bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE INHIBITORY EFFECT OF TRICHODERMA SPECIES AND OTHER SOIL MICROFUNGI ON FORMATION OF MYCORRHIZA BY LACCARIA BICOLOR IN VITRO
Authors: SUMMERBELL RICHARD C. 
Published: April 2006

SummaryTen microfungal isolates from the rhizosphere of mycorrhiza of black spruce were tested for their ability to inhibit formation of mycorrhiza by Laccaria bicolor (Maire) Orton on axenically cultivated black spruce seedlings. Two Trichoderma species, T. viride Pers. and T. polysporum (Link ex Pers.) Rifai, were strongly antagonistic towards mycorrhizal colonization. This antagonism was seen both in trials where Trichoderma and L. bicolor were inoculated together and in a trial designed to allow establishment of the mycorrhizal fungus in the rhizosphere prior to a challenge with T. viride. Despite its antagonism in flask trials, T. viride did not parasitize the hyphae of L. bicolor in agar culture. Two other soil fungi, Tolypocladium inflatum Gams and Trichosoporon beigelii (Küch et Rab.) Vuill., also had small but significant inhibitory effects on the formation of mycorrhiza in flask trials. However, a variety of Mucoralean fungi, heavily sporulating soil Hyphomycetes and non‐sporulating root‐associated Hyphomycetes had no deleterious effect on the process. It is concluded that Trichoderma spp. are likely to be significant antagonists of mycorrhizal colonization in vivo, particularly in fumigated soils.
THE FORM, DISTRIBUTION AND SEASONAL ACCUMULATION OF CALCIUM IN KIWIFRUIT LEAVES
Authors: CLARK C. J. , SMITH G. S. , WALKER G. D. 
Published: April 2006

SummarySeasonal changes in the content of Ca and Mg in leaf blades collected from mature kiwifruit [Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa] vines in a high‐producing orchard were measured by a sequential fractionation procedure (14 M acetic acid, 0.25 M HC1 and residual). Total Ca and Mg concentrations decreased within the first 4 weeks of growth, but increased linearly thereafter to be 1322 and 197 μmol g−1 dry weight, respectively, by leaf fall. Total quantities of Ca and Mg accumulated at this time were approximately 2500 and 380 μmol per blade. Calcium oxalate, dissolved in the HC1 extract, was the predominant fraction at every harvest, accounting for up to 79 % of the total Ca content shortly after leaf emergence, and decreasing to 42 % at leaf fall. The quantity of physiologically active Ca (acetic acid‐soluble) ranged from a minimum of 15 % (8 weeks after emergence) to a maximum of 41 % at the end of the season. Forms of Ca remaining in the solid residue after extraction made only a minor contribution (3 to 21 %) to the total content at any time during the season. In contrast, however, 89 to 96% of the total Mg was extracted by acetic acid at every harvest, with the remainder dissolved by HC1. Scanning electron microscopy and X‐ray microanalysis of the lamina of mature leaves indicated the presence of two crystalline, Ca‐rich products which differed in their morphology, location and distribution. Large styloids (120 to 270 μm in length) were concentrated in idioblasts adjacent to vascular tissue, while bundles of four‐sided raphides, containing wedge‐shaped apices, were located predominantly between the major transport vessels of the vascular tissue. X‐ray diffraction analysis of crystalline isolates confirmed that both morphological forms are calcium oxalate monohydrate (whewellite).
THE PROCESSES OF ANTHER DEHISCENCE AND POLLEN DISPERSAL
Authors: KEIJZER C. J. 
Published: April 2006

SummaryThe process of anther opening was followed in different species by means of light and electron microscopical techniques, stereo microscopical observation inside living tissues and micromanipulation. From these data and a review of the mainly very old literature on this subject, the opening process is outlined. It consists of the following stages: (1) Expansion of the epidermis and endothecium cells and deposition of U‐shaped wall thickenings inside the latter. (2) Enzymatic opening of the septum between two locules. (3) Mechanical rupture of the tapetum. (4) Mechanical opening of the stomium by the centripetal force of the highly turgescent epidermis and endothecium. (5) Outward bending of the locule walls by the centrifugal force of the dehydrating epidermis and endothecium. Steps (4) and (5) clearly reflect the mechanical functions of the two latter tissues. The roles of the other anther tissues and the filament during the earlier stages are discussed.
THE HISTORY OF ENDEMIC FLORA OF ST HELENA: A RELICTUAL SERIES
Authors: CRONK Q. C. B. 
Published: April 2006

