bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of some triazole fungicides on intracellular pH and on cell membrane permeability in leaves of Elodea densa (Planch.) Casp.*
Authors: ROMANI G. , BEFFAGNA N.
Published: April 2006

summary

Recent data obtained in this laboratory have shown that a number of triazole fungicides induce in leaves of barley and Elodea densa an early release of solutes and an inhibition of H+ extrusion. This paper deals with the early effects of two triazoles, penconazole and flusilazol, on intracellular pH and plasmamembrane permeability in Elodea densa leaves.

Different effects were found at low (0.1–0.15 mM) or at high (0.3–0.5 mM) triazole concentrations. At the low concentrations the triazoles induced a marked intracellular acidification (corresponding to an acidification of both the cytosol and the vacuole) as evaluated by the weak acid and weak base distribution method. For higher triazole concentrations (0.3–0.5 mM) the intracellular pH became very close to that of the external medium (pH 5.5), and cytosolic and vacuolar pH measurements became unreliable. Triazoles at concentrations higher than 0.1–0.15 mM induced an early and very marked increase in net efflux of K+ and Cl−. At these ‘toxic’ concentrations the sorbitol‐permeable space (apparent free space) was increased from about 20% to more than 90%. These results suggest that triazoles at low ‘sub‐toxic’ concentrations inhibit some mechanism involved in the regulation of intracellular pH (possibly the plasmalemma proton pump), whilst at higher concentrations they induce a non‐specific increase in passive permeability of the plasmamembrane.
Arsenic, cobalt and nickel tolerances in two populations of Silene vulgaris (Moench) Garcke from Ontario, Canada
Authors: PALIOURIS GEORGIA , HUTCHINSON THOMAS C.
Published: April 2006

summary

A population of Silene vulgaris (Moench) Garcke collected from mine tailings near the town of Cobalt, Ontario was compared in its metal tolerance with a population collected at an uncontaminated site (Baymouth, Ontario). Seedlings of the Cobalt population were tolerant to elevated levels of arsenic, cobalt and nickel, both compared with the Baymouth population and with other literature reports for this species. However, the tolerance indices in the Cobalt plants for these toxic elements did not correlate well with their concentration in water extractions in the mine soils.

Indices of arsenic tolerance, based on the inhibition of root growth in 12 d experiments, showed a similar response to that in a 28 d experiment for both populations. The latter however, appeared to be a more accurate indicator of As tolerance in S. vulgaris, because the longer‐term tolerance indices had lower standard deviations and higher probabilities for tolerance than the short‐term tolerance indices. Reduced uptake of As occurred in the roots of tolerant individuals compared with non‐tolerant individuals at a low As treatment. At a higher arsenic exposure, however, arsenic entered the roots of tolerant individuals. A partial exclusion or reduced translocation of arsenic to the shoots then appeared to operate in the shoots of tolerant individuals, i.e. arsenic levels were higher in shoots of non‐tolerant plants. At the highest arsenic exposure, where the individuals from the Cobalt population were no longer tolerant, this exclusion pattern broke down. From a preliminary selection experiment, some arsenic tolerant individuals occurred in the Baymouth population. This suggests that under circumstances of arsenic contamination this population also has the potential to develop a tolerance to high arsenic exposure.
Responses of growth, photosynthesis, and leaf conductance to white light irradiance and end‐of‐day red and far‐red pulses in Fuchsia magellanica Lam.
Authors: APHALO P.J. , GIBSON D. , Di BENEDETTO A. H.
Published: April 2006

summary

The response of Fuchsia magellanica Lam. – a shade‐tolerant perennial – to white light photon flux density and end‐of‐day red and far‐red light irradiation was studied to evaluate the role that different morphological and functional alterations play in whole‐plant acclimation to shade. The estimated relative growth rate of plants growing under a photon flux density of 30μmol m2 s1 was 71 % of that of those growing under 450μmol m−2 s−1. The proportion of total dry weight allocated to shoots was higher in low light plants, but the proportion of shoot dry weight allocated to leaf blades was not affected by any of the treatments. The estimated relative growth rate, specific leaf area and leaf conductance were not affected by end‐of‐day irradiation. In low light plants the specific leaf area was higher, and at saturating photon flux density photosynthesis was lower on a leaf area basis, but was not on a leaf dry weight basis. Dark respiration was higher in high light plants when expressed on an area basis, but not when expressed on a dry weight basis. During the normal photoperiod, leaf conductance measured in darkness was higher in high light plants than in low light ones, which is consistent with the higher stomatal density observed in these plants. The cross‐sectional area of the petioles was slightly reduced in low light in spite of a large increase in the area of individual leaves. Low irradiance affected the display of leaves, decreased leaf thickness and increased chlorophyll content per unit dry weight. End‐of‐day far‐red resulted in plants with more erect branches. Both low photon flux density and far‐red enhanced internode elongation. The effect of end‐of‐day irradiations was bigger in low light than in high light, which is the opposite to what is observed in shade‐avoiders. The relatively small difference in mean growth rate can be explained by changes in specific leaf area, shoot: root dry weight partition ratio, and by the shape of the photosynthetic light response curve. However when comparing photosynthetic rates on a dry weight basis low light plants do not seem to be at a disadvantage under high light.
Relationship of nutrients in water with biomass and nutrient accumulation of submerged macrophytes of a tropical wetland
Authors: SHARDENDU  , AMBASHT R. S.
Published: April 2006

