A Lack of Nuclear DNA Content Variability Among Wheat Near Isolines Differing in Aluminium Response

Nucleotypic variation has been speculated to play a role inthe adaptation of crop species to environmental stress. Theobjective of this study was to determine if nuclear DNA contentvariability was associated with aluminium (Al) tolerance inwheat. Six wheat (Triticum aestivumL.) near isolines (differingin Al response), two recurrent parents (Al sensitive), and onedonor parent (Al tolerant) were all analysed for nuclear DNAcontent using flow cytometry. A 1.7% variation in nuclear DNAcontent was observed among the nine wheat lines. No associationbetween Al response and nuclear DNA content was observed. Allof the wheat near isolines had a nuclear DNA content similarto their recurrent parent. The wheat genome appears to be stablewith no unusual inheritance of nuclear DNA content observed.Flow cytometric analysis proved to be sensitive enough to detectnuclear DNA content variability at the level of 0.5% variationamong wheat lines.Copyright 1999 Annals of Botany Company Genome size,Triticum,breeding, near isogenic.     

Aluminium Effects on ATPase Activity and Lipid Composition of Plasma Membranes in Sugar Beet Roots

The effect of aluminium (Al) in vivo and in vitro on root plasmamembranes has been studied in two sugar beet (Beta vulgarisL.) cultivars, Monohill (Al-sensitive) and Regina (relativelyAl-tolerant). Although Al in vitro inhibited the MgATPase inan uncompetitive way for both cultivars raised in the absenceof Al, the specific K⁺-activation of the MgATPase was only inhibitedby Al in cv. Monohill. Arrhenius analysis of the MgATPase activity showed that theeffect of Al in vitro depended on whether or not the plantswere exposed to Al in vivo. Al treatment in vitro of the MgATPasefrom control plants cultivated at a low pH (5·4) causedan increase in the phase transition temperature from 17 to 22°C. Only at a higher pH range (pH 6·1) could a secondtransition temperature be induced (at 9 °C). By additionof Al in vitro to plants cultivated with Al at pH 5·4,the slopes of the activity plots did not change. Aluminium changedthe K_m of the ATPase for MgATP in an opposite way by treatmentin vivo and in vitro. Lipid analyses of the plasma membranes showed that the acylcomposition differed little following Al treatment in vivo,but that the ratio of phosphatidylcholine: phosphatidylethanolamineincreased. The changes correlated with the observed change inthe K_m for the MgATPase. We conclude that the main effect ofAl on the MgATPase is not due to the formation of an Al-ATPcomplex. Instead, Al may bind to the membrane-bound enzyme(s)and/or modify the lipid environment. Key words: Aluminium, ATPase, Beta vulgaris, lipids     

Patterns of Root Respiration Associated with the Induction of Aluminium Tolerance in Phaseolus vulgaris L.

Aluminium (Al) tolerance in an Al-tolerant cultivar of Phaseolusvulgaris L. (‘Dade’) was found to be an inducibletrait. Upon exposure to 10 µM Al, the rate of root elongationwas inhibited in comparison to controls. During the following72 h, the rate of elongation returned to levels comparable tocontrols. In contrast, root elongation of an Al-sensitive cultivar(‘Romano’) did not recover after exposure to Al.In Dade, the resumption of root elongation following exposureto Al was accompanied by increased rates of root respiration,whereas respiration rates slowly declined over the 72 h treatmentperiod in Romano. When partitioned into growth and maintenanceexpenditures, a larger proportion of root respiration of Dadeexposed to Al was allocated to maintenance processes, potentiallyreflecting diversion of energy to metabolic pathways that offsetthe adverse effects of Al toxicity. Romano did not show sucha pattern and respiration associated with both growth and maintenancewas reduced after exposure to Al. Root and shoot growth of bothcultivars were also measured to determine the effects of long-term(21 d) exposure to 10 µM Al. Dade plants exposed to Alexhibited enhanced growth in comparison to controls, whereasRomano plants were characterized by reduced shoot and root growth.Modelling the time-course of root respiration and measuringthe long-term growth responses to Al is a valuable method ofelucidating respiratory costs of stress tolerance. Key words: Aluminium, differential tolerance, maintenance respiration, Phaseolus vulgaris, root respiration     

