MORPHOGENESIS IN SPIEODELA OLIGORRHIZA: EFFECTS OF PYRIMIDINE BASE ANALOGUES ON INITIATION, ELONGATION AND DIFFERENTIATION OF FRONDS

The effect of four pyrimidine base analogues and their antidoteson S. oligorrhiza was studied. FUdR stopped cell division at concentrations of 4 10^–7M and higher. This effect could be nullified by the additionof 4 10^–6 M thymidine. Neither uridine nor uracil hadan antidotal effect on FUdR. FU (8 10^–6 M or higher concentration) affected celldivision, frond elongation and differentiation, and could notbe counteracted by either thymidine or uracil. TU (8 10^–4 M) rather specifically inhibited differentiationof frond tissues, while not preventing cell division or theinitiation of new generations. Uracil and uridine at about equimolarconcentrations completely counteracted the TU effect. AzU (10^–3 M) suppressed cell division, frond elongationand frond differentiation. When thymidine (10^–3 M) wasadded simultaneously with AzU only cell elongation and differentiationof fronds were inhibited, but cell division proceeded. 10^–3M uracil (but not uridine) counteracted all effects of AzU. ¹ Based on a portion of the senior author's Ph.D. Thesis.     

Effects of Fusicoccin in 'Isolated' Guard Cells of Commelina communis L

The effects of 3 ? 10^–2 mol m^–3 FC on rubidium fluxesand contents in isolated guard cells of Commelina communis L.have been studied using ⁸⁶RbCl. Fusicoccin causes a marked stimulationof influx and an immediate, apparently irreversible, decreasein efflux of ⁸⁶Rb. The effect on influx is usually more importantin determining the new net flux of Rb. Observed fluxes differmarkedly from those predicted by the Goldman-Hodgkin-Katz equation,suggesting that FC does not act solely via an effect upon theplasmalemma potential. Fusicoccin appears to have a more directeffect upon the ion movements associated with changes in stomatalaperture than either ABA or transfer to the dark. Observed changesin Rb content cannot account fully for the osmotic changes associatedwith aperture increase. Key words: Fusicoccin, Guard cells, Ion fluxes, Commelina communis     

Induction of Cell Division in Leaf Cells of Coconut Palm by Alteration of pH and its Correlation with Glyoxalase-I Activity

Cell division in suspension cultures obtained from leaf cellsof coconut was influenced by pH of the culture media. A 3-foldincrease in cell number was obtained at pH 7.0 compared to suspensionsgrowing at pH 5.0. The pH of both cells and media changed after48 h of growth. Internal cell pH showed a significant increasewhen cultures were grown at pH 7.0 and 8.0 and increased onlyslightly at pH 5.0 and 6.0. Glyoxalase-I activity of cells insuspension culture was found to be pH-depcndent, showing maximumactivity at pH 7.0. Glutathione, a co-enzyme for the substratemethylglyoxaJ for glyoxalase-I, produced a 2-fold increase incell number at a concentration of 5 x 10^–3 mol dm ^–3.The polyamine, spermidine, promoted cell division maximallyat a concentration of 10^–6 mol dm^–3. Methylglyoxal-bis(guanylhydrazone), an inhibitor of spermidine biosynthesis,strongly inhibited cell division giving maximum inhibition ata concentration of 3 x 10^–6 mol dm ^–3. These resultsindicate a positive correlation between cell division and glyoxalase-Iactivity. Key words: Cocos nucifera, glyoxalase-I, pH, spermidine     

Inhibitory effect of lycorine on cell division and cell elongation

Lycorine, an alkaloid isolated from bulbs of Amarillidaceae,was found to be a powerful inhibitor of cell division and elongation.Adding different concentrations of lycorine from 10^–6M to 10^–4 M in an appropriate growth-medium strongly inhibitedcell division in explants of lettuce pith parenchyma. The sameresult was obtained with liquid yeast cultures growing exponentially. Lycorine-treated meristematic cells of the primary roots ofVicia faba also showed rapid inhibition of the mitotic indexwhile interphase cells increased proportionately. Lycorine alsoinhibited endogenous and auxin-induced cell elongation in Avenacoleoptiles and pea segments. Since both cell division and cell elongation require proteinsynthesis and RNA synthesis, the assumption is that lycorineprobably inhibits one of the two syntheses. ¹This study was supported by a contract between the NationalResearch Council of Italy and University of Bari, Instituteof Botany. (Received November 27, 1972; )     

