Oxygen-mediated cold-acclimation in cucumber (Cucumis sativus) seedlings

Cold acclimation of etiolated cucumber seedlings, consisting of cooling at 12°C for 48 h followed by a warming period at 25°C, led to tolerance to subsequent chilling at 2°C. Tolerance, as evidenced by freedom from chilling injury and continued growth, developed during the warming period in a time-course manner for 12 h but decreased with prolonged warming. A similar increase and subsequent decrease was also observed in the content of palmitic, linoleic and linolenic acids in total lipid fraction from cucumber hypocotyl tissue. During the warming period supra-ambient oxygen stimulated, whereas subambient oxygen inhibited, the increase in fatty acid content as well as development of chilling tolerance. A strong correlation between oxygen-mediated changes in fatty acid content and associated development of cold tolerance suggests that both these processes are interrelated. Cold acclimation, but not cold stress, led to an increase followed by a decrease in CO₂ evolution suggesting that a respiratory upsurge is yet another feature of cold acclimation in cucumbers.     

Differential chilling sensitivity in cucumber (Cucumis sativus) seedlings

Cucumber ( Cucumis sativus L. cv. Poinsett 76) seeds were chilled at 2.5°C in a study of the chilling sensitivity and recovery of radicle tissue. The effect of chilling on radicle growth and the production of carbon dioxide and ethylene was measured. Chilling sensitivity of radicles increased as they grew from 1 to 7 mm in length. The length, not the age of the radicles, determined the level of chilling sensitivity. Apical tissue was most sensitive to chilling and slowest to recover from chilling, followed by subapical and basal tissue. Our data demonstrate that the chilling sensitivity of young seedling radicles differs along their length and that the rapid chilling-induced inhibition of elongation is probably due to an inability of meristematic cells to remain viable and active when chilled.     

Callus growth and plant regeneration in diverse cultivars of cucumber (Cucumis sativus L.)

The growth and differentiation of callus tissues derived from cotyledons of ten cultivars ofCucumis sativus L. were investigated. Cotyledonary explants from all ten cultivars formed callus tissue on Murashige and Skoog (MS) medium supplemented with 0.5 M 2,4-dichlorophenoxyacetic acid and 5 M 6-benzylaminopurine. Fresh weight of the callus tissues averaged 1 to 8 g per flask after five weeks of culture. Shoot development was achieved in three cultivars, Hukchinju, Manchoonchoungjang and Seoul, on MS medium supplemented with 0.5 M -naphthaleneacetic acid and 5 M 6-benzylaminopurine. Reducing the 6-benzylaminopurine concentration to 0.01 M resulted in root formation on callus tissues and on shoots transferred to this medium. All cultivars gave the same response in tests of root formation, but shoot regeneration from callus culture of cucumber cotyledons was dependent on genotype with cultivar Manchoonchoungjang exhibiting the best shoot differentiation capability among the genotypes examined. Examination of mitotic metaphase from the regenerants revealed that all were tetraploid.     

Changes in polyamine pattern mediates sex differentiation and unisexual flower development in monoecious cucumber (Cucumis sativus L.)

Changes in the levels of polyamines are associated with fundamental physiological processes such as embryogenesis, induction of flowering, fruit development and ripening, senescence, and responses to environmental stresses, but the role of polyamines in sex differentiation and unisexual flower development has not been deeply studied. To extend the knowledge on the regulatory mechanisms of flowering in monoecious plant (producing unisexual flowers), we investigated the morphogenesis and free polyamine levels in Cucumis sativus during sex differentiation and unisexual flower development in vitro using histocytological and biochemical methods. As shown in our study, floral development in vitro was undisturbed and flowers of both sexes were produced. Sex differentiation relied on preventing the development of generative organs of the opposite sex, as we observed carpel repression in male flowers and stamen repression in female flowers. Pollen viability was negatively correlated with female flower development on the same node. Biochemical analysis revealed increased accumulation of aliphatic amines (tri, tetra‐amines) in generative (flower buds and flowers) compare to vegetative (axillary buds and leaves) organs. Undifferentiated floral buds contained elevated levels of agmatine, cadaverine, spermidine and spermine. Sex differentiation was associated with significantly decreased levels of agmatine and cadaverine. Our results showed that female flowers contained higher levels of total polyamine than male flowers. The increased level of cadaverine was associated with macrogametogenesis and female flower maturation. Putrescine was important for male flower development. Such results support the hypothesis that aliphatic amines are involved in unisexual flower development.     

