bluuebunny/crossref_metadata_2025 huggingface dataset:
NITROGEN FIXATION BY MEMBERS OF THE STICTACEAE (LICHENES) OF NEW ZEALAND
Authors: GREEN T. G. A. , HORSTMANN J. , BONNETT H. , WILKINS A. , SILVESTER W. B.
Published: May 2006

Forty‐four species of New Zealand lichens, including 22 species of Pseudocyphellaria and seven of Sticta, were assayed for nitrogenase activity by acetylene reduction. Nitiogen fixation was confirmed by 15N enrichment studies. Ten species, all with green algal phycobionts, showed no detectable nitrogenase activity; the remainder, including all species of Pseudocyphellaria and Sticta, assayed positively. Fixation rates were found to be species specific ranging from 0·2 to 52 nmol g‐1 min‐1. Nitrogen fixing lichens showed a species specific range of total nitrogen content and all had greater values than non‐fixing species. Further analysis of nitrogen fixation in Sticta and Pseudocyphellaria species by plotting a graph of acetylene reduction against nitrogen content showed a highly significant positive relationship; also species of like chemical strain grouped together, and in any one chemical strain lichens with solely blue‐green phycobionts possessed higher rates. The possibility exists that these lichens could provide a significant input of nitrogen into some native forests in New Zealand.
THE EFFECT OF ORTHOPHOSPHATE CONCENTRATION AND EXOGENOUSLY SUPPLIED SUGARS ON THE DISTRIBUTION OF NEWLY FIXED CARBON IN SUGAR BEET LEAF DISCS
Authors: HEROLD A. , McGEE E. E. M. , LEWIS D. H.
Published: May 2006

The apportioning of newly fixed carbon in leaf discs of sugar beet (Beta vulgaris L.) is dependent on the incubation medium. Concentration of orthophosphate (Pi) influences the distribution of carbon between chloroplast starch and the cytoplasm, and the proportion of 14C incorporated into sucrose. In the presence of exogenous sucrose and glucose, starch synthesis is enhanced and gross changes in cytoplasmic metabolite pools occur. These observations are discussed in relation to sink/source interactions of whole plants. In the presence of mannose, which sequesters cytoplasmic Pi in leaves of sugar beet as mannose‐6‐phosphate, sucrose synthesis is severely inhibited and maltose accounts for up to 30 % of the fixed carbon. This is related to earlier reports of unusual accumulation of maltose.
GROWTH OF PARASPONIA IN AGAR TUBE CULTURE AND SYMBIOTIC EFFECTIVENESS OF ISOLATES FROM PARASPONIA SPP.
Authors: TRINICK M.J.
Published: May 2006

The symbiosis between Rhizobium and Parasponia andersonii was examined under a range of nutrient regimes in agar tube culture. Nodule initiation and nitrogen fixation were stimulated with ‘starter’ nitrogen. Nitrogenase activity of plants in tubes was similar to plants in Leonard jars or pots and resembled, when expressed on a nodule weight basis, the activity of other non–legumes rather than legumes.

Fifteen isolates of Rhizobium from Parasponia were compared for effectiveness in nitrogen fixation in controlled environment cabinets. All rhizobia produced nodules and only one failed to fix nitrogen. The others varied in their degree of effectiveness, the least effective yielded only 70 % of the plant top weight of the best symbiotic combination. A few ineffectively nodulated plants occurred in all rhizobial treatments. Their presence was considered to be a result of host variability rather than environmental factors.
GERMINATION OF THE LIGHT‐SENSITIVE SEEDS OF CUCUMIS ANGUR1A AND RUMEX OBTUSIFOLIUS: EFFECTS OF TEMPERATURE
Authors: Felippe G. M.
Published: May 2006

Summary

The effect of temperature and exposure to far red light were compared using positively photoblastic seeds of Cucumis and negatively photoblastic seeds of Rumex. Short exposure of Cucumis seeds to 45°C was without effect but exposure at 0°C for 1 to 3 h promoted subsequent germination in white light at a constant temperature of 25°C. In contrast, white light alternating temperatures 25/10 and 25/5°C fully counteracted the inhibitory effect of light on germination of Cucumis seeds.

The temperature pairs 15/35, 20/35, and 25/35°C were tested with both Rumex (in darkness) and Cucumis (in light). Seeds of both species had their germination strongly promoted by the 15/35°C pair. The pair 25/35°C had a promotive effect in Rumex and no effect in Cucumis, while the pair 20/35°C was very effective for Rumex but much less so for Cucumis.

In experiments in which the alternating pair 25/5°C was combined with far red (followed by darkness and white light), Rumex and Cucumis seeds behaved similarly. With both, when far red was given during the 5°C period followed by light or darkness at 25°C germination was promoted (but the inhibitory effect was completely reversed only where far red was followed by white light). When far red was given at 25°C followed by white light or darkness during the 5°C period germination was not promoted. Thus, both positively and negatively photoblastic seeds show the same behaviour in relation to light and temperature when exposed to far red.
THE GERMINATION OF FOUR ANNUAL STRAND‐LINE SPECIES
Authors: IGNACIUK R. , LEE J. A.
Published: May 2006

Summary

The germination of four strand‐line annuals, Atriplex glabriuscula, Atriplex lacimata, Cakile maritima and Salsola kali, was studied in the field and laboratory. Germination in the field began approximately 1 month after the spring equinox. Thus, seedling establishment was not directly affected by high spring tides. The relative importance of the various biological and environmental factors influencing the timing of germination of these species is discussed.

