bluuebunny/crossref_metadata_2025_split huggingface dataset:
IS ABSCISIC ACID A UNIVERSALLY ACTIVE CALCIUM AGONIST?
Authors: HUDDART H. , SMITH R. J. , LANGTON P. D. , HETHERINGTON A. M. , MANSFIELD T. A. 
Published: May 2006

SUMMARYRecent studies of the control of stomatal aperture by abscisic acid (ABA) have suggested that its cellular action depends on the availability of calcium ions, which appear to function as secondary messengers. Stimulus‐response coupling may, therefore, be similar to that found in many animal tissues.We report here preliminary evidence that ABA has a profound effect on some mammalian tissues and on a cyanobacterium. Studies on smooth muscles from the vas deferens and bladder of rat showed that 10−6 M ABA enhanced field stimulation responses by about 25 %. This effect was inhibited by the calcium‐channel blocker, nifedipine. In K+‐depolarized bladder smooth muscle in which the fast calcium channels were voltage‐inactivated, 10−6 M ABA augmented contracture tension, and enhanced the slow tonic phase of the response which is known to be dependent on the activity of slow calcium channels. Comparative studies using ABA and the synthetic calcium agonist BAY K 8644 suggested that there are close parallels in the mode of action of the two compounds. Heal smooth muscle was remarkably sensitive to ABA, showing enhancement of K+ contracture tension by up to 400% at only 10−9 to 10−8 M ABA.In cultures of Nostoc 6720, low concentrations of ABA (about 10 −7 M) caused a substantial increase in the heterocyst/vegetative cell ratio. Addition of ABA further enhanced the increase in heterocyst content caused by increases in the concentration of Ca2+ in the medium. These observations provide further support for the proposal that ABA functions as a calcium agonist, a concept consistent with similarities between the action of ABA and the calcium ionophore A23187. In cultures of Nostoc 6720, high (> 10−5 M) concentrations of ABA had an inhibitory effect, and some evidence of a similar dose‐response relationship was found in mammalian tissues.Preliminary studies using 45Ca2+ suggested that ABA stimulates the influx of calcium into both vasa deferentia and Nostoc 6720. It is concluded that ABA may function as a calcium agonist when applied to a wide range of prokaryotic and eukaryotic cells. A recent observation that it is present in the brain of some mammals suggests that this ‘plant hormone’ may be of much wider biological significance than hitherto recognized. The similar responses of plant, animal and cyanobacterial cells to ABA might indicate the presence of cellular mechanisms which have been genetically conserved through many stages of evolution.
LONG DAY CONTROL OF FLOWERING IN POA NEMORALIS IN CONTROLLED AND NATURAL ENVIRONMENTS
Authors: HEIDE OLA M. 
Published: May 2006

SUMMARYFlower initiation and development in a local population of Poa nemoralis L. were studied in controlled and natural environments at As, Norway, 59° 40′ N. At temperatures ranging from 6 to 21 °C flowering occurred in long days (LD) only. At 12 h photoperiod the plants remained vegetative for at least 145 d. The critical photoperiod for floral initiation was about 14 h at IS and 21°C, slightly longer at 9 °C. A minimum of two LD cycles was required for floral induction at 15 °C when flower development took place in 12 h photoperiod, while more than four LD cycles were required for flower development in 8 h photoperiod. Viviparous proliferation of inflorescences resulted from marginal LD induction and subsequent flower development in short days (SD). The observed critical photoperiods agreed well with the time of floral initiation in the field, the critical photoperiod being reached as soon as growth is initiated in the spring. It is concluded that P. nemoralis is an obligatory long day plant with no SD or low temperature vernalization requirement.
THE ACTIVITY AND CHARACTERIZATION OF ACID PHOSPHATASES IN ENDOMYCORRHIZAL FUNGI OF THE ERICACEAE
Authors: Straker C. J. , Mitchell D. T. 
Published: May 2006

