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1.
Alloteropsis semialata (R.Br.) Hitchcock is a widely distributedgrass species known to show marked morphological, anatomicaland physiological variation. An unusual feature of this grassis that it shows both C3, and C4 photosynthetic pathways withthe respective anatomy related to these pathways in one speciesand within a single environment. This study investigates ultrastructuraldifferences between C3 and C4 forms of A. semialata, and showsdistribution of chlorenchyma in the two forms, at light microscopelevel. Quantitative assessment shows marked differences in mesophylland Kranz sheath cells with regard to size and organelle content;also in distribution of starch grains, lipid droplets and organellesin the mesophyll cells of both forms. These differences arediscussed in relation to the C3/C4 syndrome. Measurements were made using a Digiplan electronic planimeteron transmission electron micrographs of mature leaves sectionedtransversely at mid-lamina, and on drawings of leaf sectionsshowing the distribution of chlorenchymatous tissue. Alloteropsis semialata(R.Br.) Hitchcock, leaf structure, chlorenchyma, ultrastructure, C3-photosynthesis, C4-photosynthesis  相似文献   

2.
During germination in the light, the endosperm, containing ahigh proportion of reserve fat (composed largely of shorter-chain(C8 to C14 saturated fatty acids), is slowly invaded by theexpanding haustorium (cotyledon). Free fatty acids accumulatein the endosperm, preferential hydrolysis of longer-chain saturatedacids (C14 to C18 occurring under conditions of slow growth.Lipids are absorbed by the haustorium, the process being superficiallysimilar in certain respects to intestinal fat absorption. Whencomplicating factors are removed, absorption is found to beunselective during disappearance of 75 per cent, of the endospermlipids. Amounts of lipid in the haustorium are low compared with thehigh concentration in the surrounding endosperm and, beforephotosynthesis starts, losses through respiration account fora large part of the reserves which disappear. No free fattyacids are present in the haustorium. Breakdown of fatty acids is relatively unspecific, althoughthe acids characteristic of the haustorium (C16 C18, oleic andlinoleic acids) are metabolized some what less rapidly thanthe shorter-chain saturated acids (C8 to C14 characteristicof the endosperm fat. Both root and shoot have a low fat content. The fatty-acid compositionof the former changes little during growth, but in the shootlinolenic acid increases proportionately during leaf expansionin the light.  相似文献   

3.
The paralytic shellfish poison prducing dinoflagellate Gymnodiniuncatemrum was subjected to changes in salinity, phosphate, ammoniumand nitrate using continuous culture and batch culture methods.In contrast with other algae, this species showed very slowchanges in the concentration of intracellular amino acids, inthe Gln:Glu ratio, and, in contrast with Alrsandnum spp., onlyslow changes in toxin content, during such events as N-feedingof Ndeprived cells or during nutrient deprivation. This organismwas found to be very susceptible to disturbance; maximum growthrates around 0.25–0.3 day–1 with a minimum C:N massratio of 5.5, were attained when cultures were only disturbedby sampling once a day. P-deprived cells were larger (twicethe usual C content of 4 ng C cell–1 and volume of 20pl). The content of free amino acids was always low (5% of cell-N),with low contributions made by arginine (the precursor for paralyticshellfish toxins). Cells growing using ammonium had the lowestC:N ratios and the highest proportion of intracellular aminoacids as arginine. The toxin profile (equal mole ratios of dcSTX,GTX5, dcGT2/3 C1 and C2, and half those values for C3 and C4)was stable and the toxin concentration varied between 0.2 and1 mM STX equivalents (highest when ammonium was not limiting,lowest in P-deprived cells, though as the latter were largertoxin per cell was not so variable). Decreased salinity didnot result in increases in toxin content. Significant amountsof amino acids (mainly serine and glycine, with a total oftenexceeding 4 µM) accumulated in the growth medium duringbatch growth even though the cultures were not bacteria free. 4Present address: Instituto Español de Oceanografia,Apdo 1552, 36280, Vigo, Spain  相似文献   