Plasma Membrane Permeability of Root-Tip Cells Following Temporary Exposure to Al Ions Is a Rapid Measure of Al Tolerance among Plant Species

No correlations were recognized between Al tolerance among fourplant species, rice (Oryza sativa L.), maize (Zea mays L.),pea (Pisum sativum L.), and barley (Hordeum vulgare L.), inrank order of Al tolerance, and cation exchange capacities ofroot-tip (0-1 cm) cells or of their cell walls. The plasma membraneof root-tip of Al sensitive plant species (pea and barley) wasconsiderably permeabilized with elongation of root in Al-freesolution following 0.5 h pretreatment with Al. K⁺ release fromand Al permeation into the protoplasts isolated from the root-tipof Al-sensitive plant species were more significant than thosefor Al-tolerant plant species (rice and maize) on 10 or 30 mintreatment with Al. The permeability of the plasma membrane forprotoplasts isolated from Al sensitive plant species was considerablyincreased by treatment with hy-potonic Al-free control solutionfollowing 10 min pretreatment with Al. To our knowlege, theseare the most rapid responses to Al ions reported to date, i.e.,within 0.5 h in whole plant and within 10 min in protoplast.These results suggest that a temporary contact with Al ionsirreversibly alters the plasma membrane of root-tip cells ofAl-sensitive plant species: the cells become more leaky andrigid due to binding of Al ions to the plasma membrane. (Received January 5, 1998; Accepted February 26, 1998)     

Distribution and mobility of aluminium in an Al-accumulating plant, Fagopyrum esculentum Moench

Buckwheat (Fagopyrum esculentum Moench. cv. Jianxi) accumulateshigh concentrations of Al in the leaves without showing anytoxicity. To understand the accumulation mechanism of Al inbuckwheat, the distribution and mobility of Al in buckwheatwere investigated. Relatively long-term treatment (28 d) withAl led to a decrease in Al concentration from old to young leaves,while a short-term (1 d) exposure to Al resulted in a uniformdistribution of Al in the leaves. When the fourth leaf was wrappedinside a transparent plastic bag to suppress transpiration,the Al concentration of this leaf was only one-quarter of thatin the corresponding leaf without wrappng. Within a leaf, theAl concentration at the margins was much higher than that inthe centre. These results indicate that Al distribution in theleaves is controlled by both rate and duration of transpiration.The mobility of Al between old and new leaves was studied byfirst growing plants in a solution with Al, followed by culturein a solution without Al. The Al content in the two new leavesappeared after removal of external Al was very low, whereasthat in the old leaves did not decrease but continued to increase.The increased Al content was found to be translocated from Alremaining in the roots. It is concluded that Al is not mobileonce it is accumulated in the leaf. Key words: Accumulation, aluminium, buckwheat, distribution, mobility, transpiration.     

Quantitative Estimation of Aluminium Toxicity in Cultured Tobacco Cells: Correlation between Aluminium Uptake and Growth Inhibition

The relationship between aluminium (Al) uptake and growth inhibitionwas studied in tobacco cells (Nicotiana tabacum L. cv. Samsun;nonchlorophyllic cell line) in suspension culture. Cells atthe logarithmic phase of growth were treated with 100 µMA1C1³ in modified Murashige-Skoog medium prepared without P_iand EDTA (pH 4.0) for up to 21 h. After treatment, the inhibitionof cell growth by Al was estimated from the growth of the Al-treatedcells relative to that of the control cells during post-treatmentculture. Neither Al uptake nor the inhibition of the growthoccurred with less than a 10-h exposure but then both parametersincreased rapidly, reaching maximum values after an 18-h exposure.When cells were treated with AlCl₃ at various concentrationsfor 18 h, the extent of growth inhibition was found to be afunction of the Al content of the cells. The dose-response curve(Al uptake versus growth inhibition) resembled the curve expectedfor "single-hit" kinetics. Extrapolation from the curve suggestedthat the uptake of 1 x 10¹¹ Al atoms per cell is the minimumdose that inhibits cell growth. Cells of stationary phase wereresistant to Al and did not take up Al, an indication that theuptake of Al depends on the active growth of cells. Resultsof several types of experiment (hematoxylin staining, washingwith chelators, digestion of cell walls) indicated that Al wasincorporated inside the cells. Together, therefore, our resultssuggest that the amount of Al absorbed by the cells is a determiningfactor in the inhibition of growth by Al. ¹Present address: Department of Biology, Faculty of Science,Hirosaki University Hirosaki, Aomori, 036 Japan     

