bluuebunny/crossref_metadata_2025 huggingface dataset:
Vegetation history of Orkney, Scotland; pollen records from two small basins in west Mainland
Authors: BUNTING M. J.
Published: April 2006

summary

Pollen analysis was carried cut on sediment sequences from two small basins situated 6 km apart in the hills of west Mainland, Orkney, At both sites, vegetation development from the late glacial until after the arrival of Neolithic people is recorded. An initial late glacial heath, interrupted by a herbaceous phase indicating the Younger Dryas, was replaced by tallherb and grassland vegetation. The Saksunarvatn ash layer was recorded, coinciding with the arrival ofCorylus avellanain the islands at around 9.2 ka BP. Extensive woodland developed at about 8000 yr BP, predominantlyBetula–CoryhuswithSalix, alnus glutinosa. QuercusandPinus sylvestrisoccasionally present. The woodland was locally affected by Mesolithic human activity and finally lost at around 5kaBP, partly as a consequence of Neolithic human activity. Mire development was actively proceeding in both basins after the woodland decline. The records illustrate the importance of human activity in the development of the treeless, varied landscape seen in Orkney today.
Molecular markers in plant ecology
Authors: BACHMANN KONRAD
Published: April 2006

Various methods from molecular biology reveal sequence polymorphisms in organelle and nuclear DNA that can be used as highly informative markers for the structure and dynamics of genomes at the level of populations and individuals. Molecular markers that can be determined without regard to the phenotype permit an unbiased comparison of the adaptation of organisms to their environment, its genetic basis and its effect on evolution. Several marker types used in ecological research and their uses and limitations arc briefly discussed. PCR‐based methods, especially arnitrary‐primer‐based RAPDs, are likely to be most widely used and receive most attention. The limited use of DNA markers for overall quantitative (phenetic) comparisons of ‘genetic variability’ and ‘generic distance’ is stressed and fheir power as qualitative markers for any and all relevant regions in the genome is emphasized. Specific applications relevant to plant ecology are illustrated. These are: identification of organism and genotype even where morphology is of little help, as in mycorrhiza; identification of clones in asexually‐reproducing species, even when they are widespread and intermingled; determining if genetic variation in elonal populations comes from mutations within elonal lines or from independent origins of clonal lines; reconstructing the genotype phylogeny and fruit dispersal of elonal (apomicuc) and inbred selling organisms, measuring the degree of outcrossing by offspring exclusion analysis; detecting and analyzing introgression and characterizing reeombinant genotypes in hybrid zones relative to differential adaptive responses: tracing the phylogenetic origin and extent of ecologically differentiated races or species; characterizing the genetic basis, mapping and isolating the genes responsible for special adaptive responses. In a final outlook, 1 speculate about unconventional sources of genetic variation affecting the ecological characteristics of plants that will become accessible to experimental analysis with the new molecular methods.

ContentsSummary403I.Introduction404II.Most ecological applications concern markers in the nuclear geonome404III.DNA polymorphisms differ from allozyme pohmorphisms404IV.Types of molecular marker405V.The application of markers in ecology409VI.From marker to character413VII.Outlook414References414
Gene expression during leaf senescence
Authors: SMART CATHERINE M.
Published: April 2006

Leaf senescence is a hiphly‐controlled sequence of events comprising the final stage of development. Cells remain viable during the process and new gene expression is required. There is some similarity between senescence in plants and programmed cell death in animals. In this review, different classes of senescence‐related genes are defined and progress towards isolating such genes is reported. A range of internal and external factors which appear to cause leaf senescence is considered and various models for the mechanism of senescence‐ initiation are described. The current understanding of senescence at the wrganelle and molecular levels is presented. Finally, same ideas are mooted as to why senescence occurs and why it should be studied further.

ContentsSummary419I.Introduction420II.Internal factors that cause senescence423III.External factors that cause senescence427IV.What is the mechanism of senescence initiation?428V.Progress in the understanding of organelle senescence431VI.Progress in the understanding of senescence at the molecular level434VII.The control of senescence in animals and plants440VIII.Why is senescence necessary?441IX.Why study senescence?441References442
Chlorophyll development in mature lysigenous and schizogenous root aerenchymas provides evidence of continuing cortical cell viability
Authors: ARMSTRONG JEAN , ARMSTRONG WILLIAM
Published: April 2006

The‘greening’of mature aerenchymatous adventitious roots of Phragmrtes auttralis (Cav.) Trin. ex Steudel, rice, maize, Atorm calamus L., and Epilobium hirsutum L., when exposed to light was found to be due to chloroplast development in the cortex. In Phragmites, maize and rice, which are characterized by lysigenous cortical aerenchymos, chlomplasts developed not only in normally intact cortical cell layers adjacent to the exodermis/hypodermis and endodermis, but also in isolated radial cellular strands (and isolated cells) between the lacunae, cells which had failed to collapse during the active phase of aerenchyma development. The observation provides conclusive evidence for the continuing viability and the potential for active metabolism of the non‐lysed cells of lysigenous aerenchymas.