summary

The paper describes monthly biomass, seasonal and annual net primary productivity and monthly and seasonal nutrient content of four submerged macrophytes in a lentic wetland situated in the campus of Banaras Hindu University. The seasonal variation of six nutrients (NO3 ‐N, PO4‐P, K, Ca, Mg, Na) in water is described and their mean concentrations used in multiple regression equations to examine the relationship between nutrients in water, plant biomass and nutrient accumulation in plant body. Hydrilla verticillata (L.f.) Royle, Potamogeton crispus L., P. pectinatus L. and Aponogeton natans (L.) Engle and Krause are the constituent species. Plants show rapid growth in post‐monsoon and pre‐winter months. All the four species showed biomass accumulation in the rainy season. The highest rate of production in the submerged zone was 0.73 g m−2 d−1 and the minimum was 0.29 g m−2 d−1. Maximum annual production of any species was 69 g m−2 in P. pectinatus. In all the four species the nutrient concentration decreased in the following order: calcium > nitrogen > potassium > magnesium > sodium > phosphorus. Seasonal variation of nutrient content was dependent on the period of germination, growth and development of the species. Nitrogen, phosphorus and potassium were higher in the season of growth of particular species and calcium was higher when plants matured. There was no definite trend for sodium, though magnesium varied with species. Uptake and accumulation of nutrients in submerged plants largely depend upon nutrient concentration of water, except nitrogen which was also dependent on biomas change. Sources of nutrient for plants are both sediment and water. Translocation of potassium from the overlying water to the mud by Hydrilla plants is possible as there is reduction in potassium concentration of water around Hydrilla.
Architectural analysis of plant root systems 2. Influence of nutrient supply on architecture in contrasting plant species
Authors: FITTER A. H. , STICKLAND T. R.
Published: April 2006

summary

Two components of root architecture (topology and link lengths) were measured in a group of 13 dicotyledon and eight grass species, under both high and low nutrient supply rates. Predictions were made, based on a simulation analysis, that root systems from plants grown in low nutrient conditions and those from plants characteristic of such conditions should have the more herringbone topology (branching principally on main axis) and longer links. Both these predictions were confirmed for the dicots, but data from grasses agreed with the predictions only in terms of geometry (link lengths) and not topology. The ecological character of the species was assessed on the assumption that species of low inherent relative growth rate were characteristic of infertile soils, Taxonomic patterns were also evident, indicating that some variation in root system architecture may be historical rather than adaptive.
Relationship between root cortical senescence and growth of wheat as influenced by mineral nutrition, Idriella bolleyi (Sprague) von Arx and pruning of leaves
Authors: LASCARIS D. , DEACON J. W.
Published: April 2006

summary

Severe deficiencies of nitrogen or calcium enhanced the rate of root cortical death (RCD) when wheat seedlings were grown in perlite in a glasshouse; less severe deficiencies had no effect on RCD even though they significantly reduced both root and shoot growth. Heavy pruning of leaves curtailed root growth but did not affect the rate of RCD in the presence or absence of the weakly pathogenic fungus, Idriella bolleyt (Sprague) von Arx. The results suggest that RCD is less responsive to environmental manipulations than is seedling growth, so RCD is unlikely to be part of a stress‐response mechanism in cereals whereby assimilates or mineral nutrients are mobilized or remobilized to growing tissues.
Effects of air pollution and water stress on leaf blight and twig cankers of London planes [Platanus×acerifolia (Ait.) Willd.] caused by Apiognomonia veneta (Sacc. & Speg.) Höhn.
Authors: VON SURY ROMAN , FLÜCKIGER WALTER
Published: April 2006

summary

Potted 2‐year‐old cuttings of London plane trees [Platanus×acerifolia (Ait.) Willd.] were raised under well‐watered (WW) or water stress (WS) conditions in two semi‐open‐top chambers and fumigated with ambient air (AA) and filtered air (FA). In the FA chamber, charcoal and Reox‐Purafil† filters removed 65–100% of O3, 50–90% of NOx, and 80–95 % of SO2.

After leaf inoculations in spring with conidia of Apiognomonia veneta (Sacc. & Speg.) Höhn., significantly fewer and smaller lesions appeared on AA than on FA trees. The WS treatment led to an additional, highly significant suppression of leaf blight. In winter, WW trees inoculated with mycelium of A. veneta developed significantly larger cankers in the AA than in the FA chamber. Under WS conditions, canker formation was somewhat reduced in AA and was similar in both chambers. The production of Apiognomonia conidia on necrotic bark in spring, however, was stimulated by the WS treatment, whereas no differences in conidiation were found between AA and FA. Germination and growth of A. veneta in vitro were both significantly suppressed in the AA chamber compared with the FA. In the laboratory, 50 nl O3/l significantly reduced the germination of A. veneta but the addition of an equal concentration of NO2 (up to 100 nl/l) had no effect. After one year of exposure, initial shoot growth of WW London planes was significantly inhibited under AA conditions and a delay of bud burst was also observed. It is concluded that the longer duration of tree dormancy in AA positively affected the development of Apiognomonia cankers.

