bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbohydrate composition and invertase activity of the leafy liverwort Porella platyphylla
Authors: MARSCHALL MARIANN , PROCTOR MICHAEL C. F. , SMIRNOFF NICHOLAS
Published: March 2003

The major soluble carbohydrates in the desiccation‐tolerant leafy liverwort Porella platyphylla (L.) Lindb. are sucrose and a homologous series of fructans including the trisaccharide 1‐kestose. Exogenous glucose and fructose (10 mol m−3) did not affect the composition of the soluble carbohydrate pool. Sucrose caused an increase in the fructan pool. Sucrose also inhibited photosynthetic oxygen evolution and respiration. The fructan pool was maintained in preference to sucrose during dark starvation. Low temperature and low water potential increased the fructan pool whereas desiccation increased the proportion of high molecular weight fructan. Acid invertase activity was detected in a taxonomically diverse range of liverworts but was very low or undetectable in a range of mosses. The invertase activity from P. platyphylla was partially purified by ammonium sulphate precipitation. The reaction products of the partially purified enzyme were equimolar glucose and fructose. Kestose and higher DP fructans were not detected suggesting that, at least under the assay conditions used, the enzyme does not have sucrose∶sucrose fructosyl transferase activity. The pH optimum was 4·5–5 and the Km for sucrose was 1·7 mol m−3. Pyridoxal hydrochloride (5 mol m−3) caused 50% inhibition. The coexistence of sucrose and invertase suggests that either the invertase is inactive in vivo or is in a different subcellular compartment from sucrose. The pH response shows that it would have very low activity at cytosolic pH. A large acidic vacuole was detected in P. platyphylla leaf cells by neutral‐red staining in which either invertase or sucrose could be sequestered. Rehydrating desiccated P. platyphylla for 10 min resulted in a 60% loss of extractable invertase activity. By contrast, extractable malate dehydrogenase activity increased during rehydration. Rehydrating desiccated leaves caused an increase in glucose and fructose suggesting that the sucrose pool was susceptible to invertase at this time. It is suggested that the partial inactivation of invertase during rehydration minimizes sucrose hydrolysis while membrane structure and subcellular compartmentation are re‐established.
Intra‐specific variation in the photosynthetic responses of cyanobiont lichens from contrasting habitats
Authors: SMITH E. C. , GRIFFITHS H. , WOOD L. , GILLON J.
Published: March 2003

The photosynthetic properties of cyanobiont lichens from contrasting habitats were measured to identify whether the increased assimilation rates which characterized Peltigera membranacea (Ach.) Nyl. from an exposed habitat were correlated with increased carbon‐concentrating mechanism (CCM) activity. The results were contrasted with data obtained from two populations of Peltigera praetextata (Flörke ex Sommerf.) Zopf collected from dry and damp microhabitats within a shaded woodland and Peltigera leucophlebia (Nyl.) Gyelnik, which has been shown to lack a carbon‐concentrating mechanism. The differences in assimilation rates between the cyanobiont lichens were not accounted for by differences in chlorophyll content. Peltigera membranacea from the exposed habitat which had the highest assimilation rates had the lowest Gamma; and K0·5 values and accumulated the greatest Ci‐pool indicating that increased Ci accumulation contributed towards the higher assimilation rates shown by these species. The convexity of the light response curve for the cyanobiont lichens decreased with increasing assimilation rates. This might have indicated a diversion of electron transport to energize the carbon‐concentrating mechanism. The apparent quantum efficiency of CO2 assimilation (ΦCO2) was correlated with the genus of lichen photobiont. All cyanobiont lichens had comparable values for ΦCO2 which were greater than that of the tripartite Peltigera leucophlebia. Light compensation points reflected the exposure of the habitats with higher compensation points characterizing the cyanobiont population from the exposed crag and the tri‐partite population from the open grassland. Carbon isotope discrimination values for organic matter and measured instantaneously were the same for all cyanobiont lichens and were comparable with values recorded for species with a carbon‐concentrating mechanism. Carbon isotope measurements for P. leucophlebia were typical of those recorded for species without a carbon‐concentrating mechanism. Variation in source isotope signature and refixation of respiratory CO2 were considered to be significant factors in determining organic matter and instantaneous carbon‐isotope discrimination. These factors might have masked any subtle variation in carbon‐isotope discrimination which resulted from variable CCM activity. The functional significance of increased carbon‐concentrating mechanism activity in cyanobiont lichens occupying exposed habitats is discussed.
Field and laboratory experiments on net uptake of nitrate and ammonium by the roots of spruce (Picea abies) and beech (Fagus sylvatica) trees
Authors: GESSLER ARTHUR , SCHNEIDER STEPHAN , VON SENGBUSCH DOMINIK , WEBER PAUL , HANEMANN ULRIKE , HUBER CHRISTIAN , ROTHE ANDREAS , KREUTZER KARL , RENNENBERG HEINZ
Published: March 2003

During the vegetation periods 1994 and 1995, net uptake of nitrate and ammonium by roots of adult spruce (Picea abies (L.) Karst) and beech (Fagus sylvatica L.) trees was studied at a field site exposed to high loads of N (‘Höglwald’, Germany). In addition, uptake experiments were carried out under controlled conditions with young spruce and beech trees grown at normal N supply.

