bluuebunny/crossref_metadata_2025 huggingface dataset:
Daily and seasonal courses of leaf conductance and abscisic acid in the xylem sap of almond trees [Prunus dulcis (Miller) D. A. Webb] under desert conditions
Authors: WARTINGER A. , HEILMEIER H. , HARTUNG W. , SCHULZE E.‐D.
Published: April 2006

Individual 1‐ to 4‐year‐old almond trees [Prunus dulcis (Miller) D. A. Webb] were grown in lysimeters of different volumes, filled with loess. Once per year, at the beginning of each growing season, the lysimeters were watered to field capacity, and consequently each tree experienced a seasonal drought in relation to the amount of available water depending on soil volume and tree age. Measurements of leaf conductance were performed on youngest fully expanded, sun‐exposed leaves in climatized cuvettes. Leaf water potential was measured with a pressure chamber, which was also used for collecting xylem sap. Abscisic acid concentration of the xylem sap was determined with ELISA.

There was no consistent diurnal relationship between abscisic acid concentration in xylem sap and leaf conductance. During a drying cycle, however, there was an inverse relationship between maximum leaf conductance and daily average abscisic acid concentration in xylem sap. With soil drying, the concentration of abscisic acid in xylem sap initially increased to a maximum in summer but decreased again towards autumn. Thus, during the first part of the drying cycle the predawn water potential of the leaf was significantly correlated with abscisic acid concentration in xylem sap. As predawn water potential becomes more negative during the first part of the drying cycle, the decline in maximum leaf conductance correlates with an increase in concentration of abscisic acid in xylem sap. With further decrease in predawn water potential towards the end of the drying cycle, the stomata remained closed even though there was a decreasing concentration of abscisic acid in the xylem sap.

We conclude that the concentration of abscisic acid in xylem sap is not related to leaf conductance during the course of a day from end of May to September. However, during the course of a drying cycle the range of maximum leaf conductance seems to be dependent on the concentration of abscisic acid in xylem sap.
A comparison of maturation drying, germination, and desiccation tolerance between developing seeds of Acer pseudoplatanus L. and Acer platanoides L
Authors: HONG T. D. , ELLIS R. H.
Published: April 2006

Differences in maturation drying and desiccation tolerance during seed development were detected between the two contrasting Acer spp., Norway maple (Acer platanoides L.), which shows orthodox seed storage behaviour, and sycamore (A. pseudoplatanus L.), which shows recalcitrant seed storage behaviour. In both species, the onset of germinability (150 d tests at 5 °C) occurred after percentage seed moisture content had begun to decline, but before net loss in seed moisture. The onset of germinability in Norway maple occurred 4 wk before physiological maturity (i.e. 4 wk before the end of the increase in seed dry matter), whereas in sycamore it occurred some ten weeks before physiological maturity when the seeds were only 60 % filled. Seeds of Norway maple were able to tolerate enforced rapid desiccation to 10% moisture content (f. wt) at physiological maturity, when maturation‐drying had reduced seed moisture content to 54 %. Between 2 and 4 wk later seed moisture content rapidly declined naturally to 25 %, at which value the fruits were shed. In contrast, a constant rate of maturation‐drying was observed in sycamore. The seeds were shed at 58 % moisture content and, in almost all cases, the seeds were intolerant of rapid desiccation to c. 10 % moisture content throughout seed development. A very small proportion of sycamore seeds did survive rapid desiccation when harvested between 6 September and 4 October, but no seeds survived desiccation to 5 % moisture content or below. A comparison of the germination of sycamore seeds harvested on four dates and dried to various moisture contents showed that the seeds tolerated greater desiccation as they matured between 12 July and 20 September, but there was no further change thereafter. The results are therefore compatible with previous classifications of seed storage behaviour in each species, and with the view that the initial decline in seed moisture content stimulates the developmental switch which results in the onset of germinability in both orthodox and recalcitrant seeds.
Water relations, thallus structure and photosynthesis in Negev Desert lichens
Authors: PALMER ROBERT J. , FRIEDMANN E. IMRE
Published: April 2006

The role of lichen thallus structure in water relations and photosynthesis was studied in Ramalina maciformis (Del.) Bory and Teloschistes lacunosus (Rupr.) Sav. Water‐vapour adsorption and photosynthesis are dependent upon thallus integrity and are significantly lower in crushed thalli. Cultured phycobiont (Trebouxia sp.) cells are capable of photosynthesis over the same relative humidity range (> 80 % RH) as are intact lichens. Thus, water‐vapour adsorption by the thallus and physiological adaptation of the phycobiont contribute to the ability of these lichens to photosynthesize in an arid environment. Despite differences in their anatomical structure and water‐uptake characteristics, their CO2 incorporation is similar. The two lichens use liquid water differently and they occupy different niches.
Ecophysiology of microcolonial fungi and lichens on rocks in northeastern Oregon
Authors: PALMER F. E. , STALEY J. T. , RYAN B.
Published: April 2006

In this study of rocks in eastern Oregon, air and rock temperatures and moisture were monitored, along with the abundance and distribution of micro‐colonial fungi (MCF) and lichens, for 2 yr. Conditions were suitable for MCF growth during all but the winter months with the most favorable conditions occurring in spring and autumn. In these seasons moisture was frequent and the absorption of solar irradiation by rocks increased the surface temperatures considerably above the very cool air temperatures.