We suggest that ambient air pollutants suppressed leaf blight through a direct effect on the germinating conidia of A. veneta but that the enhancement of twig canker formation was rather due to effects on the host tree.
Short term effects of bisulphite on pollution‐tolerant and pollution sensitive populations of Sphagnum cuspidatum Ehrh. (ex. Hoffm.)
Authors: BAXTER R. , EMES M. J. , LEE J. A.
Published: April 2006

summary

Moss tissue from two distinct populations of Sphagnum cuspidatum from N, Wales (‘unpolluted’) and the S. Pennines (‘polluted’) was exposed to 0.2 mM HSO3− over a 24–26 h period. The rates of HSO2−, disappearance in the bathing solution were monitored in conjunction with tissue dark respiration, net photosynthetic rate and chlorophyll a fluorescence induction kinetics. Slow disappearance of HSO3− in the presence of moss tissue from N. Wales (40% of initial concentration remaining after 24 h) resulted in a rapid (< 2 h) loss of photosynthetic oxygen evolution, and a gradual marked decline in tissue dark respiration and chlorophyll fluorescence quenching. In the S. Pennine tissue, rapid HSO3− disappearance in the growth medium (complete after < 4 h) resulted in a marked recovery of photosynthetic and respiratory pathways after the initial inhibitory effects of HSO3− on these processes. Pretreating S. Pennine moss tissue with EDTA prior to exposure increased HSO3− residence time with consequent rapid decline in net photosynthetic rate, rendering the response of the moss similar to that from N. Wales (‘unpolluted’ site).

In a second experiment, identical moss samples from the two study sites were exposed to 0.2 mM HSO3− for a period of 24 d. One set of plants from each population was prewashed in 5mM EDTA to remove extracellularly‐bound cations prior to HSO3− exposure. Growth decrease was greater in the unpretreated moss N. Wales (74% with respect to tissue not exposed to HSO3−) than that from the S. Pennines (45.5%). After 10 days the pigments of the former were visibly bleached. No bleaching was observed in the latter.

In the moss from N. Wales, removal of the extracellular cations with EDTA only slightly enhanced the effect of HSO3− on growth, whilst in the S. Pennine plants EDTA pretreatment resulted in a further growth reduction of 13%.

The differential response of the moss from the two sites is discussed as a function of the extracellular transition metal concentration (Notably Fe) associated with the plants.
Seasonal variations in acidic pollutant inputs and their effects on the chemistry of stemflow, bark and epiphyte tissues in three oak* woodlands in N.W. Britain
Authors: FARMER A. M. , BATES J. W. , BELL J. N. B.
Published: April 2006

summary

Rainfall, throughfall and stemflow chemistry, bark chemistry and gaseous air pollutant levels were monitored for one year within three Quercus petraea (Mattuschka) Liebl. woodlands in north west Britain. Tissue chemistry of the epiphytic lichen Lobaria pulmonaria (L.) Hoffm. and the moss Isothecium myosuroides Brid. were also studied at the sites in which they were abundant. The sites were found to differ in the levels of acidic and nutrient inputs, bark chemistry and levels of gaseous pollutants, although the latter were low at all the sites. The epiphyte tissue chemistry responded to changes in stemflow chemistry across the season. At Borrowdale, Cumbria, where acid sensitive lichens have declined, stemflow was always of a low pH (3.5–4.5) and low nutrient content. The tissues of I. myosuroides at this site had low concentrations of nutrient cations, but a high nitrogen content, possibly due to a high nitrate input in the rainfall. It is concluded that acid precipitation will affect epiphytes by reducing the bark's buffering capacity and increasing its acidity. The extent to which this occurs will depend on tree species, soil chemistry and the nature of the atmospheric inputs. This is discussed in the context of the concept of critical loads for acidifying deposition.
Effects of phosphate supply on the phosphorus status, dry mass and photosynthesis of wheat infected with powdery mildew
Authors: ZULU J. N. , FARRAR J. F. , WHITBREAD R.
Published: April 2006

summary

Wheat grown hydroponically on three concentrations of inorganic phosphate (0, 0.33 and 3.30 mol m−3 P1) was infected with Erysiphe graminis when 12 d old. Large differences in P status, but small differences in growth due to Pi supply, were seen in uninfected controls 5 and 8 d later. Mildew, did not alter the P content of any part of the plants, but did increase the rate of respiration of infected leaves. Whilst mildew reduced the photosynthetic rate of leaves on plants grown at high Pi concentrations to about 50% of non‐infected controls, an interaction between the effects of mildew and Pi concentration resulted in a fall of photosynthesis to very low rates in plants grown on zero Pi.
Soil mediated effects of phosphorus supply on the formation of mycorrhizas byScutellispora calospora(Nicol. & Gerd.) Walker & Sanders on subterranean clover
Authors: THOMSON B. D. , ROBSON A. D. , ABBOTT L. K.
Published: April 2006

