68
EDWARD C. CANTINO AND JAMES S. LOVETT
identified, then the availability of synchronized, single-generation
cultures of organisms such as Blastocladiella
can be exploited fully to
pursue their role in differentiation.
In relation to an OC cell, a growing RS cell is metabolically blocked,
and the quality and quantity of these blocks depend upon the stage of
exponential growth selected. Thus, one can choose a stage with the
desired combination, grow a billion cells or so to this exact point in
ontogeny, and then pursue the nature of the metabolic relationships
involved with whatever approaches are currently employed in the study
of such phenomena in other micro-organisms (e.g., see discussion in
Adelberg, 1953). As the pattern of these metabolic blocks is altered
during development, their relationship to growth and morphogenesis of
the cell can be evaluated.
E. The Transition Between Exponential Growth and Differentiation
The developmental sequence which occurs subsequent to exponential
growth of Blastocladiella is very different in RS and OC cells. In the
latter, it involves a rapid transition to zoospore differentiation and then
discharge without delay ; i.e., a lengthy intervening period of maturation
and/or dormancy does not occur. On the other hand, the RS cell
undergoes a prolonged and apparently obligatory period of intracellular
synthesis and rearrangement before spores can be differentiated and
their release subsequently induced. Because of this, we shall first take up
the differentiation and maturation of an RS cell; having done so, we
will then discuss the processes of cleavage and discharge of spores which
occur in OC and RS types.
In both of the morphological pathways available to
Blastocladiella,
there is a stage in development beyond which the system becomes
irreversibly committed to one pathway or the other. The point at which
this occurs depends upon the previous history of the plant. It can be
located, chronologically, by addition of the RS inducer (bicarbonate) to
OC cells growing in its absence, and by withdrawal of inducer from RS
cells growing in its presence. In each case, reversal results in a change in
the direction of development towards the structure and function of the
opposite cell type. By such means, OC and RS cells were shown to have
become irreversibly committed after 60% and 43% of their respective
generation times (Cantino, 1952 ; Lovett and Cantino, 1960b).
For OC cells, very little is known concerning the significance of this
phenomenon in terms of intracellular events. On the other hand, a
considerable amount of information is available about RS morphogenesis. Unfortunately, our understanding of the process has not kept
pace with accumulation of the facts.
EDWARD C. CANTINO AND JAMES S. LOVETT
identified, then the availability of synchronized, single-generation
cultures of organisms such as Blastocladiella
can be exploited fully to
pursue their role in differentiation.
In relation to an OC cell, a growing RS cell is metabolically blocked,
and the quality and quantity of these blocks depend upon the stage of
exponential growth selected. Thus, one can choose a stage with the
desired combination, grow a billion cells or so to this exact point in
ontogeny, and then pursue the nature of the metabolic relationships
involved with whatever approaches are currently employed in the study
of such phenomena in other micro-organisms (e.g., see discussion in
Adelberg, 1953). As the pattern of these metabolic blocks is altered
during development, their relationship to growth and morphogenesis of
the cell can be evaluated.
E. The Transition Between Exponential Growth and Differentiation
The developmental sequence which occurs subsequent to exponential
growth of Blastocladiella is very different in RS and OC cells. In the
latter, it involves a rapid transition to zoospore differentiation and then
discharge without delay ; i.e., a lengthy intervening period of maturation
and/or dormancy does not occur. On the other hand, the RS cell
undergoes a prolonged and apparently obligatory period of intracellular
synthesis and rearrangement before spores can be differentiated and
their release subsequently induced. Because of this, we shall first take up
the differentiation and maturation of an RS cell; having done so, we
will then discuss the processes of cleavage and discharge of spores which
occur in OC and RS types.
In both of the morphological pathways available to
Blastocladiella,
there is a stage in development beyond which the system becomes
irreversibly committed to one pathway or the other. The point at which
this occurs depends upon the previous history of the plant. It can be
located, chronologically, by addition of the RS inducer (bicarbonate) to
OC cells growing in its absence, and by withdrawal of inducer from RS
cells growing in its presence. In each case, reversal results in a change in
the direction of development towards the structure and function of the
opposite cell type. By such means, OC and RS cells were shown to have
become irreversibly committed after 60% and 43% of their respective
generation times (Cantino, 1952 ; Lovett and Cantino, 1960b).
For OC cells, very little is known concerning the significance of this
phenomenon in terms of intracellular events. On the other hand, a
considerable amount of information is available about RS morphogenesis. Unfortunately, our understanding of the process has not kept
pace with accumulation of the facts.