Complex structure of the ribosomal DNA spacer of Cucumis sativus (cucumber)

Summary The nuclear 18 S, 5.8 S and 25 S ribosomal RNA genes (rDNA) of Cucumis sativus (cucumber) occur in at least four different repeat types of 10.2, 10.5, 11.5, and 12.5 kb in length. The intergenic spacer of these repeats has been cloned and characterized with respect to sequence organization. The spacer structure is very unusual compared to those of other eukaryotes. Duplicated regions of 197 bp and 311 bp containing part of the 3 end of the 25 S rRNA coding region and approximately 470 bp of 25 S rRNA flanking sequences occur in the intergenic spacer. The data from sequence analysis suggest that these duplications originate from recombination events in which DNA sequences of the original rDNA spacer were paired with sequences of the 25 S rRNA coding region. The duplicated 3ends of the 25 S rRNA are separated from each other mostly by a tandemly repeated 30 bp element showing a high GC-content of 87.5%. In addition, another tandemly repeated sequence of 90 bp was found downstream of the 3flanking sequences of the 25 S rRNA coding region. These results suggest that rRNA coding sequences can be involved in the generation of rDNA spacer sequences by unequal crossing over.     

Light modulation and in vitro effects of adenine nucleotides on leaf nitrate reductase activity in cucumber (Cucumis sativus)

Nitrate reductase (NR, EC 1.6.6.1) activity in attached cucumber ( Cucumis sativus L. cv. Ashley) leaves changed rapidly and reversibly during light/dark transitions, especially when assayed in the presence of free Mg²⁺. Light decreased and darkness increased the sensitivity of the enzyme to inhibition by Mg²⁺. The NR activation state, i.e. activity in the presence of Mg²⁺ relative to activity in the absence of Mg²⁺, increased with light intensity up to 400 μmol m⁻² s⁻¹ PAR (photosynthetically active radiation). When a desalted crude extract from illuminated leaves was preincubated with ATP, NR was gradually inactivated. Inactivation was only observed when activity was assayed in the presence of Mg²⁺. The ATP-inactivated NR remained inactive after removing the excess of ATP by gel filtration and it did not occur in partially purified NR preparations. NR extracted from darkened attached leaves was markedly activated when preincubated with 5'-AMP. These results support the view that inactivation/activation of cucumber-leaf NR in response to light/dark signals most likely involves phosphorylation/dephosphorylation of the enzyme catalysed by endogenous proteins. A substantial activation of NR by preincubation with 5'-AMP was also observed when activity was assayed in the absence of Mg²⁺, thus indicating that 5'-AMP can directly activate NR. Irradiation of an extract from darkened leaves containing FAD promoted a partial activation of NR. This effect was observed both in the +Mg²⁺ and in the −Mg²⁺ assay, indicating that activation was caused by photoexcited flavin and did not involve dephosphorylation of the enzyme.     

Endogenous salicylic acid accumulation is required for chilling tolerance in cucumber (Cucumis sativus L.) seedlings

Salicylic acid (SA) is an important plant hormone, and its exogenous application can induce tolerance to multiple environmental stresses in plants. In this study, we examine the potential involvement of endogenous SA in response to chilling in cucumber (Cucumis sativus L.) seedlings. A low temperature of 8 °C induces a moderate increase in endogenous SA levels. Chilling stimulates the enzymatic activities and the expression of genes for phenylalanine ammonia-lyase (PAL) and benzoic acid-2-hydroxylase rather than isochorismate synthase. This indicates that the PAL enzymatic pathway contributes to chilling-induced SA production. Cucumber seedlings pretreated with SA biosynthesis inhibitors accumulate less endogenous SA and suffer more from chilling damage. The expression of cold-responsive genes is also repressed by SA inhibitors. The reduction in stress tolerance and in gene expression can be restored by the exogenous application of SA, confirming the critical roles of SA in chilling responses in cucumber seedlings. Furthermore, the inhibition of SA biosynthesis under chilling stress results in a prolonged and enhanced hydrogen peroxide (H₂O₂) accumulation. The application of exogenous SA and the chemical scavenger of H₂O₂ reduces the excess H₂O₂ and alleviates chilling injury. In contrast, the protective effects of SA are negated by foliar spraying with high concentrations of H₂O₂ and an inhibitor of the antioxidant enzyme. These results suggest that endogenous SA is required in response to chilling stress in cucumber seedlings, by modulating the expression of cold-responsive genes and the precise induction of cellular H₂O₂ levels.     

