Theory and Practice in Measuring In-Vitro Extensibility of Growing Plant Cell Walls

This chapter summarizes four extensometer techniques for measuring cell wall extensibility in vitro and discusses how the results of these methods relate to the concept and ideal measurement of cell wall extensibility in the context of plant cell growth. These in-vitro techniques are particularly useful for studies of the molecular basis of cell wall extension. Measurements of breaking strength, elastic compliance and plastic compliance may be informative about changes in cell wall structure, whereas measurements of wall stress relaxation and creep are sensitive to both changes in wall structure and wall-loosening processes, such as those mediated by expansins and some lytic enzymes. A combination of methods is needed to obtain a broader view of cell wall behavior and properties connected with the concept of cell wall extensibility .

Assay of Plasma Membrane H+-ATPase in Plant Tissues under Abiotic Stresses

Plasma membrane (PM) H⁺-ATPase, which generates the proton gradient across the outer membrane of plant cells, plays a fundamental role in the regulation of many physiological processes fundamental for growth and development of plants. It is involved in the uptake of nutrients from external solutions, their loading into phloem and long-distance transport, stomata aperture and gas exchange, pH homeostasis in cytosol, cell wall loosening, and cell expansion. The crucial role of the enzyme in resistance of plants to abiotic and biotic stress factors has also been well documented. Such great diversity of physiological functions linked to the activity of one enzyme requires a suitable and complex regulation of H⁺-ATPase. This regulation comprises the transcriptional as well as post-transcriptional levels. Herein, we describe the techniques that can be useful for the analysis of the plasma membrane proton pump modifications at genetic and protein levels under environmental factors.

Variation in cucumber (Cucumis sativus L.) fruit size and shape results from multiple components acting pre-anthesis and post-pollination

Morphological, QTL, and gene expression analyses indicate variation in cucumber fruit size and shape results from orientation, timing, and extent of cell division and expansion, and suggest candidate gene factors. Variation in cucumber (Cucumis sativus L.) fruit size and shape is highly quantitative, implicating interplay of multiple components. Recent studies have identified numerous fruit size and shape quantitative trait loci (QTL); however, underlying factors remain to be determined. We examined ovary and fruit development of two sequenced cucumber genotypes with extreme differences in fruit size and shape, Chinese Long '9930' (CL9930), and pickling type 'Gy14'. Differences were observed in several independent factors that can influence size and shape: ovule number, rate and period of cell division in longitudinal and cross section in ovaries and fruit, timing and rate of fruit expansion in length and diameter, and cell shape. Level and timing of expression of select fruit growth stage marker genes and candidate fruit size gene homologs associated with cucumber fruit size and shape QTL were examined from 5-day pre-anthesis to 20-day post-pollination. Our results indicate that variation in fruit size and shape results from differences in cell number and shape in longitudinal and cross section, driven in turn by differences in orientation, timing, and duration of cell division and expansion, both pre- and post-anthesis, and suggest candidate genes contributing to determination of cucumber fruit size and shape.

Isolation and functional characterization of CsLsi1, a silicon transporter gene in Cucumis sativus

Cucumber (Cucumis sativus) is a widely grown cucurbitaceous vegetable that exhibits a relatively high capacity for silicon (Si) accumulation, but the molecular mechanism for silicon uptake remains to be clarified. Here we isolated and characterized CsLsi1, a gene encoding a silicon transporter in cucumber (cv. Mch-4). CsLsi1 shares 55.70 and 90.63% homology with the Lsi1s of a monocot and dicot, rice (Oryza sativa) and pumpkin (Cucurbita moschata), respectively. CsLsi1 was predominantly expressed in the roots, and application of exogenous silicon suppressed its expression. Transient expression in cucumber protoplasts showed that CsLsi1 was localized in the plasma membrane. Heterologous expression in Xenopus laevis oocytes showed that CsLsi1 evidenced influx transport activity for silicon but not urea or glycerol. Expression of cucumber CsLsi1-mGFP under its own promoter showed that CsLsi1 was localized at the distal side of the endodermis and the cortical cells in the root tips as well as in the root hairs near the root tips. Heterologous expression of CsLsi1 in a rice mutant defective in silicon uptake and the over-expression of this gene in cucumber further confirmed the role of CsLsi1 in silicon uptake. Our results suggest that CsLsi1 is a silicon influx transporter in cucumber. The cellular localization of CsLsi1 in cucumber roots is different from that in other plants, implying the possible effect of transporter localization on silicon uptake capability.

Impedance Flow Cytometry: A Novel Technique in Pollen Analysis

INTRODUCTION

An efficient and reliable method to estimate plant cell viability, especially of pollen, is important for plant breeding research and plant production processes. Pollen quality is determined by classical methods, like staining techniques or in vitro pollen germination, each having disadvantages with respect to reliability, analysis speed, and species dependency. Analysing single cells based on their dielectric properties by impedance flow cytometry (IFC) has developed into a common method for cellular characterisation in microbiology and medicine during the last decade. The aim of this study is to demonstrate the potential of IFC in plant cell analysis with the focus on pollen.

METHOD

Developing and mature pollen grains were analysed during their passage through a microfluidic chip to which radio frequencies of 0.5 to 12 MHz were applied. The acquired data provided information about the developmental stage, viability, and germination capacity. The biological relevance of the acquired IFC data was confirmed by classical staining methods, inactivation controls, as well as pollen germination assays.

RESULTS

Different stages of developing pollen, dead, viable and germinating pollen populations could be detected and quantified by IFC. Pollen viability analysis by classical FDA staining showed a high correlation with IFC data. In parallel, pollen with active germination potential could be discriminated from the dead and the viable but non-germinating population.

CONCLUSION

The presented data demonstrate that IFC is an efficient, label-free, reliable and non-destructive technique to analyse pollen quality in a species-independent manner.

Phloem transcriptome signatures underpin the physiological differentiation of the pedicel, stalk and fruit of cucumber (Cucumis sativus L.)

Cucumber is one of the most important vegetables grown worldwide due to its important economic and nutritional value. The cucumber fruit consists morphologically of the undesirable stalk and the tasty fruit; however, physiological differentiation of these two parts and the underlying molecular basis remain largely unknown. Here we characterized the physiological differences among the pedicel, stalk and fruit, and compared the respective phloem transcriptomes using laser capture microdissection coupled with RNA sequencing (RNA-Seq). We found that the pedicel was characterized by minor cell expansion and a high concentration of stachyose, the stalk showed rapid cell expansion and high raffinose accumulation, and the fruit featured transition from cell division to cell expansion and high levels of monosaccharides. Analyses of transcriptome data indicated that cell wall- and calcium ion binding-related genes contributed to the cell expansion in the pedicel and stalk, whereas genes implicated in cell cycle and hormone actions regulated the transition from cell division to cell expansion in the fruit. Differential sugar distribution in these three phloem-connected tissues resulted from tissue-specific sugar metabolism and transport. Enrichment of transcription factors in the stalk and fruit may facilitate nutrient accumulation in these sink organs. As such, phloem-located gene expression partially orchestrated physiological differentiation of the pedicel, stalk and fruit in cucumber. In addition, we identified 432 cucumber-unique genes and five phloem markers guiding future functional studies.

Mechanistic study of programmed cell death of root border cells of cucumber (Cucumber sativus L.) induced by copper

Programmed cell death (PCD) in root border cells (RBCs) induced by Copper (Cu) has been little studied. This study explored whether Cu induced PCD in RBCs of cucumber or not and investigated the possible mechanisms. The results showed that the percentage of apoptotic and necrotic RBCs increased with increasing concentration of Cu treatment. A quick burst of ROS in RBCs was detected, while mitochondrial membrane potential (ΔΨm) decreased sharply with Cu treatment. Caspase-3 like protease activity showed a tendency of increase with Cu treatment. The potential of Cu to induce PCD in RBCs of cucumber was first proved. Our results showed that ROS generation and mitochondrial membrane potential loss played important roles in Cu-induced caspase-3-like activation and PCD in RBCs of cucumber, which provided new insight into the signaling cascades that modulate Cu phytotoxicity mechanism.

