NON-FILAMENTOUS AQUATIC FUNGI
41
Blastocladiella
britannica produces uniflagellate spores which subsequently give rise to larger, coenocytic plants. And, much like Rhizidiomyces in particular, its multinucleate thallus at maturity is globose—a
nearly perfect sphere in fact—and bears rhizoidal appendages. But in
the RS strain of the fungus, two, clear-cut, alternate developmental
paths exist. One of these leads to a thick-walled, brown, and pitted cell
(a resistant sporangium) ; the other is directed towards a thin-walled cell
which (vide Rhizidiomyces)
produces a long discharge tube. However, in
contrast to Rhizidiomyces,
the protoplast of B. britannica is cleaved into
spores within the parent cell ; it is the spores themselves, and not the
multinucleate protoplasts, which are discharged through exit tubes. On
solid media, the developmental route can be selected and controlled at
will by the simple expedient of providing or withholding illumination.
In the presence of white light, thin-walled cells are formed which
discharge spores; in its absence, the brown, pitted, resistant sporangial
cells appear instead. On the other hand, cells of the TW strain can only
embark upon the path which leads to the thin-walled cells, whether or
not light is provided. With the methods (Horenstein and Cantino, 1962)
worked out so far, all these things can be reproduced in agitated, liquid
cultures, wherein half a million spores or more are induced to germinate
simultaneously and to develop synchronously for a single generation
along one pathway or the other. The points of no return for both of the
ontogenetic routes have been established ; i.e., the stages in development
beyond which removal or imposition of illumination no longer causes a
shift from one morphogenetic pathway to the other.
With abundant plant material at any stage in ontogeny thus available
for chemical and enzymatic work on a per-cell basis, single-generation
cultures of B. britannica provide an ideal system for the definitive study
of a photomorphogenetic phenomenon.
III. Blastocladiella emersonii—a Model System for
Experimental Studies of Differentiation
By now, the reader is well aware that we have been trying to 'make a
pitch'—to wit: that large, synchronized, single-generation cultures of
non-filamentous water-fungi have a great deal to offer to the morphologist interested in the chemistry and physics of an organism, to the
chemist and the physicist who would like to apply his experiences and
skills to the solution of morphological problems, and to any experimentalist who wishes to pursue in depth the molecular basis for cell
differentiation. We are reminded of Knox's recent comment (Knox,
1961) to the effect that, while there has been much intensive study of
the chemistry of adaptive change, these efforts have involved very few
41
Blastocladiella
britannica produces uniflagellate spores which subsequently give rise to larger, coenocytic plants. And, much like Rhizidiomyces in particular, its multinucleate thallus at maturity is globose—a
nearly perfect sphere in fact—and bears rhizoidal appendages. But in
the RS strain of the fungus, two, clear-cut, alternate developmental
paths exist. One of these leads to a thick-walled, brown, and pitted cell
(a resistant sporangium) ; the other is directed towards a thin-walled cell
which (vide Rhizidiomyces)
produces a long discharge tube. However, in
contrast to Rhizidiomyces,
the protoplast of B. britannica is cleaved into
spores within the parent cell ; it is the spores themselves, and not the
multinucleate protoplasts, which are discharged through exit tubes. On
solid media, the developmental route can be selected and controlled at
will by the simple expedient of providing or withholding illumination.
In the presence of white light, thin-walled cells are formed which
discharge spores; in its absence, the brown, pitted, resistant sporangial
cells appear instead. On the other hand, cells of the TW strain can only
embark upon the path which leads to the thin-walled cells, whether or
not light is provided. With the methods (Horenstein and Cantino, 1962)
worked out so far, all these things can be reproduced in agitated, liquid
cultures, wherein half a million spores or more are induced to germinate
simultaneously and to develop synchronously for a single generation
along one pathway or the other. The points of no return for both of the
ontogenetic routes have been established ; i.e., the stages in development
beyond which removal or imposition of illumination no longer causes a
shift from one morphogenetic pathway to the other.
With abundant plant material at any stage in ontogeny thus available
for chemical and enzymatic work on a per-cell basis, single-generation
cultures of B. britannica provide an ideal system for the definitive study
of a photomorphogenetic phenomenon.
III. Blastocladiella emersonii—a Model System for
Experimental Studies of Differentiation
By now, the reader is well aware that we have been trying to 'make a
pitch'—to wit: that large, synchronized, single-generation cultures of
non-filamentous water-fungi have a great deal to offer to the morphologist interested in the chemistry and physics of an organism, to the
chemist and the physicist who would like to apply his experiences and
skills to the solution of morphological problems, and to any experimentalist who wishes to pursue in depth the molecular basis for cell
differentiation. We are reminded of Knox's recent comment (Knox,
1961) to the effect that, while there has been much intensive study of
the chemistry of adaptive change, these efforts have involved very few