bluuebunny/crossref_metadata_2025 huggingface dataset:
COMPETITION FOR POLLINATORS IN THE ECOLOGY OF CENTAUREA SCABIOSA L. AND CENTAUREA NIGRA L.
Authors: LACK ANDREW J.
Published: May 2006

Observations are presented on: (a) the numbers of insects foraging on Centaurea scabiosa and Centaurea nigra per available capitulum of each species; (b) the numbers of insect visits to each capitulum of C. scabiosa and C. nigra in 30 min intervals; (c) the numbers of insect visits to rayed capitula compared with ray less capitula; (d) the number of successful pollinations. The study was carried out on the Devil's Ditch, Cambridgeshire where C. nigra is rayless, and on Hod Hill, Dorset where C. nigra is rayed, with a few results from a garden trial set out in the Cambridge Botanic Garden.

In the counts of insects in each area of the Devil's Ditch the numbers recorded feeding on each Centaurea species per capitulum were approximately proportional to the nectar reward of each species.

On Hod Hill the number of insect visits to C. nigra plants from which rays had been removed was half to three‐quarters of the number of visits to rayed capitula. This is very similar to the difference on the Devil's Ditch between the number of visits to C. scabiosa (rayed) and C. nigra (rayless), and this difference may therefore be a result simply of the possession of ray florets in C. scabiosa but not in C. nigra. The difference between the two species on Hod Hill was greater (C. scabiosa receiving two to three times as many visits as C. nigra) although C. nigra possesses ray florets and therefore resembles C. scabiosa. Some bees were observed visiting C. scabiosa selectively on Hod Hill but none did so on the Devil's Ditch.

On the Devil's Ditch both species had similar numbers of styles successfully fertilized on nearly all dates. Hod Hill on most dates a similar number of styles was fertilized in each species, but on a few dates C. scabiosa had more successful fertilizations than C. nigra. It is concluded that competition for pollinators is not a strong selective factor in Centaurea on the Devil's Ditch but may be a factor promoting the later flowering and the possession of ray florets in C. nigra on Hod Hill. Competition for pollinators may have been more important as a selection pressure in the past when less suitable habitat was available.
THE EFFECT OF TEMPERATURE ON PHYTOCHROME CONTROLLED HYPOCOTYL EXTENSION IN SINAPIS ALBA L.
Authors: WALL J. K. , JOHNSON C. B.
Published: May 2006

The effect of temperature on phytochrome control of hypocotyl elongation has been investigated using light‐grown seedlings of Sinapis alba. Temperature markedly affects the way in which these seedlings respond to both light quality and light quantity. The strong fluence rate dependence observed at 25 °C is not present at 10 °C and it is suggested that under conditions prevailing in the seedlings’natural environment phytochrome will measure only light quality.
STIMULATION AND INHIBITION BY BICARBONATE OF STOMATAL OPENING IN EPIDERMAL STRIPS OF COMMELINA BENGHALENSIS
Authors: MRINALINI T. , LATHA Y. K. , RAGHAVENDRA A. S. , DAS V. S. R.
Published: May 2006

The effect of 0 to 100μM bicarbonate on stomatal opening in epidermal strips of Commelina benghalensis was examined in the presence or absence of fusicoccin in light or darkness. Low concentrations of bicarbonate (up to 10 μM in the absence and 25 μM in presence of fusicoccin) stimulated stomatal opening while higher concentrations inhibited. The enhancement of opening by low concentrations of bicarbonate and phosphoenol pyruvate (PEP), and prevention of bicarbonate stimulation by malate or oxaloacetate suggested PEP carboxylase as a CO2 sensor in the guard cells. However, the inhibition of PEP carboxylase did not completely suppress the opening caused by fusicoccin. The action of fusicoccin therefore appears to involve a site other than CO2 fixation, presumably through the stimulation of proton excretion.
ECTOMYCORRHIZA FORMATION IN EUCALYPTUS
Authors: MALAJCZUK NICHOLAS , MOLINA RANDY , TRAPPE JAMES M.
Published: May 2006

Ectomycorrhiza formation by 11, geographically distinct Eucalyptus species and Pinus radiata with 23 diverse ectomycorrhizal fungi was examined in pure culture syntheses. Few differences occurred between the Eucalyptus species in their ability to form ectomycorrhizas with several fungi, thus indicating no evidence for host‐fungus specificity within Eucalyptus. Pinus radiata and most Eucalyptus species formed ectomycorrhizas in common with several broad‐host‐ranging fungi. However, fungus species which are known to associate exclusively with members of the Pinaceae, e.g. Suillus and Rhizopogon species, did not form ectomycorrhizas with any Eucalyptus species and vice versa. Possible incompatibility between several host‐fungus combinations was characterized by host accumulation of phenolic compounds in epidermal and cortical cells. These results are discussed relevant to better understanding degrees and processes of ectomycorrhiza host‐fungus specificity and compatibility and to practical considerations in reforestation of exotic plantations.
FINE STRUCTURE OF THE ENDOTHECIUM AND DEVELOPING XYLEM IN PHASEOLUS VULGARIS
Authors: WHATLEY JEAN M.
Published: May 2006

Differentially thickened wall bars are formed in cells of the anther endothecium as well as in the xylem. In Phaseolus vulgaris both types of wall bar appear to be lignified. As thickening takes place, Golgi bodies become numerous, endoplasmic reticulum proliferates and both types of organelle occupy characteristic sites within the cell. Thickening begins at an early stage of xylem development but in the endothecium it is long delayed. Subsequent loss of cytoplasm is associated with increasing vacuolation of xylem elements, but may be associated with plasmolysis in the endothecium.
POLLINATION ECOLOGY OF STERNBERGIA CLUSIANA (KER‐GAWLER) SPRENG. (AMARYLLIDACEAE)
Authors: DAFNI AMOTS , WERKER ELLA
Published: May 2006

Sternbergia clusiana is pollinated by two main types of pollinators, Apis mellifera and various Syrphidae. The honey bees collect nectar and pollen from the shorter inner whorl of stamens and from the lowermost part of the funnel‐shaped perianth tube. The hover flies visit mainly the appendages on the outer perigone and the longer stamen whorl. These appendages were found to secrete a sugar solution as well as polysaccharides and lipids. The latter probably attract the flies.