Soil Solution Chemistry Controlling the Field Distribution of Melica ciliata L.

Germination, establishment and growth of Melica ciliata L.,an 'acidifuge' species of rocky habitats in Europe, were studiedexperimentally and related to chemical properties of the soilsolution, including pH, base cation composition, Al concentrationand speciation, and Mn concentration. M. ciliata failed to establishin acid leptite soil. However, it was able to grow in solutionat pH 3·6 and exhibited vigorous growth at pH 3·9,a typical soil solution pH of leptite sites, which Melica isunable to colonize. Higher concentrations of Mn than those measuredin any leptite soil solutions did not influence growth. Exposureto 0·037 mmol l^-1 (1 mg l^-1) of Al³⁺, a concentrationusually exceeded in the soil solution of leptite sites, severelyretarded root growth. Speciation technique applied to Al insoil solutions obtained by centrifugation demonstrated a closerelationship between H⁺ and Al concentrations and, in particular,between H⁺ and free ionic (quickly reacting) Al species. Soilsolution concentrations of free ionic Al proved to be < 0·002mmol l^-1 in sites lacking Melica , but often > 0·10mmol l^-1 in site lacking Metalica . It is concluded that theinability of M. ciliata to establish in acid soils is not primarilydue to the high H⁺ concentration but to the high soil solutionconcentrations of Al, especially free Al ionic species at lowsoil pH.Copyright 1993, 1999 Academic Press Melica ciliata, distribution, soil solution, pH, aluminium speciation, manganese, base cations, iron     

Organic Acid Exudation by Wild Herbs in Response to Elevated Al Concentrations

In acidic soils, monomeric aluminium (Al³⁺) can reach levelsthat are toxic to plants, thus preventing many species fromgrowing there. Organic acids chelate Al and render it non-toxic.It has been shown that exudation of organic acids by Al-tolerantcrops increases their tolerance to Al. We have extended thisobservation to wild plants by comparing the ability of ten herbsto exude organic acids in response to elevated Al levels. Wehypothesized that exudation of organic acids was related tothe ability of plants to grow on Al-rich soils. Two grasseswere grown in rhizotrons in soils with 41 and 63 µM reactiveAl. Organic acids were sampled from root tips connected to anintact plant-root system.Deschampsia flexuosa (L.) Trin. exudedmore malic acid when grown in the soil with the highest Al content.Five forbs and five grasses were also exposed to three Al levels(0, 25 and 75 µM) in a hydroponic system.Rumex acetosellaL. and Viscaria vulgaris Bernh. increased exudation of oxalicacid and Galium saxatile auct. non L. and Veronica officinalisL. increased exudation of citric acid in response to elevatedAl. The distribution of the forbs in the field as describedby soil pH was negatively related to the amount of organic acidsexuded in response to Al. In contrast, none of the grasses exudedhigher amounts of organic acids with increasing Al concentrationin the hydroponic experiment. Copyright 2001 Annals of BotanyCompany Citrate, malate, aluminium detoxification, rhizotron, hydroponics, rhizosphere, Carex pilulifera,Deschampsia flexuosa , Festuca gigantea, Galium saxatile, Geum urbanum, Holcus mollis,Milium effusum , Rumex acetosella, Veronica officinalis, Viscaria vulgaris     

Specific Secretion of Citric Acid Induced by Al Stress in Cassia tora L.

