bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of soil compaction on phosphorus uptake and growth of Trifolium subterraneum colonized by four species of vesicular–arbuscular mycorrhizal fungi
Authors: NADIAN H. , SMITH S. E. , ALSTON A. M. , MURRAY R. S. , SIEBERT B. D.
Published: March 2003

The ability of four species of vesicular–arbuscular mycorrhizal (VAM) fungi to increase phosphorus uptake and growth of clover plants (Trifolium subterraneum L.) at different levels of soil compaction and P application was studied in a pot experiment. Dry matter in the shoots and roots of clover plants decreased with increasing soil compaction. Colonization by Glomus intraradices Schenck & Smith and Glomus sp. City Beach WUM16 increased plant growth and P uptake up to a bulk density of 1·60 Mg m−3, although the response was smaller as soil compaction was increased. Glomus etunicatum Becker & Gerdeman and Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe had no effect on the shoot d. wt and P uptake when the bulk density of the soil was 1·40 and 1·60 Mg m−3, respectively. Soil compaction to a bulk density of 1·60 Mg m−3 had no effect on the percentage of root length colonized by G. intraradices and Glomus sp. City Beach, but total root length colonized decreased as soil compaction was increased. Decreased P uptake and growth of clover plants colonized by G. intraradices and Glomus sp. City Beach, with increasing soil compaction up to a bulk density of 1·60 Mg m−3, was mainly attributed to a significant reduction in total root length colonized and in the hyphal biomass. Soil compaction, which increased bulk density from 1·20 to 1·75 Mg m−3, reduced the O2 content of the soil atmosphere from 0·16 to 0·05 m3 m−3. The absence of any observable mycorrhizal growth response to any of the four species of VAM fungi in highly compacted soil (bulk density = 1·75 Mg m−3) was attributed to the significant decrease in the O2 content of the soil atmosphere, change in soil pore size distribution and, presumably, to ethylene production.
Actin versus tubulin configuration in arbuscule‐containing cells from mycorrhizal tobacco roots
Authors: GENRE A. , BONFANTE P.
Published: March 2003

The involvement of the cytoskeleton in symbiotic interactions such as arbuscular mycorrhizas has received little attention. In this paper, we examine the organization of actin in tobacco mycorrhizal roots and compare actin and tubulin patterns within arbuscule‐containing cells.

Our results show drastic reorganization of microfilaments and microtubules upon fungal infection and how those new cytoskeletal patterns relate to the host cytoplasm rearrangement and the intracellular fungal structures. Whereas in uninfected cells a network of cortical and perinuclear actin filaments was observed, in infected cells actin filaments closely follow the fungal branches and envelop the whole arbuscule in a dense coating network. Microtubules are less closely connected with the fungus surface. They run across the whole arbuscule mass, linking branches to each other and to the host cell cortex and nucleus.

These major differences between the two cytoskeletal components are used to advance some suggestions concerning their contribution to structural functions in the plant–fungus interactions during the mycorrhizal symbiosis.
Major Biological Issues Resulting from Anthropogenic Disturbance of the Nitrogen Cycle (The Third New Phytologist Symposium, Lancaster University, UK, 3–5 September 1997)
Authors: MANSFIELD TERRY , GOULDING KEITH , SHEPPARD LUCY
Published: March 2003

A two‐day Discussion Meeting of the Royal Society, ‘The Nitrogen Cycle’, held in London in June 1991 (Stewart & Rosswall, 1992) reviewed the considerable progress made in understanding the N cycle in agricultural, forest and aquatic systems. The meeting included some discussion of the concerns which were already being expressed at that time over nitrate in water supplies, and the impacts of nitrogenous gases on tropospheric chemistry, the greenhouse effect and the ozone layer. Since then, disquiet over the impacts of nitrogenous compounds on the environment has increased, and numerous papers have been published on many aspects of the problem. We now have much better understanding of the size and scale of the perturbation of the N cycle, and several review papers have highlighted the complexity of the formidable issues that are challenging environmental scientists (Vitousek, 1994; Galloway et al., 1995; Vitousek et al., 1997).
Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings II. Photosynthetic capacity and water relations
Authors: CENTRITTO MAURO , MAGNANI FEDERICO , LEE HELEN S. J. , JARVIS PAUL G.
Published: March 2003