summary

A split‐root technique was used to separate plant and soil mediated effects of phosphorus (P) supply on the formation of mycorrhizas byScutellispora calospora(Nicol. & Gerd.) Walker & Sanders on subterranean clover (Trifolium subterraneumL.). There were 10 split‐root treatments, incorporating four concentrations of P (0, 18, 105 and 280 μg P g−1soil) ranging from severely deficient for plant growth to luxurious. Increasing the supply of P to plants decreased the percentage of root length infected and the total length of roots infected byS. calospora.Applications of 18 and 105 μg P g−1soil to half of the root system of plants reduced the percentage of root length infected in that half of the root system and in the other half of the root system to the same extent. The effects of severely deficient and moderately deficient rates of P on infection byS. calosporawere therefore mediated through the plant. These effects could be related directly to effects of P supply in decreasing the concentrations of soluble carbohydrates in roots because carbohydrate concentrations in roots did not differ between each half of the root system. In contrast to the concentrations of soluble carbohydrates in roots, the length of roots and the concentrations of P in roots were generally greater in the half of the root system that received the highest application of P. Applications of 280 μg p g−1soil to half of the root system of plants also reduced the percentage of root length infected byS. calosporain both halves of the root system but to a greater extent in the half that received 280 μg P g−1soil. This effect was associated with greater length of roots, higher concentrations of P in roots and higher concentrations of P in the soil in the half of the root system that received 280 μg P g−1soil. We concluded that the effects of luxury amounts of P on infection byS. calosporacould be mediated through the soil.
The effect of soil disturbance on vesicular—arbuscular mycorrhizal fungi in soils from different vegetation types
Authors: JASPER D. A. , ABBOTT L. K. , ROBSON A. D.
Published: April 2006

summary

The infectivity of vesicular–arbuscular (VA) mycorrhizal fungi in three soils from different vegetation types was compared before and after disturbance. The relative quantities of infective propagules in the disturbed soils were estimated by an infectivity test after the soils were diluted. Spare numbers and mycorrhizal roots were also quantified in each soil.

The mycorrhizal colonization of clover roots in the infectivity st was not decreased after soil from an annual pasture had been disturbed. In contrast, in both a forest soil and a heathland soil, the percentage root length colonized of test plants was almost halved if the soils had been disturhtd. In the pasture soil up to 10 times or 25 times more propaguies survived disturbance than in the forest soil or the heathland soil respectively. The large number of propaguies may allow the VA mycorrhizal fungi in the pasture soil to maintain maximum infectivity after soil disturbance.
Colonization of wheat Triticum vulgare L.) by N2‐fixing cyanobacteria: I. A survey of soil cyanobacterial isolates forming associations with roots
Authors: GANTAR M. , KERBY N. W. , ROWELL P. , OBREHT Z.
Published: April 2006

summary

A variety of heterocystous, N2‐fixing cyanobacteria, isolated from soils, were identified as members of the genera Nostoc, Anabaena and Cylindrospermum. These isolates were tested for their ability to form associations with the roots of wheat seedlings grown in liquid culture. Two types of associations were recognized: loose associations with cyanobacterial filaments growing between root hairs, which were typical of the Anabaena isolates, and tight associations of microcolonies in intimate association with the root surface, which were restricted to certain Nostoc isolates. Differences in nitrogenase activities of the free‐living and associated cyanobacteria, together with the effects of added nitrate, indicate that nitrogenase activity may be influenced by the plant and/or its products.
Evolution of resistance to fungal parasitism in natural ecosystems
Authors: HEATH MICHELE C.
Published: April 2006

summary

It is argued that the resistance of non‐host plants to plant parasitic fungi is the result of parasite‐non‐specific basic resistance rather than the consequence of specific recognition of each fungal parasite. In crop plants, and probably wild plant species, this basic resistance in maintained by a mixture of passive and active defenses that exhibit inter‐, and possibly intra‐, specific differences. Many, if not all, of the components of basic resistance not only defend the plant against stresses in addition to those exerted by plant parasitic fungi, but also have other roles in plant structure and function. Therefore, these components may be subject to random effects and multiple selection pressures of which fungal parasitism may be a minor component. Nevertheless, the coupling of the recognition of fungal products or activities with the inducible components of basic resistance seems to have occurred early in plant evolution, although not necessarily in response to selective pressures exerted by ancient fungi.

It is suggested that in natural ecosystems, parasite‐specific resistance should have no selective advantage until the fungus has established sufficient basic compatibility (by means of specific pathogenicity factors) with its host species that the plant's fitness is reduced. This resistance may not necessarily be the result of‘gene‐for‐gene1interactions, and may be difficult to distinguish from pathovar‐specific, ‘residual’ basic resistance resulting from fungal genotypes differing in their complement of pathogenicity factors such that each one is able to completely overcome the basic resistance of only some genotypes of the host. Superimposed on any co‐evolutionary changes in plant and fungus are longer‐term changes in basic resistance that may eventually change a susceptible host into a non‐host if the fungus cannot produce the necessary new or modified pathogenicity factors. Major determinants of the evolutionary paths followed by any interacting plant and fungus are the actual mechanisms of plant resistance and fungal pathogenicity or virulence. Therefore, the complex web of interactions that exists today reflects the evolutionary path that each organism has followed as well as more recent selective pressures on the interactions themselves.