Distributions of MCF and lichens were studied in detail on ten granite rocks at one site. While MCF were most numerous on southern rock exposures, this appeared to be because this exposure was least favorable for lichen growth. MCF appeared to precede lichens in colonizing recently fractured, exposed rock surfaces. The ability of the MCF to grow in the dark as well as the light may be an important factor favouring growth of MCF relative to lichens, especially in the summer when daytime air and rock temperatures were too high to permit growth. However, conditions on some areas of the rocks were especially favourable for lichen growth and in these places lichens effectively dominated the MCF for surface area. A list of lichen species observed at this and nearby locations is provided.

14CO2 release from [14C]acetate was used as a measure of MCF activity at 10–12 °C and 25 °C under different conditions of moisture. Moderate respiration was found at 10–12 °C and respiration occurred with a 2 h period of air drying. In contrast, MCF on rocks air dried for several weeks and subsequently dried for 18 h over H2SO4 did not become active during incubation for 2 h following wetting.
Effect of degree of soil disturbance on mycorrhizal colonization and phosphorus absorption by maize in growth chamber and field experiments
Authors: McGONIGLE T. P. , EVANS D. G. , MILLER M. H.
Published: April 2006

Prior studies have established that phosphorus absorption by maize from undisturbed soil is greater than from soil which has been disturbed since the previous period of growth. Those experiments were conducted under controlled conditions and with only two disturbance treatments, namely disturbance of the soil by hand sufficient that it will pass a 5 mm sieve, and no disturbance at all. We present here two experiments in which additional treatments of intermediate degrees of disturbance are included.

In a growth chamber experiment, cutting the soil into 1, 2 or 4 cm cubes reduced the phosphorus absorption and shoot dry matter, but the reduction was not as great as that after hand disturbance of the soil. In a field experiment, the phosphorus absorption and shoot dry matter found in a conventional tillage and no‐till treatments were less than in hand‐planted no‐till plots, but greater than with severe soil disturbance. In both experiments increases in shoot dry mass and shoot phosphorus concentration in the less disturbed treatments were not accompanied by an increase in mycorrhizal colonization. This is inconsistent with earlier studies in which colonization was greater in undisturbed soil.

Since it has now been demonstrated that increased colonization is not a necessary component in the process whereby lack of disturbance results in improved plant performance, the role of mycorrhizas in this effect should be reconsidered. If mycorrhizas are important in this respect then this can only be by means of changes in the external mycelium. However, without experimental confirmation this interpretation is speculative.
Direct and indirect effects of VA mycorrhizal fungi and rhizosphere microorganisms on acquisition of mineral nutrients by maize (Zea maysL.) in a calcareous soil
Authors: KOTHARI S. K. , MARSCHNER H. , RÖMHELD V.
Published: April 2006

Maize (Zea maysL.) was grown in a fertilized calcareous soil in pots which were separated by 30 μm nylon nets into three compartments, a central one for root growth and two outer ones for hyphal growth. The treatments comprised of sterilised soil, either inoculated with rhizosphere microorganisms together withGlomus mosseae(Nicol. & Gerd.) Gerdemann & Trappe, with rhizosphere microorganisms alone, or non‐inoculated (sterile control).

In the mycorrhizal treatment concentrations of P and Zn were increased in shoot and roots, as was uptake of P and Zn per unit root dry weight or per unit root length. Copper concentration in roots of mycorrhizal plants, and total uptake and uptake per unit root dry weight or per unit root length of Cu was also increased. The higher acquisition of P, Zn and Cu in the mycorrhizal plants is ascribed to VA mycorrhizaper se(hyphal uptake and translocation to the host). Besides these direct effects, VA mycorrhizal fungi and rhizosphere microorganisms affected the acquisition of other nutrients mostly through alteration of root morphology. In both mycorrhizal and sterile treatments, the decreased concentrations of Ca and Si in the shoot but increased concentrations in the roots seem to be related to restricted apoplasmic solute transport across the endodermal barrier due to decreased number of lateral roots.

The concentration of K in both shoot and roots, and Fe in shoot were lower in mycorrhizal plants due to reduced root length. Manganese concentration was also distinctly lower in both shoot and roots in mycorrhizal and sterile treatments, an effect which is attributed to the decrease in Mn reduction in the rhizosphere. Irrespective of nutrient, the uptake per unit root length was higher in mycorrhizal plants, probably due to hyphal contribution and increased supply of nutrients to the root surface by mass flow. Soil analysis indicates hyphal translocation of K but not Mg.

The results demonstrate that effects of VA mycorrhizal infection on root morphology and rhizosphere microorganisms have to be considered in interpretations of mycorrhizal effects on mineral nutrient acquisition.
Field use of 32P to measure phosphate uptake by birch mycorrhizas
Authors: DIGHTON JOHN , MASON PHILIP A. , POSKITT JAN M.
Published: April 2006

32P was used to determine phosphorus uptake by different mycorrhizas of birch in the field. Time of year and location of the application of 32P were the dominant variables influencing uptake into the canopy. There was evidence of differential uptake by the three mycorrhizal types selected. Where Hebeloma mycorrhizas were more frequent, a significantly greater rate of phosphorus uptake per unit leaf weight occurred than where Laccaria or Lactarius were more frequent. The method shows potential for field evaluation of efficiency of nutrient uptake by mycorrhizas, although a number of factors need to be taken into account in determining uptake. In locating areas for 32P injection, it was found that the distribution of mycorrhizal types on roots did not always reflect the distribution of the corresponding fruitbodies.
Root colonization by four closely related genotypes of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton – comparative studies using electron microscopy
Authors: WONG KEN K. Y. , MONTPETIT DIANE , PICHÉ YVES , LEI JIYU
Published: April 2006