Cherry seedlings (Prunus avium) were grown from seed for two growing seasons in three ambient [CO2] (∼350 μmol mol−1) and three elevated [CO2] (ambient+∼350 μmol mol−1) open‐top chambers, and in three outside blocks. A drying cycle was imposed in both the growing seasons to half the seedlings: days 69–115 in the first growing season, and in the second growing season days 212–251 on the same seedlings which had already experienced drought. Stomatal conductance was significantly reduced in elevated [CO2]‐grown, unstressed seedlings in both the first and second growing seasons, but was not caused by a decrease in stomatal density. Droughted seedlings showed little or no reduction in stomatal conductance in response to elevated [CO2]. However, stomatal conductance was highly correlated with soil water status. Photosynthetic rate increased significantly in response to elevated [CO2] in both water regimes, leading to improvement in instantaneous transpiration efficiency over the whole duration of the experiment, but there was no relationship between instantaneous transpiration efficiency and long‐term water use efficiency. The Amax was strongly reduced in the second growing season, but unaffected by [CO2] treatment. Although photosynthetic rate was not down‐regulated, Rubisco activity was decreased by elevated [CO2], possibly because of the increased leaf carbon: nitrogen ratio which had occurred by the ends of the two growing seasons. Elevated [CO2] did not improve plant water relations (for example, bulk leaf – water potential, osmotic potentials at full and zero turgor, relative water content at zero turgor, bulk modulus of elasticity of the cell) and thus did not increase water‐stress tolerance of cherry seedlings.
Role of external calcium in homeostasis of intracellular pH in the cyanobacterium Anabaena sp. strain PCC7120 exposed to low pH
Authors: GIRALDEZ‐RUIZ N. , BONILLA I. , FERNANDEZ‐PIÑAS F.
Published: March 2003

The role of external Ca2+ in the homeostasis of intracellular pH (pHi) of Anabaena sp. strain PCC7120 in response to a decrease in the external pH (pHex) has been studied in cell suspensions. Increase in cytoplasmic pH after acid shock is dependent on the presence of Ca2+ in the medium. The observed Ca2+‐mediated alkalization of the cytoplasm depends on the extent of the shift in external pH. Acid pH shifts resulted in an increased permeability of the cytoplasmic membrane to protons, which could be reversed by increasing the concentration of Ca2+ in the medium. Thus, the ability of Ca2+ to increase cytoplasmic pH might be correlated with an inhibition of net proton uptake by increasing concentrations of external Ca2+ under these conditions. This combined response resulted in the generation and maintenance of a larger pH gradient (ΔpH) at acid external pH values. All Ca2+ channel blockers tested, such as verapamil and LaCl3, inhibited the observed Ca2+‐mediated response. On the other hand, the Ca ionophore calcimycin (compound A23187) was agonistic, and stimulated both cytoplasmic alkalization and inhibition of net proton uptake. The protonophorous uncoupler carbonylcyanide m‐chlorophenyl hydrazone, inhibited this Ca2+‐mediated response, whereas monensin, an inhibitor of the Na+/H+ antiporter, had no significant effect. The results of the present study suggest that an influx of Ca2+ from the extracellular space is required for the regulation of cytoplasmic pH in Anabaena sp. strain PCC7120 exposed to low external pH values.
Energy requirement for foliage formation is not constant along canopy light gradients in temperate deciduous trees
Authors: NIINEMETS ÜLO
Published: March 2003

Foliage construction cost (glucose requirement for formation of a unit foliar biomass, G, kg glu kg−1), chemical composition and morphology were examined along a light gradient across the canopies in five deciduous species, which ranked according to increasing shade‐tolerance as Populus tremula <Fraxinus excelsior <Tilia cordata = Corylus avellana <Fagus sylvatica. Light conditions in the canopy were estimated by a hemispheric photographic technique, allowing ranking of sample locations according to long‐term light input incident to the sampled leaves (relative irradiance). G and foliage carbon concentration increased with increasing relative irradiance in F. excelsior, T. cordata and C. avellana, but wereindependent of irradiance in F. sylvatica and P. tremula. However, if G of non‐structural‐carbohydrate‐free dry mass was considered, it also increased with increasing relative irradiance in P. tremula. A positive correlation between the concentration of carbon‐rich lignin and irradiance, probably a result of the acclimation to greater water stress at higher light, was the major reason for the light‐dependence of G. Lignin concentrations were highest in more shade‐tolerant species, resulting in greatest carbon concentrations in these species. Since carbon concentration and G are directly linked, the leaves of shade‐tolerant species were also more expensive to construct. As the result of these effects, G increased faster with increasing leaf dry mass per area which was mainly determined by relative irradiance, in shade‐tolerators. Given that shade‐tolerant species had lower leaf dry mass per area at common irradiance and that this saturated at lower relative irradiance than leaf dry mass per area in the intolerant species, it was concluded that enhanced energy requirements for foliage construction might constrain species morphological plasticity and the upper limit of leaf dry mass per area attainable at high light.
Continuity of ectomycorrhizal fungi in self‐regenerating boreal Pinus sylvestris forests studied by comparing mycobiont diversity on seedlings and mature trees
Authors: JONSSON L. , DAHLBERG A. , NILSSON M‐C. , KÅRÉN O. , ZACKRISSON O.
Published: March 2003

