The "Point of no Return" Concept in Cell Division. The Effects of Some Metabolic Inhibitors on Synchronized Chlorella pyrenoidosa

The coarse of growth and cell division in synchronized cultures of Chlorella pyrenoidosa was studied after the addition of metabolic inhibitors at differing times during the cell cycle (14 h light - 10 h darkness with nitrate as nitrogen source. 12 h light: 12 h darkness with urea as nitrogen source). Dinitrophenol (DNP) added to a final concentration of 0.3 mM at any time in the synchronization cycle, the compound remaining in the suspension from the time of addition to the end of the dark period, inhibited spore formation completely. Growth measured as increase in cell volume was less sensitive to the action of the inhibitor. Chloramphenicol (CAP) added dining the 0–5 h interval to a final concentration of 0.1 mM resulted in 80 per cent inhibition of cell division. Similar treatment started at successive times thereafter resulted in a gradual decrease of the inhibition. Treatment at the 14th hour and during the dark period did not affect the sporulation. Similar experiments with 0.9 mM puromycin added at various times during the illumination period gave almost complete inhibition of cell division, while the growth was reduced by only 25 per cent. para-Fluorophenylalanine (p-FPhe) at 3.3 × 10^?2 mM stopped cell division nearly completely irrespective of addition time in the light period. Addition during the dark period also prevented an increase in the number of tree cells. In this case about half of the cells produced spores which were not released. It is concluded that DNP inhibits all stages of preparation for cell division, as well as the division process itself. With CAP a genuine transition point of preparation for cell division was observed, although its interpretation as related to protein synthesis is somewhat uncertain. With puromycin and p-FPhe no transitions were observed.     

INTERACTIONS OF LIGHT/DARK CYCLES AND NITROGEN PULSES ON THE TIMING OF CELL DIVISION IN THE NITROGEN-LIMITED MARINE DIATOM CYLINDROTHECA FUSIFORMIS (BACILLARIOPHYCEAE)1

Cell division in most eukaryotic algae grown on alternating periods of light and dark (LD) is synchronized or phased so that cell division occurs only during a restricted portion of the LD cycle. However, the phase angle of the cell division gate, the time of division relative to the beginning of the light period, is known to be affected by growth conditions such as nutrient status and temperature. In this study, it is shown that the phase angle of cell division in a diatom, Cylindrotheca fusiformis Reimann and Lewin, is affected by the N-limited growth rate; cell division occurred later in the dark period (12:12 h LD cycle) when the growth rate was infradian (D = 0.42 d^?1) than when it was ultradian (D = 1.0 d^?1). Nitrogen-pulses did not affect the phase angle of the division gate, but could shift the time of peak cell division activity within the division gate. The effects, if any, of N-pulses were dependent upon the growth rate and the time of day that the pulses were administered. These responses indicate that the timing of cell division in this diatom is not determined solely by the zeitgeber from the LD cycle, but rather that a LD cycle control mechanism and a N-mediated control mechanism are both involved and are somewhat interdependent. In addition, an increase in protein was observed immediately after administering a N-pulse to C. fusiformis in the ultradian growth mode indicating that the accumulation of protein can be uncoupled from the cell division cycle.     

THE PRODUCTION OF EXTRACELLULAR POLYSACCHARIDE BY THE UNICELLULAR RED ALGA PORPHYRIDIUM AERUGINEUM1,2

The unicellular red alga Porphyridium aerugineum was shown to be encapsulated by an amorphous, water-soluble, polyanionic polysaccharide of high molecular weight. The encapsulating polysaccharide is qualitatively identical with polysaccharide found dissolved in large quantity in the culture medium. The kinetics of extracellular polysaccharide production as a function of cell age was studied. Rates of production (on a per cell basis) of both encapsulating and dissolved polysaccharides are greatest in stationary phase light-grown cultures. Dissolved polysaccharide was quantitatively isolated by precipitation with cetyl pyridinium chloride, conversion to the calcium salt, and reprecipitation with ethanol. The procedure yields a spectrally pure product, which is composed of glucose, galactose, xylose, and 2 undetermined, sugar components, and has a sulfate content of 7.6% by weight. Electron microscopy of Porphyridium revealed that Golgi vesicles transport, polymerized polysaccharides to and through the cell membrane. Similar vesicles were observed in the multicellular Pseudogloiophloea, indicating that the Golgi complex plays a crucial role in the production of extracellular polysaccharides by the red algae. H¹⁴CO₃^- pulse-label experiments resulted in labeled extracellular polysaccharide in which all the constituent components contained ¹⁴C. Rates of excretion of polysaccharide were found, to follow a cyclic pattern, correlated generally with the division cycle, of the cell.     

