Guns and butter: a no cost defense against predation for Chrysomela confluens

Summary Chrysomela confluens produces a salicylaldehyde-based defensive secretion which is very effective against generalist predators and apparently produced at no cost. If no cost defenses are common, then one of the basic assumptions in the plant-herbivore literature, i.e. tradeoffs among defense, reproduction, and growth, must be reconsidered. We examined the effectiveness of this defense by exposing defended larvae and larvae whose secretion had been removed to a generalist predator. Larvae which had their secretions intact were attacked by only 7% of the ants which encountered them, and none of these larvae suffered serious damage. In contrast, those which had been milked of their secretions immediately prior to exposure were attacked in 48% of such encounters, and two-thirds of the larvae were killed. Larvae which had been milked 24 or 72 h before exposure, then allowed to regenerate their defenses, were attacked at rates indistinguishable from larvae that had not been milked. Thus regenerated defenses are just as effective as original defenses. We also tested the hypothesis that the cost of defense production and maintainence would be reflected in reductions in developmental rates and final adult mass and increases in leaf consumption rate. We found that larvae which were milked daily of their secretions manifested no measurable cost of recharging reservoirs. Milked larvae grew and fed at the same rates as their control sibs, and became adults of equal or slightly larger size. The liberation of glucose from salicin, a precursor present in leaves of salicaceous hosts, during the production of salicylaldehyde apparently provides enough of an energetic benefit to offset the cost of maintaining an effective defense. Consistent with this hypothesis, we did not find that milked larvae compensated for increased nutritional or salicin demands by increasing their feeding rates. Although this patterns is familiar to chemical ecologists it is generally unappreciated in the plant-herbivore literature. It is likely that many arthropod herbivore defensive systems come at little or no cost, given the intimacy of association between herbivores and their food plants. Sequestration of host plant defensive chemicals which eliminates the cost of synthesis is common in arthropods. The de novo synthesis of chemical defenses may be less costly than expected if it is integrated into other parts of an insects metabolism. Calculations based on the bond energies or molecular constitution of the compounds will not yield a complete perception of cost. Tests over the life of the herbivore, coupled with an understanding of the herbivore's metabolism, are necessary.     

植物对重金属耐性的分子生态机理

植物适应重金属元素胁迫的机制包括阻止和控制重金属的吸收、体内螯合解毒、体内区室化分隔以及代谢平衡等。近年来,随着分子生物学技术在生态学研究中的深入应用,控制这些过程的分子生态机理逐渐被揭示出来。菌根、根系分泌物以及细胞膜是控制重金属进入植物根系细胞的主要生理单元。外生菌根能显著提高寄主植物的重金属耐性,根系分泌物通过改变根际pH、改变金属物质的氧化还原状态和形成络合物等机理减少植物对重金属的吸收。目前,控制菌根和根系分泌物重金属抗性的分子生态机理还不清楚。但细胞膜跨膜转运器已得到深入研究,相关金属离子转运器被鉴定和分离,一些控制基因如铁锌控制运转相关蛋白(ZIP)类、自然抵抗相关巨噬细胞蛋白(Nramp)类、P_1B-type ATPase类基因已被发现和克隆。金属硫蛋白(MTs)、植物螯合素(PCs)、有机酸及氨基酸等是植物体内主要的螯合物质,它们通过螯合作用固定金属离子,降低其生物毒性或改变其移动性。与MTs合成相关的MT-like基因已经被克隆,PCs合成必需的植物螯合素合酶(PCS), 即γ-Glu-Cys二肽转肽酶(γ-ECS) 的编码基因已经被克隆,控制麦根酸合成的氨基酸尼克烟酰胺(NA)在重金属耐性中的作用和分子机理也被揭示出来。ATP 结合转运器(ABC)和阳离子扩散促进器(CDF) 是植物体内两种主要膜转运器,通过它们和其它跨膜方式,重金属被分隔贮藏于液泡内。控制这些蛋白转运器合成的基因也已经被克隆,在植物中的表达证实其与重金属的体内运输和平衡有关。热休克蛋白(HSP)等蛋白类物质的产生是一种重要的体内平衡机制,其分子机理有待进一步研究。重金属耐性植物在这些环节产生了相关响应基因或功能蛋白质,分子克隆和转基因技术又使它们在污染治理上得到了初步的应用。     

