bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECTS OF SHADE ON XYLEM DEVELOPMENT IN SEEDLINGS OF EUCALYPTUS GRANDIS HILL EX. MAIDEN
Authors: DOLEY D.
Published: May 2006

Summary

Seedlings of Eucalyptus grandis were grown under light regimes of 12·6 and 2·8 E m−2 day−1 for 7 weeks, during which time secondary xylem development was studied. The rate of cambial cell division was approximately 50% greater in the high light than in the low light treatment. Rates and durations of fibre expansion were similar, but the rate of wall thickening was almost three times as great in the high as in the low light treatment. Also, the duration of fibre wall thickening was estimated to be 7 days in high light as compared with 21 days in low light. Secondary vessel lumen area and the cross sectional area of vessels per unit area of leaf surface were greater in high than in low light plants, although the proportion of xylem cross sectional area occupied by vessels did not differ significantly between treatments.
A COMPARATIVE STUDY OF ESTABLISHMENT OF PLANTAGO CORONOPUS L. FROM SEEDS SOWN RANDOMLY AND IN CLUMPS
Authors: WAITE S. , HUTCHINGS M. J.
Published: May 2006

Summary

This paper reports the results of a study of the establishment of Plantago coronopus L. seeds in the field. Seeds were introduced at a range of densities into plots with intact vegetation, and plots from which the vegetation was removed. Seeds were also sown in a variety of clump sizes on to non‐vegetated plots. The aim of this experiment was to determine whether the density‐dependent germination patterns exhibited by this species in laboratory experiments could also be observed in the field.

All treatments exhibited similar patterns of seedling recruitment although different conditions of planting showed quantitatively different responses. During the first 4 weeks after sowing there was rapid seedling recruitment followed by mortality which balanced this recruitment. Eight weeks after sowing, seedling densities were not significantly different from the starting densities in any of the treatments. In particular, the chance of a seed forming an established seedling was not increased when seeds were sown in clumps, thus calling into doubt the ecological benefits of density‐dependent germination responses which have been proposed in previous laboratory studies of the phenomenon. Factors influencing germination and establishment were investigated by means of an autocorrelation matrix. Recruitment of seedlings into the population appears to be limited by the number of adult and seedling plants already present in the population.
PHOTOSYNTHETIC CAPACITIES AND BIOLOGICAL STRATEGIES OF GIANT‐CELLED AND SMALL‐CELLED MACRO‐ALGAE
Authors: RAVEN J. A. , SMITH F. A. , GLIDEWELL S. M.
Published: May 2006

Summary

Data are presented which show that the photosynthetic and respiratory characteristics of the giant‐celled alga Chaetomorpha darwinii are those of a shade plant (denned physiologically in terms of rates of photosynthesis at light and inorganic carbon source saturation, and the irradiance required to saturate photosynthesis and to compensate respiration by photosynthesis). This is in agreement with previous suggestions that giant‐celled algae have the characteristics of ‘shade plants’, while small‐celled macroalgae can be either ‘sun plants’ or ‘shade plants’. A comparison of giant‐celled algae with small‐celled macro‐algae in terms of ecological strategies has been made, using previously published data on Enteromorpha intestinalis, Chaetomorpha linum (‘fugitive’small‐celled), Chaetomorpha darwinii, Hydrodictyon africanum (‘stressed’ giant‐celled), Cham corallina (‘canopy‐dominant’/‘stressed’ giant celled) and Laminaria digitata (‘canopy‐dominant’ small celled), as well as new data on net and mass spectrometric measurements of O2 exchange in L. digitata. It is suggested that the ability of giant‐celled algae to compete as ‘canopy dominants’ may be related to cytoplasmic streaming in the ‘absence of many (or any) plasmodesmatal barriers to diffusion providing an efficient means of long‐distance transport in a differentiated plant, as an alternative to phloem‐type translocation in small‐celled ‘canopy dominants’. The significance of the giant‐celled habit in ‘stressed’ macroalgae is not clear, although the absence of giant‐celled algae from the ‘fugitive’ category may be related to their limited capacity for rapid growth relative to small‐celled algae.
THE REGULATION OF K+ UPTAKE BY RYEGRASS AND WHITE CLOVER ROOTS IN RELATION TO THEIR COMPETITION FOR POTASSIUM
Authors: DUNLOP JAMES , GLASS A. D. M. , TOMKINS B. D.
Published: May 2006

Summary

The regulation of K+ influx into roots of Westerwolds ryegrass (Lolium multiflorum Lam.) and white clover (Trifolium repens L.) seedlings has been studied. In low salt plants the absorption isotherms had the same Michaelis constants (Km) but ryegrass had a greater maximum rate of influx (Vmax) than white clover. When the potassium contents of the roots were increased the difference in Vmax diminished but the Kms increased, the value for white clover increasing much more rapidly than the value for ryegrass. The data gave very similar Hill plots for both species which suggests that the molecular mechanisms responsible for the regulation of potassium absorption have strong similarities. The practical implications of the findings are considered and it is suggested that under conditions where competition for potassium is important the specific rate of potassium absorption for ryegrass could be two to five times faster than that for white clover.
VEGETATIONAL CHANGE AND THE INFLUENCE OF PREHISTORIC MAN IN THE SOMERSET LEVELS
Authors: BECKETT S. C. , HIBBERT F. A.
Published: May 2006

Summary

Pollen analysis and radiocarbon dating of profiles from three sites in the Somerset Levels has allowed the construction of both pollen percentage and influx diagrams. The results are used to discuss the timing of vegetational change within the area of study and to quantify further the effect of man on such changes as are recorded.
INFLUENCE OF PLANT INTERACTIONS ON VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTIONS. I. HOST AND NON‐HOST PLANTS GROWN TOGETHER
Authors: OCAMPO J. A. , MARTIN J. , HAYMAN D. S.
Published: May 2006

