Managing the breakup

How cells set the where and when of cytokinesisCompared with the complex choreography required to sort chromosomes during mitosis, cytokinesis might seem fairly simple. But ensuring that the contractile ring of actin and myosin pinches off daughter cells also takes some fancy footwork. Two independent groups (1, 2) offer fresh details about how cells cue cytokinesis at the right time and place.Open in a separate windowFOCAL POINT Top: Asymmetry might set the cytokinesis clock, Dannel McCollum (left) and Juan Carlos García-Cortés (right) determined. The cytokinesis-triggering septum initiation network (indicated by a bright dot on the spindle pole body) turns on only in one side of these yeast cells. Bottom: Eric Griffis (left) and Ron Vale (right), together with James Spudich, reveal that microtubules and the motor protein Kinesin-6 help dictate where cytokinesis occurs. Here, Kinesin-6 (green) has migrated to the equator of a mitotic cell.Cytokinesis can''t begin until the chromosomes have separated, and to forestall multiple divisions it has to end when the daughter cell is independent. García-Cortés and McCollum (1) show that mitotic cells stay on this schedule thanks to a team of proteins that sparks cytokinesis but also initiates its own shutdown.In the fission yeast Schizosaccharomyces pombe, the septum initiation network, or SIN, instigates cytokinesis. The mystery was how cells commit SIN at the right time. The SIN activator Spg1 rides on the spindle pole bodies that anchor the mitotic spindle. Previous work (3) showed that the protein Etd1, which turns on Spg1, amasses at the ends of the cell. García-Cortés and McCollum wondered whether the lengthening of the spindle as chromosomes pull apart might bring Spg1 and Etd1 together, thereby activating SIN. To test that idea, the researchers followed Spg1 activation in cells dosed with a drug that halts spindle elongation. In cells where drug exposure came after the spindle had stretched out, Spg1 turned on as normal. But if the cells entered mitosis after addition of the drug—and thus could not lengthen their spindles—Spg1 remained inactive. The researchers also found that tethering Spg1 to Etd1 prompted cells to divide again and again, further evidence that the rendezvous between the two proteins spurs cytokinesis when chromosome separation is complete.

“It provides a mechanism for how cells can know when they''ve finished cytokinesis.”

A complication to the story—Spg1 and SIN only flip on in half of the cell—might explain how cells determine when to curtail cytokinesis. After the contractile ring has tightened, SIN triggers the elimination of Etd1 in the cell half where Spg1 was turned on. In turn, that leads to the shutdown of Spg1 and then SIN. According to the researchers, asymmetry of SIN signaling might serve as an indicator that the cytoplasm has been divided. “It provides a mechanism for how cells can know when they''ve finished cytokinesis,” says senior author Dannel McCollum. What researchers don''t understand is how the cell chooses which end will activate Spg1 and SIN.Even if a cell''s timing is impeccable, cytokinesis will go awry if the contractile ring assembles at the wrong location. The findings from Vale, Spudich, and Griffis (2) suggest that the molecular motor Kinesin-6 helps designate where the cell will split.Previous studies have shown that the GTPase RhoA (4) is the master regulator of cytokinesis and switches on in the cleavage furrow. Why it activates there isn''t clear. Other studies indicate that certain microtubules dictate the site of the contractile ring (5). Kinesin-6, which hauls RhoA effectors, might connect these two mechanisms.The team used total internal reflection fluorescence microscopy to follow Kinesin-6 and myosin in Drosophila cells that were just entering anaphase. They observed that myosin filaments disappeared from the poles of the fly cells and appeared again at the equator—both changes require Kinesin-6. Contrary to some other studies, the researchers didn''t observe the molecules traveling en masse from one location to the other. Instead, the researchers think that myosin filaments at the poles dissolve and then reform at the equator.Kinesin-6 itself has to concentrate at the cleavage furrow. The researchers found that the molecules first hop on the tips of growing microtubules. Microtubules that reach the cell center stabilize and form bundles. Eventually, all of a cell''s Kinesin-6 accumulates on microtubule tips or in a broad swath around the cell''s midsection. The work suggests that Kinesin-6 helps demarcate the cleavage furrow by delivering RhoA activators that spur the formation of myosin filaments at the cell equator. “Our data suggest that the process of building the contractile ring is largely due to the concentration of positive factors, rather than a directed delivery of negative factors,” says co-author Eric Griffis. What triggers myosin disassembly at the poles and reassembly at the cleavage furrow remains unclear.     