4.
冯姗  张耀洲 《昆虫学报》2006,49(5):726-732
锌带蛋白(zinc ribbon protein )是锌指类蛋白的一种,它的Cys4 Zn(2+)结合位点由3个β2片层折叠而成,而不是α螺旋结构。锌带结构与锌指结构同为转录因子结合核酸的结构域,锌带蛋白作为转录相关因子在调节基因表达活性等方面具有重要作用。在对家蚕 Bombyx mori蛹cDNA文库测序中,发现一个新的编码家蚕锌带蛋白基因的EST序列(GenBank 登录号DY230964),以此序列为信息探针检索家蚕EST数据库,通过同源筛选,获得一个新的家蚕锌带蛋白基因cDNA全序列并经RT-PCR检测和克隆、测序验证,结果表明与电子克隆序列完全一致。我们将其命名为 BmZNRD1 (Zinc Ribbon Domain Containing 1)(GenBank登录号DQ432055)。该基因全长为675 bp,由363 bp的开放阅读框序列(ORF)、10 bp的5′端非翻译区序列(5′UTR)和302 bp 的3′端非编码区序列(3′ UTR)组成,其编码的120个氨基酸序列与其他真核生物间具有较高的同源性(达60%左右),预测分子量为13.54 kD, 等电点为6.8。BmZNRD1编码的氨基酸序列是一种锌带蛋白,推测有2个功能结构域,分别是位于N-端的Cx2Cx14Cx2C和C-端的Cx2Cx24Cx2C,其中C-端保守氨基酸序列Cx2Cx6Yx3QxRSADEx2TxFx2Cx2C在生物进化中保守性很高,从酵母、果蝇、线虫到两栖类、哺乳类都有发现该结构域的存在,与酵母RNA聚合酶A亚单位9和转录相关蛋白有很高的相似性,推测其具有相同的功能。将BmZNRD1基因cDNA序列与家蚕基因组序列进行比对,结果表明该基因具有3个外显子,2个内含子,外显子/内含子边界符合经典的GT-AG规则。 关键词: 家蚕; 锌带蛋白基因; 电子克隆; 基因克隆; 序列分析  相似文献   

5.
The kinetic properties of phosphoenolpyruvate (PEP) carboxylasehave been studied among several Flaveria species: the C3 speciesF. cronquistii, the C3–C4 species F. pubescens and F.linearis, and the C4 species F. trinervia. At either pH 7 or8, the maximum activities (in µmol.mg Chl–1.h–1)for F. pubescens and linearis (187–513) were intermediateto those of the C3 species (12–19) and the C4 species(2,182–2,627). The response curves of velocity versusPEP concentration were hyperbolic for the C3 and C3–C4species at either pH 7 or 8 while they were sigmoidal for theC4 species at pH 7 and hyperbolic at pH 8. The Km values forPEP determined from reciprocal plots were lowest in the C3 species,and of intermediate value in the C3–C4 species comparedto the K' values of the C4 species determined from Hill plotsat either pH 7 or 8. Glucose-6-phosphate (G6P) decreased theKm values for PEP at both pH 7 and 8 in the C3 and C3–C4species. In the C4 species, G6P decreased the K' values at pH8 but increased the K' values at pH 7. In all cases, G6P hadits effect by influencing the activity at limiting PEP concentrationswith little or no effect on the maximum activity. At pH 8 andlimiting concentrations of PEP the degree of stimulation ofthe activity by G6P was greatest in the C4 species, intermediatein F. linearis, a C3–C4 species, and lowest in the C3species. In several respects, the PEP carboxylases of the C3–C4Flaveria species have properties intermediate to those of theC3 and C4 species. (Received April 30, 1983; Accepted August 22, 1983)  相似文献   

