bluuebunny/crossref_metadata_2025 huggingface dataset:
CHRONOLOGY AND DYNAMICS OF VEGETATION CHANGE IN THE PRAIRIE‐WOODLAND REGION OF SOUTHERN MINNESOTA, U.S.A. *
Authors: GRIMM ERIC C.
Published: May 2006

The pollen and sediment stratigraphy of Wolsfeld Lake and French Lake in the Big Woods of southern Minnesota was investigated. Wolsfeld Lake is in the northeastern Big Woods, and French Lake is in the western Big Woods about 1.5 km from the prairie‐woodland border. During the mid‐postglacial, most of the present Big Woods was prairie. Oak woodland began invading prairie about 5000 years ago in the eastern Big Woods, then expanded westward, becoming established near French Lake 2400 years ago. Topography and water bodies, which control fire frequency, strongly influenced where and when woodland invaded prairie. Oak woodland persisted until 300 years ago, when Ulmus, Ostrya virginiana, Tilia americana and Acer saccharum rapidly expanded and became dominant. The changes from prairie to oak woodland and from oak woodland to ‘bigwoods’ must have required reductions in fire frequency, which were probably caused by increased precipitation and possibly decreased temperatures. About 100 years before the expansion of bigwoods, sediment influx increased at the coring site in Wolsfeld Lake, probably because of an increase in runoff and, therefore, precipitation. A conceptual model is presented in which climatic changes trigger vegetation changes, but interactions among the existing vegetational pattern, fire, and topography cause climatic thresholds for vegetation change to vary in space and time.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN FIELD‐GROWN CROPS
Authors: JAKOBSEN TVER , ERIK NIELSEN NIELS
Published: May 2006

Development of infection by vesicular‐arbuscular mycorrhiza (VAM) was studied in some field‐grown crops. An infection plateau was reached within the first month after seedling emergence of spring barley, oats and peas. During the rest of the growth period the proportion of root length infected by VAM remained at about 50% in the cereals and 75% in the peas. In the spring, infection levels were low in winter wheat, winter rye and winter barley, and development of infection was slower in them than in the spring‐sown crops.

VAM infection was also studied in relation to soil depth and root density. The proportion of root length infected decreased markedly below 40 cm soil depth. Root density varied greatly between crops, whereas the absolute length of infected roots was similar in all crops. This indicates that susceptibility to infection was independent of host species.

The results are discussed in relation to final phosphorus uptake and dry‐matter production, and it is proposed that a relatively low soil‐phosphorus availability was counterbalanced, to some extent, by a well‐developed VAM infection.
NITROGEN ASSIMILATION IN MYCORRHIZAS. I. PURIFICATION AND PROPERTIES OF THE NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE‐SPECIFIC GLUTAMATE DEHYDROGENASE OF THE ECTOMYCORRHIZAL FUNGUS CENOCOCCUM GRANIFORME
Authors: MARTIN FRANCIS , MSATEF YAMINA , BOTTON BERNARD
Published: May 2006

The nicotinamide adenine dinucleotide phosphate‐specific glutamate dehydrogenase (L‐gluta‐mate: NADP+ oxido‐reductase, ECI .4.1 .4) of the ectomycorrhizal Ascomycete Cenococcum graniforme was purified twofold to electrophoretic homogeneity. The native enzyme was shown to have a molecular weight of 320000 and to be composed of six identical subunits with a molecular weight of 48 000. The pH optimum for the animating reaction was 7.6 NADP‐GDH showed a negative co‐operativity with respect to ammonia (Km1:2mM, Km2:8 mM). The Km values for α‐ketoglutarate and NADPH were 2 mM and 0.03 mM, respectively. The physical and kinetics properties of this enzyme are similar with those reported for NADP‐GDH of other fungi.

Cross‐reactivity of a rabbit monospecific antiserum raised against the NADP‐GDH from Sphaerostilbe repens, a saprophytic Ascomycete, was tested against the enzyme of C. graniforme. The immunochemical homology of both enzymes are low suggesting that a substitution occurs in amino acid residue of the protein.
WATER DEFICIT AND THE GROWTH AND ANATOMY OF THE RADISH FLESHY AXIS
Authors: JOYCE D. C. , ASPINALL D. , EDWARDS G. R.
Published: May 2006

Radish (cv. Mars) plants were subjected to different water deficits during the expansion of the fleshy axis, and cell division and expansion in the various tissues of the axis were measured both during stress and in recovery. Water deficit inhibited both cell division and cell expansion in all axis tissues, but there was no evidence that the relationship between the various tissues was disturbed. The walls of parenchyma cells significantly thickened during a period of water deficit and staining with toluidine blue suggests that this was due to lignification. When water stress was relieved, cell expansion in the pericycle cells out‐stripped the recovery of cell division.
EFFECTS OF PRETREATMENT WITH PHOSPHATE IN NATURAL POPULATIONS OF AGROSTIS CAPILLARIS L.
Authors: McCain S. , Davies M. S.
Published: May 2006

Clones of six populations of Agrostis capillaris L., collected from contrasting soils, were grown in sand culture for 6 months supplied with either 1 or 40 mg P dm−3 with weekly applied solutions (low and high P‐pretreatments. Plants from the low P‐pretreatment were extremely P‐deficient. Individual unrooted tillers of the pretreated plants were subseqently grown in sand culture for 10 weeks with main treatments of 1 and 40 mg P dm−3. High P‐pretreated plants produced higher yields than low P‐pretreated plants in the 1 mg P dm−3 treatment, demonstrating a distinct P ‘carry‐over’ effect.