Ultrastructural changes associated with the induction of premature chromosome condensation in Vicia faba root meristem cells

Key message

PCC induction is regulated by several signaling pathways, and all observed effects associated with PCC induction are strongly dependent on the mechanism of action of each PCC inducer used.

Abstract

Electron microscopic observations of cells with symptoms of premature chromosome condensation (PCC) showed that the interphase chromatin and mitotic chromosomes differed with respect to a chemical compound inducing PCC. Induction of this process under the influence of hydroxyurea and caffeine as well as hydroxyurea and sodium metavanadate led to a slight decrease in interphase chromatin condensation and the formation of chromosomes with a considerably loosened structure in comparison with the control. Incubation in the mixture of hydroxyurea and 2-aminopurine brought about clear chromatin dispersion in interphase and very strong mitotic chromosome condensation. Electron microscopic examinations also revealed the characteristic features of the structural organization of cytoplasm of Vicia faba root meristems, which seemed to be dependent on the type of the PCC inducer used. The presence of the following was observed: (i) large plastids filled with starch grains (caffeine), (ii) mitochondria and plastids of electron dense matrix with dilated invaginations of their internal membranes (2-aminopurine), and (iii) large mitochondria of electron clear matrix and plastids containing protein crystals in their interior (sodium metavanadate). Moreover, since caffeine causes either the most effective loosening of chromatin fibrils (within the prematurely condensed chromosomes) or induction of starch formation (in the plastids surrounding the nuclei), this may be a proof that demonstrates the existence of a link between physical accessibility to chromatin and the effectiveness of cellular signaling (e.g., phosphothreonine-connected).     

Effect of psychostimulants on responses of neocortical neurons to afferent and subcortical stimuli

The effect of psychostimulants on unit responses of the pericruciate region of the cortex during sensory and subcortical stimulation was studied in experiments on 52 immobilized cats. Amphetamine (2 mg/kg) caused a definite increase in the number of spontaneously active cortical cells. Caffeine (40 mg/kg) had a weaker action. After administration of psychostimulants afferent stimuli more often induced tonic changes in the spontaneous unit activity. More polymodal neurons were found. Phasic responses were often facilitated but were recorded at the same frequency as in the control. Amphetamine and caffeine weakened inhibition of the unit discharges during stimulation of the caudate nucleus and potentiated activation caused by stimulation of the reticular formation. The character of interaction between sensory and reticular (caudate) stimuli was not modulated by the psychostimulants although its scale and intensity were varied. The possible role of the effects of amphetamine and caffeine in therapeutic psychostimulation is discussed.     

Effects of high osmotic potential of a medium on mitotic cycle in roots ofVicia faba L

The present paper deals with the effects of osmotic potential of a medium on cell reproduction and elongation of the roots ofVicia faba L. andVicia sativa L. As the osmoticum polyethylene glycol (PEG 4000) in various concentrations ranging from 5 % to 25 % (i.e. fromca.-0.11 up to -1.27 MPa) has been used. The results show that at higher concentrations than 7.5 %, the growth of roots is slowed down and at the concentration of 25 % PEG this decrease in growth rate is as much as 6 fold compared with the control. The mitotic cycle is prolonged, however, only 1.86 times. Thus, the inhibition of root growth is caused mainly by the inhibition of cell elongation. Concerning the effect of high osmotic potential on mitotic cycle it was found that the roots after immersion into 25% PEG are able to overcome this osmotic stress and after 6 h to renew the mitotic activity. The S phase of the cycle is the most sensitive to this factor and even after mitotic activity was renewed it showed a slower rate in comparison with the control.     

Hemmung der Cytokinese und Bildung von Riesenzellen beiPoterioochromonas malhamensis durch organische Bleiverbindungen und andere Agenzien

Summary Organic lead compounds inhibit cytokinesis of the chrysophycean flagellatePoterioochromonas malhamensis leading to giant, multinucleate cells. This action on cytokinesis is compared with the long-time effects of various compounds with better known subcellular activities.Calcium (10 mM), and cytochalasin B (up to 100 g/ml) do not visibly influence cytokinesis. Caffeine (1 mM) totally inhibits multiplication of the algae whereas calcium has only a slight and cytochalasin has no effect on this parameter.The other reference-compounds (colchicine, sodium cacodylate, deuterium oxide, local anesthetics, and sodium dodecylsulfate) all inhibit cell multiplication, simultaneously leading to giant multinucleate cells, obviously by inhibition of cytokinesis.The most potent inhibitor of cytokinesis is triethyl lead which was shown to be 250× more effective than colchicine in respect to the molar concentrations.The comparison of the effects of tetraethyl lead and triethyl lead with the reference agents leads to the conclusion that organic lead compounds might inhibit cytokinesis ofPoterioochromonas malhamensis by disintegrating peripheral microtubules and/or by interfering with structures and functions of membranes.

