西瓜嫁接体发育中木质素合成及代谢相关酶活性的变化

研究了西瓜/葫芦嫁接体发育过程中砧木和接穗部分木质素含量及其代谢相关酶的活性变化.结果表明,嫁接体发育过程中木质素生物合成加快,砧木及接穗部分的过氧化物酶(POD)、过氧化氢酶(CAT)、苯丙氨酸解胺酶(PAL)、肉桂醇脱氢酶(CAD)等的活性均明显高于对照,接穗和砧木中POD活性在15 d内持续升高,H2O2含量和CAT活性于嫁接后9~12 d出现高峰,砧木中PAL于9 d时有活性高峰而接穗一直保持较高活性而没有活性高峰,木质素含量和CAD活性持续增长,葫芦砧木木质素的代谢水平高于西瓜接穗.     

外源水杨酸调控水稻化感抑草作用及其分子生理特性

为了探讨外源水杨酸（SA）调控水稻化感抑草效应的可行性,研究了不同浓度的外源SA对强化感水稻PI312777抑草效应的影响及其生理生化特性,并运用实时定量RT-PCR(FQ-PCR)技术检测SA介导的关键酶苯丙氨酸解氨酶基因（ZB8）的相对表达量.结果表明：外源SA能够诱导水稻化感抑草效应增强,而且这种诱导效应与SA的浓度和处理时间相关.叶面喷施SA后,PI312777对稗草的抑制率显著提高,其根系活力、超氧化物歧化酶（SOD）和过氧化物酶（POD）活性增强,过氧化氢酶（CAT）活性降低;而伴生杂草稗草的相应生理指标的变化趋势则相反.PI312777植株中的苯丙氨酸解氨酶（PAL）活性增强,总酚含量升高.0.2 mmol·L^-1的SA诱导水稻化感抑草效应最显著,该浓度下目的基因ZB8的相对表达丰度随处理时间先上调后下调,在24 h达到表达高峰.     

砀山酥梨果实苯丙氨酸解氨酶基因cDNA克隆及序列分析

为了研究梨石细胞形成与木质素合成的关系,以砀山酥梨果实为材料,通过基于同源性的RT—PCR方法,克隆木质素合成途径中的关键酶苯丙氨酸解氨酶（PAL）基因。同时利用基因数据库资料对克隆的PAL序列进行比较分析。结果表明,从砀山酥梨果实中克隆的PAL基因eDNA片段长度为585bp,推断其编码195个氨基酸序列。该序列包含与其它植物PAL相同的活性催化位点,经序列分析和同源性比对,该氨基酸序列与其它植物PAL氨基酸序列的同源性在90％以上。系统进化树分析表明,砀山酥梨PAL氨基酸序列与蔷薇科的甜樱桃PAL氨基酸序列聚类关系最近。     

Acid-labile handles for Fmoc solid-phase synthesis of peptide N-alkylamides

Summary By analogy to established methodology for the preparation of C-terminal peptide amides by 9-fluorenylmethyl-oxycarbonyl (Fmoc) chemistry, in conjunction with the acidolyzable 5-(4-Fmoc-aminomethyl-3,5-dimethoxyphenoxy)valeric acid (PAL, 1) handle, the present paper reports on 5-(4-(N-Fmoc-N-alkyl)aminomethyl-3,5-dimethoxyphenoxy)valeric acid [(R)PAL, 2] handles that can be used for synthesis of peptide N-alkylamides. The key step in the preparation of these handles was the NaBH₃CN-mediated reductive amination (60 to 85% yields; R=CH₃, CH₃CH₂, C₆H₅CH₂CH₂, 4-NO₂C₆H₅) of 5-(4-formyl-3,5-dimethoxyphenoxy)valeric acid (4), an aldehyde precursor to PAL. The (R)PAL handles (2a and b) were applied to the preparation of LHRH analogues. After anchoring of handles to PEG-PS supports, peptide chain assemblies were carried out, and treatments with TFA-thioanisolephenol-1,2-ethanedithiol (87:5:5:3) for 90 min at 25 °C, followed by aqueous workups, provided the expected products in excellent yields and purities as supported by HPLC and mass spectrometric characterization.Taken in part from the Ph.D. Thesis of M.F. Songster, University of Minnesota, 1996. Preliminary reports of this work were presented at the 14th American Peptide Symposium, Columbus, OH, June 18–23, 1995 (poster P047), and at the Fourth International Symposium on Solid Phase Synthesis and Combinatorial Chemical Libraries, Edinburgh, Scotland, UK, September 12–16, 1995.     