A rapid and sensitive assay method for Al-chelating activitywas established to screen Al-chelating substances secreted fromroots of Al-resistant species in response to Al stress. Fromone Al-resistant species, Cassia tora L., an Al-chelating substancewas detected in the root exudates when they were exposed toSO µM Al in 0.5 mM CaCl₂ solution at pH 4.5; the dominantcomponent was identified as citric acid. The secretion of citricacid was very low during the first 4 h after initiation of Altreatment, but increased markedly thereafter. A 3-h pulse with50 µM Al also induced significant secretion of citricacid after 6 h. The lag between Al addition and secretion ofcitric acid suggests that inducible processes are involved.A dose-response experiment showed that the amount of secretedcitric acid increased with increasing external concentrationsof Al. Eight-d treatment of P deficiency did not induce thesecretion of citric acid. Exposure to 50µM of either lanthanum(La³⁺) or ytterbium (Yb³⁺) did not induce the secretion of citricacid either. These findings indicate that the secretion of citricacid is a response specific to Al stress in .C. toraand constitutesa mechanism of Al resistance. (Received April 23, 1997; Accepted June 25, 1997)     

Al Binding in the Epidermis Cell Wall Inhibits Cell Elongation of Okra Hypocotyl

Al inhibits root elongation at micromolar concentrations, butthe mechanisms leading to this process are unknown. In thesestudies, Al-induced inhibition of cell elongation was examinedusing hypocotyl of okra (Abelmoschus esculentus Moench cv. ClemsonSpineless) as an experimental model. One-h exposure to Al (0.5mM A1Cl₃) in the presence of 10 µM auxin in 0.5 mM CaCl₂,pH 4.0 significantly inhibited auxin-induced cell elongationof okra hypocotyl segments. Elongation was further suppressedwith increasing Al concentrations up to 1 mM. Treatment of thehypocotyl with 1 mM citrate for 10 minutes after 2-h exposureto Al resulted in significant recovery of elongation. The amountof Al in the cell wall relative to the total in the tissue was96.0, 96.2, and 85.4%, respectively, following 1-, 2-, and 3-hexposure to the Al solution. The total and cell wall Al contentwas decreased by half after the citrate desorption treatment.Further-more, 95% of Al was found in the epidermis, and 95%of the Al in the epidermis was associated with the cell wall.Experiments using split hypocotyl segments showed that Al exposureincreased the outward bending of hypocotyl segments, suggestingthat the epidermis elongation was specifically inhibited byAl. Al inhibited the autolysis of epidermis by about 20%, buthad little effect on the autolysis of core tissue. Taken together,these results suggest that Al binding in the epidermal cellwall inhibits critical components in cell wall loosening mechanism,resulting in inhibition of cell elongation.     

Mechanical Stress Elicits Nitric Oxide Formation and DNA Fragmentation in Arabidopsis thaliana

The effect of mechanical stress (centrifugation) on the inductionof nitric oxide (NO) formation and DNA fragmentation was investigatedin leaf cells of Arabidopsis thaliana. Centrifuged and non-centrifugedleaves from wild-type and nitrate reductase (NR)nia1, nia2 doublemutant, defective in the assimilation of nitrate, were labelledwith 4,5-diaminofluorescein diacetate (DAF-2 DA) to visualizein vivo NO production. After these treatments, DNA fragmentationwas detected by the terminal deoxynucleotidyl transferase-mediateddUTP nick end in situ labelling (TUNEL) method. Exposure toan NO-releasing compound, sodium nitroprusside (SNP) mimickedthe cell response to centrifugation (20 g). The involvementof endogenous NO as a signal in mechanical stress and in DNAfragmentation was confirmed by inhibition of NO production usinga nitric oxide synthase (NOS) inhibitor viz. N^G-monomethyl-L -arginine (L -NMMA). These results indicate that NOS-likeactivity was present in A. thaliana leaves and was increasedby mechanical stress. The effect of leaf-wounding on nitricoxide production was identical to that of centrifugation. Experimentswith A. thaliana NR mutant also showed that NO bursts were inducedby mechanical and wounding stresses and that NO was not a by-productof NR activity. A positive and significant correlation betweenNO production and DNA fragmentation was recorded for both centrifugedand non-centrifuged cells. Our results suggest that factorsother than NO contribute to DNA damage and cell death, and furthermore,that an inducible form of NOS is present in A. thaliana. Copyright2001 Annals of Botany Company Arabidopsis thaliana, cell death, DNA fragmentation, NO, plant stress, wounding     