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Verwendete Abkürzungen im Text CB Cytochalasin B - KE Karminessigsäure - KV kontraktile Vakuole - LV Leukosinvakuole - MT Mikrotubuli - SDS Na-Dodecyl-sulfat - TEL Tetraäthylblei - TriEL Triäthylblei     

Inhibition of deoxyribonuclease activity associated with soybean chloroplasts

The effects of spermidine, pH, ethylene diamine tetracetic acid (EDTA), and adenosine triphosphate (ATP) on deoxyribonuclease (DNase) activity associated with the chloroplasts of soybean (Glycine max (L.) Merr.) were investigated. Chloroplast DNase activity was found to be partially inhibited by either 10 mM spermidine, 20 mM EDTA, or 20 mM ATP. DNase activity was also partially inhibited at non-neutral pH's. Nearly complete inhibition was achieved with use of 30 mM EDTA, pH 10, or a combination of 10 mM spermidine and 10 mM EDTA.     

Properties of intratetanic individual contractile responses in rat slow skeletal muscles during modulation of sarcoplasmic reticulum Ca<Superscript>2+</Superscript> release

In control experiments (n = 16), during direct stimulation of m. Soleus by trains of 5, 10 and 50 stimuli at a rate of 20 Hz a biphasic change was detected in the amplitude of the last contractile responses (LCR_N) depending on N, where N is the number of individual contractile responses in the tetanus. Thus, an initial decrease in LCR_N amplitudes (down to 54 ± 8% for LCR₅) was followed by a subsequent increase (up to 218 ± 14% for LCR₅₀) and significant shortening of their half-relaxation time compared to the initial response (down to 44 ± 8% for LCR₅₀). Caffeine at concentrations of 5 (n = 6) and 10 (n = 4) mM exacerbated LCR₅ depression (down to 31 ± 8% and 15 ± 4%, respectively) against the background of arising characteristic stationary contracture responses. The subsequent increase in the LCR_N amplitude was substantially lower than in control experiments (114 ± 18% and 46 ± 9% for LCR₅₀ compared to the initial response at 5 and 10 mM of caffeine, respectively). The LCR₅₀ half-relaxation time during the effect of caffeine at both concentrations also remained considerably shorter than that of individual responses recorded both in the presence of caffeine and in control experiments. In contrast to the control and caffeine effects, LCR₅ and LCR₁₀ amplitudes during the effect of 10 μM of dantrolene (n = 5) remained at the level close to that of the first response (102 ± 7% and 106 ± 8%, respectively), while the LCR₅₀ amplitude displayed a considerably smaller increase (to 143 ± 14%) than observed in control muscles. Besides, dantrolene further enhanced muscle relaxation at rest. Caffeine (10 mM), as applied in the presence of dantrolene, restored the dynamics of changes in amplitude–temporal characteristics of last contractile responses to values approximating those in control. The amplitude–temporal characteristics of action potentials recorded extracellularly in individual m. Soleus muscle fibers did not change significantly during the transition from single to train stimulation under the same protocol as in mechanographic experiments. These data may be interpreted in support of the previously advanced hypothesis on the implication of Ca²⁺-induced Ca²⁺ release in skeletal muscles under their tetanic stimulation as an additional mechanism of excitation–contraction coupling [1, 2].     

Sister chromatid exchanges in Vicia faba

The relationship between chromosomal aberrations and sister chromatid exchanges (SCE's) after treatment of Vicia faba root tips with thiotepa, caffeine and 8-ethoxycaffeine (EOC) was studied by using a modified fluorescent plus Giemsa (EPG) technique. At concentrations which had little effect on the frequency of chromosomal aberrations, thiotepa strongly increased the frequency of SCE's, provided that the chromosomes were allowed to replicate between treatment and fixation. Frequently, the size of the exchanged material was smaller than the diameter of the chromatid. Post-treatments with caffeine of roots previously exposed to thiotepa strongly increased the frequency of aberrations, but had little effect on the frequency of SCE's. In contrast to thiotepa, EOC caused only a slight increase in the frequency of SCE's even at concentrations which produced a high frequency of chromosomal aberrations. Thus, there was not a close correlation between SCE's and chromosomal aberrations. Single-strand exchanges between the DNA double helices in sister chromatids were not detected.     