SummaryWhen the endemic plant species of St Helena are ordered according to their increasing taxonomic isolation, their corresponding ‘sister groups’ show a ‘relictual series’ of increasing geographical disjunction. This is best explained by progressive extinction and evolution in continental areas rather than by particularly high rates of evolutionary change on the island (i.e. the taxonomically isolated endemics are ancient relicts). Few of the supposed trends of oceanic island evolution are convincingly evident in the flora of St Helena. St Helena was formed in the Miocene, and it is likely that the relict genera colonized St Helena from Southern Africa before the wet forest flora in this area largely disappeared as the climate deteriorated from the late Miocene onwards.
EVIDENCE FOR CALCIUM‐MEDIATED REGULATION OF HETEROCYST FREQUENCY AND NITROGENASE ACTIVITY IN NOSTOC6720
Authors: SMITH R. J. , HOBSON S. , ELLIS I. R. 
Published: April 2006

SummaryThe proportion of heterocysts (heterocyst frequency) in cultures of Nostoc 6720 varied with the Ca2+ concentration present in the growth medium, the proportion increasing from 5 to 9 % as the Ca2+ concentration was increased from 10−5 to 10−4 M. The total nitrogenase activity of the culture declined by 20% whereas the activity per heterocyst decreased by 30%. In the 10−4 to 10−3 M range of Ca2+ concentrations, which includes those employed in most standard media, the heterocyst frequency and nitrogenase activity did not change. At Ca2+ concentrations above 2 × 10−3 M the heterocyst frequency decreased and this decrease was associated with a lower growth rate.The presence of the calcium ionophore A23187 increased the heterocyst content of the culture and total nitrogenase activity, but still decreased the nitrogenase activity per heterocyst. The effects of A23187 and Ca2+ concentration were additive and demonstrated a positive interaction between Ca2+ and the ionophore. In contrast, the Ca2+ antagonist, lanthanum, decreased the heterocyst frequency and, at concentrations below 10−8 M, stimulated nitrogenase activity. At higher concentrations of lanthanum, growth, heterocyst frequency and nitrogenase activity were markedly diminished; cell degradation occurred at concentrations in excess of 10−4 M.An analysis of the intra‐ and extracellular binding of 45Ca2+ showed that decreasing the Ca2+ concentrations in the medium from 10−4 to 10−5 M lowered the intracellular Ca2+ content. In the presence of A23187, intracellular Ca2+ increased. The lanthanum treatment was exceptional in that the intracellular Ca2+ was increased about four‐fold.These results are interpreted as favouring the hypothesis that a Ca2+‐mediated regulatory process modulates heterocyst frequency and nitrogenase activity in Nostoc 6720.
COMPARATIVE STUDIES OF PLANT GROWTH AND DISTRIBUTION IN RELATION TO WATERLOGGING
Authors: WALDREN S. , DAVIES M. S. , ETHERINGTON J. R. 
Published: April 2006

SummaryThe tolerance of Geum rivale L. and G. urbanum L. to soil waterlogging was investigated by growing plants in a compost under a variety of flooding regimes. Chemical analyses showed that high concentrations of available ammonium, iron and manganese but almost no nitrate could be extracted from this compost if conditions became sufficiently reducing, though a considerable period of flooding was required for such reducing conditions to develop. This slow rate of reduction may be due to the absence of an anaerobic microflora in the loam base of the compost.Waterlogging caused a reduction in root biomass and a change in the distribution of living roots of both species such that rooting was restricted to the surface zones of flooded soil. G. rivale possessed a rhizome‐like caudex, which is virtually absent in G. urbanum, and it is suggested that this may facilitate adventitious rooting which aids survival in waterlogged soil. The numbers of leaves, shoot apices and leaves per apex were reduced by flooding in G. urbanum but not in G. rivale. The responses of the two species to transient flooding, soil volume and soils with and without a previous flooding history are discussed in relation to their distribution.
SCANNING ELECTRON MICROSCOPY OF CRYOFIXED MYCORRHIZAS OF SITKA SPRUCE, PICE A SITCHENSIS (BONG.) CARR.: A COMPARISON WITH CRITICAL POINT‐DRIED MATERIAL
Authors: ALEXANDER CLARE , JONES D. , McHARDY W. J. 
Published: April 2006

