title: Ultrastructure of compatible and incompatible interactions in phloem sieve elements during the stylet penetration by cotton aphids in melon.
abstract: Resistance of the melon line TGR-1551 to the aphid Aphis gossypii is based on preventing aphids from ingesting phloem sap. In electrical penetration graphs (EPGs), this resistance has been characterized with A. gossypii showing unusually long phloem salivation periods (waveform E1) mostly followed by pathway activities (waveform C) or if followed by phloem ingestion (waveform E2), ingestion was not sustained for more than 10 min. Stylectomy with aphids on susceptible and resistant plants was performed during EPG recording while the stylet tips were phloem inserted. This was followed by dissection of the penetrated leaf section, plant tissue fixation, resin embedding, and ultrathin sectioning for transmission electron microscopic observation in order to study the resistance mechanism in the TGR. The most obvious aspect appeared to be the coagulation of phloem proteins inside the stylet canals and the punctured sieve elements. Stylets of 5 aphids per genotype were amputated during sieve element (SE) salivation (E1) and SE ingestion (E2). Cross-sections of stylet bundles in susceptible melon plants showed that the contents of the stylet canals were totally clear and also, no coagulated phloem proteins occurred in their punctured sieve elements. In contrast, electron-dense coagulations were found in both locations in the resistant plants. Due to calcium binding, aphid saliva has been hypothesized to play an essential role in preventing/suppressing such coagulations that cause occlusion of sieves plate and in the food canal of the aphid's stylets. Doubts about this role of E1 salivation are discussed on the basis of our results.
authors.affiliation: Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain.|Laboratory of Entomology, Wageningen University, Wageningen, the Netherlands.
authors.forename: Elisa
authors.initials: E
authors.lastname: Garzo
authors.affiliation: Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Fernández-Pascual
authors.affiliation: Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain.
authors.forename: Cesar
authors.initials: C
authors.lastname: Morcillo
authors.affiliation: Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Fereres
authors.affiliation: Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora", Universidad de Málaga-CSIC (IHSM-UMA-CSIC), Algarrobo-Costa, Málaga, Spain.
authors.forename: M Luisa
authors.initials: ML
authors.lastname: Gómez-Guillamón
authors.affiliation: Laboratory of Entomology, Wageningen University, Wageningen, the Netherlands.
authors.forename: W Fred
authors.initials: WF
authors.lastname: Tjallingii
mesh_terms: D000818:Animals; D001042:Aphids / Q000502:physiology*; D028463:Cucumis melo / Q000502:physiology*; D004553:Electric Conductivity; D005247:Feeding Behavior / Q000502:physiology; D046529:Microscopy, Electron, Transmission; D052585:Phloem / Q000502:physiology*; D018515:Plant Leaves / Q000648:ultrastructure; D010940:Plant Proteins / Q000737:chemistry; D012463:Saliva / Q000737:chemistry; D012472:Salivation / Q000502:physiology
chemical_list: D010940:Plant Proteins
keywords: Aphis gossypii Glover; Cucumis melo L.; feeding behavior; insect-plant resistance; phloem defense response; watery saliva