Mannitol and hexoses are components of Buller's drop

Abstract

The mechanism of ballistospore self-propulsion by basidiomycetes involves the hygroscopic adsorption of water vapour by a drop of liquid (Buller's drop) on the hilar appendix of the spore until it makes contact with another expanding drop, the adaxial drop on the face of the spore above it. Aliquots of liquid from Buller's drop have been collected from Itersonilia perplexans using micropipettes. Analysis of the droplets by microfluorescence assays indicated the presence of mannitol and hexoses. Using the same technique, washings from basidiospore deposits of I. perplexans, containing the evaporated remnants of Buller's drops and the adaxial drops carried away by the spores on discharge, were further shown to contain mannitol and hexoses. Glc analyses of washings from spore deposits of a range of basidiomycetes also indicated the presence of mannitol and hexoses. Calculations based on the estimated concentrations of mannitol and hexoses in Buller's drop from Itersonilia show that the concentration of solutes is sufficient to bring about the condensation of water vapour from a saturated atmosphere and thus to cause the growth of Buller's drop at rates previously measured. When brought close to, but not in contact with, the surface of an agar plate, crystals of pure mannitol rapidly deliquesced. Mannitol and hexoses contribute significantly to the hygroscopic nature of Buller's drop in basidiomycetes.