bluuebunny/crossref_metadata_2025 huggingface dataset:
The use of sieving during standard pollen pre‐treatment of samples of fossil deposits to enhance the concentration of large pollen grains
Authors: BOWLER MÁIRE , HALL VALERIE A.
Published: April 2006

Small pollen grains and fine particles of the organic matrix in samples of a coarse detritus mud and a blanket peal deposit were removed by sieving through 30μ polyester mesh after digestion with KOH and acetolysis during standard pollen pre‐treatment. The technique enhanced the number of large pollen grains m the sample. There was also an increase in the range of taxa which produce huge grains. The method provided a means of estimating the ratio of any scarce large pollen grain to the total grain sum in samples prepared by standard methods of pre‐treatment.
Spatio‐temporal analysis of climate–tree ring relationships
Authors: TESSIER L.
Published: April 2006

summary

This paper is concerned with the value of the ecological information provided by response functions. Two questions are considered. The first deals with the spatial reproducibility of response functions depending on the tree population and the location of the meteorological station that yielded the climatic data. The second concerns the temporal stability of the response function. The climate–ring‐width relationships are calculated for six Populations of Pinus silvestris (L.). Twelve meteorological stations are involved in this calculation, over the period 1890–1980, divided in five sequences of 50 years. Analogies and differences between response functions are investigated using multi‐dimensional analysis (principal component analysis and cluster analysis).

Spatial analysis reveals that the climate ring‐width relationship mainly depends on the population habitat. The temporal analysis shows that instability is linked with the evolution of the habitat, more especially with the expansion of the forest cover.
Interglacial pollen and plant macrofossils from Langdon River, western Tasmania
Authors: COLHOUN ERIC A. , VAN DE GEER GUUS , HILL ROBERT S. , BIRD TREVOR
Published: April 2006

summary

Pollen and plant macrofossils from Langdon liner give an interglacial floral record for western Tasmania. The location of the site between the ice limits of the Last or Margaret Glaciation and the Penultimate or Henty Glaciation indicate that it cannot be younger than the Last Interglacial. The sequence of vegetation changes shows the succession Casuarina Phyllocladus‐Nothofagus with Casuarina as pioneer and Nothofagus as representing Maximum wet forest development. After the maximum the presence of Phyllocladus‐Nothofagus‐Eucalyptus‐Microstrobos suggests deterioration to subalpine woodland/shrubland, and Compositae, Gramineae‐Microstrobos to alpine shrubland and herbland. The sequence represents most of a glacial‐interglacial‐glacial cycle Of environmental changes that occurred before 43 000 14C yr B.P.

Very high Casuarina values occur in the early part at the interglacial sequence which contrasts with the Holocene where Eucalyptus is more important than Casuarina. Otherwise the sequence of Phyllocladus, Nothofagus, Eucryphia‐Anodopetalum is the same as for Holocene forest development. The interglaeial ‘optimum’ is marked by the occurrence of Pomaderris apetala type and Dicksonia antarctica.

There is some similarity with the Casuarina curves in the Lake George interglacials before the Last Interglacial. But, on the whole, there is more similarity with interglacial rainforest development in western South Island, New Zealand Only one cycle of vegetation change is recognized at Langdon River which is unlike New Zealand and central Chilean records from 40‐42° S which in different ways record a mid Last Interglacial climatic deterioration.
Changes in ultrastructure of Golgi apparatus during the cell cycle in a synchronous culture of Catharanthus roseus
Authors: HIROSE S. , KOMAMINE A.
Published: April 2006

summary

Changes in the ultrastructure of the Golgi apparatus during the cell cycle were investigated using a highly synchronized cell division system in a Catharanthus roseus (L.) G. Don suspension culture. During the G2 phase and cytokinesis, diameters of the dictyosomes and the number of cisternae significantly increased. Electron micrographs of cells in cytokinesis suggested that dictyosomes were dividing into two. Numerous secretory vesicles were associated with the dictyosomes in cells of the second G1 phase, the time when cell wall synthesis is most active. Structural changes in the Golgi apparatus are discussed in relation to the cell cycle and changes in cell wall synthesis.
Glutamine synthetase isoforms in the green hydra symbiosis
Authors: REES T. A. V. , SHAH N. , STEWART G. R.
Published: April 2006

summary

The occurrence of glutamine synthetase isoforms in the green hydra symbiosis has been investigated using ion‐exchange chromatography. There were three isoforms which were designated algal cytosolic, chloroplastic and host isoenzymes. Comparison of the proportions of algal isoforms from the intact association with those from nitrogen‐replete and nitrogen‐starved cultures of a Chlorella strain originally isolated from green hydra, suggests that symbionts in the intact association may be nitrogen‐deficient.
Some relationships between leaf anatomy and photosynthetic characteristics of willows
Authors: PATTON LINDA , JONES MICHAEL B.
Published: April 2006

summary

The photosynthetic light response curves and stomatal conductance of four cultivars of Salix viminalis, S. burjatica and S. × dasyclados were measured using leaves growing on unshaded plants from the field. Light saturated rates of net photosynthesis (Pn, max) ranged from 13.9 to 22.5 μ mol m−2 s−1. Cultivars of S. viminalis had the highest values of Pn. max but the lowest stomatal conductances, and as a consequence they also had the highest water use efficiency.

