Photochlorophyll Biosynthesis in Cucumber (Cucumis sativus, L.) Cotyledons

The formation of protochlorophyllide and protochlorophyllide phytyl ester was investigated during etioplast biogenesis in order to study the biosynthetic relation of these two compounds. Protochlorophyllide accumulates slowly during the first 2 days of germination, its rate of formation increases sharply during the 3rd day, and then it decreases. Protochlorophyllide phytyl ester starts accumulating a day later; its formation coincides with the initiation of xanthophyll biosynthesis. Kinetic analysis of specific radioactivities after ¹⁴C labeling of the protochlorophyll pools does not support the currently accepted conversion of protochlorophyllide into protochlorophyllide phytyl ester, but suggests that both compounds originate simultaneously from a common precursor pool.     

High-Throughput Sequencing Identifies Novel and Conserved Cucumber (Cucumis sativus L.) microRNAs in Response to Cucumber Green Mottle Mosaic Virus Infection

Seedlings of Cucumis sativus L. (cv. ''Zhongnong 16'') were artificially inoculated with Cucumber green mottle mosaic virus (CGMMV) at the three-true-leaf stage. Leaf and flower samples were collected at different time points post-inoculation (10, 30 and 50 d), and processed by high throughput sequencing analysis to identify candidate miRNA sequences. Bioinformatic analysis using screening criteria, and secondary structure prediction, indicated that 8 novel and 23 known miRNAs (including 15 miRNAs described for the first time in vivo) were produced by cucumber plants in response to CGMMV infection. Moreover, gene expression profiles (p-value <0.01) validated the expression of 3 of the novel miRNAs and 3 of the putative candidate miRNAs and identified a further 82 conserved miRNAs in CGMMV-infected cucumbers. Gene ontology (GO) analysis revealed that the predicted target genes of these 88 miRNAs, which were screened using the psRNATarget and miRanda algorithms, were involved in three functional categories: 2265 in molecular function, 1362 as cellular components and 276 in biological process. The subsequent Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that the predicted target genes were frequently involved in metabolic processes (166 pathways) and genetic information processes (40 pathways) and to a lesser degree the biosynthesis of secondary metabolites (12 pathways). These results could provide useful clues to help elucidate host-pathogen interactions in CGMMV and cucumber, as well as for the screening of resistance genes.     

黄瓜霜霉病抗性遗传分析

通过2个抗感杂交组合,采用多世代联合的分离分析方法研究了黄瓜霜霉病抗性的遗传机制.结果显示,2个组合的最适遗传模型分别是2对加性-显性-上位性主基因 加性-显性-上位性多基因模型和2对等加性主基因 加性-显性多基因模型.组合I最优模型的主基因遗传率是56.84%~87.16%,多基因遗传率是0~34.93%;2个主基因的加性效应均为-15.191,加性效应较强,显性效应较弱,它们之间的加性与加性和加性与显性上位性效应较强.组合Ⅱ最优模型的主基因和多基因遗传率分别为48.92%和42.11%;2个主基因的加性效应皆为-13.505,显性效性均为0,它们之间不存在互作效应.结果表明,黄瓜霜霉病抗性,以加性效应为主,主基因遗传力较高,但是微效多基因效应也占相当的比重,所以,在霜霉病抗性育种中,要重视主基因,同时兼顾多基因效应.     

Genetic Diversity and Population Structure of Cucumber (Cucumis sativus L.)

