Ultrastructure of hyphal tip bursting in Penicillium chrysogenum.

Hyphae around the periphery of colonies of Penicillium chrysogenum were subjected to hypotonic shock by flooding them with distilled water at 25 degrees C, which provoked bursting of hyphal tips. A minority of hyphal tips (26%) burst rapidly within 1.8 s of the flooding, but bursting continued to occur such that the majority of peripheral tips (51%) were found to have burst around colonies maintained in the flooded state for 2 h. Electron microscopy of burst tips indicated that cytoplasm was released through a small hole with a mean diameter of 337 +/- 70 nm formed at or near to the hyphal apex. Woronin bodies were observed amongst the cytoplasm extruded from such tips. Burst apices were found to be plugged with an irregular deposition of electron-dense material similar in appearance to that which has been observed plugging septal pores in ageing regions of this organism.