Cytogenetic studies on the effect of chronic gamma irradiation onVicia faba

Vicia faba seeds (cv. Giza 1) were planted in the Inshas gamma radiation field where they were chronically irradiated during the whole life of the plant. The percentage of the induced abnormal P.M.Cs, as well as the frequency of abnormal P.M.Cs in the different meiotic stages were proportional with the given doses. The main types of chromosome aberrations were anaphase and telophase bridges, fragmentation and lagging chromosomes. The nearest plants to the source showed an inhibition of shoot growth, flower and seed sterility and irregular branching. At the dosage levels used irradiation had no effect on pollen fertility. Seeds of the 1st filial generation were used for both mitotic and meiotic studies. The percentage of the mitotic abnormalities was proportional with the doses. The most dominant type of anomaly was the presence of micronuclei in the different stages of mitosis and in the resting cells. Irradiation affected also other types of anomaliese.g. lagging chromosomes, fragments, bridges...etc. Meiosis, and pollen fertility (2nd generation) were normal.     

The influence of selenium and caffeine on chemical carcinogenesis in rats,mutagenesis in bacteria,and unscheduled DNA synthesis in human lymphocytes

The influence of sodium selenite (Na₂SeO₃) and caffeine on chemical carcinogenesis induced in rats by diethylnitrosamine (DEN), N-nitrosomorpholine (NM), andN-methyl-N-nitro-N-nitrosoguanidine (MNNG) was investigated. A dose-dependent inhibitory effect of Na₂SeO₃ (l–10 ppm) on hepatocarcinogenesis induced by DEN was demonstrated. Na₂SeO₃ also increased the latency period for stomach tumor formation in rats treated with MNNG. Combined treatment of rats with Na₂SeO₃ plus vitamin C added to the diet resulted in a slight inhibition of NM-induced liver carcinogenesis. Supplementation of diet with Na₂SeO₃ plus butylated hydroxytoluene, vitamin C, and vitamin E did not reveal any additive inhibitory effect compared to the inhibitory effect of Na₂SeO₃ given alone. Caffeine (600 rag/L) reduced the number of liver tumors induced in rats by DEN. Preliminary experiments have indicated that combined treatment of rats with selenium and caffeine could result in more effective inhibition of DEN-induced liver carcinogenesis. Further experiments are being conducted to study the influence of selenium and caffeine on mutagenic activity of 1-methyl-l-nitrosourea (MNU) inSalmonella typhimurium TA 1535. The pretreatment of bacteria cells with Na₂SeO₃ (3–10 p.g/mL) increased the mutagenic response of bacteria to MNU. A synergistic stimulation of mutagenic activity of MNU was observed in bacteria pretreated simultaneously with Na₂SeO₃ and caffeine. In addition the influence of Na₂SeO₃ on UDS induced by DEN in human lymphocytes was investigated. The trace element inhibited the UDS up to 82%. The possible role of potentiation by NazSeO3 of the cell killing effect of DEN in inhibition of liver carcinogenesis was discussed.     

Studies on the regulatory complex of rabbit skeletal muscle: Contributions of troponin subunits and tropomyosin in the presence and absence of Mg2+ to the acto-S1 ATPase activity