In the field, nitrate was not taken up by the roots of spruce trees in appreciable amounts. This was also true for beech except during September 1995. Apparently, beech trees was capable of taking up nitrate, but the environmental condition prevailing at the field site usually prevented net uptake. Net uptake of ammonium in both tree species showed a seasonal course, with maximum rates in mid summer. Rates of ammonium uptake by both species correlated with soil temperature at the field site.

Laboratory experiments on the influence of root temperature on uptake of nitrate indicated that uptake rates at temperatures found in the field were low compared with the uptake capacity at optimum temperature. At temperatures of 10 and 15°C, frequently found in the soil at the field site, net uptake of nitrate by spruce and beech amounted to c. 16% and 11%, respectively, of maximum uptake at 25°C. By contrast, net uptake of ammonium at 10°C reached 73% and 31% of the maximum uptake for spruce and beech trees, respectively. Independent of temperature, rates of nitrate uptake were considerably lower than those of ammonium. In young spruce and beech trees, net uptake of nitrate was significantly inhibited by ammonium at nitrate∶ammonium ratios found in the soil solution at the forest site. Preincubation of roots of both species, with amino acids present in the phloem of adult trees at the field site, led to an increase in the amino acid pool in the roots. For spruce trees a correlation between inhibition of uptake of nitrate and enrichment of the roots with the amino compounds Glu, γ‐amino butyric acid (Gaba), Gln, and Asn was observed. In beech trees, enrichment of Asp and Gln in the roots correlated with a decrease in net uptake of nitrate. The results of laboratory experiments on the effects of temperature, the nitrate to ammonium ratio in the nutrient solution, and amino acid enrichment in the roots are discussed with special emphasis on the patterns of net uptake of ammonium and nitrate observed in the field.
The use of isotopic dilution techniques to evaluate the interactive effects of Rhizobium genotype, mycorrhizal fungi, phosphate‐solubilizing rhizobacteria and rock phosphate on nitrogen and phosphorus acquisition by Medicago sativa
Authors: TORO M. , AZCÓN R. , BAREA J. M.
Published: March 2003

A pot experiment was designed to evaluate the interactive effects of multiple microbial inoculation treatments and rock phosphate (RP) application on N and P acquisition by alfalfa plants using 15N and 32P isotopes. The microbial inocula consisted of a wild type (WT) Rhizobium meliloti strain, its genetically modified (GM) derivative, which had an enhanced competitiveness, the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, and a phosphate‐solubilizing rhizobacterium (Enterobacter sp.). Inoculated micro‐organisms became established in the root tissues and/or in the rhizosphere soil of alfalfa plants (Medicago sativa L.). The GM Rhizobium strain did not interfere with AM formation. Inoculated phosphate‐solubilizing rhizobacteria established in the alfalfa rhizosphere, but the level of establishment was lower where the natural population of phosphate‐solubilizing bacteria was stimulated by AM inoculation and RP application. The stimulation of these indigenous bacteria was also greater in the rhizosphere of alfalfa nodulated by the GM Rhizobium. Improvements in N and P accumulation in alfalfa corroborate beneficial effects of the improved GM Rhizobium on AM performance, in RP‐amended plants. Inoculation with Enterobacter did not improve the AM effect on N or P accumulation in the RP‐added soil, but it did in the non RP‐amended controls. Measurements of the 15N∶14N ratio in plant shoots indicated enhanced N2 fixation rates in Rhizobium‐inoculated AM‐plants, over that achieved by the same Rhizobium strain in non‐mycorrhizal plants. Regardless of the Rhizobium strain and of whether or not RP was added, AM‐inoculated plants showed a lower specific activity (32P∶31P) than did their comparable non‐mycorrhizal controls, suggesting that the plant was using otherwise unavailable P sources. The phosphate‐solubilizing, AM‐associated, microbiota could in fact release phosphate ions, either from the added RP or from the indigenous ‘less‐available’ phosphate. Deficiency in Ca concentration in soil solution in the neutral test soil might benefit P solubilization. The proportion of plant P derived either from the labelled soil P (labile P pool) or from RP was similar for AM inoculated and non‐mycorrhizal controls (without Enterobacter inoculation) for each Rhizobium strain, but the total P uptake, regardless of the P source, was far higher in AM‐plants. Enterobacter inoculation seems to improve the use of RP in the rhizosphere of non‐mycorrhizal plants inoculated with the WT Rhizobium.
Diversity of an early successional plant community as influenced by ozone
Authors: BARBO D. N. , CHAPPELKA A. H. , SOMERS G. L. , MILLER‐GOODMAN M. S. , STOLTE K.
Published: March 2003

