bluuebunny/crossref_metadata_2025 huggingface dataset:
Imbalanced nuclear ratios, post‐germination mortality and phenotype—genotype relationships in allopatrically‐derived heterokaryons of Heterobasidion annosum
Authors: RAMSDALE MARK , RAYNER ALAN D. M.
Published: April 2006

summary

Twelve heterokaryotic strains of Heterobasidion annosum (Fr.) Bref. containing nuclei and mitochondria derived from British and North European populations were prepared by pairing homokaryotic strains and isolating hyphal tips from either side of interaction interfaces. Conidia derived from the heterokaryons had high germinability and were predominantly uninucleate. The nuclear genotypes recovered from these conidia were predominantly nonresident in origin, reflecting the marked asymmetry m nuclear ratios (as high as 9:1) in favour of invasive nuclei that developed in the mycelium. In spite of this asymmetry, the heterokaryons had similar phenotypes to the resident homokaryons that they were derived from.

Whereas the relative ability of sib‐related nuclei to become established in a homokaryon was about equal in sympatric protoplasm, it could be very different in allopatric protoplasm. Post‐germination mortality due to the cessation of development following transfer of germlings to fresh medium was on average similar for allopatric and sympatric conidia, but there was a marked trend for reduction in mortality as nuclear ratio asymmetry increased. Homokaryons derived via conidia from a common heterokaryon exhibited less somatic incompatibility when paired together than did the original, basidiospore‐derived strains.

These findings indicate that phenotype–genotype relationships resulting from allopatric matings, such as could occur following geographical transposition, are liable to differ radically from those in sympatric matings and so have potentially profound effects on resident population structure.
Occurrence of genets of Armillaria spp. in four mountain forests in Central France: the colonization strategy of Armillaria ostoyae
Authors: LEGRAND PHILIPPE , GHAHARI SEPIDEH , GUILLAUMIN JEAN‐JACQUES
Published: April 2006

summary

Four forests each of 4–8 ha were investigated in Central France: (1) a pure beech stand harbouring only the saprophytic species Armillaria gallica and A. cepistipes; (2) a pure beech stand with the same species plus A. ostoyae; (3) an ancient beech stand to which conifers had been introduced 60 yr ago, and in which A. ostoyae was becoming the dominant species with A. gallica and A. cepistipes still present; (4) a young pine stand on an old conifer site, where A. ostoyae was exclusive and pathogenic. A total of 764 isolates was obtained from rhizomorphs, fruiting bodies and mycelia from stumps. Mapping of genets of the different Armillaria species was carried out on the four sites by testing for somatic incompatibility. This allowed comparison of the number, area and distribution of the genets of the different species. There was complete overlap of the genets of A. ostoyae with those of A. cepistipes or A. gallica, suggesting different colonization strategies. By contrast, the genets of A. gallica and A. cepistipes overlapped only rarely, suggesting similar colonization strategies. Two different genets of the same species intermingled only in a limited area along their border. In the conifer plantation, A. ostoyae tended to colonize the stumps whereas the other two species prevailed as rhizomorphs in the litter, but the competition was evolving in favour of A. ostoyae. At the fourth site, where the stumps had been uprooted and the pine seedlings had been left to grow, a large number of small genets of A. ostoyae was observed, suggesting recent infection by basidiospores.
A comparison of different methods for the identification of genets ofArmillariaspp.
Authors: GUILLAUMIN JEAN‐JACQUES , ANDERSON JAMES B. , LEGRAND PHILIPPE , GHAHARI SEPIDEH , BERTHELAY SUZANNE
Published: April 2006

summary

In a previous study, somatic incompatibility (SI) was used to map the genotypes (or genets) of threeArmillariaspecies(A. ostoyae, A. gallica, A. cepistipes)at four forest sites. A total of 109 genets was identified among 764 isolates of the three species. The object of the present study was to compare SI with three other methods of distinguishing genets: Random Amplified Polymorphic DNAs (RAPD), mating‐type alleles, and isoenzyme analysis. RAPDs and mating‐type alleles were used with 73 isolates belonging to 36 genets identified on the basis of SI reactions. A few isolates were assayed for isoenzyme polymorphism. RAPDs, mating‐type alleles, and SI were equal in their ability to distinguish genets in the populations tested. In three cases, isolates distinguished by SI reactions included two subgroups with different RAPD phenotypes. In two cases groups distinguished by different SI reactions shared the same set of mating‐type alleles. Isoenzyme analysis showed interspecific differences and a few differences between the genets of the same species. These results validate the use of SI as a routine method for epidemiological studies ofArmillariaspp.

TheEcoRI fragment profiles of mitochondrial DNA of the same group of isolates were also assayed. The analysis regrouped the genets into ‘mitochondrial types’ sharing a common cytoplasm and possibly closely related to one another through sexual reproduction. Each mitochondrial type consisted of one to five different genets.
Effects of phosphorus and ectomycorrhiza on maritime pine seedlings (Pinus pinaster)
Authors: CONJEAUD C. , SCHEROMM P. , MOUSAIN D.
Published: April 2006