Electron microscopy was used to compare four closely related genotypes of Laccaria bicolor (Maire) Orton (the two sib‐monokaryons m4 and m10 having been crossed twice to give the two dikaryons d1 and d2) which showed substantially different ectomycorrhizal structures on roots of Pinus banksiana Lamb. All four strains incorporated into mucilage on long roots but only the most compatible strain dl formed thick mantles with closely packed hyphae at surfaces of both long and short roots. At the inner Hartig net found in short roots, hyphae of dl showed a highly convoluted morphology whereas other strains formed roundish hyphal cross sections. The rare Hartig nets formed by m4 occasionally showed highly distorted root cell walls adjacent to hyphae. The occurrence of extracellular glycofibrils during initial hypha‐root contact was rare for all four fungal strains whereas substantial tannin‐like deposits were frequently found in root cortical cells.
Comparative ozone sensitivity of old and modern Greek cultivars of spring wheat
Authors: BARNES J. D. , VELISSARIOU D. , DAVISON A. W. , HOLEVAS C. D.
Published: April 2006

Ten cultivars of spring wheat, bred and introduced in Greece between 1932 and 1980, were exposed to ozone (180 μg m−3) or to charcoal‐filtered air (< 4 μg O3 m−3) for 21 d. Ozone sensitivity was assessed by recording the extent of visible injury, effects on mean relative growth rate (R̄) and changes in fast fluorescence kinetics. Ozone significantly (P < 0.01) depressed the mean relative growth rate (R̄) and there were significant (P < 0.01) differences in response between cultivars. Moreover, there was a highly significant (P < 0.002) negative relationship between the reduction in R̄ and the year of introduction; the more modern the cultivar the greater its sensitivity to ozone. Ozone reduced root growth relative to the shoot, but the effect varied with cultivar. Although all varieties developed typical visible symptoms of ozone damage, there was little relationship between the extent of this damage and effects on growth, or changes in fluorescence.

After 18 d fumigation there were significant (P < 0.001) changes in fast fluorescence kinetics in leaves that had not developed visible symptoms of injury. The ozone‐induced reduction in t1/2 was closely related (r= 0.92, P < 0.002) to the depression in R̄, indicating that a fluorescence assay based upon changes in the rise in fluorescence between Fo and Fm can be used to distinguish between genotypes of contrasting ozone sensitivity. It is concluded from this study that inadvertent selection by plant breeders may have resulted in modern varieties of some crop plants that are considerably more sensitive to ozone than their predecessors. Possible explanations for this phenomenon are discussed.
Rapid‐cycling Brassica species: anther culture potential of B. campestris L. and B. napus L.
Authors: ASLAM FERRE N. , MACDONALD MARY V. , INGRAM D. S.
Published: April 2006

summary

A study was made of the production of embryoids by cultured anthers of rapid‐cycling populations of Brassica campestris L. and Brassica napus L. In the case of B. campestris, best results were obtained when anther donors were grown at 24 °C with continuous light; anthers were excised from 1.6–2.00 mm buds with the pollen at the mid‐uninucleate stage of development and were cultured on a solidifed Brassica anther culture medium of Keller & Armstrong (K), and when incubation was at 35 °C for 1 day, followed by 30 °C for 1 day and then continuous incubation at 25 °C. The response to anther culture of B. napus was generally very poor compared with that of B. campestris but the best results were obtained when anther donors were grown at 18 °C with continuous light; anthers were excised from 2.1–2.5 mm long buds with the pollen at the mid‐uninucleate stage of development, were cultured on a liquid formulation of K medium, and incubation was at 35 °C for 1 day, followed by 30 °C for 6 days and then continuous incubation at 25 °C.
The discrete root epidermis of floating plants
Authors: CLOWES F. A. L.
Published: April 2006

summary

The reason why roots of some floating plants have a discrete epidermal meristem was investigated by comparing rates of anticlinal and periclinal division in shells of tissue during early development of lateral primordia of Pistia stratiotes L., which has such an epidermis, with those of Eichhornia crassipes (C. F. P. Martius) Solms‐Laub., which has not. The main factor involved is the timing and extent of the expansion of the primordium in relation to the availability of cells that can switch their divisions to anticlinal planes conformably with the growth of contiguous cells. The greater growth rate of the primordia of Pistia at the critical early stage forces the proximal cells of the endodermis‐derived tissue to divide only anticlinally immediately after their initiation by periclinal divisions and until the pole of the root forms a quiescent centre. It thus creates a monostromatic shell between the root cap and the pericycle‐derived tissue.
Relation of shoot growth phases in seedling oak to development of the tap root, lateral roots and fine root tips
Authors: HARMER RALPH
Published: April 2006

summary

Seedlings of Quercus robur L. were grown in tubes containing peat and perlite and observations of the periodicity of root and shoot growth were made. Root and shoot growth were not closely coupled. The rate of elongation of the tap root was approximately constant and did not decline during periods of stem growth and leaf expansion. The complexity of the root system increased throughout growth; tap roots emerged without lateral roots but by the start of the third flush of shoot growth plants had about 10 metres of lateral root and 6500 root tips. There were about 6 first order laterals per cm of tap root but the relationships between length of the lateral root system, number of root tips and tap root length changed during growth. There was no evidence that rhythmic growth in oak is related to an unfavourable root:shoot ratio caused by rapid growth of the shoot and leaves during a flush.
The effect of soil compaction on wheat during early tillering
Authors: ATWELL B. J.
Published: April 2006

