Transport number effects in the transverse tubular system and their implications for low frequency impedance measurement of capacitance of skeletal muscle fibers

Summary It has been shown in an earlier paper that the slow transient decrease in conductance, somtimes referred to as creep, obtained with small-to-medium hyperpolarizing current or voltage pulses is due to K⁺ transport number differences across the walls of the transverse tubular system. Using the same basic numerical analysis and the parameters already obtained experimentally in the previous paper for frog skeletal muscle in a sulphate Ringer's solution, this paper predicts the equivalent membrane capacitance and dynamic resistance due to transport number effects for very low amplitude and low frequency sinusoidal currents from the phase lag of the voltage response behind the current. Such sinusoidal currentper se give rise to an equivalent capacitance which increased from less than 1F·cm^–2 at 10 Hz to about 16F·cm^–2 at 0.01 Hz and to an equivalent dynamic membrane resistance which increases from its instantaneous slope resistance value of 11.7kcm² at 10 Hz to about 16kcm² at 0.01 Hz. Similar small sinusoidal components of current superimposed on depolarizing and hyperpolarizing pulses (25–45 mV) give rise to even greater capacitances at low frequencies (e.g., 24–28F·cm^–2 at 0.01 Hz). The response due to large sinusoidal currents was also investigated. These transport number effects help to explain the small discrepancies obtained by some workers between experimental and predicted values of skeletal muscle fiber impedances measured in the 1–10 Hz range and would seem to be critical for the interpretation of any skeletal muscle fiber impedance studies done at frequencies less than 1 Hz.     

Evidence for chromosomal replicons as units of sister chromatid exchanges

Chromosomal replicons have been described as the cytological counterpart of DNA replicon clusters and have previously been studied in vitro using premature chromosome condensation-sister chromatid differentiation (PCC-SCD) techniques. Chromosomal replicons are visualized as small SCD segments in S-phase cells, and measurement of these segments can provide estimates of relative chromosomal replicon size corresponding to DNA replicon clusters functioning coordinately in S-phase. Current hypotheses of sister chromatid exchange (SCE) formation postulate that sites of SCE induction are associated with active replicons or replicon clusters. We have applied the PCC-SCD technique to in vivo studies of mouse bone marrow cells that have been treated with cyclophosphamide (CP) for two cell cycles. We have been able to visualize chromosomal replicons, as well as SCEs which have been induced in vivo by CP treatment, simultaneously in the same cells. Chromosomal replicons visualized as small SCD segments were measured in PCC cells classified at early or late S-phase based on SCD segment size prevalence. Early S-phase (E/S) PCC cells contained 90% of the SCD segments measured clustered in a segment size range of 0.1 to 0.8 m with a peak value around 0.3 to 0.6 m regardless of CP treatment. As the cells progressed through S-phase, late S-phase (L/S) PCC cells were characterized by the appearance of larger SCD segments and even whole SCD chromosomes in addition to small SCD segments. A concentration of units around 0.4 to 1.0 m was found for L/S SCD segment size distributions regardless of CP treatment with an apparent bimodal profile. Our in vivo data support the existence of a subunit organization of chromosomal replication with a basic functional unit being 0.3 to 0.6 m in size. In addition, we have found that this chromosomal unit of replication or chromosomal replicon does not seem to be functionally perturbed by the mutagen CP. We also found that small SCD segments of 0.4 to 0.7 m in length were involved in the formation of an SCE, suggesting that both spontaneous and CP-induced SCEs occur between chromosomal replicons. These findings provide direct cytogenetic evidence to support a replicon cluster/chromosomal replicon model for SCE formation.     

Uptake and Retention of Selenite and Selenomethionine in cultured K-562 cells

The selenium uptake and retention have been studied in K-562 cells exposed to selenite or selenomethionine. In the uptake experiments the cells were exposed to two doses of selenite (5 or 50 M) or selenomethionine (10 or 50 M). In the retention study the cells were treated for 2 h with the above mentioned doses of the selenocompounds before being observed at different times. The selenium uptake in cells exposed to selenite 5 M began to saturate at 8 h, but increased again between 48 and 96 h. In cells exposed to selenite 50 M the selenium uptake never reached a maximum, however, at 48 and 96 h the cell viability decreased strongly. The two doses of selenite showed different retention patterns, with a relatively small cellular decrease of selenium after treatment with selenite 5 M compared to treatment with 50 M of selenite. The selenium uptake in cells exposed to selenomethionine 10 M or selenomethionine 50 M began to saturate at 24 h and 48 h, respectively. The retention patterns were similar for both selenomethionine doses with a continuous decrease of the selenium concentration during the whole observation period. The results indicated a more controlled uptake and retention pattern of selenomethionine compared to selenite.     