Control at the level of substrate supply—an alternative in the regulation of phenylpropanoid accumulation in plant cells

The problem of the intracellular mechanisms responsible for the control of accumulation of phenylalanine-derived polyphenols in plants is considered. Possible control functions of phenylalanine ammonia lyase (PAL) in this process are critically discussed and experimental facts are surveyed providing evidence that substrate (phenylalanine) supply rather than enzymic (PAL) activity is the most likely limiting factor in controlling phenylpropanoid accumulation. These facts involve: frequent lack of consistent correlation between changes in the level of PAL and accumulation rate of phenylpropanoids, high deaminating capacity of PAL markedly exceeding the level required to sustain the formation of polyphenols in most tissues, stimulatory action of phenylalanine on polyphenol accumulation when administered externally, very low and constant levels of free endogenous phenylalanine in plant tissues, and the existence of balanced relationship between protein metabolism and the formation of flavonoids and cinnamic acid derivatives in plants.     

NO对银杏悬浮细胞生长及黄酮类物质合成的影响

以硝普钠(sodium nitroprusside,SNP)为一氧化氮(NO)的供体,向银杏悬浮细胞培养液中加入不同浓度的SNP,研究外源NO对银杏悬浮细胞生长状况、过氧化氢酶(CAT)活性、苯丙氨酸解氨酶(PAL)活性和黄酮类物质生物合成的影响.结果表明,低浓度SNP有利于银杏悬浮细胞生长,而高浓度SNP可以促进黄酮类物质的合成.银杏悬浮细胞在添加0.5和10 mmol/L SNP的培养基中培养16 d时,细胞干重分别为对照组的134%和73%;在添加10 mmol/L SNP的培养基中培养20 d时,细胞中黄酮类物质的含量为对照组的136%.同时,10 mmol/L SNP促进银杏悬浮细胞PAL和CAT活性显著升高.NO专一性淬灭剂c-PITO(carboxyl phenyltetramethylimidazoleoxide)抑制SNP对银杏悬浮细胞生长、CAT活性、PAL活性和黄酮类物质含量的促进作用,说明SNP是通过其分解产物NO影响细胞生长和黄酮类物质的合成.根据这些结果推测,NO可能通过触发银杏悬浮细胞的防卫反应,激活了细胞中黄酮类物质的生物合成途径.     

Anatomy and Phenylpropanoid Metabolism in the Incompatible Interaction of Lycopersicon esculentum and Cuscuta reflexa

A time-dependent correlation of anatomical and chemical defence reactions was shown during the incompatible reaction of tomato against the phanerogamic parasite Cuscuta reflexa. Microscopical analysis of the infection sites at the tomato stem revealed the elongation of epidermal, hypodermal and collenchymatic cells beneath the parasitic prehaustorium. After 9–11 days of infection the elongated cells had collapsed forming a visible brownish plaque at the tomato stem followed by a scalariform tissue with lignified and suberized cell walls. Concomitantly, an enhanced accumulation of soluble phenolic compounds (chlorogenic acid and an unidentified hydroxycinnamic acid derivative), as well as a stimulation of peroxidases, was observed. In contrast, PAL activity was not increased. Whereas the stimulation of phenylpropanoid metabolism could also be induced by artificial wounding, the described anatomical changes were only observed during attack of Cuscuta.     

Effect of exogenous application of gibberellic acid on color change and phenylalanine ammonia-lyase, chlorophyllase, and peroxidase activities during ripening of strawberry fruit (Fragaria x ananassa Duch.)

The effect of exogenously applied gibberellic acid (GA₃) on the postharvest color change of strawberry fruit was evaluated through their external color and surface color parameters. A significant delay on color evolution was observed in fruits treated with GA₃. The evolution of activities of phenylalanine ammonia-lyase (PAL), chlorophyllase, and peroxidase was also analyzed. PAL activity increased during strawberry ripening, but in fruits treated with GA₃ the increase in such activity was slower, and, probably as consequence, the development of red color was delayed. Moreover, the activity of chlorophyllase and peroxidase, enzymes possibly involved in chlorophyll metabolism, decreased during strawberry ripening. However, a delay was observed in the decrease of such activities in GA₃-treated fruits.Abbreviations PAL phenylalanine ammonia-lyase - GA₃ gibberellic acid₃ - PVPP polyvinylpolyprrolidone - CEAU chlorophyllase enzymic activity unit - PEAU peroxidase enzymic activity unit - LSD least significant difference. Fellow of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) de la República Argentina. Author for correspondence.Members of the Research Career of the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) de la República Argentina.     

An inactivator of phenylalanine ammonia-lyase from gherkin hypocotyls

A factor capable of the reversible inactivation of PAL in vitro has been demonstrated in extracts of gherkin hypocotyls. Kinetics of the interaction between enzyme and inactivator indicate that PAL and the factor form a freely reversible complex. The properties of the inactivator are discussed in relation to its proposed role in the regulation of PAL activity in dark- and light-grown tissue.     

Sur la presence de deux isoenzymes de la phenylalanine-ammoniac-lyase chez Aesculus hippocastanum

By using the normal techniques of protein separation, two forms of PAL with different properties have been separated from the glandular tissue of Aesculus hippocastanum. A hypothesis is proposed for correlating the isoenzyme activities with the accumulation of flavonoid compounds and benzoic acids in the trichomes.