Plants of populations from nutrient‐deficient sites were not slower growing or less responsive to P than those from more fertile sites, and plants of the very acidic soil populations were particularly vigorous. However the populations from colliery spoil appeared to be more efficient at utilizing P when P supply was low.

There were no differences between P‐pretreatments in yield at 40 mg P dm−3 but, depending on population, low P‐pretreated plants accumulated between 5 and 55% more P in expanded leaf material than plants of the high P‐pretreatment. This indicates that the increases in rates of P uptake and translocation induced by P‐deficiency, frequently reported in short‐term investigations, may persist for several weeks. The relationship between initial and final P‐status of shoots was examined using genetic variability within populations as the basis of correlations. No simple linear relationship between these variables existed and possible reasons for this are discussed.

The greatest increase in P concentration in shoots at 40 mg P dm−3 as a consequence of low P‐pretreatment occurred in a population from colliery spoil and it is suggested that this, together with a high efficiency of utilization of P, may be part of an adaptive physiological strategy.
INDOLE‐3‐ACETIC ACID PRODUCTION BY MYCORRHIZAL FUNGI DETERMINED BY GAS CHROMATOGRAPHY‐MASS SPECTROMETRY
Authors: EK M. , LJUNGQUIST P. O. , STENSTRÖM ELNA
Published: May 2006

A method for determining indole‐3‐acetic acid (IAA) production in mycorrhiza‐forming fungi was developed. Culture medium and the fungal mycelium were, extracted with ethyl ether together with deuterated IAA as an internal standard, and the extracts thereafter evaporated to dryness. The dry extracts were then silylated in pyridine with BSTFA and analysed by gas chromatography‐mass spectroscopy. Compared to other methods the procedure required a minimum of preparatory work, gave good reproducibility and a standard deviation of acceptable level for studies involving biological material.

The method was used to study IAA production in 16 mycorrhiza‐forming fungi. Results indicated large differences in the ability of the fungal strains to produce IAA. Pisolithus tinctorius 185, a strain previously shown by other workers to give a strong root infection in field experiments, produced the largest amount of IAA. Several other fungi showing high IAA values also infected plant roots with relative ease in laboratory experiments.
THE PATTERN OF PRODUCTION WITHIN INDIVIDUAL UMBILICARIA LICHEN THALLI
Authors: LARSON D. W.
Published: May 2006

Predictive simulation models of lichen growth and distribution should be sensitive to the pattern of production and growth within thalli, and yet little work has dealt directly with the problem of intrathallus variability in production and thus growth.

It has been assumed for many years that lichens show marginal or apical growth as a result of the allocation of local supplies of photosynthate to the proliferating tissues. Only recently have intrathallus gradients in photosynthetic activity been demonstrated in foliose and fruticose species which mirror the observed pattern of growth. This present study aimed to determine whether there was intrathallus variation in production in the form of production gradients in Umbilicaria lichens.

Discs of tissue were removed from large thalli of four species of Umbilicaria and sampled for net CO2 exchange under constant conditions. The results were plotted as maps of physiological activity both on a weight and area basis, but showed an absence of clear intrathallus gradients in activity. This suggests that production is diffuse over the entire surface of the thallus and thus the growth pattern is diffuse.

These results are interpreted to mean that not all lichens grow apically and that greater research effort should be directed towards discovering the extent of variation in growth pattern amongst various families of lichens.
VARIATION AND POLYPLOIDY WITHIN LOWLAND POPULATIONS OF THE BETULA PENDULA/B. PUBESCENS COMPLEX
Authors: GILL J. A. , DAVY A. J.
Published: May 2006

Variation and cytotype distribution have been studied in secondary birch woodland where intermediates between Betula pendula and B. pubescens appear to predominate. Trees at three sites in lowland eastern England, with contrasting soil conditions, were examined.

Thirty‐eight of the trees studied proved to be tetraploid (2n= 56) and the remaining 12 were diploid (2n= 28); no triploids or aneuploids were detected.

Principal Components Analysis of up to 20 biometric characters of leaves, catkins, fruits and achenes revealed an essentially continuous pattern of variation. The diploid trees displayed rather limited variation and corresponded fairly well with B. pendula. In contrast, the tetraploids showed very great variation which included that normally associated with both species and most of the possible kinds of intermediate. The same pattern of variation was evident in several discontinuous variables and also in measurements of pollen diameter and guard‐cell length made on 20 trees at one site (Holme Fen).

Variation was in part site‐dependent, suggesting that the different environments were influencing phenotype. Twenty trees at one site (Dersingham) were located on a topographic gradient from bog to heath; here there was a strong correlation between the loadings of individual trees on the principal axes of variation and the elevation of those trees on the gradient. This indicates a morphological cline which might be determined by site‐wetness. The cline was not associated with polyploidy, as it was mostly attributable to variation within the tetraploids.
THE RELATIONSHIP BETWEEN NITRATE REDUCTASE AND PLANT PRODUCTIVITY IN AGROSTIS SPECIES
Authors: HARRIS P. , WHITTINGTON W. J.
Published: May 2006

Summary

Although many ecological and agricultural experiments have sought to prove that nitrate reductase activity (NRA) could be directly related to productivity, this has proved to be difficult. The experiments indicate that Agrostis tenuis and A. stolonifera may differ in both productivity and NRA but the results are much affected by environmental factors such as temperature, plant density and probably by variety. The environment can apparently determine whether the products of NRA are directed into storage protein or directly into growth. Thus, while NRA should always be correlated with total plant nitrogen, experiments may show a negative, positive or no relationship at all between growth and NRA depending on the environments imposed during the period of observation because alternatives exist for the utilization of reduced nitrate.
UPTAKE OF METHYLAMINE BY SYMBIONTS OF THE LICHEN, CLADONIA CONVOLUTA (ALGAL SYMBIONT: TREBOUXIA)
Authors: TAPPER R. C.
Published: May 2006