Light dependency of the mating process in Closterium acerosum

Sexual cell division and activation of gametangial cells forconjugation in Closterium acerosum were induced by light. L₂₀₀cells conjugated at maximum level under the following conditions;(i) a light intensity higher than 1,000 lux in a 16-hr lightand 8-hr dark regime and (ii) an illumination time longer than12 hr at 3,000 lux. L₂₀₀ cells also conjugated under continuousillumination at 3,000 lux. The action spectrum for the activation of gametangial cellshad peaks around 450, 611 and 665 nm. 3-(4'-Chlorophenyl)-l,l-dimethylurea (CMU) inhibited the accumulationof carbohydrates and sexual cell division at 10^–5 M andthe activation of gametangial cells for conjugation at 10^–4M. (Received August 15, 1977; )     

On the causes of interspecific differences in the growth-irradiance relationship for phytoplankton. Part I. A comparative study of the growth-irradiance relationship of three marine phytoplankton species: Skeletonema costatum, Olisthodiscus luteus and Gonyaulax tamarensis

Three marine phytoplankton species (Skeletonema costatum, Olisthodiscusluteus andGonyaulax tamarensis) were grown in batch culturesat 15°C and a 14:10 L:D cycle at irradiance levels rangingfrom 5 to 450 µEinst m^–2 s^–1. At each irradiance,during exponential growth, concurrent measurements were madeof cell division, carbon-specific growth rate, photosyntheticperformance (both O₂ and POC production), dark respiration,and cellular composition in terms of C, N and chlorophyll a.The results indicate that the three species were similar withrespect to chemical composition, C:N (atomic) = 6.9 ±0.4, photo-synthetic quotient, 1.43 ± 0.09, and photosyntheticefficiency, 2.3 ±0.1 x 10^–3 µmol O₂ (µgChl a)^–1 h^–1 (µEinst m^–2 s^–1)^–1.Differences in maximum growth rate varied as the –0.24power of cell carbon. Differences in growth efficiency, werebest explained by a power function of Chl a:C at µ = 0.Compensation intensities, ranged from 1.1 µEinst m^–2s^–1 for S. costatum to 35 forG. tamarensis and were foundto be a linear function of the maintenance respiration rate.The results indicate that interspecific differences in the µ–Irelationship can be adequately explained in terms of just threeparameters: cell carbon at maximum growth rate, the C:Chl aratio (at the limit as growth approaches zero) and the respirationrate at zero growth rate. A light-limited algal growth modelbased on these results gave an excellent fit to the experimentalµ–I curves and explained 97% of the observed interspecificvariability. ¹Present address: Lamont-Doherty Geological Observatory Columbiaof University, Palisades, NY 10964, USA     

Hormonal Control of Xylogenesis in Pith Parenchyma Explants of Lactuca

The time course of xylem differentiation was determined in explantsof lettuce pith parenchyma (Lactuca sativa L. cv. Romana) culturedon Murashige and Skoog (1962) medium using different concentrationsof auxin (IAA) and one cytokinin (zeatin or kinetin). Increasinglevels of auxin from I mg 1^–1 to 15 mg 1^–1 in thepresence of a constant level of a cytokinin (zeatin or kinetin)yielded up to 10 mg 1^–1 IAA, an increase in the numberof tracheary element formations. Cytokinin concentrations aboveand below o.1 mg 1^–1 interacting with an optimal xylogenicamount of auxin inhibited xylogenesis. The IAA (10 mg 1^–1)-zeatin(0.1 mg ^1–1) treatment produced the greatest number oftracheids, while kinetin compared to zeatin did not producesuch an effect. The different effectiveness of zeatin and kinetinin inducing tracheary element formations was not due to a differentcapacity of the two cytokinins to stimulate cell division butit seems likely that zeatin, because of interaction with IAA,is more active than kinetin in the determination of the dividingcells in a specific type of cytodifferentiation. The IAA (10mg 1^–1)-zeatin (0.1 mg 1^–1) treatment produced about6.9 per cent tracheids with respect to cell division while IAA(10 mg 1^–1)-kinetin (0.1 mg 1^–1) produced 4.2 percent. These results are discussed with reference to the problemsof hormonal control of xylem differentiation.     

