Induction of Haploid Fruiting by Mechanical Injury in Schizophyllum Commune

SUMMARY

The present paper reports the results of investigations concerning a number of mutually interacting factors that affect the fruiting response of haploid mycelia of S. commune to mechanical injury. Older as well as younger hyphae were found competent to fruit in response to injury. The density of hyphae in an injured fragment, however, was positively correlated with the ability to respond. A number of genes, which had previously been found to inhibit haploid fruiting responses to extramycelial fruiting inducing substances (FIS), were similarly found to inhibit the response to injury; moreover, in a cross between injury-responsive and injury-unresponsive mycelia a factor was found to segregate which might represent a new gene regulating haploid fruiting. Mycelia which had suffered graduated degrees of injury—from large cube inocula to no injury whatever—were subjected to a series of abrupt nutritional transfers, and it was found that the fruiting response to nutrient shifts (a) depended Qualitatively on the extent of the injury, but could be independent therefrom, (b) was independent of the “direction” of the transfer, i.e., to media of higher versus lower nutrient content, (c) was positively affected in uninjured mycelia only by the subsequent nutrient environment, except where the most minimal medium which supports vegetative growth was used. The responses of haploid mycelia to FIS were conclusively found to be independent of any prior history of injury. Several hypotheses concerning the possible mechanism(s) of the injury response are presented: (a) release of fruiting-induced substances—injury substances—in the injured area, (b) alteration of the O₂ and/or CO₂ partial pressures in the vicinity of injured mycelial portions, and (c) translocational response to injury which gathers material and energy reserves necessary for fruiting from the remainder of the mycelium to injured areas.