Seedlings and old trees of Scots pine in self‐regenerating, old, virgin boreal forest in northern Sweden were compared in terms of the species composition of their associated ectomycorrhizal (EM) fungi. The natural regeneration of seedlings was mimicked by annual seeding for 10 yr (1986–1995) in intact field vegetation at three sites. In 1995, all seedlings were harvested, and 171 were examined for mycorrhizas. Twenty‐five soil cores were taken in order to study the mycorrhizas on the established trees. Most short roots were mycorrhizal. Using mycorrhizal morphology and restriction fragment length polymorphisms (RFLP) analysis, we were able to distinguish 43 ectomycorrhizal taxa. Fourteen of these taxa were identified using a sporocarp and mycelial culture based internal transcribed spacer (ITS)‐RFLP reference database, and another three were identified by mycorrhizal morphology. Cenococcum geophilum, Piloderma croceum and Suillus variegatus were present on the seedlings, irrespective of age, as well as on the old trees. At one forest, 23 ectomycorrhizal taxa were found as mycorrhizas, of which 10 occurred on both seedlings and old trees. These 10 species accounted for 92 and 73% of the mycorrhizas on the seedlings and old trees, respectively. A 3‐yr survey of ectomycorrhizal sporocarps at the same site revealed 62 EM taxa. The degree of similarity between the composition of EM species reflected by sporocarps and by mycorrhizas, was low. Ectomycorrhizal species present in our ITS‐RFLP database constituted 7.5–19% of the mycorrhizas on seedlings and old trees, whereas they constituted 80–95% of the total production of epigeous sporocarps. The unidentified taxa comprised 70–87% of the mycorrhizas. Our findings support the view that the species composition of mycorrhizas colonizing naturally regenerated seedlings in forests is similar to that of mycorrhizas colonizing surrounding trees. We suggest that the concept of the mycelial network be expanded in order to embrace both the significance of interconnections between different trees as well as the continuity or perpetuation of EM fungal communities.
Effects of repeated harvesting of forest residues on the ectomycorrhizal community in a Swedish spruce forest
Authors: MAHMOOD SHAHID , FINLAY ROGER D. , ERLAND SUSANNE
Published: March 2003

The use of biofuels has been proposed as one possible substitute for fossil fuels, which contribute substantially to the increase in [CO2] in the atmosphere. However, increased harvesting of forest residues for biofuel might affect the availability of base cations, P and N, as well as the development, community dynamics and function of ectomycorrhizas. This in turn might influence nutrient uptake and tree growth. In this study we investigated the effects of repeated forest residue harvesting on ectomycorrhizal species colonizing spruce roots in the humus layer of a 35‐yr‐old forest. Harvesting significantly decreased the thickness of the humus layer as well as decreasing the numbers of ectomycorrhizal root tips both per metre root length and per unit humus volume. Changes in mycorrhizal community structure were studied by ITS typing with the use of PCR–RFLP analysis. In total, 19 different ITS types were found on two different sampling occasions (autumn and spring); 11 of these were common to both samplings. Nine of the ITS types were identified to at least the genus level by comparison with RFLP patterns of identified fruiting bodies or axenic cultures. Five species, Cortinarius sp. 2, Thelephora terrestris (Ehrenb.) Fr., Lactarius theiogalus (Bull.∶Fr.) S. F. Gray s.st. Neuhoff, Tylospora fibrillosa Donk and Tö‐96‐12, occurred on over 5% of the total sampled root tips. Together these five types colonized 63% of the mycorrhizas screened. A similarity index assessment showed no shift in mycorrhizal community structure as a result of harvesting. Our findings suggest that the repeated removal of forest residues might have a strong effect on the quantity and development of ectomycorrhizal roots in the organic horizon, but little effect on the species composition of the community.
Purification and characterization of an alkaline invertase from shoots of etiolated rice seedlings
Authors: LIN CHUNG‐LIANG , LIN HUI‐CHIAO , WANG AI‐YU , SUNG HSIEN‐YI
Published: March 2003

One alkaline invertase and two acid invertase activities were detected in the shoots of etiolated rice (Oryza sativa) seedlings. The alkaline invertase (AIT) was purified to homogeneity through steps of ammonium sulphate fractionation, concanavalin A‐Sepharose affinity chromatography (non‐retained), DEAE‐Sephacel chromatography and preparative electrophoresis. The pH optimum of AIT was 7.0 and the molecular mass, determined by gel filtration, was 240 kDa. It is apparently a homotetrameric enzyme (subunit molecular mass 60 kDa). The isoelectric point was 4.4 by isoelectric focusing. The best substrate of the enzyme was sucrose, with a Km of 2.53 mM. The enzyme also hydrolysed raffinose, but not maltose or lactose, so it is a β‐D‐fructofuranosidase. It gave negative glycoprotein staining. Of the hydrolysis products, fructose was a competitive inhibitor and glucose was a non‐competitive inhibitor. Treatment with an alkaline phosphatase could activate AIT, whereas other proteins such as BSA, concanavalin A and urease had no effect on the enzyme activity. The enzyme activity was inhibited by Tris, thiol reagents and heavy metal ions.
Tansley Review No. 104
Authors: McLAUGHLIN S. B. , WIMMER R.
Published: March 2003

