Endophage-ectophage ratios and plant defense

Summary Endophagous folivores, which are concealed inside leaf tissue for much of their life cycle, or which live externally but feed internally, should be more successful on heavily defended plants than ectophagous species. This is because endophages are more facile at feeding selectively and can manipulate tissue development to avoid physical and chemical defenses and to enhance nutrition. As a result, endophage-ectophage ratios should increase on more heavily defended hosts. This pattern will likely be strengthened by negative asymmetrical interactions with ectophages and pathogens, which may displace endophages from lightly defended hosts. The hypothesis predicts that endophages should be particularly abundant in resource-poor habitats which seem to support a preponderance of heavily defended hosts. Although data do not yet exist for a rigorous test, several observed cases where endophage distributions seem biased toward heavily defended hosts are at least consistent with the hypothesis. Plant defense levels may have little influence on the total number of herbivores associated with a host, but I suggest that guild structure can be profoundly altered.     

防卫基因PAL,LOX和PBZ1在水稻白叶枯病成株抗性中的作用(英文)

为了探讨水稻白叶枯病成株抗性是否与防卫基因相关 ,通过RT PCR研究了几种防卫基因PAL、LOX、PBZ1、Cht 1和PR1a的表达 ,同时也分析了PAL和LOX的酶活性变化 .结果表明 ,苗期PAL受病原菌诱导上调表达 ,而成株期病原菌和伤害均可诱导PAL上调表达 ,且成株期诱导表达强于苗期 .LOX在苗期和成株期都可受病原菌诱导表达 ,但成株期表达强于苗期且更持久 .PBZ1在苗期和成株期均受病原菌和伤害诱导表达 ,但成株期表达较苗期早且更强 .PR1a和Cht1没检测到期望的扩增片段 .PAL和LOX的酶活性分析结果与基因表达分析结果一致 .因此 ,PAL、LOX和PBZ1在苗期和成株期的表达差异可能与水稻白叶枯病成株抗性相关 .     

湛江市红树林资源及其可持续利用

广东省湛江市现有红树林面积7242.0hm²,人工造林未成林25.6hm²,天然更新红树林509.4hm²,另有红树林宜林地9688.6hm²。红树林及其伴生植物主要有木榄(Bruguiera gymnorrhiza)、秋茄(Kandelia candel)、无瓣海桑(Sonneratia apetala)等15科24种。由于毁林养虾、养鱼等导致1980～2001年占用红树林地面积6363.6hm²。从总体上看,湛江红树林种类多,群落类型丰富;红树林面积大幅减少,影响区域社会经济发展;除乡土种外,无瓣海桑是一种较成功的外来引树种;宜林地多,但人工造林保存率不高;破坏红树林,挖塘养殖依然较普遍。为了实现湛江红树林的可持续发展,需要加强下列工作:建立自然保护区加强对现有红树林湿地的保护;开展红树林湿地生态系统资源监测和鸟类环志;科学规划后加快红树林的恢复和重建;积极推动退塘还林并合理利用红树林;依法保护管理好红树林;多途径筹集保护资金;加强红树林、湿地的保护和宣传。     

Chemical defensive substances of soft corals and gorgonians

Despite lack of efficient physical protection in the highly competitive and hostile environment, the marine invertebrates including soft corals and gorgonians can survive, mainly relying on their chemical defensive system by a series of secondary metabolites accumulating in their bodies or releasing to their surroundings. The chemical defensive functions of these secondary metabolites were found to serve as antipredatory, antimicrobial, allelopathy and antifouling agents. Study on chemical defensive substances from corals and gorgonians is one of the most important topics in marine chemical ecology. The research results could help us to understand the chemical ecological relationships between corals and their surrounding organisms. The research strategy and methodology played an enlightening role in the discovery of bioactive natural products and the generation of new drug lead compounds from marine sources. The chemical defensive substances from soft corals and gorgonians were reviewed. This review focused on the structures of these secondary metabolites as well as their functions including antipredatory, allelopathy and antifouling activities.     

