bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

summaryWheat 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

summaryA 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

summaryThe 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

summaryA 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

summaryIt 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

summarySeedlings 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

summaryTo 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

summaryThe 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

summaryThe 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

summaryThin 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

summaryA 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

summaryThis 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

summarySubterranean 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

summaryThe 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

summaryThe 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.