bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigating microclimatic influences on ozone injury in clover (Trifolium subterraneum) using artificial neural networks
Authors: BALLS G. R. , PALMER‐BROWN D. , SANDERS G. E.
Published: April 2006

summary

Microclimatic factors interact during ozone episodes to influence the sensitivity of plants to ozone and thus are likely Co modify the amount of injury development. This paper investigates these interactions in an ozone‐sensitive cultivar of clover (Trifolium subterraneum cv. Geraldton). Experiments were conducted using a glasshouse‐based closed‐chamber exposure system in which the plants were exposed for 7 h to either charcoal‐filtered air (CF) or CF plus ozone at concentrations ranging from 40 to 160 ppb. The microclimatic conditions inside the chambers ranged from 16 to 36 C, 0‐9‐3‐6 kPa vapour pressure deficit (VPD), and 80–460 μmol m−2s−1Photosynthetically Active Radiation (PAR). Seven days after ozone exposure, the extent of foliar ozone injury was scored visually. The assessment scoring system was validated by pigment analysis. The data from these exposures were analysed using artificial neural networks (ANNs), the principles of which are described in the paper. Two ANNs were used, one to investigate the effects of microclimate on the threshold AOT40 (dose accumulated above a threshold of 40 ppb) above which injury developed, the other to determine the extent of visible injury development. Both networks used temperature. VPD, PAR and AOT40 as inputs. Testing with previously unseen data showed that the networks produced accurate predictions of the threshold and extent of injury for a range of ozone doses and microclimatic conditions. For example, the injury score network predicted that at 100 μmol m2s1PAR and 1 kPa VPD an AOT40 of 150 ppb h was required to produce an injury score of 1, whereas in conditions of 400 μmol m−2s−1s′ PAR and 3.5 kPa VPD, an AOT40 of 460 ppb h was required. Analysis of the weightings of components of the trained networks indicated that VPD and PAR had a stronger influence on the response to ozone than did temperature. Furthermore, this approach revealed that microclimate had a greater influence on the extent of ozone injury than on the threshold for injury.
Nitrogen source regulates the biosynthesis of NADP‐glutamate dehydrogenase in the ectomycorrhizal basidiomycete Laccaria bicolor
Authors: LORILLOU SOPHIE , BOTTON BERNARD , MARTIN FRANCIS
Published: April 2006

summary

NADP‐glutamate dehydrogenase (NADP‐GDH) is a key enzyme of N assimilation in ectomycorrhizal fungi, but little is known about its regulation. In the present study. the effects of N source and concentration cm NADP‐GDH specific activity, polypeptide content and biosynthesis have been investigated in the ectomycorrhizal basidiomycete Laccaria bicolor S238N. Mycelium was transferred from NH+4‐rich medium to either NO−3‐rich or N‐free medium. Under both these conditions, intracellular NH.−3 and glutamine content decreased dramatically. The specific activity of NADP‐GDH was simultaneously increased 3 4.5‐fold. Immunological analysis using anti‐GDH antibodies showed that depression of enzyme activity resulted from increased concentration of the GDH polypeptide. In addition, assessment of the steady‐state biosynthesis of NADP‐GDH by in vivo labelling of proteins demonstrated that the observed changes in enzyme concentration are explained by differences in the relative rate of enzyme biosynthesis. These results suggested that the source of N regulates synthesis of NADP‐GDH and that this regulation is under transitional and/or transcriptional control.
Phosphorus nutrition of an obligately mycorrhizal plant treated with the fungicide benomyl in the field
Authors: MERRYWEATHER JAMES , FITTER ALASTAIR
Published: April 2006

summary

We controlled arbuscular mycorrhizal (AM) fungi in the routs of bluebell (Hyacinthoides non‐scripta L. Chouard ex Rothm.) in the field by immersina otherwise undisturbed colonies in a fungicide suspension. Monthly application of benomyl successfully reduced root colonization by AM fungi throughout a 2 yr experimental period. Benonlyl had lit) effect on the availability of soil phosphorus (P), but reduced the P concentration of all parts of the plant (bulb, roots, leaves and inflorescences). Unlike the vegetative parts, flowers and seed of benomyl‐treated plants had the same P concentration as untreated plants at the end of the first season. However, at the final harvest after two growing seasons flower P concentration had been reduced by treatment. H. non‐scripta appears to protect reproductive structures from P deficiency when the plant is deprived of P, suggesting that A.M plays an important role in fitness determination. This is the first demonstration that depriving a plant growing in its natural environment of mycorrhiza on a long‐term basis can reduce P acquisition. Taken with data from experiments in controlled conditions, it confirms that H. non‐scripta is an obligately mycorrhizal species.
Transmissible reproductive changes following physiological adaptation to salinity in Sorghum bicolor
Authors: AMZALLAG G. NISSIM
Published: April 2006

