Imari Koike1, Sachi Watanabe2, Karin Okazaki2, Ken-Ichiro Hayashi3, Hiroyuki Kasahara4,5, Koichiro Shimomura1, Mikihisa Umehara6,7. 1. Graduate School of Life Sciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun, Gunma, 374-0193, Japan. 2. Department of Applied Biosciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun, Gunma, 374-0193, Japan. 3. Department of Biochemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama, Okayama, 700-0005, Japan. 4. Institute of Global Innovation Research, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu-shi, Tokyo, 183-8509, Japan. 5. RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan. 6. Graduate School of Life Sciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun, Gunma, 374-0193, Japan. umehara@toyo.jp. 7. Department of Applied Biosciences, Toyo University, 1-1-1 Izumino, Itakura-machi, Ora-gun, Gunma, 374-0193, Japan. umehara@toyo.jp.
Abstract
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. 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.
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. 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.
Authors: Pankaj Dhonukshe; Ilya Grigoriev; Rainer Fischer; Motoki Tominaga; David G Robinson; Jirí Hasek; Tomasz Paciorek; Jan Petrásek; Daniela Seifertová; Ricardo Tejos; Lee A Meisel; Eva Zazímalová; Theodorus W J Gadella; York-Dieter Stierhof; Takashi Ueda; Kazuhiro Oiwa; Anna Akhmanova; Roland Brock; Anne Spang; Jirí Friml Journal: Proc Natl Acad Sci U S A Date: 2008-03-12 Impact factor: 11.205