Plant Physiol, October 2000, Vol. 124, pp. 813-822
Gibberellin-Induced Changes in Growth Anisotropy Precede
Gibberellin-Dependent Changes in Cortical Microtubule Orientation in
Developing Epidermal Cells of Barley Leaves. Kinematic and Cytological
Studies on a Gibberellin-Responsive Dwarf Mutant, M489
Carol L.
Wenzel,1
Richard E.
Williamson, and
Geoffrey
O.
Wasteneys*
Plant Cell Biology Group, Research School of Biological Sciences,
Australian National University, G.P.O. Box 475, Canberra, Australian
Capital Territory 2601, Australia
We conducted kinematic and cytological studies on "between
vein" epidermal cells of the gibberellin (GA)-deficient M489 dwarf mutant of barley (Hordeum vulgare L. Himalaya). GAs
affect radial and axial components of cell expansion and cortical
microtubule orientation. Adaxial cells in particular expand radially
after leaving the elongation zone (EZ), probably as part of leaf
unrolling. Exogenous gibberellic acid corrects the mutant's short,
wide blades, short EZ, and slow elongation rate. Cell production rates
increase more on the adaxial than on the abaxial surface. Cells spend
equal periods of time elongating in dwarf and tall plants, but relative elemental growth rates start to decline sooner in the dwarf. GA increased the rate at which longitudinal wall area increased because the increased axial growth more than compensated for reduced radial growth. In dwarf leaves, increased radial expansion was detected in
basal parts of the EZ before cortical microtubules lost transverse orientation in the distal elongation zone. We conclude that loss of
microtubule orientation is not required for low GA levels to reduce
growth anisotropy.
1
Present address: The Plant Lab, Biology
Department, York University, York YO10 5DD, UK.
*
Corresponding author; e-mail geoffw{at}rsbs.anu.edu.au; fax
61-2-6249-4331.
© 2000 American Society of Plant Physiologists