The effects on germination of salinity and temperature and various interactions between these two factors were characterized. From experiments designed to determine the nature of the inhibition of germination by saline solutions, it was concluded that, in the Atriplex spp., the inhibition was purely osmotic but, in C. maritima and S. kali, ionic toxicity is important. The potential for dispersal of strand‐line species by sea‐currents depends upon the buoyancy of the fruit and the ability of the seed to survive prolonged immersion in seawater. Laboratory experiments showed that the four species differed considerably in these characteristics.
SOME CHARACTERISTICS OF PHOSPHOENOLPYRUVATE CARBOXYLASE ACTIVITY FROM LEAF EPIDERMAL TISSUE IN RELATION TO STOMATAL FUNCTIONING
Authors: WILLMER C. M.
Published: May 2006

Summary

PEP carboxylase from Commelina communis leaf epidermis was characterized. Activity was optimal at concentrations of 2 to 3 mM bicarbonate and 5 mM PEP at pH 8·3. The temperature optimum was between 35 and 40°C and the activation energy was 9·1 kcal mol‐1. At saturating substrate concentrations and at pH 8·3, malate inhibited PEP carboxylase activity; slight inhibition occurred at 2·0 mM (the lowest concentration tested) while 13·5 mM caused 50% inhibition. At saturating substrate concentrations KC1 and mannitol, both up to concentrations of 250 mM, had no significant inhibitory effect upon PEP carboxylase activity although, thereafter, marked inhibition occurred in the KC1 medium (concentrations of mannitol higher than 250 mM were not tested). 10 ‐4 M ABA had no effect on PEP carboxylase activity from Tulipa gesneriana leaf epidermis.

The effects of a number of factors were tested both on PEP carboxylase activity and also on stomatal opening in epidermal strips of C. communis. After 1 h, maximum apertures and maximum opening rates occurred at 35°C. The activation energy for stomatal opening was 9·3 kcal mol ‐1. The effects of malate on stomatal opening in C. communis epidermis were complex: At pH 4·1 to 4·3, 10 mM monosodium malate saturated the opening response; widest openings also occurred at pH 4·0 with no opening at pH 2·7 and some opening at pH 5·0, 6·0 and 7·0.

PEP carboxylase from C. communis epidermal tissue behaved, in most respects, very similarly to PEP carboxylase from C4 leaves. Correlations between the effects of the factors on PEP carboxylase activity and stomatal opening were difficult to make. However, temperature effects were remarkably similar. The effects of osmotica on PEP carboxylase activity suggested that inhibition due to high K+, Cl‐ or other osmoticum in the guard cell cytoplasm would be negligible. It was also concluded that ABA does not control stomatal movements via its effect on PEP carboxylase.
SODIUM NUTRITION OF PASTURE PLANTS II. EFFECT OF SODIUM CHLORIDE ON GROWTH, CHEMICAL COMPOSITION AND THE REDUCTION OF NITRATE NITROGEN
Authors: SMITH G. S. , MIDDLETON K. R. , EDMONDS A. S.
Published: May 2006

The effect of increasing concentrations of sodium chloride in the root zone on growth, chemical composition and nitrate reductase activity of perennial ryegrass and timothy was investigated in a glasshouse pot experiment. For ryegrass, a natrophile, sodium chloride had little effect on growth, whereas for timothy, a natrophobe, growth was severely depressed by comparatively low concentrations of salt. The result also indicate that translocation of sodium into the leaves of timothy took place readily only after the accumulation sites in the roots and lower stems had been saturated with this element. This means that relatively large quantities of sodium chloride were needed to produce concentrations of sodium in the leaves of timothy as high as those normally found in the leaves of ryegrass. Sodium chloride increased the uptake of total and nitrate‐nitrogen but, in contrast, depressed the uptake of potassium by ryegrass and timothy It was therefore concluded that the marked stimulation by sodium chloride of nitrate reductase activity in both species was more the result of the increased uptake of nitrates than a specific effect of this salt on the enzyme. The practical implications of these results are discussed.
MULTIPLE METAL TOLERANCES IN THE GRASS DESCHAMPSIA CESPITOSA (L.) BEAUV. FROM THE SUDBURY SMELTING AREA
Authors: COX R. M. , HUTCHINSON T. C.
Published: May 2006

Summary

An investigation was conducted into the multi‐element tolerance of the grass Deschampsia cespitosa growing around a nickel/copper smelting complex at Coniston, near Sudbury, Ontario. Tolerances for nickel, copper, aluminium, zinc, lead and cadmium in this population were compared with those of control populations growing on uncontaminated pastures. Distinctive population differences were found in distributions of copper and nickel tolerances, indicating that elevated tolerance to these elements had evolved in the Coniston population. More subtle differences between the populations in aluminium, zinc and lead tolerance were also noted, with increased tolerances showing in the smelter area population, despite a lack of elevation in zinc and lead levels in the soils. Various individuals in the Coniston population demonstrated a positive response to nickel and copper at levels as high as 0.3 μg cm‐3 in water culture. This ‘need’ for the metals was reflected in the seed population from Coniston which germinated and survived better in the copper/nickel‐contaminated soils than in the control soil. In contrast, germination of the control seed population was uniformly good, but seedling survival was poor on the metal contaminated soils compared with that of the Coniston seedlings. The relevance of these findings to evolution of multi‐metal tolerances and the possible uses of the species for reclamation are discussed. The occurrence of coincidental metal tolerances is considered.
RECIPROCAL TRANSFER OF NUTRIENTS BETWEEN ERICACEOUS PLANTS AND A CLAVARIA SP.*
Authors: Englander L. , Hull R. J.
Published: May 2006

Summary

A close physiological relationship between some ericaceous plants, Rhododendron sp. and Pieris japonica, and a member of the genus Clavaria is indicated by radioisotope translocation studies. [14C] photosynthate from host leaves was detected in Clavaria fruiting bodies and 25P applied to Clavaria fruiting bodies was detected in plant roots. Possible transfer mechanisms, including that of a mycorrhizal association, are discussed.
PHYSIOLOGICAL‐ENVIRONMENTAL INTERACTIONS IN LICHENS XI. SNOWCOVER AND NITROGENASE ACTIVITY
Authors: MacFARLANE J. D. , KERSHAW K. A.
Published: May 2006