The Effect of L-Phenylalanine on Phenylalanine Ammonia-lyase and Cell Division in Artichoke Callus Culture

5 x 10^–5 M L-phenylalanine overcame the inhibitory effectof white light on cell division in artichoke callus culturesand increased extractable phenylalanine ammonia-lyase (PAL)activity compared to cultures grown in the presence of 5 x 10^–4M phenylalanine The lower concentration of the amino acid alsoenhanced rates of uptake and incorporation of ¹⁴C labelled phenylalaninethroughout G₁ and S. Differences between the two concentrationswere greatest during S with a 4-fold increase in uptake anda 3-fold increase in incorporation It is suggested thereforethat the capacity of 5 x10^–5 M phenylalanine to offsetthe light effect is due to an indirect stimulatory effect onamino acid and protein metabolism Increased levels of extractablePAL activity would then be reflected by this general stimulationof protein synthesis. Helianthus tuberosus L, Jerusalem artichoke, callus culture, cell division, phenylalanine ammonia-lyase     

The Effects of Fusicoccin on Anion Fluxes in Isolated Guard Cells of Commelina communis L.

Clint, G. M. 1987. The effects of fusicoccin on anion fluxesin isolated guard cells of Commelina communis L.—J. exp.BoL 38: 863–876. The effects of 3?10^–2 mol m^–3 fusicoccin (FC) onbromide fluxes and contents in isolated guard cells of Commelinacommunis L. have been studied using K⁸²Br at pH 3?9 and pH 6?7.At pH 3?9 FC caused a reduction in both the influx and the effluxof ⁸²Br, whereas at pH 6?7 FC had no effect on the influx butcaused a transient increase in the efflux of ⁸²Br. There wasno obvious change in bromide content with FC treatment at eitherpH. The behaviour of the anion fluxes in response to FC suggeststhat FC does not act solely via a hyperpolarization at the plasmalemma.A redistribution of bromide between the intracellular compartmentssuggests that anion flux from the cytoplasm to the vacuole maybe stimulated by FC at pH 3?9. The failure of guard cells toincrease their anion content on treatment with FC despite anincrease in stomatal aperture and in cation content suggeststhat in FC-induced stomatal opening excess cation is balancedby organic acid synthesis within the guard cell. Key words: Fusicoccin, guard cells, ion fluxes, Commelina communis     

Colony growth and evidence for colony multiplication in Phaeocystis pouchetii (Prymnesiophyceae) isolated from mesocosm blooms

Using well plates of Phaeocystis pouchetii colonies isolatedfrom experimental mesocosms in western Norway, increases incolony size and division were documented. Median longest lineardimensions increased 0–7 µm h^–1; literaturePhaeocystis globosa values are 0.9–4.7 µm h^–1.Ten to twelve percent of colonies divided at rates of 0.21–0.28divisions day^–1. Daughter colonies were 100 µm smallerthan mother colonies. Colonies delayed 3.5–4.9 days tofirst division, compared with literature values of 4–5days for P. globosa. This study provides the first experimentalevidence for colony division of wild P. pouchetii.     

Growth and grazing rates of Protoperidinium hirobis Abe, a thecate heterotrophic dinoflagellate

Growth and feeding rates of a laboratory-reared small thecateheterotrophic dinoflagellate, Protoperidinium hirobis Abè,grown on the diatom Leptocylindrus danicus, were measured inbatch cultures. Ingestion rates were determined directly bythe enumeration of empty diatom frustules produced by dinoflagellatefeeding. Both growth and feeding rates saturated at diatom concentrationsof {small tilde} 10⁴ cells ml^–1, and reached maximum valuesof 1.7 divisions day^–1 and 23 diatoms grazer^–1 day^–1,respectively. This rate of cell division is notably high comparedto photosynthetic dinoflagellates, which seldom grow fasterthan 1 division day^–1. A maximal clearance rate of 0.5µl h^–1 was measured. Mean cell size varied proportionallywith food abundance, with food-saturated cells having doublethe mean volume of food-depleted cells. Tuning of cell divisionand grazing rate patterns were also examined; while mitosisoccurred chiefly during the dark period, no diel variationsin feeding rate were detected. These rates represent the firstdirect growth and ingestion measurements to be made for a thecateheterotrophic dinoflagellate. They serve to underscore one functionthese dinoflagellates perform within the microzooplanktonicfood web: that of transforming large diatoms into particlesmore easily ingested by microzooplankters.     