It is suggested that each pollinator is attracted by a different nectary type and that the modes of pollination prevent competition between the different pollinators and are to be interpreted as maximizing the floral attraction in the harsh season of flowering (September to December).
NITROGEN METABOLISM OF HALOPHYTES.
Authors: AHMAD I. , LARHER F. , MANN A. F. , McNALLY S. F. , STEWART G. R.
Published: May 2006

Summary

Ion‐exchange chromatography on DEAE‐Sephacel revealed the presence of two forms of glutamine synthestase (GSI and GSII) in leaf tissue and one form in root tissue of the angiosperm halophyte, Triglochin maritima. The chromatographic characteristics of GSI and the root enzyme were similar but there were differences in their stability, GSI being considerably more stable than the root enzyme. The characteristics of GSI and GSII exhibited some differences, GSII showed negative cooperativity with respect to glutamate and had a pH optimum of 8−0 compared with 7.2 for GSI. GSI was found to be unstable, particularly in the presence of inorganic salts. Compounds such as glycine betaine, proline and sorbitol, which are thought to function as compatible osmotic solutes in halophytes, were found to stabilize GSII.
AN ELECTRON PARAMAGNETIC RESONANCE (EPR) STUDY OF THE UPTAKE OF VANADYL BY WHEAT PLANTS
Authors: McPHAIL D. B. , LINEHAN D. J. , GOODMAN B. A.
Published: May 2006

Summary

Electron paramagnetic resonance (EPR) spectroscopy has been used to monitor, in vivo, the uptake of the vanadyl ion by wheat plants. The use of high levels of vanadyl ion produced, in the plant, high molecular weight complexes with EPR parameters similar to those obtained from cellulose–vanadyl derivatives. With lower vanadyl concentration, low molecular weight complexes were observed and interpreted as arising from vanadyl‐amino acid complexes. Low molecular weight complexes with similar parameters were obtained from root washings.
PHOTOSYNTHESIS IN DESICCATED SHOOTS OF POLYTRICHUM
Authors: PENNY M. G. , BAYFIELD N. G.
Published: May 2006

Summary

The desiccation responses of four species of Polytrichum were examined. The relationship between CO2 assimilation and shoot water content was similar in Polytrichum commune and Polytrichum piliferum, the species most dissimilar in ecological requirements. There were, however, considerable differences between species in recovery following various desiccation treatments.

Continuous desiccation was found to be more damaging than the same total period of desiccation interrupted by periods of wetting. Polytrichum piliferum was least affected by any of the desiccation treatments. Desiccation to 76 % r.h. was found to suppress the photosynthetic rate of both Polytrichum commune and Polytrichum piliferum after rewetting more than treatment at 55% or 90% r.h. Subsequent recovery was generally better following the 90% r.h. treatment.

Slow desiccation of Polytrichum commune was substantially less damaging than rapid drying.
ULTRASTRUCTURAL ASPECTS OF ENDOMYCORRHIZA IN THE ERICACEAE
Authors: BONFANTE‐FASOLO P. , GIANINAZZI‐PEARSON V.
Published: May 2006

Summary

The ultrastructural features of the dissociated mycorrhizal symbionts Pezizella ericae Read and Calluna vulgaris L. Hull, grown in pure culture, and of the modifications occurring in both fungus and root cells during their reassociation in axenic culture have been studied in detail. Growing (apical/subapical and vacuolated zones) and non‐growing (ageing zone) regions can be distinguished in colony margins of Pezizella ericae in pure culture. In axenic mycorrhiza cultures the general morphology of the fungus remains the same with living hyphae closely resembling those in the active growing region. However, the external hyphae around roots develop an abundant fibrillar sheath which has a polysaccharide‐protein composition and the possibility that this may play a role in recognition and adhesion phenomena in ericoid mycorrhizae is discussed.

Metachromatic vacuolar granules, which are very common in pure cultures of Pezizella ericae, are often present in external hyphae around axenic mycorrhizal roots but are very rarely observed in intracellular fungal hyphae. The general ultrastructural organization of these axenically produced ericoid mycorrhizae is compared to that reported for natural infections in several ericaceous species.
ESTABLISHMENT AND DEVELOPMENT OF A POPULATION OF ORCHIS SIMIA LAMK. IN THE NETHERLANDS, 1972 TO 1981
Authors: WILLEMS J. H.
Published: May 2006

Summary

Observations in chalk grassland in South Limburg, Netherlands, were made over a 10‐year period on the development of a population of Orchis simia which probably originated from a single individual.

The original plant (‘mother plant’) flowered for 10 successive years and, in years when the inflorescence was not damaged by grazing animals, produced viable seed. The species is clearly self‐compatible.

Juvenile plants with only one or two narrow leaves were found for the first time 4 years after the mother plant had flowered. Thereafter, recruitment to the population occurred annually, but the number of new plants in any one year was low (5 to 13). Some juvenile plants flowered 3 years after appearing above ground, while others have still to flower after 6 years above ground. Only those plants which had developed four or five leaves in the rosette with a minimum leaf area of more than 60 cm2 flowered.

