Plant Growth and Development (IMAGE) University of Würzburg Caption Plants whose direction of growth is switched from vertical to horizontal in experiments have to reorient spatially. The hormone auxin plays an important role in this process. In wild type plants, for example, the root tip immediately starts to grow back in the direction of the gravitational stimulus -- this is clearly visible already after six hours (upper plant, yellow arrow). A mutant in which the gene for the AUX1 auxin transporter is defective is not able to translate the gravitational stimulus into 'correct' growth. The root tip has no orientation (lower plant). Credit Photo: Dirk Becker Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.