Also, spores can stick together and form spore clumps. In some cases, the whole sporangium, or parts of it, together with contained spores break away from the false indusium and are shed as a whole. The ultra-lightweight spores travel through air with a maximum velocity of ~5 m s -1, and a launch acceleration of ~6300g is measured. Separation and liberation of spores from the sporangia are induced by relaxation of the annulus (the ‘throwing arm’ of the sporangium catapult) and conservation of momentum generated during this process, which leads to sporangium bouncing. High-speed cinematography allowed for analyses of fast sporangium motion and for tracking ejected spores.
The complex folding kinematics and functional morphology of false indusia are being described, and we discuss scenarios of movement initiation and passive hydraulic actuation of these structures. Sporangia are being produced on the undersides of so-called false indusia, which are situated at the abaxial surface of the pinnule margins, and become exposed by a desiccation-induced movement of these pinnule flaps. In this review we provide an up to date overview of the field while identifying what we consider to be the key gaps in knowledge associated with germination of Bacillales spores, suggesting also technical approaches that may provide fresh insight to this unique biological process.We investigated the different processes involved in spore liberation in the polypod fern Adiantum peruvianum (Pteridaceae). Despite this relative simplicity, and research effort spanning many decades, comprehensive understanding of key molecular and biochemical details and, in particular signal transduction mechanisms associated with spore germination, has remained elusive. Whereas the process by which spores are formed in response to nutrient starvation – sporulation – involves the orchestrated interplay between hundreds of distinct proteins, the process by which spores return to life – germination – is a much simpler affair, requiring a handful of receptor and channel proteins complemented with specialized peptidoglycan lysins. How might a microbial cell that is entirely metabolically dormant – and which has the ability to remain so for extended periods of time – irreversibly commit itself to resuming vegetative growth within seconds of being exposed to certain amino acids or sugars? That this process takes place in the absence of any detectable ATP or de novo protein synthesis, and relies upon a pre-formed apparatus that is immobilised, respectively, in a semi-crystalline membrane or multi-layered proteinaceous coat, only exacerbates the challenge facing spores of Bacillales species when stimulated to germinate.
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