Double or Nothing? Cell Division and Cell Size Control

Size is a fundamental property that must be tightly regulated to ensure that cells and tissues function efficiently. Dynamic size control allows unicellular organisms to adapt to environmental changes, but cell size is also integral to multicellular development, affecting tissue size and structure. Despite clear evidence for homeostatic cell size maintenance, we are only now beginning to understand cell size regulation in the actively dividing meristematic tissues of higher plants. We discuss here how coupled advances in live cell imaging and modelling are uncovering dynamic mechanisms for size control mediated at the cellular level. We argue that integrated models of cell growth and division will be necessary to predict cell size and fully understand multicellular growth and development. Size is fundamental to the structure and function of cells and tissues.To maintain cell size in populations of actively dividing cells, a careful balance between cell growth and division must be established.Advances in live cell imaging and lineage tracking, together with computational modelling, are allowing hypotheses based on the behaviour of unicellular organisms to be tested in multicellular tissues of higher plants.Cell size homeostasis as observed at the tissue level appears to be an emergent property of a dynamic system that links cell growth, cell size, and cell-cycle progression at the level of individual cells, and is dependent on environmental and developmental conditions.