bluuebunny/crossref_metadata_2025_split huggingface dataset:
Past and present variability in leaf length of evergreen members of Nothofagus subgenus Lophozonia related to ecology and population dynamics
Authors: JORDAN GREGORY J. , HILL ROBERT S. 
Published: April 2006

SUMMARYThe lengths of fossil leaves of Nothofogus cunninghamii, and of closely related fossil species from sediments older than the Middle Pleistocene showed greater variation than fossil leaves from younger sediments and extant leaves from modern sediment samples and forest floor litter. Leaf sizes of samples of the other two extant evergreen species of Nothofagus subgenus Lophazonia, N. moorei and N.menziesii, were no more variable than modern N.cunninhamii. Leaf lengths of modern and Middle‐Late Pleistocene N. cunninhamii and of modern N. menziesii were more or less unimodal in distribution, whereas the leaves of N. moorei follow bimodal distributions, and leaves from the Early Pleistocene Regatta Point and the Oligocene Link‐ Rapid River sediments tended to be bimodal and highly variable. Leaf lengths from the Oligo‐Miocene Monpeelyata sediments were also highly variable, but the sample size was too small to determine if they follow bimodal distributions. The bimodality and high variability in the older sites are unlikely to have been due to taphonomic processes. Thus, within population variability appears to have declined during the Late Tertiary‐Early Pleistocene, although the presence of cryptic species in the fossil record could also explain the results. Both a decline in variability within species, and the extinction of Nothofugus species, are consistent with a well documented Late Cainozoic decline in rainforest diversity in Tasmania. Log transformed leaf lengths of modern forest floor litter samples of N. cunninhamii were Strongly correlated with climatic parameters, particularly summer temperature, suggesting that this parameter is a strong determinant of leaf size in N. cunninhamii Changes in N. cunninhamii leaf lengths within Middle Pleistocene sediments were associated with floristic changes interpreted as transitions in glacial/interglacial cycles but these changes were small compared with changes predicted Iron climatic correlation of extant samples, probably because of limited Emetic variability in local populations at the time of deposition.
The branch roots of Zea
Authors: WANG X. L. , McCULLY M. E. , CANNY M. J. 
Published: April 2006

SUMMARYThe late metaxylem (LMX) in the first‐order branch roots of maize matures slowly. Fully lignified elements remain as individual cells of mean diameter 67 μm and length about 2 mm for considerable distances proximal from the tip of branches that retain an active meristem (indeterminate branches). Such branches, depending on their age, have from 0 to 45%, of the Total length of LMX conduits mature and open for unrestricted conduction of the transpiration stream. In determinate branches (those that have lost their meristem), up to 60% of LMX length is open for conduction. The closed portion of the xylem conduits is at the distal end of the branches. In both indeterminate, and the youngest determinate branches, immature, living xylem elements provide the block in the conduits. Later, progressive decay in the determinate branches passes basipetally beyond the immature elements, bus the distal ends of the conduits remain closed, plugged initially by mucilaginous materials apparently of root origin, and subsequently by invading microbes. It is proposed that the closed ends of the xylem conduits restrict leakage from the more proximal regions, and also prevent their blockage by embolisms. The presence of mature LMX conduits open for unrestricted water conduction is consistent with the major role in water uptake assigned to the branch roots in earlier studies.
Evaluation of air pollution phytotoxicity in a seasonally dry tropical urban environment using three woody perennials
Authors: PANDEY J. , AGRAWAL M. 
Published: April 2006

SUMMARYA two‐year study was conducted in the urban environment of Varanasi, India, to evaluate plant responses to urban air pollution. Three species including a shrub (Carissa carandas L.) and two tree species (Delonix regia Rafin and Cassia fistula L.) were grown in pots at selected study sites. Changes in plant performance were considered in relation to the status of ambient air quality.Reductions in plant height, basal diameter, canopy area, plant biomass and chlorophyll, ascorbic acid and nitrogen contents in leaves were correlated with air pollution level at different sites. The magnitude of response indicated the relative sensitivity of the three species in the order D. regia > C. fistula > C. carandas. Shifts in relative contribution of photosynthate to leaf production and shoot growth appear to be a pollution‐induced adaptive response in C. carandas. The study shows that the urban air pollution level at Varanasi is detrimental to the growth of plants.
Impact of O3 and SO2 on reproductive development in oilseed rape (Brassica napus L.)
Authors: BOSAC C. , ROBERTS J. A. , BLACK V. J. , BLACK C. R. 
Published: April 2006