Uptake and metabolism of pyrrolizidine alkaloids in<Emphasis Type="Italic"> Longitarsus</Emphasis> flea beetles (Coleoptera: Chrysomelidae) adapted and non-adapted to alkaloid-containing host plants

Several Longitarsus flea beetle species sequester pyrrolizidine alkaloids acquired from their Asteraceae and Boraginaceae host plants. We carried out feeding and injection experiments using radioactively labeled pyrrolizidine alkaloids to investigate the physiological mechanisms of uptake, metabolism and storage of alkaloids in adult beetles. We examined six Longitarsus species belonging to different phylogenetic clades in a comparative approach. All species that accepted pyrrolizidine alkaloids in a preceding food choice study showed the ability both to store pyrrolizidine alkaloid N-oxides and to metabolize tertiary pyrrolizidine alkaloids into their N-oxides. Regardless of whether the beetles' natural host plants contain pyrrolizidine alkaloids or not, these species were found to possess an oxidizing enzyme. This oxygenase appears to be specific to pyrrolizidine alkaloids: [³H]Atropine and [¹⁴C]nicotine, two alkaloids not related to pyrrolizidine alkaloids, were neither stored nor N-oxidized by any of the tested species. One species, L. australis, that strictly avoids pyrrolizidine alkaloids behaviorally, exhibited a lack of adaptations to pyrrolizidine alkaloids on a physiological level as well. After injection of tertiary [¹⁴C]senecionine, beetles of this species neither N-oxidized nor stored the compounds, in contrast to L. jacobaeae, an adapted species that underwent the same treatment. L. jacobaeae demonstrated the same efficiency in N-oxidation and storage when fed or injected with tertiary [¹⁴C]senecionine.Communicated by G. Heldmaier     

Merkel cell polyomavirus large T antigen disrupts lysosome clustering by translocating human Vam6p from the cytoplasm to the nucleus

Merkel cell polyomavirus (MCV) has been recently described as the cause for most human Merkel cell carcinomas. MCV is similar to simian virus 40 (SV40) and encodes a nuclear large T (LT) oncoprotein that is usually mutated to eliminate viral replication among tumor-derived MCV. We identified the hVam6p cytoplasmic protein involved in lysosomal processing as a novel interactor with MCV LT but not SV40 LT. hVam6p binds through its clathrin heavy chain homology domain to a unique region of MCV LT adjacent to the retinoblastoma binding site. MCV LT translocates hVam6p to the nucleus, sequestering it from involvement in lysosomal trafficking. A naturally occurring, tumor-derived mutant LT (MCV350) lacking a nuclear localization signal binds hVam6p but fails to inhibit hVam6p-induced lysosomal clustering. MCV has evolved a novel mechanism to target hVam6p that may contribute to viral uncoating or egress through lysosomal processing during virus replication.     

Packed-Bed Bioreactors Under the Influence of Chemical Modulators

This report considers the behaviour of packed-bed immobilized enzyme reactors operating in the presence of substrate and/or product sequestrators. In some cases, enzyme inhibition by the reaction product and presence of chemical modulators are also considered. For each case, an appropriate analytical model is developed. Using numerical simulations, it is shown that reactor performance is impaired by substrate sequestration. This effect can be partially reversed when competitive sequestration by product or modulator is operational.

In addition, a comparison is made between some of the predicted characteristics of the reactor and experimental data. It reveals the capabilities and limitations of the models employed.     

