植物诱导性直接防御

众所周知,植物对植食性昆虫危害的反应表现在3个方面：直接防御,间接防御,和耐害性。直接防御是指植物自身所具有的能影响寄主植物感虫性的所有特性。植物对昆虫危害的直接防御包括：限制食物供给,降低营养价值,减少偏嗜程度,破坏组织结构和抑制害虫代谢途径。目前已知的防御化合物主要包括植物次生代谢物质、昆虫消化酶（蛋白）抑制剂、蛋白酶、凝集素、氨基酸脱氨酶和氧化酶。植物在防御某种昆虫为害时多个因素往往具有累加效应或协同作用,并且对一种昆虫起主导作用的因素在防御另一种昆虫时可能仅仅起次要作用甚至根本不起作用。因此,对寄主植物基因表达、蛋白水平和活性以及代谢物含量在不同时空条件下进行广泛的定量和定性的高通量分析,不仅可以促进对植物直接防御机制的全面理解,而且有助于在农业生产中加快对作物抗性的特定靶标的鉴定。     

Mechanisms of plant defense against insect herbivores

Plants respond to herbivory through various morphological, biochemicals, and molecular mechanisms to counter/offset the effects of herbivore attack. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by induced responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be engineered genetically, so that the defensive compounds are constitutively produced in plants against are challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.     

Associational effects and the maintenance of polymorphism in plant defense against herbivores: review and evidence

Many plant species have evolved defense traits against herbivores. Associational effects (AEs) refer to a kind of apparent interaction where the herbivory risk to a focal plant species depends on the composition of other plant species in a neighborhood. Despite ample evidence for AEs between different plant species, this point of view has rarely been applied to polymorphism in defense traits within a plant species. The purpose of this review is to highlight an overlooked role of conspecific AEs in maintaining polymorphism in antiherbivore defense. First, I present a general review of AE between plant species and its role in the coexistence of plant species. This viewpoint of AE can be applied to genetic polymorphism within a plant species, as it causes frequency‐ and density‐dependent herbivory between multiple plant types. Second, I introduce a case study of conspecific AEs in the trichome‐producing (hairy) and glabrous plants of Arabidopsis halleri subsp. gemmifera. Laboratory and semi‐field experiments illustrated that AEs against the brassica leaf beetle Phaedon brassicae mediate a minority advantage in defense and fitness between hairy and glabrous plants. Combined with a statistical modeling approach, field observation revealed that conspecific AEs can maintain the trichome dimorphism via negative frequency‐dependent selection in a plant population. Finally, I discuss spatial and temporal scales at which AEs contribute to shaping genetic variation in antiherbivore defense in a plant metapopulation. Based on the review and evidence, I suggest that AEs play a key role in the maintenance of genetic variation within a plant species.     

Molecular mechanisms of insect adaptation to plant defense: Lessons learned from a Bruchid beetle

Plants can accumulate, constitutively and/or after induction, a wide variety of defense compounds in their tissues that confer resistance to herbivorous insects. The naturally occurring plant resistance gene pool can serve as an arsenal in pest management via transgenic approaches. As insect‐plant interaction research rapidly advances, it has gradually become clear that the effects of plant defense compounds are determined not only by their toxicity toward target sites, but also by how insects respond to the challenge. Insect digestive tracts are not passive targets of plant defense, but often can adapt to dietary challenge and successfully deal with various plant toxins and anti‐metabolites. This adaptive response has posed an obstacle to biotechnology‐based pest control approaches, which underscores the importance of understanding insect adaptive mechanisms. Molecular studies on the impact of protease inhibitors on insect digestion have contributed significantly to our understanding of insect adaptation to plant defense. This review will focus on exposing how the insect responds to protease inhibitors by both qualitative and quantitative remodeling of their digestive proteases using the cowpea bruchid–soybean cysteine protease inhibitor N system.     

Interactions between plants and herbivores: A review of plant defense

Ecologists have long ignored or underestimated the importance of plant–herbivore interactions owing to the diversities of herbivores, plant defensive strategies and ecological systems. In this review, we briefly discussed the categories of herbivores. Then we reviewed the major types of plant defenses against herbivores. Selective forces of herbivore pressures have led to the evolution of various defensive mechanisms in plants, which can be classified into (i) resistance traits that reduce the amount of damage received, including physical, chemical, and biotic traits; (ii) tolerance mechanisms that decrease the impact of herbivore damage, and (iii) escape strategies that reduce the probability of plants to be found by herbivores. These strategies have been studied at different levels from molecular genetics and genomics, to chemistry and physiology, to community and ecosystem ecology. We summarized the development of the methodology for studying plant defenses against herbivores. Particularly, 24 of those hypotheses and models, which are influential in the international community concerning the relationship between plants and herbivores, including the defensive mimicry hypothesis, the compensatory continuum hypothesis, the slow-growth-high-mortality hypothesis, etc, were introduced and grouped into four categories according to plant defense strategies in the present review. Finally, we also reviewed the research progress of plant–herbivore interactions in China, and discussed the perspectives of studies on plant–herbivore interactions.     

