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.     

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。     

5-Aminolevulinic Acid Induced Photodynamic Reactions in Thylakoid Membranes of Cucumber (Cucumis sativus L.) Cotyledons

The cucumber (Cucumis sativus L.) plants were sprayed with 20 mM 5-aminolevulinic acid or distilled water (control) and incubated in dark for 14 hr. The thylakoid membranes prepared from the intact chloroplasts, isolated from the above plants in dark, were illuminated with low light intensity (100 W/m2) for 30 min. Due 10 photodynamic reactions, the photochemical function of photosystem II was damaged by 50% in treated thylakoids whereas it was only slightly (8%) affected in control thylakoids. The photosystem I was, however, not affected. The exogenous electron donors, MnCl2, diphenyl carbazide and NH2OH failed to restore the photosystem II activity suggesting that the photodynamic damage had taken place very close to photosystem II reaction center. Singlet oxygen scavenger, histidine, could protect the photosystem II activity while superoxide radical scavengers, superoxide dismutase and 1, 2-dihydroxybenzene-3, 5-disulphonic acid disodium salt, and hydroxyl radical scavenger, formate, failed to protect the same.     

Effects of Acifluorfen on Endogenous Antioxidants and Protective Enzymes in Cucumber (Cucumis sativus L.) Cotyledons

The herbicide acifluorfen (2-chloro-4-(trifluoromethyl)phenoxy-2-nitrobenzoate) causes strong photooxidative destruction of pigments and lipids in sensitive plant species. Antioxidants and oxygen radical scavengers slow the bleaching action of the herbicide. The effect of acifluorfen on glutathione and ascorbate levels in cucumber (Cucumis sativus L.) cotyledon discs was investigated to assess the relationship between herbicide activity and endogenous antioxidants. Acifluorfen decreased the levels of glutathione and ascorbate over 50% in discs exposed to less than 1.5 hours of white light (450 microeinsteins per square meter per second). Coincident increases in dehydroascorbate and glutathione disulfide were not observed. Acifluorfen also caused the rapid depletion of ascorbate in far-red light grown plants which were photosynthetically incompetent.

Glutathione reductase, dehydroascorbate reductase, superoxide dismutase, ascorbate oxidase, ascorbate free radical reductase, peroxidase, and catalase activities rapidly decreased in acifluorfen-treated tissue exposed to white light. None of the enzymes were inhibited in vitro by the herbicide. Acifluorfen causes irreversible photooxidative destruction of plant tissue, in part, by depleting endogenous antioxidants and inhibiting the activities of protective enzymes.

     

Photosynthesis Is Not Involved in the Mechanism of Action of Acifluorfen in Cucumber (Cucumis sativus L.)

The possible role of photosynthesis in the mechanism of action of the herbicide acifluorfen (2-chloro-4-(trifluoromethyl)phenoxy-2-nitrobenzoate; AF) was examined. The sensitivity to AF of cotyledons of cucumber (Cucumis sativus L.) which had been grown under far red light (FR) and white light were compared. FR grown tissues which were photosynthetically imcompetent were hypersensitive to AF under white light and had approximately the same relative response to AF under blue and red light as green, white-light-grown tissues. Ultrastructural damage was apparent in FR-grown, AF-treated tissues within an hour after exposure to white light, with cytoplasmic and plastidic disorganization occurring simultaneously. In cucumber cotyledon tissue which had been greening for various time periods, there was no correlation between photosynthetic capacity and herbicidal efficacy of AF. PSII inhibitors (atrazine and DCMU) and the photophosphorylation inhibitor, tentoxin, had no effect on AF activity. Atrazine did not reduce AF activity at any concentration or light intensity tested, indicating that there is no second, photosynthetic-dependent mechanism of action operating at low AF concentrations or low fluence rates. Carbon dioxide-dependent O₂ evolution of intact chloroplasts of spinach (Spinacia oleracea L.) had an AF I₅₀ of 125 micromolar compared to 1000 micromolar for cucumber, whereas AF was much more herbicidally active in tissues of cucumber than of spinach. Differences in activity could not be accounted for by differences in uptake of AF. Our results indicate that there is no photosynthetic involvement in the mechanism of action of AF in cucumber.     