In Acortis and Epitobium, chloroplast development occurred in the cells of the schisogettmts cortical aerenchymas. In Phragmites, chloroplasts also developed in the non‐aerenchymatous cortex of illuminated fine basal lateral roots.
Experimental evidence for the autonomy of ray differentiation in Ficus sycomorus L.
Authors: LEV‐YADUN SIMCHA
Published: April 2006

Wounding or partial girdling leaving only a narrow cambial bridge resulted in changes in the xylem structure in stems and branches of Ficus sycomorus. Wounding inhihiitd the formation of fibre bands, induced tyiosis and differentiation of narrow vessels, and resulted in partially differentiated tissues. Partial girdling of mature trunks resulted in the formation of either a strip of traumatic xylem or a parenchymal strip in which all axial components failed to differentiate but the radial system was not affected and the rays continued to form. The differentiation of rays without an axial system is indicative of the autonomy of the radial signal system that participates in the regulation of ray formation.
Mechanisms of deposition of epicuticular wax in leaves of broccoli, Brassica oleracea var. capitata L.
Authors: ANTON L. , EWERS F. W. , HAMMERSCHMIDT R. , KLOMPARENS K. L.
Published: April 2006

Broceeli (Brassika oleraceo L. var. capitata L.) leaf waxes were labelled with [2‐14Cjacetate and examined during synthesis and deposition using microautoradiography. Waxes were viewed with light microscopy and scanning electron microscopy (SEM), including cryo‐SEM. In microautoradiography, silver grains resulting from radioactive decay of labelled waxes seemed to be distributed randomly throughout the cuticle. This random distribution supports the hypothesis of diffusion or complex anastomosing pores as the mechanism of epicuriculur wax position. The hypothesis of wax‐depositing pores running perpendicular to the leaf surface is not supported.
Identification of the ectomycorrhizal basidiomycete Tylospora fibrillosa Donk by RFLP analysis of the PCR‐amplified ITS and IGS regions of ribosomal DNA
Authors: ERLAND S. , HENRION B. , MARTIN F. , GLOVER L. A. , ALEXANDERS I. J.
Published: April 2006

Sitka spruce mycorrhizas, macroscopically identified as being formed by Tylospora fibritiosa Donk, were sampled from a young and on old plantation and the mycobionts were isolated into pure culture. DNA was extracted and fragments of the ribosomal DNA (rDNA) were amplified using the polymerase chain reaction (PCR). The primers were directed to conserved regions of fungal rDXA and hybridize to a wide range of fungi. One amplified region includes the internal spacer (ITS) region which has a low degree of conservation. The JTS amplification products, which were approximately 600 base pairs (bp), were digested with a variety of restriction endonucleases in order to detect restriction fragment length polymorphisms (RFLPs). The RFLPs clearly separated T. fibrillosa from other ectomycorrhizal species but there were only minor differences between the T. fibrillosa isolates. PCR amplification of the ITS region, digestion with the endonudeasc HinfI and examination of the RFLPs produced proved to be a rapid method by which to distinguish T. fibriHosa from a large number of other basidiomyictes. The method was also applied to DNA extracted, from single mycotrhizal root tips. The imergenic spacer region (1GS) of the rDNA is more variable than the ITS region in several fungal species. The 5’end of the 25S and the intergenic region between the 25S and the 5S genes were amplified and analyzed as above. Polymorphisms between T. fibritiosa isolates within this region were limited and RFLPs were not useful m discriminating between isolates, suggesting a low genetic variability in this species.
Pollination density ‐ effects on pollen germination and pollen tube growth in Betula pubescens Ehrh. in northern Sweden
Authors: HOLM S. O.
Published: April 2006

The aim of this study was to test the hypothesis that increased pollination enhances the probability of‘pollen competition’in Betula pubescent. In an in vitro test, the germination of pollen from three B. pubescens trees, increased with increasing pollen density (r2= 0·82, 0·81 and 0·82, respectively). Pollen tubes grew at different rates in styles when testing different paternal/maternal combinations. Evidence was obtained to suggest that these differences might be attributed to both maternal and paternal effects. Further, increasing the number of tubes per style tended to increase the length of the longest tube per style, but had no significant effect on the mean length of the tubes. The r values, for the correlations of lengths with numbers of pollen tubes per style, were lower in two natural B pubescens populations than in the data from a controlled pollination experiment, is concluded that selection among male gametes may occur after supplementary pollination in B. pubescens, but in natural situations, pollen deposition is usually too low for pollen Selection to be a common occurrence.
A one‐year study on carbon, water and nutrient relationships in a tropical C3‐CAM hemi‐epiphyte, Clusia uvitana Pittier
Authors: ZOTZ GERHARD , WINTER KLAUS
Published: April 2006

