Reappraisal of nuclear DNA content of rodlet cells compared to several cell types from some freshwater teleosts, using two methods of microdensitometry

Nuclear DNA contents of rodlet cells from Catostomus commersoni, Semotilus atromaculatus and Cyprinus carpio were compared with nuclear DNA of erythrocytes and larger cells of the same species, using scanning microdensitometry and averaging microdensitometry. This study reappraises the work of Barber & Westermann (1983), which employed averaging microdensitometry only, and compared rodlet cell nuclear DNA only with erythrocyte DNA. In addition, this work considers sources of error in both methods of microdensitometry, and comments upon the use of microdensitometry of either method as a mechanism for making distinctions among the DNA contents of cells of different types. The results of the present work consistently indiate no significant differences within species between nuclear DNA content of rodlet cells and larger teleost cells, using either method of microdensitometry. Because of the lack of statistically significant difference in DNA content between nuclei of rodlet cells and those of known teleost cells, it has been concluded that the rodlet cell itself is probably of teleost origin. However, the method indicates nothing about the origin of the rodlets, which have also been shown to contain DNA, but are Feulgen-negative.     

New observations on the rodlet cell (Rhabdospora thelohani) in the white sucker Catostomus commersoni (Lacépède): LM and EM studies

Light and electron microscopic studies of the morphological features of immature and mature rodlet cells in Catostomus commersoni are presented emphasizing the cells' association with epithelial tissues. The peripheral fibrillar layer is lacking from the apex and from the base of the cell. A cytoplasmic extension from the base may be a feeding mechanism whereby the rodlet cell obtains nutrient at the expense of adjacent cells leaving intercellular spaces often containing myelin figures. RNAase digestion studies demonstrate the presence of RNA in the electron dense rodlet core.
The structure and histochemistry of the rodlets which do not appear to disintegrate upon expulsion from the cell are compared to the cytoplasmic inclusions of both normal fish cells and protozoan parasites. The possible association of the rodlet cell with various pathological conditions is briefly reviewed and the authors conclude that it is premature to disregard the possibility that this cell could be a parasite or infective agent.     

Trypanosoma danilewskyi: host specificity and host's effect on morphometrics

Carassius auratus, Barbus conhus, Danio malabaricus, Catostomus commersoni, Notropis cornutus, Etheostoma caeruleum, and Ictalurus nebulosus were susceptible to Trypanosoma danilewskyi by intraperitoneal inoculation. Trypanosomes isolated from all species of susceptible fishes were infective to goldfish. No trypanosomes were detected in inoculated Semotilus atromaculatus, Ambloplites rupestris, Lepomis gibbosus and Perca flavescens. Fifty specimens were measured from each of 3 C. auratus, 2 B. conhus, 2 C. auratus inoculated with an isolate from a C. commersoni, 2 C. commersoni, and 2 E. caeruleum, for statistical analyses. The distance of the kinetoplast from the posterior end, length of free flagellum, nuclear length, and area of nucleus were similar among samples from the same host but differed significantly among samples from different host species. After discriminate analysis, samples from goldfish clustered into a tight group while those from the other fishes formed a loose cluster along the first canonical axis. Using the jacknife method of correct classification, 93% of trypanosomes from C. auratus, 36% from C. commersoni, 61% from C. commersoni-C. auratus, 25% from B. conhus, and 40% from E. caeruleum, could be correctly assigned to host species. However, only 1% of trypanosomes from C. commersoni would be classified as coming from C. auratus, 4% for C. commersoni-C. auratus, 0% for B. conhus, and 7% for E. caeruleum.     

Infection by a black spot-causing species of Uvulifer and associated opercular alterations in fishes from a high-desert stream in Wyoming

Black spot is a common disease syndrome of freshwater fishes. This study provides information on the rank of density of the black spot agent and opercular bone alterations associated with at least one digenean, Uvulifer sp., infecting native and non-native catostomids and cyprinids of the Upper Colorado River Basin. We evaluated the density rank of pigmented metacercariae and associated alterations in the operculum of the bluehead sucker Catostomus discobolus, flannelmouth sucker C. latipinnis, white sucker C. commersoni, catostomid hybrids, roundtail chub Gila robusta, and creek chub Semotilus atromaculatus, sampled from Muddy Creek, Wyoming, USA in 2003 or 2004. All fish species contained individuals that exhibited gross signs of the black spot agent. Bluehead and flannelmouth suckers had 100% prevalence of infection. Although the other suckers and chubs contained encysted metacercariae in at least one individual, the presence of pigmented metacercariae was not apparent (i.e. based on gross observations) in many individuals. Catostomids had higher densities of metacercariae than cyprinids, as shown by frequency distributions of density ranks. Opercular holes (i.e. holes that completely penetrated the opercle and were in direct association with the pigment associated metacercariae) and pockets (depressions on the external surface of the opercle associated with metacercariae) were abundant among catostomids but rare among cyprinids.     