Observations on anatomical characteristics of leaves used for photosynthesis measurements indicated a significant positive correlation between Pn. max and the ratio of the exposed surface area of mesophyll cells to leaf surface area (Ames/A) and chlorophyll content, and a significant negative correlation between Pn, max and area of fully expanded leaves.

These observations show that there are a number of selection criteria based on both physiological and anatomical measurements which may be used to select for potentially high yielding willows.
The time‐course of disease suppression and antibiosis by the ectomycorrhizal fungus Paxillus involutus
Authors: DUCHESNE LUC C. , PETERSON R. L. , ELLIS BRIAN E.
Published: April 2006

summary

Seedlings of Pinus resinosa Ait. grown in test tubes were inoculated with the ectomycorrhizal fungus Paxillus involutus Fr. and, one day later, with a spore suspension of the root pathogenic fungus Fusarium oxysporum Schlecht emend, Sny. & Hans f.sp. pini. Controls consisted of seedlings inoculated with plugs of sterile modified Melin Norkrans medium and F. oxysporum. Seedling survival was counted, sporulation of F. oxysporum was measured, and ethanol extractions of the rhizosphere were made, 1, 2, 3, 4, 5, 6, 8, 10 and 14 d after inoculation with the pathogen. The ethanol extractives were concentrated and assayed for fungitoxic activity by measuring the germination of F. oxysporum microconidia. Dead seedlings were first observed 3 d after inoculation with the pathogen. Sporulation of F. oxysporum was reduced significantly 3 d after seedling inoculation with P. involutus when compared with controls lacking P. involutus. The fungitoxic activity of the rhizosphere of the seedlings inoculated with P. involutus was greater than the fungitoxic activity of the rhizosphere of control seedlings, increasing strongly 2.4 d after inoculation with the pathogen. Suppression of Fusarium root rot by P. involutus may, therefore, be the result of antibiosis by this ectomycorrhizal fungus.
Spatial dynamics and interactions of the woodland fairy ring fungus, Clitocybe nebularis
Authors: DOWSON C. G. , RAYNER A. D. M. , BODDY LYNNE
Published: April 2006

summary

The extension rates of Clitocybe nebularis (Batsch ex Fr.) Kummer strains on 2% malt agar were only 30–40%, of those, up to 3.4 mm d−1, observed in woodland at equivalent exponential mean temperatures. Extension of mature field systems was accomplished by mycelial annuli or arcs 30‐40 cm wide, differentiated into a leading edge of mycelial cords followed by a zone of dense, diffuse mycelium which bleached litter components, and a trailing edge of greyish, Used mycelium. Disruption of mature annuli by natural obstacles or experimental re‐orientation within the mycelial band resulted in regression of the affected segment of mycelium. Localized lysis following encounter with an obstacle by immature patches of mycelium with a diameter of 30–50 cm, led to polarized development of the residual mycelium.

Strains from different fruit bodies were somatically compatible when paired on 2% malt agar if sampled from the same ring, but incompatible if from different rings, resulting in mutual antagonism and formation of a persistent demarcation zone. By contrast, collision between adjacent systems in woodland culminated in mutual obliteration of the interaction fronts. C nebularis was non‐combative when paired against other decomposer basidiomycetes on 2% malt agar, being either replaced or deadlocked but not replacing mycelia of these fungi.

The implications of these observations are discussed in terms of emerging concepts of ecological strategies, foraging theory and polarity in mycelial collectives.
Glandular trichomes and essential oils in developing peppermint leaves
Authors: MAFFEI MASSIMO , CHIALVA FRANCO , SACCO TOMMASO
Published: April 2006

summary

The trichome number and the variability in mono and sequisterpene distribution of peltate trichomes within a leaf was investigated during development of peppermint (Mentha×piperita L.) leaves. A larger number of peltate trichomes was initiated on adaxial epidermises than abaxial epidermises, but during leaf development a greater gland number was produced on abaxial epidermises. Evidence showed that the trichome number was not fixed at the time of leaf emergence. On both epidermises, the trichome distribution was found to change with its position on the leaf. A striking monoterpene composition variability was present among individual trichomes and between different parts of the leaf. Different rates of peltate trichome development and distribution as well as significant differences in trichome number and density were found between the epidermises. A clear and opposite trend was found between menthone and menthol percentages during development. Menthone and menthol were also found to be present in larger amounts on adaxial epidermises, whereas neomenthol and isomenthol had highest percentages on abaxial epidermises. Of the total oil collected from peltate trichomes, 60%, was composed of menthone. isomenthol, menthol and neomenthol and of the remaining 40 %, more than half was represented by other mono and sesquiterpenes while the final percentage was made up of a few unidentified early eluting compounds of high Volatility.
Responses of Cynoglossum officinale L. and Senecio jacobaea L. to various degrees of defoliation *
Authors: PRINS A. H. , VERKAAR H. J. , VAN DEN HERIK M.
Published: April 2006

summary

Effects of various degrees of defoliation on Cynoglossum officinale and Senecio jocobaea were studied under favourable growing conditions. Regrowth was found in both species, but did not overcompensate for defoliation. The physiological mechanisms responsible for regrowth after defoliation were found to relate either to an increase in net assimilation rate or to an increase in relative investment in aboveground parts. The morphological mechanism behind regrowth involved an increase in leaf area ratio. In almost completely defoliated plants, a combination of both mechanisms was found. The time needed to re‐establish the same amount of biomass as control plants differed between the species and between levels of defoliation. These differences in recovery time after defoliation are discussed in relation to decrees of herbivory found m natural situations.
The control of the cell cycle in microbial symbionts
Authors: Hill D. J.
Published: April 2006