Colletotrichum orbiculare Regulates Cell Cycle G1/S Progression via a Two-Component GAP and a GTPase to Establish Plant Infection

Morphogenesis in filamentous fungi depends on appropriate cell cycle progression. Here, we report that cells of the cucumber anthracnose fungus Colletotrichum orbiculare regulate G1/S progression via a two-component GAP, consisting of Budding-uninhibited-by-benomyl-2 (Bub2) and Byr-four-alike-1 (Bfa1) as well as its GTPase Termination-of-M-phase-1 (Tem1) to establish successful infection. In a random insertional mutagenesis screen of infection-related morphogenesis, we isolated a homolog of Saccharomyces cerevisiae, BUB2, which encodes a two-component Rab GAP protein that forms a GAP complex with Bfa1p and negatively regulates mitotic exit. Interestingly, disruption of either Co BUB2 or Co BFA1 resulted in earlier onset of nuclear division and decreased the time of phase progression from G1 to S during appressorium development. S. cerevisiae GTPase Tem1p is the downstream target of the Bub2p/Bfa1p GAP complex. Introducing the dominant-negative form of Co Tem1 into Co bub2Δ or Co bfa1Δ complemented the defect in G1/S progression, indicating that Co Bub2/Co Bfa1 regulates G1/S progression via Co Tem1. Based on a pathogenicity assay, we found that Co bub2Δ and Co bfa1Δ reduced pathogenesis by attenuating infection-related morphogenesis and enhancing the plant defense response. Thus, during appressorium development, C. orbiculare Bub2/Bfa1 regulates G1/S progression via Co Tem1, and this regulation is essential to establish plant infection.

Fruit removal increases root-zone respiration in cucumber

BACKGROUND AND AIMS

Many attempts have been made to avoid the commonly observed fluctuations in fruit initiation and fruit growth in crop plants, particularly in cucumber (Cucumis sativus). Weak sinks of the fruit have been assumed to result in low sink/source ratios for carbohydrates, which may inhibit photosynthesis. This study focuses on the effects of low sink-source ratios on photosynthesis and respiration, and in particular root-zone respiration.

METHODS

Mature fruit-bearing cucumber plants were grown in an aerated nutrient solution. The root containers were designed as open chambers to allow measurement of CO2 gas exchange in the root zone. A similar arrangement in a gas-exchange cuvette enabled simultaneous measurements of CO2 exchange in the shoot and root zones.

KEY RESULTS

Reducing the sinks for carbohydrates by removing all fruit from the plants always resulted in a doubling of CO2 exchange in the root zone within a few hours. However, respiration of the shoot remained unaffected and photosynthesis was only marginally reduced, if at all.

CONCLUSIONS

The results suggest that the increased level of CO2 gas exchange in the root zone after removing the carbon sinks in the shoot is due primarily to the exudation of organic compounds by the roots and their decomposition by micro-organisms. This hypothesis must be tested in further experiments, but if proved correct it would make sense to include carbon leakage by root exudation in cucumber production models. In contrast, inhibition of photosynthesis was measurable only at zero fruit load, a situation that does not occur in cucumber production systems, and models that estimate production can therefore ignore (end-product) inhibition of photosynthesis.

Evidence of programmed cell death induced by reconditioning after cold stress in cucumber fruit and possible involvement of ethylene

BACKGROUND

Cucumber fruit is susceptible to chilling injury (CI), which could be accelerated significantly with subsequent shelf-life. This type of CI culminates in deterioration of organs and eventually leads to cell death. In this study, evidence of programmed cell death (PCD), involving cell death induced by cold stress, was investigated in cucumber. Harvested cucumber (Cucumis sativus L. cv. Zhexiu-1) fruits were stored at 2 °C for 3, 6 or 9 days and subsequently transferred to 20 °C for 2 days.

RESULTS

Significant cell death acceleration was observed upon reconditioning after 9 days' cold stress when the hallmark of PCD - DNA laddering - was clearly observed. Further evidence of nuclear DNA cleavage was confirmed by the in situ TdT-mediated dUTP nick end labeling (TUNEL) assay. Chromatin condensation and nucleus distortion were observed by nuclear staining of DPI. Ethylene burst was observed upon reconditioning after 9 days of consecutive cold stress.

CONCLUSION

The features of PCD process induced by reconditioning after cold stress in cucumber fruit may be mainly attributed to ethylene burst.

Single-copy gene-based chromosome painting in cucumber and its application for chromosome rearrangement analysis in Cucumis

Chromosome painting based on fluorescence in situ hybridization (FISH) has played an important role in chromosome identification and research into chromosome rearrangements, diagnosis of chromosome abnormalities and evolution in human and animal species. However, it has not been applied widely in plants due to the large amounts of dispersed repetitive sequences in chromosomes. In the present work, a chromosome painting method for single-copy gene pools in Cucumis sativus was successfully developed. Gene probes with sizes above 2 kb were detected consistently. A cucumber karyotype was constructed based on FISH using a cocktail containing chromosome-specific gene probes. This single-copy gene-based chromosome painting (ScgCP) technique was performed by PCR amplification, purification, pooling, labeling and hybridization onto chromosome spreads. Gene pools containing sequential genes with an interval less than 300 kb yielded painting patterns on pachytene chromosomes. Seven gene pools corresponding to individual chromosomes unambiguously painted each chromosome pair of C. sativus. Three mis-aligned regions on chromosome 4 were identified by the painting patterns. A probe pool comprising 133 genes covering the 8 Mb distal end of chromosome 4 was used to evaluate the potential utility of the ScgCP technique for chromosome rearrangement research through cross-species FISH in the Cucumis genus. Distinct painting patterns of this region were observed in C. sativus, C. melo and C. metuliferus species. A comparative chromosome map of this region was constructed between cucumber and melon. With increasing sequence resources, this ScgCP technique may be applied on any other sequenced species for chromosome painting research.

Characterization and expression profiling of cucumber kinesin genes during early fruit development: revealing the roles of kinesins in exponential cell production and enlargement in cucumber fruit

Rapid cell division and expansion in early fruit development are important phases for cucumber fruit yield and quality. Kinesin proteins are microtubule-based motors responsible for modulating cell division and enlargement. In this work, the candidate kinesin genes involved in rapid cell division and expansion during cucumber fruit development were investigated. The morphological and cellular changes during early fruit development were compared in four cucumber genotypes with varied fruit size. The correlation between the expression profiles of cucumber kinesin genes and cellular changes in fruit was investigated. Finally, the biochemical characteristics and subcellular localizations of three candidate kinesins were studied. The results clarified the morphological and cellular changes during early cucumber fruit development. This study found that CsKF2-CsKF6 were positively correlated with rapid cell production; CsKF1 and CsKF7 showed a strongly positive correlation with rapid cell expansion. The results also indicated that CsKF1 localized to the plasma membrane of fast-expanding fruit cells, that CsKF2 might play a role in fruit chloroplast division, and that CsKF3 is involved in the function or formation of phragmoplasts in fruit telophase cells. The results strongly suggest that specific fruit-enriched kinesins are specialized in their functions in rapid cell division and expansion during cucumber fruit development.