Regulation of Mitochondrial Function and Biogenesis in Cucumber (Cucumis sativus L.) Cotyledons during Early Seedling Growth

The aim of this work was to characterize the respiratory metabolism of the greening cotyledons of cucumber (Cucumis sativus L.) during early seedling growth and to investigate how this is integrated with changes in mitochondrial biogenesis and function. In light-grown cotyledons, lipid mobilization extended from germination to 6 days postimbibition, reaching a maximum at 3 to 4 days postimbibition. The rate of dark oxygen uptake reached a maximum at 2 days postimbibition in dark-grown and 3 days postimbibition in light-grown cotyledons. Development of photosynthetic capacity occurred from 4 to 7 days postimbibition. In dark-grown cotyledons, lipid mobilization extended beyond 7 days postimbibition, and there was no greening or acquisition of photosynthetic competence. Measurements of mitochondrial function indicated that the respiratory capacity of the tissue changed such that during lipid mobilization there was a much greater capacity for the operation of the nondecarboxylating portion of the citric acid cycle (succinate to oxaloacetate), whereas during the development of photosynthetic function the activity of the remainder of the cycle (oxaloacetate to succinate) was induced. Comparison of the maximum capacities for mitochondrial substrate oxidations in vitro with the rates of in vivo substrate oxidations, predicted from the rate of lipid breakdown, indicated that mitochondria in this tissue operate at or below state 4 rates, suggesting limitation by both availability of ADP and substrate.     

Genetics and Resistance Mechanism of the Cucumber (Cucumis sativus L.) Against Powdery Mildew

Journal of Plant Growth Regulation - Powdery mildew (PM) is one of the most severe foliar diseases in cucumbers (Cucumis sativus L.), but the inheritance of PM resistance remains unclear. The...     

Wavelength Effect on the Action of a N-Phenylimide S-23142 and a Diphenylether Acifluorfen-Ethyl in Cotyledons of Cucumber (Cucumis sativus L.) Seedlings

Specific wavelengths of light required for expression of phytotoxic activity of S-23142 (N-[4-chloro-2-fluoro-5-propargyloxy]phenyl-3,4,5,6-tetra- hydrophthalimide) and acifluorfen-ethyl (ethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitro benzoic acid) were determined in cotyledons of cucumber seedlings using the Okazaki Large Spectrograph. Leakage of amino acids from the cotyledons was measured as an indication of the phytotoxic activity. The wavelength effects showed common major peaks of activity at 550 and 650 nanometers and a minor peak at 450 nanometers for both herbicides, indicating a common primary photoreaction. Concomitant application of DCMU (3-[3,4-dichlorophenyl]-1,1-dimethylurea) with S-23142 had little influence on the effective wavelengths for S-23142 activity. Light of 450 and 650 nanometers was relatively less effective in achlorophyllous tissue grown in far red light than in green tissue. These results strongly suggest that the phytotoxic action of S-23142 and diphenylethers involves multiple photoreactions and that one of the photoreceptor pigments may be chlorophyll or its related pigment, although photosynthesis is not involved.     

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.     

5-Aminolevulinic Acid Induced Photodynamic Damage of the Photosynthetic Electron Transport Chain of Cucumber (Cucumis sativus L.) Cotyledons

Cucumber (Cucumis sativus L. cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid (ALA) and then incubated in dark for 14 hours. Upon transfer to sunlight (800 watts per square meter) the plants died after 5 hours of exposure due to photosensitization reaction of metalloporphyrins. Due to the photodynamic damage, photosystem II (PSII), photosystem I (PSI), and whole chain reactions were impaired. PSII activity was more susceptible to photodynamic damage than PSI. The variable fluorescence was significantly reduced in ALA-treated plants within 1 hour of exposure to sunlight. At low temperature (77°K), the PSI fluorescence peak height (F₇₃₄) was drastically reduced and blue shifted by 6 nanometers. The photodynamic damage was irreversible; rather, it continued upon dark incubation of ALA-treated cucumber plants exposed to sunlight for 15 minutes. In the latter experiment, continued production of malondialdehyde during dark treatment suggests the degradation of unsaturated membrane lipids.     

Peroxidase and Glucose-6-phosphate Dehydrogenase Levels in Cotyledons of Cucumis sativus (L.)

