Figure 4.

Mitotic response to nitrogen deprivation. Wild-type and cdr2 null strains (KGY69 and KGY1475) were grown to midlog phase in minimal medium, and then separated on the basis of size by centrifugal elutriation. The smallest newborn cells were collected and split between two cultures, and each half was filtered, washed, and released into minimal medium (A and B) or minimal medium lacking nitrogen (C, D, E, F, and G). Samples were collected initially every 20 min for 6 h (A and B) or every 30 min for 12 h (C and D), and the percentage of binucleate (B and D) and cells containing a septum (A and C) were determined microscopically. From 12–48 h, samples were collected less frequently, and total cell number (E) and DNA content (F) were determined by Coulter counting and flow cytometry, respectively. Samples of cells grown in medium lacking nitrogen were also collected to measure average cell length at 0, 24, and 48 h and cell length at the first peak of septation (3.3 h for wild type and 5.5 h for cdr2 null) (G).