Diel (24 h) courses of CO2 and water‐vapour exchange of leaves of hemi‐epiphytic plants of Clusia uvitana Pittier (Clusiaceae) were measured under natural tropical conditions in the semi‐evergreen moist forest of Barro Colorado Island, Panama, from January 1991 until January 1992. Plants were studied at two sites, in the crown of a 47‐m tall tree (Ceiba pentandra) and on the shore of Lake Gatun, at a height of about 2–4 m. The following results were obtained: (1) Diel carbon gain was mainly a function of photosynthetic photon fluence rate (PPFR) on individual days. PPFR also strongly affected CAM activity. A leafless period of the host tree Ceiba pentandra resulted in higher incident PPFRs and slightly lower nighttime temperatures in the canopy of C uvitana; this led to increases in both daytime and nighttime CO2 fixation. (2) In fully mature sun leaves from the two sites, nocturnal net uptake of atmospheric CO2 occurred on almost all of the 71 days measured and nocturnal carbon gain was enhanced during the dry season. (3) In C. uvitana at the Lake site, 24‐h carbon gain during the wet and dry season was similar to C. uvitana at the Ceiba site during the leafless period of the host tree. Overall CAM activity was lower at the Lake site. (4) Recycling of respiratory CO2 was a major route for nocturnal acid synthesis. Nocturnal net uptake of atmospheric CO2 was closely correlated with changes in titratable acidity, but accounted for only about 30% of the nocturnal increase in organic acids. (5) Mature shade leaves performed CAM only during the dry season, whereas in the wet season they showed atmospheric CO2 uptake exclusively in the light. (6) Independent of exposure or season, leaves less than about 12 wk old showed a C3 pattern of diel gas exchange and the level of titratable acidity was high day and night. (7) The annual carbon budget of outer canopy leaves of C uvitana in the Ceiba site was 1780 g CO2 m‐2 a‐1 and the average long‐term water‐use efficiency was 23 × 10‐3 g CO2 g‐1 H2O. (8) Vegetative growth was strongly seasonal. Branch length increment and leaf area development was much higher in the wet season. Mineral element contents in these evergreen plants showed no age‐related changes, but a significant proportion of elements was retrieved before abscission.
Transfer of phosphate from fungus to plant in VA mycorrhizas: calculation of the area of symbiotic interface and of fluxes of P from two different fungi to A Allium porrum L.
Authors: SMITH S. E. , DICKSON S. , MORRIS C. , SMITH F. A.
Published: April 2006

The aim of the work described in this paper was to calculate the fluxes of phosphate (P) across the intraradical interfaces between two vesicular‐arbuscular mycorrhizal fungi [Glomus mosseae (Nicol. & Gerd.) Gerdemann and Trappe and Glomus sp.‘ City Beach’(WL'M 16)] and Allium porrum L. The inflows of P into roots via the fungi were calculated from inflows into mycorrhizal and non‐mycorrhizal plants for four harvest periods up to 84 d. The areas of interface between intercellular hyphae and roots, and arbuscules and roots were calculated for the same harvest periods using image analysis of sections in which the fungus was stained with nitroblue tetrazolium. The imagination of the arbuscular interface was calculated using methods based on previously published data. The fungi colonized the roots to approximately the same extent (% infection), but G. mosseae produced more intercellular hyphae and arbuscules, and hence larger interfacial areas than Glomus sp. City Beach (WUM 16).

Hyphal inflows were higher for Glomus sp. City Beach (WUM 16) than G. mosseae for all except the last harvest period, but because of the lower interfacial areas, fluxes via this fungus were higher (3‐7‐12‐8 nmol m‐2 s‐1) than for G, mosseae (0‐8‐3‐2 nmol nmol m‐2 s‐1. These fluxes are in the same range as values for P influx into plant cells and considerably larger than efflux from the fungal hyphae of ecto and ericoid mycorrhizal fungi measured in cultured mycelia. We conclude that enhanced efflux from the fungus must be essential for symbiotic phosphorus uptake by plants via VA mycorrhizal fungi.
Phosphorus, soluble carbohydrates and the competition between two arbuscular mycorrhizal fungi colonizing subterranean clover
Authors: PEARSON J. N. , ABBOTT L. K. , JASPER D. A.
Published: April 2006

We investigated the competition between two arbuscular mycorrhizal fungi, Glomus sp. [isolate WUM 10(1)] and Scutellospora calospora [isolate WUM 12(3)] during the colonization of subterranean clover at four concentrations of soil phosphorus (P). When the clover seedlings were 4 wks old we collected data for plant growth, P uptake, mycorrhizal colonization and soluble carbohydrate status of the roots. The percent and total colonization by Glomus sp. was reduced to a much greater extent than S. calospora when the soil P status was increased. When both fungi were inoculated together, S. calospora was unaffected by the presence of Glomus sp. or the P status of the soil; Glomus sp., however, was reduced to a far greater extent when in the presence of S. calospora than compared to when it was inoculated alone, Associated with the decreases in colonization by Glomus sp., when inoculated alone, with S. calospara and with increases in the level of P applied to the soil, were decreases in the concentration of soluble carbohydrates within the root. We propose that root carbohydrates directly influence the outcome of competition between these two isolates during the colonization of subterranean clover.
The effect of rain in the dry‐season on the formation of vesicular‐arbuscular mycorrhizas in the growing season of annual clover‐based pastures
Authors: BRAUNBERGER P. G. , ABBOTT L. K. , ROBSON A. D.
Published: April 2006

In a mediterranean climate with hot dry summers and cool winter growing seasons, rain in summer may initiate seed germination and seedling emergence in annual clover‐based pastures. If soil moisture becomes limiting and the seedlings die before the onset of winter rains then a‘false break’has occurred. The effect of false breaks on the formation of mycorrhizas in subterranean clover (Trifolium subterraneum L.) in the winter growing season was investigated.

Undisturbed cores were collected in the summer from two annual clover‐based pastures in Western Australia. The cores were treated with one or two false breaks, or left dry. For each false break, 3 centimetres of water were applied to the surface of the core over a 3 day period and then the cores were let dry in glasshouse conditions. The second false break and the growing season were initiated after the complete death of plants that had emerged in the previous cycle. The growing season was simulated by watering all cores to field capacity and planting to a uniform stand of subterranean clover.