Summary

Mycorrhizal infections formed by different endophytes were examined in 10 crop species grown separately and in pairs in sterilized and unsterile soils. No infection was observed in cabbage, kale, rape or swede (in the supposedly non‐mycorrhizal family Cruciferae) and only traces were seen in sugar beet (supposedly non‐mycorrhizal Chenopodiaceae) when these plants were grown alone. However, slight (< 5 %) infection (cortical mycelium and vesicles, but no arbuscules) developed in some when a mycorrhizal host plant was present and there were many clumps of endophyte mycelium on their root surfaces, usually attached to entry points which had often aborted. Glomus fasciculatus‘E3’ was a more infective endophyte than Gigaspora margarita. Infection was usually well developed in the host plants barley, lettuce, maize, potato and onion. It was depressed only in a few pairs but no more by the presence of a ‘non‐host’ plant than by a host plant. The results suggest that the barriers to mycorrhizal infection in ‘non‐hosts’ are intrinsic and more probably related to characteristics of the root cortex or epidermis than to any infection‐inhibiting factors that might be released in root exudates.
CARBOHYDRATE METABOLISM IN THE LEAFY LIVERWORT, PLAGIOCHILA ASPLENIOIDES (L.) DUM. VAR. MAJOR NEES
Authors: SULEIMAN A. A. A. , LEWIS D. H.
Published: May 2006

Summary

Volemitol, sucrose and starch are the principal photosynthetic products of the leafy liverwort Plagiochila asplenioides (L.) Dum. var. major Nees. but the quantitatively most abundant carbohydrates, fructans, do not rapidly incorporate 14C from 14CO2. The limited amount of starch present turns over rapidly but sucrose and especially volemitol do so very slowly and much 14C incorporated during a short pulse remains in these compounds after prolonged periods in the dark (up to 4 months). The liverwort grows under these conditions and 14C incorporated during the pulse passes into insoluble polymers. Loss of chlorophyll is also slow and tissue is photosynthetically viable after such long periods in the dark. Exogenous glucose, fructose and sucrose are absorbed and metabolized in the dark similarly to CO2 in the light except that there is enhanced incorporation into fructans. Exogenous mannitol is absorbed but poorly metabolized.

Results are discussed in relation to polyol‐ and fructan‐containing angiosperms and algae, and from both biochemical and ecological viewpoints.
SEASONAL CHANGES IN NEAR INFRARED REFLECTANCE RATIO AND SANDING CROP BIOMASS IN A SALT MARSH COMMUNITY DOMINATED BY HALIMIONE PORTULACOIDES (L.) AELLEN
Authors: JENSEN ARNE
Published: May 2006

Summary

Near infrared (715 to 1000 nm) reflected radiation and standing crop biomass were measured in a Halimione portulacoides shrub community during the growing seasons of 1975 and 1976. The amount of near infrared radiation that was reflected was strongly correlated with the total standing crop of photosynthetic tissue. During the growing season of 1977 the quantity of near infrared radiation reflected from the vegetation was used to predict the amount of standing crop of photosynthetic tissue in the community. The predicted values were within 10 % of the measured values obtained by the use of a harvest technique. In addition the amount of reflected near infrared radiation was found to be strongly correlated with leaf area index of the vegetation.
POLLEN ANALYSES OF SEDIMENTS FROM LOUGH INE AND BALLYALLY LOUGH, CO. CORK, S.W. IRELAND
Authors: BUZER JENNY S.
Published: May 2006

Summary

Pollen analyses of post‐glacial sediments from the marine Lough Ine and freshwater Ballyally Lough are described.

Lough Ine was found to have been formerly a freshwater basin. The oldest sediments, banded clays with no microfossils, were probably glacial outwash deposits. These were overlain by post‐glacial sediments; late‐glacial deposits were missing. By comparison with radiocarbon‐dated diagrams from other sites the marine transgression is tentatively dated at c. 4000 b.p. The lowest sediments from Ballyally Lough can be assigned to Mitchell's zone VI, the Boreal period.

The post‐glacial vegetational development of both loughs and the surrounding area is discussed.
PHOTOSYNTHESIS BY AQUATIC PLANTS: EFFECTS OF UNSTIRRED LAYERS IN RELATION TO ASSIMILATION OF CO2 AND HCO3−AND TO CARBON ISOTOPIC DISCRIMINATION
Authors: SMITH F. A. , WALKER N. A.
Published: May 2006

Summary

We review and reassess experimental evidence which indicates that the unstirred layers of solution bathing aquatic plant cells or organs represent a major factor limiting their rate of photosynthesis under natural conditions. Unstirred layers may also limit membrane transport of HCO3− where this occurs. Some authors have suggested that aquatic plants carry out C4photosynthesis and cite in support measurements of discrimination between 13C and 12C. We propose that this discrimination can also be a manifestation of the presence of unstirred layers or membrane transport or both.
THE SECRETORY CYCLE OF DIONAEA MUSCIPULA ELLIS
Authors: ROBINS R. J. , JUNIPER B. E.
Published: May 2006

Summary

The fine structure of the digestive glands of Dionaea muscipula is described and the changes that occur in the cells following stimulation were examined quantitatively. Significant cyclic alterations were found in the volume of the vacuole and of the labyrinthine walls. The architecture of these walls was examined in detail. The mitochondria were shown to become considerably more condensed and often to adopt elongated profiles. The endoplasmic reticulum showed a decrease in area, but appeared to change from a storing to a synthetic role, acquiring numerous polysomes. These obSérvations are discussed in terms of the function of the gland.
THE SECRETORY CYCLE OF DIONAEA MUSCIPULA ELLIS.
Authors: ROBINS R. J. , JUNIPER B. E.
Published: May 2006