summary

The purpose of this study was to determine how ectomycorrhizal infection and phosphorus nutrition affect biomass, photosynthesis and root respiration in the host plant. Maritime pine (Pinus pinasterSoland.inAit.) seedlings grown in containers filled with perlite–vermiculite were inoculated with the ectomycorrhizal fungusHebeloma cylindrosporum(strain D3.25.9) and given 0 or 0.5 mM phosphate in the nutrient solution.Hebeloma cylindrosporuminfection increased net photosynthesis and root respiration rates compared with those of non‐mycorrhizal plants, but there was an accompanying 35 % depression in growth. The addition of phosphorus to non‐mycorrhizal plants induced a rise in tissue phosphorus content which made them similar m that respect to mycorrhizal plants but did not result in increased photosynthesis. The nitrogen content of mycorrhizal plants was, moreover, lower than that of the control group. The data recorded were consistent with the photosynthate source‐sink hypothesis. The increase in fixed carbon in mycorrhizal plants was unable to compensate for the increased carbon cost of the mycorrhizal root system.
An experimental study of growth in relation to morphology and shoot water content in maritime Antarctic mosses
Authors: FOWBERT J. A.
Published: April 2006

summary

The dependence of shoot growth and growth form on water availability was studied experimentally in six species of maritime Antarctic moss. Under all conditions the largest growth increments were observed in the hydric species Brachythecium austro‐salebrosum and Drepanocladus uncinatus. The xeric Andreaea depressinervis grew the least. Lateral shoot production varied within and between species. Over 50 % of the biomass produced in D. uncinatus was derived from lateral shoot production, whereas Polytrichum alpestre produced very few lateral shoots and A. depressinervis produced none. Leaf density and leaf size also varied with total water content.

In all species growth ceased at total water contents of 100% d. wt or less. However, the total water content at which maximum growth was observed differed between species. Racomitrium austro‐georgicum (mesic/xeric) had the lowest optimum for growth at 370% of d. wt and D. uncinatus (hydric) exhibited maximum growth between 890 and 2300% d. wt. Optimum total water contents for growth were greater than those at full turgor and published optima for net assimilation.

Growth and total water content of these Antarctic mosses were similar to those reported for temperate species.
A molecular characterization of the Gunnera–Nostoc symbiosis: comparison with Rhizobium– and Agrobacterium– plant interactions
Authors: RASMUSSEN ULLA , JOHANSSON CHRISTINA , RENGLIN ANNA , PETERSSON CARL , BERGMAN BIRGITTA
Published: April 2006

summary

The Gunnera‐Nostoc symbiosis is a N2‐fixing endosymbiosis between an angiosperm and a prokaryote, in some respects showing similarities to legume‐rhizobial symbioses as well as to pathogenic Agrobacterium‐plant interactions. We here describe the results of a molecular comparison of these systems, along with a characterization of the Gunnera mucilage which is important for Gunnera–Nostoc communication.

Nostoc DNA sequences homologous to the rhizobial nodEF, nodMN, exoY genes, along with the nod box, were identified by heterologous hybridization, whereas no homologues to either nodABC, nodD1 or nodD2 were found. Nevertheless, no anti‐Nod protein antibodies recognized any Nostoc protein, either in normally grown or mucilage‐induced cells. Furthermore, probes containing the agrobactenal chvA, chvB and picA genes also hybridized with Nostoc DNA, whereas virA and virG genes did not.

Using rhizobia with nod gene–lacZ fusions as reporters, Gunnera mucilage and seed rinse were shown to possess nod gene‐inducing activity.

The mucilage secreted by the Gunnera stem gland, the organ susceptible to Nostoc infection, was composed of arabinose and galactose in relative molar proportions of 1.00:0.25, with an additional 0.13 molar parts of glucuronic acid. It showed a reaction on dot blot assays with the arabinogalactan protein‐specific monoclonal antibody MAC 207, indicating that it contains arabinogalactan proteins.
Phragmites die–back: bud and root death, blockages within the aeration and vascular systems and the possible role of phytotoxins
Authors: ARMSTRONG J. , ARMSTRONG W. , VAN DER PUTTEN W. H.
Published: April 2006

summary

Die‐back and healthy stands of Phragmites australis (Cav.) Trin. ex Steud in the UK and Hungary were compared in terms of stand architecture, plant morphology and anatomy, sediment redox potential and sulphide levels, plant resistance to internal Poiseuille gas flow, and convective flow characteristics of culms. Compared with healthy sites, die‐back sites were characterized by lower sediment redox potentials, and in Hungary by very high sulphide levels. Plants at die‐back sites showed a markedly clumped distribution, with fewer new shoots and fewer old flower heads than those at healthy sites, a high incidence of dead and decaying rhizomes and roots, and dead ‘overwintering’ and ‘growing season’ buds, and occasional prematurely senesced culms. Dead and stunted adventitious roots with short peg‐like laterals were very common, and there was abnormal lignification and suberization within the cortex and epidermis/hypodermis of adventitious root apices, and in the epidermis of lateral roots. Callus was found blocking the internal aeration pathways in root aerenchyma, root‐rhizome junctions, rhizome nodes and the bases of buds and culms. Blockages of the vascular elements of both xylem and phloem in rhizomes and roots were also common. At the die‐back sites, callus accounted for a greater resistance to gas flow from the dead aerial culms into the rhizome system. Compared with healthy culms, prematurely senesced culms from die‐back sites exhibited smaller potentials for aerating the rhizome system by humidity‐induced convection.