The height of the flowering stem and number of flowers on the inflorescence at the mother plant varied considerably from year to year but in every year it was more vigorous than the juvenile plants. New plants were also developed by vegetative means, but this method of reproduction is considered to be unimportant compared with spread by means of seeds.
BRANCHING PATTERNS OFLINDERA BENZOINBENEATH GAPS AND CLOSED CANOPIES
Authors: VERES JOHN S. , PICKETT S. T. A.
Published: May 2006

Summary

Lindera benzoin, a major forest shrub in central New Jersey, was studied in order to determine whether branching and biomass allocation differ between plants growing under open and closed canopies. Higher bifurcation ratios (ratio of numbers of distal to proximal branches) of open canopy plants combined with large interbranch distances, long internodes and large branch angles to the horizontal reveal a branching pattern very different from that of closed canopy plants. Plants under closed canopies possessed a higher proportion of leaf to total biomass.

The ratio of overlapping leaf area to total leaf area did not differ between subsamples of the two groups, possibly due to small sample sizes. Leaf area, leaf biomass and branch biomass, for developmentally equivalent third order samples, were found to be greater in the open canopy group. The high productivity ofLinderain gaps, its branching characteristics, including, e.g. spiral leaf insertion and short interbranch distance, and a failure to adjust allocation in shady habitats as do some species, suggest that it is basically a multilayer plant that can effectively change branch presentation and leaf orientation in shady habitats. Thus,Linderamay be particularly well suited to exploiting both the small gaps and closed canopy matrix of old growth forests.
REGULATION OF SEED‐GERMINATION TIMING BY MOIST CHILLING IN WESTERN HEMLOCK
Authors: CAMPBELL ROBERT K. , RITLAND STANLEY M.
Published: May 2006

Existence of a natural system is proposed, in which duration of winter chilling of seeds of western hemlock, Tsuga heterophylla (Raf.) Sarg., regulates timing of germination in spring. Seeds from 12 populations (from Oregon and Washington, U.S.A.) were germinated in 12 combinations of three chilling durations and four germination temperatures. Embryo development rates, calculated as 100/Y where Y= days to 50% germination, increased directly with temperature, and the relation could be described by an empirical logistic equation. Chilling increased embryo developmental rates at all germination termperatures, altering coefficients in the equation and the shape of the resulting temperature‐response curve. Each population, deviated slightly from the average curve for each chilling duration. Population deviations were described by a complex cline based on latitude, elevation, and distance from the ocean of the parent tree. Results are discussed as being consistent with Levins' dormancy‐strategy hypothesis.
RESPONSES OF SIX SPECIES OF VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI AND THEIR EFFECTS ON SOYBEAN AT FOUR SOIL TEMPERATURES
Authors: SCHENCK N. C. , SMITH GEORGE S.
Published: May 2006

The effects of four soil temperatures on colonization of soybean roots, sporulation and enhancement of plant growth by six species of vesicular‐arbuscular (VA) mycorrhizal fungi were tested. The mean values for all fungus and plant variates in three tests were generally greatest at 30 °C and lowest at 18 °C. Four fungus species, Glomus claroideum, Glomus clarum, Gigaspora pellucida, and Gigaspora gregaria, produced the greatest number of spores per gramme of colonized root at 24 °C, while Glomus mosseae and Acaulospora laevis reached their maximum at 30 °C. Gigaspora gregaria had its maximum percentage of root colonization at 36 °C, Glomus mosseae reached its maximum at 24 °C, while all other species had maximum root colonization at 30 °C. Glomus claroideum and Acaulospora laevis were the only species which had maximum root colonization and sporulation occurring at the same temperature, 30 °C. Spore diameter was generally less at 30 than 24 °C, but this varied with fungus species and test. Soybean flower numbers, pod set and seed yield varied considerably in the three tests, but plant height was little affected by soil temperature or by fungus species. Generally, plants colonized with Glomus mosseae had an increased plant response and those colonized with Acaulospora laevis had a depressed plant response. There was considerable variation in plant response to various combinations of temperature and fungus species, with both growth stimulatory and growth repressive effects occurring.
CARBOHYDRATE METABOLISM IN THE FUNGUS DENDRYPHIELLA SALINA
Authors: METCALF E. , JENNINGS D. H.
Published: May 2006

The effect of 3‐O‐methyl glucose on the carbohydrate metabolism of, and loss of 14C‐labelled compounds from, mycelium of Dendryphiella salina pretreated with [U‐14C]mannitol was investigated. Though concentrations of mycelial glycerol were higher than previously reported, the results for other internal carbohydrates were generally similar. In particular, the sugar reduced the concentration of mannitol. Loss of radioactivity into the medium was increased by 3‐O‐methyl glucose. The pattern of loss cannot yet be explained but since there was no loss of labelled mannitol or arabitol, unspecific membrane damage seems unlikely.
SEQUENTIAL ANALYSIS OF PLANT GROWTH
Authors: JOLLIFFE P. A. , EATON G. W. , DOUST J. LOVETT
Published: May 2006

Plant growth analysis, demographic analysis and yield component analysis are three procedures used to study relationships underlying plant growth and development. Previously, it has been shown that demographic analysis is qualitatively different from plant growth analysis. This paper demonstrates how plant growth analysis and yield component analysis can be merged into a composite procedure, sequential plant growth analysis. The composite approach treats some of the traditional indices of plant growth, including leaf area ratio, leaf area index, unit leaf rate, relative growth rate, crop growth rate and harvest index, as yield components. Regression analysis is used to assess quantitatively the contributions of individual yield components to variations in growth and yield. Fitted curves and trends in coefficients of determination are both used to follow the time course of relationships during development. A study of vegetative growth in bean plants is used to illustrate the composite procedure.
THE DEVELOPMENT OF ENDOMYCORRHIZAL ROOT SYSTEMS
Authors: BUWALDA J. G. , ROSS G. J. S. , STRIBLEY D. P. , TINKER P. B.
Published: May 2006