Knowing the extent and structure of genetic variation in germplasm collections is essential for the conservation and utilization of biodiversity in cultivated plants. Cucumber is the fourth most important vegetable crop worldwide and is a model system for other Cucurbitaceae, a family that also includes melon, watermelon, pumpkin and squash. Previous isozyme studies revealed a low genetic diversity in cucumber, but detailed insights into the crop''s genetic structure and diversity are largely missing. We have fingerprinted 3,342 accessions from the Chinese, Dutch and U.S. cucumber collections with 23 highly polymorphic Simple Sequence Repeat (SSR) markers evenly distributed in the genome. The data reveal three distinct populations, largely corresponding to three geographic regions. Population 1 corresponds to germplasm from China, except for the unique semi-wild landraces found in Xishuangbanna in Southwest China and East Asia; population 2 to Europe, America, and Central and West Asia; and population 3 to India and Xishuangbanna. Admixtures were also detected, reflecting hybridization and migration events between the populations. The genetic background of the Indian germplasm is heterogeneous, indicating that the Indian cucumbers maintain a large proportion of the genetic diversity and that only a small fraction was introduced to other parts of the world. Subsequently, we defined a core collection consisting of 115 accessions and capturing over 77% of the SSR alleles. Insight into the genetic structure of cucumber will help developing appropriate conservation strategies and provides a basis for population-level genome sequencing in cucumber.     

黄瓜黄绿叶突变性状的遗传分析

在深绿叶的“地串”黄瓜品种单株自交后代群体中,分离出性状稳定的黄绿叶突变株系。遗传分析表明,突变株系的黄绿叶性状受一对隐性核基因控制。该性状在幼苗期表现,突变株能正常生存、繁殖,是一种可利用的形态标记。控制此性状的基因符号暂定名为yg1。 Abstract:A yellow green leaf character mutation in cucumber was isolated from a population of selfed individual plant of dark green leaf ‘De Chuan' cultivar.Genetic analysis showed that the yellow green leaf character was controlled by one pair of recessive nuclear genes.The character expressed at the seedling stage and the mutant plant have the ability to viable and propagate.It could be used as a morpholmarker.This yellow green leaf gene was provisionally designated as yg1.     

A New Glabrous Gene (csgl3) Identified in Trichome Development in Cucumber (Cucumis sativus L.)

Spines or trichomes on the fruit of cucumbers enhance their commercial value in China. In addition, glabrous mutants exhibit resistance to aphids and therefore their use by growers can reduce pesticide residues. Previous studies have reported two glabrous mutant plants containing the genes, csgl1 and csgl2. In the present study, a new glabrous mutant, NCG157, was identified showing a gene interaction effect with csgl1 and csgl2. This mutant showed the glabrous character on stems, leaves, tendrils, receptacles and ovaries, and there were no spines or tumors on the fruit surface. Inheritance analysis showed that a single recessive gene, named csgl3, determined the glabrous trait. An F₂ population derived from the cross of two inbred lines 9930 (a fresh market type from Northern China that exhibits trichomes) and NCG157 (an American processing type with glabrous surfaces) was used for genetic mapping of the csgl3 gene. By combining bulked segregant analysis (BAS) with molecular markers, 18 markers, including two simple sequence repeats (SSR), nine insertion deletions (InDel) and seven derived cleaved amplified polymorphism sequences (dCAPs), were identified to link to the csgl3 gene. All of the linked markers were used as anchor loci to locate the csgl3 gene on cucumber chromosome 6. The csgl3 gene was mapped between the dCAPs markers dCAPs-21 and dCAPs-19, at genetic distances of 0.05 cM and 0.15 cM, respectively. The physical distance of this region was 19.6 kb. Three markers, InDel-19, dCAPs-2 and dCAPs-11, co-segregated with csgl3. There were two candidate genes in the region, Csa6M514860 and Csa6M514870. Quantitative real-time PCR showed that the expression of Csa6M514870 was higher in the tissues of 9930 than that of NCG157, and this was consistent with their phenotypic characters. Csa6M514870 is therefore postulated to be the candidate gene for the development of trichomes in cucumber. This study will facilitate marker-assisted selection (MAS) of the smooth plant trait in cucumber breeding and provide for future cloning of csgl3.     

Characteristics of Radial Solution Flow in Roots of Cucumber (Cucumis sativus L.)

