bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulphite‐induced changes of sulphur metabolism in the lichen alga Trebouxia sp
Authors: SCHLEE D.
Published: April 2006

Solutions of sodium sulphite have been used to simulate the effect of gaseous sulphur dioxide on the lichen alga Trebouxia sp. The uptake and the metabolism of inorganic and organic [35S]compounds such as sulphate, sulphite, and cysteine were investigated in cells of Trebouxia under conditions of sulphite preincubation (sulphite‐stressed cells: 3 d pretreatment with 50 mmol m‐3 and 5 mol m‐3 solutions of sodium sulphite). Metabolism was similar, regardless of whether the Trebouxia was provided with [35S]sulphate or ‐sulphite. In sulphite‐stressed cells, uptake and incorporation into ethanol‐soluble compounds, especially cysteine and methionine, was significantly decreased. In Trebouxia exogenous [35S]cysteine is metabolized only at a very low rate.
Effects of an experimentally applied increase in ammonium on growth and amino‐acid metabolism of Sphagnum cuspidatum Ehrh. ex. Hoffm. from differently polluted areas
Authors: BAXTER R. , EMES M. J. , LEE J. A.
Published: April 2006

Sphagnum cuspidatum Ehrh. ex. Hoffm. was removed from a relatively remote moorland site at the Migneint, N. Wales and from Holme Moss, S. Pennines — a site that has been subjected to atmospheric pollution deposition for a period of at least the last 200 yr.

When exposed to elevated ammonium (NH4+) concentrations (0·1 and 1·0 mM) under laboratory conditions for a period of 30 d, S. cuspidatum from N. Wales showed a marked reduction in growth, whereas in the S. Pennine population, growth was stimulated above that of the untreated control tissue at both 0·1 and 1·0 mM NH4+. The largest growth stimulation, however, was seen at 0·1 mM.

The effects of increased NH4+ in the growth medium on tissue total chlorophyll concentration after 30 d exposure were similar in moss from both study sites. There was a small linear decline in chlorophyll concentration with increasing ammonium concentration.

Moss from both sites was exposed to 0·1 mM NH4+ for a period of 20 d. There was a marked difference in the response of the different moss populations as indicated by changes in the concentrations of the individual amino acids; notably a dramatic transient increase in glutamine (three‐fold), arginine (19‐fold), and asparagine (fourfold) in the moss from N. Wales. In contrast, in the S. Pennine moss, changes in tissue amino‐N concentration were very much smaller. Possible mechanisms to account for the intraspecific differences in response of the moss from the two study sites to increased ammonium concentrations are discussed.
The role of carbohydrate storage and redistribution in the source‐sink relations of wheat and barley during grain filling — a review
Authors: SCHNYDER HANS
Published: April 2006

Two types of source contribute photosynthate for grain filling in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), current photosynthate transferred directly to the grain and photosynthate redistributed from reserve pools in vegetative tissues. Reserve pools provide the substrate needed to maintain transport and the supply of assimilate to grains during the dark period of the diurnal cycle and during the latter part of grain filling, when the photosynthetic apparatus is senescing and the rate of dry matter accumulation of grains exceeds the rate of dry matter accumulation of the total crop. In addition reserve pools provide a means by which the current rates of photosynthate production and of photosynthate use in grain filling are allowed to proceed (at least in part) independently from each other. There is evidence that all photosynthetic organs (leaves, glumes and exposed portion of the peduncle) contain one or more diurnal carbohydrate storage pools. Diurnal storage of sucrose seems to be much more important than the transient storage of starch. There is little evidence for fructan pools serving a role as a net source of carbon during the dark period of the diurnal cycle. However, fructan is the most important longer‐term reserve carbohydrate of vegetative tissues. Fructan accumulation occurs mainly in the extended internodes and leaf sheaths and usually terminates within three weeks following anthesis, after which fructan is gradually lost until grain maturity. The accumulation and loss of fructan are greatly influenced by environmental conditions and treatments that alter the longer‐term balance between photosynthate production by the plant and photosynthate use in grain filling. Observations are consistent with the view that fructan accumulation in expanded vegetative tissue is not competitive with grain filling, but the fructan pools accept surplus photosynthate during periods of low demand by grains and provide photosynthate during longer‐term deficits in current photosynthate production. Even under optimal conditions for photosynthesis it is likely that half or more of the photosynthate in mature grains is temporarily deposited in one or more reserve pools before being transferred to the grain. Neither the efficiency of reserve utilization in grain filling nor its potential variability in different genotypes and environments are known. Also, very little is known about the mechanisms that control the partitioning of photosynthate between the grain and reserve pools and the allocation to different types of reserve pools. Future progress in the understanding of photosynthesis‐yield relationships will likely depend to a great extent on improved knowledge of the controls that govern photosynthate deposition and redistribution in the different pools of reserve carbohydrate.
Element localization in mycorrhizal roots of Pteridium aquilinum (L.) Kuhn collected from experimental plots treated with cadmium dust
Authors: TURNAU K. , KOTTKE I. , OBERWINKLER F.
Published: April 2006