A model of infection of roots by vesicular–arbuscular mycorrhizas, presented earlier (Buwalda et al., 1982), is used to study the effects of phosphorus on the spread of infection in root systems. Two hosts, with contrasting responses to mycorrhizal infection (wheat and leek), were grown at a range of phosphorus levels, and sequential measurements of growth and concentrations of phosphorus in plants, and infection of roots, were made. Increasing levels of phosphorus in the soil increased concentrations of phosphorus in the plants and reduced the percentage of root length infected in both hosts, but the effect was greater in wheat. Fitting the model showed that the inherent rate of spread of the fungus was not significantly altered by applications of phosphorus. However, the maximum proportion of the root system which could become infected was reduced, especially in wheat. Some implications of this finding on our understanding of the mycorrhizal symbiosis are discussed.
ASULAM RESISTANCE IN EMBRYOIDS OF CELERY TISSUE CULTURES
Authors: MERRICK M. M. A. , COLLIN H. A.
Published: May 2006

Embryogenic cell suspensions were filtered and the globular embryoids and embryogenic aggregates exposed to the herbicide Asulam at a concentration of 8 × 10−5 M in liquid culture for 1 week; the suspension was then plated in an Asulam‐free agar medium. The surviving embryoids were allowed to develop into plants which eventually flowered and the seed was collected. Cultures were also re‐initiated from the young plants and tested for the presence of Asulam resistance. Undifferentiated and differentiated cell lines were isolated from the selected plantlets and both were shown to be resistant to Asulam. Since the plants did not set viable seed it was not possible to test the progeny. However, the presence of resistance in the tissue cultures derived from the plants developed from selected embryoids suggested the selection procedure involving embryoids, rather than undifferentiated cells, was successful in producing a source of Asulam resistance which was possibly due to a mutation.
MYCORRHIZAL SYNTHESIS BETWEEN CISTACEAE AND TUBERACEAE
Authors: GIOVANNETTI G. , FONTANA A.
Published: May 2006

Cistus incanus ssp. incanus was tested with six Tuber species to prove its ectomycorrhizal development; the same was done with Tuber melanosporum and five Cistus species. Cistus incanus L. ssp. incanus formed ectomycorrhizas with Tuber albidum Pico, T. brumale Vitt., T. aestivum Vitt. and T. rufum Pico. The five Cistus species (Cistus albidus L., C. laurifolius L., C. salvifolius L., C. crispus L. and C. monspeliensis L.) developed ectomycorrhizas with Tuber melanosporum Vitt. These Cistaceae may be used as shrubby plants and as colonizers in truffle cultivations; the variety of their environmental and ecological requirements is such that it would be possible to increase the types of soil and number of places where truffles can be grown.
COMPARATIVE EFFECTS OF FOLIAR‐OR SOIL‐APPLIED NITRATE ON VESICULAR‐ARBUSCULAR MYCORRHIZAL INFECTION IN MAIZE
Authors: AZCÓN R. , GOMEZ‐ORTEGA M. , BAREA J. M.
Published: May 2006

Various concentrations of nitrate were applied either to the rooting medium (soil) or to the foliage of maize (Zea mays L.) plants inoculated or not inoculated with the vesicular‐arbuscular mycorrhizal fungus Glomus mosseae.

Certain levels of foliar‐applied nitrate and of soil‐applied nitrate had similar effects on growth of non‐mycorrhizal plants and on concentrations of nitrogen and phosphorus in their shoots. However, when the effects of these concentrations on inoculated plants were compared, plants with soil‐applied nitrate always developed much less infection.

These results are further evidence that soil nitrate influences mycorrhizal development by acting on the establishment of infection rather than on spread within the root.
A POLLEN CALENDAR FOR SIENA (CENTRAL ITALY): PRELIMINARY DATA*
Authors: MURGIA M. , DE DOMINICIS V. , CRESTI M. , SILVESTRI S.
Published: May 2006

A preliminary investigation on airborne pollen in Siena was carried out for 1978 using a Burkard trap. For each day pollen grains were counted according to family and expressed in number of grains trapped per m3 of air. The highest concentrations of airborne pollen grains occur in March with the Cupressaceae, Corylaceae, Butulaceae, Salicaceae and in May‐July with the Poaceae, Pinaceae, Urticaceae, Fagaceae and Oleaceae.
EFFECTS OF BENZO‐18‐CROWN‐6 ON ABAXIAL AND ADAXIAL STOMATAL OPENING AND ITS ANTAGONISM WITH ABSCISIC ACID
Authors: PEMADASA M. A.
Published: May 2006

Summary

Abaxial and adaxial stomatal responses to benzo‐18‐crown‐6 (a synthetic K+ionophore), alone and in combination with abscisic acid (ABA), were examined on isolated epidermes ofCommelina communis. Increasing ionophore concentration progressively suppressed abaxial opening, while up to an optimum concentration it enhanced adaxial opening although higher concentrations caused closure; stomatal K+changed correspondingly. Increasing KCl progressively alleviated the ionophore‐induced closure. The effects of the ionophore and ABA were strongly antagonistic. Benzo‐18‐crown‐6 is postulated to eliminate an inherent disparity in permeability to K+between the membranes of abaxial and adaxial guard cells by making them more permeable. In normal abaxial functioning a net K+gain promotes wide opening, but the ionophore‐enhanced permeability results in a net K+loss causing closure, because the intensified efflux down a concentration gradient outweighs the influx driven by a proton pump. The normally low adaxial K+accumulation is attributed to an inherently restricted membrane permeability which benzo‐18‐crown‐6 is postulated to alleviate progressively with increasing concentration; an enhanced permeability up to an optimum level allows a net K+gain producing wide apertures, but any further increase in permeability leads to a net K+loss, like that in abaxial guard cells, causing closure. The progressive reduction of the ionophore‐induced closure with increasing external KCl supply and the strong antagonistic interaction between the ionophore and ABA support this postulation. The results suggest that the normal disparity in abaxial and adaxial opening is linked specifically with differential K+accumulation in the guard cells.
RHYTHMS OF ACIDITY AND CO2 PRODUCTION IN ORCHID FLOWERS
Authors: GOH C. J.
Published: May 2006

