bluuebunny/crossref_metadata_2025 huggingface dataset:
Ambient ozone effects on forest trees of the eastern United States: a review
Authors: CHAPPELKA ARTHUR H. , SAMUELSON LISA J.
Published: March 2003

Tropospheric ozone can affect crop yield and has been reported to cause reductions in growth and biomass of forest tree species in laboratory and glasshouse studies. However, linkages between growth and ambient ozone concentrations in the field are not well established for forest trees. Ambient ozone concentrations have been shown to cause foliar injury on a number of tree species throughout much of the eastern USA. Symptom expression is influenced by endogenous and exogenous factors and, therefore, ozone‐exposure/tree‐response relationships have been difficult to confirm. Clearly defined, cause‐effect relationships between visible injury and growth losses due to ozone have not been validated. Generalizations of sensitivity of forest trees to ozone are complicated by tree development stage, microclimate, leaf phenology, compensatory processes, within‐species variation and other interacting stresses. In general, decreases in above‐ground growth at ambient ozone levels in the eastern USA appear to be in the range of 0–10% per year. However, these conclusions are based on a small number of tree species, with the vast majority of studies involving individual tree seedlings in a non‐competitive environment. Comparative studies of small and large trees indicate that seedlings are not suitable surrogates for predicting responses of mature trees to ozone. Process‐level modelling is a promising methodology that has been recently utilized to assess ozone effects on a stand to regional scale, indicating that ozone is affecting forest growth in the eastern USA. The extent and magnitude of the response is variable and depends on many edaphic and climatic factors. It is imperative when conducting assessment exercises, however, that forest biologists constantly keep in mind the tremendous variability that exists within natural systems. Scaling of single site/physiological response phenomena from an individual tree to an ecosystem and/or region necessitates further research.
Differential expression of phenylalanine ammonia‐lyase genes in barley induced by fungal infection or elicitors
Authors: KERVINEN T. , PELTONEN S. , TEERI T. H. , KARJALAINEN R.
Published: March 2003

Gene‐specific probes were used to assess the expression patterns of four different phenylalanine ammonia‐lyase (pal) genes in infected or elicitor‐treated leaves and suspension‐cultured cells of barley. Genes corresponding to hpal2, hpal3, hpal4, and hpal6 were all induced by mercuric chloride and fungal infection by Bipolaris sorokiniana Sacc. (Shoem.) in barley (Hordeum vulgare L. cv. Pokko) leaves, but with considerable variation in their expression level and timing. The expression patterns of hpal2 and hpal6 were similar, both showing a rapid, strong induction after treatment with mercuric chloride and a slower induction after fungal inoculation, whereas the more divergent hpal3 was induced at a later time and at a lower level after both treatments. Hpal4 was expressed with timing like that of hpal2 and hpal6 in infected or mercuric chloride‐treated leaves but its expression was much weaker. Hpal2 and hpal4 were induced in elicitor‐treated, suspension‐cultured barley cells, whereas the expression of hpal3 was nearly undetectable, and hpal6 was strongly and constitutively present. All pal genes except hpal4 were developmentally regulated, but differentially expressed in various barley tissues. The results suggest that the four pal genes studied here might be responsible for the activation of different branches in the phenylpropanoid biosynthesis of barley.
Germination and post‐germination growth to carrot seedling emergence: predictive threshold models and sources of variation between sowing occasions
Authors: FINCH‐SAVAGE W. E. , STECKEL J. R. A. , PHELPS K.
Published: March 2003

Cumulative germination curves were recorded for carrot (Daucus carota L.) seeds at a range of constant temperatures (T) and water potentials (Ψ) in the laboratory and under variable soil conditions in 15 seed‐bed environments in the field. A single base temperature (Tb), a distribution of base water potentials (Ψb(G)) for percentiles (G) of the population and the hydrothermal time constant (Hg) were determined from laboratory data. Although less effective at low Ψ, it was possible, using these germination parameters, to satisfactorily describe the effect of T and Ψ on germination rates under constant conditions according to the threshold models of thermal and hydrothermal time. These models were applied to field data with the condition that the germination process ceased if T<Tb for thermal time and additionally Ψ<Ψb(G) for hydrothermal time.

