bluuebunny/crossref_metadata_2025_split huggingface dataset:
The survival of infective hyphae of vesicular–arbuscular mycorrhizal fungi in dry soil: an interaction with sporulation
Authors: JASPER D. A. , ABBOTT L. K. , ROBSON A. D. 
Published: April 2006

SUMMARYContrary to previous evidence, the hyphae of a vesicular–arbuscular (VA) mycorrhizal fungus, Acaulospora laevis Gerd. and Trappe, did not remain infective in soil for a length of time, and at a level of dryness, equivalent to that occurring in seasonally‐dry field soils. A possible interaction between the survival of hyphae and the timing of sporulation was therefore examined in a second experiment. We tested the hypothesis that hyphae of A. laevis and Scutellospora calospora (Nicolson and Gerdemann) Walker and Sanders, will only remain infective in dry soil if sporulation has not commenced. The capacity of the hyphae of A. laevis to remain infective, in undisturbed soil that had been allowed to dry, depended on the stage of the life cycle reached at the time of the onset of drying. If sporulation had commenced, then infectivity quickly declined as the soil dried. In contrast, infective hyphae of S. calospora survived for at least 11 wk, regardless of the timing of the commencement of drying of the soil in relation to sporulation. Quantifying entry points was an important measure for assessing the survival of infective hyphae, complementing the measure of total mycorrhiza formation by the test plants.
The relative contribution of hyphae and roots to phosphorus uptake by arbuscular mycorrhizal plants, measured by dual labelling with 32P and 33P
Authors: PEARSON J. N. , JAKOBSEN I. 
Published: April 2006

SUMMARYThe aim of this investigation was to measure the relative contribution of hyphae and roots to the total uptake of phosphorus by mycorrhizal plants. Cucumber plants were grown in three‐compartment systems where 32P was applied to a lateral root‐free compartment (HC) and 33P applied to an identical lateral compartment with both roots and hyphae (RHC). The cucumber seeds were sown into the main root compartment (RC) which was inoculated with one of the following three arbuscular mycorrhizal fungi: Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders [isolate WUM 12(2)]; Glomus sp. [isolate WUM 10(1)]; Glomus caledonium (Nicol. & Gerd.) Trappe & Gerdemann (isolate RIS 42) or left uninoculated to represent a control treatment. The plants were harvested at 17 and 27 d. The hyphal uptake of 32P from the HC increased as follows –S. calospora ≥ Glomus sp. ≥G. caledonium. The uptake of 32P from the HC was equivalent to 7, 21 and 109 % of the uptake of 33P from the RHC in plants colonized by S. calospora, Glomus sp. and G. caledonium, respectively. This indicates that the relative contribution of the roots in total P uptake varied greatly between the three mycorrhizal treatments. Although 33P uptake was variable within treatments, the P uptake systems of roots colonized by G. caledonium appeared to be inactive when compared to hyphal 32P uptake. This may have been due to feedback mechanisms being activated because of the high hyphal P uptake. The roots colonized by S. calospora had higher rates of root‐P uptake compared with the control roots, suggesting that the root‐P uptake systems have been stimulated by the presence of the fungus. This would ensure that the P supply was sufficient to maintain photosynthesis in this symbiosis where the fungus gives only little P in return for its use of plant carbon substrate from the host.
Symbiosis‐related polypeptides associated with the early stages of ectomycorrhiza organogenesis in birch (Betula pendula Roth)
Authors: SIMONEAU P. , VIEMONT J. D. , MOREAU J. C. , STRULLU D. G. 
Published: April 2006

SUMMARYAs a preliminary step towards elucidation of the molecular basis of ectomycorrhiza differentiation, polypeptide changes at different stages of mycorrhiza development were analyzed in birch (Betula pendula Roth). Time‐sequencing of the stages in the infection process of clonal plants inoculated with a compatible isolate of Paxillus involutus Batsch revealed that by 8 d mature ectomycorrhizas were obtained. Total phenol‐extracted proteins of roots during the ‘mycorrhiza formation stage’ (2–8 d post‐inoculation) were separated by two‐dimensional polyacrylamide gel electrophoresis and the resulting patterns compared with non‐mycorrhizal roots and mycelium. Alteration in the concentration of polypeptides from the host plant roots was limited even after 8 d of contact between the symbionts. However, seven novel polypeptides were detected 4 d after inoculation, three of them being already present in 2‐d‐old ectomycorrhizas. These findings demonstrate that symbiosis‐related polypeptides accumulate in ectomycorrhizal roots prior to any of the morphological changes characterizing the symbiotic state.
Modern pollen deposition in cave sites: experimental results from New York State
Authors: BURNEY DAVID A. , BURNEY LIDA PIGOTT 
Published: April 2006