CONTENTS

Summary
331

I.
Introduction
331

II.
Basic premises
332

III.
Mechanisms and evolution of basic resistance
332

IV.
Parasite‐specific resistance
336

V.
Induced resistance
341

VI.
Conclusions
341

Acknowledgements
342

References
342
Short‐term competition for phosphate between two genotypes of Arabidopsis thaliana (L.) Heynh.
Authors: KRANNITZ P. G. , AARSSEN L. W. , LEFEBVRE D. D.
Published: April 2006

summary

Seedlings from two genotypes of Arabidopsis thaliana (L.) Heynh. that had similar uptake kinetics for inorganic phosphate (P1), but differed in the levels to which they could deplete P, from solution (different Cmin values), were placed together for 21 h in the absence of exogenous P1 to determine the effect of differences in Cmin on short‐term competition for P1, as reflected by the movement of the phosphate isotope, 32P. P1‐starved seedlings were grown at two photon flux densities (30 and 90 μmol−2 S−l). Genotype LC (with the lower Cmin) was better able to deplete a 2.5 μM P1 solution than genotype HC. We predicted that when placed together in a P1‐free solution, the Cmindifferences between the genotypes would result in a continual transfer of P1 from genotype HC to LC. This did not occur, since genotypes LC and HC did not differ in the proportion of 32P obtained from labelled HC seedlings. However, LC obtained 1.3 times more 32P from HC than HC obtained from LC, for seedlings grown at both the lower (P < 0.05) and the higher (P < 0.001) photon flux densities.

Differences in Cmin between the genotypes were more pronounced for seedlings grown at the higher photon flux density. Here, genotype LC obtained significantly more 32P from genotype HC than it did from seedlings of its own genotype (P < 0.001). Genotype HC obtained less 32P from seedlings LC than it did from those of its own genotype, for seedlings grown at both photon flux densities (P < 0.001).
Phosphorus depletion and pH decrease at the root–soil and hyphae–soil interfaces of VA mycorrhizal white clover fertilized with ammonium
Authors: LI XIAO‐LIN , GEORGE ECKHARD , MARSCHNER HORST
Published: April 2006

summary

To study phosphorus (P) depletion and soil pH changes at the root–soil interface (rhizosphere) and at the hyphaesoil interface, mycorrhizal and non‐mycorrhizal white clover (Trifolium repensL.) plants were grown for 7 wk in two sterilized soils (Luvisol and Cambisol) in pots comprising five compartments: a central one for root growth, two adjacent compartments, separated from the central compartment by a nylon net of 30 μm mesh size, for growth of vesicular‐arbuscular (VA) mycorrhizal [Glomus mosseae(Nicol. & Gerd.) Gerdemann & Trappe] hyphae (hyphal compartments), and two outer compartments, separated from the hyphal compartments by a 0.45 μm membrane, which neither roots nor hyphae could penetrate (bulk soil compartments). Phosphorus was supplied as Ca(H2PO4)2at a rate of 50 mg P kg−1soil in the root compartment and 150 mg P kg−1soil in the hyphal and bulk soil compartments. Nitrogen was supplied as (NH4)2SO4at the rate of 300 mg N kg−1soil uniformly to all compartments.

In both soils, shoot dry weight and P uptake were much higher in mycorrhizal plants compared with non‐mycorrhizal plants. Hyphae of VA mycorrhizal fungi contributed 70% (Cambisol) or 80% (Luvisol) to total P uptake of mycorrhizal plants. In the hyphal compartments, concentrations of both H2O‐extractable soil P (Cambisol and Luvisol) and NaHCO3‐extractable soil P (Luvisol) were decreased drastically. Soil P depletion profiles developed not only at the root‐soil interface (rhizosphere), but also at the hyphae‐soil interface and extended several millimetres from the hyphae surface into the soil. Likewise, the soil pH was decreased at the root‐soil interface, in the hyphal compartment and also at the hyphae‐soil interface.

The results demonstrate that, similarly to roots, hyphae of VA mycorrhizal fungi have the ability to form a P depletion zone and a zone of altered pH in the adjacent soil. Thus, as well as at the root‐soil interface, soil conditions at the hyphae–soil interface may also differ considerably from conditions in the bulk soil.
Effects of excess nitrogen on carbohydrate concentration and mycorrhizal development of Pinus sylvestris L. seedlings
Authors: WALLANDER HÅKAN , NYLUND JAN‐ERIK
Published: April 2006

summary

The interaction of nitrogen supply, carbohydrate availability and ectomycorrhiza has been the subject of several studies and has been interpreted as the regulatory mechanism of the symbiosis. Only a few studies have simultaneously examined the effect of external nitrogen supply on the internal concentration of N, the internal sugar pool and, in a quantitative way, the extent of mycorrhizal colonization. The latter has usually been estimated with low accuracy through root tip counting only.

Using ergosterol as a quantitative descriptor of fungal biomass, several of the basic assumptions of the carbohydrate theory have been re examined in a semi‐hydroponic cultivation system, where Scots pine seedlings mycorrhizal with Laccaria bicolor (Maire) Orton were grown at an approximately constant relative growth rate on a nutrition regime based on a balanced basic medium supplemented with excess ammonium or nitrate. Mycorrhizal biomass was strongly correlated with the shoot nitrogen. High nitrogen availability did not significantly affect internal sugar concentrations. The development of mycorrhiza significantly reduced sugar concentrations in both roots and shoots. The difference between ammonium and nitrate in reducing mycorrhizal development was due to differences in uptake alone. The findings tend to invalidate a basic assumption of the carbohydrate theory, that of high nitrogen availability leading to reduced sugar concentration, the latter limiting mycorrhizal development. The results also conflict with the view that the host's sugar concentration is elevated in the presence of mycorrhiza.
Nitrate reduction in seedlings of carob (Ceratonia siliqua L.)
Authors: CRUZ C. M. , SOARES M. I. M. , MARTINS‐LOUÇÃO M. A. , LIPS S. H.
Published: April 2006

summary

The distribution of nitrate reduction in young carob plants (Ceratonia siliquaL. cv. Mulata) was studied. Plants (three months old) were grown in aerated nutrient solutions under greenhouse conditions. Reduction of nitrate was estimated both in the leaves and in the roots by: (a) accumulation of nitritein vitro, (b) accumulation of nitritein vivoand (c) disappearance of nitratein vivo.Disappearance of nitratein vivooffered the closest estimation of the rate of nitrate reduction.

