Main conclusion Endogenous auxin determines the pattern of adventitious shoot formation. Auxin produced in the dominant shoot is transported to the internodal segment and suppresses growth of other shoots. Abstract Adventitious shoot formation is required for the propagation of economically important crops and for the regeneration of transgenic plants. In most plant species, phytohormones are added to culture medium to induce adventitious shoots. In ipecac ( Carapichea ipecacuanha (Brot.) L. Andersson), however, adventitious shoots can be formed without phytohormone treatment. Thus, ipecac culture allows us to investigate the effects of endogenous phytohormones during adventitious shoot formation. In phytohormone-free culture, adventitious shoots were formed on the apical region of the internodal segments, and a high concentration of IAA was detected in the basal region. To explore the relationship between endogenous auxin and adventitious shoot formation, we evaluated the effects of auxin transport inhibitors, auxin antagonists, and auxin biosynthesis inhibitors on adventitious shoot formation in ipecac. Auxin antagonists and biosynthesis inhibitors strongly suppressed adventitious shoot formation, which was restored by exogenously applied auxin. Auxin biosynthesis and transport inhibitors significantly decreased the IAA level in the basal region and shifted the positions of adventitious shoot formation from the apical region to the middle region of the segments. These data indicate that auxin determines the positions of the shoots formed on internodal segments of ipecac. Only one of the shoots formed grew vigorously; this phenomenon is similar to apical dominance. When the largest shoot was cut off, other shoots started to grow. Naphthalene-1-acetic acid treatment of the cut surface suppressed shoot growth, indicating that auxin produced in the dominant shoot is transported to the internodal segment and suppresses growth of other shoots.

中文翻译：

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内源性生长素决定了吐根节间不定芽的形成模式

主要结论 内源性生长素决定了不定芽形成的模式。在优势枝条中产生的生长素被运输到节间段并抑制其他枝条的生长。摘要 经济上重要作物的繁殖和转基因植物的再生都需要不定芽的形成。在大多数植物物种中，将植物激素添加到培养基中以诱导不定芽。然而，在吐根（ Carapichea ipecacuanha (Brot.) L. Andersson）中，不经植物激素处理即可形成不定芽。因此，吐根培养使我们能够研究内源性植物激素在不定芽形成过程中的影响。在无植物激素培养中，不定芽在节间段的顶端区域形成，并且在基底区域检测到高浓度的IAA。为了探索内源性生长素与不定芽形成之间的关系，我们评估了生长素转运抑制剂、生长素拮抗剂和生长素生物合成抑制剂对吐根不定芽形成的影响。生长素拮抗剂和生物合成抑制剂强烈抑制不定芽形成，通过外源施用的生长素恢复。生长素生物合成和转运抑制剂显着降低了基部区域的 IAA 水平，并将不定芽形成的位置从顶端区域转移到节段的中间区域。这些数据表明，生长素决定了在吐根节间段上形成的芽的位置。只有一个形成的嫩芽生长旺盛；这种现象类似于顶端优势。当最大的枝条被切断时，其他枝条开始生长。切割表面的萘-1-乙酸处理抑制了枝条的生长，表明在优势枝条中产生的生长素被转运到节间段并抑制了其他枝条的生长。