Effects of short term iron citrate treatments at different pH values on roots of iron-deficient cucumber: a Mössbauer analysis

Alkaline pH values and bicarbonate greatly reduce the mobility and uptake of Fe, causing Fe deficiency chlorosis. In the present work, the effects of pH and bicarbonate on the uptake and accumulation of Fe in the roots of cucumber were studied by Mössbauer spectroscopy combined with physiological tests and diaminobenzidine enhanced Perls staining. Mössbauer spectra of Fe-deficient cucumber roots supplied with 500 μM (57)Fe(III)-citrate at different pH values showed the presence of an Fe(II) and an Fe(III) component. As the pH was increased from 4.5 to 7.5, the root ferric chelate reductase (FCR) activity decreased significantly and a structural change in the Fe(III) component was observed. While at pH 4.5 the radial intrusion of Fe reached the endodermis, at pH 7.5, Fe was found only in the outer cortical cell layers. The Mössbauer spectra of Fe-deficient plants supplied with Fe(III)-citrate in the presence of bicarbonate (pH 7.0 and 7.5) showed similar Fe components, but the relative Fe(II) concentration compared to that measured at pH values 6.5 and 7.5 was greater. The Mössbauer parameters calculated for the Fe(II) component in the presence of bicarbonate were slightly different from those of Fe(II) alone at pH 6.5-7.5, whereas the FCR activity was similarly low. Fe incorporation into the root apoplast involved only the outer cortical cell layers, as in the roots treated at pH 7.5. In Fe-sufficient plants grown with Fe(III)-citrate and 1mM bicarbonate, Fe precipitated as granules and was in diffusely scattered grains on the root surface. The "bicarbonate effect" may involve a pH component, decreasing both the FCR activity and the acidification of the apoplast and a mineralization effect leading to the slow accumulation of extraplasmatic Fe particles, forming an Fe plaque and trapping Fe and other minerals in biologically unavailable forms.

Size-topology relations in packings of grains, emulsions, foams, and biological cells

Particulate packings in 3D are used to study the effects of compression and polydispersity on the geometry of the tiling in these systems. We find that the dependence of the neighbor number on cell size is quasilinear in the monodisperse case and becomes nonlinear above a threshold polydispersity, independent of the method of creation of the tiling. These size-topology relations can be described by a simple analytical theory, which quantifies the effects of positional disorder in the monodisperse case and those of size disorder in the polydisperse case and is applicable in two and three dimensions. The theory thus gives a unifying framework for a wide range of amorphous systems, ranging from biological tissues, foams, and bidisperse disks to compressed emulsions and granular matter.

A revised architecture of primary cell walls based on biomechanical changes induced by substrate-specific endoglucanases

Xyloglucan is widely believed to function as a tether between cellulose microfibrils in the primary cell wall, limiting cell enlargement by restricting the ability of microfibrils to separate laterally. To test the biomechanical predictions of this "tethered network" model, we assessed the ability of cucumber (Cucumis sativus) hypocotyl walls to undergo creep (long-term, irreversible extension) in response to three family-12 endo-β-1,4-glucanases that can specifically hydrolyze xyloglucan, cellulose, or both. Xyloglucan-specific endoglucanase (XEG from Aspergillus aculeatus) failed to induce cell wall creep, whereas an endoglucanase that hydrolyzes both xyloglucan and cellulose (Cel12A from Hypocrea jecorina) induced a high creep rate. A cellulose-specific endoglucanase (CEG from Aspergillus niger) did not cause cell wall creep, either by itself or in combination with XEG. Tests with additional enzymes, including a family-5 endoglucanase, confirmed the conclusion that to cause creep, endoglucanases must cut both xyloglucan and cellulose. Similar results were obtained with measurements of elastic and plastic compliance. Both XEG and Cel12A hydrolyzed xyloglucan in intact walls, but Cel12A could hydrolyze a minor xyloglucan compartment recalcitrant to XEG digestion. Xyloglucan involvement in these enzyme responses was confirmed by experiments with Arabidopsis (Arabidopsis thaliana) hypocotyls, where Cel12A induced creep in wild-type but not in xyloglucan-deficient (xxt1/xxt2) walls. Our results are incompatible with the common depiction of xyloglucan as a load-bearing tether spanning the 20- to 40-nm spacing between cellulose microfibrils, but they do implicate a minor xyloglucan component in wall mechanics. The structurally important xyloglucan may be located in limited regions of tight contact between microfibrils.

The origin and composition of cucurbit "phloem" exudate

Cucurbits exude profusely when stems or petioles are cut. We conducted studies on pumpkin (Cucurbita maxima) and cucumber (Cucumis sativus) to determine the origin and composition of the exudate. Morphometric analysis indicated that the exudate is too voluminous to derive exclusively from the phloem. Cold, which inhibits phloem transport, did not interfere with exudation. However, ice water applied to the roots, which reduces root pressure, rapidly diminished exudation rate. Sap was seen by microscopic examination to flow primarily from the fascicular phloem in cucumber, and several other cucurbit species, but primarily from the extrafascicular phloem in pumpkin. Following exposure of leaves to 14CO2, radiolabeled stachyose and other sugars were detected in the exudate in proportions expected of authentic phloem sap. Most of this radiolabel was released during the first 20 s. Sugars in exudate were dilute. The sugar composition of exudate from extrafascicular phloem near the edge of the stem differed from that of other sources in that it was high in hexose and low in stachyose. We conclude that sap is released from cucurbit phloem upon wounding but contributes negligibly to total exudate volume. The sap is diluted by water from cut cells, the apoplast, and the xylem. Small amounts of dilute, mobile sap from sieve elements can be obtained, although there is evidence that it is contaminated by the contents of other cell types. The function of P-proteins may be to prevent water loss from the xylem as well as nutrient loss from the phloem.

Characterization of an ethylene-inducible, calcium-dependent nuclease that is differentially expressed in cucumber flower development

• Production of unisexual flowers is an important mechanism that promotes cross-pollination in angiosperms. We previously identified primordial anther-specific DNA damage and organ-specific ethylene perception responsible for the arrest of stamen development in female flowers, but little is known about how the two processes are linked. • To identify potential links between the two processes, we performed suppression subtractive hybridization (SSH) on cucumber (Cucumis sativus L.) stamens of male and female flowers at stage 6, with stamens at stage 5 of bisexual flowers as a control. • Among the differentially expressed genes, we identified an expressed sequence tag (EST) encoding a cucumber homolog to an Arabidopsis calcium-dependent nuclease (CAN), designated CsCaN. Full-length CsCaN cDNA and the respective genomic DNA sequence were cloned and characterized. The CsCaN protein exhibited calcium-dependent nuclease activity. CsCaN showed ubiquitous expression; however, increased gene expression was detected in the stamens of stage 6 female flowers compared with male flowers. As expected, CsCaN expression was ethylene inducible. It was of great interest that CsCaN was post-translationally modified. • This study demonstrated that CsCaN is a novel cucumber nuclease gene, whose DNase activity is regulated at multiple levels, and which could be involved in the primordial anther-specific DNA damage of developing female cucumber flowers.

Phloem unloading follows an extensive apoplasmic pathway in cucumber (Cucumis sativus L.) fruit from anthesis to marketable maturing stage

The phloem unloading pathway remains unclear in fruits of Cucurbitaceae, a classical stachyose-transporting species with bicollateral phloem. Using a combination of electron microscopy, transport of phloem-mobile symplasmic tracer carboxyfluorescein, assays of acid invertase and sucrose transporter, and [(14)C]sugar uptake, the phloem unloading pathway was studied in cucumber (Cucumis sativus) fruit from anthesis to the marketable maturing stage. Structural investigations showed that the sieve element-companion cell (SE-CC) complex of the vascular bundles feeding fruit flesh is apparently symplasmically restricted. Imaging of carboxyfluorescein unloading showed that the dye remained confined to the phloem strands of the vascular bundles in the whole fruit throughout the stages examined. A 37 kDa acid invertase was located predominantly in the cell walls of SE-CC complexes and parenchyma cells. Studies of [(14)C]sugar uptake suggested that energy-driven transporters may be functional in sugar trans-membrane transport within symplasmically restricted SE-CC complex, which was further confirmed by the existence of a functional plasma membrane sucrose transporter (CsSUT4) in cucumber fruit. These data provide a clear evidence for an apoplasmic phloem unloading pathway in cucumber fruit. A presumption that putative raffinose or stachyose transporters may be involved in soluble sugars unloading was discussed.

