bluuebunny/crossref_metadata_2025 huggingface dataset:
Suberization and bud formation in tobacco explants
Authors: WILMS F. H. A. , NEELISSEN J. A. M. , KROH M.
Published: April 2006

Wound‐healing and floral bud formation were studied in explants of Nicotiana tabacum L. Examination of sectioned material by conventional light microscopy, fluorescence microscopy and electron microscopy showed that suberin is formed in cells at the cut surface in close contact with the medium, after 4–7 days of culture.

The number of cells depositing suberin depended on the agar concentration in the medium. In explants cultured on a medium with low agar concentration (0‐2 % agar), fewer cells showed suberin deposition and more callus cells without suberin were found. Explants cultured on a medium with high agar concentration (5 % agar) formed a complete layer of cells with suberin deposition.

In tobacco explants floral determination occurred within 4 days after explantation. The inability of the explants to form floral buds after this period is probably due to barrier formation by suberin.
Effects of interactions between nutrient supply and rust infection of Senecio vulgaris L. on competition with Capsella bursa‐pastoris (L.) Medic.
Authors: PAUL N. D. , AYRES P. G.
Published: April 2006

Senecio vulgaris L., either healthy or inoculated with rust (Puccinia lagenophorae Cooke), was grown in monoculture or in mixture with Capsella bursa‐pastoris (L.) Medic, under high or low nutrient conditions. At harvests made 7, 9, and 11 weeks after sowing, uninfected S. vulgaris progressively outcompeted C. bursa‐pastoris under nutrient‐rich conditions. Rust infection eliminated the competitive advantage of S. vulgaris over C. bursa‐pastoris under high nutrient conditions. In contrast, under low nutrient conditions C. bursa‐pastoris outcompeted uninfected S. vulgaris and infection with P. lagenophorae resulted in no additional competitive disadvantage to its host. The reduced competitiveness of rusted S. vulgaris under high nutrient conditions was associated with reductions in root growth in mixtures that were greater than those caused by rust in monocultures.

The effects of nutrient supply, rust infection and competition on tissue concentrations of nitrogen, phosphorus and potassium were complex and often influenced by interactions between these factors. Increasing the nutrient supply increased nitrogen concentrations ([N]) in S. vulgaris, as did rust infection, but the effects of infection were confined to monocultures. In general [N] in C. bursa‐pastoris showed rather less variation. Phosphorus concentrations ([P]) in C. bursa‐pastoris increased with nutrient supply but under nutrient‐rich conditions were reduced by competition. In S. vulgaris [P] increased with increasing nutrient supply and with infection but in both cases responses were confined to monoculture. Potassium concentration ([K]) in S. vulgaris was increased by rust, especially in mixtures. In C. bursa‐pastoris [K] under high nutrient levels was higher in mixtures than in monoculture.

The mechanisms by which the effects of rust on host competitiveness differed under high and low nutrient conditions are considered and the implications for our understanding of the role of rusts in natural vegetation are discussed.
Salt tolerance in the halophytic wild rice, Porteresia coarctata Tateoka
Authors: FLOWERS T. J. , FLOWERS S. A. , HAJIBAGHERI M. A. , YEO A. R.
Published: April 2006

While members of the genus Oryza are very sensitive to salinity, salt concentrations as high as 20% of that of seawater had no adverse effect on the growth of the tropical wild rice (Porteresia coarctata Tateoka) in experiments undertaken in a greenhouse in the UK. P. coarctata plants accumulated sodium and chloride ions in the leaves, but maintained a Na: K ratio as low as 0.7, even after 6 weeks of growth in 25% artificial seawater (ASW) where the Na: K ratio was 34. This ability to maintain a high K: Na ratio in the leaves is in part a consequence of the secretion of ions from the leaves. The ratio of Na: K in the secreted salt (more than 5 for plants growing in 25% ASW) is similar to that measured by X‐ray microanalysis in the vacuoies of hairs found in folds of the adaxial surface of the leaf lamina, suggesting that the secretions emanate from these hairs. The salt secreted by the hairs is an important factor in the salt‐balance of the leaves: the consequences of these findings for the transfer of salt‐tolerance from this species into cultivated rice are discussed.
Kinetics of exchange of ions between artificial precipitation and maple leaf surfaces
Authors: SCHERBATSKOY TIMOTHY , TYREE MELVIN T.
Published: April 2006

Experiments were conducted to test the hypothesis that ion exchange between precipitation and leaves does not involve rapid transcuticular ion permeation. The kinetics of exchange of ions between artificial precipitation and sugar maple (Acer sacckarum Marsh.) leaf surfaces were evaluated by measuring ion concentrations in individual drops at pH 5.4 or 3.8 after time periods on the leaf ranging from 4 to 128 min. Similar experiments were conducted in which leaves, were immersed in artificial precipitation solutions. These experiments indicated that (1) mechanisms of exchange differed with ion species, (2) solution pH had significant effects on the rate of exchange, and (3) rates of ion diffusion through cuticles were small. Cu2+and Pb2+were rapidly adsorbed to the leaf surface at pH 5.4, but not at pH 3.8. Zn2−concentrations were unchanged by any treatment. K+, Ca2+, and Mg2+were released from the leaf surface, and this effect was greater at pH 3.8 than pH 5.4. Apparent permeability coefficients calculated from the kinetics of these experiments indicated net exchange was dominated by cuticle surface adsorption for Cu2+and Pb2+, and cuticular permeation for K+, Ca2+, and Mg2+. The magnitude of cuticular permeation, however, was small; calculated half‐times for cation efflux from foliage were of the order of 10 days, assuming continuous precipitation. These experiments support the hypothesis that permeation of ions through cuticles during precipitation events may not occur at biologically significant rates.
The cause of peat erosion: a palaeolimnological approach
Authors: STEVENSON A. C. , JONES V. J. , BATTARBEE R. W.
Published: April 2006

