NON-FILAMENTOUS AQUATIC
FUNGI
47
Finally, a word or two about the chemical composition of these various
organelles is appropriate here. The spores contain approximately 15 /xg
of DNA and some 220 />tg of RNA per mg dry wt. (Turian and Cantino,
1959a). Judging from early cytochemical observations, the Feulgennegative nuclear cap in the swarmers of the related Allomyces is largely
RNA (Turian, 1956, 1958). For B. emersonii, the same conclusion can be
drawn, but on the basis of chemical rather than cytological parameters.
Clean nuclear caps, devoid of contaminating cytoplasm, nuclei, and
nucleoli, have actually been isolated in sufficient quantity to permit
direct chemical and physical analyses (Lovett, 1963). The isolated caps
contain 40% RNA and 60% protein; they account for some 18% of the
total dry mass, and 69% of the total RNA of the spore. The amino-acid
composition of whole nuclear caps is very similar to that reported for
ribosomes from a variety of higher and lower organisms. The contents of
the isolated nuclear caps have also been extracted and found to consist
of small ribonucleoprotein particles quite uniform in size. At a magnesium
concentration of 0-005M, practically all of these particles have a
sedimentation coefficient of 835. They contain 63% RNA, 37% protein,
latent ribonuclease, and an RNA base ratio (CMP: AMP: UMP: GMP;
1·00: 1-42: 1-27: 1-72) similar to ribosomes isolated from many sources.
These results leave very little doubt in our minds that the nuclear cap
in the spore of Blastocladiella is a 'package' of ribosomes. On the basis of
more indirect evidence from cytochemistry and electron microscopy,
Blondel and Turian (1960) recently suggested that the caps in the
gametes of Allomyces are also nucleoprotein organelles.
It is important to emphasize (a) that the cellular framework described
in the foregoing paragraphs—and in particular, the nuclear cap—exists
only in the spore and nowhere else; and (b) that this arrangement of
organelles is maintained only so long as the spore retains its flagellum
and does not germinate. Thus, a major question naturally arises: what
is the significance of this internal superstructure for the swimming
spore? While we cannot supply an answer that is plain and positive, we
can—and would like to try to—make a guess.
The length of time the spore will swim about can vary widely. If the
spore is placed in water and thus deprived of all exogenous nutrition, it
can swim about continuously for hours. Surely, in a state of such apparent
restlessness, the spore mass (initially, ca. 1-13 χ 10
_4
/xg; Lovett and
Cantino, 1960b) must decrease greatly, for its endogenous Q 02 is at least
100 at the start (McCurdy and Cantino, 1960; Cantino and Lovett,
1960).
But in any case, with all of this activity, the spore must be well
supplied with (a) a potential pool of chemical energy capable of providing
rather long-range maintenance requirements; (b) the enzymatic
FUNGI
47
Finally, a word or two about the chemical composition of these various
organelles is appropriate here. The spores contain approximately 15 /xg
of DNA and some 220 />tg of RNA per mg dry wt. (Turian and Cantino,
1959a). Judging from early cytochemical observations, the Feulgennegative nuclear cap in the swarmers of the related Allomyces is largely
RNA (Turian, 1956, 1958). For B. emersonii, the same conclusion can be
drawn, but on the basis of chemical rather than cytological parameters.
Clean nuclear caps, devoid of contaminating cytoplasm, nuclei, and
nucleoli, have actually been isolated in sufficient quantity to permit
direct chemical and physical analyses (Lovett, 1963). The isolated caps
contain 40% RNA and 60% protein; they account for some 18% of the
total dry mass, and 69% of the total RNA of the spore. The amino-acid
composition of whole nuclear caps is very similar to that reported for
ribosomes from a variety of higher and lower organisms. The contents of
the isolated nuclear caps have also been extracted and found to consist
of small ribonucleoprotein particles quite uniform in size. At a magnesium
concentration of 0-005M, practically all of these particles have a
sedimentation coefficient of 835. They contain 63% RNA, 37% protein,
latent ribonuclease, and an RNA base ratio (CMP: AMP: UMP: GMP;
1·00: 1-42: 1-27: 1-72) similar to ribosomes isolated from many sources.
These results leave very little doubt in our minds that the nuclear cap
in the spore of Blastocladiella is a 'package' of ribosomes. On the basis of
more indirect evidence from cytochemistry and electron microscopy,
Blondel and Turian (1960) recently suggested that the caps in the
gametes of Allomyces are also nucleoprotein organelles.
It is important to emphasize (a) that the cellular framework described
in the foregoing paragraphs—and in particular, the nuclear cap—exists
only in the spore and nowhere else; and (b) that this arrangement of
organelles is maintained only so long as the spore retains its flagellum
and does not germinate. Thus, a major question naturally arises: what
is the significance of this internal superstructure for the swimming
spore? While we cannot supply an answer that is plain and positive, we
can—and would like to try to—make a guess.
The length of time the spore will swim about can vary widely. If the
spore is placed in water and thus deprived of all exogenous nutrition, it
can swim about continuously for hours. Surely, in a state of such apparent
restlessness, the spore mass (initially, ca. 1-13 χ 10
_4
/xg; Lovett and
Cantino, 1960b) must decrease greatly, for its endogenous Q 02 is at least
100 at the start (McCurdy and Cantino, 1960; Cantino and Lovett,
1960).
But in any case, with all of this activity, the spore must be well
supplied with (a) a potential pool of chemical energy capable of providing
rather long-range maintenance requirements; (b) the enzymatic