Gravimorphogenesis and ultrastructure of the fungus Flammulina velutipes grown in space, on clinostats and under hyper-G conditions

The D-2-mission provided the facilities to cultivate the higher basidiomycete Flammulina velutipes (Agaricales) in space for about 8 days. Gravimorphogenesis of developing fruiting body primordia in weightlessness was documented in comparison to cultures incubated on a 1×g reference centrifuge in space. Chemical fixation of fruiting bodies took place for later ultrastructural analysis. The μg-grown fruiting bodies exhibited random orientation compared to the 1×g-cultures where fruiting bodies showed exactly negative gravitropic orientation. Weightlessness did not impair fruiting body morphogenesis and growth although flat and helically twisted stipes were observed. Ultrastructural analyses of μg-, 1×g- and 20×g-samples did not reveal sedimentable cell components. Gravitropic bending involves growth inhibition at the upper side of a horizontally oriented transition zone, the graviperceptive region of the stipe. The fastest ultrastructural response to the altered direction of the accelerational force is the accumulation of cytosolic vesicles at the lower part of this region. They contribute to the expansion of the central vacuole and therefore to the differential enlargement of the lower side of the stipe.