summary

The development of the photosynthetic microbial symbionts of lichens and Azolla are compared. Both have more rapidly dividing cells at the growing point and slower rates of cell division in the mature regions of the host symbiont. Cell size, numbers and differentiation (function) were studied in these different stages of development. Anabaena cell number in the mature leaf cavities of Azolla increases more or less linearly. When fern growth was stopped with cycloheximide treatment, cell division in Anabaena at the apex was also arrested. In lichens, photobiont cell size increases with thallus age, us does Anabaena in Azolla. Lichen photobiont cells became larger in slower growing thalli. The pattern of photosynthetic carbon and nitrogenase functions change during thallus development. These observations together with others are used to suggest two separately operating controls on the symbiotic cell cycle: (1) nutrient supply for cell maintenance and cell growth; (2) constraint or stimulation of commitment to divide. The separate operation of these controls leads to symbiont cells being in two possible states: (1) phase I which are generative cells associated with growing host tissues and (2) phase II which are differentiated cells in the mature regions of the host.
Functional aspects of phosphorus uptake and carbon translocation in incompatible ectomycorrhizal associations between Pinus sylvestris and Suillus grevillei and Boletinus cauipes
Authors: FINLAY R. D.
Published: April 2006

summary

Pinus sylvestris L. and Larix eurolepis Henry seedlings were grown together in non–sterile laboratory microcosms containing functional mycelial networks of one of three different ectomyeorrhizal Fungi. The fungi used were Suillus bovinus (Fr.) O. Kuntze, and two Fungi which are commonly considered to be specific to Larix spp., Suillus grevillei (Klotzsch) Sing, and Boletirms cavipes (Opat.) Kalchbr. Patterns of mycorrhizal infection, transport of labelled assimilate and phosphorus uptake within the microcosms were studied in order to evaluate tine functional attributes of associations formed between P. sylvestris and the two‘larch specific’fungi. Fungal colonization of lateral roots and accumulation of labelled assimilate from adjacent plants fed with 14CO2 was significantly greater in the roots of Pinus plants when the ectomycorrhizal fungus was S. bovinu, and significantly greater in Larix roots when the fungus was V. grevillei or li. cavipes. Kctomycorrhizas formed between P. sylvestris and Ii, cavipes were fully functional in terms of transfer of labelled assimilate to the fungal mycelium. In mixed communities infected by B. caripes, myeclial uptake and translocation of 32P‐labelled orthophosphate was significantly greater to Larix plants than to Pinus plants. Formation of sheathed lateral roots on the Pinus plants was low. There was some autoradiographic evidence of phosphorus translocation from mycorrhizal pine roots to stem and leaf tissue hut levels of activity in the shoots were low, indicating limited translocation across the host‐fungus interface.
Infectivity and effectivity of indigenous vesicular‐arbuscular mycorrhizal fungi from contiguous soils in southwestern Wyoming, USA
Authors: HENKEL T.W. , SMITH W. K. , CHRISTENSEN M.
Published: April 2006

summary

In a greenhouse experiment, the degree of infectivity as well as effects on shoot hiomass, phosphorus concentration, and drought response in Agropyron smithii Rydb. were compared for species assemblages of vesicular‐arbuscular (VA) mycorrhizal fungi. Assemblages were collected from dissimilar soils across a 55 m elevational gradient in the xeric sagebrush‐steppe of southwestern Wyoming. Collection sites and soils were designated as ridgetop (RT), midslope (MS), and base (B|. All assemblages of mycorrhizal fungi were tested in their parent soils as well as the other two soils. In the phosphorus (P)‐deficient (10 mg kg −1) RT soil, the indigenous mycorrhizal fungi produced significantly greater concentrations of P in the shoot of the host ((0‐335 °) than did the fungi from the B site (0‐250%). In the non‐mycorrhizal plants the concentration of P in the shoot was 0.185%. The RT fungi also generated the highest levels of infection, plus greatest arbuscule and vesicle production in both the RT and MS soils. The B soil had the highest available 1’content (51 mg kg ‐1) and mean shoot P concentrations were not significantly different among plants of the different treatments grown in this soil. Inefectivity was also reduced in the B soil. This reduction in mycorrhizal activity was attributed to the high‐P availability in the H soil. Although shoot dry weight was either unaffected or possibly reduced by mycorrhizas in all soils, stomatal response to drought was not affected by mycorrhizas m any of the soils. The greater effectiveness of the RT inoculum for increasing P concentration in the shoot of A. smithii when grown in the RT soil, as well as the greater infectivity of this inoculum, may indicate adaptation in these mycorrhizal fungi to low‐P soil conditions. The relatively low infectivity and effectivity of the B fungi in the RT soil also suggests that these fungi may be less adapted to low‐P soil conditions. Thus, differences in ineffectivity and effectivity may occur among native VA mycorrhizal fungi when the parent soils are dissimilar yet contiguous.
Effect of different inocula of vesicular‐arbuscular mycorrhizal fungi on manganese content and concentration in red clover (Trifolium pratense L.) plants
Authors: ARINES J. , VILARIÑO A. , SAINZ MARIA
Published: April 2006