summary

A 3 wk exposure to 150 mm NaCl induced adaptation to salinity in 8‐d‐old seedlings of Sorghum bicolor (L.) Moench. This treatment, defined as standard adaptation treatment, modified the expression of the reproductive traits, and the relationship between vegetative and reproductive organs, The adaptation response was accelerated when 8‐d‐old seedlings were sprayed daily with abscisic acid (ABA) for 10 d. Adaptation was also enhanced when seedlings were exposed to salinity on day 5, instead of day 8, after germination. These adaptation treatments, applied during the early vegetative development, influenced the expression of late reproductive characters. Thus besides the direct disturbing effect of NaCl, the adaptation process also has a specific influence on the expression of the sexual characters, Offspring of adapted plants were exposed to a standard adaptation treatment. The expression of the reproductive traits of the progeny was generally less perturbed than in their parents, where treatment influenced characters such as fertility, plant height and seed size of the progeny. Therefore, the adaptation process induced stabile and transmissible changes in the expression of the reproductive characters, All analogy between changes induced by salt adaptation in Sorghum plants and somaelorial variations is suggested. The evolutionary significance of the adaptation response is discussed.
Micro‐scale patterns of modern pollen deposition within three alpine plant communities*
Authors: PARDOE H. S.
Published: April 2006

summary

Few studies have examined patterns of pollen deposition or the relationship between vegetation and pollen assemblages at the small scale. This paper examines the representation of both individual taxa and whole plant communities in modern pollen spectra. Micro‐scale variations in modern pollen deposition were studied in three alpine plant communities on Storbreen glacier foreland, southern Norway: a pioneer community; a Salix‐shrub community; and an ericaceous heath community. The relationships between vegetation and modern pollen deposition and the variability of these relationships at the local scale were investigated within 16 × 1 m2‐quadrats. The data were classified using two‐way indicator‐species analysis (TWINSPAN) and ordinated using detrended‐correspondence analysis (DCA). In addition, the pollen and vegetation data were ordinated simultaneously, using canonical correspondence analysis (CCA). The effect of removing arboreal pollen from the pollen sum was examined. The three plant communities were distinguished successfully by multivariate statistical techniques, using; both pollen data and vegetation data. However, within the communities there was high variability in pollen deposition, which was most pronounced in the Salix‐shrub community. The abundance of individual taxa in the vegetation was compared with their representation in the pollen spectra. The strongest relationships were shown by Salix Ericales, Empetrum and Lycopodium. Certain taxa showed consistent, reproducible patterns of behaviour. These patterns provided valuable evidence for separating contrasting plant communities. Comparison of modern pollen‐vegetation relationships of this kind with pollen data from Holocene and Pleistocene sites is important to improve the reconstruction of past plant communities. Statistical analyses showed that for the majority of taxa a moss polster consisting of 20 subsamples was necessary to reduce the effect of microscale variability in this environment to acceptable levels.
Late‐glacial and early Holocene vegetation of Snowdonia
Authors: INCE JOHN
Published: April 2006

summary

Detailed pollen and lithostratigraphic analyses of lake deposits at Clogwyngarreg provide a comprehensive record of vegetational and environmental change in the lowlands of Snowdonia, north Wales during the late‐glacial and early Holocene. A radiocarbon determination suggests that the low lands were ice free by at least c. 13 500 BP. and thiit by that time open habitat herhaceous taxa, including abundant Rumex spp. were colonizing the recently deglaciated ground. The initial pioneer grassland communities Were gradually invaded by Juniperus and Betula, hut the development of birch woodland was limited. An interstadial episode, the lute‐glacial lnterstadial (Windermere Interstadial) is recognized in the sequence of plant succession that culminated m the establishment of juniper. A significant decline in Juniperus pollen frequencies and an increase in Cramineae, in the absence of an expansion in birch woodland, suggests that environmental conditions in the mid‐ to late‐late ‐glacial Interstadial were less favourable m juniper than those of the early‐middle Interstadial. Towards the top of the Interstadial organic sequence fluctuations in the Juniperus pollen curve, coupled with high Isoetes spore values and the deposition of a stone horizon, suggest local instability and re‐working prior to the deposition of Loch Lomond (Younger Dryas) Stadial mini‐rofjenic sediments. By c. 11 000 BP widespread solifluction and increasingly severe environmental conditions led to a breakup of existing plant communities and a proliferation of open habitat and disturbed ground taxa. During the Loch Lomond (Younger Dryas) Stadial, glaciers reoccupied the higher cwms of Snowdonia. Climatic amelioration, marking the Holocene at c. 10 000 yr BP, was characterized by a rapid expansion of Juniperus at Clogwyngarreg and evidence for early Holocene woodland development is presented.
Antioxidant responses to drought in sunflower and sorghum seedlings
Authors: ZHANG JINGXIAN , KIRKHAM M. B.
Published: April 2006

summary

To determine if antioxidant responses to drought differ between C3 and C4 plants, we grew Sorghum bicolor (C4) and Helianthus annuus (C3) under either watered or dry conditions in a growth chamber. Levels of leaf enzymatic antioxidants (ascorbate peroxidase, catalase, guaiacol peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase and superoxide dismutase), nonenzymatic antioxidants (ascorbate, glutathione and carotenoids) and stress parameters (Chl and malondialdehyde [MDA]) were determined. Under watered and drought conditions, Chl contents and leaf relative water contents (RWC) were higher in sorghum than in sunflower; however, MDA levels were higher in sunflower than in sorghum. Under watered conditions, inherent levels of antioxidants were not consistently higher or lower in sorghum than in sunflower. In response to drought, levels of antioxidants, Chl and MDA showed increase, decrease or remained unchanged depending on crop, duration of drought and kind of antioxidants. Duration of drought was divided arbitrarily into three stages. At an early stage of drought (watering had stopped for 3–4 d) when soil water content (WC) and leaf RWC had decreased only in sunflower, drought generally did not affect levels of antioxidants and stress parameters. At a middle stage of drought (watering had stopped for 5–6 d) when soil WC had decreased for both sorghum and sunflower but leaf WC and RWC had decreased only in sunflower, drought changed levels of some antioxidants in sunflower and sorghum. At a late stage of drought (watering had stopped for 7–8 d) when soil WC, leaf WC and RWC had decreased in sorghum and sunflower, most parameters studied were affected by drought. Because of the differential effect of drought, levels of antioxidants were not consistently higher or lower in sorghum than in sunflower under drought. These results show that, under both drought and watered conditions, sorghum does not have consistently higher or lower antioxidant levels than sunflower, and that antioxidant responses to drought differ in C3 and C4 plants.
Ammonium assimilation by young plants of Hordeum vulgare in light and darkness: effects on respiratory oxygen consumption by roots
Authors: RIGANO C. , DI MARTINO RIGANO V. , VONA V. , CARFAGNA S. , CARILLO P. , ESPOSITO S.
Published: April 2006