Summary

Calcium occupies a unique position among plant nutrients both chemically and functionally. Its chemical properties allow it to exist in a wide range of binding states and to serve in both structural and messenger roles. Despite its importance in many plant processes, Ca mobility is low, making Ca uptake and distribution rate a limiting process for many key plant functions. Ca plays an essential role in regulating many physiological processes that influence both growth and responses to environmental stresses. Included among these are: water and solute movement, influenced through effects on membrane structure and stomatal function; cell division and cell wall synthesis; direct or signaling roles in systems involved in plant defense and repair of damage from biotic and abiotic stress; rates of respiratory metabolism and translocation; and structural chemistry and function of woody support tissues. Forest trees, because of their size and age capacity, have been examined for evidence of limitations imposed by the timing and level of Ca supply. Examination of Ca physiology and biogeochemical cycling for forested systems reveals many indications that Ca supply places important limitations on forest structure and function. These limitations are likely to be most significant with older trees, later successional stages, high levels of soil acidity and/or high canopy Ca leaching losses, or under conditions where plant competition is high or transpiration is limited by high humidity or low soil moisture. Evidence of structural and physiological adaptations of forests to limited Ca supply; indicators of system dysfunction at many levels under reduced Ca supply; and the positive responses of diverse indicators of forest vitality in liming experiments indicate that Ca is more important to forest function and structure than has generally been recognized. Lack of recognition of Ca limitations is due in part to that fact some important plant functions are controlled by changes in very small physiologically active pools within the cytoplasm, and whole‐leaf Ca levels may not reflect these limitations. An additional aspect is the fact that Ca availability has declined significantly for many forests in just the past few decades. Additional research on the role of Ca supply in resistance of forests to disease, changes in structural integrity of woody tissues, restrictions on rooting patterns and function, and uptake of other nutrients, notably N, is needed. Increased understanding of the physiological ecology of Ca supply can be anticipated to provide important insights that will aid in future protection and management of both natural and commercial forest systems.

contents

Summary

I.
introduction – a hypothesis
374

II.
effects of calcium on physiological processes
376

III.
calcium uptake and distribution at the whole‐plant level
382

IV.
ecosystem processes and calcium supply
387

V.
plant and ecosystem responses to human alterations in calcium supply
391

VI.
conclusion
407

VII.
evaluation of the hypothesis
410

Acknowledgements
411

References
411
Acquisition and allocation of resources in two waterlogging‐tolerant grasses
Authors: RUBIO GERARDO , LAVADO RAUL S.
Published: March 2003

This study focuses on the following questions: (i) whether reductions in root:shoot ratio have a cost in terms of nutrient balance of the plant, and (ii) whether changes in resource‐allocation patterns are proportional among different resources. Our approach was to analyse the variations in the allocation pattern induced by soil waterlogging. A pot experiment was conducted to analyse the effects of waterlogging on biomass, phosphorus (P) and nitrogen (N) accumulation of Paspalum dilatatum and Danthonia montevidensis, two waterlogging‐tolerant grasses. When changing from oxic to anoxic conditions, a common response of these and other waterlogging‐tolerant grasses is a reduction in allocation to below‐ground resources. It was observed that (i) the reduction in root:shoot ratio caused by waterlogging did not have a cost in terms of capacity for nutrient uptake; (ii) resource partitioning within aerial parts was less sensitive to treatments than partitioning between roots and shoots; and (iii) biomass does not appear to be a useful currency for evaluating nutrient‐allocation patterns, as the allocation of P and N was inadequately represented by biomass. The results presented here indicate that the existence of compensation mechanisms reduces the predictive value of the partition of resources for the capacity of plants to acquire resources. Data on the allocation of nutrients in relation to biomass suggest that the assumptions of independence in the allocation pattern between biomass and limiting nutrients under the effects of environmental factors can be extended.
Interactions of chronic exposure to elevated CO2 and O3 levels in the photosynthetic light and dark reactions of European beech (Fagus sylvatica)
Authors: GRAMS THORSTEN E. E. , ANEGG SABINE , HÄBERLE KARL‐HEINZ , LANGEBARTELS CHRISTIAN , MATYSSEK RAINER
Published: March 2003

Young trees of European beech (Fagus sylvatica) acclimated for one growing season to ambient (c. 367 μl l−1) or elevated CO2 levels (c. 660 μl l−1) were exposed during the subsequent year to combinations of the same CO2 regimes and ambient or twice‐ambient ozone (O3) levels (generated from the database of a rural site). By the end of June, before the development of macroscopic leaf injury, the raised O3 levels had not affected the light and dark reactions of photosynthesis. However, acclimation to elevated CO2 had resulted in lowered chlorophyll and nitrogen concentrations, whereas photosynthetic performance, examined over a wide range of parameters from light and dark reactions, remained unchanged or showed only slight reductions (e.g. apparent electron transport rate, ETR; apparent quantum yield of CO2 gas exchange, ΦCO2; apparent carboxylation efficiency, CE; and photosynthetic capacity at light and CO2 saturation, PC). In August, after the appearance of leaf necroses, plants grown under ambient CO2 and twice‐ambient O3 conditions declined in both the photosynthetic light reactions (optimum electron quantum yield, Fv/Fm, non‐photochemical energy quenching, NPQ, reduction state of QA, apparent electron quantum yield, ΦPSII, maximum electron transport rates) and the dark reactions as reflected by CE, ΦCO2, as well as the maximum CO2 uptake rate (i.e. PC). CE, ΦCO2 and PC were reduced by c. 75, 40 and 75%, respectively, relative to plants exposed to ambient CO2 and O3 levels. By contrast, plants exposed to twice‐ambient O3 and elevated CO2 levels maintained a photosynthetic performance similar to individuals grown either under ambient CO2 and ambient O3, or elevated CO2 and ambient O3 conditions. The long‐term exposure to elevated CO2 therefore tended to counteract adverse chronic effects of enhanced O3 levels on photosynthesis. Possible reasons for this compensatory effect in F. sylvatica are discussed.
Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions
Authors: MUNNÉ‐BOSCH SERGI , NOGUÉS SALVADOR , ALEGRE LEONOR
Published: March 2003