An early successional plant community was exposed to various ozone concentrations for two growing seasons (1994–1995) in open‐top chambers in Auburn, Alabama, USA. The ozone treatments were: AA, ambient air (open plots); CF, carbon‐filtered air (c. 0·5×ambient air), 1×, non‐filtered air, and 2×, twice ambient air. Vegetative canopy cover exhibited a pattern of accumulation in the spring, with maximum canopy cover attained in summer, then senescence of foliage in the autumn 1994. This pattern was not observed in 1995 as a result of a drought during the spring and summer. Varying ozone exposures caused shifts in the competitive interactions between plants, thereby altering community structure. Higher canopy cover, vertical canopy density (layers of foliage), species richness, diversity, and evenness existed in the CF treatments than in the other treatments. In addition, winged sumac (Rhus copallina L.) became a major component of the CF treatments only during 1995. Surprisingly, blackberry (Rubus cuneifolius Pursh.), a species considered ozone‐sensitive, based on visible injury, dominated canopy cover within the 2× treatments, 41 and 33% of total canopy cover in 1994 and 1995, respectively. From these results it is concluded that plant communities existing in areas where lower ozone concentrations are prevalent might be more complex and diverse than those existing in areas with higher ozone concentrations.
Diversity of ectomycorrhizal fungi in Britain: a test of the species–area relationship, and the role of host specificity
Authors: NEWTON A. C. , HAIGH J. M.
Published: March 2003

The host range of ectomycorrhizal (ECM) fungi in Britain was examined by compilation of a data matrix from published literature sources, based primarily on accounts of sporocarp associations with particular host genera. Information was gathered for 577 species of ECM fungi belonging to 51 genera, and 25 genera of host trees, representing the majority of ECM fungal species and host genera recorded in Britain.

Pronounced variation was recorded in the number of ECM fungal species associated with different host genera, with over 200 species recorded with Betula, Fagus, Pinus and Quercus. There was a positive linear relationship (r2=0·47, P=0·007) between the number of species of ECM fungi associated with different host genera and the total area occupied by each tree genus in Britain (both values log‐transformed). There was also variation in the number of species of ECM fungi which were apparently specific to particular host genera, values ranging from zero (in 15 genera) to >40 in the case of Betula and Fagus. In total, 233 fungal species appeared to be specific to a single host genus (i.e. 40% of those surveyed). Comparison of the ECM mycota associated with different host genera by PCA accounted for 17% of the total variation, with genera belonging to the Fagaceae (Quercus, Fagus and Castanea) tending to cluster together, indicating a degree of overlap in their ECM associates. Exotic conifer species, which displayed a lower ECM diversity than would be expected from their distributional areas, were characterized by a high degree of overlap with the ECM associates of Pinus and Betula.

These results indicate that the abundance of different genera of host trees and variation in host specificity could provide a basis for understanding patterns of diversity in ECM fungi within Britain.
Comparison of the light‐limited growth of the nitrogen‐fixing cyanobacteria Anabaena and Aphanizomenon
Authors: DE NOBEL W. T. (PIM) , MATTHIJS HANS C. P. , VON ELERT ERIC , MUR LUUC R.
Published: March 2003

The effect of simultaneous N2 fixation and light limitation on the growth of two strains of Anabaena sp. Bory de St. Vincent and Aphanizomenon flos‐aquae (L.) Ralfs was investigated using continuous cultures. Under severely light‐limited conditions, Aphanizomenon showed a broader absorption spectrum (due to the presence of phycoerythrin), a higher maximum efficiency of photosynthesis, a higher steady‐state N2 fixation activity and a higher growth affinity for light than did Anabaena. On the other hand, under light saturation, Anabaena showed a higher maximum rate of O2 production and a higher maximum specific growth rate than Aphanizomenon. These monoculture results characterize Anabaena and Aphanizomenon, in relative terms, as a ‘sun’ and a ‘shade’ species respectively, and are in accordance with field observations. The difference between the two species in their acclimatory response is discussed in terms of a species‐specific alteration of the PSI∶PSII stoichiometry. Besides the species‐specific modulation of the accessory pigments, such an acclimation would provide a biochemical basis for the observed physiological differences. The monoculture results were used to differentiate the niches of the two species and suggested that Aphanizomenon would competitively displace Anabaena under N2‐fixing, light‐limited conditions. However, when both species were grown together, Anabaena became dominant and seemed to be the superior competitor for light. In order to explain this finding, the possible effects of release of allelopathic compounds, or dynamic aspects of light supply, are discussed.
Plant defence genes are induced in the pathogenic interaction between bean roots and Fusarium solani, but not in the symbiotic interaction with the arbuscular mycorrhizal fungus Glomus mosseae
Authors: MOHR UWE , LANGE JÜRG , BOLLER THOMAS , WIEMKEN ANDRES , VÖGELI‐LANGE REGINA
Published: March 2003

Plant roots enter symbiotic as well as pathogenic interactions with fungi in the rhizosphere. We studied the response of bean (Phaseolus vulgaris L. cv. Saxa) roots to infection by the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe and the pathogen Fusarium solani (Mart.) Sacc. f. sp. phaseoli (Burkholder) Snyder & Hansen. In a time‐course study of the symbiotic interaction between bean roots and G. mosseae, covering all stages of mycorrhiza development, we detected little change in the expression of the defence‐related genes chitinase, β‐1,3‐glucanase and phenylalanine ammonia‐lyase compared with non‐mycorrhizal control roots. The only difference observed was a transient increase in chalcone synthase transcripts at later stages of mycorrhizal root colonization. In interactions with the pathogen, a marked induction of chitinase and phenylalanine ammonia‐lyase expression was observed at the level of both the transcripts and enzyme activities. Class I β‐1,3‐glucanase levels strongly increased at the transcript level, but there was little change in the overall β‐1,3‐glucanase enzyme activity. In the non‐host interaction between common bean and Fusarium solani (Mart.) Sacc. f. sp. pisi (Linford) Snyder & Hansen defence responses increased only slightly and transiently, if at all.
Effects of nitrogen addition on the stress sensitivity of Calluna vulgaris
Authors: POWER S. A. , ASHMORE M. R. , COUSINS D. A. , SHEPPARD L. J.
Published: March 2003