Summary

The influence of a long term snowcover on the rates of nitrogenase activity in the lichens Peltigera canina var. praetextata and P. canina var. rufescens has been investigated. In accordance with the existing literature, only very low rates of nitrogenase activity could be detected after several months of snowcover. These low rates of activity result from prolonged darkness rather than an inactivation of the nitrogenase enzyme by low temperature. The subsequent recovery of nitrogenase activity after snowmelt is very largely controlled by the presence of radiant energy with temperature playing a subordinate role.
NITROGENASE ACTIVITY ASSOCIATED WITH THE RHIZOSPHERE OF AMMOPHILA ARENARIA L. AND EFFECT OF INOCULATION OF SEEDLINGS WITH AZOTOBACTER
Authors: WAHAB A. M. ABDEL , WAREING P. F.
Published: May 2006

Summary

A marked gain in nitrogen was obtained when plants of Ammophila arenaria L. were grown in pots in dune sand and supplied with nitrogen‐free nutrient solution. Nitrogenase activity was associated with the roots but the estimated rates of nitrogen‐fixation based upon the acetylene reduction technique were less than one‐tenth of those obtained by the Kjeldahl method. Significant rates of acetylene reduction were also demonstrated both for detached roots taken from plants growing naturally in sand dunes and from measurements made in situ in the field, but the estimated rates of nitrogen fixation were much lower than calculated rates of nitrogen gain by actively‐growing plants. Some possible reasons for this discrepancy are discussed. Acetylene reduction was greatly stimulated by the addition of glucose, suggesting that nitrogen fixation by micro‐organisms in the rhizosphere is limited by the supply of root exudates. Seedlings of Ammophila grown under aseptic conditions and inoculated with Azotobacter showed greatly increased growth compared with that of uninoculated seedlings.
POLLEN ALLELOPATHY—A NEW PHENOMENON
Authors: KANCHAN SUKHADA , CHANDRA JAYA
Published: May 2006

SUMMARY

White dust spread on the leaves and stigmatic surface of Crotalaria pellida L. and Desmodium heteracarpon (L.) DC var. strigosum Meeuwen growing in the midst of a Parthenium hysterophorus L. stand was found to be clusters of Parthenium pollen. The fruit set in those species was poor. It was found that Parthenium pollen grains contained growth inhibitors which inhibited fruit set in many test species when artificially dusted on the stigmatic surface. In culture conditions the germination and pollen tube growth of the test species were inhibited in the presence of Parthenium pollen or their extract. The plant produces on an average 3375 million pollen grains per square metre areas of the stand. The pollen grains disperse in dusters of 600 to 800 each and are carried great distances by wind. Pollen grains deposited on leaves in large quantity also reduce the chlorophyll content in these species.
THE ROLE OF ELECTRICITY IN PLANT MOVEMENTS
Authors: SIMONS P.J.
Published: May 2006

A survey has been made of the different types of reversible movements in the plant kingdom (including those of carnivorous traps, leaves, floral parts, root tips, cytoplasmic streaming, cilia and flagella) and it is suggested that many are mediated by changes in electrical potential. Many touch‐sensitive movements in higher plants are regulated by propagating electrical signals (action potentials), which relay excitation from the site of stimulation to the motor organ(s), where collapse of sensitive motor cells is brought about. The resulting change in volume of the motor cells causes movement of the entire motor organ. In some cases additional localized changes in electrical potential (receptor potentials) can be induced by external stimuli, which convert specific characteristics of the stimulus into an electrical analogue before triggering an action potential.

The role of electrical activity in other plant movements is more speculative. Action potentials do not arise in light‐ or endogenous rhythm‐regulated movements, but changes in the membrane potential of motor cells concerned with these movements may also help to drive the ionic transport which leads to their turgor‐mediated motion. The significance of electrical activity associated with intracellular movements is less certain, but may become the focus of increasing attention as the regulation of actin‐directed cellular movements is further investigated. Electrical impulses comparable to those in higher plants may, however, regulate ciliar and flagellar activity in the motile gametes and spores of lower plants. Thus, it is clear that electrophysiology is an important aspect of many plant movements, and bears a remarkable similarity to excitation in animal nervous systems.
ISOLATION OF POLYSOMES AND POLY(A)‐CONTAINING RNA FROM CHLORELLA FUSCA VAR. VACUOLATA
Authors: LEONARD J. C. , DUNHAM S.M. , THURSTON C. F.
Published: May 2006

Ribonuclease activity in 120000 g supernatant extracts of Chlorella fusca var. vacuolata showed maximal activity at pH 5 and minimal activity at about pH 7·5 in the range 5 to 8·6. Dithiothreitol, high salt concentration and 100 mM tris significantly inhibited ribonuclease activity although the extent of inhibition was not uniform at all pH values. Heparin, poly‐vinylsulphate and sodium dodecylsulphate were largely ineffective as ribonuclease inhibitors under the same conditions.

Polysomes were isolated using the method of Jackson and Larkins (1976) without the addition of heparin but including 10 mM dithiothreitol. Sucrose density gradient centrifugation analysis revealed profiles of polysomes consisting mainly of SOS ribosomes and containing a high proportion of large polysomes when cells were treated with 2·5μgml‐l cycloheximide before harvesting. The yield of polysomal material was about 50 A250 units per 1010C. fusca cells. Total RNA extracted from C. fusca was analyzed by acrylamide gel electrophoresis in 98 % formalide. Cells broken by liquid nitrogen grinding gave RNA preparations which were much less degraded than when the French pressure cell was used for cell disruption. Of three methods tested for isolation and deproteinization of RNA, phenol‐cresol deproteinization of extracts in trisbuffered triisopropylnaphthalene sulphonate/p‐amino salicylate gave the highest yield of RNA and was consistent with the conditions established for minimizing ribonuclease activity. Re‐extraction of the phenol phase was necessary to obtain a high yield particularly of poly(A)‐containing RNA. C. fusca cells growing exponentially in the light gave a greater proportion of poly(A)‐containing RNA than light‐limited cells.

