g/hm~2的苄嘧磺隆对谷子叶片内最大光化学量子产量(the maximum photochemical efficiency,MPE)、表观光合电子传递速率(photosynthetic electron transport rate,ETR)、光化学淬灭系数(photochemical quenching,PQ)和非光化学淬灭系数(non-photochemical quenching,NPQ)的影响均不显著。苄嘧磺隆推荐剂量300 g/hm~2施药7 d后,晋谷21号叶片内过氧化物酶(peroxidase,POD)活性、总抗坏血酸、还原型抗坏血酸(ascorbate acid,AsA)和还原型谷胱甘肽(reduced glutathione,GSH)含量分别较对照显著增加18.60%、22.85%、74.80%和...