植物叶绿素的降解

文章介绍近几年来植物叶绿素降解途径以及与其相关几种酶的研究进展。     

植物叶绿素降解途径及其分子调控

文章介绍了近年来在叶绿素降解产物结构解析和关键酶基因克隆方面的最新成果,以及在此基础上的叶绿素降解途径修正及其分子调控机理研究。     

植物叶片衰老过程中叶绿素降解代谢研究进展

本文对近年来植物叶片衰老过程中叶绿素降解代谢研究进展作一介绍,包括叶绿素降解产物分离、检测和命名;叶绿素降解途径及降解酶系。此外,对叶绿素降解意义及今后研究趋势进行了评述。     

植物体内的叶绿素降解与滞绿突变体

文章介绍植物体内叶绿素降解途径和滞绿突变体的新类型研究进展。     

植物叶片衰老过程中叶绿素降解代谢研究进展

 本文对近年植物叶片衰老过程中叶绿素降解代谢研究进展作一介绍,包括叶绿素降解产物分离、检测和命名;叶绿素降解途径及降解酶系。此外,对叶绿素降解意义及今后研究趋势进行了评述。     

衰老叶片中叶绿素的降解

综述了近年来关于衰老叶片中叶绿素降解的研究情况,包括叶绿素代谢的中间产物、终产物、主要代谢途径、代谢酶及代谢途径在细胞内的定位及代谢调节方面的研究进展。     

植物病原菌产生的降解酶及其作用

综述了植物病原微生物产生的降解酶的种类、作用方式、在致病中的地位及研究进展,阐明了细胞壁降解酶的双重作用：即作为病原物侵染的致病因子及作为植物防卫反应的激发子,为寄主一病原物分子互作提供一定的参考。     

植物叶绿素合成、分解代谢及信号调控

叶绿素(Chlorophyll, Chl)合成是决定植物光合效率的重要性状, 是决定作物产量的重要因素。参与植物Chl合成、分解代谢及信号调控的基因数目众多, 其中任何一个基因发生突变都有可能引起Chl含量的变化, 从而表现为各种叶色异常甚至导致植株死亡。自然或人工创造突变体, 对于Chl相关基因的功能分析非常必要。目前, Chl突变体己广泛应用于基础研究和生产实践。文章就该研究领域内的最新研究进展进行了概述。     

植物病原茵产生的降解酶及其作用

综述了植物病原微生物产生的降解酶的种类、作用方式、在致病中的地位及研究进展,阐明了细胞壁降解酶的双重作用即作为病原物侵染的致病因子及作为植物防卫反应的激发子,为寄主一病原物分子互作提供一定的参考.     

Chlorophyll Metabolism in Higher Plants VI. Involvement of Peroxidase in Chlorophyll Degradation

The following phenolics were found to be essential for peroxidase-dependentchlorophyll bleaching: 2,4-dichlorophenol (DCP), p-coumaricacid (HCA), phenol, p-hydroxyphenylacetic acid, p-hydroxybenzoicacid, p-hydroxyacetophenone, resorcinol and umbelliferone. Mostof them are monophenols with electron-attracting groups at thep-position. The short-lived radicals generated by horseradishperoxidase (HRP)-phenolics-H₂O₂ reaction might be involved inthis reaction. Tobacco leaf enzyme preparation with peroxidaseactivity for guaiacol could also degrade chlorophyll with suchphenolics. In addition, tobacco leaf methanol extract couldsubstitute for chlorophyll bleaching as an electron donor inthe absence of phenolics. In place of free H₂O₂, the glycolate-glycolateoxidase (GOX) system could degrade chlorophyll in [peroxidase$phenolics]-dependentbleaching. This chlorophyll bleaching system was inhibited by peroxidaseinhibitors, radical scavengers, reducing reagents, and carotenoids.Ascorbate and glutathione stopped chlorophyll bleaching withGSSG reductase and NADPH. The role of ascorbate and glutathionein peroxidase activity for controlling the chlorophyll degradationrate is discussed. (Received January 28, 1985; Accepted July 23, 1985)     

24-Epibrasinolide Delays Chlorophyll Degradation and Stimulates the Photosynthetic Machinery in Magnesium-Stressed Soybean Plants

