No.42 - è¾²æ¥­ç”Ÿç‰©è³‡æºç ”ç©¶æ‰€

MECHANISM OF BRASSINOSTEROID SIGNALING
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plants under dark conditions causes phenotypes similar to those displayed by brassinosteroiddeficient
mutants, such as shortened hypocotyl, cotyledon opening, and de-etiolation. In the light,
plants treated with the Brz displayed dwarf and highly greened leaves (Asami et al., 2000, Asami
and Yoshida, 1999). In the stem tissues, development of the vascular bundle cells was inhibited by
Brz. (Nagata et al., 2001)
The Brz also revealed the regulation of chloroplast development by brassinosteroid. In the
cotyledon of dark-germinated plant, the mRNA of chloroplast genes; i.e., cab and rbcS, did not
expressed. But, in the cotyledon of dark-germinated plant with Brz, these chloroplast genes
expression was detected (Asami et al., 2000, Nagata et al., 2000). After 2 hour light emission to
these dark-germinated plant, the Brz-treated plant harbored very quick developed chloroplast that
contained more numbered thylakoid membrane layer that Brz-untreated plant. These result
revealed that plastid development was regulated brassinosteroid. (Fig. 2)
Brassinosteroid receper BRI1
The Arabidopsis bri1 mutant was also identified by its dwarf phenotype, but brassinosteroid
treatment did not recover the dwarfism to wild-type phenotype and did not inhibit the elongation of
the roots of this mutant (Clouse et al., 1996, Li and Chory, 1997) (Fig. 3). Study of bri1 revealed
that BRI1 is a critical component in brassinosteroid signaling, and that mutation in its BRI1 gene
Fig. 2 Brz effect to the plant.
Brz treatment of plants under dark conditions causes photomorphogenesis such as shortened
hypocotyl, cotyledon opening. In the light, plants treated with the Brz displayed dwarf and highly
greened leaves. The Brz also revealed the regulation of chloroplast development by brassinosteroid.