Leaves consistently showed rates of nitrate reduction lower than those in roots, regardless of assay method. Lowering root temperature had no marked effect on the distribution of nitrate reductase activity in the plant; increasing nitrate concentration in the shoot, however, markedly increased leaf nitrate reduction. The relatively low level of nitrate reductase in leaves appears to be caused mainly by a limitation of nitrate transport from root to shoot. Nitrate reduction takes place in both the root and the shoot of young carob plants with the shoot accounting for approximately 20% of total nitrate reduction in the plant.
Natural tolerance of cyanobacteria to the herbicide glyphosate
Authors: POWELL H. A. , KERBBY N. W. , ROWELL P.
Published: April 2006

summary

Synechocystis PCC 6803 and Anabaena variabilis ATCC 29413 showed a high degree of tolerance to the herbicide glyphosate, applied as the free acid, the monoisopropylamine salt or the commercial formulation (Roundup > R). Differential toxicity between herbicide formulations was observed (Roundup > isopropylamine salt > free acid) and correlated with their rates of uptake. There was no evidence of glyphosate degradation. Shikimate accumulation, together with partial alleviation of inhibition by aromatic amino acids, suggests that the target site for glyphosate is in the pathway of aromatic amino acid biosynthesis.
Secondary embryogenesis from thin cell layers of Brassica napus ssp. oleifera
Authors: SHU W. , LOH C. S.
Published: April 2006

summary

Thin cell layers approximately 1 × 8 mm in size were excised from secondary embryoids of Brassica napus ssp. oieifera cv. Primor. Further secondary embryogenesis was observed in about 35% of the thin cell layers cultured on a medium without the addition of plant growth regulators. In one experiment using 168 thin cell layers, the explants showing embryogenesis produced an average of 23 embryoids per explant. Secondary embryogenesis was found to be inhibited with the addition of high concentrations of auxin or cytokinin to the culture medium. Callus, root, shoot, and leafy structures were obtained depending on the type and concentration of auxin and cytokinin used. The embryoids from thin cell layers were capable of producing further secondary embryoids.
The interpretation of in vitro measurements of fructosyl transferase activity: an analysis of patterns of fructosyl transfer by fungal invertase
Authors: CAIRNS ANDREW J. , ASHTON JENNIFER E.
Published: April 2006

summary

A commercially available invertase preparation from yeast was analysed by native gel electrophoresis and shown to contain the large and small forms of yeast invertase but no specific fructosyl transferase. Both invertase isoforms catalysed the synthesis of the trisaccharides isokestose, neokestose and kestose from 600 mol m−3 sucrose at pH 5.

The hydrolytic and fructosyl transferase properties of the unfractionated invertase preparation were analysed under conditions similar to those used for the analysis of sucrose : sucrose fructosyl transferase (SST) from grasses. The sucrose concentration kinetics of the transferase gave a Km of between 224–308 mol m−33 which is similar to that reported for SST from graminaceous and other plant species. The sucrose Km of the hydrolase was estimated at between 11–34 mol m−3.

The transferase and hydrolase activities of yeast invertase could be distinguished on the basis of their responses to reaction temperature and pH, and in these respects, the data reproduced the results of grass SST studies. These observed differences in properties can be explained in terms of changes in reaction sucrose concentration and the differential kinetic properties of the hydrolase and transferase activities.

The two activities could not be distinguished on the basis of their temperature‐stability characteristics or their responses to pyridoxal HCI. Pyridoxal HCI was shown to cause acidification of enzyme reactions and the direct effects of this compound on the transferase and hydrolase activities were thus difficult to interpret.

The results are discussed with respect to the evidence for separate SST and invertase activities in mixed enzyme systems derived from grass tissues.
On the relationship between specific root length and the rate of root proliferation: a field study using citrus rootstocks
Authors: EISSENSTAT DAVID M.
Published: April 2006

summary

This study tested two hypotheses: (1) species with roots that have a high length to dry mass ratio or specific root length (SRL) also have the potential for high rates of root growth in small volumes of favourable soil and (2) variation in average root diameter fully accounts for variation in SRL. To minimize differences among shoots, the study used 13‐year‐old ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] trees budded to rootstocks representing a range of genotypes. Soil cores 7.4 cm in diameter and 14.2 cm deep were extracted from beneath the canopy, and the soil was sieved free of roots and replaced. Root length, diameter and dry weight of the roots in the disturbed soil and adjacent undisturbed soil were evaluated 5, 10, 19 and 40 weeks following soil replacement. The disturbed soil had a higher water content than the undisturbed soil for the first three sampling dates. Averaged across rootstocks, root length density increased in a linear fashion in the disturbed soil and was comparable to that in the undisturbed soil by 40 weeks. Mean root diameter of the fibrous roots (< 2 mm) declined with age. Rootstocks with the highest SRL had the most rapid rate of root proliferation (cm cm−3 wk−1) (r= 0.94) and the greatest rate of water extraction at 19 weeks (r= 0.79). Although variation in root diameter contributed to rootstock variation in SRL, the data also suggested that rootstocks of high SRL had roots with lower tissue density than those of low SRL (P < 0.05). The potential trade‐offs of constructing root systems of high SRL are discussed.
Magnesium requirements of subterranean clover (Trifolium subterraneum L.) either reliant on symbiotic nitrogen fixation or supplied with nitrate
Authors: SCOTT B. J. , ROBSON A. D.
Published: April 2006

