RNA Synthesis in Phaseolus Chloroplasts: I. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLAST PREPARATIONS FROM PHASEOLUS VULGARIS L. LEAVES AND SOLUBILIZATION OF THE RNA POLYMERASE

Chloroplast preparations from the young primary leaves of Phaseolusvulgaris L. cv. Canadian Wonder carry out the DNA-dependentincorporation of UTP into RNA at rates between 8 and 14 pmolUTP µg^–1 chlorophyll h^–1. It is estimatedthat 90% of the activity was localized in the chloroplasts.The incorporation proceeded for between 20 and 30 min at 35°C. The maximum rates of RNA synthesis were attained atpH 8.3, in the presence of 15 mM MgCl₂. Chloroplasts were alsoactive, to a lesser extent, with 1.5 mM MnCl₂. The simultaneouspresence of MnCl₂ and MgCl₂ resulted in inhibition of activity.Nuclear material prepared from young P. vulgaris leaves incorporatedUTP at a rate of about 12 pmol UTP µg^–1 DNA h^–1.On a chloroplast (Tritonsoluble) DNA basis chloroplast activitywas over 40-fold that of nuclei. Methods of solubilizing chloroplastRNA polymerase were explored. Yields of over 75% were achieved,but methods suitable for one species were not always successfulwhen applied to another. The highest yields of the P. vulgarisenzyme were obtained using EDTA and KCl. All methods resultedin solubilization of DNA. RNA synthesis by the soluble P. vulgarisenzyme proceeded for more than 40 min at 35 °C.     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum. Growth, Ion and Water Relations and Gas Exchange in Response to Altered Salinity

Clipson, N. J. W. 1987. Salt tolerance in the halophyte Suaedamaritima L. Dum. Growth, ion and water relations and gas exchangein response to altered salinity.—J. exp. Bot. 38: 1996–2004. Shoot and root fresh and dry weights and shoot sodium, chlorideand potassium contents were measured and shoot relative growthrates calculated in seedlings of Suaeda maritima over a periodof 11 d following a raising of culture solution salinity from0 to 200 mol m₃– NaCl. Growth, growth rates and sodiumand chloride contents, as compared to plants growing in theabsence of salt were increased whilst potassium contents declined.Shoot sodium accumulation rate and the rate of transport ofsodium from root to shoot, osmotic potential, and rates of photosynthesisand transpiration were also measured for up to 72 h after transferof plants originally growing at 0 and 200 mol₃– NaCl to200 and 400 mol m₃– NaCl respectively. Ion uptake andtransport rates were maximal 6-12 h after transfer and thendeclined to new steady-state levels within 48 h; osmotic potentialswere lowered over a 72 h period on average by approximately1·0 MPa; and after 9 h photosynthetic and transpirationrates were reduced by about 20percnt; and 30% respectively.Results are discussed in terms of the ability of halophytesto adjust to fluctuating salinity and to salt tolerance mechanismsin general. Key words: Suaeda maritima, salinity, gas exchange, growth, ion and water relations     

Aldosterone induces ras methylation in A6 epithelia

Aldosterone increases Na⁺ reabsorption by renalepithelial cells: the acute actions (<4 h) appear to be promoted byprotein methylation. This paper describes the relationship betweenprotein methylation and aldosterone's action and describesaldosterone-mediated targets for methylation in cultured renal cells(A6). Aldosterone increases protein methylation from 7.90 ± 0.60 to 20.1 ± 0.80 methyl ester cpm/µg protein. Aldosteronestimulates protein methylation by increasing methyltransferase activityfrom 14.0 ± 0.64 in aldosterone-depleted cells to 31.8 ± 2.60 methyl ester cpm/µg protein per hour in aldosterone-treated cells. Three known methyltransferase inhibitors reduce thealdosterone-induced increase in methyltransferase activity. One ofthese inhibitors, the isoprenyl-cysteine methyltransferase-specificinhibitor,S-trans,trans-farnesylthiosalicylic acid, completely blocks aldosterone-induced protein methylation and also aldosterone-induced short-circuit current. Aldosterone inducesprotein methylation in two molecular weight ranges: near 90 kDa andaround 20 kDa. The lower molecular weight range is the weight of smallG proteins, and aldosterone does increase both Ras protein 1.6-fold andRas methylation almost 12-fold. Also, Ras antisense oligonucleotidesreduce the activity of Na⁺ channels by about fivefold. Weconclude that 1) protein methylation is essential foraldosterone-induced increases in Na⁺ transport;2) one target for methylation is p21^ras; and3) inhibition of Ras expression or Ras methylation inhibits Na⁺ channel activity.