SUMMARYResults from two years of pollen trapping experiments in New York State show that pollen spectra inside the three caves studied are highly similar to the pollen rain outside the caves. Statistical comparisons of modern pollen spectra derived from Tauber traps, speleothems, moss polsters, and nearby pond sediments suggest that pollen deposition inside caves can provide a reliable index of the regional and local vegetation, directly comparable to the more conventional spectra derived from lake sediments and moss polsters. Because of the relatively low pollen influx inside caves, however, stochastic and episodic forms of particle transport may influence pollen deposition inside caves in proportions that are unique to each site. With careful attention to site parameters such as entrance size, pollen preservation, and modes of sedimentation, investigators could make greater use of caves in palynological studies.
The genetics of metal tolerance in vascular plants
Authors: MACNAIR MARK R. 
Published: April 2006

SUMMARYIn many parts of the world soils are detrimental to plant growth owing to elevated levels of metal ions, caused either by natural processes or by the result of man's activities. Many plants have evolved ecotypes or varieties that are able to grow more‐or‐less normally on these soils. This paper reviews our knowledge of the genetics of this phenomenon.The nature of tolerance and the problems of its measurement are discussed. Tolerance is frequently measured by an index produced by comparing growth in a contaminated environment with growth in a control environment. It is argued that this measurement is inappropriate for many genetical studies, and that it is frequently more useful to use growth at a single critical level of metal as a measure of tolerance.Polygenic inheritance provides a null hypothesis that has to be tested in a genetical analysis. Examples of major genes for tolerance to aluminium, arsenic, boron, cadmium, copper and manganese are discussed. Even where major genes have been demonstrated, it is probable that other minor genes, ‘modifiers’, are present as well. Because of the nature of tolerance as a character, dominance and epistasis are likely to vary with the level of metal at which an analysis is performed. Tolerance is generally found to be dominant at some levels of the metal. Studies which have mapped tolerance genes, particularly to aluminium and salt, are discussed.The specificity of tolerance is a matter of some confusion. Some studies indicate that tolerances evolve independently to different metals, but others have suggested that tolerance to one metal may often confer a degree of tolerance to some other metals.Very little is known about the molecular genetics of tolerance, and the mechanisms of tolerance to most metals. The possible role of phytochelatins and metallothionein‐like proteins in metal tolerance is discussed.The distribution of tolerance in natural populations suggests that tolerance is a disadvantage in uncontaminated environments, but how this ‘cost’ arises is not known. There is some evidence that the disadvantage to tolerance may be associated more with the modifiers of tolerance than with the primary tolerance gene.The study of the genetics of tolerance is of importance in planning breeding programmes to produce tolerant crops for use in areas where metal contamination is a limiting factor in productivity. It can also assist in understanding the mechanisms of tolerance, as exemplified by the study of the mechanism of arsenic tolerance in Holcus lanatus. Important areas for further research are discussed.

Contents

Summary
541

I.
Introduction
542

II.
Introduction
542

III.
Transmission genetics of tolerance
544

IV.
Specificity of tolerance
550

V.
Molecular genetics of tolerance
552

VI.
Ecological genetics of tolerance
553

VII.
Conclusions
555

Acknowledgements
556

References
556
Further evidence for a correlation between nodulation genotypes in alfalfa (Medicago sativa L.) and mycorrhiza formation
Authors: BRADBURY S. M. , PETERSON R. L. , BOWLEY S. R. 
Published: April 2006