summary

Subterranean clover was grown in solution culture with Mg supplied at 0, 10, 20, 30, 40, or 80 μM in factorial combination with nitrogen (N), supplied either symbiotically or as calcium nitrate (500 μM). External requirements for Mg, as assessed by the concentration in the medium required for maximum growth, were similar for plants irrespective of N source and were in the range 21 to 24 μM. Similarly, internal requirement was assessed by the critical concentration of Mg in whole shoots at 1100μg g−1 and there was no difference between plants reliant on symbiotic N2−fixation and those supplied with Ca(NO3)2. However, because of the effects of added Ca(NO3)2 on the distribution of Mg within plants, a higher minimum concentration of Mg in the youngest open leaf (YOL) was required for uninhibited growth by plants reliant on N2 fixation.

The concentration of N in shoots increased with increasing Mg in solution and Mg‐deficient plants contained a lower proportion of total shoot N as protein. This occurred both in plants reliant on N2 fixation or supplied with nitrate. Thus Mg appeared to be required in greater amounts for protein synthesis than for either nodule formation or N2‐fixation.
Stimulation of vesicular‐arbuscular mycorrhiza formation and growth of white clover by flavonoid compounds
Authors: SIQUEIRA J. O. , SAFIR G. R. , NAIR M. G.
Published: April 2006

summary

The effects of flavonoid compounds on VA mycorrhiza root colonization and growth of white clover (Trifolium repens L.) plants under growth chamber conditions are reported. The isoflavonoids, formononetin and biochanin A, previously identified from clover roots, stimulated colonization and growth of clover, while several other flavonoid compounds were inactive when tested at concentrations of 5 mg 1−1. The flavone, chrysin, when applied at concentrations higher than those tested for formononetin and biochanin A, also increased root colonization and plant growth. The stimulatory effects of the isoflavonoids on plant growth were mediated by VA mycorrhizal fungi and were dependent on concentration, period of growth and soil spore density. Maximum responses were found when 5 mg 1−1 solutions were applied to soil containing 2 to 4 VA mycorrhiza spores g−1 of soil. These results may provide insights on the molecular mechanisms of host‐fungus interaction and for the development of technology to exploit the potential of the indigenous VA mycorrhizal fungi in field soil.
Tocopherols and leaf age in Xanthium strumarium L.
Authors: MOLINA‐TORRES J. , MARTINEZ M. L.
Published: April 2006

summary

The concentration of tocopherol in the leaves of Xanthium strumarium L., plants growing under vegetative conditions, were analysed to determine whether they are maintained constant in the different leaves, during the light period throughout the vegetative growth of the plant, α‐ and γ‐Tocopherols were present in this tissue. A relation between tocopherol content and leafage was observed. α‐Tocopherol accumulated with the age of the leaf. γ‐Tocopherol was present in low concentrations throughout the life of the leaf.
Responses of potato plants to sulphur dioxide, water stress and their combination
Authors: QIFU MA , MURRAY FRANK
Published: April 2006

summary

The effects of SO2, and water stress, singly and in combination on potato plants (Solanum tuberosum L. cv. Russet Burbank) were studied by exposing them to one of three SO2 concentrations (2, 110 and 300 nl 1−1) and one of two levels of soil moisture (well‐watered and water‐stressed). Visible leaf injury attributable to SO2 toxicity was observed after 6 weeks of fumigation with 300 nl 1−1 SO2 and 9 weeks of fumigation with 110 nl 1−1 SO2. Leaf, stem and tuber growth were significantly reduced by 300 nl 1−1 SO2 and water stress. Exposure to 300 nl 1−1 SO2 under well‐watered conditions induced an increase of the shoot: root (including tuber) ratios but not for the ratios (excluding tuber) early in the season, indicating a strong effect of the treatment on tuber growth. With progress of the season, water stress usually reduced both ratios.

SO2−induced growth reductions in well‐watered plants were mostly significant, but usually not in water‐stressed plants, indicating a protective function of soil water stress in the response of plants to SO2. This could be caused by reduced SO2 uptake in water‐stressed plants, as the well‐watered plants showed much higher leaf sulphur concentrations than did the water‐stressed plants at the same SO2 concentrations.
Simulated acid rain and the reproduction of mountain birch [Betula pubescens ssp. tortuosa (Ledeb.) Nyman]: a cautionary tale
Authors: NEUVONEN S. , NYYSSÖNEN T. , RANTA H. , KIILUNEN S.
Published: April 2006