The effects of low levels of nitrogen addition (7·7 and 15·4 kg N ha−1 yr−1) on plant sensitivity to biotic and abiotic stress were studied at a lowland heath in the south of England that has received N treatments since 1989. Larval growth rates and adult weights of heather beetles were found to be significantly higher when insects were reared on plants that had received additional N, with implications for insect survival and reproductive success. Electrolyte leakage measurements failed to reveal any significant impact of N addition on plant sensitivity to frost episodes in early winter. In April, however, there was some evidence of slightly decreased frost hardiness in plants receiving additional N. Accelerated spring bud burst also suggested earlier physiological activity in N‐treated plots. The rate of water loss from excised shoots of Calluna vulgaris (L.) Hull was significantly faster in plants receiving additional N, although no difference in plant water potential was measured in the field after a prolonged dry spell. Whilst experimental N addition had only a small effect on plant sensitivity to abiotic stress, the relationship between enhanced deposition and increased insect performance was clear, with the potential for substantially increased insect damage at deposition rates around the critical load contributing to the formation of gaps in the Calluna canopy.
Ammonia: emission, atmospheric transport and deposition
Authors: ASMAN WILLEM A. H. , SUTTON MARK A. , SCHJØRRING JAN K.
Published: March 2003

The global emission of ammonia (NH3) is about 54 Mt N. The major global sources are excreta from domestic animals and fertilizers, but oceans, biomass burning and crops are also important. About 60% of the global NH3 emission is estimated to come from anthropogenic sources. NH3‐N emissions are of the same order as the NOx‐N emissions on both global and European scales. Emitted NH3 returns to the surface mainly in the form of dry deposition of NH3 and wet deposition of ammonium (NH4+). In countries with high NH3 emission densities, dry deposition of NH3 from local sources and wet deposition of NH4+ from remote sources dominate the deposition. In countries with low NH3 emission densities only wet deposition of NH4+ from remote sources dominates the deposition. Surface exchange of NH3 is essentially bi‐directional, depending on the NH3 compensation point concentration of the vegetation and the airborne concentration. In general, the compensation point is larger for agricultural than semi‐natural plants, and varies with plant growth stage. According to basic thermodynamics the leaf tissue or stomatal compensation point of NH3 doubles for each increase of 5°C. However, exchange of NH3 does not only occur through the stomata, but it can also be deposited to leaf surfaces, as well as emitted back to the atmosphere from drying leaf surfaces. Atmospheric transport and deposition models can be used to interpolate NH3 concentrations and depositions in space and time, to calculate import/export balances and to estimate past or future situations. Adverse effects on sensitive ecosystems caused by high N deposition can be reduced by lowering the emissions and, to a limited extent, also by removing sources close to the ecosystem to be protected.
A comparison of arbuscular and ectomycorrhizal Eucalyptus coccifera: growth response, phosphorus uptake efficiency and external hyphal production
Authors: JONES MELANIE D. , DURALL D. M. , TINKER P. B.
Published: March 2003

Eucalyptus coccifera Hook., a plant capable of forming both arbuscular mycorrhizas and ectomycorrhizas, was used to compare the effects of the two mycorrhizal types on phosphorus uptake and C allocation. Seedlings were grown in a P‐deficient soil/sand mixture inoculated with peat/vermiculite spawn of Laccaria bicolor (Maire) Orton or Thelephora terrestris (Ehrh.) Fr.; or with 250‐μm sievings from leek colonized by Glomus caledonium (Nicol. & Gerd.) Trappe & Gerde., Glomus sp. type E3 or Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe or with autoclaved spawn (non‐mycorrhizal control). Before the 89‐d harvest, a subset of the harvested plants was labelled with 14C (45–60‐min pulse, 202‐h chase). Growth promotion and the increase in seedling P content was largest in the two ectomycorrhizal treatments. Production of fluorescein diacetate‐stained external hyphae was three to seven times higher by ectomycorrhizal (ECM) fungi compared with arbuscular mycorrhizal (AM) fungi and was highly correlated with P uptake and shoot weight. Phosphorus inflow rates of ECM and AM seedlings were 3·8 times, and 2·0–2·7 times those of non‐mycorrhizal seedlings. Phosphorus acquisition efficiencies were similar (11·2 and 10·0 μmol P mmol−1C for T. terrestris and Glomus E3 plants, respectively) for the two mycorrhizal types, and appeared to be greater than in uninoculated plants (7.2 μmol P mmol−1C) grown at the same P level.
Primary and secondary host plants differ in leaf‐level photosynthetic response to herbivory: evidence from Alnus and Betula grazed by the alder beetle, Agelastica alni
Authors: OLEKSYN J. , KAROLEWSKI P. , GIERTYCH M. J. , ZYTKOWIAK R. , REICH P. B. , TJOELKER M. G.
Published: March 2003