Low salt roots of Cucumis sativus L. cv. Burpeeana Hybrid weresubjected to iso-ionic treatments in which the external solutionconcentration of K⁺ was maintained at 14 mM. Solution concentrationof varied from 0 to 14 mM, other anions compensating. When Cl^– was the compensating ion, its concentrationin the exudate increased during the first 4 h and thereafterwas nearly the same as that of the external solution in alltreatments containing I mM or more. After 8 h of equilibration the concentration in the exudate increased almost exactly as its concentrationin the external solution. Rates of exudation and K⁺ transportwere almost constant between I and 14 mM KNO₂. More Cl^–was transported from solutions of similar Cl– concentrationwhen was also present. When water transport was inhibited with mannitol in treatments containing both KNO₃and KCI, exudate concentrations of K⁺ and were increased, but exudate concentration of Cl^– was notsignificantly affected except at the highest Cl     

Comparative Study of β-Glucosidase from Cotyledons and Fruits of Cucumber, Cucumis sativus

This study was conducted to compare the β-glucosidase of cotyledons and fruits of Cucumis sativus L. cv. Chipper. The concentration of the enzyme was followed throughout the growth period of each organ. The greatest concentration of the enzyme did not correspond with the most rapid period of growth. Each enzyme was characterized kinetically. The Michaelis constant of the cotyledon β-glucosidase for p-NO₂-phenyl-β-D-gluco-pyranoside was 1.57 mM, and was 0.35 mM for the fruit enzyme. The enzymes from the two sources also differed in affinity for glucono-1,5-lactone, a competitive inhibitor of β-glucosidases, susceptibility to inhibition by saccharides, and heat stability. The two organs apparently contain different forms of β-glucosidase.     

光合菌对黄瓜光合及抗氧化同工酶的影响

以2种基因型的黄瓜(Cucumis sativus)为材料, 研究光合菌(PSB)的喷施对植物生物量、净光合速率(Pn)、叶片PSII 的最大光化学效率(Fv/Fm)及抗氧化同工酶代谢的影响。结果表明, 喷施PSB均能诱导2种基因型黄瓜的生物量显著增加, 并伴随Pn的显著提高。但是, 2种基因型黄瓜的Fv/Fm并不受PSB喷施的影响; PSB能使总过氧化物歧化酶(SOD)和抗坏血酸过氧化酶(APX)活性提高, 并使它们的多数同工酶的活性上调, 这些同工酶活性的增加在叶绿体中表现更为明显(如 Cu/Zn-SOD、Fe-SOD 和 sAPX)。研究结果表明, PSB能通过增强黄瓜抗氧化酶体系的活性改善植株的抗氧化能力, 从而在植株的生长和光合作用方面起到促进作用。     

光合菌对黄瓜光合及抗氧化同工酶的影响

以2种基因型的黄瓜（Cucumis sativus）为材料,研究光合菌（PSB）的喷施对植物生物量、净光合速率（Pn）、叶片PSII的最大光化学效率（Fv／Fm）及抗氧化同工酶代谢的影响。结果表明,喷施PSB均能诱导2种基因型黄瓜的生物量显著增加,并伴随Pn的显著提高。但是,2种基因型黄瓜的Fv/Fm并不受PSB喷施的影响：PSB能使总过氧化物歧化酶（soo）和抗坏血酸过氧化酶（APX）活性提高,并使它们的多数同工酶的活性上调,这些同工酶活性的增加在叶绿体中表现更为明显（如Cu／Zn-SOD、Fe-SOD和sAPX）。研究结果表明,PSB能通过增强黄瓜抗氧化酶体系的活性改善植株的抗氧化能力,从而在植株的生长和光合作用方面起到促进作用。     

黄瓜花性别分化和内源激素的关系

黄瓜雌花中GA3 和IAA含量均高于雄花 ;雌花在大孢子母细胞时期以后直到发育成熟 ,IAA含量持续增加 ,雄花中IAA含量则下降 ;ZT含量增加有利于大小孢子母细胞的形成而ABA含量增加则有利于四分体的形成。高水平的ZT/IAA和低水平的GA3 /ZT有利于大孢子母细胞和花粉粒的形成 ,大孢子四分体在高水平的GA3 /ZT和低水平的ZT/IAA下形成。雌性系黄瓜经硝酸银处理后茎尖中GA3 增加、IAA和ZT减少 ,有利于雄性分化 ;强雄性系黄瓜经乙烯利处理后 ,茎尖中GA3 下降 ,IAA和ZT增加 ,有利于雌性分化。据此认为内源IAA可能是黄瓜性别发育的关键性激素     

