bluuebunny/crossref_metadata_2025_split huggingface dataset:
INORGANIC NUTRITION OF THE PROTONEMATA OF SPHAGNUM PAPILLOSUM LINDB., S. MAGELLANICUM BRID. AND S. CUSPIDATUM EHRH.
Authors: BOATMAN D. J. , LARK P. M. 
Published: May 2006

SummaryThe gametophores of Sphagnum spp. normally grow on peat and in oligotrophic waters, but attempts to grow the protonemata of S. papillosum, S. cuspidatum and S. magellanicum in natural waters failed. When the spores were sown on a cellophane disc in contact with a standard culture solution in special culture chambers however, protonemata consisting of a thallus with filaments developed from the spores of all three species. When the culture solution was diluted × 10, × 100 and × 1000, the size of the thalloid part of the protonemata became progressively less and the filamentous part was relatively more extensive. S. magellanicum failed to germinate when the solution was diluted × 100. The effect of reducing the concentration of each of the major ions individually was investigated and it was found that the thallus decreased in size as the concentration of phosphate was decreased. The protonemata failed to respond in a consistent way to nitrate and developed satisfactorily in the complete absence of the ion.Natural waters were collected from five ombrotrophic mire sites in Scotland and the phosphate level raised to that of the 0.1 standard solution by adding sodium dihydrogen phosphate. In about half of the cultures (spread throughout the five waters) the form of the protonemata (S. papillosum only) was similar to that of protonemata in 0.1 standard cultures. When spores were immersed in culture solution, very small protonemata only developed.It is concluded that protonemata of the species of Sphagnum used are unlikely to develop in mire pools because (a) the concentration of phosphate is too low and (b) the protonemata are unable to develop properly when completely immersed.
THE MECHANISM OF MYCELIAL STRAND INDUCTION IN SERPULA LACRIMANS: A POSSIBLE EFFECT OF NUTRIENT DISTRIBUTION
Authors: WATKINSON SARAH C. 
Published: May 2006

SummaryExperiments were carried out on the conditions favouring strand formation in the mycelium of Serpula lacrimans. The mechanism of strand production proposed by Garrett and Butler (1960) was taken as a working hypothesis.Colonies of the fungus were grown on a liquid medium of a nutrient composition found previously to induce stranding. In one set of cultures this medium was renewed daily by slow perfusion of fresh medium through the culture vessels, continued over a 6‐week period. In a parallel set of cultures the medium remained static and was not renewed over the same period. Strands formed only in these static cultures and not in the perfused ones. When the fungus was grown from a nutrient‐rich food base over media at a range of lower concentrations it was found that there was an optimal lower concentration for strand formation. Another state of nutrient supply that favoured the formation of strands occurred when mycelium growing out from a food base over a non‐nutrient medium encountered and began to colonize a fresh food base. This observation, first made on Helicobasidium purpureum by Valder (1958), was repeated using Serpula lacrimans and it was also shown by using 14C‐labelled glucose that carbon was transported between old and new food bases. Further experiments using 14C as a tracer showed that there was a loss of substances containing carbon from intact hyphae and from strand‐forming mycelium.The significance of these results is discussed, and it is suggested that to Garrett's original hypothesis might be added the proposition that nutrient leakage from older hyphae is part of the process of strand induction.
SOME GENETIC FACTORS AFFECTING SEEDLING EMERGENCE IN RASPBERRIES
Authors: JENNINGS D. L. 
Published: May 2006

SummaryThe emergence of raspberry seedlings derived from two diallel crosses was studied, and also the effects on emergence of applying auxin to fruits 7 days after pollination. In one diallel, emergence was poor and the variations present were largely determined by maternal effects. In the other it was better and the largest variations were determined by inbreeding depression effects. In most cases maternal effects on emergence were negatively correlated with maternal effects on endosperm size, while inbreeding effects were associated with reductions in embryo size. Maternal interaction effects were of minor importance and were probably correlated with effects on the endocarp. The auxin treatments had variable consequences according to their effects on the seed tissues. It is concluded that the factors which determined seedling emergence would tend to maintain heterozygosity and should therefore be regarded as part of the breeding system.
DIPLOID‐TETRAPLOID SYMPATRY IN DACTYLIS(GRAMINEAE)
Authors: BORRILL MARTIN , LINDNER RUTH 
Published: May 2006

