bluuebunny/crossref_metadata_2025_split huggingface dataset:
Jurassic aeolian oolite on a palaeohigh in the Sundance Sea, Bighorn Basin, Wyoming
Authors: KILIBARDA ZORAN , LOOPE DAVID B. 
Published: June 2006

ABSTRACTAeolian limestones are widespread in the Quaternary record and have been identified in outcrops and cores of late Palaeozoic strata. These rocks have been interpreted as a low latitude signal of glacio‐eustatic sea level fluctuations and have not been previously reported from the Mesozoic or from other episodes of earth history generally believed to have been non‐glacial. Numerous lenticular bodies of cross‐stratified oolite lie near the contact between the lower and upper members of the mudstone‐dominated lower Sundance Formation (Middle and Upper Jurassic) in the Bighorn Basin of north‐central Wyoming, USA. The lenses, up to 12 m thick, contain sedimentary structures diagnostic of aeolian deposition. Inversely graded laminae within thick sets of cross‐strata were deposited by climbing wind ripples. Adhesion structures and evenly dispersed lag granules are present in flat‐bedded strata at the bases of several of the oolite bodies. Thin sections reveal abundant intergranular micrite of vadose origin. The lenses appear to represent virtually intact, isolated aeolian bedforms that migrated across a nearly sand‐free deflation surface. When the Sundance Sea transgressed the dunes, a thin (<1 m thick), wave‐rippled, oolite veneer formed on the upper surface of the aeolianite. Previous workers, primarily on the basis of sedimentary structures in the veneer, interpreted the oolite lenses as tidal sand bodies.The dunes provide clear evidence of widespread subaerial exposure on the crest and north flank of the Sheridan Arch. This structural high was delineated by previous workers who demonstrated thinning of pre‐upper‐Sundance Formation strata and localized development of ooid shoals. Ooids that formed in shoals on the windward (southern) side of the palaeohigh were exposed and deflated during lowstand. Thin, scour‐filling ooid grainstone lenses that crop out in the southern part of the study area represent remnants of the marine beds that sourced the aeolianites. Farther north (down‐wind), oolitic dunes prograded over thinly laminated lagoonal silts. When relative sea level began to rise, the uncemented dunes were buried under fine‐grained marine sediment as the lee side of a low‐relief island was inundated.
PLASTID DEVELOPMENT IN THE PRIMARY LEAF OF PHASEOLUS VULGARIS: VARIATIONS BETWEEN DIFFERENT TYPES OF CELL
Authors: WHATLEY JEAN M. 
Published: June 2006

SummaryDuring the period of cellular differentiation, plastids in all cells throughout the primary leaf of Phaseolus vulgaris undergo the same sequence of structural changes. However plastids in different types of cell can, at an early stage, be distinguished from each other quantitatively, i.e. in size, in the amount of starch accumulated, and, later, in the extent of their thylakoid systems. These quantitative differences depend in part on the position of the cell within the lamina and in part on the type of cell involved, and they persist throughout development. Further modifications in plastid structure affect only a few specialized types of cell. These later modifications in plastid structure take place only as the cells become fully differentiated.Plastid division occurs in two separate phases, during seed development on the parent plant and during germination. It is probable that differing rates of plastid division and cell division in epidermal, palisade and mesophyll cells during early stages of germination are responsible for the characteristically different numbers of plastids present in each type of cell in the mature leaf.
ENDOGENOUS AUXIN AND CYTOKININ CHANGES DXJRING EMBRYOID DEVELOPMENT IN CELERY TISSUE CULTURES
Authors: AL‐ABTA SAHERA , COLLIN H. A. 
Published: June 2006

SummaryEmbryoids as embryonic cell masses, globular, heart and torpedo forms were grown on medium in the presence and absence of the growth regulators, 2,4‐dichlorophenyoxyacetic acid (2,4‐D) and kinetin. The early phase, up to the globular stage of development, was dependent on a supply of 2,4‐D and kinetin for continued cell division and growth, whereas the later stages did not require an external supply of growth regulators and their development was in fact inhibited if an external supply was provided. The early dependent phase and the later independent phase in the embryoids corresponded to the heterotrophic and autotrophic phases of embryo development in the intact plant. An analysis of endogenous auxin and cytokinin in the different stages of embryoid development showed a relatively low auxin content with little change at each stage. The cytokinins however showed both quantitative and qualitative changes with an increase in total cytokinin in the mature embryoids and plantlets then a decline in the intact plant.
EFFECTS OF LIGHT AND GROWTH REGULATORS ON GERMINATION AND RADICLE GROWTH OF LETTUCE SEEDS HELD UNDER HIGH‐TEMPERATURE STRESS AND WATER STRESS
Authors: HEGARTY T. W. , ROSS HEATHER A. 
Published: June 2006