Neither model accurately predicted germination patterns in the field. However, the pattern of germination was adequately described in most situations by a modified threshold model in which the predicted progress towards germination was unaffected by soil Ψ, provided it remained above Ψb(G), and was therefore more rapid under variable seed bed conditions than hydrothermal time. In this modified threshold model, the condition Ψ<Ψb(G) had to be fulfilled at the initiation of radicle extension before germination occurred. This result implies that the initiation of radicle growth operates as a moisture‐sensitive step that can determine germination and seedling emergence timing under variable soil‐moisture conditions.

Seedling emergence was also recorded in the field and used to determine, separately, the impact of germination and post‐germination growth on the variation in seedling emergence patterns. The analysis suggests that delays in seedling emergence occur largely in the germination phase, but that seedling losses and variation in the spread of seedling emergence times within the population occur largely during the post‐germination growth phase.
Cyanobiont specificity in some Nostoc‐containing lichens and in a Peltigera aphthosa photosymbiodeme
Authors: PAULSRUD PER , RIKKINEN JOUKO , LINDBLAD PETER
Published: March 2003

The cyanobacterial symbionts in some Nostoc‐containing lichens were investigated using the nucleotide sequence of the highly variable cyanobacterial tRNALeu (UAA) intron. When comparing different Nostoc‐containing lichens, identical intron sequences were found in different samples of the same lichen species collected from two remote areas. This was true for all species where this comparison was made (Peltigera aphthosa (L.) Willd., P. canina (L.) Willd. and Nephroma arcticum (L.) Torss.). With one exception, a specific intron sequence was never found in more than one lichen species. However, for two of the species, Peltigera aphthosa and Nephroma arcticum, two different cyanobionts were found in different samples. By examining a P. aphthosa photosymbiodeme it could be shown that the same Nostoc is present in both bipartite and tripartite lobes of this lichen. It is thus possible for one cyanobiont/Nostoc to form the physiologically different symbioses that are found in bipartite and tripartite lichens. The connection between photobiont identity and secondary chemistry is discussed, as a correlation between differences in secondary chemistry and different cyanobionts/Nostocs in the species Peltigera neopolydactyla (Gyeln.) Gyeln. was observed. It is concluded that more knowledge concerning the photobiont will give us valuable information on many aspects of lichen biology.
Effects of carbon dioxide and nitrogen enrichment on a plant–insect interaction: the quality of Calluna vulgaris as a host for Operophtera brumata
Authors: KERSLAKE J. E. , WOODIN S. J. , HARTLEY S. E.
Published: March 2003

Calluna vulgaris L. (Hull) is not one of the usual hosts of the winter moth, Operophtera brumata L., but outbreaks have caused extensive damage to heather moorland in Scotland in recent years. This study investigated the potential role of environmental change in such outbreaks by rearing O. brumata larvae on C. vulgaris plants grown in open‐top chambers for 20 months with enriched CO2 (600 ppm) and nitrogen supply (average 52·5 kg N ha−1 yr−1) in factorial combination. This prolonged exposure to elevated CO2 caused no change in shoot growth, photosynthesis or foliar C∶N ratio of C. vulgaris, even with increased N supply, indicating that the absence of response was not due to N limitation. Increased N supply itself resulted in increased shoot growth and a decrease in tissue C∶N ratio. Phenolic content did not change in response to either CO2 or N enrichment, contrary to the predictions of the carbon/nutrient balance hypothesis. In line with the absence of plant response, there was no effect of CO2 on the development of Operophtera brumata on C. vulgaris, and so continued increase in atmospheric CO2 concentration is unlikely to affect directly O. brumata outbreaks on heather moorland. Operophtera brumata showed increased larval development, growth rate and pupal weight on N‐treated plants, correlated both to the decrease in foliar C∶N ratio, and to the increase in shoot extension which was predictive of survivorship. Thus, increased atmospheric N deposition, or increased rates of mineralization in a warmer environment, might increase the severity of O. brumata outbreaks on C. vulgaris. Since the combination of high N availability and disturbance of heather canopy by herbivory is known to result in increased dominance of grasses, it is suggested that this could lead to further degradation of moorland in upland Britain.
Susceptibility of ectomycorrhizal and non‐mycorrhizal Scots pine (Pinus sylvestris) seedlings to a generalist insect herbivore, Lygus rugulipennis, at two nitrogen availability levels
Authors: MANNINEN A.‐M. , HOLOPAINEN T. , HOLOPAINEN J. K.
Published: March 2003

