COMPARISON OF BIOLOGICAL-ACTIVITIES OF GIBBERELLINS AND GIBBERELLIN-PRECURSORS NATIVE TO THLASPI-ARVENSE L

Field pennycress (Thlaspi arvense L.) is a winter annual weed with a cold requirement for stem elongation and flowering. The relative abilities of several native gibberellins (GAs) and GA-precursors to elicit stem growth were compared. Of the eight compounds tested, gibberellin A1, (GA1), GA9, and GA20 caused stem growth in noninduced (no cold treatment) plants. No stem growth was observed in plants treated with enf-kaurene, ent-kaurenol, ent-kaurenoic acid, GA53, or GA8. Moreover, of the biologically active compounds, GA9 was the most active followed closely by GA1. In thermoinduced plants (4-week cold treatment at 6°C) that were continuously treated with 2-chlorocholine chloride to reduce endogenous GA production, GA9 was the most biologically active compound. However, the three kaurenoid GA precursors also promoted stem growth in thermoinduced plants, and were almost as active as GA20. No such increase in activity was observed for either GA8 or GA53. The results are discussed in relation to thermoinductive regulation of GA metabolism and its significance to the initiation of stem growth in field pennycress. It is proposed that thermoinduction results in increased conversion of enf-kaurenoic acid to GAs through the C-13 desoxy pathway and that GA9 is the endogenous mediator of thermoinduced stem growth in field pennycress.