Plant growth, development, and cellular organization

The plant body of a typical angiosperm consists of two major organ systems: the root and the shoot. The shoot is composed of stems, leaves, and flowers, and each major organ in turn is composed of tissues that represent collections of one or more specialized cell types. All growth and organ formation of the plant body are initiated and controlled by regions of active cell division termed “meristems.” Meristems are composed of two categories of cells: the dividing initials and the immediate undifferentiated derivatives of cell division. The derivatives subsequently become differentiated and change into different types of mature cells and tissues. Following fertilization, the plant body begins development as a single-celled zygote that undergoes embryogenesis. After a series of early cell divisions, a globose proembryo is formed. During the later stages of embryo development, the embryonic axis of the plant body is formed along with the root and shoot apical meristems from which the rest of the plant body develops following seed germination. One of the most distinctive structural features of plant cells is the surrounding cell wall, typically composed of carbohydrate cellulose. Cell walls play important roles in plant development, cell-to-cell communication, physiology and environmental adaptation, and stress response.