bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal changes in water use of ash trees exposed to ozone episodes
Authors: WILTSHIRE J.J.J. , UNSWORTH M. H. , WRIGHT C. J.
Published: April 2006

Young ash trees (Fraxinus excelsior L.) growing in the field were exposed to episodes of 150 nl 1‐1 ozone, or to clean air, in open‐top chambers at the University of Nottingham, Sucton Bonington Campus, UK, in the summer of 1992. The episodes were for 8 h daily and for 1‐4 in succession, with a seasonal total of 27 d. From late‐June until mid‐September 1942, flow of water in the stems of individual trees was measured using a heat balance method. Short‐term effects of ozone exposure on stem flow were not detected. However, in the longer‐term, daily integrated stem flow values for the ozone treatment decreased throughout the measurement period relative to the clear air treatment. Further data analysis showed that integrated stem flow values for morning, evening and for the more stable central part of the day changed in a similar way, but this was statistically significant only for the evening period. No treatment differences, however, were detected in night‐time water use values.

This response was probably mediated by changes in stomatal resistance and, if applicable to other species, has important implications for the long‐term growth of trees in regions where photochemical ozone is common.
Late Epipalaeolithic wood remains from el‐Wad Cave, Mount Carmel, Israel
Authors: LEV‐YADUN SIMCHA , WEINSTEIN‐EVRON MINA
Published: April 2006

Thirty‐two Early Natufian (13‐11 k years BP) pieces of charcoal were found in the recent excavations of el‐Wad Cave, Mount Carmel, Israel. These includedTamarixsp. (10 pieces),Quercus calliprinosWebb (10),Quercus ithaburensisDecne. (three),Quercussp. (two),Salixsp., probablyacmophyllaBoiss, (four),Cupressus sempervirensL. (one), andMyrtus communisL. (one), and an unidentified dicotyledonous plant. These finds indicate that the Natufians used various local woody plants in their economy, in a Mediterranean climate similar to that of the present, during the closing stages of the Pleistocene.
Rates of diffusion into roots of maize
Authors: CANNY M.J. , HUANG C.X.
Published: April 2006

The rate at which solutes may move in the cell wall apoplast of roots was assessed by measuring the diffusivity (D) of a dye, sulphorhodamine G (SR), in freshroots of field‐grown maize. Pieces of axile and branch roots from regions with soil sheaths (with immature late metaxylem) and without sheaths (with mature late metaxylem) were placed in SR solution for 5, 20 and 80 min, removed, rinesed and freeze‐substituted. The water‐soluble SR was retained in position in the tissues during anhydrous embedding and sectioning. The distance of radial penetration of the dye was measured from micrographs taken in the fluorescence microscope. Fick's aecond law was used to calculate values of D. The values are expressed relative to the value of D in water (Daq). Mature axile roots uniformly gave values of D=Duq/1000. In immature axile roots D varied from 0 (no penetration through the hypodermal walls) through Duq/1000 to D aq/40 (the maximum value found). This variation probably arises from a developmental sequence. with D high in the region to 10 cm from the tip. zero in the region 10‐25 cm from the tip, and low further back (merging with values for mature roots). In branches of both immature and mature roots also, D was highly variable, from zero to Daq/40. SR was found to penetrate through the endodermis of axes and branches, following sub‐microscopic paths around the lining of pits in the secondary walls. It is concluded that soil solutes probably enter roots at the outermost layer of cells, and that the cell wall apoplast is most unlikely to be a path for flowing water.
Salt stress‐induced changes in superoxide dismutase isozymes in leaves and mesophyll protoplasts from Vigna unguiculata (L.) Walp.
Authors: HERNÁNDEZ JOSE A. , DEL RÍO LUIS A. , SEVILLA FRANCISCA
Published: April 2006

The effect of salt stress (NaCl and/or KCl) on the specific activity of superoxide dismutase (SOD) isozymes in leaves from cowpea plants and in mesophyll protoplasts from cowpea leaves was examined. In leaves, mitochondrial Mn‐SOD was significantly decreased by 35 mM (up to 35%) and 100 mM NaCl (up to 60%), whereas, under the same conditions, cytosolic and mitochondrial Cu, Zn‐SOD I was slightly diminished and chloroplastic Cu, Zn‐SOD II did not show a response. In protoplasts, the specific activity of SOD isozymes was decreased as a function of both the salt concentration and the type of salt used Mn‐SOD was again the most salt‐sensitive isozyme, but in contrast to whole leaf preparations. Cu, Zn‐SOD II in protoplasts was markedly inhibited by NaCl and Cu, Zn‐SOD I showed an intermediate sensitivity. KCl concentrations equivalent to those of NaCl were less effective in inhibiting the SOD isozymes, suggesting the existence of specificity for certain ions. In protoplasts salt inhibition of SODs was reversible. However, Mn2+ was necessary for total recovery of Mn‐SOD activity in NaCl‐treated protoplasts. The in vitro results suggested a competitive inhibition of SOD isozymes by salts. A possible competitive inhibition of SOD activity in salt‐treated cowpea plants was also suggested. Finally, the possible correlation between plant response to NaCl and the potential of SOD isozymes was analyzed.
Canopy photosynthesis of CO2‐enriched lettuce (Lactuca sativa L.). Response to short‐term changes in CO2, temperature and oxides of nitrogen
Authors: CAPORN S. J. M. , HAND D. W. , MANSFIELD T. A. , WELLBURN A. R.
Published: April 2006

The canopy net photosynthesis (Pn) of lettuce (Lactuca sativa L. ev.‘Ambassador’) was analyzed under controlled conditions simulating the winter glasshouse atmosphere. Prior to measurements the plants were grown in CO2‐enriched air of 1000 μmol mol−1, at a photosynthetic photon flux density (PPFD) of 280 μmol m2 s−1 (400–700 nm) and a day/night air temperature of 16/13 °C.

