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EDWARD C. CANTINO AND JAMES S. LOVETT
(e) At this stage, using the nuclear cap and the refractile granules on
the mitochondrion as the most suitable markers, the following events
occur. The nuclear cap rotates within the cell (through 270 degrees or more)
and turns in an opposite direction to the curve of the flagellum. Simultaneously, the flagellum gets shorter and eventually disappears within
the body of the cell. During the rotation of the cap, the spore itself does
not turn. Similarly, the granules attached to the giant mitochondrion do
not move significantly from their original position until the cap has
finished turning; at that time, the granules lose their grouping and
become dispersed more or less in a curved line through the cytoplasm of
the cell. It has been revealed by electron microscopy that, at this stage,
the mitochondrion begins to change in texture and in shape.
(f) The cell, now a perfect sphere, remains in this position until the
first germ tube—the precursor of the cell's rhizoidal system—makes its
appearance. By this time, the nuclear cap has completely disappeared.
This rather startling series of events occurs in a very short period—a
matter of minutes under normal circumstances—in the life of the
organism. And yet, it has raised so many questions, most of them as yet
unanswered, that this phase of ontogeny deserves serious attention as a
major research project.
What sort of trigger mechanism induces the sequence of flagellar
movements to begin with? We do not know, and comparative biology
does not shed much light upon the mystery. The internal rotation of the
cap and its associated nuclear apparatus, without a corresponding
twisting of the spore itself, and the irreversible retraction of the tail
which immediately ensues, represent a point of no return for the spore.
It is most tempting to look upon the rotation of the nuclear assembly as
the causa sine qua non for retraction of the tail, and thus for germination.
Indeed, the reciprocal or complimentary relationship between the
sudden twist of the flagellum, and the rotation of the cap in an opposite
direction could be interpreted to mean that the nuclear apparatus and
its associated cap is winding in the tail. This may, in fact, not be quite as
absurd as it may sound, for certain observations with the electron
microscope would be consistent with the thought ; the evidence, however,
is insufficient and the question remains unresolved.
We may also ask : what induces the sudden dissolution of the nuclear
cap after the flagellum has been retracted? Without retraction of the
tail, the cap never disappears; following retraction, it always does so.
It thus appears as if an obligatory sequence of events is involved. Does
this exclusive package of ribosomes simply play a passive role until the
flagellum is absorbed, or does it also function in some active way in its
intact form? Does this massive ribosomal aggregate control amino-acid
sequences if, indeed, protein synthesis and turnover does occur within
EDWARD C. CANTINO AND JAMES S. LOVETT
(e) At this stage, using the nuclear cap and the refractile granules on
the mitochondrion as the most suitable markers, the following events
occur. The nuclear cap rotates within the cell (through 270 degrees or more)
and turns in an opposite direction to the curve of the flagellum. Simultaneously, the flagellum gets shorter and eventually disappears within
the body of the cell. During the rotation of the cap, the spore itself does
not turn. Similarly, the granules attached to the giant mitochondrion do
not move significantly from their original position until the cap has
finished turning; at that time, the granules lose their grouping and
become dispersed more or less in a curved line through the cytoplasm of
the cell. It has been revealed by electron microscopy that, at this stage,
the mitochondrion begins to change in texture and in shape.
(f) The cell, now a perfect sphere, remains in this position until the
first germ tube—the precursor of the cell's rhizoidal system—makes its
appearance. By this time, the nuclear cap has completely disappeared.
This rather startling series of events occurs in a very short period—a
matter of minutes under normal circumstances—in the life of the
organism. And yet, it has raised so many questions, most of them as yet
unanswered, that this phase of ontogeny deserves serious attention as a
major research project.
What sort of trigger mechanism induces the sequence of flagellar
movements to begin with? We do not know, and comparative biology
does not shed much light upon the mystery. The internal rotation of the
cap and its associated nuclear apparatus, without a corresponding
twisting of the spore itself, and the irreversible retraction of the tail
which immediately ensues, represent a point of no return for the spore.
It is most tempting to look upon the rotation of the nuclear assembly as
the causa sine qua non for retraction of the tail, and thus for germination.
Indeed, the reciprocal or complimentary relationship between the
sudden twist of the flagellum, and the rotation of the cap in an opposite
direction could be interpreted to mean that the nuclear apparatus and
its associated cap is winding in the tail. This may, in fact, not be quite as
absurd as it may sound, for certain observations with the electron
microscope would be consistent with the thought ; the evidence, however,
is insufficient and the question remains unresolved.
We may also ask : what induces the sudden dissolution of the nuclear
cap after the flagellum has been retracted? Without retraction of the
tail, the cap never disappears; following retraction, it always does so.
It thus appears as if an obligatory sequence of events is involved. Does
this exclusive package of ribosomes simply play a passive role until the
flagellum is absorbed, or does it also function in some active way in its
intact form? Does this massive ribosomal aggregate control amino-acid
sequences if, indeed, protein synthesis and turnover does occur within