summary

Three sterilized acid soils were inoculated with vesicular‐arbuscalar (VA) mycorrhizal fungi. Inocula consisted of mixtures of line + coarse type endophytes (Glomus tenue(Greenall) Hall plus either G. mosseae (Nicol and Gerd), G. fasciculatum (Thaxter sensu Gerd) Gerdemann and Trappe, G, epigaeum Daniels and Trappe or G. macrocarpum Tul and Tul var. geosporum, and native inocula). Red clover (Trifolium pratense L.) was seeded in pots and grown in a glasshouse for four months, Root colonization by VA mycorrhizal fungi, plant growth and Mn content and concentration in shoots and roots, were studied. Mycorrhiza depressed the Mn concentration in shoots and roots of plants growing in all three soils, and the Mn uptake in one of them. On average, Mn concentration in mycorrhizal plants was 45% in shoots and 20% in roots of that found in non‐mycorrhizal controls.
Cell wall bound‐phenols in roots of vesicular‐arbuscular mycorrhizal plants
Authors: CODIGNOLA A. , VEROTTA L. , SPANU P. , MAFFEI M. , SCANNERINI S. , BONFANTE‐FASOLO P.
Published: April 2006

summary

This paper examines the qualitative and quantitative chemical composition of phenols occurring in the cell wall of vesicular‐arhuscular (YA) mycorrhizal and non‐mycorrhizal roots of Allium porrum L. and Ginkgo bilnba L. their localization at the cellular level, and the phenylalanine ammonia lyase (PAL) activity of these tissues. Constitutive phenols occurred in both species of plants, and did not change when the symbiont Cully colonized the roots. Cell wall bouncl‐phenols were more abundant in A. porrum than in C. biloba, and PAL activity was higher too. Tyrosol, 2‐(4‐hydroxyphenyl ethanol), was identified as the most abundant component in A. porrum, where it occurred with vanillic, syringic and ferulic acids. In G. biloba, p‐coumaric, protocathecuic, vanillic and ferulic acids were found. Cell‐wall bound phenols (revealed by UV fluorescence and by transmission electron microscopy) were localized in the epidermal and hypodermal cells, but did not usually occur in the cortical cells, where the fungus developed arbuscules.

We show that cell wall bound‐phenols are constitutive compounds in leek and in ginkgo:, and that the VA mycorrhizal fungus does not activate metabolic pathways leading to the synthesis of new phenols as antimicrobial substances, at least in the host cell walls.
Sensitivity of white clover to ambient ozone in Switzerland
Authors: BECKER K. , SAURER M. , EGGER A. , FUHRER J.
Published: April 2006

summary

Ozone (O3) in ambient air was investigated as a possible cause of visible damage to leaves of white clover (Trifolium repens L.) in agricultural areas of Switzerland. Differences in the sensitivity of five commonly mown cultivars were studied, namely Ladino Sacramento, Ladino California, Alban, Sonja and Milkanova. Plants were grown in pots and exposed to O3 using three different experimental systems: (i) exposure to ambient air, (ii) exposure in open‐top chambers to filtered air, unfiltered air, or unfiltered air to which O3 was added from 09.00 until 17.00 h during a four‐day period, (iii) exposure under controlled environmental condition to filtered air with or without O3 added daily. Occurrence of injury symptoms on field‐grown plants was recorded during the summers of 1987 and 1988.

Ozone exposure produced visible injury expressed as small necrotic flecks on the tipper leaf surface. Irrespective of the experimental system used, the following order in O3 sensitivity was observed: L. Sacramento ≤ L. California ≪ Alban ≤ Sonja ≤ Milkanova. Injury symptoms were seen when plants were exposed to ambient O3 or to unfiltered air in open‐top chambers, but not in charcoal‐filtered air. In ambient air, symptoms in the most sensitive cultivars appeared after episodes with 1‐h maximum concentrations of above 120‐140μg m−3 occurring on several consecutive days. The symptoms of injury could be reproduced in controlled‐environment fumigation experiments using concentrations comparable to those observed in ambient air.

Plants of the different cultivars grown under controlled environmental conditions did not differ in superoxide dismutase or peroxidase activity, or in the content of fructose, sucrose or glucose. Differences in O3−sensitivity between cultivars were related to differences in stomatal density and to some degree to the length of the stomatal pore. Stomatal densities were related to leaf conductance, transpiration, and rate of water loss by excised leaves. Leaves of Milkanova (resistant) had higher 313values than L. California (sensitive). Compared with filtered air, exposure to unfiltered ambient air or O3–amended air in open‐top chambers caused a change in δ13 value in leaves of L. California (sensitive), but not in leaves of Milkanova (resistant).

It is concluded that ambient levels of O3 in Switzerland can be sufficient to produce visible leaf injury in sensitive white clover cultivars characterized by a high gas‐phase conductance of the leaves, that the isotopic composition of leaf tissue could be used as an indicator of O3 sensitivity in different cultivars, and that ambient levels of O3 can change the isotopic composition of the leaf tissue in sensitive species.
The potential for evolution of tolerance to sodium chloride, calcium chloride, magnesium chloride and seawater in four grass species
Authors: ASHRAF M. , MCNEILLY T. , BRADSHAW A. D.
Published: April 2006

summary

To examine the contrasting genetic potentials of different species, which would allow or prevent the evolution of tolerance to naturally saline environments, the growth of selected tolerant and normal lines of Agrostis stolonifera L., A. capillaris L., Holcus lanatus L., and Lolium perenne L., in NaCl, CaCl2, MgCl2 and seawater solutions was examined.

