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     

麦红吸浆虫不同滞育期四种糖代谢酶活力分析

海藻糖是麦红吸浆虫Sitodiplosis mosellana (Gehin)滞育期间储藏能量的主要物质,为弄清其在滞育期的积累机理,本文测定了麦红吸浆虫滞育前后和滞育期糖原磷酸化酶（Gpase）、己糖激酶（HK）、磷酸果糖激酶（PFK）和醛缩酶（ALD）这4种糖代谢酶活力的变化。结果表明: 麦红吸浆虫滞育前后这些糖代谢酶活力明显不同,滞育后Gpase 活力显著提高,糖酵解有关酶HK,PFK和ALD活力降低;滞育解除后,Gpase 活力降低,HK,PFK和ALD活力升高。滞育期间,4种糖代谢酶的活力均与滞育发育有关;同时Gpase 和PFK的活力也与环境温度有关,即夏、冬季高于春、秋季;同期不同滞育状态幼虫比较,裸露幼虫HK,PFK和ALD活力总是略高于结茧幼虫,Gpase则相反。滞育当年与第2年同期幼虫4种糖代谢酶的活力无显著差异。     

Modulation of Sucrose Content by Fructose 2,6-bisphosphate during Photosynthesis in Rice Leaves Growing at Different Light Intensities

Reddy, A. R. and Das, V. S. R. 1987. Modulation of sucrose contentby fructose 2,6-bisphosphate during photosynthesis in rice leavesgrowing at different light intensities.—J. exp. Bot. 38:828–833. The relationship between the rate of CO₂ fixation and sucroseconcentration in the leaves of rice (Oryza sativa L.) grownat different light intensities was investigated. Maximum sucrosecontent coincided with maximum rates of CO₂ fixation, achievedat a photon flux density of 1600 µmol m^–2 s^–1.The levels of sucrose and fructose 2,6-bisphosphate were alsocompared in the leaves under different light intensities. Fructose2,6-Msphosphate accumulated during growth at low light. Theactivity of fructose-6-phosphate 2-kinase was high in the leavesgrown at low light while that of fructose-2,6-bisphosphatasewas low. The activities of phosphoglucose isomerase and phospho-glucomutasewere slightly increased by growth at low light The activitiesof UDP glucose pyrophosphorylase were adversely affected invitro with increased concentrations of fructose 2,6-bisphosphatewhile those of sucrose phosphate synthase were moderately affected.Phosphoglucose isomerase and phosphoglucomutase were activatedby fructose 2,6-bisphosphate (8-0 mmol m^–3) by 12-15%.The results suggested that low light intensities during growthresult in an accumulation of fructose 2,6-bisphosphate whichmodulates the key enzymes of sucrose biosynthesis thus regulatingcarbon flow under conditions of limited photosynthesis. Key words: Oryza sativa, photosynthesis, sucrose synthesis, fructose 2,6-bisphosphate, light     

Light-induced Increase in Sucrose Phosphate Synthetase Activity in Leaves of Lolium temulentum

Mature leaves of Lolium temulentum L. were assayed for sucrosephosphate synthetase activity at different times during thephotoperiod. There was a rapid increase in activity at the onsetof illumination which was not observed in leaves maintainedin darkness. The activity prior to illumination was insufficientto catalyse the rates of sucrose synthesis observed in illuminateddetached leaves; after 15 min illumination the two processeswere of similar magnitude. Lolium temulentum L., darnel, sucrose phosphate synthetase, enzyme activity, light, sucrose, starch     

Multiple effects of the inhibitory protein of ethylene production on cellular metabolisms

