Figure 4.

Timing of Arabidopsis sepal epidermal cell division and entry into endoreduplication is variable. (A) Wild type sepals (the outermost, green, floral organs) have a diversity of cell sizes on the outer epidermis ranging from giant cells (false colored red in SEMs) to small cells (not colored). A stochastic computational model that accounts for cell cycle length and entry into endoreduplication can accurately predict the distribution of sepal cell sizes from wild-type plants. In the model, cells are colored according to the number of endocycles they have undergone (red = 3, purple = 2, green = 1, and blue = 0). (B,C) Changing the expression of cyclin dependent kinase inhibitors (CKI) alters the probability of entry into endoreduplication and the resulting cell size distribution. As the model predicts, (B) plants overexpressing cyclin-dependent kinase inhibitor KRP1 form ectopic giant cells, but islands of small cells remain between giant cells. Note that the sepals curve outward. (C) Likewise the model predicts that plants mutant for cyclin-dependent kinase inhibitor LGO continue to have variable smaller cell sizes. Note that the sepals curve slightly inward. (D) The duration of the cell cycle amongst sepal cells is highly variable and ranges from 12 to more than 60 h. (E) A histogram of the cell sizes produced in the random model (red dashed line) is not significantly different from measured cell sizes in the sepal (blue line). This figure is modified and reprinted from Roeder et al. (2010) under the Creative Commons Attribution license.