We tested how nitrogen availability affects suitability of ectomycorrhizal (ECM) and non‐mycorrhizal Pinus sylvestris (L.) for a polyphagous insect herbivore. Seedlings grown on sterile agar at two N levels, were infected or not with the ECM fungus Cenococcum geophilum (Sow.) Ferd. & Winge. Ultrastructural observations showed that C. geophilum formed well‐developed ectomycorrhizas in pine roots. After mycorrhizal establishment, oviposition preference of the polyphagous tarnished plant bug (Lygus rugulipennis Popp.) was determined in three different experiments. The duration of these experiments and the amount of irradiance were different. Nitrogen level or mycorrhizal treatment did not have significant effects on oviposition preference. However, mycorrhizal seedlings were favoured as an oviposition site at the lower N level, but only in expt 1. Total or individual terpene, total resin acid and total or individual sugar concentrations in pine shoots were not altered by treatment. Total phenolics concentration in pine shoots and roots was also the same in different treatments. Of individual resin acids, the concentration of dehydroabietic acid was increased after mycorrhizal treatment. Total resin acid, abietic acid and sandaraco pimaric acid concentrations correlated negatively with the number of Lygus eggs, but the correlations were only marginally significant. Of individual terpenes, β‐pinene and bornylacetate concentrations had a significant positive correlation with the number of Lygus eggs. Greater amounts of N predictably increased total N concentration in pine seedlings in expts 1 and 2, but mycorrhizal infection increased total nitrogen concentration only in expt 3. Total N concentration did not correlate with the number of Lygus eggs in expts 1 and 2. An early stage of mycorrhizal development did not provide mycorrhizal benefits to the host plant as a higher nutrient concentration or as increased growth. These results suggest that host–plant quality might be involved in selection of oviposition site by L. rugulipennis, but ectomycorrhizal infection at this level does not seem to be an important mediator.
Barley yellow dwarf virus: effects on carbohydrate metabolism in oat (Avena sativa) during cold hardening
Authors: LIVINGSTON D. P. , GILDOW F. E. , LIU SHU‐YEN
Published: March 2003

Barley yellow dwarf virus (BYDV) causes significant losses in yield and in overwintering ability of winter cereals. Mechanisms by which the physiology of plants is affected by the virus are not clear. To see how carbohydrates in the crown of winter cereals were affected by BYDV, fructan isomers of degree of polymerization (DP) 3–5, fructan DP>6 and the simple sugars, glucose, fructose and sucrose, were measured before and during cold hardening in three oat (Avena sativa L.) cultivars, ‘Wintok’, ‘Coast Black’ and ‘Fulghum’. On a fresh weight basis fructan DP>6 decreased by 50% in infected ‘Wintok’ and ‘Coast Black’ and by 25% in ‘Fulghum’. Two DP3, one DP4 and one DP5 isomer were significantly higher than non‐infected controls. The percentages of simple sugars in infected crowns were significantly higher than controls in all three cultivars in every week except the first week of hardening. Crude enzyme extracts from BYDV infected plants incubated with sucrose suggested higher invertase and lower sucrose‐sucrosyl transferase activity. When incubated with 1‐kestose and neokestin, no significant difference was found in fructose fructosyl transferase or in hydrolase activity. The activity of unidentified enzymes catalysing the synthesis of larger (DP>5) fructan was altered by BYDV. The decrease of carbohydrates in the crown induced indirectly by BYDV may alter the plant's capacity to regenerate tillers in the spring. The ability of plants to prevent or tolerate carbohydrate fluctuations induced by BYDV infection may be an important genetically regulated characteristic for developing virus‐resistant cultivars.
Leaf structure and specific leaf mass: the alpine desert plants of the Eastern Pamirs, Tadjikistan
Authors: PYANKOV VLADIMIR I. , KONDRATCHUK ALEXANDRA V. , SHIPLEY BILL
Published: March 2003