SUMMARYThe flowering racemes of Brassica napus L. cv. Tapidor were exposed independently from the vegetative component to 200 nl l−1, 100 nl l−1 O3/30 nl l−1 SO2, In all cases, a single 6 h exposure significantly increased bud abortion, and abscission 2 and 5 d after treatment. Similar results were obtained using cv. Libravo, although the effect of 100 nl l−1 O3 was significant only after 2 d. Exposure to 30 nl l−1 SO2 did not enhance bud abortion and abscission in either variety. Longer term measurements for up to 25 d revealed a trend to wards sustained losses of fertile sites in those pollutant treatments which had exhibited demonstrable, effects after 2 and/or 5 d. However, the number of fertile sites present was comparable to or even higher than in the controls, indicating that compensation for the initial losses must have occurred. Following exposure, plants of cv. Tapidor tended to develop longer total raceme lengths and greater numbers of raceme branches, and those of cv. Libravo a greater number of raceme branches. Indicating possible methods by which new fertile sites may have been produced. The significance of these observations for the reproductive development of field‐grown oilseed rape is discussed.
A basidiomycete isolated from a Pisonia mycorrhiza forms sheathing mycorrhizas with transfer cells on Pisonia grandis R. Br.
Authors: CAIRNEY J. W. G. , REES B. J. , ALLAWAY W. G. , ASHFORD A. E. 
Published: April 2006

SUMMARYA basidiomycete isolated from a mycorrhiza of glasshouse‐crown Pisonia grandis R. Br. (Nyctaginaceae) produced sheathing mycorrhizas with transfer ceils when inoculated on to roofs of Pisonia grandis in pots. Mycorrhizal synthesis was successful on Pisonia grandis in sterilized natural soil rich in phosphorus, nitrogen, potassium and calcium, but unsuccessful in a range of other substrates of low nutrient status. The same fungus produced ectomycorrhizas, with a sheath and some intercellular penetration, on short lateral runts of Picea sitchensis (Bong.) Carr (Pinaceae) seedling in growth pouches, but did not on Eucalyptus pilularis Smith (Myrtaceae).
The effects of polyamine biosynthesis inhibitors on growth, enzyme activities and polyamine concentrations in the mycorrhizal fungus Laccaria proxima
Authors: ZARB J. , WALTERS D. R. 
Published: April 2006

SUMMARYDifluoromethylarginine (DFMA) and difluoromethylornithine (DFMO) are inhibitors of the polyamine biosynthetic enzymes arginine decarboxylase (ADC) and ornithine decarboxylese (ODC), respectively, DFMO is a potential fungicide acting on fungal ODC.This report examines the effects of DFMA and DFMO on polyamine concentrations and metabolism, and on the activities of enzymes of polyamine biosynthesis and breakdown in the mycorrhizal fungus Laccaria proxima. Data indicate that L. proxima possesses both ADC and ODC activities: DFMA depleted putrescine and did not inhibit ODC activity; incubation of mycelium with a [U‐14C]arginine substrate led to [14C]putrescine formation DFMA completely inhibited the formation of polyamines from [U‐14C]arginine DFMO inhibited bound biosynthetic enzyme activity and the formation of putrescine from [U‐14C]ornithine. Therefore, L. proxima may not be susceptible to fungicidal DFMO application.
Improved nitrogen uptake and transport from 15N‐labelled nitrate by external hyphae of arbuscular mycorrhiza under water‐stressed conditions
Authors: TOBAR R. , AZCÓN R. , BAREA J. M. 
Published: April 2006

