Plant hormones regulate growth and development by diffusing through plants. The five major plant hormones are auxin, cytokinin, gibberellin, abscisic acid, and ethylene. Auxin stimulates root growth and the response of plant growth to the environment. Cytokinin stimulates cell division and new shoot growth. Gibberellin promotes stem elongation and controls flowering and seed production cycles. Abscisic acid induces dormancy, and ethylene induces fruit ripening and flower/leaf senescence. These hormones often work in balance or opposition to regulate growth throughout a plant's life cycle.