Palaeoecological analyses of two lake sediment cores from the Round Loch of Glenhead, Galloway, S.W. Scotland and Loch Laidon, Ratinoch Moor, Central Scotland have been conducted to elucidate the cause of the observed blanket peat erosion in their catchments. Both simple physical measurements such as percentage loss on ignition and the pollen and diatom record reveal clearly the onset of peat erosion in these catchments. Accurate dating of erosion is still problematical. Nevertheless, some of the competing hypotheses that have been advanced to explain blanket peat erosion are evaluated. Acid deposition cannot be responsible for the peat erosion in these two catchments since the combined use of 211Pb and 14C dating suggests that erosion was initiated between c. AD 1500 and AD 1700, an age well before the effects of atmospheric deposition are documented by the core. However, it remains to he resolved what the effects have been of land‐management changes such as grazing, burning and climatic effects, such as the Little Ice Age.
Ascomycete mycorrhizas from pot‐grown silver‐fir seedlings (Abies alba Mill.)
Authors: BERNDT R. , KOTTKE I. , OBERWINKLER F.
Published: April 2006

Four types of ascomycete mycorrhizas were found on seedlings of Abies alba grown in pot cultures on mineral soil. One type was formed by Cenococcum graniforme Ferd. & Winge; the fungal partners of the other three types could not be identified. The macroscopic and microscopic characteristics are described. One mycorrhiza appeared to be identical with Type 15 of Haug & Oberwinkler, found in natural spruce stands. Senescent stages of this type are also described. Ultrastructural investigations showed that the dolipore seemed to be the main distinguishing feature between ascomycete and basidiomycete mycorrhizas. Differences in the matrix of the interface and the fungal wall were not stable enough to be used as a distinguishing feature between asco‐ and basidiomycetes. Dead fungal cells were isolated from the living tissue by plugging of septa with Woronin bodies and walling‐over of the plugged septa. Subsequently these isolated dead cells could be colonized by the fungus. The predominant mycorrhization of the fir seedlings by ascomycetes in pot culture with mineral soil is discussed.
15N natural abundance as a possible marker of the ectomycorrhizal habit of trees in mixed African woodlands
Authors: HÖGBERG PETER
Published: April 2006

The partial contribution by fixed nitrogen in N2‐fixing plants can be estimated if the 15N natural abundance of non‐N2‐fixing reference species, which derive their N from the soil, deviates from that of atmospheric N2 (the 15N natural abundance method). Data from Tanzanian miombo woodland showed a significant difference (= 1.0‐2.5 δ15N%0) in 15N abundance between ectomycorrhizal and vesicular‐arbuscular (VA) mycorrhizal reference species. This finding casts doubt upon arbitrary selection of reference species, and also raises the possibility of using 15N abundance as a marker of the ectomycorrhizal habit. It is suggested that the higher 15N abundance of ectomycorrhizal tree species could result from differences in discrimination during uptake or from greater utilization of organic N.
Variation in [75Se]selenate uptake and partitioning among tomato cultivars and wild species
Authors: SHENNAN C. , SCHACHTMAN D. P. , CRAMER G. R.
Published: April 2006

Eight Lycopersicon esculentum cultivars and six wild taxa from four Lycopersicon species were tested for their ability to transport and distribute Se under low and high sulphate salinity conditions. Plants were exposed to [75Se]selenate for 1 h. Significant variation was observed in both morphological and transport characteristics that control the short‐term uptake and accumulation of selenate in tomato species.

Among L. esculentum cultivars under low salinity, selenate uptake ranged from 126‐184 pmol g f. wt root−1 h−1 and shoot 75Se concentrations ranged from 40‐66 pmol g f. wt shoot−1. Shoot accumulation was affected by both specific root weight (SRW, root fresh weight/total plant fresh weight) and uptake of the cultivar. Distribution of tracer between root accumulation and transport to the shoot, expressed on a root weight basis, was similar in all cultivars. High sulphate salinity reduced uptake to around 22 pmol g f. wt root−1 h−1 in all cultivars and only small differences in shoot 75Se concentration (7.4‐10.5 pmol g f. wt shoot−1) were observed, indicating that root uptake rate was the primary determinant of shoot 75Se concentration under these conditions. In the low‐salinity treatment wild accessions showed a wider range of uptake rates (52–190 pmol g f. wt root−1 h−1) and shoot Se concentrations (12–79 pmol g f. wt shoot−1) than the cultivars. High sulphate salinity had a less inhibitory effect on Se uptake in the wild taxa than in the cultivars, with uptake rates of 18–63 pmol g f. wt root−1 h−1 and shoot concentrations of 7–28 pmol g f. wt shoot−1 measured. Differences in uptake, partitioning and SRW all contributed to the variation in shoot 75Se uptake in these taxa at both salinity levels.