The regulatory roles of the components of the troponin-tropomyosin complex in the presence and absence of Mg²⁺ on the acto-S1 ATPase have been examined. The effect of free Mg²⁺ on the inhibition of the acto-S1 ATPase by rabbit skeletal troponin (Tn) was studied at S1 to actin ratios ranging from 0.17:1 to 2.5:1. These studies were performed using two Mg²⁺ concentrations: 2.5 mM Mg²⁺-2.5 mM ATP, conditions considered to have low free Mg²⁺; and 5.0 mM Mg²⁺-2.5 mM ATP, conditions providing a high free Mg²⁺ concentration of ～2.5 mM. In the presence of high free Mg²⁺ (2.5 mM ATP-5.0 mM MgCl₂) the Tn inhibition of acto-S1-TM ATPase increased by approximately 40–50% over a range of S1 to actin ratios of 0.17:1 to 2.5:1. The effect of free Mg²⁺ on increasing quantities of Tn in the absence or presence of tropomyosin was studied independently at two S1 to actin ratios (1:1 and 2:1). In the absence of TM, at 5 mM Mg²⁺ there is an additional 38% (1:1 S1 to actin) or 37% (2:1) decrease in the ATPase activity by Tn compared to 2.5 mM Mg²⁺. Similarly, in the presence of TM and Tn, Mg²⁺ exerts its effect at both S1 to actin ratios. Significantly, the inhibition by the IT complex in the presence of TM is unaffected by free Mg²⁺. Furthermore, ultracentrifugation binding studies using¹⁴C-iodoacetamide-labeled Tn and TM established that the Tn-TM regulatory complex was firmly bound to F-actin at both Mg²⁺ concentrations, indicating that faciliation of binding to F-actin by Mg²⁺ is not responsible for the increased inhibition. Hence, it is concluded from the data that Mg²⁺ binding and by analogy Ca²⁺ binding to the Ca²⁺-Mg²⁺ sites of TnC promotes muscle relaxation by inducing inhibition of the actomyosin ATPase, whereas Ca²⁺ binding to the Ca²⁺-specific sites promotes contraction by potentiating the ATPase. The inhibition of the acto-S1-TM ATPase by TnT has also been further examined. The data indicate that TnT exerts the same level of inhibition upon the ATPase as TnI or Tn. The inhibitory activity requires TM, and occurs to the same extent under conditions where TM alone would have either a potentiating (2:1 S1 to actin) or an inhibitory (1:1 S1 to actin) effect upon the ATPase. In the presence of TM the IT complex is a more effective inhibitor than either TnI, TnT, or Tn. The inhibitory activity of the IT complex is partially released by TnC in the absence of Ca²⁺. These observations, in conjunction with those by Chong, Asselbergs, and Hodges, which showed that the inhibition by TnT is partially released by TnC plus Ca²⁺, indicate that the role of TnT involves more than anchoring Tn to the thin filament.     

Anticancer effect of calycopterin via PI3K/Akt and MAPK signaling pathways,ROS-mediated pathway and mitochondrial dysfunction in hepatoblastoma cancer (HepG2) cells

Calycopterin is a flavonoid compound isolated from Dracocephalum kotschyi that has multiple medical uses, as an antispasmodic, analgesic, anti-hyperlipidemic, and immunomodulatory agents. However, its biological activity and the mechanism of action are poorly investigated. Herein, we investigated the apoptotic effect of calycopterin against the human hepatoblastoma cancer cell (HepG2) line. We discovered that calycopterin-treated HepG2 cells were killed off by apoptosis in a dose-dependent manner within 24 h, and was characterized by the appearance of nuclear shrinkage, cleavage of poly (ADP-ribose) polymerase and DNA fragmentation. Calycopterin treatment also affected HepG2 cell viability: (a) by inhibiting cell cycle progression at the G2/M transition leading to growth arrest and apoptosis; (b) by decreasing the expression of mitotic kinase cdc2, mitotic phosphatase cdc25c, mitotic cyclin B1, and apoptotic factors pro-caspases-3 and -9; and (c) increasing the levels of mitochondrial apoptotic-related proteins, intracellular levels of reactive oxygen species, and nitric oxide. We further examined the phosphorylation of extracellular signal-related kinase (ERK 1/2), c-Jun N-terminal kinase, and p-38 mitogen-activated protein kinases (MAPKs) and found they all were significantly increased in HepG2 cells treated with calycopterin. Interestingly, we discovered that treated cells had significantly lower Akt phosphorylation. This mode of action for calycopterin in our study provides strong support that inhibition of PI3K/Akt and activation of MAPKs are pivotal in G2/M cell cycle arrest and apoptosis of human hepatocarcinoma cells mediated by calycopterin.     