summary

Barley plants (Hordeum vutgare L.) grown for 10 d in nitrogen‐free hydroponic culture, after a rapid initial phase absorbed supplied NH4+ at a constant rate of 15.1 ±1.2 μ mol h−1 g−1f. wt in the light, arid at a rate of 13.81 ± 1.6 μ mol h−1 g−1 f. wt in darkness. Ammonium‐grown plants assimilated NH4+ at a rate of 7.5 ± 0.33 μmol h−1 g−1 f. wt and at a 50% lower rate in darkness. Nitrogen‐free grown plants showed low concentrations of free amino acids in both root and shoot tissues. Supplying NH4+ caused an immediate increase in the concentration of free amino in the root tissues of both illuminated and darkened plants over a 120 mm period. The increase in concentration of glutamine then exhibited a lag period of 120 min, after which it resumed, but to a very small extent. Glutamine also accumulated in shoot tissue of illuminated plants at increasing rates, attaining a concentration which, 8 h after NH4+ supply, was 1.61‐fold greater than that attained in the roots. In shoots of darkened plants, by contrast, the concentration of glutamine increased slowly and was always smaller than that in the root tissue. Overall formation of glutamine (in shoots and roots) occurred at decreasing rates during the first 4 h, and then at increasing rates. The increase was more pronounced in illuminated plants than in darkened plants, liven 24 h after NH4+ was supplied, glutamine content in root tissue was lower than that in shoot tissue. However, 48 h later, the concentrations of glutamine in root and shoot were similar, attaining values that were almost 47‐fold (in root) and 134‐fold (in shoot) greater than initial values. Significant levels of asparagine were detected in the root and in the shoot 24 h after adding NH4+. These increased further during the succeeding period. Ammonium supply caused a transitory drop in the concentration of ATP in root tissue, along with noticeable transitory variations in glucose‐6‐P concentration. A permanent decrease in free glucose concentration was also detected. Addition of NH4+ caused 2‐ and 1.43‐fold increases in respiratory oxygen consumption by roots of illuminated and darkened plants, respectively. Both in the light and in the dark, the root tissue accumulated methylammonium up to a concentration of 55–67 μmol h−1 g−1f. wt. Methylammonium was never found in shoot tissue of either illuminated or darkened plants. Methylammonium stimulated respiration of root barley plants by a factor of 1.2. Regulatory aspects of NH4+ metabolism are discussed.
The phosphorus requirement of N2‐fixing and urea‐fed Acacia mangium
Authors: RIBET JÉRǑME , DREVON JEAN‐JACQUES
Published: April 2006

summary

The fast‐growing leguminous tree Acacia mangium Willd, was grown for at least 22 wk in aerated solution culture either under N2‐fixing conditions or with 2 mmol urea per plant per wk. Inorganic phosphorus was supplied at between 1 and 100 μmol P1 per plant per wk: the latter was determined to be the optimum P supply for growth. The external P requirement for growth and the efficiency of utilization of internal P were similar for both N sources. However, shoot growth and the concentrations of N and P in leaves were decreased by P deficiency to a slightly higher extent in N2‐fixing plants than in urea‐fed plants. Even though P deficiency limited nodule growth more drastically than it did shoot growth, the fraction of P allocated to both nodules and nodule nitrogenase activity (acetylene reduction) increased with P deficiency. It is concluded that this increase in nitrogenase activity reflects a higher N requirement per unit nodule mass in P‐deficient plants and that, once nodules are fully functional the efficiency of utilization of internal P in N2‐fixing A. mangium is high compared with that of other N2‐fixing legumes.
Effects of elevated carbon dioxide and arbuscular mycorrhizal infection onTrifolium repens
Authors: JONGEN MARJAN , FAY PETER , JONES MICHAEL B.
Published: April 2006

summary

Trifolium repensL. cv. aran was grown for 58 d at ambient (350 μol mol−1) and elevated (700 μol mol−1) atmospheric CO2, wish and without the arbuscular mycorrhizal fungusGlomus mosseae(Nicol. & Gerd.) Gerd. & Trappe cv. YV. Plant biomass, mycorrhizal infection, non‐structural carbohydrates, C, N and P content were examined. Elevated CO2(a) significantly increased above‐ and below‐ground biomass, (b) decreased specific leaf area and specific root length, (c) decreased tissue %N and increased the C:N ratio, and (d) significantly increased total non‐structural carbohydrates. InoculatingT. ripenswithGlomus mosseae(a) significantly increased above‐ and below‐ground biomass. (b) increased the total root length and total leaf area, and (c) significantly decreased tissue of Evidence of an increased influence of mycorrhiza on the P nutrition ofT. repensat elevated CO2was found in the 22%, increase in leaf total P (P< 005) of mycorrhizal plants grown at elevated CO2compared with non‐mycorrhizal plants. No significant interactions were found between CO2and mycorrhiza treatments.

