bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rapid identification of genetic variation of ectomycorrhizal fungi by amplification of ribosomal RNA genes
Authors: HENRION B. , TACON F. LE , MARTIN F. 
Published: April 2006

SUMMARYThere is a clear requirement to develop sensitive methods for detecting denned isolates of ectomycorrhizal fungi within the complex microbial communities of natural ecosystems and reforestation sites. We present a method that permits the rapid identification of an ectomycorrhizal isolate using enzymatic amplification (polymerase chain reaction) of DNA extracted either from pure cultures or ectomycorrhizas. A set of oligonucleotide primers capable of amplifying full‐length nuclear 17S and 25S ribosomal RNA genes, together with the ribosomal internal transcribed spacer and intergenic spacer, have been designed and could be used for amplifying target sequences from a wide range of ectomycorrhizal genera. Length polymorphism in the amplified rDNA and restriction endonuclease analysis of nearly 6‐0 kbp of amplified rDNA provided useful criteria for the rapid typing of isolates from different genera and species. Restriction endonuclease analysis of amplified DNA from 26 isolates representing four species of Laccaria (L. bicolor, L. laccata, L. proxima, L. tortilis) yielded up to 20 scored RFLPs and revealed interspecific and intraspecific polymorphism. Most of the polymorphisms were located within the regions corresponding to the internal transcribed spacer and intergenic spacer. The degree of variation observed was sufficient to discriminate several isolates from the same species. Genetic variation was correlated to some extent with geographical origin of the isolates. However, RFLPs of the rRNA genes cannot unambiguously discriminate all selected isolates within Laccaria species, requiring the development of additional DNA probes. Alone, or in combination with other DNA probes, the amplified rDNA genes may serve in the determination of pure fungal cultures and in the characterization of genetic variation of field ectomycorrhizal populations.
The distribution of some fungal and bacterial endophytes in maize (Zea mays L.)
Authors: FISHER P. J. , PETRINI O. , SCOTT H. M. LAPPIN 
Published: April 2006

SUMMARYEndophytic bacteria and fungi were isolated from healthy maize plants collected in a field in Devon. The average bacterial counts in the stem core tissues showed that the plant parts closer to the soil were more heavily colonized by bacteria than those near the top of the plants, and that the lower and middle part of the stems hosted the most frequently isolated bacterial species. Of the fungal species isolated, 12 had a relative importance of more than 10% in the core, 15 in the epidermis, and only 5 in the leaves. In general the distribution patterns were different among the three tissue types studied, with core and epidermis of the stems showing almost equal colonization frequencies and the leaves being most heavily colonized. More fungal species were recovered from the core and epidermis of the stem than from the leaves. The fungi most frequently isolated showed some patterns of tissue specificity, with Alternaria alternata almost exclusively associated with the leaves and Aureobasidium pullulans var. melanigerum most often present in the epidermal tissues.Assays showed low fungal colonization of seeds taken from freshly matured cobs and of seeds dried for 8 wk before testing, in contrast to higher colonization frequencies observed for the seeds used for planting. The mean values for fungal isolations in the stem pieces mostly in contact with the soil flora or close to the ground were lower than those of the more centrally placed sections. These areas of low fungal infection yielded the highest bacterial counts. The potential role of bacterial endophytes in biological control is briefly discussed.
The response of spring wheat (Triticum aestivum L.) to ozone at higher elevations. III. Responses of leaf and canopy gas exchange, and chlorophyll fluorescence to ozone flux
Authors: GRIMM A. GRANDJEAN , FUHRER J. 
Published: April 2006