     

Development of Ethylene Biosynthesis in Pear Fruits at --1 {degrees}C

Knee, M. 1987. Development of ethylene biosynthesis in pearfruits at — 1 °C.—J. exp. Bot. 38: 1724–1733. The regulation of ethylene synthesis in pear fruits was investigated.During storage for 60 d at — 1 °C the rate of ethylenesynthesis increased 100-fold but the concentration of 1-aminocyclopropane-l-carboxylicacid (ACC) increased only 2-fold and ACC synthase activity waslow. On transfer to 15 °C after storage at — 1 °Cethylene synthesis increased 10-fold within 10 h but ACC synthaseactivity only increased rapidly after 24 h; the decline in ACClevels during the first 16 h at 15 °C was insufficient tosustain ethylene synthesis. Ethylene synthesis was further investigatedusing discs cut from the mid cortex of pear fruits. Synthesiswas inhibited by aminoethoxyvinylglycine (AVG) and amino-oxyaceticacid at all stages of ripening. The rate of synthesis and ACCsynthase activity increased rapidly after slicing of pears heldat — 1 °C but more slowly in discs cut from pearsimmediately after harvest. Cycloheximide (CHI) inhibited theseincreases and reversed increases resulting from pre-incubationof discs. A combination of CHI and AVG abolished the capacityof discs to synthesize ACC and ethylene production was curtailed.Cordycepin and actinomycin-D were less effective as inhibitorsof the development of ethylene synthesis and ACC synthase activitythan as inhibitors of incorporation of 5-[³H] uridine into totalRNA or poly A rich RNA. The ability of discs to develop ethylenesynthesis and ACC synthase activity in the presence and absenceof cordycepin increased concurrently during storage of wholefruits at — 1 °C. This suggested that mRNA for ACCsynthase was formed at — 1 °C. Key words: 1-Aminocyclopropane-l-carboxylic acid, ethylene, fruit ripening, Pyrus communis L. (fruit ripening)     

Isoforms of NADP-dependent Malic Enzyme in Tissues of the Greening Maize Leaf

Scagliarini, S., Pupillo, P. and Valenti, V. 1988. Isoformsof NADP-dependent malic enzyme in tissues of the greening maizeleaf.—J. exp. Bot. 39: 1109–1119. The compartmentation of the isoforms of NADP-dependent malicenzyme (E.C. 1.1.1.40 [EC] ) has been studied in cell-free extractsand in enzymatically-isolated protoplasts of mesophyll tissue(MT) and bundle sheath (BS) strands of greening maize leaves.The etiolated leaf of 10-d-old seedlings contains a cytosolicisozyme with a pl of 5.4 ?0.1 at low specific activity (s.a,45 ? 3 nmol min^–1 mg^–1 protein), found both in MTand BS. The green leaf on the other hand contains the dominantBS chloroplast isozyme with pl 4.6 ? 0.2 at a s.a, of 370 ?40 nmol min^–1 mg^–1 protein (3.2 ? 0.5 µmolmin^–1 mg^–1 chl) and a minor, previously undescribedisoform with pl 6.5 ? 0.1 also localized in the BS at a s.a.of 38 ? 6 nmol min^–1 mg^–1 protein. Green MT protoplastshave only traces of pl 4.6 isozyme. After illumination of dark-grown seedlings, the total leaf activityshows a rapid increase (1.5-fold within 2 h), attributed mainlyto the pl 5.4 isozyme of MT protoplasts and BS strands. Thisis followed by a large increase of enzyme activity due to thecontinued rise of pl 5.4 isozyme for about 24 h and, after aninitial lag of a few hours, to the accumulation of pl 4.6 isozyme.After 18 h illumination, pl 4.6 and 5.4 isozyme activities tendto decline in the MT whereas they are still increasing in theBS, particularly the former. This pl 4.6 species has becomethe major one by 48 h illumination. The final pattern of greenleaves is established around 96 h light, when the chloroplastisozyme has attained its maximum level, the pl 5.4 isozyme ofBS strands has been superceded by the pl 6.5 species (also supposedto be cytosolic) and MT protoplasts retain little residual activity.Some metabolic implications of the changing pattern of NADP-dependentmalic isozymes during maize leaf greening are discussed. Key words: C₄, isozymes, malic enzyme, photodifferentiation, Zea mays     