It is suggested that die‐back in Phragmites might be brought about and perpetuated at least partly by phytotoxins which induce (a) blockages within the aeration pathways due to callus development, (b) stunting of roots and the development of abnormal root wall lignification and suberisation causing interference with water and mineral absorption, and (c) internal blockages causing interference with vascular transport. A tentative scheme for Phragmites die‐back is presented.
Waterlogging and survival in Sesleria albicans
Authors: DIXON JEAN M.
Published: April 2006

summary

The performance of Sesleria albicans Kit. ex Schultes, a species usually found in dry limestone habitats, but also recorded in wet places, was examined over a period of 2 yr along a soil‐water gradient. This supplied a ‘dry’ end with the water‐table 22 cm below the surface, grading to a ‘wet’ end with the water‐table at the surface, providing static waterlogged conditions. The performance of plants (judged from measurements of tussock diameter, plant height, panicle length, counts of the number of panicles and spikelets per panicle, and shoot and root d. wt) was progressively impaired with increasingly waterlogged conditions. Previously waterlogged ramets recovered when removed to non‐waterlogged soil, showing that waterlogging had stunted but not killed the roots.

The effects of waterlogging were demonstrated by a pot experiment to be similar in three different types of soil. Differences in the performance of S. albicans in these (determined by counts of the number of tillers, number of nodal axes and measurements of leaf length, root length, and shoot and root d. wt) were a result of factors other than waterlogging, since the differences were maintained in both waterlogged and normally watered soil.

Although performance of S. albicans was adversely affected in static waterlogged soils, none of the plants died, even after 2 yr. Possible explanations for the survival of S. albicans were sought.
The role of mycorrhizas in the response ofPinus taedaseedlings to elevated CO2
Authors: LEWIS J. D. , STRAIN B. R.
Published: April 2006

summary

The effects of mycorrhizal status, phosphorus supply and CO2, partial pressure on production and allocation of biomass in seedlings from two populations ofPinus taedaL. were examined. Seedlings from a North Carolina and a Florida population were grown in sterile soil in a full‐factorial experiment with one of two phosphorus treatments (low P, high P) and at one of two CO2partial pressures (35.5, 71.0 Pa). One half of the seedlings were inoculated withPisolithus tinctorius(Pers.) Coker & Couch hyphae and spores. Seedlings were harvested 60, 90 and 120 d after emergence. Elevated CO2significantly increased total seedling dry mass in all treatments at all three harvests. Phosphorus limitation reduced seedling growth, and mycorrhizas increased seedling growth in seedlings limited by phosphorus supply. Generally, however, there were no interactions between CO2, phosphorus supply and mycorrhizal status on dry mass of seedlings. Mycorrhizas probably did not affect the response of dry mass to elevated CO2, because phosphorus limitation did not reduce response of dry mass to elevated CO2, Phosphorus‐limited seedlings responded to elevated CO2, as a result of increased phosphorus uptake, resulting from increased total root dry mass, and increased phosphorus use efficiency. Although mycorrhizal colonization did not affect the response of biomass to elevated CO2, it significantly reduced the response of needle area. As a result, specific leaf area (leaf area per unit plant biomass) was lower in mycorrhizal seedlings grown in elevated CO2than in mycorrhizal seedlings grown in ambient CO2Because there were no effects on relative growth rate or seedling dry mass, reductions in specific leaf area suggest that elevated CO2reduced the relative cost of the symbiosis.
Facilitation of plant phosphate acquisition by arbuscular mycotrhizas from enriched soil patches
Authors: CUI MUYI , CALDWELL MARTYN M.
Published: April 2006

summary

Mycorrhizal contribution to nutrient acquisition from spatially heterogeneous soil was investigated using two‐way comparisons of non‐mycorrhizal and arbuscular mycorrhizal Agropyron desertorum (Fisch. ex Link) Schult. in soil with either a patchy or a uniform nutrient distribution. Double‐labelling allowed a comparison between acquisition of an ion of lower abundance and mobility, phosphate (P), and an ion of higher abundance and mobility, nitrate. As expected, root density increased in enriched‐nutrient patches relative to either unenriched soil or to soil where the same quantity of nutrients was applied to the entire soil volume (uniform‐nutrient treatment). However, the increase of local root density in patches was less for mycorrhizal plants than for non‐mycorrhizal plants. Mycorrhizal infection enhanced plant acquisition of labelled P relatively more in the enriched patches (patchy‐nutrient treatment) than in soil with uniform nutrient distribution, both when expressed on a shoot mass and on a root‐length basis. As expected, plant nitrate acquisition and shoot nitrogen concentration were not significantly affected by either mycorrhizal infection or patterns of soil nutrient distribution. Hence, arbuscular mycorrhizas can enhance root P acquisition and, thus, contribute to plant exploitation of soil P heterogeneity.
Facilitation of plant phosphate acquisition by arbuscular mycorrhizas from enriched soil patches
Authors: CUI MUYI , CALDWELL MARTYN M.
Published: April 2006

summary

Effects of arbuscular mycorrhizas (AM) on plant exploitation of soil nutrient heterogeneity were studied with non‐mycorrhizal and mycorrhizal Agropyron desertorum (Fisch. ex Link) Schult. in two‐compartment containers. A central cylindrical plant compartment was separated from an outer hyphal compartment by two layers of stainless‐steel screen with a 2 mm air gap between the screen layers. Patchy or uniform nitrate (NO2−) and phosphate (P) distribution patterns were created in the outer compartment. Only AM hyphae could cross the double‐screen barrier to access those nutrients. Mycorrhizal plants acquired significantly more labelled P in both the patchy‐ and the uniform‐nutrient treatments than did non‐mycorrhizal plants. Mycelia in root‐free soil delivered similar amounts of P from the more distant rich patches to mycorrhizal plants as from the uniform and more proximate labelling. The uptake of a more mobile and abundant element, nitrate, was not affected significantly by either mycorrhizal infection or by nutrient distribution patterns in the root‐free soil. Despite a lower root:shoot mass ratio, mycorrhizal plants had significantly greater shoot phosphorus concentration than did nonmycorrhizal plants. There was no significant difference in P uptake or phosphorus concentration between the two nutrient distribution patterns for mycorrhizal plants, indicating that AM hyphae can explore the root‐free soil for available P and transport it to host plants equally well when P was distributed in either patchy or uniform patterns in the root‐free soil.
Growth and mineral nutrition of non‐mycorrhizal and mycorrhizal Norway spruce (Picea abies) seedlings grown in semi‐hydroponic sand culture
Authors: ELTROP LUDGER , MARSCHNER HORST
Published: April 2006