Estimation and Analysis of Cucumber (Cucumis sativus L.) Leaf Cellular Heat Sensitivity

Triphenyl tetrazolium chloride (TTC) reduction by cucumber (Cucumis sativus L. cv Poinsett 76 and cv Ashley) leaf discs was used as a viability assay to examine the effect of temperature pretreatment on the tissue response to acute hyperthermia. Semi-logarithmic plots of TTC reduction as a function of incubation time at different temperatures from 40 to 60[deg]C resembled the heat survival curves of animal cells. Heat inactivation rates were obtained and subjected to "quasi" Arrhenius analyses by analytical methods derived from the animal studies. The Arrhenius plots of TTC reduction rates for cv Ashley leaf discs preincubated at 25 or 37[deg]C and for cv Poinsett 76 preincubated at 37[deg]C were linear with the same activation energy (Ea) of about 80 kcal mol-1. The Arrhenius plot of cv Poinsett 76 preincubated at 25[deg]C was nonlinear with an Ea of about 80 kcal mol-1 at temperatures below 46[deg]C and an Ea of about 27.5 kcal mol-1 at temperatures above 47[deg]C. The significance of these differences is discussed in terms of the role of protein denaturation in the thermal sensitivity of cucumber disc reduction of TTC and the applicability of these methods to the analysis of plant cellular heat sensitivity.     

几个影响黄瓜子叶体细胞胚胎发生的因素

黄瓜品种“叶三旱”是体细胞胚胎发生的理想基因型 ;愈伤组织诱导阶段和胚胎发生阶段分别采用 9%和 6 %的蔗糖浓度 ,可促进体细胞胚胎发生 ;胚诱导培养基中添加 6 BA 0 .5mg·L-1,体细胞胚胎发生率较高 (达到 6 7.8% ) ;愈伤组织诱导阶段甘露醇与蔗糖配合使用 ,可提高体细胞胚胎发生率 (高达 82 .2 % )。     

Induction by Electric Currents of Ethylene Biosynthesis in Cucumber (Cucumis sativus L.) Fruit

The effects of an electric current on ethylene biosynthesis were investigated in cucumber (Cucumis sativus L.) fruit that were producing almost no ethylene. Direct currents at 0.5 to 3.0 milliamperes induced much ethylene synthesis, with a rapid continuous increase in the rate, which reached a peak within 5 to 6 hours and then decreased. The rate of production was greater with a stronger current. Ethylene production was not observed after the use of a sine-wave alternating current (60 hertz) at 3 milliamperes, the magnitude at which a direct current had the greatest effect. The activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ethylene forming enzyme (EFE) increased before the rise in ethylene production. ACC synthase and EFE were activated sixfold and fourfold, respectively, by 2 hours. The concentration of ACC increased linearly up to 6 hours and then decreased. Ethylene induction by an electric current was suppressed almost completely by the infiltration of the cucumbers with 5 millimolar aminooxyacetic acid, an inhibitor of ACC synthase, and was also suppressed 70% by 5 millimolar salicylic acid, an inhibitor of EFE. The results indicate that the ethylene induced by the direct current was synthesized via the ACC-ethylene pathway as a result of electrical stress, a new kind of stress to be identified.     

Flower Formation In vitro by Hypocotyl Explants of Cucumber (Cucumis sativus L.)

