芥子油苷-黑芥子酶系统及其在植物防御和生长发育中的作用

本文对十字花科（Cruciferae）植物体内的芥子油苷-黑芥子酶系统在生物、非生物胁迫和生长发育中的研究进展作了介绍。     

植物芥子油苷代谢与硫营养

文章简要介绍芥子油苷积累、代谢及其防御作用受环境供硫水平调控的研究进展。     

植物芥子油苷代谢及其转移

芥子油苷是一类含氮、含硫的植物次生代谢产物,主要分布于十字花科植物。芥子油苷及其降解产物具有多种生化活性,在植物防御方面也有重要作用。简要介绍芥子油苷的分布、合成、降解和在植物体内的转移。     

芥子油苷在十字花科植物与昆虫相互关系中的作用

芥子油苷(glucosinolate, GS)是十字花科植物重要的次生代谢物,对调节十字花科植物与昆虫间的关系起着重要作用.由于GS及其代谢产物具有一定的毒性,因此它是十字花科植物抵御广食性植食昆虫攻击的有力手段.而寡食十字花科植物的昆虫由于具备多种GS应对机制,因此可通过GS这一十字花科植物特有的次生代谢物进行寄主选择.被植食性昆虫摄入的GS不仅可以影响天敌的生长发育,而且还对天敌有一定的驱避作用.而虫害后十字花科植物释放的GS代谢产物又可作为天敌的寄主选择信息.本文结合该领域的一些最新研究成果,从GS对植食性昆虫的毒性、寡食性害虫的寄主选择、植食性昆虫对GS的适应机制、虫害对GS-黒芥子酶系统的诱导,以及GS对天敌的影响等方面对GS如何影响植物与昆虫间的相互关系进行了综述,并就今后该领域的研究方向、研究方法提出建议.     

环境对植物芥子油苷代谢的影响

芥子油苷是一类含氮、含硫的植物次生代谢物质,主要分布于十字花科植物.芥子油苷及其降解产物具有多种生化活性,近年来人们更多地关注芥子油苷代谢与植物生存环境的相互作用以及与其它物质代谢途径的相互联系.介绍了温度、光、水分、硫营养、CO2浓度以及重金属污染等非生物环境对芥子油苷代谢影响的研究概况.     

植物中的吲哚族芥子油苷与生长素代谢途径的关系

文章介绍了植物中的吲哚族芥子油苷代谢与生长素合成途径相互关系的研究进展。     

环境胁迫下植物的化感作用及其诱导机制

植物化感作用是生态学研究中一个十分活跃的领域,对植物为什么和在什么条件下释放化感物质这一重要问题有不同的认识。在对环境胁迫下植物化感作用的变化及环境胁迫因子对化感物质听诱导机制等方面进行了评述后,指出植物化感化质的产生和释放是植物在环境胁迫的选择压力下形成的,植物化感作用是植物在进化过程中产生的一种对环境的适应性机制。     

芥子油苷在甘蓝蚜寄主部位选择行为中的作用

利用刺吸电位技术（EPG）记录甘蓝蚜Brevicoryne brassicae在芥菜Sinapis alba 不同部位上的取食行为,同时用高压液相色谱（HPLC）分析芥菜相应部位的芥子油苷(glucosinolates)含量,据此分析芥子油苷在甘蓝蚜对寄主部位偏好行为中的作用。选择芥菜三个部位进行取食行为记录和化学分析,即新出完全叶(第7片)的叶片、叶柄,以及花茎。相对于其它两个部位,甘蓝蚜的口针在花茎上用较少的刺探次数和较短的时间到达韧皮部;一旦口针进入韧皮部持续吸食阶段,蚜虫在三个部位的取食行为没有太大的差异。只在花茎的表皮和皮层中测定到较高含量的白芥子苷（glucosinalbin）。因此,本实验的结果证明,白芥子苷是甘蓝蚜寄主部位选择的关键信号化学物质或取食促进剂。     

植物化感作用(Allelopathy)及其作用物的研究方法

综述了植物化感作用室内培养和田间试验的研究方法,重点评述了化咸物质的提取、分离、纯化、鉴定和检测方法,并提出了进一步研究需关注的问题。     

植物内生真菌化感作用的研究现状

植物内生真菌能产生酚类、萜类和生物碱类等多种类型的化感物质,它们在植物的生长发育、抗生物胁迫和非生物胁迫方面发挥重要作用。对植物内生真菌的化感作用及其所产生的化感物质进行了综述,并展望了其化感作用的应用前景。     

The role of glucosinolates and the jasmonic acid pathway in resistance of Arabidopsis thaliana against molluscan herbivores

