The water mold, Achlya bisexualis grows in the form of large, aseptate hyphae that lend themselves to diverse physical techniques, light microscopy, and simple surgical procedures. This proposal is based upon the ability to measure and manipulate the hydrostatic pressure gradient. A pressure probe has been constructed adapted from U. Zimmermann's original design, which permits the recording of turgor from growing hyphae and other eukaryotic microorganisms. The magnitude of the pressure, its genesis and regulation and its function as the driving force for extension will be studied. The pressure probe should also permit adjustments to the hydrostatic pressure, and may serve as the basis for the development of a simple microinjection system. Fungal hyphae extend by polarized secretion, laying down new cell wall and plasma membrane at the apex. The driving force for extension is supplied by turgor pressure, and cells yield to this global stress by localized, controlled wall synthesis. The goals of this research are to understand how precursor vesicles are transported to the apex and what confines their exocytosis to that site; how the polarized pattern of growth is maintained; how polarized patterns arise anew, as in the emergence of branches; and how the work of surface enlargement is done. The results of this research will contribute new information about the mechanisms of polarized growth in a fungal system.