Male reproductive effect of arsenic in mice

Arsenic, a known human carcinogen, was given to mice via drinking water as sodium arsenite at a dose 53.39, 133.47, 266.95 and 533.90 mol l for 35 days. A decrease in the activity of 17 HSD along with increase in LDH, GT activity were observed at 533.90 mol l. The observed sperm count, motility and morphological abnormalities in sperm were similar to control at lower dose levels. However at 533.90 mol l a significant decrease in sperm count and motility along with increase in abnormal sperm were noticed. Significant accumulation of arsenic in testes and accessory sex organs may be attributed to the arsenic binding to the tissues or greater cellular uptake. No effects were observed on indices studied for reproductive effects at 53.39 mol l arsenic close to which human being are exposed through drinking water under the present set of experimental conditions.     

Combined effect of cytochalasin a and adenosine triphosphate onPhysarum polycephalum

Summary Physarum polycephalum microplasmodia exposed to 1.6×10^–5 M cytochalasin A evidenced intracellular cytoplasmic condensation, slow contraction, and eventual breaks at discrete surface areas, within one hour. Other cytochalasins tested (CB or CD) did not substitute for CA. CA effects on plasmodia were not abolished by immediate washing or media replacement. In nutrient medium, CA plus ATP (375 M) produced within minutes herniation (blebbing) and plasmodial disruption. The order of addition of reagents was important; ATP added simultaneously with or prior to CA stimulated the phenomenon, whereas initial addition of CA resulted in no such dynamic response. Several other nucleotides (e.g., AMP, cAMP) could substitute for ATP; however, such changes were not observed with 5-adenylylimidodiphosphate. Blebbing was not abolished in the presence of 2,4-dinitrophenol. In minimal medium, it was best stimulated by simultaneous addition of Ca⁺⁺ and Mg⁺⁺. Preincubation of CA with L-cysteine or with -mercaptoethanol negates its individual or nucleotide-combined effects. Yet, 10^–5 M ethacrynic acid, a sulfhydryl-reactive liposoluble drug, in the presence of ATP does not mimic the blebbing response. These observed effects, which take place at or near the plasmodial surface, presumably reflect acceleration of normal contractile processes inPhysarum. Abbreviations CA cytochalasin A - CB cytochalasin B - CD cytochalasin D - AMP adenosine 5-monophosphate - ADP adenosine 5-diphosphate - ATP adenosine 5-triphosphate - di-butyryl-cAMP di-butyryl-cyclic adenosine 35-monophosphate - di-butyrylcGMP di-butyryl-cyclic guanosine 35-monophasphate. This work was supported by a grant (AI-11902) from the U.S. Public Health Service.     

Carcinogenic potential and genomic instability of beryllium sulphate in BALB/c‐3T3 cells

Occupational exposure to beryllium (Be) and Be compounds occurs in a wide range of industrial processes. A large number of workers are potentially exposed to this metal during manufacturing and processing, so there is a concern regarding the potential carcinogenic hazard of Be. Studies were performed to determine the carcinogenic potential of beryllium sulfate (BeSO₄) in cultured mammalian cells. BALB/c3T3 cells were treated with varying concentrations of BeSO₄ for 72 h and the transformation frequency was determined after 4 weeks of culturing. Concentrations from 50–200 g BeSO₄/ml, caused a concentrationdependent increase (9–41 fold) in transformation frequency. Nontransformed BALB/c3T3 cells and cells from transformed foci induced by BeSO₄ were injected into both axillary regions of nude mice. All ten Beinduced transformed cell lines injected into nude mice produced fibrosarcomas within 50 days after cell injection. No tumors were found in nude mice receiving nontransformed BALB/c3T3 cells 90 days postinjection. Gene amplification was investigated in Kras, cmyc, cfos, cjun, csis, erbB2 and p53 using differential PCR while random amplified polymorphic DNA fingerprinting was employed to detect genomic instability. Gene amplification was found in Kras and cjun, however no change in gene expression or protein level was observed in any of the genes by Western blotting. Five of the 10 transformed cell lines showed genetic instability using different random primers. In conclusion, these results indicate that BeSO₄ is capable of inducing morphological cell transformation in mammalian cells and that transformed cells induced by BeSO₄ are potentially tumorigenic. Also, cell transformation induced by BeSO₄ may be attributed, in part, to the gene amplification of Kras and cjun and some BeSO₄induced transformed cells possess neoplastic potential resulting from genomic instability.     

