Main conclusion Tissue-specific occurrence and formation of endogenous sesquiterpene lactones has been assessed and suggests physiological function as antagonists of auxin-induced plant growth in sunflower. Abstract Sunflower, Helianthus annuus , accumulate high concentrations of bioactive sesquiterpene lactones (STL) in glandular trichomes, but in addition, structurally different STL occur in only trace amounts in the inner tissues. The spatial and temporal production of these endogenous STL during early phases of plant development is widely unknown and their physiological function as putative natural growth regulators is yet speculative. By means of HPLC and MS analysis it was shown that costunolide, dehydrocostuslactone, 8-epixanthatin and tomentosin are already present in dry seeds and can be extracted in low amounts from cotyledons, hypocotyls and roots of seedlings during the first days after germination. Semi-quantitative and RT-qPCR experiments with genes of the key enzymes of two independent routes of the endogenous STL biosynthesis confirmed the early and individual expression in these organs and revealed a gradual down regulation during the first 72–96 h after germination. Light irradiation of the plants led to a fast, but transient increase of STL in parts of the hypocotyl which correlated with growth retardation of the stem. One-sided external application of costunolide on hypocotyls conferred reduced growth of the treated side, thus resulting in the curving of the stem towards the side of the application. This indicates the inhibiting effects of STL on plant growth. The putative function of endogenous STL in sunflower as antagonists of auxin in growth processes is discussed.

中文翻译：

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内源性倍半萜内酯的空间和发育合成支持向日葵生长调节功能

主要结论 对内源性倍半萜内酯的组织特异性发生和形成进行了评估，并表明其作为向日葵中生长素诱导的植物生长的拮抗剂的生理功能。摘要 向日葵（Helianthus annuus）在腺毛中积累高浓度的生物活性倍半萜内酯（STL），但此外，结构不同的STL仅在内部组织中出现微量。在植物发育的早期阶段这些内源性 STL 的时空产生是广泛未知的，它们作为推定的天然生长调节剂的生理功能尚属推测。通过 HPLC 和 MS 分析表明，木香内酯、脱氢木香内酯、8-表黄素和毛绒素已经存在于干燥的种子中，并且可以从子叶中少量提取，发芽后最初几天的幼苗下胚轴和根。内源性 STL 生物合成的两条独立途径的关键酶基因的半定量和 RT-qPCR 实验证实了这些器官中的早期和个体表达，并揭示了在发芽后的前 72-96 小时内逐渐下调。植物的光照射导致下胚轴部分的 STL 快速但短暂的增加，这与茎的生长迟缓有关。在下胚轴上单侧外部应用科斯塔内酯会降低处理侧的生长，从而导致茎向应用侧弯曲。这表明STL对植物生长的抑制作用。