Cryptobia cataractae from the blood of Semotilus atromaculatus: structure and division in the fish

A cryptobiid was found in the blood of 2 of 9 Semotilus atromaculatus from a tributary of the Saugeen River in Ontario, Canada. Blood inoculation produced an infection in 2 uninfected S. atromaculatus but not in any Oncorhynchus mykiss, Catostomus commersoni, or Carassius auratus. The flagellate was identified as Cryptobia cataractae, based on host restriction. Cryptobia cataractae occurred as slender and broad forms (body width 3.0-8.7 microns). The length of the anterior flagellum was equal to body length, whereas that of the free recurrent flagellum was half body length. Cryptobia cataractae divided by equal binary fission that produced elongate, slender daughter cells.     

Observations on rodlet cells found in the vascular system and extravascular space of angelfish (Pterophyllum scalare scalare)

In the angelfish ( Pterophyllum scalare scalare ) numerous rodlet cells were found in the large post-orbital blood vessel caudal to the eye and in the surrounding extravascular space. Within the vessel the rodlet cells formed striking regular arrays, along the inner aspect of the wall. The rodlets within the cells were positive to PAS but negative to Sudan Black B, Masson's, and the Fuelgen stain. The capsule around the cells was negative for all these stains. These rodlet cells appeared to be traversing the vessel endothelium, and to be pushing the endothelium aside without damaging it. Some discharged their contents into the vessel, but we never observed the release of intact rodlets. The nuclei of rodlet cells in actual contact with the vessel were at the end of the cell more distant from the endothelial wall. Cell-to-cell adhesion structures or communications junctions between rodlet cells and the endothelium were not evident. A putative rodlet cell precursor in the extravascular space contained large electron-dense granules, and extended pseudopodia that contacted nearby rodlet cells. Based on their morphology, tissue distribution, and their behaviour, we conclude that the rodlet cell is an endogeneous teleost cell type, and possibly represents a form of matured granulocyte.     

Reduced transglutaminase-catalyzed cross-linking of exogenous amines to membrane proteins in sickle erythrocytes

In order to determine the capacity of sickle cells to undergo transglutaminase-catalyzed cross-linking of membrane proteins, human normal and sickle erythrocytes were incubated with [ring-2-14C]histamine in the presence of Ca2+ and ionophore A23187. The [14C]histamine incorporation into membrane components was observed in freshly prepared erythrocytes. Incorporation of radioactivity into spectrin and Band 3 membrane components was significantly (P less than 0.001) less in sickle erythrocytes than in normal cells. Transglutaminase deficiency was excluded by the finding of increased activity of this enzyme in sickle cells from patients with reticulocytosis. The incorporation of [3H]spermine into red cell membranes was also less in sickle erythrocytes than in normal cells under the same conditions of incubation used for [ring-2-14C]histamine. Sickle erythrocytes were more permeable to these amines than normal cells. It is proposed that the gamma-glutamyl sites of membrane proteins in sickle erythrocytes are less accessible for transglutaminase-catalyzed cross-linking to histamine and polyamines in vitro, perhaps due to prior in vivo activation of this enzyme by the increased calcium in sickle cells and/or shielding secondary to altered membrane organization.     

Microsatellite analysis of different ploidy offspring of artificial gynogenesis in Cyprinus carpio

Gynogenesis was induced by using UV-irradiated spermatozoa of blunt snout bream Megalobrama amblycephala to activate eggs of common carp Cyprinus carpio. The maternal genome was then duplicated by cold shock in 0 to 4° C cold water to retain the second polar body. Two kinds of fry, normal fry and abnormal tortuous fry, were hatched. Their DNA content was measured by flow cytometry. The normal fry were identified as diploid, representing the successful gynogenesis in C. carpio whereas the abnormal tortuous fry were haploid. Ten microsatellite loci were used to study the genetic diversity among C. carpio, diploid gynogenetic C. carpio and unduplicated haploid tortuous fry. The results indicated that the genetic homozygosity of gynogenetic C. carpio was significantly higher than that of C. carpio. The genetic homozygosity of the haploid C. carpio was intermediate between that of gynogenetic C. carpio and C. carpio. It might be easier for the allogenetic DNA fragments to be integrated into the haploid genome than into diploid gynogenetic genome.     