Summary

The cellular mechanisms involved in the storage and synthesis of secretory proteins in the glands of the carnivorous plant Dionaea muscipula were examined. Important roles for a sub‐compartment of the vacuole and smooth endoplasmic reticulum were demonstrated by high‐resolution autoradiography and cytochemistry. It is shown, for the first time in a carnivorous plant, that de novo protein synthesis occurs during the secretory phase of activity and that part of this protein is directly secreted.
THE RESPONSE OF ROOT ACID PHOSPHATASE ACTIVITY TO HEAVY METAL STRESS IN TOLERANT AND NON‐TOLERANT CLONES OF TWO GRASS SPECIES
Authors: COX R. M. , HUTCHINSON T. C.
Published: May 2006

Summary

The inhibition by zinc of phosphatase activity in dialysed root extracts was determined for zinc‐tolerant and non‐tolerant clones of Anthoxanthum odoratum L. Similarly the inhibition by copper of this enzyme activity in root extracts of copper‐tolerant and non‐tolerant clones of Deschampsia cespitosa (L.) Beauv. was also determined. It was found for both species that the relationship between the in vitro percentage inhibition of enzymatic activity and the tolerance index of each clone, changed after exposure to sub‐lethal concentrations of the respective metal in water culture. The enzyme activity in the root extracts of the tolerant clones was found to be significantly less inhibited by the particular metal, than those of the non‐tolerant clones only when the plants were previously exposed to the particular metal in vivo. Since exposure of the roots to metal appeared to induce a positive reaction in tolerant material, it is suggested that physiological and biochemical investigations of metal tolerance may be more informative if plants that have been pre‐stressed by a particular metal are used. This should enable a better recognition of adaptive components of metabolism. Examples of such an approach and its implications are discussed.
THE SECRETORY CYCLE OF DIONAEA MUSCIPULA ELLIS. V. THE ABSORPTION OF NUTRIENTS
Authors: ROBINS R. J. , JUNIPER B. E.
Published: May 2006

Summary

The absorption pathway is studied, using chloride ion as a marker, in relation to the ultrastructure of the gland. The relative importance of the symplast and apoplast as pathways of absorption is considered and it is suggested that the former is the primary route for metabolites moving into the leaf. Quantitative ultrastructural evidence is presented to support this. It is shown that the labyrinthine walls have a highly polar distribution and it is proposed that this is partially concerned with absorption, but has a more important role in the excretion of water. A model is proposed to explain bi‐directional flow within the gland.
MORPHOLOGICAL AND PHYSIOLOGICAL VARIATIONS IN CLONES OF ASTERIONELLA FORMOSA HASSALL
Authors: HAPPEY‐WOOD CHRISTINE M. , HUGHES DAVID I.
Published: May 2006

Summary

The morphology of Asterionella formosa isolated from two contrasting lakes has been studied. During four months in culture the valve length of five isolates decreased. Greater variation in valve length was observed in the strain from Llyn Coron, resulting in the separation of two morphologically distinct clones from the original isolate. Two cultures of the diatom from Llyn Padarn exhibited a more regular decrease in cell size. All strains had similar chlorophyll‐a levels in relation to cell volume.

Most rapid growth, but smallest yields, in batch cultures, were characteristic of the two large‐celled clones from Llyn Coron, whereas the small‐celled clone from this lake exhibited the slowest growth rate, but maximum yield. Thus morphological change which is accompanied by physiological differences may occur in a culture derived from a single parent colony. The growth characteristics of the two strains from Llyn Padarn were more similar than those of the three isolates from Llyn Coron.

The rapidly growing large‐celled strain from Llyn Coron had a high photosynthetic rate. So had one isolate from Llyn Padarn, but a large proportion of fixed carbon was lost extra‐cellularly by this strain, which may account for its slower growth rate. Photosynthetic rates of the small‐celled isolate from Llyn Coron and the second isolate from Llyn Padarn were low. A range of photosynthetic efficiencies were recorded and these were related positively to the maximum photosynthetic rate. The rapidly photosynthesizing Padarn strain, which had the lower chlorophyll‐a content per cell, was the most efficient. The pattern of distribution of photosynthate for this strain from Padarn differed from the other isolates. In addition to the large proportion lost extracellularly, it had a higher level of protein synthesis. The presence of extracellular products reduced the photosynthetic rate, and differences were noted in the response to light intensity between A. formosa from the two lakes.

Morphological and physiological variations were confirmed in A. formosa. The situation is complex, since morphologically similar strains isolated on different occasions from Llyn Padarn showed contrasting physiological behaviour and, during culture, morphological types were distinguished in the isolate from Llyn Coron, which also differed physiologically.
THE GENECOLOGY OF LAWN WEEDS
Authors: WARWICK S. I.
Published: May 2006

Results from an experiment in which trampling was simulated indicated that in Plantago major and Poa annua the genetically‐determined prostrate growth forms were in general better able to withstand trampling damage than the corresponding erect growth forms. The effects of trampling stress were found to differ between species, between treatments for each species, and in the degree to which different aspects of growth and reproduction appear to be affected within a given species. Estimates of coefficients of selection acting against the erect growth forms were particularly high for reproductive characters, with values of 0.78 to 0.79 for Plantago major and 0.46 to 0.66 for Poa annua.

