Formation and division of giant mitochondria during the cell cycle of Euglena gracilis Z in synchronous culture I. Some characteristics of changes in the morphology of mitochondria and oxygen-uptake activity of cells

Changes in the morphology of mitochondria of Euglena gracilisZ cells were followed with an electron microscope during thecell cycle in a synchronous culture under photoautotrophic conditions.Giant mitochondria were temporarily formed, most probably byfusion of smaller forms, in the cells at an intermediate stagein the growth phase of the cell cycle. Formation of the giantmitochondria was accompanied by a striking decrease in the oxygen-uptakeactivity of the cells, and the division of giant mitochondriainto smaller forms by a re-increase in the activity. ¹ This work was reported in part at the 28th Annual Meetingof the Japanese Society of Electron Microscopy, May 1972. (Received November 8, 1973; )     

Interspecific and intraspecific mitochondria-induced cytoplasmic transformation in yeasts

Spheroplasts from respiratory-deficient (rho^–) yeastswere transformed into rho⁺ cells by incubation with mitochondriaprepared from respiratory-sufficient (rho+) yeasts in the presenceof polyethylene glycol 4000 and CaCl₂. Spheroplasts of buddingyeast rho^– strains were also transformed into rho⁺ cellsby treatment with mitochondria prepared from heterospecificbudding or fission yeast strains. All the transformed regeneratantsyielded rho⁺ yeast colonies which bore chromosomal genetic characteristicsof the spheroplasts used and cytoplasmic genetic characteristicsof the mitochondria used. These indicate that mitochondrialgenes or mitochondria themselves introduced by the incubationfunctioned normally in the rho^– cells regardless of thespecies difference of the recipient spheroplasts. ¹A preliminary report appeared in ref. 17. (Received October 31, 1978; )     

The annual cycle of planktonic ciliates in nearshore waters at Signy Island, Antarctica

The abundance and biomass of marine planktonic ciliates in BorgeBay, Signy Island, were determined at monthly intervals betweenApril 1990 and June 1991. At least 24 different ciliate taxawere recorded from samples preserved in Lugol's iodine, includingthe tintinnids Codonellopsis balechi, Cymalocylis convallaria,Laackmaniella naviculaefera and Salpingella sp., and the aloricatetaxa Didinium sp. and Mesodinium rubrum. Ciliate abundance andbiomass exhibited a clear seasonal cycle with high values duringthe austral summer and low values in the austral winter. Abundanceranged from 0.3 10³l^–1 in September to 2.3 10³l^–1in January, while biomass ranged from 0.5 µg C l^–1in October to 12.6 µg C l^–1 in December. Small ciliatesdominated abundance throughout the year, and biomass duringwinter. Larger ciliates contributed most to biomass during summer.Aloricate ciliates were common throughout the year, while tintinnidscontributed substantially to abundance and biomass only duringsummer. Salpingella sp. was the commonest tintinnid, but C.convallariacontributed most to tintinnid biomass. The seasonal patternof ciliate abundance and biomass matched that of chlorophylla concentration and bacterial biomass, suggesting tight trophiccoupling between ciliates and other components of the pelagicmicrobial community. ¹Present address: Scott Polar Research Institute, Universityof Cambridge, Lensfield Road, Cambridge CB2 1ER, UK     

Synthetic rates of chloroplast and cytoplasmic ribosomal ribonucleic acids during the cell cycle of Chlorella

By feeding radioisotopic precursors of RNA ([5-³H]uracil and[5-³H]uridine) to cells of Chlorella ellipsoidea at variousstages in the cell cycle effected by autotrophic synchronousculture, we examined synthetic rates of the chloroplast andthe cytoplasmic ribosomal ribonucleic acids (chl-rRNA and cyt-rRNA,respectively). The net incorporation of the precursors intochl-rRNA was higher than that into cyt-rRNA in the early stagesof the cell cycle, and vice versa in the late stages. The specificactivity of chl-rRNA was extremely high, and this phenomenonwas likely to be intrinsic to small cells at the start of thecell cycle under autotrophic conditions, namely, cell-cyclestagespecific. We conclude that algal cells grown autotrophicallysynthesize chl-rRNA at a distinctly higher rate than cyt-rRNAin the early stages of the cell cycle. (Received July 21, 1978; )     

Electron microscope studies of the vegetative cellular life cycle of Chlamydomonas reinhardi Dangeard in synchronous culture II. Association of mitochondria and the chloroplast at an early developmental stage