The Effect of Temperature Change on Leakage from Pea Seeds

Intact seeds of P. sativum and P. elatius leaked electrolytes,sugars and proteins for as long as 48 h after the beginningof imbibition. Initial leakage was higher at 25 °C thanat 5 °C, but its extent was much greater at the lower temperature.Transfer of seed from 5 °C to 25 °C after 5 h imbibitionresulted in leakage for 48 h at the initial rate at 5 °C.The transfer from 25 °C to 5 °C gave leakage at a rateequivalent to the initial rate at 25 °C. The results arediscussed in relation to behaviour of membranes and to the sensingof the initial temperature. Key words: Pisum sativum, P. elatius, Leakage, Electrolytes, Sugars, Proteins, Temperature     

Induction of chitinase and {beta}-1,3-glucanase activity in sunflower suspension cells in response to an elicitor from Phytophthora megasperma f. sp. glycinea (Pmg). Evidence for regulation by ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC)

In heterotrophic cell suspensions of sunflower (Helianthus annuusL. cv. Spanners Allzweck) the effect of Pmg elicitor, a fungalelicitor preparation from Phytophthora megasperma f. sp. glycinea,on the induction of chitinase and ß-1,3-glucanaseactivity was studied in relation to changes in ethylene biosynthesis.Dose-response experiments with Pmg elicitor showed that theonset of the induction of intracellular chitinase and ß-1,3-glucanaseactivity coincided or followed a transient rise in ethyleneand particularly endogenous 1-aminocyclopropane-1-carboxylicacid (ACC) levels within 5 h of application. Treatment with5 µg ml^–1 elicitor stimulated ethylene and ACC levels1.6-fold and 4-fold, relative to control, respectively. Themolar ratio of ACC to ethylene changed from approximately 3:1in controls to 9:1 in treated cells. During further incubation,ethylene formation and, to a lesser degree, ACC levels declinedand the ACC/ethylene ratio increased to 56:1 in elicitor-treatedcells. On a protein basis, the activities of ß-1,3-glucanaseand chitinase increased approximately 5-fold and 8-fold, respectively,48 h after elicitor application. Additional treatment with theACC synthesis inhibitor aminoethoxyvinyiglycine (AVG) decreasedelicitor-induced enzyme activities and the levels of both ethyleneand ACC. Elicitor effects on chitinase and ß-1,3-glucanaseactivities could be fully restored when ACC was additionallyapplied. Concomitantly, the ACC/ ethylene ratio increased. Neithertreatments with ACC alone, which simultaneously increased internalACC and ethylene levels, nor treatments with AVG alone, whichsimultaneously reduced ACC and ethylene levels, could generallystimulate chitinase or ß-1,3-glucanase activitiesin the cells. It is suggested that ACC functions as a promotingfactor in the induction of chitinase and ß-1,3-glucanaseactivity triggered by Pmg elicitor and appears to reverse aninhibiting influence of ethylene. Key words: 1-Aminocyclopropane-1-carboxylic acid, chitinase, ß-1,3-glucanase, ethylene, Helianthus cellsuspension cultures, Phytophthora megasperma-elicitor     

Studies on chromatin-associated protein phosphokinase of submandibular gland from isoproterenol-treated rats

Water-soluble chromatin from rat submandibular gland nuclei was isolated, and had a DNA: RNA:protein ratio of 8:1:20. The spectral properties of this preparation were similar to those described for chromatins from other tissues. The rat submandibular gland chromatin possessed protein phosphokinase activity. It was able to incorporate ³²P from [γ-³²P]-ATP into chromatin proteins, and into dephospho-phosvitin. The chromatin-associated protein phosphokinase activity (measured with dephospho-phosvitin as substrate) required Mg²⁺, Na⁺ or K⁺ and dithiothreitol for optimal activity. A single injection of isoproterenol influenced the activity of this enzyme system, so that it was decreased at 2 h, showed a transient increase at 4 h, and a large increase at 10–16 h after the injection. This event appears to precede the increase in ribosomal RNA induced by Ipr [13]. By 48 h the chromatin-associated protein kinase returned to the normal control levels. These changes appeared to be commensurate with the corresponding alterations in the non-histone acidic protein complement of these chromatins. Actinomycin D or cycloheximide, when administered 30 min prior to isoproterenol, blocked the increase in chromatin-associated protein kinase at 4 as well as 10 h after the injection of isoproterenol. Injection of pilocarpine did not influence the chromatin-associated protein phosphokinase activity. Dichloroisoproterenol appeared to be antagonistic to the influence of isoproterenol in mediating changes in chromatin-associated protein kinase. The results suggest that the isoproterenol-induced increase in chromatin-bound protein phosphokinase which precedes the increase in RNA synthesis is related to the eventual onset of DNA synthesis in rat submandibular gland stimulated by isoproterenol. The chromatin-bound protein phosphokinase activity (or activities) may have a regulatory role on gene action, mediated through the control of phosphorylation of nuclear non-histone acidic proteins [26].     

