Protochlorophyll Biosynthesis in a Cell-free System from Higher Plants

A cell free system prepared from etiolated cucumber (Cucumis sativus, L) in tris-sucrose buffer is able to incorporate delta-aminolevulinic acid-4- (14)C into the two components of protochlorophyll: protochlorophyllide and protochlorophyllide ester. The activity is associated with the etioplasts. Optimal incorporation is obtained at pH 7.7. For the formation of protochlorphyllide ester, oxygen, reduced glutathione, methyl alcohol, magnesium, inorganic phosphate, and nicotinamide adenine dinucleotide are required. For the formation of (14)C-protochlorophyllide, adenosine triphosphate, and coenzyme A are required in addition to the above. The requirement for methyl alcohol is highly specific, and the methyl group appears to be incorporated into the protochlorophyll molecules. A biosynthetic scheme resulting in the parallel production of (14)C-protochlorophyllide and (14)C-protochlorophyllide ester from (14)C-Mg protoporphyrin monoester is presented.     

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)     

高等植物赤霉素生物合成及其调节研究进展

主要介绍近年来高等植物中生物活性GAs的生物合成,拟南芥GA生物合成途径中关键酶基因（GA1－GA5）的克隆和GA3基因CYP701A3的母（Saccharomyces cerevisiae）中的成功表达。评述了活性GAs对赤霉不生物合成的反馈抑制作用和反馈调节中信号的传递和接收问题。高等植物中光周期对GA生物合成的调节主要是在20－氧化和／或3β－羟基化步骤。     

Terpene Biosynthesis in Cell-free Extracts and Excised Shoots from Wedgwood Iris

Excised shoots and cell-free extracts prepared from Wedgwood iris (Iris hollandica Hoog. “Wedgwood”) shoots metabolized ¹⁴C-labeled mevalonic acid (MVA). By using cell-free extracts, the ¹⁴C from MVA-1-¹⁴C was recovered as ¹⁴CO₂, while that from MVA-2-¹⁴C was recovered as neutral terpenes, acid-hydrolyzable terpenes, or ¹⁴CO₂. Also, under optimal incubation conditions, 12.8 nanomoles R-MVA-2-¹⁴C was incorporated into neutral terpenes per milligram fresh weight per hour. In contrast, excised shoots incorporated only 0.58 nanomoles R-MVA-2-¹⁴C per mg fresh weight per hour. Labeled products identified from the cell-free system were squalene, farnesol, geranylgeraniol, and compounds that are converted to farnesol and geranylgeraniol after alkaline hydrolysis. Squalene and a 4,4-dimethylsterol were identified as products from excised shoots but not the terpene alcohols or the alkaline-hydrolyzable compounds.     

高等植物脱落酸的生物合成及其调控

介绍了近年来高等植物体内ABA的合成部位,ABA生物合成缺陷型突变体,ABA生物合成途径及其调控的最新研究进展。     

高等植物脱落酸生物合成途径及其酶调控

脱落酸(ABA)生物合成一般有两条途径:C15直接途径和C40间接途径,前者经C15法呢焦磷酸(FPP)直接形成ABA;后者经由类胡萝卜素的氧化裂解间接形成ABA,是高等植物ABA生物合成的主要途径.9-顺式环氧类胡萝卜素氧化裂解为黄质醛是植物ABA生物合成的关键步骤,然后黄质醛被氧化形成一种酮,该过程需NAD为辅因子,酮再转变形成ABA-醛,ABA-醛氧化最终形成ABA.在该途径中,玉米黄质环氧化酶(ZEP)、9-顺式环氧类胡萝卜素双加氧酶(NCED)和醛氧化酶(AO)可能起重要作用.     

高等植物油菜素内酯的生物合成及信号转导研究进展

综述了近年来发现的植物油菜素内酯生物合成缺陷型及反应不敏感型突变体,BR生物合成的早期C 6氧化和晚期C 6氧化途径,参与合成的酶以及BR信号转导等方面的研究进展,并提出了这一问题今后研究的前景.     

植物叶绿素的降解

简要介绍了植物叶绿素降解及其机制的研究进展。     

Biosynthesis of Ureides from Purines in a Cell-free System from Nodule Extracts of Cowpea [Vigna unguiculata (L) Walp.

The synthesis of ¹⁴C-labeled xanthine/hypoxanthine, uric acid, allantoin, allantoic acid, and urea from [8-¹⁴C]guanine or [8-¹⁴C]hypoxanthine, but not from [8-¹⁴C]adenine, was demonstrated in a cell-free extract from N₂-fixing nodules of cowpea (Walp.). The ¹⁴C recovered in the acid/neutral fraction was present predominantly in uric acid and allantoin (88-97%), with less than 10% of the ¹⁴C in allantoic acid and urea. Time courses of labeling in the cell-free system suggested the sequence of synthesis from guanine to be uric acid, allantoin, and allantoic acid. Ureide synthesis was confined to soluble extracts from the bacteroid-containing tissue, was stimulated by pyridine nucleotides and intermediates of the pathways of aerobic oxidation of ureides, but was completely inhibited by allopurinol, a potent inhibitor of xanthine dehydrogenase (EC 1.2.1.37). The data indicated a purine-based pathway for ureide synthesis by cowpea nodules, and this suggestion is discussed.     