At an intermediate stage in the growth phase of the cell cycleof Chlamydomonas reinhardi, mitochondria and the chloroplastassociated with each other in a characteristic manner. Aftertemporary association with the chloroplast, mitochondria seemto fuse into giant forms as reported previously. ¹ This work was reported in part at the 27th Annual Meetingof the Japanese Society of Electron Microscopy, May 1971. (Received June 7, 1972; )     

Mitochondrial alterations in human gastric carcinoma cell line

We compared mitochondrial function, morphology, and proteome in the rat normal gastric cell line RGM-1 and the human gastric cancer cell line AGS. Total numbers and cross-sectional sizes of mitochondria were smaller in AGS cells. Mitochondria in AGS cells were deformed and consumed less oxygen. Confocal microscopy indicated that the mitochondrial inner membrane potential was hyperpolarized and the mitochondrial Ca²⁺ concentration was elevated in AGS cells. Interestingly, two-dimensional electrophoresis proteomics on the mitochondria-enriched fraction revealed high expression of four mitochondrial proteins in AGS cells: ubiquinol-cytochrome c reductase, mitochondrial short-chain enoyl-coenzyme A hydratase-1, heat shock protein 60, and mitochondria elongation factor Tu. The results provide clues as to the mechanism of the mitochondrial changes in cancer at the protein level and may serve as potential cancer biomarkers in mitochondria. two-dimensional gel electrophoresis proteomics; biomarker; cancer     

Organic Acid Metabolism in Cellular Organelles of Vigna cylindrica (Mitorisasage) Cotyledons

In starchy cotyledons of Vigna cylindrica (L.) Skeels (Mitorisasage)during seed germination, the enzymes of the glyoxylate cyclewere located in the matrix of mitochondria. Glyoxysomes wereabsent. The glyoxylate cycle in the mitochondria supplies organicacids to the tricarboxylic acid cycle. In mitochondria, isocitratelyase activity was much higher than malate synthase activity.Part of the glyoxylate thus produced in mitochondria may benonenzymatically converted to formate by H₂O₂ and the formatethen converted to CO₂ by peroxidase or by formic dehydrogenase.The activity of superoxide dismutase, which supplies H₂O₂, washigher in mitochondria than in peroxisomes. The remaining glyoxylatein mitochondria is possibly converted to glycine by alanine-glyoxylateaminotransferase or transported to peroxisomes which lackedisocitrate lyase activity but had high malate synthase activity.In peroxisomes, glyoxylate may be also produced from urate,as is suggested by the fairly high activities of uricase, allantoinaseand allantoicase. Judging from the enzyme distribution, Vignaperoxisomes should be capable of producing malate, oxalacetate,citrate, isocitrate and a-ketoglutarate. ¹Present address: Department of Horticulture, College of Agricultureand Animal Science, Yeugnam University, Gyeongsan 632, Korea. (Received May 27, 1987; Accepted October 7, 1987)     

Effects of Acriflavine on the Formation of the Plasma Membrane of Escherichia coli

When cells of acriflavine-sensitive (acrA) and acriflavine-resistant(acrA⁺) Escherichia coli K-12 strains were treated with a ratherhigh concentration (100 µg ml^-1) of acriflavine in mediumthat had been adjusted to pH 8.1, distinct whirlpool-like structuresderived from the plasma membrane appeared not only in the acrAcells but also in the acrA⁺ cells. Chemical analysis was performedto determine the lipid composition of the cells by thin-layerchromatography on silica gel and gas-liquid chromatography.The amount of total fatty acids was significantly higher inthe acrA cells than in the acrA⁺ cells, when cells were culturedin the presence of acriflavine. This difference seems to becaused by the greater accumulation of unsaturated fatty acids(palmitoleic and cis-vaccenic acid) in the acrA mutant cellsthan in the acrA⁺ cells and by the acceleration of this accumulationas a result of the presence of the dye. A comparison of phospholipidcontents between the acrA and acrA⁺ cells cultured under acriflavine-freeconditions showed that the former cells contained more phosphatidylethanolamine(PE) and, in particular, more cardiolipin (CL) than the lattercells. However, the situation was reversed in the case of phosphatidylglycerol(PG). Addition of acriflavine to the medium led to a markedincrease in levels of PE and CL in both acrA and acrA⁺ cellsbut an increase in levels of PG was found only in the acrA⁺cells. (Received October 13, 1992; Accepted May 31, 1993)     

Tricarboxylic Acid Cycle Activity in Mitochondria from Soybean Nodules and Cotyledons