Pteridium aquilinum (L.) Kuhn roots collected from plots localized in a Pino‐Quercetum forest, treated 10 yr before with 2000 Mg km−2 of cadmium dust, were examined. The ultrastructure of endomycorrhizal roots and element distribution, determined using the electron energy loss spectroscopy, is given. The cytoplasm of the mycorrhizal fungus was found to contain more Cd, Ti and Ba than that of the host cells of the fern. Within polyphosphate granules present in fungal vacuoles beside Fe, S, N and Al which were reported by other authors, Cd, Ti and B were localized. Within fern cells Cd, Al, Fe, Zn and Cu were found to be accumulated both in plastids, especially in electron‐opaque, globular or crystalloid material, and on the surface of transfer cell wall ingrowth.
Genotype/nutrition interactions in the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnesi
Authors: GAY G. , MARMEISSE R. , FOUILLET P. , BOULETREAU M. , DEBAUD J.C.
Published: April 2006

Intraspecific variability in mycelial growth of the ectomycorrhizal basidiomycete Hebeloma cylindrosporum Romagnesi has been studied within 20 sib‐monokaryons, each being the progeny of one wild dikaryon fruiting in vitro, and the 50 synthesized dikaryons obtained from all the compatible fusions of these monokaryons. The interaction between fungal diversity and nutrition was also studied.

The range of variation in mycelial growth (expressed as mg protein per culture) among the sib‐monokaryons was the same as that recorded among the synthesized dikaryons. The average growth of both mono‐ and dikaryons was highest on a synthetic medium containing nitrate as the sole nitrogen source, but showed the greatest variation. Fungal growth was approximately halved when nitrate was replaced by ammonium, and was intermediate on an organic nutrient‐rich medium. A decrease from 24 mM to 24 /M concentration of phosphorus reduced the average growth of the mycelia 40‐fold.

The variation in mycelial growth in the synthesized dikaryons involved additive and non‐additive genetic components. Their ratio was variable depending on the nutrient conditions. In all cases but one, the interactive component was higher than the additive one.

From an ecological point of view, these results emphasize the tremendous effect of nutrition on the phenotypic expression of fungal growth. Their possible significance for the dynamics of natural populations of ectomycorrhizal fungi is discussed.
Antioxidant response and winter hardiness in red spruce (Picea rubens Sarg.)
Authors: DOULIS A. G. , HAUSLADEN A. , MONDY B. , ALSCHER R. G. , CHEVONE B. I. , HESS J. L. , WEISER R. L.
Published: April 2006

Antioxidant metabolism has been examined in red spruce growing at two sites with similar levels of ozone pollution but different winter temperatures. The northern site was Whiteface Mountain, New York with a latitude of 44° 31′(NY). The southern site was Whitetop Mountain, Virginia with a latitude of 36° 54′(VA). The northern site has lower winter temperatures. At the NY site two populations of trees were denned with respect to cold tolerance. An effort was made to establish a temporal relationship between the antioxidant capacity of conifer needles on one hand and the different stages of winter hardening/dehardening, and the induction of dormancy, on the other. The hypothesis tested was that winter injury of red spruce was due to an increased demand for glutathione at levels exceeding the inherent capacity of the needles and/or the altered activities of glutathione reductase.

In the autumn, as temperatures began to decrease, photosynthetic potential decreased as spruce entered dormancy. At the same time, cold tolerance (measured as needle electrolyte leakage) gradually increased. Glutathione metabolism appeared to be coupled to these processes. At both sites, seasonal changes in glutathione levels were observed. These changes were found to coincide temporally with the onset and cessation of dormancy (as measured by decline in photosynthetic activity). The same pattern was observed at the northern and the southern site with the winter increases being greater at the former. Glutathione began to increase as soon as needles entered dormancy and began hardening. Glutathione reductase activities closely followed the dehardening process during spring, while glutathione concentration continued to stay relatively high with prehardening levels reached only by summer. At the northern site during the winter, cold‐tolerant trees had significantly higher glutathione reductase activities compared with cold‐sensitive ones. Based on these data, it is proposed that individuals that cannot respond to the increased demand for glutathione reductase activity during the hardening, winter and dehardening periods, become susceptible to winter injury.
Fructan content of wheat seedlings(Triticum aestivumL.) under hypoxia and following re‐aeration
Authors: ALBRECHT G. , KAMMERER S. , PRAZNIK W. , WIEDENROTH E. M.
Published: April 2006

We studied fructan accumulation in wheat seedlings (Triticum aestivumL. cv. Alcedo) caused by oxygen shortage around the root. Plants were cultivated in either nitrogen‐flushed or aerated nutrient solution. In response to the nitrogen treatment there was an accumulation of soluble carbohydrates in shoots as well as in roots. The main contribution was due to fructans. The content of fructo‐oligosaccharides had been increased five‐fold in the roots and seven‐fold in the shoots. This is incompatible with the assumption that higher substrate consumption follows enhanced fermentation under oxygen shortage. Re‐aeration of the nitrogen‐flushed nutrient solution resulted in enhanced consumption of stored carbohydrates, mainly of fructans, accompanied by high growth rates of the roots. The possibility of utilizing fructans quickly if oxygen is available is a possible advantage for plants adapted to hypoxia. Particularly however, it is suggested that the low energy requirements for sucrose: sucrose fructosyl transferase, allowing fructan synthesis even under oxygen shortage, may improve the fitness of plants to survive temporary hypoxia in the rhizosphere.
Fructosyltransferase activities from Lolium rigidum Gaudin
Authors: JOHN J. A. ST. , BONNETT G. D. , SIMPSON R. J.
Published: April 2006