One cultivar (UC82B) was tested under high chloride salinity. Uptake was reduced by 40% relative to the low salt control, compared with the 87% reduction observed under high sulphate salinity. The apparent inhibition in the presence of chloride salinity could be explained by the 40% reduction in selenate activity calculated for this solution relative to the control. Reduced selenate activity was insufficient to account entirely for the reduced uptake observed in this taxon under high sulphate salinity. In contrast, after allowing for reduced selenate activity, uptake by L. pennellii LA716 was little affected by an increase in sulphate from 2.9 and 38 mM, showing that considerable variation in selectivity of the transport system for selenate versus sulphate exists among Lycopersicon species.
The relationship of light and plant geometry to self‐thinning of an aquatic annual herb,Murdannia keisak(Commelinaceae)
Authors: DUNN CHRISTOPHER P. , SHARITZ REBECCA R.
Published: April 2006

Self‐thinning was examined in shaded and unshaded populations ofMurdannia keisak(Hask.) Hand.‐Mazz. (Commelinaceae). Four mathematical descriptions of self‐thinning were compared: (1) the traditional – 3/2 thinning rule in which mean plant biomass is regressed on density; (2) principal components regression of mean plant biomass and density; (3) total stand biomass regressed on density, and (4) principal components regression of total stand biomass and density. Most slopes conform to the expected ones; however, confidence intervals reported here and in the literature are wide which may reduce the ecological value of the thinning lineper se.

In addition, plants grown in full sun form significantly fewer branches than those in shade. This difference in geometry results in differences in mean plant volume, in plant packing, and thus, in different thinning trajectories.
Stimulatory effects of SO2 on growth of Eucalyptus rudis Endl.
Authors: CLARKE KAREN , MURRAY FRANK
Published: April 2006

summary

Eucalyptus rudis Endl. saplings were exposed to either 274 μg m−3 SO2 or 132 μg m−3 SO2 for 8 h d−1, over 123 d, in open‐top chambers. Exposure to 132μg m−3 SO2 increased the height of the plants and increased the average area and dry weight of leaves. Exposure to 274 μg m−3 SO2 increased the concentration of total sulphur in the leaves and increased the number of leaves abscised. Sulphur accumulation in the leaves decreased as the duration of exposure increased.
A CHECK‐LIST OF MYCORRHIZA IN THE BRITISH FLORA–SECOND ADDENDA AND ERRATA
Authors: HARLEY J. L. , HARLEY E. L.
Published: April 2006

Preamble

The check‐list of mycorrhiza in the British flora was first published in February 1987 as a supplement of Vol. 105, No. 2 of this journal. A first list of Addenda and Errata, together with an Index, was published in December 1987 in Vol. 107, No. 4, pp. 741–749. This second list of Addenda and Errata is available as a reprint uniform in size with the check‐list to those who subscribed to it, gratis on request to the Executive Editor. Those wishing to obtain the checklist and both addenda may obtain copies by sending a cheque for £8 (sterling only) payable to the New Phytologist Trust, to the Executive Editor, The New Phytologist, Department of Animal and Plant Sciences, The University of Sheffield, Sheffield, S10 2TN, UK, together with an adhesive label addressed to themselves. Requests should not be sent to the authors.

The authors wish to reinforce their previous description of this checklist by emphasizing that it is designed to enable scholars to find and study what has been written about the mycorrhiza of species of the British Flora and does not provide detailed information. The authors would gratefully receive information of errors in the list or further information and reprints of papers concerning mycorrhiza in British plants which have not yet been included in this list, where the work was conducted using European material (not material collected outside Europe).
Does calcium in xylem sap regulate stomatal conductance?
Authors: ATKINSON C. J. , MANSFIELD T. A. , DAVIES W. J.
Published: April 2006

Whole plants and individual leaves of Commelina communis and Triticum aestivum were used to study the influence of changes in apoplastic Ca on the regulation of gas‐exchange, in particular stomatal conductance (g) and transpiration (E). Plants grown in nutrient solution at a low concentration of Ca (1 mol m−3) were used in experiments where rapid changes in Ca concentration were induced via the rhizosphere or by direct entry into the xylem. Solutions containing Ca2+ ions were applied directly to the leaf surface and also through the cut end of detached leaves and via a xylem feeding system to attached leaves. Putative Ca‐channel blockers (lanthanum chloride and verapamil hydrochloride), which are believed to deny Ca entry into the cytoplasm, were also used to provide more information about the nature of the action of Ca on the guard cells.