Short‐term changes in CO2 concentration significantly changed the initial gradient of the photosynthetic response to incident PPFD. Maximum photosynthetic efficiency of the crop increased from 0·041 mol CO2 mol photons−1 (equivalent to 8·2 μg CO2 J−1 and 9·4% on an energy basis) at 350 μmol mol−1 to 0·055 mol CO2 photons−1 (10·9 μg CO2 J−1 and 12·7% on an energy basis) at 1000 μmol mol−1. Transfer from low to high CO2 also lowered the light compensation point, but did not affect dark respiration. The large response of Pn to transient changes in CO2 indicated that the lettuce canopy did not acclimate to growth in 1000 μmol CO2 mol−1, in contrast with the effect of growth in high CO2on Pn in single mature leaves reported earlier.

A reduction in air temperature from 16 to 6 °C at a concentration of 1000 μmol CO2 mol−1 halved the rate of dark respiration and reduced the light compensation point, but had no direct effect on the maximum efficiency with which the crop utilized light. Subsequently at low light (below 200 μmol m−1 s−1) Pn was greater at 6 than 16 °C. Between a PPFD of 250 and 300 μmol m−2 s−1 canopy Pn was similar at all temperatures.

Addition of 2·0 μmol mol−1 nitric oxide to an atmosphere of 1000 μmol CO2 mol−1 caused a rapid and reversible reduction of canopy Pn, which was greater at the lowest temperatures. The average inhibition was 6·6 at 16 °C and 28·8% at 6 °C; this was not explained by differences in the rate of pollutant uptake, which was less in the cooler conditions.

The results are discussed in relation to development of optimal growing conditions for production of glasshouse lettuce at low light and low temperature during winter in the UK.
Time course of oxidant stress biomarkers in flag leaves of wheat exposed to ozone and drought stress
Authors: FANGMEIER A. , BRUNSCHÖN S. , JÄGER H.‐J.
Published: April 2006

Protein content, catalase activity (CAT), non‐specific peroxidase activity (POD), ascorbic acid content (AsA) and malondialdehyde content (MDA) were estimated in flag leaves of spring wheat exposed to ozone and drought stress in open‐top chambers. Four harvests were carried out at different developmental stages to estimate the time course of these parameters. Senescence was enhanced by ozone which was reflected in the time course of the oxidant stress biomarkers. Protein content decreased, and POD and MDA increased only after the leaves had experienced high doses of ozone, whereas AsA levels were raised in ozone‐treated plants after only a short exposure period. CAT did not significantly respond to ozone treatment, but, ozone accelerated the progress of its time course. Drought stress did not influence the time course of any of the estimated parameters, but led to somewhat increased levels of AsA.
Pathogenesis‐related proteins in ozone‐exposed Norway spruce [Picea abies (Karst) L.]
Authors: KÄRENLAMPI SIRPA O. , AIRAKSINEN KIRSTI , MIETTINEN ANU T. E. , KOKKO HARRI I. , HOLOPAINEN JARMO K. , KÄRENLAMPI LAURI V. , KARJALAINEN REIJO O.
Published: April 2006

In a search for biochemical markers indicating the impact of ozone on plants. Pathogenesis related (PR) proteins were studied. The following observations were made: (1) PR‐proteins are present in gymnosperms, exemplified by Norway spruce (Picea abies) and (2) ozone induces PR‐proteins in Norway spruce. Studies were made by Western blot analysis using antibodies raised against seven PR‐proteins; five from tobacco (PR‐1a, ‐1b, ‐1c, ‐P and ‐Q) and two from maize (PRm 6 and 7). Each antibody recognized specific proteins in spruce needles. A more detailed study was done with the antibodies against tobacco PR‐P (endochitinase) and maize PRm 6 (β‐1,3‐glucanase). Exposure to ozone increased the contents of proteins recognized by both antibodies. In control trees, anti‐PR‐P antibody recognized a protein of about 28 kD while in the ozone‐exposed trees a form with a slightly faster migration rate in SDS‐PAGE predominated. In contrast, in the range of 34–44 kD, a family of proteins was recognized by anti‐PRm 6 antibody upon induction by ozone. In this same size range, a strong bund of 37 KD appeared in the total protein pattern, corresponding to about 5 to 10% of total protein. N‐terminal sequencing revealed a typical homology pattern shared by β‐1,3‐glucanases. This was also reflected by the enzymatic level Where ozone was shown to increase β‐1,3‐glucanase activity. By inducing pathogenesis‐related proteins, ozone may modify the response of spruce to pathogens.
Genetics of ectomycorrhizal symbiosis
Authors: ROSADO S. C. S. , KROPP B. R. , PICHÉ Y.
Published: April 2006