summary

Growth, nitrogen uptake and mineral nutrient concentrations in the plant tissues were determined in non–mycorrhizal and mycorrhizal Norway spruce (Picea abies (L.) Karst.) seedlings grown under controlled conditions in a semi‐hydroponic culture system with quartz sand as substrate and a percolating nutrient solution. The culture system allowed the determination of nutrient uptake rates in mycorrhizal root systems with an intact extramatrical mycelium. The rate of infection of the roots by the mycorrhizal fungi Pisolithus tinctorius and Laccaria laccata was high but the rate of infection by Paxillus involutus was low.

When supplied with ammonium nitrate, the d. wt of the roots and particularly of the shoots was significantly lower in mycorrhizal than in non–mycorrhizal plants. Despite the lower root d. wt, the number of root tips and the root branching ratio (number of root tips per unit root length) were significantly higher in mycorrhizal plants infected with L. laccata and P. tinctorius than in non–mycorrhizal plants. The depletion of ammonium in the external solution was faster than the depletion of nitrate. Nitrate uptake rates increased at ammonium concentrations below 400μM. The maximal N uptake rates (Vmax), calculated after Lineweaver–Burk, were significantly higher for ammonium than for nitrate. The N uptake rates did not differ significantly between non–mycorrhizal and mycorrhizai plants. The concentrations of N, P, K, Ca and Mg tended to be higher in the smaller mycorrhizal than in the larger non–mycorrhizal plants. A significant increase in mineral nutrient concentration in mycorrhizal compared with non–mycorrhizal plants was found only for N concentrations in the needles of mycorrhizal plants infected with P. tinctorius.

When they were supplied with ammonium ((NH4), SO4) as source of N, but not when they were supplied with nitrate (KNO3), the d. wt was lower in mycorrhizal plants infected with P. tinctorius than it was in non‐mycorrhizal plants. Therefore, N uptake rates were increased in mycorrhizai plants with P. tinctorius only when they were supplied with ammonium but not with nitrate.

The insignificant differences in uptake rates of N, P, K, Ca and Mg between non–mycorrhizal and mycorrhizal plants indicate that at unlimited spatial nutrient availability the contribution of the extramatrical mycelium to nutrient uptake by mycorrhizal plants was small. It is suggested that the decreased growth of mycorrhizal plants is due to the demand of the mycorrhizal fungus for photosynthates, i.e. source limitation.
Growth and mineral nutrition of non‐mycorrhizal and mycorrhizal Norway spruce (Picea abies) seedlings grown in semi‐hydroponic sand culture
Authors: ELTROP LUDGER , MARSCHNER HORST
Published: April 2006

summary

In seedlings of Norway spruce(Picea abies(L.) Karst.), grown in semi‐hydroponic sand culture, mycorrhizal infection decreased growth (Eltrop & Marschner, 1996). Possible reasons for this growth depression were investigated in the present study by comparing the plant and fungal biomass distribution and carbon partitioning between non‐mycorrhizal and mycorrhizal(Pisolitlius tinctorius)plants supplied with ammonium or nitrate as source of N.

Despite the high mycorrhizal infection rate (55–71% of total root tips), the amount of fungal biomass in roots and extramatrical mycelium of mycorrhizal plants accounted for less than 3% of plant dry matter and was significantly lower in nitrate‐ than in ammonium‐supplied plants.

The CO2assimilation rates were higher in mycorrhizal than in non‐mycorrhizal plants supplied with ammonium as well as those supplied with nitrate. High light intensity considerably increased CO2assimilation rates. The respiration rates of the intact root systems were significantly increased in ammonium‐supplied mycorrhizal plants compared with non‐mycorrhizal plants. The amount of CO2lost in root respiration as a percentage of the amount of CO2gained in photosynthesis (respiratory quotient), ranged from 49.3% at 30°C root zone temperature and low light intensity (290 μmol m−2S−1) to 11.7% at 10 °C and high light intensity (990 μmol m−2s−1). In ammonium‐supplied plants grown at 22 °C and low light intensity, the proportion of carbon lost by root respiration was significantly higher in mycorrhizal than in non‐mycorrhizal plants. This increase in root respiration was of the same order of magnitude (7.4 %) as the decrease in dry matter production by mycorrhizal plants (10.1 %). In nitrate‐supplied plants, no significant difference in the respiratory quotient was found between non‐mycorrhizal and mycorrhizal plants. The respiration rate per unit d. wt of the fungal mycelium was estimated to account for 31.3 % (ammonium supply) and 8.3 % (nitrate supply) of that of the total mycorrhizal root system although the dry weight accounted for only 4. % (ammonium supply) and 2.5 % (nitrate supply). Accordingly, the respiration rate was calculated to be 11.1 times higher with ammonium supply, and 3.4 times higher with nitrate supply, than that of the root tissue. The carbohydrate concentrations in shoots and roots were not consistently different between non‐mycorrhizal and mycorrhizal plants.

