PLANT PHYSIOLOGY , Vol 114, Issue 4 1267-1272, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Restoration of Phototropic Responsiveness in Decapitated Maize Coleoptiles
R. Kaldenhoff and M. Iino
Julius-von-Sachs-Institut fur Biowissenschaften, Universitat Wurzburg, Mittlerer Dallenbergweg 64, 97082 Wurzburg, Germany (R.K.)
The literature indicates that the tip of maize (Zea mays L.) coleoptiles
has the localized functions of producing auxin for growth and perceiving
unilateral light stimuli and translocating auxin laterally for
phototropism. There is evidence that the auxin-producing function of the
tip is restored in decapitated coleoptiles. We examined whether the
functions for phototropism are also restored by using blue-light conditions
that induced a first pulse-induced positive phototropism (fPIPP) and a
time-dependent phototropism (TDP). When the apical 5 mm, in which
photosensing predominantly takes place, was removed, no detectable fPIPP
occurred even if indole-3-acetic acid (lanolin mixture) was applied to the
cut end. However, when the blue-light stimulation was delayed after
decapitation, fPIPP became inducible in the coleoptile stumps supplied with
indole-3-acetic-acid/lanolin (0.01 mg g-1), indicating that phototropic
responsiveness was restored. This restoration progressed 1 to 2 h after
decapitation, and the curvature response became comparable to that of
intact coleoptiles. The results for TDP were qualitatively similar, but
some quantitative differences were observed. It appeared that the overall
TDP was based on a major photosensing mechanism specific to the tip and on
at least one additional mechanism not specific to the tip, and that the
tip-specific TDP was restored in decapitated coleoptiles with kinetics
similar to that for fPIPP. It is suggested that the photoreceptor system,
which accounts for fPIPP and a substantial part of TDP, is regenerated in
decapitated coleoptiles, perhaps together with the mechanism for lateral
auxin translocation.
