bluuebunny/crossref_metadata_2025_split huggingface dataset:
ORIGIN OF REDUCTANT FOR REDUCTION OF NITRATE AND NITRITE IN RICE AND WHEAT LEAVES IN VIVO
Authors: RAMARAO C. S. , SRINIVASAN  , NAIK M. S. 
Published: May 2006

SUMMARYMalonate inhibited completely anaerobic dark reduction of nitrate in rice leaves and the inhibition was reversed by fumarate. Under dark anaerobic conditions l4CO2 evolution from endogenously labelled substrates was dependent on nitrate reduction. When nitrate reduction was inhibited by tungstate or cyanide, 14CO2 evolution was inhibited and conversely, when 14CO2 evolution via the citric acid cycle was inhibited by malonate, nitrate reduction was inhibited. These results suggest a mitochondrial origin of NADH for nitrate reduction and this suggestion was confirmed by following the evolution of 14CO2 from endogenous substrates, mostly organic acids, labelled in darkness. In comparison with the reduction of nitrite in light, the dark aerobic reduction of accumulated nitrite was very slow and commenced only after a time lag of 20 min. This could be a detoxification mechanism for the removal of nitrite which does not normally accumulate in the leaves under natural conditions. NADH acted as a physiological reductant for dark aerobic nitrite reduction.
ULTRASTRUCTURE AND ELECTRON‐PROBE MICROANALYSIS OF THE METACHROMATIC VACUOLAR GRANULES OCCURRING IN TAXUS MYCORRHIZAS
Authors: STRULLU D. G. , GOURRET J. P. , GARREC J. P. , FOURCY A. 
Published: May 2006

SUMMARYNumerous metachromatic vacuolar granules occur in the hyphae of the fungal symbiont of Taxus baccata mycorrhizas. These granules exist in the trunks and in proliferating arbuscules but they are absent in lysed arbuscules. Direct microanalysis with an electron probe shows that they have a high phosphorus and calcium content. Potassium and magnesium are also present but in lesser quantities. The concentration of phosphorus and calcium is higher in the granules than in the light part of the vacuoles. The concentration of phosphorus also is higher in the granules than in the nuclei of the root cells and the concentrations of calcium are greater than those measured in the pecto‐cellulosic wall of root cells. The role of calcium in the metabolism of phosphorus within the tissues of mycorrhizas still remains unknown.
CELL PROLIFERATION IN ECTOTROPHIC MYCORRHIZAS OF FAGUS SYLVATICA L.
Authors: CLOWES F. A. L. 
Published: May 2006

SUMMARYThe organization of the meristem and rates of cell proliferation in its regions have been investigated by continuous labelling of DNA and stathmokinetic experiments. Mycorrhizas bearing intact fungal sheaths and those in which the apices had grown through the sheaths were compared with uninfected roots.Despite low overall rates of mitosis the restricted meristems of mycorrhizal roots have quiescent centres of non‐cycling cells, the numbers of which fluctuate periodically. At one time the quiescent centre may comprise only the cells at the pole of the stele, at others these plus from one to seven tiers of axial cells belonging to the cortical complex distal to the stelar pole. This flux in cell cycling forces an exchange in roles between cortical cells and cap initials which produces further changes in the organization of planes and rates of cell division.Roots which have escaped from the fungal sheath have higher rates of mitosis and larger meristems than those with intact sheaths, but the cap meristems of the latter contribute over a quarter of the total production of cells by the whole apex compared with a much smaller fraction in escaped roots. The fungal sheath must therefore contend with the production of as many as 50 cap cells per day and this problem is discussed.
EFFECT OF CALCIUM ON THE UPTAKE AND TOXICITY OF LEAD IN HORDEUM VULGARE L. AND FESTUCA OVINA L.
Authors: GARLAND C. J. , WILKINS D. A. 
Published: May 2006

SUMMARYThe effect of increasing calcium concentration on root growth and the uptake of lead from solutions of lead nitrate, by both barley seedlings and lead‐tolerant and non‐tolerant plants of Festuca ovina, are described. Lead uptake into the roots of all plants declined linearly with the logarithm of increasing calcium nitrate concentration up to 12.72 mM. Root extension growth in each lead solution increased as calcium concentration was raised, and this increase was greater than could be accounted for by the diminishing lead uptake; a second influence of calcium may thus be indicated. The regression of root growth, or tolerance index, on root lead content may be a useful indicator of sensitivity to the metal.
ECO‐PHYSIOLOGICAL ASPECTS OF INTER‐SPECIFIC AND SEASONAL VARIATION IN NITRATE UTILIZATION IN THE GENUS AGROSTIS
Authors: OSBORNE B. A. , WHITTINGTON W. J. 
Published: May 2006