It was concluded that increased root respiration was mainly responsible for the growth reduction in mycorrhizal compared with non‐mycorrhizal plants, whereas the production of fungal biomass in the extramatrical mycelium of mycorrhizal plants was of minor importance.
The effect of long‐term ozone fumigation on the growth, physiology and frost sensitivity of Calluna vulgaris
Authors: FOOT J. P. , CAPORN S. J. M. , LEE J. A. , ASHENDEN T. W.
Published: April 2006

summary

Calluna vulgaris (1) Hull, plants were fumigated in open‐top chambers with ambient charcoal‐filtered air, or 70 nl 1−1 (70 ppb) ozone, for 8 h a day, five days a week. Ozone treatment during the winter increased the frost sensitivity of plants as measured by electrolyte leakage following a controlled frosting regime. Root growth was decreased and the allometric root‐.shoot ratio (k) was reduced by the ozone treatment, reflecting a decrease in the partitioning of carbon to the roots. There was no significant effect of ozone on instantaneous net photosynthesis. There was a significant increase in anthocyanin content in ozone‐fumigated plants, but no effect on chlorophyll content. In contrast with the effects of wintertime exposure, plants treated during summer showed no significant responses. These results suggest that Calluna vulgaris can be adversely affected by prolonged ozone episodes in the field, particularly if these are followed by or coincide with frosting temperatures.
Does temperature stress induce nectar secretion in Mediterranean plants?
Authors: PETANIDOU THEODORA , SMETS ERIK
Published: April 2006

summary

We studied the effect of temperature on nectar secretion in Thymus capitatus, a typical labiate of phrygana (i.e. the garrigue of the East Mediterranean Basin). Experiments were carried out at controlled temperatures in a climatic chamber. We measured the nectar standing crop of the flowers at the end of the first day of their anthesis. All nectar values (i.e. volume per flower, sugar content and concentration) increased with temperature up to 38° C, as long as the plants were not water stressed. However, in the open and under normal temperate conditions (i.e. at relatively low temperatures) nectar secretion depended more on changes in solar irradiance than on temperature.

Under the same conditions, nectar secretion in Ballota acetabulosa, a species that is sympatric and coflowering with T. capitatus, was affected neither by light nor temperature. Since in the wild these two species are found in different microhabitats (full sun and shade, for T. capitatus and B. acetabulosa, respectively), we attribute the differences we observed to the differential natural adaptation of the plants to these factors. We conclude that T. capitatus is very well adapted to the Mediterranean conditions. By performing optimally as a nectar source at high temperatures, it can support a very large insect fauna that visits its flowers for nectar. It is in fact a temperature–induced cornucopian species.
Effects of pollutants in snowmelt onKiaeria starkei, a characteristic species of late snowbed bryophyte dominated vegetation
Authors: WOOLGROVE C. E. , WOODIN S. J.
Published: April 2006

summary

Areas which experience prolonged snowlie and possess a distinctive bryophyte‐dominated vegetation are termed snowbeds. Snow is a very efficient scavenger of atmospheric pollution. Because of the dynamics of snowmelt, much of the pollutant load of a snowpack is released in a highly concentrated episode known as the ‘acid flush’. This flush is received by the underlying vegetation when it is covered by the snow and also when it has been exposed after snow cover. Concentrations of pollutants which are already occurring in the meltwater of Scottish snowbeds are shown to be causing damage to the underlying bryophytes. Damage is greatest when the pollutants are received by the plants when out of snow cover. Recovery from the damage is slow and in some cases the plants show no signs of recovery 4 wk after exposure to polluted snow meltwater. Given the very short growing season available to the plants, damage persisting for so long could impinge on the plants'potential for survival. The long‐term threat to these sensitive communities is a serious one.
Habitat differentiation in a narrow hybrid zone between diploid and tetraploid Anthoxanthum alpinum
Authors: FELBER‐GIRARD M. , FELBER F. , BUTTLER A.
Published: April 2006

summary

Populations of diploid and autotetraploid Anthoxanthum alpinum A. & D. Löve formed a narrow hybrid zone in a study area in the Swiss Prealps. Detailed vegetation analyses were performed along transects in several contact zones between the two cytotypes. The vegetation differed according to the position in the hybrid zone. When considering the hybrid zone as a whole, and for one transect that was analysed in detail, there was strong evidence for habitat segregation between the cytotypes. Vegetation transitions, habitat preference and segregation of the two cytotypes differed according to location in the hybrid zone. The origin and dynamics of the hybrid zone are discussed.
Effects of nitrogen limitation and starvation on Chroococcidiopsis sp. (Chroococcales)
Authors: BILLI DANIELA , CAIOLA MARIA GRILLI
Published: April 2006