A partial separation of sucrose: sucrose fructosyltransferase (SST) activity from invertase activity extracted from leaves of Lolium rigidum Gaudin was achieved by gel filtration. The SST activity was purified 54‐fold with a ratio of SST activity to invertase activity of 1.1:1. The partially purified SST activity eluted with an apparent molecular mass of about 68000, had an optimum pH of 55 and a Km of 0.2 M. When incubated with sucrose concentrations ranging from 10 to 600 mM the partially purified SST activity produced mainly 1‐kestose and some 6‐kestose (10–15% of trisaccharide produced). SST and invertase activities declined during storage at — 25 °C with invertase activity declining at a faster rate. After the loss of invertase activity in storage, the partially purified SST activity synthesized only 1‐kestose. When incubated with 1‐kestose the partially purified SST activity synthesized neokestose (1.9 nkat ml−1), nystose (2.2 nkat ml−1) and an unidentified tetrasaccharide (1.4 nkat ml−1) indicating that the fructosyltransferase preparation also had FFT‐like activity. The partially purified invertase had significant sucrose‐hydrolyzing activity (25 nkat ml−1) and contained no measurable SST activity when incubated with 10–400 mM sucrose, but produced trisaccharide (1‐kestose and 6‐kestose, ratio 15:1) when incubated with 600 mM sucrose. L. rigidum does not normally accumulate 6‐kestose. The optimum pH of the sucrose‐hydrolyzing activity was 4–5 and the optimum pH of the fructosyltransferase activity of the invertase preparation was 55. The partially purified invertase did not have significant FFT‐like activity. The results support the hypothesis that SST activity synthesizes only 1‐kestose, which is a key intermediate in the synthesis of fructan in L. rigidum.
How to quantify differences in epicuticular wax morphology of Picea abies (L.) Karst. needles
Authors: TUOMISTO H. , NEUVONEN S.
Published: April 2006

Because researchers seldom possess unlimited resources, planning is needed to maximize the ratio of information gained to work needed. The aim of the present study was to find reasonable sampling and observation schemes for documenting regional differences in the impact of air pollution on the morphology of epicuticular needle wax. One‐year‐old Picea abies (L.) Karst. needles were collected in Southern Finland at two sites with different air pollution levels. In both sites, samples were taken from four trees, and within each tree, from three heights and four compass directions. The epicuticular wax of the needles was investigated under a scanning electron microscope (SEM) by estimating the relative abundances of eight wax types representing both tubular and degraded forms. Two ways are proposed to convert these data to index values, and the usefulness of this approach is evaluated. The differences between the two sites were significant, the needles from the urban site showing, on average, less‐preserved wax types than those from the rural site. Variation among individual trees within each site was pronounced, which proved the necessity of sampling several trees. There was also marked variation among the needles taken from the same tree, but this showed no consistent pattern with respect to sampling height or compass direction. Analysis of the variance at different hierarchical levels (among trees, among needles and within needles) suggested that the sampling effort is better invested when it is spread among several tree individuals than when it is concentrated on the detailed study of fewer trees.
Wall extensibility: its nature, measurement and relationship to plant cell growth
Authors: COSGROVE DANIEL J.
Published: April 2006

Expansive growth of plant cells is controlled principally by processes that loosen the wall and enable it to expand irreversibly. The central role of wall relaxation for cell expansion is reviewed. The most common methods for assessing the extension properties of plant cell walls (‘wall extensibility’) are described, categorized and assessed critically. What emerges are three fundamentally different approaches which test growing cells for their ability (a) to enlarge at different values of turgor, (b) to induce wall relaxation, and (c) to deform elastically or plastically in response to an applied tensile force. Analogous methods with isolated walls are similarly reviewed. The results of these different assays are related to the nature of plant cell growth and pertinent biophysical theory. I argue that the ‘extensibilities’ measured by these assays are fundamentally different from one another and that some are more pertinent to growth than others.

‘That's a great deal to make one word mean,’ Alice said in a thoughtful tone.

‘When I make a word do a lot of work like that’ said Humpty Dumpty,‘I always pay it extra’.

‘Oh!’ said Alice. She was too much puzzled to make any other remark.

Lewis Carroll, Through the Looking‐glass

CONTENTS

Summary
1

I.
Introduction
1

II.
The nature of wall expansive growth
2

III.
Techniques for measuring wall extensibility
4

IV.
Concluding remarks and prospectus
20

Acknowledgements
20

References
20
Mycorrhiza‐like interaction between the achlorophyllous gametophyte of Lycopodium clavatum L. and its fungal endophyte studied by light and electron microscopy
Authors: SCHMID E. , OBERWINKLER F.
Published: April 2006

The mycorrhiza‐like association of mature gametophytes of Lycopodium clavatum and an endophytic fungus was studied by means of light and electron microscopy. Fine aseptate hyphae of the fungus formed very regular dense hyphal coils and numerous small vesicles of different stages in the cortical cells. Extended infections occurred within preformed spaces between the cells of the storage tissue. These spaces probably arose by degeneration of the host cells. Several hyphae grew within them and were partly swollen or irregularly lobed and branched. They were embedded in a heterogeneous material, probably of host origin. Arbuscles were not established during the interaction. All fungal structures degenerated in the older host tissues that remained intact. The fungus contained bacterium‐like organelles. Elliptic interphase spindle‐pole bodies of the fungus were attached to the outer nuclear envelope. The host‐fungus interaction in the gametophyte of L. clavatum cannot be related to any type of mycorrhizal association described to date. It is therefore called the ‘Lycopodioid mycothallus interaction’.
Accumulation of photoassimilate by Peronospora viciae (Berk.) Casp. and leaves of Pisum sativum L.: evidence for nutrient uptake via intercellular hyphae
Authors: CLARK J. S. C. , SPENCER‐PHILLIPS P. T. N.
Published: April 2006