Interactions between glucosinolate- and myrosinase-containing plants and the sawfly Athalia rosae

Several insects have specialised on using Brassicaceae as host plants. Therefore, they evolved metabolic pathways to cope with the defensive glucosinolate–myrosinase system of their diet. Larvae of the turnip sawfly, Athalia rosae L. (Hymenoptera: Tenthredinidae), incorporate various glucosinolates from their hosts into their haemolymph. The ability to sequester these metabolites makes A. rosae a useful model system to study mechanisms of glucosinolate metabolism in this species compared to other specialists, and to study effects of sawfly feeding on levels of glucosinolates and their hydrolysing enzymes in plants. The levels of plant metabolites might in turn directly affect the performance of the insect. On the one hand, costs for glucosinolate uptake and avoidance of myrosinase activity were postulated. On the other hand, sequestration of glucosinolates can be part of the insect’s defence against several predators. Here, the findings on glucosinolate metabolic pathways are compared between different herbivores and the sawfly. The impact of different glucosinolate levels and myrosinase activities on the performance of A. rosae is discussed. Furthermore, effects of feeding by A. rosae larvae on the chemical composition and enzyme activities of various Brassicaceae species are summarised. Induction patterns vary not only between different plant species and cultivars but also due to the inducing agent. Finally, the plant–herbivore interactions are discussed with regard to the sawflies’ defence abilities against different carnivore guilds.     

Inhibition of autophagosome formation by the benzoporphyrin derivative verteporfin

Autophagy enables cells to degrade and recycle cytoplasmic materials both as a housekeeping mechanism and in response to extracellular stress such as nutrient deprivation. Recent studies indicate that autophagy also functions as a protective mechanism in response to several cancer therapy agents, making it a prospective therapeutic target. Few pharmacological inhibitors suitable for testing the therapeutic potential of autophagy inhibition in vivo are known. An automated microscopy assay was used to screen >3,500 drugs and pharmacological agents and identified one drug, verteporfin, as an inhibitor of autophagosome accumulation. Verteporfin is a benzoporphyrin derivative used in photodynamic therapy, but it inhibits autophagy without light activation. Verteporfin did not inhibit LC3/Atg8 processing or membrane recruitment in response to autophagic stimuli, but it inhibited drug- and starvation-induced autophagic degradation and the sequestration of cytoplasmic materials into autophagosomes. Transient exposure to verteporfin in starvation conditions reduced cell viability whereas cells in nutrient-rich medium were unaffected by drug treatment. Analysis of structural analogs indicated that the activity of verteporfin requires the presence of a substituted cyclohexadiene at ring A of the porphyrin core but that it can tolerate a number of large substituents at rings C and D. The existence of an autophagy inhibitor among FDA-approved drugs should facilitate the investigation of the therapeutic potential of autophagy inhibition in vivo.     

Cyanogenic glucosides in the biological warfare between plants and insects: the Burnet moth-Birdsfoot trefoil model system

Cyanogenic glucosides are important components of plant defense against generalist herbivores due to their bitter taste and the release of toxic hydrogen cyanide upon tissue disruption. Some specialized herbivores, especially insects, preferentially feed on cyanogenic plants. Such herbivores have acquired the ability to metabolize cyanogenic glucosides or to sequester them for use in their own predator defense. Burnet moths (Zygaena) sequester the cyanogenic glucosides linamarin and lotaustralin from their food plants (Fabaceae) and, in parallel, are able to carry out de novo synthesis of the very same compounds. The ratio and content of cyanogenic glucosides is tightly regulated in the different stages of the Zygaena filipendulae lifecycle and the compounds play several important roles in addition to defense. The transfer of a nuptial gift of cyanogenic glucosides during mating of Zygaena has been demonstrated as well as the possible involvement of hydrogen cyanide in male assessment and nitrogen metabolism. As the capacity to de novo synthesize cyanogenic glucosides was developed independently in plants and insects, the great similarities of the pathways between the two kingdoms indicate that cyanogenic glucosides are produced according to a universal route providing recruitment of the enzymes required. Pyrosequencing of Z. filipendulae larvae de novo synthesizing cyanogenic glucosides served to provide a set of good candidate genes, and demonstrated that the genes encoding the pathway in plants and Z. filipendulae are not closely related phylogenetically. Identification of insect genes involved in the biosynthesis and turn-over of cyanogenic glucosides will provide new insights into biological warfare as a determinant of co-evolution between plants and insects.