Poly(A)‐containing RNA was separated from total RNA and from polysomes on a column of oligo(dT)‐cellulose. This fraction, isolated from total RNA consisted mostly of molecules between 2 × 106 and 0·5 × 106 daltons, but a significant proportion of smaller molecules was present when polysomes were first isolated as the starting material. Poly(A)‐tracts obtained by oligo(dT)‐cellulose chromatography of 14C‐labelled poly(A)‐containing RNA were up to about 450 nucleotides in length with tracts 300 nucleotides long apparently most abundant. When the data were corrected for the increase in radioactivity with tract length and the logarithmic distribution of tract sizes on polyacrylamide gels, smaller tracts were shown to be predominant.
QUANTIFYING VESICULAR‐ARBUSCULAR MYCORRHIZAE: A PROPOSED METHOD TOWARDS STANDARDIZATION *
Authors: BIERMANN BRENDA , LINDERMAN R. G.
Published: May 2006

A standard method for the quantification of root colonization by vesicular‐arbuscular (VA) mycorrhizal fungi is needed. From the examination of roots from three different host species, the estimation of the percentage of the length of root segments containing V A mycorrhizal fungal structures was found to be more accurate than the determination of the percentage of root segments with VA mycorrhizal fungal structures. It was no more time consuming, and was not influenced by segment size. Examination of a minimum of seven samples, each with 25 randomly selected 0‐5 to 10 cm root segments, was needed for confidence limits to be within 10% of the mean It is proposed that, for the sake of comparability between studies, this procedure be adopted as a standard method.
VARIATION IN THE INFECTION OF SILENE DIOICA (L.) CLAIRV. BY USTILAGO VIOLACEA (PERS.) FUCKEL IN NORTH WEST ENGLAND
Authors: LEE J. A.
Published: May 2006

The infection of populations of Silene dioica by Ustilago violacea was studied in four areas of north‐west England. Infection showed wide variation in each area but was not readily related to shade stress from trees or shrubs, nor was percentage infection simply related to shoot density. Infected male shoots predominated early in the season, but later, infection was greater in females. Overall, female plants had a higher percentage of infection than males and, in some populations, over a third of the reproductive capacity was lost. Infection reduced the growth of male plants but produced a large increase in the number of flowers on female plants. The results are discussed in relation to the spread of the disease and to the effects of the fungus on the population dynamics of S. dioica.
SUPPRESSION OF AXILLARY BUDS OF ITS HOST BY PARASITIZING CUSCUTA I. COMPETITION AMONG SINKS AND INDIRECT INHIBITION
Authors: TSIVION Y.
Published: May 2006

The drastic inhibition of elongation imposed by parasitizing Cuscuta on the lateral shoots of a decapitated pea plant was studied in order to gain further understanding of the relationship between this parasite and its host. Reduction in host‐bud length was caused by the parasite as well as by a growing, partially shaded, lateral shoot of the host. The results were interpreted as competition between sinks on a common pool of photosynthates produced by the host. In such competition, the less efficient sink is weakened.

An influence of the parasite which is not directly related to competition for nutrients is effected through the xylem of the host. This was demonstrated by inhibition of lateral buds by a parasite attached below a girdle that separated the buds from the parasite.
THE PHYTOSOCIOLOGY AND ECOLOGY OF SCRAGH BOG, CO. WESTMEATH
Authors: O'CONNELL MICHAEL
Published: May 2006

Scragh Bog, a mire of some 23 ha, harbours plant communities representative of the more important stages in hydroseral succession. These communities are described, classified and mapped according to Zürich‐Montpellier methodology. Fen communities constitute the major part of the vegetation cover and that dominated by Schoenus nigricans forms the basis of a new subassociation within the Cirsio‐Schoenetum nigricantis Br.‐Bl. et Tx. 1952. Other new syntaxa proposed are the Erico‐Sphagnetum plumulosi, the Carici limosae‐Sphagnetum contort and the Salici‐Betuletum pubescentis pyroletosum. Environmental conditions, as assessed by water table, pH and Kcorr measurements and mineral analyses of surface waters, are considered in relation to the vegetation cover. Mineral analyses were performed on Sphagnum plumulosum and other bryophyte species which are important as initiators of the climax raised bog community. Growth measurements were also performed on 5. plumulosum. The significance of the vegetation cover as well as the factors influencing the future rate of succession are discussed.
THE PAST AND PRESENT VEGETATION OF THE CAENLOCHAN NATIONAL NATURE RESERVE, SCOTLAND II. PALAEOECOLOGICAL INVESTIGATIONS
Authors: HUNTLEY BRIAN
Published: May 2006

The existence within the Scottish Highlands of small areas of extreme floristic richness, especially with respect to taxa of northern and montane distribution patterns, is discussed. Possible hypotheses to account for the existence of such areas are considered and the importance of site history is stressed.

palaeoecological studies made at two sites within the Caenlochan N.N.R. are described. On the basis of these studies the past flora, vegetation and probable land‐use are reconstructed for the Flandrian (post‐glacial) period. Six chronological units are recognized within this period.

