Synthesis of brassinolide and its biosynthetic precursors using methyl 3-hydroxy-2-methylpropionate

Formal synthesis of plant hormones that belong to the group of 24α-methylbrassinosteroids, including brassinolide and its biosynthetic precursors with one hydroxyl group in their side chain, was performed. Stereochemistry of a methyl group at the C24 atom was provided by the choice of the desired enanthiomer of methyl-3-hydroxy-2-methylpropionate and by the sequence of its conversions into the chiral intermediate that was necessary for the formation of the C23–C28 fragment of the side chain. The (22R,23R)-diol group was introduced by the Sharpless asymmetric dihydroxylation of the intermediate Δ²² -steroids, the products of consecutive reactions of attachment of a low-molecular sulfone to the steroid C22-aldehyde, acetylation, and reductive desulfurization of the intermediate β-acetoxysulfones. Reduction of 22-acetoxy-23,25-disulfones was shown to proceed with the preservation of the functional group at atom C22.     

Uzu Mutation in Barley (Hordeum vulgare L.) Reduces the Leaf Unrolling Response to Brassinolide

A sensitive method to examine the brassinolide (BL) response of barley (Hordeum vulgare L.) using dark-grown leaf segments was established based on the known method for wheat. BL responses of 53 dwarf isogenic lines of barley were examined, and two lines were found having a uzu gene that doesn't respond significantly. These results indicate that uzu dwarfism may be caused by the non-responding character to BL.     

Brassinosteroid functions in a broad range of disease resistance in tobacco and rice

Brassinolide (BL), considered to be the most important brassinosteroid (BR) and playing pivotal roles in the hormonal regulation of plant growth and development, was found to induce disease resistance in plants. To study the potentialities of BL activity on stress responding systems, we analyzed its ability to induce disease resistance in tobacco and rice plants. Wild-type tobacco treated with BL exhibited enhanced resistance to the viral pathogen tobacco mosaic virus (TMV), the bacterial pathogen Pseudomonas syringae pv. tabaci (Pst), and the fungal pathogen Oidium sp. The measurement of salicylic acid (SA) in wild-type plants treated with BL and the pathogen infection assays using NahG transgenic plants indicate that BL-induced resistance does not require SA biosynthesis. BL treatment did not induce either acidic or basic pathogenesis-related (PR) gene expression, suggesting that BL-induced resistance is distinct from systemic acquired resistance (SAR) and wound-inducible disease resistance. Analysis using brassinazole 2001, a specific inhibitor for BR biosynthesis, and the measurement of BRs in TMV-infected tobacco leaves indicate that steroid hormone-mediated disease resistance (BDR) plays part in defense response in tobacco. Simultaneous activation of SAR and BDR by SAR inducers and BL, respectively, exhibited additive protective effects against TMV and Pst, indicating that there is no cross-talk between SAR- and BDR-signaling pathway downstream of BL. In addition to the enhanced resistance to a broad range of diseases in tobacco, BL induced resistance in rice to rice blast and bacterial blight diseases caused by Magnaporthe grisea and Xanthomonas oryzae pv. oryzae, respectively. Our data suggest that BDR functions in the innate immunity system of higher plants including dicotyledonous and monocotyledonous species.     

极小种群海南假韶子叶片光合特性和叶绿素荧光参数的动态变化

探讨海南省极小种群物种海南假韶子(Paranephelium hainanensis)的光合生理特性,以期为该物种的保护和利用提供科学依据。应用Li-COR便携式光合仪和FC1000-H便携式植物荧光成像系统测定海南假韶子的光合特性、叶绿素荧光参数的动态变化。结果表明:海南假韶子成年树和林下幼苗在7月和11月时净光合速率(P_n)和蒸腾速率(T_r)的日变化均呈明显"双峰"曲线,成年树的最大P_n达9.24μmol·m^-2·s^-1,最大T_r为3.34μmol·m^-2·s^-1,其光合能力显著强于幼苗;海南假韶子成年树初始荧光值(F₀)在7月和11月最大值分别为323.04和135.87,F_m在7月和11月最大值分别为502.78和307.76,但幼苗的F₀和F_m均低于成年树;成年树F_v/F_m...     