Leaf Development in Lolium temulentum L.: Progressive Changes in Soluble Polypeptide Complement and Isoenzymes

Ougham, Helen J., Jones, Thomas W. A. and Evans, Mair LL. 1987.Leaf development in Lolium temulentum L.: progressive changesin soluble polypeptide complement and isoenzymes.—J. exp.Bot. 38: 1689–1696. The spectrum of soluble polypeptides extracted from segmentsof the developing 4th leaf of Lolium temulentum simplified withincreasing distance from the leaf base. Most of the metabolicallyimportant isoenzymes analysed also exhibited gradients of activitywith respect to distance from the base, and in some cases twoor more contrasting gradients were observed for a given enzyme. Key words: Gradients, isoenzymes, leaves, Lolium temulentum,, soluble polypeptides     

ABA in Roots and Leaves of Flooded Pea Plants

Zhang, J. and Davies, W. J. 1987. ABA in roots and leaves offlooded pea plants.—J. exp. Bot. 38: 649–659. Roots of potted pea (Pisum sativum L. cv. Feltham First) seedlingswere flooded with tap water. Within a few hours of the startof the flooding treatment the content of free ABA in roots increasedcompared to contents of roots of unflooded control plants butthis increase was not statistically significant until the beginningof the second day after flooding. Approximately 36 h after firstflooding significant increases in the free-ABA content of leaveswere detected. This was 14 h after significant increases inthe amount of ABA in the roots of the same plants. There wasmarked diurnal variation in free-ABA content of leaves and rootsof plants that had been flooded for several days, with maximumcontents recorded 3 h or more after the beginning of the lightperiod. Very rapidly after the lights were switched oft ABAcontents declined. On day 3 of the flooding treatment, therewas more than a 5-fold decrease in the free-ABA content of leaveswithin a few hours of the beginning of the dark period. Radio-immunoassaysuggested that a very large proportion of the total ABA in theplant was in a bound form. This form of ABA increased substantiallyas the flooding period progressed. The importance of variation in ABA content for the control ofwater relations and gas exchange of flooded plants is discussed. Key words: Flooding, Pisum sativum, ABA, water relations     

The Use of Organic and Inorganic Compounds to Increase the Accumulation of Indole Alkaloids in Catharanthus roseus (L.) G. Don Cell Suspension Cultures

Smith, J. I, Smart, N. J., Kurz, W. G. W. and Misawa, M. 1987.The use of organic and inorganic compounds to increase the accumulationof indole alkaloids in Catharanthus roseus (L.) G. Don cellsuspension cultures.—J. exp. Bot. 38: 1501–1506. The addition of sodium chloride, potassium chloride or sorbitolto 5–d–old cell suspension cultures of Catharanthusroseus stimulated an increase in the intracellular accumulationof catharanthine and other indole alkaloids within 48–72h. The magnitude of the response depended upon the concentrationof the compound added. The use of such inexpensive and readilyavailable compounds to increase the yields and reduce the requiredculture times has considerable potential for the productionof useful secondary metabolites from cell cultures of C. roseusand other plant species.     