The inferred floristic and vegetational history is compared with that for other sites. The conclusion is reached that the present rich flora and diverse vegetation of the Caenlochan N.N.R. represents the joint survival from late‐glacial times of many montane taxa in a locality peculiarly‐suited to their needs and relatively undisturbed by man until the recent past.
FACTORS AFFECTING THE VESICULAR‐ARBUSCULAR INFECTION AND MYCORRHIZAL DEPENDENCY OF THIRTEEN WHEAT CULTIVARS
Authors: AZCÓN R. , OCAMPO J. A.
Published: May 2006

Wheat cultivars inoculated with Glomus mosseae show different degrees of mycorrhizal infection and mycorrhizal dependency. Mycorrhizal dependency was affected by root and root/shoot (R/S) ratio dry wts, but neither mycorrhizal dependency nor mycorrhizal infection levels were directly affected by N, P, K, Ca or Mg concentrations in plant tissues.

Absence of mycorrhizal infection in some wheat varieties was associated with lack of sugar exudation from the roots rather than with the sugar content of the roots. VA infection led to a decrease in the reducing and total sugar content of root extracts, and this effect was correlated with the degree of mycorrhizal infection.
CHANGES IN THE LEAVES OF FINGER MILLET DUE TO VA MYCORRHIZAL INFECTION
Authors: KRISHNA K. R. , SURESH H. M. , SYAMSUNDER JOSHI , BAGYARAJ D. J.
Published: May 2006

Anatomical and histochemical differences in the leaves of non‐mycorrhizal and mycorrhizal Eleusine coracana Gaertn. (finger millet) were studied. Striking increases in the thickness of leaves, size of midrib vein, major vein, minor vein, last vein, motor cells, mesophyll cells and number of plastids were noticed in the leaves of mycorrhizal plants. The leaves of mycorrhizal plants contained higher amounts of insoluble polysaccharides and insoluble proteins. These features are discussed from the view point of the effect of endomycorrhizas on the stimulation of plant growth.
BIOLOGICAL CONTROL OF ROOT‐INFECTING BASIDIOMYCETES BY SPECIES OF BACILLUS AND CLOSTRIDIUM
Authors: TAYLOR J. B. , GUY ESMÉ M.
Published: May 2006

The effect of flooding was studied on eight basidiomycete fungi growing on pieces of wood which were buried and flooded for 12 weeks. None of the fungi was re‐isolated from the flooded site, and the cause of the phenomenon was investigated, using a bioassay with Peniophora sacrata as the test fungus. When four Bacillus spp. and three Clostridium spp. from this site were added together to McCartney bottles containing soil and P. sacrata, and then flooded, the fungus was killed, but not when single bacterial species were used. This potential was present in 24 of 32 soils in the southwest Pacific.
VARIABILITY IN SEEDLING PROGENIES AND THE EFFECT OF LIGHT REGIMES DURING SEED PRODUCTION ON INTERSPECIFIC HYBRIDS OF POA
Authors: WILLIAMSON CYNTHIA J.
Published: May 2006

Variability in seedling characters of 11 families derived from Poa ampla × P. pratensis and P. longifolia × P. pratensis hybrids was examined using univariate and multivariate methods.

The determinants from within‐family dispersion matrices based on seedling characters enabled separation of the phenotypically very variable families from the more uniform ones. Comparable results were obtained from visual assessment of intra‐family variability on mature, spaced plants which suggested that it was possible at the seedling state to distinguish between families derived from predominantly amphimictic and predominantly apomictic seed respectively.

Ramets from 11 plants lifted from the field were kept in three light regimes and in natural daylight during inflorescence and seed development. Inflorescences, seed and resulting seedling progenies all responded to an increase in length of photoperiod and total daily irradiance. Variability in seedling characters was also affected which indicated that the light regime during embryo sac and seed development may influence the proportion of apomictic seed which matures. There was no consistent trend in this response among the hybrids examined.
Studies ON THE TOLERANCE TO SULPHUR DIOXIDE OF GRASS POPULATIONS IN POLLUTED AREAS
Authors: AYAZLOO M. , BELL J. N. B.
Published: May 2006

Dactylis glomerata, Festuca rubra, Holcus lanatus, Lolium perenne and Phleum bertolonii were collected from one or more of three sites with differing pollution characteristics in the north of England, and screened for tolerance to both acute and chronic sulphur dioxide injury in comparison with either bred cultivars or individuals of the same species collected from clean areas. Selection for tolerance was detected in all species and at all sites, suggesting that this is widespread in the field.

Differential response to chronic injury was manifested as effects on senescence, dry matter production, and/or partition of assimilate between roots and shoots. No correlation was found between the degree of acute and chronic injury at either the intraspecific or interspecific levels, which may indicate independent physiological mechanisms for these. Tolerance may evolve within 17 to 25 years. The significance of the evolution of SO2 tolerance for grasslands at polluted sites is discussed.
BIOCHEMICAL EXPLANATIONS OF MORE THAN ADDITIVE INHIBITORY EFFECTS OF LOW ATMOSPHERIC LEVELS OF SULPHUR DIOXIDE PLUS NITROGEN DIOXIDE UPON PLANTS
Authors: WELLBURN A. R. , HIGGINSON CAROLYN , ROBINSON DEBORAH , WALMSLEY CHRISTINE
Published: May 2006

Three clones of Lolium perenne L. known to show different sensitivities to SO2 pollution, together with other grasses (Dactylis glomerata L., Phleum pratense L. and Poa pratensis L.), were fumigated with low levels of SO2, NO2 and SO2+ NO2. Ratios of glutamate dehydrogenase activity (GDH) to that of glutamine synthetase (GS) were significantly raised by SO2 (6·8 parts 10‐8 for 11 weeks) or SO2+ NO2 in the SO2‐sensitive cloned cultivar S23 of L. perenne and by SO2+ NO2 in cloned Lolium perenne material which has high resistance to SO2 (S23 Bell resistant). In Lolium derived from Pennine upland (Helmshore clone) GDH/GS ratios were unchanged in the presence of SO2 or SO2+ NO2 but all three clones showed slight elevations in ratios in response to NO2 fumigation alone.

