bluuebunny/crossref_metadata_2025_split huggingface dataset:
PHOSPHOLIPIDS AND PLANT MEMBRANE PERMEABILITY
Authors: Simon E. W. 
Published: May 2006

SUMMARYCurrent views on membrane construction are presented as a basis for discussing certain modifications of structure that may render membranes leaky, allowing solutes to diffuse from them. Biophysical experiments on dehydrated membranes indicate that, when their water content is reduced below 20%, they no longer adopt the lipid bilayer conformation. When dry seeds, spores or lichens are placed in water, soluble cell constituents leak from them for a few seconds or minutes until membrane integrity is re‐established; the same may apply also to the liberation of solutes from pollen grains. Moreover, there are indications that ‘dry’ in this context means having less than about 20% water.Some plants are sensitive to chilling, their tissues becoming leaky when exposed to temperatures between 0 and 10°C. This chilling‐induced leakage, attributed to a phase change in all the phospholipids of which the membrane is composed occurs at a slightly lower temperature than the change in the activation energy of membrane‐bound enzymes.At senescence, leaf tissues become leaky and may eventually dry out. So much phospholipid disappears from senescing cotyledons of cucumber that there is no longer sufficient to fabricate complete and intact membranes around the cells. Treating cucumber cotyledons with iodoacetate also causes a loss of phospholipids, allowing solutes to leak out of the cells.It is possible that exposing seeds or mature plant tissues to oxygen at pressures of 1 or more atm renders them leaky because of lipid peroxidation.
REGENERATION IN ROOT CUTTINGS OF TARAXACUM OFFICINALE I. THE NATURE AND LEVELS OF ENDOGENOUS HORMONES
Authors: BOOTH A. , SATCHUTHANANTHAVALE R. 
Published: May 2006

SUMMARYThe levels of auxins, cytokinins and gibberellins in extracts of fresh roots of Taraxacum were estimated by bioassay after chromatography. Auxin activity, largely confined to a single zone on chromatograms, had the RF and chromogenic properties of IAA and ranged from 45 to 85 μg kg‐1 fresh weight of roots (in IAA equivalents). Similar auxin activity was found in root diffusates collected in agar gel. Most of the cytokinin activity was present in the zone RF 0.6‐0.8 on chromatograms developed in a n‐butanol: acetic acid: water solvent. The cytokinin was not characterized but its level in kinetin equivalents was in excess of 500 μg kg‐1 fresh weight of roots. Gibberellin activity was of the order of 1 μg kg‐1 in GA3 equivalents.
AGEING IN EXCISED ROOTS OF TOMATO II. THE EFFECTS OF GROWTH HORMONES ON AGEING IN GLUCOSE
Authors: WESTON GEOFFREY D. 
Published: May 2006

SUMMARYCulture of roots for 7 days in 1.5% glucose medium drastically enhanced ageing on subsequent subculture in 1% sucrose medium. NAA, GA, BA, ABA and ethylene enhanced the ageing of roots cultured in 1% sucrose medium, but counteracted the effect of pretreatment in 1.5% glucose. Reduction of growth during the glucose pretreatment by low temperature counteracted the effect of glucose on ageing; in contrast, reduction of growth by a high concentration of mannitol did not affect ageing. Exposure of roots to glucose for 72 h was required to produce the effects of glucose. It is postulated that cell division may be required during the glucose treatment for glucose to affect ageing.
FURTHER STUDIES ON POLLINATION ECOLOGY IN FICUS SYCOMORUS II. POCKET FILLING AND EMPTYING BY CERATOSOLEN ARABICUS MAYR
Authors: GALIL J. , EISIKOWITCH D. 
Published: May 2006

SUMMARYFilling of pockets with pollen by the agaonid wasp Ceratosolen arabicus Mayr (Chalcidoidea, Hymenoptera) was studied in Ficus sycomorus L. at Magadi, Kenya. The phenology of the fig during the male phase (D) was observed in detail and various techniques were devised in order to ensure the normal behaviour of the wasps in spite of the bisection of the fig and the strong illumination necessary for carrying out the observations. It was found that in fig‐halves tightly enclosed with cellophane paper during the second morning of the male phase, the emerging wasps filled their pockets with pollen from anthers previously detached by the male wasps. It was established that the cutting of anthers is a separate, specific action and not merely a byproduct of the tunnelling of the syconial wall that takes place afterwards. In the filling act itself, the role of the combs–rows of stiff bristles along the inner margin of each foreleg coax was established. Pollen was lifted by the arolia of the forelegs from the open anthers to the underside of the thorax and shovelled from there by the coxal combs into the thoracic pockets which gaped widely due to the bending of the body.An analysis of the responses of the wasps to various environmental conditions leads to the conclusion that the size of the cavity is a critical factor in the behaviour of the wasps in the fig of F. sycomorus. The possible role of light for pocket filling in the subdued illumination of the intact fig cavity is discussed.
EVIDENCE FOR THE PRESENCE OF A ‘FACTOR’ IN ELYSIA VIRIDIS WHICH STIMULATES PHOTOSYNTHATE RELEASE FROM ITS SYMBIOTIC CHLOROPLASTS
Authors: GALLOP ANGELA 
Published: May 2006