Summary

The uptake of methylamine by Trebouxia and its associated fungal partner in the lichen, Cladonia convoluta, has been examined directly using quantitative autoradiography. Uptake of methylamine by Trebouxia is about five times that by the fungal symbiont. The membrane permeability of methylamine measured for both symbionts is higher than can be accounted for by the permeation of the uncharged molecule and provides evidence for the presence of a membrane transport system for protonated methylamine.
ELICITATION OF ACCUMULATION OF TERPENOID ALDEHYDE PHYTOALEXINS IN VERTICILLIUM DAHLIAE‐NFECTED COTTON
Authors: MACE M. E.
Published: May 2006

Summary

Stem stele tissues of Verticillium wilt‐resistant (Seabrook Sea Island 12B2) cotton plants were examined for location of the pathogen and localization of terpenoid aldehyde accumulation 5 days after inoculation with Verticiliium dahliae. Mycelia of V. dahliae were confined to the vessel lumina. Terpenoid aldehyde phytoalexins were detected histochemically in fresh sections as red Sb‐chelates after application of the terpenoid aldehyde‐specific SbCl3 reagent. Most terpenoid aldehydes were detected as diffuse deposits in and around colonized xylem vessels; however, some were localized in solitary xylem parenchyma cells appressed to vessel walls or in solitary xylem and pith parenchyma cells removed from any V. dahliae‐colonized vessels. Thus, physical contact with the pathogen is not required for elicitation of terpenoid aldehyde accumulation.
GENETIC COMPONENTS OF MORPHOLOGICAL VARIATION IN SALIX REPENS
Authors: FOWLER NORMA , ZASADA J. , HARPER J. L.
Published: May 2006

Summary

The presence of statistically significant levels of genetic variation in a series of quantitative morphological characters in a dune population of Salix repens L. was demonstrated by the comparison of half‐sibs grown in the glasshouse from field‐collected seed. Although the plants showed considerable phenotypic differentiation between ridges and slacks in the natural population, only the amount of branching could be shown to be genetically different between plants grown from cuttings from the two environments. Comparison of plants grown from different collections of cuttings showed that these were genetically different for a variety of other morphological characters, although this variation was not correlated with ridge or slack origin. Analysis of the number of collections of this dioecious species containing male or female flowers, or flowers of both sexes, indicates that even within areas 0–5 m in diameter several different clones frequently occur.
THE FITNESS OF THE COPPER TOLERANCE GENE OF MIMULUS GUTTATUS IN UNCONTAMINATED SOIL
Authors: MACNAIR M. R. , D. WATKINS A.
Published: May 2006

Summary

Two experiments looking for differences in fitness between plants of Mimulus guttatus heterozygous for the copper tolerance gene and homozygous for the non‐tolerance gene are described. Experiment 1 used self thinning to look for intraspecific competition; no differences in fitness between the genotypes could be detected. Experiment 2 looked at various fitness‐related characters in spaced plants, and again no difference in fitness was apparent. In both experiments, the trends were for increased fitness of the tolerant genotype. These results may help to explain why metal tolerant plants are often found in non‐tolerant populations at low frequency.
INTERACTIONS OF VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION AND HEAVY METALS IN PLANTS
Authors: GILDON A. , TINKER P. B.
Published: May 2006

The degree of infection of onions with the vesicular–arbuscular mycorrhizal fungus Glomus mosseae was strongly reduced by additions of zinc, copper, nickel or cadmium to the soil medium, and could be completely eliminated by heavy rates of application. A split pot experiment was used to show that zinc translocated within the plant from other roots was effective in decreasing infection levels. Despite this, clover plants growing on areas which had been heavily contaminated with metal were found to be strongly infected with mycorrhizal fungi. A comparison of G. mosseae isolated from these plants with the isolate used at Rothamsted showed the former to be much more tolerant of zinc and cadmium in the soil. There was some indication that mycorrhizal infection, particularly with the tolerant isolate, could protect plants against the effects of heavy metal additions. These infections might be very important in revegetation of polluted sites.
ESTERASE POLYMORPHISM AND GROWTH FORM DIFFERENTIATION IN POA ANNUA L.
Authors: DARMENCY H. , GASQUEZ J.
Published: May 2006

Leaf esterase polymorphism in eight populations of Poa annua L., from two habitat types (four opportunist and four semi‐permanent populations), was demonstrated to be controlled by nine loci. Frequencies at five loci were studied. Locus Est 1 proved highly correlated with growth form: homozygotes AA were prostrate, whereas homozygotes BB were erect. All populations were polymorphic both for esterase isozymes and growth form. Mean frequencies of prostrate and erect plants were 12 and 88% respectively in opportunist populations, and 32 and 68% in semi‐permanent populations. The outcrossing rate was strongly dependent upon plant density, but in both types of habitat, prostrate and erect plants appeared to be able to exchange genes.
THE INFLUENCE OF LIGHT ON THE GERMINATION OF A VENA FA TUA L. (WILD OAT) SEED AND ITS ECOLOGICAL SIGNIFICANCE
Authors: HILTON JANET R. , BITTERLI C. J.
Published: May 2006