Infected cells of soybean (Glycine max) nodules require NADH,ATP, and 2-oxoglutarate for ammonia assimilation. The role ofmitochondria in nodule metabolism was investigated by determiningtheir respiratory properties and comparing them with cotyledonmitochondria. Nodule mitochondria oxidized malate at a ratetwice that of any other NAD-linked substrate although theirmalic enzyme activity was very low, accounting for only 12%of malate oxidation at pH 6.4 compared to 56% for cotyledonmitochondria. The reduction of NAD⁺ in mitochondria of noduleson adding malate (determined by fluorescence) was rapid andreached a stable level, whereas in cotyledon mitochondria theNADH level declined rapidly as oxaloacetate accumulated. Anoxaloacetate scavenging system in the mitochondrial reactionmedium increased malate oxidation by cotyledon mitochondria4-fold, but increased that of nodule mitochondria by less than50%. This demonstrates that the efflux of oxaloacetate by theoxaloacetate carrier is highly regulated by the extra-mitochondrialoxaloacetate concentration in cotyledon mitochondria comparedto nodule mitochondria. The activity of TCA cycle enzymes, exceptmalate and succinate dehydrogenases, was low in nodule mitochondria.Their oxaloacetate export during malate oxidation was rapid.The aspartate amino transferase activity associated with nodulemitochondria was sufficient to account for significant formationof 2-oxoglutarate from oxaloacetate and glutamate. These resultssuggest that nodule mitochondria operate a truncated form ofthe TCA cycle and primarily oxidize malate to provide oxaloacetateand ATP for NH₃ assimilation. Key words: Glycine max (L.), nitrogen fixation, gluconeogenesis, respiration     

Studies on frost hardiness in Chlorella ellipsoidea III. Changes in O2 uptake and evolution during hardening and after freeze-thawing

Chlorella ellipsoidea cells at an intermediate stage in theripening phase of the cell cycle were hardened at 3?C. Oligomycin(OGM) and 3-(3,4-dichiorophenyl)-1,1-dimethylurea (DCMU) addedduring hardening in the light inhibited the development of frosthardiness, suggesting that mitochondria and chloroplasts wereinvolved in the hardening process. The O₂-uptake activity in unhardened cells increased duringhardening in the light while the O²-evolution activity decreased,when these activities were measured at 25?C. The increase inO₂ uptake was suppressed by OGM and DCMU and the decrease inO₂ evolution was stimulated by OGM. While the algal hardinessin the dark was very limited, the addition of glucose duringhardening in the dark caused a remarkable development of frosthardiness. These results suggest that mitochondria and chloroplastsclosely interact at low temperature, and the former plays aprincipal role in the hardening process and the latter servesas substrate-donor in the light. The O₂ evolution in cells which survived freezing was remarkablydecreased by freeze-thawing while the O₂ uptake was hardly affected.The freeze-injured chloroplasts were repaired during the followingincubation. OGM inhibited the repair of freeze-injured chloroplasts.From the results, mitochondria seem to change their membranesinto a structure hardier than chloroplasts, and ATP synthesizedby mitochondria seems to be essential for the repair of freeze-injuredchloroplasts. ¹ Present address: Department of Public Health, Faculty of Medicine,Kyushu University, Maidashi 3-1-1, Higashiku, Fukuoka 812, Japan. (Received November 9, 1977; )     

DNA damage-induced [Zn(2+)](i) transients: correlation with cell cycle arrest and apoptosis in lymphoma cells

Reactive changes in free intracellularzinc cation concentration ([Zn²⁺]_i) weremonitored, using the fluorescent probe Zinquin, in human lymphoma cells exposed to the DNA-damaging agent VP-16. Two-photon excitation microscopy showed that Zinquin-Zn²⁺ formscomplexes in cytoplasmic vesicles. [Zn²⁺]_iincreased in both p53^wt (wild type) and p53^mut(mutant) cells after exposure to low drug doses. In p53^mutcells noncompetent for DNA damage-induced apoptosis, elevated [Zn²⁺]_i was maintained at higher drug doses,unlike competent p53^wt cells that showed a collapse of thetransient before apoptosis. In p53^wt cells, the[Zn²⁺]_i rise paralleled an increase in p53and bax-to-bcl-2 ratio but preceded an increase in p21^WAF1,active cell cycle arrest in G₂, or nuclear fragmentation.Reducing [Zn²⁺]_i, usingN,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, caused rapid apoptosis in both p53^wt andp53^mut cells, although cotreatment with VP-16 exacerbatedapoptosis only in p53^wt cells. This may reflectchanged thresholds for proapoptotic caspase-3 activation incompetent cells. We conclude that the DNA damage-induced transient isp53-independent up to a damage threshold, beyond which competent cellsreduce [Zn²⁺]_i before apoptosis.Early stress responses in p53^wt cells take place in anenvironment of enhanced Zn²⁺ availability.

