Characterization and partial purification of three glycosidases from castor bean endosperm

α-Mannosidase and β-N-acetylhexosaminidase, which could function in the cleavage of glycosidic linkages in the native Ricinus communis lectins, and β-galactosidase were purified some 100-fold from the endosperm tissue of castor bean seedlings. The procedure used ammonium sulphate precipitation followed by chromatography on CM-cellulose, hydroxyapatite and Sephacryl S-300 to separate the three activities. All three glycosidases were present, with the lectins, in the protein bodies of dry seed and increased in activity during the time that lectins are broken down in the vacuoles. The enzymes show optimal activity in the range pH 3–5.5. The α-mannosidase had a K_m of 0.77 mM for p- nitrophenyl-α-D-mannopyranoside. The β-galactosidase showed a K_m of 1.39 mM for p-nitrophenyl-β-D-galactopyranoside. The β-N-acetylhexasominidase had a K_m of 0.47 mM for p-nitrophenyl-N-acetyl-β-N-glucosamide and a K_m of 0.33 mM for p-nitrophenyl-N-acetyl-β-D-galactosamide. Effects of competitive inhibitors and cations were described.     

Endosperms and embryos of mature dry castor bean seeds contain active ribosomes

Mature dry endosperms and embryos of castor bean contain ribosomes which are capable of catalysing protein synthesis in vitro. This observation contradicts previous reports that ribosomes are absent from mature dry endosperms. On hydration of the mature seeds the polyribosome content of both embryos and endosperms increases. These polyribosomes are lost on subsequent dehydration but, again, ribosomes are conserved. REFERENCES     

The relationship of the pyridine nucleotide cycle to ricinine biosynthesis in Ricinus Communis

Quinolinic acid-6-¹⁴C feeding experiments were performed using Ricinus communis L. plants to determine the efrect of selected inhibitors on the incorporation of this precursor into the alkaloid, ricinine, and into the pyridine nucleotide cycle intermediates. Administration of azaserine and azaleucine resulted in a decrease in the incorporation into ricinine and an increase in the radioactivity remaining in quinolinic acid. Administration of excess ricinine and ethionine yielded similar results. This mutual inhibition indicated an interdependency between the conversion of quinolinic acid to ricinine and to the pyridine nucleotide cycle intermediates.     

Mixed function oxidases from germinating castor bean endosperm

Homogenates from germinating castor bean endosperm were fractionated by sucrose density gradient centrifugation and examined for mixed function oxidase activity. Activity of cinnamic acid 4-hydroxylase and p-chloro-N-methylaniline N-demethylase was highest in the endoplasmic reticulum fraction. Activity of both enzymes is dependent on NADPH and on molecular oxygen; both activities are inhibited by carbon monoxide. When challenged with a number of potential inhibitors the enzymes responded in ways fairly typical of mixed function oxidases from other plants and animals. The N-demethylase appears to be specific for N-methylarylamines. In the absence of NADPH, cumene hydroperoxide is able to support N-demethylation. The mechanistic significance of this activity is discussed.     

Diethylene glycol disulfide from castor bean cell suspension cultures

Diethylene glycol disulfide was isolated from castor bean cell suspension cultures. Incubation of suspension cultures with Na₂³⁵SO₄ resulted in the incorporation of radioactivity into the isolated diethylene glycol disulfide. Diethylene glycol disulfide was detected in cells (430 nmol/g cells) and in cell-free growth medium (41.5 nmol/ml).     