Effects of indoleacetic, p-chlorophenoxyisobutyric and 2,4,6-trichlorophenoxyacetic acids on three phases of rooting in Azukia cuttings

In adventitious root formation of disbudded epicotyl cuttingstaken from light-grown, 5-day-old Azukia angularis seedlings,indoleacetic acid (IAA), 1 x 10^–4 M, applied during thefirst day showed no effect, but enhanced the effect of IAA,1 x 10^–4 M, applied during the second day. Treatment duringthe second day promoted rooting by about 70%, and a combinationof treatments for the first and second days promoted rootingsome 200%. p-Chlorophenoxyisobutyric acid (PCIB), 3 x 10^–4M, and2,4,6-trichlorophenoxyacetic acid (2,4,6-T), 2 x 10^–44M, applied the first day also enhanced the effect of IAA, 2x 10^–4 M, applied the second day. When applied the second day, PCIB, 2 x 10^–4M, increasedthe number of root primordia or clusters of small cells, butnot die number of protruded roots. Formation of the cell clusterwas inhibited by 2,4,6-T, 3 x 10^–4M, applied the secondday. Rooting processes in Azukia cuttings seem to include at leastthree phases: the first phase is induced not only by IAA butalso by PCIB or 2,4,6-T, the second phase is induced by IAAor PCIB and the diird phase depends specifically on IAA. (Received October 28, 1970; )     

Direct Organogenesis from Petiole and Thin Cell Layer Explants in Sugar Beet Cultured In Vitro

Detrez, C., Tetu, T., Sangwan, R. S. and Sangwan-Norreel, B.S., 1988. Direct organogenesis from petiole and thin cell layerexplants in sugar beet cultured in vitro.—J. exp. Bot.39: 917–926. Plant regeneration was obtained by direct bud formation frompetiole as well as from thin cell layer explants taken fromsugar beet (Beta vulgaris L.) plants grown in vitro. The budswere mainly induced in the blade-petiole transition zone ofthe explants. High frequency bud regeneration was observed inpetiole and thin layer explants of 10 different breeding linesof sugar beet tested. Organogenesis resulted when petiole explantsexcised from 8-d-old seedlings grown on half-strength Murashigeand Skoog medium (MS) containing 3.0 mg dm^–3 naphthaleneacetic acid (NAA), 3.0 mg dm^–3 6-benzylaminopurine (BAP)and 1.0 mg dm^–3 2, 3, 5, triiodobenzoic acid (TIBA) werecultured on MS with 3.0 mg dm^–3 NAA and 3.0 mg dm^–3BAP. Thin cell layer strips isolated from shoot apices culturedon MS medium supplemented with 0–9 mg dm^–3 BAP or1.0 mg dm^–3 indolebutyric acid (IBA) formed adventitiousbuds on MS medium containing 0–5 mg dm^–3 NAA + 5.0mg dm^–3 BAP. Histological studies confirmed the sub-epidermalorigin of shoots. Key words: Beta vulgaris, direct organogenesis, in vitro culture, petiole, regeneration, thin cell layer     

DNA Levels in Dividing and Developing Plastids in Expanding Primary Leaves of Avena sativa

The amounts of plastid DNA in the primary leaves of 4-d-oldlight- and dark-grown seedlings of Avena sativa were measuredby microspectrofluorometry using the DNA-fluorochrome DAPI (4',6-diamidino-2-phenylindole). In the light-grown primary leaves (40–45 mm long) therewas a marked increase in DNA level per plastid from 10.2 to18.5 ? 10^–15 g between 2.0 mm and 10 mm from the leafbase, resulting from the rate of plastid DNA synthesis beinghigher than the rate of plastid division. Beyond 30 mm the plastidDNA level was reduced to 14 ? 10^–15g due to chloroplastdivision rates being higher than the rate of plastid DNA synthesis,while from 20 mm plastid DNA levels were constant at 2.2 ? 10^–12g per cell, which corresponds to 16000 plastome copies per cell. Observations of dark-grown leaves establish that, in Avena,light is not necessary for plastid division and the dark-grownleaf cells accumulate higher amounts of plastid DNA than light-grownleaf cells. Plastid nucleoids showed a change of distribution after completionof plastid DNA synthesis in light-grown leaves. A change inthe distribution of plastid nucleoids was also observed duringthe greening of etioplasts of dark-grown leaves while plastidDNA level remained constant. Such changes in plastid nucleoiddistribution appear to be independent of plastid DNA synthesisand correlate with the formation of grana stacks. Key words: Avena sativa, microspectrofluorometry, plastid DNA     