Acid Phosphatase Activity in Karri (Eucalyptus diversicolor F. Muell.) in Relation to Soil Phosphate and Nitrogen Supply

O'Connell, A. M. and Grove, T. S. 1985. Acid phosphatase activityin karri (Eucalyptus diversicolor F. Muell.) in relation tosoil phosphate and nitrogen supply.—J. exp. Bot. 36: 1359–1372 Soluble acid phosphatase activity was measured in tissues ofkarri (Eucalyptus diversicolor F. Muell.) seedlings and fiveyear old karri trees to which P and N fertilizer had been applied.Addition of P from 0 to 1250 mg P kg^–1 soil with a basaltreatment of other nutrients produced significant increasesin growth, P content and P concentration of karri seedlings.In each of five plant components (shoot tips, partly expandedleaves, mature leaves, young stems and old stems) soluble acidphosphatase activity was greatest at low levels of added P anddecreased with increasing soil P supply. The range of acid phosphataseactivity (0·5-6·5 µmol NPP g^–1 f.wt.min^–1) was similar to that reported for a number of agriculturaland horticultural plants. Enzyme activity was highest for shoottips and lowest for old stems. However, the relative changein activity with decreasing soil P supply was greatest for stems(4·3 fold) and least for shoot tips (2·7 fold) Mature leaves of seedlings grown in ‘high P’ and‘low P’ soil at four levels of added N showed, inaddition to the effect of P, a significant N-P interaction onsoluble acid phosphatase activity. In leaf samples from fiveyear old karri trees there was a significant decrease in solubleacid phosphatase with increasing P fertilization. Addition ofN fertilizer had no significant effect on enzyme activity, probablybecause added N had little effect on foliar N concentrations Exponential models relating (1) plant growth to enzyme activityand (2) plant growth to P concentration in stems and matureleaves of plants grown in soil with a range of added P accountedfor 78–92% and 63–87%, respectively, of the variationin top dry weight. The results suggest that for the diagnosisof plant P status, (1) stem components may be the most appropriatetissue to sample, and (2) nutrient and enzyme assays may complementeach other, P concentration being most useful where P supplyis adequate and phosphatase activity where P supply limits growth Key words: Phosphatase activity, Eucalyptus diversicolor, nutrients, phosphorus, nitrogen, forests     

Sidestream smoke exposure enhances rapidly adapting receptor responses to substance P in young guinea pigs

Bonham, A. C., K. S. Kott, and J. P. Joad. Sidestreamsmoke exposure enhances rapidly adapting receptor responses to substance P in young guinea pigs. J. Appl.Physiol. 81(4): 1715-1722, 1996.We determinedthe effect of sidestream tobacco smoke (SS) exposure on responses oflung rapidly adapting receptors (RARs), peak tracheal pressure (Ptr),and arterial blood pressure (ABP) to substance P in young guinea pigs.Guinea pigs were exposed to SS or filtered air fromday 8 to days41-45 of life. They were then anesthetized andgiven three doses of intravenous substance P (1.56-4.94 nmol/kg).SS exposure augmented substance P-evoked increases in RAR activity(P = 0.029 by analysis of variance) but not substance P-evoked increases in peak Ptr or decreases in ABP.Neurokinin 1-receptor blockade (CP-96345, 400 nmol/kg) attenuatedsubstance P-evoked increases in RAR activity(P = 0.001) and ABP(P = 0.009) but not in peak Ptr(P = 0.06). Thus chronic exposure toSS in young guinea pigs exaggerates RAR responsiveness to substance P. The findings may help explain the increased incidence of airwayhyperresponsiveness and cough in children chronically exposed toenvironmental tobacco smoke.

     

The Nuclear Endoreduplication Cycle in Metaxylem Cells of Primary Roots of Zea mays L.

The nuclear DNA content of metaxylem cells in roots of Zea mayscv. Golden Bantam reaches 16C or 32C by successive rounds ofDNA endoreduplication. Each phase of endoreduplication (endo-S)is separated by a non-DNA synthetic phase (endo-G). These phasesseem to occur in zones at fixed distances from the root tip.The duration of the phases in two of the endoreduplication cycles(4C–8C, 8C–16C) has been estimated in two ways.The first makes use of the rate of movement of cells throughthe positions along the root where the different phases of thecycle are occurring, the second uses labelling with methyl-[³H]thymidineand autoradiography. Both methods indicate that the endo-S phaseswhich cause the nuclear DNA content to rise from 4C to 8C andfrom 8C to 16C last 8–10 h, and that the intervening endo-Gphase lasts 8–12 h. DNA endoreduplication keeps pace withthe increase of nuclear volume; cell volume increases at a morerapid rate, however. Comparison of the endoreduplication cyclein the metaxylem with the mitotic cycle in the adjoining filesof parenchyma cells shows that the mitotic cells complete theircycle more slowly. DNA synthesis, endoreduplication cycle, mitotic cycle, root apex, Zea mays     

