Metabolism of Tritiated Gibberellins A(4) and A(9) in Norway Spruce, Picea abies (L.) Karst. : Effects of a Cultural Treatment Known to Enhance Flowering

Shoots of mature grafted propagules of Picea abies (L.) Karst. metabolized [³H]gibberellin A₄ (GA₄) to at least 14 acidic substances, two of which were tentatively identified by gas-liquid radiochromatography as GA₂ (possibly an artifact) and GA₃₄. [³H]GA₉ was converted into a number of metabolites, one of which was chromatographically similar to, but not identical with, GA₄. Metabolism was maximally 61 and 57% over 48 hours for GA₄ and GA₉, respectively, and was correlated with the rate of change (i.e. increase followed by decrease) in endogenous GA-like substances as shoot elongation progressed. Propagules covered with a clear plastic film, a treatment which promotes flowering, metabolized [³H]GA₄ more slowly than did control plants in the open. Inasmuch as a GA_4/7 mixture can also promote flowering in P. abies, the retarded metabolism of [³H]GA₄ may reflect the manner in which trees under plastic metabolize endogenous GA-like substances. If so, then the stimulating effect of this cultural treatment on flowering may come about through an increased level of endogenous, less polar GA-like substances.