SUMMARYThe vesicular‐arbuscular (VA) mycorrhizal status of three alfalfa (Medicago sativa L.) nodulation genotypes (nod+fix+, nod+fix− and nod−fix−) was investigated using pot cultures of three fungal species from two genera (Glomus monosporum Gerd. & Trappe, Glomus fasciculatum (Thaxter) Gerd. & Trappe emend. Walker & Koske and Gigaspora margarita Becker & Hall). Roots of the nod+fix+ genotype developed complete VA mycorrhizas with each fungus. Roots of the nod+fix− and nod−fix− genotypes did not develop normal VA mycorrhizal symbioses. Roots of the nod− fix− genotype had significantly more appressoria than roots of the other genotypes. Aborted appressoria were unable to penetrate the cortical cells of roots of nod+fix− and nod− fix− genotypes. Measurement of appressorium length, width and approximate contact area revealed significant differences in the size of appressoria produced by each VA mycorrhizal fungus on each alfalfa nodulation genotype. Histological studies of nod+fix+ and nod− fix− genotypes colonized by Glomus versiforme (Karsten) Berch showed the presence of electron‐dense material in aborted appressoria on roots of the nod−fix− genotype but not in appressoria on roots of the nod+fix+ genotype.
Influence of the host on three sub‐Arctic annual facultative root hemiparasites
Authors: SEEL W. E. , PRESS M. C. 
Published: April 2006

SUMMARYGrowth, mineral accumulation and above‐ground dry‐matter partitioning were measured in three sub‐Arctic annual facultative root hemiparasites, Rhinanthus minor L., Euphrasia frigida L. and Melampyrum sylvaticum L., growing either unattached or attached to a host plant. Attached plants were at least an order of magnitude taller than unattached plants, and individuals produced a total above‐ground biomass up to three orders of magnitude greater than that produced by unattached plants. Attached plants produced a greater number of branches, leaves, buds, flowers and ripe seed capsules. Leaf size was greater in attached than unattached plants. For two species, Rhinanthus minor and Euphrasia frigida, the response of individuals attached to a legume was compared to the response of those attached to a grass. Stimulation of parasite growth was greater with a legume host than with a grass. The architecture of parasites on legume hosts differed greatly from those either on grasses or unattached, with those on legumes often having a considerably greater number of second order branches. Above‐ground biomass partitioning was affected by attachment to a host, and was a function of host type. Unattached plants of all three species of parasite accumulated foliar element concentrations within the same order of magnitude as their hosts. Element concentrations in attached plants were sometimes, but not always, greater than those of their hosts. Element concentrations, especially N, were greatest in those parasites attached to a legume.
The deposition of atmospheric ammonia and its effects on plants
Authors: PEARSON JOHN , STEWART GEORGE R. 
Published: April 2006

SUMMARYAcross Europe, total nitrogen deposition is increasing and, of this total, atmospheric ammonia can contribute up to 50–80%. Average deposition of ammonia in the UK is likely to be around 15–20 kg ha−1yr−1, while in The Netherlands, which has some of the highest rates of deposition, this value is likely to be between 40 and 50 kg ha−1yr−1. It is argued that because of the processes of assimilation and nitrification this ammonia is an acidifying pollutant.Ammonia taken up by plants is most likely to be directly assimilated and this uptake can have a strong effect on the nutrient imbalances of the plant. With root uptake in particular, anions are taken up in preference to cations. However, simple soil/plant nutrient measurements are unlikely to be a definitive means of monitoring ammonia pollution. This is because the processes of ammonia metabolism and acidification affect soil ion activity, mycorrhizas, plant uptake, and foliar leaching. These effects interact with acidityper se, and are compounded by the strong correlative co‐deposition of ammonia with sulphur. Evidence for uptake of gaseous and wet deposited ammonia by leaves is presented.The exact mechanism of ammonia toxicity is still not really clear, but could be due to physiological perturbation, rather than to the direct toxicity of the ion. Assimilation of ammonia by leaves releases protons which can cause cellular acidosis, and has important implications for acid‐base regulation in cells. This regulation depends on intrinsic features of the plant's metabolism, that is in turn dependent on the ecology of root versus leaf nitrogen nutrition under normal conditions. Certain species are more acidic in a leaf physiological sense and tend to be prone to damage by pollutants.Likewise, acidic habitats are particularly prone to damage through both eutrophication and the different capacities of plants both to utilize and to buffer against this nitrogen enrichment. The current evidence from The Netherlands suggests that the part this plays in perturbing the ecosystem should not be underestimated.ContentsSummary283I.Introduction284II.Emission and deposition of ammonia284III.Is ammonia toxic?288IV.The eflfects of ammonia deposition289V.Throughfall versus foliar uptake293VI.Physiological effects on ahove‐ground parts296VII.Conclusions301Acknowledgements302References302
The control of exocytosis in plant cells
Authors: BATTEY NICHOLAS H. , BLACKBOURN HUGH D. 
Published: April 2006