The Role of Maturation Drying in the Transition from Seed Development to Germination: III. INSOLUBLE PROTEIN SYNTHETIC PATTERN CHANGES WITHIN THE ENDOSPERM OF Ricinus communis L. SEEDS

Kermode, A. R., Gifford, D. J. and Bewley, J. D. 1985. The roleof maturation drying in the transition from seed developmentto germination. III. Insoluble protein synthetic pattern changeswithin the endosperm of Ricinus communis L. seeds.—J.exp. Bot. 36: 1928–1936. Immature seeds of Ricinus communisL. cv. Hale (castor bean) removed from the capsule at 30 or40 days after pollination (DAP) can be induced to germinateby being subjected to drying. This desiccation–inducedswitch from development to germination is mirrored by a change,upon subsequent rehydration, in the pattern of insoluble proteinsynthesis within the endosperm storage tissue. During normaldevelopment from 25–40 DAP there is rapid synthesis ofthe insoluble (11S) crystalloid storage protein. At later stagesof development (45 and 50 DAP), crystalloid protein synthesisdeclines markedly and synthesis of new insoluble proteins commences.Following premature drying at 30 or 40 DAP, the pattern of insolubleprotein synthesis upon rehydration is virtually identical tothat following imbibition of the mature seed. Proteins synthesizedduring normal late development (at 45 and 50 DAP) are producedup to 48 h after imbibition; a subsequent change in the patternof insoluble protein synthesis occurs between 48 and 72 h. Thus,in contrast to the rapid switch in the pattern of soluble proteinsynthesis induced by drying, insoluble protein syntheses withinthe endosperm are redirected towards those uniquely associatedwith a germination/growth programme only after a considerabledelay following mature seed imbibition, or following rehydrationof the prematurely dried seed. Nevertheless, these results supportour contention that drying plays a role in the suppression ofthe developmental metabolic programme and in the permanent inductionof a germination/growth programme. Key words: Desiccation, crystalloid storage proteins, castor bean, seed development, seed germination     

RNA Polymerase Activity During Breakage of Seed Dormancy by Low Temperature Treatment of Fruits of Acer platanoides (Norway Maple)

Slater, R. J. and Bryant, J. A. 1987. RNA polymerase activityduring breakage of seed dormancy by low temperature treatmentof fruits of Acer platanoides (Norway maple).—J. exp.Bot. 38:1026–1032. Endogenous RNA polymerase activity has been characterized innuclei isolated from embryo axes of Acer platanoides. Optimalactivity was recorded at 4·0 mol m^–3 MgCl₂ and50 mol m^–3 (NH₄)₂SO₄ and total activity could be inhibitedby up to 30% by -amanitin. Stratification of fruits leads toa stimulation of RNA polymerase activity. A minimum of 3 d coldtreatment is required with at least 3-fold stimulation recordedafter 10 d at 4°C. The increased enzyme activity is resistantto -amanitin suggesting an effect on RNA polymerase I. Key words: Acer platanoides, RNA polymerase, seed dormancy     

Nuclear Chromatin Structure in Relation to Cell Differentiation and Cell Activation in the Cap and Quiescent Centre of Zea mays L.

Barlow, P. W. 1985. Nuclear chromatin structure in relationto cell differentiation and cell activation in the cap and quiescentcentre of Zea mays L —J. exp. Bot. 36: 1492–1503.Nuclear chromatin structure has been analysed by electron microscopyof thin sections of cells in four zones of the root cap—meristem,central, slime-secreting and outermost cells—and alsoin the quiescent centre of the root before and after decapping.The chromatin pattern has been related to the DNA and RNA syntheticactivity of the nuclei. During cap cell maturation there wasa progressive condensation of the chromatin and this was accompaniedby some reduction of RNA synthesis. The degree of condensationwas estimated from the area and number of pieces of electrondense chromatin which increased and decreased, respectively,during cap maturation. The volume fraction of condensed chromatinwas also estimated but, in the cap, was not found to be a goodindicator of nuclear activity. The outermost cells of the capshowed the greatest degree of chromatin condensation but werestill active in RNA synthesis. Microdensitometry of their nuclearDNA contents gave an indication of loss of DNA in some of thenuclei. Decapping activated DNA and RNA synthesis in the quiescentcentre and also stimulated a decondensation of chromatin: thenumber of condensed pieces of chromatin increased, and theirsize and volume fraction both decreased 4 h after decapping.The number of pores per unit length of nuclear envelope profilewas also estimated. In the cap this number increased duringcap maturation; in the activated quiescent centre the numberremained constant except for a small rise 4 h after decapping Key words: Zea mays, chromatin, root cap, quiescent centre     