NaCl tolerant lines of all four species had significantly greater root growth in NaCl, CaCl2, solutions, and seawater than unselected lines, but in MgCl., only the NaCl tolerant lines of H. lanatus had significantly longer roots than the unselected line.

Screening of seedlings in solution culture in all four species, for tolerance to the same salt solutions, suggested that variability was available in each species for enhanced tolerance to each salt. When the selected material was tested as adults, the superior tolerance in response to increased seawater concentration remained for all lines in all species except those of A. capillaris and H. lanatus.

The results suggest that all four species have genetic potential for the evolution of salt tolerance. The failure of some of these species to evolve salt tolerant populations in nature is likely to be due to other factors in naturally saline environments, for which the necessary adaptive genetic potential is lacking.
Characteristics of plant species which store different types of reserve carbohydrates
Authors: BROCKLEBANK K. JANE , HENDRỲ GEORGE A. F.
Published: April 2006

summary

The occurrence of the three principal reserve carbohydrates, starch, fructan and sucrose, is documented in 20 native British species over four seasons. Species containing two of the reserve carbohydrates in different combinations were present in each of three common habitats.

Sucrose reserves Undergo considerable depletion after winter. Starch depletion also occurs in many though not all species. In contrast, fructan is stored in high concentrations which are not subject to depletion. This indicates the fructan has functions other than as a source of consumable carbohydrate, one of which may be as an osmotic regulator.

Fructan is associated with relatively restricted phenologies associated with early‐season, low‐temperature growth. In contrast, the Storage of starch or sucrose as a principal reserve carbohydrate is associated with the broadest variation in phenological patterns. There is, however, no indication that fructan has a unique or specific‐role in low temperature tolerance as similar attributes are shown to be present in a number of non‐fructan species.

In relation to herbivore nutrition, each type of carbohydrate is made relatively unavailable either in space (starch and fructan) or in time (sucrose). The consequences of these various characteristics are considered in relation to plant evolution and Survival.
Adaptive speciation in Mimulus: an ecological comparison of M. cupriphilus with its presumed progenitor, M. guttatus
Authors: MACNAIR M. R. , MACNAIR V. E. , MARTIN B. E.
Published: April 2006

summary

The ecology of a recently evolved species, Mimulus cupriphilus, was compared with its presumed progenitor, M. guttatus. Both species live sympatrically as annuals on two small copper mines in Calaveras county, California, USA. There are almost no other species present in the areas where Mimulus dominates. The production of seed by the two species was compared. The relationship between capsule number and plant height differs, with M. cupriphilus having the steeper slope, so that at any particular height it produces more capsules. Mean seed number per capsule, and the relationship between seed number and size of plant, also varies between the two species. M. cupriphilus is normally sell‐fertilizing, and thus has a higher probability that a capsule will he fertilized than M. guttatus, which relies more on fertilization by insects. The various parameters can be combined to produce a predicted relationship between size of plant and seed production. When plants are small, M. cupriphilus will produce more seeds, but at heights greater than about V cm M. guttatus will be fitter. The overall resource allocation pattern also reveals that M. cupriphilus devotes a greater proportion of its dry weight to seed and capsule production. These results show that in the habitat where the two species co‐exist, arid deserted copper mines, the derived species is better adapted.
Pollen allelopathy among sympatric grassland species: in vitro evidence in Phleum pratense L.
Authors: MURPHY STEPHEN D. , AARSSEN LONNIE W.
Published: April 2006

summary

Pollen extracts from live locally‐common grassland species in eastern Ontario, Canada were tested for in vitro allelopathic effect on the pollen germination of 17 sympatric target species in 1987. The flowering phenologies of the test and target species were recorded to determine if any phenologically‐divergent species showed evidence of in vitro pollen‐allelopathic interactions. Phleum pratense L. demonstrated pollen‐allelopathic effects on all targets except Linaria vulgaris Hill. P. pratense also exhibited significant phenological divergence with seven of the target species. Pollen extracts from Agrostis stolonifera L., Melilotus alba Desr., and Vicia cracca L. inhibited pollen germination in some of the target species, but the results suggest that these effects were pH‐mediated. The pollen extract of Erigeron annuus (L.) Pers. did not cause inhibition of pollen germination in any of the target species. Further tests with pollen extract of P. pratense and another 23 sympatric target species were performed in 1988. Pollen germination was significantly inhibited in all but two of these species: A. stolonifera and P. pratense. Hence the pollen of P. pratense was not auto‐allelopathic. The breeding system, relatively tall growth habit and relatively large quantity of pollen produced all support the in vitro evidence of P. pratense as a pollen‐allelopathic species.
Characterization of a stigmatic component fromPapaver rhoeasL. which exhibits the specific activity of a self‐incompatibility (S–) gene product
Authors: FRANKLIN‐TONG VERNONICA E. , RUUTH ERIK , MARMEY PHILIPPE , LAWRENCE MICHAEL J. , FRANKLIN F. CHRISTOPHER H.
Published: April 2006

summary

Extracts prepared from stigmatic tissue ofPapaver rhoeasL. have been fractionated and monitored for S–gene product activity. A basic glycoprotein, with an apparent MW of 22 kDa, which exhibits the specific activity expected of a protein encoded by the self–incompatibility (S–) gene has been identified. Similar preparations using extracts from other tissues have revealed that this protein is unique to mature stigma tissue.
Aluminium—phosphate interactions in wheat
Authors: de MIRANDA L. N. , ROWELLO D. L.
Published: April 2006