6.
Kleczkowski, L. A. and Randall, D. D. 1987. Immunologicallydistinct forms of adenylate kinase in leaves: comparison ofsubunit size of adenylate kinase from C3 and C4 plants.—J.exp. Bot. 38: 1440–1445. Antibodies prepared against maize leaf adenylate kinase (E.C.2.7.4.3 [EC] ) cross-reacted with the enzyme isolated from leavesof both C3 and C4 plants. The immunoreaction was very specificas judged by the presence of a single band on Western immunoblotscontaining proteins from leaf extracts of several species. Themolecular weight (M1) of adenylate kinase determined by meansof the immunoblotting was 29 kD and 27 kD for C4 and C3 species,respectively. For both C3 and C4 plants, the antibodies failedto precipitate all adenylate kinase activity in leaf extracts,while they were 100% effective in pelleting the enzyme frommaize mesophyll chloroplasts. This indicated the presence ofat least two immunologically distinct forms of adenylate kinasein leaves. It is suggested that the observed differences in molecular structure(M1s) of adenylate kinase from C3 and C4 species might be responsiblefor distinct catalytic and functional properties of the enzymein these two groups of plants. The irrununologically-determinedoccurrence of distinct pools of adenylate kinase in leaves supportsprevious evidence obtained by means of subcellular fractionationstudies.  相似文献   

7.
C3和C4植物光合途径的适应性变化和进化   总被引:1,自引:0,他引:1       下载免费PDF全文
 高等植物大多为C3植物, C4植物和景天酸代谢(Crassulacean acid metabolism, CAM)植物是由C3植物进化而来的。C4途径的多源进化表明, 光合途径由C3途径向C4途径的转变相对简单。该文分析研究了植物光合途径的进化前景, 指出C4植物是从C3植物进化而来的高光效种类, 且地质时期以来降低的大气CO2浓度和升高的大气温度以及干旱和盐渍化是C4途径进化的外部动力。C3植物的C4途径的发现说明植物的光合途径并非是一成不变的, C3和C4植物的光合特征具有极大的可塑性, 某些环境的变化会引起植物光合途径在C3和C4途径之间转变。C3植物具有的C4途径是环境调控的产物, 是对逆境的适应性进化结果, 因而光合途径的转变也适用于干旱地区植被的适应性生存机理研究。该文还利用国外最新的C4光合进化模型介绍了植物在进化C4途径中所经历的7个重要时期(从分子基础到形态基础、结构基础, 再到物质代谢水平、光合酶活水平, 直到C3和C4途径协调运转时期, 最后达到形态与功能最优化阶段), 并结合全球气候变化的特点对国内外相关领域的研究进行了分析, 总结了植物光合途径的适应性转变和进化的研究成果, 为今后的相关工作提出建议。  相似文献   

8.
Phosphorus responses of C3 and C4 species   总被引:2,自引:0,他引:2  
An hypothesis was formulated that phosphorus (P) partitioningin tissues of C4 leaves would permit C4 plants to resist P deficiencybetter than C3 plants. To test this hypothesis, 12 C3, C4, andC3–C4 intermediate species were grown at adequate, deficient,and severely deficient P supply in a solid-phase-buffered sandculture system to characterize photosynthetic and growth responses.Species differed considerably in response to P stress. The growthof C3 species was more sensitive to P supply than C4 species,but C3 and C4 species had similar photosynthetic P use efficiency,and C4 species did not have low leaf P content, contrary toour hypothesis. In fact, leaf photosynthetic rates were notcorrelated with growth responses. Moncots had lower leaf P contentand better maintenance of leaf production under P stress thandicots, because of greater inhibition of branching (dicots)than of tillering (monocots). The most P efficient species inthis survey was Brachiaria, a C4 monocot that increased rootbiomass allocation under stress while maintaining P allocationto the shoot. It is concluded that C4 species are not inherentlymore P efficient than C3 species, but that monocots are moreP efficient than dicots, because of contrasting P and biomassallocation under stress. Key words: Phosphorus deficiency, C3 plants, C4 plants, growth response  相似文献   