SUMMARYTissues of Elysia viridis contain a ‘factor’ which stimulates release of fixed 14C from isolated Codium chloroplasts and also from the symbiotic algae of Anemonia sulcata. This ‘factor’ appears to be thermolabile, non‐particulate, and only occurs in effective amounts in the chloroplast‐containing tissues of the animal. So far, attempts to mimic the action of Elysia homogenates by varying the pH of the medium, or by adding Codium homogenates, fructose 1,6 di‐phosphatase or‘2C‐glucose to it, have failed.
LIPID METABOLISM IN LEAVES OF TUSSILAGO FARFARA DURING INFECTION BY PUCCINIA POARUM
Authors: LÖSEL D. M. , LEWIS D. H. 
Published: May 2006

SUMMARYFollowing infection by Puccinia poarum, there is an accumulation of lipid in leaf tissue of Tussilago farfara. Most of this increase is in the fungus, which accounts for nearly half of the dry weight of mature aecial pustules. While the lipid content of infected tissue rises to more than three times that of healthy leaves, that of the uninfected parts of diseased leaves is reduced by one‐third. Aerial pustules accumulate a high proportion of neutral lipid, particularly triglycerides and fatty acids. As infection progresses, a loss of chloroplast glycolipids and phosphatidyl glycerol is accompanied by increases in phosphatidyl ethanolamine and phosphatidyl choline and the formation of phosphatidyl serine, which is not readily detectable in healthy leaf tissue. The lipid changes following rust infection have been compared with those of senescing Tussilago leaves.Both neutral lipids and phospholipids incorporated more photosynthetically assimilated C in rust‐infected tissue than in healthy leaves. Greatest differences were in free fatty acids, triglycerides, phosphatidyl ethanolamine and phosphatidyl choline with significant increases also in sterols, phosphatidyl inositol and phosphatidyl serine. Whereas three‐quarters of the activity incorporated from 14CO2 into lipid appears in the neutral lipids of diseased tissue, in healthy tissue these contain only one‐quarter.
A COMPARISON OF NEGATIVE RELATIVE GROWTH RATES IN SHADED SEEDLING
Authors: MAHMOUD A. , GRIME J. P. 
Published: May 2006

SUMMARYSeedlings of the shade‐tolerant species, Deschampsia flexuosa, were subjected to shade treatments under controlled conditions of daylength, temperature, irradiance, relative humidity and mineral nutrient supply. Dry matter production was compared with that of seedlings of the shade‐intolerant species, Agrostis tennis and Festuca ovina. The three species did not differ markedly with respect to their light intensity compensation points. A more promising explanation for the shade tolerance of Deschampsia flexuosa lies in the extremely low negative relative growth rates which seedlings exhibit at light intensities below the compensation point.
GROWTH CHARACTERISTICS OF THE‘ROGUE’TOMATO
Authors: CALVERT A. 
Published: May 2006

SummaryA faster than normal rate of leaf production in the rogue tomato leads to earlier flowering in summer. In winter, growth of the inflorescence is less than the normal, often resulting in abortion.In the rogue there is an early short‐term stimulation of growth of all axillary buds. This, together with a smaller leaf area and shorter internodes, creates the characteristic rogue appearance. In general, however, the pattern of axillary growth along the stem is similar in rogue and normal plants; an observation which provides little support for the theory that the rogue appearance is due to loss of apical dominance.Neither removal of the first two leaves nor IAA application influences the rate of leaf initiation in the rogue as it does in the normal, indicating the possibility that the rogue has a modified auxin control system.
PLANT GROWTH RESPONSES TO VESICULARARBUSCULAR MYCORRHIZA
Authors: HAYMAN D. S. 
Published: May 2006