Problems in the design of experiments investigating trampling stress are discussed.
COMPARISON OF THE ONION PLANT (ALLIUM CEPA) AND ONION TISSUE CULTURE. II. STIMULATION OF FLAVOUR PRECURSOR SYNTHESIS IN ONION TISSUE CULTURES
Authors: SELBY C. , TURNBULLF A. , COLLIN H. A.
Published: May 2006

Onion callus was exposed to high concentrations of a number of intermediates involved in the synthesis of S‐trans‐prop‐1‐enyl‐L‐cysteine sulphoxide, the major flavour precursor in the intact onion plant. The intermediates were sodium sulphate, L‐valine, methacrylic acid and S‐(2‐carboxypropyl)‐L‐cysteine. Growth was reduced or totally inhibited at the highest concentration (50 to 100 HIM) Of All the intermediates but, except for methacrylic acid which was inhibitory at all concentrations, a limited growth occurred at the lower concentrations (10 to 20 mM) of the other compounds. The only treatment which caused the callus to produce an onion odour on crushing the tissue was when S‐(2‐carboxypropyl)‐L‐cysteine was incorporated in the culture medium; this result indicated that the callus was capable of the final stages in the synthesis of S‐Jram‐prop‐1‐enyl‐L‐cysteine sulphoxide. The presence of this pathway was confirmed by feeding smaller amounts of L‐cysteine, L‐valine and S‐(2‐carboxy‐propyl)‐L‐cysteine (1 and 3 mM) and separating the amino acids and flavour precursors by t.l.c. electrophoresis. S‐trans‐prop‐1 ‐enyl‐L‐cysteine sulphoxide was found only when S‐(2‐carboxypropyl)‐L‐cysteine was present in the medium. When S‐ethyl and S‐propyl‐L‐cysteine were fed to the callus these compounds were oxidized to their sulphoxides showing that an oxidase system for the S‐alkyl cysteines was present in the callus.
RESPONSE OF CROP PLANTS TO VA MYCORRHIZAL INOCULATION IN AN UNSTERILE INDIAN SOIL
Authors: BAGYARAJ D. J. , MANJUNATH A.
Published: May 2006

Inoculation of three crop plants, viz. cotton, cowpea and finger millet to inoculation with the VA mycorrhizal fungus, Glomus fasciculatus, in an unsterile Indian soil low in available phosphorus significantly increased their root and shoot weights. The phosphorus and zinc content of inoculated plants were higher. Inoculated plants did not differ significantly from uninoculated plants in manganese content.
MITOSIS IN THE ROOT CAP OF ZEA MAYS
Authors: CLOWES F. A. L.
Published: May 2006

The rate of mitosis and the probability of the plane of mitosis have been determined for every cell of the cap meristem. of Zea. Overall rates decrease from the central files outwards and from the proximal to the distal tiers. This also applies to transverse divisions, but highest rates in the longitudinal plane occur nearer the periphery of the proximal tier. All the cells show some probability of dividing in both planes and the transition from predominantly transverse divisions at the axis to mostly longitudinal divisions near the periphery is smooth.

The meristem is very sensitive to the way the plants are treated not only in the aggregate rate of cell production, but also in the disposition of cell production across the meristem.
LEAF‐CANOPY‐INDUCED SEED DORMANCY IN A GRASSLAND FLORA
Authors: SILVERTOWN JONATHAN
Published: May 2006

The germination of 27 species from calcareous grassland was tested in three light treatments in the laboratory: in darkness, under tungsten lamps and under a leaf‐canopy. Germination was significantly lower under a leaf‐canopy than in the dark in 17 species. The phenomena of leaf‐canopy induced dormancy was not associated with the life‐span of species, though there was a weak, negative relationship with seed weight amongst 20 perennials in the sample. It is suggested that the co‐existence of species at high density in calcareous grasslands may, in part, be explained by differences in germination response to fine‐grained variations in the light environment at the soil surface.
THE LATE DEVENSIAN AND FLANDRIAN VEGETATIONAL HISTORY OF CROSE MERE, SHROPSHIRE
Authors: BEALES PETER W.
Published: May 2006

The vegetational history of Crose Mere, north Shropshire, is reconstructed by means of pollen analysis, lithostratigraphy and radiocarbon dating. Pollen diagrams from a core representing the Flandrian and Late Devensian are presented. Eleven radiocarbon dates were obtained from the Flandrian and these allowed the estimation of pollen deposition rates from pollen concentrations.

The pattern of vegetational changes shows close similarities with those from the lowlands of north‐west England notably the appearance of Pinus sylvestris after Corylus avellana, Ulmus and Quercus in the forest succession. The effects of man on the environment are traced and four main agricultural episodes are distinguished after the ‘elm decline’ at about 5300 B.P.

Comparison of pollen percentage and absolute data highlights the problem of interpreting pollen deposition rates from a basin with uneven sedimentation and the possibility of resuspension of freshly deposited sediments.
RELATIVE HARDINESS TO FREEZING OF LAMINAE, ROOTS AND TILLERS OF TALL FESCUE
Authors: PEARCE R. S.
Published: May 2006

summary

Tall fescue (Festuca arundinacea Schreb. cv. S. 170) plants grown in the field and in controlled environments (mainly differing in temperature; photoperiod 12 or 16 h) were divided into laminae, roots and trimmed tillers and these were exposed to frost in a bath. Laminae and tillers hardened as much in some controlled environments as they did in the field (measured in December); a photon flux density of 110 μ mol m−2 s−1 was adequate for this. Generally, growth at low temperatures increased the hardiness of laminae and tillers; roots from plants grown at 16/14°C or at 6/4°C (day/night) were equally hardy. Laminae were hardier when they were taken from plants grown in nutrient depleted soil. The hardiness of the laminae to extension of the period of exposure (from 45 min to 24 h) was not increased by growth in 6/4°C.