This study examines interrelationships between eight leaf attributes (specific leaf mass, area, dry mass, lamina thickness, mesophyll cell number per cm2, mesophyll cell volume, chloroplast volume, and number of chloroplasts per mesophyll cell) in field‐grown plants of 94 species from the Eastern Pamir Mountains, at elevations between 3800 and 4750 m. Unlike most other mountain areas, the Eastern Pamirs, Karakorum system, Tadjikistan provide
localities where low temperatures and radiation combine with moisture stress at high altitudes. For all the attributes measured, significant differences were found between plants with different mesophyll types. Leaves with dorsiventral palisade structure (dorsal palisade, ventral spongy mesophyll cells) had thicker leaves with larger but fewer mesophyll cells, containing more and larger chloroplasts. These differences in mesophyll type are reflected in differences in the total surface of mesophyll cells per unit leaf area (Ames/A) or volume (Ames/V). Plants with isopalisade leaf structure (palisade cells under both dorsal and ventral surfaces) are more commonly xerophytes and their increased values of Ames/A and Ames/V decrease CO2 mesophyll resistance, which is an important adaptation to drought. Path analysis shows the critical importance of mesophyll cell volume in leading to the covariance between the different leaf attributes and hence to specific leaf mass (SLM), even though mesophyll cell volume is not itself strongly correlated with SLM. This is because mesophyll cell volume increases SLM through its effects on leaf thickness and chloroplast number per cell, but decreases SLM through its negative effect on mesophyll cell density.
Profiles of photosynthetic oxygen‐evolution within leaves of Spinacia oleracea
Authors: HAN T. , VOGELMANN T. , NISHIO J.
Published: March 2003

Oxygen evolution was measured from mesophyll tissues in spinach leaves using a photoacoustic technique. The photosynthetic capacity of individual cell layers was measured by directing microscopic beams of light, 40 μm wide, to cells exposed within a leaf cross section. The resulting profile for oxygen‐evolution potential was relatively flat, indicating a uniform capacity for photosynthesis in leaf mesophyll tissues. Two experimental approaches were used to estimate the photosynthetic performance of individual mesophyll cell layers when white light was applied to the adaxial leaf surface. These experiments indicated that oxygen was produced relatively uniformly across the mesophyll and that oxygen evolution increased with irradiance of the white light applied to the leaf surface. The measured profiles for oxygen evolution and capacity are flatter than previous measurements of profiles of fixed carbon and estimates of profiles for absorbed light within spinach leaves.
Competition under high and low nutrient levels among three grassland species occupying different positions in a successional sequence
Authors: SCHIPPERS PETER , SNOEIJING INEKE , KROPFF MARTIN J.
Published: March 2003

To clarify the role of seasonal change, competitive response and nutrient availability in the competitive asymmetry of grassland species a competition experiment was conducted on Holcus lanatus, Anthoxanthum odoratum and Festuca ovina, which represent a successional sequence of decreasing nutrient availability. Seven harvests were taken over two growing seasons. At each harvest the dry weight of plant parts, dead leaves, leaf area and plant height were measured. Three key traits that determine the successional status of the species were studied: specific leaf area, specific shoot height, and dead leaf fraction.

The response of these traits to competition appeared to be limited and insufficient to change the competitive relations in the experiment. However, all three traits showed marked seasonal changes which resulted in superior growth and survival in winter of the species adapted to nutrient‐poor environments. The findings support the theory that competitive asymmetry increases at higher nutrient levels. It is postulated that the directionality of light makes it possible for the dominant species to monopolize this resource more easily than nutrients.
Phialophora graminicola, a dark septate fungus, is a beneficial associate of the grass Vulpia ciliata ssp. ambigua
Authors: NEWSHAM K. K.
Published: March 2003

Seedlings of the annual grass Vulpia ciliata ssp. ambigua were grown in sterilized sand with a dark septate root fungus, Phialophora graminicola, which had been isolated from a natural population of the grass. Tiller number and shoot, root and total biomass of seedlings grown with P. graminicola were enhanced relative to uninoculated control plants in a growth room and a glasshouse experiment. Root length of seedlings grown with P. graminicola was significantly increased, but no effects of the fungus on root diameter, number of root hairs or specific root length were recorded. Root nitrogen content and shoot, root and total phosphorus contents of seedlings grown with the fungus were enhanced, but shoot nitrogen concentration of these plants was reduced. Shoot biomass and specific root length of inoculated plants were positively associated with the number of P. graminicola colonies re‐isolated from roots. These data indicate that P. graminicola acts as a beneficial associate of V. ciliata ssp. ambigua seedlings under controlled conditions.
Xylem hydraulic characteristics of subtropical trees from contrasting habitats grown under identical environmental conditions
Authors: VANDER WILLIGEN C. , SHERWIN H. W. , PAMMENTER N. W.
Published: March 2003