SUMMARYExocytosis is a key event in plant cells, linking the internal and external environments. Cell‐wall precursors, membrane material, and soluble and membrane‐associated proteins are supplied by exocytosis and allow cells to grow and differentiate. In this review, we describe exocytotic systems in plants and summarize information on how exocytosis is controlled and itself controls cell development. Mechanisms regulating exocytosis in other organisms are outlined and some critical directions for future research on plant exocytosis are suggested.

Contents

Summary
307

I.
Introduction
307

II.
Exocytotic systems
309

III.
The mechanism of exocytosis
322

IV.
Conclusions and future research
329

Acknowledgements
331

References
331
Immunocytochemical localization of Fe‐SOD in different cells of Anabaena cylindrica Lemm. grown at two different photon irradiances
Authors: CAIOLA MARIA GRILLI , CANINI ANTONELLA 
Published: April 2006

SUMMARYSuperoxide dismutase (SOD) converts superoxide radicals into hydrogen peroxide and molecular oxygen and therefore represents the primary defence against oxygen damage. Using antibodies against Anabaena cylindrica Lemm. iron‐SOD, the isoenzyme was localized by immunogold labelling in vegetative cells, heterocysts and akinetes of the cyanobacterium Anabaena cylindrica grown at different light intensities. At a low photon irradiance (25 μmol photons m−2 s−1), the density of iron‐SOD labelling was similar in vegetative cells and in heterocysts, whereas in akinetes only 60 % of the gold particles were present as compared with the other cell types. At a higher photon irradiance (140 μmol photons m−2 S−1), iron‐SOD labelling increased by 100% in both vegetative cells and in heterocysts but did not change in akinetes. The cultures grown at the photon irradiance of 140 μmol photons m−2 s−1 showed a rate of photosynthetic oxygen evolution 40 % higher than that of cultures grown at the lower photon irradiance. The increase of SOD labelling in vegetative cells is in line with the increased photosynthetic oxygen evolution induced by light. The unchanged SOD labelling observed in the akinetes suggests that light intensity does not seem to affect the oxidative metabolism due to respiratory activity.
Long‐term effects of drought on photosynthesis of adult oak trees [Quercus petraea (Matt.) Liebl. and Quercus robur L.] in a natural stand
Authors: EPRON DANIEL , DREYER ERWIN 
Published: April 2006

SUMMARYEffects of drought on photosynthesis of two co‐occurring oak species (Quercus robur and Q. petraea) have been assessed under natural conditions in a 30‐y‐old stand. Leaf conductance and net CO2 assimilation rates have been measured at midday in situ during two successive summers (1991 and 1992). Chlorophyll a fluorescence parameters were monitored before dawn during the summer of 1991. A severe drought was imposed on two trees per species, resulting in decreases of pre‐dawn leaf potential to about –2.0 MPa during both years. Both species showed the same overall response to drought: gradual decrease of net assimilation and leaf conductance but maintenance at substantial levels down to strong water deficits, stability of the pre‐dawn photochemical efficiency of PS II during the whole period of drought, and declines in pre‐dawn fluorescence (both basic and maximal levels) owing probably to changes in the optical properties of leaves during maturation. It was concluded that both species displayed a strategy of tolerance to drought, and they displayed efficient protection mechanisms against permanent high irradiance damage. Slight differences were observed between both species, Q. robur displaying smaller leaves, lower chlorophyll contents, and a larger stomatal conductance at equivalent net assimilation rates than Q. petraea. Significance of these findings is discussed in relation to the ecological requirements known for each of these species.
Nickel and zinc tolerance and co‐tolerance in populations of Deschampsia cespitosa (L.) Beauv. subject to artificial selection
Authors: VON FRENCKELL‐INSAM BEATRIX A. K. , HUTCHINSON THOMAS C. 
Published: April 2006