In all the experimental systems used, the short‐term application of 8 mol m−3 Ca induced reductions in both g and E, but when longer‐term changes in the calcium concentrations in the xylem sap were induced through changes in Ca supply from the rhizosphere, no change in g was apparent. These experiments raise important questions about how plants with an abundant supply of calcium in the rhizosphere prevent high concentrations of apoplastic calcium from interfering in the stomatal mechanism. The data presented do not preclude the possibility that a pulse of calcium ions delivered into the xylem could be used in root–shoot communication.
An altered phosphate uptake system in arsenate‐tolerant Holcus lanatus L.
Authors: MEHARG ANDREW A. , MACNAIR MARK R.
Published: April 2006

The mechanism of phosphate and arsenate uptake was investigated in arsenate‐tolerant and non‐tolerant genotypes of Holcus lanatus L. It appeared that arsenate and phosphate were taken up by the roots by the same uptake system in both genotypes, although the uptake system had a much greater affinity for phosphate than arsenate. In non‐tolerant plants the uptake of both anions was much greater than for tolerant plants at low phosphate and arsenate concentrations. High‐affinity uptake appeared to be absent in the tolerant plants for both arsenate and phosphate. The absence of this high‐affinity uptake is discussed in terms of arsenate tolerance in this species. The identification of a mutant with only one phosphate uptake system provides further evidence that ‘normal’ uptake of ions occurs via two distinct transport systems. The theoretical and ecological implications of this altered phosphate uptake mechanism are considered.
Utilization of AlPO4 as a phosphorus source by ectomycorrhizal Pinus rigida Mill. seedlings
Authors: CUMMING JONATHAN R. , WEINSTEIN LEONARD H.
Published: April 2006

Mycorrhizal infection of roots of Pinus rigida Mill, seedlings by Pisolithus tinctorius Coker & Couch maintained normal foliar P relations when seedlings were exposed to Al in solution. To investigate how this symbiosis aids in P acquisition in the presence of Al, seedlings were grown in sand culture with solutions containing between 1 and 50 μM NaH2PO4 (Pi) with or without insoluble AlPO4 in the substrate. Mycorrhizal seedlings had a higher affinity for Pi than non‐mycorrhizal seedlings as judged by superior growth and foliar P contents at all Pi levels tested. In addition, mycorrhizal seedlings, but not nonmycorrhizal seedlings, effectively extracted P from AlPO4 through the dissolution of this insoluble salt. Measurement of matrix solution pH indicated that increased proton production, in association with high proliferation of mycorrhizal roots under P‐limiting conditions, led to increased AlPO4 solubilization.
Tansley Review No. 27 The control of carbon partitioning in plants
Authors: WARDLAW IAN F.
Published: April 2006

This review reports on the processes associated with carbon transfer and metabolism in leaves and growing organs and the role of long‐distance transport and vascular links in the regulation of carbon partitioning in plants. Partitioning is clearly influenced by both the supply and demand for photosynthate and is moderated by vascular connections and the storage capacity of the leaves and pathway tissues. However there appears to be little more than circumstantial evidence either that short distance transfer of carbon within either the source or the sink, or that long‐distance transport in the phloem, are limiting photosynthesis or growth directly. Although individual biochemical and physiological processes relating to photosynthesis and growth may be well understood, the factors primarily responsible for the control of carbon partitioning in plants have not been clearly identified. There is a need for a greater understanding of organ initiation and development (source and sink formation and potential size), the clear identification of whether growth is sink or source limited (including possible sink‐controlled photosynthesis) and a detailed assessment of the role of storage in buffering developmental and environmental changes in sink and source activity. Also more information is needed on the role of hormonal and nutritional factors in regulating source and sink activity (organ interactions not directly associated with carbon transfer).

CONTENTSSummary341I.Introduction342II.General source‐sink relationships342III.Control at the source345IV.The utilization of photosynthate: sink characteristics and limitations353V.Vascular constraints and temporary storage360VI.Concluding comments366Acknowledgements366References367
The association of Morchella rotunda (Pers.) Boudier with roots of Picea abies (L.) Karst
Authors: BUSCOTAND F. , KOTTKE I.
Published: April 2006

A histo‐cytological study of Norway spruce [Picea abies (L.) Karst.] roots connected to ascocarps of Morchella rotunda (Pers.) Boudier revealed that hyphae of morel were associated with all parts of the root system. The main suberized roots were surrounded by a mycelial sheath. The finer rootlets were enveloped by a cottony mycelium and their absorbing root tips were found to be ectomycorrhizal. Morel hyphae also invaded the oldest parts of a heterobasidiomycete ectomycorrhiza.
Copper tolerance and copper uptake ofLotus purshianus(Benth.) Clem. & Clem. and its symbioticRhizobium lotiderived from a copper mine waste population
Authors: WU LIN , LIN SHEN‐LIN
Published: April 2006

Lotus purshianus(Benth.) Clem, and Clem., growing on a copper mine waste in Northern California, exhibits copper tolerance. Effective nitrogen fixation (acetylene reduction) is seen in copper‐enriched soils. When subcultured in liquid culture,Rhizobium lotiisolated from root nodules ofL. purshianusgrowing on the copper mine, showed considerably greater copper tolerance than did rhizobium isolated from plants growing in a nearby field. No difference was detected in either the pattern of copper uptake or concentration in plant tissue between tolerant and non‐tolerantL. purshianus.However, a copper accumulation mechanism associated with copper tolerance was found in the symbiotic rhizobium. The successful colonization of copper enriched soil by this legume species is accomplished by the evolution of copper tolerance in both the legume plant and its symbiont. The copper tolerance of the plant and rhizobium may have evolved independently.
Relationship of colonization and sporulation by VA mycorrhizal fungi to plant nutrient and carbohydrate contents*
Authors: DOUDS DAVID D. , SCHENCK N. C.
Published: April 2006