The conflicting reports on the influence of light on the germination of A. fatua L. (wild oat) seed may be due to the use of seed of different types and of differing dormancy status. In an attempt to resolve these uncertainties we tested 30 stocks of seed of known type and dormancy status. Light promoted the germination of three types of partially‐dormant seed but had no effect on fully‐dormant and fully non‐dormant seed. The magnitude of the promotory effect was similar in all stocks tested irrespective of the level of dormancy. Following the application of dormancy‐breaking treatments germination of fully dormant seed was also promoted by light. The photoreceptor involved was shown to be phytochrome.
THE RESPONSE OF HAPLOID SECONDARY EMBRYOIDS AND SECONDARY EMBRYOGENIC TISSUES OF WINTER OILSEED RAPE TO TREATMENT WITH COLCHICINE
Authors: LOH C.‐S. , INGRAM D. S.
Published: May 2006

It was shown by experiment that the treatment of cultured haploid detached secondary embryoids and secondary embryogenic tissues of Brassica napus ssp. oleifera with colchicine resulted in diploidy, tetraploidy and mixaploidy. The proportions of the different ploidy levels so induced depended on the concentration of colchicine used and the duration of treatment. The highest levels of diploidization were obtained by exposing the tissues to 0.05 % colchicine in 2% dimethylsulphoxide for 72 h. The capacity for secondary embryogenesis was retained in colchicine‐induced diploid, tetraploid and mixaploid tissues, and the majority of the resulting second generation secondary embryoids were of the same ploidy as the parental material. This indicates the stability of the secondary embryogenic potential irrespective of changes in ploidy level. It is suggested that the ability to produce secondary embryoids is a consequence of haploidy and homozygosity. That the phenomenon is not a consequence of growth in culture is indicated by the fact that secondary embryoids are also produced occasionally on mature glasshouse‐grown plants regenerated from secondary embryoids. It is concluded that a system is now available for the continuous production of large numbers of haploid and homozygous diploid plants, and plants of other ploidy types, all derived from the same haploid anther embryoid. Such a system will be of value for oilseed rape breeding and for genetical and biochemical studies of somatic embryogenesis.
PLANT GROWTH RESPONSES TO VESICULAR‐ARBUSCULAR MYCORRHIZA
Authors: BÅÅTH E. , HAYMAN D. S.
Published: May 2006

The effect of pre‐inoculation with vesicular‐arbuseular mycorrhiza (VAM) on Verticillium wilt of tomato was assessed in a glasshouse trial. Inoculation with Verticillium albo‐atrum decreased plant growth compared to non‐inoculated controls, irrespective of the mycorrhizal status of the plant. Mycorrhizal plants were slightly smaller than non‐mycorrhizal ones. Addition of extra phosphorus to the soil enhanced plant growth but this enhancement was totally eliminated by Verticillium. It is not expected, therefore, that VAM could affect the severity of disease caused by Verticillium even under conditions where VAM would normally have been beneficial for plant growth. The lowest percentage mycorrhizal infection was found on plants with the most severe disease symptoms.
SEASONAL VARIATION IN FROND MORPHOLOGY AND CHLOROPLAST PHYSIOLOGY OF THE INTERTIDAL ALGA CODIUM FRAGILE (SURINGAR) HARIOT
Authors: BENSON E. E. , RUTTER J. C. , COBB A. H.
Published: May 2006

The life cycle of Codium fragile shows strong seasonal trends with respect to frond morphology and chloroplast physiology. The period of maximum carbon fixation, pigment content and chloroplast size occurs during the early winter when competition from other algae is small and the variation in tidal amplitude decreased. At this time of year the alga may be able to accumulate nutrient reserves as evidenced by the seasonal variation in chloroplast alkali: acid‐soluble polyphosphate ratios. In the summer when the physical environment is more extreme (due to prolonged tidal exposure) and competition from other algae greater, photosynthetic rates, pigment concentration and chloroplast size are reduced and the alga enters the reproductive phase. This part of the life cycle is accompanied by the development of frond hairs which may increase nutrient uptake and the mobilization of stored polyphosphates sequestered during the winter vegetative phase. It is proposed that these seasonal trends in frond morphology and chloroplast physiology may constitute an ecologically advantageous growth strategy in C. fragile.
PHYSIOLOGICAL RESPONSES OFRIVULARIA ATRATO SALINITY: OSMOTIC ADJUSTMENT IN HYPOSALINE MEDIA
Authors: REED R. H. , STEWART W. D. P.
Published: May 2006

The metabolic responses of the topshore cyanobacterium (blue‐green alga)Rivularia atra(Roth) Born, et Flah. have been studied over the salinity range from 0 to 100% sea water. Photosynthetic competence is maintained throughout, showing only minor variation in response to salinity change. Nitrogenase activity is highest in hyposaline media (5 to 25% sea water), decreasing to approximately 55 to 60% in full‐strength sea water. The principal low molecular weight, ethanol‐soluble carbohydrate present within cells ofR. atrais the disaccharide trehalose, occurring at concentrations up to 232 mmol kg−1(cell water) within cells incubated in 100% sea water. Trehalose concentration was found to be dependent upon the salt concentration of the bathing medium, suggesting that it played a role in the maintenance of positive turgor under conditions of varying salinity. Approximately 10 to 12% of the total intracellular trehalose pool was released upon ‘downshock’ [transfer from 100% sea water to 0% (fresh water)]. Regular release of such quantities of carbohydrate in response to ‘downshock’, e.g. on exposure to rain or freshwater at low tide, may be locally important in providing fixed carbon for associated heterotrophic organisms, although it represents a negligible input of fixed carbon to the marine littoral environment.
AN 15N INVESTIGATION INTO NITROGEN ASSIMILATION IN HYDROPONICALLY‐GROWN BARLEY (HORDEUM VULGARE L. CV. CLIPPER) IN RESPONSE TO NITRATE, AMMONIUM AND MIXED NITRATE AND AMMONIUM NUTRITION
Authors: LEWIS O. A. M. , CHADWICK S.
Published: May 2006

Barley plants (Hordeum vulgare L. cv. Clipper) were grown in pH‐controlled, aerated solution culture with 2 mM inorganic 14N supplied as nitrate alone, ammonium alone or 1 :1 nitrate+ ammonium. At the 20th day of growth the 14N feeding solutions were replaced by 15N feeding solutions and the plants grown in these media for 4 and 8 h before harvesting.