Adverse effects caused by inadequate magnesium (Mg) supply (deficiency or excess) often cause oxidative stress in chloroplasts and a decline in photosynthetic activity. However, 24-epibrassinolide (EBR) is a natural, biodegradable, and ecologically viable plant growth regulator with multiple roles in plant metabolism. This research aims to determine whether the foliar application of EBR (1) can delay chlorophyll degradation and/or (2) mitigate oxidative stress on the photosynthetic process in magnesium-stressed soybean plants. The experiment followed a completely randomized factorial design with two concentrations of 24-epibrassinolide (0 and 0.1 mM EBR, described as – EBR and?+?EBR, respectively) and three Mg supplies (0.0225, 2.25 and 225 mM Mg, described as low, control and high supply of Mg). Inadequate Mg supplies (deficiency and excess) negatively interfered with photosynthetic pigments, chlorophyll fluorescence and gas exchange. However, exogenous EBR sprayed in plants under high Mg maximized superoxide dismutase (37%), catalase (34%), ascorbate peroxidase (48%) and peroxidase (49%), protecting against oxidative stress and delaying chlorophyll degradation. Concomitantly, plants sprayed with this steroid had increases in Mg content, improving the photochemical efficiency and gas exchange because Mg plays an essential role during the light capture process.

     

Enzymatic Degradation of Chlorophyll in Chenopodium album

The breakdown of chlorophyll (Chi) in crude extracts of Chenopodiumalbum (white goose foot) in the dark was examined. Derivativesof pheophorbide were formed when Chi or chlorophyllide wasincubated with depigmented crude extracts. The formation ofpheophorbide was completely prevented by heat treatment of extracts,indicating that the reaction was enzymatic, and the presenceof a Mg-releasing enzyme, the so called Mg-dechelatase, waspostulated. This hypothesis was strongly supported by the observationthat the formation of pheophorbide was inhibited by 51% by 10mM MgCl₂. Analysis by high-performance thin-layer chromatography(HPTLC) and liquid chromatography (HPLC) showed that the appearanceof chlorophyllide , pheophorbide 13²-hydroxychlorophyllide and pyropheophorbide was accompanied by a concomitant decreasein levels of Chi The formation of 13²-hydroxychloro-phyllide was not clearly an enzymatic reaction and requires furtherexamination. It appears that Chl is degraded in a crude extractof C. album via the following enzymatically catalyzed reactions (Received September 10, 1990; Accepted November 15, 1990)     

高等植物叶绿素生物合成的研究进展

叶绿素是植物叶绿体内参与光合作用的重要色素,其功能是捕获光能并驱动电子转移到反应中心.整个叶绿素生物合成过程(L-谷氨酰-tRNA→叶绿素a→叶绿素b)需要15步反应,涉及15种酶,迄今在模式植物拟南芥中已分离到27个编码这些酶的基因,完成了以拟南芥为代表的被子植物叶绿素生物合成全部基因的克隆.本文主要对近年来国内外有关植物叶绿素的生物合成过程及相关酶基因的克隆、生物合成途径中2个关键步骤(σ-氨基酮戊酸(ALA)合成和Mg离子插入原卟啉Ⅸ的调节)、影响叶绿素生物合成的主要因素(光、温度、营养元素等),以及叶绿素生物合成相关酶的其他生物学功能等的研究进展进行综述.     

Chlorophyll Biosynthesis in a Cell-free System from Higher Plants

A crude homogenate obtained from greening cucumber (Cucumis sativus, L.) cotyledons in tris-sucrose, pH 7.7, containing coenzyme A, glutathione, potassium phosphate, pH 7.7, methyl alcohol, magnesium, nicotinamide adenine dinucleotide, and adenosine triphosphate, is able to incorporate 4-(14)C-delta-aminolevulinic acid into chlorophyll a and b in the presence of oxygen. If the homogenates are prepared from etiolated cotyledons which have been exposed to light for two and one-half hours, (14)C-chlorophyll a is synthesized. However, when the homogenates are prepared from cotyledons illuminated for four and one-half hours, both (14)C-chlorophyll a and b are produced.