Detection of Chlorophyll Breakdown Products in the Senescent Leaves of Higher Plants

The determination of intermediary breakdown products of chlorophyllsin senescent leaves of higher plants was performed by high-performanceliquid chromatographic technique that had been newly developedto separate and identify the oxidation products of chlorophylls,in particular monopyrrole derivatives [Suzuki et al. (1999)J. Chromatogr. A 839: 85]. In six plants tested, degradationproducts were detected only in the senescent leaves of plantsincluding barley (Hordeum vulgare), except for radish (Raphanussativus), in which they were found both in pre- and senescentcotyledons. In the senescent cotyledons of barley, three degradationproducts, hematinic acid, methyl ethyl maleimide, and the putativedegraded C-E-ring derivative, methyl vinyl maleimide dialdehyde,were detected. In addition to above three products, methyl vinylmaleimide was also found in both pre- and senescent cotyledonsof radish. These products decreased during senescence with anaccumulation of unknown compound(s), probably degraded monopyrrolederivatives. The degradation process and amounts of breakdownproducts of chlorophylls depend largely on plant species andvary with length of senescence. To conclude, it is likely thatchlorophylls are degraded into low-molecular-weight hydrolyticcompounds through monopyrroles. (Received March 10, 1999; Accepted June 11, 1999)     

高等植物中异黄酮合成代谢及其调控

异黄酮是植物次级代谢过程中产生的酚类物质,豆科等植物中含量丰富,在动植物体内有着广泛的生理作用。本文综述了高等植物中异黄酮的合成代谢途径及其关键酶以及调控机理。     

高等植物脱落酸生物合成的酶调控

高等植物ABA的生物合成开始于细胞质内的甲瓦龙酸 (MVA)或位于叶绿体内的丙酮酸_硫胺素焦磷酸 (TPP) ,经一系列反应最后在质体或胞质中形成的。除胁迫或植物发育中生理变化引起的诱导外 ,ABA的合成还受到一系列酶的调控 ,其中 ,玉米黄质环氧化酶 (ZE) ,9_顺环氧类胡萝卜素双加氧酶(NCED)和醛氧化酶 (AO)可能起到重要的调节作用。本文介绍近年来ABA生物合成酶调控的研究进展。     

高等植物花生长和花色素苷生物合成的信号调控

介绍了赤霉素、光和糖信号对花生长和花色素苷生物合成过程的调控及调控机制的研究进展。     

Biosynthesis of Carotenoids in the Chloroplasts of Algae and Higher Plants

Physiological, biochemical, and genetic aspects of carotenoid biosynthesis in the chloroplast membranes of green algae and higher plants are discussed starting from the earliest stages of biosynthesis of key C₅-isoprene units. The latter are synthesized either from acetate (C₂) to mevalonic acid (C₆) or from glucose (C₆) by forming glyceraldehyde 3-phosphate (C₃) and pyruvate decarboxylation product (C₂) through intermediate compounds to isopentenyl diphosphate (C₅). In all organisms, the further carotenoid synthesis from isopentenyl diphosphate and its isomer dimethylallyl diphosphate (C₅) proceeds through their transformation into geranyl diphosphate (C₁₀), farnesyl diphosphate (C₁₅), geranylgeranyl diphosphate (C₂₀) and phytoene (C₄₀). Phytoene desaturation (dehydrogenation) to carotene, neurosporene, and lycopene, and all steps of their cyclization to , and carotenes are discussed in detail. The synthesis of xanthophylls in chloroplasts is presented as the sequential formation of hydroxy-, epoxy- and oxo- groups. Genetic control of biosynthesis, as well as the localization and functional role of carotenoids in the chloroplast membranes of plants and algae are briefly discussed.     

高等植物体中植酸合成、代谢及其生理作用

本文对植酸及其存在形式、代谢、调控及在高等植物内的生理作用作了介绍。     

叶绿素生物合成的分子调控

介绍了叶绿素生物合成的分子调控研究进展,并对今后这一领域的研究作了展望。     

Some Physical Characteristics of the Enzymes of l-Tryptophan Biosynthesis in Higher Plants

Anthranilate synthetase, phosphoribosyltransferase, phosphoribosyl anthranilate isomerase, and indoleglycerol phosphate synthetase were examined in partially purified extracts of the monocotyledon, Zea mays and the dicotyledon, Pisum sativum. The plant extracts were chromatographed on DEAE-cellulose and Sephadex G150. The molecular weights of the enzymes were determined and found to be similar to those observed for many bacteria. None of the plant tryptophan enzyme activities was aggregated in vitro as is also the case with most bacteria. This is in contrast with the complex aggregation patterns observed in other eucaryotic organisms that have been examined (fungi and Euglena gracilis). The tryptophan enzymes from peas and corn were generally similar but some differences in stability were observed.     

Mevalonate Biosynthesis in Plants

Referee: Guiseppe Inesi, M.D., Ph.D., Professor and Chairman, School of Medicine, Dept. of Biochemistry and Molecular Biology, Univeristy of Maryland, Baltimore.