Although slugs and snails play important roles in terrestrial ecosystems and cause considerable damage on a variety of crop plants, knowledge about the mechanisms of plant immunity to molluscs is limited. We found slugs to be natural herbivores of Arabidopsis thaliana and therefore investigated possible resistance mechanisms of this species against several molluscan herbivores. Treating wounded leaves with the mucus residue (‘slime trail’) of the Spanish slug Arion lusitanicus increased wound‐induced jasmonate levels, suggesting the presence of defence elicitors in the mucus. Plants deficient in jasmonate biosynthesis and signalling suffered more damage by molluscan herbivores in the laboratory and in the field, demonstrating that JA‐mediated defences protect A. thaliana against slugs and snails. Furthermore, experiments using A. thaliana mutants with altered levels of specific glucosinolate classes revealed the importance of aliphatic glucosinolates in defending leaves and reproductive structures against molluscs. The presence in mollusc faeces of known and novel metabolites arising from glutathione conjugation with glucosinolate hydrolysis products suggests that molluscan herbivores actively detoxify glucosinolates. Higher levels of aliphatic glucosinolates were found in plants during the night compared to the day, which correlated well with the nocturnal activity rhythms of slugs and snails. Our data highlight the function of well‐known antiherbivore defence pathways in resistance against slugs and snails and suggest an important role for the diurnal regulation of defence metabolites against nocturnal molluscan herbivores.     

Allelopathic potential of glucosinolates (mustard oil glycosides) and their degradation products against wheat

A number of glucosinolates and isothiocyanates were tested for their allelopathic potential against wheat. Most of the glucosinolates showed no activity against wheat, with the exception of glucobrassicin which was moderately active, as was sinapine thiocyanate. Isothiocyanates showed high activity against wheat germination and seedling growth. The most active compound, 2-phenethyl ITC completely inhibited wheat germination at 500 ppm. Allyl ITC showed high activity whereas other isothiocyanates tested were only moderately active. The data is discussed in relation to the possible use of some mustard species for effective weed control.     

植物次生代谢及其与环境的关系

人类对植物次生代谢产物（天然产物）的早期研究源于它们的应用价值,近些年来人们越来越认识到植物次生代谢产物广泛的生物学效应,开始重新评价这些化合物在植物生命活动以及生态系统中可能扮演的角色。植物的次生代谢是植物在长期进化中与环境（生物的和非生物的）相互作用的结果,次生代谢产物在植物提高自身保护和生存竞争能力、协调与环境关系上充当着重要的角色。介绍了植物次生代谢及其产物的特点,概述了植物次生代谢与温度、水分、光照、养分、CO2浓度、UV-B辐射、环境污染等非生物环境以及与化学防御、化感作用、菌根共生、微生物病害的关系。研究植物次生代谢与环境的关系,可以从更深的层次发掘植物与环境的内在联系,为全面、深入认识植物与环境的相互关系提供新的研究途径,同时也有利于人类更有效、合理地利用植物的次生代谢产物。     

Differential roles of glucosinolates and camalexin at different stages of Agrobacterium‐mediated transformation

Agrobacterium tumefaciens is the causal agent of crown gall disease in a wide range of plants via a unique interkingdom DNA transfer from bacterial cells into the plant genome. Agrobacterium tumefaciens is capable of transferring its T‐DNA into different plant parts at different developmental stages for transient and stable transformation. However, the plant genes and mechanisms involved in these transformation processes are not well understood. We used Arabidopsis thaliana Col‐0 seedlings to reveal the gene expression profiles at early time points during Agrobacterium infection. Common and differentially expressed genes were found in shoots and roots. A gene ontology analysis showed that the glucosinolate (GS) biosynthesis pathway was an enriched common response. Strikingly, several genes involved in indole glucosinolate (iGS) modification and the camalexin biosynthesis pathway were up‐regulated, whereas genes in aliphatic glucosinolate (aGS) biosynthesis were generally down‐regulated, on Agrobacterium infection. Thus, we evaluated the impacts of GSs and camalexin during different stages of Agrobacterium‐mediated transformation combining Arabidopsis mutant studies, metabolite profiling and exogenous applications of various GS hydrolysis products or camalexin. The results suggest that the iGS hydrolysis pathway plays an inhibitory role on transformation efficiency in Arabidopsis seedlings at the early infection stage. Later in the Agrobacterium infection process, the accumulation of camalexin is a key factor inhibiting tumour development on Arabidopsis inflorescence stalks. In conclusion, this study reveals the differential roles of GSs and camalexin at different stages of Agrobacterium‐mediated transformation and provides new insights into crown gall disease control and improvement of plant transformation.     