Induction of biosynthetic enzymes for avenanthramides in elicitor-treated oat leaves

The accumulation of oat (Avena sativa L.) phytoalexins, avenanthramides, occurred in leaf segments treated with oligo-N-acetylchitooligosaccharides. The amount of avenanthramide A, the major oat phytoalexin, reached a maximum 36–48 h after elicitor treatment. This accumulation was preceded by a marked increase in enzyme activities of phenylpropanoid pathway members, including phenylalanine ammonia-lyase (EC 4.3.1.5), cinnamate 4-hydroxylase (EC 1.14.13.11) and 4-coumarate:CoA ligase (EC 6.2.1.12). These enzyme activities reached a maximum 6–12 h after elicitor treatment, when the avenanthramides were produced most rapidly. Both phenylalanine ammonia-lyase and 4-coumarate:CoA ligase activities decreased thereafter to undetectable levels 72 h after treatment, while cinnamate 4-hydroxylase activity showed a second increase 48 h after treatment. Among the chitooligosaccharides tested, tetra- and pentasaccharides most effectively induced these enzyme activities in a dose-dependent manner. The elicitor-induced 4-coumarate: CoA ligase accepted all hydroxycinnamic acids occurring in the avenanthramides as substrates, with the exception of avenalumic acid. These findings indicate that accumulation of the avenanthramides results from de-novo synthesis through the general phenylpropanoid pathway and that early biosynthetic enzymes function as regulatory points of carbon flow to the avenanthramides. Received: 3 December 1998 / Accepted: 27 January 1999     

Muscle glycogen accumulation after endurance exercise in trained and untrained individuals

Hickner, R. C., J. S. Fisher, P. A. Hansen, S. B. Racette,C. M. Mier, M. J. Turner, and J. O. Holloszy. Muscle glycogen accumulation after endurance exercise in trained and untrained individuals. J. Appl. Physiol. 83(3):897-903, 1997.Muscle glycogen accumulation was determined in sixtrained cyclists (Trn) and six untrained subjects (UT) at 6 and either48 or 72 h after 2 h of cycling exercise at ~75% peakO₂ uptake(O_{2 peak}), which terminated with five 1-min sprints. Subjects ate 10 gcarbohydrate · kg¹ · day¹for 48-72 h postexercise. Muscle glycogen accumulation averaged 71 ± 9 (SE) mmol/kg (Trn) and 31 ± 9 mmol/kg (UT) during the first 6 h postexercise (P < 0.01) and 79 ± 22 mmol/kg (Trn) and 60 ± 9 mmol/kg (UT) between 6 and 48 or 72 h postexercise (not significant). Muscle glycogenconcentration was 164 ± 21 mmol/kg (Trn) and 99 ± 16 mmol/kg(UT) 48-72 h postexercise (P < 0.05). Muscle GLUT-4 content immediately postexercise was threefoldhigher in Trn than in UT (P < 0.05)and correlated with glycogen accumulation rates (r = 0.66, P < 0.05). Glycogen synthase in theactive I form was 2.5 ± 0.5, 3.3 ± 0.5, and 1.0 ± 0.3 µmol · g¹ · min¹in Trn at 0, 6, and 48 or 72 h postexercise, respectively;corresponding values were 1.2 ± 0.3, 2.7 ± 0.5, and 1.6 ± 0.3 µmol · g¹ · min¹in UT (P < 0.05 at 0 h). Plasmainsulin and plasma C-peptide area under the curve were lower in Trnthan in UT over the first 6 h postexercise(P < 0.05). Plasma creatine kinaseconcentrations were 125 ± 25 IU/l (Trn) and 91 ± 9 IU/l (UT)preexercise and 112 ± 14 IU/l (Trn) and 144 ± 22 IU/l(UT; P < 0.05 vs.preexercise) at 48-72 h postexercise (normal: 30-200 IU/l).We conclude that endurance exercise training results in an increasedability to accumulate muscle glycogen after exercise.