Somatic mosaicism for a newly identified splice-site mutation in a patient with adenosine deaminase-deficient immunodeficiency and spontaneous clinical recovery.

Absent or severely reduced adenosine deaminase (ADA) activity produces inherited immunodeficiency of varying severity, with defects of both cellular and humoral immunity. We report somatic mosaicism as the basis for a delayed presentation and unusual course of a currently healthy young adult receiving no therapy. He was diagnosed at age 2 1/2 years because of life-threatening pneumonia, recurrent infections, failure of normal growth, and lymphopenia, but he retained significant cellular immune function. A fibroblast cell line and a B cell line, established at diagnosis, lacked ADA activity and were heteroallelic for splice-donor-site mutation in IVS 1 (+1GT-->CT) and a missense mutation (Arg101Gln). All clones (17/17) isolated from the B cell mRNA carried the missense mutation, indicating that the allele with the splice-site mutation produced unstable mRNA. In striking contrast, a B cell line established at age 16 years expressed 50% of normal ADA; 50% of ADA mRNA had normal sequence, and 50% had the missense mutation. Genomic DNA contained the missense mutation but not the splice-site mutation. All three cell lines were identical for multiple polymorphic markers and the presence of a Y chromosome. In vivo somatic mosaicism was demonstrated in genomic DNA from peripheral blood cells obtained at 16 years of age, in that less than half the DNA carried the splice-site mutation (P < .002, vs. original B cell line). Consistent with mosaicism, erythrocyte content of the toxic metabolite deoxyATP was only minimally elevated. Somatic mosaicism could have arisen either by somatic mutation or by reversion at the site of mutation. Selection in vivo for ADA normal hematopoietic cells may have played a role in the return to normal health, in the absence of therapy.     

On the kinetics of erythroid cell differentiation in fetal mice. II. DNA and hemoglobin measurements of individual erythroblasts during gestation

Microspectrophotometric absorption measurements were used to determine the hemoglobin content of erythroid cells derived from the yolk sac during gestation of fetal C3H mice, from day 9 to day 15. Using the DNA content as a marker for the mitotic state between 2C and 4C phase, five successive cell generations and their mean hemoglobin contents were distinguished: 12 pg (pg, picogram = 10^?12 gm). 22.2 pg, 37 pg, 50 pg and 56 pg. In the final state, nucleated erythrocytes contained 98 ± 22 pg hemoglobin. Erythroid cells derived from the liver were measured on day 15 of fetal gestation. The hemoglobin content of proerythroblasts was below 0.3 pg. The two cell generations in the basophilic state had 0.6 pg and 1.7 pg respectively. Polychromatic erythroblasts yielded a hemoglobin content of 5.1 pg in the first cell generation and 7.5 pg in the second one. Orthochromatic erythroblasts contained 8 pg, reticulocytes 12 pg and mature erythrocytes 28 ± 7 pg hemoglobin. Calculations based on these data suggest that the rate of total hemoglobin synthesis is similar in both yolk sac and liver erythropoiesis. The difference between the final hemoglobin content in nucleated erythrocytes of yolk sac origin and that in hepatic erythrocytes can be explained by the different cell generation times.     

Flow cytometric analyses in embryogenic and non-embryogenic callus lines of Cyclamen persicum Mill.: relation between ploidy level and competence for somatic embryogenesis

