Promotion of Flower Induction in Transgenic Eucalyptus camadulensis Trees by Paclobutrazol

This paper reports a series of experiments in which paclobutrazol was applied to 6-mo-old transgenic Eucalyptus camadulensis grafts to examine its relative effects on precocious flowering, growth, and levels of gibberellin (GA), abscisic acid (ABA), indoleacetic acid (IAA), and paclobutrazol residues in the shoot apex. Paclobutrazol was effective in promoting precocious flowering in E. camadulensis. Responses to a trunk injection and soil drenching persisted for up to 2 yr, but growth responses were not expressed for another year. Paclobutrazol reduced internode length, and leaves appear less green. Paclobutrazol induced aerial roots at the basal portion of the grafts. Assessment of seed yield per capsule and subsequent germination tests showed no deleterious effects on seed development or quality. Paclobutrazol is known to block gibberellin production early in the biosynthesis pathway, but it cannot inhibit endogenous gibberellin biosynthesis, including GA1, GA3, GA4,GA8, GA20, GA24, and GA53 during flower bud initiation. Paclobutrazol treatment reduced endogenous ABA and IAA levels by about 1/3. During flower bud initiation, paclobutrazol residues in the shoot apex as determined by pyrolysis-gas chromatography-mass spectrometry were 34.7, 0.31, and 0 μg.g-1 dry weight in the 1st to 3rd yr after treatment, respectively

本研究报道了一系列实验：将多效唑（paclobutrazol）施用于6月龄转基因坎杜桉（Eucalyptus camadulensis）嫁接苗，以探究其对提前开花、植株生长，以及茎尖（shoot apex）内赤霉素（gibberellin，GA）、脱落酸（abscisic acid，ABA）、吲哚乙酸（indoleacetic acid，IAA）含量与多效唑残留量的相对影响。多效唑可有效诱导坎杜桉提前开花。树干注射（trunk injection）与土壤浇灌（soil drenching）两种施药方式的持效期可达2年，但生长相关效应延迟1年才显现。多效唑可缩短节间长度（internode length），并使叶片色泽变淡；同时可诱导嫁接苗基部产生气生根（aerial roots）。对每蒴果（capsule）种子产量的评估及后续发芽试验（germination tests）结果显示，多效唑对种子发育与品质无不良影响。已知多效唑可在赤霉素生物合成途径（biosynthesis pathway）早期阻断其合成，但在花芽分化期（flower bud initiation）无法抑制内源赤霉素的生物合成，涉及的赤霉素亚型包括GA1、GA3、GA4、GA8、GA20、GA24及GA53。多效唑处理可使内源脱落酸与吲哚乙酸含量降低约1/3。在花芽分化期，经热解气相色谱-质谱联用法（pyrolysis-gas chromatography-mass spectrometry）测定，处理后第1至3年茎尖内的多效唑残留量分别为34.7、0.31及0 μg·g⁻¹干重。