     

Vertical distribution, life cycle and production of the chaetognath Sagitta crassa in Tokyo Bay, Japan

The daytime vertical distribution of Sagiita crassa in TokyoBay was examined from February 13, 1988 to February 20, 1989.High densities of larger-size chaetognaths were found near thesea bottom, whereas the smaller animals tended to inhabit theupper layers. This feature of distribution is discussed in relationto the distribution of their main food organisms, e g. Pseudodiaptomusmarinus, Acartia omoru, Centropages abdomialis and Oithona davisae.The two periods of replacement of two morphs were confirmedby the variation only in mean body length of this chaetognath,unlike the previous authors who made additional morphologicalobservations. It was hypothesized that S.crassa has at leastfive generations Two generations, including mostly the largerforms, had higher growth rates than the generation consistingmainly of the small form. Yearly respiration of S.crassa was8.2 g C m^–Abstract. Yearly production of this animal wasestimated to be 3.8 g C m^–. A feeding estimate revealedthat chaetognaths require a prey production of 13.1 g C m^–year^–1. The impact of this chaetognath on the prey populationin Tokyo Bay and the propriety of an estimated value of annualproduction of S crassa is discussed.     

Effects of the ovarian cycle on sympathetic neural outflow during static exercise

We comparedreflex responses to static handgrip at 30% maximal voluntarycontraction (MVC) in 10 women (mean age 24.1 ± 1.7 yr) during twophases of their ovarian cycle: the menstrual phase (days 1-4) and the follicularphase (days10-12). Changes in muscle sympathetic nerve activity (MSNA; microneurography) in response tostatic exercise were greater during the menstrual compared withfollicular phase (phase effect P = 0.01). Levels of estrogen were less during the menstrual phase(75 ± 5.5 vs. 116 ± 9.6 pg/ml, days 1-4 vs.days 10-12;P = 0.002). Generated tension did not explain differences in MSNA responses (MVC: 29.3 ± 1.3 vs. 28.2 ± 1.5 kg, days 1-4 vs.days 10-12;P = 0.13). In a group of experiments with the use of ³¹P-NMRspectroscopy, no phase effect was observed forH⁺ andH₂PO₄ concentrations(n = 5). During an ischemicrhythmic handgrip paradigm (20% MVC), a phase effect was notobserved for MSNA or H⁺ orH₂PO₄ concentrations,suggesting that blood flow was necessary for the expression of thecycle-related effect. The present studies suggest that, during statichandgrip exercise, MSNA is increased during the menstrual compared withthe follicular phase of the ovarian cycle.

     

The seasonal abundance of the phototrophic ciliate Mesodinium rubrum in Southampton Water, England

The abundance of the marine phototrophic planktonic ciliateMesodinium rubrum was monitored throughout an annual cycle attwo stations in the Southampton Water estuary. Seasonal changesin the concentration of nitrate, ammonia and phosphate weremonitored both at the inner estuary station (NW Netley) andouter estuary station (Calshot). Nutrient levels in the winterwere similar at both stations, and were diminished during sequentialdiatom blooms dominated initially by Sketetonema costatum andthen by Rhizosolenia dclicatula. Nitrate was reduced to a seasonalminimum in the outer estuary following these spring diatom blooms,but in the inner estuary was sustained >500 µg I^–1until the onset of the M.rubrum bloom. During the developmentof a visible red tide of M.rubrum in June/July at NW Netley,nutrient concentrations were considerably reduced. Cell numbersof M.rubrum varied between 2 and 3 cells ml^– during winterto >400 cells ml^–1 during the bloom at NW Netley, whereasat Calshot cell abundance did not increase above 25 cells ml^–1at any time of the year. At NW Netley, dense accumulations ofthe ciliate occurred over restricted depth intervals duringthe bloom and possible factors influencing the observed verticaldistribution of cells are considered. ¹Present address: Biology Department, Faculty of Science, AddisAbaba University, PO Box 1176, Addis Ababa, Ethiopia     

Studies of mitochondria1 migration in Physarum polycephalum I. Reversible induction of mitochondrial migration and its inhibition by cytochalasin B