Effect of Transverse Gravity Stimulation, Gibberellin and Indoleacetie Acid upon Polar Transport of IAAC14 in the Stem of Helianthus annuus

Using IAA^C14, polar transport has been studied in Helianthus annuus shoots in which stem elongation was inhibited by a transverse gravity stimulus induced by horizontal orientation of the plant with daily rotation. Marked inhibition of polar transport of IAA ^C14 occurred in the treated plants. A similar degree of inhibition occurred in the upper and lower halves of non-rotated horizontally trained shoots. Horizontal orientation of stem segments during the transport test had no consistent effect upon IAA transport. Pretreatment of erect plants with gibberellin greatly enhanced IAA^C14 transport and also reduced the inhibitory effect of horizontal orientation. Pretreatment of erect plants with non-radioactive IAA or ethylene inhibited transport of IAA ^C14 and induced the same symptoms in the shoot as the transverse gravity stimulus. The similarities between the response of the auxin transport system to gravity stimulation, IAA and ethylene are discussed.     

Silencing of the <Emphasis Type="Italic">CCNB1, Her2</Emphasis>, and <Emphasis Type="Italic">PKC</Emphasis> genes by small interfering RNA differently retards the division of different human cancer cell lines

Deregulation of genes encoding proteins responsible for cell cycle control frequently accompanies cell malignization and switches the cell program from differentiation and apoptosis to uncontrollable proliferation. We used siRNAs targeted to HER2, protein kinase C (PKC), and cyclin B1 (CCNB1) mRNAs to evaluate the therapeutic potential of the suppression of genes coding for key cell cycle regulators in different human cancer cells. The CCNB1, HER2, or PKC mRNA levels were efficiently reduced within 48 h after transfection with siCycB1, siHER2 or siPKC, respectively. Silencing of HER2, PKC, and CCNB1 substantially reduced the growth rates of all cell lines under study except HL-60 but did not affect cell death or apoptosis. The most pronounced inhibition of cell division was induced by siCycB1 in SK-N-MC cells and by siPKC in MCF-7 cells. We conclude that the selected siRNAs inhibit tumor cell division, and the investigated genes can be promising targets in cancer treatment.     

Change in Electrophoretic Pattern of Ribonuclease during Dormancy and Growth of Bird-cherry Buds

A morphactin formulation containing methyl-2-chloro-9-hydroxyfluorene-9-carboxylate as the major component caused abnormal stem growth in Pinus radiata D. Don seedlings when applied as a bark band. The banded region swelled due to increased cell division in the periderm and cambium. The abnormal stem development in treated trees did not cause a localized girdling effect. The morphactin treatment inhibited shoot elongation and root growth. Treated trees exposed to ¹⁴CO₂ translocated significantly less assimilate to the roots than did control trees although fixation of ¹⁴CO₂ by the shoots was not reduced. Label from a bark band of ¹⁴C-morphactin was rapidly translocated to the roots indicating that direct inhibition of root growth by the inhibitor probably occurred.     

Initial CD34+ cell-enrichment of cord blood determines hematopoietic stem/progenitor cell yield upon ex vivo expansion