Summary

Acidity fluctuations typical of Crassulacean acid metabolism (CAM) were observed in flowers of CAM orchids such as Arachnis, Aranda, Dendrobium and Vanda hybrids, but not in flowers of a C2 orchid, Oncidium Goldiana. The range of fluctuation was however, much smaller in the flowers than in the leaves. Dark 14CO2 fixation yielded labelled malate while day fixation resulted in labelled intermediates of C3 photosynthesis. A diurnal CO2 production rhythm was observed in flowers of both CAM and C3 orchids irrespective of fragrance production.
WATER POTENTIAL MEASUREMENT, WATER COMPARTMENTATION AND WATER FLOW IN DACTYLIS GLOMERATI L. LEAVES
Authors: ROY J. , BERGER A.
Published: May 2006

Summary

When measuring the water potential of leaf samples in a dew‐point hygrometer, it takes several hours to achieve a constant value. It is demonstrated that this is due to water potential gradients within the sample which occur only if the leaf is actively transpiring.

Water potentials have been measured on the same leaf or plant using a pressure chamber, a sample dew‐point hygrometer and an in situ hygrometer. Relatively good agreement was found in plants with zero or low transpiration, but results diverged widely when transpiration was high. It is suggested that divergences occur because the methods refer to different compartments of the leaf separated by resistances to water flow. The pressure chamber measures the water potential of the xylem vessels (ψxw), the sample hygrometer gives a value (ψcw) close to the water potential of the vacuoles and the in situ hygrometer yields a value (ψaw) close to the water potential around the evaporation sites. ψawshould logically be the most negative, but this was not always the case. On the other hand, ψxw was always and up to 10 × 105 Pa less negative than ψcw.

These findings question the validity of the calibration of the pressure chamber against psychrometers or hygrometers and are relevant to the topic of water pathway in leaves.
SILICON DEPOSITION AND ANATOMICAL STUDIES IN THE INFLORESCENCE BRACTS OF FOUR PHALARIS SPECIES WITH THEIR POSSIBLE RELEVANCE TO CARCINOGENESIS
Authors: SANGSTER A. G. , HODSON M. J. , PARRY D. WYNN
Published: May 2006

Summary

Inflorescence bracts of four grasses, Phalaris canariensis, P. minor, P. paradoxa and P. arundinacea, were investigated using light microscopy, scanning electron microscopy and electron‐probe microanalysis to determine their anatomy and silicon depositional patterns.

The heaviest silicon accumulation detected was associated with the outer (abaxial) epidermis of the lemma. Preferential deposition sites were located in the cell walls of the macrohairs, the walls and lumina of the long cells, and external to the epidermis, forming a thin layer of extracellular sheet or cuticular silica. Occasional silicification of internal tissues occurred in two forms, either as elongated, pointed fibres of the dendriform type, resulting from the infilling of lumina and pits of hypoderm fibres, or as rows of spongy mesophyll cells and intercellular spaces.

Dimensions and silicon levels, recorded for the various siliceous structures indicated that the macrohairs and the friable sheets formed by silicification of the abaxial epidermal cells were a potential source of sharp, elongated siliceous fibres falling into the critical size range for classification as being carcinogenic. The seeds of all four Phalaris species are known contaminants of the cereal crops of the Middle East, and have been implicated as factors in the high incidence of oesophageal cancer in north‐east Iran.
LIMITED INDEPENDENT GROWTH OF A VESICULAR–ARBUSCULAR MYCORRHIZAL FUNGUS IN VITRO
Authors: HEPPER CHRISTINE M.
Published: May 2006

Summary

The hyphae developing from germinating resting spores of the vesicular‐arbuscular mycorrhizal fungus Glomus caledonius remain viable and can continue to grow after they have been detached from their parent spores. This new growth is at least as extensive as that present at the time when the spore was detached and is dependent on nutrients in the medium.
A COMPARISON OF GROWTH EFFICIENCY AND SPECIFIC RATE OF DARK RESPIRATION OF UNINFECTED AND VESICULAR‐ARBUSCULAR MYCORRHIZAL PLANTS OF TRIFOLIUM SUBTERRANEUM L.
Authors: SILSBURY J. H. , SMITH S. E. , OLIVER A. J.
Published: May 2006

Summary

Small swards of mycorrhizal and non‐mycorrhizal subterranean clover plants were grown in an artificial rooting medium in pots so as to form a closed canopy, by which time plants were about 5 weeks old and had 30 % infection in mycorrhizal roots. Specific rates of dark respiration of mycorrhizal and uninfected populations of plants were compared in an incubation chamber after exposure of the sward to standard light flux density and temperature on a 12 h day/12 h night cycle. Growth efficiencies were measured by exposing a sward to variable light flux density at constant temperature and monitoring the CO2‐exchange rate.

The dark respiration rate of whole plants decreased during darkness from an initial value measured immediately after the start of incubation to one about 20% lower after 12 h. Rates for excised roots decreased to about 35% of the initial value. When compared on the same basis the specific rate of dark respiration of mycorrhizal plants did not differ from that of uninfected plants. Likewise, mycorrhizal plants and uninfected plants displayed the same growth efficiency, for both used about 30 % of the net CO2 gain during the light period for purposes of biosynthesis. This parameter was not affected by phosphate nutrition. Mycorrhizal and uninfected plants responded to change in light flux density in a similar manner.