SummarySeeds of two cultivars of lettuce (Lactuca sativa L.), untreated or soaked in acetone containing kinetin and gibberellic acid (K + GA3), were germinated in light or dark at a range of (high) temperatures and at a range of water potentials. In addition, untreated and treated seeds were germinated at 20°C in the light and then transferred to the same high temperatures or to low water potentials. In both cvs light and K + GA3 promoted germination at high temperatures and at low water potentials, although the cvs differed quantitatively in their responses. The upper temperature limit of germination in the light, and of radicle growth after germination, were similar in treated and untreated seeds respectively, suggesting that light and K + GA3 in combination may have completely removed the specific high‐temperature block to germination. Although light and K + GA3 increased the tolerance of germination to water stress, germinated, untreated seeds were able to grow at even lower water potentials. The K + GA3 treatment, whilst promoting germination under high temperature or water stress, reduced radicle growth subsequent to germination, thus providing support for the possibility that, in germination, the initiation of cell elongation has a degree of metabolic independence of the other processes associated with growth.
SOME ASPECTS OF CARBON METABOLISM AND TRANSLOCATION IN ONIONS
Authors: STEER B. T. , DARBYSHIRE B. 
Published: June 2006

SummaryIn the first six leaves of plants of Allium cepa L. cv. Creamgold grown from seed, the carbohydrate content per unit fresh weight within the leaf is highest in the leaf base and lowest at the tip. Soluble protein content is highest at the leaf tip and decreases down the leaf. The activity of ribulose bisphosphate carboxylase per unit fresh weight is constant in the upper leaf but is lower in the leaf sheath.During growth, ribulose bisphosphate carboxylase activity reaches a maximum when leaves are at about 50 % of final size. Thereafter activity decreases even though leaf growth continues. After short exposures to 14CO2, 80 % of 14C in the leaf is recovered in sucrose. Carbon is rapidly translocated from the upper leaf to the leaf base and to a lesser extent to roots and unemerged leaves. The rapid carbon translocation is consistent with the absence of non‐structural polysaccharide pools in the upper leaf segments.
MOVEMENTS OF ABAXIAL AND ADAXIAL STOMATA
Authors: PEMADASA M. A. 
Published: June 2006

SummaryA comparative study was made of diurnal movements, and responses to a range of light intensities, of abaxial and adaxial stomata on normal and inverted leaves of Stachytarpheta indica by microscopic examination of epidermal strips fixed in absolute ethanol. Additional observations were made on Coreopsis grandifiora, Crotalaria retusa and Tridax procumbens. The natural diurnal movements in the field and light‐induced opening in the laboratory and accompanied changes in concentrations of starch and potassium in the guard cells were all substantially more pronounced in the shaded abaxial stomata than in the exposed adaxial stomata on normal leaves. The effect of leaf inversion was to accentuate these differences considerably. Carbon dioxide‐free air was not effective in overcoming the differences in opening ability of abaxial and adaxial stomata. The differential behaviour of abaxial and adaxial stomata is related, to a great extent, to differential changes in concentrations of starch and potassium in abaxial and adaxial guard cells. The greater photosensitivity of abaxial stomata is a widespread phenomenon occurring in both monocotyledons and dicotyledons irrespective of differences in stomatal density; the adaptive significance of this phenomenon is briefly mentioned.
THE EFFECT OF EMBRYONAL AXIS ON THE DEVELOPMENT OF PHOTOSYNTHETIC ACTIVITY IN APPLE SEEDLINGS
Authors: MACIEJEWSKA U. 
Published: June 2006