summary

Laboratory experiments showed that mountain birch pollen u as sensitive to the acidity of the incubation solution : the percentage of pollen germination was significantly reduced (compared to control, pH 5.6) at pH 4.0 and the length of the longest germ tube was reduced by nearly 50% at pH 4.6. On the other hand, the pollen germination percentage was not significantly affected by treating the male catkins of mountain birch with acid spray down to pH 3.0. Furthermore, a field experiment with simulated acid rain did not show any significant treatment effects either on the number or size of female catkins or on the seed germination capability of mountain birch. There are several mechanisms which may compensate and buffer the effects of acidity on the reproduction of trees.
Seasonal changes in the pigments, carbohydrates and growth of red spruce as affected by exposure to ozone for two growing seasons
Authors: AMUNDSON R. G. , ALSCHER R. G. , FELLOWS S. , RUBIN G. , FINCHER J. , VAN LEUKEN P. , WEINSTEIN L. H.
Published: April 2006

summary

Three‐year‐old red spruce seedlings were exposed to various concentrations of ozone, from 0.4 to 3 times ambient, for two consecutive growing seasons in open‐top chambers in Ithaca, NY, USA. Exposures, which varied with changes in daylength, were from 30 May to 14 December 1987 and 1 June to 1 December 1988. Seedling biomass, foliar pigments and carbohydrate content of roots and shoots were assessed once or twice per month. Tree biomass increased through the summer and declined slightly in late autumn, regardless of ozone treatment. Biomass and contents of sugar and starch of 1988 fixed growth declined linearly with exposure to increasing levels of ozone. Rates of decline in total shoot biomass and old shoot biomass increased linearly with exposure to increasing concentrations of ozone, but tree height was not affected. Seasonal means of starch content of roots decreased linearly with increasing doses of ozone, but in contrast seasonal mean sugar content and rate of sugar accumulation of roots increased linearly. Chlorophyll a and chlorophyll b contents were not affected by ozone.

These data are consistent with the concept that ozone stress is cumulative, since effects on biomass and carbohydrate content of roots and shoots were not detected after the first year of exposure, but were detected after the second year of treatments. Furthermore, biomass was reduced by ozone only in tissues that were initiated during the first year of exposures and developed during the second year of exposures (1988 fixed growth).
Sensitivity of frost resistance and growth in citrus and avocado to chronic ozone exposure
Authors: EISSENSTAT D. M. , SYVERTSEN J. P. , DEAN T. J. , YELENOSKY G. , JOHNSON J. D.
Published: April 2006

summary

The effects of elevated levels of ozone on growth and frost resistance were studied using broadleaf‐evergreen citrus and avocado trees. ‘Ruby Red’ grapefruit (Citrus parodist L.) trees on either Volkamer lemon (Citrus volkanieriana Ten. & Pasq.) or sour orange (Citrus aurantium L.) rootstocks and ‘Simmonds’ or ‘Pancho’ avocado trees (Persea americana Mill.) on the rootstock ‘Waldin’ were exposed to ozone in open‐top chambers for 4 months in 1988 and for 8 months in a second experiment in 1989. The ambient ozone concentration, averaged over a 12 h day, was 30‐1 nl 1−1 in 1988 and 39‐1 nl 1−1 in 1989 during the exposure period. Citrus tree growth, estimated by total leaf mass, was unaffected by ozone concentrations of 3 × ambient in either year but the growth of avocado in 1989 was reduced 20 and 61 % by ozone concentrations at 2 × and 3 × ambient, respectively. Frost resistance, estimated by electrolyte leakage from leaf disks and from survival of leaves, stems and whole plants following exposure to freezing temperatures, was often diminished in avocado and citrus at 3 × ambient ozone, but occasionally was increased at 2 × ambient. The effects of chronic ozone exposure on frost resistance were generally subtle; 3 x ambient ozone exposure in 1989 compared to 0.3 × only caused the temperature for 50% electrolyte leakage (LT30) to increase less than 1 °C (− 5.3 to −4.8 °C) in citrus and about 2 °C (− 8.0 to −5.8 °C) in avocado. Nevertheless, the tests for frost resistance on whole plants indicated that these differences could have a substantial impact on stem and plant survival if the frost was at a critical temperature. The likelihood that chronic ozone exposure currently affects citrus frost resistance in Florida appears slight.
Late‐ and post‐glacial vegetational change at Black Loch, Fife, eastern Scotland – a multiple core approach
Authors: WHITTINGTON GRAEME , EDWARDS KEVIN J. , CUNDILL PETER R.
Published: April 2006

summary

Percentage and absolute (concentration and ‘influx’) pollen diagrams are presented from four locations within a small lake (Black Loch) in eastern Scotland. Two lake marginal cores extend back to lateglacial times but material recovered from the more central cores provides data over only the last c. 3500 years. Two cores are radiocarbon dated (a total of 25 dates) and provide a chronological framework for catchment events. The differences in pollen histories between cores serve to exemplify the dangers of reliance upon single profiles, but the similarities are sufficiently strong to enable useful comparisons to be made and to permit a comprehensive reconstruction of vegetational history for the site. Of particular note is the apparent early arrival of Corylus (c. 8600 BP) and Alnus (c. 7300 BP), the local presence of Pinus and the existence of multiple elm declines. Human impacts upon the vegetational landscape are demonstrable from at least Neolithic times onwards and the presence of Cannabis sativa pollen is strong from c. 985 BP. The planting of woodland on Sanded estates over the last few centuries is clearly represented.