Mycorrhizal colonization in the growing season was decreased by false breaks with little difference between One and two false breaks. In one soil, the percentage of the root length containing arbuscules (AC%) at 14 d after planting in the growing season was decreased from 52 to 33% by false breaks and at 42 d after planting from 16 to 46%. In the other soil, the AC% at 28 d after planting in the growing season was decreased from 72 to 55% by false breaks. Assessment of the morphology of the mycorrhizas indicated that colonization by fine endophytes was decreased but colonization by Acaulospora spp., Glomus spp. and Scutellospora and Gigaspora spp. was not decreased by false breaks. Shoot phosphorus concentration at 14 d after planting and shoot dry mass at 42 d after planting were decreased by false breaks in only one soil.
Fungal endophytes from the leaves and twigs of Quercus ilex L. from England, Majorca and Switzerland
Authors: FISHER P. J. , PETRINI O. , PETRINI L. E. , SUTTON B. C.
Published: April 2006

Leaves of Quercus ilex taken from sites in England, Majorca and Switzerland have been studied to detect the influence of the geographic position of the host within and outside its native range on the composition of its endophytic fungal assemblages. Samples of stem tissue of Q. ilex collected from the Swiss trees were also studied to confirm tissue‐specific differences. Sixty different fungal taxa were isolated, but only 28 were frequent. Of the total number of isolates from the leaves from the Swiss, British and Spanish sites 87%, 31% and 63%, respectively, were coelomycetes. Four species of Phomopsis, which includes Phyllosticta ilicina (=Phomopsis ilicina v. d. Aa, ined.), were the most frequent endophytes of leaves and were either absent or rare in the twig units. Two distinct kinds of sterile mycelia were common in twigs. Swiss and Spanish trees possessed fungal assemblages distinct from those present in Britain. Naturalized stands were distinguished from native stands by the presence of rather cosmopolitan and non‐specific fungal taxa, rare or absent in the samples collected in the native stands. Samples derived from the native stands were colonized by more host‐specific fungi. The relative frequency of two sterile mycelia in the Swiss and Spanish sites determined their separation. Phyllosticta (Phomopsis) ilicina, the most numerous leaf colonizer, was virtually absent from the bark and the xylem. The frequent occurrence of coelomycetes as endophytes of woody trees is briefly discussed.
Late‐glacial and Holocene vegetation history of the Flow Country, northern Scotland
Authors: CHARMAN DANIEL J.
Published: April 2006

The vegetation history of an important conservation area, the Flow Country in northern Scotland, is described using the results of pollen analysis from two closely spaced cores from the Cross Lochs, eastern Sutherland. Buried lake sediments and shallower surface peats yield a continuous record covering the Devensian Late‐glacial and the Holocene. The earliest Late‐glacial pollen spectra recovered suggest a transition from open habitat to more stable communities, dominated by *Empetrum heath. This Windermere Interstadial vegetation shows some variability, with a phase of increased growth of juniper and birch, followed by deteriorating climate and less stable soil conditions in the transition to the Stadial, with Huperzia selago and Salix. There are poorly defined Loch Lomond Stadial and Stadial‐Holocene transition periods, characterized by Rumex/Oxyria, after which much warmer, Holocene conditions occur, with a succession of birch‐juniper and birch‐hazel woodland. Birch persists in small amounts locally, but the presence of other arboreal pollen is thought to be mostly due to long distance pollen transport. From c. 5500 BP, the landscape is largely treeless, apart from a brief phase of local pine forest c 4500–4000 BP. These changes are compared with other pollen records for northern Scotland. The trends in the Late‐glacial vegetation are broadly similar to those displayed by other sites, although many of the changes appear to be less extreme than for areas to the south and west. The lack of Artemisia during the Loch Lomond Stadial in the east Sutherland and Caithness area is particularly noteworthy. This may imply more extensive snow cover. The early Holocene is similar to the rest of northern Scotland, but invasion of Betula was more rapid and the later growth of this genus and hazel was not so dense. The lack of pine in the early Holocene allies the site with eastern Caithness and the Northern Isles, rather than north‐west Scotland and the Grampians. It is suggested that the effects of early human populations on such marginal forest areas may have been underestimated in the past. The paradoxical existence of pine macrofossils with no pollen evidence in several areas of Scotland is explained, at least in part, by the lack of temporal precision of pollen diagrams rather than by low pollen productivity, extremely localized occurrences of the species or strong prevailing winds.
Immunomagnetic isolation of viable intracellular hyphae of Colletotrichum lindemuthianum (Sacc. & Magn.) Briosi & Cav. from infected bean leaves using a monoclonal antibody
Authors: PAIN NAOMI A. , GREEN JONATHAN R. , GAMMIE FIONA , O'CONNELL RICHARD J.
Published: April 2006

A method is described for isolating intracellular hyphae (IH, i.e. infection vesicles and primary hyphae) of Colletotrichum lindemuthianum (Sacc. & Magn.) Briosi & Cav. from infected leaves‐of bean (Phaseolus vulgaris L.). 1H were recovered from homogenates of infected leaves after filtration through a 45 μm nylon mesh and isopyenic centrifugation on Percoll. 1H were then affinity‐purified by immunomagnetic separation using Dynabeads coated with monoclonal antibody UB25, specific for IH surface glycoproteins. The method yielded 7 × 104 IH g‐1 f. wt leaf tissue, with 27% purity and 62% viability, as judged by staining with fluorescein diacetate. The Viability of isolated IH was confirmed by their ability to grow in nutrient medium and by the normal ultrastructure of their cytoplasm. The host plasma membrane and matrix layer which surround IH in planta were absent from isolated IH. Staining with lectins. Calcofluor and aniline blue showed that the walls of IH contain N‐acetylgalactosamine. α‐linked mannose residues and β‐linked polysaccharides, including‐chitin and β‐1,3‐glucans. Potential uses of the isolated IH are discussed.
Inorganic carbon acquisition by aquatic photolithoatrophs of the Dighty Burn, Angus, U.K.: uses and limitations of natural abundance measurements of carbon isotopes
Authors: RAVEN J. A. , JOHNSTON A. M. , NEWMAN J. R. , SCRIMGEOUR C. M.
Published: April 2006