SUMMARYEndomycorrhizal fungi were isolated from the root systems of Vaccinium macrocarpon Aiton, Rhododendron ponticum L., Calluna vulgaris (L.) Hull (Ericaceae) and also from a South African erica, Erica hispidula L. They were grown on a liquid medium containing inositol hexakisphosphate, fractionated into cytoplasmic, extracellular and wall‐ and membrane‐bound fractions and assayed for acid phosphatase. Extracellular phosphatase was demonstrated in all cultures but its activity was highest in the endophyte of E. hispidula. The wall‐ and membrane‐bound acid phosphatase was the dominant fraction in the European endophytes. The extracellular acid phosphatase of high P‐fed (3.23 mM P) mycelia of the endophytes of E. hispidula had the greatest activity (76% of total activity), whereas in low P‐fed (0.1 mM P) mycelia both wall and extracellular fractions contributed almost equally to form 80% of total activity. All the fractions contained an acid phosphatase of 173858 MW with a broad pH optimum of 2.0 to 6.0 but a smaller enzyme of 68028 MW with a pH optimum of 6.5 also occurred in the wall fraction from low P‐fed mycelia. All the enzymes were inhibited by fluoride, molybdenum, arsenate, cyanide, mercury and phosphate but stimulated by EDTA, citrate and the ferric ion at low concentrations. A wide substrate specificity was demonstrated with maximum affinity for inorganic pyrophosphate, high affinities for α and β‐naphthyl phosphate, phenyl phosphate and a‐glycerophosphate and a low affinity for phytic acid. The low molecular weight enzyme was the only one which hydrolysed organic anhydrides (ATP, ADP and AMP).
MICROPROPAGATION OF CHESTNUT AND CONDITIONS OF MYCORRHIZAL SYNTHESES IN VITRO
Authors: STRULLU D. G. , GRELLIER B. , MARCINIAK D. , LETOUZÉ R. 
Published: May 2006

SummaryChestnut (Castanea sativa Mill.) was cloned in vitro. Mycorrhizal syntheses were obtained between cloned plants and Paxillus involutus (Batsch.) Fr. In the case studied, MNM nutrient solution did not favour the development of the host plants. The composition of an original nutrient solution was determined for the mycorrhizal infection of chestnut in vitro. The mycorrhizas obtained were studied by scanning electron microscopy.
VESICULAR–ARBUSCULAR MYCORRHIZA IN NATURAL VEGETATION SYSTEMS
Authors: FRANCIS R. , FINLAY R. D. , READ D. J. 
Published: May 2006

SummaryThe role of inter‐plant hyphal bridges formed by vesicular‐arbuscular (VA) mycorrhizal mycelia was investigated using double pots in which donor plants were grown in the mycorrhizal (M) or non‐mycorrhizal (NM) condition with root systems split so that they could be supplied with nutrients in the donor pot. Plantago lanceolata L. and Festuca ovina L. were grown in intra‐and inter‐specific combination as donors and receivers. The normally non‐mycorrhizal species Arabis hirsuta L. was included as an additional potential receiver. Nutrient solution or distilled water was applied to the donor pot and the patterns of growth responses, and of nitrogen and phosphorus accumulation were compared in receiver plants with and without mycelial interconnections.Yields of M receivers were significantly higher than those of NM plants in all combinations of plants at the second or third harvest, except in the case of the intra‐specific combination of Plantago. A. hirsuta showed no response to nutrient application. Mycorrhizal infection of receivers in the distilled water treatment produced a relatively small response indicating that improved exploitation of sand in the receiver pots was not the cause of growth stimulation in M receivers.Yield increases were associated with higher total N contents of the mycorrhizal receiver plants in three of the species combinations and of P content in all combinations, by the third harvest the gain in P concentration being relatively greater than that of N.The results confirm that VA infection can provide channels for direct inter‐plant nutrient transfer and that transfer is sufficient to sustain significant enhancement of both growth and nutrient composition of receivers, in some cases within six weeks of commencement of the treatment. The probable physiological and ecological significance of these observations is discussed.
DIFFERENTIAL (HOST‐SPECIFIC) ACCUMULATION OF ZOOSPORES OF PYTHIUM ON ROOTS OF GRAMINACEOUS AND NON‐GRAMINACEOUS PLANTS
Authors: MITCHELL R. T. , DEACON J. W. 
Published: May 2006

SummaryZoospores of Pythium graminicola Subramanian and P. arrhenomanes Drechs., which characteristically infect the Gramineae, differed from spores of P. aphanidermatum (Edson) Fitzp. and P. ultimum Trow, which have wide host ranges, by accumulating to a greater degree on roots of graminaceous as compared with non‐graminaceous plants. These differential responses occurred with wild plants collected from field sites or grown in a glasshouse, but not with cultivated cereals and dicotyledonous plants (Antirrhinum majus L. and Lycopersicon esculentum Mill.) grown in a glasshouse. Differential responses involved mainly encystment and accumulation of encysted spores, rather than taxis.Root mucigel was implicated in zoospore accumulation. Host‐differences in this respect did not occur with damaged roots; treatment of roots with methylene blue or periodate (but not alcian blue or Calcofluor) prevented or reduced zoospore encystment without markedly affecting accumulation of motile zoospores.
PHYSIOLOGICAL AND ANATOMICAL ASPECTS OF PHOTOSYNTHESIS OF TWO AGROSTIS SPECIES AT A SUB‐ANTARCTIC ISLAND
Authors: PAMMENTER N. W. , DRENNAN PHILLIPPA M. , SMITH V. R. 
Published: May 2006