Peroxidase and glucose-6-phosphate dehydrogenase become increasinglyactive in cucumber cotyledons excised from the plant althoughthere is a fall in total protein content. The increases areinhibited by dinitrophenol, D, and L-threo-chloramphenicol,cycloheximide, puromycinj and actinomycin D, and it is concludedthat the enzymes are synthesized de novo. Disc electrophoresisof cotyledon extracts revealed three bands of peroxidase, oneof which becomes much enhanced in excised cotyledons. Citrullineaccumulates markedly in excised cotyledons. If the shoot ofcucumber plants is cut away above the cotyledons, very largeincreases in peroxidase and glucose-6-phosphate dehydrogenaseare observed although yellowing and protein loss are delayed.     

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     

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.     

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     

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.     

Embryogenic Suspension Culture and Plant Regeneration from Suspension-Derived Proto-plasts of Cucumber (Cucumis sativus L.)

Fast growing embryogenic cell suspension culture was established when embryogenic callus derived from cotyledon protoplasts of cucumber was transferred into a liquid culture. So far the cell line has been subcultured for two years and retained the ability of embryogenesis and plant regeneration. Experimental data showed that the concentration of ABA or sucrose had a dramatic effect on embryogenesis and synchronization of embryoid development. Low level of sucrose concentration (1%) facilitated the precocious germination of the embryoids while 1 mg/l of ABA or 7–9% of sucrose was found to be effective for reducing callusing of the cultures and synchronisticly controlling the embryoids at globular or late globular stage. Embryogenic cells taken from 3–5 days after subculture were enzymatically digested. A large amount of viable protoplasts was isolated. Protoplasts were cultured in a DPDK1 medium either by means of drop or thin layer liquid culture or by means of sodium alginate encapsulation culture. Actively dividing cells formed cell colonies and globular embryoids which were transferred onto a solidified agar medium or directly into a liquid medium to form a shaken culture. The embryoids would proliferated continuously. Embryoids eventually developed into plantlets when they were transferred onto a 1/2 MSO medium devoid of phytohormones.     

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.     

黄瓜白色果皮基因遗传规律及定位研究

以黄瓜嫩果深绿色果皮自交系1507(P1)和白色果皮自交系1508(P2)为亲本,构建6世代遗传群体(P1、P2、F1、F2、BC1P1、BC1P2),对黄瓜嫩果白色果皮基因(w)进行遗传规律分析和基因定位研究。结果表明,黄瓜白色果皮性状由隐性单基因(w)控制,深绿色对白色为显性。利用F2群体,结合分离群体分组分析法筛选得到了14个与w基因相关的SSR标记,构建了该基因的SSR连锁群,将其定位到黄瓜3号染色体上,两侧的标记为SSR23517和SSR23141,遗传距离分别为4.9cM和1.9cM。侧翼标记之间的物理距离为1 150kb,在该区域中共预测了500个候选基因。该研究对w基因的初步定位,为该基因精细定位及分子标记辅助选择育种奠定了良好的基础。     

全雌性黄瓜中3个肌动蛋白基因片段的克隆和表达分析

通过1次PCR扩增从全雌性黄瓜中同时获得了长度分别为1 186bp、955 bp和870bp的3个肌动蛋白基因片段Act1、Act2和Act3(GenBank登记号:DQ115881,DQ115882和DQ115883).序列分析表明,3个肌动蛋白基因片段与GenBank中收录的肌动蛋白基因序列高度同源,与GenBank中收录的全长肌动蛋白基因(如AF386514.1、AF059484.1和AB010922.1等)的第2、第3个外显子和第2个内含子相对应.Act1中1-580 bp、984～1 186 bp,Act2中1-580 bp、753-955bp,Act3中1-580 bp、668-870 bp为外显子编码区,其余为内合子序列,3个基因内含子的两端序列均符合典型的"GT-AG"规则.RT-PCR分析表日月,Act1仅在根中表达,Act2在根和雌花中表达,而Act3在所有检测的器官(包括根、茎、叶、卷须,雌花和幼果)中都表达,提示黄瓜根的生长发育需要多种肌动蛋白基因的参与,而Act2和Act3可能与黄瓜雌性系的形成发育有关.