bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cellular and molecular defence‐related root responses to invasion by arbuscular mycorrhizal fungi
Authors: GIANINAZZI‐PEARSON VIVIENNE , DUMAS‐GAUDOT ELIANE , GOLLOTTE ARMELLE , ALAOUI A. TAHIRI‐ , GIANINAZZI S. 
Published: April 2006

SUMMARYArbuscular mycorrhizal (AM) fungi, which date from the Devonian era, must have dealt very early on with problems of plant defence, a tactic which has enabled them to colonize roots of most extant plant taxa. Conversely, plants forming arbuscular mycorrhiza must exert some sort of control over the fungi during symbiotic interactions since mycelial proliferation within roots is confined to the cortical parenchyma tissue. Plants possess a panoply of defence mechanisms which are triggered by microbial attack. Here we review present‐day knowledge of defence‐related root responses to colonization by AM fungi, and assess their possible implications in the symbiosis. Weak, transient, unco‐ordinated or extremely localized activation of inducible defence responses occurs during compatible interactions in AM which differs from that in plant–pathogen interactions. When symbiosis‐related plant genes are mutated, typical defence responses are associated with resulting root resistance to arbuscular mycorrhizal fungi whilst, contrastingly, plants constitutively expressing defence genes are unaffected in their symbiotic capacities. The mechanisms by which plants can modulate defence responses during symbiotic interactions and the way in which A1V1 fungi might contend with these are discussed.
Ecological implications of recognition events in the pre‐infection stages of root pathogens
Authors: DEACON J. W. 
Published: April 2006

SummaryHost‐specificity and recognition by root‐infecting pathogens are reviewed, with emphasis on fungi but drawing parallels with other root parasites, symbionts and rhizosphere micro‐organisms. Two major levels of specificity are identified: family‐specific parasitism, exemplified by many parasites that characteristically infect Gramineae, and the possibly recent segregation of pathogen species into crop‐specific strains. In both of these cases there are examples where host‐specificity is paralleled by host‐recognition in the pre‐infection stages, including host‐specific triggering of propagule germination. The pre‐infection sequence of zoosporic pathogens (Pythium, Phytophthora, Aphanomyces spp.) is reviewed. These fungi seem to have both general (low‐affinity) and host‐specific (high‐affinity) receptor‐based recognition systems for chemotaxis to root diffusates and for induction of encystment by host surface components. Zoospores orientate (dock) during encystment, and the cysts germinate from a fixed point, whereas the non‐motile spores of at least some root parasites (e.g. Idriella bolleyi) can germinate from any point, which is influenced by the host.The possession of both general and host‐specific recognition systems by a parasite could enable it to exploit rhizosphere niches or to invade compromised plants in the absence of preferred hosts. Evidence from graminicolous (family‐specific) Pythium spp. suggests that host‐specific recognition is quantitative rather than absolute but, when compounded over successive cycles of infection, is a powerful selective mechanism.
Mycorrhizal diversity in arctic and alpine tundra: an open question
Authors: GARDES M. , DAHLBERG A. 
Published: April 2006

SUMMARYCurrent knowledge of mycorrhizal diversity in arctic and alpine tundra is based mainly on static surveys of mycorrhizal associations of plant taxa and fruiting patterns of selected ectomycorrhizal fungal species in specific habitats. Within these limitations, it appears that: (1) non‐mycorrhizal plants are widespread and predominate in certain plant communities; (2) typical arbuscular mycorrhizal associations are ubiquitous in low arctic and alpine areas but that the level of root colonization is highly variable; (3) root colonization by dark septate fungi is a common event but that their ecological significance is still unknown; (4) a large number of ectomycorrhizal fungal species are present as symbionts of a relatively few widely distributed shrubs and herbaceous plant taxa; (5) ericaceous plants with erieoid mycorrhizas dominate large arctic and alpine areas covered by heath communities. Physical environmental features strongly limit and shape species diversity in arctic and alpine tundra. Cold‐dominated environments provide extreme conditions for the establishment and functioning of mycorrhizal associations. Therefore, such systems are simple models to address the ecology and evolution of mycorrhizal symbioses. Molecular methods to identify mycorrhizal fungi on plant roots will resolve questions related to the structure and dynamics of communities of mycorrhizal fungi in arctic and alpine tundra.
Lux gene technology – a strategy to optimize biological control of soil‐borne diseases
Authors: WHITE DUNCAN , LEIFERT CARLO , RYDER MAARTEN H. , KILLHAM KEN 
Published: April 2006