The involvement of hydrogen peroxide in plant responses to stresses

The role of reactive oxygen species, especially H₂O₂, in plant response to stresses has been the focus of much attention. Hydrogen peroxide has been postulated to play multiple functions in plant defence against pathogens. (1) H₂O₂ may possess direct microbicidal activity at the sites of pathogen invasion. (2) It is used for cell-wall reinforcing processes: lignification and oxidative cross-linking of hydroxyproline-rich proteins and other cell-wall polymers. (3) It was found to be necessary for phytoalexin synthesis. (4) H₂O₂ may trigger programmed plant cell death during the hypersensitive response that restricts the spread of infection. (5) H₂O₂ has been suggested to act as a signal in the induction of systemic acquired resistance and (6) it induces defence genes. Recently H₂O₂ has been proposed to be involved in the signal transduction pathways leading to acclimation and protection from abiotic stresses. The present review discusses new insights into the function of H₂O₂ in plant responses to biotic and abiotic stresses.     

Genome size evolution is associated with climate seasonality and glucosinolates,but not life history,soil nutrients or range size,across a clade of mustards

Background and AimsWe investigate patterns of evolution of genome size across a morphologically and ecologically diverse clade of Brassicaceae, in relation to ecological and life history traits. While numerous hypotheses have been put forward regarding autecological and environmental factors that could favour small vs. large genomes, a challenge in understanding genome size evolution in plants is that many hypothesized selective agents are intercorrelated.MethodsWe contribute genome size estimates for 47 species of Streptanthus Nutt. and close relatives, and take advantage of many data collections for this group to assemble data on climate, life history, soil affinity and composition, geographic range and plant secondary chemistry to identify simultaneous correlates of variation in genome size in an evolutionary framework. We assess models of evolution across clades and use phylogenetically informed analyses as well as model selection and information criteria approaches to identify variables that can best explain genome size variation in this clade.Key ResultsWe find differences in genome size and heterogeneity in its rate of evolution across subclades of Streptanthus and close relatives. We show that clade-wide genome size is positively associated with climate seasonality and glucosinolate compounds. Model selection and information criteria approaches identify a best model that includes temperature seasonality and fraction of aliphatic glucosinolates, suggesting a possible role for genome size in climatic adaptation or a role for biotic interactions in shaping the evolution of genome size. We find no evidence supporting hypotheses of life history, range size or soil nutrients as forces shaping genome size in this system.ConclusionsOur findings suggest climate seasonality and biotic interactions as potential forces shaping the evolution of genome size and highlight the importance of evaluating multiple factors in the context of phylogeny to understand the effect of possible selective agents on genome size.     

The microRNA miR393 re-directs secondary metabolite biosynthesis away from camalexin and towards glucosinolates

flg22 treatment increases levels of miR393, a microRNA that targets auxin receptors. Over-expression of miR393 renders plants more resistant to biotroph pathogens and more susceptible to necrotroph pathogens. In contrast, over-expression of AFB1, an auxin receptor whose mRNA is partially resistant to miR393 degradation, renders the plant more susceptible to biotroph pathogens. Here we investigate the mechanism by which auxin signalling and miR393 influence plant defence. We show that auxin signalling represses SA levels and signalling. We also show that miR393 represses auxin signalling, preventing it from antagonizing SA signalling. In addition, over-expression of miR393 increases glucosinolate levels and decreases the levels of camalexin. Further studies on pathogen interactions in auxin signalling mutants revealed that ARF1 and ARF9 negatively regulate glucosinolate accumulation, and that ARF9 positively regulates camalexin accumulation. We propose that the action of miR393 on auxin signalling triggers two complementary responses. First, it prevents suppression of SA levels by auxin. Second, it stabilizes ARF1 and ARF9 in inactive complexes. As a result, the plant is able to mount a full SA response and to re-direct metabolic flow toward the most effective anti-microbial compounds for biotroph resistance. We propose that miR393 levels can fine-tune plant defences and prioritize resources.     

The glutathione-deficient mutant pad2-1 accumulates lower amounts of glucosinolates and is more susceptible to the insect herbivore Spodoptera littoralis

Plants often respond to pathogen or insect attack by inducing the synthesis of toxic compounds such as phytoalexins and glucosinolates (GS). The Arabidopsis mutant pad2-1 has reduced levels of the phytoalexin camalexin and is known for its increased susceptibility to fungal and bacterial pathogens. We found that pad2-1 is also more susceptible to the generalist insect Spodoptera littoralis but not to the specialist Pieris brassicae . The PAD2 gene encodes a γ-glutamylcysteine synthetase that is involved in glutathione (GSH) synthesis, and consequently the pad2-1 mutant contains about 20% of the GSH found in wild-type plants. Lower GSH levels of pad2-1 were correlated with reduced accumulation of the two major indole and aliphatic GSs of Arabidopsis, indolyl-3-methyl-GS and 4-methylsulfinylbutyl-GS, in response to insect feeding. This effect was specific to GSH, was not complemented by treatment of pad2-1 with the strong reducing agent dithiothreitol, and was not observed with the ascorbate-deficient mutant vtc1-1 . In contrast to the jasmonate-insensitive mutant coi1-1 , expression of insect-regulated and GS biosynthesis genes was not affected in pad2-1 . Our data suggest a crucial role for GSH in GS biosynthesis and insect resistance.