Stimulation by hexose esters of lactate production by rat erythrocytes,insensitivity to 3-O-methyl-D-glucose and inhibition by 2-deoxy-D-glucose and its tetraacetic ester

Selected esters of D-glucose were recently proposed as tools to provide the sugar to cells, whilst bypassing the carrier system for hexose transport across the plasma membrane. In the present study, -D-glucose pentaacetate, -D-glucose pentaacetate, -D-mannose pentaacetate and, to a lesser extent, 6-O-acetyl-D-glucose, all tested at a 1.7 mM concentration, were found to increase lactate production above basal value in rat erythrocytes. Over 90 min incubation, the increment in lactate production ranged from about 1.2 (-D-glucose pentaacetate) to 0.6 (6-O-acetyl-D-glucose) mol/l of erythrocytes. Little or no change in lactate production was observed in cells exposed to -L-glucose pentaacetate, -D-glucose pentaethylsuccinate, -D-galactose pentaacetate or -D-galactose pentaacetate. The metabolic response to -D-glucose pentaacetate was resistant to 3-O-methyl-D-glucose (10-80 mM) which suppressed, however, that evoked by D-glucose. D-mannoheptulose (10 mM) virtually failed to affect the response to D-glucose and its pentaacetate ester. On the contrary, 2-deoxy-D-glucose (10.6 mM) inhibited to the same relative extent (55% decrease) lactate production in erythrocytes exposed to either unesterified D-glucose or -D-glucose pentaacetate. The tetraacetic ester of 2-deoxy-D-glucose was more efficient than unesterified 2-deoxy-D-glucose in inhibiting lactate production from -D-glucose pentaacetate. It is proposed that selected esters of saccharides represent useful tools to bypass defects in hexose transport, and to increase their nutritional or therapeutic efficiency.     

A comparison of male and female recombination frequency in wheat using RFLP maps of homoeologous group 6 and 7 chromosomes

A novel approach was used to compare male and female recombination rates in wheat. Doubled haploid lines were developed from an F₁ using two distinct approaches: the anther-culture technique and the Hordeum bulbosum system, from which sets of lines were developed from male and female meioses, respectively. The genotype of the lines was established at RFLP and isozyme markers polymorphic on chromosomes of homoeologous groups 6 and 7, and male and female linkage maps were calculated using this information. The markers in one segment of chromosome 6B exhibited disturbed segregation frequencies in the anther-culture population. The male and female maps differed significantly in recombination frequency between some markers on two chromosomes, and these were consistent in direction within chromosomes and inconsistent in direction between chromosomes. In two of the four chromosomes studied the male map was much longer than the female map. These results suggest that significant differences may exist in male and female recombination frequencies in bread wheat which are specific to certain chromosomal segments but are inconsistent in direction between chromosomes. Other factors, such as environmental influences, may also be important in creating differences.     

Optimization of in vivo tumor targeting in SCID mice with divalent forms of 741F8 anti-c-erbB-2 single-chain Fv: effects of dose escalation and repeated i.v. administration