Aluminium and the Hydraulic Conductivity of Quercus rubra L. Root Systems

Two hydroponic experiments were conducted to determine the effectsof brief and prolonged AI³⁺ exposures on the hydraulic conductivity(Lp) of northern red oak (Quercus rubra L.) root systems. RootLp was determined using the pressure chamber method of Fiscus(1977). In the first experiment, 28- to 40-d-old seedlings weretreated for 4 d with complete nutrient solutions containingone of three Al concentrations (0.04, 1.85 or 3.71 mol m^–3)and either 0 or 50 mmol m^–3 P. Neither Lp nor daily transpirationwas affected by treatment. In Experiment II, seedlings were grown for 48–63 d incomplete solutions containing one of three Al concentrations(0, 0.75 or 2.00 mol m^–3) and either 10 or 250 mmol m^–3Ca. Lp and leaf area to root length ratio (LA/RL) were reducedwhen (AI³⁺/ Ca²⁺), the solution activity ratio, was 2.9 andhigher. Lp and LA/RL were also negatively correlated with Alconcentration and Al/Ca concentration ratio in the roots. Lpwas positively correlated with LA/RL in both experiments. Itis unclear whether Lp in the second experiment was reduced directlyby solution and root chemistry or whether Lp changed in responseto altered leaf/root balance. Key words: Al phytotoxicity, Al x Ca interaction, Quercus rubra, root hydraulic conductivity     

Effect of inhibitors of nucleic acid and protein synthesis on the reappearance of "light interruption rhythm" in a long-day duckweed, Lemna gibba G 3

Effects of several inhibitors of DNA, RNA and protein synthesison the reappearance of a once faded-out light interruption rhythmin a long-day duckweed, Lemna gibba G 3, were studied. The reappearancewas not affected by inhibitors of RNA and protein synthesis;i.e., 2-thiouracil, 8-azaguanine, ethionine and chloramphenicol,but was suppressed by inhibitors of DNA synthesis; i. e., 5-fluorodeoxyuridine,5-fluorouracil and mitomycin C only when these were appliedduring the light period for perturbation. We concluded that synthesis of a new DNA species during thelight period was required for the recurrence of this rhythm. (Received September 25, 1968; )     

Early Replication of Highly Repeated DNA Sequences during Dedifferentiation of Carrot

When carrot explants are placed on an agar medium containingphytohormones, a satellite DNA begins to replicate earlier thanthe bulk DNA during the first cell division cycle. The majorityof this early replicating satellite DNA was previously shownto have an identical buoyant density to ribosomal DNA (rDNA)(Hase et al. 1982). Molecular sizes of EcoRI-digests of ³H-labeledDNA were analyzed in the present study by gel electrophoresisfollowed by fluorography. Most of the labeled DNA bands didnot correspond to EcoRI-digests of carrot rDNA. The resultsindicated that the majority of the early replicating satelliteDNA is not rDNA, but probably a type or types of highly repeatedDNA sequences. (Received June 6, 1985; Accepted November 4, 1985)     

Inoculation with Azospirillum lipoferum Affects Growth and Gibberellin Status of Corn Seedling Roots

Maize (Zea mays L., hybrid Cargill 147) seedlings, grown inaseptic conditions, were inoculated with three strains of Azospirillumlipoferum (Al op 33, Al iaa 320, and ATCC 29708) or culturedin different concentrations of indol-3-acetic acid (IAA) orgibberellin A₃ (GA₃). After 48 h, root length, root surfacearea, root dry weight, and shoot dry weight were measured inall treatments. Gibberellin content was evaluated in selectedroots of control and Azospirillum inoculated seedlings by gaschromatography-mass spectrometry-selected ion monitoring withthe use of deuterated gibberellins as internal standards. Thethree strains of A. lipoferum, IAA (2 ng ml^–1), and GA₃(40 to 400 pg ml^–1) significantly enhanced root growth.Improvement of root hair growth and density was obtained mainlywith A. lipoferum strain Al op 33 and GA₃ 40 pg ml^–1.GA₃ was identified by gas chromatography-mass spectrometry (byboth, full scan and selected ion monitoring) in a free acidfraction from roots of the seedlings inoculated with A. lipoferum.In the roots of the non inoculated seedlings GA₃ was found afterhydrolysis of a fraction expected to contain glucosyl conjugates. (Received April 26, 1993; Accepted September 27, 1993)     

