Plant Meristems and Organogenesis: The New Era of Plant Developmental Research

The principles behind the process of body formation in multi-cellular organisms have long intrigued biologists. Body forma-tion in flowering plants is initiated from a single zygotic cell. Proliferation of the cell leads to the formation of an embryo, in which two distinctive meristems (groups of stem cells), the embryonic shoot apical meristem (SAM) and the root apical meristem (RAM), as well as other embryonic tissues and organs, begin to form. After germination, the SAM develops shoot organs and tissues by proliferation and differentiation of cells in peripheral regions, whereas the RAM differentiates several types of root tissues in proximal and distal directions to form the root proper and the root cap, respectively. Both meristems maintain the stem cell population by self-renewal. The lateral root meristem and the axial meristem are formed de novo during plant growth. After a period of vegetative growth, flow