SUMMARYThe occurrence of co‐tolerance to four heavy metals was investigated among seedlings selected from three different non‐tolerant Canadian and German Deschampsia cespitosa (L.) Beauv. populations. Plants selected following screening of seedlings in solution containing Ni or Zn ions, subsequently showed enhanced tolerance to Ni and Zn, respectively. ‘Nickel screened’ seedlings exhibited no increased tolerance to Zn.‘Zinc screened’ seedlings, in contrast, had somewhat elevated tolerance to Ni in two of the three populations tested (Elm and Cypress Lake). Thus, co‐tolerance may be a population‐specific rather than a species‐specific response. Individual Elm plants screened for Ni response did not have elevated Zn tolerance, whereas‘Zn screened’ seedlings did show elevated Ni tolerance. This confirms the result from the population tolerance tests. We conclude that co‐tolerance is not a reciprocal process. While the selection for one metal may confer elevated tolerance to a second, selection for the second may not confer tolerance to the first.
Root porosities and radial oxygen losses of Rumex and Plantago species as influenced by soil pore diameter and soil aeration
Authors: ENGELAAR W. M. H. G. , VAN BRUGGEN M. W. , VAN DEN HOEK W. P. M. , HUYSER M. A. H. , BLOM C. W. P. M. 
Published: April 2006

SUMMARYThe effects of hypoxia in ballotini and quartz sand with respectively large and small soil pore diameters on root porosity was studied for Rumex palustris Sra., Rumex acetosa L. and Plantago major L. ssp. major. Under hypoxic conditions R. palustris produced large root pores when large soil pores were present. Absence of such large soil pores resulted in the collapse of the root structure and a reduced root growth. Increases in intercellular spaces in P. major roots seemed to result in a higher root porosity upon hypoxia, a small soil pore diameter or a combination of both but this was not significant. Only a limited number of roots with large root pores was produced. The morphological structure of P. major roots without large root pores remained intact also in soils with a small soil pore diameter. R. acetosa only slightly increased its root porosity upon hypoxia and its morphological structure also remained intact when soil pore diameter was small. Radial oxygen loss (ROL) was found in R. palustris roots when grown in waterlogged, uncompacted soils. P. major had some roots with ROL in all treatments except in waterlogged, compacted soil. R. acetosa did not produce any roots showing ROL. Under field conditions aerenchyma is of no use in water saturated, compacted soils. This explains why a species like R. palustris only grows on hypoxic soil when it is not compacted, in contrast to P. major which will grow on moist, compacted soils. R. acetosa cannot be found on either very moist or heavily compacted soil, since it does not produce a healthy root system under these conditions.
Sugar uptake by protoplasts of the ectomycorrhizal fungus, Amanita muse aria (L. ex fr.) Hooker
Authors: CHEN XIAO‐YA , HAMPP RÜDIGER 
Published: April 2006

SUMMARYProtoplasts have been isolated from the ectomycorrhizal fungus, Amanita muscaria, for the first time. Yields were about 108 protoplasts per g fr. wt of mycelial suspension cultures treated with a combination of Novozym 234, chitinase and cellulase Onozuka R‐10, and osmotically supplemented by 0–55 M sorbitol or 035 M KC1. Silicon oil filtration was used to investigate the uptake of metabolites by protoplasts using labelled compounds. About 66% of the initial protoplast population passed the oil layer after 50 s of centrifugation. Both glucose (as well as 3‐O‐methylglucose) and fructose were taken up by the protoplasts but not sucrose and mannitol. The Km for glucose (fructose) uptake was 1.25 mM (11.3), Vmax was 18 (30) pmoles (106 protoplasts min)−1. Uptake of fructose was strongly inhibited by glucose but not vice versa; uptake of both was not inhibited by sucrose. The much higher affinity for glucose than for fructose suggests that glucose should be the main carbohydrate source for this fungus. Treatment of protoplasts with 10 μM antimycin A lowered cellular ATP/ADP ratios to well below 1 and significantly inhibited uptake of sugars.