Comparison of the distribution of the repetitive DNA sequences in three variants of Cucumis sativus reveals their phylogenetic relationships

Repetitive DNA sequences with variability in copy number or/and sequence polymorphism can be employed as useful molecular markers to study phylogenetics and identify species/chromosomes when combined with fluorescence in situ hybridization (FISH). Cucumis sativus has three variants, Cucumis sativus L. var. sativus, Cucumis sativus L. var. hardwickii and Cucumis sativus L. var. xishuangbannesis. The phylogenetics among these three variants has not been well explored using cytological landmarks. Here, we concentrate on the organization and distribution of highly repetitive DNA sequences in cucumbers, with emphasis on the differences between cultivar and wild cucumber. The diversity of chromosomal karyotypes in cucumber and its relatives was detected in our study. Thereby, sequential FISH with three sets of multi-probe cocktails (combined repetitive DNA with chromosome-specific fosmid clones as probes) were conducted on the same metaphase cell, which helped us to simultaneously identify each of the 7 metaphase chromosomes of wild cucumber C. sativus var. hardwickii. A standardized karyotype of somatic metaphase chromosomes was constructed. Our data also indicated that the relationship between cultivar cucumber and C. s. var. xishuangbannesis was closer than that of C. s. var. xishuangbannesis and C. s. var. hardwickii.

Wavelength swept amplified spontaneous emission source for high speed retinal optical coherence tomography at 1060 nm

The wavelength swept amplified spontaneous emission (ASE) source presented in this paper is an alternative approach to realize a light source for high speed swept source optical coherence tomography (OCT). ASE alternately passes a cascade of different optical gain elements and tunable optical bandpass filters. In this work we show for the first time a wavelength swept ASE source in the 1060 nm wavelength range, enabling high speed retinal OCT imaging. We demonstrate ultra-rapid retinal OCT at a line rate of 170 kHz, a record sweep rate at 1060 nm of 340 kHz with 70 nm full sweep width, enabling an axial resolution of 11 μm. Two different implementations of the source are characterized and compared to each other. The last gain element is either a semiconductor optical amplifier or an Ytterbium-doped fibre amplifier enabling high average output power of >40 mW. Various biophotonic imaging examples provide a wide range of quality benchmarks achievable with such sources.

The action of herbicides on fatty acid biosynthesis and elongation in barley and cucumber

BACKGROUND

Herbicides that affect lipid metabolism have been used commercially for many years. Here, napropamide, diphenamid, dimethachlor and cafenstrole are compared; these have all been classified by the Herbicide Resistance Action Committee (HRAC) as K(3) herbicides and inhibitors of cell division and/or synthesis of very-long-chain fatty acids (VLCFAs). In addition, spiro-decanedione A and pinoxaden dione are compared as inhibitors of lipid synthesis through inhibition of acetyl-CoA carboxylase (ACCase).

RESULTS

Whereas the chloracetamide dimethachlor and the carboxyamide cafenstrole potently inhibited VLCFA synthesis in both barley and cucumber, the acetamides napropamide and diphenamid which are also classified as K(3) herbicides and likewise the unclassified herbicide cinmethylin did not. The graminicide pinoxaden dione inhibited de novo fatty acid synthesis in barley, but not in cucumber, and correspondingly inhibited the plastid form of maize ACCase much more than the cytosolic form (IC(50) values of 0.1 and 17 microM). By contrast, spiro-decanedione A exhibited herbicidal effects not only on grasses but also on broad leaves, strongly inhibited maize cytosolic ACCase and inhibited synthesis of VLCFAs in cucumber.

CONCLUSIONS

The acetamides napropamide and diphenamid, which do not inhibit VLCFA synthesis, should be classified separately from K(3) herbicides that do. Pinoxaden dione and spiro-decanedione A represent new classes of chemicals acting on plant lipid synthesis.

Identification and mapping of molecular markers linked to the tuberculate fruit gene in the cucumber (Cucumis sativus L.)

Warty fruit is one of the highly valuable external quality traits related to the market values of cucumber. Genetic analysis has shown that a single dominant gene, Tu (Tuberculate fruit), determines the warty fruit trait in the cucumber plant. An F(2) population (247 individuals) from the cross of S06 x S52 was used for the mapping of the Tu/tu locus. By combining bulked segregant analysis with the sequence-related amplified polymorphism (SRAP) and simple sequence repeat (SSR) markers, 15 markers (9 SRAPs and 6 SSRs) linked to the Tu/tu locus were identified. Of nine SRAP markers, three closely linked to the Tu/tu locus were successfully converted into sequence characterized amplified region (SCAR) markers. The Tu/tu locus was mapped between the co-dominant SSR marker SSR16203 and the SCAR marker C_SC933, at a genetic distance of 1.4 and 5.9 cM, respectively. Then the linked SSR markers in the study were used as anchor loci to locate the Tu/tu locus on cucumber chromosome 5. Moreover, the validity analysis of the C_SC69 and C_SC24 markers was performed with 62 cucumber lines of diverse origins, showing that the two SCAR markers can be used for marker-assisted selection (MAS) of the warty fruit trait in cucumber breeding. The information provided in this study will facilitate the map-based cloning of the Tu/tu gene.

Changes of alternative oxidase activity, capacity and protein content in leaves of Cucumis sativus wild-type and MSC16 mutant grown under different light intensities

In vitro studies demonstrated that alternative oxidase (AOX) is biochemically regulated by a sulfhydryl-disulfide system, interaction with alpha-ketoacids, ubiquinone pool redox state and protein content among others. However, there is still scarce information about the in vivo regulation of the AOX. Cucumis sativus wild-type (WT) and MSC16 mutant plants were grown under two different light intensities and were used to analyze the relationship between the amount of leaf AOX protein and its in vivo capacity and activity at night and day periods. WT and MSC16 plants presented lower total respiration (V(t)), cytochrome oxidase pathway (COP) activity (v(cyt)) and alternative oxidase pathway (AOP) activity (v(alt)) when grown at low light (LL), although growth light intensity did not change the amount of cytochrome oxidase (COX) nor AOX protein. Changes of v(cyt) related to growing light conditions suggested a substrate availability and energy demand control. On the other hand, the total amount of AOX protein present in the tissue does not play a role in the regulation neither of the capacity nor of the activity of the AOP in vivo. Soluble carbohydrates were directly related to the activity of the AOP. However, although differences in soluble sugar contents mostly regulate the capacity of the AOP at different growth light intensities, additional regulatory mechanisms are necessary to fully explain the observed results.

Chromatin structural rearrangement during dedifferentiation of protoplasts of Cucumis sativus L

This paper reports on the structural rearrangement of satellite DNA type I repeats and heterochromatin during the dedifferentiation and cell cycling of mesophyll protoplasts of cucumber (Cucumis sativus). These repeats were localized in the telomeric heterochromatin of cucumber chromosomes and in the chromocenters of interphase nuclei. The dramatic reduction of heterochromatin involves decondensation of subtelomeric repeats in freshly isolated protoplasts; however, there are not a great many remarkable changes in the expression profile. In spite of that, reformation of the chromocenters, occurring 48 h after protoplast isolation, is accompanied by recondensation of satellite DNA type I; however, only partial reassembly of these repeats was revealed. In this study, FISH and a flow cytometry assay show a correlation between the partial chromocenter and the repeats reassembly, and with the reentry of cultivated protoplasts into the cell cycle and first cell division. After that, divided cells displayed a higher variability in the expression profile than did leaves' mesophyll cells and protoplasts.