Non-protein amino acids in plant defense against insect herbivores: representative cases and opportunities for further functional analysis

Chemical defense against herbivores is of utmost importance for plants. Primary and secondary metabolites, including non-protein amino acids, have been implicated in plant defense against insect pests. High levels of non-protein amino acids have been identified in certain plant families, including legumes and grasses, where they have been associated with resistance to insect herbivory. Non-protein amino acids can have direct toxic effects via several mechanisms, including misincorporation into proteins, obstruction of primary metabolism, and mimicking and interfering with insect neurological processes. Additionally, certain non-protein amino acids allow nitrogen to be stored in a form that is metabolically inaccessible to herbivores and, in some cases, may act as signals for further plant defense responses. Specialized insect herbivores often possess specific mechanisms to avoid or detoxify non-protein amino acids from their host plants. Although hundreds of non-protein amino acids have been found in nature, biosynthetic pathways and defensive functions have been elucidated in only a few cases. Next-generation sequencing technologies and the development of additional plant and insect model species will facilitate further research on the production of non-protein amino acids, a widespread but relatively uninvestigated plant defense mechanism.     

Iron withholding: A defense against viral infections

A variety of laboratory and clinical investigations during the past 15 years have observed that one of the dangers of excessive iron is its ability to favor animal viral infections. The metal is essential for host cell synthesis of virions and can also impair defense cell function and increase oxidative stress. In both animal models and humans, viral infections cause upregulation of the iron withholding defense system. Factors that suppress the system enhance viral progression; factors that strengthen the system augment host defense. Procedures designed to reinforce the system are being developed and tested; some of these may become useful adjuncts in prevention and management of viral diseases.     

The influence of plant carbon dioxide and nutrient supply on susceptibility to insect herbivores

The carbon/nutrient ratio of plants has been hypothesized to be a significant regulator of plant susceptibility of leaf-eating insects. As rising atmospheric carbon dioxide stimulates photosynthesis, host plant carbon supply is increased and the accompanying higher levels of carbohydrates, especially starch, apparently dilute the protein content of the leaf. When host plant nitrogen supply is limited, plant responses include increased carbohydrate accumulation, reduced leaf protein content, but also increased carbon-based defensive chemicals. No change, however, has been observed in the concentration of leaf defensive allelochemicals with elevated carbon dioxide during host plant growth. Insect responses to carbon-fertilized leaves include increased consumption with little change in growth, or alternatively, little change in consumption with decreased growth, as well as enhanced leaf digestibility, reduced nitrogen use efficiency, and reduced fecundity. The effects of plant carbon and nutrient supply on herbivores appear to result, at least in part, from independent processes affecting secondary metabolism.     

植物细胞培养技术提高次生代谢物产量的方法(综述)

介绍植物细胞培养技术提高次生代谢物产量的方法。     

Specialist and generalist herbivores exert opposing selection on a chemical defense

* Plant defense traits often show high levels of genetic variation, despite clear impacts on plant fitness. This variation may be partly maintained by trade-offs in the defense against multiple herbivore species, for example between generalists and coevolved specialists. Despite a long-standing discussion in the literature on the subject, no study to date has specifically manipulated specialist and generalist herbivores independently of one another to determine whether the two guilds exert opposing selection pressures on specific defensive traits. * In two separate experiments, the dominant specialist and generalist herbivores of Brassica nigra were independently manipulated to test whether the composition of the herbivore community altered the direction of selection on a major defensive trait of the plant, sinigrin concentration. * It was found that generalist damage was negatively correlated but specialist loads were positively correlated with increasing sinigrin concentrations; and sinigrin concentration was favored when specialists were removed, disfavored (past an intermediate point) when generalists were removed and selectively neutral when plants faced both generalists and specialists.     

植物对植食性哺乳动物的化学防卫

综述植物次生合物防卫植食性哺乳动物食的研究进展,植物组织的次生化合物主要为酚类、萜类及含N类化合物,植物对动物觅食的化学防卫对策以次生化合物的各类而有差异,次生化合物通过对动物的食物摄入、消化、代谢,以及敏殖活动的效应,以抵御动物的觅食。将植物化学防卫与动物适应对策相结合,探讨动物－植物协同进化模式,是该研究领域的主要发展趋势。     

Heterologous chitinase gene expression to improve plant defense against phytopathogenic fungi

Agricultural crops worldwide suffer from a vast array of fungal diseases which cause severe yield losses. Upon interaction with a pathogen, plants initiate a complex network of defense mechanisms, among which is a dramatic increase in chitinase activity. Chitinases are capable of hydrolyzing chitin-containing fungal cell walls and are therefore thought to play a major role in the plant’s response. One of the strategies to increase plant tolerance to fungal pathogens is the constitutive overexpression of proteins involved in plant-defense mechanisms. The level of protection observed in transgenic plants harboring heterologous chitinase genes varies, depending on the particular combination of enzyme, plant and pathogen tested. Nevertheless, most of these transgenic plants exhibit increased tolerance to fungal diseases relative to their non-transgenic counterparts. The combined expression of chitinases with other plant-defense proteins such as glucanases and ribosome-inactivating proteins further enhances the plant’s resistance to fungal attack. Received 29 January 1997/ Accepted in revised form 01 July 1997     

植物和刺吸式口器昆虫的诱导防御与反防御研究进展

刺吸式口器昆虫在长期的进化过程中形成特殊的口针结构,用于专门吸食植物韧皮部筛管细胞的汁液成分.以蚜虫为例,它们在取食过程中分泌的胶状唾液和水状唾液将有效的降低植物防御反应,其中水状唾液包含的大量酶类不仅可以帮助蚜虫穿刺植物韧皮部,刺探到筛管细胞,同时也是植物感受蚜虫为害的激发因子,诱导出植物防御反应和相关抗性基因的表达...     

