Exodermis structure controls fungal invasion in the leafless epiphytic orchid Dendrophylax lindenii (Lindl.) Benth. ex Rolfe

Leafless and shootless epiphytic orchids rely essentially on CAM photosynthesis in roots for carbon gain. However, it is believed that a proportion of carbon is obtained by endomycorrhizal associations. In this study, we show that Dendrophylax lindenii possesses a dimorphic exodermis with smaller, thin-walled passage cells that are depleted in flavonoids. No hyphae succeeded in penetrating into the cortex from a non-passage cell, but 20% of the hyphae in contact with a passage cell managed to penetrate into the cortex. The passage cells represent 40% of the amount of cells in the centre of the side that touches the substrate, but no passage cells are observed in the upper side of the root. This distribution and density of exodermal passage cells define a strategy for controlling the extent and location of fungal invasion in the orchid root. This strategy provides a mechanism for restricting fungal growth to the lower cortex and thus maximising carbon gain from photosynthesis while enabling further trophic exchanges from mycorrhizal associations

A mechanistic model to predict distribution of carbon among multiple sinks.

International audienceFor over 35 years, biological scientists have come to rely on the research protocols and methodologies in the critically acclaimed Methods in Molecular Biology series. The series was the first to introduce the step-by-step protocols approach that has become the standard in all biomedical protocol publishing. Each protocol is provided in readily-reproducible step-by-step fashion, opening with an introductory overview, a list of the materials and reagents needed to complete the experiment, and followed by a detailed procedure that is supported with a helpful notes section offering tips and tricks of the trade as well as troubleshooting advice. These hallmark features were introduced by series editor Dr. John Walker and constitute the key ingredient in each and every volume of the Methods in Molecular Biology series. Tested and trusted, comprehensive and reliable, all protocols from the series are indexed in PubMed

Computational complementation: a modelling approach to study signalling mechanisms during legume autoregulation of nodulation

Autoregulation of nodulation (AON) is a long-distance signalling regulatory system maintaining the balance of symbiotic nodulation in legume plants. However, the intricacy of internal signalling and absence of flux and biochemical data, are a bottleneck for investigation of AON. To address this, a new computational modelling approach called ‘‘Computational Complementation’’ has been developed. The main idea is to use functional-structural modelling to complement the deficiency of an empirical model of a loss-of-function (non-AON) mutant with hypothetical AON mechanisms. If computational complementation demonstrates a phenotype similar to the wild-type plant, the signalling hypothesis would be suggested as ‘‘reasonable’’. Our initial case for application of this approach was to test whether or not wild-type soybean cotyledons provide the shoot-derived inhibitor (SDI) to regulate nodule progression. We predicted by computational complementation that the cotyledon is part of the shoot in terms of AON and that it produces the SDI signal, a result that was confirmed by reciprocal epicotyl-and-hypocotyl grafting in a real-plant experiment. This application demonstrates the feasibility of computational complementation and shows its usefulness for applications where real-plant experimentation is either difficult or impossible

Carbon allocation in fruit trees: from theory to modelling

International audienceCarbon allocation within a plant depends on complex rules linking source organs (mainly shoots) and sink organs (mainly roots and fruits). The complexity of these rules comes from both regulations and interactions between various plant processes involving carbon. This paper presents these regulations and interactions, and analyses how agricultural management can influence them. Ecophysiological models of carbon production and allocation are good tools for such analyses. The fundamental bases of these models are first presented, focusing on their underlying processes and concepts. Different approaches are used for modelling carbon economy. They are classified as empirical, teleonomic, driven by source–sink relationships, or based on transport and chemical/biochemical conversion concepts. These four approaches are presented with a particular emphasis on the regulations and interactions between organs and between processes. The role of plant architecture in carbon partitioning is also discussed and the interest of coupling plant architecture models with carbon allocatio