Hypocotyl explants of cucumber (Cucumis sativus L.) producedcallus when grown in Murashige and Skoog medium with 0.5 or1.0 µM benzyladenine and 1.5 or 5.0 µm 2, 4-D. Somaticembryos and adventitious buds were formed when callus was transferredto medium without growth regulators. Flowers that were formedin vitro were either staminate or pistillate. Cucumis sativus L, cucumber, embryogenesis, organogenesis, flowering in vitro     

离体培养黄瓜子叶诱导雌花的研究

采用添加Spd和IAA的MS培养基培养离体黄瓜子叶,研究了Spd和IAA对雌花诱导的协同作用,及昼夜温差、培养基中N素和pH值对雌花诱导的影响。结果表明,分别添加Spd、IAA时的雌花诱导率和单株雌花数偏低或为0,12 mg·L^-1 Spd与0.01mg·L^-1 IAA 配合时的诱导效果明显高于单独处理的,而对照组未见雌花,说明Spd和IAA对雌花诱导的协同作用显著。在0、2、6、10℃昼夜温差,60、70、80、90 mmol·L^-1的N素含量和pH 5.4、5.8、6.2、6.6的培养条件下,70 mmol·L^-1 N、6℃温差和pH 6.2时的雌花诱导效果较好,表明适当提高昼夜温差、培养基中N素和pH值有利于黄瓜子叶的雌花诱导。     

黄瓜多样性固定核心样本集的构建与评价

利用149对具有多态性的In Del引物对473份黄瓜初选核心种质自交系进行遗传多样性分析。采用3种方法 12种取样比例对该初级遗传多样性固定群体进行抽样获得候选多样性固定核心样本集(GDFCC),使用等位基因数(Na)、有效等位基因数(Ne)、Shannon's信息指数(I)、基因多样性指数(gene diversity)、多态性信息含量(PIC)、总等位位点数(total number of loci)、等位位点保留百分率(retention rate of loci)评价候选多样性固定核心样本集的多样性和代表性,结果表明,采用逐级聚类+稀有基因优先取样法并按照15%取样比例构建出的多样性固定核心样本集的效果较好。比较发现,该核心样本集的Ne、I、基因多样性指数和PIC值均接近或高于初级遗传多样性固定群体,且对原始群体的等位位点的保留百分率为99.68%。入选多样性固定核心样本集的材料来自15个国家和国内18个省市。该研究为今后黄瓜优异基因资源的挖掘利用提供了代表性强、覆盖度广、遗传稳定的研究群体,将有利于黄瓜种质资源的高效研究利用。     

Ultrahigh-Density Linkage Map for Cultivated Cucumber (Cucumis sativus L.) Using a Single-Nucleotide Polymorphism Genotyping Array

Genotyping arrays are tools for high-throughput genotyping, which is beneficial in constructing saturated genetic maps and therefore high-resolution mapping of complex traits. Since the report of the first cucumber genome draft, genetic maps have been constructed mainly based on simple-sequence repeats (SSRs) or on combinations of SSRs and sequence-related amplified polymorphism (SRAP). In this study, we developed the first cucumber genotyping array consisting of 32,864 single-nucleotide polymorphisms (SNPs). These markers cover the cucumber genome with a median interval of ~2 Kb and have expected genotype calls in parents/F₁ hybridizations as a training set. The training set was validated with Fluidigm technology and showed 96% concordance with the genotype calls in the parents/F₁ hybridizations. Application of the genotyping array was illustrated by constructing a 598.7 cM genetic map based on a ‘9930’ × ‘Gy14’ recombinant inbred line (RIL) population comprised of 11,156 SNPs. Marker collinearity between the genetic map and reference genomes of the two parents was estimated at R² = 0.97. We also used the array-derived genetic map to investigate chromosomal rearrangements, regional recombination rate, and specific regions with segregation distortions. Finally, 82% of the linkage-map bins were polymorphic in other cucumber variants, suggesting that the array can be applied for genotyping in other lines. The genotyping array presented here, together with the genotype calls of the parents/F₁ hybridizations as a training set, should be a powerful tool in future studies with high-throughput cucumber genotyping. An ultrahigh-density linkage map constructed by this genotyping array on RIL population may be invaluable for assembly improvement, and for mapping important cucumber QTLs.