Two Brazilian wheat varieties (Triticum aestivum L., varieties IAC‐5 and Jupateco) were grown in solution culture with three concentrations of P (1, 5 and 20 μg ml‐1) and no Al, then transferred to three concentrations of Al (0, 2.5 and 12.5 μg ml‐1) and no P and afterwards returned to the first solutions. In the first growth period the tolerant variety IAC‐5 absorbed and translocated more P to the shoots than the sensitive one. In the second period A1 restricted both root growth and the translocation of P from root to shoot, and led to movement of P from shoots to roots in plants with low P contents, the sensitive variety again being most affected. The amount of P translocated to the roots was approximately equal to the increase in isotopically‐exchangeable P in the roots. In the third period, root P taken up in the first period was translocated to the shoots in amounts approximately equal to the total exchangeable P in the roots, along with freshly absorbed P. After the second period tissue was ground and filtered to give a filtrate (predominantly cell contents) and a residue (predominantly cell walls). The A1: P ratio (μmol g‐1 dry matter) in the contents was about 1:7, and in the walls it was 1:2. The latter value may indicate the composition of aluminium phosphate precipitated in the walls. Tolerance of soil acidity is associated with the ability of roots to translocate P to shoots in the presence of A1 and may also depend on the ability to move P down to roots growing in acid subsoils.
Interactions between fluorescent pseudomonads and VA mycorrhizal fungi
Authors: PAULITZ T. C. , LINDERMAN R. G.
Published: April 2006

Cucumber seeds were treated with rifampin‐resistant derivatives of Pseudomonas putida (A12, NI or R‐20) or R‐20 or P. fluorescens (2–79 or 3871) and planted in soils with and without added inoculum of the VA mycorrhizal fungi Glomus intraradices Schenck & Smith or G. etunicatum Becker & Gerdemann. Populations of Pseudomonas spp. in the combined rhizosphere‐rhizoplane soil were determined at 1–9 weeks after planting by dilution plating on a selective medium. At 1–3 weeks, the populations of all strains except R–20 were 1.5 to 7 times lower in the rhizosphere of cucumber roots colonized by G. intraradices, when compared to nonmycorrhizal plants. However, this effect was less consistent in 3‐ to 9‐week‐old plants. No significant difference was detected in populations of Pseudomonas strains between roots colonized by G. etunicatum and nonmycorrhizal roots. Strains 3871 and 2‐79, which are antibiotic producers, delayed the germination of G. etunicatum spores in raw soil, but by seven days no significant differences in frequency of germination were detected. None of the fluorescent Pseudomonas strains affected the colonization of cucumber roots by G. etunicatum, as determined by measurements of mycorrhizal inoculum density root colonization relationships.
Uptake, translocation and assimilation of nitrogen from 15N‐labelled ammonium and nitrate sources by intact ectomycorrhizal systems of Fagus sylvatica infected with Paxillus involutus
Authors: FINLAY R. D. , EK H. , ODHAM G. , SÜDERSTRÖM B.
Published: April 2006

The uptake and assimilation of nitrogen from 15N‐labelled ammonium and nitrate sources was followed in intact ectomycorrhizal systems containing Fagus sylvatica L. plants infected with the fungus Paxillus involutus (Mich. ex Pers.) Cohen & Couch. Plants were grown in flat perspex observation chambers containing non‐sterile peat; the fungal mycelium growing from a host plant was allowed to cross a barrier and to colonize an area of peat from which roots had been excluded. Labelled ammonium chloride or sodium nitrate was fed to the mycelium, and the shoot, root and mycelial tissues analysed for total and 15N‐labelled amino acid contents after a feeding period of 72 h. Both free and protein‐incorporated amino acids were analysed. Labelled nitrogen was incorporated into a range of free amino acids, the principal sinks for assimilation being alanine, aspartate/asparagine and glutamate/glutamine. The spectrum of labelling in protein‐incorporated amino acids was wider with significant incorporation into the above compounds but additional assimilation of nitrogen as glycine, valine, serine, leucine, isoleucine and arginine. In total 78% of the nitrogen assimilated was incorporated into proteinaceous material. Label was incorporated from both nitrogen sources but the levels of enrichment in most free and protein‐bound amino acids were usually higher in systems supplied with ammonium than in those supplied with nitrate. The mean amount of nitrogen assimilated From nitrate was only 62% of that assimilated from ammonium.
Fungi in healthy stems and branches of American beech and aspen: a comparative study
Authors: CHAPELA I. H.
Published: April 2006

Fungi inhabiting healthy stems and branches of American beech and aspen were induced to develop within the wood by drying sections of these organs. The two tree species were similar in that tile water content of the wood strongly determined fungal development, with a high water content preventing fungal growth for at least 25 weeks, fast drying resulting in poor development and slow drying inducing very fast growth of fungi within the wood. Fungal assemblages thus obtained were strongly dominated by ascomycetes and coelomycetes.

Although some fungal species appeared on both tree species, assemblages of fungi obtained from each tree species were clearly different, even though samples of each were obtained from the same site and all experimental conditions were identical for both.