The effects of an inhibitory protein of ethylene productionisolated from etiolated mung bean hypocotyls (Planta 113: 115,1973) were investigated. Etiolated mung bean hypocotyl segmentsincubated with IAA for 3 hr (1st incubation) to induce ethylene-producingactivity were incubated for 1 hr with IAA in the presence ofthe inhibitory protein and a radioactive material to measuremetabolic activity. Under the conditions where ethylene productionwas inhibited 80% or more by the protein, RNA synthesis, proteinsynthesis and phosphate uptake were suppressed 55–60,65–80, and 60–75%, respectively. Conversion of 1-¹⁴C-acetateto CO₂, lipid, basic and neutral fractions was also inhibited,but the degrees of inhibition were much less than those forthe other processes. When the segments pretreated with the inhibitoryprotein during the 1st incubation period were washed free ofthe protein and assayed for their metabolic activities, theinhibition of RNA and protein syntheses and of phosphate uptakewas partially restored, while ethylene-producing activity wasfully restored to the control level. Similar reversible inhibitoryeffects were also observed for those metabolic activities inthe tissue segments not treated with IAA, thus not producinginduced ethylene. Oxygen uptake and conversion of U-¹⁴C-glucoseto CO₂ were not affected by the inhibitory protein. The possibilitythat the inhibitory protein acts on cell surface membranes andthe modified membranes affect the regulatory mechanism of cellularmetabolism is discussed. ¹ This investigation was supported in part by grants from theMinistries of Education (B-248009), and of Agriculture and Forestryof Japan. (Received November 4, 1977; )     

The Nicotinamide Biosynthetic Pathway Is a By-Product of the RNA World

Many of the biosynthetic pathways, especially those leading to the coenzymes, must have originated very early, perhaps before enzymes were available to catalyze their synthesis. While a number of enzymatic reactions in metabolism are known to proceed nonenzymatically, there are no examples of entire metabolic sequences that can be achieved in this manner. The most primitive pathway for nicotinic acid biosynthesis is the reaction of aspartic acid with dihydroxyacetone phosphate. We report here that nicotinic acid (NAc) and its metabolic precursor, quinolinic acid (QA), are produced in yields as high as 7% in a six-step nonenzymatic sequence from aspartic acid and dihydroxyacetone phosphate (DHAP). The biosynthesis of ribose phosphate could have produced DHAP and other three carbon compounds. Aspartic acid could have been available from prebiotic synthesis or from the ribozyme synthesis of pyrimidines. These results suggest that NAD could have originated in the RNA world and that the nonenzymatic biosynthesis of the cofactor nicotinamide could have been an inevitable consequence of life based on carbohydrates and amino acids. The enzymes of the modern pathway were later added in any order. Received: 22 May 2000 / Accepted: 7 August 2000     

Biosynthesis of Anthraquinone by Cells of Galium mollugo L. Grown in a Chemostat with Limiting Sucrose or Phosphate

Growth and anthraquinone biosynthesis by Galium cells were examinedin steady-state substrate-limited conditions using a chemostatcontinuous culture technique. Steady-state growth was obtainedin both sucrose- and phosphate-limiting conditions for periodsup to 60 d. In sucrose-limiting conditions three growth rateswere investigated with doubling times (t_d) of 25 h, 35 h and40 h, and phosphate-limited growth was obtained at t_d= 35 h.The kinetics of the growth response to a change in limitingsubstrate concentration in sucrose-limiting conditions was examinedand found to follow closely that predicted by the applicationof Monod's (1950) model obtained for micro-organisms. The anthraquinone content of cells grown in phosphate and sucroselimitation was uniformly similar and at a relatively low level(0.68 mg g^–1 dry wt.). When the substrate limitation wasrelieved by the addition of the limiting substrate, either phosphate,or sucrose, anthraquinone synthesis was markedly stimulated.The addition of the anthraquinone precursor, orthosuccinyl benzoicacid (OSB) greatly enhanced anthraquinone synthesis in phosphate-limitingconditions but not in sucrose-limited cells. The results show that growth limitation by phosphate and bysucrose causes a suppression of the rate of synthesis of thesecondary metabolite anthraquinone in Galium cells and suggeststhat the metabolic point of suppression is different in eachcase. Key words: Anthraquinone biosynthesis, Galium, Continuous culture, recursor feeding     

Nucleotide pools in suspension-cultured cells of Datura innoxia

A general picture of the metabolic events which govern to growth behaviour of a batch culture of suspended dedifferentiated cells of Datura innoxia is obtained by following both the uptake and accumulation of the medium phosphate and sucrose by the cells, and the synthesis of RNA, protein and starch. The results are compared with the changes in the nucleotide pools described in the preceding paper. The sequence of formation and the regulatory dependencies of cellular pools of phosphate, sucrose, nucleotides and RNA in the production of proteins, starch and cell mass, and in the control of proliferation and cell growth are discussed. Furthermore, the importance of the maintenance pools for metabolic survival during starvation is emphasized.     