The interactions between genotypes of Pinus elliottii and the ectomycorrhizal fungus Pisolithus tinctorius (Pt) were investigated to assess genetic variability and heritability of root morphology and ectomycorrhizal traits. Seedlings from 15 open‐pollinated pine families, which were either uninoculated or inoculated with Pt and grown under controlled conditions in growth pouches, were analyzed for the following traits: number of shoot roots (SRN), root dry weight (RDW), shoot/root dry weight ratio (SRR), number of ectomycorrhizes (ECN), percentage ectomycorrhizal colonization (ECP) and development of extramatrical mycelium (EMD). There were significant increases in SRN and SRR in inoculated seedlings and significant family variation for RDW and SRR traits. A significant inoculation × family interaction was observed for SRN, but not for RDW and SRR. The individual narrow‐sense heritabilities for SRN, RDW and SRR were, respectively, 0·55, 1·00 and 0·68 (inoculated) and 0·43, 1·00 and 0·25 (uninoculated). The higher heritabilities for the ectomycorrhizal traits were 0·60, 0·81 and 0·53 for ECN, ECP and EMD, respectively. The higher heritabilities of root morphology traits for inoculated seedlings indicates that the mycorrhizal condition of plants should be an important factor in increasing root quality from genetic selection, especially on poor sites where the plants are more dependent on mycorrhizal. The relatively strong genetic control of ectomycorrhizal traits indicates a great potential for selecting individuals in tree breeding programs.
Photostimulation of seed germination during soil tillage
Authors: SCOPEL A.L. , BALLARE C.L. , RADOSEVICH S.R.
Published: April 2006

We conducted intensively replicated field experiments in the Willamette Valley. Oregon, USA, in order to study the role of light in triggering seed germination during soil tillage. We found that the normal practice of cultivating agricultural land during daytime can increase germination of buried seed populations between 70 and 400 above the levels recorded following nighttime cultivations. Experimental reduction of the irradiance under the tillage implements during daytime cultivation decreases the number of dicotyledonous seedlings emerged. while strong artificial illumination (>300μmol m−2 s−1; 400–800nm) of the soil surface under the implements during nighttime tillage significantly increases seedling densities. These results suggest that the enhancement of seed germination caused by daytime tillage, compared with nighttime tillage, is due to light that penetrates into the soil during the actual disturbance. The detection by the seeds of this very short exposure to sunlight requires a high photosensitivity. which provides an adaptive‘purpose’for the evolution of the very‐low‐fluence response mechanism in phytochrome‐controlled seed germination. Seedling emergence induced by nighttime control tillage was considerable in some experiments. suggesting that light perceived by seeds after cultivation or other microenvironmental factors affected by tillage may be important in triggering germination in disturbed soil.
Responses of white clover to gaseous pollutants and acid mist: implications for setting critical levels and loads
Authors: ASHENDEN T. W. , BELL S. A. , RAFAREL C. R.
Published: April 2006

summary

White clover plants (Trifolium repens L. cv. ‘Grasslands Huia’) were exposed to combinations of gaseous pollutants and acid mists for 15 wk. The treatments were (a) charcoal‐filtered air (control), (b) 40 ppb SO2+ 40 ppb NO2, (e) 40 ppb Oa with additional peaks of 2 × 3 h at 80 ppb and 1 × 1 h at 110 ppb O3 and (d) SO2+NO2+O3 (a combination of treatments b and c), these being combined with acid mist treatments (6 mm wk1) with solutions at pHs of 2.5, 3.5, 4.5 and 5.6. All gaseous pollution treatments resulted in substantial reductions in plant dry weights with additive effects of SO2+ NO2 and O3 in the SO2+ NO2+O2 treatment. There was a lower dry weight, averaged over all gas pollution treatments, for plants exposed to pH 2.5 compared with pH 4.5 or pH 5.6 mists. An interactive effect of gas x mist treatments revealed that effects of acid mists on plant dry weights were overridden by the more toxic O3 and SO2+ NO2+ O3 gas exposures. Net photosynthesis was reduced in plants exposed to pH 2.5 and pH 3.5 mists compared with plants exposed to pH 5.6 mist. Rates of stomatal conductance were reduced by exposure to the gaseous pollution treatments but not to acid mists. Water loss was greater after 55 h for leaves detached from plants exposed to all gaseous pollution treatments compared with ones from control plants. There was a greater loss of water from detached leaves exposed to pH 2.5 compared with pH 5.6 mist. The quantities (loads) of S + N in gaseous form resulting in decreased growth of T. repens were calculated to be much lower than those applied in mists with no adverse effects. It is concluded that the concepts of critical levels and critical loads of pollutants need considerable refinement for realistic assessments of the threat of pollutants to vegetation.
Growth, photosynthesis and carbohydrate utilization in submerged Scirpus maritimus L. during spring growth
Authors: CLEVERING O. A. , VAN VIERSSEN W. , BLOM C. W. P. M.
Published: April 2006

summary

The importance of underwater photosynthesis and the use of reserve‐carbohydrates were assessed in submerged Scirpus maritimus L. during spring growth. Submerged plants were grown in outdoor ponds (90 cm deep) using different initial tuber sizes (mean 8.9 and 16.2 g f. wt) and different light treatments (0, 40, 70 and 100% of full daylight). After shoot emergence the recovery from shading and darkness was studied.

The period of submerged growth lasted 9 wk. During this period the mean relative growth rate (RGR) was independently affected by shading and tuber size. At the end of this period dry weight of plants grown in darkness was only 50% of that of plants grown in full daylight or shade (70 or 40% of full daylight), whereas that of plants from small tubers was only 67% of that from large ones. As a result plants grown from small tubers in darkness had only 33% of the dry weight of those grown from large tubers in full daylight or shade.

Despite these large differences in total dry weight at the end of the submerged period, shoot length remained unaffected by shading and tuber size. Shoots grown in darkness were strongly etiolated, with a slower rate of leaf appearance, but with longer leaves, than those grown in full daylight or shade. Only after emergence was shoot length as well as dry matter production greater in plants grown previously in full daylight or shade than in darkness, and greater in plants grown from large than from small tubers.