summary

Wheat (Triticum aestivum L. ev. Eradu) was grown in the field on a deep loamy sand which had either a compact soil layer (compact soil) between 10 and 55 cm depth or a deep‐tilled profile (loosened soil). Concentrations of metabolites were affected by the presence of mechanical impedance. The concentrations of soluble sugars (including glucose, fructose and sucrose), free amino acids and inorganic ions (K+, Na+, NH4+, Cl−, NO3−, H2PO4−, SO42−) in consecutive 1 cm root segments of the seminal roots are reported. When tissues equidistant from the apex were compared, the concentrations of free amino acids were greater in roots from loosened soil; soluble sugars were also more concentrated in roots from loosened soil except in the apical 1 cm of the root. However, comparing root tissues of the same age (calculated from elongation rates), showed that concentrations of soluble sugars were smaller in roots from loosened soil. Potassium, Na+, Cr and SO42 were present in fairly constant concentrations along the terminal 4 cm of the root; NO3− and H2PO4 showed more distinct gradients along the axis. Roots from loosened soil had higher NO3 and lower SO42− concentrations than those from compact soil. The total concentration of solutes assayed was 19–31 % smaller in roots growing in compact soil than in roots from loosened soil. Soluble sugar concentrations in shoots as a whole were 21 % greater in plants taken from compact soil than those from loosened soil, suggesting that the lower shoot growth rates of the former were not the result of carbohydrate shortage.
Morphological aspects of in vitro co‐cultivation of Frankia alni subsp. pommerii Lalonde (strain ACN1AG) and Frankia elaeagni (Schröter) Becking (strain EANlpec) with larch (Larix×eurolepis Henry) cells
Authors: LALIBERTÉ S. , LALONDE M.
Published: April 2006

summary

This study describes the establishment of in vitro co‐cultures between the microsymbiont Frankia and cells from the non‐actinorhizal plant Larix×eurolepis Henry. Co‐cultures with strains from the two host‐plant specificity groups Alnus and Elaeagnus are compared, namely Frankia alni subsp. pommerii Lalonde strain ACN1AG and Frankia elaeagni (Schroter) Becking strain EANlpec. Larch cell clumps expanded when co‐cultivated with Frankia strain ACNlAG. The actinomvcete proliferated and hyphae developed at the surface of the clumps, in intercellular spaces, in middle lamellae and, more rarely in the plant cell wall. Conversely co‐cultivation of larch cells and Frankia strain EANlpec was highly detrimental for both partners. Dual colonies became degenerate, with the appearance of necrotic plant cells and senescent Frankia structures. The plant cell wall seemed to show a hypersensitive reaction to the presence of the actinomvcete.
Stimulation of hyphal growth of the VA mycorrhizal fungus Gigaspora margarita by suspension‐cultured Pueraria phaseoloides cells and cell products
Authors: PAULA M. A. , SIQUEIRA J. O.
Published: April 2006

summary

The effects of suspension‐cultured Pueraria phaseoloides Benth. (pueraria) cells and cell products on growth of hyphae of the VA mycorrhizal fungus Gigaspora margarita Becker & Hall in liquid media were examined. Addition of 6‐d‐old cell cultures of pueraria cells at a concentration of 25 cells ml−1 of medium caused a 3.9‐fold increase in hyphal growth. Higher cell concentrations resulted in less growth stimulation. Cell exudates or extracts (cell products) at a concentration of 25 μl−1 of medium also stimulated hyphal growth. Successive cell additions, or transfer of the spores into fresh media containing pueraria cells, resulted in no additional hyphal growth. Spores soaked in exudates or extracts showed faster and more vigorous growth when plated on an agar medium than those soaked in a control solution. It is suggested that suspension‐cultured pueraria cells stimulate hyphal growth of VA mycorrhizal fungi by accumulating and leaking very active metabolites into the medium.
Carbon flow into soil and external hyphae from roots of mycorrhizal cucumber plants
Authors: JAKOBSEN I. , ROSENDAHL L.
Published: April 2006

summary

Cucumber (Cucumis sativus L.) plants grown in PVC tubes with a partially sterilized soil‐sand mixture were inoculated with the vesicular‐arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter) Gerdemann & Trappe emend. Walker & Koske or left uninoculated. The soil column of each PVC tube was divided into a root and a hyphal compartment by a mesh bag (60 μm), which retained the roots but allowed external hyphae to pass. Inoculated plants rapidly became infected and an extensive mycelium developed. Three weeks after seedling emergence plants were labelled with 14CO2 for 16 h. The distribution of 14C within the plants and the 14C flow into external hyphae and soil were measured during an 80 h chase period. Below‐ground respiration in mycorrhizal plants accounted for 27% of the photo assimilated 14C. Organic 14C in the soil represented 3˙1 % of the fixed 14C, and 26 % of this was located in external hyphae.

Based on conservative assumptions concerning dry weight of internal mycorrhizal infection and growth yield of the fungus, it was estimated that mycorrhizal events consumed 20 % of photoassimilated 14C. The specific incorporation of C by the external mycelium in the hyphal compartment was 41 μg C mg−1 dry wt. d−1.

