The force from without

摘要

It seems that the epidermis is the cell layer through which growth-promoting plant hormones called brassinosteroids exert their effect on cell expansion — a finding that puts a new perspective on classical views of plant growth. Brassinosteroids are growth-promoting plant hormones, and their absence, or the absence of their main transmembrane receptor protein, creates dwarfed plants. In the past few years, both the brassinosteroid biosynthetic pathway and the molecular signalling route from the brassinosteroid receptor to intracellular gene-transcription factors have been elucidated. That information, and the ability to restore normal growth selectively in specific plant cell layers, has now allowed Savaldi-Goldstein and co-workers (page 199 of this issue) to clarify the pivotal role of a single cell layer — the outermost layer, known as the epidermis — in plant growth.