The 13C/12C ratio (expressed as δ13C) of benrhic photolithotrophs. in the Dighn Water (= Burn) were measured fur comparison with that of the potential inorganic carhun sources. CO2 and HCO3‐, in the Burn. The Burn water contains an average of 65.7 mmol m‐3 CO2 with δ13C of ‐14.7% and 1600 mmol m‐3 HCO3‐ with δ13C of ‐4.%. δ13C values of riparian vegetation were also measured as contributors, after respiration in the soil or the Burn, to the δ13C of inorganic carbon in the Burn. The potential range of differences in 13C/12C between dissolved CO2 and plant organic C is set by the intrinsic 13c/12C discrimination (α value) in CO2 fixation by Rubisco. Main results and conclusions are. as follows, (i) A literature survey suggests that there is no convincing evidence that the α, Values (rate constant for 12CO2 fixation relative to that for 13CO2 fixation by Rubisco in the absence of CO2 transport limitation) for the‘lower plants’in the Burn (diatoms, green and red algae, mosses) are significantly different from the well‐established αp values for the flowering plum enzyme. (ii) In confirmation of earlier work, the semi‐erect 'streamer’gametophytes of the red alga Lemanea mamillosa and the moss Fontinalis antipyetica have δ13C values which can only be interpreted in terms of diffusive CO2 entry with minimal limitation of photosynthesis by CO‐ diffusion, (iii) The serui‐erect grren alga Cladophora glomerata and the flowering plant Ranunculus penicillatus ssp. pseudofluitons (formerly var. calcareus) are‐ both able to use HCO3‐. Their δ13C values indicate that, if the HCO3‐ ‐use system does not (as is likely) discriminate significantly between 13C and 12C, then a substantial fraction of the inorganic C made available to Rubisco must return to the medium, carrying 13C‐inorganic C not fixed by Rubisco. (iv) Two sets of δ13C data from different hydrodynamic regimes distance from leading edge of a flat stone; different size of thalli) show that the attainable differences in situ in thickness of the diffusion boundary layer do not alter the fractional limitation of photosynthesis of Cladophora by external diffusion of inorganic C, considered with HCO3 use. (vi) The entrusting red alga Hildenbrandia rivularis has a δ13C value suggestive of CO2 as the inorganic C source, but not entirely ruling nut HCO3‐. Marine species of both Hildenbrundia and Cladophora have δ13C values which, even when corrected for source inorganic C δ13C values, are 10%, more positive than the freshwater species. (vii) Mats of pennate diatoms were shown by pH‐drift to by able to use HCO3‐; the relatively high (i.e. not very negative) δ12C value of these mats could relate to a relatively‘non‐leaky’HCO3‐ aequisition mechanism and/or to limitation by external diffusion (e.g. through the mat).
Hydraulic architecture, water relations and vulnerability to cavitation ofClusia uvitanaPittier: a C3‐CAM tropical hemiepiphyte
Authors: ZOTZ GERHARD , TYREE MELVIN T. , COCHARD HERVÉ
Published: April 2006

Clusia uvitana Pittíer (Clusiacea) is a tropical hemiepiphyte that has been shown to display a high plasticity in the expression of CAM in response to the environment. When water is available CO2is taken up mostly during the‐ day. This study of the water relations and hydraulic architecture has revealed that leaf water potentials, £ ranged from 0‐7 to ‐0.9 MPa and changed very little with time or water availability. The absolute hydraulic conductivity of stem segments(K,)and the specific conductivity (K1) were comparable to many other temperate and tropical species, but the leaf specificity conductivity (K1) was 1/3 to 1/30 that of many other species. So stems supported high leaf areas per unit of hydraulic conductivity.C uvitanawas very vulnerable to cavitation, reaching 50 % loss of hydraulic conductivity at stem £=1.3 MPa. The species survives in spite of low K1and high xylem vulnerability, because the CAM physiology insures low transpiration rates and high ability to evade dehydration.
Origin of the epidermis in root meristems
Authors: CLOWES F. A. L.
Published: April 2006

A survey of root meristems shows that in general, closed meristems, those with separate regions generating outer and inner tissues, derive the epidermis with the cortex in monocotyledons and with the cap in dicotyledons. Open meristems, where the cells between the stelar pole and cap divide transiently producing an unstable boundary between the cap and the rest of the root, also show a distinction between the classes, monocotyledons displaying greatest affinity between epidermis and cortex, dicotyledons between epidermis and cap.

Exceptions in monocotyledons occur where there is a discrete epidermal meristem, an anticlinally dividing, monostromatic sheet of cells between cortex and cap. This condition has been reliably found only in a few floating plants and it is associated with the root being derived from both pericycle and endodermis of the mother organ. This is uncommon as a permanent feature in angiosperms though not confined to those with discrete epidermises. The mother tissue producing the epidermis depends on the species. In many other monocotyledons with closed meristems the epidermis is functionally discrete, for the branching of the epidermal cell files from, the cortical files is seen within the quiescent centre, i.e. it occurred during the meristem's initiation.