The importance of external VA mycorrhizal hyphae for the distribution of plant‐derived C in the soil volume and as a substrate source for the soil biota is discussed.
Occurrence of unilateral genetic transfer and genomic replacement between strains of Stereum hirsutum from non‐outcrossing and outcrossing populations
Authors: AINSWORTH A. M. , RAYNER A. D. M. , BROXHOLME S. J. , BEECHING J. R.
Published: April 2006

summary

Populations of the wood‐decaying basidiomycete, Stereum hirsutum (Willd. ex Fr.) S. F. Gray, from different geographical regions, reproduce either by outcrossing or non‐outcrossing. Outcrossing generates variable progeny whilst non‐outcrossing results in clonal sub‐populations.

Pairings between single‐basidiospore‐derived strains from non‐outcrossing and outcrossing populations commonly result in mutual rejection or mycelial invasion of the outcrosser by the non‐outcrosser. However, on the basis of both morphological evidence and studies of DNA restriction fragment length polymorphisms, some pairings result in unilateral transfer of nuclear DNA from the non‐outcrosser into the outcrosser. In some combinations the resultant putative heterokaryon may be stable and give rise to variable basidiospore progeny with unusual development and non‐self recognition responses and at least one mating‐type specificity evidently transferred from the non‐outcrosser. In other combinations, genomic takeover by the non‐outcrosser has been demonstrated, leading respectively to the emergence of mycelial sectors or production of basidiospore progeny in which solely or predominantly non‐outcrossing nuclear DNA is associated with outcrossing mitochondrial DNA.

These observations add a new perspective to the selective pressures influencing sexual outcrossing and non‐outcrossing and the role and interplay of these breeding strategies in reproductive isolation and speciation.
Stump colonization byArmillaria luteobubalinaand other wood decay fungi in an age series of cut‐over stumps in karri (Eucalyptus diversicolor) regrowth forests in south‐western Australia
Authors: PEARCE M. H. , MALAJCZUK N.
Published: April 2006

summary

As part of a study of interactions betweenArmillaria luteobubalinaWatling and Kile and other wood decay fungi, we conducted a three‐year floristic survey of fungal colonization of 150 eucalypt stumps (left after clearfelling of mature forest) in a series of karri (Eucalyptus diversicolorF. Muell.) regrowth stands of different ages. Certain fungi showed preferences for different eucalypt species or parts of stumps in their choice of food base. A successional trend of fungal species was evident in the age series of stumps (0–16 yr after logging). There was no significant relationship between the absence ofA. luteobubalinaand the presence of other fungal species on stumps, but there was a significant correlation between the percent stump base colonized byA. luteobubalinaand presence of other fungi, indicating some degree of natural suppression ofA. luteobubalina.More than 80 wood decay fungi were observed on stumps, some of which are cosmopolitan, such asCoriolus versicolor(L. ex Fr.) Quel. andStereum hirsutum(Wild, ex Fr.) S.F. Gray, but a number of which are yet undescribed.
Effects of water on the decomposition and release of nutrients from cow pats
Authors: DICKINSON C. H. , CRAIG G.
Published: April 2006

summary

Decomposition of cow pats was studied using artificially placed pats which were either covered, uncovered or irrigated with additional water. Weight losses were recorded and these showed that there was little difference between the irrigated and uncovered treatments whereas the covered dung decayed extremely slowly. These dung pats were also analysed for their nutrient content, as was the surface horizon of the underlying soil. The results showed that nutrient losses from the dung were not paralleled by a concomitant increase in the soil, which implies that considerable quantities of nutrients were removed from the soil almost as quickly as they left the dung. It is suggested that this implies considerable root activity under the cow pats, perhaps commencing almost as soon as they are laid.
The influence of ozone, acid mist and soil nutrient status on Norway spruce [Picea abies(L.) Karst.]
Authors: BARNES J. D. , EAMUS D. , BROWN K. A.
Published: April 2006

summary

Three‐year old Norway spruce [Picea abies(L.) Karst.] trees of clonal stock originating from medium altitude in southern Germany were transplanted in May 1986 into two acid brown‐earth soils which differed particularly in the amounts of exchangeable Ca2+and Mg2+. During the summers of 1987 and 1988 trees were exposed in large‐scale fumigation chambers (solardomes) to ozone at 200 or 40 (control) μg m−3Acid (pH 3˙6) or control mist (pH 5˙5) solution was applied daily to trees in each half of the solardomes. In late autumn (1988) the light response of CO2exchange, and the chlorophyll and soluble carbohydrate contents of needles were determined. Ozone and/or acid mist treatment had only minor (< 10%) effects on the light‐saturated rate of photosynthesis which were not statistically significant in plants from either soil. Needles from trees raised on the richer soil and exposed to a combination of ozone and acid mist showed a significant increase in the apparent quantum yield of photosynthesis which was associated with an increase in chlorophyll content. Ozone (alone) stimulated the rate of dark respiration by 40 and 58 % for trees grown in richer and poorer soils, respectively, and this was associated with a decrease in ethanol‐soluble carbohydrate content of needles. Where significant interactions between ozone and acid mist were found, they were generally antagonistic. The reduction in the ethanol‐soluble carbohydrates would be expected to reduce frost hardiness, and may contribute to the increased sensitivity of ozone‐treated needles to freezing, which has been reported in previous studies.
Cation‐exchange properties and adaptation to soil acidity in bryophytes
Authors: BÜSCHER P. , KOEDAM N. , VAN SPEYBROECK D.
Published: April 2006

