talk session 6 ASHFORD, ANNE , GEOFF HYDE & LARA PERASSO. School of Biological Science, The University of New South Wales, Sydney NSW 2052, Australia - Fungal vacuoles, endosomes and transport Vacuole systems of Pisolithus tinctorius labelled with 6- carboxyfluorescein can form pleiomorphic dynamic networks in the hyphal tips. We have been able to visualise these networks unstained by DIC optics, showing that their form and motility are not dependent on loading of fluorochrome. Tubules may also be seen connecting the larger vacuoles in mature hyphae, indicating that the system has potential for transport in both tip and mature regions. The integrity and motility of tubules is dependent on microtubules but not microfilaments. In the presence of anti-microtubule drugs tubules disappear leaving a series of rounded vacuoles, while cytochalasin apparently has no effect. Experiments using these drugs could provide the opportunity to separate transport via vacuoles from cytoplasmic streaming. Various characteristics including motility suggest that the vacuolar networks are equivalent to animal cell endosomal networks which interconnect and transfer material by fusion and fission rather than vesicle transport. Both endosomal networks and vacuolar networks have varicosities that progressively move along tubules. Endosomal varicosities are multivesicular bodies that are sites of molecular sorting and transport within linear, continuous compartments. Multivesicular bodies are very common in electron micrographs of hyphae, and we propose that similar mechanisms may operate in fungi. We are studying this using the styryl dye FM 4-64 which labels vacuolar membranes. Vacuoles of Pisolithus tinctorius contain high levels of phosphorus. We have suggested that at least some of this phosphorus is polyphosphate which occurs in a dispersed form rather than as granules. This view is further supported by the very low frequency of granules in live, unlabelled and fluorochrome- labelled vacuole systems.