The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary (Rosmarinus officinalis) and lavender (Lavandula stoechas), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψpd) from c.−0.4 to c.−1.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis. A similar decrease in CO2 assimilation rates by c. 75% was observed in water‐stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO2:mol H2O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water‐
stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought‐induced damage to photosystem II, as indicated by the maintenance of the ratio Fv:Fm throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water‐stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15‐d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water‐stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought.
Characterization of two arbuscular mycorrhizal fungi in symbiosis with Allium porrum: colonization, plant growth and phosphate uptake
Authors: DICKSON S. , SMITH S. E. , SMITH F. A.
Published: March 2003

Two arbuscular mycorrhizal fungi, Scutellospora calospora and Glomus sp. ‘City Beach’, were grown in soil conditions suitable for colonization of Allium porrum. Effects on plant growth and phosphate uptake were examined. Isolates of S. calospora (including the one used here) have been shown by others to vary in their stimulation of plant growth, and appear to be inefficient in the transfer of P from the fungus to the host. Our hypothesis was that such isolates of S. calospora may be more aggressive colonizers than other fungi, thus preventing growth increases or producing strong growth depressions in the host plant. In fact, inoculation with either fungus increased growth of plants in their respective soils both low in P (P0) and with added P (P1) by 42 d. The effect on growth due to mycorrhizal symbiosis (i.e. mycorrhizal growth response, % MGR) at 42 d was higher in plants grown in P0 soil. Plants colonized by Glomus sp. ‘City Beach’ had a greater % MGR than plants colonized by S. calospora. Both fungi colonized plants to high levels. The percentage of root length colonized was higher in P0 soil than in P1 soil at 21 d. The internal development of S. calospora appeared less affected by addition of P than Glomus sp. ‘City Beach’ at the early harvests. Formation of arbuscules followed the same trends as total colonization. Shoot P concentration was significantly higher in mycorrhizal plants than in non‐mycorrhizal plants, by 21 d in P1 soil and by 28 d in P0 soil. Different percentage responses to added P based on total plant dry weight (% PGR) were observed at 28 and 42 d between the plants colonized by the two fungi. The increased P content due to mycorrhizal colonization (% MPR) differed with soil P. For both fungi grown in their respective soils, the response was greater in plants grown in P0 soil. Although the isolate of S. calospora used is an aggressive arbuscular mycorrhizal fungus with some hosts, it promotes a strong positive plant growth response in A. porrum after a mild initial growth depression.
Effects of cadmium on growth of Helianthus annuus seedlings: physiological aspects
Authors: DI CAGNO R. , GUIDI L. , STEFANI A. , SOLDATINI G. F.
Published: March 2003

Sunflower seedlings (Helianthus annuus hybrid Select) were grown in a complete nutrient solution in the absence or presence of Cd2+ (10 and 20 μM). Analyses were performed to establish whether there was a differential effect of Cd2+ on mature and young leaves. After 7 d the growth parameters as well as the leaf area had decreased in both mature and young leaves. Accumulation of Cd2+ in the roots exceeded that in the shoots. Seedlings treated with Cd2+ exhibited reduced contents of chlorophyll and CO2 assimilation rate, with a greater decrease in young leaves. The photochemical efficiency of photosystem II (PSII) was not altered by Cd2+ treatment in either mature or young leaves, although during steady‐state photosynthesis in young leaves there was a significant alteration in the following parameters: quantum yield of electron transport by PSII (ΦPSII), photochemical quenching (qP), non‐photochemical quenching (qNP), and excitation capture efficiency of PSII (Φexc).
Confocal ratio imaging of cytoplasmic pH during germ tube growth and appressorium induction by Magnaporthe grisea
Authors: JELITTO T. C.
Published: March 2003

The role of cytosolic pH (pHc) in growing germ tubes of the filamentous fungus Magnaporthe grisea was analysed by confocal ratio imaging of the pH‐sensitive fluorescent dye 5(6)‐carboxyseminaphthorhodafluor‐1 (SNARF‐1). The cytosol of these cells was successfully loaded with the acetoxymethyl ester of the dye and the pHc was visualized and quantified during conidium germination, germ tube growth and appressorium induction by simultaneous dual‐emission confocal ratio imaging. Calibrations of the free acid in vitro and calibrations in vivo produced results indicating a similar dynamic response in the pH range 6.0–8.0 for both methods. The pHc in growing germ tubes was consistently pH 7.2±0.1 during all developmental stages analysed. Only slight changes in pHc (<0.1 pH unit) were found in response to alkaline external pH (pH 8.0). No changes in pHc occurred in response to an acidic extracellular pH (pH 6.0) or to the presence of nutrients. There was no observation of either pronounced gradients or changes in pHc in growing germ tubes accompanying conidium germination, germ tube growth or early appressorium formation.
A thermal time basis for comparing the germination requirements of some British herbaceous plants
Authors: TRUDGILL D. L. , SQUIRE G. R. , THOMPSON K.
Published: March 2003

