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Plant Physiol. 2017 Dec;175(4):1593-1607. doi: 10.1104/pp.17.01270. Epub 2017 Oct 30.

Gradients in Wall Mechanics and Polysaccharides along Growing Inflorescence Stems.

Author information

1
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
2
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802.
3
Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831.
4
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 meihong@mit.edu dcosgrove@psu.edu.
5
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802 meihong@mit.edu dcosgrove@psu.edu.

Abstract

At early stages of Arabidopsis (Arabidopsis thaliana) flowering, the inflorescence stem undergoes rapid growth, with elongation occurring predominantly in the apical ∼4 cm of the stem. We measured the spatial gradients for elongation rate, osmotic pressure, cell wall thickness, and wall mechanical compliances and coupled these macroscopic measurements with molecular-level characterization of the polysaccharide composition, mobility, hydration, and intermolecular interactions of the inflorescence cell wall using solid-state nuclear magnetic resonance spectroscopy and small-angle neutron scattering. Force-extension curves revealed a gradient, from high to low, in the plastic and elastic compliances of cell walls along the elongation zone, but plots of growth rate versus wall compliances were strikingly nonlinear. Neutron-scattering curves showed only subtle changes in wall structure, including a slight increase in cellulose microfibril alignment along the growing stem. In contrast, solid-state nuclear magnetic resonance spectra showed substantial decreases in pectin amount, esterification, branching, hydration, and mobility in an apical-to-basal pattern, while the cellulose content increased modestly. These results suggest that pectin structural changes are connected with increases in pectin-cellulose interaction and reductions in wall compliances along the apical-to-basal gradient in growth rate. These pectin structural changes may lessen the ability of the cell wall to undergo stress relaxation and irreversible expansion (e.g. induced by expansins), thus contributing to the growth kinematics of the growing stem.

PMID:
29084904
PMCID:
PMC5717741
DOI:
10.1104/pp.17.01270
[Indexed for MEDLINE]
Free PMC Article

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