SummaryThe development of photosynthetic activity in cotyledons from non‐dormant apple embryos and embryos in a state of dormancy was studied during the culture of intact embryos, of single cotyledon with axis, and of isolated cotyledons. The embryonal axis was found to stimulate the development of photosynthetic activity in the cotyledons. In non‐dormant embryos the influence of the axis on the assimilation of CO2 by cotyledons became apparent at an early stage of culture; in the dormant embryos it was noted first after 10 to 12 days. No influence of the embryonal axis was observed on chlorophyll biosynthesis in cotyledons. The photosynthetic rate was always higher in cotyledons from non‐dormant embryos than in those from dormant ones. However, the chlorophyll content was similar in cotyledons from both groups of embryos. It is concluded that the interaction of the embryonal axis and cotyledons in the development of photosynthetic activity in seedlings depends on the physiological state of the embryo.
WATER RELATIONS OF WHEAT ALTERNATED BETWEEN TWO ROOT TEMPERATURES
Authors: KIRKHAM M. B. 
Published: June 2006

SummaryWater potentials, osmotic potentials and stomatal resistances were measured daily in a growth room during a 16‐day period, in growing leaves of a drought‐sensitive and a drought‐resistant winter wheat (Triticum aestivum L. em. Thell.), which had the roots maintained under one of three root‐temperature treatments: (1) constant temperature of 24°C (about the optimum); (2) constant temperature of 34°C (10° above the optimum and near the high temperature limit for growth); and (3) alternating temperature of 24 h at 24°C followed by 24 h at 34°C. Air temperature was constant at 24°C.Water and osmotic potentials, stomatal resistances, and height of plants maintained at the 34°C root temperature were intermediate between those grown at 24°C (highest potentials, lowest resistances, tallest) and those alternated daily between the two temperatures (lowest potentials, highest resistances, shortest). Previous work showed that potentials, stomatal resistances, and growth of wheats subjected to constant root temperatures of 25, 29 and 33°C were linearly related to root temperature with lowest potentials, highest resistances, and least growth at the high temperature. Even though alternated plants in this experiment were at an average root temperature of 29°C, they grew the poorest. The wheat plants, therefore, did not integrate a root temperature stress in the same manner over ‘time’ as they did over ‘space’.The results showed that the stomatal resistance, water and osmotic potentials, and height of wheat seedlings, maintained at a constant root temperature 10°C higher than the optimum, were about halfway between those of plants grown at the optimum and those alternated daily between the optimum and the optimum‐plus‐10 °C root temperature.
DESICCATION EFFECTS AND CATION DISTRIBUTION IN BRYOPHYTES
Authors: BROWN D. H. , BUCK G. W. 
Published: June 2006

SummaryAnalysis of the cations in a range of bryophytes, using a differential ion displacement technique, has shown that potassium is mainly soluble within the cells, calcium is bound, exchangeably, to sites in the cell wall and is insoluble within the cell and magnesium is present in all three locations. After desiccation, soluble ions either leak into the rehydrating solution (e.g. potassium and some magnesium) or become bound to the cell‐wall exchange sites (e.g. most of the magnesium). Leakage of intracellular ions can be used as a measure of membrane damage. An index of desiccation resistance (based on potassium retention within the cells after storage at 52 and 100% r.h.) is related to the availability of water in each bryophyte's habitat and is significantly correlated with the total potassium content of the plant. Reduced cation leakage occurred after material was transferred from either 52 or 0% r.h. to 100% r.h., indicating the ability of bryophytes to recover from such desiccation stress. An index of recovery is presented which shows that most bryophytes, unless excessively stressed, are able to repair the damage caused by desiccation.
CYTOCHEMICAL LOCALIZATION OF GLUTAMATE DEHYDROGENASES DURING CARPOPHORE DEVELOPMENT IN COPRINUS CINEREUS
Authors: ELHITI M. M. Y. , BUTLER R. D. , MOORE D. 
Published: June 2006