Field‐grown trees of Alnus incana (L.) Moench, Alnus glutinosa (L.) Geartner and Betula pendula Roth displayed pronounced differences in responses of light‐saturated net photosynthesis (Asat) to herbivory by the alder beetle (Agelastica alni L., Galerucinae), a specialized insect which primarily defoliates alders. We found that photosynthetic rates of grazed leaves increased following herbivory in Alnus but not in Betula. Area‐ and mass‐based Asat of grazed leaves declined linearly with increasing amount of leaf perforation in B. pendula, by as much as 57%. By contrast Alnus glutinosa and Alnus incana increased area‐based rates of Asat by 10–50% at all levels of leaf grazing. Given increased Asat in the remaining portion of grazed leaves, a net reduction in photosynthesis per leaf occurred only when the proportion of leaf area grazed exceeded 40% for Alnus incana and 23% for Alnus glutinosa. Since vein perforation by Agelastica alni was observed much more frequently in leaves of Betula than in Alnus, we hypothesized that declining Asat in herbivorized Betula was related to this disruption of water transport. A field experiment with artificial leaf perforation demonstrated a greater decline in Asat in vein‐perforated Betula leaves than perforated leaves with midrib veins intact. However, regardless of leaf perforation regime, birch never showed post‐perforation increases in Asat. In all species, rates of transpiration of grazed leaves linearly increased and water‐use efficiency decreased with increased amount of leaf perforation. In grazed Alnus incana leaves, increasing leaf area consumption by Agelastica alni resulted in an increase of total phenols, a reduction in starch content and no changes in nitrogen concentration in the remaining portion. The increase in photosynthesis in Alnus incana might be related to declining leaf starch concentration or increasing stomatal conductance, but was unrelated to leaf nitrogen concentration. These gas exchange and leaf chemistry measurements suggest that in contrast to B. pendula, Alnus incana and Alnus glutinosa, which are the major host species for Agelastica alni, possess leaf‐level physiological adaptations and defence mechanisms which can attenuate negative effects of herbivory by the alder leaf‐beetle.
A new sampler for extracting undisturbed surface peat cores for growth pot experiments
Authors: BUTTLER A. , GROSVERNIER P. , MATTHEY Y.
Published: March 2003

The sampler extracts uncompressed cores of 13·3 cm in diameter, up to 70 cm long, from the surface layers of peat. It has two close‐fitting concentric cylindrical tubes, the outer one acting as a cutter and the inner one as a collector. As the outer tube is introduced by rotation into the peat, the cut core is collected in the inner tube which is maintained in a fixed position during the rotation phase and then pushed down stepwise. This limits friction between the peat core and the wall of the corer and prevents compression or distortion of the peat. These problems are also reduced by means of three skew cutters allowing the peat to be supported during the slicing action. Air can penetrate between the tubes to the lower end of the core, suppressing any suction effect during withdrawal. The sampler has been tested and has worked satisfactorily in many different peat types.
Chitin and ergosterol combined to measure total and living fungal biomass in ectomycorrhizas
Authors: EKBLAD ALF , WALLANDER HÅKAN , NÄSHOLM TORGNY
Published: March 2003

We have studied the chitin and ergosterol contents of ectomycorrhizal roots in three sets of experiments to evaluate them as indicators of fungal biomass. The first set of experiments showed that ageing had a marked effect on ergosterol concentrations. The ergosterol content of 7‐month‐old, brown, shrunken Pinus sylvestris L.–Paxillus involutus (Fr.) Fr. mycorrhizas was found to be only 10% of that found in white, turgid, 1‐ or 4‐month‐old specimens. This supports the hypothesis that the compound is a good indicator of living fungal biomass. Ageing had a lesser effect on chitin concentrations since the chitin levels found in 7‐month‐old mycorrhizas were still 60% of the levels found in 1‐ and 4‐month‐old specimens.

Consequently, the chitin∶ergosterol ratio increased from about 14 to 19 in 1‐ and 4‐month‐old mycorrhizas respectively to about 110 in 7‐month‐old mycorrhizas. In the second set of experiments, we found that variation in plant growth had no effect on the chitin∶ergosterol ratio in whole root systems of either Alnus incana (L.) Moench or Pinus sylvestris mycorrhizal with Paxillus involutus. In the third set of experiments, we found a constant relationship between the two marker concentrations in 10‐month‐old root systems of Pinus sylvestris, regardless of fungal species involved, using Paxillus involutus, Piloderma croceum Erikss. & Hjorts and Suillus variegatus (Fr.) O. Kuntze as test organisms. Taken together, the results of this study suggest that both chitin and ergosterol give reliable, but different, relative measures of fungal biomass in mycorrhizal roots. Furthermore, we demonstrate that, in combination, the two chemical markers can be used to estimate both total and living fungal biomass (derived from the chitin∶ergosterol ratio).
Effects of drought on non‐mycorrhizal and mycorrhizal maize: changes in the pools of non‐structural carbohydrates, in the activities of invertase and trehalase, and in the pools of amino acids and imino acids
Authors: SCHELLENBAUM L. , MÜLLER J. , BOLLER T. , WIEMKEN A. , SCHÜEPP H.
Published: March 2003