Effects of catechins on Agrobacterium-mediated genetic transformation of Camellia sinensis

In this study, recalcitrance of tea plant ( Camellia sinensis) to Agrobacterium-mediated genetic transformation was investigated with an emphasis on specialized compounds in tea. Chemical constituents in tea leaves and calli were extracted into liquid Luria–Bertani (LB) medium to determine their biological activities on Agrobacterium growth, virulence, and plant transformation efficiency. Compared to the control Agrobacterium grown in LB medium, tea leaf extract containing 6.5 mg mL^?1 catechins resulted in an 84.6 % reduction of Agrobacterium growth, a 73–36 % suppression of expression for the six virulence (vir) genes, browning of infected tobacco explant wounds, and an absence of transient or stable transformation events. Tea callus extract, containing 0.22 mg mL^?1 catechins, did not significantly affect Agrobacterium growth or tobacco transgenic hairy root generation, whereas it enhanced the expression of some vir genes. Treatment with authentic catechin mixtures (other than caffeine) dissolved in LB resulted in suppression of Agrobacterium growth, vir gene expression, and tobacco transformation efficiency. Our data suggest that catechins are the key active constituents in tea leaves. Transient transformation efficiencies of tea leaves were much lower than those of tobacco leaves as indicated by the GUS (β-glucuronidase) assay, probably a result of inhibition by the catechins present in tea leaves. Lower transformation efficiencies of tea calli suggested that additional plant factor(s) might also exert inhibitory effects on tea plant transformation. Agrobacterium rhizogenes ATCC 15834 induced transgenic roots from the tea explants with 15–20 % efficiency. Our data suggested catechins inhibition of tea gene transformation could be overcome by using optimized strains of Agrobacterium.     

Effects of Inhibitors of Myosin Light Chain Kinase and Other Protein Kinases on the First Cell Division of Sea Urchin Eggs

We investigated effects of protein kinase inhibitors on the first cell division in sea urchin eggs on the assumption that phosphorylation of myosin is requisite for the formation and/or the contraction of the contractile ring. ML-7 or ML-9, which inhibits myosin light chain kinase (MLCK), inhibited cytokinesis with a half maximal inhibition at 0.1–0.2 mM. The nuclear division was accomplished normally at 0.2–0.25 mM where the cytokinesis was completely blocked. Fluorescent staining of actin filaments with rhodamine-labeled phalloidin revealed that the contractile ring was not formed in the cleavage-inhibited eggs. H-7 which inhibits cAMP-dependent protein kinase, cGMP-dependent protein kinase and protein kinase C arrested the process of the division at mid-cleavage at 0.25–0.3 mM and at metaphase or anaphase at 0.5 mM. H-8 and HA1004, which inhibit cAMP-dependent and cGMP-dependent protein kinases did not show significant effect at millimolar order. In the presence of micromolar concentrations of staurosporine which preferentially inhibits protein kinase C and MLCK small mitotic apparatuses were formed, in which chromosomes did not form the metaphase plate. The role of phosphorylation in the cell division is discussed.     

Adiponectin-Induced Antitumor Activity on Prostatic Cancers through Inhibiting Proliferation

Adiponectin, an adipose tissue-derived hormone, has been studied intensively for the past decade because of its anti-inflammatory, anti-atherogenic, and anti-diabetic properties. Recent advances suggest that adiponectin also plays an important role in the development and progression of various cancers. Accumulating evidence suggests that adiponectin may have an important protective role in carcinogenesis. Adiponectin circulates at high concentrations in human plasma. Plasma levels of adiponectin are approximately 50 % lower in obese than in lean subjects. An association between low plasma levels of adiponectin and higher risk of developing prostate and other cancers was recently reported. Obesity and overweight have also been associated with increased mortality from cancer. To test the hypothesis that adiponectin exerts direct antiproliferative and/or pro-apoptotic effects on cancer cells, we used the PC-3 human prostate adenocarcinoma cell line. The proliferation rate of the PC-3 cells was measured using the MTT method, and apoptosis was examined by quantifying the DNA fragmentation using an ELISA assay. In addition, adiponectin receptor 1 (AdipoR1) and AdipoR2 mRNA expression was detected using RT-PCR. Adiponectin diminished the proliferation rate of PC-3 cells; this effect was significant after 48–96 h of treatment. The presence of receptor expression suggested that the effect of adiponectin on cell proliferation was most likely specific and adiponectin receptor-mediated. Adiponectin induced no apoptosis of PC-3 cells over 48 h. We conclude that adiponectin inhibits proliferation but causes no apoptosis of PC-3 prostate cancer cells.     

