A Model for the Development of the Rhizobial and Arbuscular Mycorrhizal Symbioses in Legumes and Its Use to Understand the Roles of Ethylene in the Establishment of these two Symbioses

We propose a model depicting the development of nodulation and arbuscular mycorrhizae. Both processes are dissected into many steps, using Pisum sativum L. nodulation mutants as a guideline. For nodulation, we distinguish two main developmental programs, one epidermal and one cortical. Whereas Nod factors alone affect the cortical program, bacteria are required to trigger the epidermal events. We propose that the two programs of the rhizobial symbiosis evolved separately and that, over time, they came to function together. The distinction between these two programs does not exist for arbuscular mycorrhizae development despite events occurring in both root tissues. Mutations that affect both symbioses are restricted to the epidermal program. We propose here sites of action and potential roles for ethylene during the formation of the two symbioses with a specific hypothesis for nodule organogenesis. Assuming the epidermis does not make ethylene, the microsymbionts probably first encounter a regulatory level of ethylene at the epidermis–outermost cortical cell layer interface. Depending on the hormone concentrations there, infection will either progress or be blocked. In the former case, ethylene affects the cortex cytoskeleton, allowing reorganization that facilitates infection; in the latter case, ethylene acts on several enzymes that interfere with infection thread growth, causing it to abort. Throughout this review, the difficulty of generalizing the roles of ethylene is emphasized and numerous examples are given to demonstrate the diversity that exists in plants

A Review of the Effects of Major Atmospheric Pollutants on Pollen Grains, Pollen Content and Allergenicity

International audienc

The Weight-loss Practices of Working Class Women in France

International audienceThis paper focuses on weight loss methods used by working-class women. It is based on the results of a qualitative investigation conducted among women who participated in a Food Education Programme in the north of France, the area with the highest obesity rate in the country. We show that the women interviewed used three types of techniques (physical, restrictive or culinary) to lose weight. The study offers new evidence that social class is particularly relevant in weight loss practices in view of both somatic culture and relationships to employment. We also have highlighted the key role played by intra- and intergenerational mobility, especially when daughters’ upward mobility acts as inverse socialisation. We also demonstrate that the strength of family relationships is of particular importance. Watching one’s weight and dieting are more likely to occur when food is central to family exchanges, especially in the context of France where mealtimes are still a crucial moment in family life