9.
Leaf alcohol (cis-3-hexenol) and leaf aldehyde (trans-2-hexenal)are responsible for the green odor in leaves and fruits. cis-3-Hexenal,a precursor of cis-3-hexenol and trans-2-hexenal, was producedfrom linolenic acid by a homogenate of Farfugium japonicum (Japanesesilver) leaves. n-Hexanal was produced from linoleic acid bya homogenate of the leaves. The enzyme system catalyzing formationof C6-aldehydes from linolenic and linoleic acids was localizedin chloroplast lamellae, and required oxygen for reaction. C18-unsaturatedfatty acids such as linolenic acid, linoleic acid and -linolenicacid, which have carboxyl groups and cis-1, cis-4-pentadienesystems including a double bond at C-12, acted as substrates,and C6-aldehydes (cis-3-hexenal or n-hexanal), but not C9-aldehydes,were produced from them. The properties of the enzyme systemin chloroplasts were as follows: optimal pH 7.0; stable at pH5 to 7; thermolabile and no activity at 50?C. These propertieswere very similar to those of tea chloroplasts. The enzyme systemcould be solubilized from chloroplasts by 2% Triton X-100, butwas very unstable in solubilized form. (Received July 9, 1976; )  相似文献   

10.
Leaves of three C4 plants, Setaria italica, Pennisetum typhoides,and Amaranthus paniculatus possessed five- to ten-fold higheractivities of a (Na+-K+)-dependent ATPase than those of twoC3 plants, Oryza sativa and Rumex vesicarius. Na+-K+ ATPasefrom leaves of Amarathus exhibited an optimal pH of 7?5 andan optimal temperature of 35 ?C. It required 40 mM K+ and 80mM Na+ for maximal activity. Ouabain partially inhibited (Na+-K+)-dependentATPase activity in leaves of C4 plants. Ouabain also blockedthe movement of label from initially formed C4 acids into endproducts in leaves of only C4 plants, Setaria and Amaranthusbut not in a C3 plant, Rumex. We propose that Na+-K+ ATPasemay mediate transfer of energy during active transport of C4acids from mesophyll into the bundle sheath.  相似文献   

11.
When grown in pots and well-watered, the relative growth ratesof the above ground parts of two species of Moricandia (M. arvensis,an intermediate C3–C4 species, and M. moricandioides,a C3 species) were inferior to those of two cultivated Brassicaspecies (B. campestris and B. napus). The Moricandia specieshad thicker leaves (greater d.wt per unit leaf area) with morechlorophyll than the Brassica species and had slightly greaterrates of photosynthesis per unit leaf area at an irradiance(400–700 nm) of 2000 µmol quanta m–2 s –1.Leaves of M. arvensis, known to have a CO2 compensation pointbetween that of C3 and C4 species, had a lower ratio of theintercellular to atmospheric partial pressure of CO2 (C1/Ca)and a greater instantaneous water use efficiency (WUE) thanthose of M. moricandioides and the Brassica species. Carbon isotope discrimination (  相似文献   

12.
Both malate and aspartate were decarboxylated at the 4-carbonposition by isolated bundle sheath strands of C4 plants butto different extents depending upon the species. In Digitariasanguinalis, an NADP-malic enzyme (NADP-ME) species, 100 µMoxalic acid blocked malate decarboxylation through NADP-ME withoutaffecting aspartate decarboxylation which apparently occursthrough NAD-ME. In several phosphoenolpyruvate carboxykinase(PEP-CK) type C4 species, 200 µM 3-mercaptopicolinic acid(3-MPA), an inhibitor of PEP-CK, specifically inhibited themalate decarboxylation and partially inhibited aspartate decarboxylation.The aspartate decarboxylation insensitive to 3-MPA may occurthrough NAD-ME. Neither inhibitor prevented C4 acid decarboxylationin bundle sheath cells of NAD-ME species. The inhibitors thusserved to differentiate between the decarboxylation of C4 acidsin PEP-CK and NADP-ME type C4 species through their major decarboxylasefrom that of their less active decarboxylation through NAD-ME. 1 Present address: Department of Biochemistry and Microbiology,Rutgers University, New Brunswick, NJ 08903, U. S. A. (Received January 28, 1977; )  相似文献   

