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At least 217 records · Page 12Linked to original sources
PubMed1997

Single cell gel electrophoresis on peripheral blood leukocytes of patients with oral squamous cell carcinoma.

The single cell gel electrophoresis (SCGE) assay, also known as the comet assay, is a cytogenetic technique for measuring and analyzing DNA single stranded breaks (SSB) and/or alkali labile sites within individual cells. Peripheral blood leukocytes of 22 oral squamous cell carcinoma (OSCC) patients were subjected to SCGE and the DNA damage levels (SSB) were quantified with respect to clinical staging and histopathologic grading. Highly statistically significant differences in DNA damage levels were found between normal subjects and patients with OSCC of the same age group. DNA damage levels were altered in all clinical stages and histopathological grades of oral squamous cell carcinoma. The differences were generally significant between all the clinical stages of OSCC, while in histopathologic grading the results were significant only between grades I and III. The results support the concept of a systemic host response in malignancy.

Adult↗
PubMed1983

Protective effects of differentiation inducers on natural killer sensitivity of K 562 cells: Analysis at a single-cell level.

K 562 cells induced to differentiate by sodium butyrate (SB) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) were studied for their capacities to be bound and killed by large granular lymphocytes (LGL) in a single-cell cytotoxicity assay in agarose. After SB treatment, K 562 cells were less efficient in binding to LGL, whereas the frequency of killer cells among bound LGL was unaffected. When TPA was used to induce K 562 differentiation, the binding of LGL to their target and the lytic efficiency of the bound LGL were both diminished when compared to control K 562 cells. It has been demonstrated that the expression of structures involved in the binding of natural killer (NK) effectors to their targets could be correlated with the target-differentiation stage. It is shown that phorbol-ester treatment can also affect NK target structures involved in the killing step.

Animals↗
PubMed1989

Autologous and allogenic natural cell mediated cytotoxicity at the single cell level: divergent effects of interferons and interleukin 2 on binding and lysis.

In order to evaluate their divergent effects on binding and lysis of the NCMC, rH IFN-alpha and rH IL-2 were used for the in vitro-preincubation of normal donors' PBL, which were then tested as effector cells against K562 and the long-term cultured melanoma cell line RIMA in the SCCA. Both lymphokines significantly augmented the cytolysis of K562 without relevant influence on the conjugate formation. However, against RIMA IFN-alpha additionally amplified the binding affinity. This in keeping with the other authors' opinion that IFNs have target-specific effects at the single cell level, with the principal activation of already conjugated pre-killer cells against all the target cell lines tested. We performed a therapy-follow-up of the i.p. administration of rH IFN-gamma to patients with ovarian carcinomas in vivo. With the SCCA we detected a significant correlation of the duration of therapy with the autologous cytotoxicity in the ascitic compartment. In one case the increase of this parameter was even exponential. However, the countercurrent trend of the conjugate formation delayed and reduced the activation of the autologous total killer activity. This relative stagnation resulted in the inadequate clinical response of two patients. Moreover, we observed a discrepancy in the development of the autologous and allogeneic SCCA-parameters suggesting strong effects of the peritumorally administered IFN directly on the effusion tumor cells.

Adenocarcinoma↗
PubMed1997

DNA damage in breast epithelial cells: detection by the single-cell gel (comet) assay and induction by human mammary lipid extracts.

