DIVERSITY AND DYNAMICS OF THE SPITZENKORPER IN GROWING HYPHAL TIPS OFHIGHER FUNGI

The Spitzenkorper, located in the apex of growing hyphae of septate fu ngi, has been portrayed previously as a spheroid complex containing a cluster of apical (secretory) vesicles which sometimes encloses a diff erentiated core area. With the aid of computer-enhanced video microsco py and phase-contrast optics, we studied 32 fungi in the Ascomycetes, Deuteromycetes, Hyphomycetes, Basidiomycetes, and Agonomycetes. The Sp itzenkorper appeared as a highly dynamic and pleomorphic multicomponen t complex capable of changing shape, size, and position within the hyp hal apex during growth. The main theme of this study is to demonstrate two kinds of morphological diversity/variation in Spitzenkorper from diverse fungi: (a) inherent diversity-Spitzenkorper features character istic of particular fungi, and (b) dynamic pleomorphism-gradual or rap id changes in size, shape, and position of the Spitzenkorper within a single hyphal tip. Several components associated with the Spitzenkorpe r were identified: (a) vesicle cluster, (b) vesicle cloud, (c) differe ntiated core region(s) within the Spitzenkorper, (d) apical granules, (e) cytoplasmic filaments. Eight morphological patterns of Spitzenkorp er organization are described in the higher fungi based on the shape a nd distribution of their components. An additional (ninth) pattern was recognized in the chytridiomycete Allomyces macrogynous from recent w ork by others. All these patterns appeared to be conserved at the genu s level. In all patterns but one, a core region was observed by light microscopy. The Spitzenkorper not only exhibited spontaneous dynamic p leomorphism but also reacted to stress conditions (light, mechanical, and electrical fields). These reactions include migration of the Spitz enkorper back into the subapical zone and/or disassembly of its compon ents. The understanding and conceptualization of this dynamic complex is problematic and should remain flexible enough to encompass the dive rsity of Spitzenkorper patterns and the dynamic pleomorphism of this s pecialized apical apparatus which appears to drive hyphal tip growth i n the higher fungi.