[Effects of root zone hypoxia on respiratory metabolism of cucumber seedlings roots]

With the seedlings of Lübachun No. 4, a hypoxia-resistant cultivar, and Zhongnong No. 8, a hypoxia-sensitive cultivar, as test materials, and by the method of solution culture, this paper studied the effects of root zone hypoxia on their roots' respiratory metabolism. The results showed that root zone hypoxia inhibited the tricarboxylic acid (TCA) cycle significantly, But accelerated the anaerobic respiration of cucumber roots. Under root zone hypoxia stress, the decrement of succinic dehydrogenase (SDH) and isocitric dehydrogenase (IDH) activities and the increment of lactate dehydrogenase (LDH) activity and lactate and pyruvate contents were lesser in Lübachun No. 4 than in Zhongnong No. 8 seedlings roots, but conversely, the increment of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) activities and alcohol and alanine contents in Lübachun No. 4 seedlings roots were higher than those in Zhongnong No. 8 seedlings roots. On the 8th day of hypoxia stress, the ADH activity and alcohol and alanine contents increased by 409.30%, 112.13% and 30.64% in Lübachun No. 4 roots and by 110.42%, 31.84% and 4.78% in Zhongnong No. 8 roots, respectively, compared with the control. No significant differences in the alanine aminotransferase (AlaAT) activity and acetaldehyde content were observed between the two cultivars. It was concluded that the acceleration of alcohol fermentation and the accumulation of alanine were in favor of the enhancement of root zone hypoxia tolerance of cucumber roots.

Comparison of heavy metal effect on the proton pumps of plasma membrane and tonoplast in cucumber root cells

The effects of 10 microM cadmium, copper and nickel on the activities of vacuolar membrane and plasma membrane (PM) ATP-dependent proton pumps was investigated in Cucumis sativus L. root cells. It was demonstrated that vacuolar H+-ATPase (EC 3.6.3.14) and PM H+-ATPase (EC 3.6.3.6) differed in sensitivity to heavy metals. Exposure of cucumber seedlings to Cd, Cu and Ni had no significant effect on the activity of the vacuolar proton pump and, in the case of Ni, also on the activity of the PM proton pump. In contrast, Cd and Cu ions diminished both ATP hydrolysis and proton transport in plasma membranes. Transcript levels of genes encoding PM enzyme as well as the subunit A of tonoplast enzyme in roots stressed with heavy metals were similar to the control. Cd, Cu and Ni were accumulated in cucumber roots with similar efficiency, but their relative distribution between the symplast and apoplast differed. To explain the mechanism of heavy metal action on the plasma membranes of cucumber roots, the MDA content, as a lipid peroxidation product, and fatty acid composition were analyzed. It was shown that exposure of plants to Cd, Cu and Ni did not enhance the lipid peroxidation in the PM fraction. However, all metals caused an increase in the saturation of PM fatty acids and a decrease in the length of the fatty acid chain.

Continuous UV-B irradiation induces morphological changes and the accumulation of polyphenolic compounds on the surface of cucumber cotyledons

Sharp-headed and globular-headed trichomes are found on the surface of cucumber (Cucumis sativus L.) cotyledons. Most sharp-headed trichomes consist of three cells. Toluidine blue O stains sharp-headed but not globular-headed trichomes. The effect of continuous ultraviolet-B (UV-B; 290-320 nm) irradiation on the surface of cucumber cotyledons was examined with respect to the two trichome types. Continuous UV-B irradiation induced cell division at or under the basal part of sharp-headed trichomes, resulting in an increase in the number of cell layers from three to six. In parallel, the area stained by toluidine blue O expanded to include epidermal cells surrounding sharp-headed trichomes. Regions of alkali-induced fluorescence due to the presence of polyphenolic compounds coincided with areas stained by toluidine blue O. In contrast, continuous UV-B irradiation did not cause morphological changes in globular-headed trichomes. Thus, continuous UV-B irradiation causes the accumulation of polyphenolic compounds in cucumber cotyledons and induces specific morphological changes in or around sharp-headed trichomes. UV-B exposure also increases lignin content in this tissue. Therefore, continuous UV-B irradiation may induce the specific accumulation of polyphenolic compounds, especially stress lignins, in and near sharp-headed trichomes.

A nitrite transporter associated with nitrite uptake by higher plant chloroplasts

Chloroplasts take up cytosolic nitrite during nitrate assimilation. In this study we identified a nitrite transporter located in the chloroplasts of higher plants. The transporter, CsNitr1-L, a member of the proton-dependent oligopeptide transporter (POT) family, was detected during light-induced chloroplast development in de-etiolating cucumber seedlings. We detected a CsNitr1-L-green fluorescent protein (GFP) fusion protein in the chloroplasts of leaf cells and found that an immunoreactive 51 kDa protein was present in the isolated inner envelope membrane of chloroplasts. CsNitr1-L has an isoform, CsNitr1-S, with an identical 484 amino acid core sequence; however, in CsNitr1-S the 120 amino acid N-terminal extension is missing. Saccharomyces cerevisiae cells expressing CsNitr1-S absorbed nitrite from an acidic medium at a slower rate than mock-transformed control cells, and accumulated nitrite to only one-sixth the concentration of the control cells, suggesting that CsNitr1-S enhances the efflux of nitrite from the cell. Insertion of T-DNA in a single CsNitr1-L homolog (At1g68570) in Arabidopsis resulted in nitrite accumulation in leaves to more than five times the concentration found in the wild type. These results show that it is possible that both CsNitr1-L and CsNitr1-S encode efflux-type nitrite transporters, but with different subcellular localizations. CsNitr1-L may possibly load cytosolic nitrite into chloroplast stroma in the chloroplast envelope during nitrate assimilation. The presence of genes homologous to CsNitr1-L in the genomes of Arabidopsis and rice indicates that facilitated nitrite transport is of general physiological importance in plant nutrition.

The selection of mosaic (MSC) phenotype after passage of cucumber (Cucumis sativus L.) through cell culture — a method to obtain plant mitochondrial mutants

Mosaic (MSC) mutants of cucumber (Cucumis sativus L.) appear after passage through cell cultures. The MSC phenotype shows paternal transmission and is associated with mitochondrial DNA rearrangements. This review describes the origins and phenotypes of independently produced MSC mutants of cucumber, including current knowledge on their mitochondrial DNA rearrangements, and similarities of MSC with other plant mitochondrial mutants. Finally we propose that passage of cucumber through cell culture can be used as a unique and efficient method to generate mitochondrial mutants of a higher plant in a highly homozygous nuclear background.

In situ reverse transcription PCR on plant tissues

In situ detection techniques allow specific nucleic acid sequences to be exposed in morphologically preserved tissue sections. In combination with immunocytochemistry, in situ detection can relate microscopic topological information to gene activity at the transcript or protein levels in specific tissues. The advantage of in situ methods over the conventional techniques (e.g., Northern blot, reverse transcription polymerase chain reaction [RT-PCR], or real-time PCR) is that they allow the investigation of the putative spatial distribution of nucleic acid products activity in a heterogeneous cell population. In this chapter, we describe a protocol for in situ RT-PCR detection of specific messenger RNA in cucumber (Cucumis sativus), although this protocol can be used for any plant species, floral buds, and somatic embryo tissue sections on glass microscope slides. A successful in situ RT-PCR procedure requires the optimization of many conditions related to the tissue types used, for example, a cell's age, size, and composition, which may influence the detection of RT-PCR products, as well as specific transcript availability. Moreover, parameters, such as the fixation time, thermal cycling set-up, and the time of detection of RT-PCR products, also should be optimized. The importance of the other factors also is estimated in the protocol. In addition several types of controls that are necessary for a trustworthy in situ RT-PCR method are being discussed.