summary

Cation‐exchange processes of plant tissue are often hypothesized to affect ion uptake. Fixation of cations on exchange sites could either withdraw cations from further uptake, or concentrate them for the absorption sites. For a number of bryophyte taxa (Atrichum undulatum(Hedw.) P. Beauv.,Homalothecium sericeum(Hedw.) B.S.&G.,Leucobryum glaucum(Hedw.) Angstr.,Mnium hornumHedw.,Plagiomnium undulatum(Hedw.) T. Kop.,Polytrichum formosumHedw.), these contrasting hypotheses were tested by studying cation‐exchange properties and soil preference of populations with respect to soil acidity and soil exchangeable cations (Al, H, Fe, Mn, Ca, Mg, K). Acidiphilous and acidicline taxa (preference for soils with pH < 5) with relatively lower cation‐exchange capacities tolerate high exchangeable aluminium levels and low calcium levels. Neutrocline taxa (preference for soils with pH > 5) with higher cation‐exchange capacity avoid aluminium in the substrate and thrive on calcium‐rich substrates. Cation‐exchange properties therefore do not protect mosses against potentially toxic cations such as aluminium through a sequestration mechanism. However cation exchange sites may increase the availability of cations. High cation‐exchange capacity was indeed shown to favour fixation of aluminium over calcium ions and hence a low capacity is a prerequisite for taxa adapted to acid soils.
Proteolytic activity during senescence of plants
Authors: HUFFAKER R. C.
Published: April 2006

summary

Although information has rapidly developed concerning the intracellular localization of plant proteins, relatively few reports concern the intracellular location of endo‐ and exo‐proteolytic activities. Relatively few proteases have been purified, characterized, and associated with a specific cellular location. With the exception of the processing proteases involved in transport of proteins across membranes, little progress has yet been made concerning determination of in vivo products of specific proteases.

Information on the turnover of individual proteins and the assessment of rate‐limiting steps in pathways as proteins are turned over is steadily appearing. Since chloroplasts are the major site of both protein synthesis and, during senescence, degradation, it was important to show unambiguously that chloroplasts can degrade their own constituents. Another important contribution was to obtain evidence that the chloroplasts contain proteases capable of degrading their constituents. This work has been more tenuous because of the low activities found and the possibility of contamination by vacuolar enzymes during the isolation of organelles.

The possible targeting of cytoplasmic proteins for degradation by facilitating their transport into vacuoles is a field which hopefully will develop more rapidly in the future.

Information on targeting of proteins for degradation via the ubiquitin (Ub) degradation pathway is developing rapidly. Future research must determine how much unity exists across the different eukaryotic systems. At present, it has important implications for protein turnover in plants, since apparently Ub is involved in the degradation of phytochrome.

Little information has been developed regarding what triggers increased proteolysis with the onset of senescence, although it appears to involve protein synthesis. Thus far, the evidence indicates that the complement of proteases prior to senescence is sufficient to carry out the observed protein degradation. This field of study has great practical implications, e.g. maintaining photosynthesis during seed‐fill in order to obtain greater crop yields. The current use of ‘stay green’ variants in the populations of several crop plants to produce increased yields shows the potential for future development.

The near future should see exciting discoveries in these areas of research that will have far reaching effects on the construction of transgenic plants for future research accomplishments and agricultural use.

CONTENTS

Summary
200

I.
Introduction
200

II.
Protein turnover
201

III.
Proteases
201

IV.
Plant proteases
202

V.
Senescence
203

VI.
Proteolytic activity during senescence
205

VII.
Chloroplasts
207

VIII.
Proteolytic activities associated with chloroplasts
209

IX.
Proteolytic activities associated with stromal fractions
210

X.
Thylakoid proteins
211

XI.
Proteolytic activities associated with thylakoid fractions
214

XII.
Targeting proteins for degradation
215

References
223
Spectral properties and net photosynthesis of Aster tripolium L. and Halimione portulacoides (L.) Aellen leaves under saline and hypoxic conditions
Authors: LORENZEN BENT , SKOVHUS KARIN , JENSEN ARNE
Published: April 2006

summary

Spectral properties of leaves of Aster tripolium L. and Halimione portulacoides (L.) Aellen grown under saline and hypoxic conditions were studied in relation to the net photosynthesis (Pn) of the leaves. Cuttings of A. tripolium and of H. portulacoides were grown in aerated or nitrogen flushed nutrient solution under glasshouse conditions. During a 13 d period both Pn and the directional spectral reflectance and transmittance of the adaxial surface of marked leaves was recorded. At the end of the experiment the water content and total chlorophyll content of the leaves was determined. The chlorophyll content and Pn of the leaves were highly correlated. Between 56 and 67 % of the variation in Pn could be accounted for by changes in chlorophyll content. Light absorption by the plant pigment was negatively correlated to the reflectivity. More than 91 % of the variation in reflectivity could be accounted for by changes in absorption. However, Pn of the two species grown under saline and hypoxic conditions was poorly or not correlated to spectral reflectance (r2= 0.07–0.14), and only 12–14% of the variation in absorptance could be accounted for by changes in Pn. The low correlation between Pn and spectral properties may be due to asymptotic spectral characteristics when chlorophyll content exceeded 2 mg g−1 d. wt and to changes in respiration and stomatal conductance that may influence Pn independent of reflectance.
Rates of apoplastic diffusion in wheat leaves
Authors: CANNY M. J.
Published: April 2006

