Micro-tubers of Solanum tuberosum were inoculated with several arbuscular mycorrhizal fungi (AMF) when used as propagule for the production of plantlets in pots with sterilized soil. The inoculation with AMF resulted in higher fresh weight and reduced plant loss. The effectiveness of fungal strains differed significantly. Inoculation of micro-propagated potato plantlets with AMF was carried out in seedling plates and under field conditions and the yield of tubers investigated. All tested fungi colonized the root systems of micro-propagated potato plants, but revealed strainand environment-specific differences. Overall, the inoculation of micro-propagated plant material with AMF inoculum improved both, mini-tuber production in the seedling plate and tuber production in the field. The results underline the importance of mycorrhiza use in potato production systems.
Mechanosensory organelles (MOs) are specialized subcellular entities where force-sensitive channels and supporting structures (e.g., microtubule cytoskeleton) are organized in an orderly manner. The delicate structure of MOs needs to be resolved to understand the mechanisms by which they detect forces and how they are formed. Here, we describe a protocol that allows obtaining detailed information about the nanoscopic ultrastructure of fly MOs by using serial section electron tomography (SS-ET). To preserve fine structural details, the tissues are cryo-immobilized using a high-pressure freezer followed by freeze-substitution at low temperature and embedding in resin at room temperature. Then, sample sections are prepared and used to acquire the dual-axis tilt series images, which are further processed for tomographic reconstruction. Finally, tomograms of consecutive sections are combined into a single larger volume using microtubules as fiducial markers. Using this protocol, we managed to reconstruct the sensory organelles, which provide novel molecular insights as to how fly mechanosensory organelles work and are formed. Based on our experience, we think that, with minimal modifications, this protocol can be adapted to a wide range of applications using different cell and tissue samples. Key features • Resolving the high-resolution 3D ultrastructure of subcellular organelles using serial section electron tomography (SS-ET). • Compared with single-axis tilt series, dual-axis tilt series provides a much wider coverage of Fourier space, improving resolution and features in the reconstructed tomograms. • The use of high-pressure freezing and freeze-substitution maximally preserves the fine structural details.
As the start of this booklet, we begin this chapter by providing a definition on "what is mechanosensory transduction" at the cell biological level and listing the fundamental questions in this emerging field. We then briefly introduce "mechanotransduction in physiology" and "mechanotransduction in diseases," which aim to integrate this cell biological process into the physiological and pathological contexts. Finally, we summarize the mechanotransduction processes in three model systems: (1) the bacterial cell, (2) the C. elegans touch-sensitive receptor, and (3) the vertebrate hair cell. We focus on how mechanotransduction contributes to the functions of these cells and the molecular basis of the mechanosensory transduction in each model cell.
In Chap. 4 , we discussed the working mechanisms of several fly mechanoreceptors. These mechanoreceptors have developed striking structural-mechanical features that couple the environmental signals to the proximity of the mechanosensory cells. These proximal stimuli are then transformed by a transduction apparatus, often associated with the cell membrane, to the electrochemical signals in cells, which then initiates the neuronal impulses. In this chapter, we will discuss the core components of mechanotransduction apparatus at the molecular level, including the mechanotransduction channel and the gating spring. Two bona fide mechanotransduction channels are identified in Drosophila melanogaster, i.e., NompC/TRPN and DmPiezo. One molecular candidate for gating spring is identified, i.e., the ankyrin-repeat domain of NompC. In this chapter, we will introduce the structure, function, and physiology of these molecules and discuss their working mechanisms in fly mechanoreceptors.
Mechanoreceptor cells develop specialized mechanosensory organelles (MOs), where force-sensitive channels and supporting structures are organized in an orderly manner to detect forces. It is intriguing how MOs are formed. Here, we address this issue by studying the MOs of fly ciliated mechanoreceptors. We show that the main structure of the MOs is a compound cytoskeleton formed of short microtubules and electron-dense materials (EDMs). In a knock-out mutant of DCX-EMAP, this cytoskeleton is nearly absent, suggesting that DCX-EMAP is required for the formation of the MOs and in turn fly mechanotransduction. Further analysis reveals that DCX-EMAP expresses in fly ciliated mechanoreceptors and localizes to the MOs. Moreover, it plays dual roles by promoting the assembly/stabilization of the microtubules and the accumulation of the EDMs in the MOs. Therefore, DCX-EMAP serves as a core ultrastructural organizer of the MOs, and this finding provides novel molecular insights as to how fly MOs are formed.
In Chap. 1 , we provided a general introduction for mechanotransduction. We feel that before going to the biological details (molecule, structures, etc.), it may help to provide the readers an overall picture on how an ideal system may work. We think that a theoretical model that depicts the operation of a mechanotransduction system may serve this purpose well. In this chapter, we introduce a classical model for cell mechanotransduction, i.e., the "gating-spring" model, which was proposed over 30 years ago based on the remarkable experimental work and data analysis on hair cells. We add some of our understanding of this model at the end of this chapter.
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