During the submerged period, the relative depletion rate of reserve‐carbohydrates increased with time, but remained unaffected by shading and tuber size. The reserve‐carbohydrates were replenished after plants emerged

It was concluded that both underwater photosynthesis and tuber size had a large impact on total dry matter production in S. maritimus. They did not, however, affect the ability of S. maritimus to emerge from 90 cm deep water.
Induction of mycorrhiza‐like structures and defence reactions in dual cultures of spruce callus and ectomycorrhizal fungi
Authors: SIRRENBERG ANKE , SALZER PETER , HAGER ACHIM
Published: April 2006

summary

Heterotrophic spruce (Picea abies [L.] Karst.) callus cells were grown in dual culture with ectomycorrhizal fungi (Amanita muscaria [L.] Pers., Lactarius deterrimus Gröger, Hebeloma crustuliniforme [Bull.] Quél., Suillus variegatus [Sw.: Fr.] O.K.) or with the pathogenic fungus Heterobasidion annosum [Fr.] Bref. Spruce cells stimulated growth of the mycorrhizal fungi, whereas growth of the pathogenic fungus was not affected. Two of the mycorrhizal fungi, 5. variegatus and L. deterrimus, caused hypersensitive reactions in spruce cells. In contact with the surface of the plant cells the mycorrhizal fungi developed densely interwoven lobed, hand‐ and fan‐shaped structures. They resembled morphological features occurring in the hyphal mantle and Hartig net of ectomycorrhizas. The ectomycorrhizal fungi did not show altered branching patterns when growing on cellophane sheets. These results demonstrate that callus cells of the host P. abies are able to stimulate fungal growth and to induce ectomycorrhizal fungi to form mycorrhiza‐like structures which normally are only generated in the presence of host roots.
Acclimation of tomato to different carbon dioxide concentrations. Relationships between biochemistry and gas exchange during leaf development
Authors: VAN OOSTEN J.‐J. , WILKINS D. , BESFORD R. T.
Published: April 2006

summary

Tomato plants were transferred to different CO2 mole fractions (350, 700, 1050 and 1400μmol CO2 mol−1) 31 d after sowing (2% of full expansion) and the light saturated rate of photosynthesis (Pmax) of the unshaded 5th leaf was measured at either an ambient CO2 mole fraction, C2 of 350 μmol CO2 mol−1 (Pmax (350)) or at the mole fraction of CO2 at which the plants were grown. At 60% nd 95% leaf expansion, Pmax of high CO2 grown plants measured at growth CO2, was greater than the Pmax (350) of the ambient CO2 grown plants. However, by leaf maturity, Pmax(growth CO2) declined linearly as growth CO2 concentration increased. Pmax (350) of plants exposed to elevated CO2 up to 60% le f expansion had not acclimated to high CO2 At 95% leaf expansion, Pmax(350) was smaller in the high CO2 grown plants. Pmax (350) w s predicted from Rubisco in vitro carboxylation capacity using tomato Rubisco kinetic constants. By 95% leaf expansion, high CO2 grown plants showed similarities to the response of plants to low nitrogen supply, in terms of Rubisco nd chlorophyll content. The observed nd theoretical relationships between the initial slopes of the Pmax/C1 responses nd Rubisco activity were statistically equivalent. Both short‐term and long‐term effects of elevated CO2 on dark respiration (Rn) were also investigated at two stages of leaf development (50 nd 100% expansion). Rn (growth CO2) was smaller for the high CO2 grown plants compared with the control plants, whereas Rn (350) was either equal or greater for the plants grown in high CO2
Regulation of assimilate partitioning in flowering plants of the monopodial orchid Aranda Noorah Alsagoff
Authors: CLIFFORD P. E. , NEO H. H. , HEW C. S.
Published: April 2006

summary

Radiocarbon dosing of leaves and source‐sink manipulation treatments were used to clarify how assimilate partitioning is regulated in flowering plants of a monopodial Aranda orchid. The inflorescence was the dominant sink for all test leaves that were selected to determine patterns of 14C‐assimilate partitioning. Defoliation treatments had only minor effects on the distribution of 14C‐assimilate between the inflorescence and vegetative apical shoot. Excision of the inflorescence resulted in greater proportions of l4C‐assimilate being sent to all other sinks. Loss of the vegetative apical shoot had a quite different effect in that greater proportions of 14C‐assimilate were exported only to the inflorescence. Rates of 14C assimilation of remaining leaves were often raised in defoliated plants although this effect was not consistent for a single, residual leaf unless the vegetative apical shoot was also excised. Our results highlight the complexity of source‐sink relationships in indeterminate plant types showing simultaneous vegetative and reproductive growth. We suggest that inflorescence growth in monopodial orchids such as Aranda is primarily source‐limited although significant sink limitations for assimilate gain by the inflorescence exist because of a modulating effect of the vegetative apical shoot on inflorescence sink strength and the ability of source leaves to respond positively to increased sink demand.
The structure and function of the vegetative mycelium of ectomycorrhizal plants
Authors: BENDING GARY D. , READ DAVID J.
Published: April 2006

summary

The relationships between colonization of fermentation horizon organic matter (FHOM) by an ectomycorrhizal fungus and the activities of enzymes involved in key processes of nitrogen (N) and phosphorus (P) mobilization were investigated. FHOM was collected from a birch forest and placed in transparent observation chambers with (M) or without (NM) plants of Betula pendula Roth, the roots of which were infected by Paxillus involutus (Fr.) Fr. The fungus colonized the FHOM of the M chambers, and after different periods of occupation the activities of protease, polyphenol oxidase, peroxidase and phosphomonoesterase were determined in colonized and uncolonized substrate.