It is concluded that when CO2 fluxes are measured on a whole‐plant basis over a 24 h period, mycorrhizal and uninfected plants of subterranean clover grown as swards, have essentially similar carbon economies.
HYPOXANTHINE AND ALLANTOIN AS NITROGEN SOURCES FOR THE GROWTH OF SOME FRESHWATER GREEN ALGAE
Authors: PRASAD P. V. DEVI
Published: May 2006

Summary

Six freshwater green algae, viz. Scenedesmus obliquus, Scenedesmus pannonicus, Chlorella glucotropa, Crucigenia tetrapedia, Tetradesmus cumbricus and Stichococcus mirabilis, were examined for their ability to utilize hypoxanthine and allantoin as sole nitrogen sources for growth in light. All the six algae could utilize both hypoxanthine and allantoin for growth. None of the algae needed any significant period of adaptation and growth was often as rapid on hypoxanthine/allantoin as it was on nitrate. Higher concentrations (3 mat) of the purines inhibited the growth of Stichococcus mirabilis and Crucigenia tetrapedia, possibly because of the formation of intracellular pools of the purines. Activity of the enzyme nitrate reductase was not markedly affected by growth on either hypoxanthine or allantoin. It is concluded that the ready utilization of hypoxanthine and allantoin indicates the operation of the standard pathway of purine catabolism, i.e. hypoxanthine → xanthine → uric acid → allantoin → end products, in these algae.
THE INFLUENCE OF LIGHT ON THE GERMINATION OF SENECIO VULGARIS L.
Authors: HILTON JANET R.
Published: May 2006

Summary

Achenes of Senecio vulgaris L. show a strong positive requirement for white or red light to attain maximal germination at 20 °C. The response to light is mediated by the photoreversible photoreceptor phytochrome. The light requirement can also be satisfied by short daily irradiations with red light (660 nm) and far‐red light given at the end of daily red light photoperiods depresses germination to Cedeximately 60%. It is suggested that Pfr, the active form of photochrome, once formed, persists for between 8 and 10 h. The interactions between light, KNO3 and constant temperatures between 0 and 30 °C have also been studied.
Ca2+‐ AND MG2+‐STIMULATED ATPases FROM ROOTS OF PLANTAGO SPECIES: RESPONSE TO DIFFERENT LIGHT ENERGY FLUXES
Authors: KUIPER DAAN
Published: May 2006

Summary

Plants of four Plantago species: P. major L ssp. major L, P. lanceolata L, P. media L and P. coronopus L were grown at two light energy fluxes. In all species, except P. major spp major, the growth of the root was more depressed with low light than that of the shoot, resulting in an increased shoot to root ratio. The shoot to root ratio of P. major ssp major was similar at both light energy fluxes.

The Ca2+‐ and Mg2+‐stimulated ATPase activity of microsomal preparations of the roots was also studied. The capacity values (Vmax) of both ATPase activities were usually low in P. major ssp. major and the highest Vmax value for the Ca2+‐stimulated ATPase activity was demonstrated in P. media. Both ATPase activities (Ca2+ and Mg2+) were lower in plants grown with low light except in P. major ssp major, which showed the same Vmax values for enzyme activity in plants grown at both light levels.

The lack of response of P. major ssp major to different light energy fluxes is interpreted as a lack of phenotypic plasticity of this species. The data are compared with previous results on plasticity as a response to mineral nutrition. Phenotypic plasticity is discussed as a factor in the plant's strategy for survival.
ACTIVITY OF NITRATE REDUCTASE IN TRIFOLJUMSUBTERRANEUM: EFFECTS OF MYCORRHIZAL INFECTION AND PHOSPHATE NUTRITION
Authors: OLIVEER A. J. , SMITH S. E. , NICHOLAS D. J. D. , WALLACE W. , SMITH F. A.
Published: May 2006

Summary

Activity of nitrate reductase (NADH‐dependent), measured by in vitro methods, was present in both roots and shoots of non‐mycorrhizal Trifolium subterraneum. As expected, the activity was dependent upon the amount of nitrate supplied and was closely related to the concentration of nitrate in the tissues.

Mycorrhizal plants had a greater capacity to synthesize the enzyme in both roots and shoots than non‐mycorrhizal plants when both were grown under phosphate‐limiting conditions. This conclusion was reached from the results of two types of experiment: (1) when constant (relatively low) amounts of nitrate were supplied to the plants each day, the specific activity of the enzyme in the roots declined over the period of the experiment (52 days) as the plants grew larger. There was also a decline in shoots of mycorrhizal plants. However, when the nitrate supply was increased fourfold, the stimulation of activity was considerably greater in the roots of mycorrhizal plants than in non‐mycorrhizal plants; (2) interactions between mycorrhizal infection, phosphate nutrition and nitrate reductase activity were investigated in plants which received different amounts of nitrate according to size. At the two lowest levels of additional soil phosphate (0 and 0.2 mmol phosphate per kg), there was a large mycorrhizal growth response accompanied by reduction in root: shoot ratio, increase in the phosphate concentration in the tissues and considerable stimulation of nitrate reductase activity, both on fresh weight and whole plant bases. This stimulation (together with changes in root: shoot ratio and phosphate concentration) was also apparent at 0.4 mmol phosphate per kg in the absence of any overall mycorrhizal growth response. At 0.67 mmol phosphate per kg, there was neither a growth response nor any stimulation of enzyme activity.

