Microtubules regulate tip growth and orientation in root hairs ofArabidopsis thaliana

Authors

  • Tatiana N. Bibikova,

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    • Present address: Plant Molecular Science Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.

    • These authors contributed equally to this work.

  • Elison B. Blancaflor,

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    • These authors contributed equally to this work.

  • Simon Gilroy

    1. Department of Biology, The Pennsylvania State University, 208 Mueller Laboratory, University Park, PA 16802, USA
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*For correspondence (fax +814 865 9131; e-mail sxg12@psu.edu).

Summary

The polarized growth of cells as diverse as fungal hyphae, pollen tubes, algal rhizoids and root hairs is characterized by a highly localized regulation of cell expansion confined to the growing tip. In apically growing plant cells, a tip-focused [Ca2+]c gradient and the cytoskeleton have been associated with growth. Although actin has been established to be essential for the maintenance of elongation, the role of microtubules remains unclear. To address whether the microtubule cytoskeleton is involved in root hair growth and orientation, we applied microtubule antagonists to root hairs ofArabidopsis. In this report, we show that depolymerizing or stabilizing the microtubule cytoskeleton of these apically growing root hairs led to a loss of directionality of growth and the formation of multiple, independent growth points in a single root hair. Each growing point contained a tip-focused gradient of [Ca2+]c. Experimental generation of a new [Ca2+]c gradient in root hairs pre-treated with microtubule antagonists, using the caged-calcium ionophore Br-A23187, was capable of inducing the formation of a new growth point at the site of elevated calcium influx. These data indicate a role for microtubules in regulating the directionality and stability of apical growth in root hairs. In addition, these results suggest that the action of the microtubules may be mediated through interactions with the cellular machinery that maintains the [Ca2+]c gradient at the tip.

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