Structure-activity relationship of brassinosteroids

Takatsuto, Suguru; Yazawa, Naoto; Ikekawa, Nobuo; Takematsu, Tetsuo; Takeuchi, Yoshinori; Koguchi, M

doi:10.1016/0031-9422(83)80135-6

Cited by 103 publications

(61 citation statements)

References 20 publications

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“…Fig. 2) was less than that reported in auxin assays with Avena coleoptiles (12, 13), but was similar in magnitude to that observed in light-grown tomato hypocotyls following treatment with brassinosteroids (20). Analogs of IAA reported to have growth promotory activity (pCPA, 2,4-D, 2,4,5-T, and aNAA) (17) stimulated elongation of normal hypocotyls, while the inactive isomers of pCPA and aNAA, oCPA and ,BNAA, respectively, were either ineffective or only marginally effective in inducing elongation (Table II).…”

Section: Resultssupporting

confidence: 68%

Insensitivity of the Diageotropica Tomato Mutant to Auxin

Kelly¹,

Bradford²

1986

Plant Physiol.

137

106

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The sensitivity of excised hypocotyl segments to indoleacetic acid (IAA) in two assays, ethylene production and elongation, was determined in the ethylene-requiring tomato (Lycopersicon esculentum Mill.) mutant, diageotropica (dgt), and its isogenic parent, cv VFN8. Endogenous (uninduced) ethylene synthesis rates were slightly lower in dgt hypocotyls than in VFN8 hypocotyls. Ethylene production was essentially unaffected by IAA in dgt, but was stimulated up to 10-fold by 10 micromolar IAA in VFN8. Elongation of dgt hypocotyls was also insensitive to concentrations of IAA as high as 100 micromolar, as compared to significant elongation of VFN8 hypocotyls in response to 0.1 micromolar IAA. A range of IAA analogs active in VFN8 was also ineffective in stimulating elongation of dgt hypocotyls, suggesting that the differences were not due to rapid metabolism of IAA by dgt tissues. Auxin-induced elongation of VFN8 hypocotyls was unaffected by 2,3,5-triiodobenzoic acid and naphthylphthalamic acid, indicating that polar auxin transport was not a factor in these experiments. Exogenous and auxin-induced ethylene had no effect on the elongation respone of either genotype, nor did exogenous ethylene restore the sensitivity of dgt hypocotyls to IAA. Despite their apparent insensitivity to auxin, dgt hypocotyls elongated dramatically and synthesized ethylene rapidly in response to 1.2 micromolar fusicoccin. These results suggest that the primary effect of the dgt mutation is to reduce the sensitivity of the tissue to auxin. As altered regulation of ethylene synthesis is only one symptom of this fundamental deficiency, dgt should more properly be considered to be the auxin-insensitive tomato mutant.

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Section: Resultssupporting

confidence: 68%

Insensitivity of the Diageotropica Tomato Mutant to Auxin

Kelly¹,

Bradford²

1986

Plant Physiol.

137

106

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“…Numerous studies of structure/activity relationships for brassinosteroids have shown that minor structural modifications can result in loss of biological activity, although structural requirements vary somewhat with the assay system used (Thompson et al, 1982;Takatsuto et al, 1983;Arteca et al, 1985). Such strict structural requirements for activity are consistent with the hypothesis that BR effects are mediated by a protein receptor.…”

Section: Discussionmentioning

confidence: 58%

“…It has been shown previously that exogenously applied auxins lead to increased hypocotyl lengths in VFN but not in dgt tomatoes (Kelly and Bradford, 1986) and that BR promotes elongation of wild-type tomato hypocotyls (Takatsuto et al, 1983). Figure 5B shows that BR also promotes elongation in the dgt mutant and that BR does not cause rapid induction of the SAUR homolog in either genotype.…”

Section: Br Lnduces Elongation But Not Saur Cene Expression In An Auxmentioning

confidence: 55%

Investigation of Gene Expression, Growth Kinetics, and Wall Extensibility during Brassinosteroid-Regulated Stem Elongation

Zurek¹,

Rayle²,

McMorris³

et al. 1994

Plant Physiol.

125

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Brassinosteroids promote stem elongation in a variety of plants but little is known about the mechanism of action of these plant growth regulators. We investigated a number of physiological and molecular parameters associated with brassinosteroid-enhanced elongation. Continuous growth recordings of soybean (Glycine mar 1. cv Williams 82) epicotyls showed that there was a 45-min lag before 0.1 f i~ brassinolide (BR) exerted a detectable effect on elongation. BR caused a marked increase in Instron-measured plastic extensibility, suggesting that BR may promote elongation in part by altering mechanical properties of the cell wall (wall loosening). Structure-function studies suggested that the dimensions of the brassinosteroid side chain were critical for promotion of elongation and expression of BRU1, a gene regulated specifically by active brassinosteroids. Auxin-BR interactions were examined by using small auxin up RNA (SAUR) gene probes and the auxininsensitive diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.). We have shown that in wild-type tomato, which elongates in response to exogenous auxin, a transcript of identical size to the soybean SAUR 15A is strongly induced within 1 h by 50 f i~ 2,4-dichlorophenoxyacetic acid or indoleacetic acid, whereas in the dgt mutant, which does not elongate in response to auxin, no transcript is expressed. Furthermore, BR promotes equal elongation of hypocotyls in both wild-type and dgt tomatoes but does not rapidly induce the SAUR 15A homolog in either genotype. BR does not cause rapid induction of SAUR 6B in elongating soybean epicotyls but does lead to increased expression after 18 h. This late BR activation of SAUR 6B is controlled, at least in part, at the transcriptional leve1 and i 5 not accompanied by an increase of free indoleacetic acid in the tissue. We conclude that although both BR and auxin affect wall relaxation processes, BR-promoted elongation in soybean and tomato stems acts via a mechanism that most likely does not proceed through the auxin signal transduction pathway.Brassinosteroids are growth-promoting natural products with structural similarities to animal steroid hormones (Mandava, 1988). The wide distribution of brassinosteroids in the plant kingdom, their marked effect on cell proliferation and elongation at nanomolar levels, and their interactions with

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“…Numerous structure-function analyses have defined the specific requirements for BR activity (McMorris etal., 1994;Takatsuto et al, 1983). These include a cis-vicinal glycol at C-2 and C-3, a keto or lactone function at C-6 and hydroxylation (with proper stereochemistry) of the C-17 side chain.…”

Section: De-etiolated Mutants Take On a New Identity As Genetic Lesiomentioning

confidence: 99%