VACUOLE MOTILITY AND TUBULE-FORMING ACTIVITY IN PISOLITHUS-TINCTORIUSHYPHAE ARE MODIFIED BY ENVIRONMENTAL-CONDITIONS

Motile tubular vacuole systems have been visualised using DIC optics i n living hyphae of Pisolithus tinctorius without loading of any fluore scent tracer. Adding new medium, with or without the tracer CFDA, alte rs the motility of this system and increases the number of tubules. Th is response has been shown in individual hyphal tip cells and quantifi ed in populations of tip cells. Vacuoles with motile tubules are also demonstrated in more basal cells of the hyphae, within 600 mu m of the growing hyphal front. The vacuoles in these cells show more limited m otility, but similarly respond to addition of new medium by increased motility and tubular activity. This demonstration that the vacuole sys tem in more mature regions is both motile and interconnected as in the tips, and similarly responds to changes in external conditions, suppo rts the hypothesis that the vacuole system may play a role in long-dis tance transport. Vacuoles in the most mature cells, more than 600 mu m behind the hyphal growth zone are not motile. They do not respond to these stimuli and remain spherical and isolated. There are many explan ations for this and the present lack of response does not exclude the transport hypothesis. The findings further support the concept that tu bular vacuole systems are equivalent to animal endosomal/lysosomal sys tems and have implications for their motility, especially their plasti city in response to external stimuli, such as fluorescent tracers.