Hardiness of the different parts of tall fescue was compared using the highest temperature at which significant damage occurred. Laminae from the hardiest plants were hardier than the tillers; on other occasions the hardiness of laminae and tillers was close. Roots (from controlled environments) were less hardy than laminae and tillers. The hardinesses of laminae and tillers were not correlated, partly because the tillers de‐hardened during a prolonged period of growth at 6/4°C; this may have been related to reproductive development. With the exception of the last point, the observations suggest that the relative degree of frost hardening of the different parts might often be related to the likely relative intensity of the frost to which they might be exposed.
MICROBIAL EFFECTS ON THE GERMINATION AND SEEDLING GROWTH OF BARLEY
Authors: HARPER S. H. T. , LYNCH J. M.
Published: May 2006

Summary

Barley seed was treated with micro‐organisms, or their metabolites and germinated and grown under conditions that in the absence of treatment were known to be favourable for plant development.

There was a range of inhibitory and stimulatory effects of micro‐organisms on germination and on the weight and lengths of the roots and coleoptile.

There were consistent positive correlations between the lengths of the longest root and of the total root system and between the lengths of the coleoptile and of the total root system.
SODIUM NUTRITION OF PASTURE PLANTS I. TRANSLOCATIGN OF SODIUM AND POTASSIUM IN RELATION TO TRANSPIRATION RATES
Authors: SMITH G. S. , MIDDLETON K. R. , EDMONDS A. S.
Published: May 2006

A study of transpiration rates, and of uptake and translocation of sodium and potassium, has supported a previous classification made for certain pasture and fodder species. The plants termed natrophiles were found to have relatively high transpiration rates and to translocate relatively large amounts of absorbed sodium from root systems into leaves. Plants termed natrophobes had lower transpiration rates and translocated less sodium from roots to leaves. In contrast, potassium was readily translocated by both natrophiles and natrophobes; consequently, compared with natrophobes, natrophiles had low K/Na ratios in their leaves. In general, transpiration rate was less associated with absorption of sodium by roots than with translocation of sodium from roots to aerial parts. The practical and ecological implications of these results are discussed.
EFFECT OF POTASSIUM NUTRITION ON LEAF ANATOMY AND NET PHOTOSYNTHESIS OF PHASEOLVS VULGARIS L.
Authors: O'TOOLE J. C. , TREHARNE K. , TURNIPSEED M. , CROOKSTON K. , OZBUN J.
Published: May 2006

Summary

Low levels of potassium (K+) nutrition resulted in a decrease in dry wt of leaves, stems and roots of two contrasting bean cultivars, Michelite (M‐62) and Redkote (RK). A decrease in eel! size and compaction of cells per unit area, resulting in decreased leaf thickness, and degradation of chloroplasts, and loss of cell wall integrity accompanied the decrease in percent K+ of leaf tissue.

Net photosynthesis rate decreased below a threshold level of about 1% K+ in the leaf tissue with corresponding nutrient solution levels of between 1·2 and 0·3 mequiv. K+1‐1. Below this critical level, both stomatal and mesophyll diffusion resistances to CO2 increased markedly. Varietal differences for these responses suggests differences in efficient utilization of the element rather than differential ability to absorb K+.
TRANSLOCATION AND TRANSFER OF NUTRIENTS IN VESICULAR‐ARBUSCULAR MYCORRHIZAS. III. POLYPHOSPHATE GRANULES AND PHOSPHORUS TRANSLOCATION
Authors: COX G. , MORAN K. J. , SANDERS F. , NOCKOLDS C. , TINKER P. B.
Published: May 2006

Summary

X‐ray microanalysis has confirmed, and measured, the phosphorus content (0·03 g cm‐3) of cytochemically‐demonstrated polyphosphate granules in onion mycorrhizas. The volume occupied by the granules measured from stereoscopic high‐voltage electron micrographs of thick sections was 0·8 % of the fungal volume, and cytoplasmic streaming rates of the extra‐matrical mycelium in soil measured in the light microscope were around 12·6 cm h‐1. From these data a flux rate of about 2·7 × 10‐8 mol P cm‐2 s‐1 has been calculated, which fulfils the hypothesis that phosphorus is translocated in the fungus by means of the transport of polyphosphate granules by cytoplasmic streaming.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS
Authors: MACFARLANE J. D. , KERSHAW K. A.
Published: May 2006

Summary

Data are presented which fully corroborate previous provisional findings that two populations of Peltigera canina differ quite markedly, when air‐dry, in their response to heat stress. In addition, observations upon a number of other species are described, and it was shown that thallus temperatures as low as 25 °C can severely stress Peltigera scabrosa.

The design of the stress treatment paralleled naturally occurring stress periods and temperature levels found under summer field conditions. Stress effects were assessed by monitoring nitrogenase activity, net photosynthetic rates and respiration rates. The mycobiont usually has a much greater tolerance of thermal stress than the algal component, so that net photosynthetic rates of the lichens are seriously impaired whilst concurrent respiration rates can be fully maintained. This probably accounts for the extreme temperatures required by previous workers to induce a stress effect when this was defined solely by a reduction of respiration rates.

The significance of these findings is discussed in relation to the ecology and geographical distribution of lichens.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS X. LIGHT AS AN ECOLOGICAL FACTOR
Authors: KERSHAW K. A. , MACFARLANE J. D.
Published: May 2006

Summary

Little attention has been paid to the potential importance of light in the ecology of lichens. Data is presented which shows that Peltigera canina var. praetextata from a woodland floor can rapidly acclimate to low or high light levels and thus maintain a given level of photosynthesis irrespective of the leaf canopy status. This photosynthetic adjustment takes place naturally in the field during leaf fall in October. P. scabrosa shows a similar response to low light and furthermore, acclimation to low levels of illumination can readily take place in air‐dry material. In contrast populations of Peltigera aphthosa collected from the dense shade of spruce in northern Ontario are extremely sensitive to quite modest levels of ‘high’ light, with pronounced damage occurring under 350 μE m‐3 8‐1 illumination. Contrasting populations of P. aphthosa collected from open habitats are not affected by this level of illumination.

