Organization and dynamics of the Spitzenkoerper in growing hyphal tips
Abstract
In order to study apical growth in fungi, a slide culture chamber for light microscopic observation of growing hyphal tips was designed. This slide culture chamber is easy to build, stable, inexpensive, and effective with oil immersion lenses. It allows growing hyphal tips to be observed with minimal stress at high magnification. With the use of computer-enhanced video microscopy and phase-contrast optics, more than 30 fungi were studied. These fungi were mainly represented in the Ascomycetes and Basidiomycetes. Several components within the Spitzenkorper were identified: (a) the vesicle cluster, (b) the vesicle cloud, (c) two different kinds of differentiated internal core structures, (d) apical granules, and (e) cytoplasmic filaments. The Spitzenkorper is a highly dynamic and pleomorphic complex, that is maintained within the apical crown of the cell during hyphal growth. Two kinds of variation in the morphological organization of the Spitzenkorper were found: (a) inherent--according to the kind of organism, and (b) pleomorphic--within a given organism. Eight morphological patterns of Spitzenkorper were identified based on the shape, refractive index, and distribution of its components. The Spitzenkorper reacted to stress conditions (light, mechanical, and electric field). Some of these reactions included the migration of the Spitzenkorper into the subapical zone and disassembly of its components. In some fungi, mainly in the Ascomycetes, multiple Spitzenkorper were observed. In addition to the typical main Spitzenkorper, smaller satellite Spitzenkorper appeared a few micrometers behind the hyphal apex. These satellite Spitzenkorper increased in size, migrated along the plasma membrane, and merged with the main Spitzenkorper. Four developmental stages were identified from the time the satellites first became visible until they merged with the main Spitzenkorper. Localized cell enlargement was associated with stationary satellites, indicating that satellite Spitzenkorper are functional as sources of new cell surface before they reach the main Spitzenkorper, therefore, they may account for some variations in the profiles of growing hyphae. Imaged by electron microscopy, satellites consisted of small clusters of apical vesicles surrounding a group of microvesicles located next to the plasma membrane. Thus, the observation of satellites represents the evidence in favor of directional mass transport of vesicle towards the hyphal apex. The occurrence of pulsed growth during apparent steady growth of hyphal apices was also demonstrated in this study. (Abstract shortened by UMI.)
Degree
Ph.D.
Advisors
Bracker, Purdue University.
Subject Area
Botany|Plant pathology
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