78
EDWARD C. CANTINO AND JAMES S. LOVETT
Simultaneously, however, the activity of several enzymes levels off, that
of others decreases, the total soluble-protein remains constant but its
composition is altered, the pool of free amino-acids and orthophosphate
drops rapidly, and that of soluble organic phosphorus, adenine, and
some ribonucleotides increases. Most of these substances reach maximal
levels by 48 hours, but melanin, lipid, and RNA continue to increase to
at least 60 hours. This is hardly the picture of a static system !
1. RS Cells vs. Bacterial
Endospores
At this point, then, it is pertinent to ask : what purpose is served by
all this internal turmoil within the cell? To seek at least a partial answer,
it may be worthwhile to compare briefly the RS cell of
Blastocladiella
with resting cells in other organisms and with its homologue in the
closely-related, filamentous fungus Allomyces. In the latter, RS cells are
produced abundantly on the diploid sporophyte without special
treatment ; no exogenous bicarbonate inducer is required to trigger their
formation. In fact, thin-walled zoosporangia and resistant sporangia
frequently occur on the same plant. Although the RS cells on Allomyces
are smaller and different in shape than those of Blastocladiella,
they
share the same basic architecture; i.e., a thick pitted wall impregnated
with melanin. Indeed, the cytoplasm even contains carotene (Turian and
Cantino, 1959b), as is true for B. emersonii. Both can remain viable in an
air-dried condition for many years—fair testimony to their important
function of ensuring survival of the organism during periods of unfavourable environment.
From one important point of view, however, these two structures
appear to be significantly different. The RS cell in Allomyces is the seat
of meiosis in its life-history (Emerson and Wilson, 1949). The haploid
meiospores derived therefrom, instead of producing another parental
generation as does B. emersonii, give rise to a haploid gametophytic
generation. Thus, in Allomyces the RS cell serves two functions: it tides
the fungus over adverse conditions, and it houses its mechanism for
chromosome reduction. Blastocladiella,
on the other hand, clearly has
retained the first function but, to all intents and purposes, has lost the
second. Although B. emersonii does form orange (male?) thalli which
indulge in a non-conventional and seemingly perverse sort of "sex'
(Cantino and Hyatt, 1953a; Cantino and Horenstein, 1954), it never
displays its gender in the customary way. It would be most interesting
to know if its loss of functional sexuality occurred concomitantly with
acquisition of its bicarbonate response or, alternatively if they arose
independently. In this sense, it is perhaps worth emphasizing that
Blastocladia (see Section II, B), which is even more sexless than Blastocladiella in that it produces no orange plants at all, forms RS cells only
EDWARD C. CANTINO AND JAMES S. LOVETT
Simultaneously, however, the activity of several enzymes levels off, that
of others decreases, the total soluble-protein remains constant but its
composition is altered, the pool of free amino-acids and orthophosphate
drops rapidly, and that of soluble organic phosphorus, adenine, and
some ribonucleotides increases. Most of these substances reach maximal
levels by 48 hours, but melanin, lipid, and RNA continue to increase to
at least 60 hours. This is hardly the picture of a static system !
1. RS Cells vs. Bacterial
Endospores
At this point, then, it is pertinent to ask : what purpose is served by
all this internal turmoil within the cell? To seek at least a partial answer,
it may be worthwhile to compare briefly the RS cell of
Blastocladiella
with resting cells in other organisms and with its homologue in the
closely-related, filamentous fungus Allomyces. In the latter, RS cells are
produced abundantly on the diploid sporophyte without special
treatment ; no exogenous bicarbonate inducer is required to trigger their
formation. In fact, thin-walled zoosporangia and resistant sporangia
frequently occur on the same plant. Although the RS cells on Allomyces
are smaller and different in shape than those of Blastocladiella,
they
share the same basic architecture; i.e., a thick pitted wall impregnated
with melanin. Indeed, the cytoplasm even contains carotene (Turian and
Cantino, 1959b), as is true for B. emersonii. Both can remain viable in an
air-dried condition for many years—fair testimony to their important
function of ensuring survival of the organism during periods of unfavourable environment.
From one important point of view, however, these two structures
appear to be significantly different. The RS cell in Allomyces is the seat
of meiosis in its life-history (Emerson and Wilson, 1949). The haploid
meiospores derived therefrom, instead of producing another parental
generation as does B. emersonii, give rise to a haploid gametophytic
generation. Thus, in Allomyces the RS cell serves two functions: it tides
the fungus over adverse conditions, and it houses its mechanism for
chromosome reduction. Blastocladiella,
on the other hand, clearly has
retained the first function but, to all intents and purposes, has lost the
second. Although B. emersonii does form orange (male?) thalli which
indulge in a non-conventional and seemingly perverse sort of "sex'
(Cantino and Hyatt, 1953a; Cantino and Horenstein, 1954), it never
displays its gender in the customary way. It would be most interesting
to know if its loss of functional sexuality occurred concomitantly with
acquisition of its bicarbonate response or, alternatively if they arose
independently. In this sense, it is perhaps worth emphasizing that
Blastocladia (see Section II, B), which is even more sexless than Blastocladiella in that it produces no orange plants at all, forms RS cells only