Within a week after treatment with NO2, all grasses had significantly higher nitrite reductase activities than similar plants given clean air, SO2 or SO2+ NO2 treatments. The presence of SO2 appeared to destroy the ability of the plant to respond to NO2, and this inhibition of a potential detoxification mechanism of nitrite is believed to be one of the main reasons why the SO2+ NO2 combination exhibits more than additive effects upon the growth of grasses.

All three clones of Lolium perenne and also Phleum pratense showed enhanced ATP formation in the presence of low (6·8 parts 10‐8 for 20 weeks) levels of NO2, but reduced cyclic photophos‐phorylation in the presence of either SO2 or SO2+ NO2. At higher levels of shorter duration (25 parts 10‐8 for 11 days), rates of ATP formation, ATP content and energy charge ratios were higher in NO2 fumigated tissue than in controls, but lower in SO2+ NO2 treated tissue, although basic electron transport systems were unaffected. It is believed that the principal effect of the pollutant combination is upon proton gradients within the photosynthetic membranes leading to general deficiency in ATP which is necessary both for growth and the repair of secondary pollutant damage elsewhere.

Parts 10‐8 (parts per hundred million) = quantity in μ m‐3× (1/mol. wt × 106) × 0·0224 × 108 at s.t.p. * for 11 weeks) or SO2+ NO2 in the SO2‐sensitive cloned cultivar S23 of L. perenne and by SO2+ NO2 in cloned Lolium perenne material which has high resistance to SO2 (S23 Bell resistant). In Lolium derived from Pennine upland (Helmshore clone) GDH/GS ratios were unchanged in the presence of SO2 or SO2+ NO2 but all three clones showed slight elevations in ratios in response to NO2 fumigation alone.
CONTROL OF DEVELOPMENT IN CHENOPODIUM ALBUM L. BY SHADELIGHT: THE EFFECT OF LIGHT QUANTITY (TOTAL FLUENCE RATE) AND LIGHT QUALITY (RED.FAR‐RED RATIO)
Authors: MORGAN D. C. , SMITH HARRY
Published: May 2006

In nature, fluence rate and the red.far‐red ratio are reduced in shadelight beneath vegetation; both show similar exponential decays with increasing canopy density. An assessment of the degree to which each of these factors controls development in natural shade was made by comparing Chenopodium album plants grown under vegetational shade with those grown under the controlled environment light treatments of low fluence rate, and combined low fluence rate and low red: far‐red ratio. The observations of stem extension and specific leaf area from vegetational shade were entirely consistent with the effects of the controlled environment light treatments. The increase of specific leaf area in natural shade was probably due to the low fluence rate; the initial rapid stem extension in natural shade was probably due to the reduced red: far‐red ratio. There is good evidence to suggest that the latter is a phytochrome‐controlled phenomenon.
THE REPRODUCTIVE BIOLOGY OF ASCLEPIAS TUBEROSA
Authors: WYATT ROBERT
Published: May 2006

Individual flowers of the self‐incompatible milkweed Asclepias tuberosa are available to pollinators for 7 or 8 days; however, there is a large overlap in flowering time (4 to 5 weeks) within and among inflorescences on a single plant and therefore the possibility of high levels of self‐pollination. Pollinator activity closely follows availability of flowers, although the more rapid decline of the former may indicate switching of pollinators to other plant species flowering simultaneously. These observational data are combined with experimental crossing data to write probability functions for a simple multiplicative model incorporating both extrinsic and intrinsic factors determining fruit‐set. Fruit‐set predictions from the model are very close to the 033% observed in natural populations of A. tuberosa.
MEGASPORES WITH MULTIFURCATE AND BIFURCATE PROCESSES FROM OLD RED SANDSTONE FACIES OF TOURNASIAN AGE, FROM THE TAFF GORGE, SOUTH GLAMORGAN, WALES
Authors: ALLEN K. C. , ROBSON J.
Published: May 2006

Seven megaspore species referable to the genera Hystricosporites and Ancyrospora are described from rocks of lowest Tournasian age in South Wales. Three species, Hystricosporitespyramidalis, Hystrictosporites proximo‐tuberculatus, and Ancyrospora cambrica are new, and Hystricosporites bedfordi is a recombination. Further information is added to previously described species, particularly on the exinal layers. The problems of separating the two genera are discussed.
NITROGEN ASSIMILATION, ROOT GROWTH AND WHOLE PLANT RESPONSES OF SOYBEAN TO ROOT TEMPERATURE, AND TO CARBON DIOXIDE AND LIGHT IN THE AERIAL ENVIRONMENT *
Authors: Jr RUFTY THOMAS W. , Jr RAPER C. DAVID , JACKSON WILLIAM A.
Published: May 2006

Vegetative soybean plants were exposed to root temperatures of 18, 24, and 30 °C in each of three aerial environments varying in light and CO2. Under high light (700 mUE m‐2 s‐1) at ambient CO2 (400 mUl l‐1) nitrate absorption and root growth were less at 18 and 30°C than 24°C. Both nitrate absorption and root growth were more sensitive to increasing root temperature under low light (325 μE m‐2 s‐1) and less sensitive under enriched CO2 (1000 μl l‐1). As indicated by dry matter accumulation, net flux of photosynthate to the roots was correlated with the changes in aerial environment. It was concluded from these relationships that the variation in root growth and nitrate uptake resulted from altered utilization of carbohydrates in the roots and that altered utilization of carbohydrates with increasing root temperature resulted from disproportionate partitioning of carbohydrate among root functions.