The proportion ofT. repensroot length colonized byGlomus mosseae wasnot affected byCO2concentration. The percentage mycorrhizal infection was 29% at ambient CO2and 35%, et al elevated CO2. However, exposure to elevated CO2significantly increased the total mycorrhizal foot length from 3.4 to 6.1 m per plant.

The results show little evidence that the role of arbuscular mycorrhiza in the growth and nutrition ofT. repenswould increase if atmospheric CO2were to increase as predicted.
Phosphodiesterase as mycorrhizal P sources
Authors: LEAKE J. R. , MILES W.
Published: April 2006

summary

These results provide the first account of the breakdown and utilization of DNA by an ericoid mycorrhizal fungus, and of its phosphodiesterase activity in vitro. Hymenoscyphus ericae (Read) Korf & Kernan grew well on DNA as a sole source of phosphorus (P), achieving greater mycelium dry weight than on an equivalent concentration of P supplied as orthophosphate. Some characteristics of the production and activity of extracellular (culture filtrate) and cell‐wall bound phosphodiesterase in H. ericae are reported. At least part of the phosphodiesterase activity is attributed to the exonuclease F nucleotide diesterase on the basis of its high affinity for a specific substrate of this enzyme, The pH optima for extra‐cellular and cell‐wall‐bound diesterase are acidic (pH 4.0–5.5), with considerable activity maintained in the pH range typical of organic soils under ericaceous plants (pH 3.0–4.5). The production of phosphodiesterase was not substrate‐induced, since highest specific activity for wall‐bound enzyme was found in culture grown without organic or inorganic P. The results are discussed in relation to the ecology and biology of acid organic soils on which ericaceous plants are dominant.
Phosphodiesters as mycorrhizal P sources
Authors: MYERS M. D. , LEAKE J. R.
Published: April 2006

summary

Mycorrhizal plants of Vaccinium mocrocarpon Aiton used nuclei from salmon sperm as a sole source of phosphorus (P) and achieved similar yields, P content and P concentration to plants crown with orthophosphate. Mycorrhizal infection significantly increased the effectiveness of utilization of both inorganic and organic (nuclei) sources of P by Vaccinium but in the case of the organic source this involved providing access to P which was completely unavailable to the uninfected plants. The results provide further support for the view that ericoid mycorrhizas have a crucial role in direct recycling of nutrients from organic matter, independent of the mineralizing activities of saprotrophic micro‐organisms.
The physiology of basidiomycete linear organs
Authors: GRAY S. N. , DIGHTON J. , JENNINGS D. H.
Published: April 2006

summary

Autoradiography and quantitative image analysis were used to measure 137Cs distribution and translocation through mycelia of A. gallica Marxmuller & Romagn. and A. ostoyae (Romagn.) Herink growing in small microcosms in the laboratory. Rhizomorphs of A. gallica were labelled with 134Cs in the field, and the translation of radiolabel measured after excavation and destructive harvesting. The flux of radiocaesium through rhizomorphs was estimated to be greater than through undifferentiated hyphae, and greater through rhizomorphs growing in the field than through rhizomorphs grown across homogeneous media in the laboratory'. Differentiation within mycelia resulting in melanization or rhizomorph formation cave rise to increased heterogeneity in the 137Cs distribution through laboratory microcosms compared with that through microcosms containing undifferentiated mycelia. Radiocaesium leaked from undifferentiated hyphae into the surrounding medium, but melanized regions of the mycelium appeared to be conservative for radiocaesium. These findings provide further evidence for the importance of filamentous fungi in determining the distribution and rate of release of radiocaesium currently present in the environment as a result of weapons testing and the accident at the Chernobyl nuclear reactor.
Ion compartmentation in the red algaCaloglossa leprieuriiin response to salinity changes: freeze‐substitution and X‐ray microanalysis
Authors: MOSTAERT ANIKAS S. , ORLOVICH DAVID A. , KING ROBERT J.
Published: April 2006

summary

The elemental content of cell compartments in the euryhaline red macroalgaCaloglossa leprieurii(Montague) J. Agardh subjected to different salinities, was determined by X‐ray microanalysis of freeze‐substituted thin sections. Duty are given for three compartments; cell wall, vacuole and cytoplasm. The most abundant elements detected were potassium, sodium and chlorine, with a Sulphur peak in the cell wall indicating the presence of sulphated polysaccharides. With salinity upshock the cytoplasm is maintained low in K, Na and Cl, whereas in the vacuoles they increased. High levels of K and Na located in the cell wall reflect cation binding to negatively charged polysaccharides. Hyposaline shock resulted in decreased K, Na and Cl levels in all compartments, though K was retained in the cytoplasm. Results are discussed with regard to the role of ion compartmentation in the salt tolerance of this alga, and the cation exchange properties of the cell wall are emphasized.
Cation ratios inCladonia portentosaas indices of precipitation acidity in the British Isles
Authors: HYVÄRINEN M. , CRITTENDEN P. D.
Published: April 2006

