Woronin bodies of filamentous fungi

Abstract

Woronin originally reported observation of the fungal organelles which Buller subsequently named Woronin bodies, as highly refractive particles occurring on either side of the septum. This description presented light-microscopists with some difficulty in identifying these organelles precisely and led to frequent confusion with other organelles of similar size, such as lysosomes. The advent of the electron microscope provided more specific structural detail and the now generally recognised description of Wironin bodies as approximately spherical, electron-dense, single membrane-bound inclusions found in close association with the septal pore. Such specifically defined organelles occur only in the filamentous ascomycete and deuteromycete fungi. Their chenical composition has not yet been determined, but enzyme digestion studies have indicated that they are largely composed of protein and not of ergosterol as was once thought. It has long been believed that these organelles function in an emergency response to hyphal damage, being moved into and so plugging septal pores. This would prevent excessive loss of cytoplasm wwhich would otherwise result from hyphal rupture, because of the cytoplasmic continuity between hyphal compartments provided by the presence of septal pores. Recently, it has been demonstrated that Woronin bodies do function in this way, and that the initial Woronin body plug becomes consolidated into a seal by subsequent deposition of new material over the cytoplasmic side of the plug and septal plate. The plugging process has been found to be very rapid and to occur extensively within the mycelium in the immediate vicinity of severe damage. The mechanism by which Woronin bodies are moved into the septal pore remains unknown, but working hypotheses have been proposed, based on simple bulk flow transport or alternatively on the involvement of a contractile system. These relatively neglected organelles are therefore clearly of vital importance to many filamentous fungi, and notably to most species of current industrial significance. Continuing investigation of the function and composition of Woronin bodies presents the prospect of manipulating these organelles and the emergency plugging response they mediate, in a commercially useful manner.