Graduate School of Life Sciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun, Gunma, 374-0193, Japan.
Department of Applied Biosciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun, Gunma, 374-0193, Japan.
Planta. 2020 Mar 5;251(3):73. doi: 10.1007/s00425-020-03367-5.
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. 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.
内源性生长素决定不定芽形成的模式。在优势芽中产生的生长素被运输到节间段，并抑制其他芽的生长。不定芽的形成是经济上重要的作物繁殖和转基因植物再生所必需的。在大多数植物物种中，植物激素被添加到培养基中以诱导不定芽的形成。然而，在金鸡纳（Carapichea ipecacuanha（Brot.）L. Andersson）中，不定芽可以在没有植物激素处理的情况下形成。因此，金鸡纳的培养允许我们研究内源性植物激素在不定芽形成过程中的作用。在没有植物激素的培养中，不定芽形成于节间段的顶端区域，并且在基部区域检测到高浓度的 IAA。为了探讨内源生长素与不定芽形成的关系，我们评估了生长素运输抑制剂、生长素拮抗剂和生长素生物合成抑制剂对金鸡纳不定芽形成的影响。生长素拮抗剂和生物合成抑制剂强烈抑制不定芽的形成，而外源生长素可以恢复不定芽的形成。生长素生物合成和运输抑制剂显著降低了基部区域的 IAA 水平，并将不定芽形成的位置从顶端区域转移到节间段的中间区域。这些数据表明生长素决定了金鸡纳节间段上形成的芽的位置。只有一个形成的芽生长旺盛；这种现象类似于顶端优势。当最大的芽被切断时，其他芽开始生长。萘乙酸处理切口表面抑制芽的生长，表明优势芽中产生的生长素被运输到节间段并抑制其他芽的生长。
