NON-FILAMENTOUS AQUATIC FUNGI
69
1. The Point of No Return in RS
Morphogenesis
When these studies of Blastocladiella
were begun, the multiple
generation cultures then in use imposed a severe restriction upon what
could be done, and biochemical studies of RS morphogenesis had to be
limited to the terminal stages in development (Cantino, 1956). Nonetheless, with them it was shown that the bicarbonate-induced pathway led
to the formation of an RS cell possessing a thick, pitted, chitinous, wall
impregnated with melanin (Fig. 2). Such cells contained obvious lipid
globules and y-carotene, had a very low respiratory rate, lacked aketoglutaric dehydrogenase and cytochrome oxidase activities, and
possessed other characteristics not shared by OC cells (Cantino and
Turian, 1959).
When synchronous culture techniques were devised however, :t
became possible to follow the complete cycle through a single generation
of RS cells, and furthermore, to do this under conditions where large
samples of a single, synchronized RS population could be removed and
analysed as a function of time and stage in development. Under these
conditions (i.e., 10
7 cells/litre of a vigorously-aerated medium containing
8-9 χ ΙΟ
-3 M sodium bicarbonate at 24° C; Lovett and Cantino, 1960b),
growth in size stops at 36 hours, or 43% of the cell's normal 84-hour
generation time. Dry weight per cell, on the other hand, continues to
increase up to 48 hours. An important point, here, is that termination of
increase in size corresponds exactly with (a) the completion of a crosswall (the formation of which begins at 32 hours) delimiting the terminal
RS cell, and (b) the time at which the cell becomes irreversibly committed to RS formation (Lovett and Cantino, 1960b). Many other
striking events occur at this time. For example (see Fig. 5), intracellular
pools of soluble amino-acids and inorganic phosphorus start to drop
rapidly; oxygen consumption, already greatly depressed relative to its
original level in the spore, begins to decline further; net synthesis of
protein and DNA stops ; and the activity of many enzymes decreases.
During the same period, however, synthesis of chitin, lipid, melanin,
polysaccharide and RNA continues for some time without interruption
(Cantino and Lovett, 1960; Lovett and Cantino, 1960b; McCurdy and
Cantino, 1960; Cantino, 1961a, b; Cantino and Goldstein, 1961). This
recitation of the changes known to occur is far from complete; it is
enough, however, to emphasize that a high degree of biochemical
differentiation is associated with formation of the cross-wall and
morphological differentiation and that together, these somehow
culminate in the establishment of an irreversible, morphogenetic
system.
69
1. The Point of No Return in RS
Morphogenesis
When these studies of Blastocladiella
were begun, the multiple
generation cultures then in use imposed a severe restriction upon what
could be done, and biochemical studies of RS morphogenesis had to be
limited to the terminal stages in development (Cantino, 1956). Nonetheless, with them it was shown that the bicarbonate-induced pathway led
to the formation of an RS cell possessing a thick, pitted, chitinous, wall
impregnated with melanin (Fig. 2). Such cells contained obvious lipid
globules and y-carotene, had a very low respiratory rate, lacked aketoglutaric dehydrogenase and cytochrome oxidase activities, and
possessed other characteristics not shared by OC cells (Cantino and
Turian, 1959).
When synchronous culture techniques were devised however, :t
became possible to follow the complete cycle through a single generation
of RS cells, and furthermore, to do this under conditions where large
samples of a single, synchronized RS population could be removed and
analysed as a function of time and stage in development. Under these
conditions (i.e., 10
7 cells/litre of a vigorously-aerated medium containing
8-9 χ ΙΟ
-3 M sodium bicarbonate at 24° C; Lovett and Cantino, 1960b),
growth in size stops at 36 hours, or 43% of the cell's normal 84-hour
generation time. Dry weight per cell, on the other hand, continues to
increase up to 48 hours. An important point, here, is that termination of
increase in size corresponds exactly with (a) the completion of a crosswall (the formation of which begins at 32 hours) delimiting the terminal
RS cell, and (b) the time at which the cell becomes irreversibly committed to RS formation (Lovett and Cantino, 1960b). Many other
striking events occur at this time. For example (see Fig. 5), intracellular
pools of soluble amino-acids and inorganic phosphorus start to drop
rapidly; oxygen consumption, already greatly depressed relative to its
original level in the spore, begins to decline further; net synthesis of
protein and DNA stops ; and the activity of many enzymes decreases.
During the same period, however, synthesis of chitin, lipid, melanin,
polysaccharide and RNA continues for some time without interruption
(Cantino and Lovett, 1960; Lovett and Cantino, 1960b; McCurdy and
Cantino, 1960; Cantino, 1961a, b; Cantino and Goldstein, 1961). This
recitation of the changes known to occur is far from complete; it is
enough, however, to emphasize that a high degree of biochemical
differentiation is associated with formation of the cross-wall and
morphological differentiation and that together, these somehow
culminate in the establishment of an irreversible, morphogenetic
system.