The presence of DNA damage in primary cultures of human mammary epithelial cells (HMECs), and the ability of extracts of human mammary lipid to cause such damage, has been investigated. Lipid extracts, prepared by a solid-phase procedure, and HMECs were obtained from breast tissue removed from healthy women (ages 18-50 years) who were resident in the UK and undergoing elective reduction mammoplasties. DNA single strand breaks (SSBs) were detected using the single-cell gel assay (comet assay) with alkaline electrophoresis (pH 12.3) and quantified by measuring comet tail length (CTL) (microm). Untreated HMECs and HMECs incubated (30 min, 37 degrees C) with a mammary lipid extract, with or without DNA-repair inhibitors hydroxyurea (HU) and cytosine arabinoside (ara-C), were examined. Ionizing radiation was used as a positive control. An active lipid extract gave a linear dose-response over the range 2.0-12.2 g equivalents. When MCL-5 cells, a line of metabolically-competent human lymphoblastoid cells, were used to compare the DNA-damaging properties of lipid extracts from six different donors, significant interindividual variations (median CTLs were 15.0, 53.5, 32.5, <4.0, <4.0 and 77.5 microm respectively) were observed. In eight subjects, the donors' HMECs were examined both before and after treatment with extracts of that donor's own lipid. Pre-existing DNA damage was detected in untreated HMECs from some donors (median CTLs 22.0-37.5 microm) that was not present in others (median CTLs 4.0-11.5 microm), and increases in CTL could be induced by incubation with the matching lipid extract (8 g equivalent) in more than half (five out of eight) the subjects examined (median CTL up to 111.0 microm). There was a tendency for the most active lipid extracts to be those obtained from donors whose HMECs also contained the most pre-existing DNA SSBs. The results of this pilot study may prove to be significant in relation to the initiation of breast cancer.

Adult↗
PubMed2003

Monitoring liposome-mediated delivery and fate of an antisense drug in cell extracts and in single cells by capillary electrophoresis with laser-induced fluorescence.

Capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection was used for evaluation of the effectiveness of delivery and fate of a model 25-mer DNA-based phosphorothiate antisense drug in cells. The antisense molecule was delivered to the cells through a simple incubation and by using a cationic liposome (Cytofectin GS 3815). The cationic lipid interacted with the negatively charged antisense to form a more positively charged complex. It was observed that uptake of the liposome-antisense complex by the cell was dependent on concentration of lipid, duration of transfection, and the cell type. The antisense drug interacted with intracellular components such as proteins and additional steps were needed to quantify the free antisense. Proteinase-K was able to release antisense from proteins. However, the addition of sodium dodecyl sulfate (SDS) to the sample or running buffer was more effective than Proteinase-K to release both naked and liposome-bound antisense from the cellular materials. Analysis of single HeLa cells for uptake of the unbound and liposome-complexed antisense revealed averages of 8.9x10(-19) moles and 4.9x10(-18) moles, respectively. The amount of uptake, however, varied greatly among individual cells and depended on the delivery method. With liposome-mediated delivery, the relative standard deviation (RSD) for the amount of antisense in individual cells was 130%, while the variation was much smaller (RSD = 45%) when the cells were incubated with the unbound antisense. These uptake variations agreed with those obtained from flow cytometry analysis.

Cell Extracts↗
PubMed1979

Mechanism of cell-mediated cytotoxicity at the single cell level. II. Evidence for first-order kinetics of T cell-mediated cytolysis and for heterogeneity of lytic rate.

The kinetics and rate of T cell-mediated cytolysis was assessed by measuring the times required for lysis of isolated target cells by single cytotoxic lymphocytes. Single target cell lysis was determined microscopically by observing trypan blue uptake as a function of time of incubation of effector-target conjugates in agarose. Lysis of EL-4 target cells by alloimmune peritoneal exudate lymphocytes was initiated without a lag and was essentially complete at 2 hr. Both zero-order and first-order kinetics equations were analyzed for fit to the 0 to 2 hr lysis values. Statistically, the zero-order kinetic function could be rejected (p greater than 0.05), but the first-order kinetics function (p less than 0.01) could not. This strong evidence for first-order kinetics of T cell-mediated cytolysis implies that within each CTL-target cell population, cytolysis occurs exponentially as a random decay process and that one event in the entire process of cytolysis is rate limiting. The first-order equation was then applied to measurements of the rate of cytolysis in many different individual effector-target cell combinations. Significant differences in the lytic rate were apparent when either the effector or target cell were varied, with the rate constants spanning a 5-fold range. The heterogeneity of lytic rates is consistent with the hypothesis that lytic efficiency is a function of both the effector and target cells used.