Since umbilical cord blood (UCB), contains a limited hematopoietic stem/progenitor cells (HSC) number, successful expansion protocols are needed to overcome the hurdles associated with inadequate numbers of HSC collected for transplantation. UCB cultures were performed using a human stromal‐based serum‐free culture system to evaluate the effect of different initial CD34⁺ cell enrichments (Low: 24 ± 1.8%, Medium: 46 ± 2.6%, and High: 91 ± 1.5%) on the culture dynamics and outcome of HSC expansion. By combining PKH tracking dye with CD34⁺ and CD34⁺CD90⁺ expression, we have identified early activation of CD34 expression on CD34^? cells in Low and Medium conditions, prior to cell division (35 ± 4.7% and 55 ± 4.1% CD34⁺ cells at day 1, respectively), affecting proliferation/cell cycle status and ultimately determining CD34⁺/CD34⁺CD90⁺ cell yield (High: 14 ± 1.0/3.5 ± 1.4‐fold; Medium:22 ± 2.0/3.4 ± 1,0‐fold; Low:31 ± 3.0/4.4 ± 1.5‐fold) after a 7‐day expansion. Considering the potential benefits of using expanded UCB HSC in transplantation, here we quantified in single UCB units, the impact of using one/two immunomagnetic sorting cycles (corresponding to Medium and High initial progenitor content), and the average CD34⁺ cell recovery for each strategy, on overall CD34⁺ cell expansion. The higher cell recovery upon one sorting cycle lead to higher CD34⁺ cell numbers after 7 days of expansion (30 ± 2.0 vs. 13 ± 1.0 × 10⁶ cells). In particular, a high (>90%) initial progenitor content was not mandatory to successfully expand HSC, since cell populations with moderate levels of enrichment readily increased CD34 expression ex‐vivo, generating higher stem/progenitor cell yields. Overall, our findings stress the importance of establishing a balance between the cell proliferative potential and cell recovery upon purification, towards the efficient and cost‐effective expansion of HSC for cellular therapy. J. Cell. Biochem. 112: 1822–1831, 2011. © 2011 Wiley‐Liss, Inc.     

Regulation of root anaerobiosis and carbon translocation by light and root aeration in Isoetes alpinus

The activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15–0.35 × 10^?6 mol g^?1 fresh weight s^?1) over the entire plant depth range (3–7 m depth), and was intermediate to that developed in excised roots after 1‐week exposure to either dissolved oxygen at air‐saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot‐to‐root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of ¹⁴C‐labelled photo‐assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high ¹⁴C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning.     

Impaired cell proliferation in regenerating liver of 3 β-hydroxysterol Δ14-reductase (TM7SF2) knock-out mice

The liver is the most important organ in cholesterol metabolism, which is instrumental in regulating cell proliferation and differentiation. The gene Tm7sf2 codifies for 3 β-hydroxysterol-Δ¹⁴-reductase (C14-SR), an endoplasmic reticulum resident protein catalyzing the reduction of C14-unsaturated sterols during cholesterol biosynthesis from lanosterol. In this study we analyzed the role of C14-SR in vivo during cell proliferation by evaluating liver regeneration in Tm7sf2 knockout (KO) and wild-type (WT) mice. Tm7sf2 KO mice showed no alteration in cholesterol content. However, accumulation and delayed catabolism of hepatic triglycerides was observed, resulting in persistent steatosis at all times post hepatectomy. Moreover, delayed cell cycle progression to the G1/S phase was observed in Tm7sf2 KO mice, resulting in reduced cell division at the time points examined. This was associated to abnormal ER stress response, leading to alteration in p53 content and, consequently, induction of p21 expression in Tm7sf2 KO mice. In conclusion, our results indicate that Tm7sf2 deficiency during liver regeneration alters lipid metabolism and generates a stress condition, which, in turn, transiently unbalances hepatocytes cell cycle progression.     

Serine palmitoyltransferase inhibitor myriocin induces growth inhibition of B16F10 melanoma cells through G(2) /M phase arrest

Objectives: Melanoma is the most aggressive form of skin cancer, and it resists chemotherapy. Candidate drugs for effective anti‐cancer treatment have been sought from natural resources. Here, we have investigated anti‐proliferative activity of myriocin, serine palmitoyltransferase inhibitor, in the de novo sphingolipid pathway, and its mechanism in B16F10 melanoma cells. Material and methods: We assessed cell population growth by measuring cell numbers, DNA synthesis, cell cycle progression, and expression of cell cycle regulatory proteins. Ceramide, sphingomyelin, sphingosine and sphingosine‐1‐phosphate levels were analysed by HPLC. Results: Myriocin inhibited proliferation of melanoma cells and induced cell cycle arrest in the G₂/M phase. Expressions of cdc25C, cyclin B1 and cdc2 were decreased in the cells after exposure to myriocin, while expression of p53 and p21^waf1/cip1 was increased. Levels of ceramide, sphingomyelin, sphingosine and sphingosine‐1‐phosphate in myriocin‐treated cells after 24 h were reduced by approximately 86%, 57%, 75% and 38%, respectively, compared to levels in control cells. Conclusions: Our results suggest that inhibition of sphingolipid synthesis by myriocin in melanoma cells may inhibit expression of cdc25C or activate expression of p53 and p21^waf1/cip1, followed by inhibition of cyclin B1 and cdc2, resulting in G₂/M arrest of the cell cycle and cell population growth inhibition. Thus, modulation of sphingolipid metabolism by myriocin may be a potential target of mechanism‐based therapy for this type of skin cancer.     

