The hen egg white protein composition has not yet been fully defined. To improve the knowledge of this biological fluid, the most usual and recently developed electrophoretic methods have been used: SDS-PAGE, native-PAGE, isoelectric focusing (IEF), and 2-dimensional electrophoresis (2DE). Seven of the major known proteins were thus identified in at least one electrophoretic system. Isoforms of ovotransferrin, ovalbumin, and ovomucoid were visualized when pI was used for the separation. Two-dimensional electrophoresis allowed separation of a very large number of spots. In each of the four systems, some components were revealed but not identified, and unknown spots were particularly numerous with 2DE. With this technique, many spots corresponding to small acidic proteins were highlighted, among which was the Ch21 protein, whose presence in hen egg white was thus confirmed. This study thus constitutes, to our knowledge, the first proteomic investigation of hen egg white.

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SummaryWhen a potential pathogen attempts to infect a plant, biochemical and molecular communication takes place and leads to the induction of plant defence mechanisms. In the case of efficient defence, visible symptoms are restricted and the pathogen does not multiply (incompatible interaction); when defence is inefficient, the plant becomes rapidly infected (compatible interaction). During the last 30 years, a growing body of knowledge on plant-pathogen interactions has been gathered, and a large number of studies investigate the induction of various plant defence reactions by pathogens or by pathogenderived compounds. However, as most papers focus on incompatible interactions, there is still a lack of understanding about the similarities and differences between compatible and incompatible situations. This review targets the question of specificity in Solanaceae-pathogen interactions, by comparing defence patterns in plants challenged with virulent or avirulent pathogens (or with pathogen-associated molecular patterns from these). A special emphasis is made on analysing whether defence reactions in Solanaceae depend primarily on the type of elicitor, on the plant genotype/species, or on the type of interaction (compatible or incompatible).

Lipopolysaccharides (LPS), ubiquitous cell surface components of Gram-negative bacteria, are directly implicated in plant/pathogen interactions. However, their perception by the plant, the subsequent signal transduction in both compatible and incompatible interactions, as well as the defence reactions induced in compatible interactions are as yet poorly understood. We focused on biochemical and physiological reactions induced in cell suspensions of three Solanaceae species (tobacco, tomato, and potato) by purified lipopolysaccharides from PECTOBACTERIUM ATROSEPTICUM (PA), a pathogen of potato, and PSEUDOMONAS CORRUGATA (PSC), a pathogen of tomato. LPS PA and LPS PSC caused a significant acidification of potato, tomato, and tobacco extracellular media, whereas laminarin (a linear beta-1,3 oligosaccharide elicitor) induced an alkalinisation in tobacco and tomato, but not in potato cell suspensions. None of the two LPS induced the formation of active oxygen species in any of the hosts, while laminarin induced H (2)O (2) production in cells of tobacco but not of tomato and potato. In tomato cells, LPS PA and LPS PSC induced a strong but transitory stimulation of lipoxygenase activity, whereas laminarin induced a stable or slightly increasing LOX activity over the first 24 h of contact. In tobacco, LOX activity was not triggered by either LPS, but significantly increased following treatment with laminarin. In potato, neither LPS nor laminarin induced LOX activity, in contrast with concentrated culture filtrate of PHYTOPHTHORA INFESTANS (CCF). These results demonstrate that LPS, as well as laminarin, are perceived in different ways by SOLANACEAE species, and possibly cultivars. They also suggest that defence responses modulated by LPS depend on plant genotypes rather than on the type of interaction.