Little is known about molecular responses in plants to phloem feeding by insects. The induction of genes associated with wound and pathogen response pathways was investigated following green peach aphid (Myzus persicae) feeding on Arabidopsis. Aphid feeding on rosette leaves induced transcription of two genes associated with salicylic acid (SA)dependent responses to pathogens (PR-1 and BGL2) 10-and 23-fold, respectively. Induction of PR-1 and BGL2 mRNA was reduced in npr1 mutant plants, which are deficient in SA signaling. Application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA, suggesting that wild-type SA-dependent responses do not influence resistance to aphids. Twofold increases occurred in mRNA levels of PDF1.2, which encodes defensin, a peptide involved in the jasmonate (JA)-/ethylene-dependent response pathway. Transcripts encoding JA-inducible lipoxygenase (LOX2) and SA/JA-inducible Phe-ammonia lyase increased 1.5to 2-fold. PDF1.2 and LOX2 induction by aphids did not occur in infested leaves of the JA-resistant coi1-1 mutant. Aphid feeding induced 10-fold increases in mRNA levels of a stress-related monosaccharide symporter gene, STP4. Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding.

Phloem feeding involves unique biological interactions between the herbivore and its host plant. The economic importance of aphids, whiteflies, and other phloem-feeding insects as pests has prompted research to isolate sources of resistance to piercing-sucking insects in crops. However, little information exists about the molecular nature of plant sensitivity to phloem feeding. Recent discoveries involving elicitation by plant pathogens and chewing insects and limited studies on phloem feeders suggest that aphids are capable of inducing responses in plants broadly similar to those associated with pathogen infection and wounding. Our past work showed that compatible aphid feeding on leaves of Arabidopsis thaliana induces localized changes in levels of transcripts of genes that are also associated with infection, mechanical damage, chewing herbivory, or resource allocation shifts. We used microarray and macroarray gene expression analyses of infested plants to better define the response profile of A. thaliana to M. persicae feeding. The results suggest that genes involved in oxidative stress, calcium-dependent signaling, pathogenesis-related responses, and signaling are key components of this profile in plants infested for 72 or 96 h. The use of plant resistance to aphids in crops will benefit from a better understanding of induced responses. The establishment of links between insect elicitation, plant signaling associated with phloem feeding, and proximal resistance mechanisms is critical to further research progress in this area.

No abstract

Diverse organisms simultaneously exploit plants in nature, but most studies do not examine multiple types of exploiters like phytophagous insects and fungal, bacterial, and viral plant pathogens. This study examined patterns of induction of antipathogenic peroxidase enzymes and phenolics after infection by the cucurbit scab fungus, Cladosporium cucumerinum, and then determined if induction mediated ecological eects on Colletotrichum orbiculare, another fungal pathogen, and two insect herbivores, spotted cucumber beetles, and melon aphids. Peroxidase induction occurred in inoculated,`local,' symptom-bearing leaves 3 days after inoculation, and in`systemic,' symptom-free leaves on the same plants 1 day later. Phenolics were elevated in systemic but not in local leaves 3 days after inoculation. Detached systemic leaves from plants inoculated with C. cucumerinum developed signi®cantly fewer and smaller lesions after challenge with C. orbiculare. Spotted cucumber beetles did not show consistently signi®-cant preferences for infected versus control leaf disks in comparisons using local or systemic leaves, but trends diered signi®cantly between leaf positions. In no-choice tests, beetles removed more leaf area from local but not from systemic infected leaves compared to control leaves, and melon aphid reproduction was enhanced on local infected leaves. In the ®eld, cucumber beetle and melon aphid densities did not dier between infected and control plants. Antipathogenic plant chemical responses did not predict reduced herbivory by insects. Other changes in metabolism may explain the positive direction and spatially dependent nature of plant-mediated interactions between pathogens and insects in this system.

This paper examines the effect of graphite and silicon carbide reinforcements on the pitting behavior of graphite/aluminum (Gr/Al) and silicon carbide/aluminum (SiC/A1) metal matrix composites. Electrochemical corrosion tests were performed on both Gr/A1 and SiC/A1 composite specimens. Identical tests were completed on powder metallurgy processed aluminum and wrought aluminum of the same composition. The electrochemical behavior of the SiC/A1 composites was essentially identical to that of the powder processed and wrought aluminum alloys; however, the pitting attack on the SiC/Al composites was distributed more uniformly across the surface, and the pits penetrated to significantly less depths. The presence of graphite in the Gr/A1 composites did not cause an electropositive shift in corrosion potential as anticipated, but caused a substantial decrease in resistance to passive film breakdown. This effect is the predominant reason for the poor performance of Gr/At composites in marine environments.Interest in implementation of metal matrix composites (MMC) in marine applications is rapidly expanding due to the materials' higher strength and modulus than that which can be attained by conventional alloying. Utilization of MMC in marine environments requires adequate corrosion resistance. To date, composites considered for marine application are typically aluminum-based, specifically 5000 series or 6061 Al, with reinforcements of graphite (Gr) and silicon carbide (SIC). It has been reported tl~at aluminum alloys suffer localized attack by pitting in chloride environments (1, 2). A reinforcement of Gr or SiC added to the aluminum matrix could potentially decrease the corrosion resistance as compared to an unreinforced alloy due to the structure of the composite. Continuous graphite/aluminum (Gr/A]) composites typically consist of Gr/Al wires (graphite multifilament tows infiltrated with aluminum) diffusion bonded between aluminum foils. This composite configuration could promote wicking of the electrolyte (thereby increasing the corrosion rate) at the foil-to-wire and wire-to-wire interfaces once pitting corrosion progresses through the aluminum foils. The structure of the discontinuous silicon carbide/aluminum (SiC/A1) composites, that of silicon carbide whiskers or particles blended into a powder aluminum matrix could increase the probability of pitting/crevice corrosion at exposed SiC-A1 interfaces in the composite. Dull et al. (3,4) studied the Gr/A1 system in 3.5% NaC1.They concluded that the corrosion rate was slightly higher for Gr/AI relative to 6061 aluminum alloy controls. The explanation for this increased corrosion rate was galvanic corrosion at the graphite fiber-aluminum interface.Trzaskoma et al. (5) studied the SiC/A1 system in 0.1N NaC1. They concluded that the SiC whiskers did not influence the susceptibility of 6061 aluminum to pit initiation, but promoted the development of a smaller size pit morphology relative to 6061 aluminum controls.In this research, both SiC/A1 and Gr/A1 composites were evalua...

Beam-Line FIG. 3. Implementation of detectors in the πM1 area in a Geant4 [10] simulation. The beam strikes the thin scintillator beam hodoscope and three GEM chambers, passes through a hole in the annular veto scintillator, enters the cryotarget vacuum chamber and strikes one of the targets, then exits the vacuum chamber and goes through the beam monitor. Scattered particles are detected by two symmetric spectrometers, each with two straw chambers wrapped in RF shielding and two planes of scintillator paddles.

No abstract

No abstract