Transient synchronization of the Chlamydomonas cell division cycle during acclimation to limiting CO2
Steven Dillard, Kyujung Van and Martin H. Spalding
Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA
Chlamydomonas reinhardtii acclimates to nutrient limitations by induction or de-repression of genes whose gene products are beneficial for acquisition of the limiting nutrient and/or for tolerance of the limitation. Acclimation to limiting CO2 or inorganic carbon has been studied fairly extensively with regard to the mechanisms underlying the induced inorganic carbon acquisition systems, the systems needed to tolerate limiting CO2 conditions and the signal transduction pathway involved in recognizing and responding to the limiting CO2. However, little is known about how acquisition to limiting nutrients, such as CO2, interact with the cell division cycle (CDC) beyond the response to complete withdrawal of the nutrient. To investigate the effects of CO2 limitation on the CDC of Chlamydomonas, flow cytometry was used to monitor the CDC of both synchronous and non-synchronous cultures during acclimation to a limiting CO2 concentration. When faced with CO2 limitation, non-synchronous cultures of Chlamydomonas undergo transient synchronization as those cells past the "commitment" point of the CDC undergo division, while the remainder of the cells arrest their growth in early G1 phase, with the result that the cells all accumulate in early G1 phase, appearing transiently synchronized until acclimated sufficiently to limiting CO2 for growth to resume.
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