In the nitrate‐fed plants at both harvests most of the absorbed and assimilated 16N was found in the shoot. Xylem sap analyses showed that 66% of the 16N supply to the shoot was as nitrate indicating that the shoot was the main organ of nitrate assimilation. In the ammonium‐fed plants there was considerable accumulation of 15N ammonium in the root, where the assimilatory pools saturated quickly with 16N and the highest content of organic 16N was found (in the 4 h harvest). Xylem sap analysis showed that 93% of the 15N exported from root to shoot was as organic N (mainly glutamine) with very little ammonium present, indicating that the root was the major organ of ammonium assimilation. The high 15N shoot content at the 8 h harvest suggested however, that the shoot was the major destination of the root assimilated N. In the mixed‐feed plants, combined root and shoot assimilation was evident, 29 % of the 15N in the xylem sap being in the form of nitrate, indicating a suppression of nitrate ion absorption by ammonium ions.

The highest rate of 15N incorporation into organic N, (24.8 μg h−1per plant) occurred in the mixed N‐fed plants (the largest and more robust plants), followed by the ammonium‐fed plants (24.8 μg h−1per plant) (the smallest, least robust plants) and the nitrate‐fed plants (5.6 μg h−1per plant). The lower N assimilation by the nitrate‐fed plants is ascribed mainly to decreased uptake of the nitrate ion in comparison to the ammonium ion.

It appears that, for maximum growth and N assimilation of hydroponically‐grown barley, a mixed nitrate‐ammonium N source is required. Nitrate is poorly absorbed but appears to be necessary for the optimum growth of ammonium fed plants by increasing shoot N assimilation or by providing additional electron accepting potential to the roots. The situation could be markedly different in soil grown plants where the ammonium ion is not so readily available.
THE RELATIONSHIP BETWEEN COMBINED NITROGEN UPTAKES AND NITROGEN FIXATION IN AZOLLA‐ANABAENA SYMBIOSIS
Authors: ITO OSAMU , WATANABE IWAO
Published: May 2006

The assimilation and distribution in Azolla pinnata of nigrogen from three different sources of nitrogen–ammonium, nitrate and dinitrogen–were compared. Neither ammonium nor nitrate supplied at 1 mM for 4 days, inhibited acetylene reduction activity (ARA). At higher concentrations, the ARA was less inhibited by nitrate than by ammonium. Of the three nitrogen sources tested, nitrate‐nitrogen was the least available and mobile in Azolla.

After incubation with 15N‐labelled nitrogen sources leaves were divided into six branches ranging from young to the old and the distribution of 15N among those branches determined. Ammonium and dinitrogen were preferentially assimilated into younger branches and nitrate into older ones.

Alternative labelling with either dinitrogen or combined nitrogen showed that dinitrogen fixation took place simultaneously with the assimilation of ammonium or nitrate, and was less inhibited by nitrate than by ammonium. After 4 days of incubation, about a half of the total nitrogen in Azolla comprised nitrogen newly incorporated from both the medium and atmosphere, and of this about 70 and 30% originated from ammonium and nitrate at 10 mM respectively.

It is suggested that, even when Azolla is grown on a medium containing combined nitrogen, Anabaena in the leaf cavities still fixes atmospheric nitrogen and supplies it to the host plants, and that each nitrogen source is incorporated and translocated in a characteristic manner.
NECTAR GUIDE COLOUR CONTRAST: A POSSIBLE RELATIONSHIP WITH POLLINATION STRATEGY
Authors: PENNY J. H. J.
Published: May 2006

A quantitative photographic survey was made of the spectral structure of the colours of a random selection of wild and cultivated flowers, in the insect and human visible spectra. The survey revealed that the majority of insect‐pollinated flowers possessed nectar guides, of which three types were recognized. Analysis of the contrasts between the nectar guides and the petals revealed that they were apparently most conspicuous in the insect‐visible spectrum. Cultivars were found to have a significantly lower incidence of nectar guides and were also apparently more conspicuous in the human visible spectrum. These results were discussed in relation to possible floral colour adaptation to insect pollinator attraction.
A MODULAR APPROACH TO ANALYSIS OF PLANT GROWTH
Authors: PORTER J. R.
Published: May 2006

The previous paper in this series argued that whole plant development is best viewed as a population‐type process in which attention is focused on the production of modular plant parts. This approach is of more relevance to quantifying whole plants architecture than conventional growth analysis. The present paper describes an experiment in which the growth of two cultivars of Fuchsia was followed as a developing system of meristems. The noted features of growth and development were the changes in numbers of meristems as the plants produced flowers, the age distribution of vegetative meristems and the probabilities of transition between different modular states as the plant developed.
SODIUM IONS CAN ELIMINATE THE NORMAL DISPARITY IN ABAXIAL AND ADAXIAL STOMATAL OPENING ON ISOLATED EPIDERMES
Authors: PEMADASA M. A.
Published: May 2006