Five evergreen subtropical tree species growing under identical environmental conditions were investigated to establish which hydraulic properties are genotypically rigid and which show phenotypic plasticity. Maximum xylem‐specific conductivity (ks) correlated well with the anatomical characteristics (conduit diameter and density) for the four angiosperms Tecomaria capensis, Trichilia dregeana, Cinnamomum camphora and Barringtonia racemosa; the anatomy of the gymnosperm Podocarpus latifolius was not assessed. Huber values (functional xylem cross‐sectional area ∶ leaf area) varied inversely with ks among species. Maximum leaf‐specific conductivity was similar in the five unrelated species. Vulnerability of xylem to cavitation differed between species, as did the relationship between transpiration and water potential. Models of these parameters and isolated midday readings confirm that these trees operate at similar maximum leaf‐specific conductivity (kl) values. The data are consistent with the hypothesis that conductivity characteristics (kl, ks) are influenced by environment, whereas vulnerability to cavitation is genetically determined.
Isolation of sucrose: sucrose 1‐fructosyltransferase (1‐SST) from barley (Hordeum vulgare)
Authors: LÜSCHER M. , HOCHSTRASSER U. , BOLLER T. , WIEMKEN A.
Published: March 2003

The enzyme sucrose: sucrose 1‐fructosyltransferase was partially purified from barley leaf growth zones. Four steps (ammonium sulphate precipitation and polyethylene glycol precipitation, followed by chromatography on Concanavalin A‐sepharose and hydroxylapatite) yielded a 35‐fold purification. The resulting preparation of 1‐SST which still contained a number of different activities related to fructan metabolism, was subjected to preparative isoelectric focusing, and sections of the gel were analysed individually for 1‐SST and related activities, using sucrose and 1‐kestose as substrates. This procedure yielded a 196‐fold purification and revealed the presence of two isozymes of 1‐SST with pI values of 4.93 and 4.99, as determined by analytical isoelectric focusing of the corresponding fractions. Both isozymes produced glucose and 1‐kestose when incubated with sucrose. In addition, small amounts of 6‐kestose and tetrasaccharides were formed. In particular, one of the two 1‐SST isozymes yielded fructose when incubated with 1‐kestose, indicating that it also acts as a fructan exohydrolase. The other isozyme exhibited less fructan exohydrolase activity. Nystose was also degraded by the fructan exohydrolase activity but less than 1‐kestose, whereas 6‐kestose was not a substrate for the enzyme. Incubation of both 1‐SSTs with different concentrations of sucrose showed that the enzyme was not saturated even at 500 mM. As for the barley sucrose: fructan 6‐fructosyltransferase, both isozymes of 1‐SST yielded two polypeptide bands of molecular weight 50 and 22 kDa upon sodium dodecylsulphate polyacrylamide gel electrophoresis, suggesting their close relationship to invertase (composed of two subunits of similar size), as previously reported for other plants.
33P translocation in the thallus of the mat‐forming lichen Cladonia portentosa
Authors: HYVÄRINEN M. , CRITTENDEN P. D.
Published: March 2003

The extent of vertical migration of 33P in thalli of the heathland lichen Cladonia portentosa was investigated under field conditions. 33P‐labelled orthophosphate was introduced into the bottom 25 mm of podetia cut to a length of 50 mm from the apices. The distribution of label was scanned using a molecular imager immediately after incubation, and after growing for 8 wk and 6 months. Differences in the relative distribution of label between podetia harvested at the beginning and the end of the experiment showed that there had been a significant migration of 33P upwards out of the labelled 25 mm stratum towards the apex. This was confirmed by statistically significant changes in the median (md) and the 90 percentile of total relative distribution of 33P label. In a control treatment in which label was introduced into the apical 25 mm of podetia, which were then grown inverted (top down), no upward movement of label was detected. By contrast, a statistically significant reduction in the md of the distribution indicated migration downwards towards the thallus apex. The results are consistent with the hypothesis that P is recycled within podetia of mat‐forming lichens, migrating from degrading basal regions upwards to the growing apices following a source–sink relationship.
Axis elongation can occur with net longitudinal orientation of wall microfibrils
Authors: PAOLILLO DOMINICK J.
Published: March 2003