Vesicular‐arbuscular (VA) mycorrhizal fungi typically produce spores either within roots of a host plant or in the soil. Experiments were conducted to examine the effects of plant nutrition, as measured by tissue N, P, K, and soluble sugar concentrations, upon colonization of roots of Paspalum notatum Fliigge and sporulation within roots by Glomus intraradix Schenck & Smith and in the soil by Acaulospora longula Spain & Schenck and Gigaspora margarita Becker & Hall. Plants receiving a balanced nutrient solution without P consistently had the greatest percentage root length colonized by VA mycorrhizal fungi. Glomus intraradix produced more spores per root weight under conditions of nonmycotrophy, when plants received either water only or KH2PO4 only in the nutrient‐poor soil used in these experiments. Gigaspora margarita and A. longula produced more spores in the soil when plants received the balanced nutrient solution without P. Similarly contrasting responses were seen when sporulation inside and outside the roots was correlated to plant nutrient and soluble sugar concentrations. The P‐tolerant, intraradical‐sporulating, VA mycorrhizal fungus G. intraradix sporulated heavily when N: P ratios of host tissue were imbalanced toward P. Acaulospora longula and G. margarita produced more spores in the soil when plant tissue N:P ratios were imbalanced toward N.
Growth of five families of Pinus taeda L during three years of ozone exposure
Authors: ADAMS M. B. , KELLY J. M. , TAYLOR G. E. , EDWARDS N.T.
Published: April 2006

Loblolly pine (Pinus taeda L.) seedlings of five half‐sib families were grown for 3 yr in the field in open‐top chambers. The seedlings were fumigated during the growing seasons (approximately April‐October) with ozone at the following target levels: subambient (CF), ambient (AMB), and ambient+ 60 ppb (AMB +). At the end of the three growing seasons, no significant ozone effects on diameter, height or total biomass of the seedlings were detected, and no statistically significant ozone‐family interactions were detected. Analysis of growth trends suggest that drought during the second and third growing seasons may have interacted with the ozone treatments. The importance of long‐term studies under realistic field conditions is discussed.
Pollen and related studies at Kinloch, Isle of Rhum, Scotland, with particular reference to possible early human impacts on vegetation
Authors: HIRONS KENNETH R. , EDWARDS KEVIN J.
Published: April 2006

The Inner Hebridean island of Rhum lies between the once wooded mainland of north‐west Scotland and the now largely treeless islands of the Outer Hebrides. Rhum is more exposed than the nearby larger islands and is of particular interest since it has been occupied by humans for at least 8500 years. Pollen, charcoal and radiocarbon studies were carried out on a peat profile from Kinloch in the most sheltered eastern part of the island, some 300 m from the site of the earliest known Mesolithic occupation site in Scotland.

From an estimated 7800 BP, the local mire surface was open with some hazel and willow scrub. Alder replaced willow at c. 6500 BP and with hazel, remained the dominant woody vegetation until c. 4000 BP when both were reduced and by which time evidence for agriculture is discernible. A period of reduced Alnus and Corylus between 5950 and 5700 BP, with high concentrations of charcoal, may result from human influence. An Alnus reduction dated to between 5250 and 4950 BP may have been caused by changes in mire hydrology. The woodland was more open than that at nearby mainland sites but it was comparable to well‐wooded sites on Skye and Mull. Birch was notably less significant at the Rhum site and the preponderance of Alnus along with persistently high Osmunda values may indicate that adaptation to exposure and salt tolerance were important factors in determining the character of the early postglacial vegetation.
Salinity induced structural changes in meristematic cells of barley roots
Authors: HUANG CHENG X. , van STEVENINCK REINHARD F. M.
Published: April 2006

summary

Structural changes occurring in meristematic cells of barley (Hordeum vulgare L. cv. California Mariout) in response to moderate salinity treatment were studied. In the apical region of the root, salt caused an increase in vacuolation which may provide a means for accumulation of excess ions. Salt treatment also caused many plastids in the cortical cells in this region to adopt varying amoeboid shapes, often appearing to enclose part of the cytoplasm which was less dense than the surrounding cytoplasm. This suggested that plastid morphology may allow or alternatively result from adaptive changes in protein synthesis or cvtoplasmic composition.
A split‐root experiment shows that iron is required for nodule initiation in Lupinus angustifolius L.
Authors: TANG CAIXIAN , ROBSON ALAN D. , DILWORTH MICHAEL J.
Published: April 2006

summary

A split‐root system was used to examine the effect of iron on nodule initiation and development in lupins (Lupinus angustifolius L. cy. Yandee) in solution culture. An inoculum of Bradyrhizobium was added to one half of the root system which then received either 0‐05 or 2‐5 μM iron, in various combinations. Where inoculum was present along with a low concentration of iron, the numbers of nodule initials and nodules were markedly decreased, irrespective of whether or not the shoots of the plant were adequately supplied with iron. The limitation to nodule formation was independent of host plant growth. Where half of the roots were given 2–5 μM iron, plants translocated little iron to the roots grown in the other compartment at 0.05 μm iron. Foliar application of iron obviated deficiency symptoms in the shoot but did not increase nodulation. We conclude that, for nodule initiation, iron is required either in the external solution or within the root.
A test of mycorrhizal benefit in an early successional plant community
Authors: GANGE A. C. , BROWN V. K. , FARMER L. M.
Published: April 2006