Exceptions in dicotyledons occur in the Nymphaeales. In their closed meristems the epidermis is part of the cortical complex and in their open meristems its affinity with the cortex is manifest by early separation of the cap creating a cylindrical cleft in some genera. Differentiation of epidermal trichoblasts is also by a mode more characteristic of monocotyledons. Nelumbo roots, previously described as lacking an epidermis, as in gymnosperms, have closed meristems of dicotyledonous type and epidermises without distinctive trichoblasts, supporting Nelumbno's transfer from the Nymphaeales.

The survey has corrected many errors of observation and interpretation in the literature enabling better use to be made of the mode of origin of root epidermises in discussing evolution and the new reclassification of angiosperms.
Is acclimation required for success in high light environments? A case study using Mycelis muralis (L.) Dumort (Asteraceae)
Authors: OSBORNE BRUCE A. , CLABBY GERRY T. , HORSLEY DAVID , NOLAN PETER F.
Published: April 2006

In the field significant differences in maximum photosynthetic O2‐exchange rate (Pm) were found between leaves of Mycelis muralis (L.) Dumort (Asteraceae) collected from woodland and exposed habitats, with the highest values in the exposed sites‐ However, there were no differences in the Pm of leaves collected from plants growing in grikes (fissures in the limestone pavement), of exposed limestone pavement, despite a greater than four‐fold difference in the integrated daily irradiance. Leaves of plants from the open pavement had lower photon yields (ø1) and higher dark respiration rates and light compensation points, in comparison to shaded plants. Under controlled environmental conditions the highest Pm of leaves from plants subjected to variations in irradiance were found at the intermediate (8‐6 mol photon m‐2 d‐1 growth light level used. At the highest growth irradiance 17.3 mol photon m‐2 d‐1 used in the laboratory both Pm and øl were reduced, although the latest plant biomass was found at this irradiance. No changes were found in the chlorophyll a:b ratio over the same range of irradiances. Examination of plant populations of M. muralis, collected from open or shaded habitats and exposed to growth irradiances that covered the range over which increases in photosynthesis were, observed in the laboratory (0.86‐8.6 mol photon m‐2 d‐1), resulted in changes in leaf structure and pigment composition. The chlorophyll a:b ratio was low and largely independent of irradiance or the origin of the plant population. Differences in total chlorophyll content were small with the lowest values m the Durrow woodland populations at both irradiances. No variations were found in a number of chloroplast thylakoid structural features. In particular, the ratio of oppressed to non‐appressed membranes was unchanged by growth at the two irradiances, consistent with an invariant chlorophyll a:b ratio. Based on peaks in the difference spectra the woodland populations had mi enhanced in vivo absorption at λlD= 650 and 706 nm when grown at low irradiance. These peaks were absent from the population collected from the open limestone pavement. The significance of the enhanced absorption at low irradiance and the possibility that these peaks represent long‐wavelength forms of chlorophyll a (λlD = 706) and b (λlD = 650) is discussed. A particular feature of plants grown at high irradiance was an enhanced anthocyanin content in comparison to those grown at low irradiance. This was associated with an increase in absorptance. particularly in the green region (λlD = 550 nm) of the visible spectrum. Overall these results suggest that complete acclimation of photosynthesis and an ability to modulate light‐harvesting is not a prerequisite, for success in a high light environment.
Past and present variability in leaf length of evergreen members of Nothofagus subgenus Lophozonia related to ecology and population dynamics
Authors: JORDAN GREGORY J. , HILL ROBERT S.
Published: April 2006

The lengths of fossil leaves of Nothofogus cunninghamii, and of closely related fossil species from sediments older than the Middle Pleistocene showed greater variation than fossil leaves from younger sediments and extant leaves from modern sediment samples and forest floor litter. Leaf sizes of samples of the other two extant evergreen species of Nothofagus subgenus Lophazonia, N. moorei and N.menziesii, were no more variable than modern N.cunninhamii. Leaf lengths of modern and Middle‐Late Pleistocene N. cunninhamii and of modern N. menziesii were more or less unimodal in distribution, whereas the leaves of N. moorei follow bimodal distributions, and leaves from the Early Pleistocene Regatta Point and the Oligocene Link‐ Rapid River sediments tended to be bimodal and highly variable. Leaf lengths from the Oligo‐Miocene Monpeelyata sediments were also highly variable, but the sample size was too small to determine if they follow bimodal distributions. The bimodality and high variability in the older sites are unlikely to have been due to taphonomic processes. Thus, within population variability appears to have declined during the Late Tertiary‐Early Pleistocene, although the presence of cryptic species in the fossil record could also explain the results. Both a decline in variability within species, and the extinction of Nothofugus species, are consistent with a well documented Late Cainozoic decline in rainforest diversity in Tasmania. Log transformed leaf lengths of modern forest floor litter samples of N. cunninhamii were Strongly correlated with climatic parameters, particularly summer temperature, suggesting that this parameter is a strong determinant of leaf size in N. cunninhamii Changes in N. cunninhamii leaf lengths within Middle Pleistocene sediments were associated with floristic changes interpreted as transitions in glacial/interglacial cycles but these changes were small compared with changes predicted Iron climatic correlation of extant samples, probably because of limited Emetic variability in local populations at the time of deposition.
The branch roots of Zea
Authors: WANG X. L. , McCULLY M. E. , CANNY M. J.
Published: April 2006