Animals↗
PubMed2026

scSurv: a deep generative model for single-cell survival analysis.

MOTIVATION: Single-cell omics analysis has unveiled the heterogeneity of various cell types within tumors. However, no methodology currently reveals how this heterogeneity influences cancer patient survival at single-cell resolution. Here, we introduce scSurv, combining a Cox proportional hazards model with a deep generative model of single-cell transcriptome, to estimate individual cellular contributions to clinical outcomes. RESULTS: The accuracy of scSurv was validated using both simulated and real datasets. This method identifies cells associated with favorable or adverse prognoses and extracts genes correlated with their contribution levels. In melanoma, scSurv reproduces known prognostic macrophage classifications and facilitates hazard mapping through spatial transcriptomics in renal cell carcinoma. We also identified genes consistently associated with prognosis across multiple cancers and demonstrated the applicability of this method to infectious diseases. scSurv is a novel framework for quantifying the heterogeneity of individual cellular effects on clinical outcomes. AVAILABILITY: The implementation of scSurv is available on GitHub (https://github.com/3254c/scSurv) and Zenodo (https://doi.org/10.5281/zenodo.17793054).

Humans↗
PubMed2004

Inward rectifying currents stabilize the membrane potential in dendrites of mouse amacrine cells: patch-clamp recordings and single-cell RT-PCR.

PURPOSE: To explore the possible existence of inward rectifying currents in the distal dendrites of amacrine cells. METHODS: Patch-clamp recordings were made from amacrine cells in a new horizontal slice preparation of mouse retina. Single-cell RT-PCR studies were performed after the patch-clamp recordings. RESULTS: In contrast to results from vertical slices or dissociated cells, all amacrine cells tested demonstrated inward rectifying currents, IIR. Within the limits of our sample, this current did not depend on the morphological and physiological type of the amacrine cell. Amacrine cells from which the dendrites had been removed did not possess detectable amounts of IIR. Pharmacological experiments with ZD7288 (100 microM) and single-cell RT-PCR from recorded cells revealed that IIR includes an h-current (I(H)) carried by hyperpolarization-activated cyclic nucleotide gated channels (HCN), HCN1 and/or HCN2 subtypes. In the presence of extracellular Cs+ (5 mM), which greatly suppressed IIR, the resting membrane conductance was reduced. IIR suppressed the generation of oscillatory potentials. Intracellular cAMP (8-cpt-cAMP, 1 mM) activated IIR. CONCLUSIONS: IIR appears to occur within dendrites of many amacrine cells, where it tends to stabilize the resting membrane potential. HCN1 and/or HCN2 channels contribute to IIR in amacrine cells. Dendritic IIR would be expected to contribute to functional independence of the distal dendrites of amacrine cells that express it.

Amacrine Cells↗
PubMed2026

Identification of Drug-resistant Cell Subpopulations in Colorectal Cancer Through Single-cell Analysis and Exploration of Potential Therapeutic Strategies.

