In plants, undifferentiated meristem tissue provides stem cells to produce roots and shoots. The root meristem contains a few of these stem cells in a region called the quiescent center. Ortega-Martínez et al . studied Arabidopsis plants with a defect in a gene that controls ethylene biosynthesis and found that it produced more of the gaseous hormone ethylene. The quiescent center cells in these mutants went through more cell divisions than normal, resulting in extra stem cells in the root meristem. Adding exogenous ethylene also increased quiescent cell division, and blocking its synthesis in the mutants prevented extra divisions. O. Ortega-Martínez, M. Pernas, R. J. Carol, L. Dolan, Ethylene modulates stem cell division in the Arabidopsis thaliana root. Science 317 , 507-510 (2007). [Abstract] [Full Text]