The maintenance of the correct day length during air‐dry storage is also very important since a rapid alteration of daylength produces a marked although temporary photosynthetic decline. On the other hand continuous daylight induces a rapid and continuous decline of photosynthesis probably leading eventually to the death of the phycobiont.
THE LOCATION AND SIZE OF THE EXTENSION ZONE OF EMERGING WHEAT LEAVES
Authors: KEMP D. R.
Published: May 2006

Summary

The length of the extension zone (LEZ) of emerging wheat leaves varied with the stage of leaf development and between leaves with the length of the encircling sheath (LES). The ratio LEZ/LES varied from 0·60 when the leaf tip emerged from the encircling sheath to 0·35 when the ligule emerged. The relationship between LEZ/LES and an index of leaf development (DI), defined as the sheath length of the growing leaf relative to LES, was: LEZ/LES= 0·632 exp (‐0.622.DI); (r= 0.91). 14C incorporation studies supported the measurement of extension zone location and length.

There appeared to be a small zone of non‐expanding tissue, within the extension zone, around the ligule, but it was not a major discontinuity within the whole extension zone. The relative extension rate of the extension zone declined by only 50 % from leaf tip to ligule emergence whereas the relative extension rate of the whole leaf declined by 90 % over the same interval.

There was little variation in protein and carbohydrate concentrations around the upper limit of the extension zone in emerging leaves. For studies of leaf growth in wheat where it is not possible to measure LEZ, harvesting the lower 50 % of the enclosed part of an emerging leaf would adequately sample the extension zone.
THE EFFECT OF INORGANIC NITROGEN ON THE MAJOR ENZYMES OF AMMONIUM ASSIMILATION IN GRASSLAND PLANTS
Authors: TAYLOR A. A. , HAVILL D. C.
Published: May 2006

Naturally occurring grassland plants possess the enzymic potential for assimilation of ammonium via the glutamate dehydrogenase and glutamine synthetase/glutamate synthase pathways. In the majority of species, high exogenous ammonium concentrations enhanced the levels of root and shoot GDH and reduced the levels of root glutamine synthetase. However, the enzyme response to increasing nitrate or ammonium availability was relatively small and suggested that these species are not adapted for major changes in the form or availability of nitrogen.
A FIELD SURVEY OF MYCORRHIZAL ASSOCIATIONS IN FERNS OF PAKISTAN
Authors: IQBAL S. H. , YOUSAF M. , YOUNUS M.
Published: May 2006

Roots of the ferns examined in this investigation were constantly mycorrhizal. A mixture of several endophytes infecting a root system was a usual feature of them. Vesicular‐arbuscular endophytes predominated over endophytes with a septate mycelium. Ectomycorrhizal fungi with a septate mycelium bearing clamp‐connections ran longitudinally inside the cortex and occasionally these hyphae formed a mantle on the outside of the roots. A displacement of endotrophic mycorrhizas by ectomycorrhizal fungi occurred in Adiantum vemistum D. Don when growing under pine forest. Heavy arbuscular and vesicular infections occurred throughout the period of investigation. Several spore types were present in each rhizosphere.
INFLUENCE OF PHOSPHATE SOURCE ON VESICULAR‐ARBUSCULAR MYCORRHIZAE OF BOUTELOUA GRACILIS
Authors: ALLEN MICHAEL F. , SEXTON JAMES C. , Jr MOORE THOMAS S. , CHRISTENSEN MARTHA
Published: May 2006

Non‐mycorrhizal and vesicular‐arbuscular mycorrhizal Bouteloua gracilis infected with Glomus fasciculatus were grown in defined media containing different phosphate sources and compared with respect to phosphate content and form, biomass, chlorophyll concentration, and root phosphatase activity. The phosphate sources were sodium monobasic phosphate, a mixture of sodium monobasic phosphate and calcium phytate, and calcium phytate. Inositol and inositol plus calcium were added to the sodium phosphate medium as additional treatments. Mycorrhizal infection was highest in roots of plants grown in the presence of phytate (75%). Lower root infection levels were noted in plants from the sodium phosphate (19%) and mixed phosphate (22%) media. No penetration by fungi occurred in plants from the sodium phosphate plus inositol or inositol and calcium media. Dry wts of non‐mycorrhizal plants were highest when grown in media containing phytate and sodium phosphate plus inositol and calcium followed in decreasing order by sodium phosphate plus inositol, mixed phosphates, and sodium phosphate. Mycorrhizal infection increased leaf dry wt in plants from the sodium phosphate medium and root dry wt from the phytate medium. Phosphate concentrations in the plants were highest when grown in mixed phosphate medium followed by sodium phosphate and phytate. Mycorrhizal infection always increased significantly leaf phosphate concentrations but increased root phosphate concentrations only in the phytate medium. Phosphates were found predominantly as organically‐bound compounds in leaves of mycorrhizal plants whereas in leaves of non‐mycorrhizal plants, most of the phosphate was inorganic. Chlorophyll concentrations increased significantly with mycorrhizal infection with no change in a/b ratios. Mycorrhizal plants grown in the phytate medium had substantially higher alkaline phosphatase activity than did non‐mycorrhizal plants; acid phosphatase activity was not affected by mycorrhizal condition.

