NON-FILAMENTOUS AQUATIC FUNGI
83
encourage a continued search for further understanding of such a
general morphogenetic mechanism.
2. Intracellular Events and Ultimate Function in an RS Cell
We should like to turn our attention, now, to the intracellular events
which are directed toward the ultimate function of the RS cell, whether
or not it has properly done its job in bearing the brunt of adverse
environmental conditions; that is, its ultimate role as the producer of
the next generation of spores. A structure of major consequence is the
nuclear cap (see Section III, A). It is known that in Allomyces, basophilic
material aggregates in the form of organelles, called chromospheres,
when meiospores are differentiated within the RS cell (Wilson, 1952).
Such chromospheres, when isolated and analysed (Rorem and Machlis,
1957), contained 12% RNA and 60% protein. It was suggested that
these structures were the precursors of the nuclear caps finally laid down
in meiospores, a proposal reinforced by cytochemical demonstrations
that RNA occurs in the nuclear caps of motile gametes (Turian, 1955,
1956). Subsequent work confirmed these observations (Turian, 1956,
1958; Blondel and Turian, 1960) and led to the further thought (hinted
at by Rorem and Machlis) that the nuclear cap might be an aggregate of
ribosomes.
Because of the potential significance of the origin and function of such
organelles in interpretations of morphogenesis, we looked for RNA
transformations in maturing RS cells (Cantino, 1961b). In brief,
synthesis of total RNA continues until the RS cell is nearly mature.
However, this RNA consists of both NaCl-soluble and NaCl-insoluble
fractions. Soon after the morphogenetic point of no return, the NaClinsoluble RNA begins to accumulate linearly up to ca. 60 hours. During
this same period in ontogeny, the NaCl-soluble RNA (which includes
essentially all the RNA in a young RS cell at 30 hours) decreases to about
half of its original level. At the end of this transformation, the base
ratios of the NaCl-soluble RNA which remains in the RS cell are the
same as those of the newly-formed NaCl-insoluble RNA; all four
nucleotides are present in equimolar quantities. And yet, before the
point of no return, the base ratios of the NaCl-soluble RNA are unequal
(CMP : AMP : UMP : GMP, 1 00 : 1-33 : 1 08 : 1-27), as they are in the
NaCl-soluble RNA extractable from an OC cell (Cantino, 1961b) and
also (Lovett, 1963) from the zoospore itself. (Incidentally, Heyes' recent
observations on expanding root-cells provokes a quick comparison:
during the increase in RNA per cell, its base composition also changes
and is due to an alteration in the proportion of two kinds of RNA with
different extraction properties.)
The coincident increase in both the NaCl-insoluble RNA fraction and
83
encourage a continued search for further understanding of such a
general morphogenetic mechanism.
2. Intracellular Events and Ultimate Function in an RS Cell
We should like to turn our attention, now, to the intracellular events
which are directed toward the ultimate function of the RS cell, whether
or not it has properly done its job in bearing the brunt of adverse
environmental conditions; that is, its ultimate role as the producer of
the next generation of spores. A structure of major consequence is the
nuclear cap (see Section III, A). It is known that in Allomyces, basophilic
material aggregates in the form of organelles, called chromospheres,
when meiospores are differentiated within the RS cell (Wilson, 1952).
Such chromospheres, when isolated and analysed (Rorem and Machlis,
1957), contained 12% RNA and 60% protein. It was suggested that
these structures were the precursors of the nuclear caps finally laid down
in meiospores, a proposal reinforced by cytochemical demonstrations
that RNA occurs in the nuclear caps of motile gametes (Turian, 1955,
1956). Subsequent work confirmed these observations (Turian, 1956,
1958; Blondel and Turian, 1960) and led to the further thought (hinted
at by Rorem and Machlis) that the nuclear cap might be an aggregate of
ribosomes.
Because of the potential significance of the origin and function of such
organelles in interpretations of morphogenesis, we looked for RNA
transformations in maturing RS cells (Cantino, 1961b). In brief,
synthesis of total RNA continues until the RS cell is nearly mature.
However, this RNA consists of both NaCl-soluble and NaCl-insoluble
fractions. Soon after the morphogenetic point of no return, the NaClinsoluble RNA begins to accumulate linearly up to ca. 60 hours. During
this same period in ontogeny, the NaCl-soluble RNA (which includes
essentially all the RNA in a young RS cell at 30 hours) decreases to about
half of its original level. At the end of this transformation, the base
ratios of the NaCl-soluble RNA which remains in the RS cell are the
same as those of the newly-formed NaCl-insoluble RNA; all four
nucleotides are present in equimolar quantities. And yet, before the
point of no return, the base ratios of the NaCl-soluble RNA are unequal
(CMP : AMP : UMP : GMP, 1 00 : 1-33 : 1 08 : 1-27), as they are in the
NaCl-soluble RNA extractable from an OC cell (Cantino, 1961b) and
also (Lovett, 1963) from the zoospore itself. (Incidentally, Heyes' recent
observations on expanding root-cells provokes a quick comparison:
during the increase in RNA per cell, its base composition also changes
and is due to an alteration in the proportion of two kinds of RNA with
different extraction properties.)
The coincident increase in both the NaCl-insoluble RNA fraction and