The effect of temperature on germination rate was assessed for seeds of 31 wild plant species and four cultivated species growing in the UK. The temperature at which seed first germinated ranged from 2 °C (Brassica rapa) to 11 °C (several species). As the temperature progressively increased, the percentage of seed that germinated rapidly increased to near 100%, whereas the duration for germination progressively decreased up to the thermal optimum. Above the thermal optimum, the duration for germination initially remained constant, and then rapidly increased until the thermal maximum was exceeded when no seed germinated. To assess the effect of temperature on germination rates, the reciprocal of the duration (1/duration) for 50% germination was calculated and regressed against temperature. For most species a linear regression accounted for >90% of the variation in germination rates for temperatures up to the thermal optimum. From the regressions, the base temperatures (Tb, below which no germination is expected) and the thermal constant (S, expressed in degree days) for 50% germination were calculated. The extremes were the alpine species Dryas octopetala, which had a high Tb (c. 12.0 °C) and low S (26 degree days), and Saxifraga tridactylites which had a low estimated Tb (c. −1.8 °C) and a high S (136 degree days). The estimated value of S increased with increasing percentage germination, and although S varied considerably between species with similar values of Tb, a weak inverse relationship between Tb and S was indicated. A thermal time approach was shown to be useful when analysing and comparing thermal requirements for germination of the seed of wild plant species. It showed, for example, that percentage germination often decreased as temperatures approached Tb, and that for some seed germination ceased at temperatures well above Tb.
Subcellular compartmentation of elements in non‐mycorrhizal and mycorrhizal roots of Pinus sylvestris: an X‐ray microanalytical study. I. The distribution of phosphate
Authors: BÜCKING HEIKE , HEYSER WOLFGANG
Published: March 2003

The inter‐ and intracellular distribution of phosphate in non‐mycorrhizal and ectomycorrhizal roots of Pinus sylvestris was analysed by energy‐dispersive X‐ray spectroscopy after cryofixation, freeze‐drying, pressure infiltration with resin and dry cutting of the material. The results show (1) that in non‐mycorrhizal roots the distribution of phosphate across the root cross section is relatively homogenous, (2) that the intracellular distribution of phosphate depends on the external supply, and (3) that the phosphate absorption can be increased by a supply of NH4. Under phosphate starvation, the phosphate is mainly localized in the cell cytoplasm, whereas under high external phosphate this element accumulates in the vacuoles of cortical cells. It can be inferred that at low external conditions phosphate is mainly located in the cytoplasm of cells to protect metabolism from deficiency, that phosphate is translocated to the shoot via symplastic and apoplastic pathways, and that especially the vacuolar pool size is regulated by the external phosphate supply. The nutrition of the host plant under phosphate starvation was improved by a mycorrhizal infection with Suillus bovinus. However, this effect might not be the same for all ectomycorrhizal infections and supply conditions. With high external phosphate an ectomycorrhizal infection with S. bovinus had no effect on intracellular phosphate within the roots, the shoot contents of mycorrhizal plants were less than those of non‐mycorrhizal seedlings and translocation rate across the mycorrhizal interface appeared to be independent of the availability of phosphate. Intracellular phosphate in fungal cells of mycorrhizal roots was independent of the external supply and seemed to be regulated by the formation of polyphosphates. A supply of (NH4)2HPO4, which led to an increase in cytoplasmic phosphate levels in the hyphae of the Hartig net of the Paxillus involutus mycorrhiza also led to higher phosphate in the plant cell compartments. Therefore, it can be inferred that the translocation of phosphate from fungus to host plant across the mycorrhizal interface is regulated by the phosphate concentration in the cytoplasm of the Hartig net and by the efflux rate into the interfacial apoplast.
Leaf metabolic and morphological responses of dwarf willow (Salix herbacea) in the sub‐arctic to the past 9000 years of global environmental change
Authors: BEERLING D. J. , RUNDGREN M.
Published: March 2003