SummaryThe known zones of contact between diploid and tetraploid Dactylis are reviewed, and two well‐documented examples of intermixed and morphologically similar diploids and tetraploids are considered in detail. The relict subspecies mairei is accompanied, in its particular habitat, by a tetraploid counterpart. The evidence suggests this to be an example of autotetraploidy, the diploid and tetraploid components of which have been preserved by isolation in a specialized relict habitat.In Dactylis interploid sympatry appears to have arisen in two ways–by changes in the original habitat, whereby morphologically dissimilar and spatially isolated diploids and tetraploids become intermixed, or by the formation of autotetraploids which co‐exist in the‘dipioid’habitat and may subsequently be modified by hybridization with other diploids or tetraploids with which they come in contact.No triploid or tetraploid hybrids were discovered in the seedling progeny of dipioid Kerrata plants, hut the numbers screened are considered insufficient. Direct formation of tetraploid hybrids as a consequence of the functioning of unreduced gametes by dipioid parents can be a more effective‘genetic bridge’than the backcrossing of triploid hybrids. Further study of mixed diploid‐tetraploid stands is therefore required to determine the frequency and effectiveness of this phenomenon in natural populations.
CELL DIVISION IN CYANOPHORA PARADOXA
Authors: PICKETT‐HEAPS JEREMY 
Published: May 2006

SummaryMitosis in the nucleus of Cyanophora paradoxa is shown to be generally typical of other eukaryotic cells. Basal bodies and the flagella apparatus appear to replicate before nuclear division. At preprophase, microtubules approach the nucleus from the periphery of the cell to form the usual extranuclear spindle by prophase; at this stage the nucleolus begins its breakdown, which is soon complete. The spindle poles, clearly defined by the orientation of microtubules, never contained any obvious structural component, and basal bodies were never associated with the spindle. By prometaphase, breakdown of the nuclear envelope is accompanied by invasion of the nucleus by the extranuclear microtubules. During anaphase, two plates of chromosomes separate inside the spindle containing both continuous and chromosomal microtubules. Remnants of the nuclear envelope often coat the chromosomes. Cleavage, initiated by early anaphase, is achieved by an asymmetric, longitudinal constriction of the cell membrane, which passes between the replicated flagellar apparatuses. The plane of cleavage was always oriented at right angles to the spindle axis, and did not involve any detectable microfibrillar elements. Telophase nuclei reform as normal. These observations indicate that the host cell of the symbiotic pair cannot be considered as a dinoflagellate as had been previously suggested.Division of the cyanelles is independent of nuclear division in the host, which therefore contains variable numbers of these symbionts. ‘Wall’ material is secreted into the furrow of the cleaving cyanelles. Furthermore, a very characteristic organelle was discovered in many cells invariably appressed to the cyanelles. Its dense granular contents were contained within a single unit membrane, and it was also frequently associated with endoplasmic reticulum. It was always inserted into the cleavage of dividing cyanelles and apparently it divided along with them, so that each daughter cyanelle remained associated with one of these inclusions. This organelle is thought to be a peroxisome and its possible significance in the host‐cyanelle relationship (and also in the evolution of chloroplasts) is briefly indicated.
THE CYTOKININS OF CULTURED SYCAMORE CELLS
Authors: MACKENZIE I. A. , STREET H. E. 
Published: May 2006

SummaryTwo cytokinin fractions, active in the tobacco and soybean callus bio‐assays, have been obtained from sycamore cells cultured in a cytokinin‐free medium. One of these (Cyt 1) corresponds in its properties to an uncharacterized cytokinin detected in water melon and cucumber seeds. The second fraction (Cyt 2) is coincident with zeatin riboside in chromatographic properties. No evidence was obtained for the presence of a ‘nicotinamide‐like’ cytokinin.The ‘staled’ culture medium which had supported the growth of sycamore cells contained Cyt 1 activity, low Cyt 2 activity and a cytokinin coincident with zeatin in chromatographic mobility.There is a rapid rise in the cytokinin activity in the cells during the lag phase which precedes active division in batch culture. Later the cytokinin activity per cell and per unit volume of culture progressively declines.
LEAF ABSCISSION IN COLEUS
Authors: HALLIDAY M. B. W. , WANGERMANN ELISABETH 
Published: May 2006

