Metabolism of Gibberellin A(12) and A(12)-Aldehyde in Developing Seeds of Pisum sativum L

Metabolism of ¹⁴C]gibberellin (GA) A₁₂ (GA₁₂) and ¹⁴C]gibberellin A₁₂-aldehyde (GA₁₂-aldehyde) was examined in cotyledons and seed coats from developing seeds of pea (Pisum sativum L.). Both were metabolized to only 13-hydroxylated GAs in cotyledons but to 13-hydroxylated and non-13-hydroxylated GAs in seed coats. The metabolism of ¹⁴C]GA₁₂ was slower in seed coats than in cotyledons. ¹⁴C]GA₁₂-aldehyde was also metabolized to conjugates in seed coats. Seed coat ¹⁴C]-metabolites produced from ¹⁴C]GA₁₂-aldehyde were isolated by high-performance liquid chromatography (HPLC). Conjugates were base hydrolyzed and the free GAs reisolated by HPLC and identified by gas chromatography-mass spectrometry. ¹⁴C]GA₅₃-aldehyde, ¹⁴C]GA₁₂-aldehyde conjugate, and ¹⁴C]GA₅₃-aldehyde conjugate were major metabolites produced from ¹⁴C]GA₁₂-aldehyde by seed coats aged 20-22 days or older. The dilution of ¹⁴C in these compounds by ¹²C, as compared to the supplied ¹⁴C]GA₁₂-aldehyde, indicated that they are endogenous. Feeding ¹⁴C]GA₅₃-aldehyde led to the production of ¹⁴C]GA₅₃-aldehyde conjugate in seed coats and shoots and also to 13-hydroxylated GAs in shoots. Labeled GAs, recovered from plant tissue incubated with either ¹⁴C]GA₁₂, ¹⁴C]GA₁₂-aldehyde, or ³H]GA₉, were used as appropriate markers for the recovery of endogenous GAs from seed coats or cotyledons. These GAs were purified by HPLC and identified and quantified by gas chromatography-mass spectrometry. GA₁₅, GA₂₄, GA₉, GA₅₁, GA₅₁-catabolite, GA₂₀, GA₂₉, and GA₂₉-catabolite were detected in seed coats, whereas GA₉, GA₅₃, GA₄₄, GA₁₉, GA₂₀, and GA₂₉ were found in cotyledons. The highest GA levels were for GA₂₀ and GA₂₉ in cotyledons (783 and 912 nanograms per gram fresh weight, respectively) and for GA₂₉ and GA₂₉-catabolite in seed coats (1940 and > 1940 nanograms per gram fresh weight, respectively).