These results suggest that form of the phosphate in the root environment influences mycorrhizal establishment and effect of mycorrhizae on plant growth.
THE UPTAKE OF 2‐OXOGLUTARATE AND PYRUVATE BY ISOLATED PEA CHLOROPLASTS
Authors: PROUDLOVE M. O. , THURMAN D. A.
Published: May 2006

The uptake of 2‐oxoglutarate and pyruvate by intact, isolated pea chloroplasts has been studied by centrifugal filtration. Inhibition of 2‐oxoglutarate transport by malate, fumarate, oxaloacetate and glutamate suggested that a dicarboxylate carrier is operating. This carrier is substrate saturated at approximately 1 mM and shows a Vmax of 32 μmol (mg chlorophyll)‐1 h‐1 and has a Km of 0·19 mM. Pyruvate enters pea chloroplasts mainly by diffusion, but at low external concentrations of the keto‐acid uptake may be carrier mediated with a Vmax of 6·5 μmol (mg chlorophyll)‐1 h‐1 and a Km of 0·33 mM. A number of compounds related to pyruvate, and also α‐cyano‐4‐hydroxycinnamic acid, failed to inhibit pyruvate movement.
NITRATE AVAILABILITY UNDER LOW IRRADIANCE AND ITS EFFECT ON NITRATE REDUCTASE ACTIVITY
Authors: UDAYAKUMAR M. , DEVENDRA R. , REDDY V. SREENIVASA , SASTRY K. S. KRISHNA
Published: May 2006

Leaf nitrate reductase (EC 1.6.6.1, NADH: nitrate oxidoreductase) (NR) activity decreased on exposure to low irradiance and the decrease was dependent upon duration of exposure. The observed decrease was associated with a decrease in the rate of xylem exudation and nitrate concentration resulting in lesser supply of nitrate to the tops. Continuous nitrate supply to excised leaves in shade or even in the dark resulted in a high NR activity, suggesting that lack of reducing power was not the main cause for lower NR activity. Further, when excised leaves were deprived of nitrate, even in light, NR activity decreased with time. In leaves with their petioles dipped in water, the NR activity decreased and on retransfer to KNO3 within 105 min the activity increased, suggesting that continuous nitrate supply was essential for maintaining high NR activity.
MYCORRHIZAL INFECTION AND GROWTH OF TRIFOLIUM SUBTERRANEUM: USE OF STERILIZED SOIL AS A CONTROL TREATMENT
Authors: SMITH F. A. , SMITH S. E.
Published: May 2006

Effects of mycorrhizal infection on the growth of Trifolium subterraneum have been studied by comparing plants grown in sterilized soil/sand mixtures with plants grown in untreated soil/sand mixtures. The original soil contained a high level of endomycorrhizal inoculum. The aim was to consider whether this approach is valid, bearing in mind the possible effects of sterilization (γ‐irradiation or autoclaving) on soil properties. Plants in the untreated soil/sand mixtures became significantly larger than plants in the sterilized soil/sand mixtures about 4 weeks after planting. This response was associated with rapid infection by vesicular‐arbuscular mycorrhizal fungi; it still occurred when nitrate replaced N2 as the nitrogen source for the plants. Addition of soluble phosphate enhanced the growth of the non‐mycorrhizal plants to a level similar to that of the mycorrhizal plants. Mixing sterilized and untreated soil did not depress mycorrhizal infection or growth. These results indicate that the growth difference was a classic mycorrhizal response, and did not reflect toxic effects of soil sterilization. The growth of Brassica oleracea (broccoli), which does not form mycorrhizas, was better on sterilized soil.
TECHNIQUES FOR STUDYING THE INFECTION OF PLANTS BY VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI UNDER AXENIC CONDITIONS
Authors: HEPPER CHRISTINE M.
Published: May 2006

Methods of growing axenic seedlings infected by vesicular arbuscular mycorrhizal fungi are described, using agar, paper or glass as a support. Two of the techniques are particularly suitable for studying the interaction between the fungus and the host plant, for example the germination of the spore inoculum, hyphal growth around the roots before the symbiosis has been initiated and the early stages of root penetration.
THE RELATIONSHIP BETWEEN PHOSPHATE ABSORPTION AND OXYGEN UPTAKE IN EXCISED BEECH MYCORRHIZAS
Authors: HARLEY J. L. , McCREADY C. C.
Published: May 2006

When mycorrhizal rootlets of beech are aged for several days in water, their respiration rate falls. If phosphate is applied, the respiratory rate rises and the rise in oxygen consumption is proportional to phosphate uptake in replicate samples aged for equivalent times. The ratio of μg‐atom phosphorus to μg‐atom oxygen absorbed is usually around or just below unity, but it varies with the state of the tissues to values as low as 0·28. High values of this ratio in the later state of ageing may be spurious because, in senescent mycorrhizas, phosphate penetrates non‐metabolically. High values in fresh mycorrhizas occur because the rate of phosphate‐induced oxygen uptake is low but it rises faster than that of phosphate uptake in the early stages of ageing. The conclusion is drawn that the processes of phosphate absorption and polyphosphate formation are often 20 to 30% efficient with respect to respiratory oxidative phosphorylation. The linear relationship of total oxygen consumption to phosphate absorption observed in fresh mycorrhizas is due to the pre‐emption of a portion of total phosphorylation by polyphosphate production.
PRELIMINARY INVESTIGATIONS INTO THE STRUCTURE OF THE ROOTS OF THE MANGROVES, AVICENNIA MARINA AND BRUGUIERA GYMNORRHIZA, IN RELATION TO ION UPTAKE
Authors: LAWTON JUNE R. , TODD ANN , NAIDOO D. K.
Published: May 2006

The structure of the roots of Avicennia marina (Forsk.) Vierh., a salt excretor, and Bruguiera gymnorrhiza (L.) Lam., an excluder (non‐excretor), differed in the length and thickness of the root cap, phenolic content, the development of the Casparian strip in the endodermis and in the differentation of the vascular tissues.