Autoradiography showed that accumulation of label by hyphae of Peronospora viciae (Berk.) Casp., in leaflets of Pisum sativum L. exposed to 14CO2, was up to 4.5 times greater in the susceptible cv. Krupp Pelushka than the resistant cv. Early Onward. Concentrations of label were similar in apoplastic solutions from both cvs, although a greater volume was available in Early Onward. Uninfected Krupp Pelushka assimilated more label from 14CO2 than Early Onward; para‐chloro‐mercuribenzene sulphonic acid (PCMBS) treatment and infection reduced assimilation by Krupp Pelushka but not Early Onward. Infected leaf tissue from Early Onward assimilated more label than Krupp Pelushka from [14C]sucrose supplied to the apoplast. Transient treatment with PCMBS reduced assimilation of [14C]sucrose into infected plant tissue to 30 and 61 % of untreated levels, in Early Onward and Krupp Pelushka respectively. In contrast, autoradiography of hyphal fragments showed that the fungus accumulated 1.4 times more label from [14C]sucrose than without PCMBS. The different nutrient status of leaves of Early Onward and Krupp Pelushka, and evidence that label from sucrose is accumulated by intercellular hyphae directly from the apoplast, are discussed in relation to the role of haustoria and mechanisms of compatibility.
Wound‐healing in Vaucheria longicaulis Hoppaugh var. macounii Blum.
Authors: TORNBOM LAURIE , OLIVEIRA LUIS
Published: April 2006

The sequence of events leading to wound‐healing and resumption of growth are studied by light microscopy including the use of differential interference contrast optics in Vaucheria longicaulis Hoppaugh var. macounii Blum. Wound‐healing has been divided into four stages. In stage 1, a wound‐healing vesicle is rapidly extruded from the wound site. Loss of turgor pressure, as observed by the appearance of plasmolysis, is seen along the length of the filament. In stage 2, the wound‐healing vesicle is sealed‐off from the filament. Organelles then accumulate at the barrier created by the sealing‐off process. This is followed by chloroplast retraction from and return to the wound site, concurrent with the restoration of turgor pressure in late stage 2. In stage 3 chloroplasts again retract from and return to the wound site, in preparation for stage 4 that finally leads to the resumption of growth on the part of the healed filament.

The effect of wound healing on organelle distribution has been studied with the use of selective fiuorochromes. The distribution of nuclei, identified by DAPI staining, remains largely unchanged after wounding. Mitochondria and probable lipid bodies (designated RBIs) are identified by staining with DiOC6 and Rhodamine B, respectively. Their presence in the wound‐healing vesicle cytoplasm and accumulation along the wound site points to the existence of an efficient mechanism of ATP synthesis in support of the energy requirements associated with the healing process. CTC fluorescence along the wound site and wound vesicle cytoplasm suggests that Ca2+‐based exocytosis is important in both wound‐healing vesicle expansion and its sealing‐off from the filament.
Combination effect of NaCl salinity, nitrogen form and calcium concentration on the growth, ionic content and gaseous exchange properties of Triticum aestivum L. cv. Gamtoos
Authors: HAWKINS H.‐J. , LEWIS O. A. M.
Published: April 2006

The effects of NaCl salinity have been investigated with respect to the growth response, ionic content and gas exchange characteristics of wheat plants (Triticum aestivum L. cv. Gamtoos) raised on nitrate or ammonium nutrition at different Ca2+ concentrations in the nutrient medium. Salinity up to 100 mM reduced the biomass production, moisture content and water use efficiency of both NO3− and NH4+‐supplied wheat but the biomass production of NO3+‐supplied wheat was reduced to a far greater degree than that of NH4+‐supplied wheat. There was no clear trend in the photosynthetic response of these plants to moderate salinity stress (50 mM NaCl). The stomatal conductances and transpiration rates of NH4+‐supplied wheat were between 20 and 40 % lower than those of NO3−‐supplied wheat, depending on the degree of salinity stress; at higher salinity (70–100 mM NaCl) the moisture content of NH4+‐supplied plants was c. 10% higher than that of NO3+‐supplied salinized plants. An increase in Ca2+ concentration from 0.5 to 5.0 mM resulted in an increase in biomass production, moisture content, shoot:root ratio, K+ content and a decrease in Na+ content of 50 mM NaCl‐stressed, NO3+‐supplied plants. Supplemental Ca2+ had no effect on the biomass production, shoot: root ratio or moisture content of 50 mM NaCl‐stress, NH4+‐supplied plants relative to the controls.
Effect of NaCl salinity, nitrogen form, calcium and potassium concentration on nitrogen uptake and kinetics in Triticum aestivum L. cv. Gamtoos
Authors: HAWKINS H.‐J. , LEWIS O. A. M.
Published: April 2006

