Frustration-induced inherent instability and growth oscillations in pollen tubes

Abstract

In a seed plant a pollen tube is a vessel that transports male gamete cells to an ovule to achieve fertilization. It consists of one elongated cell, which exhibits growth oscillations, until it bursts completing its function. Up till now, the mechanism behind the periodic character of the growth has not been fully understood. An attempt to understand these oscillations lead us to an attractive scenario: We show that the mechanism of pressure-induced symmetry frustration occuring in the wall at the perimeter of cylindrical and approximately hemispherical parts of a growing pollen cell, together with the addition of cell wall material, suffices to release and sustain mechanical self-oscillations and cell extension in pollen tubes. At the transition zone where symmetry frustration occurs and one cannot distinguish either of the involved symmetries, a kind of 'entangled state' appears where either single or both symmetry(ies) can be realized by the system. We anticipate that testifiable predictions made by the model may deliver, after calibration, a new tool to estimate turgor pressure from oscillation period of the growing cell. Since the mechanical principles apply to all turgor regulated walled cells including those of plant, fungal and bacterial origin, the relevance of this work is not limited to the case of the pollen tube.