Irradiance and daylength effects on growth and chemical composition of Gyrodinium aureolum Hulburt in culture

For Gyrodinium aureolum significant irradiance and daylengtheffects were found on the division rate and on the growth-relevantChla-normalized photosynthetic rate (^gP^B). Optimum conditionsof irradiance and daylength were found at 230 µmol m^–2s^–1 and 14 h for the division rate, and at >260 µmolm^–2 s^–1 and <6 h for ^gP^B.^gP^B showed no photoinhibition,while the division rate decreased markedly at irradiances abovesaturation. This difference and the difference in optimum irradiancebetween the division rate and ^gP^B are explained by a decreasein cellular Chla/carbon ratio with increasing irradiance. Thecellular content of carbon and nitrogen decreased significantlywith increasing irradiance. Total phosphorus was independentof irradiance and daylength. Below the saturation irradiancefor ^gP^B the daily Chla-normalized carbon yield may be describedas an exponential function of the daily irradiance (irradiancex daylength).     

Isolation, Culture, and Plant Regeneration of Protoplasts of Two Shrubby Oxalis Species from South America

Protoplasts were successfully isolated from internodal callustissues of both Oxalis glaucifolia and O. rhombeo-ovata whenthey were digested in a solution containing 0.1% (w/v) MacerozymeR-10, 0.5% (w/v) cellulase Onozuka R-10 and 0.3 mmol m^–3sucrose. Protoplasts proliferated to give cell colonies on Gamborget al.'s B5 medium supplemented with 0.3 mmol m^–3 mannitol,0.5 mg dm^–32, 4-D, and 2.0 mg dm^–3 kinetin. Calluswas produced upon transfer of cell colonies to Murashige andSkoog medium containing 2.0 mg dm^–3 l-naphthaleneaceticacid (NAA) and 0.1 mg dm^–3 kinetin for O. glaucifolia,or with 5.0 mg dm^–3 NAA and 0.5 mg dm^–3 6-benzylaminopurine,for O. rhombeo-ovata. Plants were regenerated from O. glaucifoliaprotoplasts on a medium containing 0.1 mg dm–3 NAA, 1.0mg dm^–3 kinetin and 1.0 mg dm^–3 gibberellic acid,but only vascular nodules were differentiated by O. rhombeo-ovataprotoplast-derived calli. Key words: Tissue culture, protoplasts, plant regeneration, Oxalis spp     

Effects of Fusicoccin and Abscisic Acid on Sugar and lon Transport from Plant Glands

Fusicoccin (FC) inhibited net excretion of Cl^– by theglands of the pitchers of the carnivorous plant Nepenthes hookeriana;of Na⁺ and Cl^– by the salt glands of the halophytes Limoniumvulgare and L. pectinatum and of K⁺ in the nectar of Acer platanoidesflowers. It had no effect on K⁺ elimination with nectar of Impatienswalleriana (extrafloral nectaries) and Abutilon striatum. Abscisicacid (ABA) stimulated net excretion of K⁺ and Cl^– in Nepenthesand of Na⁺ and Cl^– in Limonium but had no effects on K⁺in nectar. Thus, FC and ABA had opposing effects on ion excretionby the salt eliminating glands of Limonium and Nepenthes. Bothcompounds, however, had similar effects on sugar secretion ofnectary glands which was either inhibited or unaffected by FCand ABA. It is suggested that the effects of FC and ABA on ion excretionby gland cells could be reconciled with literature showing FC-stimulationand possible ABA-inhibition of proton pumps at the plasmalemmaof plant cells. Nepenthes hookeriana, Limonium vulgare, Limonium pectinatum, Acer platanoides, salt-glands, nectaries, excretion, fusicoccin, abscisic acid, proton pump     