A comparative study was made of the effects of KCl and NaCl on abaxial and adaxial stomatal responses to light, CO2and indole‐3‐acetic acid (IAA) on isolated epidermes ofCommelina communis. Although K+and Na+were equally capable of promoting opening, NaCl masked the responses to light, CO2and IAA normally occurring in KCl; thus a specific requirement of K+for normal stomatal responses is suggested. NaCl produced equally wide abaxial and adaxial stomatal apertures, so eliminating the disparity in their opening normally found in KCl; the Na+‐stimulated opening was not a result of a stimulation of K+accumulation in the guard cells. The results suggest that the normal disparity in abaxial and adaxial stomatal opening is specifically linked with differential K+accumulation in the guard cells.
BIOCHEMICAL EFFECTS OF SULPHUR DIOXIDE ON PROLINE METABOLISM IN THE ALGA TREBOUXIA SP.
Authors: EWALD D. , SCHLEE D.
Published: May 2006

Cells of the green alga Trebouxia sp. treated with Na2SO3 (5 × 10−5 to 5 × 10−3 M) for 4, 24, 48, and 72 h show a decreased content of proline and an increase in alanine dependent on incubation time and sulphite concentration.

The activity of the NAD‐dependent proline dehydrogenase (EC 1.5.1.2, alternative name, pyrroline‐5‐carboxylate reductase) was measured. In vitro sulphite uncompetetively inhibited the enzyme. In vivo, sulphite concentrations up to 5 × 10−4 M led to enhanced enzyme activity.

It is suggested that sulphite influences the proline content in Trebouxia via the last enzyme of proline synthesis, proline dehydrogenase.
MORPHOLOGICAL FEATURES OF SYNTHESIZED ECTOMYCORRHIZAE OF ALNUS CRISP A AND A. RUGOSA*
Authors: GODBOUT C. , FORTIN J. A.
Published: May 2006

The ability of two shrubby alders to form ectomycorrhizae with known species of fungus was investigated. Frankia‐ inoculated seedlings of Alnus crispa and Alnus rugosa were raised in growth pouches and inoculated with a pure culture inoculum of potential ectomycorrhizal fungi. Ten of the 46 species of fungi used formed ectomycorrhizae with both Alnus species. Only Alpova diplophloeus showed a well distributed Hartig net; others had a net only proximally, while others had none. These patterns are discussed in terms of more or less rapid Hartig net development. The Hartig net was always confined to the epidermal layer of the root, never completely surrounding it. This situation appears to predominate in the Angiosperms. Colonization of young actinorhizae by Alpova diplophloeus led to the formation of ectomycorrhizal structures.
THE EFFECTS OF SALT WATER AND SOIL TYPE UPON THE GERMINATION, ESTABLISHMENT AND VEGETATIVE GROWTH OF HOLCUS LANATUS L. AND LOLIUM PERENNE L.
Authors: WATT T. A.
Published: May 2006

Holcus lanatus is the dominant grass over large areas of thin peat soil on the western sea‐cliffs of Lundy Island, exposed to salt spray. Its tolerance of artificial sea water (ASW) on peat or loam soils when grown alone or in mixture with either an agricultural cultivar of H. lanatus, Massey Basyn or with ‘Aberystwyth S. 23’Lolium perenne was investigated. Under salt spray, on peat soil, ‘Lundy’H. lanatus had the highest tillering ability and, unlike the others, its yield was unaffected by the spray. When high levels of salt were applied to the soil, the yield of L. perenne was lowest when it was grown on peat and was also in competition with ‘Lundy’H. lanatus. On peat soil, the agricultural cultivar of H. lanatus was more productive than L. perenne. It was also at least as productive as ‘Lundy’H. lanatus when grown on peat with a high level of salt in the soil solution.

When immersed in a solution of ASW, the leaves of L. perenne retained approximately 17 times more salt than did those of either ‘Lundy’ or ‘Massey’H. lanatus. There was no evidence for sodium ions being adsorbed on to the cuticle of any of the grasses. ‘Seeds’ of both L. perenne and ‘Massey’H. lanatus germinated readily in 40% ASW. However, germination of ‘Lundy’H. lanatus‘seeds’ was much reduced at this salt level, especially from intact spikelets, although they germinated readily when transferred to fresh water. The establishment of ‘Lundy’H. lanatus under 120 kg ha−1 day−1 of sea‐salt was slower than that of the other two grasses.
CYANOBACTERIAL MOTILITY AS A TEST OF THE QUANTITATIVE SIGNIFICANCE OF PROTICITY TRANSMISSION ALONG MEMBRANES
Authors: RAVEN J. A.
Published: May 2006

Summary

A quantitative analysis of energy transmission along membranes by diffusion of buffered protons in the aqueous (N and P) phases on either side of the membrane is presented. In thylakoids of plants with chlorophylls a and b, where proton motive force (pmf)‐generators and pmf‐consumers are laterally separated by up to 1 μm, energy transmission by diffusion of buffered protons in the aqueous phase can occur at the observed in vivo rate with less than a 10% decrement in pmf available to consumers relative to its value at pmf‐generators. However, in motile cyanobacteria, it is concluded that motility cannot be maintained in non‐illuminated portions of the trichome by transmission of proticity along the plasmalemma when the mean distance of transmission exceeds a few micrometres. The transmitted effect of illumination is probably an informational rather than an energetic effect. Energy transmission by lateral proticity transport is essentially a diffusive process, and is subject to similar constraints to those related to the transport of ‘chemical’ energy (e.g. as ATP): suggestions that energy transmission by lateral proticity movement can occur over distances, and at velocities, similar to those of nervous transmission apply to transient states and do not reflect steady‐state power transmission.
EFFECTS OF PERIODS OF LOCALIZED WATER STRESS ON SUBSEQUENT NUTRIENT UPTAKE BY BARLEY ROOTS AND THEIR ADAPTATION BY OSMOTIC ADJUSTMENT
Authors: SHONE M. G. T. , FLOOD ANN V.
Published: May 2006

