20 Plant Cell Growth

Abstract

The production of plant cells is confined mainly to meristems, small specialized growth zones found in shoots, roots, and lateral areas of the plant. Meristems are highly organized structures where rapidly cycling cells are produced from a small central mass of cells that proliferate very slowly if at all, analogous to stem cells in animals. New progeny cells are displaced toward the periphery of a meristem where they progressively differentiate and organize into organs. The meristems are therefore dynamic structures continuously traversed by a flux of cells that divide and grow at different rates depending on their position in the meristem. The shoot and root meristems are defined during embryogenesis. Lateral meristems, mediating radial growth, and meristems of secondary roots are formed later during the development of the young plant. New meristems can also form spontaneously in culture from an undifferentiated mass of proliferating cells, thereby allowing the regeneration of a plant. Meristematic cells (Fig. 1) are small (~5 μm), densely packed with cytoplasm, and, in defined regions of the meristem, grow to a specific size before dividing. Growing and dividing meristematic cells display a high level of metabolic activity and macromolecular synthesis as required to generate new cell mass (Woodard et al. 1961). The nutrients needed to sustain the high growth rate of meristematic cells (sink tissue) are provided by the rest of the plant body.

“SOLID” VERSUS “LIQUID” GROWTH
During the development of organs, cells lose their capacity to divide and can enlarge up to one thousand times...