>Several students speculated about what the
>pollen tube is made of, whether it grows through cell division or cell
>expansion, whether it is a part of the male gametophyte, or formed of
>stylar tissue (or the dissolving of stylar tissue).
The pollen tube is the extension of a single cell of the pollen grain
(or male gametophyte) the tube cell. You can demonstrate that this
growth does not require any contribution of the style other than
sucrose, calcium, and boron, since pollen grains of many species will
successfully germinate in a liquid medium containing these three
ingredients. Incredibly the tubes that extend from these pollen
grains can become hundreds of times longer than the original pollen
grain within only several hours. The growth rate can be as fast as 1
cm/ hour in some species. No cell division occurs during this
growth, instead it is a type of growth known at tip-growth in which
new cell wall material is added to the growing tip by the fusion of
golgi-derived vesicles with the plasma membrane. Taiz and Zeiger's
Plant Physiology text has a good description of the molecular
processes involved in this growth.
Mark D. Spiro
Department of Biology
Bucknell University
Lewisburg, PA 17837
spiro at bucknell.edu
phone: (570) 577-3486
fax: (570) 577-3537
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