The late metaxylem (LMX) in the first‐order branch roots of maize matures slowly. Fully lignified elements remain as individual cells of mean diameter 67 μm and length about 2 mm for considerable distances proximal from the tip of branches that retain an active meristem (indeterminate branches). Such branches, depending on their age, have from 0 to 45%, of the Total length of LMX conduits mature and open for unrestricted conduction of the transpiration stream. In determinate branches (those that have lost their meristem), up to 60% of LMX length is open for conduction. The closed portion of the xylem conduits is at the distal end of the branches. In both indeterminate, and the youngest determinate branches, immature, living xylem elements provide the block in the conduits. Later, progressive decay in the determinate branches passes basipetally beyond the immature elements, bus the distal ends of the conduits remain closed, plugged initially by mucilaginous materials apparently of root origin, and subsequently by invading microbes. It is proposed that the closed ends of the xylem conduits restrict leakage from the more proximal regions, and also prevent their blockage by embolisms. The presence of mature LMX conduits open for unrestricted water conduction is consistent with the major role in water uptake assigned to the branch roots in earlier studies.
Evaluation of air pollution phytotoxicity in a seasonally dry tropical urban environment using three woody perennials
Authors: PANDEY J. , AGRAWAL M.
Published: April 2006

A two‐year study was conducted in the urban environment of Varanasi, India, to evaluate plant responses to urban air pollution. Three species including a shrub (Carissa carandas L.) and two tree species (Delonix regia Rafin and Cassia fistula L.) were grown in pots at selected study sites. Changes in plant performance were considered in relation to the status of ambient air quality.

Reductions in plant height, basal diameter, canopy area, plant biomass and chlorophyll, ascorbic acid and nitrogen contents in leaves were correlated with air pollution level at different sites. The magnitude of response indicated the relative sensitivity of the three species in the order D. regia > C. fistula > C. carandas. Shifts in relative contribution of photosynthate to leaf production and shoot growth appear to be a pollution‐induced adaptive response in C. carandas. The study shows that the urban air pollution level at Varanasi is detrimental to the growth of plants.
Impact of O3 and SO2 on reproductive development in oilseed rape (Brassica napus L.)
Authors: BOSAC C. , ROBERTS J. A. , BLACK V. J. , BLACK C. R.
Published: April 2006

The flowering racemes of Brassica napus L. cv. Tapidor were exposed independently from the vegetative component to 200 nl l−1, 100 nl l−1 O3/30 nl l−1 SO2, In all cases, a single 6 h exposure significantly increased bud abortion, and abscission 2 and 5 d after treatment. Similar results were obtained using cv. Libravo, although the effect of 100 nl l−1 O3 was significant only after 2 d. Exposure to 30 nl l−1 SO2 did not enhance bud abortion and abscission in either variety. Longer term measurements for up to 25 d revealed a trend to wards sustained losses of fertile sites in those pollutant treatments which had exhibited demonstrable, effects after 2 and/or 5 d. However, the number of fertile sites present was comparable to or even higher than in the controls, indicating that compensation for the initial losses must have occurred. Following exposure, plants of cv. Tapidor tended to develop longer total raceme lengths and greater numbers of raceme branches, and those of cv. Libravo a greater number of raceme branches. Indicating possible methods by which new fertile sites may have been produced. The significance of these observations for the reproductive development of field‐grown oilseed rape is discussed.
A basidiomycete isolated from a Pisonia mycorrhiza forms sheathing mycorrhizas with transfer cells on Pisonia grandis R. Br.
Authors: CAIRNEY J. W. G. , REES B. J. , ALLAWAY W. G. , ASHFORD A. E.
Published: April 2006

A basidiomycete isolated from a mycorrhiza of glasshouse‐crown Pisonia grandis R. Br. (Nyctaginaceae) produced sheathing mycorrhizas with transfer ceils when inoculated on to roofs of Pisonia grandis in pots. Mycorrhizal synthesis was successful on Pisonia grandis in sterilized natural soil rich in phosphorus, nitrogen, potassium and calcium, but unsuccessful in a range of other substrates of low nutrient status. The same fungus produced ectomycorrhizas, with a sheath and some intercellular penetration, on short lateral runts of Picea sitchensis (Bong.) Carr (Pinaceae) seedling in growth pouches, but did not on Eucalyptus pilularis Smith (Myrtaceae).
The effects of polyamine biosynthesis inhibitors on growth, enzyme activities and polyamine concentrations in the mycorrhizal fungus Laccaria proxima
Authors: ZARB J. , WALTERS D. R.
Published: April 2006

Difluoromethylarginine (DFMA) and difluoromethylornithine (DFMO) are inhibitors of the polyamine biosynthetic enzymes arginine decarboxylase (ADC) and ornithine decarboxylese (ODC), respectively, DFMO is a potential fungicide acting on fungal ODC.