INTRODUCTION: The therapeutic efficacy of Colorectal Cancer (CRC) is often compromised by resistance to the standard chemotherapy agent oxaliplatin. METHODS: This study obtained single-cell RNA sequencing (scRNA-seq) data from the Gene Expression Omnibus (GEO) database. Differentially Expressed Genes (DEGs) between resistant and sensitive epithelial subpopulations were identified, followed by enrichment analysis. Pseudotemporal trajectory and cell-cell communication were analyzed using Monocle2 and CellChat, respectively. The candidate drug was predicted by Connectivity Map (cMAP) analysis. External validation included assessment of the EpC2 signature in an oxaliplatin-resistant cell line dataset (GSE76092), survival analysis using The Cancer Genome Atlas (TCGA) cohorts, and re-analysis of the GSE179784 dataset to assess the reproducibility of EpC2-like subpopulations and their DNA Damage Repair (DDR) scores. RESULTS: Cell subpopulations were divided into 10 clusters. Among them, epithelial cells comprised 5 subpopulations, with EPC2 identified as a potential oxaliplatin-resistant subset. DEGs were enriched in the TNF and IL-17 pathways. External validation confirmed the enrichment of EpC2 in resistant cell lines and its association with poor survival. Pseudotemporal trajectory revealed that epithelial cells underwent state transitions, forming two distinct branches. The resistant group exhibited enrichment in RNA splicing and NF-&#x3ba;B pathways. Cell-cell communication analysis revealed interactions involving MDK- NCL and PPIA-BSG. Dasatinib was predicted as a candidate drug. DISCUSSION: We identified an oxaliplatin-resistant subpopulation of Epithelial Cells (EpC2) in CRC, elucidated its multi-layered resistance mechanisms, and integrated multi- omics and cMAP database analyses to predict a potential intervention drug. CONCLUSION: This study provided potential therapeutic possibilities for oxaliplatin resistance, contributing to CRC treatment.

Humans↗
PubMed1995

Hodgkin and Reed-Sternberg cells do not carry T-cell receptor gamma gene rearrangements: evidence from single-cell polymerase chain reaction examination.

Hodgkin and Reed-Sternberg (H&RS) cells are generally accepted to be the neoplastic cells of Hodgkin's disease (HD), even though they represent only a minority of the cellular infiltrate in affected tissues. Recent immunologic studies and Southern blot analyses of DNA extracted from whole lymph node tissue favored, but did not convincingly prove a lymphoid origin of H&RS cells. To detect rearrangements of the T-cell receptor gamma chain (TCR gamma) genes at the single-cell level as an indication of early T-cell lymphoid differentiation, we isolated H&RS cells by micromanipulation from cytospin preparations of fresh biopsy material. TCR gamma chain rearrangement was detected by polymerase chain reaction using four "forward primers" that were constructed corresponding to all four V families and two "reverse primers" corresponding to consensus sequences of J segments. Rearrangements of all V families in combination with the different J segments were detected in human peripheral blood and tonsillar T cells. Although rearrangements of TCR gamma chain genes were shown in single cells of 10 of 10 T-cell leukemias, no rearrangement of these genes was found in single H&RS cells from 13 consecutive patients with HD. Our results indicate that H&RS cells from the vast majority of cases are not derived from T cells. This finding may have implications for the pathogenesis of HD and the development of more effective treatment regimens.

Base Sequence↗
PubMed2004

A three-dimensional flow control concept for single-cell experiments on a microchip. 2. Fluorescein diacetate metabolism and calcium mobilization in a single yeast cell as stimulated by glucose and pH changes.

Using a three-dimensional flow control concept to manipulate and retain a single yeast cell in a microchip, we were able to study the kinetics of intracellular metabolism and calcium mobilization at the single-cell level, as stimulated by glucose and pH changes. As a model study, the fluorogenic substrate fluorescein diacetate (FDA) was chosen to study how the intracellular carboxylesterase metabolize it. A single yeast cell was first cultured in the microchip. Thereafter, under a constant concentration of FDA, influx of FDA into the yeast cell occurred and FDA was hydrolyzed or metabolized. It was found that changes in both pH and glucose stimulated the FDA metabolism in a yeast cell, and the stimuli can elicit multiple responses from the cell. Since it was carried out within the microchip, the whole experiment on one single yeast cell could last for as long as 10 h. The dormant cell, budding cell, and pretreated budding cell (in low-pH buffer) of yeast resulted in different responses. Experimental data provided details on the FDA metabolism at the single-cell level and revealed strong correlations between FDA metabolism and calcium mobilization. Furthermore, efflux of the FDA metabolite fluorescein could start spontaneously if there was glucose in the medium. The experiments on a single cell were of the "human cell conservation" style because the cell responded to the reagent changes implemented by the human researcher. A mathematical model was also developed to study the influx-hydrolysis-efflux processes of the FDA metabolism using single-cell fluorescent data. These long overdue single-cell experiments are now rendered possible using the three-dimensional flow control in the microchip.