13.
Enzymes of the C4, C3 pathway and photorespiration have beenanalyzed for P. hians and P. milioides, which have chlorenchymatousbundle sheath cells in the leaves. On whole leaf extracts thelevels of PEP carboxylase are relatively low compared to C4species, RuDP carboxylase is typical of C3 species, and enzymesof photorespiratory metabolism appear somewhat intermediatebetween C3 and C4. Substantial levels of PEP carboxylase, RuDPcarboxylase, and photorespiratory enzymes were found in bothmesophyll and bundle sheath cells. Low levels of C4-acid decarboxylatingenzymes may limit the capacity for C4 photosynthesis in P. hiansand P. milioides. The results on enzyme activity and distributionbetween mesophyll and bundle sheath cells are consistent withCO2 fixation via C3 pathway in these two species. 1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and bythe University of Wisconsin Research Committee with funds fromthe Wisconsin Alumni Research Foundation; and by the NationalScience Foundation Grant BMS 74-09611. (Received September 16, 1975; )  相似文献   

14.
The capacity for C4 photosynthesis in Panicum milioides, a specieshaving reduced levels of photorespiration, was investigatedby examining the activity of certain key enzymes of the C4 pathwayand by pulse-chase experiments with 14CO2. The ATP$P1 dependentactivity of pyruvate,P1 dikinase in the species was extremelylow (0.14–0.18 µmol mg chlorophyll–1 min–1).Low activity of the enzyme was also found in Panicum decipiensand Panicum hians (related species with reduced photorespiration)and in Panicum laxum (a C3 species). The antibody to pyruvate,P1dikinase caused about 70% inhibition of the ATP$P1 dependentactivity of the enzyme in P. milioides. The activity of NAD-malicenzyme and NADP-malic enzyme in P. milioides was equally low(approximately 0.1–0.2 µmol mg chlorophyll–1min–1) and similar to the activity in P. decipiens, P.hians and P. laxum. Photosynthetic pulse-chase experiments underatmospheric conditions showed a typical C3-like pattern of carbonassimilation including the labelling of glycine and serine asexpected during photorespiration. During the pulse with 14CO2only about 1% of the labelled products appeared in malate and2–3% in aspartate. During a chase in atmospheric levelsof CO2 for up to 6 min there was a slight increase in labellingin the C4 acids. The amount of label in carbon 4 of aspartatedid not change during the chase, indicating little or no turnoverof the C4 acid via decarboxylation. The results indicate thatunder atmospheric conditions P. milioides assimilates carbondirectly through the C3 pathway. Photorespiration as indicatedby the CO2 compensation point may be repressed in the speciesby a more efficient recycling of photorespired CO2. (Received June 8, 1982; Accepted July 22, 1982)  相似文献   

15.
The quantum yields of photosynthetic O2 evolution were measuredin 15 species of C4 plants belonging to three different decarboxylationtypes (NADP-ME type, NAD-ME type and PEP-CK type) and 5 speciesof C3 plants and evaluated relative to the maximum theoreticalvalue of 0.125 mol oxygen quanta-1. At 25°C and 1% CO2,the quantum yield in C4 plants averaged 0.079 (differences betweensubgroups not significant) which was significantly lower thanthe quantum yield in C3 plants (average of 0.105 for 5 species).This lower quantum yield in C4 plants is thought to reflectthe requirement of energy in the C4 cycle. For the C4 NADP-MEtype plant Z. mays and NAD-ME type plant P. miliaceum, quantumyields were also measured over a range of CO2 levels between1 and 20%. In both species maximum quantum yields were obtainedunder 10% CO2 (0.105 O2 quanta-1 in Z. mays and 0.097 O2 quanta-1in P. miliaceum) indicating that at this CO2 concentration thequantum yields are similar to those obtained in C3 plants underCO2 saturation. The high quantum yield values in C4 plants undervery high CO2 may be accomplished by direct diffusion of atmosphericCO2 to bundle sheath cells, its fixation in the C3 pathway,and feedback inhibition of the C4 cycle by inorganic carbon. (Received June 6, 1995; Accepted August 15, 1995)  相似文献   