In wheat plants it was found that salinity stress (50 mM NaCl) and an increase in the exogenous Ca2+ supply (to 5 mM) had a differential influence on N uptake capacity depending on the N source (NO3− or NH4+). In NO3−supplied wheat plants which had not been supplied with supplemental calcium, a salinity of 50 mM NaCl reduced the N uptake rate of the root by 30 %, reduced the Fmax of NO3− uptake by 38 % and the N concentration of the plants by 35 %. In NH4+supplied plants (which were not affected by a change in calcium concentration) a salinity of 50 mM resulted in a reduction in the N concentration by 16 % (only in the root), a reduction in the Fmax of NH4+uptake by 50 %, while the N uptake rate by the plant was reduced by 16 %. In salt‐stressed NO3−supplied wheat, an exogenous Ca24 concentration of 5 mM resulted in a 65 % increase in Vmax of NO3− uptake, a 58% increase in NO3− uptake rate by the shoot per g root and a 61 and 5 % increase in shoot and root N concentration respectively. Increased exogenous concentrations of either Ca2+ or K+ had no effect on NH4+ uptake. Kinetic calculations indicate that the inhibitory activity of NaCl on both NO3− and NH4+ uptake was one of noncompetitive inhibition. When NO3−, but not NH4+, was the N source, Ca2+ at a concentration of 5 mM partially ameliorated the NaCl‐mediated inhibition of NO3− uptake.
Orientation of the lateral roots of trees
Authors: COUTTS M. P. , NICOLL B. C.
Published: April 2006

Sitka spruce [Picea sitchensis (Bong.) Carr.] plants were grown under controlled conditions in specially designed boxes in which the plagiogravitropic lateral roots grew out from moist peat into an air space at one side. In one treatment the air was saturated with water vapour. In the other a linear horizontal gradient of water vapour pressure was maintained between the vertical peat surface and a porous membrane made from black cloth. Near the peat surface the vapour pressure gradient was equivalent to a soil water‐potential gradient of about 0.48 MPa mm−1.

The angles of the roots before and after emergence from the peat were measured in different planes. In the saturated air treatment there was no significant change of angle after emergence but roots which emerged into the air with the humidity gradient grew more slowly and showed a marked change of direction. This deflection had two components; there was some tendency for the roots to be attracted to the moist peat surface (hydrotropism), and there was also a downward component (gravitropism). Mean deviation from the angle of emergence which would have resulted from a hydrotropic response alone was 58°, while deviation from the true gravitropic position was only 31°. Therefore under the conditions of the experiment the gravitropic response was considerably stronger than the hydrotropic one.

The implications of these results are discussed for the growth of roots in soils, where water potential gradients generally do not seem to be sufficient to cause hydroptropic curvature. However, there was an enhanced gravitropic response of the tips of lateral roots subject to water stress and this may help control the orientation of roots near the soil surface.
Structure of fructan oligomers in cheatgrass (Bromus tectorum L.) *
Authors: CHATTERTON N. J. , HARRISON P. A. , THORNLEY W. R. , BENNETT J. H.
Published: April 2006

Leaves of field‐grown cheatgrass (Bromus tectorum L.) plants were sampled during early spring when day‐ and night‐time temperatures were relatively cool. Fructan oligomers with a degree of polymerization (DP) 3–6 were extracted and purified using gel and anion‐exchange chromatography. The structures of 13 cheatgrass fructans were established. They included two trisaccharides [1‐kestotriose (1‐kestose) and 6‐kestotriose (6‐kestose)], four tetrasaccharides [(1.1)‐kestotetraose (nystose), (1&6)‐kestotetraose (bifurcose), (6,1)‐kestotetraose and (6,6)‐kestotetraose], three pentasaccharides [(1,1&6)‐kestopentaose, (1&6,6)‐kestopentaose and (6;1&6)‐kestopentaose] plus four hexasaccharides [(1,1,1&6)‐kestohexaose (1&6,6,6)‐kestohexaose, (6;1&6,6)‐kestohexaose and (6;1,6&6)‐kestohexaose]. All fructans larger then DP 4 contained a branch point. Each member of the dominant series(1&6)‐kestotetraose, (1&6,6)‐kestopentaose and (1&6,6,6)‐kestohexaose, is a branched fructan in which two fructose moieties are linked to the fructose subunit of each sucrose molecule. Thus the dominant series is built upon (1&6)‐kestotetraose. Fructans larger than DP 3 with exclusively 2→1‐ or 2→6‐linkages were absent except for a very small amount of (6,6)‐kestotetraose. The unique fructan structures synthesized in cheatgrass, wheat and oats illustrate diversity in the enzymology of fructan biosynthesis among grass species.
The survival of infective hyphae of vesicular–arbuscular mycorrhizal fungi in dry soil: an interaction with sporulation
Authors: JASPER D. A. , ABBOTT L. K. , ROBSON A. D.
Published: April 2006

Contrary to previous evidence, the hyphae of a vesicular–arbuscular (VA) mycorrhizal fungus, Acaulospora laevis Gerd. and Trappe, did not remain infective in soil for a length of time, and at a level of dryness, equivalent to that occurring in seasonally‐dry field soils. A possible interaction between the survival of hyphae and the timing of sporulation was therefore examined in a second experiment. We tested the hypothesis that hyphae of A. laevis and Scutellospora calospora (Nicolson and Gerdemann) Walker and Sanders, will only remain infective in dry soil if sporulation has not commenced. The capacity of the hyphae of A. laevis to remain infective, in undisturbed soil that had been allowed to dry, depended on the stage of the life cycle reached at the time of the onset of drying. If sporulation had commenced, then infectivity quickly declined as the soil dried. In contrast, infective hyphae of S. calospora survived for at least 11 wk, regardless of the timing of the commencement of drying of the soil in relation to sporulation. Quantifying entry points was an important measure for assessing the survival of infective hyphae, complementing the measure of total mycorrhiza formation by the test plants.
The relative contribution of hyphae and roots to phosphorus uptake by arbuscular mycorrhizal plants, measured by dual labelling with 32P and 33P
Authors: PEARSON J. N. , JAKOBSEN I.
Published: April 2006