To study the response of non‐mycorrhizal and mycorrhizal maize plants to drought, the changes in the pools of non‐structural carbohydrates and amino acids were analysed in leaves and roots of two maize cvs. Plants well colonized by the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) (60% of root length infected) and comparable non‐mycorrhizal plants were subjected to moderate drought stress by reducing the water supply. This stress induced a conspicuous increase in the trehalose pool in the mycorrhizal roots, probably because it was accumulated by the fungal symbiont. Furthermore, glucose and fructose were accumulated in leaves and roots of non‐mycorrhizal plants but not in the mycorrhizal ones. Starch disappeared completely from the leaves of both mycorrhizal and non‐mycorrhizal plants in response to drought. Activities of soluble acid invertase and trehalase were also measured. Acid invertase activity increased during drought in the leaves of both non‐mycorrhizal and mycorrhizal plants whilst in the roots it was unaffected in non‐mycorrhizal plants and decreased in the mycorrhizal ones. Without drought stress, trehalase activity was considerably higher in the leaves and roots of mycorrhizal plants than in those of non‐mycorrhizal plants. It increased conspicuously during drought, primarily in the leaves of non‐mycorrhizal plants. A drought‐induced accumulation of amino acids as well as imino acids was found in roots and leaves of both mycorrhizal and non‐mycorrhizal plants; leaves of mycorrhizal plants accumulated more imino acids than those of non‐mycorrhizal ones. Our results show that drought stress and the presence of a mycorrhizal fungus have a considerable effect on carbon partitioning, imino acid and amino acid accumulation in maize plants.
Photosynthate costs associated with the utilization of different nitrogen–forms: influence on the carbon balance of plants and shoot–root biomass partitioning
Authors: ZERIHUN AYALSEW , McKENZIE BRUCE A. , MORTON JAMES D.
Published: March 2003

The photosynthate costs of processes (amino acid and protein synthesis and turnover, and pH regulation) associated with the utilization of nitrate (NO3−), ammonium (NH4+) or glutamine (Gln) for plant growth were estimated. Based on these estimates, the effects of these forms of nitrogen (N) on the carbon balance of plants and on shoot–root biomass allocation were evaluated. The results indicated that NO3− as an N source for plant growth is not substantially more expensive to utilize than either NH4+ or Gln, particularly in the long term when costs due to protein turnover dominate the total costs of N utilization. It is also suggested that the photosynthate use in processes associated with N assimilation has little impact on the carbon balance of plants, and hence on shoot–root biomass allocation.
Induction of genes for the stress proteins PR‐10 and PAL in relation to growth, visible injuries and stomatal conductance in birch (Betula pendula) clones exposed to ozone and/or drought
Authors: PÄÄKKÖNEN E. , SEPPÄNEN S. , HOLOPAINEN T. , KOKKO H. , KÄRENLAMPI S. , KÄRENLAMPI L. , KANGASJÄRVI J.
Published: March 2003

Well watered (WW) or drought‐stressed (DS) saplings of ozone‐sensitive and ozone‐tolerant (less sensitive) birch (Betula pendula Roth) clones were exposed for 43 d to 0 nl l−1 or 100 nl l−1 ozone. Relative growth rates of leaves, stem, and roots, leaf discolouration, stomatal conductance and induction of genes encoding stress‐related proteins PR‐10, PAL and a LEA‐group protein BP8 were determined. In general, both ozone and drought stress, singly and in combination, increased transcript levels of PR‐10 in both clones. This was related to lower induction of PAL (except in older leaves of the tolerant clone), and increased proportions of visibly injured and yellowed leaves in ozone‐exposed plants. The clones differed in their stomatal conductance and growth responses. In the less sensitive clone 2, ozone did not affect growth rates, but high stomatal conductance was observed in WW ozone‐exposed plants. The more sensitive clone 5 showed, on the contrary, reduced growth rates and low stomatal conductance in WW ozone plants. Interestingly, clone 2 was sensitive to drought stress alone, whereas clone 5 was highly sensitive to ozone and drought stress experienced together. The results show that appearance of visible injuries (necrotic flecks) and enhanced yellowing of leaves coincided with the induction of genes for stress proteins PR‐10 and PAL. The short‐term growth responses, however, seemed to be separate processes. Additionally, stomatal conductance was related to leaf injuries and growth rates in a complicated manner, emphasizing the complex nature of ozone sensitivity/tolerance mechanisms in birch.
Comparison of Gaeumannomyces‐ and Phialophora‐like fungal pathogens from maize and other plants using DNA methods
Authors: WARD ELAINE , BATEMAN GEOFFREY L.
Published: March 2003

Several DNA‐based techniques, developed for identifying and differentiating fungi in the Gaeumannomyces–Phialophora complex associated with take‐all diseases of cereals and grasses, were used to compare fungi from maize. Maize isolates obtained as G. graminis (Sacc.) Arx & H Olivier var. tritici Walker, from the UK, having been identified by ascospore morphology and in pathogenicity tests on wheat, were indistinguishable from isolates of the same variety obtained from wheat. Isolates of G. graminis (Sacc.) Arx & H Olivier var. maydis Yao et al., recently described as the maize take‐all fungus from China, were identical in DNA tests to the anamorphic fungus Phialophora radicicola Cain and almost identical to Phialophora zeicola Deacon & Scott, whose description was originally based on isolates from South Africa and France. These species appear to represent the holomorph of the same fungus. The late wilt pathogen of maize, from India and Egypt, commonly known as Cephalosporium maydis Samra et al., but suggested as being the Phialophora anamorph of a Gaeumannomyces species, was closely related to other Gaeumannomyces species included in the tests.
Microtubule and actin filament organization during stomatal morphogenesis in the fern Asplenium nidus. II. Guard cells
Authors: APOSTOLAKOS P. , GALATIS B.
Published: March 2003