Activities of protease and polyphenol oxidase increased in organic matter that had been occupied for 28–50 d, and remained elevated in FHOM that had been occupied for 50–98 d. However, although activity of phosphomonoesterase increased in FHOM that had been colonized for 28–50 d, amounts in FHOM colonized for 50–98 d decreased to below that found in uncolonized material. No difference in peroxidase activity was detected between colonized and uncolonized organic matter. The results are discussed in relation to the role of ectomycorrhizal fungi in nutrient cycling processes in temperate forest ecosystems.
Identification of ribosomal DNA polymorphisms among and within spores of the Glomales: application to studies on the genetic diversity of arbuscular mycorrhizal fungal communities
Authors: SANDERS IAN R. , ALT MONICA , GROPPE KATHLEEN , BOLLER THOMAS , WIEMKEN ANDRES
Published: April 2006

summary

Little information currently exists on species diversity in communities of arbuscular mycorrhizal fungi (AMF), mainly owing to difficulties in identification of field extracted spores on the basis of morphology. The possibility was explored to identify individual AMF spores from the field on the basis of a molecular marker, namely the nuclear ribosomal DNA encoding the highly conserved 5.8S rRNA with the two flanking internal transcribed spacers (ITS region), known to vary between species. A technique involving polymerase chain reaction followed by restriction fragment length polymorphism analysis (PCR–RFLP) was developed to amplify and characterize the ITS region from single AMF spores. PCR reactions with extracts from single spores of three AMF species, raised under glasshouse conditions, yielded reproducibly a single amplification product of the ITS region in sufficient amounts to allow cleavage with several restriction enzymes. The size of the ITS region, c. 600 base pairs, varied only slightly between species. Digestion of the PCR products with the restriction enzymes Hinfl and Taq I resulted in banding patterns that were reproducible for different individual spores of a given species, but showed clear differences between the three species tested. The sum of the fragment sizes was sometimes greater than the size of the original PCR product, e.g. in Glomus mosseae. Clones of the amplification product from a single spore of this fungus were obtained and sequenced. This yielded two closely related but different sequences, indicating that two different ITS regions co‐existed in the spore. The RLFP pattern of the amplification product of the spore was a result of an amalgamation of these two sequences. The technique was applied to AMF spores collected from a species‐rich grassland. Spores were sorted into morphological groups on the basis of their colour, size, and shape, and then subjected to PCR–RFLP analysis. In some morphological groups, a large percentage of spores failed to yield an amplification product, probably because they had lost their contents. A group of Glomus spores yielding amplification products in the majority of cases was further investigated: PCR RFLP analysis on 10 individual spores from the field produced 10 different patterns. Similar results were obtained with other groups of spores. The results suggest that the diversity in natural AMF communities and the genetic diversity within individual spores might he much greater than previously thought.
Sensitivity of seedlings of black cherry (Prunus serotina Ehrh.) to ozone in Great Smoky Mountains National Park
Authors: NEUFELD HOWARD S. , LEE E. HENRY , RENFRO JAMES R. , HACKER W. DAVID , YU BEN‐HUI
Published: April 2006

summary

The response of seedlings of black cherry (Prunus serotina Ehrh.) to ozone was evaluated in Great Smoky Mountains National Park using open‐top chambers during the growing seasons of 1989 and 1992. Two separate sets of seedlings were each exposed to various concentrations of ozone (charcoal‐filtered; 0.5 × (not used in 1989), 1.0 ×, 1.5 ×, and 2.0 × modified ambient) in two different seasons. Seasonal indices of exposure (SUM00, SUM06 and AOT40) for the 1.0 × treatments were 39.2, 1.9, and 1.62 ppm h respectively, in 1989, and 63.1, 0.9, and 0.78 ppm h, respectively, in 1992. No significant chamber effects were noted, except for reduced height growth in open plots compared with 1.0 × chambers in 1992. In both years, the 2.0 × treatment reduced total, leaf, root, and shoot‐I‐root biomass, although some of these changes were only marginally significant in 1992. Stem biomass was significantly reduced in 1989, but not 1992. Leaf area, count and weight were all highly correlated, and showed significant reductions in both years. The leaf area ratio (leaf area/total weight) was reduced in 1989, but not in 1992. Height was not affected by ozone, but diameter was reduced only in 1989. Chamber‐to‐chamber variation for biomass and leaf variates was greater in 1992, and as a result, significance levels were lower. Weibull functions were fitted to chamber means, and showed significant near‐linear declines for most components when log‐transformed data were plotted against the SUM06 and AOT40 indices. Individual Weibull models for the 1989 and 1992 data sets, and combined models over both years, were developed. Combined models were adequate for describing ozone responses for all biomass components, as determined by the likelihood ratio test. The data show‐that the two years of exposure produced similar, but not identical effects, despite large differences in initial size of the seedlings and in seasonal ozone dynamics. Leaf and root biomass were most sensitive to ozone (as determined by the slope of decrease with increasing SUM06), whereas stem biomass was least sensitive. Black cherry seedlings are shown to be among the most sensitive to elevated ozone of the 21 tree species examined to date in Great Smoky Mountains National Park.
Gametes with the somatic chromosome number: mechanisms of their formation and role in the evolution of autopolyploid plants
Authors: BRETAGNOLLE F. , THOMPSON J. D.
Published: April 2006