Calcium↗
PubMed2005

Single-cell microinjection of cytochrome c can result in gap junction-mediated apoptotic cell death of bystander cells in head and neck cancer.

BACKGROUND: Gap junction intercellular channels are required for metabolic cooperation between cells and regulate normal tissue homeostasis by means of the transfer of small molecules between contacting cells. Not surprisingly, the gap junction phenotype is frequently lost during carcinogenesis in human tissues (including those of the upper aerodigestive tract), freeing individual cancer cells from the growth control signals of normal surrounding tissues and less aggressive adjacent cancer cells. We hypothesized that gap junctional intercellular communication (GJIC) could mediate a bystander effect (apoptotic cell death) in squamous cell carcinoma of the head and neck (SCCHN) cells adjacent to individually targeted SCCHN cells. METHODS: Single-cell microinjection of cytochrome c was used to induce apoptosis in target SCCHN cells with endogenous GJIC activity and in an SCCHN cell line with exogenously introduced GJIC activity. Apoptosis was followed in target and surrounding bystander cells through light and time course microscopic characterization. All of the preceding experiments were carried out in the absence and presence of 18-beta-glycerretinic acid, a pharmacologic inhibitor of GJIC. RESULTS: When cytochrome c was introduced into SCCHN cells with endogenous GJIC activity through single-cell microinjection, bystander effects (apoptosis of nontarget cells) were observed. When GJIC activity was blocked with the specific pharmacologic inhibitor of gap junctions, 18-beta-glycerretinic acid, a bystander effect was never seen in GJIC active SCCHN cell lines. CONCLUSIONS: Gap junction intercellular channels can mediate a bystander effect in SCCHN. Inconsistencies in our data will be discussed in the context of recent advances in this field, as well as our future research directions.

Apoptosis↗
PubMed1992

Expression of cell growth and bone specific genes at single cell resolution during development of bone tissue-like organization in primary osteoblast cultures.

Primary cultures of calvarial derived normal diploid osteoblasts undergo a developmental expression of genes reflecting growth, extracellular matrix maturation, and mineralization during development of multilayered nodules having a bone tissue-like organization. Scanning electron microscopy of the developing cultures indicates the transition from the uniform distribution of cuboidal osteoblasts to multilayered nodules of smaller cells with a pronounced orientation of perinodular cells towards the apex of the nodule. Ultrastructural analysis of the nodule by transmission electron microscopy indicates that the deposition of mineral is confined to the extracellular matrix where cells appear more osteocytic. The cell body contains rough endoplasmic reticulum and golgi, while these intracellular organelles are not present in the developing cellular processes. To understand the regulation of temporally expressed genes requires an understanding of which genes are selectively expressed on a single cell basis as the bone tissue-like organization develops. In situ hybridization analysis using 35S labelled histone gene probes, together with 3H-thymidine labelling and autoradiography, indicate that greater than 98% of the pre-confluent osteoblasts are proliferating. By two weeks, both the foci of multilayered cells and internodular cell regions have down-regulated cell growth associated genes. Post-proliferatively, but not earlier, initial expression of both osteocalcin and osteopontin are restricted to the multilayered nodules where all cells exhibit expression. While total mRNA levels for osteopontin and osteocalcin are coordinately upregulated with an increase in mineral deposition, in situ hybridization has revealed that expression of osteocalcin and osteopontin occurs predominantly in cells associated with the developing nodules. In contrast, proliferating rat osteosarcoma cells (ROS 17/2.8) concomitantly express histone H4, along with osteopontin and osteocalcin. These in situ analyses of gene expression during osteoblast growth and differentiation at the single cell level establish that a population of proliferating calvarial-derived cells subsequently expresses osteopontin and osteocalcin in cells developing into multilayered nodules with a tissue-like organization.