Ammonium ion transport—a cause of cell death

Ammonium can be transported into the cell by ion pumps in the cytoplasmic membrane. Ammonia then diffuse out through the cell membrane. A futile cycle is created that results in cytoplasmic acidification and extracellular alkalinisation. Ammonium transport can be quantified by measuring the extracellular pH changes occurring in a cell suspension (in PBS) after addition of ammonium. By using this technique, in combination with specific inhibitors of various ion pumps, it was shown that ammonium ions are transported across the cytoplasmic membrane by the Na⁺K⁺2Cl^--cotransporter in both hybridoma and myeloma cells. Further, the Na⁺/H⁺ exchanger, which regulates intracellular pH by pumping out protons, was shown to be active during ammonium exposure. The viability of hybridoma cells suspended in PBS and exposed to NH _inf4 ^sup+ for only 90 min, was reduced by 11% (50% necrosis and 50% apoptosis). A control cell suspension did not loose viability during this time. Turning off the activity of the Na⁺/H⁺ exchanger (by amiloride) during ammonium exposure decreased viability further, while inhibiting transport itself (by bumetanide) restored viability to the same level as for the control experiment with bumetanide alone. These results show that one effect of ammonia/ammonium on cell physiology is specifically related to the inward transport of ammonium ions by membrane bound ion pumps.Abbreviations q _pH specific rate of pH increase (pH units per min and 10⁶ cells per ml)     

Oryzalin,a dinitroaniline herbicide,binds to plant tubulin and inhibits microtubule polymerization in vitro

The effects of oryzalin, a dinitroaniline herbicide, on chromosome behavior and on cellular microtubules (MTs) were examined by light microscopy and immunogold staining, respectively, in endosperm cells from Haemanthus katherinae Bak. Brief treatments with 1.0·10^-8 M oryzalin reduced markedly the migration rate of anaphase chromosomes and 1.0·10^-7 M oryzalin stopped migration abruptly. Oryzalin (1.0·10^-7 M) depolymerized MTs and prevented the polymerization of new MTs at all stages of the mitotic cycle. The chromosome condensation cycle was unaffected by oryzalin. Endothelial cells from the heart of Xenopus leavis showed no chromosomal or microtubular rearrangements after oryzalin treatment. The inhibition by oryzalin of the polymerization of tubulin isolated from cultured cells of Rosa sp. cv. Paul's scarlet was examined in vitro by turbidimetry, electron microscopy and polymer sedimentation analysis. Oryzalin inhibited the rapid phase of taxol-induced polymerization of rose MTs at 24°C with an apparent inhibition constant (K _i ) of 2.59·10⁶ M. Shorter and fewer MTs were formed with increasing oryzalin concentrations, and maximum inhibition of taxol-induced polymerization occurred at approx. 1:1 molar ratios of oryzalin and tubulin. Oryzalin partially depolymerized taxol-stabilized rose MTs. Ligand-binding experiments with [¹⁴C]oryzalin demonstrated the formation of a tubulin-oryzalin complex that was time- and pH-dependent. The tubulin-oryzalin interaction (24°C, pH 7.1) had an apparent affinity constant (K _app) of 1.19·10⁵ M^-1. Oryzalin did not inhibit taxol-induced polymerization of bovinebrain MTs and no appreciable binding of oryzalin to brain tubulin or other proteins was detected. The results demonstrate pharmacological differences between plant and animal tubulins and indicate that the most sensitive mode of action of the dinitroaniline herbicides is the direct poisoning of MT dynamics in cells of higher plants.Abbreviations MT microtubule - SIB sucrose isolation buffer - TO tubulin-oryzalin complex     