summary

The production of 2n gametes in plants, i.e. gametes with a somatic chromosome number, is considered to be the dominant process involved in the origin of polyploid plants. In this review, we provide a synthesis of current knowledge concerning the production of 2n gametes. Firstly, we describe the different methods used to detect and quantify the production of 2n gametes in plants, which include morphological and flow cytometry screening of the occurrence of 2n pollen, the analysis of crosses among diploid and tetraploid parents and the instigation of micro‐and mega‐sporogenesis. Secondly, the high level of inter‐ and infra‐specific variation in 2n gametes production is described. Thirdly, the various cytological anomalies responsible for the production of 2n gametes are reviewed, with particular reference to the relative genetic consequences of the first and second restitution divisions that give rise to 2n gametes. Fourthly, the significance of 2n gametes in crop plant improvement is discussed, in relation to somatic chromosome doubling to obtain new polyploid varieties. In particular, we compare the genetic and yield consequences of methods based on unilateral and bilateral sexual polyploidization. Finally, we outline how knowledge of the variety of mechanisms involved in 2n gamete production have increased our understanding of the evolutionary significance of polyploidy and the population biology of polyploid plants.

Contents

Summary
1

I.
Introduction
2

II.
Methods used to detect the presence and frequency of 2n gametes
3

III.
Frequency of 2n gamete production
5

IV.
Mechanisms of formation and the influence of external factors
6

V.
The genetic consequences of First Division Restitution (FDR) and Second Division Restitution (SDR)
12

VI.
2n gametes and the unilateral and bilateral sexual polyploidization of crop plants
13

VII.
The evolutionary significance of 2n gamete production
15

Acknowledgements
18

References
18
Occurrence of ectomycorrhizas on ericaceous and coniferous seedlings grown in soils from the Oregon Coast Range
Authors: SMITH JANE E. , MOLINA RANDY , PERRY DAVID A.
Published: April 2006

summary

Seedlings of Gaultheria shallon, Pseudotsuga menziesii, Rhododendron macrophyllum, and Tsuga heterophylla were grown together in the greenhouse in soils from three young managed Douglas fir forests in the Oregon Coast Range. The objective of the study was to evaluate the ability of ericaceous plants and overstory conifers to share compatible mycorrhizal fungi in order to assess potential mycorrhizal linkages. Ericoid mycorrhizal fungi were examined in Gaultheria and Rhododendron to assess their assumed presence in soils of the Pacific Northwestern region of the United States. Nine ectomycorrhizal types were recognized on the conifers and two on the Ericaceae. All nine ectomycorrhizal types occurred on both conifer species, and the two ectomycorrhizal types on the ericaceous hosts resembled types associated with the conifer hosts. Ectomycorrhizal fungi occurred on all the conifer seedlings and in trace amounts on 26% of the ericaceous seedlings in the study. Ericoid mycorrhiza developed on all the ericaceous seedlings.
Localization of β (1–3) glucan in walls of the endomycorrhizal fungi Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe and Acaulospora laevis Gerd. & Trappe during colonization of host roots
Authors: LEMOINE M. C. , GOLLOTTE A. , GIANINAZZI‐PEARSON V.
Published: April 2006

summary

Previous studies showed that cell walls of endomycorrhizal fungi belonging to the Acaulosporaceae and Glomaceae contain β (1–3) glucan polymers as well as chitin. Indirect immunolabelling with monoclonal and polyclonal antibodies has been used to investigate the distribution of these structural polysaccharides in cell walls of Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe and Acaulospora laevis Gerd. & Trappe as they interact with pea and tobacco roots, respectively. The (l‐3) glucans were detected in the walls of external hyphae, and of hyphal coils and intercellular hyphae developing in outer root tissues. The glucan component was alkali‐insoluble but treatment with chitinase resulted in solubilization of most of the β(1–3) glucans from the fungal wall. A decrease in immunolabelling was associated with thinning out of the hyphal wall as the fungi colonized deeper in the host root, and β(1–3) glucans could not be detected in walls of intercellular hyphae or arbuscules in the parenchyma cortical tissue. The molecular configuration of cell walls of G. mosseae and A. laevis is discussed in relation to fungal morphogenesis and the symbiotic state in endomycorrhiza.
Soil phosphate status modifies response of mycorrhizal and non‐mycorrhizal Senecio vulgaris L. to infection by the rust, Puccinia lagenophorae Cooke
Authors: WEST H. M.
Published: April 2006

summary

The impact of rust infection (Puccinia lagenophorae Cooke) on growth of mycorrhizal and non‐mycorrhizal Senecio vulgaris L. was examined under three levels of phosphorus fertilization. Seeds were then collected from infected and control plants and germination, seed chemistry and offspring vigour were examined. Rust infection did not become established on plants which were phosphorus limited, but on hosts fed with medium or high levels of P, the proportion of total leaf number exhibiting infection was a function of leaf production. Capitula production was decreased by rust infection and increased by mycorrhizal colonization in plants fed with a medium concentration of P. In plants fed with a high P concentration, leaf number was reduced by rust infection of mycorrhizal plants, whilst rust was deleterious to both mycorrhizal and non‐mycorrhizal plants grown with a medium P supply. However, the effects of the rust were less marked in the mycorrhizal plants. Seed production and weight were unaffected by fungal treatments, although percentage germination of the resultant seeds was reduced by maternal mycorrhizal colonization and enhanced in seed from rusted, mycorrhizal plants grown at high soil P. The amount of total C, N and P was also reduced by maternal mycorrhizal infection at high soil P and increased in seeds from rusted, mycorrhizal mothers. Vigour of offspring produced from treated mother plants was influenced by mycorrhizal × phosphorus and rust × phosphorus interactions with respect to bud and leaf numbers. Mycorrhizal infection of mother plants grown with a medium P supply benefited the offspring as increased leaf and bud production was observed, but rusted mothers at the same P level produced offspring with reduced leaf number and potential fecundity.
Comparison of hydraulic architecture of woody plants of differing phylogeny and growth form with special reference to freestanding and hemi‐epiphytic Ficus species from Panama
Authors: PATIÑO SANDRA , TYREE MELVIN T. , HERRE E. ALLEN
Published: April 2006