Summary

Drought and low soil water potentials depress nutrient uptake by roots, but their capacity for recovery when the soil is re‐wetted has received less study. We investigated the uptake in barley of labelled phosphate and calcium from sand culture following periods of drought or treatment with polyethylene glycol 4000 (PEG) of the surface layers of the sand, with the lower portion of the root system receving ample nutrients and water. Drought diminished uptake and translocation of both nutrients and caused death of fine lateral roots, but after 3 days of re‐wetting, uptake per unit fresh weight of roots was comparable with that of well‐watered control plants despite apparent collapse of some of the cortical cells of the seminal axes. The activity of new nodal roots that grew during the 3‐day re‐wetting period alleviated the earlier depression of nutrient absorption. Effects of PEG (−0.8 MPa) were less severe and nodal roots grew through this medium with no apparent damage. The tips of these roots seemed to become osmotically adjusted largely by enhancement of their sugar content, but we found little evidence of such adjustment in those parts of the seminal axes exposed to PEG. Rapid growth of nodal roots assisted by osmotic adjustment may be of adaptive significance in ensuring resumption of nutrient and water uptake following periods of water deficit.
POPULATION DIFFERENTIATION IN FESTUCA RUBRA L. AND AGROSTIS STOLONIFERA L. IN RESPONSE TO SOIL WATERLOGGING
Authors: DAVIES M. S. , SINGH A. K.
Published: May 2006

Summary

Two populations of Agrostis stolonifera and seven populations of Festuca rubra from salt marsh and inland habitats were grown on a free draining soil and at two levels of soil waterlogging. The growth of A. stolonifera was stimulated by soil waterlogging while that of F. rubra was depressed. There was no difference between the two populations of A. stolonifera in growth response to waterlogging but the inland population had a greater Fe concentration in the shoots when grown on waterlogged soil than the salt marsh population. In F. rubra the yield of the salt marsh populations was generally less depressed by soil waterlogging than that of populations from free draining soils; the salt marsh populations also had lower concentrations of Fe and Mn in the shoot on the continuously waterlogged soil than the inland populations. It is concluded that the evolution of a degree of waterlogging tolerance has occurred in the salt marsh populations of F. rubra in response to the periodic flooding by sea water in their native habitats.
THE EFFECT OF SALINITY ON LEAF WATER RELATIONS AND CHEMICAL COMPOSITION IN THE SUB‐ANTARCTIC TUSSOCK GRASS POA COOKII HOOK F.
Authors: PAMMENTER N. W. , SMITH V. R.
Published: May 2006

Summary

Isolated tillers of the sub‐Antartic Maritime tussock grass Poa cookii responded to high concentrations of NaCl (0.3 to 0.7 M) in the root medium by markedly accumulating Na in the older leaves. Concomitant with this was a decline in leaf water potential (φ), osmotic potential (φ) and fresh weight: dry weight ratio. Inorganic solutes accounted for a greater proportion of the measured φ in older than in younger leaves and Na was the most important cation contributing to measured values of φ and φ Changes in the K, Ca and Mg concentrations in leaves exposed to NaCl in the root medium were related to changes in leaf water content rather than to remobilization of these elements within the plant. The results are interpreted as demonstrating a mechanism preventing injuriously high levels of Na in young, metabolically active tissue, rather than an osmoregulatory phenomenon. This suggests that P. cookii cannot be considered to be a true halphyte despite its frequent occurrence in the salt spray zone of many sub‐Antarctic islands.
VESICULAR‐ARBUSCULAR MYCORRHIZA IN FIELD‐GROWN CROPS II. EFFECT OF INOCULATION ON GROWTH AND NUTRIENT UPTAKE IN BARLEY AT TWO PHOSPHORUS LEVELS IN FUMIGATED SOIL
Authors: JAKOBSEN I.
Published: May 2006

Summary

The effect of inoculation with vesicular–arbuscular mycorrhizal fungi on the growth of barley in the field was studied at two levels of soil P on plots fumigated with methyl bromide. During the vegetative phase, growth and P uptake was influenced only by soil P; P uptake in the period from earing until maturity was negligible in uninoculated plots. Final production of dry matter was increased by 20 % on average by inoculation and by 40 % by soil P. In contrast, the final P uptake was increased by 100% by inoculation and only by 50% by soil P. Concentrations of bromide in shoots were high and inoculation increased the uptake of bromide, Zn and Cu significantly. Mycorrhizal infection in inoculated plots was first observed 25 days after seedling emergence, and final infection levels were c. 50% in contrast to 12 % without inoculation. The introduced endophyte had spread 30 cm horizontally during the growth period of 96 days.
ORIGINS OF DECAY IN LIVING DECIDUOUS TREES: THE ROLE OF MOISTURE CONTENT AND A RE‐APPRAISAL OF THE EXPANDED CONCEPT OF TREE DECAY
Authors: BODDY LYNNE , RAYNER A. D. M.
Published: May 2006

Summary

It is argued that the development of decay in living hardwoods can best be explained in terms of the unsuitability of functional sapwood for mycelial establishment owing to its high moisture content and lack of easily assimilable nutrients other than within living cells. Decay occurs when these limitations are removed by any mechanisms which prevent or interfere with the normal functioning of sapwood. Recent concepts of decay in living trees have implied an active host defence against infection. This view is discussed against the alternative that non‐specific mechanisms which maintain sapwood function will, by their very nature, prevent establishment of ‐ycelium of decay and stain fungi. The significance of mixed microbial communities in the development of decay is discussed, particularly in relation to the supposed requirement for specific sequences to overcome host defences.
A HOLOCENE POLLEN DIAGRAM FROM LYNCH'S CRATER, NORTH‐EASTERN QUEENSLAND, AUSTRALIA
Authors: KERSHAW A. P.
Published: May 2006