Complete sequence and organization of the cucumber (Cucumis sativus L. cv. Baekmibaekdadagi) chloroplast genome

The nucleotide sequence of the cucumber (Cucumis sativus L. cv. Baekmibaekdadagi) chloroplast genome was completed. The circular double-stranded DNA, consisting of 155,527 bp, contained a pair of inverted repeat regions (IRa and IRb) of 25,187 bp each, which were separated by small and large single copy regions of 86,879 and 18,274 bp, respectively. The presence and relative positions of 113 genes (76 peptide-encoding genes, 30 tRNA genes, four rRNA genes, and three conserved open reading frames) were identified. The major portion (55.76%) of the C. sativus chloroplast genome consisted of gene-coding regions (49.13% protein coding and 6.63% RNA regions; 27.81% LSC, 9.46% SSC and 18.49% IR regions), while intergenic spacers (including 20 introns) made up 44.24%. The overall G-C content of C. sativus chloroplast genome was 36.95%. Sixteen genes contained one intron, while two genes had two introns. The expansion/contraction manner of IR at IRb/LSC and IR/SSC border in Cucumis was similar to that of Lotus and Arabidopsis, and the manner at IRa/LSC was similar to Lotus and Nicotiana. In total, 56 simple sequence repeats (more than 10 bases) were identified in the C. sativus chloroplast genome.

Cucumber (Cucumis sativus L.)

We describe two novel Agrobacterium tumefaciens-based methods of cucumber transformation. The first involves direct regeneration from leaf microexplants selected on kanamycin-containing medium. The second involves regeneration from a long-term established embryogenic suspension culture emitting green autofluorescence (GAF) and selection on medium containing hygromycin. In the latter method, GAF was used as a reporter, thereby allowing a simple and reliable identification of transgenic cells with a high regeneration capacity. (No false positives were observed.) The transformation efficiency in the leaf microexplants fluctuated from 0.8 to 6.5% of the primary explants, whereas in the embryogenic suspension-cultured cells it varied from 6.4 to 17.9% of the aggregates. In the GAF method, the step involving the elimination of the Agrobacterium cells by antibiotics could be omitted; however, this reduced the transformation efficiency to about 3%. The time required from inoculation to regenerated plant in the greenhouse was the same for both methods, but the GAF method required more preinoculation time than the leaf microexplant method.

Preferential localization of abscisic acid in primordial and nursing cells of reproductive organs of Arabidopsis and cucumber

Abscisic acid (ABA) is known to function in plant stress responses and seed dormancy, and much is known about its detailed mechanisms of signal transduction. Recent studies suggest that this hormone may also play important roles in sugar signaling and assimilate distribution during fruit development. However, little is known about the role of ABA in actively growing or differentiating fruits and other plant organs or tissues. To explore whether ABA functions during the early development of reproductive organs, we carried out ABA immunolocalization using monoclonal antibodies. The specific ABA accumulation pattern was verified by gas chromatography-mass spectrometry (GC-MS). ABA was not only detected in primordial cells of flower organs, but was also detected in nursing cells (e.g. tapetum and integuments), which function in supplying nutrition for germ cell development. These findings suggest that, in addition to its well-known function as a 'negative hormone', ABA may play some 'positive' roles during plant development, including possible involvement in the regulation of assimilate distribution.

Cucurbit phloem serpins are graft-transmissible and appear to be resistant to turnover in the sieve element-companion cell complex

Serpins are unique inhibitors of serine proteases that are located in various plant tissues and organs. An orthologue of the pumpkin (Cucurbita maxima) phloem serpin CmPS-1 was amplified from cucumber (Cucumis sativus) RNA by RT-PCR, cloned, and designated as CsPS-1 (GenBank accession no. AJ866989). Alternative amino acid sequences in the reactive centre loop suggest distinct inhibitory specificity between CmPS-1 and CsPS-1. A difference in the electrophoretic mobility of these serpins was used in heterografts to establish that serpins are phloem-mobile. Immuno light microscopy revealed that the phloem serpins are localized exclusively to sieve elements (SE), while the phloem filament protein CmPP1, used as a reference, is localized to both SEs and companion cells (CCs). Similar to CmPS-1, CsPS-1 accumulates over time in phloem exudates, indicating that serpins differ from other phloem-mobile proteins whose concentrations appear to be stable in phloem exudates. These differences could reflect alternative mechanisms regulating protein turnover and/or inaccessibility of protein degradation. The functionality of the pore/plasmodesma units connecting SEs and CCs was tested with graft-transmitted CmPP1 as a transport marker. The occurrence of CmPP1 in the CCs of the Cucumis graft partner shows that translocated 88 kDa phloem filament protein monomers can symplasmically exit the SE and accumulate in the CC. By contrast, serial sections probed with the serpin antibody demonstrate that the 43 kDa serpin does not enter CCs. Collectively, these data indicate that CCs play a decisive role in homeostasis of exudate proteins; proteins not accessing the CCs accumulate in SEs and display a time-dependent increase in concentration.

The perisperm-endosperm envelope in Cucumis: structure, proton diffusion and cell wall hydrolysing activity

BACKGROUND

and Aims The envelope surrounding the embryo in cucurbit seed, which consists of a single layer of live endosperm cells covered by lipid- and callose-rich layers, is reported to show semi-permeability and also to act as the primary barrier to radicle emergence. Structure, development and permeability of the envelope and activity of cell wall hydrolases during germination of cucumber and muskmelon seeds were investigated.

METHODS

Sections of seeds were stained with aniline blue and Sudan III. Proton diffusion and endo-beta-mannanase activity were detected by tissue printing. A gel-diffusion assay was performed to quantify endo-beta-mannanase activity, while the activity of beta-glucanase was determined with laminarin as the substrate and glucose formation measured using the GOD-POD method.

KEY RESULTS

The lipid layer differentiated during seed development in cucumber in the epidermis of a multilayered nucellus, whereas the callose layer appeared to develop outside the endosperm cell layer. Accordingly, the envelope has been called the perisperm-endosperm (PE) envelope. Chloroform treatment of seeds, which resulted in a substantial reduction in Sudan staining of the lipid layer, also enhanced the permeability of the PE envelope to 2,3,5-triphenyltetrazolium chloride. Proton diffusion occurred when the PE envelopes from seeds had their inner surface in contact with bromocresol purple-containing agarose gels, but not when their outer surface was in contact. Substantial endo-beta-mannanase activity was present in the caps of the PE envelopes, whereas a marked increase in beta-glucanase activity was observed in radicles prior to germination.

CONCLUSIONS

The lipid layer seems to contribute to the semi-permeability of the PE envelope. The diffusion of protons might create an acidic environment conducive to the activity of cell wall hydrolases, namely endo-beta-mannanase (EC 3.2.1.78) and beta-glucanase [beta(1-->3)glucanohydrolase; EC 3.2.1.6], which, in turn, may play a role in the weakening of the PE envelope necessary for the protrusion of the radicle in cucumber and muskmelon seeds.

Development of a simple algorithm for the detection of chilling injury in cucumbers from visible/near-infrared hyperspectral imaging

Hyperspectral images of cucumbers under a variety of conditions were acquired to explore the potential for the detection of chilling-induced damage in whole cucumbers. Region of interest (ROI) spectral features of chilling injured areas, resulting from chilling treatment at 0 degrees C, showed the reduction of reflectance intensity over the period at post-chilling room temperature (RT) storage. A large spectral difference between good, smooth skins and chilling-injured skins occurred in the 700-850 nm visible/near-infrared (NIR) region. Both simple band ratio algorithms and principal component analysis (PCA) were attempted to discriminate the ROI spectra of good cucumber skins from those of chilling injured ones. Results revealed that both the dual-band ratio algorithm (R(811nm)/R(756nm)) and a PCA model from a narrow spectral region of 733-848 nm can detect chilling-injured skins with a success rate of over 90%. The results also suggested that chilling injury is relatively difficult to detect at the initial post-chilling RT stage, especially during the first 0-2 days in storage, due to insignificant manifestation of chilling induced symptoms.

