Abstract
The vegetative mycelium of Agaricus bisporus supplies developing white button mushrooms with water and nutrients. However, it is not yet known which part of the mycelium contributes to the feeding of the mushrooms and how this depends on growth conditions. Here we used photon counting scintillation imaging to track translocation of the 14C-radiolabeled metabolically inert amino acid analogue α-aminoisobutyric acid (14C-AIB). Translocation to the periphery of the mycelium was observed in actively growing vegetative mycelium with a velocity of up to 6.6 mm h−1, which was 30-fold higher than the growth rate. Furthermore, 14C-AIB translocated to neighboring colonies after fusion by anastomosis depending on the relative growth rate in these colonies. When mushrooms started to develop, translocation of 14C-AIB was redirected to the fruiting bodies via mycelium and hyphal cords. More abundant mycelial cord formation and a 5-fold higher rate of translocation was observed for cultures growing directionally from inoculum located at one side of the substrate, when compared to non-directional growth (inoculum mixed throughout the substrate). The maximum translocation distance was also greater (≥50 and 22 cm, respectively). In conclusion, 14C-AIB translocation switches between vegetative growth and towards developing mushrooms, especially via cords and when source–sink relationships change.
Highlights
The white button mushroom Agaricus bisporus is a high quality food that is rich in protein and fibre and contains useful vitamins, minerals and anti-cancer polysaccharides
We assessed whether growth-induced bulk flow induces movement of water and nutrients to the growing periphery of the colony, and what the speed of that movement was using photon counting scintillation imaging (PCSI, Tlalka et al, 2002, 2007). 14C-AIB was loaded at the Phase III (PIII)-PII compost interface after 2/3 of the surface area of the PII compost had been directionally colonised from the PIII compost (Fig. 1D). 14C-AIB predominantly moved in the direction of the growing periphery and hardly within the PIII compost inoculum
Symmetric growing colonies that had been inoculated from a single rye grain spawn, produced less predominant cords (Fig. 4G). 14C-AIB was loaded on the rye grain inoculum and translocated with 3.68 ± 0.31 mm hÀ1 towards the colony margin (Fig. 4G-L, Movie S2)
Summary
The white button mushroom Agaricus bisporus is a high quality food that is rich in protein and fibre and contains useful vitamins, minerals and anti-cancer polysaccharides. This fungus produces mushrooms after extensive colonisation of the substrate by a mycelial network. After 16e19 days incubation at 25 C, the colonised PIII compost is transported to the growers, where it is topped with a layer of casing soil. This initiates phase IV (PIV), during which mushrooms are produced in 2e3 flushes at weekly intervals
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