Determining relative abundance of specific DNA sequences in flow cytometrically sorted maize nuclei

A wide breadth of DNA content variation has been reported amongmaize lines. While the extent of this variation has been welldocumented, few studies have focused on its cause. Some of thenuclear DNA content variation has been explained by the presenceof B chromosomes or knobs. However, variation in these two structuresdoes not account for all of the observed variation. In orderto identify other fluctuating DNA sequences, a rapid and reliablemethod of estimating relative abundance of DNA sequences neededto be developed. The potential of flow cytometry in conjunctionwith spot hybridization for determining relative abundance ofspecific DNA sequences in maize was studied. Different numbersof G1 phase nuclei were sorted on nitrocellulose filters andnon-radioactive hybridization and signal detection performed.Results from these experiments revealed a significant, positivelinear correlation between the amount of target sequence andsignal density using both knob (R = 0.98) and ribosomal spacer(R =0.99) DNA sequences. In addition, G1 phase nuclei of eightinbred lines differing in the amount of knob heterochromatin,were sorted on to filters and the non-radioactive hybridizationand signal detection performed. A significant, positive linearcorrelation between C-band number and signal density (R =0.83;P = 0.0051) as well as between per cent heterochromatin andsignal density (R=0.96;P = 0.0002) was observed. These resultsindicate the usefulness of flow cytometry for spot hybridizationin determining the relative abundance of DNA sequences in themaize genome. Key words: Flow cytometry, copy number, non-isotope labelling, spot hybridization, flow sorting, Zea mays L.     

Replicon Size, Mean Rate of DNA Replication and the Duration of the Cell Cycle and its Component Phases in Eight Monocotyledonous Species of Contrasting DNA C Values

Various aspects of the cell cycle were measured in the apicalmeristem of primary and seminal roots of eight monocotyledonousangiosperms: Oryza sativa (0.6 pg), Zea mays (2.4 pg), Pennisetumamericanum (2.5 pg), Aegilops umbellulata (5.1 pg), Hordeumvulgare (5.5 pg), Triticum monococcum (6.2 pg), Secale cereale(8.6 pg) and Tulipa kaufmanniana (22.6 pg), representing a 38-foldvariation in DNA C values. Using 4-d-old roots of the firstseven species and 21-d-old Tulipa roots, replicon size and ratesof replication were determined by DNA fibre autoradiography,and the duration of the cell cycle and its component phasesby the percentage labelled mitoses method. When tested withDNA C value, no significant relationships existed for repliconsize, rate of DNA replication or duration of G 1. Significantpositive linear relationships were found between DNA C valueand cell cycle duration, duration of mitosis and G2 durationwhen all data were tested, but not when the Tulipa data wereexcluded. The only characters significantly related to DNA C value whenthe Tulipa data were included or excluded were the durationof S-phase, and the ratio of the interval required for a repliconto replicate its allotted DNA (Rs) to the duration of S-phase(Ds). The Rs: Ds ratio is a measure of synchrony of repliconactivation, and the higher the DNA C value the lower this ratiobecame. We concluded that there was a nucleotypic effect ofDNA C value on this ratio and that the interval between activationof replicons became protracted and hence S-phase lengthenedas C value increased. Cell cycle, NA C value, DNA replication, replicon, S-phase     

The mitochondrial genome of the lizard Calotes versicolor and a novel gene inversion in South Asian draconine agamids

