Ν ON-FILAMENTOUS AQUATIC FUNGI
81
the RS cell (at which time, vigorous lactic acid production occurs;
Cantino and Goldstein, 1961) while the cytochrome oxidase therein is nil
(Cantino and Hyatt, 1953c).
Perhaps it would be too much to ask that the correlation found in
bacteria between the degree of dormancy and the presence of dipicolinic
acid (Powell, 1953) apply as well to Blastocladiella;
unfortunately, we
have not been able to detect this acid in RS cells (Cantino, unpublished
notes).
Another piece of evidence, while having nothing to do directly with
sporulation, might help plug some gaps in this puzzle. Ephrussi and
Slonimski (1950) demonstrated that in yeast, a cytochrome system is
lost during cellular adaptation to anaerobic growth, but that it can be
induced to reappear by placing the organism once again under aerobic
conditions. This observation may be relèvent to the loss of the cytochrome system in a dormant cell. One possible explanation invokes the
thought that this terminal electron transport system is inducible by
oxygen and/or repressed by bicarbonate (and/or carbon dioxide). If a
cell is removed from its exogenous supply of oxygen (as in yeast), or if,
alternatively, the cell's wall simply becomes thick and impermeable to
it (as may possibly be true for Blastocladiella,
bacteria, and/or Neurospora), the presence of increased concentrations of bicarbonate (or C0 2 )
and/or lower partial pressures of oxygen might either repress activity of
the cytochrome oxidase pathway, or somehow lead to its destruction.
In cases of extensive turnover occurring during sporulation, the net
result could be its loss. Whether or not such a control system exists
remains to be determined, but such a regulatory role for C0 2 and/or
bicarbonate would fit well with our ideas ; it would provide, as well, a
mechanism for control of terminal electron transport under conditions
where the latter becomes superfluous—or even deleterious—to the cell.
The impressive way in which an increase in the concentration of the
bicarbonate inducer (above that needed for normal RS cells) brings
about additional abnormal thickening of the characteristic chitinous
wall appears, so far, to be unique for Blastocladiella (Lovett and Cantino,
1960c). The quantitative nature of the response suggests that chitin
synthesis, though obviously constitutive in that it occurs in OC cells as
well, exemplifies yet another biosynthetic pathway subject to the
regulatory influence of bicarbonate during morphogenesis. There is no
way of knowing, at the moment, if bicarbonate exerts its effect directly
upon the rate of chitin synthesis, or if it does so indirectly by an alteration in some other system—one which might, for instance, simply
provide increased quantities of essential substrates. In any event, if a
higher order of genetic regulation of development is involved in
Blastocladiella,
as suggested earlier, this flexible and experimentally
81
the RS cell (at which time, vigorous lactic acid production occurs;
Cantino and Goldstein, 1961) while the cytochrome oxidase therein is nil
(Cantino and Hyatt, 1953c).
Perhaps it would be too much to ask that the correlation found in
bacteria between the degree of dormancy and the presence of dipicolinic
acid (Powell, 1953) apply as well to Blastocladiella;
unfortunately, we
have not been able to detect this acid in RS cells (Cantino, unpublished
notes).
Another piece of evidence, while having nothing to do directly with
sporulation, might help plug some gaps in this puzzle. Ephrussi and
Slonimski (1950) demonstrated that in yeast, a cytochrome system is
lost during cellular adaptation to anaerobic growth, but that it can be
induced to reappear by placing the organism once again under aerobic
conditions. This observation may be relèvent to the loss of the cytochrome system in a dormant cell. One possible explanation invokes the
thought that this terminal electron transport system is inducible by
oxygen and/or repressed by bicarbonate (and/or carbon dioxide). If a
cell is removed from its exogenous supply of oxygen (as in yeast), or if,
alternatively, the cell's wall simply becomes thick and impermeable to
it (as may possibly be true for Blastocladiella,
bacteria, and/or Neurospora), the presence of increased concentrations of bicarbonate (or C0 2 )
and/or lower partial pressures of oxygen might either repress activity of
the cytochrome oxidase pathway, or somehow lead to its destruction.
In cases of extensive turnover occurring during sporulation, the net
result could be its loss. Whether or not such a control system exists
remains to be determined, but such a regulatory role for C0 2 and/or
bicarbonate would fit well with our ideas ; it would provide, as well, a
mechanism for control of terminal electron transport under conditions
where the latter becomes superfluous—or even deleterious—to the cell.
The impressive way in which an increase in the concentration of the
bicarbonate inducer (above that needed for normal RS cells) brings
about additional abnormal thickening of the characteristic chitinous
wall appears, so far, to be unique for Blastocladiella (Lovett and Cantino,
1960c). The quantitative nature of the response suggests that chitin
synthesis, though obviously constitutive in that it occurs in OC cells as
well, exemplifies yet another biosynthetic pathway subject to the
regulatory influence of bicarbonate during morphogenesis. There is no
way of knowing, at the moment, if bicarbonate exerts its effect directly
upon the rate of chitin synthesis, or if it does so indirectly by an alteration in some other system—one which might, for instance, simply
provide increased quantities of essential substrates. In any event, if a
higher order of genetic regulation of development is involved in
Blastocladiella,
as suggested earlier, this flexible and experimentally