16.
The response of two speciality vegetable crops, New Zealandspinach (Tetragonia tetragonioides Pall.) and red orach (Atriplexhortensis L.), to salt application at three growth stages wasinvestigated. Plants were grown with a base nutrient solutionin outdoor sand cultures and salinized at 13 (early), 26 (mid),and 42 (late) d after planting (DAP). For the treatment saltconcentrations, we used a salinity composition that would occurin a typical soil in the San Joaquin Valley of California usingdrainage waters for irrigation. Salinity treatments measuringelectrical conductivities (ECi) of 3, 7, 11, 15, 19 and 23 dSm-1were achieved by adding MgSO4, Na2SO4, NaCl and CaCl2to thebase nutrient solution. These salts were added to the base nutrientsolution incrementally over a 5-d period to avoid osmotic shockto the seedlings. The base nutrient solution without added saltsserved as the non-saline control (3 dS m-1). Solution pH wasuncontrolled and ranged from 7.7 to 8.0. Both species were saltsensitive at the early seedling stage and became more salt tolerantas time to salinization increased. For New Zealand spinach,the salinity levels that gave maximal yields (Cmax) were 0,0 and 3.1 dS m-1and those resulting in a 50% reduction of biomassproduction (C50) were 9.1, 11.1 and 17.4 dS m-1for early, midand late salinization dates, respectively. Maximal yield ofred orach increased from 4.2 to 10.9 to 13.7 dS m-1as the timeof salinization increased from 13, to 26, to 42 DAP, respectively.The C50value for red orach was unaffected by time of salt imposition(25 dS m-1). Both species exhibited high Na+accumulation evenat low salinity levels. Examination of K-Na selectivity dataindicated that K+selectivity increased in both species withincreasing salinity. However, increased K-Na selectivity didnot explain the increased salt tolerance observed by later salinization.Higher Na-Ca selectivity was determined at 3 dS m-1in New Zealandspinach plants treated with early- and mid-salinization plantsrelative to those exposed to late salinization. This correspondedwith lower Cmaxand C50values for those plants. Lower Ca uptakeselectivity or lower Ca levels may have inhibited growth inyoung seedlings. This conclusion is supported by similar resultswith red orach. High Na-Ca selectivity found only in the early-salinizationplants of red orach corresponded to the lower Cmaxvalues measuredfor those plants. Copyright 2000 Annals of Botany Company New Zealand spinach, Tetragonia tetragonioides Pall., red orach, Atriplex hortensis L., salinity, stage of growth, ion accumulation, selectivity, plant nutrition  相似文献   

17.
Total peroxidase activities and peroxidase isozymes were comparedamong 10 bush- and vine-squash cultivars of Cucurbita maximaDuch. and C. pepo (L.) Several qualitative variations of isozymeswere detected between C. maxima and C. pepo, and some differenceswere evident among varieties of C. pepo. There were no qualitativedifferences between genetically similar bush and vine strains.Quantitative differences were difficult to resolve, althoughit did appear that in varieties of C. maxima exhibiting lowlevels of peroxidase activity, isozymes C3, C4, and C6 wereless intense. Depending upon the cultivars compared, total peroxidase activityin bush forms was either higher or lower than, or the same astheir vine counterparts. Since the major bush genes in the varietiesstudied are believed to be allelic, the results indicate thatthe over-all genotype of squash varieties can influence therelative expression of peroxidase activity between bush andvine forms.  相似文献   

18.
The extent to which photorespiration occurs in CrassulaceanAcid Metabolism (CAM) plants has received limited attention.No comparative studies of C3 and CAM development have been made.To address this problem, activities of several photorespiratoryenzymes were measured in a facultative CAM plant—Mesembryanthemumcrystallinum L.—during induction of CAM by water stress(NaCl-treatment). Salt-treatment over a 22 d period produceda progressive change in metabolism from C3 to CAM. This wasconfirmed by (I) changes in gas exchange from C3 fixation tothe characteristic CAM pattern of nocturnal CO2 uptake; (2)increases in did acid fluctuation and (3) a 30-fold increasein phosphoenol pyruvate (PEP) carboxylase activity. In contrast,no significant changes were observed in the activities of glycollateoxidase (GO), NAD-dependent-hydroxypyruvate reductase (HPR),glutamine synthetase (GS) or glutamate dehydrogenase (GDH) whenplants were induced into CAM. Ion exchange chromatography onDEAE Sephacel detected only one GS isoenzyme (GS2, chloroplastic)at all stages of CAM induction, Western blot analysis, however,detected an additional, although minor, band of GS1 (cytosolic),in C3 plants, which disappeared following CAM induction. Ourresults show that, after development of CAM, these plants stillretain the capacity to photorespire. This may be an essentialrequirement of CAM plants growing in habitats with variablerainfall. When water availability is high, stomata may openin the light allowing ribulose bisphosphate carboxylase oxygenase(Rubisco) activity and photorespiration to occur. The inherentcapacity to photorespire would allow plants to survive variableperiods of rainfall. Key words: Mesembryanthemum, C3, CAM, photorespiration  相似文献   

