Functional organisation of the endomembrane network in the digestive gland of the Venus flytrap: revisiting an old story with a new microscopy toolbox.

Up-to-date imaging approaches were used to address the spatiotemporal organisation of the endomembrane system in secretory cells of Dionaea muscipula. Different 'slice and view' methodologies were performed on resin-embedded samples to finally achieve a 3D reconstruction of the cell architecture, using ultrastructural tomography, array tomography, serial block face-scanning electron microscopy (SBF-SEM), correlation, and volume rendering at the light microscopy level. Observations of cryo-fixed samples by high-pressure freezing revealed changes of the endomembrane system that occur after trap activation and prey digestion. They provide evidence for an original strategy that adapts the secretory machinery to a specific and unique case of stimulated exocytosis in plant cells. A first secretion peak is part of a rapid response to deliver digestive fluids to the cell surface, which delivers the needed stock of digestive materials 'on site'. The second peak of activity could then be associated with the reconstruction of the Golgi apparatus (GA), endoplasmic reticulum (ER) and vacuolar machinery, in order to prepare for a subsequent round of prey capture. Tubular continuum between ER and Golgi stacks observed on ZIO-impregnated tissues may correspond to an efficient transfer mechanism for lipids and/or proteins, especially for use in rapidly resetting the molecular GA machinery. The occurrence of one vacuolar continuum may permit continuous adjustment of cell homeostasy. The subcellular features of the secretory cells of Dionaea muscipula outline key innovations in the organisation of plant cell compartmentalisation that are used to cope with specific cell needs such as the full use of the GA as a protein factory, and the ability to create protein reservoirs in the periplasmic space. Shape-derived forces of the pleiomorphic vacuole may act as signals to accompany the sorting and entering flows of the cell.

Structural Features of Carnivorous Plant (Genlisea, Utricularia) Tubers as Abiotic Stress Resistance Organs.

Carnivorous plants from the Lentibulariaceae form a variety of standard and novel vegetative organs and survive unfavorable environmental conditions. Within Genlisea, only G. tuberosa, from the Brazilian Cerrado, formed tubers, while Utricularia menziesii is the only member of the genus to form seasonally dormant tubers. We aimed to examine and compare the tuber structure of two taxonomically and phylogenetically divergent terrestrial carnivorous plants: Genlisea tuberosa and Utricularia menziesii. Additionally, we analyzed tubers of U. mannii. We constructed phylogenetic trees using chloroplast genes matK/trnK and rbcL and used studied characters for ancestral state reconstruction. All examined species contained mainly starch as histologically observable reserves. The ancestral state reconstruction showed that specialized organs such as turions evolved once and tubers at least 12 times from stolons in Lentibulariaceae. Different from other clades, tubers probably evolved from thick stolons for sect. Orchidioides and both structures are primarily water storage structures. In contrast to species from section Orchidioides, G. tuberosa, U. menziesii and U. mannii form starchy tubers. In G. tuberosa and U. menziesii, underground tubers provide a perennating bud bank that protects the species in their fire-prone and seasonally desiccating environments.

Fine structure of Aldrovanda vesiculosa L: the peculiar lifestyle of an aquatic carnivorous plant elucidated by electron microscopy using cryo-techniques.

The aquatic carnivorous plant Aldrovanda vesiculosa L. is critically endangered worldwide; its peculiar lifestyle raises many questions and poses problems both intriguing on their own and relevant to conservation. While establishing a culture system for its propagation and restoring its natural habitat in Hozoji pond in Saitama, Japan, we conducted ultrastructural observations to examine the various aspects of Aldrovanda's way of life. Electron microscopic observation in combination with cryo-techniques produced novel information which could not be obtained by other methods. Some of the results are: phosphorous is stored in petiole cells of turions during winter; mucilaginous guides are provided for pollen tubes in parietal placental ovaries; storage of potassium in the vicinity of the midrib of carnivorous leaves may contribute to the rapid closing of the carnivorous leaves; dynamic sequential changes of the ultrastructure of digestive glands are involved in the synthesis and secretion of digestive enzymes, including protease and acid phosphatase. These results should contribute significantly to our understanding of Aldrovanda and the detailed mechanisms of its life.