Influence of light on the morphological changes that take place during the development of the Flammulina velutipes fruit body

We show that fruit bodies of Flammulina velutipes can be induced in complete darkness after a sharp temperature reduction (23° to 16°C). However, the fruit bodies that form in complete darkness have a long stipe with an undeveloped pileus on the top (pinhead fruit bodies) and are thinner and whiter than the normal fruit bodies which are formed in the light. This finding suggests that F. velutipes fruit bodies cannot mature in complete darkness. However, when we irradiated the fruit bodies that had formed in complete darkness, a pileus developed immediately, and 4 days later the separation between the stipe and the pileus could be observed. Immediately after light exposure, the stipe also thickened and became increasingly pigmented. The stipe elongation was inhibited until 8 days after light exposure, although stipe elongation progressed very quickly thereafter. Basidospores were also visible in the gills 8 days after light exposure. We consider that the basidiospore development is involved in this rapid stipe elongation, which aids the effective dispersal of basidiospores.