Single-chain Fv molecules in monovalent (sFv) and divalent [(sFv')₂] forms exhibit highly specific tumor targeting in mice as a result of their small size and rapid systemic clearance. As a consequence, there is a rapid reversal of the sFv blood/tumor gradient, resulting in diminished retention of sFv species in tumors. In this report we investigate two distinct strategies, dose escalation and repetitive intravenous (i.v.) dosing, aiming to increase the absolute selective retention of radiolabeled anti-c-erbB-2¹²⁵I-741F8 (sFv')₂ in c-erbB-2-overexpressing SK-OV-3 tumors in mice with severe combined immunodeficiency (SCID). A doseescalation strategy was applied to single i.v. injections of¹²⁵I-741F8 (sFv')₂. Doses from 50 g to 1000 g were administered without a significant decrease in tumor targeting or specificity. High doses resulted in large increases in the absolute retention of¹²⁵I-741F8 (sFv')₂. For example, raising the administered dose from 50 g to 1000 g increased the tumor retention 24 h after injection from 0.46 g/g to 9.5 g/g, and resulted in a net increase of greater than 9 /g. Over the same dose range, the liver retention rose from 0.06 g/g to 1 g/g, and resulted in a net increase of less than 1 g/g. The retention of 9.5 g/g in tumor 24 h fllowing the 1000-g dose of (sFv')₂ was comparable to that seen 24 h after a 50-g dose of¹²⁵I-741F8 IgG, indicating that the use of large doses of (sFv')₂ may partially offset their rapid clearance. When two doses were administered by i.v. injection 24 h apart, the specificity of delivery to tumor observed after the first dose was maintained following the second injection. Tumor retention of¹²⁵I-741F8 (sFv')₂ was 0.32 g/g at 24 h and 0.22 g/g at 48 h following a single injection of 20 g/g, while 0.04 g/ml and 0.03 g/ml were retained in blood at the same assay times. After a second 20-g injection at the 24-h assay time, tumor retention increased to 0.49 g/g, and blood retention was 0.06 g/ml, at the 48-h point. These results suggest that multiple high-dose administrations of radiolabeled 741F8 (sFv')₂ may lead to the selective tumor localization of therapeutic radiation doses.Supported by National Cancer Institute (NCI) National Cooperative Drug Discovery Group grant U01 CA51880, CA06927, an appropriation from the Commonwealth of Pennsylvania, and the Bernard A. and Rebecca S. Bernard Foundation     

β-Alanine metabolism and high salinity stress in the sea anemone,Bunodosoma cavernata

Summary During high salinity stress, -alanine accumulates to high levels in the sea anemone,Bunodosoma cavernata. Following a salinity increase from 26 to 40 -alanine increased 28-fold from 1.5 to 41.9 moles/g dry weight. Both whole animal studies and experiments with cell free homogenates indicate that under high salinity conditions an increase in the rate of -alanine synthesis from aspartic acid as well as a decrease in the rate of -alanine oxidation are responsible for the observed accumulation of -alanine. The rate of aspartic acid decarboxylation to -alanine is about 3 times greater in anemones acclimated to 40 than for those in normal salinity water (26). -alanine oxidation to CO₂ and acetyl-CoA proceeds 2.5 to 3 times slower in high salinity adaptedB. cavernata than in those acclimated to normal salinity. There is always a rapid degradation of uracil to -alanine, but this does not change with salinity.Abbreviations CASF cold acid soluble fraction - FAA free amino acids - MES 2(N-morpholino) ethane sulfonic acid - NPS ninhydrin positive substances - PCA perchloric acid - TCA trichloroacetic acid     

The human leukocyte test system

Summary Leukocyte cultures were set up with X-irradiated whole blood (200 R). Cells starting with their DNA synthesis between 25 and 35 h after culture initiation (early replicating cells) were pulse-labeled with tritiated thymidine ([³H] TdR). Mitoses were collected with colcemid in adjacent intervals from 36 up to 72 h after culture initiation. At fixation times of 50, 56, 62, and 72 h enough mitoses for a determination of the frequencies of chromosomal aberrations (dicentric and ring chromosomes) were found. After that the preparations were processed for autoradiography. All mitoses analyzed for chromosomal aberrations were re-analyzed for labeling, and the frequencies of chromosomal aberrations in labeled (=early replicating cells) and unlabeled (=late replicating cells) mitoses were compared. At all fixation times, higher frequencies of dicentric chromosomes were found in labeled as compared to unlabeled mitoses, indicating a higher sensitivity of early replicating cells to X-irradiation in the G₀ stage of the cell cycle.     