SUMMARYThe significance of the external mycelium of arbuscular mycorrhiza for uptake and transport of N from 15N‐labelled nitrate in benefiting plant nutrition, was evaluated under either well‐irrigated or water‐stressed conditions. Plants of lettuce (Lactuca sativa L.) were grown under controlled conditions in a neutral agricultural soil/sand mix either non‐mycorrhizal or in association with the arbuscular‐mycorrhizal fungus, Glomus fasciculatum (Taxter sensu Gerd.) Gerd. and Trappe. The pots comprised a two‐compartment system, where a fine nylon mesh screen prevented the development of roots in a hyphal compartment. 15NO3− was applied to this hyphal compartment where access of the root was not possible. At harvest, the 15N enrichment in plant tissues was the same for both mycorrhizal and non‐mycorrhizal plants under optimal water supply conditions. However, under water‐stressed conditions, where the mass flow and diffusion of NO3− ions to the roots can be affected, the 15N enrichment was four times higher in mycorrhizal than in non‐mycorrhizal plants. This provides evidence of hyphal transport of N from a nitrate source, supporting the view that arbuscular mycorrhiza can be important for the N‐nutrition of plants in relatively dry agricultural soil where nitrate is actually the predominant nitrogen form.
Mycorrhizal fungi and reproduction of field populations of Abutilon theophrasti Medic. (Malvaceae)
Authors: KOIDE ROGER T. , SHUMWAY DURLAND L. , MABON STEPHEN A. 
Published: April 2006

SUMMARYThe effects of inoculation with mycorrhizal fungi and phosphorus amendment on reproduction of Abutilon theophrasti Medic, were documented over two years in the field. In Year 1 all plots were thinned to a common and relatively low density (12 plants m−2). Mycorrhizal infection significantly increased capsule and seed production. Phosphorus amendment had little effect on these characters, possibly due to low soil moisture content. In Year 2 following natural recruitment, inoculated (M) plots were much more dense than uninoculated (NM) plots. In contrast with the results from Year 1, however, individual plains in M plots produced fewer capsules than those in NM plots in Year 2 because capsule production in Year 2 was density‐dependent. Based on these results and others, we suggest that in monospecific stands of Abutilon, mycorrhizal infections have the greatest effects on fecundity at low densities. At higher densities, density‐dependent forces may reduce the importance of mycorrhizal infections to reproductive effort of a single plant. Our results highlight the necessity of examining the effects of mycorrhizal fungi in natural populations and communities.
Accumulation of amino acids in some boreal forest plants in response to increased nitrogen availability
Authors: NÄSHOLM ANN‐BRITTEDFAST TORGNY , ERICSSON ANDERS , NORDÉN LARS‐GÖSTA 
Published: April 2006

SUMMARYAccumulation of amino acids in response to application of 500 kg N ha−1 as a single dose of NH4NO3, was measured for four common Swedish forest species. Addition of N resulted in increased levels of especially glutamine and arginine in Vaccinium myrtillus L. and in V. vitis‐idaea L., whilst, in fertilized Deschampsia flexuosa L., asparagine and glutamine were most prominent. In Epilobium angustifolium L. glutamine and arginine increased most after fertilization. In a second study, five different forest species, V. myrtillus, V. vitis‐idaea, D. flexuosa, Pleurozium schreberi Wild. and Polytrichum commune Menz. were studied in a Norway spruce fertilization experiment. In this experiment, plots had been irrigated with a complete mixture of nutrients during the growing period for five subsequent years. Arginine in Pl. schreberi, glutamine in P. commune and asparagine in D. flexuosa were all elevated on fertilized plots, while in fertilized V. vitis‐idaea and V. myrtillus only minor increases of amino acid concentrations were found. In a third investigation, amino acid concentrations were measured in Pl. schreberi, Hylocomium splendens L., V. myrtillus, V. Vitis‐idaea and D. flexuosa growing on different plots in an area with relatively high nitrogen deposition. The plots were divided into two groups, one characterized by high, and one by low concentration of arginine in spruce needles from trees growing on the same plot. Asparagine in D. flexuosa, arginine and asparagine in Pl. schreberi and arginine in H. splendens were significantly higher in plants from plots with high concentrations of arginine in needles of Norway spruce. Differences between species in the metabolism of nitrogen during conditions of high nitrogen supply are discussed as well as possible usage of specific amino acids in the studied species as indicators of nitrogen saturation.
Fire and age structure of Scots pine and Norway spruce in northern Sweden during the past 700 years
Authors: ENGELMARK OLA , KULLMAN LEIF , BERGERON YVES 
Published: April 2006