Changes in the activities of some enzymes of carbohydrate metabolism in Amaryllis vittata pollen suspension cultures

Amaryllis vittata pollen grown in suspension cultures utilizeexogenous carbohydrates for starch synthesis and pollen tubegrowth; tube growth is influenced by both monosaccharides andoligosaccharides in the culture medium but not by ribose andxylose. The level of starch in germinating pollen was influencedby the availability of exogenous carbohydrates. Specific activitiesof some enzymes of glycolysis and pentose phosphate pathwaysvaried during pollen germination. The activities of all theenzymes, except glucose-6-phosphate dehydrogenase, showed moreor less pronounced increase initially, followed by a generaldecrease in later stages. The increase in the enzyme activitieswas affected by the presence of cycloheximide in the incubationmedium. (Received October 20, 1977; )     

Changes in RNA and Protein Metabolism Associated with Alterations in the Germination Efficiency of Sunflower Seeds

Precise knowledge of seed quality after harvest and during storageis of particular importance for seed producers. We analyseddifferent sunflower seed lots (Helianthus annuusL.) characterizedby extremes of germination ability. We used RNA analysis tostudy possible changes in gene expression in seeds unable togerminate. Total RNA content was very small in dry seeds showinga low germination ability. Capacity for total RNA synthesisat the onset of imbibition was also reduced in these seeds.In addition, correlations were found between these parametersand germination ability at 19 °C. We demonstrated a highcorrelation between the amount of total RNA in the dry seed,the capacity of RNA synthesis at the onset of imbibition andthe seed moisture content at the time of the harvest. The abilityof dry seed mRNAs to be translatedin vitrowas also reduced andseven polypeptides, from stored mRNAs, were characteristic ofthe cotyledons from high germinability seeds. Germination canthus be affected at several levels including membrane, enzymaticand nucleic acid deteriorations. Gene expression; germination ability; Helianthus annuusL.; marker; protein; RNA; seed; sunflower     

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; )     

RNA synthesis required for DNA replication in Vicia seed embryos

The synthesis of DNA and RNA during germination of Vicia seedswas examined. Incorporation of ³H-thymidine into DNA reacheda maximum at about 32 hr after the beginning of imbibition,and RNA synthesis was shown to precede DNA replication. Sedimentationanalyses of ³H-uridine-labeled RNAs indicated that the embryossynthesize all types of rRNA, heterodisperse RNA and 4–5SRNA before and also during the phase of DNA replication. Actinomycin-treatments at lower concentrations (50 or 100 µg/ml)resulted in the specific inhibition of rRNA synthesis. Suchinhibition did not lead to a large reduction in ³H-thymidineincorporation during the replication phase. However, DNA synthesiswas drastically inhibited by a higher level (200 µg/ml)of actinomycin D. The results strongly suggest the involvementof synthesis of heterodisperse RNA in DNA replication. (Received May 28, 1976; )     

Some Aspects of Phosphate Nutrition in the Root System of Broad Bean (Vicia faba)

An attempt was made, using radiophosphate, to trace the movementof phosphate in the root systems of Vicia faba during the period0 to 2 hours after commencement of uptake. The results showthat phosphate inserted at an isolated point is first distributedabout the root systems of turgid plants and tends to accumulatetemporarily in the lateral roots before large-scale movementup the plant axis begins. This increased concentration in thelaterals, which is not thought to represent metabolic accumulation,is at a maximum at 75 minutes in turgid plants but in wiltedplants it terminates more rapidly. It is affected by potassiumcyanide solutions.     

Correlation between the rate of protein and nucleic acid synthesis and the intensity of various glucose metabolic pathways in rat liver cells

A sharp and strong suppression of protein synthesis by cycloheximide in liver cells of starving rats is paralleled with activation of RNA synthesis and glucose-6-phosphate dehydrogenase production. Subsequent reconstitution and stimulation of protein synthesis (6-12 hrs after cycloheximide injection) result in activation of hexokinase. Upon stimulation of DNA synthesis (48-60 hrs after cycloheximide injection) the activity of both enzymes is very low. Since glucose-6-phosphate dehydrogenase appears to be the limiting step of glucose decay via the pentose phosphate pathway, and hexokinase is the limiting step of glycolysis, it was assumed that RNA synthesis predominantly occurs via the pentose phosphate pathway, while that of proteins via glycolysis.     