SUMMARY Lux gene technology is based on the transformation of environmental bacteria with genes of the lux operon from the marine bacteria Vibrio fischeri and V. hurveyi. Transformed strains are bioluminescent and thus provide a rapid and very accurate tool for the study of population dynamics, metabolic activity and spatial distribution of specific bacteria in environmental samples. This review summarizes the recent progress in using lux‐marked rhizobacteria to optimize biological control methods for soil‐borne diseases. Special emphasis has been placed on the advantages and limitations of the new technology.
A model for the partitioning of photosynthetically fixed carbon during the C3‐CAM transition in Sedum telephium
Authors: BORLAND ANNE M. 
Published: April 2006

SUMMARY Sedum telephium is a succulent plant in which CAM‐cycling is rapidly induced or enhanced in response to drought stress. Diel measurements of leaf malate content and gas exchange demonstrate that as drought stress increased, daytime uptake of CO2 declined and less respiratory CO2 was lost at night as a result of re‐fixation by phosphoenolpyruvate carboxylase (PEPC) with subsequent accumulation of malate. The enhancement of CAM‐cycling in response to drought stress under high and low photon flux density (PFD) results in up to fourfold increases in daily water use efficiency. Moreover, potential conservation of water resulting from CAM‐cycling varied from 4 to 77 % of total daytime transpiration, depending on PFD and severity of drought. Measurements of instantaneous C‐isotope discrimination demonstrated the activation of PEPC activity in vivo with a minimal direct contribution from C4 carboxylation to net CO2 uptake during the day. The δ13C composition of carbohydrates and organic acids indicated that products of malate breakdown are preferentially directed towards starch during the day, which subsequently supplies phosphoenolpyruvate (PEP) for the dark reactions of CAM. The data are summarized using a model which quantitatively describes the source of carbon in the leaf during the day (C3 or C4) and the partitioning of this carbon between the generation of substrate for CAM, production of respiratory CO2 or export. The resulting carbon budgets illustrate that the breakdown of starch at night increases up to twofold with severe drought stress, whilst the flux of carbon into starch during the day is maintained or even increased, largely at the expense of the soluble sugar pool. Overall, under high PFD the enhancement of CAM‐cycling permits continued growth under conditions of severe drought, albeit at a reduced rate. However, under low PFD, the induction of CAM‐cycling serves mainly as a maintenance mechanism whereby water is conserved and a positive carbon balance is preserved by recycling carbon skeletons at the expense of growth during periods of severe water shortage.
Estimations of apoplastic concentrations of K+ and Ca2+ in the vicinity of stomatal guard cells
Authors: DE SILVA D. L. R. , HONOUR SARAH J. , MANSFIELD T. A. 
Published: April 2006

SUMMARYA method which determines the null point for stomatal aperture has been used to estimate the apoplastic concentrations of potassium and calcium adjacent to the stomatal guard cells of Commelina communis. These two ions are contributors to important aspects of stomatal physiology: the determination of guard cell turgor (K+) and intracellular signalling (Ca2+) when the guard cells respond to the various stimuli that effect changes in stomatal aperture. We obtained estimates of apoplastic K+ concentrations in the range of 50–75 mol m‐3, which are in general agreement with those of Bowling (1987). Ca2+ concentrations appear to be in the region of 0·05 mol m‐3 adjacent to the guard cells even though much higher concentrations (up to 4 mol m‐3) may be delivered to the leaf in the xylem sap. Thus it is suggested that the gradient in apoplastic Ca2+ may be very large over short distances, and may be strictly controlled by cells within the epidermis.
The genotoxicity of Zn(II) and Cd(II) in Allium cepa root meristematic cells
Authors: BORBOA L. , DE LA TORRE C. 
Published: April 2006

SUMMARYApplications of 5 × 10‐4m Zn(II) and 3 × 10‐5m Cd(II) depressed but did not block root growth in Allium cepa L. Both heavy metals were indirect clastogens at these moderate concentrations, for they induced the appearance of chromosomal bridges, but no breaks were detected in the first anatelophases. On the other hand, Zn and Cd respectively potentiated six and eleven times the direct clastogenic effect of the β‐irradiation produced by [3H]thymidine incorporation into DNA. The chromosomal breaks at mitosis were more abundant when [3H] was incorporated into early replicating DNA. On the other hand, when the incorporation took place in the last half of interphase, the subsequent G2 as well as the prophase were extended (1·7‐fold for Zn and 2·7‐fold for Cd), and the Sexcess lesions were repaired before anaphase. The whole cycle experienced 1·5 and 2·0‐fold increases in the presence of Zn and Cd in relation to that in control meristems (15 h).
Factors determining the growth curve of the foliose lichen Parmelia conspersa
Authors: ARMSTRONG R. A. , SMITH S. N. 
Published: April 2006