Ice‐core records of the concentration of atmospheric CO2 and its stable isotope ratio (δ13Ca) have shown that the global C cycle has not remained in steady‐state over the past 11000 yr, implying a possible change in vegetation activity over this period. Here we evaluated the ecophysiological responses of the dwarf willow (Salix herbacea) over the past 9000 yr by measuring the stable carbon isotope composition and stomatal characters of a unique, well dated, high‐latitude (68 °N) sub‐fossil leaf sequence. After correction for corresponding changes in δ13Ca, a 9000‐yr record of variations in the ratio of intercellular (ci) to atmospheric (ca) CO2 concentration was established. Intercellular∶atmospheric CO2 concentration ratios provide a time‐integrated indicator of the set‐point of leaf gas exchange, and the historical variations revealed in this record have been interpreted as an impact of environmental changes on leaf gas exchange. The sequence shows a progressive fall in ci/ca 9000–3000 yr BP as well as the climatic effects of the Medieval Warm Period, the Little Ice Age and the post‐industrial CO2 rise. Leaf stomatal index (proportion of epidermal cells as stomata), but not stomatal density, was significantly (P<0.01) correlated with Holocene atmospheric CO2 variations. A process‐based interpretation of the changes in ci/ca was made using two different coupled photosynthesis‐stomatal conductance models. Calculated in this way, S. herbacea photosynthetic rates were relatively stable throughout the Holocene whilst stomatal conductance progressively declined. Both, however, showed the marked effects of the Medieval Warm Period and the Little Ice Age. Overall, the results demonstrate that S. herbacea leaf metabolism, like the global C cycle, has not remained in steady state during the Holocene but has responded to changes in atmospheric CO2 concentration and short‐term climatic oscillations.
Symbiotic germination and development of myco‐heterotrophic plants in nature: ontogeny of Corallorhiza trifida and characterization of its mycorrhizal fungi
Authors: McKENDRICK S. L. , LEAKE J. R. , TAYLOR D. L. , READ D. J.
Published: March 2003

The processes of symbiotic germination and seedling development were analysed in the myco‐heterotrophic orchid Corallorhiza trifida, seeds of which were buried in ‘packets’ either adjacent to or at varying distances from
adult plants in defined communities of ectomycorrhizal tree species. Germination occurred within eight months
of burial under Betula–Alnus and within seven months under Salix repens. It was always associated with
penetration of the suspensor by a clamp‐forming mycorrhizal fungus. Four distinct developmental stages were
defined and the rates of transition through these stages were plotted. There was no evidence of a relationship
between extent of germination or rate of development and the presence of naturally distributed plants of C. trifida
at the spatial scale of 1 m. The best germination and the most rapid rate of development of C. trifida seedlings
occurred in a Salix repens community located at a considerable distance from any extant C. trifida population.
Determination of internal transcribed spacer (ITS) RFLPs and of gene sequences of the fungi involved in
symbiotic germination and growth of C. trifida, revealed them to belong exclusively to the Thelephora–Tomentella
complex of the Thelephoraceae. These fungi are known also to be ectomycorrhizal associates of trees. It is
hypothesized that the rate of growth of the C. trifida seedlings is determined by the ability of the fungal symbionts to transfer carbon from their ectomycorrhizal co‐associates.
Terpenes and the thermotolerance of photosynthesis
Authors: Singsaas Eric L.
Published: March 2003

A walk through the forest is a good way to become aquainted with the variety of terpenes emitted by plants. The most fragrant of these are the monoterpenes, which lend a distinctive smell to trees (e.g. α‐ and β‐pinene from pines), mints (e.g. menthol from peppermint), fruits (e.g. limonene from citrus) and flowers (e.g. geraniol from roses). In addition to adding fragrance, phytogenic hydrocarbons play an important role in atmospheric chemistry. This was recognized as early as 1960 by Fritz Went who noted that blue hazes often formed above forested areas (Went, 1960). This idea was picked up by US President Ronald Reagan who accused trees of polluting the atmosphere, although in truth phytogenic hydrocarbons only contribute to pollution in air that is already contaminated by industry or automobile exhaust (Feshenfeld et al., 1992).

Terpenes serve a variety of functions in plants including deterring herbivores and attracting pollinators. Until recently, the function of terpene emission from some groups of plants, which do not store the terpenes in their tissues, has been a mystery. Following the discovery that isoprene, a hemiterpene, increases the thermotolerance of photosynthesis in some species (Sharkey & Singsaas, 1995; Singsaas et al., 1997), Loreto et al. (1998) discovered that thermotolerance of the monoterpene‐emitting oak, Quercus ilex, increases when leaves are fumigated with monoterpenes. Now, a report by Delfine et al. in this issue (pp. 27–36) provides further support for the hypothesis that terpenes play a role in thermotolerance of leaves and suggests, intriguingly, that the mechanism by which this occurs is not limited to plants that make these compounds.
Spatial patterns of photobiont diversity in some Nostoc‐containing lichens
Authors: PAULSRUD PER , RIKKINEN JOUKO , LINDBLAD PETER
Published: March 2003

Patterns of photobiont diversity were examined in some Nostoc‐containing lichens using the nucleotide sequence
of the cyanobacterial tRNALeu (UAA) intron. Lichen specimens collected in northwestern USA were analysed and
the sequence data were compared with tRNALeu(UAA) intron sequences previously obtained from lichens in
northern Europe. Generally, it is the species identity of a lichen rather than the geographical origin of the specimen
that determines the identity of the cyanobiont. Identical intron sequences were found in Peltigera membranacea
specimens collected in Oregon (USA) and in Sweden, and very similar sequences were also found in Nephroma
resupinatum thalli collected in Oregon and Finland. Furthermore, in mixed assemblages where two Peltigera
species grew in physical contact with each other, the different lichen species housed different photobiont strains.
There is however not a one‐to‐one relation between mycobiont and photobiont as some intron sequences were
found in more than one lichen species, and different intron sequences were found in different samples of some
lichen taxa. Peltigera venosa exhibited a higher level of photobiont diversity than any other lichen species studied,
and several intron sequences could for the first time be obtained from a single thallus. It is not clear whether this
is evidence of lower cyanobiont specificity, or reflects an ability to exhibit different degrees of lichenization with
different Nostoc strains. In one specimen of P. venosa, which contained bipartite cyanosymbiodemes and tripartite, cephalodiate thalli, both thallus types contained the same intron sequence.
Gloomy predictions – modelling photoautotrophy in low‐light environments
Authors: Reynolds C. S.
Published: March 2003