The uptake and distribution of lanthanum, used as a marker for ion movement differed in the two species. Though both had similar root concentrations, the amount of lanthanum in the leaves of Avicennia marina was significantly higher than that in stem and root, whereas in Bruguiera gymnorrhiza it was significantly lower. The barrier to lanthanum transport, probably located in the hypocotyl, is discussed in relation to the anatomy of the root and the uptake of salt under natural conditions.
ABAXIAL AND ADAXIAL STOMATAL BEHAVIOUR AND RESPONSES TO FUSICOCCIN ON ISOLATED EPIDERMIS OFCOMMELINA COMMUNISL.
Authors: PEMADASA M.A.
Published: May 2006

Summary

A comparative study was made of the behaviour of abaxial and adaxial stomata on isolated epidermis ofCommelina communisincubated under controlled conditions. The degree of opening and of K+accumulation, and the responsiveness to light, carbon dioxide, abscisic acid and KC1 concentration were substantially higher in abaxial than in adaxial stomata; thus their differential behaviour is mainly a result of inherent, rather than of environmental, differences between the two epidermes. The isolation of guard cells, by killing other epidermal cells, failed to annul the disparity, suggesting that any difference in subsidary cell resistance between the two epidermes is not responsible for this phenomenon. Fusicoccin was able to overcome the smaller opening of adaxial stomata, indicating that there is no fundamental difference in the potential opening ability between abaxial and adaxial stomata. Even in a medium free of KC1, fusicoccin stimulated exceptionally high K+accumulation in adaxial guard cells, demonstrating that endogenous K+available in the adaxial epidermis is sufficient for wide opening. Accordingly, an inherent metabolic condition of adaxial stomatal cells appears to prevent them opening as wide as abaxial stomata. The effectiveness of fusicoccin to produce exceptionally wide adaxial apertures suggests that, when necessary, the proton pump can operate as efficiently in adaxial as in abaxial guard cells.
COMPARATIVE INOCULUM POTENTIAL OF SPORES OF SIX VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI
Authors: DANIELS B. A. , McCOOL P. M. , MENGE J. A.
Published: May 2006

Summary

Using the most probable number method, differences in inoculum potential between six vesicular‐arbuscular (VA) mycorrhizal fungal isolates were demonstrated. Inoculum of Glomus mosseae had the highest inoculum potential while G. constrictus, and G. fasciculatus isolate 92, and isolate 0–1 were approximately 1/5, 1/6 and 1/12 as effective. G. fasciculatus isolate 185 and G. epigaeus were approximately 1 /50 as effective. These differences were not correlated with differences in spore viability or germinability since approximately 75 % germination occurred in all species after 3 weeks. While G. mosseae has the largest spore size and had the highest inoculum potential, no further correlation between spore size and inoculum potential was observed. The rate of increase of infection by these six VA mycorrhizal fungi differed more when equal spore numbers were used as inoculum than when equalized inoculum potentials were used. The percentage root infection, subjected to the multiple infection correction, was regressed against log of inoculum density and yielded slopes of 063 to 070 for all VA mycorrhizal fungi tested. The inoculum density‐infection relationships of mycorrhizal fungi are discussed with respect to Baker's epidemiological models.
EFFECT OF PHYSICAL FACTORS ON GAMETANGIAL INDUCTION, FERTILIZATION AND SPOROPHYTE DEVELOPMENT IN THE MOSS BRYUM ARGENTEUM GROWN IN VITRO
Authors: CHOPRA R. N. , BHATLA S. C.
Published: May 2006

Summary

Cultures of Bryutn argenteum, a dioecious moss, were raised aseptically from single spores. Normal gametophytes were formed at 25 ± 2 °C in 3500 to 4000 lx of continuous illumination. Gametangial formation in both male and female clones is affected by temperature, light intensity and photoperiod. Both sexes exhibit maximum gametangial formation at 25 ± 2 °C. Lowering of temperature to 10 ± 2 °C lowers the response. Light intensity within the range 1800 to 2000 lx is optimum for gametangial induction. Higher light intensities favour vegetative growth. Bryum behaves as a quantitative day‐neutral plant, since it becomes fertile even in an 8 h photoperiod. Gametangial induction increases with increasing day‐length, and the best response is observed with continuous illumination.

Flooding of mixed cultures is necessary for fertilization. Although sporophytes appear in cultures maintained both at 18 ± 2 °C and at 25 ± 2 °C, the higher temperature is more favourable for the proper development of capsules.
DIATOM ANALYSES OF SEDIMENTS FROM LOUGH INE, CO. CORK, SOUTHWEST IRELAND
Authors: BUZER JENNY S.
Published: May 2006

Summary

Diatom analyses of a sediment core from the marine Lough Ine are described. Diatom diagrams have been divided into four assemblage zones, LID 1 to 4, and these are used to interpret the post‐glacial history of the lough.

The oldest diatom‐containing sediments recovered are attributable to Mitchell's pollen zone V, the Boreal Period. The lough was fresh water and very productive at this time, having a predominantly alkaliphilic, planktonic diatom flora, dominated by Cyclotella spp. During zones LID 1 and 2, Fragilaria spp. became dominant and productivity decreased. A slight tendency to more neutral or acid conditions is noted. Epiphytic diatoms increased in frequency. Zone LID 3 covers the marine transgression into Lough Ine, tentatively dated at c. 4000 B.P. The transgression appears to have been a gradual process. This is illustrated by successive peaks of diatoms indifferent to salt, halophilous, mesohalobous, estuarine and truly marine. Total numbers of diatoms in the sediments dropped dramatically during the marine transgression. This was partly a result of the change in sediment type. The marine transgression was completed in zone LID 4, where Paralia sulcata and other benthic marine species dominate the sediments.