SUMMARYGrowth curves of the foliose lichen Parmelia conspersa (Ehrh. ex Ach.) Ach. were obtained by plotting radial growth rate (RGR, mm yr‐1) of the fastest measured lobe, the slowest measured lobe, a randomly selected lobe, and by averaging a sample of lobes from each thallus against thallus diameter. Growth curves derived from the fastest‐growing lobe and by averaging lobes were asymptotic and could be fitted by the growth model of Aplin and Hill. Mean lobe width increased with thallus size, reaching a maximum at approx. 4· cm thallus diameter. In four out of six thalli, radial growth of lobes over 4 months was positively correlated with initial lobe width or area. The RGR of isolated lobes was unaffected until the base of the lobe was removed to within 1–2 mm of the tip. The concentration (μg mg‐1 biomass) of ribitol, arabitol and mannitol was greater in the marginal lobes of large than in small thalli. These results suggested that the growth curve of P. conspera is determined by processes that occur within individual marginal lobes and can be explained by the Aplin and Hill model. Changes in lobe width and in the productive capacity of individual lobes with thallus size are likely to be more important factors than the degree of translocation within the lobe in determining the growth curve.
Aerial dispersal of lichen soredia in the maritime Antarctic
Authors: MARSHALL WILLIAM A. 
Published: April 2006

SUMMARYAn aerobiological monitoring programme was carried out for over a year on Signy Island, South Orkney Islands, Antarctica. Collections were made using arrays of rotorod samplers at three sites. Lichen soredia were found to be the most abundant air borne propagules, more so than ascospores, the sexual propagules of lichen fungi. The dominance of soredia over ascospores appeared to decrease with increasing maturity of fellfield sites. No correlations were found with temperature, relative humidity or wind speed. Collections at 1 m above ground level were shown not to be significantly different to those at 0·15 m at two of the sites. Size range distribution also differed at two of the sites. Soredial clumps in excess of 100 μm in diameter were collected at 1 m above ground level and at some distance from potential source plants, though most fell in the range 30–60 μm. Peaks in numbers of air borne soredia were found after winter snow melt, demonstrating that soredial production continues at subzero temperatures.
Effects of soil pH on the ectomycorrhizal response ofEucalyptus urophyllaseedlings
Authors: AGGANGAN NELLY S. , DELL BERNARD , MALAJCZUK NICHOLAS 
Published: April 2006

SUMMARYTo examine the effects of soil pH on ectomycorrhizal formation and function onEucalyptus urophyllaS. T. Blake, seedlings inoculated with nine ectomycorrhizal fungi (seven isolates ofPisolithusspp.,Scleroderma cepaandLaccaria laccatacollected under eucalypt stands in Australia and the Philippines) were transplanted into pots containing a non‐sterile acid (pH 4·6) sandy loam amended with four levels of CaCO3that raised the soil pH from 4·6 to 6·6 (5 mM CaCl2). Pots were placed in temperature‐controlled water baths (28 ± 2 °C) inside an evaporatively cooled glasshouse for 9 wk.Increase in soil pH from 4·6 to 6·6 significantly decreased plant d. wt and shoot nutrient content of uninoculated and inoculated seedlings. Inoculation with fourPisolithusspp. (H445, H2144, M56 and H4003) significantly increased the growth ofE. urophyllaseedlings at pH 4·6. At pH 6·6, eight ectomycorrhizal isolates significantly improved total d. wt compared with those of the uninoculated seedlings.Pisolithusisolates stimulated seedling growth more thanL. laccatawhereasS. cepawas ineffective at all pH levels. Total d. wt of H445 inoculated plants grown in P‐deficient (8 mg P kg‐1soil) soil was 147% more than that of uninoculated plants given the same P rate and was 70% that of plants fertilized with 64 mg P kg‐1soil (P64) at pH 46. At soil pH 5·8 and 6·6, M56 was the best growth‐promoter forE. urophylla.These results indicate that soil pH can significantly alter the development and function of ectomycorrhizal fungi. Soil pH did not significantly affect mycorrhizal formation by the different ectomycorrhizal fungi. However, the percentages of mycorrhizal root tips formed by the different ectomycorrhizal fungi differed significantly.Pisolithusisolate H445 formed the highest percentage of colonized roots and highest total d. wt at pH 4·6 and 5·2, implying its potential for commercial use in acidic conditions.
Xylem recovery from cavitation‐induced embolism in young plants of Laurus nobilis: a possible mechanism
Authors: SALLEO SEBASTIANO , GULLO M. ASSUKTA LO , DE PAOLI DOROTEA , ZIPPO MANUELA 
Published: April 2006