summary

The fungicide ‘Rovral’ (iprodione) was applied in granular form in an attempt to reduce VA mycorrhizal infection of plants during the early stages of secondary plant succession, namely the first year of colonization of bare ground. In 7 out of 11 plant species examined, infection levels were reduced by the fungicide. Four of these also showed reduced cover abundance as a result of fungicide application. Since three were annual forbs, which as a plant life‐history grouping comprised 73 % of the community, total cover of the vegetation (as measured by point quadrats) was significantly reduced by the fungicide. In three species, reduced infection levels did not appear to result in reduced vegetation cover. The reasons for this are discussed in relation to the dependency of plants on mycorrhizal infection. It was found that fewer plant species recruited into communities where iprodione was applied. The implications of these results, in terms of the role that mycorrhizas play in the structuring of early successional plant communities, are discussed.
Nuclear features in infected roots of Ophrys lutea Cav. (Orchidaceæe)
Authors: BARROSO J. , PAIS M. S.
Published: April 2006

summary

In mycorrhizas of Ophrys lutea Cav., nuclear hypertrophy occurs in infected cells and in some neighbouring uninfected ones. Hypertrophied nuclei are amoeboid in shape and possess numerous nuclear pores. The increase in nuclear volume is associated with an increase of the number of nucleoli from 1 to 2–4. These nucleoli possess well defined granular and fibrillar components and several vacuoles. Nuclear bodies of different sizes are associated with the nucleoli or lie free in the nucleoplasm near the nuclear envelope. Silver impregnation reveals that both the fibrillar component of the nucleolus and the nuclear bodies are argyrophilic. Some nucleolar‐associated bodies do not react with the silver stain. After regressive staining with EDTA, the chromatin, the nucleolar fibrillar component and the nuclear bodies lying free in the nucleoplasm are bleached. The nuclear bodies may be transient accumulations of ribonucleoproteins migrating into the cytoplasm.
Responses of rust (Puccinia lagenophorae Cooke) to nutrient supply in groundsel (Senecio vulgaris L.) and effects of infection on host nutrient relations
Authors: PAUL N. D. , LAXMI K. ARUNA , AYRES P. G.
Published: April 2006

summary

Senecio vulgaris (groundsel), healthy or inoculated with rust (Puccinia lagenophorae), was grown in a nutrient‐poor sand‐soil mixture amended with a compound fertiliser to provide a range of nutrient regimes. The greatest number of pustules per plant occurred on unamended soil but fertiliser addition increased the sporulating area of each pustule: the leaf area occupied by pustules was unaffected by nutrient supply. Since total leaf area increased with increasing nutrient supply, the percentage of total area that was infected declined. Plant and root dry weights increased with nutrient supply and decreased with rust infection. Infection also reduced root fresh weight and length, which were little changed by nutrient supply, but reduced leaf area only under the most nutrient‐rich conditions.

The ratios of root length: leaf area (R:L) and, especially, root:shoot dry weight (R:S) were reduced by infection. Root length per unit root weight was increased by infection when expressed on the basis of dry weight but not on the basis of fresh weight.

Conversely, increasing nutrient supply decreased root length:weight only on the basis of fresh weight. The concentrations of P and K per unit dry weight were increased in rusted leaves but that of N was unchanged. Because infection increased the dry weight: fresh weight ratio (d. wt:f. wt) of leaves, concentrations of P and K on a fresh weight basis increased by up to 3‐fold over those in controls and that of N was also substantially increased. On a dry weight basis, the concentration of N and K, but not P, increased in the roots of rusted plants. However, since d. wt:f. wt of roots was decreased in infected plants, the concentrations of N and K were unchanged on a fresh weight basis and that of P was significantly reduced.

Rates of uptake of N, P and K were significantly increased in rusted plants both on the basis of root dry weight and root length. This was attributed to increased ‘shoot demand’ on each unit of root which, in turn, reflected the decreased R:S and R:L of infected plants.
Ultrastructural and histochemical studies on interactions between Vitis vinifera L. and Uncinula necator (Schw.) Burr.
Authors: HEINTZ C. , BLAICH R.
Published: April 2006

summary

Host‐parasite interactions between the grapevine Vitis vinifera L. and the powdery mildew Uncinula necator (Schw.) Burr, were studied by light microscopy and histochemistry, scanning and transmission EM. The lobed appressoria (10 μm diam) of the fungus adhered to the host cuticle because of their shape and the production of a soluble adhesive substance. Each formed a penetration peg (0–3 μm diam) which, after penetration into the epidermal cell, developed into a globular haustorium consisting of a nucleated central body with fingerlike lobes, embedded in a matrix. The surrounding extra haustorial membrane was derived from the transformed plasmalemma of the host cell. As a defence mechanism the walls of the host cell and neighbouring cells were encrusted with silica and phenolic substances associated with cell wall bound peroxidase activity. Penetration may have been blocked by the formation of a papilla composed of different layers containing carbohydrates, silica and phenolic substances. Cells forming a thick papilla were not infected. In cells with old infections, callose deposits could be observed in walls and/or around the haustorial neck and papilla, and sometimes around the whole haustorium.
Effect of VA mycorrhizal fungi and rhizosphere microorganisms on root and shoot morphology, growth and water relations in maize
Authors: KOTHARI S. K. , MARSCHNER H. , GEORGE E.
Published: April 2006

summary

Maize (Zea mays L.) was grown in fertilized calcareous soil in pots which were separated by 30 μm nylon nets into three compartments, the central one for root growth and the two outer ones for hyphal growth. The size of each compartment was 40 × 25 × 3 cm. The treatments comprised of sterilized soil, either inoculated with rhizosphere microorganisms (other than VA mycorrhizal fungi), with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe] or remained non‐inoculated (sterile control). As inoculum for rhizosphere microorganisms the roots with adhering rhizosphere soil of non‐mycorrhizal maize plants was used.