Purification and characterization of arginine decarboxylase from cucumber (Cucumis sativus) seedlings

A simple, reproducible and rapid protocol for the purification of arginine decarboxylase fromCucumis sativus seedlings has been standardised. The purification steps involved ion-exchange chromatography on diethylaminoethyl-cellulose followed by gel filtration on Sephadex G-l 50. The purified enzyme preparation migrated as a single stainable band on Polyacrylamide gels at both basic and acidic pH, but under denaturing and reducing conditions on sodium dodecyl sulphate-polyacrylamide gels resolved into polypeptides of molecular weight 48,000,44,000 and 15,000. However, in the absence of 2-mercaptoethanol on electrophoresis on sodium dodecyl sulphate-polyacrylamide gels, the enzyme moved as single band with a molecular weight of 150,000. Evidence was obtained to indicate that these three polypeptides were probably derived from a single larger molecular weight enzyme. On storage of the purified protein, the 48,000 species was preferentially degraded to smaller polypeptides. The preliminary data suggested that the 48,000 and 44,000 species shared many common tryptic peptides as revealed by finger printing of the [¹²⁵I ]-labelled protein. The purified enzyme was a glycoprotein and had aK _m of 0.5 mM for arginine. Its activity was stimulated by dithiothrietol and pyridoxal phosphate. EDTA did not inhibit the enzyme activity. Mn²⁺ at 1 mM stimulated arginine decarboxylase activity but was inhibitory at higher concentration     

Auxin,biosynthesis of ethylene and sex expression in cucumber (Cucumis sativus)

Ethylene production, level of 1-aminocyclopropane-1-carboxylic acid (ACC) and activity of the ethylene forming enzyme (EFE) were higher in apices of gynoecious cucumber (Cucumis sativus cv. Alma) as compared to monoecious cucumber (C. sativus cv. Elem). Application of indole-3-acetic acid (IAA) enhanced ethylene and ACC production in both cultivars. The stimulatory effect of IAA was more pronounced in gynoecious apices. Induction of ethylene production and accumulation of ACC resulting from treatment with IAA were effectively blocked by aminoethoxyvinylglycine (AVG). Content of endogenous IAA, measured by an enzyme immunoassay, was lower in gynoecious cucumber as compared to monoecious one. Treatment of gynoecious plants with the antiauxins -(p-chlorophenoxy)isobutyric acid (PCIB) and -naphthaleneacetic acid (-NAA) did not inhibit female sex expression.It appears that although exogenous IAA enhances ACC and ethylene production, endogenous IAA might not have a major role in the control of sex expression in cucumber of the Beit-Alfa type.Prof. Rudich passed away in May 1986.     

Aspartyl proteinase from cucumber (Cucumis sativus) seeds. Preparation and characteristics

Aspartyl proteinase (EC 3.4.23) from cucumber seeds was purified by ammonium sulphate fractionation, chromatography on immobilized pepstatin and gel filtration on Sephacryl S-200. The preparation obtained, homogeneous on polyacrylamide-gel electrophoresis in acidic and alkaline media, has a molecular mass of 42,000, pI of 5.2, and shows the highest activity with denatured haemoglobin at pH 3.2. The proteinase is stable in slightly alkaline medium, whereas it is inactivated in acidic medium, especially in the presence of NaCl. The enzyme activity is affected neither by the inhibitors of serine proteinases, sulfhydryl-proteinases and metalloproteinases, nor by divalent metal ions, whereas the enzyme is inactivated by the inhibitors of aspartyl proteinases: 1,2,3-epoxy(p-nitrophenoxy)propane, diazoacetyl-DL-norleucine and pepstatin.     

Oxidative stress in cucumber (Cucumis sativus L) seedlings treated with acifluorfen

Treatment of diphenyl ether herbicide acifluorfen-Na (AF-Na) to intact cucumber (Cucumis sativus L cv Poinsette) seedlings induced overaccumulation of protoporphyrin IX in light (75 mumole m-2 s-1). The extra-plastidic protoporphyrin IX accumulated during the light exposure disappeared within two hours of transfer of acifluorofen-treated seedlings to darkness. The dark disappearance was due to re-entry of migrated protoporphyrin IX into the plastid and its subsequent conversion to protochlorophyllide. In light, protoporphyrin IX acted as a photosensitizer and caused generation of active oxygen species. The latter caused damage to the cellular membranes by peroxidation of membrane lipids that resulted in production of malondialdehyde. Damage to the plastidic membranes resulted in damage to photosystem I and photosystem II reactions. Dark-incubation of herbicide-sprayed plants before their exposure to light enhanced photodynamic damage due to diffusion of the herbicide to the site of action. Compared to control, in treated samples the cation-induced increases in variable fluorescence/maximum fluorescence ratio and increase in photosystem II activity was lower due to reduced grana stacking in herbicide-treated and light-exposed plants.     