This report examines the effects of DFMA and DFMO on polyamine concentrations and metabolism, and on the activities of enzymes of polyamine biosynthesis and breakdown in the mycorrhizal fungus Laccaria proxima. Data indicate that L. proxima possesses both ADC and ODC activities: DFMA depleted putrescine and did not inhibit ODC activity; incubation of mycelium with a [U‐14C]arginine substrate led to [14C]putrescine formation DFMA completely inhibited the formation of polyamines from [U‐14C]arginine DFMO inhibited bound biosynthetic enzyme activity and the formation of putrescine from [U‐14C]ornithine. Therefore, L. proxima may not be susceptible to fungicidal DFMO application.
Improved nitrogen uptake and transport from 15N‐labelled nitrate by external hyphae of arbuscular mycorrhiza under water‐stressed conditions
Authors: TOBAR R. , AZCÓN R. , BAREA J. M.
Published: April 2006

The significance of the external mycelium of arbuscular mycorrhiza for uptake and transport of N from 15N‐labelled nitrate in benefiting plant nutrition, was evaluated under either well‐irrigated or water‐stressed conditions. Plants of lettuce (Lactuca sativa L.) were grown under controlled conditions in a neutral agricultural soil/sand mix either non‐mycorrhizal or in association with the arbuscular‐mycorrhizal fungus, Glomus fasciculatum (Taxter sensu Gerd.) Gerd. and Trappe. The pots comprised a two‐compartment system, where a fine nylon mesh screen prevented the development of roots in a hyphal compartment. 15NO3− was applied to this hyphal compartment where access of the root was not possible. At harvest, the 15N enrichment in plant tissues was the same for both mycorrhizal and non‐mycorrhizal plants under optimal water supply conditions. However, under water‐stressed conditions, where the mass flow and diffusion of NO3− ions to the roots can be affected, the 15N enrichment was four times higher in mycorrhizal than in non‐mycorrhizal plants. This provides evidence of hyphal transport of N from a nitrate source, supporting the view that arbuscular mycorrhiza can be important for the N‐nutrition of plants in relatively dry agricultural soil where nitrate is actually the predominant nitrogen form.
Mycorrhizal fungi and reproduction of field populations of Abutilon theophrasti Medic. (Malvaceae)
Authors: KOIDE ROGER T. , SHUMWAY DURLAND L. , MABON STEPHEN A.
Published: April 2006

The effects of inoculation with mycorrhizal fungi and phosphorus amendment on reproduction of Abutilon theophrasti Medic, were documented over two years in the field. In Year 1 all plots were thinned to a common and relatively low density (12 plants m−2). Mycorrhizal infection significantly increased capsule and seed production. Phosphorus amendment had little effect on these characters, possibly due to low soil moisture content. In Year 2 following natural recruitment, inoculated (M) plots were much more dense than uninoculated (NM) plots. In contrast with the results from Year 1, however, individual plains in M plots produced fewer capsules than those in NM plots in Year 2 because capsule production in Year 2 was density‐dependent. Based on these results and others, we suggest that in monospecific stands of Abutilon, mycorrhizal infections have the greatest effects on fecundity at low densities. At higher densities, density‐dependent forces may reduce the importance of mycorrhizal infections to reproductive effort of a single plant. Our results highlight the necessity of examining the effects of mycorrhizal fungi in natural populations and communities.
Accumulation of amino acids in some boreal forest plants in response to increased nitrogen availability
Authors: NÄSHOLM ANN‐BRITTEDFAST TORGNY , ERICSSON ANDERS , NORDÉN LARS‐GÖSTA
Published: April 2006

Accumulation of amino acids in response to application of 500 kg N ha−1 as a single dose of NH4NO3, was measured for four common Swedish forest species. Addition of N resulted in increased levels of especially glutamine and arginine in Vaccinium myrtillus L. and in V. vitis‐idaea L., whilst, in fertilized Deschampsia flexuosa L., asparagine and glutamine were most prominent. In Epilobium angustifolium L. glutamine and arginine increased most after fertilization. In a second study, five different forest species, V. myrtillus, V. vitis‐idaea, D. flexuosa, Pleurozium schreberi Wild. and Polytrichum commune Menz. were studied in a Norway spruce fertilization experiment. In this experiment, plots had been irrigated with a complete mixture of nutrients during the growing period for five subsequent years. Arginine in Pl. schreberi, glutamine in P. commune and asparagine in D. flexuosa were all elevated on fertilized plots, while in fertilized V. vitis‐idaea and V. myrtillus only minor increases of amino acid concentrations were found. In a third investigation, amino acid concentrations were measured in Pl. schreberi, Hylocomium splendens L., V. myrtillus, V. Vitis‐idaea and D. flexuosa growing on different plots in an area with relatively high nitrogen deposition. The plots were divided into two groups, one characterized by high, and one by low concentration of arginine in spruce needles from trees growing on the same plot. Asparagine in D. flexuosa, arginine and asparagine in Pl. schreberi and arginine in H. splendens were significantly higher in plants from plots with high concentrations of arginine in needles of Norway spruce. Differences between species in the metabolism of nitrogen during conditions of high nitrogen supply are discussed as well as possible usage of specific amino acids in the studied species as indicators of nitrogen saturation.
Fire and age structure of Scots pine and Norway spruce in northern Sweden during the past 700 years
Authors: ENGELMARK OLA , KULLMAN LEIF , BERGERON YVES
Published: April 2006

The performance ofPinus sylvestrisL. andPicea abies(L.) Karst has been studied in relation to the fire regime from the 1200s up to present in an old‐growth boreal forest area, The J‐shaped age distribution of pine during the study period, suggests a stationary pattern in the landscape. The spruce age structure (from the 1600s onwards) also points towards a J‐shape, although with slight deviations. No significant changes in total pine or spruce regeneration occurred in response to the significantly prolonged fire cycle (from 187 to 371 yr) around 1870. This break in the fire cycle might possibly have a climatic background.