During the initial phases of elongation of pea internodes, oat and rice coleoptiles, oat mesocotyls, soybean hypocotyls and dandelion peduncles, net transverse orientation of cellulose wall microfibrils (Mfs) was found in the outer epidermal wall. This paper demonstrates that in all these axes, with the exception of rice coleoptile, net longitudinal orientation of microfibrils occurs in the outer epidermal wall in portions of the axes that were still elongating at the time of sampling. The timing of the transition to net longitudinal orientation and whether the transition proceeded acropetally or basipetally varied with the type of axis under study. The variability of the relationship between extension and the transition from net transverse to net longitudinal orientation suggests that factors other than extension are important in determining the transition. Layers of longitudinal wall microfibrils may be added to the extending epidermal wall to bolster its tensile strength commensurate with its function during and after extension. Attention is drawn to the parallels between the concept of tissue tension in growing axes and the concept that the epidermis functions as a stressed skin in the support of mature plant parts in primary growth.
Comparative stem‐growth rates of Mediterranean trees under background and naturally enhanced ambient CO2 concentrations
Authors: TOGNETTI ROBERTO , CHERUBINI PAOLO , INNES JOHN L.
Published: March 2003

Ring widths of five Mediterranean forest tree species (Arbutus unedo, Fraxinus ornus, Quercus cerris, Quercus ilex and Quercus pubescens) growing close to a natural source of CO2 in Tuscany, Italy and at a nearby control site were compared. At the CO2‐enriched site, trees have been growing for decades under elevated CO2 concentrations. They originated from parent trees that also grew under elevated CO2 in natural conditions, and they have been continuously exposed to elevated CO2 throughout their growth. Tree‐ring series from each of the species were prepared. Assigning calendar dates to rings was difficult but possible, and ring‐width series were built for all species. The ring‐width data were analysed using a two‐sided t‐test to assess if there was a difference between the radial growth at the CO2‐enriched site and the control site. The cumulative basal area at the same cambial age at both sites was also compared using a Wilcoxon test. Radial growth of trees at the CO2‐enriched site was not significantly different from growth at the control site. For each species, year by year, radial growth at the CO2‐enriched site was tested against the control site and significant differences were found in only a few years; these differences were not synchronous with extreme climatic events. The expected increase in above‐ground productivity, as one of the ecosystem responses to increasing CO2 during drought stress, was not observed in this Mediterranean woody plant community, despite being water‐limited. Other resource limitations, such as low nutrient availability (common in the Mediterranean region), may have counteracted the positive effect of elevated CO2 under drought stress, or trees may have acclimated to the high CO2.
Effects of salinity on xylem structure and water use in growing leaves of sorghum
Authors: BAUM STUART F. , TRAN PHONG N. , SILK WENDY K.
Published: March 2003

Within the growth zone, salt‐affected leaves of sorghum (Sorghum bicolor) had narrower protoxylem and metaxylem cells than controls. Leaf width and cross‐sectional area were also reduced, so that the salt treatment had no effect on the area of protoxylem per area of leaf cross section. Dye uptake studies suggested that in controls most of the veins, but in salt‐affected leaves only half of the veins, are functional in water transport. Volumetric water flow was greatly diminished in the salt‐affected plants. The reduced flow rate was largely explained by the salt‐induced decrease in leaf surface area. Some decreases in flow rates per unit leaf mass or area were also produced by salinity, particularly in late developmental stages. Not surprisingly, leaf conductance measured with a diffusion porometer did not appear to be correlated with the diameter of the protoxylem or metaxylem elements. By contrast, published values of water deposition rates are strongly related to the size of the protoxylem elements: the rates of water deposition into the growing leaf tissue are proportional to the square of the protoxylem radius. Thus environmentally produced change of the hydraulic architecture of monocot leaves may cause change in local growth rates.
Double chitin synthetase mutants from the corn smut fungus Ustilago maydis
Authors: CHAVEZ‐ONTIVEROS JEANETT , MARTINEZ‐ESPINOZA ALFREDO D. , RUIZ‐HERRERA JOSE
Published: March 2003