The aim of this investigation was to measure the relative contribution of hyphae and roots to the total uptake of phosphorus by mycorrhizal plants. Cucumber plants were grown in three‐compartment systems where 32P was applied to a lateral root‐free compartment (HC) and 33P applied to an identical lateral compartment with both roots and hyphae (RHC). The cucumber seeds were sown into the main root compartment (RC) which was inoculated with one of the following three arbuscular mycorrhizal fungi: Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders [isolate WUM 12(2)]; Glomus sp. [isolate WUM 10(1)]; Glomus caledonium (Nicol. & Gerd.) Trappe & Gerdemann (isolate RIS 42) or left uninoculated to represent a control treatment. The plants were harvested at 17 and 27 d. The hyphal uptake of 32P from the HC increased as follows –S. calospora ≥ Glomus sp. ≥G. caledonium. The uptake of 32P from the HC was equivalent to 7, 21 and 109 % of the uptake of 33P from the RHC in plants colonized by S. calospora, Glomus sp. and G. caledonium, respectively. This indicates that the relative contribution of the roots in total P uptake varied greatly between the three mycorrhizal treatments. Although 33P uptake was variable within treatments, the P uptake systems of roots colonized by G. caledonium appeared to be inactive when compared to hyphal 32P uptake. This may have been due to feedback mechanisms being activated because of the high hyphal P uptake. The roots colonized by S. calospora had higher rates of root‐P uptake compared with the control roots, suggesting that the root‐P uptake systems have been stimulated by the presence of the fungus. This would ensure that the P supply was sufficient to maintain photosynthesis in this symbiosis where the fungus gives only little P in return for its use of plant carbon substrate from the host.
Symbiosis‐related polypeptides associated with the early stages of ectomycorrhiza organogenesis in birch (Betula pendula Roth)
Authors: SIMONEAU P. , VIEMONT J. D. , MOREAU J. C. , STRULLU D. G.
Published: April 2006

As a preliminary step towards elucidation of the molecular basis of ectomycorrhiza differentiation, polypeptide changes at different stages of mycorrhiza development were analyzed in birch (Betula pendula Roth). Time‐sequencing of the stages in the infection process of clonal plants inoculated with a compatible isolate of Paxillus involutus Batsch revealed that by 8 d mature ectomycorrhizas were obtained. Total phenol‐extracted proteins of roots during the ‘mycorrhiza formation stage’ (2–8 d post‐inoculation) were separated by two‐dimensional polyacrylamide gel electrophoresis and the resulting patterns compared with non‐mycorrhizal roots and mycelium. Alteration in the concentration of polypeptides from the host plant roots was limited even after 8 d of contact between the symbionts. However, seven novel polypeptides were detected 4 d after inoculation, three of them being already present in 2‐d‐old ectomycorrhizas. These findings demonstrate that symbiosis‐related polypeptides accumulate in ectomycorrhizal roots prior to any of the morphological changes characterizing the symbiotic state.
Modern pollen deposition in cave sites: experimental results from New York State
Authors: BURNEY DAVID A. , BURNEY LIDA PIGOTT
Published: April 2006

Results from two years of pollen trapping experiments in New York State show that pollen spectra inside the three caves studied are highly similar to the pollen rain outside the caves. Statistical comparisons of modern pollen spectra derived from Tauber traps, speleothems, moss polsters, and nearby pond sediments suggest that pollen deposition inside caves can provide a reliable index of the regional and local vegetation, directly comparable to the more conventional spectra derived from lake sediments and moss polsters. Because of the relatively low pollen influx inside caves, however, stochastic and episodic forms of particle transport may influence pollen deposition inside caves in proportions that are unique to each site. With careful attention to site parameters such as entrance size, pollen preservation, and modes of sedimentation, investigators could make greater use of caves in palynological studies.
The genetics of metal tolerance in vascular plants
Authors: MACNAIR MARK R.
Published: April 2006

In many parts of the world soils are detrimental to plant growth owing to elevated levels of metal ions, caused either by natural processes or by the result of man's activities. Many plants have evolved ecotypes or varieties that are able to grow more‐or‐less normally on these soils. This paper reviews our knowledge of the genetics of this phenomenon.

The nature of tolerance and the problems of its measurement are discussed. Tolerance is frequently measured by an index produced by comparing growth in a contaminated environment with growth in a control environment. It is argued that this measurement is inappropriate for many genetical studies, and that it is frequently more useful to use growth at a single critical level of metal as a measure of tolerance.

Polygenic inheritance provides a null hypothesis that has to be tested in a genetical analysis. Examples of major genes for tolerance to aluminium, arsenic, boron, cadmium, copper and manganese are discussed. Even where major genes have been demonstrated, it is probable that other minor genes, ‘modifiers’, are present as well. Because of the nature of tolerance as a character, dominance and epistasis are likely to vary with the level of metal at which an analysis is performed. Tolerance is generally found to be dominant at some levels of the metal. Studies which have mapped tolerance genes, particularly to aluminium and salt, are discussed.

The specificity of tolerance is a matter of some confusion. Some studies indicate that tolerances evolve independently to different metals, but others have suggested that tolerance to one metal may often confer a degree of tolerance to some other metals.