Although differences occurred in the amount of nitrogen translocated out of the root, nitrogen accumulation in the shoot was primarily a function of nitrate absorbed. Restrictions in dry matter accumulation in the shoot were similar to restrictions observed in the root. A decrease in emergence of new leaves was often the first response observed, with decreases in leaf area and dry wt occurring later. The integrated plant response to moderate root temperature stress is interpreted as evidence for an interdependent plant system, predominantly regulated by carbohydrate flux to the root and nitrogen flux to the shoot.
THE STRUCTURE OF THE SPORES OF GIGASPORA MARGARITA
Authors: SWARD R. J.
Published: May 2006

Light and electron microscopy have been used to study the changes that accompany germination in the spores of Gigaspora margarita. Regular germination is achieved following surface sterilization of the spores and the possible role played by sodium hypochlorite in spore activation is discussed. Following spore activation there is considerable redistribution of cytoplasm with a subsequent accumulation of cytoplasmic and wall material in the region of the bulbous‐shaped attachment. Germ‐tube development occurs in this region without the production of peripheral compartments that have been described for other spore types. The possible significance of this feature and the mode of germ‐tube wall development are discussed.
COMPARATIVE WATER RELATIONS AND PHOTOSYNTHESIS OF MYCORRHIZAL AND NON‐MYCORRHIZAL BOUTELOUA GRACILIS H.B.K. LAG EX STEUD.
Authors: ALLEN MICHAEL F. , SMITH WILLIAM K. , Jr MOORE THOMAS S. , CHRISTENSEN MARTHA
Published: May 2006

The rangeland grass, Bouteloua gracilis was inoculated with its mycorrhizal symbiont, Glomus fasciculatus, to determine the influence of vesicular‐arbuscular mycorrhizae on water status, stomatal behaviour and photosynthesis as well as gross plant morphology, biomass and phosphorus content. Mycorrhizal infection increased transpiration rates by over 100% with 50 to 70% lower leaf resistances to water vapour diffusion. Leaf xylem pressure was not different between mycorrhizal and non‐mycorrhizal plants indicating that whole‐plant resistance to water transport was reduced by more than 50%. Photosynthetic rates under saturating light conditions increased 68% with infection as a consequence of a 33% reduction in stomatal resistance and a 67% reduction in mesophyll resistance to CO2 uptake. Mycorrhizal infection did not affect biomass or gross plant morphology after 30 weeks of growth, but increased chlorophyll and phosphate concentrations by 28% and 70% respectively. These physiological changes indicate that mycorrhizae may substantially alter survival ability of Bouteloua gracilis.
DEVELOPMENTAL CHANGES IN LEAF EPICUTICULAR WAXES IN RELATION TO FOLIAR PENETRATION
Authors: BAKER E. A. , HUNT GRACE M.
Published: May 2006

Changes in surface properties during expansion of the leaves of eight plant species have been examined in relation to the uptake of 1‐naphthylacetic acid. Rates of wax production ranged from 0·1 ng cm‐2 h‐1 for sugar beet leaves to 6.2 nm cm‐2 h‐1 for leaves of Eucalyptus globulus. Individual leaves of all species maintained different rates of wax production at their adaxial and abaxial surfaces. Rates of synthesis of wax fractions and their constituent homologues varied with surface and leaf age. The homologue distribution shifted towards components of longer chain length as the leaves expanded. Morphological changes in wax deposits were small and limited largely to increases or decreases in the density of the plate waxes. Rates of penetration of 1‐naphthylacetic acid varied between species, between leaf surfaces and with age of tissue. The highest rates of uptake were confined to the period when the leaves expanded most rapidly. The decrease in penetration rate with increase in age of the tissue, common to most plants, was greatest for grape vine and Eucalyptus globulus leaves both of which maintained high rates of wax production during expansion.
EFFECT OF COPPER DEFICIENCY ON PHENOLIC AND OTHER CONSTITUENTS OF WHEAT CELL WALLS
Authors: ROBSON A. D. , HARTLEY R. D. , JARVIS S. C.
Published: May 2006

Summary

Before decreasing yield significantly, copper deficiency affected the amounts of phenolic compounds released (by treatment with sodium hydroxide) from the cell walls separated from young leaves of wheat. Effects of changes in copper supply on the amounts of phenolic compounds released followed closely its effect on copper concentration in the plant parts. More ferulic and less p‐icoumaric acid was released from the walls of young leaves of copper‐deficient plants than from those of copper‐adequate ones; these differences were less marked in older than in younger leaves. Copper deficiency decreased the lignin, hemicellulose and acetyl contents of cell walls only in severely deficient plants.
CELL DEATH AND CELL WALL PAPILLAE IN THE RESISTANCE OF OAK SPECIES TO POWDERY MILDEW DISEASE
Authors: EDWARDS M. C. , AYRES P. G.
Published: May 2006

Summary

A quantitative study was made of the infection processes of Microsphaera alphitoides, powdery mildew, on seedlings of three oak species, Quercus robur (leaves highly susceptible until mature), Q. cerris (moderately resistant) and Q. borealis (highly resistant), to determine the mechanisms underlying their different resistances to disease. Some inhibition of spore germination occurred on mature leaves of Q. robur, and on leaves of Q. cerris and Q. borealis, but the number of appressoria formed from germinated spores was not affected either by oak species or leaf age. Formation of elongating secondary hyphae (ESH) from appressoria was strongly inhibited on mature leaves of Q. robur and on leaves of Q. cerris, and was completely inhibited on leaves of Q. borealis. At this stage of infection, host resistance was expressed most effectively.