summary

Since the movement of water in leaves beyond the veins is not apoplastic, solutes excluded from the symplast move in the apoplast by diffusion. Estimates of the diffusivities (D) of sulphorhodamine G (SR) in the apoplast of wheat leaves are presented, measured by the analysis of advancing profiles of fluorescence of SR over a range of times from 7 to 90 min. The greatest values of D were found from vein sheaths, over the surface of fibre extensions where present, to and along the inner periclinal walls of the epidermises. The value along the lower epidermis (D = 8 × 1(T8 cm2 s1) was consistently twice that in the upper epidermis. SR diffused radially into the fibre walls of the vein extensions at a much lower rate (D= 10−10 cm2 s−1). At these rates the visible fluorescence occupied much of the apoplast between the veins after about 1 h. These findings suggest that useful generalizations may be gained from investigations of the spread of natural solutes of the transpiration stream in cell wall material.
Studies on the tolerance to sulphur dioxide of grass populations in polluted areas
Authors: WILSON G. B. , BELL J. N. B.
Published: April 2006

summary

Clones of Lolium perenne L., chosen as sensitive or tolerant to sulphur dioxide (SO2) injury, were employed in a half‐dialled crossing programme to carry out an analysis of the genetic basis of tolerance to acute SO2 concentrations. Their progeny were fumigated with SO2 and the percentage injury on the foliage scored and subjected to an analysis of variance designed to test an additive dominance model. The genetic analysis indicated that dominance was towards SO2 susceptibility. Further analysis of the relationship between variance and covariance of members of the same parental array supported this finding and suggested that only a few genes were involved. The results show clearly that the relative sensitivity of L. perenne to acute SO2 concentrations is heritable, with significant additive and non‐additive components. A comparison with the very limited number of other studies on the genetic basis of SO2 tolerance, suggests that it is highly variable between species.
Explant cultures of maize (Zea mays L.) raised under water‐deficit and waterlogged conditions
Authors: DHINGRA JYOTI H. R. , VARGHESE T. M.
Published: April 2006

summary

Root‐tip segments excised from plants grown under conditions of water deficit and waterlogging did not exhibit any significant change in the extent of callus induction over controls when cultured on Murashige and Skoog's (MS) medium supplemented with 2,4–D alone or in combination with L‐proline. On the other hand, the mesocotyls cultured on medium with 2,4–D showed an increase in the extent of callus induction which was further improved by the addition of L‐proline. The root tip callus from plants grown under water deficit conditions showed increases in both fresh and dry weight over controls on MS medium supplemented with 2 mg 1–1 2,4‐D while mesocotyl segments from plants grown in the presence of 5 % polythylene glycol‐6000 produced heavier calli on 2,4‐D supplemented media. The addition of L‐proline to the medium favoured an increase in both fresh and dry weights of root tip callus but failed to bring about a similar change in mesocotyl callus.

Waterlogging pre‐treatment resulted in an increase in fresh weight of root tip callus over control on 2,4‐D supplemented medium but not with the mesocotyl callus. Further, addition of proline to the medium enhanced both fresh and dry weights of root tip callus but did not affect the weights of the callus of mesocotyl origin. The pre‐conditioning treatment did not modify the regeneration potential of the explants. The biochemical basis of such a differential behaviour of the two explant types is discussed in the light of available information.
Nutrient supply, nutrient demand and plant response to mycorrhizal infection
Authors: KOIDE ROGER T.
Published: April 2006

summary

One of the most dramatic effects of infection by vesicular‐arbuscular mycorrhizal fungi on the physiology of the host plant is an increase in phosphorus absorption. When phosphorus is limiting, the maximum extent to which mycorrhizal infection can improve plant performance is thus predicted to be a function of the phosphorus deficit of the plant, the difference between phosphorus demand and phosphorus supply. Phosphorus demand is defined as the rate of phosphorus absorption that would result in optimum performance of the plant as measured by growth rate, reproduction or fitness. The phosphorus supply is defined as the actual rate of phosphorus absorption under the prevailing conditions. Variation among plant taxa in morphological, physiological or phenological traits which affect either phosphorus demand or phosphorus supply (and thus phosphorus deficit) is predicted to lead to variation in potential response to mycorrhizal infection. The actual response to mycorrhizal infection is predicted to be a function of the increase in phosphorus uptake due to mycorrhizal infection and the phosphorus utilization efficiency of the plant. Demonstrated variability in responsiveness to mycorrhizal infection among plant taxa suggests that mycorrhizal fungi may play an important role in determining the structure of plant communities.

Mycorrhizal infection may alter the phosphorus deficit or phosphorus utilization efficiency independently from its direct effect on phosphorus uptake, making the prediction of response to mycorrhizal infection based on the traits of non‐mycorrhizal plants quite difficult. For example, infection may at times increase the rate of phosphorus accumulation beyond that which can be currently utilized in growth, reducing the current phosphorus utilization efficiency. Such momentary ‘luxury consumption’ of phosphorus may, however, serve a storage function and be utilized subsequently, allowing mycorrhizal plants ultimately to outperform non‐mycorrhizal plants.