summary

Chroococcidiopsis sp. cells from hot desert rock (Timna National Park, Israel) were grown in modified BG‐11 medium which was either N‐free or which contained different concentrations of nitrogen, provided as nitrate. The life cycle, ultrastructure and physiological activities of the cyanobacterium were investigated over a period of 4 months. No alterations were detected in cells grown in medium containing 250 or 125 μg N ml−1. In contrast, cells grown in medium with 62 μg N ml−1 or lacking nitrogen occurred only as isolated viable forms, after 3 months and 1 month of growth, respectively. In these cells a decrease in the content of cellular chlorophyll and phycocyanin paralleled undetectable O2 evolution and depressed O2 uptake. In addition, such isolated cells were characterized by a multilayered envelope, whereas, in the cytoplasm, vesiculated thylakoids and glycogen granules were observed. N‐limited and N‐starved cells recovered their cellular organization and physiological activities upon N repletion. These ‘survival’ cells had a spore‐like form, and were functionally comparable to akinetes.
Experimental studies of growth and regenerative capacity in the foliose lichen Xanthoria parietina
Authors: HONEGGER ROSMARIE
Published: April 2006

summary

A series of outdoor culturing experiments on artificial ceramic substrata was set up to test the regenerative capacity of thallus fragments of the foliose lichen Xanthoria parietina (L.) Th. Fr. which had been dissected along an axis from the growing marginal pseudomeristem to the apothecia‐covered central areas. This dorsiventrally organized macrolichen (photobiont: Trebouxia arboricola De Puymaly) is capable of regenerating new lobes along wound margins or cut edges in any part of the thallus, including the thalline margin of apothecial disks. In semithin sections of central thalline areas of non‐disturbed thalli, where fungal and algal cells have reached their mature dimensions and where a high percentage of oversized Trebouxia cells imply an arrested cell cycle, small islets of actively growing and dividing fungal and algal cells were found within the algal layer. These are likely to be the sites where primordial stages of new lobes initiate after wounding. In nature, apothecia‐covered central thalline areas of X. parietina usually lose their contact with the substratum and break off along drought‐stress induced cracks. When landing on a suitable substratum, detached thallus fragments were found to regenerate new lobes in the same manner as artificially dissected samples, thus serving as propagules of the symbiotic state of this ecologically very successful lichen species.
Resource re‐allocation following fruit removal in cucurbits: patterns in two varieties of squash
Authors: EL‐KEBLAWY ALI , LOVETT‐DOUST J.
Published: April 2006

summary

The effects of removal of marketable‐sized fruits on investment toward male, female and vegetative activities were evaluated using two monoecious varieties of cultivated squash, Cucurbita pepo, cv. Striato d'Itaha o di Napoli, and cv. Zucchini Black. Leaf and flower demography were used to examine potential trade‐offs among these activities. Treated individuals produced more leaves, but individual leaf life expectancies were lower than those of controls. Fruit removal also significantly stimulated the production of male and female flowers, fruit and total above‐ground biomass. By contrast, permitting the extended process of fruit maturation in controls significantly decreased the overall production of both male and female flowers. There was no significant difference in total fruit mass between treated and control individuals. However, production of female and male flowers was labile, and responsive to the resource relationships operating within the plant. Treated plants produced more female (potentially fruit‐bearing) flowers as their fruits were harvested, and both groups of plants produced more male flowers at the end of the season. Overall, the squash cultivar produced almost twice as many male flowers as the zucchini cultivar; the harvesting treatment enhanced male flower production later in the season, and did so earlier in squash than in zucchini. Since reduced fruit production is achieved through reduced production of female flowers rather than through abortion of early fruits, and this precedes the period where resource limitation is anticipated, it is concluded that available resources do not directly prevent fruit development. The results are interpreted in the light of recent artificial selection for one to two large fruits per plant in the case of the squash cultivar and many smaller fruits in the case of the zucchini.
Growth response of grasses to elevated CO2: a physiological plurispecific analysis
Authors: ROUMET C. , BEL M. P. , SONIE L. , JARDON F. , ROY J.
Published: April 2006

summary

The effect of CO2 enrichment on the growth and the economy of carbon and nitrogen of 11 Mediterranean grass species was investigated in order to determine the underlying causes of the large variation observed between species in their responses to elevated CO2. Plants were grown for 26–43 d (depending on species growth rate) under productive conditions at ambient (350 μmol mol−1) and elevated (700 μmol mol−1) concentrations of CO2. Plant parameters were determined at a common biomass of 0.15 g to determine the CO2 effect independent of ontogenic effects.

The effect of CO2 on RGR ranged from −6.7 to 22.5%, with a mean stimulation of 10.3%. Averaged over the 11 species, the growth enhancement resulted from an increase in net assimilation rate per unit leaf d. wt. (narw) of 10.6 %. This was the result of a large increase (18.7%) in nar per unit leaf area (NARa) associated with a 8.1% decrease in the specific leaf area (sla). This decrease in sla was due to a large increase of the non‐structural carbohydrates. The increase in shoot activity was balanced by a 70.6% increase in the specific absorption rate of nitrogen (sar). AS a result, plant nitrogen content was not modified. Leaf nitrogen productivity was significantly increased (14.9%). Shoot vs. root allocation of biomass and nitrogen was not modified.

An analysis across the 11 species of the relationships between the stimulation of rgb and the alteration in rgr components showed a significant correlation only with increases in narw, sar and nitrogen productivity. The co‐ordinated increase in these three parameters constitutes a single response syndrome, whose intensity is responsible for most of the species variability.
Effects of elevated CO2 on stem growth, vessel area and hydraulic conductivity of oak and cherry seedlings
Authors: ATKINSON C. J. , TAYLOR J. M.
Published: April 2006

summary

Plants of Quercus robur L. and Prunus avium L. ×P. pseudocerasus Lind, were grown in either ambient (350 vpm) or elevated (700 vpm) CO2. The intention was to examine the effects of elevated CO2 on the morphological and functional development of the stem. The relationships between stem longitudinal transport capacity and development were explored in several ways: stem hydraulic function was related to stem cross‐sectional area, supplied leaf area and total stem vessel lumen area.

