No.42 - è¾²æ¥çç©è³æºç 究æ
No.42 - è¾²æ¥çç©è³æºç 究æ
No.42 - è¾²æ¥çç©è³æºç 究æ
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Gamma Field Symposia, No. 42, 2003 Institute of Radiation Breeding<br />
NIAS, Japan<br />
MECHANISM OF BRASSINOSTEROID SIGNALING<br />
53<br />
MECHANISM OF BRASSINOSTEROID SIGNALING<br />
Takeshi NAKANO, Shigeo YOSHIDA and Tadao ASAMI<br />
Plant Functions Lab., RIKEN<br />
2-1 Hirosawa, Wako 351-0198<br />
Introduction<br />
Steroid hormones, compounds with a signature tetracyclic structure, are synthesized<br />
downstream of the isoprenoid pathway in many organisms. In animals, steroid hormones regulate<br />
embryonic and adult cell development, and also act on neurons, heart tissue, sperm, oocytes and<br />
other organs and cells. In insects, the steroid hormone ecdysone also controls metamorphosis and<br />
reproduction. Brassinolide is the most bioactive form in all plant steroids and the first purification<br />
and determination of the structure was done in using of chemicals from bee-collected rape pollen.<br />
Brassinosteroids, plant steroid hormones that are widely distributed throughout the plant kingdom,<br />
have biological effects on many plant growth processes, such as stem and pollen tube elongation,<br />
leaf development, and xylem development. Brassinosteroids can also regulate chloroplast that is<br />
closely associated with the unique plant organelle. As these steroids can regulate each organism<br />
specific organ development, steroids are interesting in the aspect of molecular evolution (Clouse,<br />
2001, Fujioka and Yokota, 2003).<br />
Brassinosteroid biosynthesis<br />
In the past decade, Arabidopsis brassinosteroid biosynthetic mutants such as det2 (Li et al.,<br />
1996), dwf4 (Choe et al., 1998) and cpd (Szekeres et al., 1996) had been identified and<br />
characterized (Fig. 1). Before the screening of these mutants, the importance of brassinosteroid for<br />
plant growth had not been confirmed yet. Brassinosteroid feeding for plant could not cause so<br />
drastic change on plant phenotype and some visible effects might be thought as similar to other<br />
known phytohormones. But, these brassinosteroid-deficient mutants have a pleiotropic dwarf<br />
phenotype with very short stem, shorten and waving leaves, and dark greened leaves. Gibberellin<br />
deficient mutants were known to similar to the dwarf phenotype, but these brassinosteroid-deficient<br />
mutants did not showed the germination inhibition and the late flowering that were observed in<br />
gibberellin deficient mutants. Then, brassinosteroids could be identified as special and unique<br />
bioactivity in comparison with another known phytohormones, and had participated in actual
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