Abstract

Polar expansion is a widespread phenomenon in plants spanning all taxonomic groups from the Charophycean Green Algae to pollen tubes in Angiosperms and Gymnosperms. Current data strongly suggests that many common features are shared amongst cells displaying polar growth mechanics including changes to the structural features of localized regions of the cell wall, mobilization of targeted secretion mechanisms, employment of the actin cytoskeleton for directing secretion and in many cases, endocytosis and coordinated interaction of multiple signal transduction mechanisms prompted by external biotic and abiotic cues. The products of polar expansion perform diverse functions including delivery of male gametes to the egg, absorption, anchorage, adhesion and photo-absorption efficacy. A comparative analysis of polar expansion dynamics is provided with special emphasis on those found in early divergent plants.

Highlights

  • The developmental dynamics of pollen tube growth represent a spectacular example of anisotropic cell expansion in eukaryotes

  • Root hairs develop by a comparable polar expansion mechanism that leads to structures that are used for water and mineral absorption, anchorage, and communication with soil microbiota

  • Though polar expansion is far less common than ―diffuse‖ expansion dynamics in plants cells, it is widely exhibited across the taxonomic spectrum of plants, yielding a diverse assortment of specialized cells with distinct and varied functions (Table 1)

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Summary

Introduction

The developmental dynamics of pollen tube growth represent a spectacular example of anisotropic cell expansion in eukaryotes. This growth mechanism entails finely-tuned and highly-coordinated interactions of the tube’s cell wall biosynthetic and secretory machinery with the cytoskeletal system as well as multiple, cross-talking signal transduction pathways [1]. These activities are focused at a Plants 2013, 2 precisely defined ―softened‖ (i.e., loosened) zone in the cell wall located at the pollen tube tip [2]. A comparative analysis of the mechanisms involved in polar expansion phenomena is presented

Common Components and Processes Associated with Polar Expansion in Plants
Expansins
Exo- and Endocytosis
Actin Binding Proteins
Microtubules
Phosphoinositides
Reactive Oxygen Species
Polar Growth Mechanisms in Early Divergent Plants
Physcomitrella Patens and Mosses
Polar Expansion in Primitive Vascular Plants
The Pollen Tube
Root Hairs
Findings
Conclusions

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