Animals↗
PubMed2025

Predicting and comparing transcription start sites in single cell populations.

The advent of 5' single-cell RNA sequencing (scRNA-seq) technologies offers unique opportunities to identify and analyze transcription start sites (TSSs) at a single-cell resolution. These technologies have the potential to uncover the complexities of transcription initiation and alternative TSS usage across different cell types and conditions. Despite the emergence of computational methods designed to analyze 5' RNA sequencing data, current methods often lack comparative evaluations in single-cell contexts and are predominantly tailored for paired-end data, neglecting the potential of single-end data. This study introduces scTSS, a computational pipeline developed to bridge this gap by accommodating both paired-end and single-end 5' scRNA-seq data. scTSS enables joint analysis of multiple single-cell samples, starting with TSS cluster prediction and quantification, followed by differential TSS usage analysis. It employs a Binomial generalized linear mixed model to accurately and efficiently detect differential TSS usage. We demonstrate the utility of scTSS through its application in analyzing transcriptional initiation from single-cell data of two distinct diseases. The results illustrate scTSS's ability to discern alternative TSS usage between different cell types or biological conditions and to identify cell subpopulations characterized by unique TSS-level expression profiles.

Transcription Initiation Site↗
PubMed2004

A three-dimensional flow control concept for single-cell experiments on a microchip. 1. Cell selection, cell retention, cell culture, cell balancing, and cell scanning.

An ideal microchip for single-cell experiments should be able to allow us to culture cells, to select any desired single cell from a group, to retain the cell for convenient cellular signal detection, and to deliver any buffer or reagent directly to the cell at any time during continual detection and observation. Most importantly, any negative impact on the live cell should be minimized. To accomplish all these functions, we developed a three-dimensional liquid flow control concept and employed special liquid flow fields to manipulate and retain a single yeast cell freely in the chip. A zero-speed point was controlled to retain the cell for three-dimensional cell balancing and cell scanning. A dispersive flow delivered reagents at a high speed to very near the cell and provided them to the cell at a low speed. No force stronger than its gravitational force was exerted on the cell, which could be balanced on different positions on an arc-sloping wall, thus minimizing any negative impact on the cell due to strong liquid flows. Specifically, we demonstrate on-chip single-cell culture, cell wall removal, and reagent delivery. Subsequently, single-cell fluorescence detection was performed, and noise filtering and background correction were applied for data processing.

Cell Culture Techniques↗
PubMed2025

SLB-msSIM: A Spectral Library-Based Multiplex Segmented SIM Platform for Single-Cell Proteomic Analysis.

Mass spectrometry (MS)-based single-cell proteomics, while highly challenging, offers unique potential for a wide range of applications to interrogate cellular heterogeneity, trajectories, and phenotypes at a functional level. We report here the development of the spectral library-based multiplex segmented selected ion monitoring (SLB-msSIM) method, a conceptually unique approach with significantly enhanced sensitivity and robustness for single-cell analysis. The single-cell MS data is acquired by a multiplex segmented selected ion monitoring (msSIM) technique, which sequentially applies multiple isolation cycles with the quadrupole using a wide isolation window in each cycle to accumulate and store precursor ions in the C-trap for a single scan in the Orbitrap. Proteomic identification is achieved through spectral matching using a well-defined spectral library. We applied the SLB-msSIM method to interrogate cellular heterogeneity in various pancreatic cancer cell lines, revealing common and distinct functional traits among PANC-1, MIA-PaCa2, AsPc-1, HPAF, and normal HPDE cells. Furthermore, for the first time, our novel data revealed the diverse cell trajectories of individual PANC-1 cells during the induction and reversal of epithelial-mesenchymal transition (EMT). Collectively, our results demonstrate that SLB-msSIM is a highly sensitive and robust platform, applicable to a wide range of instruments for single-cell proteomic studies. SUMMARY: We present the SLB-msSIM method, a conceptually unique approach in mass spectrometry-based single-cell proteomics that significantly enhances sensitivity and robustness. This innovative platform enables detailed analysis of the proteome landscape, capturing cellular heterogeneity, trajectories, and phenotypes at a single-cell resolution. Utilizing the SLB-msSIM technique, we identified both common and distinct functional traits among various pancreatic cancer cell lines and normal cells. Moreover, our study unveiled new insights into the diverse cell trajectories of individual cancer cells during the induction and reversal of epithelial-mesenchymal transition (EMT). In summary, the SLB-msSIM method offers a highly sensitive and robust platform for single-cell proteomic studies, with broad applicability across different instruments.

