Cell Polarity in Plants Linked to Endocytosis

The phytohormone auxin acts as a versatile trigger in many aspects of plant development. Scientists have known for some time that auxin is transported from the top to the bottom of a plant, and that the local concentration of auxin is important for the growth direction of stems, the growth of roots, and the sprouting of shoots. Different cellular responses, in many instances, are mediated by the phytohormones based on its graded distribution on plant cells. The so-called PIN proteins, localized in the cell membrane, play a vital role in cell to cell auxin distribution. Scientists, however, have long been puzzled why the PIN proteins only showed up at the bottom of a cell.

A Ghent University-led, international team of scientists have revealed a rather unusual mechanism. They found out that PIN proteins are made in the protein factories of the cell and are transported all over the cell membrane. They are engulfed by the cell membrane in a process called endocytosis. After endocytosis, the PIN proteins are then ‘recycled’, that is they disconnect from the membrane and move back to the cell. The proteins are subsequently transported to the bottom of the cell, where they are again incorporated in the cell membrane.

The scientists said that it is unclear why plants use a complex mechanism, but a plausible explanation is that this mechanism enables a quick response when plant cells feel a change in the direction of gravity.

For more information, read the article at http://www.vib.be/NR/rdonlyres/E8FB2BC8-3D32-4D76-BFC1-9609FA07C689/2745/20081027_ENG_JiriFriml_mechanismupanddown2.pdf The paper published by Nature is available at http://dx.doi.org/10.1038/nature07409