A complete mitochondrial DNA (mtDNA) sequence was determinedfor the lizard Calotes versicolor (Reptilia; Agamidae). The16,670-bp genome with notable shorter genes for some protein-codingand tRNA genes had the same gene content as that found in othervertebrates. However, a novel gene arrangement was found inwhich the proline tRNA (trnP) gene is located in the light strandinstead of its typical heavy-strand position, providing thefirst known example of gene inversion in vertebrate mtDNAs.A segment of mtDNA encompassing the trnP gene and its flankinggenes and the control region was amplified and sequenced forvarious agamid taxa to investigate timing and mechanism of thegene inversion. The inverted trnP gene organization was sharedby all South Asian draconine agamids examined but by none ofthe other Asian and African agamids. Phylogenetic analyses includingclock-free Bayesian analyses for divergence time estimationsuggested a single occurrence of the gene inversion on a lineageleading to the draconine agamids during the Paleogene period.This gene inversion could not be explained by the tandem duplication/randomloss model for mitochondrial gene rearrangements. Our availablesequence data did not provide evidence for remolding of thetrnP gene by an anticodon switch in a duplicated tRNA gene.Based on results of sequence comparisons and other circumstantialevidence, we hypothesize that inversion of the trnP gene wasoriginally mediated by a homologous DNA recombination and thatthe de novo gene organization that does not disrupt expressionof mitochondrial genes has been maintained in draconine mtDNAsfor such a long period of time.     

Effect of Laurie Acid on Cell Division, Macromolecular Synthesis and Membrane Lipid Organization in Escherichia coli

Laurie acid (1 mg/ml) sharply suppressed the cell division ofan acrA mutant strain of Escherichia coli K12. However, thewild type acrA^$ strain was resistant to the fatty acid. Capricacid and myristic acid were not so toxic. Laurie acid inhibitedboth DNA and protein synthesis of the acrA mutant strain, withthe former being more sensitive than the latter. On the otherhand, DNA polymerase activity of toluene-treated cells was stimulatedrather than inhibited by the presence of 1 mg/ml of lauric acid.Fatty acid composition of phospholipids in the inner membranewas largely altered by the addition of lauric acid. These resultssuggest that addition of lauric acid to the medium causes adisorganization of the membrane lipids in the acrA mutant celland activities of DNA polymerase and other intramembranous enzymesare consequently inhibited. ¹Present address: Osaka City Institute of Public Health andEnvironmental Sciences. Osaka 543, Japan. (Received January 28, 1983; Accepted November 15, 1983)     

The Role of DNA Synthesis During Hypocotyl Elongation in Light and Dark

Fluorodeoxyuridine, an inhibitor of DNA synthesis, did not affectgermination and post-germinative growth in the aerial part oflettuce and Haplopappus gracilis seedlings when grown in thelight. In the dark, however, elongation of the hypocotyl wasinhibited by fluorodeoxyuridine, strikingly in lettuce and onlyslightly in Haplopappus gracilis. This could imply that thecontrolling mechanism of hypocotyl elongation is in some casesrelated to DNA synthesis, either because mitotic processes (oftenlittle taken into account in considering hypocotyl growth) areinvolved in the elongation of hypocotyls only when they aregrown in the dark, or because DNA synthesis affects cell elongationdirectly, or through the production of a greater number of endopolyploidcells in the dark. Using mainly autoradiographic and cytofluorimetricmethods, these possibilities were tested. Besides lettuce (Lactucasativa L. var. Great Lakes) and H. gracilis (Nutt.) Gray, radish(Raphanus sativus L. var. Tondo rosso quarantino) and soybean(Soya hyspida Sieb. and Zucc. var. Tokyo) seedlings were alsostudied. Fluorodeoxyuridine drastically inhibits cell elongation onlywhen it is preceded or accompanied by mitotic or endomitoticevents. Need for DNA synthesis during hypocotyl elongation,as well as during early post-germinative growth, seems to beof particular importance when endomitotic processes are involved. DNA synthesis, elongation, endoreduplication, fluorodeoxyuridine, Haplopappus gracilis (Nutt.) Gray, Lactuca sativa L., Raphanus sativus L., Soya hyspida Sieb and Zucc