SUMMARYNitrate utilization, as judged by dry matter production and nitrate reductase activity, was examined in species of the genus Agrostis and compared with species of Lolium and Poa. A. setacea had the lowest ability to utilize nitrate which correlated with its restricted ecological distribution in areas of low nitrate availability. In contrast, A. tenuis which may also be found in low nitrate sites, exhibited a higher nitrate reductase activity but lower dry matter production than the species A. stolonifera and L. multiflorum, both of which are characteristic of sites with higher nitrate availability. A high potential to utilize nitrate may be important in low nitrate areas subjected to marked fluctuations in supply. Correlations between nitrate utilization and growth were, in general, non‐significant and often negative. The results suggest that the efficiency of incorporation of reduced nitrogen into plant structure may bring about differences between species in the production of dry matter. Significant variations between species and response to nitrate were found in relation to the time of year. Maximum enzyme activities were found during the winter months with little change, after a drop in activity in the early spring, during the growth period. The peaks in activity found may not represent nitrate utilization but rather the induction of high levels of enzyme with little subsequent reduction of nitrate. Variation in soil pH did not modify the seasonal pattern and had little overall effect on either nitrate utilization or dry matter production although significant differences were found between species in both of these factors.
LONG‐DISTANCE POLLEN IN LATE WISCONSIN QUANTITATIVE ANALYSIS*
Authors: BIRKS H. J. B. 
Published: May 2006

SUMMARYIn Late Wisconsin sediments of Minnesota there occur fossil pollen and spores of certain taxa that are unlikely on ecological or phytogeographical grounds to have grown in Minnesota at that time. Long‐distance dispersal is believed to be the cause. The occurrences of 21 such types in three sites in Minnesota are analyzed statistically. Contingency‐table analysis suggests that some types occur together more commonly or more rarely than would be expected by chance. Principal co‐ordinates analysis similarly reveals groups of taxa whose pollen commonly occur together in time.The patterns within the series of occurrences, when viewed as point processes, are characterized by the techniques of statistical analysis of series of events. These analyses show that the series of occurrences ofAcer saccharum, Carya, Celtis occidentalis, Juglans cinerea, Platanus occidentalis, and probablyA. saccharinum‐typeandTilia americanapollen all have statistically significant trend and that their rates of occurrence are higher between 8300 and 10200 B.P.Athyrium filix‐feminaspores show a higher rate of occurrence between 20500 and 12000 B.P. The series of occurrences of all the other pollen types accord with a trend‐free renewal process. The series ofAcer negundo, Iva ciliata‐type, I. xatithifolia‐type, Morus rubra, andSarcobatus vermiculatuspollen are long enough to permit more detailed analysis. All these series appear to reflect a homogeneous Poisson process with random occurrences in time.Hypotheses to explain these patterns are discussed in terms of migration and population expansion to the south and east of Minnesota and of changing atmospheric circulation patterns during the Late Wisconsin. The need for more detailed series of occurrences is emphasized.
OVULE DEVELOPMENT INORNITHOGALUM CAUDATUM(LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION
Authors: TILTON VARIEN R. , LERSTEN NELS R. 
Published: May 2006

SUMMARYOrnithogalumovules are crassinucellate, and the nucellar epidermis forms a nucellar cap which is secretory. The nucellus accommodates archespore and megaspore mother cell expansion by a concurrent increase in its size. It accommodates functional megaspore and megagametophyte expansion by simultaneously undergoing growth and partial degeneration. Nucellar degeneration is centrifugal and appears to be an autolytic process rather than a result of mechanical pressure from the growing megagametophyte. Megagametophyte development is of thePolygonumtype. Mitotic divisions of the functional megaspore and its daughter cells are characterized by a perinuclear distribution of organelles. Some starch is stored in the micropylar end of the nucellus, but the majority is stored in the chalazal end around the hypostase. A strand of cytoplasm extends between the egg apparatus and antipodals. The micropylar polar nucleus moves across the central cell's vacuole in this strand to reach its mate. Antipodals initially are vacuolate but later fill with dense cytoplasm and numerous starch grains. Preliminary evidence from light microscopic investigation indicates a thin layer of wall material surrounds the egg apparatus. However, around the chalazal end of the egg this layer may be disjointed islands of wall material rather than a continuous wall. Synergid cytoplasm contains an abundance of organelles and a large filiform apparatus (FA) projects into it. In addition to the FA, synergid walls have a knobbed ingrowth around their micropylar end. We propose that the antipodals and central cell function initially as storage cells for nutrient reserves and later as nurse cells for embryo and endosperm whereas the synergids function as secretory cells which produce an agent(s) which attracts pollen tubes and, via the filiform apparatus, as cells which receive the pollen tube.
OVULE DEVELOPMENT INORNITHOGALUM CAUDATUM(LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION
Authors: TILTON VARIEN R. 
Published: May 2006

