52 Takashi HIRAYAMA and Tsutomu UGAJIN RAN1 2 RAN1 GFP RAN1 etr1 EIN3 EIN2
Gamma Field Symposia, No. 42, 2003 Institute of Radiation Breeding NIAS, Japan MECHANISM OF BRASSINOSTEROID SIGNALING 53 MECHANISM OF BRASSINOSTEROID SIGNALING Takeshi NAKANO, Shigeo YOSHIDA and Tadao ASAMI Plant Functions Lab., RIKEN 2-1 Hirosawa, Wako 351-0198 Introduction Steroid hormones, compounds with a signature tetracyclic structure, are synthesized downstream of the isoprenoid pathway in many organisms. In animals, steroid hormones regulate embryonic and adult cell development, and also act on neurons, heart tissue, sperm, oocytes and other organs and cells. In insects, the steroid hormone ecdysone also controls metamorphosis and reproduction. Brassinolide is the most bioactive form in all plant steroids and the first purification and determination of the structure was done in using of chemicals from bee-collected rape pollen. Brassinosteroids, plant steroid hormones that are widely distributed throughout the plant kingdom, have biological effects on many plant growth processes, such as stem and pollen tube elongation, leaf development, and xylem development. Brassinosteroids can also regulate chloroplast that is closely associated with the unique plant organelle. As these steroids can regulate each organism specific organ development, steroids are interesting in the aspect of molecular evolution (Clouse, 2001, Fujioka and Yokota, 2003). Brassinosteroid biosynthesis In the past decade, Arabidopsis brassinosteroid biosynthetic mutants such as det2 (Li et al., 1996), dwf4 (Choe et al., 1998) and cpd (Szekeres et al., 1996) had been identified and characterized (Fig. 1). Before the screening of these mutants, the importance of brassinosteroid for plant growth had not been confirmed yet. Brassinosteroid feeding for plant could not cause so drastic change on plant phenotype and some visible effects might be thought as similar to other known phytohormones. But, these brassinosteroid-deficient mutants have a pleiotropic dwarf phenotype with very short stem, shorten and waving leaves, and dark greened leaves. Gibberellin deficient mutants were known to similar to the dwarf phenotype, but these brassinosteroid-deficient mutants did not showed the germination inhibition and the late flowering that were observed in gibberellin deficient mutants. Then, brassinosteroids could be identified as special and unique bioactivity in comparison with another known phytohormones, and had participated in actual
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ISSN 0435-1096 Gamma Field Symposia
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The lecturers and the members of th
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KANEKO, T. KARITA, E. KASHIMA, M. K
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TANO, S. TSUCHIDA, Y. TSUTSUMI, N.
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The Symposium Committee Shigeki NAG
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- Page 19 and 20: 8 Yuji KAMIYA References AKIYOSHI,
- Page 21 and 22: 10 Yuji KAMIYA SHINOMURA, T. (1997)
- Page 23 and 24: 12 Yuji KAMIYA 8’ 8’ 273
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- Page 39 and 40: 28 Atsuhiro OKA At almost the same
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- Page 77 and 78: 68 Yoshikatsu MATSUBAYASHI are grow
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