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。     

高等植物中铁的代谢机制

铁在高等植物的生长发育中发挥着重要作用,但随着人类的耕作及土壤的盐碱化,缺铁已成为一个世界性植物营养问题。高等植物在长期的进化过程中,形成了完善的对环境铁信号响应的体系。本文围绕植物与环境的相互作用,综述了近年来植物铁营养的吸收、转运、分配和储存的研究进展,并总结了植物中铁营养代谢调控的相关机理。     

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.     

{gamma}-Aminobutyric Acid Metabolism in Plants: Part 2. Metabolism in Higher Plants

The metabolism of -aminobutyric acid (AB) has been studied inhigher plants, particularly in peas and peanuts. Transaminationappeared to form the first step in AB degradation although transaminaseactivities were very low. The relatively active AB transaminaseassociated with whole pea plants possessing nodulated rootsappears to reside almost entirely within the nodules. AB transaminationwas demonstrated conclusively in extracts of mitochondria fromcotyledons of peanut seedlings; pyruvic acid acted as a betteramino-group acceptor than -ketoglutaric acid (KG). AB transaminaseactivity present in the microsomal and soluble cytoplasmic fractionsof the cells was very low AB was not metabolized perceptibly by intact mitochondria frompeanut, but when various organic acids were supplied simultaneously,an extra uptake of oxygen occurred and was associated with ABdisappearance. Aspartate, alanine, and ammonia were formed usingthe nitrogen atom of AB. The metabolic pathway followed by the carbon skeleton of ABwas traced by supplying C¹⁴-labelled material to leaf discsof peas and to mitochondria from peanut cotyledons. Radioactivitywas incorporated into organic acids, amino-acids, and respiratorycarbon dioxide in a manner suggesting that AB was convertedinto succinate which was then metabolized by the enzymes ofthe Krebs cycle present in the plant mitochondria. Glutamic decarboxylase was shown to be present largely in thenon-particulate (soluble) cytoplasm of cells. The enzymes responsiblefor AB synthesis and degradation, glutamic decarboxylase, andAB transaminase, respectively, therefore largely reside in differentsub-cellular fractions.     

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。     

Studies on Protein Metabolism in Higher Plants

Changes in ribulose diphosphate (RuDP) carboxylase activity and the content of fraction 1 protein, which had been elucidated to be identical with protein of RuDP carboxylase, in tobacco leaves were examined with age, comparing with change in total protein content. Fraction 1 protein was determined by an immunological precipitin method developed in this experiment. Fraction 1 protein decreased with age and the rate was similar or a little larger than those of total protein and total chlorophyll. The carboxylase activity decreased more rapidly than fraction 1 protein during the senescent process. In a plant, upper leaves showed higher values of the carboxylase activity and fraction 1 protein content than lower leaves. The specific activity, RuDP carboxylase activity per unit fraction 1 protein, in upper leaves was higher than that in lower leaves.     

Studies on Protein Metabolism in Higher Plants

A leaf protease of tobacco whose activity was enhanced during curing was purified about 60 times with ammonium sulfate fractionation, ethanol precipitation, calcium phosphate gel treatment and Sephadex G-200 column chromatography, and some properties of the protease were examined. The purified enzyme showed the optimum pH at 5.5 and the optimum temperature at 60°C. The protease activity was stable between pH 4.5 and 5.5 at 50°G or at pH 5.5 below 40°C for 1 hr, but completely destroyed at 70°C during 1 hr. The protease activity was greatly activated by reducing agents such as cysteine, glutathione or mercaptoethanol and inhibited by p-chloromercuribenzoate, phenyl- mercuric acetate or silver ions. Metal ions except for silver ion and ethylenediamine tetraacetic acid did not affect the protease activity so far examined.     

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.     

高等植物脯氨酸代谢研究进展

很多植物在胁迫条件下可以通过增加合成、减少降解而在体内累积大量脯氨酸,这对于调节渗透平衡、防止渗透胁迫对植物造成伤害、清除自由基、保护细胞结构具有重要意义。脯氨酸合成、降解相关酶的编码基因大都已经克隆到,但对脯氨酸在植物发育中的具体作用、胁迫条件下脯氨酸累积的分子机理了解还比较少。概述了植物控制脯氨酸合成、降解相关酶的编码基因的研究进展情况。     

高等植物赤霉素的代谢与信号转导

赤霉素是一种重要的二萜类植物激素,有着广泛而复杂的生物学功能,调节植物整个生命周期不同阶段的生长和发育。本文在分子生物学水平上对高等植物中的赤霉素代谢以及信号转导的最新研究进展进行了总结。     

Inositol Metabolism in Plants. VI. Conversion of Myo-Inositol to Phytic Acid in Wolffiella floridana

When Wolffiella floridana, an aquatic angiosperm in the family, Lemnaceae, was grown in axenic culture under continuous light in E medium containing 1.0% sucrose and a micromolar amount of ¹⁴C-labeled myo-inositol (MI), MI was taken up by the growing plants and converted to phytic acid. After 13 weeks in labeled medium during which time there was a 1000-fold increase in fresh weight, 30% of the ¹⁴C was recovered in ethanol insoluble residue. Extraction of this residue with EDTA released 70% of the label into solution. Phytic acid, identified by paper electrophoresis, ion exchange chromatography, and hydrolysis with phytase, accounted for most of this radioactivity although some label was also found in pentaphosphate and lower phosphate esters of MI. Very little MI was converted to cell wall polysaccharides under the conditions used. Results of this study indicate that Wolffiella floridana is a convenient tissue for the study of phytic acid biosynthesis under laboratory conditions.

Lemna gibba G3, grown under short day conditions in medium of the same composition as that used for W. floridana, also formed labeled phytic acid as well as other labeled lower phosphate esters of MI.

     

高等植物中一碳化合物代谢研究进展

高等植物中一碳(C1)化合物的代谢主要包括甲醇代谢、甲醛代谢和甲酸代谢等,它们是高等植物一碳单位代谢的重要组成部分.由于C1化合物的代谢机制复杂、代谢规模非常小、参与代谢反应的酶和中间产物的含量低且不稳定等特点,相关研究报道很有限.现代生化和分子遗传学方法的综合使用使得人们对参与植物中C1化合物代谢的酶和基因有了一定程度的了解,该文主要综述了近年来有关高等植物中内源和外源C1化合物甲醇、甲醛和甲酸的来源和代谢途径方面的研究进展,并提出了该研究领域目前存在的问题和今后的研究方向.