SUMMARYSpring wheat (Triticum aestivum L., cv. Albis) was grown in open‐top chambers and exposed to four different levels of ozone (O3) from the three‐leaf stage until maturity. The aim was to examine changes in leaf and canopy gas exchange, and in chlorophyll fluorescence, in response to O3 flux. Measurements were carried out periodically between full expansion and complete senescence of flag leaves. Fluxes to the canopy of CO2 (CERc.) (corrected for soilborne CO2), water vapour (Ec) and O3 were determined by using open‐top chambers as differential systems. Water use efficiency (WUEc.) was calculated from CERc, and Ec. Leaf CO2 (CERn) and H2O (En) exchange rates, stomatal conductance (g,(H2O)), and WUEn, were analyzed with a portable gas exchange analyzer. Effects of O3 flux on structural components of photosynthesis were examined by determining variable fluorescence (defined by the Fv/Fo ratio) in leaves after 60 minutes of dark‐adaptation or during the night.The decline in CERc and CERn associated with senescence was accelerated by O3. Average CERn between flag leaf unfolding and late milk stage declined linearly with increasing O3 flux. The corresponding decline in average CERc was less pronounced. The quantitative effect of O3 flux on CERc corresponded well with the effect on grain yield. In young leaves, gs(H2O) was reduced in response to O3 but WUEn was unaffected. With progressing leaf age, WUEn declined. Thus, in the young leaves, O3 affected the stomata directly and, consequently, limitation of photosynthesis was primarily due to reduced CO2 diffusion. In contrast, in senescent leaves, the effect of O3 was mainly due to reduced carboxylation. Compared with WUEn WUEc responded differently to increasing O3 flux. During O2 fluxes at above‐ambient levels, WUEC tended to increase rather than to decrease. It is suggested that under O3 stress, factors controlling WUE at the canopy level differ from those operating at the level of single flag leaves. The decline in Fv/Fo measured after anthesis was stimulated by O2, but no effect of O3 was detected when Fv/Fo was measured during the night. This leads to the conclusion that the effect of O3 on photosynthetic structures is reversible and the reduction in photosynthesis in response to O3 flux is due to metabolic changes rather than to direct damage to structural components.
Mineral nutritional inter‐relations amongst stolons and tiller ramets in Agrostis stolonifera L.
Authors: MARSHALL C. , ANDERSON‐TAYLOR G. 
Published: April 2006

SUMMARYThe functional organization of the clonal plant Agrostis stolonifera L. was investigated in terms of the mineral nutrient inter‐relations between individual well‐established stolons and between adjacent tiller ramets on a single stolon. Tillers on developing stolons were rooted individually and treatments established in which different patterns of mineral nutrient supply were given to various parts of the clone. In the first experiment with plants consisting of 2 main stolons and where the ramets of each stolon were supplied with either nutrient solution or water, the stolons displayed distinctly independent nutrient economies irrespective of the pattern of nutrient supply. In a second experiment, where the effect of uniform or local nutrient supply to a single stolon of rooted ramets was followed, the growth of ramets was very closely related to their local nutrient supply. In a further experiment the performance of rooted and unrooted ramets was compared in contrasting nutrient regimes. When situated between ramets supplied with nutrients, the growth and development of an unrooted ramet closely matched one that was rooted and supplied with nutrient solution but greatly exceeded that of one that was rooted and given only water.The independent mineral nutrient economies displayed by individual rooted stolons and by rooted tiller ramets is discussed in relation to the underlying physiological integration of the stolon axis that allows unrooted ramets and the unrooted extending apical region of a stolon to be provided with adequate mineral resources for their growth and development.
On the ecophysiology of the Clusiaceae in Trinidad: expression of CAM in Clusia minor L. during the transition from wet to dry season and characterization of three endemic species
Authors: BORLAND A. M. , GRIFFITHS H. , MAXWELL C. , BROADMEADOW M. S. J. , GRIFFITHS N. M. , BARNES J. D. 
Published: April 2006

SUMMARYA study was made of photosynthesis and expression of crassulacean acid metabolism (CAM) in naturally exposed and shaded populations of Clusia minor L. during the transition from wet to dry season in Trinidad (mid‐February to mid‐April, 1990). At the start of the dry season, plants from exposed and shaded habitats showed a capacity for CAM either through the fixation of external or internal (respiratory) CO2. Exposed plants showed continuous uptake of CO2 over 24 h although dark fixation accounted for only a small proportion of CO2 fixed over the day. The expression of CAM was considerably enhanced as the dry season progressed with substantial increases in the overnight accumulation of titratable acidity, particularly in leaves of exposed plants. This was accompanied by a reduction in day‐time photosynthesis and an increase in dark fixation, with shaded plants showing only night‐time fixation of CO2. The magnitude of CAM in C. minor was substantial with a maximum ΔH+ of 1410 mol m‐3 measured in leaves from exposed branches. Both malic and citric acids were accumulated overnight. The highest citric:malic acid ratios were found in young leaves from exposed plants with 250 mol m‐3 malic and 125 mol m‐3 citric acid accumulated near the time of maximum CAM activity. Photosynthetic efficiency, measured as light responses of O2 evolution, also varied on a daily basis dependent on the incident photosynthetic photon flux density (PPFD). Apparent quantum yield and photosynthetic capacity showed marked reductions depending on the degree of exposure, suggesting that photoinhibitory responses are important under natural conditions. An analysis of three members of the Clusiaceae endemic to Trinidad showed that each had the capacity to induce CAM activity, despite being found in a narrow range of habitats which have higher rainfall than those of C. minor. However, despite the variable expression of CAM activity, carbon isotope composition suggested that when integrated throughout the year, carbon accumulation is predominantly mediated via the C3 pathway in all the species studied.
New pollen‐analytical researches in Corsica: the problem of Quercus ilex L. and Erica arborea L., the origin of Pinus halepensis Miller forests
Authors: REILLE MAURICE 
Published: April 2006

