Hormone Effects on the Plane of Cell Division

There is little evidence that hormones play a direct role in determining the plane of orientation of the cell plate during division. Indeed it is difficult to imagine how subcellular gradients of hormone concentration could be estab- 

In tomato root meristems, auxin causes an increase in the number of longitudinal and a decrease in the number of transverse divisions (Hughs and Street 1960), while in intercalary meristem segments from Avena stems, kinetin enhances transverse cell division and causes a shift of division within the intercalary meristem from the transverse to the longitudinal direction (Jones and Kaufman 1971). These effects were obtained only with high levels of kinetin. 

Some of these hormonal effects on cell plate orientation may be caused by alterations in cell expansion patterns. Nism and Sugano (1970), showed 

Lintilhac (1977) supported this hypothesis by showing that in Coleus stems an imposed force induces a pattern of cell wall orientation corresponding to the principal stresses generated by the force. Stress-induced alterations in the plane of cell division were also demonstrated in Jerusalem artichoke callus tissue by Yeoman and Brown (1971). Lintilhac points out that this model may explain the selective development of a single cell among a mass of apparently identical cells. The cell in the very center of the nucellus, for example, is unique in its exposure to isotropic stress, and it is this cell which divides and develops into the megasporangium. 

---