Embryogenic and non-embryogenic callus lines derived from the same diploid Cyclamen persicum genotype (`Purple Flamed') were analyzed by flow cytometry and compared to the initial plant material. The DNA content of the diploid plant in the greenhouse was 1.12 pg DNA/2C as estimated in relation to the internal standards tomato nuclei and chicken erythrocytes. In both callus lines the majority of cells contained the same amount of DNA as the initial plant, indicating that no polyploidization has taken place after 5 years of culture on medium containing 2.0 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.8 mg/l 6-(γ-γ-dimethylallylamino)purine(zip). Thus, our data suggest that in Cyclamen callus lines there was no strict correlation between the ploidy level and the ability to produce somatic embryos. Furthermore, following the proportion of cells in the three phases of the cell cycle (G0/G1, S, G2/M) during one subculture period of 4 weeks revealed high division activity within the first 2 weeks for both callus lines cultured on the 2,4-D-containing medium. However, when transferred to hormone-free medium, the division activity of the embryogenic cell line decreased markedly, corresponding to the differentiation of somatic embryos. In contrast, for the non-embryogenic callus an increase in cells in the G2/M phase was observed. Received: 22 November 1996 / Revision received: 6 January 1997 / Accepted: 20 February 1997     

Lipid peroxidation in Plasmodium falciparum-parasitized human erythrocytes.

cis-Parinaric acid (PnA) was used as a fluorescent probe to study lipid peroxidation in nonparasitized and Plasmodium falciparum-parasitized erythrocytes, upon challenge by cumene hydroperoxide and tert-butyl hydroperoxide. Parasitized erythrocytes were less susceptible toward lipid peroxidation than nonparasitized erythrocytes with which they had been cultured. Furthermore, nonparasitized erythrocytes cultured together with parasitized cells, and thereafter isolated on a Percoll gradient, were less susceptible toward lipid peroxidation than erythrocytes kept under the same experimental conditions but in the absence of parasitized cells. We concluded, therefore, that the intracellular development of the parasite leads to an increase in the resistance against oxidative stress, not only of the host cell membrane of the parasitized erythrocyte, but also in the plasma membrane of the neighboring cells. The erythrocyte cytosol of parasitized cells and/or the intraerythrocytic parasite was required for the increased protection of the host cell membrane, since ghosts prepared from parasitized erythrocytes were more susceptible to lipid peroxidation than those prepared from nonparasitized ones. Vitamin E content of parasitized erythrocytes was lower than that of nonparasitized cells. However, parasitized erythrocytes promoted extracellular reduction of ferricyanide at higher rates, which might be indicative of a larger cytosolic reductive capacity. It is suggested that the improved response of intact erythrocytes is due to an increased reduction potential of the host-erythrocyte cytosol. The role of vitamin C as a mediator of this process is discussed.     

Production and analysis of intergeneric somatic hybrids between <Emphasis Type="Italic">Brassica oleracea</Emphasis> and<Emphasis Type="Italic"> Matthiola incana</Emphasis>

The gene pool of Brassica oleracea was enriched via intergeneric somatic hybridization between B. oleracea (2n = 18) and Matthiola incana (2n = 14). One hundred and eighteen plants were obtained from 96 calli. Only four plants (H1, H2, H3 and H4) showed an intermediate phenotype from the parents; among these, H1 and H3 arose from the same callus. Random amplified polymorphic DNA (RAPD), sequence-related amplified polymorphism (SRAP), and cytological analyses confirmed that H1 and H3 were hybrids. The nuclear DNA content of the regenerated plants was determined by flow cytometry. More than half of the plants contained a nuclear DNA content of 1.3 to 3.9 pg/cell, which was higher than the content of B. oleracea but lower than that of M. incana. H1 contained 4.89 ± 0.02 pg of DNA per cell, while H3 nuclear DNA content was estimated at 4.87 ± 0.06 pg/cell. Cytological study of the root-tip cells revealed that the majority of the H1 and H3 hybrid cells contained 28 chromosomes.     

Inflammatory cells of teleostean fish: a review focusing on mast cells/eosinophilic granule cells and rodlet cells