Members only: induced systemic resistance to herbivory in a clonal plant network

The stoloniferous herb Trifolium repens was used to study the expression of induced systemic resistance (ISR) to the generalist caterpillar Spodoptera exigua in interconnected ramets of clonal fragments. The ISR was assessed as caterpillar preference in dual choice tests between control and systemically induced plants. The ISR was detected in young ramets, after inducing older sibling ramets on the same stolon by a controlled herbivore attack. However, older ramets did not receive a defense induction signal from younger ramets unless the predominant phloem flow was reversed by means of basal shading. This provides evidence for the notion that in T. repens the clone-internal expression of ISR is coupled to phloem transport and follows source–sink gradients. The inducibility of the genotypes was not linked to their constitutive ability to produce cyanide, implying the absence of a trade-off between these two defense traits. To our knowledge, this is the first study that explores ISR to herbivory in the context of physiological integration in potentially extensive clonal plant networks.     

Effects of resource level and habitat type on behavioral and morphological plasticity in Eurasian perch

Spatial and temporal heterogeneity in the environment is a common feature affecting many natural populations. For example, both the resource levels and optimal habitat choices of individuals likely change over time. One way for organisms to cope with environmental variation is to display adaptive plasticity in traits such as behavior and morphology. Since trait plasticity is hypothesized to be a prerequisite for character divergence, studies of mechanisms behind such plasticity are warranted. In this study, we looked at the interaction of two potentially important environmental variables on behavioral and morphological plasticity in Eurasian perch (Perca fluviatilis L.). More specifically, the plastic responses in activity and morphology of perch exposed to different resource levels and simulated habitat types were studied in an aquarium experiment. The resource level experienced had a large influence on plasticity in both activity and morphology. Behavioral adaptations have been thought to mediate morphological transitions, and we suggest that the morphological response to the resource level was mediated by differences in activity and growth rates. The habitat type also affected morphological plasticity but to a lesser extent, and there was no effect on activity from habitat type. Based on these results, we suggest that it is essential to include several environmental factors acting in concert when studying mechanisms behind trait plasticity. We also propose that variation in resource levels might play a key role in fostering trait plasticity in at least fish populations, while other environmental variables such as divergent habitat complexities and prey types might be less influential. Dynamics in resource levels and optimal habitat choices might thus be important factors influencing character divergence in natural populations.     

Structural and phylogenetic analyses of the GP42 transglutaminase from Phytophthora sojae reveal an evolutionary relationship between oomycetes and marine Vibrio bacteria

Transglutaminases (TGases) are ubiquitous enzymes that catalyze selective cross-linking between protein-bound glutamine and lysine residues; the resulting isopeptide bond confers high resistance to proteolysis. Phytophthora sojae, a pathogen of soybean, secretes a Ca²⁺-dependent TGase (GP42) that is activating defense responses in both host and non-host plants. A GP42 fragment of 13 amino acids, termed Pep-13, was shown to be absolutely indispensable for both TGase and elicitor activity. GP42 does not share significant primary sequence similarity with known TGases from mammals or bacteria. This suggests that GP42 has evolved novel structural and catalytic features to support enzymatic activity. We have solved the crystal structure of the catalytically inactive point mutant GP42 (C290S) at 2.95 Å resolution and identified residues involved in catalysis by mutational analysis. The protein comprises three domains that assemble into an elongated structure. Although GP42 has no structural homolog, its core region displays significant similarity to the catalytic core of the Mac-1 cysteine protease from Group A Streptococcus, a member of the papain-like superfamily of cysteine proteases. Proteins that are taxonomically related to GP42 are only present in plant pathogenic oomycetes belonging to the order of the Peronosporales (e.g. Phytophthora, Hyaloperonospora, and Pythium spp.) and in marine Vibrio bacteria. This suggests that a lateral gene transfer event may have occurred between bacteria and oomycetes. Our results offer a basis to design and use highly specific inhibitors of the GP42-like TGase family that may impair the growth of important oomycete and bacterial pathogens.     

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.     

Genetic dominance and worker interactions affect honeybee colony defense

Colonies of honeybees (Apis mellifera L.) were established thatvaried in the proportions of their workers that were of Europeanand hybrid (Africanized x European) descent. Colony defensiveresponses increased with higher proportions of hybrid workers.Colonies consisting exclusively of hybrid workers did not differin their response from "pure" Africanized colonies, suggestingthat the strong defensive behavior of Africanized workers isgenetically dominant. European workers became more defensivein colonies that also contained hybrid workers, whereas hybridworkers became less defensive in the same mixed colonies. Inmixed colonies hybrid workers were individually more likelythan Europeans to sting a leather target but not more likelyto guard the entrance.