SummaryLeaf anatomy, rates of photosynthesis, leaf N, chlorophyll, RuBP carboxylase and nitrate reductase were studied on the indigenous Agrostis magellanica Lam. and the invasive alien Agrostis stolonifera L. on Marion Island (46° 54′ S, 37° 45′ E). Leaves of A. magellanica were more deeply ridged, thicker and more sclerophyllus than those of A. stolonifera. Mesophyll cells of A. magellanica were larger but the number of cells per unit leaf area and the total area of chloroplast per unit leaf area were the same for the two species. Maximum CO2 assimilation rates for the two species did not differ (mean maxima of 9.5 and 9 μmol CO2 m−2s−1for A. magellanica and A. stolonifera respectively). At low photon flux densities, A. stolonifera showed a greater response of CO2 assimilation to photon flux density. A. magellanica exhibited temperature‐dependent photoinhibition. Leaf N, chlorophyll and RuBP carboxylase on a fresh or dry weight basis were higher in A. stolonifera but on a leaf area basis there was little difference between the species. The competitive ability of A. stolonifera on Marion Island may be related to its response to low photon flux densities or to its carbon allocation patterns (less sclerophyllous tissue means that a greater leaf area may be produced per unit carbon fixed). The lack of support tissue may limit it to sites partly sheltered from frequent gale force winds.
RE‐INVESTIGATION OF SECRETORY CAVITY DEVELOPMENT IN LYSIMACHIA (PRIMULACEAE)
Authors: LERSTEN NELS R. 
Published: May 2006

SummaryNineteenth century studies described Lysimachia cavities as schizogenous, but Guttenberg (1928) reported them as only being schizogenous initially. Inner epithelial cell walls then swelled and dissolved in mucilage secreted into the cavity. Later, as a gradually solidifying resin accumulated, epithelial cells reportedly formed a new and cellulosic cell wall. My re‐examination of cavity development in Lysimachia nummularia L., using a resin embedding method, revealed only typical schizogenous development, thus refuting Guttenberg's interpretation and supporting earlier workers.
SOIL MOISTURE INFLUENCES COLONIZATION OF PRAIRIE CORDGRASS (SPARTINA PEC TIN ATA LIND.) BY VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI
Authors: ANDERSON ROGER C. , EBBERS BERT C. , LIBERTA ANTHONY E. 
Published: May 2006

SummaryWe examined mycorrhizal development in prairie cordgrass (Spartina pectinate Lind.), a mycorrhizal plant that typically occupies wet habitats, under different soil moisture conditions. The five experimentally induced soil moisture conditions ranged from continuous saturation to allowing soil moisture tensions to reach – 15 bars and then saturating the soil 48 h later.Colonization by vesicular‐arbuscular mycorrhizal (VAM) fungi occurred under all experimental conditions but was significantly greater when plants were grown under conditions of 24 h saturation followed by 48 h of drainage than under any other moisture regime. There was a significant negative correlation between VAM fungal colonization and the weight of the rhizome‐tiller units used to propogate experimental plants. Plant growth was not significantly affected by treatment conditions and there were no significant correlations between measured plant growth response and VAM colonization.
ECTOMYCORRHIZAS OF TROPICAL ANGIOSPERMOUS TREES
Authors: ALEXANDER I. J. , HÖGBERG P. 
Published: May 2006

SummaryDetails are presented of ectomycorrhizas in seventeen genera of tropical angiospermous trees from six families. Mycorrhizas of Intsia, Melaleuca, Monotes, Neea, Tristania and Vateria are figured for the first time. Overall, the tropical mycorrhizas are of a smaller diameter than is typical for those of temperate angiosperm trees but the sheaths are thicker and the fungus can form up to about 80% by weight of the dual organ. Our observations do not support the notion of a higher degree of host/fungus specificity in the tropics than in the temperate zones.
STUDIES ON THE TOLERANCE TO SULPHUR DIOXIDE OF GRASS POPULATIONS IN POLLUTED AREAS
Authors: WILSON G. B. , BELL J. N. B. 
Published: May 2006