Summary

Pollen analysis of this core from Lynch's Crater provides a more detailed and continuous Holocene record than has been obtained previously from the site. The pattern of dry‐land vegetation changes appears broadly similar to those from other sites covering this period from the Atherton Tableland, though problems of dating do place some restriction on temporal correlations between them. Swamp forest is recorded for the first time within the region from pollen and plant macroremains, and this existed from the time of arrival of rainforest, probably about 8500 years B.P. until between 6000 and 4500 B.P. Firing by Aborigines in addition to climate change is considered to have been an important factor in swamp forest destruction and in the promotion of subsequent changes in swamp vegetation.
GENOTYPIC VARIATION IN THE RESPONSE TO SUB‐OPTIMAL TEMPERATURES OF GROWTH IN TOMATO (LYCOPERSICON ESCULENTUM MILL.)
Authors: PAUL E. M. M. , HARDWICK R. C. , PARKER P. F.
Published: May 2006

Summary

A growth analysis of plants raised under controlled environment conditions was used to examine the response to temperature of five contrasting tomato cultivars bred for outdoor production. Curves were fitted to the data of dry weight and leaf area and, to compensate for ontogenetic drift, instantaneous values of growth analysis parameters were calculated from these curves at a specific growth stage. Differences in relative growth rate which could be exploited in a breeding programme were not detected, though there were large differences in the components of relative growth rate. These were, however, compensatory within a cultivar. It was concluded that in order to select a genotype with improved growth rate it would be necessary to disrupt the compensation mechanism between the components of relative growth rate.
THE DEPENDENCE OF SUNTRACKING IN LAVATERA CRETICA L. UPON CARBON DIOXIDE AVAILABILITY
Authors: FISHER F. J. F. , WRIGHT M.
Published: May 2006

Summary

When CO2 is withheld from the leaves of Lavatera cretica L., the normal phototropic tracking response to an oblique light source becomes weakened within 60 min and after 2 h is eliminated altogether. If CO2 is also withheld throughout a preceding 24 h dark period, even the initial tracking response in the light under carbon dioxide deprivation is eliminated. Normal tracking resumes in both cases when CO2 is again provided. Alternating directions of oblique illumination, under normal atmospheric CO2 levels, produce a synchronized response cycle with a short phase lag, but carbon dioxide deprivation results in the adoption of a neutral intermediate position. The results are in accord with the hypothesis that uneven distribution patterns in photosynthetic activity, resulting from the oblique illumination of the lamina, lead to the pulvinar turgor gradients responsible for suntracking movements in this species.
INJURIES TO LICHEN ULTRASTRUCTURE CAUSED BY SULPHUR DIOXIDE FUMIGATIONS
Authors: HOLOPAINEN TOINI , KÄRENLAMPI L.
Published: May 2006

Summary

Effects of SO2 (0.05,01, 0.3 and 1.0 ppm) fumigations on the ultrastructure of the lichens Bryoria capillaris (Ach.) Brodo & D. Hawksw. and Hypogymnia physodes (L.) Nyl. were studied with a transmission electron microscope. All concentrations of SO2 caused characteristic ultrastructural symptoms. These were always observable before light microscopic and visible changes in thalli.

Sulphur dioxide injury in the Trebouxia phycobiont cells of both species began as swelling and deformation of mitochondria, stretching of the chloroplast envelope and deformation of pyrenoglobuli. Later, stretching of thylakoids and degeneration of pyrenoid, chloroplast stroma, nucleus, mitochondria and cytoplasm were observable. It was typical of the later stages of SO2injury that thylakoids remained visible for a long time. The degree of injury in the algal cells increased with increasing SO2 concentration and duration of exposure. The fungal cells showed ultrastructural symptoms, swelling of mitochondria and vesiculation of the mesosome‐like organelle, only at the highest concentration (1.0 ppm) of SO2. The experimental results are consistent with many earlier observations on natural material collected from industrial environments. Relationships between the ultrastructural and physiological changes caused by SO2 are discussed.
ANTIGENIC ANALYSIS OF ANABAENA AZOLLAE AND THE ROLE OF LECTIN IN THE AZOLLA–ANABAENA SYMBIOSIS
Authors: LADHA J. K. , WATANABE I.
Published: May 2006

Summary

Antigenic cross‐reactivity between symbiotic Anabaena azollae and its Azolla host was detected by an indirect immunofluorescence technique. Antiserum against Anabaena‐free Azolla cell extract cross‐reacted with A. azollae freshly separated from different species of Azolla, but did not cross‐react with any of the free‐living Anabaena species tested, including A. azollae (Newton), which was claimed to be isolated from Azolla.

Cell extracts of the whole Azolla‐Anabaena symbiosis and of Anabaena‐free Azolla plants both caused agglutination of human and rabbit erythrocytes whereas extracts of symbiotic A. azollae freshly separated from Azolla plants or free‐living A. azollae (Newton) did not cause haemag‐glutination. Of the several sugars tested α‐D‐galactose inhibited the haemagglutination. Free‐living A. azollae (Newton) showed no cross‐reaction at any growth phase of its life cycle with antiserum against Anabaena‐iree Azolla nor could it bind the haemagglutinating factor from the Azolla‐Anabaena symbiosis.

The possible significance of common antigens and lectin in the Azolla‐Anabaena symbiosis is discussed.