SUMMARYThe performance ofPinus sylvestrisL. andPicea abies(L.) Karst has been studied in relation to the fire regime from the 1200s up to present in an old‐growth boreal forest area, The J‐shaped age distribution of pine during the study period, suggests a stationary pattern in the landscape. The spruce age structure (from the 1600s onwards) also points towards a J‐shape, although with slight deviations. No significant changes in total pine or spruce regeneration occurred in response to the significantly prolonged fire cycle (from 187 to 371 yr) around 1870. This break in the fire cycle might possibly have a climatic background.
Tansley Review No. 82. Strategies of arbuscular mycorrhizal fungi when infecting host plants
Authors: BONFANTE PAOLA , PEROTTO SILVIA 
Published: April 2006

summaryArbuscular mycorrhizal (AM) fungi are ancient Zygomycetes, thought to have colonized the first land plants; today, they are associated with the roots of about 80% of plant species. The symbiosis they form is potentially valuable not only for developmental programmes based on low‐input agriculture, but also as a complex experimental model, where both fungal and host plant growth are regulated. Here we review some recent progress m the area of cell and molecular biology of arbuscular mycorrhizas. Particular attention is given to strategies followed by AM fungi when, as obligate biotrophs, they establish a successful symbiosis with their host plants. Four topics are analysed: (i) parameters controlling fungal growth in the absence and presence of the host root, Le. events of DNA replication and timing of the cell cycle; (ii) mechanical and enzymatic mechanisms which allow the fungus to colonize root tissues, maintaining host viability; (iii) morphological changes induced by AM fungus host cells and, in particular, the formationde novoof a subcellular compartment termed the interface, and (iv) modifications of plant gene expression during fungal colonization, including those involving structural, symbiotic and defence‐related genes.ContentsSummary3I.Introduction3II.Fungal growth and activatioti of the cell cycle5III.Molecular basis of the colonization process9IV.Plant and fungal morphogenesis during the infection process12V.AM fungi change the pattern of gene expression in host plants17VI.Conclusions18Acknowledgements470References
Partitioning and flows of ions and nutrients in salt‐treated plants ofLeptochloa fuscaL. Kunth
Authors: JESCHKE W. DIETER , KLAGGES SABINE , HILPERT ANDREA , BHATTI A. SAEED , SARWAR G. 
Published: April 2006

summaryAn empirically based modelling technique, based on the relative immobility of Ca2+in phloem, was used quantitatively to describe uptake, flow in xylem and phloem, and partitioning of K+, Na+, Mg2+, and Cl−for a 13‐d period at the end of vegetative growth of the main shoot inLeptochloa fusca(L.) Kunth grown in presence of 100 mM NaCl. The model incorporated data on net increments of the ions in the root, the stem, individual leaf sheaths and laminae (blades), and tillers, secretion of salt by glandular hairs on sheaths and laminae, and the molar ion:Ca ratios in the xylem sap. Molar ratios of uptake of Na:Cl:K were 1.27: 1.12:1, indicating an uptake selectivity of 11.3 in favour of K+against Na+. The flow pattern of K+ in the main shoot featured relatively low permanent deposition (22% of the intake into the shoot in the stem axis and 10% in leaves) but a high return flow via phloem to the root (67%) followed by cycling of K+. In the whole plant a large share (72%) of K+uptake was utilized for growth of tillers but K+cycling from shoot to root amounted to 96% of uptake. The flow pattern of Na+featured a somewhat smaller commitment (62%) to deposition in tillers. In the main shoot 33% of Na+intake was deposited in the stem and 35% in leaves. In these the sheaths incorporated by far the larger (2.8‐fold) share compared with the laminae. Of the total Na1intake, 9%, was excreted by salt glands (3.3‐fold more by laminae than sheaths) and only 31% was translocated to the root via phloem. Flows and partitioning of Cr were similar to those of Na+, but phloem transport was larger (60% of intake into the main shoot) than that of Na+. The flow patterns are discussed in relation to changes in ion concentrations of leaves with leafage and in relation to salinity tolerance. It is suggested that besides salt secretion a high efficiency in K+utilization contributes to the performance of this halophyte in presence of salt
Hydraulic conductivity of concentric root tissues of Agave deserti Engelm. under wet and drying conditions
Authors: NORTH GRETCHEN B. , NOBEL PARK S. 
Published: April 2006

