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Hyphal tips of fungi representing OQmycetes, Zygomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes were examined by light and electron microscopy and compared with respect to their protoplasmic organization. In all fungi studied, there is a zone at the hyphal apex which is rich irn cytoplasmic vesicles but nearly devoid of other cell components. Some vesicle profiles are continuous with the plasma membrane at the apices of these tip-growing cells. The subapical zones of hyphae contain an endomembrane system which includes smooth-surfaced cisternae associated with small clusters of vesicles. The findings are consistent with the hypothesis that vesicles produced by the endomembrane system in the subapical region become concentrated in the apex where they are incorporated at the expanding surface. Septate fungi (Ascomycetes, Basidiomycetes, and Deuteromycetes) have an apical body (Spitzenkorper) which is associated with growing hyphal tips. In electron micrographs of these fungi, an additional specialized region within the accumulation of apical vesicles is shown for the first time. This region corresponds on the bases of distribution among fungi, location in hyphae, size, shape and boundary characteristics to the Spitzenkorper seen by light microscopy. This structure is not universally associated with tip growth, whereas apical vesicles are widespread among tip-growing systems.

A membrane-bound adenosine triphosphatase (EC 3.6.1.3) that requires Mg++ and that is stimulated by monovalent ions has been purified 7-to 8-fold from homogenates of oat (Avena sativa L. Cult. Goodfield) roots by discontinuous sucrose-gradient centrifugation. The enzyme was substrate specific; adenosine triphosphate was hydrolyzed 25 times more rapidly than other nucleoside triphosphates. The membrane fraction containing adenosine triphosphatase was enriched in plasma membranes, which were identified by the presence of a glucan synthetase (EC 2.4.1.12), a high sterol to phospholipid ratio, and by a stain consisting of periodic acid, chromic acid, and phosphotungstic acid that is specific for plant plasma membranes. Oat-root plasma membranes and the associated adenosine triphosphatase were purified on either a 6-layer discontinuous sucrose gradient or on a simplified gradient consisting of only two sucrose layers.These results represent the first demonstration that plant plasma membranes contain an adenosine triphosphatase that is activated by monovalent ions, and this finding further implicates the enzyme in the absorption of inorganic ions by plant roots.Absorption of inorganic ions bylplant-root cells is an energyrequiring process dependent on aerobic respiration (1, 2). Furthermore, adenosine triphosphate (ATP) appears to be the energy source, since ion absorption by plant roots is inhibited by dinitrophenol (3,4), arsenate (4), and oligomycin (5-7). The mechanism of energy transfer from ATP to the ion-transport system is unknown, however, and this phenomenon represents one of the major unresolved aspects of the ion-absorption process in plants.We have suggested (8, 9) that the energy transduction process involved in ion transport of plant cells involves an adenosine triphosphatase (ATPase; EC 3.6.1.3) similar to the "transport" ATPase of animal cells (10). Plant ATPase is associated with membranes, requires MIg++, and is further activated by monovalent ions (8, 9, 11). A high correlation exists between the KCl-or RbCl-activated component of the ATPase and K+ or Rb+ absorption by root tissue (9). Also, the kinetics of monovalent-ion transport into roots and the kinetics of monovalent ion-stimulated ATPase are similar (8, 9). However, in order for this ATPase to be involved in energy transduction for ion transport, it should be associated with one or both of the membranes involved in active ion transport (i.e., either the plasma membrane or tonoplast), and this has not been demonstrated.It is difficult to isolate and identify the membrane system containing the ion-stimulated ATPase because of the ubiquity of membrane-associated ATPases in plants (12)(13)(14) and the paucity of known membrane "markers" for plant cells (14). We have recently found, however, that the membrane system containing the monovalent ion-stimulated ATPase can be separated from nearly all the other membranes on either continuous or discontinuous sucrose gradients (14). In this paper, we show that this membrane system has a high ste...

Somatic fungal hyphae are generally assumed to elongate at steady linear rates when grown under constant environmental conditions with ample nutrients. However, patterns of pulsed hyphal elongation were detected during apparent steady growth of hyphal tips in fungi from several major taxonomic groups (Oomycetes, Pythium aphanidermatum and

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