SUMMARYThe chalazal end of the egg projects beyond the synergids while the micropylar end is in contact with the nucellar epidermis. The egg nucleus and nucleolus are large and, along with most of the cytoplasm, are located chalazally while a large vacuole occupies the micropylar end. The egg cell wall is attenuated chalazally but, based on preliminary light microscope observations, it does appear to surround the entire cell in some cases. The synergids each have a large chalazal vacuole with the majority of their cytoplasm in the micropylar half of the cell. Nuclei and nucleoli are large and other organelles are numerous. Plastids and endoplasmic reticulum (ER) are more numerous chalazally while mitochondria appear to be evenly distributed. Filiform apparatus (FA) formation occurs late in synergid maturation. The FA is large, well developed, and is surrounded by a vacuolate zone. Various sized vesicles with fibrillar or flocculent contents occur within the FA. The FA stains for both protein and RNA in addition to carbohydrate which is the dominant component. The synergid walls have a knobbed ingrowth around the periphery of their micropylar end. Neither egg nor synergids store any metabolites.This information, coupled with overwhelming evidence from the literature reviewed, has led me to conclude all angiosperm synergids are active in synthesizing and, via the FA, in secreting a substance(s) which influences the final phases of pollen tube growth. Movement of materials into a megagametophyte via the FA seems unlikely, but if it does occur, it is probably an inconsistent feature and only of trivial consequence.
CESSATION OF VASCULAR ACTIVITY CORRELATED WITH APOSPOROUS DEVELOPMENT IN PTERIDIUM AQUILINUM (L.) KUHN
Authors: SHEFFIELD E. , BELL P. R. 
Published: May 2006

SUMMARYApospory has been found to occur on leaves of Pteridium aquilinum still attached to parent plants, although previous work had indicated that detachment was a prerequisite for regeneration. It is clear, however, that such recrudescence occurs only in leaves where active vascular flow has ceased, and which are also in contact with a moist surface. It is proposed that the cessation of an active vascular supply has an inductive effect. The inability of mature fronds to behave aposporously is attributed to the presence of a thick cuticle external to the superficial cells, which is thought to prevent the exchange of metabolites between frond and medium.
THE KEEL PETAL COLOUR POLYMORPHISM OF LOTUS CORNICULATUS L. IN SCOTLAND
Authors: ABBOTT RICHARD J. 
Published: May 2006

SUMMARYIn a survey of the keel petal colour polymorphism in Lotus corniculatus L. conducted at 61 coastal and inland locations in Scotland, there was a major difference in morph frequency between populations in the west and those in the east and central areas, with the dark keel being at low‐relative frequency at most western locations. When figures for east and central Scotland were considered, there was a slight but statistically significant increase in the dark keel morph with increasing latitude, a pattern which was not found in Scotland as a whole.
THE ELM DECLINE: THE DEPLETION OF A RESOURCE
Authors: GARBETT GEOFFREY G. 
Published: May 2006

SUMMARYA high‐resolution pollen diagram of the elm decline at Ellerside Moss, previously studied by Oldfield and Statham (1963), was constructed by freezing the peat core and taking samples at 02 cm intervals using a sledge microtome. Consecutive samples were counted across the most critical part of the diagram.Ivy pollen was used as an indicator of standing dead trees, but this did not provide any evidence to support the idea that disease was a major factor contributing to the elm decline. The diagram does, however, provide evidence of leaf‐fodder gathering involving elm, oak and lime during the initial stage of the elm decline followed by a period when elm only was exploited. It is argued that this resulted in a near destruction of the elm and thus initiated the partial clearance of the elm‐dominated regions and later the production of small temporary clearances throughout the forest.Using the available evidence from a number of disciplines an interpretation of the cultural and economic basis of the elm decline is offered in the light of the present findings. It is seen primarily as an over‐exploitation of a resource.
THE OCCURRENCE AND SIGNIFICANCE OF DISPENSABLE PROTEINS IN PLANTS
Authors: ADAMS C. A. , RINNE R. W. 
Published: May 2006

