cell membrane might be achieved by an active process
of endocytosis– the converse of exocytosis, which is
widely recognized to occur when vesicles fuse with
the plasma membrane and release their contents into
the surrounding environment (Figs 3.2, 3.4). How-
ever, there is still some debate about whether fungal
hyphae have an endocytotic system, and (if they do
so) whether it is equivalent to the endosomal system
commonly reported in other cell types.
The evidence for endocytosis in fungal hyphae is
based on the use of amphiphilic steryl dyes such as
FM4-64 and FM1-43, which are reported to be marker
dyes for endocytosis in many different organisms. These
vital dyes can be taken up by cells and are then visual-
ized by laser scanning confocal microscopy. Figure 3.15
shows confocal images of Neurospora crassatreated
with two of these dyes – FM4-64 which strongly labels
the plasma membrane and Spitzenkörper, and FM1-43
which labels the mitochondria but only weakly labels
the Spitzenkörper. Essentially similar labeling patterns
with FM4-64 were found when hyphae of eight dif-
ferent fungi were tested, including representatives of
Ascomycota, Basidiomycota, mitosporic fungi, and
Zygomycota (Fig. 3.16). The reasons for the different
labeling patterns of these dyes are still unclear, but the
strong labeling of the plasma membrane by FM4-64
is consistent with reports that this dye becomes inter-
calated between the outer and inner layers of the cellFUNGAL STRUCTURE AND ULTRASTRUCTURE 61
Fig. 3.14The dynamic tubular vacuolar system of living fungal hyphae, treated with a fluorescent dye that becomes
localized in the vacuoles. (a) Hypha of Penicillium expansumseen by normal bright-field microscopy, showing the pres-
ence of a septum (S). (b) The same hypha viewed by fluorescence microscopy, showing a narrow tubule (t) passing
through the septum and then branching. (c) The same hypha showing dilated vacuoles ( V ) after they have passed
through the septum. (d–f ) Hypha of Aspergillus nigerphotographed at 8-second intervals, showing a succession of
peristalsis-like movements causing the vacuolar dilations to travel along the hypha from left to right. (Courtesy of
B. Rees, V. Shepherd and A. Ashford; from Rees et al. 1994.)