Single-Cell Analysis↗
PubMed1985

Single-cell analysis of the relationship among transferrin receptors, proliferation, and cell cycle phase in K562 cells.

Multiparameter single-cell analysis by flow cytometry was used to distinguish between size-related changes in K562 cell transferrin receptor (TfR) expression and changes in membrane receptor density throughout the cell cycle and over time in culture. Light-scatter pulse-width time-of-flight, a direct and readily calibrated measure of cell diameter, was used to calculate receptor density as the average number of receptors per unit cell surface area. Cell surface TfRs were unimodally distributed over the cell population and were present throughout the cell cycle. The number of receptors increased as cells progressed through the cell cycle, but cell cycle phase was also correlated with cell volume. However, when size heterogeneity was factored out by reanalysis of listmode data, there was a clear cell-cycle effect: among cells of the same size, both the number of receptors per cell and the receptor density increased from G1 to S to G2/M. TfR expression was also followed over time in culture after dilution into fresh medium. A decrease in growth rate after four days was preceded by one to two days by a decrease in both number of TfRs per cell and mean receptor density, indicating that decreased TfR expression represented true "down-regulation" and not just decreased cell size or an increase in the proportion of smaller G1 cells. This type of analysis is generally applicable for resolving the effects of cell size heterogeneity and cell cycle on membrane protein distribution and for other studies of ligand-receptor interaction.

Cell Cycle↗
PubMed2006

Sugar concentrations along and across the Ricinus communis L. hypocotyl measured by single cell sampling analysis.

Single cell sap sampling and analysis were used to measure the longitudinal and radial distribution of sucrose, glucose and fructose in the apical cell division zone and in the basal, elongated zone of the Ricinus hypocotyl. Sucrose and hexose increased in concentration from the apex to the base of the seedling axis. In the cell division zone low hexose and sucrose concentrations prevailed in cortex and pith, with a slightly higher hexose concentration in pith cells. The sucrose concentrations in sieve tubes and in phloem were much higher than in the cortex and pith cells. In the basal zone of the hypocotyl high levels of sucrose in phloem, cortex and pith were found, therefore radial, diffusional sucrose flow away from the phloem was considered unlikely. It is proposed that radial flow of growth-water to the hypocotyl periphery together with the down-regulation of a sucrose transporter at the phloem leads to a preferential sucrose flow to the expanding cortex. The pith cells, which do not experience flow of growth-water, are probably insufficiently supplied with sucrose from the phloem resulting eventually in cell death as the plant grows. Shortage of sucrose supply, experimentally achieved by removal of the endosperm, led to sucrose hydrolysis in the pith. The sucrose levels in the other tissues decreased less. It appears that the hydrolysis to hexose was initiated to maintain the osmotic value in the pith cell sap. It is speculated that high hexose levels in the cells are indicative of insufficient sucrose supply via the phloem and that the pith cells are confronted with that situation during early seedling development.

Carbohydrate Metabolism↗