SummaryPlants produce many different kinds of proteins. Enzymes, ribosomal proteins and storage proteins have clearly defined, ubiquitous, physiological roles and are indispensable for normal plant growth. Other proteins, such as urease, β‐amylase, lectins, proteinase inhibitors and some proteinases, have a varied distribution and no clear physiological role. These proteins are dispensable in that some plant species manage without them, or with only extremely low levels, whereas other species accumulate significant quantities of the proteins. Dispensable proteins all have defined biological activities, but in most cases these activities do not explain their physiological role. Urease is able to degrade urea, but many seeds contain little or no urea. Beta‐amaylase only attacks gelatinized starch, not intact starch granules. Lectins agglutinate red blood cells. Trypsin inhibitors specifically inhibit a proteolytic enzyme from animals. These proteins may fulfill a non‐specific role as part of the cellular protein complement and therefore could presumably be replaced by other proteins in other species. The production of dispensable proteins may also be another aspect of general plant secondary metabolism which already encompasses the biosynthesis of amino acids, amines, lipids and carbohydrates. Because they are dispensable, these proteins possibly could be manipulated through plant breeding or epigenetic procedures, without accompanying deleterious side effects. The presence of large quantities of these proteins or their absence appears to have little phenotypic effect on a particular species.
PEROXIDASE ISOZYMES IN RELATION TO DEVELOPING WATER DEFICITS IN TWO ZEA MAYS L. CULTIVARS
Authors: THAKUR PARTAP S. , SINGH GURMIT , RAI VINAY K. 
Published: May 2006

Summary Zea mays L. cultivars Agati‐76 and Vijay have been scanned for peroxidase isozyme changes under varying water stress. Water stress did not induce the synthesis of any new isozyme in either cultivar, but one band with low electrophoretic mobility (RF 0·29) disappeared in leaves of the susceptible cv. Vijay. A significant inhibition of enzyme activity on a protein basis was observed in both cultivars, but to a greater extent in the susceptible cultivar, Vijay. Enhanced enzyme activity on a fresh wt basis was recorded in cv. Agati‐76 with increasing stress. Peroxidase activity declined in stressed roots of both cultivars. A highly significant negative correlation was found between enzyme activity and water saturation deficit. The possible physiological role of peroxidase in drought resistance is discussed.
AN EXPERIMENTAL INVESTIGATION OF INHIBITION OF PHYTOPLANKTON PHOTOSYNTHESIS AT LAKE SURFACES
Authors: BELAY AMHA 
Published: May 2006

SummaryPhotoinhibition of photosynthesis in natural populations of phytoplankton has been investigated in situ in Windermere, English Lake District, and Llyn Padarn, North Wales. The extent of inhibition was found to be directly related to irradiance and to increase with time of exposure. Inhibition was increased when the ultra‐violet component of sunlight was not removed by enclosure of samples in glass bottles. Supersaturation with oxygen to the extent likely to occur in the surface waters of lakes did not appear to be an important factor increasing photoinhibition. Experiments on the effect of nutrient deficiency were inconclusive. It was demonstrated that populations could recover from severe photoinhibition within periods of less than 24 h and that when the water column is stable the population in the surface water adapts to become more resistant to photoinhibition.
PHOSPHATE ACCUMULATION IN FAGUS MYCORRHIZAS
Authors: HARLEY J. L. , MCCREADY C. C. 
Published: May 2006

SummaryThe quantities of polyphosphate formed in beech mycorrhizas during uptake of KH232PO4 were estimated after extraction with cold TCA and KOH. Over an absorption period of 19 h the proportion of absorbed phosphate converted into polyphosphate increases with external phosphate concentration from 22% in 0·16 mM to 44% in 0·98 mM KH2PO4. Uptake from 64 mM phosphate results in 39 % being accumulated as polyphosphate during 2·5 h. Calculations based on the percentage of phosphate accumulated in the sheath, obtained by dissection, show that a large fraction of the phosphate in the fungus is accumulated as polyphosphate.
ABUNDANCE OF MYCORRHIZAS AND ROOT‐SURFACE MICRO‐ORGANISMS OF PLANTAGO LANCEOLATA IN RELATION TO SOIL AND VEGETATION: A MULTI‐VARIATE APPROACH
Authors: NEWMAN E. I. , HEAP ALISON J. , LAWLEY R. A. 
Published: May 2006