RNA Synthesis in the Apex of Sinapis alba in Transition to Flowering

RNA synthesis in the 1.5 mm apex during floral evocation ofSinapis alba (a long-day plant) was measured using a double-labellingtechnique to compare precursor incorporation in evoked and vegetativeapices, followed by analysis by gel electrophoresis and oligo(dT)-cellulosechromatography. In plants induced to flower by exposure to asingle long day, higher levels of RNA synthesis showed a two-phasepattern, the first increase starting very early in evocation,from 10 h after the start of the long day. This early extrasynthesis is of rRNA, and then also sRNA.² Subsequently higherlevels of RNA synthesis, especially rRNA and 5S RNA, are shownfrom 36 h. At no time was such additional synthesis of the RNAfraction retained on oligo(dT)-cellulose detected. The experimentwas repeated with plants subjected to a single displaced shortday, a treatment which also induces flowering, and similar higherRNA synthesis found in evoked apices. These results were comparedwith those obtained in two non-inductive treatments which resultin some features of floral evocation: a single short day athigh intensity light, and a single treatment with benzyladenine.Neither gave rise to additional RNA synthesis, and thus theobserved high levels of synthesis of rRNA and sRNA seem to beassociated with other features of floral evocation.     

A Biochemical Study of Spore Germination in the Blue-green Alga Anabaena doliolum

The spores of Anabaena doliolum formed in light (light spores)and after transfer to darkness (dark spores) are biochemicallydifferent in that the light spores contain chlorophyll a andphycocyanin, while dark spores seem to lack them. The apparentbiosyntheses accompanying dark-spore germination seem to proceedin the following order: RNA, chlorophyll a, phycocyanin andDNA. Results of chloramphenicol treatment indicate that proteinsynthesis precedes RNA synthesis. The biosynthetic events followingRNA synthesis show a requirement for light.     

A Cytochemical Study of DNA, RNA, and Protein in the Developing Maize Anther: II. Observations

Changes in acetic-alcohol fixable DNA, RNA, and protein werefollowed in the tapetum, sporogenous tissue, and spores of thedeveloping maize anther using standard cytochemical methodsand microdensitometry. In the tapetum, early nuclear divisionsoccur without prior DNA synthesis, giving a population of IC nuclei. Subsequent synthesis produces the equivalent of 34,000C amounts per pollen sac, 20 times more than is present in thespores before pollen mitosis. The main tapetal RNA synthesisis during the meiotic prophase, with a further period of accumulationin the interval, tetrad to young spores. In the meiocytes, theprincipal accumulation is in the early prophase, with no synthesisduring the meiotic divisions or through the tetrad period. Proteinaccumulation occurs in the tapetum up to mid-meiotic prophase;after this there is a pause, followed by further synthesis frommeiotic metaphase I to the final dissolution of the tissue.In the meiocytes, protein is accumulated through the early prophase;there is no synthesis during the meiotic mitoses or in the tetradperiod, but active accumula-tion occurs in the developing spores. The implications of these observations are discussed in relationto the function of the tapetum.     

Enhancing effects of CO2 on chloroplast regeneration in glucose-bleached cells of Chlorella protothecoides II. Role of carbamylphosphate in chloroplast regeneration

Levels of the activities of glutamine-dependent carbamylphosphatesynthetase, ornithine-and aspartate-transcabamylase and phosphoenolpyruvatecarboxylase were followed in greening cells of Chlorella prolothecoides.Among the enzymes examined the activity of carbamylphosphatesynthetase was extremely low, especially at the early phaseof greening. Arginine (but not ornithine or aspartate), when administeredto algal cells at the 24th hour of greening, stimulated thesyntheses of RNA, protein and chlorophyll in the subsequentperiod. It also affected the metabolic pathway of the ¹⁴CO₂supplied simultaneously with arginine in the presence of CMU.Arginine produced a decreased incorporation of ¹⁴C into proteinand an increased incorporation into nucleic acid. The mechanismof the action of CO₂ on chloroplast regeneration is discussed.We concluded that chloroplast regeneration in glucose-bleachedcells is limited by the synthesis of carbamylphosphate, especiallyin the early phase of greening. (Received August 19, 1975; )