summary

The relationship between rainfall chemistry and the concentrations of potassium, calcium and magnesium in the apices (top 5 mm) of the cushion‐forming; lichenCladonia portentosa(Dufour) Coem was investigated. Lichen samples, together with underlying topsoil, were collected from heathlands in close proximity to rain gauges in the UK Acid Deposition Monitoring Network, located in rural areas of the British Isles, which provide wet deposition data based on weekly bulk samples. The ratios K+: Mg2+and extracellular Mg2+: intracellular Mg2+in the lichen apices were strongly correlated with H+concentration in precipitation. It is suggested that shifts in these ratios occur owing to enhanced displacement of extracellular Mg2+by elevated H+concentration in acid rain. By contrast, there was no indication of any relationship between total acid deposition and lichen chemistry. The concentration of Mg2+in the lichen was weakly correlated with that in soil, whereas lichen Ca2+content was not correlated with either precipitation or soil chemistry. It is concluded that these ratios describing changes in lichen Mg2+content provide good biomarkers for wet‐deposited acidity.
Molecular genetics of cellular differentiation in leaves
Authors: HALL LISA N. , LANGDALE JANE A.
Published: April 2006

summary

Leaves of green plants vary widely in morphology. However, the underlying cell types and structures observed in leaves of different species are remarkably similar. Although we can adequately describe leaf development in morphological terms we cannot yet explain interactions at the cellular level. In recent years molecular genetics has been used extensively to address a variety of developmental questions. The isolation of a wide variety of mutants disrupted in numerous aspects of leaf ontogeny has led to the cloning of genes involved in various developmental processes. In this review we consider advances that have been made in understanding shoot apical meristem organization, leaf initiation and the development of leaf form. In particular we concentrate on progress, that has been made in understanding cellular differentiation in the epidermis, and within the interior of the leaf, namely the photosynthetic cells and the vasculature.

CONTENTS

Summary
533

I.
Introduction
533

II.
Shoot growth
533

III.
Leaf initiation
534

IV.
Development of leaf form
536

V.
Cellular differentiation
537

VI.
Perspectives
548

VII.
Acknowledgements
549

VIII.
References
549
Allocation of biomass and mineral elements in Melilotus segetalis (annual sweetclover): effects of NaCl salinity and plant age
Authors: ROMERO J. M. , MARAÑÓN T.
Published: April 2006

summary

The allocation of biomass and mineral elements (Ka, K, Ca, P, N, Fe, Cu, Mn and Zn) during the ontogenetic cycle of annual sweetclover (Melilotus segetalis (Brot.) Ser.) growing under favourable and saline conditions has been studied. Plants were grown in a glasshouse, in pots with siliceous substrate and watered with Hoagland solution. Half were salinized by adding 170 mol m−2N2Cl (15 dS m−1) to the solution. Eleven harvests at 15 d intervals measured the dry weight distribution within the plant and the mineral composition. Allocation relative to biomass (ARB) in each plant organ, both under favourable and salt‐stress conditions, was calculated for each mineral element, Biomass and mineral elements were allocated independently within M. segetalis, and the general pattern thanked with age and was affected by salinity. Salt‐stressed plants were smaller and invested proportionately more biomass in leaves. Na was accumulated in roots of young plants and excluded from leaves and fruits, whereas K was depleted from roots and accumulated in leaves and fruits. Immobile Ca accumulated in leaves, with age. Phloem‐mobile P and X were translocated to flowers and fruits. Fe, Cu and Zn were diluted in leaves and not affected by salt; whereas Mn concentration increased with age and salinity. The switch to reproduction and increased demand for nutrients induced drastic changes in the allocation pattern of mineral elements. Salinity induced a re‐allocation of biomass and mineral elements in all plant organs except the reproductive structures, as part of a whole‐plant response to minimize salt toxic effects, to achieve osmotic adjustment, to preserve the reproductive output, and to compensate nutrient imbalance.
The effect of fungicides on vesicular‐arbuscular mycorrhizal symbiosis
Authors: SUKARNO N. , SMITH F. A. , SMITH S. E. , SCOTT E. S.
Published: April 2006

summary

Two experiments were conducted under controlled environmental conditions to determine the effects of the three fungicides, Benlate®. Aliette® and Ridomil®, on efficiency of P uptake from the soil and transfer across the living plant‐fungal interface‐ of onion plants (Allium cepa L.) associated with Glomus sp. ‘City Beach’ (WUM 16), P applied to the soil did not apparently increase the rate of transfer (flux) of P to the plant via the fungal partner of the mytorrhiza.

Benlate reduced P inflow and transfer across the interface in one of the experiments. The rate of P uptake per m living external hyphae was not affected but, as development of living external hyphae in the soil was reduced, the contribution of the fungus to P uptake was small. Aliette reduced growth of both shoots and roots, but apparently increased the accumulation of P in the tissues compared with controls. Ridomil reduced P inflow per m of root and P uptake per m living external hyphae, hut had no effect on the rate of P transfer across the interface. This led to a reduction in the overall contribution of the fungus to P nutrition.
Direct measurement of release and assimilation of ammonia in the Gunnera–Nostoc symbiosis
Authors: SILVESTER WARWICK B. , PARSONS RICHARD , WATT PETER W.
Published: April 2006

