Plant Physiol, June 2000, Vol. 123, pp. 605-612
The Mechanic State of "Inner Tissue" in the Growing Zone of
Sunflower Hypocotyls and the Regulation of Its Growth Rate
Following Excision1
Winfried S.
Peters2* and
A. Deri
Tomos
Ysgol Gwyddorau Biolegol, Prifysgol Cymru, Bangor, Gwynedd LL57
2UW, Cymru, United Kingdom
Spontaneous growth of isolated inner tissue from the etiolated
sunflower (Helianthus annuus L.) hypocotyl growing zone
was investigated. A new preparation technique allowed measurements starting 3 s after excision. Elongation with respect to the
turgescent and plasmolized state was quantified in terms of relative
growth rates, facilitating comparison to growth in situ. Turgor and
turgor-induced strain were determined. Overall longitudinal strain in
inner tissues in situ was positive, indicating that compressive forces
exerted by peripheral tissues are outweighed by turgor-dependent
tensile stress. Inner tissue expansion following isolation depended on water uptake. Extreme plastic extension rates occurred immediately after excision, suggesting that mechanical parameters of inner tissue
in situ cannot be extrapolated from the mechanics of excised sections.
In the long term, excised inner tissue autonomously established values
of turgor, turgor-induced strain, and relative growth rates similar to
values in the living plant. These results support historic models of
tissue cooperation during organ growth, in which inner tissues actively
participate in the control of growth rates.
1
This work was supported by a North Atlantic
Treaty Organization postdoctoral research fellowship from the Deutscher
Akademischer Austauschdient (to W.S.P.).
2
Present address: AK Kinematische Zellforschung,
Biozentrum der Johann Wolfgang Goethe-Universität,
Marie-Curie-Str. 9, D-60439 Frankfurt (Main), Germany.
*
Corresponding author; e-mail
w.s.peters{at}zoology.uni-frankfurt.de; fax 49-0-69-798-29607.
© 2000 American Society of Plant Physiologists