SUMMARYXylem recovery from cavitation‐induced embolism was studied in l‐yr‐old twigs of Laurus mibilis L. Cavitation was induced by applying pre‐established pressure differentials (AP0,1) across the pit membranes of xylem conduits. ΔP0) were 1.13, 1.75 and 2.26 MPa, corresponding to about 50, 77 und 100% of the measured leaf water potential at the rurgor loss point ΔP0,1 were obtained either by increasing xylem tensions or by applying positive pressures from outside, or by a combination of the two. The percentage loss of hydraulic conductivity (PLC) did not change, regardless of how the ΔP0–1 were obtained. This confirmed that xylem cavitation was nucleated by microbubbles from outside the vessels. Positive pressures, however, amplified (up to 75%) and sped up the xylem refilling (20 min) in comparison with that measured in unpressurized twigs (c.50% in 15 h). Twigs girdled proximally to their pressurized segment 1 nun after the desired pressure value had been reached, did not recover from embolism. The later the twigs were girdled with respect to when they were tested for PLC, the higher was their recovery from embolism, suggesting that some messenger was transported in the phloem which stimulated xylem refilling. Indol‐3‐acetic acid (1AA] applied to the exposed cortex of both pressurized and unpressurized twigs, induced an almost complete recovery from PLC. We hypothesize that the refilling of cavitated xylem might be a result of an auxin‐induced increase in the phloem loading with solutes. This would cause radial transport of solutes to cavitated xylem conduits via the rays, thus decreasing their osmotic potential and making them refill. No positive xylem pressure potentials were measured during xylem recovery from PLC.
Growth and sugar accumulation in durum wheat plants under water stress
Authors: KAMELI A. , LÖSEL D. M. 
Published: April 2006

SUMMARYThe effect of water stress on growth of Trillium durum L. was investigated in relation to sugar accumulation and water status of wheat plants before, during and after a period of water stress. The slight decrease in water potential in the first few days after withholding water had no detectable effect on growth. Inhibition of growth was only apparent when the water content started to decline. Dry weight continued to increase during water stress, even under severe stress (after day 27) which was associated with n sharp rise in sugar content, accounting for 20% of the gain in dry matter between days 27 and 31. The increase in leaf length and leaf area of stressed plants fallowing re‐watering, from day 31, was owing to the leaves regaining turbidity after witting. Growth inhibition coincided with a considerable increase in sugar content. The role of growth inhibition and other factors in sugar accumulation under water stress is discussed, Photosynthesis rather than reserve starch might be the major source of sugar accumulated under water stress in durum wheat.
Tillering and partitioning of dry matter and nutrients in Lolium perenne growing with neighbours of different species: effects of nutrient supply and defoliation
Authors: MARRIOTT CAROL A. , ZUAZUA M. TERESA 
Published: April 2006

