The roles of auxin and gibberellin in reversing radiation inhibition of hypocotyl lengthening.

Inhibition of hypocotyl lengthening in Lupinus albus seedlings mediated through the high energy reaction was not reversed by 5 authentic gibberellins nor by extracted lupin "gibberellin-like" compounds. However, inhibition by continuous light was largely overcome by applying IAA (indole-3-acetic acid) to intact seedlings. In contrast, inhibition of lengthening mediated through phytochrome in its low energy mode was reversed by gibberellin. It is concluded that light antagonises hormone-regulated growth.