SummaryThe anatomical and histological development of the abscission zone is described in relation to the development of the whole leaf. The initiation of the abscission zone coincides with the change‐over from exponential to restricted growth in the blade. The response of explants from leaves at all stages of abscission zone development to a wide range of concentrations of indolyl acetic acid (IAA) applied at the distal end shows that concentrations of 10−9 M and lower accelerate, and higher concentrations retard abscission. Intact plants and excised abscission zones respond similarly. Delayed application of IAA to debladed petioles shows that it can reverse the abscission process for about 4 days after deblading. There is no evidence for an IAA‐accelerated phase in abscission. The effect of IAA is directly on the abscission zone.
THE EFFECTS OF WATER STRESS ON NITROGEN‐FIXING ROOT NODULES
Authors: SPRENT JANET I. 
Published: May 2006

SummaryThe effects of osmotic stress on nitrogen fixation and respiration of soybean root nodules were investigated. Non‐electrolytes, such as mannitol, depressed acetylene reduction when given to detached nodules in sufficient concentration to withdraw water from them. When given to the root systems of whole plants, hypotonic concentrations of mannitol had a depressing effect after 1–2 hours, the exact time depending on the size of the nodules. Equivalent concentrations of salts had a much more rapid effect on whole root systems and on detached nodules (less than 5 minutes); 100 m‐equiv./l almost stopped acetylene reduction by small nodules. These effects could not be transmitted via the roots and needed contact between salt solution and nodules. They were accompanied by a decrease in respiratory activity and were fully reversible if the root systems were flushed with water within a few hours of treatment. High salt concentrations, as in sea water, had a rapid (1–2 minutes) effect, which after 20 minutes became irreversible.The effects of salt stress are interpreted as resulting from alterations in the metabolism of the cortical cells of the nodules.
CARBOHYDRATE METABOLISM IN CHAETOMIUM GLOBOSUM
Authors: ADOMAKO D. , KAYE M. A. G. , LEWIS D. H. 
Published: May 2006

SummaryExtracts of Chaetomium globosum contained an unstable, NAD‐dependent mannitol dehydrogenase, oxidizing mannitol to fructose. The enzyme had a low affinity for its substrates but showed high activity in vitro. Compared to fructose, exogenous mannitol was poorly utilized by the fungus. Raising the pH of the medium resulted in improved growth of the fungus on mannitol, in increased formation of ketose in the medium, and in stimulation of mannitol dehydrogenase formation. By contrast, glucokinase and fructokinase activities were depressed by growth at the higher pH.The possible involvement of a mannitol dehydrogenase in the utilization of exogenous mannitol is discussed, together with the factors probably contributing to the poor growth of the fungus on mannitol and the control of cellular mannitol formation.
STUDIES IN FESTUCA
Authors: BORRILL MARTIN 
Published: May 2006

SummaryThe cytogeographic distribution and morphology of Festuca taxa in sections Bovinae and Scariosae has been compared with the results of experimental hybridization between them. Two groups have been established, the first is predominantly Moroccan and includes F. mairei (2n= 28), F. arundinacea varieties atlantigena forma pseudo‐mairei (2n= 56), letourneuxiana and cirtensis (2n= 70).These taxa are closely related to the diploid F. scariosa endemic in the Spanish Sierra Nevada. Their distinctive morphological features are due to the inclusion of the scariosa genome. The second group, predominantly European, including F. arundinacea var. glaucescens (2n= 28) and F. arundinacea var. genuina (2n= 42), is similarly associated with the diploid F. pratensis. It is suggested that evolution in this species complex involved opportunities in a previous era for hybridization between tetraploid taxa now separated geographically. From such hybrids the higher polyploids can be derived.
THE TIME OF ORIGIN OF THE FLOWERING PLANTS DETERMINED BY USING AMINO ACID SEQUENCE DATA OF CYTOCHROME C
Authors: RAMSHAW J. A. M. , RICHARDSON D. L. , MEATYARD B. T. , BROWN R. H. , RICHARDSON M. , THOMPSON E. W. , BOULTER D. 
Published: May 2006