SUMMARYThe pollen‐analytical study of eight sites (two glacial lakes and six coastal marshes) has been carried out (nine pollen diagrams, 472 pollen spectra). The total absence of Quercus ilex forest in Corsica during the Atlantic and the vegetation contrast existing at that time between the western and the eastern sides of the island are demonstrated. On the western site, Erica arborea constituted the only regional vegetation from the coast up to about 1500 m. Human action is responsible for the establishment of Quercus ilex in this climax vegetation during the Sub‐boreal. It is also shown that the only Pinus halepensis forest present today in Corsica has been introduced on the island during the nineteenth century.
The anthocerote chloroplast: a review
Authors: VAUGHN KEVIN C. , LIGRONE ROBERTO , OWEN HEATHER A. , HASEGAWA JIRO , CAMPBELL ELLA O. , RENZAGLIA KAREN S. , MONGE‐NAJERA JULIAN 
Published: April 2006

SUMMARYThis review covers previous data, together with new information from our laboratories, on the subject of the anthocerote chloroplast. Unlike all other archegoniates, most species of anthocerote have pyrenoids in their chloroplasts. The pyrenoid is the site of accumulation of the first enzyme in the C3 photosynthetic cycle, ribulose bispbosphate carboxylase/oxygenase. Unlike most algae, the hornwort pyrenoid is composed of distinct subunits, numbering up to several hundred. Pyrenoid morphology is quite variable among the genera in shape, fine structure, and distribution of inclusions. Another unique feature of the anthocerote chloroplast is the presence of thylakoids that connect adjacent granal stacks at right angles to the long axis of the granum (so‐called channel thylakoids), resulting in a 'spongy’arrangement of the thylakoid system. The granal stacks of anthocerotes are like the‘pseudograna’of green algae because they lack the highly‐curved end membranes typical of all other embryophytes. The channel thylakoids are enriched in photosystem (PS) I and the grana are enriched in PS II. The chloroplast envelope is a double membrane structure with regions of appression, much like that of other green plants. The apieal cell of the gametophyte contains chloroplasts similar to the mature chloroplasts of the thallus, although certain gametophytic tissues may contain underdeveloped plastids. Chloroplasts in cells around Nostoc colonies and in cells invaded by mycorrhizal fungi have thylakoids mainly in pairs, and small or absent pyrenoids. A number of similarly reduced plastids are noted in the placental cells at the sporophyte/gametophyte junction and in developing spores. The greatest reduction is observed in spermatid cell plastids, which at maturity consist of only a small starch grain surrounded by the envelope. Chromoplast‐like organelles are found in the cells of the antheridial jacket in some genera; these contain numerous osmiophilic globules that are probably pigment aggregations. Colourless bead‐like plastids occur in the rhizoids; these seem to develop by fragmentation of the single chloroplast in the rhizoid initials, concomitant with the loss of chlorophyll. Chloroplast division is a tightly controlled process and, in uniplastidic species, always occurs just before nuclear division, with the participation of a unique system of chloroplast‐associated microtubules. The number of chloroplasts per cell is quite variable in some genera, although most species have but a single chloroplast in each cell of the gametophyte. Chloroplast shape is also variable from ellipsoidal, dumbbell‐shaped, to irregular. These data indicate that the anthocerote chloroplast is unique among the embryophytes and are in line with the notion of an isolated position in the plant kingdom. Certain features of chloroplast morphology appear to be typical of certain genera and might prove useful in taxonomic decisions at the generic level.
Symplastic transport of Lucifer Yellow in mature leaf blades of barley: potential mesophyll‐to‐sieve‐tube transfer
Authors: FARRAR JOHN , SCHOOT CHRIS van der , DRENT PETER , van BEL AART 
Published: April 2006