SummaryCritical point‐drying is the standard method of preparation for scanning electron microscope studies of mycorrhizas. However, a number of recent studies on various biological specimens have shown disadvantages associated with this technique. These can be overcome by cryofixation, where specimens are frozen in liquid nitrogen and viewed in the frozen‐hydrated state. Three distinct types of mycorrhiza of Sitka spruce [Picea sitchensis (Bong.) Carr.] were critical point‐dried or cryofixed, and were examined for differences in the preservation of both surface features and internal morphology after fracturing or cutting the material transversely.Surface features were better preserved in frozen‐hydrated mycorrhizas than in critical point‐dried ones. Surface cementing matrix seen in the former was partially or entirely removed by critical point‐drying. Some distortion of both fungal and plant cells also occurred after the latter treatment, and cell contents retained in frozen‐hydrated specimens were often lost after critical point‐drying. Fractured frozen‐hydrated material revealed surface features of the cortical cells and lobed Hartig net hyphae.
MYCORRHIZAS IN GRASSLANDS: INTERACTIONS OF UNGULATES, FUNGI AND DROUGHT
Authors: WALLACE L. L. 
Published: April 2006

SummaryFumigated and non‐fumigated plots were planted with several species of either mycorrhizal or non‐mycorrhizal grasses. These plots were either inside or outside enclosures which allowed grazing by native North American ungulates and longhorn cattle. The morphology and growth of plants as well as the level of vesicular‐arbuscular mycorrhizal (VAM) development were followed over one growing season during which growing season precipitation was 50 % of the normal level. Grazing was the most important treatment effect, greatly reducing plant size and relative growth rates. Mycorrhizal colonization had no effect upon plant, growth rates or size. Even in grazed plots where nutrient content and soil moisture were higher, no mycorrhizal effect on plant growth was observed. Grazing did not influence VAM colonization, although grazed plants which were growing in non‐fumigated soil had significantly lower colonization levels than any other treatment.
GLUTAMINE SYNTHETASE AND AMMONIUM ASSIMILATION IN ROOTS OF ZINC‐TOLERANT AND NON‐TOLERANT CLONES OF DESCHAMPSIA CESPITOSA (L.) BEAUV. AND ANTHOXANTHUM ODORATUM L.
Authors: SMIRNOFF N. , STEWART G. R. 
Published: April 2006

SummaryThe influence of zinc on glutamine synthetase (GS) activity and ammonium assimilation in roots of zinc‐tolerant and non‐tolerant clones of Deschampsia cespitosa (L.) Beauv. and Anthoxanthum odoratum L. was studied. One isoform of GS was resolved by ion exchange chromatography in D. cespitosa roots. However, two isoforms were found in A. odoratum roots; one of these was attributed to fungal contamination and was not studied further. There was no difference in the sensitivity of partially purified GS from zinc‐tolerant and non‐tolerant clones to inhibition by zinc. Inhibition of GS by Zn was reversible and the kinetics of inhibition were studied. Methionine sulphoximine (an inhibitor of GS) induced ammonium accumulation in the roots of control and zinc‐grown roots of Zn‐tolerant D. cespitosa. Zinc inhibited incorporation of [15N]ammonium into free amino acids (determined by combined gas chromatography–mass spectrometry) in both clones of D. cespitosa, but higher concentrations were required to achieve inhibition in the tolerant clone. The labelling pattern was unaffected by zinc in both clones. The results suggest that zinc has no effect on the pathway of ammonium assimilation in zinc‐grown roots and that assimilation is via the glutamine synthetase–glutamate synthase pathway. There was no evidence to support the hypothesis that glutamate dehydrogenase functions preferentially in ammonium assimilation under conditions of environmental stress.
A 86Rb BIOASSAY TO DETERMINE THE POTASSIUM STATUS OF TREES
Authors: JONES HELEN E. , HARRISON A. F. , DIGHTON J. 
Published: April 2006