Compared to the non‐inoculated (sterile) control, inoculation with rhizosphere microorganisms did not affect shoot dry weight and morphology, but increased total root length (17 %) and root length per unit root dry weight (35%). The additional inoculation with VA mycorrhizal fungi had no influence on the shoot dry weight but increased area and dry weight of the leaf blades by about 30% and the ratio leaf blade:leaf sheath + stem (w/w) by 41 %. The most profound effect of VA mycorrhizal fungi inoculation was on root growth and morphology. Compared to the non‐inoculated control, root dry weight was decreased by 16%, root length by 31 % and root hair density and length by 41 and 43 %, respectively.

In mycorrhizal plants the transpiration rates per plant were about 30 % higher than in the other treatments and this is attributed to the larger leaf area. Water uptake rate per unit root length and per unit time was about twice as high in mycorrhizal plants. For several reasons a substantial hyphal water transport seems unlikely. The results stress the necessity of detailed studies on root morphology for interpretation of effects of mycorrhizal fungi on mineral nutrient uptake and water relations in plants.
A laboratory scale air‐lift helical photobioreactor to increase biomass output rate of photosynthetic algal cultures
Authors: LEE EDMUND T.‐Y. , BAZIN MICHAEL J.
Published: April 2006

summary

The helical air‐lift reactor of 0·315 1 capacity provides an improved way to cultivate photosynthetic organisms when compared to a 0·625 1 stirred reactor. The improvement results from an approximately three‐fold increase in the surface area: volume ratio of the reactor. Continuous operation of the helical reactor at a dilution rate of 0·025 h−1 permitted a light‐limited photosynthetic culture of Porphyridium cruentum to be maintained at a steady state biomass concentration of 4·6 g l−1 compared to 1·7 g l−1 in the stirred reactor under similar illumination. When operated at an air flow rate of 0·75 1 min−1, the volumetric oxygen transfer coefficient was 160 h−1 in the helical reactor and a Reynolds number of 2000 was obtained.
Effects of liming on ectomycorrhizal fungi infecting Pinus sylvestris L.
Authors: ERLAND SUSANNE , SÖERSTRÖM BENGT
Published: April 2006

summary

Five ectomycorrhizal fungi were studied in relation to the effects of applications of lime and wood ash to the growth substrate. Growth and survival of inoculated fungi in unsterile humus and relative root colonization frequency by inoculated and indigenous ectomycorrhizal fungi were measured. Growth of the fungi was tested in Petri dish systems with humus taken from a field site treated with lime and wood ash. The infection potential of the fungi was tested by introducing Pinus sylvestris L. seedlings into the growth systems.

Paxillus involutus (Fr.) Fr. was the only fungus affected both by the pH increase, and by the different treatments applied, in all aspects of its ecology tested (growth and survival in humus, infection potential and competitive ability). No other fungus grew saprophytically, but they showed the similar changes in infection potential in response to pH whether lime or ash had been used.
The influence of open‐top chambers on the growth and development of field bean
Authors: SANDERS G. E. , CLARK A. G. , COLLS J. J.
Published: April 2006

summary

In 1988, open‐top chambers (OTCs) based on the Raleigh (USA) design were used to investigate the effect of ambient pollutants on field‐sown Vicia faba cv, Ticol. This paper reports an aspect of this study in which the effect of the chamber itself on crop growth and development was investigated. Non‐filtered chamber (NF OTC) microclimates were typically 0.8°C warmer, with 20% less radiation and reduced wind speeds compared with open‐field sub‐plots (AA treatments). These differences are sufficient to induce alterations in the growth and development of V. faba.

Plant development progressed more quickly inside the chambers in response to the faster accumulation of thermal time. Chamber‐grown V. faba were up to 20 cm taller and had fewer branches (0.7 compared with 1.2 per plant) than plants grown in the AA treatments. Larger leaf areas developed on the NF plants, and there were fewer stomata per unit leaf area in this treatment (34 compared with 42 mm−2, P= 0.01). Enclosure within an OTC did not alter the number of flowers per plant or the number of flowers which formed pods. However, at harvest, chamber‐grown plants had a 13% higher yield than the plants grown in open‐field plots. These differences in growth are described in relation to the microclimate differences between AA and NF treatments.
The vegetational history of Glen Diomhan, North Arran, site of endemic whitebeams, Sorbus arranensis Hedl. and S. pseudofennica E.F. Warb.
Authors: STEVEN G. , DICKSON J. H.
Published: April 2006

