油菜素内酯促进绿豆上胚轴伸长与蛋白质和核酸合成的关系

用饲喂蛋白质和核酸合成的放射性前体［３ Ｈ］－Ｐｈｅ、［３ Ｈ］－尿嘧啶和［３ Ｈ］－胸腺嘧啶证实了油菜素内酯（ＢＲ）能促进绿豆上胚轴的生长和蛋白质、ＲＮＡ 及ＤＮＡ 的合成。用蛋白质和核酸合成抑制剂（ＣＨ、Ａｃｔ．Ｄ、５－Ｆｕ）进一步探讨它们对上胚轴伸长的抑制作用与蛋白质、ＲＮＡ、ＤＮＡ 和ｍ ＲＮＡ 合成之间的关系。证明了上胚轴的伸长依赖于蛋白质和核酸的合成,尤其是依赖于ｍ ＲＮＡ 的合成。说明ＢＲ是在转录水平上调节基因的表达,进而促进上胚轴的伸长     

Brassinolide-2,3-acetonide: A brassinolide-induced rice lamina joint inclination antagonist

A novel chemical tool compound that is an antagonist of brassinolide (BL, 1)-induced rice lamina joint inclination was developed. Although 2-O-, 3-O-, 22-O-, or 23-O-methylation of BL causes a critical decrease in biological activity,⁵ a crystal structure of the extracellular leucine-rich repeat (LRR) domain of BRASSINOSTEROID-INSENSITIVE I (BRI1) bound to BL3, 4 indicates that the loss of activity of the O-methylated BL may result from not only the low affinity to BRI1, but also from blocking the interaction with another BR signaling factor, a partner protein of BRI1 (e.g., BRI1-ASSOCIATED KINASE 1, BAK1). On the basis of this hypothesis we synthesized the BL 2,3-acetonide 2, the 22,23-acetonide 3, and the 2,3:22,23-diacetonide 4 to assess the possibility of 2-O- and 3-O- or/and 22-O- and 23-O-alkylated BL as an antagonist in BR signaling evoked by exogenously applied BL. The 2,3-acetonide 2 more strongly inhibited the lamina inclination caused by BL relative to the 22,23-acetonide 3, whereas the diacetonide 4 had no effect most likely due to its increased hydrophobicity. This suggested that the 2,3-hydroxyl groups of BL play a more significant role in the interaction with a BRI1 partner protein rather than BRI1 itself in rice lamina joint inclination. Taken together it was demonstrated that BL, the most potent agonist of BRI1, is transformed into an antagonist by functionalization of the 2,3-dihydroxyl groups as the acetonide. This finding opens the door to the potential development of a chemical tool that modulates protein–protein interactions in the BR signaling pathway to dissect the BR-dependent processes.     

Synthesis of [26,27-2H6]brassinosteroids from 23,24-bisnorcholenic acid methyl ester

A number of hexadeuterated brassinosteroids (BS) containing a hydroxy group at C-22 or a 22R,23R-diol function were prepared starting from 23,24-bisnorcholenic acid methyl ester for biosynthetic studies. Synthesis of the cyclic part was accomplished via the initial hydroboration-oxidation of Delta(5)-double bond. The key step in the synthesis of the side chain involved addition of (2S)-[3,4-(2)H(6)]2,3-dimethylbutylphenyl sulfone to the corresponding C-22 aldehydes.     

Semisystematic nomenclature of brassinosteroids

The assignment of the trivial name to new isolated or detected brassinosteroid is based on the trivial names of seven different brassinosteroids, with names assigned according to the plant source from which they were first isolated. To avoid some observed mistakes in assigning trivial names to these compounds and the impractical constant usage of their systematic names, we propose a semisystematic nomenclature of brassinosteroids, in which (22R,23R)-2,3,22,23-tetrahydroxy-5-campestane, the trivial name of which is 6-deoxocastasterone, is considered the functional parent compound and is named brassinostane or brassinane. A set of rules for naming the remaining natural brassinosteroids is presented.     