Mitochondrial movement in a microplasmodium of Physarum polycephalumwas studied by light microscopy using acid fuchsin stainingtechniques. The mitochondria were dispersed almost evenly inthe microplasmodium of Physarum polycephalum in highly aerobiccultures but when the microplasmodia were transferred from thehighly aerobic culture to less aerobic culture, the mitochondriamigrated toward the peripheral area of the microplasmodium andlocated themselves on a peripheral cytoplasm. Once this peripherallocalization was established in the less aerobic culture, shiftto a highly aerobic culture induced a reversion. This mitochondrialmovement was reversibly inhibited by cytochalasin B at a concentrationof 10^–4;M, suggesting that contractile proteins are essentialfor this mitochondrial migration. (Received October 13, 1979; )     

Cell Cycle Timing of Replication of the Nuclear Gene Encoding Chloroplastic NADP-Specific Glutamate Dehydrogenase Isoenzymes in Chlorella sorokiniana

In synchronized Chlorella sorokiniana cells, the NH₄⁺ inducibleNADP-specific glutamate dehydrogenase enzyme (NADP-GDH) accumulatedin a linear manner throughout the first cell cycle. Early inthe following second cell cycle, an increase in its rate ofaccumulation occurred that was proportional to the increasein total cellular DNA in the previous cell cycle. In synchronizedbacterial cells, increases in rate of linear accumulation ofinducible enzymes coincide with the time of replication of theirstructural genes. To determine whether the rate change in NADPGDHaccumulation resulted from a delay in replication of its nuclearstructural gene (gdhN) in fully induced C. sorokiniana cells,the cell cycle timing of replication of this gene was comparedto that of another nuclear gene, nitrate reductase (nia), andof a chloroplast gene, ribulose bisphosphate carboxylase large-subunit(rbcL), in synchronized cells cultured in NH₄⁺ or NO₃^–(uninduced) medium. The gdhN and nia genes replicated withinthe period of nDNA synthesis and rbcL within the period of ctDNAsynthesis in cells growing in either nitrogen source. Therefore,the delayed rate change in enzyme accumulation results froma process that regulates expression of the gdhN gene after itsreplication. (Received July 16, 1994; Accepted November 28, 1994)     

Neuromuscular fatigue after maximal stretch-shortening cycle exercise

Strojnik, V., and P. V. Komi. Neuromuscular fatigueafter maximal stretch-shortening cycle exercise. J. Appl. Physiol. 84(1): 344-350, 1998.To examinesome possible sites of fatigue during short-lasting maximally intensivestretch-shortening cycle exercise, drop jumps on an inclined sledgeapparatus were analyzed. Twelve healthy volunteers performed jumpsuntil they were unable to maintain jumping height >90% of theirmaximum. After the workout, the increases in the blood lactateconcentration and serum creatine kinase activation were statisticallysignificant (P < 0.001 and P < 0.05, respectively) but rathersmall in physiological terms. The major changes after the workout wereas follows: the single twitch was characterized by smaller peak torque(P < 0.05) and shorter time to peak(P < 0.05) and half-relaxation time(P < 0.01). The double-twitch torqueremained at the same level (P > 0.05), but with a steeper maximal slope of torque rise(P < 0.05); during 20- and 100-Hzstimulation the torque declined (both P < 0.01) and the maximal voluntarytorque changed nonsignificantly but with a smaller maximal slope oftorque rise (P < 0.01) and a higheractivation level (P < 0.05),accompanied by an increased electromyogram amplitude. These findingsindicate that the muscle response after the short-lasting consecutivemaximum jumps on the sledge apparatus may involve two distinctmechanisms acting in opposite directions:1) The contractile mechanism seemsto be potentiated through a shorterCa²⁺ transient and fastercross-bridge cycling, as implied by twitch changes.2) High-frequency action potentialpropagation shows an impairment, which is suggested as the possibledominant reason for fatigue in exercise of this type.

     

Correlation between the Starch Level and the Rate of Starch Synthesis during the Developmental Cycle of Chlorella ellipsoidea

The starch content as well as the rate of photosynthetic starchformation in Chlorella ellipsoidea was studied throughout thecell cycle. The starch level in Chlorella cells rose markedlyduring the growing phase in the light, but it started to decreaseafter about 14 to 16 hr regardless of illumination. The rateof starch synthesis, measured by the level of ¹⁴C-incorporationinto starch, increased rapidly in the growing phase until 10hr, and decreased promptly thereafter, even in the light. From these results, it was concluded that both the cellularlevel of starch and the rate of starch synthesis were a functionnot only of the light regime, but also of the stage of celldevelopment. ³ Present address: Yamada High School, Yamada-machi, Iwate Pref.028-13, Japan. (Received October 12, 1981; Accepted May 12, 1982)