Very little is known about the molecular genetics of tolerance, and the mechanisms of tolerance to most metals. The possible role of phytochelatins and metallothionein‐like proteins in metal tolerance is discussed.

The distribution of tolerance in natural populations suggests that tolerance is a disadvantage in uncontaminated environments, but how this ‘cost’ arises is not known. There is some evidence that the disadvantage to tolerance may be associated more with the modifiers of tolerance than with the primary tolerance gene.

The study of the genetics of tolerance is of importance in planning breeding programmes to produce tolerant crops for use in areas where metal contamination is a limiting factor in productivity. It can also assist in understanding the mechanisms of tolerance, as exemplified by the study of the mechanism of arsenic tolerance in Holcus lanatus. Important areas for further research are discussed.

Contents

Summary
541

I.
Introduction
542

II.
Introduction
542

III.
Transmission genetics of tolerance
544

IV.
Specificity of tolerance
550

V.
Molecular genetics of tolerance
552

VI.
Ecological genetics of tolerance
553

VII.
Conclusions
555

Acknowledgements
556

References
556
Further evidence for a correlation between nodulation genotypes in alfalfa (Medicago sativa L.) and mycorrhiza formation
Authors: BRADBURY S. M. , PETERSON R. L. , BOWLEY S. R.
Published: April 2006

The vesicular‐arbuscular (VA) mycorrhizal status of three alfalfa (Medicago sativa L.) nodulation genotypes (nod+fix+, nod+fix− and nod−fix−) was investigated using pot cultures of three fungal species from two genera (Glomus monosporum Gerd. & Trappe, Glomus fasciculatum (Thaxter) Gerd. & Trappe emend. Walker & Koske and Gigaspora margarita Becker & Hall). Roots of the nod+fix+ genotype developed complete VA mycorrhizas with each fungus. Roots of the nod+fix− and nod−fix− genotypes did not develop normal VA mycorrhizal symbioses. Roots of the nod− fix− genotype had significantly more appressoria than roots of the other genotypes. Aborted appressoria were unable to penetrate the cortical cells of roots of nod+fix− and nod− fix− genotypes. Measurement of appressorium length, width and approximate contact area revealed significant differences in the size of appressoria produced by each VA mycorrhizal fungus on each alfalfa nodulation genotype. Histological studies of nod+fix+ and nod− fix− genotypes colonized by Glomus versiforme (Karsten) Berch showed the presence of electron‐dense material in aborted appressoria on roots of the nod−fix− genotype but not in appressoria on roots of the nod+fix+ genotype.
Influence of the host on three sub‐Arctic annual facultative root hemiparasites
Authors: SEEL W. E. , PRESS M. C.
Published: April 2006

Growth, mineral accumulation and above‐ground dry‐matter partitioning were measured in three sub‐Arctic annual facultative root hemiparasites, Rhinanthus minor L., Euphrasia frigida L. and Melampyrum sylvaticum L., growing either unattached or attached to a host plant. Attached plants were at least an order of magnitude taller than unattached plants, and individuals produced a total above‐ground biomass up to three orders of magnitude greater than that produced by unattached plants. Attached plants produced a greater number of branches, leaves, buds, flowers and ripe seed capsules. Leaf size was greater in attached than unattached plants. For two species, Rhinanthus minor and Euphrasia frigida, the response of individuals attached to a legume was compared to the response of those attached to a grass. Stimulation of parasite growth was greater with a legume host than with a grass. The architecture of parasites on legume hosts differed greatly from those either on grasses or unattached, with those on legumes often having a considerably greater number of second order branches. Above‐ground biomass partitioning was affected by attachment to a host, and was a function of host type. Unattached plants of all three species of parasite accumulated foliar element concentrations within the same order of magnitude as their hosts. Element concentrations in attached plants were sometimes, but not always, greater than those of their hosts. Element concentrations, especially N, were greatest in those parasites attached to a legume.
The deposition of atmospheric ammonia and its effects on plants
Authors: PEARSON JOHN , STEWART GEORGE R.
Published: April 2006

Across Europe, total nitrogen deposition is increasing and, of this total, atmospheric ammonia can contribute up to 50–80%. Average deposition of ammonia in the UK is likely to be around 15–20 kg ha−1yr−1, while in The Netherlands, which has some of the highest rates of deposition, this value is likely to be between 40 and 50 kg ha−1yr−1. It is argued that because of the processes of assimilation and nitrification this ammonia is an acidifying pollutant.

Ammonia taken up by plants is most likely to be directly assimilated and this uptake can have a strong effect on the nutrient imbalances of the plant. With root uptake in particular, anions are taken up in preference to cations. However, simple soil/plant nutrient measurements are unlikely to be a definitive means of monitoring ammonia pollution. This is because the processes of ammonia metabolism and acidification affect soil ion activity, mycorrhizas, plant uptake, and foliar leaching. These effects interact with acidityper se, and are compounded by the strong correlative co‐deposition of ammonia with sulphur. Evidence for uptake of gaseous and wet deposited ammonia by leaves is presented.

The exact mechanism of ammonia toxicity is still not really clear, but could be due to physiological perturbation, rather than to the direct toxicity of the ion. Assimilation of ammonia by leaves releases protons which can cause cellular acidosis, and has important implications for acid‐base regulation in cells. This regulation depends on intrinsic features of the plant's metabolism, that is in turn dependent on the ecology of root versus leaf nitrogen nutrition under normal conditions. Certain species are more acidic in a leaf physiological sense and tend to be prone to damage by pollutants.

