Annu. Rev. Plant Physiol. Plant Mol. Biol. 2000. 51:349–70 Copyright °c 2000 by Annual Reviews. All rights reserved DEVELOPMENT OF SYMMETRY IN PLANTS A. Hudson Institute of Cell and Molecular Biology, University of Edinburgh, King’s Buildings, Mayfield Road, Edinburgh EH9 3JH United Kingdom; e-mail:
[email protected] Key Words asymmetry, axes, embryogenesis, lateral organs, flowers I Abstract Plant development involves specification and elaboration of axes of asymmetry. The apical-basal and inside-outside axes arise in embryogenesis, and are probably oriented maternally. They are maintained during growth post-germination and interact to establish novel axes of asymmetry in flowers and lateral organs (such as leaves). Whereas the genetic control of axis elaboration is now partially understood in embryos, floral meristems, and organs, the underlying mechanisms of axis specifica- tion remain largely obscure. Less functionally significant aspects of plant asymmetry (e.g. the handedness of spiral phyllotaxy) may originate in random events and therefore have no genetic control. CONTENTS WHAT IS SYMMETRY? ........................................... 349 ASYMMETRY IN EMBRYOGENESIS ................................ 350 Apical-Basal (A-B) Asymmetry .................................... 350 Inside-Outside Asymmetry of the Embryo ............................. 354 Bilateral Symmetry of the Embryo ................................... 356 ELABORATION OF ASYMMETRY AFTER EMBRYOGENESIS ............. 359 Phyllotaxy and Translational Symmetry in the Shoot .....................