summary

A detailed pollen analysis was undertaken of sediment from a site in Glen Catacol on the Isle of Arran, Scotland, close to Glen Diomhan National Nature Reserve which has a large though possibly declining population of the endemic whitebeams, Sorbus arranensis Hedl. and S. pseudofennica E.F. Warb. Blanket peat formation began before 7000 years BP. The results provide evidence that while parts of the glen saw the development and subsequent decline of birch, oak, hazel and alder woodland a large proportion of the surrounding vegetation has remained open throughout the Flandrian with grass‐heath similar to that which occurs over much of the glen in the present day.
The xylem wedge as a functional unit – speculations on the consequences of flow in leaky tubes
Authors: CANNY M. J.
Published: April 2006

summary

Xylem, as a mixture of elements of large and small diameter, presents a paradox when viewed as a conductor of sap flow, since the quantity carried is determined by only the largest diameter elements. The paradox may be s resolved, and an important function for the smallest elements revealed, by consideration of flow in leaky tubes. It is shown how the balance between axial flow and leakage becomes critical at a certain diameter, called the critical diameter (D0). Below D0, no axial flow can occur. When a stack of connected tracheary elements of different diameters is assembled into a xylem wedge, as in the major veins of dicotyledon leaves, this wedge will act as a functional unit. Elements with D > D0 have axial flow, but those where DD0 have only radial flow. The mixture of elements then acts to concentrate solutes of the sap in the smallest elements at the apex of the wedge, left behind as the water leaves. The balance between radial and axial flow is also self‐adjusting to changes in the longitudinal gradient of pressure. Consideration is given to the functions of these graded stacks in the metaxylem of leaves, of stem vascular bundles, within secondary wood, and in roots. It is shown how some xylem fibres may be expected to mediate exchanges of water and solutes, and may act as regulators of these exchanges in space and time. Some experimental demonstrations are presented of the predictions of this hypothesis.
Architectural analysis of plant root systems 1. Architectural correlates of exploitation efficiency
Authors: FITTER A. H. , STICKLAND T. R. , HARVEY M. L. , WILSON G. W.
Published: April 2006

summary

In order to determine whether variation in root system architecture can be said to be adaptive, it is necessary' to be able to define the costs and benefits of particular architectures. A simulation model of root growth is described that allows the development of root systems varying in several important architectural features, including topology, link lengths and radii, and branching angles. The program also estimates the exploitation efficiency of each root system, as the ratio of the volume of soil occupied by depletion zones (allowing for overlaps between competing roots) and the volume of tissue required to construct the system. Output from the model shows that high exploitation efficiency is associated with a herringbone topology (where branching is predominantly on the main axis) and with long interior and exterior links, although all these characteristics are associated with large tissue volumes and hence high construction cost, We predict, therefore, that such ‘expensive’ root systems will occur mainly in nutrient‐poor soils and on plants characteristic of such soils.
Biophysics of leaf growth of hybrid poplar: impact of ozone
Authors: FROST D. L. , TAYLOR GAIL , DAVIES W. J.
Published: April 2006

summary

Biophysical parameters controlling leaf expansion in hybrid poplar (Populus nigra L. ×P. deltoides Barer, ex Marsh =P. x euramericana) were measured for first‐year cuttings growing under controlled conditions, with or without ozone fumigation. As individual leaves expanded, leaf water potential remained constant whilst solute potential declined and turgor (P) increased from approximately 0.5 MPa to over 1.0 MPa as leaf size increased. Yield turgor (Y) measured by stress‐relaxation of leaf discs within psychrometers, increased from approximately 0.2 MPa to over 1.0 MPa during the same period. As the value of Y approached that of P, the effective turgor For growth (P – Y) declined and became zero as leaf growth ceased.

Cell wall extensibility (measured as percentage plasticity by the ‘Instron’ technique) was related to leaf growth rate such that highest values of plasticity corresponded to maximum rates of growth. As growth ceased, wall extensibility declined to very law values.

Fumigation with 50 nl 1−1 ozone for 16 h d−1 had no effect on any of the measured parameters with the result that growth and mature leaf size were unaffected by comparison with control plants receiving charcoal‐filtered air. Additional episodes of 120 nl 1−1 ozone on three consecutive days during the period of maximum leaf growth similarly had no effect on expansion or final leaf size.
Colonization of wheat (Triticum vulgare L.) by N2‐fixing cyanobacteria: II. An ultrastructural study
Authors: GANTAR M. , KERBY N. W. , ROWELL P.
Published: April 2006

summary

The infrastructure of a novel association between a N2‐feeing cyanobacterium, Nastoc sp, isolated from soil, and wheat seedlings grown in liquid culture is described. Cyanobacteria were found either as hormogonia, filaments or aseriate packages. The aseriate packages, which developed from filaments, often formed a thick layer surrounding the root surface. The packages were in intimate contact with adjacent root epidermal cells and could not be removed without damaging the epidermis. Cyanobacteria penetrated both the root epidermis and cortex and formed packages in intercellular spaces. Cyanobacteria] filaments were occasionally found within plant cells that appeared empty. Additionally, cyanobacteria were observed in association with the stem and on the surfaces of leaves. These findings demonstrate the technical feasibility of forming a novel association between a N2‐fixing cyanobacterium and a cereal.