SummaryLight and temperature greatly influenced the development of vesicular‐arbuscular mycorrhiza and growth of onions in a phosphate‐deficient soil. There were more large arbuscules and host growth was stimulated more with 25,000 lux than with 13,000 lux at 23° C and in a 14‐23° C diurnal cycle. At 14° C and 13,000 lux mycorrhiza caused no growth stimulation even in three low‐phosphate soils. At 18° C infection was much sparser in a 6 h daylength than in 12 and 18 h. Mycorrhizal Plants kept in daylengths of 6 h at 13,000 lux were 3.5 times heavier than their non‐inoculated controls. The effect of infection increased in longer daylengths and higher light intensities to 14.2 times the weight of controls with 18 h at 25,000 lux. The addition of soluble phosphate stimulated growth to the same extent as mycorrhizal inoculation did in the highest light conditions but phosphate stimulated growth more than did mycorrhiza under intermediate light conditions. The amounts of soluble carbohydrate in the roots of Plants given phosphate and in those that were mycorrhizal did not differ significantly, but there was more soluble carbohydrate in Plants growing in most light. Plants both with and without mycorrhiza contained much glucose, fructose, sucrose and an unidentified sugar with a low RF value, but there was no indication of fungal carbohydrates such as trehalose and mannitol.
TETRAD POLLEN GRAIN DEVELOPMENT AND STERILITY IN LESCHENAULTIA FORMOSA (GOODENIACEAE)
Authors: KNOX R. B. , FRIEDERICH E. 
Published: May 2006

SummaryPollen of Leschenaultia formosa R. Br. adheres as tetrads linked together on their radial walls by extensions of the bacular strands of sexine sporopollenin after release from the meiotic tetrad. Before release, the tetrads of microspores showed a thickened deposition of primexine polysaccharide on their radial walls, where only slight callose deposits were detectable.The onset of variable sterility in the tetrads was detected as early as the prevacuolate period after spore release. Sterile microspore protoplasts could not he plasmolysed and using the fluorochromatic reaction, showed leakage of fluorescein through the plasma membranes. Sterile grains showed considerable exine development and patterning, which continued until midvacuolate period, but the inner cellulosic intine, layer was absent. In the walls of fertile grains, the enzymic proteins, acid phosphatase and ribonuclease were located in the intine, as found previously with other pollens.
THE UPTAKE AND TRANSLOCATION OF 35SO2 IN SOY‐BEAN GLYCINE MAX VAR. BILOXI
Authors: GARSED S. G. , READ D. J. 
Published: May 2006

SummaryFeeding of specific leaves has been used to follow the uptake and translocation of 35SO2 in soy‐bean plants at the four‐leaf stage. The effect of leaf age and position on the translocation pattern have been examined and an analysis made of the distribution of radioactivity with time. The results are discussed with reference to data for movement of 14CO2 and foliar applied 35SO2‐4, and to the ecological implications.
THE RELATIONSHIP BETWEEN TEMPERATURE AND SEEDLING GROWTH OF TWO SPECIES WHICH OCCUR IN UPPER TEESDALE
Authors: ARNOLD SYLVIA M. 
Published: May 2006

SummarySeedlings of Plantago maritima L. and Kobresia simpliciuscula (Wahlenb.) Mackenzie were grown at 10, 14, and 18° C. Net assimilation rate and relative growth rate of Plantago seedlings increased with temperature, as did rate of leaf extension, and there was little delay in leaf emergence as temperature dropped from 18 to 10° C. Increase of temperature from 10 to 14° C had little effect on Kobresia seedlings, but growth increased significantly with a further rise to 18° C. Rate of leaf extension was unaffected by temperature but leaves grew for a shorter time, and emergence was greatly delayed at the lower temperatures. Increase in total leaf length with temperature was attributable to increase in number of leaves in Kobresia, and increase in average leaf length in Plantago. In both species successive leaves elongated at a similar rate, and temperature had no effect on leaf width. Growth responses are discussed in relation to temperature regimes measured in Teesdale.
DIFFERENCES IN XYLEM EXUDATION BY SEMINAL ROOTS OF LOLIUM VARIETIES
Authors: DUNLOP JAMES 
Published: May 2006

SummaryExudation by excised roots of eleven Lolium varieties has been studied. Data on the rate of potassium translocation, the rate of water movement through the roots, the concentration of potassium in the xylem exudate, the electrical potential gradient across the roots, and the electrochemical potential difference for potassium across the roots is reported. Each parameter showed significant variation among the varieties with only water flux grouped according to species. It is suggested that the variation in rate of potassium translocation can be attributed partly to differences in the rate of water movement through roots and partly to differences in the intensity of transport to the xylem.
ELECTRON MICROSCOPICAL STUDIES OF THE MICROFLORA OF ROOTS OF SAND DUNE GRASSES
Authors: Old K. M. , NICOLSON T. H. 
Published: May 2006