All the characteristics mentioned above strongly resemble those documented for endophytes on smaller aerial tree organs such as leaves, petioles and twigs, and for this reason the fungi obtained here were termed‘xylotropic endophytes'.

Among the dominant species found on aspen, three species with presumed pathogenic abilities were isolated. These were Cryptosphaeria populina, Cytospora chrysosperma and Hypoxylon mammatum. Hypoxylon fragifarme was the most frequently and abundantly isolated species obtained from beech.
Long‐term ozone exposure affects winter hardiness of red spruce (Picea rubens Sarg.) seedlings
Authors: FINCHER JEAN , CUMMING JONATHAN R. , ALSCHER RUTH GRENE , RUBIN GAIL , WEINSTEIN LEONARD
Published: April 2006

Red spruce (Picea rubens Sarg.) seedlings were exposed to elevated levels of ozone during a growing season and into the period of early winter frosts. Samples were taken for histological analysis, chlorophyll content, and carotenoid content. Ozone treatments increased mesophyll cell disruption after frosts in early winter. Cell injury increased with increasing ozone concentrations up to 2 × ambient. In the spring, injury was assayed by ranking trees based on overall appearance and by counting the number of shoots with brown needles. Ozone treatments had no effect on winter injury as scored by the ranking method. There was also no effect on the number of injured flushes when all trees were considered. However, when only those trees exhibiting winter injury were considered, there was a small, but statistically significant effect of ozone on the number of injured shoots. Thus, there is evidence that ozone increases injury from freezing temperatures in the autumn. Ozone slightly increases browning in the spring in sensitive trees. There were no correlations between histological injury in the autumn and appearance in the spring, indicating that there may be different aspects of the winter injury syndrome.
Tansley Review No. 18 Mechanisms of resistance and pathogenic specialization in rust‐wheat interactions
Authors: DEVERALL B. J.
Published: April 2006

Forms of resistance and pathogenic specialization in interactions between wheat and its stem and leaf rust Fungi have been selected for analysis with two hypotheses in mind. One is that phytoalexin formation is a universal defence mechanism in plants; the other is that resistance is elicited specifically by products of avirulent strains of pathogens.

A search for phytoalexins in wheat, using a range of extraction and separation procedures and a number of forms of expression of resistance, has indicated the presence of several inhibitors of fungal development but has yielded very little evidence for post‐infectional increases in the amounts of these inhibitors. No evidence for the formation of phytoalexins in wheat has been obtained. Hypersensitivity has been confirmed as being closely associated with the expression of most forms of resistance studied. Recent work with some very rapidly expressed forms of resistance to rust fungi has implicated lignification as a component of active defence in wheat, a finding in agreement with those of other workers.

The expression of resistance conferred by the Lr20 gene towards avirulent strains of the leaf rust fungus was the principal subject of explorations for elicitors. Histological observations of the sequence of events in fungal and wheat cells suggested the action of rust strain and Lr20–specific elicitors in bringing about hypersensitivity. Experimental manipulations involving heat treatments or use of epidermis‐free segments of leaves incubated on infected mesophylls gave results consistent with this interpretation. Attempts to extract specific elicitors from infected leaves failed but yielded non‐specific elicitors. Non‐specific elicitors have been obtained in intercellular washing fluids of leaves infected with strains of both the leaf and stem rust fungi. They have also been obtained from extracts of germ tubes of both species of fungus. Although not specific for any known resistance gene, the elicitors are selective for a character determined by a factor on chromosome 5 A in some wheat cultivars. A role for the non‐specific elicitors as incompatibility factors between rust fungi and wheat is suggested.

A revised hypothesis is presented in order to explain the evolution of pathogenesis in rust fungi towards wheat and it is discussed in relation to concepts of basic compatibility between pathogens and their hosts, as proposed also by others.

CONTENTS

Summary
233

I.
Introduction
234

II.
Working Ideas and Hypotheses
234

III.
The Search for Phytoalexins
235

IV.
Elicitation of Resistance
237

V.
Revised Hypothesis
240

Acknowledgements
242

References
242
Tansley Review No. 19 Environmental and endogenous controls of developmental pathways: variation and its significance in the forest pathogen, Heterobasidion annosum
Authors: STENLID J. , RAYNER A. D. M.
Published: April 2006

Cultural studies of the forest root pathogen Heterobasidion annosum (Fr.) Bref. have shown that the mycelium of the fungus possesses a high degree of developmental versatility, being able to grow in a variety of distinctive functional modes. Consequently the fungus can alternate between conidiogenous and meiotic reproductive pathways, rapid, sparsely branched and slow, densely branched mycelial extension, nutritive and non‐nutritive modes, and‘juvenile’and ‘senescent’phases. This ability is probably of considerable importance in natural infection cycles and provides an interesting model for examining interrelationships between developmental regulation and host‐pathogen interactions generally. It also raises important questions about the interface between environmental and endogenous controls of developmental pathways.