NADPH‐dependent nitrate reductase activity, more characteristic of fungi than NADH‐dependent activity, was barely detectable and similar (very low) activity was present in both mycorrhizal and non‐mycorrhizal roots. The conclusions are that mycorrhizal effects on nitrate reductase activity are largely indirect, mediated via improved phosphate nutrition and that direct involvement of the fungi in nitrate assimilation is likely to be very slight.
ULTRASTRUCTURE AND ANALYSIS, BY LASER PROBE MASS SPECTROGRAPHY, OF THE MINERAL COMPOSITION OF THE VESICLES OF TRIFOLIUM PRA TENSE ENDOMYCORRHIZAS
Authors: STRULLU D. G. , CHAMEL A. , ELOY J. F. , GOURRET J. P.
Published: May 2006

Summary

The elementary composition of the fungal vesicles of Trifolium pratense L. endomycorrhizas was determined using the laser‐probe mass spectrography. Anatomical and cytological studies were also made so as to locate and describe the Endogonaceae in the infested roots of the host plant. Results obtained with fixed and unfixed samples are compared. The fixatives and embedding procedures are not convenient for elements such as potassium. It appears that the vesicles of the Endogonaceae, in addition to their high lipid contents could act as reservoirs for many elements, the principal elements detected being K, Ca, Mg and Na.
EFFECTS OF TEMPERATURE, LEVELS OF NITRATE SUPPLY AND DURATION OF LIGHT AND GROWTH ON NITRATE REDUCTASE ACTIVITY IN AGEOSTIS TENUIS AND AGROSTIS STOLONIFERA
Authors: HARRIS P. , WHITTINGTON W. J.
Published: May 2006

Nitrate reductase activity (NRA) was assessed at several moments within the day during the early stages of establishment of tiller generated plants and seedling swards of Agrostis tenuis and A. stolonifera grown at different temperatures and levels of nitrate supply. Agrostis tennis consistently exhibited higher NRA values than A. stolonifera at initial developmental stages or low nitrate availability. The reverse situation was found to occur at high nitrate availability or in longer established plants and seedling swards. This emphasizes the difficulties in establishing consistent differences between species in NRA. Both species showed increased NRA with increased nitrate availability, increased night temperature or decreased day temperature. Agrostis stolonifera increased its NRA to a greater extent than A. tenuis as nitrate availability increased. The importance of daily and developmental variation in NRA in establishing differences between these species is discussed.
OSMOREGULATION IN HIGHER PLANTS: EFFECT OF NaCl SALINITY ON NON‐NODULATED PHASEOLUS AUREUS L.
Authors: IMAMUL HUQ S. M. , LARHER F.
Published: May 2006

Phaseolus aureus L. tolerated up to 150 mM NaClext, but with a diminished growth and an accumulation of various organic solutes characteristic of stress conditions. With increasing external salinity NH4+ accumulated in the tissues, attaining toxic concentrations at the higher levels. In consequence, the production of organic solutes such as asparagine, proline, glycine betaine and free amino acids was different from that in the control plants. Growth reduction corresponding to diminished organic matter production was due to ‘ion excess’ in the plants. NH4+ toxicity resulted in an increased accumulation of ureides and asparagine. K+, NO3−and asparagine played a key role, while sugars only a minor role as osmotica. However, a role for proline and quaternary ammonium compounds as compatible solutes in plants suffering severe salt stress can not be eliminated.
EFFECTS OF VESICULAR–ARBUSCULAR MYCORRHIZAE ON DISTICHLIS SPICATA UNDER THREE SALINITY LEVELS
Authors: BACH ALLEN EDITH , CUNNINGHAM GARY L.
Published: May 2006

Inland and coastal populations of the salt‐tolerant plant Distichlis spicata were grown under three salinity levels (0, 1000 and 2000 mg Na+ added kg−1 soil as NaCl) with and without inoculum of vesicular–arbuscular mycorrhizae. Mycorrhizal infection averaged 28% for the inland plants and 9% for the coastal plants, and was unaffected by soil salinity. Dry mass of non‐mycorrhizal plants was significantly higher at the low salinity for inland plants and at the intermediate salinity for coastal plants. Mycorrhizal roots had higher Na concentrations than did non‐mycorrhizal roots, but also had higher K and P concentrations, and thus maintained a high K/Na ratio. Leaf concentrations of Na were similar in mycorrhizal and non‐mycorrhizal plants. Excretion by salt glands may serve to maintain constant leaf Na concentrations. Stomatal conductances were the same for mycorrhizal and non‐mycorrhizal plants at all salinities. While mycorrhizae had little effect on D. spicata in this short‐term greenhouse experiment, a full evaluation might require long‐term field observations.
NADH CYTOCHROME C REDUCTASE ACTIVITY ASSOCIATED WITH A MEMBRANE FRACTION FROM PROTEIN BODIES OF LUPINUS ANGUSTIFOLIUS COTYLEDONS
Authors: PLANT A. R. , MOORE K. G.
Published: May 2006

Protein bodies (PBs) were isolated from germinating seeds of Lupinus angustifolius L. (cv. New Zealand Bitter Blue) by centrifugation in an isotonic medium. A membrane vesicle fraction was isolated from the organelle after solubilization of the protein matrix and found to have an associated NADH cytochrome c reductase. The reductase had a broad alkaline pH optimum and NADH was the favoured electron donor (Km=11.0 μM) whilst ferricyanide, dichlorophenol indophenol and cytochrome c were effective as electron acceptors. Cations were found to enhance (NH4+, Li+, Na+, K+, Rb+, Cs+, Mg2+) or decrease (Ca2+, Sr2+) the activity. Inhibitor studies enabled the partial characterization of the PB membrane NADH cytochrome c reductase and suggested that it was of a microsomal rather than mitochondrial type.
SIEVE ELEMENTS IN THE FUCALES
Authors: MOSS BETTY L.
Published: May 2006

Medullary filaments from the thalli of most of the British species of brown seaweeds belonging to the Fucales have been examined with both scanning and transmission electron microscopy (SEM and TEM). The end walls of each cell in the filament are in the form of a sieve plate. The pores, each 0.1 μm or less in diameter, are irregular in size, shape and distribution across the sieve plate. Through these small pores there is continuity of the cytoplasm. The medullary filaments provide an anatomical system throughout the thallus through which translocation can take place.
COMPARATIVE ULTRASTRUCTURAL STUDY OF THE DEGRADATION IN SOIL OF ISOLATED CUTIN FROM ILEX LEAVES AND MALUS FRUIT
Authors: MACNAMARA O. C. , BEAKES G. W. , DICKINSON C. H.
Published: May 2006