summary

Hydraulic parameters were measured in seven species of Fiats (three free‐standing and four hemi‐epiphytic) on stem segments of 3–35 mm in wood diameter. Parameters measured included Kh (water flux per unit pressure gradient), Kh (leaf specific conductivity =Kh per unit leaf area), Ks (specific conductivity =Hh per unit wood cross section), and Hv (Huber value = wood cross section per unit leaf area).

The hemi‐epiphytes tended to have less conductive stems per unit leaf area (lower Ki and invested less wood cross section per unit leaf area (lower Hv) than free‐standing species. Hydraulic parameters of Ficus are compared to 21 other temperate and tropical species to see if there is any discernible pattern in hydraulic architecture that correlates with phylogeny, growth form or habitat occupied by diverse species. Figs, as a group, had relatively high hV. and relatively low hv compared to other tropical trees.

A possible correlation between KL and transpiration and growth form is discussed.
Growth and dry matter partitioning in loblolly and ponderosa pine seedlings in response to carbon and nitrogen availability
Authors: GRIFFIN KEVIN L. , WINNER WILLIAM E. , STRAIN BOYD R.
Published: April 2006

summary

We grew loblolly pine (Pinus taeda L.) and ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings in a factorial experiment with two CO2 partial pressures (35 and 70 Pa) and two nitrogen treatments (1‐0 and 3–5 mM NH4+) for one growing season in a ‘common garden’ experiment designed to examine the extent that dry matter and nitrogen accumulation and partitioning are environmentally controlled. Ponderosa pine seedlings grown in 35 Pa CO2 and 3.5 mM NH4+ showed symptoms of nitrogen toxicity, characterized by greatly reduced growth, and moderately reduced total plant N. With the exception of this treatment combination, there were no significant differences between species in total plant dry matter or total plant nitrogen, suggesting that responses of growth to environmental conditions were stronger than heritable responses. There were however large differences in dry matter and N partitioning between the two species. Increases in leaf mass were largest in loblolly pine, whilst ponderosa pine tended to have higher root: shoot (R:S) ratios. R:S ratio of loblolly increased in response to C availability and decreased in response to N availability, whilst R: S ratio of ponderosa pine was much less responsive to resource availability. Total plant N varied with N supply, and N partitioning was related to plant growth and carbon partitioning. Carbon and N were interactive, such that an increase in the accumulation of either resource was always accompanied by an increase in the other. Over several seasons the different patterns of resource acquisition and biomass allocation that we observed in a uniform environment could potentially result in different growth rates at most resource levels. In the first season, contrary to our expectations, heritable differences in growth rate did not appear.
The combined effect of arbuscular mycorrhizas and short‐term cold exposure on wheat
Authors: PARADIS R. , DALPÉ Y. , CHAREST C.
Published: April 2006

summary

In order to investigate the effect of arbuscular mycorrhizal colonization and short‐term cold exposure on Triticum aestivum L., 7‐wk‐old seedlings of spring and winter cultivars (Glenlea and AC Ron) were submitted to a 1‐wk cold treatment when inoculated with Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe. The combined effect of arbuscular mycorrhizas and low temperature on the two cultivars was determined for several physiological parameters including biomass and chlorophyll, protein, and sugar contents. The dry biomass was higher in Glenlea than AC Ron at week five and did not significantly change at week eight in both cultivars with either the mycorrhizal or the cold treatment. The chlorophyll content was higher in mycorrhizal (M +) than non‐mycorrhizal (M‐) Glenlea at 5 °C but was unaltered in AC Ron or in either cultivar at 25 °C. The reducing and total sugar contents were higher in AC Ron than Glenlea. The non‐reducing sugar level at 5 °C was higher in M + AC Ron than M+ Glenlea and higher in M‐ than M+ Glenlea. The protein content was higher in Glenlea than AC Ron at 25 °C but remained constant regardless of the mycorrhizal or cold treatment. This study shows that the spring wheat seems to benefit more than the winter wheat from AM association after a short‐term exposure to low temperature.
Arbuscular mycorrhizas and water relations in maize under drought stress at tasselling
Authors: SUBRAMANIAN K. S. , CHAREST C. , DWYER L. M. , HAMILTON R. I.
Published: April 2006

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A greenhouse experiment was conducted to investigate the influence of an arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on drought tolerance in tropical maize. Freshly regenerated seeds of selection cycles 0 (cv. C0, drought‐sensitive) and 8 (cv. C8, drought‐resistant) of the lowland tropical population ‘Tuxpeño sequia’ were used for this study. Maize plants were subjected to drought stress for three weeks following tasselling (75–95 days after sowing). During the drought stress period, midday leaf water potential (LWP), stomatal resistance (SR) and transpiration rate (TR) were monitored daily, and green leaf area (GLA) determined at alternate days to assess the effects of mycorrhizal inoculation. Mycorrhizal plants of the cultivars CO and C8 had higher (less negative) LWP and TR, and lower SR throughout the experiment. The GLA was 27.5 % higher in mycorrhizal than non‐mycorrhizal CO plants under drought conditions. Results indicate that mycorrhizal significantly improve tolerance to moderate drought stress imposed at tasselling, especially for the sensitive CO maize cultivar.
The role of plant‐parasitic nematodes and soil‐borne fungi in the decline of Ammophila arenaria (L.) Link
Authors: DE ROOIJ‐VAN DER GOES P. C. E. M.
Published: April 2006

