Have you ever wondered why stems grow upwards and roots downwards? Why plants always seem to turn towards the light and climbing plants run up the trellis（格子，框架） rather than down? The answer is simple: auxin（植物生长素） .

But maybe not that simple, since plant hormones -- and auxin is a plant hormone -- are regulated by complex combinations of various processes. Elke Barbez, Jürgen Kleine-Vehn and Jirí Friml, connected to VIB and UGent recently identified an important new link in the transport of auxin through the plant, resulting in auxin being stored at specific sites. The results were published by the journal Nature.

Auxin surrenders its secrets

Darwin was already interested in auxin in the 19th century. Only in recent years, however, has the hormone started to relinquish（放弃） its secrets, thanks to intensive molecular research. Auxin is produced in the young, growing parts of plants and then transported throughout the plant -- to a low-lying stem for example. The stem needs to straighten out as soon as possible to be able to absorb the sun's rays efficiently; therefore more auxin will be delivered to the underside of the stem than to the topside, resulting in the underside growing faster and the stem straightening out. For the same reason, plants in front of windows will always turn to the light. This dynamic regulation of auxin transport allows plants to take optimal advantage of local and changing conditions.

A new means of transport for auxin?

The transport of auxin through the plant plays a vital role. And, from all appearances, it is not a simple matter. The VIB researchers identified an important new link and means of transport for auxin: PILS proteins. PILS proteins are vital for auxin-dependent plant growth and regulate the intracellular storage of the hormone. It is exactly this compartmentalizing of auxin that seems functionally important for the various developmental processes.

Growing crops more efficiently: the right amount of auxin in the right place

Higher auxin levels at the right moment and in the right place result in better growth and greater yields. Better regulation of auxin levels would make plants grow more efficiently. The researchers hope to contribute to the development of more efficient growing processes by continuing to unravel auxin transport processes.