summaryWater moves from the root surface to the root xylem through a series of tissues, each with properties that influence the root radial hydraulic conductivity (LR). To determine LR for intact roots, root hydraulic conductivity (LR) and axial (xylem) conductance (Kh) were measured for root segments of the desert succulent Agave deserti Engelm. As layers were successively removed, LR was calculated for each layer by considering the conductivities in series. For the distal root region, no single tissue limited LR under wet conditions, although the suberized exodermis and sclerenchyma/endodermis were more limiting per cross‐sectional area of the root than were the cortex and stele. At midroot under wet conditions, LR for the cortex was higher than in the distal region, and cortical cells were dead. After 28 d in drying soil, LR for the suberized layers decreased by over 70% and thereby became more limiting to LR of the intact segment, consistent with increases in extracted lipids in these layers. During drying, intercellular lacunae formed in the cortex due to cellular collapse, and cortical LR decreased. After 7 d of re‐wetting following drying, LR increased for all tissues, but not to its value under wet conditions, reflecting persisting losses in conductivity, especially in the suberized layers. Thus, new apical growth and the development of new laterals are necessary for the complete restoration of root system conductivity. Within 20 mm of the root tip, substantial uptake of the apoplastic tracer 8‐hydroxy‐1,3,6‐pyrenetrisulphonic acid (PTS) occurred, although the exodermis restricted PTS uptake further than 20 mm back from the root tip under wet conditions and all along the root after drying. When the exodermis was removed, PTS moved freely through the cortex in both distal and midroot regions, further suggesting that the cortical apoplast is a significant pathway for radial water flow.
Activities of free radical processing enzymes in dry sunflower seeds
Authors: REUZEAU C. , CAVALIE G. 
Published: April 2006

summaryChanges in the lipid peroxidation and the enzymatic activities of the oxygen radical detoxification were studied in dry seeds of sunflower (Helianthus annuus L.) and related to their germinability. There was a positive relationship between the total dehydrogenase activity extracted from whole seeds and germination at both 25 °C and 10 °C. Catalase and superoxide dismutase activities in embryonic axes and germination at 10 °C were negatively correlated. Glucose‐6‐phosphate dehydrogenase and total peroxidase activities were higher in seeds showing high germination capacity. A high malondialdehyde content and a high total glutathione content, were found in cotyledons of dry seeds exhibiting no germination capacity. A net decrease (20%) in the activities of catalase and glucose‐6‐phosphate dehydrogenase was found in these cotyledon fragments. Glutathione reductase and glutathione peroxidase activities were increased by 20 and 50%, respectively. Kinetic properties of glucose‐6‐phosphate dehydrogenase were also affected; the apparent Km for NAD+ was lower in seeds unable to germinate than in seeds with a high germination ability. Oxidative stress appeared to affect seed quality by lowering antioxidant defence capacity; the collapse of the oxygen radical detoxification system appeared to be the result of the ineffectiveness of the glucose‐6‐phosphate dehydrogenase activity; its potential role in oxidative stress tolerance and seed germination ability is discussed.
Continuous monitoring of gas exchange in open‐top chambers in pollution experiments: methodological aspects
Authors: DAUDET F.‐A. , CLAUSTRES J. P. 
Published: April 2006

summaryAs part of an experiment on effects of atmospheric pollution on the physiology of spruce trees (Picea abies (L.) Karsten), a method for continuous monitoring of gas exchange of young trees grown in Open Top Chambers (OTC) was developed. The basic principles and feasibility of this method are first presented in detail. The installation of a fine perforated polyethylene net over the top of the OTC, in order to reduce ingress of outer air, made it possible satisfactorily to monitor the gas exchange of the trees over long periods. Examples are given of typical measurements of net assimilation and transpiration fluxes for an experimental canopy of 15 young spruce trees to show diurnal and seasonal variation.