CONTENTS

Summary
365

I.
Introduction
366

II.
The concepts of phosphorus supply, phosphorus demand and phosphorus deficit
367

III.
Factors which affect phosphorus supply
369

IV.
Plant traits which affect phosphorus demand
370

V.
Variation in response to mycorrhizal infection
372

VI.
The effect of infection on inherent traits which influence phosphorus supply, phosphorus demand or phosphorus utilization efficiency
378

VII.
Mycorrhizal effects not related to phosphorus
380

VIII.
Conclusions
380

Acknowledgements
381

References
381
Selective interactions between different species of mycorrhizal fungi and Rhizobium meliloti strains, and their effects on growth, N2‐fixation (15N) and nutrition of Medicago sativa L.
Authors: AZCÓN R. , RUBIO R. , BAREA J. M.
Published: April 2006

summary

Three isolates of vesicular‐arbuscular (VA) mycorrhizal fungi, belonging to the species Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe, G. fasciculatum (Taxter sensu Gerd.) Gerd, and Trappe, and G. caledonium (Nicol. and Gerd.) Trappe and Gerd, were inoculated in dual combinations with six strains of Rhizobium meliloti with the aim of testing these combinations for functional compatibility with their common host plant, the legume Medicago sativa L. Symbiotic efficiency (promotion of plant growth and N and P nutrition) was found to be dependent on the particular combination of Rhizobium strain and Glomus species indicating selective and specific compatibilities between strains and isolates of the two types of microsymbiont, but also between them and the common host plant. Observed effects on plant growth were in general, though not always, related to the extent of VA mycorrhizal colonization. Although the different mycorrhizal and/or rhizobial treatments produced different effects on plant growth, the rate of nodule formation on M. sativa roots remained constant. Most mycorrhizal treatments increased the concentration and/or content of N in plant shoots but effectiveness was in the order: G. fasciculatum > G. mosseae > G. caledonium. In some cases, this increase in N‐content may be a consequence of a P‐mediated stimulation of N2‐fixation by VA mycorrhiza, as ascertained using 15N. In other instances, however, the increase seems to reflect a VA mycorrhizal‐mediated enhancement of N‐uptake from soil. VA mycorrhizal inoculation decreased the concentration of Ca and Mg in plant shoots and a buffering effect of VA mycorrhiza in situations of nutrient excess in soil is proposed.
Carbohydrate transport in discs of storage parenchyma of celery petioles
Authors: DIETTRICH BEATE , KELLER FELIX
Published: April 2006

summary

Petioles of celery leaves function successively as net importing (sink) and net exporting (source) organs during ontogeny. The parenchyma of these petioles is the main store for large amounts of D‐glucose, D‐fructose and mannitol. The mechanism of uptake of glucose and fructose into discs isolated from storage parenchyma of celery petioles was investigated. Uptake kinetics showed a biphasic response to increasing concentrations for both hexoses with a saturable component at low concentrations and a non‐saturable, linear, diffusion‐like component at higher concentrations (at least up to 16 mM). The apparent Kns‐values were an order of magnitude higher for fructose (2–3 mM) than for glucose (034 RIM) uptake. The saturable components of uptake of the two hexoses were inhibited similarly by the SH‐reagents PCMBS and NEM, the uncouplers CCCP and DNP, the ATPase inhibitor DES and the hydrophobic reagents phloretin and phlorizin. They were stimulated by the plasmalemma H+‐ATPase stimulator FC and showed a broad pH‐optimum around pH 6. Competition studies revealed that glucose uptake was very specific whereas fructose uptake was inhibited by D‐glucose, L‐sorbose and D‐tagatose. The saturable components of uptake of both hexoses were clearly turgor‐dependent. Lowering of cell turgor resulted in a linear increase of Vmax and a constant Km.

It is concluded that the saturable components of glucose and fructose uptake are of a similar, active, sugar‐proton cotransport type with carriers containing SH‐groups and interacting hydrophobically. It is suggested that two different hexose carriers might be operative, one for glucose only and one for both glucose and fructose.
Carbohydrate transport in discs of storage parenchyma of celery petioles
Authors: KELLER FELIX
Published: April 2006

summary

The sugar alcohol mannitol is, together with glucose and fructose, the main soluble carbohydrate of celery petioles. It is accumulated in the storage parenchyma of mature petioles and remobilized during senescence. The mechanisms of mannitol uptake into discs isolated from petiole parenchyma was studied. Uptake kinetics showed a biphasic response to increasing external concentrations of [14C]D‐mannitol with a predominant saturable component at low concentrations (below about 2 mM) and a linear component at higher concentrations (at least up to 16 mM). The saturable component showed an apparent Km of about 1 mM and a fairly sharp pH optimum around pH 6–5. It was stimulated by the plasmalemma H+‐ATPase stimulator FC and inhibited by the SH‐reagents PCMBS and NEM and the uncoupler DNP. CCCP was also inhibitory, but its effect could be reversed by DTT, suggesting a dual role of CCCP as SH‐reagent and uncoupler in this tissue. Competition studies with 14‐different polyols and sugars showed that uptake was very specific. The saturable uptake component was clearly turgor‐dependent. Lowering of cell turgor by treatment of increasing concentrations of the relatively nonpermeant glycinebetaine (0 to 0.8 M) resulted in a linear increase of Vmax and an unaltered Km.

It is concluded that celery petiole parenchyma contains at least a mannitol carrier at the plasmalemma which operates in an active proton‐cotransport manner. It is speculated that a superimposed mannitol carrier is present at the tonoplast and might operate by facilitated diffusion.