CONTENTS

Summary
245

I.
Introduction
245

II.
Spore germination and mycelial extension
246

III.
Production of non‐nutritive mycelium
249

IV.
Sporophore production, senescence, somatic incompatibility and extracellular enzyme production
251

V.
Discussion
254

Acknowledgements
255

References
255
Genetic variation of nitrate reductase activity in mono– and dikaryotic populations of the ectomycorrhizal fungus, Hebeloma cylindrosporum Romagnési
Authors: WAGNER F. , GAY G. , DEBAUD J. C.
Published: April 2006

Intraspecific variability in the activity of nitrate reductase (NR) has been studied in the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnési at the interstrain and intrastrain levels, the latter within a population of 11 wild dikaryotic strains collected in‘Les Landes’(SW France) at four locations less than 100 km away from one another. An attempt was made to determine whether variability within the monokaryotic and dikaryotic progeny of the HC1 fruiting strain could be used as a basis for an improvement programme involving breeding between selected monokaryons.

The NR activity of the wild strains ranged from 201 to 700 nmol NO2 synthesized h‐1 mg ‐1 fungal protein whilst that of 20 sib‐monokaryons (5 per mating type) of the HCl strain varied from 51 to 510 nmol NO2 synthesized h ‐1mg‐1 fungal protein. Fifty controlled dikaryotic myeclia were obtained from all the compatible fusions with these monokaryons. In these, variation of NR activity was of the same order of magnitude as that recorded at the interstrain level, ranging from 72 to 689 nmol NO2 synthesized h ‐1 rag ‐1 fungal protein. Analysis of the components of the variation of NR activity in these controlled dikaryons demonstrated that the additive component of this variation accounted for less than 1 % of the total observed variation. The NR activity of any one controlled dikaryon could not therefore be predicted from the activity of its parental monokaryons However 14 of the 50 controlled dikaryons e8hibited an NR activity higher than that of the HCl parental dikaryon. These results indicate that breeding with sib‐monokaryons can be used as a basis for an improvement programme of NR activity in this ectomycorrhizal Basidiomycete.
Photosynthetic characteristics, stomatal responses and water relations of Fagus sylvatica: impact of air quality at a site in southern Britain
Authors: TAYLOR GAIL , DOBSON M. C.
Published: April 2006

Transplants of beech (Fagus sylvatcia L.) were grown in open‐top chambers ventilated with either charcoal‐filtered or unfiltered air. From May until September measurements of stomatal conductance to water vapour (gs) were made on trees in the chambers. On six out of seven occasions, leaves which had expanded during the first flush (initial shoot extension, during May) in unfiltered air, had lower stomatal conductances, compared with those grown in filtered air; this was significant on three occasions (P < 0.05). Leaves which expanded later in the season (second Hush or lammas growth) responded differently to the air quality treatments, with greater stomatal conductances recorded for trees exposed to unfiltered air. Measurements of leaf (psychrometry) and shoot (pressure bomb) water relations indicated that air quality had little effect on turgor pressure (P). Values of solute (ψs) and water (ψw) potential were higher for trees grown in unfiltered air.

Trees were transported to the laboralory for measurement of photosynthesis (A), transpiration (E) and stomatal conductance (gs). Measurements of CO, uptake were also made whilst the CO, concentration within the leaf (Cf) was experimentally controlled (A/Ci analysis). This revealed that higher rates of photosynthesis for lammas leaves grown in unfiltered air were due to enhanced regeneration of RuBP (increased Jmax, P < 0.08). Carboxylation efficiency (d.A/dCf) and percentage stomatal limitation were not significantly altered by air quality. Jmax and dA/dCi were similarly reduced following exposure to drought regardless of the air quality treatment.
Photosynthesis during winter in ryegrass/white clover mixtures in the field
Authors: WOLEDGE JANE , DAVIDSON I. A. , TEWSON VERONICA
Published: April 2006

Measurements of canopy gas exchange of mixed communities of ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) in the field during winter showed that instantaneous rates of gross photosynthesis were usually little less than those of canopies of similar leaf area at similar irradiance in summer. Respiration rates per unit dry weight were on average 25% less than those of comparable swards in summer. The daily totals of net photosynthesis, however, were as little as a tenth of summer values, because of the short photoperiods and low average irradiance. Clover leaf area tended to be positioned lower in the canopy than grass leaf area, especially towards the end of winter, and clover had a lower rate of photosynthesis per unit leaf area in situ than grass.
Storage of sugars and mannitol in petioles of celery leaves
Authors: KELLER FELIX , MATILE PHILIPPE
Published: April 2006

Mannitol and sucrose are produced photosynthetically in the mesophyll and translocated in the phloem of celery leaves. The thick and fleshy petioles of these leaves act as reversible carbohydrate sinks, storing mainly mannitol, glucose and fructose but very little sucrose (less than 3.3 mg ml‐1 sap) in their parenchyma. The concentrations of soluble carbohydrates and the activities of enzymes of sucrose cleavage were asayed in the petiole parenchyma during leaf development. Mannitol (about 20 mg ml‐1 sap), glucose and fructose (about 10 to 15 mg ml‐1 sap each), changed little with development. Soluble acid invertase accounted for over 95 % of the total enzymic sucrose cleavage measured in vitro. Its activity was closely related to development with a sharp decrease during leaf maturation.

With protoplasts from petiole parenchyma and vacuoles isolated from them it was demonstrated that 28% of the total soluble acid invertase of the tissue was in the apoplast and 72 % in the vacuole. Alkaline invertase and sucrose synthase were totally cytosolic. Glucose and fructose, the main storage sugars of these protoplasts, were vacuolar in location, whereas mannitol was both cytosolic (19%) and vacuolar (81%).