A fast brassinolide-regulated response pathway in the plasma membrane of Arabidopsis thaliana

To understand molecular processes in living plant cells, quantitative spectro-microscopic technologies are required. By combining fluorescence lifetime spectroscopy with confocal microscopy, we studied the subcellular properties and function of a GFP-tagged variant of the plasma membrane-bound brassinosteroid receptor BRI1 (BRI1-GFP) in living cells of Arabidopsis seedlings. Shortly after adding brassinolide, we observed BRI1-dependent cell-wall expansion, preceding cell elongation. In parallel, the fluorescence lifetime of BRI1-GFP decreased, indicating an alteration in the receptor's physico-chemical environment. The parameter modulating the fluorescence lifetime of BRI1-GFP was found to be BL-induced hyperpolarization of the plasma membrane. Furthermore, for induction of hyperpolarization and cell-wall expansion, activation of the plasma membrane P-ATPase was necessary. This activation required BRI1 kinase activity, and was mediated by BL-modulated interaction of BRI1 with the P-ATPase. Our results were used to develop a model suggesting that there is a fast BL-regulated signal response pathway within the plasma membrane that links BRI1 with P-ATPase for the regulation of cell-wall expansion.     

Conformation of Peracetylated Cyclodextrins

Typical brassinosteroid activity was found in the alkaline hydrolysate of the n-hexane fraction of lily pollen. Two acyl conjugates of teasterone were purified from the n-hexane fraction by HPLC and analyzed by GC-MS and/or LC-MS, resulting in the identification of teasterone esters with lauric acid and myristic acid. Syntheses of the teasterone esters are also reported. The acyl conjugates of typhasterol, castasterone, and brassinolide did not occur in lily pollen. This is the first time that acyl conjugates have ever been discovered among naturally occurring brassinosteroids.     

亚适宜温光盐环境下油菜素内酯对黄瓜幼苗抗氧化系统及光合作用的影响

研究了24 表油菜素内酯(EBR)对亚适宜温光盐环境下黄瓜幼苗抗氧化系统及光合作用的影响.结果表明: 与对照相比,亚适宜温光盐环境下黄瓜幼苗叶片H₂O₂含量增加,膜脂过氧化程度加剧,膜透性增强,净光合速率(P_n)、气孔导度(g_s)、胞间CO₂浓度(C_i)和蒸腾速率(T_r)分别显著下降39.3%、40.0%、21.2%和47.2%,幼苗干物质积累减少35.9%.外源喷施EBR可提高亚适宜温光盐环境下黄瓜幼苗的抗氧化酶活性,降低H₂O₂含量及膜透性,缓解亚适宜温光盐环境下P_n、g_s、T_r的下降幅度,幼苗干物质积累增加25.9%,生长加快．EBR可通过调节亚适宜温光盐环境下黄瓜幼苗抗氧化性,减少其膜脂过氧化程度,进而维持其较高的光合性能,有效促进了亚适宜温光盐环境下黄瓜幼苗的生长．     

Brassinolide-induced elongation and auxin

Segments from the hook and subhook zone of the stem of 6-day-old etiolated Pisum sativum L. cv. Victory Freezer seedlings were used to study the relationship between brassinolide and auxin in the promotion of elongation. Minor changes in exogenous indole-3-acetic acid or4-chloroindole-3-acetic acid concentration affected the kinetics markedly and the ethylene generator ethephon overcame brassinolide-induced elongation in an antagonistic interaction. Brassinolide-induced elongation was markedly inhibited by low concentrations of the cellulose biosynthesis inhibitor 2,6-dichlorobenzonitrile, and diagnostic concentrations of the antiauxin 2-( p -chlorophenoxy) isobutyric acid did not affect brassinolide-induced elongation. As the characteristics of auxin-induced growth are not displayed in brassinolide-induced elongation of the upper stem segment, it is proposed that brassinolide does not depend on auxin as a mediator in the promotion of elongation of younger tissues but that it can interact in a very complex manner with auxin. In the elongation of more mature tissues, and in bending responses, brassinolide probably accelerates auxin effects. When split, the upper stem segment was unusual in its lack of specific response to growth regulators, and the slight relief of epidermal tension.