[Expression of CFL gene during differentiation of floral and vegetative buds in cucumber cotyledonary nodes cultured in vitro]

CFL gene, a LFY homologue, was cloned from cucumber (Cucumis sativus L.). In this paper, in situ hybridization was performed to analyze the expression pattern of CFL gene at the stage of floral and vegetative buds differentiation in cucumber cotyledonary nodes cultured in vitro. The results showed that at the stage of floral differentiation, CFL gene was strongly expressed in primordia, floral organ primordia, and each whirl of floral organs at the early stage of their formation, but weakly expressed or not expressed in floral organs after their formation (Fig. 2). At the stage of vegetative bud differentiation, CFL gene was strongly expressed in meristem, leaf primordium and young leaves, and no apparent expression signal was detected in mature tissues (Fig. 3). The results suggest that the expression of CFL gene be necessary for the differentiation and formation of floral and vegetative primordias, and it plays an important role in floral and vegetative development in cucumber. The results also indicate that CFL gene involving in mitosis initiation, mitosis controlling, and transformation of vegetative meristem to floral meristem.

A systemic small RNA signaling system in plants

Systemic translocation of RNA exerts non-cell-autonomous control over plant development and defense. Long-distance delivery of mRNA has been proven, but transport of small interfering RNA and microRNA remains to be demonstrated. Analyses performed on phloem sap collected from a range of plants identified populations of small RNA species. The dynamic nature of this population was reflected in its response to growth conditions and viral infection. The authenticity of these phloem small RNA molecules was confirmed by bioinformatic analysis; potential targets for a set of phloem small RNA species were identified. Heterografting studies, using spontaneously silencing coat protein (CP) plant lines, also established that transgene-derived siRNA move in the long-distance phloem and initiate CP gene silencing in the scion. Biochemical analysis of pumpkin (Cucurbita maxima) phloem sap led to the characterization of C. maxima Phloem SMALL RNA BINDING PROTEIN1 (CmPSRP1), a unique component of the protein machinery probably involved in small RNA trafficking. Equivalently sized small RNA binding proteins were detected in phloem sap from cucumber (Cucumis sativus) and lupin (Lupinus albus). PSRP1 binds selectively to 25-nucleotide single-stranded RNA species. Microinjection studies provided direct evidence that PSRP1 could mediate the cell-to-cell trafficking of 25-nucleotide single-stranded, but not double-stranded, RNA molecules. The potential role played by PSRP1 in long-distance transmission of silencing signals is discussed with respect to the pathways and mechanisms used by plants to exert systemic control over developmental and physiological processes.

Breakage of resistance to Cucumber mosaic virus by co-infection with Zucchini yellow mosaic virus : enhancement of CMV accumulation independent of symptom expression

Resistance to the cucumovirus Cucumber mosaic virus (CMV) in cucumber cv. Delila was manifested as a very low level of accumulation of viral RNA and capsid protein, and an absence of CMV-induced symptoms. In addition, resistance was observed at the single cell level, with a reduction in accumulation of CMV RNAs, compared to accumulation in cells of the susceptible cucumber cv. Bet Alpha. Resistance to CMV in cv. Delila was broken by co-infection with the potyvirus Zucchini yellow mosaic virus (ZYMV). Resistance breakage in cv. Delila plants was manifested by an increase in the accumulation of (+) and (-) CMV RNA as well as CMV capsid protein, with no increase in the level of accumulation of ZYMV. Resistance breakage in the resistant cultivar by ZYMV also occurred at the single cell level. Thus, synergistic interactions known to occur between a potyvirus and a cucumovirus led to resistance breakage during a double infection. However, resistance breakage was not accompanied by an increase in disease symptoms beyond those induced by ZYMV itself. On co-inoculation with an asymptomatic variant of ZYMV-AG an enhancement of CMV infection occurred without disease manifestation. Consequently, intensification of viral RNA and capsid protein accumulation can occur without a corresponding increase in disease development, suggesting that different host genes regulate viral accumulation and disease development in the CMV-resistant cucumber plants.

[Carpel development in male flowers of cucumber (Cucumis sativus. L)]

Carpel development in cucumber male flowers was studied by morphological, histochemical and isoenzyme electrophoretic analyses. The results showed that: (1) cell number of the carpel in male flowers increased continuously during the development of male flowers, and the carpel in male flowers was abundant in RNA content; (2) the carpel in male flowers at latter developmental stage was differentiated, and a placenta-like structure was formed in the carpel of male flowers during anthesis, while the ovule did not appear as that of mature female flowers; (3) The POD and esterase isoenzyme electrophoretic profiles of carpel varied from the development of male flowers, which further indicated that the carpel in mature male flowers was no longer at the stage of primordium. It could be deduced from the results that carpel of cucumber male flowers develops continuously in a distinct pattern with that of female flowers during sex expression process.

Ethylene stimulates endoreduplication but inhibits cytokinesis in cucumber hypocotyl epidermis

The effects of ethylene on cell division are generally considered inhibitory. In this study, we demonstrate that transient ethylene exposure, while suppressing cytokinesis, stimulates DNA synthesis. We monitored DNA synthesis and cytokinesis in the epidermis of cucumber (Cucumis sativus) hypocotyls, an organ whose post-germination development involves strictly limited cell division. During exposure to ethylene, DNA synthesis, assessed by the incorporation of the thymidine homolog 5-bromo-2'-deoxyuridine, was detected in 20% of the epidermal cells, whereas DNA synthesis was nearly undetectable in normal air. Cytofluorometric analysis of nuclei in affected cells showed an up to 8-fold increase in DNA content. During this time, new cell plate formation was not detected. However, shortly after ethylene was removed, DNA content was rapidly restored to 2C (diploid) levels in all cells, and new cell plate formation dramatically increased. These results demonstrate that ethylene promotes DNA synthesis and its endoreduplication but inhibits cytokinesis, thereby maintaining some cells in G2 phase.

Mosaic (MSC) cucumbers regenerated from independent cell cultures possess different mitochondrial rearrangements

Passage of the highly inbred cucumber ( Cucumis sativus L.) line B through cell culture produces progenies with paternally transmitted, mosaic (MSC) phenotypes. Because the mitochondrial genome of cucumber shows paternal transmission, we evaluated for structural polymorphisms by hybridizing cosmids spanning the entire mitochondrial genome of Arabidopsis thaliana L. to DNA-gel blots of four independently generated MSC and four wild-type cucumbers. Polymorphisms were identified by cosmids carrying rrn18, nad5-exon2, rpl5, and the previously described JLV5 deletion. Polymorphisms revealed by rrn18 and nad5-exon2 were due to one rearrangement bringing together these two coding regions. The polymorphism revealed by rpl5 was unique to MSC16 and was due to rearrangement(s) placing the rpl5 region next to the forward junction of the JLV5 deletion. The rearrangement near rpl5 existed as a sublimon in wild-type inbred B, but was not detected in the cultivar Calypso. Although RNA-gel blots revealed reduced transcription of rpl5 in MSC16 relative to wild-type cucumber, Western analyses revealed no differences for the RPL5 protein and the genetic basis of the MSC16 phenotype remains enigmatic. We evaluated 17 MSC and wild-type lines regenerated from independent cell-culture experiments for these structural polymorphisms and identified eight different patterns, indicating that the passage of cucumber through cell culture may be a unique mechanism to induce or select for novel rearrangements affecting mitochondrial gene expression.

DNA damage in the early primordial anther is closely correlated with stamen arrest in the female flower of cucumber (Cucumis sativus L.)

To investigate the regulatory mechanisms of sex expression in cucumber, morphological observations and biochemical analyses were carried out on inappropriate stamen development of female flowers of cucumber. It was found that developmental arrest of the inappropriate stamen mainly occurs at the anther primordium. This arrest is closely correlated with DNA damage, as detected by TUNEL assay, and might result from anther-specific DNase activation. It was also found that the DNA damage does not lead to cell degeneration, although chromatin condensation is observed in the anther primordia.