A rapid effect of applied brassinolide on abscisic acid concentrations in <Emphasis Type="Italic">Brassica napus</Emphasis> leaf tissue subjected to short-term heat stress

Three-week old canola (Brassica napus L.) seedlings grown at 20/16°C (day/night) were subjected to short-term (4 and 8 h) heat stress (45°C) or maintained at a normal temperature of 20°C. Half of the plants under each treatment received a 10⁻⁶ M solution of brassinolide (BL) 1 h prior to beginning the temperature treatments. The concentration (ng/g dry weight) of endogenous abscisic acid (ABA) was subsequently determined in young leaves via the stable isotope dilution method. Applied BL had no effect on endogenous ABA for plants maintained at normal temperatures. However, ABA concentration was significantly elevated by heat stress alone and doubled by heat stress + BL. These results suggest that the well-known enhancement of tolerance to high temperature stress that can be obtained by BL or 24-epi-BL applications may be caused by a brassinosteroid-induced elevation in endogenous ABA concentration.     

Metabolism of14C-labeled epibrassinolide in intact seedlings of cucumber and wheat

The metabolism of exogenously applied¹⁴C-24-epibrassinolide (¹⁴C-EBR) in seedlings of cucumber and wheat was examined. Total lipids were extracted with isopropanol and chloroform, and then partitioned with water. More than 80% of radioactivity was distributed to chloroform-phase. Concentrated chloroform-phase was applied to silica gel plate and was developed with chloroform-ethanol (5:1 v/v). Rf value of original¹⁴C-EBR was about 0.6. In cucumber leaves harvested after 2 day-culture, three peaks were detected at Rf 0.11, 0.47 and 0.84. In cucumber petioles of 2 day-culture, however, a major peak was detected at Rf 0.90. But¹⁴C-EBR was hardly metabolized in hypocotyls and roots after 2 days. In wheat leaves harvested just after pulse labeling, a peak was detected at Rf 0.63. By further analysis of this peak using ODS-HPLC, however, an original peak of¹⁴C-EBR and two metabolites having higher polarity were detected. In wheat leaves harvested after 2 day-culture, the profile of TLC scanning was similar to that just after pulse labeling, although, an original peak of¹⁴C-EBR was no longer detected by ODS-HPLC. In wheat roots,¹⁴C-EBR was hardly metabolized. These results indicate that¹⁴C-EBR occurring in leaves and petioles is metabolized to produce several kinds of metabolites.     

Metabolic Conversion of Castasterone and Brassinolide into Their Glucosides in Higher Plants

Castasterone (CS) and brassinolide (BL) were administered to mung bean (Vigna radiata) explants, Arabidopsis thaliana seedlings, and cultured Catharanthus roseus cells, and the glucosylated metabolites were analyzed using LC/MS/MS. In mung bean and C. roseus, CS-2-O-glucoside (CS-2G), -3-O-glucoside (CS-3G), -22-O-glucoside (CS-22G), and -23-O-glucoside (CS-23G) were identified as metabolites of CS, whereas BL-2G, BL-3G, and BL-23G were identified as metabolites of BL. In A. thaliana, CS and BL were converted into their respective 2-O- and 23-O-glucosides. Of the metabolites identified with BL and CS administration, BL-23G was the predominant metabolite in mung bean and A. thaliana, whereas the 3-O-glucoside of BL was abundant in C. roseus. This is the first report of the metabolic conversion of CS into CS-2G, CS-3G, CS-22G, and CS-23G, and of BL into BL-2G and BL-3G. Our results indicate that the glucosylation profiles of BL and CS vary with plant species, and that the glucosylation of CS is rather limited quantitatively, compared with that of BL.     

Physiological Actions of Brassinosteroids: An Update

In general, this overview covers literature from 1999 until early 2003. Topics covered include aspects of the biosynthesis and transport of brassinosteroids, their effects on cell division, expansion, and differentiation, and their effects on whole plants, including source-sink relations and other endogenous interactions. Some interactions with environmental signals are discussed, as well as results that may promise applications in future. Topics that warrant further investigation of the roles of BRs include phenotypic variability, reproductive physiology, senescence, branching, and apical dominance, whereas topics in which possible roles for BRs are relatively unexplored include lignification, phototropism, photoperiodism, and endogenous rhythms.