SummaryA bioassay method has been developed to test for potassium deficiency in forest trees; it is based on the metabolic uptake by excised roots of 86Rb from 5 × 10−6 M rubidium chloride solution during a period of 15 min. Betula pubescens Ehrh. seedlings were grown in sand culture supplied with Hewitt's nutrient solution containing K at concentrations between 1 and 200 mg l−1. A negative curvilinear relationship was demonstrated between uptake by the seedlings of 86Rb from the rubidium chloride solution and the concentration of K previously supplied in the growth medium. When roots of intact plants were immersed in 86Rb‐labelled solution for 15 min, less than 1% of 86Rb taken up was translocated to the shoots. A similar response curve, relating 86Rb uptake to K supplied to growing plants, was demonstrated when Picea sitchensis (Bong.) Carr seedlings were grown in peat culture with K added at 0 to 400 mg l−1. In three field trials of the bioassay, roots were excised from P. sitchensis and Pinus contorta Douglas ex Loud, growing on peat or peaty gley plots where different amounts of fertilizer had been added to give a range of degrees of K deficiency or from unfertilized, control plots. The patterns of 86Rb uptake by excised roots indicated that the method is potentially useful for the rapid determination of K deficiency in forest trees.
INDUCTION OF PHOSPHOLIPASE ACTIVITY IN THE HYPERSENSITIVE RESPONSE OF WHEAT
Authors: OCAMPO C. A. , GRAMBOW H. J. 
Published: April 2006

SummaryPhospholipase activity, probably C‐type, increased when cultivars of wheat were infected in incompatible, but not in compatible, combinations with wheat stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. & Henn) or with the non‐pathogenic crown rust of barley (P. coronata Cda. f. sp. avenae Fraser & Led.)‐ The effect was mimicked when an elicitor fraction isolated from germ tubes of the wheat stem rust was injected into leaves. The increase in phospholipase activity correlated with the hypersensitive response of leaves when infected with incompatible rust fungi or treated with fungal elicitor. This effect was not observed in healthy or in water‐injected control plants. The results suggest that membrane degradation is involved in the hypersensitive response.
THE GENETICS OF RACE‐SPECIFIC RESISTANCE IN GROUNDSEL (SENECIO VULGARIS L.) TO THE POWDERY MILDEW FUNGUS, ERYSIPHE FISCHERI BLUMER
Authors: HARRY I. B. , CLARKE D. D. 
Published: April 2006

SummaryThe inheritance of race specific resistance to five pathotypes of the powdery mildew fungus Erysiphe fischeri Blumer was studied in different lines of Senecio vulgaris L. With two exceptions, resistance was dominant over susceptibility. The exceptions were two crosses in which resistance to pathotype 3 behaved as the recessive character. The data from these crosses suggested the involvement of dominant inhibitor genes which suppressed the activity of the resistance gene. Seven different dominant resistance genes were identified in three resistant lines, two conditioned resistance to pathotype 4, two to pathotype 10 and one each to pathotypes 3, 5 and 11. The two genes conditioning resistance to pathotype 4 were unlinked, as were the two conditioning resistance to pathotype 10. The genes for resistance to pathotypes 3, 5 and 11 were clearly linked in one line and were probably linked in the other two lines. The linkage group also appears to contain one of each of the genes for resistance to pathotype 4 and 10. The expression of the two genes conditioning resistance to 4 and 10, not in the main linkage group, appeared to be reduced in one line, probably due to the activity of modifier genes. The results are consistent with the hypothesis that race‐specific resistance in S. vulgaris is controlled by a gene‐for‐gene interaction.
A CHECK‐LIST OF MYCORRHIZA IN THE BRITISH FLORA—ADDENDA, ERRATA AND INDEX
Authors: HARLEY J. L. , HARLEY E. L. 
Published: April 2006