The mean total vessel number and the total vessel lumen area per stem, for both species, was determined from basal sections of the xylem. In Primus seedlings grown in different CO2 concentrations there was no significant change in the mean vessel size or number of vessels per stem. Quercus seedlings grown at elevated CO2 showed a significant increase in both vessel number and mean vessel size. When total stem vessel area was calculated it had increased twofold for Quercus plants grown at elevated CO2.

Measured stem hydraulic conductivity was shown to increase linearly with supplied leaf area, except in Quercus seedlings grown at elevated CO2. Stem hydraulic conductivity for Quercus seedlings grown at elevated CO2 did not change with the increase in supplied leaf area. This absence of an increase in the stem hydraulic conductivity appeared to relate to changes in total stem vessel area. Despite total stem vessel area being greater at elevated CO2 than that at ambient, it similarly did not increase with supplied leaf area.

The implications of this change in the relationship between leaf area and stem hydraulic conductivity are discussed with respect to the possible effects the change might have on the plant's water balance. The possible causes and significance of the changes in xylem anatomy are also considered in relation to direct effects caused by CO2 or indirect effects on changes in cambial maturity and tree growth.
The response of Plantago major ssp. pleiosperma to elevated CO2 is modulated by the formation of secondary shoots
Authors: FONSECA F. , DEN HERTOG J. , STULEN I.
Published: April 2006

summary

The effect of elevated CO2 on the relative growth rate (RGR) of Plantago major ssp. pleiosperma was studied during the vegetative stage, in relation to plant development, by growing plants at 350 μl 1−1 or at 700 μl 1−1 CO2 in non‐limiting nutrient solution with nitrate. To minimize interference by the accumulation of non‐structural carbohydrates in the interpretation of results, RGR was expressed on a f. wt basis (RGRFW), as were all plant weight ratios. Stimulation of the RGRFW of the whole plant by elevated CO2 was transient, and did not last longer than 8 d. At the same time a transient increase in root weight ratio (RWR) was observed.

In order to investigate whether the transient effect of elevated CO2 on rgrfw was size‐dependent, the data were plotted versus total f. wt (loge, transformed). The transient period of stimulation of rgrfw and of rwr by elevated CO2 was still found, but in both CO2 treatments rgrfw decreased after a certain plant size had been reached. This size coincided with the stage at which secondary shoots started to develop, and was reached earlier in plants grown at elevated CO2. The rgr of these secondary shoots (rgrset.) was still increased when the period of whole plant stimulation of rgrfw had ended, indicating that the development of these new sinks took priority over a continuation of the stimulation of rwr. It is hypothesized that in this Plantago subspecies the response of the rgrfw of the whole plants to elevated CO2 is modulated by the formation of secondary shoots. Apparently, partitioning of the extra soluble carbohydrates at elevated CO2 to this tissue takes precedence over partitioning to the roots, resulting in a cessation of stimulation of plant rgrfw by elevated CO2.
Localizing an Ophiostoma piceae proteinase in sapwood of four tree species using polyclonal antibodies
Authors: GHARIBIAN S. , HOFFERT C. , ABRAHAM L. D. , BREUIL C.
Published: April 2006

summary

The growth and proteolytic activity of the sap‐staining fungus Ophiostoma piceae were characterized in the wood of four tree species: lodgepole pine (Pinus contorta var. latifolia Dougl.), aspen (Populus tremuloides Michx.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and Western hemlock (Tsuga heterophylla Sarg.). Proteolytic activity and growth were highest in aspen. Proteolytic activity was minimal in both Douglas fir and Western hemlock. Polyclonal antibodies raised against the major proteinase produced by O. picaea were used to immunolocalize the enzyme after fungal growth in lodgepole pine and aspen. Immunogold labelling revealed that the proteinase was localized mainly in the cell wall of O. piceae. Gold particles concentrated in a sheath which was well defined after 10 d. Labelling appeared greater in the inoculated aspen than in lodgepole pine.
Nod factor‐induced host responses and mechanisms of Nod factor perception
Authors: HEIDSTRA RENZE , BISSELING TON
Published: April 2006

Soil bacteria belonging to the genera Rhizobium, Bradyrhizobium and Azorhizobium are able to invade the roots of their leguminous host plants, where they trigger the formation of a new organ, the root nodule. At least two steps of signal exchange between the bacterium and the host plant are involved in starting the interaction. In the first step, flavonoids excreted by the plant induce the transcription of bacterial nodulation genes (nod genes). The induction of these nod genes leads to the synthesis of specific lipooligosaccharides (called Nod factors) that can induce various root responses, e.g. root hair deformation, depolarization of the root hair membrane potential, induction of nodulin gene expression, and formation of nodule primordia.

