Circumnutation and distribution of phytohormones in Vigna angularis epicotyls

Motoyuki Iida, Toshihiko Takano, Takakazu Matsuura, Izumi C. Mori, Shingo Takagi

    Research output: Contribution to journalArticlepeer-review

    5 Citations (Scopus)

    Abstract

    Circumnutation is a plant growth movement in which the tips of axial organs draw a circular orbit. Although it has been studied since the nineteenth century, its mechanism and significance are still unclear. Greened adzuki bean (Vigna angularis) epicotyls exhibited a clockwise circumnutation in the top view with a constant period of 60 min under continuous white light. The bending zone of circumnutation on the epicotyls was always located in the region 1–3 cm below the tip, and its basal end was almost identical to the apical end of the region where the epicotyl had completely elongated. Therefore, epidermal cells that construct the bending zone are constantly turning over with their elongation growth. Since exogenously applied auxin transport inhibitors and indole-3-acetic acid (IAA) impaired circumnutation without any effect on the elongation rate of epicotyls, we attempted to identify the distribution pattern of endogenous auxin. Taking advantage of its large size, we separated the bending zone of epicotyls into two halves along the longitudinal axis, either convex/concave pairs in the plane of curvature of circumnutation or pre-convex/pre-concave pairs perpendicular to the plane. By liquid chromatography–mass spectrometry, we found, for the first time, that IAA and gibberellin A1 were asymmetrically distributed in the pre-convex part in the region 1–2 cm below the tip. This region of epicotyl sections exhibited the highest responsiveness to exogenously applied hormones, and the latent period between the hormone application and the detection of a significant enhancement in elongation was 15 min. Our results suggest that circumnutation in adzuki bean epicotyls with a 60 min period is maintained by differential growth in the bending zone, which reflects the hormonal status 15 min before and which is shifting sequentially in a circumferential direction. Cortical microtubules do not seem to be involved in this regulation.

    Original languageEnglish
    Pages (from-to)165-178
    Number of pages14
    JournalJournal of Plant Research
    Volume131
    Issue number1
    DOIs
    Publication statusPublished - Jan 1 2018

    Keywords

    • Adzuki bean
    • Auxin
    • Circumnutation
    • Gibberellin
    • LC–MS

    ASJC Scopus subject areas

    • Plant Science

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