The post‐cytokinetic guard cells of Asplenium nidus display a prominent perinuclear microtubule system and a few microtubules under the periclinal walls. Afterwards, microtubules appear on the whole surface of the ventral wall, whereas those below the periclinal walls proliferate and tend to become parallel with the ventral wall. The perinuclear microtubules gradually diminish but persist in later stages of guard cell differentiation. In post‐cytokinetic guard cells, actin is found in the perinuclear cytoplasm and in the cortical cytoplasm lining all the walls. In differentiating guard cells, the following cortical microtubules and actin filament ‘systems’ appear in succession: (a) radial microtubule and actin filament arrays beneath the periclinal walls converging on the stomatal pore region, (b) anticlinal microtubule bundles, which are co‐localized with actin filaments, along the ventral wall outlining the region of the stomatal pore, (c) periclinal microtubules and actin filaments on the polar ventral wall ends. These cytoskeletal systems, except for the radial actin filaments, persist in advanced stages of guard cell differentiation. Instead of the radial actin filaments, a prominent actin filament reticulum is organized under the margins of the developing wall thickenings of the stomatal pore. In addition, an extensive endoplasmic actin filament reticulum develops around the plastids. It seems likely that the successive microtubule systems in guard cells are formed by putative microtubule organizing centres operating in a definite spatial and temporal succession. Guard cell morphogenesis is the outcome of a definite process, in which the cortical microtubule cytoskeleton plays the primary role, implicated in the deposition of cellulose microfibrils and probably of the local wall thickenings. Callose or a callose‐like glucan is deposited on the whole surface of the nascent ventral wall and in the wall regions where thickenings are deposited. Finally, the guard cells of Asplenium assume a kidney shape and display polar hypostomatic swellings. Particular structural features established in guard cell mother cells affect guard cell morphogenesis.
A comparison of visualization techniques for recording arbuscular mycorrhizal colonization
Authors: GANGE ALAN C. , BOWER ERICA , STAGG PENNY G. , APLIN DAVID M. , GILLAM ALEXANDRA E. , BRACKEN MICHAEL
Published: March 2003

The extent of arbuscular mycorrhizal colonization was assessed in 10 field‐collected plant species, representing three annual forbs, three perennial forbs, three perennial grasses and one annual grass. Each root system of each plant was split into four portions, and for each portion, mycorrhizal structures were revealed with epifluorescence microscopy (under which only arbuscules are generally visible) and three commonly used stains (Chlorazol Black E, Acid Fuchsin and Trypan Blue). The aim of the study was not to evaluate the efficacy of each method, but to compare results obtained by each under standard laboratory conditions. The recorded colonization levels of arbuscules, total arbuscular mycorrhizal fungal material and total fungal (arbuscular mycorrhizal+non‐arbuscular mycorrhizal) material differed significantly between visualization methods in a number of species. However, there were also interactions between stain and plant species, indicating that the performance of a stain is dependent on the plant species being examined. In some cases (e.g. Plantago lanceolata), each visualization method produced the same colonization level, while in others (e.g. Dactylis glomerata), each method gave a different result. These data therefore suggest that the level of mycorrhizal colonization recorded in any particular plant species at a particular time is dependent on the technique employed.
Parental environmental effects on life history traits in Arabidopsis thaliana (Brassicaceae)
Authors: ANDALO C. , MAZER S. J. , GODELLE B. , MACHON N.
Published: March 2003

Environmentally induced maternal effects on offspring phenotype are well known in plants. When genotypes or maternal lineages are replicated and raised in different environmental conditions, the phenotype of their offspring often depends on the environment in which the parents developed. However, the degree to which such maternal effects are maintained over subsequent generations has not been documented in many taxa. Here we report the results of a study designed to assess the effects of parental environment on vegetative and reproductive traits, using glasshouse‐raised maternal lines sampled from natural populations of Arabidopsis thaliana. Replicates of five highly selfed lines from each of four wild populations were cultivated in two abiotic environments in the glasshouse, and the quality and performance of seeds derived from these two environments were examined over two generations. We found that offspring phenotype was strongly influenced by parental environment, but because the parental environments differed with respect to the time of seed harvest, it was not possible to distinguish clearly between parental environmental effects and the possible (but unlikely) effects of seed age on offspring phenotype. We observed a rapid decline in the expression of ancestral environmental effects, and no main environmental effects on progeny phenotype persisted in the second generation. The mechanism of transmission of environmental effects did not appear to be associated with the quantity or quality of reserves in the seeds, suggesting that environmental effects may be transmitted across subsequent generations via some mechanism that generates environment‐specific gene expression.
Leaf life span and nutrient resorption as determinants of plant nutrient conservation in temperate‐arctic regions
Authors: ECKSTEIN R. L. , KARLSSON P. S. , WEIH M.
Published: March 2003

