86
EDWARD C. CANTINO AND JAMES S. LOVETT
RS cells of the closely related B. britannica (Horenstein and Cantino,
unpublished notes). Presumably, the events which precede cracking
are in some way associated with the breaking of dormancy and activation of the metabolic system. The phenomena which follow, and which
lead to or are associated with differentiation of the spores, may be
similar in many respects—if not all of them—to those involved in
sporogenesis of OC cells.
Because of the paucity of definitive information about spore formation
in Blastocladiella, we must rely for the moment on the results of a careful
study of gametogenesis in Allomyces (Blondel and Turian, 1960). The
basic similarity in apparent structure in the spores of these two organisms
encourages us to assume that the pattern shown by one will hold true in
many respects for the other. A brief summary of the observations made
by Blondel and Turian follows (for general discussion, see Cantino and
Turian, 1959).
After septation in the multinucleate garnetangial cells, numerous lipid
globules appear in the region immediately surrounding each nucleus;
this was labelled the 'lipid crown stage' (this unusual condition is also
seen in stained preparations of the OC cells of Blastocladiella).
Following
this, basophilic material (150-200 Â diameter particles) in the cytoplasm
—which up to this time had been dispersed uniformly—begins to
aggregate in the regions of the presumptive spore nuclei. Finally, this
results in the formation of a very dense region which is surrounded by a
double-layered cytoplasmic membrane, and contains substantially all
the basophilic material of the cell. Formation of the characteristic
nuclear cap is thus completed. While these events are going on,
membranes are laid down which delimit the nuclei and their adjacent
cytoplasm into individual packets ; flagella also make their appearance.
In the gametes which result, a layer of small mitochondria and lipid
globules surrounds the nuclear cap. The entire process described above,
from lipid crown stage to genesis of complete gametes, is accomplished
in about an hour.
The formation of zoospores in B. emersonii has not yet been examined
in great detail; however, work has been done on their ultrastructure
(cf. Section III, A, and Fig. 3). As a result, we know that two prominent
differences distinguish the gametes of Allomyces from the spores of
Blastocladiella. First, while gametes bear numerous small mitochondria
which surround the nuclear cap, zoospores possess only one very large
mitochondrion, densely packed with cristae, which is located at the base
and to one side of the nucleus. Second, in contrast to Allomyces, the
lipid globules in the spores of Blastocladiella are restricted to a narrow
region in the cell, where they lie in intimate association with the single
mitochondrion. Until the zoospores of Allomyces have been examined in
EDWARD C. CANTINO AND JAMES S. LOVETT
RS cells of the closely related B. britannica (Horenstein and Cantino,
unpublished notes). Presumably, the events which precede cracking
are in some way associated with the breaking of dormancy and activation of the metabolic system. The phenomena which follow, and which
lead to or are associated with differentiation of the spores, may be
similar in many respects—if not all of them—to those involved in
sporogenesis of OC cells.
Because of the paucity of definitive information about spore formation
in Blastocladiella, we must rely for the moment on the results of a careful
study of gametogenesis in Allomyces (Blondel and Turian, 1960). The
basic similarity in apparent structure in the spores of these two organisms
encourages us to assume that the pattern shown by one will hold true in
many respects for the other. A brief summary of the observations made
by Blondel and Turian follows (for general discussion, see Cantino and
Turian, 1959).
After septation in the multinucleate garnetangial cells, numerous lipid
globules appear in the region immediately surrounding each nucleus;
this was labelled the 'lipid crown stage' (this unusual condition is also
seen in stained preparations of the OC cells of Blastocladiella).
Following
this, basophilic material (150-200 Â diameter particles) in the cytoplasm
—which up to this time had been dispersed uniformly—begins to
aggregate in the regions of the presumptive spore nuclei. Finally, this
results in the formation of a very dense region which is surrounded by a
double-layered cytoplasmic membrane, and contains substantially all
the basophilic material of the cell. Formation of the characteristic
nuclear cap is thus completed. While these events are going on,
membranes are laid down which delimit the nuclei and their adjacent
cytoplasm into individual packets ; flagella also make their appearance.
In the gametes which result, a layer of small mitochondria and lipid
globules surrounds the nuclear cap. The entire process described above,
from lipid crown stage to genesis of complete gametes, is accomplished
in about an hour.
The formation of zoospores in B. emersonii has not yet been examined
in great detail; however, work has been done on their ultrastructure
(cf. Section III, A, and Fig. 3). As a result, we know that two prominent
differences distinguish the gametes of Allomyces from the spores of
Blastocladiella. First, while gametes bear numerous small mitochondria
which surround the nuclear cap, zoospores possess only one very large
mitochondrion, densely packed with cristae, which is located at the base
and to one side of the nucleus. Second, in contrast to Allomyces, the
lipid globules in the spores of Blastocladiella are restricted to a narrow
region in the cell, where they lie in intimate association with the single
mitochondrion. Until the zoospores of Allomyces have been examined in