SummaryScanning and transmission electron microscopy were used to study microflora of roots of three species of sand dune grasses. Observations were made on the mucigel on intact epidermal cells and the colonization of sloughing superficial root cells by bacteria and actinomycetes. Thin sections of the same root samples showed that bacteria penetrated epidermal cells either by perforating the cell wall or by exploiting the middle lamella between adjacent cells as an avenue of entry. Cortical cells of all three species contained vesicular‐arbuscular endophytes. Several phases of the mycorrhizal association could be identified.
LEAKAGE DURING IMBIBITION, RESISTANCE TO DAMAGE AT LOW TEMPERATURE AND THE WATER CONTENT OF PEAS
Authors: SIMON E. W. , WIEBE H. H. 
Published: May 2006

SUMMARYThe extent of leakage from imbibing pea embryos depends on their initial water content, leakage being very low if the embryos already have a water content of 30% or more (water potential higher than −80 bars). Seeds that have reached this degree of hydration are killed by a 20‐min exposure to liquid nitrogen.
A THEORETICAL ANALYSIS OF THE CONTRIBUTION OF ALGAL CELLS TO THE ATTENUATION OF LIGHT WITHIN NATURAL WATERS I. GENERAL TREATMENT OF SUSPENSIONS OF PIGMENTED CELLS
Authors: KIRK J. T. O. 
Published: May 2006

SUMMARYA theoretical treatment of light attenuation within suspensions of phytoplankton, which takes account of the heterogeneous distribution of pigment in the system, is described. As a measure of the effect of canopy structure on light attenuation, a new parameter, the penetration coefficient (Pλ) is introduced, this being defined as the ratio of the downward monochromatic radiation flux at a given depth in the suspension to that within an equivalent solution of the algal pigments. A set of rules is established, applicable to cells of any shape or orientation, which characterizes the relationship between the penetration coefficient and the parameters of canopy structure (cell number, size, pigment composition etc.). A standardized procedure for calculating the spectral distribution of, and the vertical attenuation coefficients for, photo‐synthetically active radiation within model phytoplankton suspensions, is outlined.
A THEORETICAL ANALYSIS OF THE CONTRIBUTION OF ALGAL CELLS TO THE ATTENUATION OF LIGHT WITHIN NATURAL WATERS II. SPHERICAL CELLS
Authors: KIRK J. T. O. 
Published: May 2006

SUMMARYA theoretical treatment of light attenuation within natural phytoplankton suspensions, developed in a previous paper, has now been applied to model suspensions of green and blue‐green algal cells and colonies, in order to obtain a quantitative assessment of the effects of changes in the phytoplankton canopy structure on light attenuation within the system. It is shown that for green algae suspended in water in which effectively all the blue light is removed by dissolved yellow substances (gelbstoff) the light attenuation properties of the suspension are rather similar to those of an equivalent solution of algal pigments: this is because the individual cells have relatively low absorption values in the spectral region (545–655 nm) in which most of the transmitted light occurs. With blue‐green algae, which have a strong absorption in this region, there can be marked differences between the light attenuation properties of suspensions and of equivalent pigment solutions. The suspensions transmit substantially more photosynthetically active radiation than the solutions: the effect increases with cell/colony size, with algal concentration and with depth, and can amount to a difference of several‐fold. Values of vertical attenuation coefficients, and increments in attenuation coefficients per unit algal concentration, for the photosynthetic waveband have been calculated, and their dependence on pigment composition and cell/colony size is demonstrated. Calculations have also been carried out to show the relationship between the phytoplankton canopy structure, and the euphotic depth and maximum sustainable standing crop, of the suspension.
THE INFLUENCE OF LIGHT ON STOMATAL DENSITY IN THE TOMATO
Authors: GAY A. P. , HURD R. G. 
Published: May 2006