我国优势油脂类生物柴油植物蓖麻的种质资源发掘和生物柴油利用

发展可再生生物质能源是解决人类能源危机和环境污染的重要途径。利用边际土地发展油脂类生物质能是生物质能的重要组成部分。蓖麻因为适应性强和油脂成份独特被誉为"理想的生物柴油植物"。蓖麻是我国优势油脂类能源植物,利用边际土地,发展蓖麻产业为我国生物柴油产业化提供原料,是我国现阶段生物柴油产业化发展的相对理想而又现实的选择,而且具有重要的发展前景和巨大的发掘潜力。立足我国现阶段生物柴油产业化的瓶颈问题,着重阐述了蓖麻种质资源发掘的现状、优良品种培育的途径和发展前景,以及利用蓖麻种子油生产商业化生物柴油的现状,以期推动我国利用边际土地发展蓖麻产业以及生物柴油商业化生产。     

Fungicidal effect of ultraviolet-C radiations in prevention of mycoflora of castor bean seeds

The effect of ultra violet (UV-C) radiation on germination and fungal flora of castor bean seeds was estimated with different doses stored up to 80?days interval. Results revealed that 20 and 40?min radiated castor bean seeds showed complete reduction in most of the fungi while germination of castor bean seeds were enhanced when UV-C radiations applied for 20?min. Increasing the radiation doses and storage period has been shown decrement in Aspergillus species colonisation.     

Comparison of homoserine dehydrogenase from different plant sources

Homoserine dehydrogenase (HSD) was partially purified from castor bean, pea and wheat seedlings. The enzyme from pea had a MW of 75 000 and no sensitivity to threonine when measured in the direction of homoserine formation (forward reaction). The enzyme purified from castor bean had a MW of 290 000–350 000 and exhibited an almost complete inhibition by 1 mM threonine. Furthermore, this enzyme exhibited a polymeric nature as shown by polyacrylamide electrophoresis of the desensitized preparation and by SDS electrophoresis of the native enzyme. In wheat two isoenzymes were separated by gel filtration on Sephadex G 200. The fast-moving fraction (HSD I) was completely inhibited by threonine and exhibited a MW of 280 000, while the slow-moving fraction (HSD II) was insensitive to threonine and had a MW of 75 000. The sensitive enzyme from wheat and castor bean showed an almost absolute requirement for K⁺. The enzyme from pea and the insensitive form from wheat did not show a requirement for K⁺. For the wheat enzyme the effect of several amino acids and the main kinetic constants were studied.     

Alkaloid biosynthesis in Croton linearis

The ability of Croton linearis to form crotonosine from linearisine has been demonstrated; the extent of this conversion appears to vary according to the sex of the plant.     

Homoserine dehydrogenase in Pisum sativum and Ricinus communis

Homoserine dehydrogenase was extracted from Ricinus communis and Pisum sativum. The kinetic parameters of the forward and reverse reactions were determined. In the forward reaction only the enzyme from Ricinus is inhibited by threonine. The response to K⁺ is different for the enzyme from the two sources.     

Biosynthesis of securinine,the main alkaloid of Securinega suffruticosa

Biosynthesis of securinine was studied by incorporation experiments in Securinega suffruticosa. Among presumed precursors tested, lysine, cadaverine, and tyrosine showed the highest incorporation into securinine. Degradation experiments revealed that cadaverine-[1,5-¹⁴C] labelled specifically the piperidine ring of securinine and the radioactivity from dl-tyrosine-[2-¹⁴C] was introduced into the C-11 lactone carbonyl. Experiments with L-tyrosine-[U-¹⁴C] and L-tyrosine-[3′,5′-³H; U-¹⁴C] prove that the remaining C₆Sz.sbnd;C₂ moiety is derived from the aromatic ring and the C-2 and C-3 or tyrosine.     

Biosynthesis of crotsparine,crotsparinine and sparsiflorine

The biosynthesis of crotsparine, crotsparinine and sparsiflorine in Croton sparsiflorus has been studied using racemic [Ar-³H]-coclaurine, isococlaurine and norcoclaurine. Tyrosine and coclaurine are shown to be precursors of all three alkaloids.     

