56
EDWARD C. CANTINO AND JAMES S. LOVETT
relative rates of synthesis of enzymes and other macromolecules and
metabolic products. Not long ago, Cohn (1957) suggested in his discussion of differential rates of protein synthesis that, ideally, one should
study enzyme formation in a single, growing cell. For all intents and
purposes, synchronized single generations of Blastocladiella provide this
very thing.
In this connection, one last thought may be appropriate. During
exponential growth, B. emersonii produces nuclei at a rapid rate; it
accomplishes this by way of mitoses in which the nuclear membranes
persist and prevent normal scatter of chromosomes until the daughternuclei are formed (Turian and Cantino, 1960). Judging from (a) the time
at which the single nucleus in the spore undergoes its first division;
(b) the speed with which such nuclei divide thereafter (Turian and
Cantino, 1959a); and (c) the number of uninucleate spores finally
produced upon cessation of growth (see Fig. 2 ; also Cantino and Hyatt,
1953a; Goldstein and Cantino, 1962), nuclear divisions occur at an
average rate of roughly one per hour during exponential growth.
However, cell walls are not laid down to delimit these nuclei from one
another until the end of the exponential phase. But then, when cell
enlargement has ceased, it does occur; the large, multinucleated cell is
cut up, very quickly, into uninucleated protoplasmic pieces. Clearly, the
factors which control nuclear division and cell enlargement, on the one
hand, and those which control cell division, on the other, function
independently. Here again, synchronized Blastocladiellas should provide
a test system (see Section III, G) well-suited for dealing with some
aspects of phenomena, well-known in other organisms, in which cell
divisions and cell elongation appear to be mutually exclusive (Scherr and
Weaver, 1953, and references therein; Falcone and Nickerson, 1958;
etc.).
A second aspect of the exponential growth of an OC cell must be
mentioned now: namely, that it is stimulated by white light. The
manifold effect of illumination upon the cell involves accelerated
consumption of bicarbonate and production of polysaccharide, alteration
of internal pools of nitrogenous and phosphorus constituents and the
activity of at least one enzyme system, depression of glycine uptake,
increased synthesis of nucleic acid, protein, and total dry weight,
acceleration of nuclear reproduction, and an extension of the organism's
generation time. Since Blastocladiella is a water-mould, this response to
light is striking; it represents, as far as we know now, the only welldocumented example of a non-chlorophyllous organism which, provided
C0 2 is available, grows more rapidly (in dry weight) in white light than
in the dark. These and other phenomena associated with the lightstimulated growth of B. emersonii are documented elsewhere (Cantino
EDWARD C. CANTINO AND JAMES S. LOVETT
relative rates of synthesis of enzymes and other macromolecules and
metabolic products. Not long ago, Cohn (1957) suggested in his discussion of differential rates of protein synthesis that, ideally, one should
study enzyme formation in a single, growing cell. For all intents and
purposes, synchronized single generations of Blastocladiella provide this
very thing.
In this connection, one last thought may be appropriate. During
exponential growth, B. emersonii produces nuclei at a rapid rate; it
accomplishes this by way of mitoses in which the nuclear membranes
persist and prevent normal scatter of chromosomes until the daughternuclei are formed (Turian and Cantino, 1960). Judging from (a) the time
at which the single nucleus in the spore undergoes its first division;
(b) the speed with which such nuclei divide thereafter (Turian and
Cantino, 1959a); and (c) the number of uninucleate spores finally
produced upon cessation of growth (see Fig. 2 ; also Cantino and Hyatt,
1953a; Goldstein and Cantino, 1962), nuclear divisions occur at an
average rate of roughly one per hour during exponential growth.
However, cell walls are not laid down to delimit these nuclei from one
another until the end of the exponential phase. But then, when cell
enlargement has ceased, it does occur; the large, multinucleated cell is
cut up, very quickly, into uninucleated protoplasmic pieces. Clearly, the
factors which control nuclear division and cell enlargement, on the one
hand, and those which control cell division, on the other, function
independently. Here again, synchronized Blastocladiellas should provide
a test system (see Section III, G) well-suited for dealing with some
aspects of phenomena, well-known in other organisms, in which cell
divisions and cell elongation appear to be mutually exclusive (Scherr and
Weaver, 1953, and references therein; Falcone and Nickerson, 1958;
etc.).
A second aspect of the exponential growth of an OC cell must be
mentioned now: namely, that it is stimulated by white light. The
manifold effect of illumination upon the cell involves accelerated
consumption of bicarbonate and production of polysaccharide, alteration
of internal pools of nitrogenous and phosphorus constituents and the
activity of at least one enzyme system, depression of glycine uptake,
increased synthesis of nucleic acid, protein, and total dry weight,
acceleration of nuclear reproduction, and an extension of the organism's
generation time. Since Blastocladiella is a water-mould, this response to
light is striking; it represents, as far as we know now, the only welldocumented example of a non-chlorophyllous organism which, provided
C0 2 is available, grows more rapidly (in dry weight) in white light than
in the dark. These and other phenomena associated with the lightstimulated growth of B. emersonii are documented elsewhere (Cantino