summary

In Gunnera, Nostoc cells invade secretory tissue forming well defined symbiotic areas within the stems and are termed internal nodules (Silvester, 1976). Excised, but intact, internal stem Nostoc nodules taken from Gunnera magellanica show light‐stimulated nitrogenase activity and release a small, but measurable, proportion of their current N2 fixation as NH3 into the external solution. When nodules are disrupted and Nostoc extracted anaerobically, 90% or more of the estimated N2 fixation is released from the Nostoc cells as NH3 into the surrounding medium. Use of 15N2 confirmed that only 12% of N2 fixed is retained within the cells of Nostoc. The remaining 88% was identified as NH3 released outside the cells. Within the intact nodule system, 15N2 uptake showed that 2–5% of recently fixed N2 remains within the Nostoc cells and up to 30% of extracellular N is in asparagine after 1 h. Evidence is presented that stimulation of nitrogenase by light in the intact Gunnera/Nostoc system produces more NH3 than can be assimilated by the host cells, resulting in significant NH3 accumulation.
Carbonic anhydrase(s) associated with lichens: in vivo activities, possible locations and putative roles
Authors: PALMQVIST KRISTIN , BADGER MURRAY R.
Published: April 2006

summary

The activity of the enzyme carbonic anhydrase (CA; E.C. 4.2.1.1) was examined in eight species of lichen in vivo by measurements of 18O exchange from doubly labelled CO2 (13C18O18O) to water, with the aim of determining whether this enzyme is present in lichens and if so to what extent it participates in physiological processes. The lichens were chosen to represent different mycobiont (Heterodera, Leptogium, Lobaria, Peltigera, Pseudocyphellaria, Xantoparmelia) and photobiont (Coccomyxa, Dictyochloropsis, Myrmecia, Nostoc, Trebouxia) genera as well as varying morphology. All lichens were found to possess considerable activity of CA, which varied by a factor of about four between the species when compared on a chlorophyl basis, and by u factor of about 10 when related to the weight. Incubation of lichen tholli with ethoxyzolamide (EZA) and acetazolamide (AZA), which inhibit intracellular and extracellular CA respectively, showed that intracellular CA was present in all of the species. Incubation with EZA also resulted in inhibition of photosynthetic CO2, uptake in all species suggesting a role of internal CA in the CO2, acquisition process in all the investigated photobiont genera. A part of the CA activity was inhibited by AZA in all except two of the four cyanobacterial Nostoc lichens, indicating the possible presence of extracellular forms of CA. This CA also appeared to be involved in the acquisition of CO2, as AZA inhibited photosynthetic CO2 uptake in these lichens. The CA inhibitors also affected CO2 efflux in the dark, i.e. fungal respiration, which was inhibited by both AZA and EZA in six of the species, suggesting that a proportion of the CA activity might be located in the mycobiont.
Potential effects of rising tropospheric concentrations of CO2 and O3 on green‐algal lichens
Authors: BALAGUER LUIS , VALLADARES FERNANDO , ASCASO CARMEN , BARNES JEREMY D. , DE LOS RIOS ASUNCION , MANRIQUE ESTEBAN , SMITH ELIZABETH C.
Published: April 2006

summary

Pormelia sulcata Taylor was used as a model to examine the effects of elevated CO2 and/or O3 on green algal lichens. Thalli were exposed for 30 d in duplicate controlled‐environment chambers to two atmospheric concentrations of CO2 (‘ambient’ [350μmol mol−1] and ‘elevated’ [700μmol mol−1] 24 h d−1) and two O3 regimes (‘non‐polluted’ air [CF, < 5 nmol mol−1] and ‘polluted’ air [15 nmol mol−1overnight rising to a midday maximum of 75 nmol mol−1]), in a factorial design. Elevated CO2, or elevated O3 depressed the light saturated rate of CO2, assimilation Asat) measured at ambient CO2, by 30% and 18%, respectively. However, despite this effect ultrastructure) studies revealed increased lipid storage in cells of the photobiont in response to CO2‐enrichment. Simultaneous exposure to elevated O3 reduced CO2‐induced lipid accumulation and reduced Asat in an additive manner. Gold‐antibody labelling revealed that the decline in photosynthetic capacity induced by elevated CO2and/or O3 was accompanied by a parallel decrease in the concentration of Rubiscoa in the algal pyrenoid (r= 0.93). Interestingly, differences in the amount of Rubisco protein were not correlated with changes in pyrenoid volume. Measurements of in vivo chlorophyll‐fluorescence induction kinetics showed that the decline in Asat induced by elevated CO2, and/or O2, was not associated with significant changes in the photochemical efficiency of photosystem (PS) II. Although the experimental conditions inevitably imposed some stress on the thalli, revealed as a significant decline in the efficiency of PS II photochemistry, and enhanced starch accumulation in the photobiont over the fornication period, the study shows that the green‐algal lichen symbiosis might be influenced by future changes in atmospheric composition. Photosynthetic capacity, measured at ambient CO2, was found to be reduced after a controlled 30 d exposure to elevated CO2, and/or O3 and this effect was associated with a parallel decline in the amount of Rubisco in the pyrenoid of algal chloroplasts.
Nickel‐accumulating plants from the ancient serpentine soils of Cuba
Authors: REEVES R. D. , BAKER A. J. M. , BORHIDI A. , BERAZAÍN R.
Published: April 2006