SUMMARYStomatal densities (stomatal number per unit leaf area) were determined on tomato plants grown at ‘high’ (100 W m−2) and ‘low’ (20 W m−2) light in a growth cabinet. The upper epidermis of a fully expanded leaf in low light had fewer than one stoma mm−2, whilst that in high light had thirty stomata mm−2. On the lower epidermis there were about eighty and 100 stomata mm−2 in low and high light respectively. Similar differences were observed on plants growing in natural light.Stomatal initiation is most active early in the development of the leaf and effects of light on initiation were greatest at this stage, being observable within 3 days of a change in light level. Since light influenced the rate and duration of all stages of leaf expansion, the final stomatal densities achieved under natural conditions varied with the light history of the leaf.Stomatal density reached a peak before the leaf had expanded to 10% of its final area. Stomatal initiation and stomatal density both decreased from then until leaf expansion ceased. Fully‐expanded leaves of plants grown continuously in the same environment had similar stomatal densities irrespective of their position on the plant.A quantitative relationship is described between stomatal density and leaf area during the growth of a leaf.
SOME ASPECTS OF TISSUE WATER RELATIONS IN THREE POPULATIONS OF EUCALYPTUS VIMINALIS LABILL.
Authors: LADIGES PAULINE Y. 
Published: May 2006

SUMMARYUsing the pressure bomb technique, measurements have been made of the tissue water relations of seedlings of three populations of Eucalyptus viminalis, and of adult shoots of trees from two contrasting sites, to facilitate an understanding of the physiological basis of intra‐specific variation in drought resistance.For both juvenile and adult material, the shoot water potential of the most drought resistant population declined most rapidly with decreasing water content. Estimates of the fraction of water in the cell walls at full turgor were also greatest for this population, averaging 0.36 for juvenile and 0.40 for adult material. Calculated values for the bulk modulus of elasticity of the walls were very variable, but tended to be higher, in adult than juvenile tissues.The results suggest that in dry habitats there has been selection for plants which, during temporary periods of drying, can maintain a water content above the critical level for cell damage. Differences between two very closely situated field populations emphasize the need to consider the role of edaphic as well as climatic factors in selection for drought resistance.
THE EFFECT OF SALT AND OSMOTIC STRESS ON THE RETENTION OF POTASSIUM BY EXCISED BARLEY AND BEAN ROOTS
Authors: NASSERY H. 
Published: May 2006

SUMMARYThe effect of different concentrations of NaCl, mannitol and CaCl2 on the retention of potassium ion by preloaded roots of barley, Hordeum vulgare, and bean, Phaseolus vulgaris, indicated that 50 mM NaCl had no effect on potassium loss, but 50 mM NaCl or more increased the rate of efflux. Barley roots appeared 10 be more sensitive to salt stress than bean roots since 100 mM NaCl caused 78% potassium loss over 6.5 h by barley as compared with 40% loss by bean roots. Mannitol up to 200 mM had no effect on the retention of potassium by barley roots but slightly increased the potassium loss from bean roots (26%). The results suggested that salt stress is more effective than osmotic stress in disrupting the membrane permeability and calcium ions can prevent the increased permeability caused by osmotic or ionic stress.
INHIBITION OF SEED GERMINATION UNDER LEAF CANOPIES IN ARENARIA SERPYLLIFOLIA, VERONICA ARVENSIS AND CERASTUM HOLOSTEOIDES*
Authors: KING T. J. 
Published: May 2006

SUMMARYThe germination of imbibed seeds of Arenaria serpyllifolia L., Veronica arvensis L. and Cerastium holosteoides Fr. is inhibited under two layers of Tilia×europaea L. leaves. The ecological significance of this phenomenon is discussed.
SOME ASPECTS OF HETEROSTYLY
Authors: YEO P. F. 
Published: May 2006

SUMMARYIt is suggested that the functional significance of each di/trimorphic structure in heterostyled flowers should be considered separately. The origin of the morphological and physiological components of heterostyly is discussed; it is suggested that the physiological incompatibility arose first and created conditions favouring selection of morphological differentiation. In this connection, the cases of Amsinckia and Narcissus tazetta are given special consideration. The restricted occurrence of tristyly is considered together with the distinctive syndrome of exserted sexual organs and sternotribic pollination in heterostyled plants. The need is emphasized to bear in mind constantly the functional aspects of heterostyly.
RADIOCARBON DATES FROM LATE‐DEVENSIAN DEPOSITS, NANT FFRANCON, CAERNARVONSHIRE
Authors: BURROWS C. J. 
Published: May 2006

SUMMARYTwo radiocarbon dates near the beginning and end of the Allerød interstadial (conventional pollen zone II) show that the timing for the event in the mountains of North Wales was similar to that elsewhere in Britain and Europe. The occurrence of a pre‐Allerød interstadial, almost certainly equivalent to the Bølling (conventional pollen zone Ib), is confirmed. Other sequences for the same period from lowland North Wales and elsewhere in Western Britain differ from the Nant Ffrancon sequence in that evidence for cooling between the Bølling and Allerød is missing, but some sequences from inland mountainous areas, or in Eastern Britain and the Continent are very similar to the Nant Ffrancon sequence.