SummaryThe NAD‐ and NADP‐linked glutamate dehydrogenases were detected in frozen sections of carpophore tissues by means of tetrazolium salt. Material at all stages of development was examined. From the earliest stages NAD‐glutamate dehydrogenase was uniformly distributed in the basidial cells of the hymenium, and as the carpophore developed an increasing proportion of cells of the subhymenium came to express enzyme activity. The NADP‐glutamate dehydrogenase (NADP‐GDH) was initially limited to basidial cells in isolated patches of the hymenium. As development proceeded the proportion of basidia exhibiting NADP‐GDH activity increased, as did the proportion of subhymenial cells showing this enzyme activity. No NADP‐GDH activity was detectable in sections of stipe tissue.
THE UPTAKE OF UREA BY THE DIATOM, PHAEODACTYLUM
Authors: REES T. A. V. , SYRETT P. J. 
Published: June 2006

SummaryUrea‐grown cells of Phaeodactylum absorbed [14C]urea by an active mechanism. Most of the urea taken up was present in the cells as free urea and the ratio of internal to external concentration could exceed 3000. The activity of the transport mechanism was greatly increased by depriving the cells of nitrogen for up to 24 h. The uptake mechanism had a high affinity for urea, the half‐saturation constant being about 1·0 μM. Active uptake of urea occurred in darkness, particularly in nitrogen‐deprived cells, but uptake was markedly stimulated by light. Uptake was not inhibited by DCMU but was abolished almost completely by 10−4m CCCP. It is concluded that active uptake is driven by phosphorylation. Uptake of [14C]urea continued until a constant level within the cells was attained, the plateau value probably resulting from a balance between rate of active uptake and rate of passive loss by diffusion.The transport mechanism was absent from cells grown with ammonium as nitrogen‐source. The urea uptake mechanism developed in such cells when they were deprived of nitrogen; cycloheximide prevented the development of the mechanism. The mechanism was lost when urea‐grown cells were incubated in ammonium medium for 24 h but ammonium (at concentrations up to 10 mM) did not inhibit short‐term uptake of urea into urea‐grown cells.
THE UPTAKE OF UREA BY CHLORELLA
Authors: BEKHEET I. A. , SYRETT P. J. 
Published: June 2006

SummaryThe uptake of 14C by urea‐grown cells of Chlorella (strain 211/8p) supplied with [14C]urea was studied. Uptake was rapid in light with an apparent half‐saturation value (Km) for urea of 16·5 μM. Uptake was inhibited competitively by thiourea. Uptake of 14C was inhibited by 6 × 10−6 DCMU in light and was very much slower in darkness; nevertheless, under these conditions, rate of loss of 14C from the medium was much the same as in illuminated non‐inhibited cultures. [14C]urea was metabolized rapidly by the cells and, in illuminated cells after a 5 min exposure to [14C]urea, less than 50 % of the soluble 14C within the cells was in [14C]urea. It is concluded that much of the measured 14C uptake may have been due to conversion of [14C]urea to 14CO2 followed by photosynthetic 14CO2 fixation. Nevertheless, when [14C]urea in the cells was extracted and separated by thin‐layer chromatgraphy, there was clear evidence of accumulation at a concentration above that in the external medium and of light stimulation of uptake. It is suggested that, in view of the rapid metabolism of [14C]urea by Chlorella, it may be preferable to study the uptake mechanism of this organism by using the urea analogue, thiourea.
THE OCCURRENCE OF A HYPERSENSITIVE REACTION IN THE PLANKTONIC DIATOM ASTERIONELLA FORMOSA HASSALL PARASITIZED BY THE CHYTRID RHIZOPHYDIUM PLANKTONICUM CANTER EMEND., IN CULTURE*
Authors: CANTER HILDA M. , JAWORSKI G. H. M. 
Published: June 2006

SummaryCulture work has shown that cells of the diatom Asterionella formosa Hassall may undergo a hypersensitive death reaction in response to infection by the chytrid Rhizophydium planktonicum Canter emend. In the clone of Asterionella studied most of the infected cells exhibited this fatal reaction. On these incompatible cells the fungus died and the encysted zoospore did not enlarge into a sporangium. However, in very rare instances a compatible cell bearing a sporangium was found. An investigation of this mainly incompatible, hypersensitive host‐parasite relationship was conducted using light microscopy and experimentation.
ULTRASTRUCTURE OF DRY SEED TISSUE AFTER A NON‐AQUEOUS PRIMARY FIXATION
Authors: THOMSON WILLIAM W. 
Published: June 2006