SUMMARYThe hypotheses that performance of Lolium perenne L. (ryegrass) differs when plants grow with conspecific or heteraspecific neighbours, and that nutrient supply and severity of defoliation modifies the effect, were tested in a target: neighbour pot experiment. Target L. perenne plants were grown with neighbours of five grass species (L. perenne, Poa pratensis L., P. trivialis L., Festuca ovina L. and F. rubra L.) and Trifolium repens L. (white clover), at three nutrient levels (high, medium and low) and three defoliation severities (no defoliation or cut every 2 wk to 4 cm or 8 cm) over a 12 wk experimental period. Performance of L. perenne plants differed depending on the species of neighbour. Tiller numbers and dry weights of clippings of L. perenne, at both individual cuts and the total accumulated over all seven cuts, were greater with P. pratensis, F. ovina or T. repens as neighbours than in a monoculture. The differences were generally confined to medium and high nutrient levels. The pattern of clippings depended on species association: clippings were similar at successive cuts except in mixtures with P pratensis, F. ovina and T. repens, where they increased until the 4–5th cuts. The total accumulated dry matter (DM) and nutrients of L. perenne and the percentage contribution of DM to the pot total were also greater in these mixtures. Individual linear regressions of tiller numbers and accumulated N for each species combination best described the relationships between L. perenne and its neighbour. Neighbouring species had no significant effect on the relative losses of dry weight of nutrients in clippings of L. perenne when expressed as a proportion of the total accumulated, but partitioning of DM to L. perenne roots (root weight ratio) was greater in associations with Poa species than in a monoculture. It was concluded that the species of neighbour affected the accumulation and partitioning of dry matter and nutrients in L. perenne and that nutrient supply, but not defoliation, modified the responses. The results are discussed in relation to species interactions in grazed swards.
Response to phosphorus supply of tropical tree seedlings: a comparison between a pioneer species Tapirira obtusa and a climax species Lecythis corrugata
Authors: RAAIMAKERS DORINNE , LAMBERS HANS 
Published: April 2006

SUMMARYThe highly‐weathered acid sandy soils in Guyana, South America, art very low in nutrients, especially in phosphorus (P) Earlier experiments demonstrated that P was growth‐limiting for some tree seedlings on these soils, but other species failed to increase their growth in response to greater P‐availability. To investigate this, we measured growth and distribution (if biomass and P of tree seedlings, of a pioneer tree species, Tapirira obtusa (Benth.) Mitchell, and of a climax tree species, Lecythis corrugata Poit., at 10 levels of P‐supply under controlled conditions in a glasshouse. At intervals of 3 wk. dry weights of plant parts and their phosphorus concentrations were measured. The pioneer and the climax species took up similar amounts of P when grown at high P‐supply. The pioneer tree T. obtusa maintained a low P concentration (0.25 mg g−1) independent of P‐supply, and used the P taken up Hi increase growth., At high P‐supply it invested little biomass in roots, and reached a relative growth rate (RGR) of 40 mg g−1 d−1. The climax, tree species, L, corrugate, maintained a low RGR of 10 mg g−1 d−1 and a constant distribution of biomass at all P‐supply rates. It stored the extra P in a structure between the stem and root derived from the former hypocotyl, which persisted for over 6 months after germination. The differences m growth and distribution of biomass and P in response to P‐supply of the two species are likely to contribute to the establishment of their seedlings in the field. If L. corrugata is capable of re‐translocating P from the hypocotyl, this storage of P has ecological advantages for long‐term survival, which might be important under low light conditions. Together with a low RGR, it enables a seedling to maintain P‐reserves until a gap occurs. In a newly created gap, P‐availability per seedling increases, and pioneers, with their higher P uptake and growth potential, can benefit from these relatively higher levels of P‐availability. This is an important advantage in high‐light gap environments where the tallest tree seedling is generally the most competitive one.
Benomyl inhibits phosphorus transport but not fungal alkaline phosphatase activity in a Glomus–cucumber symbiosis
Authors: LARSEN J. , THINGSTRUP I. , JAKOBSEN I. , ROSENDAHL S. 
Published: April 2006

SUMMARYShort‐term effects of benomyl on the arbuscular mycorrhizal fungus Glomus caledonium (Nicol. & Gerd.) Trappe and Gerdeman associated with Cucumis sativus L. were studied by measuring effects on fungal P transport and on fungal alkaline phosphatase activity. Mycorrhizal plants were grown in three compartment systems where nylon mesh was used to separate n root‐free hyphal compartment (HC) and a root + hyphal compartment(RHC) from The main root compartment (RC). Non‐mycorrhizal control plants were grown in similar growth units. After 6 wk benomyl was applied to the plants in three ways: as soil drenches to RHC or HC, or as u spray to the leaves. Benomyl was added in three concentrations. Equal amounts of 32P and 33P were added to the HC and to the RHC respectively, immediately after the application of benomyl. Plants were harvested 4–6 d later. Hyphal transport of 32P from the HC was inhibited when benomyl was applied to the HC at 10 μg g−1 soil, whereas the uptake of 32P from RHC I roots + hyphae) was reduced only at the highest dose of application to the RHC (100 μ g g−1 soil). In contrast to the marked reduction of benomyl on fungal P transport, the activity of fungal alkaline phosphatase inside the roots was unaffected by benomyl.