SummaryThe evolution of tolerance to sulphur dioxide (SO2) under differing degrees of selective pressure over the same period of time was investigated in Festuca rubra L. and Dactylis glomerata L. along a transect away from a point source (a smokeless fuel factory) in northern England. Populations of both species were sampled from eight sites along the 2 km transect, starting close to the factory. All populations were screened for relative sensitivity to acute injury, assessed as degree of leaf damage after fumigation with a high concentration of SO2. In the case of F. rubra, relative sensitivity to chronic injury was also determined, on the basis of changes in growth in response to a prolonged fumigation with a moderate concentration of SO2. Festuca rubra showed a clear cline of decreasing tolerance to acute injury with distance from the point source, but no such pattern was apparent for D. glomerata. Although the chronic fumigation produced reductions in various growth parameters for F. rubra, there was no clear indication of changes in tolerance along the transect. The pattern of evolution of acute SO2 tolerance in F. rubra is discussed in relation to the selective pressures imposed at different sites by combinations of high and low level emissions from the factory. The occurrence of tolerance to acute, but not chronic injury is in agreement with earlier work by the authors, which suggested that there was greater potential for the rapid evolution of the former at polluted sites.
REGENERATION OF SPHAGNUM
Authors: CLYMO R. S. , DUCKETT J. G. 
Published: May 2006

SummaryWhen disc‐shaped horizontal slices of peat cores, three from a bog in mid‐Wales and three from a bog in Hampshire, were kept for several months in a saturated atmosphere in a cool greenhouse numerous new shoots of Sphagnum papillosum (Lindb. S. magellanicum Brid. and S. recurvum P. Beauv. were produced.The new shoots arose on peat discs from at least 30 cm below the surface and water table and from regions in which the Sphagnum appeared to be brown and dead. A timescale, inferred from the cumulative dry mass and the peak in 137Cs concentration (which was assumed, conservatively, to reflect the 1963 peak influx), indicates that the matrix of the deepest discs from which new shoots arose was from 25 to perhaps 60 years old.Many of the new shoots of Sphagnum arose as innovations from the outer cortex of buried stems. In most cases the first leaves on these had the usual dimorphic leaf cell pattern. Other shoots, which initially produced leaves with monomorphic cells, arose from protonemata, comprising irregularly lobed plates of tissue and sparsely branched filaments with oblique cross‐walls. A few of the protonemata arose from old stems, a feature not reported before, but the vast majority had no attachment to old plants and are thought to have grown from spores.Light and air were necessary if new shoots were to appear. But very few innovations or protonemata were found in the green discs from near the surface of the core. This suggests some kind of hormonal control of innovations akin to apical dominance in vascular plants and a more general allelopathic inhibition of spore germination and protonemal growth by green Sphagnum.Fern gametophytes of at least two taxa (Dryopteris‐like and Pteridium‐like) grew on the peat discs with distribution patterns similar to those of new Sphagnum shoots. Seedlings of five taxa of vascular plants – all species growing close to the core‐sites – appeared on the peat discs but much more erratically than Sphagnum and the ferns. Stems of five species of leafy liverwort, presumed to have been derived from subterranean axes rather than from gemmae or spores, were also recorded, but no other bryophytes were seen.The discovery that morphogenesis in Sphagnum is far more fluid than hitherto assumed has far‐reaching physiological, ecological and possibly genetical implications. The development of protonemata under semi‐natural conditions, recorded here for the first time, confounds the results of culture experiments which had indicated that Sphagnum protonemata were unlikely to grow on peat.
Effects of Single‐Site Versus Biventricular Epicardial Pacing on Myocardial Performance in an Immature Animal Model of Atrioventricular Block
Authors: COJOC ANCA , REEVES JAMES G. , SCHMARKEY LAURA , STRIEPER MARGARET J. , JOYNER RONALD W. , WAGNER MARY B. , CAMPBELL ROBERT M. , VINTEN‐JOHANSEN JACOB , FRIAS PATRICIO A. 
Published: May 2006