SummaryA primary fixative of formaldehyde and glycerol is presented as an essentially non‐aqueous medium for the preservation of dry material, such as seeds, for electron microscopic studies. Good preservation of the ultrastructure of the parenchyma cells of cotyledons of dry seeds of mungbean was obtained with this fixative. In these cells the nuclei, plastids, protein bodies and mitochondria were easily identified. In some parenchyma cells, stacked arrays of ribosomes were observed that were similar to ordered arrays of rough endoplasmic reticulum although the membrane elements were poorly defined. In general, all membranes including the plasmaiemma were ill defined, suggesting that, in dry seeds, membranes are disorganized from the topical bilayered structure.
ULTRASTRUCTURE OF PHLOEM IN YOUNG RUNNER‐BEAN STEM: DISCOVERY, IN OLD SIEVE ELEMENTS ON THE BRINK OF COLLAPSE, OF PARIETAL BUNDLES OF P‐PROTEIN TUBULES LINKED TO THE PLASMALEMMA
Authors: LAWTON D. M. , NEWMAN Y. M. 
Published: June 2006

SummaryThin sections of the oldest uncrushed sieve elements in two vascular bundles have been examined by electron microscopy. They are shown to contain bundles of about 50 P‐protein tubules which are no different in appearance from tubules in immature sieve elements. Tubules in these old sieve elements have remained interlinked with ‘side‐arms’ throughout the time that the sieve elements were translocating. The accumulation of callose on each sieve element pore, which signifies senescence, may incidentally protect the tubules from changes in pressure whilst they are fixed. The generally held conclusion that P‐protein tubules change into narrow striated filaments and disperse from their parietal positions as the sieve element reaches maturity is re‐examined.In the development of the sieve element the central body of the P‐protein crystal is shown to be present very early, at a stage when the sieve element and the companion cell are otherwise still difficult to distinguish.
A RADIOCARBON‐DATED POLLEN DIAGRAM FROM LOCH OF WINLESS, CAITHNESS, NORTH‐EAST SCOTLAND
Authors: PEGLAR SYLVIA 
Published: June 2006

SummaryA pollen diagram is presented from a 6 metre continuous core taken from Loch of Winless. Ten radiocarbon age determinations have been made from the sediments in relation to pollen stratigraphical changes and the sediments are found to cover the past 12800 years.On the basis of pollen stratigraphy the diagram is divided into five local pollen assemblage zones. Zones 1 and 2 may be correlated with the younger part of the Late Devensian (sensu Mitchell et al., 1973) whilst zones 3, 4 and 5 cover the Flandrian up to the present.The most notable aspect of the vegetational history of the area inferred from the fossil assemblages is the lack of tree‐cover at any time since the last glaciation. With the climatic amelioration at the beginning of the Flandrian period (approximately 10000 years B.P.), ‘dwarf‐shrub’ and ‘dwarf‐herb’ communities typical of the Late Devensian contracted and there was a widespread expansion of rich ‘tall‐herb’ and fern‐dominated communities with some small patches of willow and hazel scrub in sheltered sites. These in turn gave way to Calluna‐dominated heaths on the well drained soils where podsolization and acidification were occurring.
A HOLOCENE VEGETATION RECORD FROM THE EASTERN SIDE OF WILSONS PROMONTORY, VICTORIA
Authors: LADD P. G. 
Published: June 2006

SummaryPollen analysis of sediment at a site on the eastern side of Wilsons Promontory (southern Australia) privides a record of the vegetation from about 13 000 B.P. to the present. A Eucalyptus forest was present on the site at first, but was replaced by a Melaleuca scrub or thicket about 11000 B.P., probably reflecting a rise in the watertable. As the sea was at least 6 km distant, this event may mark increasing rainfall near the start of the Holocene. The arrival of the sea close to the site about 7000 years ago is demonstrated by changes from a freshwater swamp to saline salt marsh, followed by succession to the low scrub swamp of the present.Regionally, the Nothofagus rainforest, which is now restricted to small isolated stands on high parts of the promontory, expanded between 11 000 and 7000 B.P. This forest is now more extensive than at 11000 B.P. but has contracted relative to the mid‐Holocene extent. From this it appears that the climate of this region during the mid‐Holocene was slightly wetter than that of the early or late Holocene.The later half of the record is in agreement with other work from the western side of Wilsons Promontory.