Isolation and characterization of two tightly linked catalase genes from castor bean that are differentially regulated

Two catalase genes,cat1 andcat2, have been isolated from the castor bean genome. They were located in the same direction on a chromosome at a distance of 2.4 kb,cat1 being on the downstream side ofcat2. The two genes contained introns at the same positions except that one of the 7 introns incat1 is missing incat2 and the corresponding introns differed in size and sequence between the two genes. The translated regions of the two genes had the same number of nucleotides and exhibited 81.3% nucleotide sequence identity. In addition to introns, the nucleotide sequences of the 5-and 3-flanking regions are highly divergent between the two genes. In etiolated seedlings,cat1 mRNA was present abundantly in endosperms and cotyledons and only in a small amount in roots. Thecat1 mRNA could not be detected in hypocotyls. By contrast,cat2 mRNA is most abundant in hypocotyls and roots, while endosperms and cotyledons contained only low levels ofcat2 mRNA. Although neithercat1 norcat2 mRNA could be detected in dry seeds, both mRNAs showed temporal accumulation in the endosperm in response to germination. These results suggest that expression of two tightly linked catalase genes of castor bean,cat1 andcat2, are differentially regulated during development.     

蓖麻根腐病抗性鉴定及其SSR标记的初步建立

蓖麻根腐病是茄腐镰孢菌(Fusarium solani)引起的根部病害,严重影响蓖麻产量。抗源缺乏制约了抗病品种的选育。为寻找抗病种质、建立抗性分子标记,该研究对252份蓖麻材料的抗性进行了表型和分子标记鉴定。结果表明:(1)浓度为1×10⁶个·mL^-1的孢子悬浮液灌根是一种有效的接种方法; 以接种后枯萎天数为基础的5级评价法,可作为鉴定标准。(2)鉴定出130份抗病材料,其中高抗为105份。(3)野生材料中抗病材料比率(66%)远高于栽培材料(35%),建议将野生材料,尤其是中国华南野生材料的研究利用作为今后抗病育种的重要方向。(4)初步建立了8个与抗性关联的SSR标记。该研究结果提供了有效的根腐病抗性鉴定方法和评价标准,筛选出了一批育种迫切需要的抗病基因资源,初步建立了可用于辅助选择的SSR标记,为蓖麻抗根腐病育种奠定了重要基础。     

Nucleic acid (cDNA) and amino acid sequences of isocitrate lyase from castor bean

A cDNA library was constructed to mRNA enriched for isocitrate-lyase mRNA from castor-bean (Ricinus communis var. zanzibarensis) endosperms. Nine clones for isocitrate lyase (EC 4.1.3.1) were identified. The insert of 2.2 kb from clone ICL4 was sequenced and proved to contain the entire coding region, 1731 bp, for isocitrate lyase. The amino acid sequence of isocitrate lyase was deduced from the nucleic acid sequence. By analogy with muscle aldolase a lysine residue that possibly takes part in the binding of the substrate was identified. The 3 untranslated region contained three putative polyadenylation addition signals and two direct repeats.     

Isolation and characterization of NAD(P)H-dehydrogenases from seeds of the castor bean

Two pyridine nucleotide dehydrogenases have been isolated from castor bean seed extracts by a combination of ion exchange chromatography on DEAE-Sepharose and gel permeation chromatography on Sephadex G-200. The enzymes were designated D-I and D-II according to their elution position on DEAE-Sepharose. Both enzymes D-I and D-II are globular proteins which have MWs of 66 000 and 60 000, respectively. Dehydrogenation is observed with both NADH and NADPH as electron donors, while the electron acceptor specificity demonstrates that the enzymes are probably NAD(P)H: quinone oxidoreductases. Successful coupling of dehydrogenase activity with that of peroxidase indicates a possible role of the enzymes in seed germination.     

Regulation of sterol biosynthesis in etiolated mung bean hypocotyl sections

The incorporation of radioactivity into sterols by transmethylation of methionine-[¹⁴C-methyl] was studied in mung bean hypocotyl sections. Young hypocotyl sections (1 cm) synthesized 4 times more radioactive sterols than older sections (5 cm). The transmethylation reactions may be rate limiting in older tissues. Wounding has only a quantitative effect on sterol biosynthesis, as seen by incorporation experiments with MVA-[2-¹⁴C]. Naphthalene acetic acid (NAA) stimulates sterol biosynthesis in both wounded surfaces and intact tissues of mung bean hypocotyl sections.