Growth of Ceratium hirundinella in a subtropical Australian reservoir: the role of vertical migration

A study into the photophysiology, growth and migration of Ceratiumhirundinella in Chaffey Reservoir in subtropical northern NewSouth Wales, Australia, revealed that a proportion of cellsformed subsurface accumulations at depths that optimized lightintensity (212–552 µmol photons m^–2 s^–1)for photosynthesis and cell growth. At high incident irradiance,Ceratium migrated downwards from the near-surface waters, avoidinghigh-light-induced, slow-recovering non-photochemical quenchingof photosystem II. Overnight deepening of the surface mixedlayer by convective cooling produced homogeneous distributionsof Ceratium with a significant proportion of the populationbelow the depth where light saturation of photosynthesis occurred.Ceratium migrated towards the surface from suboptimal lightintensities, at a velocity of 1.6–2.7 x 10^–4 m s^–1.Subsurface accumulations occurred under a variety of turbulenceintensities; however, accumulation was significantly reducedwhen the turbulent velocity scale in the mixed layer was >5x 10^–3 m s^–1, beyond which turbulent diffusion dominatedadvection by swimming. The formation of subsurface accumulationswith increased computed water column integral photosynthesisby 35% compared to a uniform cell distribution.     

Influence of K-Cl cotransporter activity on activation of volume-sensitive Cl- channels in human osteoblasts

The whole cell recording mode of the patch-clamp technique was used to study the effect of hypotonic NaCl or isotonic high-KCl solution on membrane currents in a human osteoblast-like cell line, C1. Both hypotonic NaCl or isotonic high-KCl solution activated Cl^– channels expressed in these cells as described previously. The reversal potential of the induced Cl^– current is more negative when activated through hypotonic NaCl solution (–47 ± 5 mV; n = 6) compared with activation through isotonic high-KCl solution (–35 ± 3 mV; n = 8). This difference can be explained by an increase in intracellular [Cl^–] through the activity of a K-Cl cotransporter. Potassium aspartate was unable to activate the current, and furosemide or DIOA suppressed the increase in Cl^– current induced by isotonic high-KCl solution. In addition, we used the polymerase chain reaction to demonstrate the presence of KCC1–KCC4 mRNA in the osteoblast-like cell line. From these results, we conclude that human osteoblasts express functional K-Cl cotransporters in their cell membrane that seem to be able to induce the indirect activation of volume-sensitive Cl^– channels by KCl through an increase in the intracellular ion concentration followed by water influx and cell swelling. potasium-chloride cotransporter; KCC1–KCC4; chloride channels; extracellular potassium concentration buffering     

Comparison of the Disruption of Mitosis and Cell Plate Formation in Oat Roots by DCPA, Colchicine and Propham

Holmsen, J. D. and Hess, F. D. 1985. Comparison of the disruptionof mitosis and cell plate formation in oat roots by DCPA, colchicineand propham.—J. exp. Bot. 36: 1504–1513. Concentrationsof DCPA, propham and colchicine were selected to cause from0% to greater than 60% inhibition of oat (Avena sativa L. ‘Victory’)root growth after 24 h exposure. Root growth progressively declinedas concentrations were raised from 1·0 to 5·6mmol m^–3 DCPA, 1·0–5·0 mmol m^–3propham, and 50–500 mmol m^–3 colchicine. In additionto inhibiting root growth each mitotic disrupter caused theroot tips to swell to an extent dependent upon concentration.All three compounds effectively disrupted mitosis at concentrationsthat caused less than maximal root growth inhibition. Mitoticdisruption was manifest as a reduction in the number of normalmitotic figures and an increase in the number of condensed prophase,multipolar and anaphase bridge division figures. The frequencyof each type of division figure was different for each of thethree compounds. DCPA disrupted mitosis more effectively whencompared with propham and colchicine at concentrations whichcaused the same amount of root growth inhibition. Each mitoticdisrupter also induced the formation of aberrant cell walls.DCPA was the most effective at disrupting cell plate formation,whereas colchicine was least effective. These data suggest thatthe mechanism of action of DCPA is distinct from the mechanismof colchicine or propham Key words: Avena sativa L., mitotic disruption, DCPA, colchicine, propham