The role of plant hormones in higher plant cellular differentiation. I. A critique.

Primary growth and morphogenesis in higher plants can be explained mechanistically in terms of primary types of cellular differentiation, namely, phenomena of cell division, primary wall growth, intercellular bonding and polarity. Plant hormones fulfil essential roles in regulating these types of differentiation, and it is well established that plant hormones can initiate primary growth and morphogenesis. Secondary and terminal types of cellular differentiation largely determine the usefulness of plants to man; however, regulators of these types remain poorly characterized. Secondary and terminal types need not differentiate in order for primary growth and morphogenesis to occur, and there is no conclusive evidence that factors regulating primary growth and morphogenesis also initiate subsequent types of differentiation.