19.
Summary Comparative chemical and histochemical studies were performed on formalin-fixed, surgical specimens of human small intestine from cases of Crohn's disease and normal controls. The sialic acids of the crude glycoproteins isolated from normal ileum were significantly less neuraminidase-susceptible and more C4 substituted (P<0.01) than those of the glycoproteins isolated either from normal upper small intestine (duodenum and jejunum) or from cases of Crohn's disease of the ileum. Fractionation yielded two major sialic acid-containing fractions, eluting from DEAE-cellulose with 0.2m or 0.3m sodium chloride. Both fractions contained fucose, galactose, glucosamine and galactosamine in addition to sialic acids both with and withoutO-acyl substituents at position C4 and/or in the side-chain (side-chainO-acylated sialic acids were also detected by histochemical procedures). The fractions differed significantly from one another with respect to the neuraminidase susceptibility of their sialic acids (P<0.01), the percentage of C4 (P<0.01) and side-chain substituted sialic acids (P<0.05), and the molar fucose-sialic acid ratio (P<0.05). TheO-acyl substitution patterns of the sialic acids of both the 0.2m and 0.3m fractions of the upper small intestine glycoproteins differed significantly from those of the corresponding fractions from normal ileum, while the sialic acids of the 0.2m fractions from Crohn's disease of the ileum differed significantly from normal with respect to neuraminidase susceptibility (P<0.01) and percentage C4 substitution (P<0.01); the 0.3m fractions differed only in the percentage of sialic acids substituted at C4. The differences between the sialic acids from the normal and Crohn's disease specimens were shown to be independent of either the anatomical origin of the specimen or the histopathological sub-group of the Crohn's disease specimens; no significant differences were noted between the sub-groups but all the sub-groups differed from normal.  相似文献   

20.
Excised leaves of a C3-photosynthetic type, Hordeum vulgare,a C4-type, Panicum miliaceum, and an intermediate-type, Panicummilioides, were allowed to take up through their cut ends a1 mM solution of butyl hydroxybutynoate (BHB), an irreversibleinactivator of glycolate oxidase. After 30 to 60 min in BHB,extractable glycolate oxidase activity could not be detectedin the distal quarter of the leaf blades. Following this pretreatment,recovery of 14C-glycolate from 14CO2 incorporated in a 10 minperiod was nearly maximal for each of the three plant types.Labeled glycolate was 51% of the total 14CO2 incorporated forthe C3-species, 36% for the intermediate-species, and 27% forthe C4-species Increased labeling of glycolate was compensatedfor primarily by decreased labeling of the neutral and basicfractions for the C3 and intermediate-type species. In the C4-type,label decreased primarily in the neutral and insoluble fractions,but increased in the basic fraction. A lower rate of glycolatesynthesis is indicative of a lower rate of photorespirationand consistent with a lower O2/CO2 ratio present in the bundle-sheathcells of C4-plants. We conclude that both decreased glycolatesynthesis and the refixation of photorespiratory-released CO2are important in maintaining a lower rate of photorespirationin C4-plants compared to C3 plants. Intermediate glycolate synthesisin Panicum milioldes is consistent with its intermediate levelof O2 inhibition of photosynthesis and intermediate rate ofphotorespiration. (Received May 6, 1978; )  相似文献   

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