The structure of two distinct pancreatic amylase genes in mouse strain YBR

The amylase complex on mouse chromosome 3 encodes both salivary and pancreatic amylase. It appears that one active gene is present for salivary amylase, whereas pancreatic amylase in some strains is coded by at least 4, and perhaps by more than 10, genes. Strain YBR is different from other strains in that it produces twice as much salivary amylase. Pancreatic amylase in YBR is present as two different protein forms, A and B, the sum of which amounts to only one-third of that in, for instance, strain A/J. YBR chromosomal DNA was cloned in phage , followed by restriction and heteroduplex analysis of recombinant phages carrying amylase genes. Among 32 phage isolates, 5 carried parts of the salivary amylase sequence. The remaining phage isolates contained pancreatic amylase-like sequences and represented three nonoverlapping genomic regions, i.e., one of 34 kb containing a complete gene, PAN-II; another of 41 kb with a complete but different gene, PAN-I, plus a truncated gene, PAN-1; and finally, one of 23 kb with another truncated gene, PAN-2. Parts of the amino acid sequence of A and B have previously been determined, and we report here the sequencing of a 4-kb DNA fragment from Pan-II which establishes that this gene codes for B.This work was supported by the Danish Natural Science Research Council.     

DNA variations in regenerated plants of pea (Pisum sativum L.)

Summary The aim of this study was to determine whether DNA variations could be detected in regenerated pea plants. Two different genotypes were analyzed by cytogenetic and molecular techniques: the Dolce Provenza cultivar and the 5075 experimental line. Dolce Provenza regenerated plants showed a reduction in DNA content, particularly at the level of unique sequences and ribosomal genes. Moreover, regeneration was associated with an increase in DNA methylation of both internal and external cytosines of the CCG sequence. On the other hand, the DNA content of the 5075 line remained stable after regeneration. DNA reduction was found only in 5075 plants regenerated from callus cultures maintained for long incubation periods (about a year). The DNA variations observed are discussed both in relation to the genotype source and the role of tissue-culture stress.     

Identification of beta subunit of the rhesus monkey chorionic gonadotropin (rmCG)

Chorionic gonadotropin (CG) is a placental derived hormone that plays a crucial role in successful implantation and establishment of early pregnancy in the primates. The rhesus monkey was chosen as a model to understand the feasibility of developing human DNA immuno-contraceptive. The coding region of rhesus monkey CG -subunit (rmCG) was isolated by the TDRT-PCR method. The nucleotide sequence including the leader peptide was 499 nucleotide long and encoded 166 amino acids. In comparing with the previous known primates CG -subunits, the rmCG was the highest degree of homology with baboon CG -subunit at the deduced amino acid sequence (94%), 79.5% homology with human CG -subunit and 70.4% homology with marmoset monkey CG -subunit. The eukaryotic expression vector pCMV4-rmCG inserted full-coding cDNA sequence of rmCG was constructed, and the expression of rmCG -subunit in HeLa cells transient expressing system in vitro and BALB/c mice in vivo was determined. The results demonstrated that the recombinant PCMV4-rmCG eukaryotic expression vector could express rmCG -subunit in vitro and in vivo.     

Trace metal contamination initiates the apparent auto-aggregation,amyloidosis, and oligomerization of Alzheimer’s Aβ peptides

Nucleation-dependent protein aggregation (seeding) and amyloid fibril-free formation of soluble SDS-resistant oligomers (oligomerization) by hydrophobic interaction is an in vitro model thought to propagate -amyloid (A) deposition, accumulation, and incur neurotoxicity and synaptotoxicity in Alzheimers disease (AD), and other amyloid-associated neurodegenerative diseases. However, A is a high-affinity metalloprotein that aggregates in the presence of biometals (zinc, copper, and iron), and neocortical A deposition is abolished by genetic ablation of synaptic zinc in transgenic mice. We now present in vitro evidence that trace (0.8 µM) levels of zinc, copper, and iron, present as common contaminants of laboratory buffers and culture media, are the actual initiators of the classic A1–42-mediated seeding process and A oligomerization. Replicating the experimental conditions of earlier workers, we found that the in vitro precipitation and amyloidosis of A1–40 (20 µM) initiated by A1–42 (2 µM) were abolished by chelation of trace metal contaminants. Further, metal chelation attenuated formation of soluble A oligomers from a cell-free culture medium. These data suggest that protein self-assembly and oligomerization are not spontaneous in this system as previously thought, and that there may be an obligatory role for metal ions in initiating A amyloidosis and oligomerization.     

Polygonal inequalities as a key to neuronic equations

Neuronic or decision equations, first proposed as a mathematical model of neural activity, have shown, after their exact, compact solution was found, typical behaviours that make them natural tools for General Systems studies. It is shown here that their mathematical investigation is remarkably furthered by generalizing the triangular inequality to polygonal ones. These permit the immediate computation of the tensorial expansion of linearly separable boolean functions, and exhibit clearly the connection between their continuous and discontinuous aspects.     