SUMMARYIntermediate veins of mature barley leaves were exposed by partial enzymic removal of mesophyll cells. Lucifer Yellow was iontophoresed into a variety of cell types and its symplastic transfer followed by fluorescence microscopy. Dye transfer from mesophyll cells into the parenchymatous bundle sheath (PBS) and from PBS to mestome sheath (MS) occurred readily. Dye transfer around and along both PBS and MS was rapid. Following injection into PBS or MS dye could be seen moving within sieve tubes, thus providing a demonstration of potential mesophyll‐to‐sieve tube transfer.
Regeneration of the discrete root epidermis of Pistia stratiotes L. after perturbation of the meristem
Authors: CLOWES F. A. L. 
Published: April 2006

SUMMARYPerturbation of meristems of adventitious roots of Pistia resulted in abnormal patterns of cell division in the quiescent centre including the pole of the normally discrete epidermis. Two of the methods used, radiation from incorporated tritiated thymidine and cold treatment, also produced abnormal patterns in the lateral primordial present within the apices of the adventitious roots. Cells of the monostromatic epidermal shell divided periclinically in some roots and some primordia where all previous divisions would have been anticlinal. In other meristems, the normally quiescent cells of the stelar and cortical poles grew and divided to displace the former epidermal pole and cap initials.Recovery from the perturbation resulted in the organization of a meristem which assembled a new monostromatic epidermal layer apparently discrete from the new cap initials below and the new cortical pole cells above. The new epidermal pole formed continuously with the old and, though the pattern of planes and rates of mitosis initiating and maintaining it must be determined as in normal ontogeny, some additional influence of the epidermis left intact above the region of abnormal activity appears to operate.
Increased photosynthesis and resistance to rust infection in upper, uninfected leaves of rusted broad bean (Vicia faba L.)
Authors: MURRAY D. C. , WALTERS D. R. 
Published: April 2006

SUMMARYPhotosynthesis and resistance to rust infection were studied in upper, uninfected leaves of broad bean, Vicia faba L., where the lower two leaves were infected with rust, Uromyces viciae‐fabae (Pers.) Shroet. Following inoculation of the lower leaves, rates of net photosynthesis were significantly increased in the upper, uninfected, fully‐developed leaves and the young developing leaves, compared to controls. In contrast, photosynthesis was substantially reduced in the lower, rusted leaves. When 14CO2 was fed to the upper, uninfected leaves of rusted plants, there was a considerable increase in labelled assimilate in those leaves, compared to controls. In addition, there was substantial movement of labelled assimilate into lower, rusted leaves, into young, developing leaves and into roots. On the other hand, there was a substantial reduction in labelled assimilates moving into shoot apices.Upper, uninfected leaves of rusted beans exhibited Increased resistance to rust infection. Thus, the percentage leaf area covered with rust and the number of pustules per cm2 were reduced in these leaves compared to controls. This resistance to rust infection was greatest when the upper leaves were challenged 1 d after inoculation of the lower leaves with rust and decreased with increasing time after inoculation of the lower leaves. Young, developing leaves on rusted beans also exhibited increased resistance to rust infection. When photosynthesis in the upper leaves was reduced to near control values or well below control values by shading, resistance to rust infection in those leaves was also reduced, although not in proportion to the reduction in photosynthesis. It is suggested that the increased photosynthesis in upper, uninfected bean leaves probably facilitates maximum expression of resistance to infection in those leaves.
Amino acid and amide metabolism in the hulls and seeds of developing fruits of garden pea, Pisum sativum L.
Authors: Aspartate V. , MURRAY DAVID R. 
Published: April 2006