PREAMBLEA check‐list of mycorrhiza in the British Flora was published in February 1987 as a supplement to Vol. 105, No. 2 of this journal. As stated in the Editorial Note in Vol. 105, No. 2 itself, it was intended that additions to the list should be published from time to time, and it was for this reason that species for which no information was to hand at the time the compilation was made were included in the list.In this first list of Addenda, the opportunity has been taken not only to correct mistakes in the original check‐list but also to add an Index to facilitate retrieval of information. This Index, the need for which was suggested to us by Dr E. I. Newman, is of families and genera only: species are in alphabetical order within genera. Nomenclature follows Clapham, A. R., Tutin, T. G. & Warburg, E. F. (1981), Excursion Flora of the British Isles (3rd edition). Cambridge University Press, Cambridge.The original check‐list and a copy of these addenda etc. may be obtained from the Executive Editor, The New Phytologist, Department of Botany, The University, Sheffield S10 2TN, UK on receipt of a sterling cheque for £6 made payable to The New Phytologist Trust and an adhesive label addressed to the orderer. The cheque covers cost and postage.
INCOMPATIBILITY IN CULTURED EXPLANT‐GRAFTS BETWEEN MEMBERS OF THE SOLANACEAE
Authors: PARKINSON M. , JEFFREE C. E. , YEOMAN M. M. 
Published: April 2006

SummaryThe development in culture of explant‐grafts between compatible and incompatible combinations of three solanaceous species parallels that of the corresponding whole‐plant grafts in respect of the pattern of vascular development and the functional status of the vascular system. In culture, incompatible explant‐grafts attain greater mechanical strength than corresponding whole‐plant grafts, and consequently this parameter of their development is an unsuitable criterion for judging the compatibility of explant‐grafts. The findings demonstrate that graft compatibility/incompatibility is determined by local factors operating close to the graft union, possibly at a cellular level between the opposing cells of stock and scion. Explant grafting in culture offers an ideal system for experimental analysis of the cellular basis of incompatibility in internode grafting.
AMINOPEPTIDASE FROM THE COTYLEDONS OF VICIA FABA L. VAR. MINOR SEEDS: PARTIAL PURIFICATION AND SOME PROPERTIES
Authors: CITHAREL J. , GARREAU C. 
Published: April 2006

SummaryLeucine aminopeptidase from field beans was studied in the cotyledons of dry and germinating seeds. The partially purified enzyme had a molecular weight of about 60000 (determined by gel filtration). Activity was maximal at pH 7.5, with leucine‐p‐nitroanilide or leucine naphthylamide as substrates, and was stimulated by dithiothreitol and mercaptoethanol and inhibited by Cu and Zn ions. During germination, the highest enzyme activity in the cotyledons occurred after 2d.
INOCULUM EFFICIENCY AND PATHOZONE WIDTH FOR TWO HOST‐PARASITE SYSTEMS
Authors: GILLIGAN C. A. , SIMONS S. A. 
Published: April 2006

SummaryExperiments involving direct placement of inoculum at various distances from an infection court are used to estimate the probability of infection and/or disease of seminal roots of wheat by Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici Walker and of germinating seeds of radish by Rhizoctonia solani Kühn. Two concepts underlie the relationships under investigation. These are the pathozone, which is characterized by the furthest extent of inoculum from the host from which infection is recorded (z), and infection efficiency, which is characterized by two parameters α and β. The asymptotic infection efficiency, β, is estimated by the proportion of propagules that cause infection when placed in contact with the host; a is a measure of the decline in infection efficiency of propagules of inoculum with increasing distance from the host. Three non‐linear models are used to describe the profile of infection efficiency over distance.The sensitivity of the method of placement of inoculum in detecting treatment effects is demonstrated first by showing differences in response amongst two isolates of G. graminis and two times of observation. Maximal values of z for G. graminis ranged from 4 to 8 mm, depending upon the type of inoculum of G. graminis and the growth medium used. Values of z for R. solani and germinating radish seeds varied from 12 to 16 mm for propagules comprising fragments of chopped potato soil inoculum sieved to 1 to 2 mm.The amounts and nutritional basis of inoculum influenced the probability of infection and the parameters α, β and z. Thus, for G. graminis, estimated values for α−1, β and z were greater for inoculum comprising colonized millet grains than for colonized sand particles. When seedlings of radish were exposed to clumps of propagules of R. solani, the parameters β and z increased, while β decreased with increasing clump density. Reduction in propagule size to 0.5 to 1.0 mm reduced the proportion of infected hosts. When clumps of seedlings of radish were challenged with clumps of inoculum of JR. solani, the probability of infection of clumps increased with clump density, but there was no evidence for an effect on the probability of infection of individual seedlings within a clump. The relationship between the estimates of pathozone width and infection efficiency and models for infection of subterranean organs is discussed.