We will focus on the various nod factor‐induced plant responses. We will discuss the ways these responses can be used to improve our knowledge of the mechanism of Nod factor perception. Furthermore, plant genes, in particular the sym2 allele from Afghanistan pea, encoding proteins that probably are involved in Nod factor recognition, are discussed. Based on the Nod factor‐induced plant responses and the phenotype displayed by sym2 peas, a model will be presented of how Nod factors may be perceived.
Suppression of defence responses in mycorrhizal alfalfa and tobacco roots
Authors: KAPULNIK YORAM , VOLPIN HANNE , ITZHAKI HANNAN , GANON DANA , GALILI SHMUEL , DAVID RAKEFET , SHAUL ORNA , ELAD YIGAL , CHET ILAN , OKON YAACOV
Published: April 2006

The broad host range of arbuscular mycorrhizal (AM) fungi differs from the specificity encountered in biotrophic pathogens. We summarize here the basic plant strategies of defence plant responses to colonization with pathogenic micro‐organisms and evaluate their possible involvement in AM performance. Detailed evidence is presented that, during early colonization of plant roots by symbiotic Glomus, defence‐related root responses are induced and then subsequently suppressed. In AM interactions, the broad host‐range infection capacity and the induction of defence‐related genes suggests that the compatible interaction is dominant. These results are discussed in relation to the possible conclusion that AM fungi might lack avirulence homologues or alternatively, that the factor causing suppression of the host defence response might be dominant.
Analysis of factors involved in fungal recognition responses to host‐derived signals by arbuscular mycorrhizal fungi
Authors: GIOVANNETTI MANUELA , SBRANA CRISTIANA , CITERNESI ANNA SILVIA , AVIO LUCIANO
Published: April 2006

An experimental model for the study of recognition responses by arbuscular mycorrhizal symbionts to host roots was validated by analysing the main factors which might affect such responses. Results showed that fungal responses to host‐derived signals were unaffected by the degree of sterility of the system, host age and mycorrhizal status, symbiont age, or different chemical and physical characteristics of hydrophilic membranes. Use of dialysis membranes showed that the molecules putatively eliciting fungal responses weigh less than 500 Da. Utilization of the model for studies of developmental expression of proteins and genes in arbuscular mycorrhizal symbionts is examined.
Molecular analysis of cell wall proteins expressed during the early steps of ectomycorrhiza development
Authors: TAGU DENIS , MARTIN FRANCIS
Published: April 2006

Ectomycorrhiza morphogenesis involves the differentiation of structurally specialized fungal tissues, the mantle and the Hartig net, and interfaces between symbionts. Proteins whose biosynthesis is specifically up‐ or down‐regulated have been identified in several ectomycorrhizal associations. Their spatial and temporal expressions have been characterized by cell fractionation, two‐dimensional polyacrylamide gel electrophoresis and lmmunochemical assays in the Eucalyptus spp ‐Pisolithus tinctorius symbiosis. These biochemical investigations have revealed the drastic alterations experienced by fungal cell wall polypeptides during the early stages of the ectomycorrhizal interaction. These include the increased synthesis of 32 kDa acidic polypeptides, together with the decrease in content of a major 95 kDa‐mannoprotein, gp95. Differential screening of a mycorrhiza cDNA library and large‐scale cDNA sequencing have allowed the characterization of several symbiosis‐regulated fungal genes coding for cell wall proteins (e.g. hydrophobins). In P. tinctorius, the content of hydrophobin transcripts is up‐regulated in aerial hyphae and during the mantle formation. The cell wall of the fungal partner therefore presents a novel protein composition, characteristic of the symbiotic status. A convergence of biochemical and molecular results now allows formulation of molecular models for the key role of the cell wall compartment in the early developmental stages of ectomycorrhiza formation. Clearly, we are only beginning to understand the formation of the symbiotic cell walls, their regulation and topologic specificity. Definitive information should emerge from biochemical, cytological and molecular analyses of the appropriate models.
Phylogeny of the Glomales: deciphering the past to understand the present
Authors: SIMON L.
Published: April 2006

The Glomales comprise more than 130 described species, presently classified in three families and five genera. Previous analysis of the sequence of the nuclear genes coding for the ribosornal small subunit rRNA (SSU) obtained from 12 isolates representing as many species generally corroborated the taxonomy based on morphological characters. As part of an ongoing effort to understand better the relationship between glomalean species, four new glomalean SSU sequences obtained in our laboratory are described, along with partial sequences from other laboratories. Using this enlarged dataset, a current phylogenetic tree of the Glomales was reconstructed. The dataset was also analysed to locate informative regions of the glomalean SSU that could be targeted by molecular ecologists studying the taxonomy, identification and ecology of arbuscular mycorrhizal fungi.
Inter‐ and intraspecific variation within the morphologically‐similar arbuscular mycorrhizal fungi Glomus mosseae and Glomus coronatum
Authors: DODD J. C. , ROSENDAHL S. , GIOVANNETTI M. , BROOME A. , LANFRANCO L. , WALKER C.
Published: April 2006

This collaborative investigation was aimed at using morphological and molecular characters to study inter‐ and intraspecific variation within isolates of Glomus mosseae and Glomus coronatum from different parts of the world. A secondary aim was to assess whether any divergence found was genetically based and/or correlated with the biogeographic origin of isolates. Morphological evaluations of various possible taxonomic characters including spore colour, size, sporocarp architecture and hyphal attachment morphology, showed that only spore colour could discriminate the two groups. Isozyme analysis of malate dehydrogenase and esterase loci clearly confirmed this grouping of the two species complexes. SDS profiles and cluster analysis showed the same separation on a selection of isolates from the two groups. A comparison of a representative isolate from the G. coronatum group (BEG 49) with other arbuscular mycorrhizal fungi using G. mosseae‐specific primers also provided evidence for separation of the two species complexes. The data and methodology employed provide a blueprint for future multimodal and multidisciplinary approaches to the unravelling of taxonomic problems within this ancient group of symbiotic fungi.