summary

Extraordinary uptake of nickel (Ni), reaching concentrations of 0.1–5.0%, c. 1000 times greater than those usually found in flowering plants, has been observed previously in c, 190 species that grow on Ni‐rich serpentine soils derived from ultramafic rocks in various parts of the world. These so‐called hyperaccumulators of Ni include c. 50 species from the rich ultramafic flora of New Caledonia and c. 80 species from the Brassicaceae of Mediterranean Europe and Turkey. A study of a limited part (the families Buxaceae and Euphorbiaceae) of the very large ultramafic flora of Cuba has now identified this as the home of at least 80 hyperaccumulators, the largest number jet found in any one country. The more frequent incidence here of this unusual form of plant behaviour is linked to the very long period (r. 10–30 million years) during which some of the Cuban ultramafic substrata are believed to have been continuously available for colonization; the distribution of Ni hyperaccumulators between older and younger ultrarnafic soils in Cuba mirrors the overall incidence of endemic species in these areas.
Availability of organic and inorganic phosphorus compounds as phosphorus sources for Carex species
Authors: PÉREZ CORONA M. E. , VAN DER KLUNDERT I. , VERHOEVEN J. T. A.
Published: April 2006

summary

Inorganic phosphates (ferric phosphate, calcium phosphate and aluminium phosphate) and organic forms of phosphorus (inosito) hexaphosphate and β‐glycerophosphate) were tested as phosphorus (P) sources for the growth of three Carex species from fens differing in productivity‐ and nutrient availability. Aluminium phosphate and β‐glycerophosphate were equally effective sources of P for all three Carex species as KH2PO4, which was used as a control treatment. Phosphorus from ferric phosphate and calcium phosphate was also taken up bv Carex acutiformis Ehrh., a species of high productivity from eutrophic fen areas, but not by the other two species. Only Carex lasiocarpa Ehrh., a species from P‐limited fens, showed a higher P‐uptake when grown with inositol phosphate than in the second control treatment without P. The P‐source also affected, with differences between species, the biomass allocation to the below‐ground plant parts and the area of absorption surface of the roots.

The mobilization of organic sources of P by fen Carex species found in the present study might be an important factor in the P dynamics of fens because of the high contents of organic P in the fen peat soils where these species grow. In the same way, the utilization of inorganic sources of P can play a relevant role in the P‐cycle in these systems where the discharge of ground water rich in ions can lead to the fixation of P into inorganic compounds. However, the differing abilities of the various Carex species to mobilize P from P‐pools does not explain clearly their preferential presence in different fens in relation to the P‐availability.
Plant‐affecting streptomycin‐sensitive micro‐organisms in barley monoculture soils
Authors: OLSSON STIG , ALSTRÖM SADHNA
Published: April 2006

summary

Soils from barley monoculture and from crop‐rotation plots of three long‐term field experiments were tested for their effects on barley growth in the glasshouse, using plant growth tubes. Test plants of young barley developed significantly shorter and thinner root axes when grown in soil from monoculture plots than when grown in soil from crop rotation plots, but the difference in shoot growth was only small. Addition of small doses of streptomycin sulphate neutralized the retarded root growth in soil from monoculture plots, whereas the fungicide metalaxyl induced no such effect. The difference in root growth of barley test plants could be transmitted into a soil‐free root environment by inoculation with the microflora from roots grown in soil. These findings indicate that some component(s) of rhizosphere bacteria is the causal agent of the early monoculture effect measured.
The roles of internal iron hydroxide precipitation, sulphide toxicity and oxidizing ability in the survival of Stratiotes aloides roots at different iron concentrations in sediment pore water
Authors: SMOLDERS A. J. P. , ROELOFS J. G. M.
Published: April 2006

summary

Stratiotes aloides L. is an aquatic macrophyte that occurs in waters on reduced peaty sediments which have a relatively narrow range of free‐iron content in the sediment.

Comparison of different aquatic macrophytes reveals that species from reducing sediments have much lower oxidizing ability than do species from oxidizing sediments. Compared with those other species from reducing sediments, the oxidizing ability of Stratiotes aloides is very low and probably makes the species very vulnerable to sulphide toxicity and internal precipitation of iron hydroxide.

Apoplastic iron contents were determined for Stratiotes roots growing in sediments with different free‐iron concentrations. Roots collected from sediment with a low free‐iron content appeared to have a relatively low apoplastic‐iron content whereas roots from sediments with a relatively high free‐iron concentration had a relatively high apoplastic‐iron content. In sediments with low free‐iron levels, sulphide levels are generally high.

Using light microscopy, iron hydroxide precipitates were observed around the endodermis and cortical air spaces of the roots of Stratiotes aloides growing in iron‐rich sediments. Internal iron oxidation outside the endodermis can prevent iron toxicity inside the stele and thus enable root apices to survive. The root hairs, however, die because of iron hydroxide precipitation at their base; the dead roots have the highest visible iron hydroxide content. Excessive internal iron hydroxide precipitation and the consequential early death of the roots probably explains the absence of Stratiotes aloides in locations with high free‐iron levels in sediment pore water.
Spatial heterogeneity of soil water around single roots: use of CT‐scanning to predict fungal growth in the rhizosphere
Authors: GROSE M. J. , GILLIGAN C. A. , SPENCER D. , GODDARD B. V. D.
Published: April 2006

summary

Whole‐body computed tomography X‐ray scanning (X‐ray CT) of wheat, cotton and radish growing in pots containing 350 g of a white sand: clay mixture produced images from which digital data of the volumetric water content were obtained. The volumetric water contents were spatially heterogeneous around the root and altered with the depth at which the image was taken. Data represent a ‘snapshot in time’ of the soil around single roots in a living soil–plant system.

