NON-FILAMENTOUS AQUATIC FUNGI
79
if provided with extraordinarily high levels of C0 2 . At the moment, these
observations are no more than correlations, but they may be worthy of
further experimental exploration.
Even if we assume that the RS cell of B. emersonii functions primarily
as a dormant resistant structure, we must keep the possibility in mind
that it may go through some of the motions, so to speak—however
ineffectual they may be—associated with a previous sexual function lost
somewhere along the evolutionary line. But, whatever types of nuclear
divisions are involved, the RS cell nevertheless ultimately produces
typical uniflagellate spores with nuclear caps as found in all motile
cells—gametes as well as spores—in the family Blastocladiaceae.
Aside from Allomyces, practically nothing is known concerning the
physiology of the resting spore in other aquatic fungi, thus virtually
eliminating any comparative biological help from organisms in related
quarters. Among the higher fungi, Neurospora is the only creature with
resistant dormant spores that have been well-studied experimentally.
Its ascospores result directly from meiosis. However, no significant
attention has been devoted to physiological and biochemical studies on
the origin of the dormant ascospore itself, although a great deal of it has
been devoted to germination and, in particular, the triggering effects of
heat and chemicals (Goddard, 1939; Sussman, 1961). A dormant
ascospore shares certain attributes with a resistant sporangium; i.e., a
low respiratory rate, depressed enzyme activity, and a melanized wall.
Its requirement of a heat shock (or a chemical substitute) for germination, on the other hand, differentiates it from the RS cell of B. emersonii.
This brief mention of the ascospore cannot help but bring to mind the
bacterial endospore, the most intensively studied resistant structure
produced by any micro-organism. Superficially at least, the exogenous
condition needed for endospore induction in some bacteria is also vastly
different from that required by Blastocladiella.
In Bacillus mycoides, for
example, sporulation is induced by aeration in distilled water (Hardwick
and Foster, 1953), the very treatment that reverses RS induction in
Blastocladiella! This alone might well suggest that the bacterial trigger
mechanism is quite different. This and other differences in the conditions
required for sporulation by bacteria and B. emersonii, however, may
serve to distract attention from less conspicuous and more subtle
similarities, some of which might imply a more widespread duplication
of basic processes between these two kinds of organism. The most
obvious differences may often be the most superficial, and can simply
represent alternative devices which ensure the same result in ecological
niches of widely different sorts. Thus, with respect to the issue which
confronts us now—that is, dormancy—we should try to avoid those
79
if provided with extraordinarily high levels of C0 2 . At the moment, these
observations are no more than correlations, but they may be worthy of
further experimental exploration.
Even if we assume that the RS cell of B. emersonii functions primarily
as a dormant resistant structure, we must keep the possibility in mind
that it may go through some of the motions, so to speak—however
ineffectual they may be—associated with a previous sexual function lost
somewhere along the evolutionary line. But, whatever types of nuclear
divisions are involved, the RS cell nevertheless ultimately produces
typical uniflagellate spores with nuclear caps as found in all motile
cells—gametes as well as spores—in the family Blastocladiaceae.
Aside from Allomyces, practically nothing is known concerning the
physiology of the resting spore in other aquatic fungi, thus virtually
eliminating any comparative biological help from organisms in related
quarters. Among the higher fungi, Neurospora is the only creature with
resistant dormant spores that have been well-studied experimentally.
Its ascospores result directly from meiosis. However, no significant
attention has been devoted to physiological and biochemical studies on
the origin of the dormant ascospore itself, although a great deal of it has
been devoted to germination and, in particular, the triggering effects of
heat and chemicals (Goddard, 1939; Sussman, 1961). A dormant
ascospore shares certain attributes with a resistant sporangium; i.e., a
low respiratory rate, depressed enzyme activity, and a melanized wall.
Its requirement of a heat shock (or a chemical substitute) for germination, on the other hand, differentiates it from the RS cell of B. emersonii.
This brief mention of the ascospore cannot help but bring to mind the
bacterial endospore, the most intensively studied resistant structure
produced by any micro-organism. Superficially at least, the exogenous
condition needed for endospore induction in some bacteria is also vastly
different from that required by Blastocladiella.
In Bacillus mycoides, for
example, sporulation is induced by aeration in distilled water (Hardwick
and Foster, 1953), the very treatment that reverses RS induction in
Blastocladiella! This alone might well suggest that the bacterial trigger
mechanism is quite different. This and other differences in the conditions
required for sporulation by bacteria and B. emersonii, however, may
serve to distract attention from less conspicuous and more subtle
similarities, some of which might imply a more widespread duplication
of basic processes between these two kinds of organism. The most
obvious differences may often be the most superficial, and can simply
represent alternative devices which ensure the same result in ecological
niches of widely different sorts. Thus, with respect to the issue which
confronts us now—that is, dormancy—we should try to avoid those