Challenged cells and the host cell wall around the fungal penetration point were examined by light and scanning electron microscopy (SEM). SEM studies of the leaf surface around the penetration point showed no difference between susceptible and resistant leaf surfaces and, in neither case, was there any evidence of chemical dissolution of cuticle or epicuticular wax. In light microscope investigations, limitation of ESH formation was associated with two factors. First, death of the challenged host cells occurred within 12 h of infection. This was a normal component of the resistance of Q. cerris but was uncommon in Q. robur and Q. borealis. Second, material was deposited in the form of a papilla on the inside of the epidermal cell wall, opposite the penetration point of the fungus. Large dome‐shaped papillae, which histochemical tests showed were typically lignified, were not penetrated by the fungus, while smaller, cone‐shaped, non‐lignified papillae failed to inhibit fungal development. Both types of papillae could occur in the same leaf but their frequency reflected the resistance of the host species. Lignified papillae were most common in resistant leaves.
DIRECT MEASUREMENT OF TRANSLOCATION OF CARBOHYDRATE IN THE LICHEN, CLADONIA CONVOLUTA, BY QUANTITATIVE AUTORADIOGRAPHY
Authors: TAPPER Y R.
Published: May 2006

Summary

Translocation of carbohydrate between Trebouxia and its associated fungal partner in the lichen, Cladonia convoluta, has been examined directly using quantitative autoradiography. This technique allows measurements to be made without disrupting the symbiotic association and avoids the rapid physiological changes that occur when the symbionts are isolated. The quantity of photosynthetically‐fixed carbon transferred from Trebouxia was higher than measured by previous methods. Release of carbohydrate from Trebouxia was reduced by several metabolic inhibitors indicating at least a partial dependence on energy for the overall process.
MICROBIAL FERMENTATION OF GRASS RESIDUES TO ORGANIC ACIDS AS A FACTOR IN THE ESTABLISHMENT OF NEW GRASS SWARDS
Authors: GUSSIN E. J. , LYNCH J. M.
Published: May 2006

Summary

Extracts from anaerobically decomposed shoots of a range of grass species were toxic to other grasses and clover. This phytotoxicity was less after 20 days than after 10 and seemed to be caused by organic acids. The residues produced byFestuca rubra, Alopecurus pratensisandAgrostis stoloniferawere the most toxic. After aerobic decomposition for 10 days extracts from these three species were phytotoxic, but after a further 10 days decomposition they caused a stimulation in grass and clover root growth. These results are discussed in relation to the poor establishment that sometimes follows reseeding old pasture land.
INHERITANCE OF TRIAZINE RESISTANCE IN POA ANNUA: CONSEQUENCES FOR POPULATION DYNAMICS
Authors: DARMENCY H. , GASQUEZ J.
Published: May 2006

Summary

A chloroplast triazine resistant population of Poa annua from a triazine treated area was compared with one from an adjacent untreated area. A study of morphological characters and isoenzymes showed that the resistant population contained as much polymorphism as the susceptible one. One phenotype, on an isozyme basis, was much more frequent in each habitat, suggesting the importance of natural selection in each population. The possibility of a ‘founder effect’ within the resistant population is discussed.

A dominant esterase allozyme was used to estimate the outcrossing rate giving an estimate of 13 % under greenhouse conditions. Transmission of herbicide resistance was also tested and found to be mainly inherited maternally (0·1% transmission via pollen). Paternal transmission is therefore not important for gene flow. Allogamy would appear responsible for the high degree of polymorphism found in the resistant population.
PRETREATMENT EFFECTS OF CADMIUM ON THE ROOT GROWTH OF HOLCUS LANATUS L.
Authors: BROWN HELEN , MARTIN M. H.
Published: May 2006

Summary

A cadmium tolerant and a non‐tolerant population of Holcus lanatus were subjected to a pretreatment with either no or low (0·2 μg Cd ml−1) concentrations of cadmium prior to normal tolerance testing in 1·0 μg Cd ml−1 solution. When pretreated roots were not removed prior to the tolerance test, the cadmium pretreatment resulted in significantly greater root growth of both populations in the test solution relative to plants given no cadmium pretreatment. Repeating the tolerance test on plants which had had their pretreated roots excised prior to testing showed no significant effect of any pretreatment on subsequent root growth in either population. There was an overall difference between the two populations in terms of their response to pretreatment and test concentrations in that when exposed to cadmium, plants of the tolerant population grew significantly better than those of the non‐tolerant population. The data presented provide evidence for a stimulation of cadmium tolerance following low‐level exposure of roots to cadmium. The mechanisms associated with these effects are not clear although cadmium tolerance in animals is known to show similar trends.
METAL UPTAKE IN TERRICOLOUS LICHENS
Authors: GOYAL R. , SEAWARD M. R. D.
Published: May 2006

Summary

The nature of the accumulation patterns within the lichen is assessed in terms of metal localization within the different thallus components (i.e. rhizinae, thallus without rhizinae, phycobiont, mycobiont) and the importance of substrate concentrations in controlling localization. Peltigera canina, P. polydactyla, P. rufescens, Cladonia furcata, C. impexa and C. uncialis from a wide range of natural and man‐influenced sites in the British Isles were analyzed for Cr, Cu, Fe, Mn, Ni, Pb and Zn; Cladonia spp. were used for comparative purposes. Metal accumulation capacity (μg g−1) of the rhizinae was maximum for Fe, Mn and Pb. However, the phycobiont was found to have maximal accumulation capacity for Cu, Ni and Zn. The metal accumulation capacities by rhizinae and thallus without rhizinae as well as phycobiont and mycobiont without rhizinae were found to be interrelated and were dependent upon the biologically‐available metal concentrations in their associated soils as well as the type of substrate. The total amounts (g) of metals localized within the different thallial components, from two major types of environment (i.e. with background and enhanced metal concentrations), are presented; rhizinae accumulate the highest concentrations of all metals under enhanced environments.