THE TANGLED-1 MUTATION ALTERS CELL-DIVISION ORIENTATIONS THROUGHOUT MAIZE LEAF DEVELOPMENT WITHOUT ALTERING LEAF SHAPE

It is often assumed that in plants, where the relative positions of ce lls are fixed by cell walls, division orientations are critical for th e generation of organ shapes, However, an alternative perspective is t hat the generation of shape may be controlled at a regional level inde pendently from the initial orientations of new cell walls. In support of this latter view, we describe here a recessive mutation of maize, t angled-1 (tan-1), that causes cells to divide in abnormal orientations throughout leaf development without altering overall leaf shape, In n ormal plants, leaf cells divide either transversely or longitudinally relative to the mother cell axis; transverse divisions are associated with leaf elongation and longitudinal divisions with leaf widening, In tan-1 mutant leaves, cells in all tissue layers at a wide range of de velopmental stages divide transversely at normal frequencies, but long itudinal divisions are largely substituted by a variety of aberrantly oriented divisions in which the new cell wall is crooked or curved. Mu tant leaves grow more slowly than normal, but their overall shapes are normal at all stages of their growth. These observations demonstrate that the generation of maize leaf shape does not depend on the precise spatial control of cell division, and support the general view that m echanisms independent from the control of cell division orientations a re involved in the generation of shape during plant development.