EFFECTS OF OXYGEN INDUCED CONVULSIONS ON THE UPTAKE OF ACETATE INTO RAT BRAIN LIPIDS1,2

Abstract— Rats were exposed to 5 atmospheres absolute of oxygen, and [1-¹⁴C]acetate was injected into the jugular vein either before or at the onset of electroencephalogram-defined convulsions. Levels of ¹⁴C observed 2.2 min after the injection were reduced in the total lipids of brain and elevated in the blood of convulsed rats when compared to the nonconvulsed controls. These differences between convulsed and nonconvulsed animals were less pronounced when measured 15 and 60 min after injection. Convulsions did not change the amount of ¹⁴C incorporated into the total lipids of plasma during the 60 min period studied. Six fractions obtained from total lipid extracts of brain by TEAE-cellulose showed similar ¹⁴C distributions in convulsed and control animals. The results suggest that oxygen-induced convulsions cause an impaired utilization of systemically administered acetate for fatty acid incorporation into the lipids of brain.     

RNA levels in colchicine-resistant mutants of Chlamydomonas reinhardi

A colchicine-resistant mutant of Chlamydomonas reinhardi (col⁻_{10, 12}) which appears blocked in the final stages of the cell division cycle is shown to have an RNA: protein ratio over four times that which is observed in wild-type cultures. This does not appear to be simply a consequence of reduced overall growth rate, because a comparable reduction in the overall growth rate of wild type by caffeine inhibition did not produce such a large rise in RNA content. The RNA levels in six other colchicine-resistant mutants, which have various abnormalities in colchicine-binding activity, has also been investigated. Two of them have elevated RNA levels.     

Modulation of photosynthesis and respiration in guard and mesophyll cell protoplasts by oxygen concentration

Stomatal movement is an energetic oxygen-requiring process. In the present study, the effect of oxygen concentration on mitochondrial respiratory activity and red-light-dependent photosynthetic oxygen evolution by Vicia faba and Brassica napus guard cell protoplasts was examined. Comparative measurements were made with mesophyll cell protoplasts isolated from the same species. At air saturated levels of dissolved oxygen in the protoplast suspension media, respiration rates by mesophyll protoplasts ranged from 6 to 10μmoles O₂ mg^?1 chl h^?1, while guard cell protoplasts respired at rates of 200–300 μmoles O₂ mg chl^?1 h^?1, depending on the species. Lowering the oxygen concentration below 50–60 mmol m^?3 resulted in a decrease in guard cell respiration rates, while rates by mesophyll cell protoplasts were reduced only at much lower concentrations of dissolved oxygen. Rates of photosynthesis in mesophyll cell protoplasts isolated from both species showed only a minor reduction in activity at low oxygen concentrations. In contrast, photosynthesis by guard cell protoplasts isolated from V. faba and B. napus decreased concomitantly with respiration. Oligomycin, an inhibitor of oxidative phos-phorylation, reduced photosynthesis in mesophyll cell protoplasts by 27–46% and in guard cell protoplasts by 51–58%. The reduction in both guard cell photosynthesis and respiration following exposure to low oxygen concentrations suggest close metabolic coupling between the two activities, possibly mediated by the availability of substrate for respiration associated with photosynthetic electron transport activity and subsequent export of redox equivalents.     

Exposure to hyperbaric oxygen induces cell cycle perturbation in prostate cancer cells

Summary Cell cycle synchronization of tumor cells by exposure to hyperbaric oxygenation (HBO) may increase the efficacy of chemotherapy or radiation by placing cells into a chemosensitive portion of the cycle. The purpose of the current study was to examine oxygen pressure-dependent relationships with respect to the cell cycle in prostate tumor cells in vitro. LNCaP cells were grown in an incubator at 21% O₂ and then exposed to 100% oxygen at pressures up to 6 atmospheres (atm) for 1.5 h. Cells were then returned to the incubator and evaluated for DNA content by propidium iodide and new DNA synthesis with a pulse-chase experiment. Cell cycle effects were evaluated by flow cytometry. Exposure to HBO increased the percentage of cells synthesizing new DNA in a dose-dependent fashion: 0 atm, 44%; 6 atm, 65%. Cells that synthesize new DNA accumulate in G₂/M as a function of partial pressure of oxygen. These results suggest that HBO induces cells to enter the cell cycle and accumulate in G₂/M. Cell cycle synchronization and entry of senescent cells into the cell cycle suggest that HBO may be a useful adjuvant to chemotherapy or radiation in the treatment of prostate cancer. There are two potential mechanisms of action that may make HBO efficacious in the treatment of prostate cancer. HBO may potentiate cancer chemotherapeutic agents that cause damage to DNA during DNA synthesis or HBO may inhibit cell division causing accumulation in G₂/M.     