Nutrient conservation plays an important role in plants adapted to infertile environments. Nutrients can be conserved mainly by extending the life span of plant parts and/or by minimizing the nutrient content of those parts that are abscissed. Together these two parameters (life span and resorption) define the mean residence time (MRT) of a nutrient. In this review we summarize available information on nitrogen resorption and life span, and evaluate their relationship to the MRT of nitrogen, both between and within species. Abundant information with respect to nitrogen resorption efficiency and life span is available at the leaf level. By definition, woody evergreen plants have a much longer leaf life span than species of other life‐forms. Conversely, differences in resorption efficiency among life‐forms or among plants in habitats differing in soil fertility appear to be small. Inter‐specific variation in leaf life span is much larger than intra‐specific variation (factor of >200 compared with 2, respectively), while resorption efficiency varies by about the same magnitude at both levels (factor of 3.8 compared with 2.7, respectively). The importance of resorption efficiency in determining leaf‐level MRT increases exponentially towards and above the maximum resorption efficiency observed in nature. This effect is independent of leaf life span, which may explain the lack of life‐form related differences in resorption efficiency. When scaling up from the leaf to the whole‐plant level, fundamental differences in turnover rate among different plant organs must be considered. Woody species invest c. 50% of their net productivity into their low‐turnover stems, while in herbaceous species the life span of stems is only slightly longer than that of leaves. As a result, nutrient turnover of woody (evergreen and deciduous) plants is generally lower than that of herbaceous species (herbs and graminoids) on a whole‐plant basis. At the intra‐specific level empirical data show that both biomass life span (i.e. the inverse of biomass loss rate) and resorption efficiency are important sources of variation in MRT. However, we argue that the relative importance of resorption efficiency in explaining variation in MRT is lower at the inter‐specific level, whereas the reverse is true for life span. This is because variation in MRT and life span is much larger at the inter‐specific level compared with variation in resorption efficiency. Plant traits related to nutrient conservation are discussed with respect to their implications for leaf structure, plant growth, competition, succession and ecosystem nutrient cycling.
Tansley Review No. 105.
Authors: LUNN J. E. , FURBANK R. T.
Published: March 2003

Sucrose has a central role in the metabolism of all higher plants. Here we discuss the location of sucrose synthesis in the leaves of C4 plants, the control of flux through the pathway and its response to environmental conditions, and finally some of the prospects for the genetic manipulation of sucrose metabolism in C4 plants. Much of our knowledge about sucrose synthesis in plants comes from C3 species; it is evident, from those studies of C4 species that are available, that there are many similarities between sucrose synthesis in C3 and C4 plants. However, some of the basic regulatory mechanisms common to both C3 and C4 plants seem to have been adapted for the specialized photosynthetic metabolism of C4 plants. There are also some other important differences: for example, some C4 species possess photosynthetic cells with little or no capacity for sucrose synthesis. For these reasons it is not always appropriate to extrapolate directly from C3 to C4 plants. Even where data are available from one C4 species, usually maize, it should not be assumed that all C4 plants are necessarily the same in every respect. Although C4 plants constitute a small fraction of the plant kingdom as a whole, they include a disproportionate number of agriculturally important species. C4 plants also have some advantages over C3 plants for studies of the regulation of cell‐specific gene expression and the control of metabolism. For these reasons we suggest that they are worthy of more attention by researchers.

contents

Summary
221

I.
Introduction
221

II.
Pathway of sucrose synthesis in C4 plants
223

III.
Control of sucrose synthesis in C4 plants
225

IV.
Future prospects
233

Acknowledgements
234

References
234
Exploring the relationships between reflectance and anatomical and biochemical properties in Quercus ilex leaves
Authors: OURCIVAL J. M. , JOFFRE R. , RAMBAL S.
Published: March 2003

Leaf anatomical parameters such as leaf mass per area (LMA) and biochemical composition can be used as indicators of leaf photosynthetic capacity. The aims of this study are to evaluate the potential of reflectance spectroscopy of fresh leaves for assessing and predicting various parameters, anatomical (LMA and tissue thickness) and biochemical (nitrogen concentration). This paper describes results obtained with fresh leaves of holm oak (Quercus ilex), an evergreen oak that is widely distributed from mesic to xeric habitats in the Mediterranean. Fresh leaves (560) were collected over 3 yr at six different sites, from the top to the bottom of the canopy. The reflectance of each leaf was obtained within 1 h of sampling with an NIRSystems 6500 spectrophotometer over the range 400–2500 nm. LMA was determined for all samples; biochemical and anatomical measurements were conducted over representative subsample populations of 92 and 87 leaves, respectively. Stepwise regression calibrations and partial least squares (PLS) calibrations were developed and compared with different spectral regions and mathematical treatments. Calibration equations had high coefficients of determination (r2 ranging from 0.94 for nitrogen to 0.98 for LMA and tissue thickness). The PLS regressions gave better results than stepwise regressions for all parameters studied. Compared with regressions calculated on raw spectral data, calculations on second derivatives of spectra improved results in all cases. The use of scatter corrections also improved results. These results show that visible and near‐infra red reflectance can be used for accurately predicting anatomical parameters and the nitrogen concentration of fresh holm oak leaves. The results support the suggestion that high spectral resolution imaging spectrometry can be a useful tool for assessing functional processes in forest ecosystems.