Cutin was dewaxed and removed from leaves of Ilex aquifolium L. (holly) and fruits of Malus pumila Mill, (apple) by a combination of chemical and enzymic techniques. Discs of cutin were then buried in soil under field conditions, retrieved at intervals and examined using electron microscopy. The ultrastructure of cutin before and after burial was compared with that of cuticle of intact holly leaves and apple fruits. Apple cutin was extensively eroded after being buried for 12 months, but neither apple nor holly cutin was completely degraded even after 2 years in soil. The significance of polysaccharide fibrils embedded in the cutin is discussed in relation to the patterns of cutin degradation which were observed and to the distribution of microorganisms in the decaying cutin.
SECRETION AND REDISTRIBUTION OF CHLORIDE IN THE DIGESTIVE GLANDS OF DIONAEAMUSCIPULA ELLIS (VENUS'S FLYTRAP) UPON SECRETION STIMULATION
Authors: REA P. A. , JOEL D. M. , JUNIPER B. E.
Published: May 2006

The localization of Cl− in the digestive glands of Dionaea muscipula Ellis (Venus's Flytrap) was studied by the AgCl precipitation technique. From these studies, the digestive cycle of Dionaea is considered to comprise two phases: a preparatory and a secretory phase. During the preparatory phase which ensues within 15 min of the start of stimulation, only the head cells of the gland accumulate Cl−. After about 5 h of stimulation, the vacuoles of the head cells appear to have undergone fragmentation. During the succeeding 2 h the head cells lose most of their Cl− accumulations and, at about the same time, Cl− appears in their outer walls. During the secretory phase, the onset of which can only be demonstrated after about 17 h of stimulation, Cl− can be seen in the endodermoid and basal cells of the digestive glands. At the end of the digestive cycle and during the time between the first and subsequent cycles only the basal cells show large amounts of Cl−.

The Cl− that is redistributed is shown to be of endogenous origin and the results are discussed with respect to the functional anatomy of the gland complex.
PLASTIDS IN THE ROOTS OF PHASEOLUSVULGARIS
Authors: WHATLEY J. M.
Published: May 2006

In roots of Phaseolus vulgaris plastid development takes place from the apical meristem both upwards into the root proper and downwards into the root cap. The maximum state of plastid development seems to be achieved in the cortical cells of that part of the primary root associated with mature root hairs. However in these cortical cell plastids the thylakoid system is very limited in extent and no true prolamellar bodies are formed. Farther from the apex of the root proper, in the zone of mature lateral roots, the plastids appear to have undergone dedifferentiation and to have lost whatever thylakoids they once contained. Both the rate of plastid development and the patterns of production of ancillary plastid structures, including starch and membrane–bound bodies, vary in different cell files. The differential distribution of these and other plastid features are summarized in the accompanying diagrams.
THE RELATION OF DIEL PATTERNS OF CELL DIVISION TO DIEL PATTERNS OF MOTILITY IN THE SYMBIOTIC DINOFLAGELLATE SYMBIODINIUM MICROADRIA TICUM FREUDENTHAL IN CULTURE
Authors: FITT W. K. , TRENCH R. K.
Published: May 2006

Frequency of binary fission in cultures of three strains of the symbiotic dinoflagellate Symbiodinium microadriaticum, isolated from the anemones Aiptasia tagetes, Heteractis lucida and the jellyfish Cassiopeia xamachana, was related to their diel patterns of motility. Under a 14:10 h light:dark cycle, karyokinesis, cytokinesis and motility occur diurnally. The highest frequency of cytokinesis preceded highest motility by 4 to 7 h. Karyokinesis preceded cytokinesis by 1 to 5 h. Generally, the ratio of number of dividing cells to the number of motile cells recorded in exponentially growing cultures was 1:2, suggesting that two motile cells arise from one newly divided zooxanthella. No motile cells were seen in stationary cultures. Algae grown at high irradiance (180/μE m−2 s−1) had higher growth rates and higher levels of motility than those grown at lower irradiance (15 μE m−2 s−1).

Under constant light or dark conditions, patterns of cytokinesis and motility were circadian. In darkness the rhythm tapered out after about 1 week. The patterns were evident for up to 7 days in constant dim light, but tended to dampen out with time.

These results suggest that current views of the life cycle of S. microadriaticum need to be modified, and we propose some alternatives which are consistent with our observations.
THE ECOLOGICAL INTERPRETATION OF FINE RESOLUTION POLLEN RECORDS
Authors: GREEN D. G.
Published: May 2006

Preserved pollen records with small intersample time intervals contain information about many processes in plant population and community ecology. A general approach to the ecological interpretation of these records includes the use of time series statistics, indices that reflect population or community dynamics and models of relevant ecological and sedimentological processes. While the problems inherent in traditional pollen analysis remain, the larger data sets generated by close‐interval sampling make it possible to filter out more sampling ‘noise’ and to obtain a stronger ecological ‘signal’.
A MODIFIED FIELD VERSION OF THE WINKLER DETERMINATION OF DISSOLVED OXYGEN FOR TESTING REMOTE SOURCES OF WATER
Authors: WRIGHT R. C.
Published: May 2006

Summary

A modification of a simple field method (Drew and Robertson, 1974) for the Winkler determination of dissolved oxygen is described. The modification, involving the addition of sulphuric acid and sodium azide as preserving agents rather than the precipitation of manganese hydroxides in the field, gives more accurate results when samples have to be stored before completion of the determination.