授粉对黄瓜果实发育和品质的影响

以 津绿 3号 黄瓜为试材 ,研究了授粉对黄瓜果实发育、营养成分变化及采后果形变化的影响 .结果表明 ,授粉可减少化瓜、刺激果实发育、提高果实商品性 ,并提高产量 ,其坐瓜率、商品瓜率、单瓜重及产量分别较单性结实提高 6 3.0 %、6 8.7%、2 2 .6 %和 12 7.6 % .授粉瓜和单性结实瓜均表现为随着果实发育 ,可溶性蛋白质和维生素 C含量呈减少的趋势 ,可溶性糖含量呈逐渐增长的趋势 ,游离氨基酸含量呈波动变化 ,但授粉瓜的 4种营养成分均高于单性结实瓜 .在采后 1～ 5 d,授粉瓜头部易膨大形成大头瓜 ,而单性结实瓜果形变化不大     

Effects of oxidative stress on chlorophyll biosynthesis in cucumber (Cucumis sativus) cotyledons

We conducted a series of experiments to assess the effects of oxidative stress on chlorophyll biosynthesis in the vascular plant Cucumis sativus (cucumber). Specifically, cucumber cotyledons were treated with 100 μ M methyl viologen (MV) and subsequently exposed to dark (0 μE m⁻² s⁻¹), low light (40–45 μE m⁻² s⁻¹), or high light (1500–1600 μE m⁻² s⁻¹). Following treatment, extracts of these samples were subjected to high-performance liquid chromatography (HPLC) to quantitate the accumulation of chlorophyll biosynthetic pathway intermediates. The results of these analyses revealed significant accumulation of Mg-protoporphyrin IX monomethyl ester (Mg-proto IX ME) in green (14-h illuminated) as well as in etiolated cotyledons with MV treatment. These data suggest that MV-induced oxidative stress may have inhibited Mg-proto IX ME cyclase activity. Upon exposure to high light, in the presence or absence of MV, both green and etiolated cotyledons predominantly accumulated protoporphyrin IX (Proto IX). These elevated levels of Proto IX might be attributable to attenuated activity of any or all of the following enzymes: Mg-chelatase, Fe-chelatase and protoporphyrinogen IX oxidase. We also observed that MV-induced oxidative stress impacts on chlorophyll biosynthesis to a greater extent than on photosystem II. These results demonstrate that oxidative stress impedes key steps in chlorophyll biosynthesis by either directly or indirectly inhibiting the activity of these enzymes.     

Natural variation in iron use efficiency and mineral remobilization in cucumber (Cucumis sativus)

Aims

Iron (Fe) is an essential micronutrient, and plant available Fe is often limited in alkaline soils. Fe deficiency chlorosis decreases plant growth and yield. Identification of germplasm with high and low Fe use efficiency will allow studies to better understand the genetic components for breeding Fe efficient varieties.

Methods

A screen using cucumber (Cucumis sativus) seedlings identified varieties that maintained contrasting levels of chlorophyll under Fe deficiency or limitation. A time course of mineral dynamics in cotyledons was conducted.

Results

The variety Ashley had the highest chlorophyll under Fe deficiency and per unit Fe in the leaf, while the variety Miniature White had the lowest. Ashley also maintained higher chlorophyll when challenged with low Fe or bicarbonate, accumulated greater quantities of Fe, and had higher root ferric reductase activity. Cotyledons accumulated minerals for the first several days, then Fe, P, K, and Cu were remobilized. The Fe use efficient and inefficient varieties remobilized Fe and P on different timescales.

Conclusions

Our results suggest that this screen can identify varieties for systems level studies that could elucidate factors needed for Fe use efficiency and remobilization of minerals. The time course indicated that cotyledon Fe stores did not contribute to seedling Fe use efficiency.     

多胺对盐胁迫下黄瓜 (Cucumis sativus L.)幼苗体内K+、Na+和Cl-含量及器官间分布的影响

采用营养液水培,选用耐盐性不同的两个黄瓜品种,研究了外源多胺（Put、Spd、Spm）对NaCl胁迫下黄瓜幼苗植株不同器官中K＋、Na＋和Cl-含量的影响。结果表明,NaCl胁迫后黄瓜植株体内K＋含量下降、Na＋和Cl-含量升高、K/Na比值降低,耐盐性较弱的“津春2号”体内离子含量变化幅度明显大于耐盐性较强的“长春密刺”;叶面喷施多胺抑制了K＋含量的降低,减少了Na^＋和Cl^-的积累,提高了K/Na比值及K^＋、Na^＋吸收和运输的选择性,可缓解盐胁迫的伤害,增加生物积累量,且Spd（亚精胺）的作用尤为明显。总之,外源多胺可通过调控盐胁迫下植株体内的离子平衡,提高黄瓜幼苗的耐盐性。     

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