Effects of brassinolide on the growing of rice plants

Fig. 4. Observation of roots 64 hr after the germination of seeds treated

with (A) solvent and (B) BL at 5×10−9 M.

remarkable. NSBR1, the non-steroidal brassinolide-like compound16) discovered in our laboratory, also induced the spiral

in two of ten seeds treated at 5×10−5 M (Fig. 5-B). We also examined the effect of an antagonist, the 3,4-difluoro-substituted

analog of NSBR1, which was discovered in the assay against Arabidopsis.16) As shown in Fig. 5-C, the spiral formation induced

by BL at 5×10−8 M was released by treating with an antagonist

at 1.7×10−4 M. The release of spiral induction in the roots can be

used to bioassay antagonists of BRs.

We also examined the effect of gibberellin on the growth of

roots. No spiral was induced in the root at 5×10−6 M of GA3. At

a higher concentration (5×10−5 M) of GA3, root growth was significantly inhibited. Likewise, auxins did not induce the spiral,

even at the higher concentration (5×10−5 M). Since this spiral

induction is specific to BRs and the potency can be determined

quantitatively using minimum effective concentrations, a study

of the structure–activity relationship for spiral induction by various BRs13–15) is in progress.

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Fig. 5. Spiral induction in rice seeds. (A) BL at various concentrations. (B) NSBR1 at 5×10−5 M and 2.5×10−4 M. (C) BL antagonist at 1.7×10−4 M.

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