SummaryCytochrome c sequences from nineteen plants have been used, in conjunction with those of animal and fungal origin already published, to calculate the times of origin of the animal, fungal and plant kingdoms and also of some higher plant groups. The results show that the Angio‐sperms originated at least several geological periods before the Cretaceous, which is the earliest period in the geological record in which authentic angiosperm fossils have been found.
THE INTERACTION BETWEEN GROWTH PROMOTERS IN APICAL DOMINANCE
Authors: WOOLLEY D. J. , WAREING P. F. 
Published: May 2006

SummaryPreliminary experiments with one‐node cuttings of Solanum andigena in sterile culture indicated that residual root effects, possibly due to stored cytokinins, could obscure the effects of exogenous growth promoters on lateral bud growth in rootless cuttings. Therefore two‐node cuttings, obtained from apical cuttings that had been maintained without roots for a number of days, were used in all subsequent investigations. Application of cytokinin or gibberellin to the base of rootless, two‐node cuttings promoted the growth of lateral buds as leafy, orthotropic shoots, or diageotropic stolons, respectively; simultaneous application of both hormones completely inhibited lateral bud growth. The effects of roots, 6‐benzylammopurine (BAP) and zeatin on lateral shoot growth were similar in leading to the formation of vigorous, orthotropic, leafy shoots.Indole‐3‐acetic acid (IAA) completely inhibited lateral bud growth in rootless cuttings for at least 7 days, even when BAP was included in the nutrient medium. By using [α‐14C BAP it was demonstrated that cytokinin accumulates in the lateral buds of cuttings not treated with IAA, prior to their growth as leafy shoots; evidence of a causal relationship between cytokinin accumulation and lateral shoot growth was provided by a parallel experiment using [8‐14C]‐adenine. IAA did not appear to reduce BAP or BAP‐riboside accumulation in lateral buds by diverting these cytokinins to the point of IAA application, but did promote the formation of an unknown metabolite of BAP which accumulated in stem tissue.
CELL CYCLES IN A COMPLEX MERISTEM AFTER X‐IRRADIATION
Authors: CLOWES F. A. L. 
Published: May 2006

SummaryMean rates of mitosis, determined over short intervals of time by blocking the cell cycle at metaphase, fall immediately after X‐irradiation in most parts of the root meristem of Zea mays. The fall continues for several hours and is then replaced by a rise until normal rates are reached. In the quiescent centre, however, the mean mitotic cycle shortens to one‐third of its previous duration within an hour of irradiation. The rate of mitosis then falls to nearly its previous level before rising again at the same time as the acceleration of the cycle in the other regions. Finally quiescence sets in again as the other regions return to greater mitotic activity.The observations suggest (1) that the reaction of the quiescent centre is not simply due to the relief of some inhibition imposed by the surrounding cells, (2) that something other than the different DNA levels of the various regions is in part responsible for the differential response, and (3) the resistance of the quiescent centre to irradiation is a real phenomenon requiring explanation.
ENDOGENOUS INORGANIC CARBON SOURCES IN PLANT HOTOSYNTHESIS
Authors: RAVEN J. A. 
Published: May 2006

SummaryThe quantity of CO2 arising from photorespiration in angiosperms and in algae has been estimated. Much of such CO2 arises from the metabolism of glycolate so that estimates are based on the rate of formation of glycolate and the rate at which it is metabolized (Table 1). The total CO2 production in leaves or algae in the light can then be taken as equal to the photorespiratory CO2 plus the CO2 produced by‘dark’ respiratory pathways.Methods of estimating CO2 release from illuminated green tissues are considered and the rate of decarboxylation deduced from biochemical evidence of substrate turnover is compared with the observed rate of CO2 release; the difference between these values is reassimilation (Table 1). In angiosperms with the PGA pathway, in air, reassimilation is never complete and ranges from o to 0.6 of the endogenous CO2 production. This implies that the resistance to refixation is as great or greater than the resistance to loss of endogenous CO2 to the medium and is in accord with the relative values of these resistances based on other evidence. In law oxygen environment less glycolate is produced and hence less photorespiratory CO2; the resistance to refixation is smaller and so fractional reassimilation in increased. Unicellular algae have the PGA pathway and some appear to have more efficient reassimilation than the corresponding angiosperms.The special problems of metabolism in four carbon acid plants are discussed. Such plants show essentially complete reassimilation since they do not lose CO2 when illuminated. In their leaves the resistance to escape of endogenously produced CO2 must be very much greater than the resistance to refixation. The low resistance to refixation is probably related to high levels of CO2 in chloroplasts which are generated by the‘CO2‐pump’ rather than to any peculiarities of carboxydismutase.The importance of reassimilation is discussed in relation to the influence of CO2 on various aspects of metabolism, to isotopic discrimination in CO2 fixation and to the mechanism of the use of bicarbonate in photosynthesis.
THE EFFECT OF AUXIN FROM THE SHOOT ON ROOT DEVELOPMENT IN PISUM SATIVUM L.
Authors: McDAVID C. R. , SAGAR G. R. , MARSHALL C. 
Published: May 2006