In contrast to the roles played by monocytes/macrophages, neutrophils and lymphocytes, the presence and functions of basophils, mast cells/eosinophilic granule cells, eosinophils and rodlet cells in teleosts are areas of controversy. The tissue distribution of mast cells/eosinophilic granule cells in species from a certain genus shows a characteristic pattern, and this pattern is usually also present at the family level. Functionally, the mast cells/eosinophilic granule cells of teleosts show close similarity to the mast cells of mammals. Acute tissue damage is causing mast cell/eosinophilic granule cell degranulation and release of mediators of inflammation, whereas an increase in the number of these cells is often found in chronically inflamed tissues. The mast cells/eosinophilic granule cells of teleosts show marked diversity in their staining properties, with both basophilic and acidophilic components in their granules. In some fish families, e.g. the labrids, the eosinophilic component is dominating, whereas in the pike the granules are strongly basophilic and show the metachromatic staining characteristics found in the granules of mast cells, but being more akin to the granules of the mucosal than to those of the connective tissue type of mast cells of mammals. With respect to rodlet cells, a cell type hitherto clearly demonstrated only in teleosts, a characteristic distribution pattern seems to be established in certain families. In other families rodlet cells are absent in some individuals and present in different tissues in others. However, there is a close relation between the presence of helminths or other noxious agents and the presence of rodlet cells. Massive aggregations of such cells can be seen in affected epithelia of gills or the intestinal tract, and in individuals of species from some fish families they also occur in association with mesothelial and endothelial tissues. The rodlet cell may represent a type of eosinophilic granulocyte that populates the tissues at its immature stage and mature in response to the appropriate stimuli, in a way similar to that of mast cell precursors. Present evidence points to a functional role for the rodlet cells of teleosts in host defence against parasites.     

Rodlet cells of fish in calcium deficiency in the external environment

The ultrastructure of rodlet cells from the heat kidney of the carp Cyprinus carpio L. and tilapia Oreochromis mossambicus Peters has been studied. All the investigated cells displayed a common structure. The number of rodlet cells increased after exposure of fishes in Ca(2+)-free water or in the water supplemented with NH4+ or Cd2+. The latter were found to suppress Ca(2+)-absorption from the environment.     

Histone H2A subfractions and their phosphorylation in cultured Peromyscus cells

Patterns of histone phosphorylation and histone H2A subfractionation have been compared in cultured cell lines from two species of deer mice, Peromyscus eremicus and Peromyscus boylii, which differ considerably in their content of heterochromatin but which contain essentially the same euchromatin content. DNA measurements by flow microfluorometry indicated that P. eremicus cells contained 34.2% more DNA than P. boylii cells, and C-band chromosome analysis indicated that the extra DNA in P. eremicus was present as constitutive heterochromatin. Subfraction of histone H2A by acid-urea polyacrylamide preparative gel electrophoresis in the presence of non-ionic detergent showed that each cell line contained two H2A subfractions. Incorporation of ³²PO₄ into these histones indicated that the steady state phosphorylation of the two H2A subfractions was not the same, the more hydrophobic H2A being greater than two times more phosphorylated than the less hydrophobic H2A in both cell lines. A comparison of the two cell lines indicated that the cell line with 34.2% greater constitutive heterochromatin contained a similar excess (29%) in its ratio of the more highly phosphorylated, more hydrophobic H2A subfraction to the less hydrophobic H2A subfraction. It is suggested that this enrichment of the more highly phosphorylated, more hydrophobic H2A subfraction may be related to the amount of constitutive heterochromatin present in the genome.     

Chromatin diminution in the copepod Mesocyclops edax: diminution of tandemly repeated DNA families from somatic cells.

Chromatin diminution, i.e., the loss of selected chromosomal regions during the differentiation of early embryonic cells into somatic cells, has been described in taxa as varied as ciliates, copepods, insects, nematodes, and hagfish. The nature of the eliminated DNA has been extensively studied in ciliate, nematode, and hagfish species. However, the small size of copepods, which makes it difficult to obtain enough DNA from early embryonic cells for cloning and sequencing, has limited such studies. Here, to identify the sequences eliminated from the somatic cells of a copepod species that undergoes chromatin diminution, we randomly amplified DNA fragments from germ line and somatic line cells of Mesocyclops edax, a freshwater cyclopoid copepod. Of 47 randomly amplified germ line clones, 45 (96%) contained short, tandemly repeated sequences composed of either 2 bp CA-repeats, 8 bp CAAATAGA-repeats, or 9 bp CAAATTAAA-repeats. In contrast, of 83 randomly amplified somatic line clones, only 47 (57%) contained such short, tandemly repeated sequences. As previously observed in some nematode species, our results therefore show that there is partial elimination of chromosomal regions containing (CAAATAGA and CAAATTAAA) repeated sequences during the chromatin diminution observed in the somatic cells of M. edax. We speculate that chromatin diminution might have evolved repeatedly by recruitment of RNAi-related mechanisms to eliminate nonfunctional tandemly repeated DNA sequences from the somatic genome of some species.     

