6-甲氧基-2-苯并唑啉酮(MBOA)分布不均匀是引起玉米胚芽鞘向光性运动的主要原因

采用高效液相色谱分析等方法,对玉米（ＺｅａｍａｙｓＬ．）胚芽鞘在单侧蓝光作用下产生的生物活性物质进行分析发现：１．在单侧蓝光作用下,胚芽鞘向光侧的生长抑制物质６甲氧基２苯并唑啉酮（ＭＢＯＡ）含量比背光侧多１．５倍。２．向光性刺激后,胚芽鞘向光侧和背光侧生长素的含量没有出现明显的差异。３．于胚芽鞘一侧外施ＭＢＯＡ及其类似物５,６ｄｉｍｅｔｈｏｘｙ２ｂｅｎｚｏｘａｚｏｌｉｎｏｎｅ（ＤＭＢＯＡ）和２ｃｈｌｏｒｏ５,６ｄｉｍｅｔｈｏｘｙ２ｂｅｎｚｏｘａｚｏｌｉｎｏｎｅ（ＣｌＤＭＢＯＡ）等抑制物质,均使胚芽鞘产生弯曲生长,表明引起玉米胚芽鞘向光性运动的直接原因是ＭＢＯＡ分布不均匀。     

Degradation of the benzoxazolinone class of phytoalexins is important for virulence of Fusarium pseudograminearum towards wheat

Wheat, maize, rye and certain other agriculturally important species in the Poaceae family produce the benzoxazolinone class of phytoalexins on pest and pathogen attack. Benzoxazolinones can inhibit the growth of pathogens. However, certain fungi can actively detoxify these compounds. Despite this, a clear link between the ability to detoxify benzoxazolinones and pathogen virulence has not been shown. Here, through comparative genome analysis of several Fusarium species, we have identified a conserved genomic region around the FDB2 gene encoding an N‐malonyltransferase enzyme known to be involved in benzoxazolinone degradation in the maize pathogen Fusarium verticillioides. Expression analyses demonstrated that a cluster of nine genes was responsive to exogenous benzoxazolinone in the important wheat pathogen Fusarium pseudograminearum. The analysis of independent F. pseudograminearum FDB2 knockouts and complementation of the knockout with FDB2 homologues from F. graminearum and F. verticillioides confirmed that the N‐malonyltransferase enzyme encoded by this gene is central to the detoxification of benzoxazolinones, and that Fdb2 contributes quantitatively to virulence towards wheat in head blight inoculation assays. This contrasts with previous observations in F. verticillioides, where no effect of FDB2 mutations on pathogen virulence towards maize was observed. Overall, our results demonstrate that the detoxification of benzoxazolinones is a strategy adopted by wheat‐infecting F. pseudograminearum to overcome host‐derived chemical defences.     

Enantioseparation of benzoxazolinone aminoalcohols and their aminoketone precursors,potential adrenergic ligands,by analytical and preparative liquid chromatography on amylose chiral stationary phases and characterization of the enantiomers

To obtain milligram amounts of the enantiomers of benzoxazolinone derivatives to be tested for binding to adrenergic sites, analytical HPLC methods using derivatized amylose chiral stationary phases were developed for the direct enantioseparation of benzoxazolinone aminoalcohols and their aminoketone precursors, derivatives with one or two chirals centers. The separations were made using normal phase methodology with a mobile phase of n‐hexane‐alcohol (ethanol, 1‐propanol, or 2‐propanol) in various proportions, and silica‐based amylose (tris‐3, 5‐dimethylphenylcarbamate) Chiralpak AD and (tris‐(S)‐1‐phenylethylcarbamate) Chiralpak AS columns. The effects of concentration of various aliphatic alcohols in the mobile phase were studied. The best separation was achieved on Chiralpak AS, so preparative HPLC was set up with this chiral stationary phase using a mobile phase consisting of n‐hexane‐alcohol using isocratic conditions and multiple repetitive injections. Physicochemicals properties of enantiomers were reported The effect of structural features of the solutes on discrimination between the enantiomers was examined. Limit of detection (LD) and limit of quantification (LQ) were determined using both ultra‐violet (UV) and evaporative light‐scattering detection (ELSD). Chirality, 2009. © 2008 Wiley‐Liss, Inc.     

Selection for low dormancy in annual ryegrass (Lolium rigidum) seeds results in high constitutive expression of a glucose-responsive α-amylase isoform

Background and Aims

α-Amylase in grass caryopses (seeds) is usually expressed upon commencement of germination and is rarely seen in dry, mature seeds. A heat-stable α-amylase activity was unexpectedly selected for expression in dry annual ryegrass (Lolium rigidum) seeds during targeted selection for low primary dormancy. The aim of this study was to characterize this constitutive activity biochemically and determine if its presence conferred insensitivity to the germination inhibitors abscisic acid and benzoxazolinone.

Methods

α-Amylase activity in developing, mature and germinating seeds from the selected (low-dormancy) and a field-collected (dormant) population was characterized by native activity PAGE. The response of seed germination and α-amylase activity to abscisic acid and benzoxazolinone was assessed. Using an alginate affinity matrix, α-amylase was purified from dry and germinating seeds for analysis of its enzymatic properties.

Key Results

The constitutive α-amylase activity appeared late during seed development and was mainly localized in the aleurone; in germinating seeds, this activity was responsive to both glucose and gibberellin. It migrated differently on native PAGE compared with the major activities in germinating seeds of the dormant population, but the enzymatic properties of α-amylase purified from the low-dormancy and dormant seeds were largely indistinguishable. Seed imbibition on benzoxazolinone had little effect on the low-dormancy seeds but greatly inhibited germination and α-amylase activity in the dormant population.

Conclusions

The constitutive α-amylase activity in annual ryegrass seeds selected for low dormancy is electrophoretically different from that in germinating seeds and its presence confers insensitivity to benzoxazolinone. The concurrent selection of low dormancy and constitutive α-amylase activity may help to enhance seedling establishment under competitive conditions.