Population of Aonidiella aurantii on citrus varieties in relation to their physical and chemical characteristics

Different varieties of citrus exhibit a great variation in their susceptibility to infestation by the red scale, Aonidiella aurantii. Among the thirteen varieties investigated, mandarin clemantine, santara and baladi, orange baladi and rough lemon are the most resistant; while lemon baladi, sour orange and grapefruit are the most susceptible. The susceptibility to infestation decreases with the increase of oil glands in the leaves and fruits of citrus. The total amount of nitrogen, phosphorus and carbohydrates in the leaves of different varieties shows no correlation with their susceptibility to infestation.

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Résumé Différentes variétés de Citrus montrent de grandes variations dans leur sensibilité aux attaques par Aonidiella aurantii. Parmi les 13 variétés étudiées, les plus résistantes sont: mandarine clémentine, mandarine baladi et rough lemon, tandis que lemon baladi; sour orange et pamplemousse sont les plus sensibles.La sensibilité aux infestations décroît proportionnellement avec l'accroissement du nombre des glandes à huiles essentielles sur les feuilles de citrus. La quantité totale d'azote, de phosphore et d'hydrates de carbone dans les feuilles des différentes variétés ne montre aucune corrélation avec leur sensibilité aux infestations.

     

Ganglioside-cholera toxin interactions: a binding and lipid monolayer study

Summary On t.l.c. plates ¹²⁵I-cholera toxin binds to a disialoganglioside tentatively identified as GD_lb with about 10 times less capacity than to ganglioside GM₁. Binding of labeled toxin to both gangliosides was abolished in presence of excess amounts of unlabeled B subunit. Ganglioside extracts from human or pig intestinal mucosa showed toxin binding to gangliosides GM₁ and GD_1b. In ganglioside-containing lipid monolayers the penetration of the toxin was independent of the ganglioside binding capacity.Abbreviations GM₂ Gal-NAc14Gal(3-2NeuAc)14G1c1Cer - GM₁ Gal3Ga1-NAc14Gal(32NeuAc)14G1c11Cer - GD_1a NeuAc23Ga113Gal-NAc14Gal(32NeuAc)14G1c11Cer - GD1b Gall3Gal-NAcl4Gal(32NeuAc82NeuAc)14Glc11Cer - GT_1b NeuAc23Ga113Ga1-NAcal4Gal(3-2NeuAc82NeuAc)14G1c11Cer - dpPC 1,2-hexadecanoyl-sn-glycero-3-phosphocholine - dpPE 1,2-hexadecanoyl-sn-glycero-3-phosphoethanolamine     

Binding of Amyloid Beta-Protein to Intracellular Brain Proteins in Rat and Human

Amyloid beta-protein (A), in its soluble form, is known to bind several circulatory proteins such as apolipoprotein (apo) E, apo J and transthyretin. However, the binding of A to intracellular proteins has not been studied. We have developed an overlay assay to study A binding to intracellular brain proteins. The supernatants from both rat and human brains were found to contain several proteins that bind to A 1–40 and A 1–42. No major difference was observed in the A binding-proteins from brain supernatants of patients with Alzheimer's disease and normal age-matched controls. Binding studies using shorter amyloid beta-peptides and competitive overlay assays showed that the binding site of A to brain proteins resides between 12–28 amino acid sequence of A. The presence of several intracellular A-binding (AB) proteins suggests that these proteins may either protect A from its fibrillization or alternatively promote A polymerization. Identification of these proteins and their binding affinities for A are needed to assess their potential role in the pathogenesis of Alzheimer's disease.     

Concluding remarks

On the basis of symposium contributions onChlorella, Hibbertia, Eucalyptus, Ambrosia and on numerical approaches some fundamental problems of (bio)systematics, evolution, and taxonomic categories are discussed: Methods available for analysing affinities; conflicting evidence from phenetic, biochemical, cytogenetic and other analyses; further classification problems in cases of intermediacy, etc. While sibs of various levels and their natural hierarchy often can be objectively defined, this appears impossible for particular taxonomic levels itself (e. g. species). A single objective taxonomic system of organisms is unrealistic. Certain guiding lines for relative and practicable concepts of species and genus are proposed.Presented at the symposium Speciation and the Species Concept during the XIIth International Botanical Congress, Leningrad, July 8, 1975.