Nuclear DNA Content Varies with Cell Size across Human Cell Types

Variation in the size of cells, and the DNA they contain, is a basic feature of multicellular organisms that affects countless aspects of their structure and function. Within humans, cell size is known to vary by several orders of magnitude, and differences in nuclear DNA content among cells have been frequently observed. Using published data, here we describe how the quantity of nuclear DNA across 19 different human cell types increases with cell volume. This observed increase is similar to intraspecific relationships between DNA content and cell volume in other species, and interspecific relationships between diploid genome size and cell volume. Thus, we speculate that the quantity of nuclear DNA content in somatic cells of humans is perhaps best viewed as a distribution of values that reflects cell size distributions, rather than as a single, immutable quantity.Our understanding of the complexity of multicellular organisms, and the diverse cells of which they are comprised, has dramatically increased over the past several decades. Yet, we still lack an understanding of some of the most basic features of the cells that constitute multicellular organisms. For example, the number of different cell types in an organism, or the rate at which different cells grow, divide, and die, remain poorly understood (see Niklas 2015). But perhaps most important, we lack an understanding of the size and abundance of cells that constitute an organism (see Amodeo and Skotheim 2015). Cell size, in particular, affects virtually all structural and functional attributes of multicellular organisms, from the molecular level to the whole organism level.One key feature of organisms that may vary with cell size is the amount of nuclear DNA. Across species, genome size has long been known to correlate positively with cell and nuclear volume (Price et al. 1973; Szarski 1976; Olmo 1983). But within species, too, the nuclear DNA content of somatic cells has been shown in a few instances to increase with cell size in species such as Daphnia (Beaton and Hebert 1989) and Arabidopsis (Jovtchev et al. 2006). Such increases in nuclear DNA content can have important consequences for cell function, in general, and gene expression, in particular (Hancock et al. 2008; Lee et al. 2009; De Veylder et al. 2011; Marguerat and Bähler 2012).In the case of humans, substantial differences in DNA content have been observed in many human cell types. Indeed, since Watson and Crick described the structure of DNA, studies of healthy human tissues have reported the presence of polyploid cells (Winkelmann et al. 1987; Biesterfeld et al. 1994). The cell types in which this has been observed appear to have little in common, except that they are generally stable, fully differentiated cells (Winkelmann et al. 1987). Still, these observations have done little to change the traditional view that all healthy somatic cells in the human body hold the same characteristic quantity of DNA (∼7 billion base pairs) based on the long-standing principle of DNA constancy (Mirsky and Ris 1949). Deviations from the diploid quantity of DNA in humans, like other animals, are still often viewed as exceptional, tissue-specific, or indicative of pathology. A more synthetic view of differences in nuclear DNA content across human cell types may provide some clarity on these and other issues.In this review, we compile and analyze published data to examine the extent to which nuclear DNA content varies across diverse human cell types, and whether such variation is correlated with cell size. We then compare these results with previously reported relationships between nuclear DNA content and cell size within four other species. Finally, we compare these results with the relationships between diploid genome size and cell size observed across species in several broad taxonomic groups. These analyses suggest that systematic variation in nuclear DNA content is a more ubiquitous phenomenon in human cells than was previously appreciated. However, as we later discuss, the mechanisms underlying these patterns remain in question.     

Nuclear DNA content of Solanum species grown in vitro, as determined by flow cytometry

The DNA relative content in nuclei from several Solanum species, which were used as partners for somatic hybridization, were determined using a flow cytometry method. The nuclei were isolated mechanically or via protoplasts from leaves of in vitro grown plants. In the case of S. nigrum as well as S. tuberosum cv. Bzura and dihaploid clone H8105, the nuclei were also obtained from suspension cultured cells by lysis of protoplasts. The source and the method of nuclei isolation affected the pattern of nuclear DNA in the genotypes studied. The mesophyll nuclei showed two distinct peaks on the DNA histograms, whereas the DNA peaks produced by cell suspension nuclei were broad and less distinct. The DNA content in the nuclei, calculated from the DNA histograms of the samples and a DNA standard historgam (Trout Red Blood Cells, having DNA content of 5.05 pg per nucleus), were much lower in mesophyll nuclei than in those obtained from the cell suspension for the same genotypes. The results are discussed in respect of the genetic instability of Solanum genotypes. The usefulness of a flow cytometry approach in somatic hybridization research is also discussed.