Diffusion of an organic cation into root cell walls

Uptake of a cationic dye (methylene blue) by isolated root cell walls, roots of whole transpiring seedlings, and excised roots was investigated using 7-day-old seedlings of cucumber, maize, and wheat. The number of ionogenic groups per 1 g dry and wet weight of the root cell walls, their swelling capacity (K(cw)), time-dependence of methylene blue (M(cw)) ion exchange capacity, and diffusion coefficients of the cation diffusion in the polymer matrix of the cell walls (D(cw)) were determined. The M(cw) value depended on pH (or carboxyl group dissociation); it changed in accordance with the number of carboxyl groups per 1 g cell wall dry weight. This parameter decreased in the order: cucumber > wheat > maize. For description of experimental kinetic curves and calculation of cation diffusion coefficients, the equation for ion diffusion into a cylinder of infinite length was used. The chosen model adequately described cation diffusion in cell walls and roots. Diffusion coefficient values for cucumber, wheat, and maize were 3.1*10(-8), 1.3*10(-8), and 8.4*10(-8) cm(2)/sec, respectively. There was a statistically significant linear dependence between K(cw) and D(cw) values, which characterize the same property of the polymer matrix, rigidity of its polymer structure or the degree of cross-linkage or permeability. This also confirms the right choice of the model selected for calculation of methylene blue diffusion coefficients, because K(cw) and D(cw) values were obtained in independent experiments. The coefficients determined for methylene blue diffusion in transpiring seedling roots (D(ts)) and excised roots (D(er)) depended on the plant species. The rate of methylene blue diffusion into the excised roots was either 1.5-fold lower (cucumber) or 3-4-times lower (maize, wheat) than in cell walls. The values of diffusion coefficients in roots of whole seedlings were comparable which those for the cell walls. On the basis of the experimental data and results of calculations, it is concluded that the mechanism of methylene blue uptake by plant roots involves ion exchange reactions between the organic cation and cell wall carboxyl groups, and the uptake rate is determined by the cation diffusion in the polymer matrix of the cell walls.

Nitrate transport across the tonoplast of Cucumis sativus L. root cells

Nitrate transport across the tonoplast has been studied using vacuole membranes isolated from cucumber roots grown in nitrate. The addition of NO3- ions into the tonoplast with ATP-generated transmembrane proton gradient caused the dissipation of delta pH, indicating the NO3(-)-induced proton efflux from vesicles. NO3(-)-dependent H+ efflux was almost insensitive to the transmembrane electrical potential difference, suggesting the presence of an electroneutral NO3-/H+ antiporter in the tonoplast. Apart from saturation kinetics, with respect to nitrate ions, NO3(-)-linked H+ efflux from the tonoplast of cucumber roots showed other characteristics expected of substrate-specific transporters. Experiments employing protein modifying reagents (NEM, pCMBS, PGO and SITS) indicated that a crucial role in the activity of tonoplast nitrate/proton antiporter is played by lysine residues (strong inhibition of NO3-/H+ antiport by SITS). None of the ion-channel inhibitors (NIF, ZnSO4 and TEA-Cl) used in the experiments had a direct effect on the nitrate transport into tonoplast membranes. On the other hand, every protein reagent, as well as NIF and ZnSO4, significantly affected the ATP-dependent proton transport in vesicles. Only TEA-Cl, the potassium channel blocker, had no effect on the vacuolar proton pumping activity.

[Studies on calcium sensitive period during floral differentiation of cucumber cotyledonary node cultures in vitro]

Cotyledonary nodes of cucumber cultured on calcium-free medium for 0, 1, 2, 3, 4, 5, 6d respectively, were transferred to medium with 6.0 mmol/L CaCl2 for 24h, then returned to calcium-free medium. Cotyledonary nodes cultured on calcium-free or 6.0 mmol/L CaCl2 medium for all time, were taken as controls. Results showed that cotyledonary nodes were transferred to 6.0 mmol/L CaCl2 medium for 24h during 0-3d after the beginning of culture, percentage of floral bud formation at cotyledonary nodes was increased significantly. Transferring cotyledonary nodes on the 3d day after the beginning of culture was achieved best effect, percentage of floral bud formation was up to 34.3%. We deduced that the calcium sensitive period during floral differentiation of cucumber cotyleddonary node cultured in vitro may be 0-4d after the beginning of culture.

Determination of element distribution between the symplasm and apoplasm of cucumber plant parts by total reflection X-ray fluorescence spectrometry

The distribution of Cd, Ni, Pb and Fe between the symplasm (cytoplasm) and apoplasm (cell wall) of cucumber roots and leaves was determined by total reflection X-ray fluorescence spectrometry following a special sample preparation procedure. The plants were grown in modified Hoagland nutrient solution containing Fe in chemical form of Fe(III)-citrate or Fe(III)-EDTA, as well as the heavy metal contaminants, each in concentration of 10 microM. In the roots the larger part of Pb was found in the apoplasm, while Ni and Cd were mostly in the symplasm. In the leaves however, about 50-60% of the Pb content and practically the total amount of Cd were detected in the symplasm. About 30-40% of the translocated Ni remained in the apoplasm of the leaves. The Cd-, Ni- and Pb-treatments resulted in higher total concentration of Fe in the roots, however, the relative amount of Fe in the symplasm decreased in all cases. In the leaves of the control plants the larger part (60-80%) of Fe occurs in the symplasm. Due to the heavy metal effects, the relative amount of Fe in the symplasm decreased except in the Pb-contaminated plants, where in the presence of Fe(III)-EDTA, the Pb treatment resulted in a moderate increment of Fe concentration in the symplasm.

Extracellular freezing in leaves of freezing-sensitive species

Low-temperature scanning-electron microscopy was used to study the freezing of leaves of five species that have no resistance to freezing: bean (Phaseolus vulgaris L.), tobacco (Nicotiana tabacum L.), tomato (Lycopersicon esculentum L.), cucumber (Cucumis sativus L.), and corn (Zea mays L.). In the leaves of the four dicotyledonous species, ice was extracellular and the cells of all tissues were collapsed. In contrast, in maize leaves ice was extracellular in the mesophyll, and these cells were collapsed, but the epidermal and bundle-sheath cells apparently retained their original shapes and volume. It is concluded that the leaves of the freezing-sensitive dicotyledonous species tested were killed by cellular dehydration induced by extracellular freezing, and not by intracellular freezing. Freezing injury in maize leaves apparently resulted from a combination of freezing-induced cellular dehydration of some cells and intracellular ice formation in epidermal and bundle-sheath cells.

Effect of Mentha x piperita essential oil and monoterpenes on cucumber root membrane potential

Peppermint (Mentha piperita L.) essential oil and its main components were assessed for their ability to interfere with plant plasma membrane potentials. Tests were conducted on root segments isolated from etiolated seedlings of cucumber (Cucumis sativus L.). Increasing the concentration of peppermint essential oil from 5 to 50 ppm caused a decrease in membrane potential (Vm) hyperpolarization of 10-3 mV, whereas concentrations from 100 up to 900 ppm caused an increasing depolarization of Vm (from 5 to 110 mV). When tested at 300 ppm, (+)-menthyl acetate, (-)-limonene and 1,8-cineole did not exert any significant effect on V(m), whereas (+)-menthofuran (73 mV), (+)-pulegone (85 mV), (+)-neomenthol (96 mV), (-)-menthol (105 mV) and (-)-menthone (111 mV) showed increased ability to depolarize V(m). A plot of log of octanol-water partition coefficient (K(ow)) against their depolarizing effect showed a significant negative correlation, suggesting that among all monoterpenoids increased membrane depolarization depends on lower K(ow). However, among monoterpene ketones, alcohols and furans, increased membrane depolarization is associated with a decline in water solubility. The possible effect of monoterpenoids on membrane ion fluxes is also discussed, since changes in the bioelectric potential of cells imply changes in the flux of ions across the plasma membrane