Likewise, acidic habitats are particularly prone to damage through both eutrophication and the different capacities of plants both to utilize and to buffer against this nitrogen enrichment. The current evidence from The Netherlands suggests that the part this plays in perturbing the ecosystem should not be underestimated.

ContentsSummary283I.Introduction284II.Emission and deposition of ammonia284III.Is ammonia toxic?288IV.The eflfects of ammonia deposition289V.Throughfall versus foliar uptake293VI.Physiological effects on ahove‐ground parts296VII.Conclusions301Acknowledgements302References302
The control of exocytosis in plant cells
Authors: BATTEY NICHOLAS H. , BLACKBOURN HUGH D.
Published: April 2006

Exocytosis is a key event in plant cells, linking the internal and external environments. Cell‐wall precursors, membrane material, and soluble and membrane‐associated proteins are supplied by exocytosis and allow cells to grow and differentiate. In this review, we describe exocytotic systems in plants and summarize information on how exocytosis is controlled and itself controls cell development. Mechanisms regulating exocytosis in other organisms are outlined and some critical directions for future research on plant exocytosis are suggested.

Contents

Summary
307

I.
Introduction
307

II.
Exocytotic systems
309

III.
The mechanism of exocytosis
322

IV.
Conclusions and future research
329

Acknowledgements
331

References
331
Immunocytochemical localization of Fe‐SOD in different cells of Anabaena cylindrica Lemm. grown at two different photon irradiances
Authors: CAIOLA MARIA GRILLI , CANINI ANTONELLA
Published: April 2006

Superoxide dismutase (SOD) converts superoxide radicals into hydrogen peroxide and molecular oxygen and therefore represents the primary defence against oxygen damage. Using antibodies against Anabaena cylindrica Lemm. iron‐SOD, the isoenzyme was localized by immunogold labelling in vegetative cells, heterocysts and akinetes of the cyanobacterium Anabaena cylindrica grown at different light intensities. At a low photon irradiance (25 μmol photons m−2 s−1), the density of iron‐SOD labelling was similar in vegetative cells and in heterocysts, whereas in akinetes only 60 % of the gold particles were present as compared with the other cell types. At a higher photon irradiance (140 μmol photons m−2 S−1), iron‐SOD labelling increased by 100% in both vegetative cells and in heterocysts but did not change in akinetes. The cultures grown at the photon irradiance of 140 μmol photons m−2 s−1 showed a rate of photosynthetic oxygen evolution 40 % higher than that of cultures grown at the lower photon irradiance. The increase of SOD labelling in vegetative cells is in line with the increased photosynthetic oxygen evolution induced by light. The unchanged SOD labelling observed in the akinetes suggests that light intensity does not seem to affect the oxidative metabolism due to respiratory activity.
Long‐term effects of drought on photosynthesis of adult oak trees [Quercus petraea (Matt.) Liebl. and Quercus robur L.] in a natural stand
Authors: EPRON DANIEL , DREYER ERWIN
Published: April 2006

Effects of drought on photosynthesis of two co‐occurring oak species (Quercus robur and Q. petraea) have been assessed under natural conditions in a 30‐y‐old stand. Leaf conductance and net CO2 assimilation rates have been measured at midday in situ during two successive summers (1991 and 1992). Chlorophyll a fluorescence parameters were monitored before dawn during the summer of 1991. A severe drought was imposed on two trees per species, resulting in decreases of pre‐dawn leaf potential to about –2.0 MPa during both years. Both species showed the same overall response to drought: gradual decrease of net assimilation and leaf conductance but maintenance at substantial levels down to strong water deficits, stability of the pre‐dawn photochemical efficiency of PS II during the whole period of drought, and declines in pre‐dawn fluorescence (both basic and maximal levels) owing probably to changes in the optical properties of leaves during maturation. It was concluded that both species displayed a strategy of tolerance to drought, and they displayed efficient protection mechanisms against permanent high irradiance damage. Slight differences were observed between both species, Q. robur displaying smaller leaves, lower chlorophyll contents, and a larger stomatal conductance at equivalent net assimilation rates than Q. petraea. Significance of these findings is discussed in relation to the ecological requirements known for each of these species.
Nickel and zinc tolerance and co‐tolerance in populations of Deschampsia cespitosa (L.) Beauv. subject to artificial selection
Authors: VON FRENCKELL‐INSAM BEATRIX A. K. , HUTCHINSON THOMAS C.
Published: April 2006

The occurrence of co‐tolerance to four heavy metals was investigated among seedlings selected from three different non‐tolerant Canadian and German Deschampsia cespitosa (L.) Beauv. populations. Plants selected following screening of seedlings in solution containing Ni or Zn ions, subsequently showed enhanced tolerance to Ni and Zn, respectively. ‘Nickel screened’ seedlings exhibited no increased tolerance to Zn.‘Zinc screened’ seedlings, in contrast, had somewhat elevated tolerance to Ni in two of the three populations tested (Elm and Cypress Lake). Thus, co‐tolerance may be a population‐specific rather than a species‐specific response. Individual Elm plants screened for Ni response did not have elevated Zn tolerance, whereas‘Zn screened’ seedlings did show elevated Ni tolerance. This confirms the result from the population tolerance tests. We conclude that co‐tolerance is not a reciprocal process. While the selection for one metal may confer elevated tolerance to a second, selection for the second may not confer tolerance to the first.