Abstract
Onion plants form bulbs in response to stimuli generated under long-day conditions. The stimuli seem to consist of bulbing and anti-bulbing hormones and the their ratio determines the commencement of bulb formation. However, the nature of these hormones still remains unknown. Simultaneous application of sucrose at a high concentration and an inhibitor for GA biosynthesis can induce bulb formation in vitro. Using the culture system as a bioassay method, we tried to isolate these hormones. Strong anti-bulbing activity was found in hexane-soluble fraction obtained from onion leaves and the active compounds were identified to be free linoleic and linolenic acids. On the other hand, bulb-inducing activity was found in water-soluble fraction. Purification of the active compound is now in progress.