SummaryAt 40 sites in England and South Wales, mostly in grassland, features of the soil and vegetation were measured. Three Plantago lanceolata individuals were collected from each site, nitrogen, phosphorus and potassium concentrations in the leaves were measured, and the abundance of mycorrhizal infection and of fungi and bacteria on the root surface was determined by microscopic examination of stained root segments. The results were subjected to multiple regression analysis.Mycorrhizal abundance was most significantly related to vascular plant cover (negatively) and Plantago leaf length (positively), bacteria to soil organic matter (positively), fungi to cover of non‐grasses (positively) and leaf phosphorus concentration (negatively). The ecological interpretation of these relationships is discussed.
REGULATION OF PLANT CELL GROWTH: THE CHANGING PERSPECTIVE
Authors: HANSON J. B. , TREWAVAS A. J. 
Published: May 2006

SummaryThis article outlines the main features of growth regulation by auxin and places them side‐by‐side with the physiological properties of fusicoccin. The fundamental role of the plasma membrane located H+/K+ ATPase in growth responses is examined and the information about this enzyme briefly reviewed. The effects of wounding on the activity of this enzyme are detailed and it is concluded that growth in excised tissue segments ceases not from lack of hormone but from impairment of ATPase function. An additional conclusion of major importance for hormone studies is reached; that is, that the experimentally‐realized reactivation of growth by auxin in excised tissues represents largely an accelerated recovery from injury. Furthermore the calmodulin/Ca2+ system may be an essential intermediary in this recovery step. Finally, the major area of ignorance, predisposition to growth, is considered.
TOXICITY OF GLYPHOSATE APPLIED TO ROOTS OF BARLEY SEEDLINGS
Authors: PENN D. J. , LYNCH J. M. 
Published: May 2006

SummaryThe toxicity of glyphosate to barley seedlings when applied to the entire root system in water culture was such that at pH 7.5 the minimum lethal dose was around 15 mg l−1; 3 mg l−1 caused a 23 % decrease in shoot dry wt. Barley and wheat seedlings did not differ significantly in susceptibility. The growth of seminal roots with a short (5 mm) length of the tip exposed to 500 mg l−1 glyphosate in culture solution was decreased by about 50%. Unless a large amount of the root system of an establishing crop came into contact with the rhizomes of couch grass which had been treated with glyphosate, herbicide release by the rhizomes seems likely to be unimportant.
ROOT NODULES IN THE GENUS COLLETIA
Authors: BOND G. , BECKING J. H. 
Published: May 2006

SummaryFollowing the earlier reported detection of root nodules on a species of Colletia growing in the Glasgow Botanic Gardens, the authors' enquiries have revealed that Colletia species are nodulated in some other botanic gardens, both in Europe and elsewhere. Cytological study of the nodules under the electron microscope shows that the endophyte is a procaryotic, actinomycete‐like organism consisting of septate, branching hyphae which are 0.37 to 0.53 μm in diameter and form terminal spherical vesicles 2.0 to 2.5 μm in diameter. The vesicles are internally sub‐divided and lie peripherally within the host cell. The endophyte is enclosed within a thin layer (or capsule) of material which judging by previous studies of other non‐legume nodules consists of carbohydrate‐related substances laid down by the host cytoplasm. Data from long‐term growth trials and acetylene assays show that Colletia nodules are nitrogen‐fixing and capable of satisfying the nitrogen‐needs of the host plant. Of the five genera of the Rhamnaceae that have so far been found to be nodule‐bearing, four (namely Colletia, Discaria, Trevoa and Talguenea) are in the tribe Colletieae, while the fifth genus (Ceanothus) is placed elsewhere in the family by taxonomists. A very similar situation exists in the Rosaceae as regards the distribution of nodulating genera and species. It is concluded that in these families the habit of symbiosis with a nitrogen‐fixing actinomycete probably arose, in some instances, prior to the establishment of now‐existing genera, but in others at a later stage. This conclusion is consistent with the belief that nodule symbioses were initiated in an earlier era when plants in general were subject to nitrogen stress.