Metabolism of Gibberellin A₄ by Vegetative Shoots of Douglas Fir at Three Stages of Ontogeny

Abstract

Abstract Vegetative shoots of coastal Douglas fir [ Pseudotsuga menziesii (Mirb.) Franco] seedlings rapidly metabolized 1,2[ 3 H]‐gibberllin A 4 (GA 4 ) to GA 2 , GA 34 and 6 unknown acidie, ethyl acetate‐soluble compounds. The kinetics of formation of each compound depended upon the stage of ontogeny, metabolism being most rapid during bud set and bud break and least rapid during elongation. Translocation of radioactivity was greatest at the bud set stage. By hour 72 large amounts (65%) of neutral, ehter‐soluble compunds were formed at the stage of bud break and lesser, but significant amounts (40%) at bud set. Less than 15% of the radioactivity went into neutral ether during the elongation stage. Douglas fir appears to have an efficient system for con‐version of the relatively non‐polar GA 34 . This, coupled with the formation of neutral, ether‐soluble and acidie, n ‐butanol‐soluble substances, may regulate the effective level of biologically active exogenous and/or endogenous GAs in this conifer.