Not-so-tip-growth

Abstract

In tip-growing plant cells such as pollen tubes and root hairs, surface expansion is confined to the cell apex. Vesicles containing pectic cell wall material are delivered to this apical region to provide the material necessarily to build the expanding cell wall. Quantification of wall expansion reveals that the surface expansion rates are not highest at the pole but instead in an annular region around the pole. These findings raise the question of the precise localization of exocytosis events in these cells. Recently, we used spatio-temporal image correlation spectroscopy (STICS) in combination with high temporal resolution confocal imaging to characterize the intracellular movement of vesicles in growing pollen tubes. These observations, together with the analysis of FRAP (fluorescence recovery after photobleaching) experiments, indicate that exocytosis is likely to occur predominantly in the same annular region where wall expansion rates are greatest. Therefore, tip growth in plant cells does not seem to happen exactly at the tip.

Keywords: allometric growth; cell mechanics; cell wall; cytomechanics; exocytosis; expansion; plant cell growth; pollen tube; root hair; tip growth; vesicle transport.

Figure 1

Drawing of the spatial distribution of mechanical features determining tip growth in plant cells. (A) Degree of deformation of the cell wall during its maturation. The thickness of the arrows indicates relative strain rates. (B) Position of the annular ring surrounding the pole of the tip growing cell. (C) Movement patterns of vesicles as observed with FM1–43 label.