SUMMARYPea plants (Pisum sativum L. cv. Melbourne Market), each with a single developing pod, were pulse‐fed [4‐14C]aspartate through the cut stem at stages from 11 to 32 d after full blossom. The distribution of radioactivity in soluble metabolites of the hull, seedcoats, embryo sac liquid and embryo was determined by 2‐dimensional paper chromatography and radioautography after feeding intervals of 6 h, 24 h or 48 h. At the earliest stage, radioactivity was recovered mainly in sucrose, serine, homoserine and threonine in the hull. At the 15‐16 d stage, threonine became the major derived amino compound secreted into the embryo sac, and sucrose became the predominant derivative recovered from both hull and seed tissues. Stem‐fed aspartate can therefore be transferred to stem phloem, and sucrose synthesized from aspartate in stems and leaves can be transferred to phloem in both organs.
Transfusion tissue of pine needles as a site of retrieval of solutes from the transpiration stream
Authors: CANNY M. J. 
Published: April 2006

SUMMARYThe fluorescent tracers sulphorhodamine G (SR) and pyrene trisulphonate (PTS) were used to explore the functions of cells and tissues within the pine needle, following their progress after feeding through the transpiration stream. The distributions of tracer in the needles were stabilized for fluorescence microscopy by rapid freezing and freeze‐substitution, and anhydrous embedding and sectioning. After short pulse + chase times (up to 2 h), SR and PTS accumulated at higher‐than‐xylem concentrations in the transfusion tracheids on the flanks of the vascular strand, but did not pass out through the endodermis. The accumulations occurred locally where the transpiration water was separated from the tracers and passed into the symplast of the transfusion parenchyma and endodermis. After a 24 h water chase, SR had entered the symplast through the transfusion parenchyma, and spread through the endodermis and palisade. It is argued that this is evidence of active H+‐ATPase systems lowering the external pH of the transfusion parenchyma, and characterizes these cells as scavenging cells similar to those found in the bundle sheath systems of legume leaves. The transport of SR through the endodermis and palisade is the first clear evidence that this tracer can also function as a symplastic tracer. The hypothesis that the transfusion parenchyma acts to scavenge solutes from the transpiration stream was tested by loading the stream with [14C]aspartate and examining the subsequent distribution of 14C by dry autoradiography. After a pulse + chase of (0.75 + 3) h, 14C was found concentrated in the transfusion parenchyma, and at even higher levels in the Strasburger cells. It is proposed that major functions of the transfusion tissue of gymnosperms are (a) the concentrating of solutes from the transpiration stream and (b) the retrieval from the stream of selected solutes that are returned to the phloem through the Strasburger cells, or forwarded through the endodermis to the palisade.
Temperature effect on fructan oligomer contents and fructan‐related enzyme activities in stems of wheat (Triticum aestivum L.) during grain filling
Authors: BANCAL PIERRE , TRIBOÏ EUGÈNE 
Published: April 2006

SUMMARYTwo 2 m2 stands of wheat were grown under controlled conditions from 2 d after anthesis until harvest. Day and night temperature were 18 and 10 °C respectively in crop 1, whereas they were shifted to 28 and 20 °C 5 d after anthesis in crop 2. CO2 exchange rates of the canopies were continuously measured. Samples of 20 plants were collected from each crop two or three times a week. Grain filling was monitored as were various carbohydrates and enzyme activities in stems. Sugar reserves were highly correlated with the difference between cumulative photosynthesis and dry matter stored in grains. Fructan accumulated up to 150 mg culm−1 2 wk after anthesis in crop 1; but it ceased to accumulate in crop 2 as soon as high temperature was applied, because the increased metabolic rates resulted in higher carbon requirement for grain filling. The fructan was mostly phlein or highly 2–6 linked oligomers with a degree of polymerization up to 15. 6‐Kestose was the most abundant, reaching 70 mg culm−1 in crop 1. 1‐Kestose content never exceeded 25 mg culm−1 and it remained roughly constant from anthesis to harvest. No temperature‐related difference in amount of 1‐Kestose was noticed. Four kestotetraoses were quantified, 6,6‐ followed by l&6‐kestotetraose were the most abundant of them. The (2–1) linkages in bulk kestotetraose decreased from 40 % of total at anthesis to 10 % at maximum grain fresh weight. This chemical shift of the fructan reserves in the two crops was accelerated but not enhanced by elevated temperature. (2‐l)‐Fructan exohydrolase increased as soon as temperature was enhanced. However, in both crops its activity peaked at maximum grain dry weight only. Sucrose‐sucrose fructosyl transferase was constant at 01 nkat culm−1 in crop 1, whereas its activity decreased in crop 2 when temperature increased. Little change in invertase activity can be reported in both crops later than 1 wk after anthesis.