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In coastal foredunes, Ammophila arenaria (L.) Link grows vigorously when it is buried regularly by windblown sand and degenerates at stabilized sites. Nematodes and soil‐borne fungi were found to be involved in its decline. In order to establish their role in the disease complex, seedlings of A. arenaria were inoculated with several groups of potentially harmful soil organisms that were isolated from its root zone. Inoculation of single species of fungi did not reduce the growth of the seedlings, but combining all fungi that were commonly found in the Dutch coastal foredunes significantly reduced growth to about 80% of that in sterilized soil. This indicates synergistic effects between commonly found plant pathogenic fungi. The addition of large numbers of the nematode Telotylenchus ventralis, the only species that could be successfully grown on A. arenaria in the laboratory, reduced plant growth to the same level as in non‐sterile soil, but numbers were 80 times greater than in the latter soil. Inoculation with relatively large numbers of T. ventralis in combination with the commonly occurring fungi reduced plant growth in sterilized soil to a level similar to that in non‐sterile soil. The involvement of other species of nematodes, such as Heterodera spp. or Meloidogyne maritima, in the decline of A. arenaria in non‐sterile soil could not be proven in inoculation experiments with sterile soil, but it is likely that these species may also be involved. It is concluded, therefore, that several different combinations of soil organisms can be harmful to A. arenaria, so that natural decline is not caused by one simple well defined pathosystem.
Stimulation and inhibition of pine root growth by osmotic stress
Authors: TRIBOULOT MARIE‐BÉATRICE , PRITCHARD JEREMY , TOMOS DERI
Published: April 2006

summary

The effect of osmotic stress on the regulation of extension of roots of pine seedlings (Pinus pinaster Ait.) was studied. Extension rate (r) was measured as increase in root length, and as local growth rate (LGR) along the growing region. Turgor pressure (P) was measured over the same profile using the cell pressure probe. Correlation of LGR and P allowed changes in cell wall mechanical properties to be followed.

In unstressed plants, differences in LGR along the root apex were owing to variations in the mechanical properties of the cell walls since P remained constant at 0.5 MPa along the first 10 mm of the root tip. Contrary to expectation, a moderate water stress of 0.15 MPa stimulated root growth despite a small reduction in P to 0.4 MPa. The walls of the expanding cells became looser, allowing enhanced growth in spite of reduced turgor. Examination of LGR showed that these changes occurred uniformly over the whole elongation zone. The advantage to the plant of this is discussed. Higher stresses (0.45 and 0.66 MPa) decreased cell turgor to a greater degree (≤0.3 MPa) and decreased growth rate. At the highest stress (0.66 MPa), P was maximal in cells that were still elongating, resulting in a longitudinal gradient in turgor. In both treatments LGR remained unchanged at the apex of the growing zone. Wall loosening appeared to have occurred in this region. Pine root extension is therefore modulated by changes in cell wall properties, with cell wall loosening resulting in increased growth at moderate stress. It appears that growth under higher stresses is limited by inability to maintain turgor.
Microtubule arrays in maize root cells. Interplay between the cytoskeleton, nuclear organization and post‐mitotic cellular growth patterns
Authors: BALUŠKA F. , BARLOW P. W. , HAUSKRECHT M. , KUBICA Š. , PARKER J. S. , VOLKMANN D.
Published: April 2006

summary

Results from studies with metabolic inhibitors suggest that, in growing cells of the maize root apex, nuclear metabolism is involved in the organization of the cortical microtubular arrays (CMTs) located at the cell periphery. Nucleus‐derived factors intrinsic to each individual cell are inferred as being responsible for the accomplishment of the MT‐dependent transition from the approximately isodiametric mode of cellular growth, characteristic of the immediate post‐mitotic root region, to the strictly directional cell lengthening in the elongation zone. These hypothetical factors seem to be related to RNA but not DNA synthesis, as indicated by our inhibitor studies. For instance 5‐fluorodeoxyuridine, an inhibitor of DNA synthesis, had little effect on orientation of CMTs, when these were present, and allowed the developmental switch from more or less isodiametric mode of cell growth into highly polarized cell elongation to occur. In contrast, actinomycin D, a specific inhibitor of nuclear metabolism which rapidly halts rRNA synthesis, affected both the polarity and efficacy of postmitotic cell growth and impaired the transversal arrangement of CMTs as well as inducing the appearance of prominent ‘holes’ in their bundled arrays. These latter effects of actinomycin D cannot be simply explained by its indirect effect on translation, through impairment of functional ribosome assembly, as they were visible after only 15 min. Moreover, inhibition of protein synthesis by cycloheximide resulted in a different response. There was rapid and complete loss of the preferred transverse orientation of CMTs and the individual CMTs failed to organize themselves into bundles. Endoplasmic microtubules (EMTs), located more internally between plasma membrane and nucleus, seem to be important for determining nuclear size and chromatin architecture, since whenever EMTs were caused to disintegrate (cold and anti‐MT drug treatments), meristematic nuclei swelled and their chromatin dispersed. By contrast, when EMTs were stabilized and increased in number by taxol, which specifically favours MT polymerization, the nuclei became smaller and the chromatin more condensed. Nevertheless, the mechanisms of these complex interplays between the MT cytoskeleton and the nuclear organization remain unclear.