SummaryThe effect of auxin of shoot origin on the growth and development of the root system of Pisum sativum L. cv. Kelvedon Wonder was investigated. Root growth was reduced when auxin transport from shoot to root was interrupted, but this could have been caused by a reduction in assimilate supply rather than a deficiency of auxin. Shoot removal, however, markedly reduced the number and total length of secondary roots produced and a 1% IAA–lanolin paste applied to the cut stump compensated to a large extent for shoot removal, markedly increasing secondary root growth in de‐shooted plants. It is suggested that auxin produced by the shoot may influence the growth and development of the root system.
REDUCTION OF ACETYLENE AND NITROGEN BY FIELD‐GROWN SOYBEANS
Authors: MAGUE T. H. , BURRIS R. H. 
Published: May 2006

SummaryAcetylene reduction by soybean nodules started without a lag and remained linear with time for about 80 minutes. There was no apparent injury to nodules from evacuation. Rates of reduction of acetylene increased with increasing pO2 to 1 atm; respiration did not seriously deplete the available O2 from bottles in which nodules occupied less than 20% of the volume of the bottles. Reduction of acetylene decreased markedly in nodules soaked in water. About 0.2 atm acetylene supported the most rapid reduction of acetylene, and nodules 3–5 mm in diameter were most active. Intact soybean plants, nodulated roots and detached nodules fixed nitrogen at relative rates of approximately 100/46/23. The soybean plants exhibited a diurnal cycle of acetylene reduction dependent upon light intensity and air temperature. The observed ratio of acetylene reduced to N2 reduced was approximately 2.0 rather than the often assumed theoretical value of 3.0. There was a dramatic difference among soybean varieties in the date of onset and termination of acetylene reduction. Acetylene reduction was most vigorous in plants inoculated with a mixture of effective strains of Rhizobium japonicum.
EFFECT OF ENDOGONE MYCORRHIZA ON PLANT GROWTH
Authors: DAFT M. J. , NICOLSON T. H. 
Published: May 2006

SummaryEndotrophic mycorrhiza in tomato and maize, induced by chlamydosporic varieties of Endogone macrocarpa, were examined quantitatively by estimating infection of roots, pigmentation of roots and production of ectocarpic chlamydospores. When the size of the root system was taken into account, estimates of infection showed a relationship to growth of the host. The amount of pigmentation within the root system gave a good indication of mycorrhizal intensity and was related to the size of the host at high levels of infection. The numbers of spores produced on an individual root system, given a particular treatment, were positively correlated with the size of the host. The relative merits of these different assessments of mycorrhiza are discussed.
THE RELATION OF RAY SPACING TO CAMBIAL GROWTH
Authors: CARMI A. , SACHS T. , FAHN A. 
Published: May 2006

SummaryAn experimental test was made of Bünning's (1965) hypothesis that the tangential spacing of the rays is determined by mutual inhibitory effects of the ray initials. Partial girdles of trunks of Ailanthus altissima were prepared in such a way that regions of the cambium were obtained in which cell division and differentiation occurred rapidly in the radial direction but not along the circumference of the trunk. Though the spacing of the original rays was not changed by this restricted growth, it was found that the rays grew in volume and many new rays were initiated. This result suggests that the rays differentiate along channels of a stimulus moving between the phloem and the differentiating xylem and their spacing is controlled not in the cambium but in the differentiating vascular tissues.