Herbivore induced plant volatiles: Their role in plant defense for pest management

Plants respond to herbivory through different defensive mechanisms. The induction of volatile emission is one of the important and immediate response of plants to herbivory. Herbivore-induced plant volatiles (HIPVs) are involved in plant communication with natural enemies of the insect herbivores, neighboring plants, and different parts of the damaged plant. Release of a wide variety of HIPVs in response to herbivore damage and their role in plant-plant, plant-carnivore and intraplant communications represents a new facet of the complex interactions among different trophic levels. HIPVs are released from leaves, flowers, and fruits into the atmosphere or into the soil from roots in response to herbivore attack. Moreover, HIPVs act as feeding and/or oviposition deterrents to insect pests. HIPVs also mediate the interactions between the plants and the microorganisms. This review presents an overview of HIPVs emitted by plants, their role in plant defense against herbivores and their implications for pest management.     

Elicitors and priming agents initiate plant defense responses

Biotic elicitors produced by plant pathogens or herbivore pests rapidly activate a range of plant chemical defenses when translocated to plant tissue. The fatty acid conjugate volicitin has proven to be a robust elicitor model for studying herbivore-induced plant defense responses. Here we review the role of insect-derived volicitin (N-[17-hydroxylinolenoyl]-L-glutamine) as an authentic elicitor of defense responses, specifically as an activator of signal volatiles that attract natural enemies of herbivore pests. Comparisons are drawn between volicitin as an elicitor of plant defenses and two other classes of signaling molecules, C₆ green-leaf volatiles and C₄ bacterial volatiles that appear to prime plant defenses thereby enhancing the capacity to mobilize cellular defense responses when a plant is faced with herbivore or pathogen attack.     

Effects of spatial distribution on plant associational defense against herbivory

Several studies have shown that consumption of a focal plant by herbivores depends not only on its own defense traits but also on the characteristics of the neighboring plants. A number of studies have reported on plant associational defense in relation to neighboring plant palatability but the effect of the spatial distribution of the focal plant within patches of different neighboring plants has received less attention. We conducted a manipulative experiment to determine whether and how spatial distribution of focal plants affects the associational defense between plant species. In our experimental setup sheep encountered two patches varying in spatial distribution of the focal plant within patches (dispersed or clumped) and patch quality, good patch and bad patch, where the focal plant, Lathyrus quinquenervius, was neighbored to high- (Chloris virgata) or low-palatable (Kalimeris integrifolia) species, respectively. Results showed that, when focal plants were dispersed within both patches, the risk of attack was significantly lower for focal plants in the patches with low- than high-palatable neighbors, indicating associational defense. Alternatively, when focal plants were clumped within both patches, they were consumed in bad-patch as much as in good-patch plots, which indicates the absence of associational defense. However, if the focal plants have different spatial distributions in the two patches (dispersed in good-patch and clumped in bad-patch or vice versa), sheep foraging success for focal plants was greatly reduced in dispersed spatial pattern irrespective of the palatability of neighboring plants. Therefore, we concluded that spatial distribution is as important as traits of neighboring plants in predicting vulnerability of the focal plant to grazing by generalist herbivores. The outcome of plant associational defense for different types of neighborhood strongly depends on the magnitude of herbivore foraging selectivity between and within patches, which further depended on the contrasts between plant species or between patches.     

Optimal defense strategy against herbivory in plants: Conditions selecting for induced defense, constitutive defense, and no-defense

To examine the conditions selecting for induced defense, constitutive defense, and no-defense, we developed a model of plant defense strategy against herbivory. In the model, a plant consists of two modules between which signal inducing defense compounds can be translocated. We assume three strategies: plants produce defense compounds responding to herbivory (induced defense), they have the compounds beforehand (constitutive defense), and they never produce the compounds (no-defense). We found that no-defense is optimal if the amount of biomass lost due to herbivory is small because of the growth cost of having defense compounds. The constitutive defense is optimal if the amount of biomass lost is not so small and the probability of herbivory is high. If the biomass loss is not so small but the probability of herbivory is low, the induced defense or no-defense is optimal. When the induced defense is optimal, the probability of herbivory necessarily increases in plants once herbivory has occurred. If the probability stays the same, no-defense is optimal. Thus, the behavior of herbivores, i.e., whether they remain around a plant and attack it repeatedly, affects the evolution of the induced defense.