Nativity of the macromolecule of isologous DNA as a condition for its reparative effect on radiation damage

The effect of isologous DNA on the course of postirradiation reparation of meristematic cells ofVicia faba primary roots was studied in detail. A considerable interest was devoted to determinations of fundamental qualitative and quantitative conditions of the above effect of isologous DNA. Main criteria of the effect were both mitotic activity of irradiated cellular population and dynamics of chromosome aberrations induced by radiation. One set of experiments compared the course of reparation as occurred in regard to applied dose of ionizing radiation in native isologous DNA, DNA denaturated by heat and degraded by DNAase, and post-irradiation reparation of induced damages was favorably affected by native isologous DNA only. Another set of results evaluated the dependence of positive reparative effect of native isologous DNA on the length of the molecule demonstrating that in the process of reparation the presence of a complete DNA macromolecule was not essential. The last experimental group was focused on observations on the dependence of the rate of native isologous DNA effect on concentration of applied solution of the macromolecule.     

Polysomes from expanded tobacco leaves

The isolation of intact polysomes from leaves of tobacco (Nicotiana tabacum L.) is dependent on the age and state of development of leaves. Undegraded polysomes from young leaves in the early stages of expansion can be isolated easily by extracting the leaves in ice-cold extraction buffer (200 mM tris(hydroxymethyl)aminomethylmethane(Tris)-HCl, pH 9.0; 400 mM KCl; 200 mM sucrose; 35 mM MgCl₂). Medium-size leaves give best yields of undegraded polysomes when extractions are carried out in the above buffer and in the presence of ethyleneglycol-bis-(β-amino-ethyl ether)-N,N′-tetracetic acid (EGTA) and mercaptoethanol. Isolation of polysomes from large, nearly fully expanded (mature) leaves requires all of the above plus diethyldithiocarbamate (DIECA) in the extraction medium. An extraction medium consisting of 25 mM EGTA, 0.01 M mercaptoethanol, 25 mM DIECA and 0.5% of the nonionic detergent, Nonidet-P40 (NP 40) was found to be very suitable for extraction of polysomes from all developmental stages of leaves. The polysomes extracted in the above medium showed active translation of protein in the wheat-germ in-vitro protein-synthesizing system. The translational products were similar when translations were carried out directly with polysomes or polysomal RNA, or polysomal poly(A)⁺ RNA from tobacco leaves. Poly(A)^? polysomal RNA was a poor template in the in-vitro wheat-germ system.     

Does light spectral quality affect survival and regeneration of potato (Solanum tuberosum L.) shoot tips after cryopreservation?

Cryopreservation, the storage of germplasm at ultra-low temperature is the most reliable tool for long-term preservation of plant genetic resources. Cryopreservation techniques are widely applied but the effect of light spectra on plant recovery after cryopreservation is largely unknown. Therefore, we investigated the effect of different light spectral qualities on survival and regeneration of shoot tips of potato (Solanum tuberosum L.) cultivars Agrie Dzeltenie, Maret, Bintje, Désirée and Anti cryopreserved by the DMSO-droplet method. Prior to cryopreservation, the plants were stored under cool white fluorescent light (CW). Post-cryopreservation, the plants were allowed to regenerate under six different light qualities: CW, warm white light (HQI), blue LEDs (B), red LEDs (R), red with 10 % of blue (RB) and RBF - red with 10 % of blue with addition of 20 % of far-red LEDs. The light spectral quality had a significant effect on the survival and regeneration of potato shoot tips after cryopreservation. The combination of red light with 10 % of blue (RB) doubled the regeneration percentage of all cultivars, whereas red light (R) was not suitable for regeneration after cryopreservation. Specifically, the regeneration percentages were increased in RB compared to CW from 25.5 to 52.6 % for ‘Agrie Dzeltenie’, 25.0–43.6 % for ‘Maret’, 8.1–26.1 % for ‘Bintje’, 0.0–17.1 % for ‘Anti’ and 18.2–36.6 % for ‘Désirée‘. Therefore, the modification of light spectra during the recovery phase is a promising tool for increasing the regeneration of potato shoot tips after cryopreservation.     

The sequence and duration of mitotic cycles in the apical root meristem ofVicia faba l

A study was made on the mitotic cycle times in meristematic cells of Vicia faba root tips and on the relationship between their duration and the position of a certain cell in the column of proliferating cells. For the demonstration of the sequence and duration of mitotic oycles a single-column model was used. The results of experiments show that the great variability in the duration of mitotic cycles (from 12 to l20 h)is the result of a different program of the apical meristem cells. The long duration of the cycle of initials corresponds to the sum of cycle times of their descendants.