Introduction:  Single‐site ventricular pacing results in dyssynchronous ventricular activation and may contribute to ventricular dysfunction. We evaluated epicardial biventricular (BiV) pacing as a means of maintaining synchronous ventricular activation in an acute piglet model of AV block with normal ventricular anatomy and function. Methods and Results: We used left ventricular (LV) impedance catheters and tissue Doppler imaging to assess the cardiodynamics of immature piglets (n = 6, 33–78 days, 9.35 ± 0.85 kg). Following catheter ablation of the AV node, a pacemaker was programmed 20 beats per minute above the intrinsic atrial rate. The animals were paced at 5‐minute intervals via the following AV sequential configurations: Right atrial appendage (RA)‐RV apex (RVA), RA‐LV apex (LVA), and RA‐biventricular (RVA/LVA). RA‐RVA was the experimental control. LV systolic mechanics, measured by the slope of the end‐systolic pressure–volume relationship (Ees), increased with BiV pacing (12.8 ± 3.4 mmHg/mL, P < 0.02) or single‐site LVA pacing (10.6 ± 3.4 mmHg/mL, P < 0.05) compared with single‐site RVA pacing (8.3 ± 1.4 mmHg/mL). QRS duration lengthened compared with sinus rhythm (42 ± 8 msec) with either RVA (56 ± 9 msec, P < 0.02) or LVA (54 ± 7 msec, P < 0.03), but not with BiV (48 ± 7 msec, P = 0.08) pacing. Tissue Doppler imaging showed LV dyssynchrony with RVA (septal‐to‐lateral delay 46.0 ± 51.7 msec), with return toward normal with LVA (−9.6 ± 33.6 msec, P < 0.04) or BiV (−4.1 ± 33.8 msec, P < 0.04) pacing. Conclusions: In this acute immature piglet model of AV block, LV performance improved with single‐site pacing from the LVA and BiV pacing (RVA/LVA), as compared with single‐site pacing from the RVA. These changes correlated with tissue Doppler indices of mechanical synchrony, though not necessarily with QRS duration.
Fibrillating Areas Isolated within the Left Atrium after Radiofrequency Linear Catheter Ablation
Authors: ROSTOCK THOMAS , ROTTER MARTIN , SANDERS PRASHANTHAN , JAÏS PIERRE , HOCINI MÉLÈZE , TAKAHASHI YOSHIHIDE , SACHER FRÉDERIC , JÖNSSON ANDERS , O'NEILL MARK D. , HSU LI‐FERN , CLÉMENTY JACQUES , HAÏSSAGUERRE MICHEL 
Published: May 2006

Introduction: Nonpulmonary vein sources have been implicated as potential drivers of atrial fibrillation (AF). This observational study describes regions of fibrillating atrial tissue isolated inadvertently from the left atrium (LA) following linear catheter ablation for AF. Methods and Results: We report four patients with persistent/permanent AF who underwent pulmonary vein isolation with additional linear lesions and who presented with recurrent AF (mean AF cycle length [AFCL] 175–270 ms). Further catheter ablation resulted in the inadvertent electrical isolation of significant areas of the LA in which AF persisted at the same AFCL as was measured prior to disconnection, despite the restoration of sinus rhythm (SR) in all other left and right atrial areas, strongly suggesting that these islands were driving the remaining atria into fibrillation. The disconnected areas were located in the lateral LA, including the left atrial appendage (LAA) in three patients (limited to the LAA in one) and in the posterior LA in one patient. These isolated fibrillating regions represented 15–24% of the global LA surface, as estimated by electroanatomic mapping. Conclusion: Fibrillation can be maintained within electrically isolated regions of the LA following catheter ablation of AF, demonstrating the importance of atrial drivers in the maintenance of AF. Further mapping of these drivers is needed to characterize their mechanism and thereby allow for a more specific ablation strategy.
Bone healing and graft resorption of autograft, anorganic bovine bone and β‐tricalcium phosphate. A histologic and histomorphometric study in the mandibles of minipigs
Authors: Jensen Simon Storgård , Broggini Nina , Hjørting‐Hansen Erik , Schenk Robert , Buser Daniel 
Published: May 2006

AbstractObjective: The purpose was to qualitatively and quantitatively compare the bone formation and graft resorption of two different bone substitutes used in both orthopedic and oral surgery, with autogenous bone as a positive control.Materials and methods: Three standardized bone defects were prepared in both mandibular angles of 12 adult minipigs. The defects were grafted with either autograft, anorganic bovine bone (ABB), or synthetic β‐tricalcium phosphate (β‐TCP). Sacrifice was performed after 1, 2, 4, and 8 weeks for histologic and histomorphometric analysis.Results: At 2 weeks, more new bone formation was seen in defects filled with autograft than with ABB (P∼0.0005) and β‐TCP (P∼0.002). After 4 weeks, there was no significant difference between β‐TCP and the two other materials. Defects grafted with ABB still exhibited less bone formation as compared with autograft (P∼0.004). At 8 weeks, more bone formation was observed in defects grafted with autograft (P∼0.003) and β‐TCP (P∼0.00004) than with ABB. No difference could be demonstrated between β‐TCP and autograft. β‐TCP resorbed almost completely over 8 weeks, whereas ABB remained stable.Conclusion: Both bone substitutes seemed to decelerate bone regeneration in the early healing phase as compared with autograft. All defects ultimately regenerated with newly formed bone and a developing bone marrow. The grafting materials showed complete osseous integration. Both bone substitutes may have a place in reconstructive surgery where different clinical indications require differences in biodegradability.