How plants gather their resources, harvest solar energy and convert raw materials into an increased biomass is one of the enduring fascinations of biological science. Just about every step has been charted by biochemists and few processes have escaped the determination of a rate constant by physiologists. Even the molecular biologist is busy identifying the genes that govern the processes of synthesis and assembly. Nevertheless, at higher levels of organization, of building populations and, especially, communities, the prediction of growth continues to be problematic. Thus, the development by Bright & Walsby (pp. 301–316 in this issue) of a method for calculating the daily growth of a photoautotroph in its natural environment is bound to command our attention. Their approach is ingenious and the veracity of their calculations compelling. This is exciting science.
Differences in nitrogen metabolism of Faidherbia albida and other N2‐fixing tropical woody acacias reflect habitat water availability
Authors: CAMPA CLAUDINE , DIOUF DIÉGANE , NDOYE IBRAHIMA , DREYFUS BERNARD
Published: March 2003

The activities of nitrate reductase and glutamine synthetase were evaluated in young plants of Faidherbia albida,
a tropical woody legume, fed with different N sources under hydroponic conditions. Results showed that assimilation of both NO3− and NH4+
preferentially took place in shoots. A basal amount of nitrate reductase
activity was detected in shoots of plants grown with an NO3−‐free solution or placed under N2‐fixing conditions,
and also in nodules of N2‐fixing plants. This strongly suggests that constitutive nitrate reductase activity is present
in these organs. Analyses of the soluble nitrogenous content showed that the major form of N in the different
organs was α‐amino acids (particularly amides), irrespective of the N status of the culture conditions. The same
result was obtained for nodulated plants grown in local sandy soil. In this case, amide‐N generally accounted for
more than 40% of the total soluble N. This was especially true in nodules. Ureide‐N never exceeded 9% of the
total soluble N and did not appear to increase with increasing nodule nitrogenase activity. Amides were also
predominant in three N2‐fixing Sahelian acacias (Acacia seyal, A. nilotica and A. tortilis), showing that F. albida
does not differ from Sahelian Acacia in terms of the metabolism of fixed N. However, like another Sahelian acacia
growing preferentially near water (A. nilotica), F. albida can be distinguished from acacias growing strictly in arid
zones (A. seyal and A. tortilis) in terms of initial growth, water and nitrate management.
Sexual development and sex chromosomes in hop
Authors: SHEPHARD H. L. , PARKER J. S. , DARBY P. , AINSWORTH C. C.
Published: March 2003

The stages of floral development in staminate and pistillate plants of hop (Humulus lupulus) were defined using scanning electron microscopy and light microscopy. Vegetative meristems of male and female plants are morphologically indistinguishable. On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent. The first sex‐specific differences occur extremely early in floral ontogeny. Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract. Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers. Female inflorescence meristems produce flowers arranged in ‘cones’. Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia. There is no sign of carpel development at any stage. In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl. No stamen development is observed. Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences. Bisexual flowers usually possess perianth, stamen and carpel whorls. The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium. Chimaeric central whorls consisting of fused staminoid‐carpelloid structures also occur. Sex differences in unisexual hop flowers are determined at an extremely early stage in ontogeny. The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all. Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis. The sex chromosomes of dioecious hop plants are described, as well as the chromosome constitutions of monoecious plants and those carrying bisexual flowers.
Adaptations to extreme low light in the fern Trichomanes speciosum
Authors: JOHNSON G. N. , RUMSEY F. J. , HEADLEY A. D. , SHEFFIELD E.
Published: March 2003

Trichomanes speciosum is a threatened species restricted to sheltered, very humid sites. Uniquely amongst European ferns, differing ecological tolerances of the gametophyte and sporophyte generations are manifested as widely differing distributions. The perennial, vegetatively propagating gametophyte persists in drier, colder, darker habitats than the sporophyte. In sites where the gametophyte grows, light availability was found to be < 1 μmol m2 s1 for approx. 85% of daylight hours, rarely or (in some sites) never rising above 10 μmol m2 s1. Much of the time, light was < 0.01% of full sunlight. Measurements of gas exchange and chlorophyll fluorescence yield show that these plants have optimal photosynthesis at light intensities c. 5–10 μmol m2 s1, the highest light to which they are normally exposed to in their natural environment. The absence of any capacity for reversible nonphotochemical fluorescence quenching means that there is little or no protection of the photosynthetic apparatus from light‐induced damage. We conclude that these plants are able to create what are essentially monocultures in their extreme environments only because of a combination of low metabolic rate (at low temperatures) and an ability to make efficient use of what little light is available to them by morphological and physiological means.