The volumetric water contents of soil around seedlings were assessed for the growth of two soil‐borne fungi, Gaeumannomyces graminis var. tritici and Rhizoctonia solani. The heterogeneity of water content was biologically significant: water contents around the roots of wheat, radish and cotton were of a great enough range to suggest the existence of heterogeneous sites in the rhizosphere which might favour or restrict fungal growth. In soil surrounding wheat roots, the most favourable regions for the growth of G. graminis were nearest the root, suggesting that the inner rhizosphere might be more amenable to the growth of this pathogenic fungus than the outer region of the rhizosphere, and the bulk soil.

The technique of X‐ray CT enables spatial examination of the response of soil water to environmental treatments of the soil–root system, and the non‐destructive observation of the effect of the spatial heterogeneity of volumetric water content upon fungal growth in the soil, over time and at a range of depths.
Nitrate depletion and pH changes induced by the extraradical mycelium of the arbuscular mycorrhizal fungusGlomus intraradicesgrown in monoxenic culture
Authors: BAGO B. , VIERHEILIG H. , PICHÉ Y. , AZCÓN‐AGUILAR C.
Published: April 2006

summary

The effect of the extraradical mycelium of the arbuscular mycorrhizal (AM) fungusGlomus intraradicesSmith & Schenck on nitrate uptake and on the pH of the medium was studied in a monoxenic culture with tomato(Lycopersicon esculentumMill. var. Vendor) roots obtained from root organ culture. The symbiosis was established in compartmented Petri dishes containing agar media amended with the pH indicator bromocresol purple. A pattern of pH changes was revealed as the symbiosis progressed in the media of the Petri dish compartments containing the dual, arbuscular‐mycorrhizal fungi/root, culture as well as in the media of the hyphae, root‐free compartments, in which the extraradical hyphae developed extensively, coming from the compartment containing the symbiosis. The colour changes in the media were measured spectrophotometrically, whilst maintaining the monoxenic conditions. The extraradical hyphae ofG. intraradicesstrongly increased the pH of nutrient‐free medium when supplied with nitrate, whereas the pH decreased m the absence of this N source. The hyphae developing from germinated spores and growing in axenic, nitrate‐amended media did not induce any increase in pH. Nitrogen analysis revealed that a depletion of nitrate in the media accompanied increased pH.

These results point towards an active uptake of nitrate by the extraradical mycelium ofG. intraradices, probably coupled to a H+‐symport mechanism. The pH changes induced by AM fungal hyphae and the possible influence of the establishment of a functional symbiosis on these pH changes are discussed.
A comparative study of phenolic acids associated with cell walls and cytoplasmic extracts of host and non‐host roots for AM fungi
Authors: NAGAHASHI GERALD , ABNEY GLORIA D. , DONER LANDIS W.
Published: April 2006

summary

Carrots (Daucus carota L.) are a ubiquitous host for arbuscular mycorrhizal fungi whereas sugar beets (Beta vulgaris L.) are a non‐host. Root cultures were used to compare the constitutive phenolic compounds associated with the cell wall or present in the cytoplasm of the host and non‐host. Phenolic acids were released from purified cell walls by alkaline hydrolysis and were separated and identified by HPLC, TLC and u.v. absorption spectra analyses. Two phenolic acids unique to carrot root cell walls were identified as p‐hydroxybenzoic acid (p‐HBA) and vanillic acid. Sugar beet root cell walls had ferulic acid as major constituent and contained several unique phenyl propanoids which were not identified. Caffeic acid was found only in the cytoplasm of carrot roots and was present in the conjugated form (chlorogenic acid). The sugar beet cytoplasm also contained several unidentified hydroxycinnamic acid‐type phenolics which were not found in carrot roots.
Effects of a mycophagous Collembola on the symbioses betweenTrifolium subterraneumand three arbuscular mycorrhizal fungi
Authors: LARSEN JOHN , JAKOBSEN IVER
Published: April 2006

summary

We examined the effect of the mycophagous CollembolaFolsomia CandidaWillem on the symbioses betweenTrifolium subterraneumL. and three arbuscular mycorrhizal (AM) fungi. Mycorrhizal and non‐mycorrhizal plants were grown in pots with a central mesh bag which constituted a root‐free soil compartment (RFSC) where the soil was labelled with32P. This allowed us to study hyphal P transport as affected by the presence of Collembola in the soil with roots. The hyphal P transport was monitored by measuring the32P content in leaflets sampled from the latest fully developed trifoliate leaf after 3, 4, 5 and 6 wk. Measurementsoneach plant after 6 wk furthermore included total contents of32P and31P, root length and length of hyphae inside the mesh bag. The presence ofF, Candidareduced the average hyphal32P transport from the RFSC by 12% and the average AM hyphal length in the RFSC was reduced by 30%. The root dry weights of mycorrhizal plants were also reduced by the presence of Collembola. The reduction in total hyphal32P transport was not revealed by the data from the time‐course study using leaflet samples, which demonstrates the uncertainty of analyses of AM fungal activity based solely on measurements of leaf materials.

The results from this work suggest thatF. Candidagrazed on roots and/or hyphae of AM; however, shoot yields were unaffected by this grazing. In conclusion, Collembola seemed to have little effect on the functioning of AM fungi.