Translocation of assimilates and phosphate in detached bean leaves

¹⁴C-assimilates were accumulated by the veins in the blades and transported basipetally into the petioles of detached leaves of Red Kidney bean (Phaseolus vulgaris L.). Neither process was greatly affected by mild moisture stress, age of fully enlarged leaves, or period in the dark prior to exposure to ¹⁴CO₂. However, both vein loading and transport into petioles were greatly reduced by oxygen deficiency. The basipetal transport of ³²PO₄ also did not appear to be greatly reduced by 6 or 8 days of darkness prior to the application of phosphate-³²P, followed by a transport period of 1 day in the dark. Endothall at 5 × 10⁻³ m was effective in stopping basipetal flow of ³²P. It is considered that transport in leaves may be powered by forces in the plasmodesmata of the cell walls between the border parenchyma and phloem.     

EFFECTS OF SMALL-SCALE TURBULENCE ON PHOTOSYNTHESIS,PIGMENTATION, CELL DIVISION,AND CELL SIZE IN THE MARINE DINOFLAGELLATE GOMAULAX POLYEDRA (DINOPHYCEAE)1

Several experiments were conducted to understand better the physiological mechanisms underlying growth inhibition of the dinoflagellate Gonyaulax polyedra Stein due to small-scale turbulence shear. To measure photosynthetic ¹⁴C uptake, a “phytoplankton wheel” device for rotating cultures in closed bottles was used. Turbulence was quantified biologically in the bottles by comparing growth inhibition with that in cultures with constant shear between a fixed cylinder and an outer concentric rotating cylinder (a stable Couette flow). At saturating irradiances, particulate photosynthesis (P_sat) or photosynthesis per unit chlorophyll (P^B_sat) were not inhibited completely at the highest turbulence level (26.6 rad.s^?1), and photosynthesis was less sensitive than growth. Photosynthesis per cell (P^C_sat) was increased by turbulence. In three experiments on the effects of turbulence on photosynthesis versus irradiance curves, the slope of the curve, α, for particulate photosynthesis at limiting irradiances did not change. Photosynthesis per unit chlorophyll per unit irradiance (α^B) decreased at high (but not intermediate) turbulence levels. Photosynthesis per cell per unit irradiance, α^C, increased with turbulence, suggesting an increase in photosynthetic efficiency in turbulent cultures. In two of the three experiments, respiration rates increased with turbulence, and in one experiment excretion of photosynthetically fixed ¹⁴C was not affected by motion. Ratios of accessory pigments to chlorophyll a did not change with turbulence, but pigments per cell and per dry weight increased with turbulence. These findings suggest little or no disruption of the photosynthetic apparatus. When turbulence was applied for 1 week, β-carotene increased while peridinin and diadinoxanthin decreased, suggesting inhibition of synthesis of these latter pigments by prolonged turbulence. Since cell numbers did not increase or decreased during turbulent 72–h incubations, cell division was inhibited and also the cells were very much enlarged. Increases in α^C per cell suggest that, in the sea, photo synthetic metabolism can persist efficiently without cell division during turbulent episodes. After turbulence ceases or reaches low levels again, cells can then divide and blooms may form. Thus, blooms can come or go fairly rapidly in the ocean depending on the degree of wave- and wind-induced turbulence.     

Modification of amino acid and sugar transport in uncoupler-adaptedEuglena gracilis

Uncoupler-adaptedEuglena gracilis have a greatly impaired capacity to take up and incorporate some exogenously supplied amino acids and sugars. The degree of inhibition varies widely from >90% in the case of valine or glucose to none in the case of histidine. The inhibition is due to a decreased activity of the transport mechanism itself and is not due to either a lesion in the control mechanism for endogenous amino acid or sugar synthesis nor to a direct inhibition of the transport mechanism by uncouplers.No preferential labeling of mitochondrial membranes by [¹⁴C]amino acids occurs during the process of adaptation, a time when no cell division occurs. Apparently, during the long time required for adaptation, there occurs no major modification of mitochondrial proteins which could explain the subsequent resistance to uncouplers.Contribution from the Department of Biochemistry, School of Agriculture and Life Sciences and School of Physical and Mathematical Sciences. Paper No. 5179 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, North Carolina 27607.