Using genetic crosses between single chs mutants of Ustilago maydis inoculated into maize (Zea mays) seedlings,
two classes of double mutants affected in genes coding for chitin synthetases were isolated: chs3/chs4, and
chs4/chs5. Analysis of the mutants showed almost no change in their phenotype compared with wild‐type strains.
Growth rate, effect of stress conditions, dimorphic transition and mating were not affected. The only salient
differences were increased sensitivity to osmotics at acid pH, and decrease in chitin synthetase activity, especially
when measured with CO2+, and in chitin content. Most significant was a decrease in virulence, although this
appeared to be due a factor unrelated to CHS genes. These data can be taken as further evidence that multigenic control of chitin synthetase in fungi operates as a safety mechanism to guarantee fungal viability in changing and hostile environmental conditions.
Maternal transmission of adaptive modifications in salt‐treated Sorghum bicolor: a first stage in ecotypic differentiation?
Authors: AMZALLAG G. NISSIM
Published: March 2003

Following a 3‐wk pretreatment with 150 mM NaCl, Sorghum plants were able to survive exposure to 300 mM NaCl, a lethal concentration for nonpretreated plants. This response is termed salt adaptation. Although the population was initially homogeneous, Na‐includer and Na‐excluder individuals coexisted after the achievement of the salt‐adaptation response, and a large diversity in size of the seeds produced was observed at the end of the life cycle. Offspring of salt‐adapted plants were exposed to a new salt‐adaptation treatment. Even in the absence of selection, the proportion of Na‐excluder individuals in the progeny was significantly increased. Offspring germinated from small seeds differed significantly from plants first‐exposed to a salt‐adaptation treatment, whereas offspring from large seeds displayed intermediate characteristics. This suggests that some of the adaptive changes were transmitted through embryo imprinting. The importance of this phenomenon for emergence of a newly adapted ecotype is discussed.
Genetic diversity of root‐associated fungal endophytes from Calluna vulgaris at contrasting field sites
Authors: SHARPLES J. M. , CHAMBERS S. M. , MEHARG A. A. , CAIRNEY J. W. G.
Published: March 2003

A total of 107 putative ericoid mycorrhizal endophytes were isolated from hair roots of Calluna vulgaris from two
abandoned arsenic/copper mine sites and a natural heathland site in southwest England. The endophytes were
initially grouped as 14 RFLP types, based on the results of ITS‐RFLP analysis using the restriction endonucleases
Hinf I, Rsa I and Hae III. ITS sequences were obtained for representative isolates from each RFLP type and
compared phylogenetically with sequences for known ericoid mycorrhizal endophytes and selected ascomycetes.
The majority of endophyte isolates (62–92%) from each site were identified as Hymenoscyphus ericae, but a number
of other less common mycorrhizal RFLP types were also identified, all of which appear to have strong affinities
with the order Leotiales. None of the less common RFLP types was isolated from C. vulgaris at more than one
field site. Neighbour‐joining analysis indicated similarities between the endophytes from C. vulgaris and mycorrhizal endophytes isolated from other Ericaceae and Epacridaceae hosts in North America and Australia.
Why are annual plants rarely spring ephemerals?
Authors: McKENNA MARGARET F. , HOULE GILLES
Published: March 2003

The period of active growth for spring ephemeral plants coincides with the period of high light, water and nutrient availability between snow melt and canopy closure in the understorey of deciduous forests in eastern North America. However, low temperatures prevail during this period and might restrict the performance of these plants. Remarkably, this peculiar phenology is extremely rare among annual plants. To understand better the role of light and water availability and of temperature in the phenology of spring ephemeral plants, we investigated the effects of two temperature regimes (low: 16/7 °C and high: 21/14 °C), three water availability levels (saturated, control and drought), and three photosynthetically active photon flux densities: low (85–100 μmol m−2 s−1); intermediate
(182–196 μmol m−2 s−1); high
(437–454 μmol m−2 s−1) on the growth and reproduction of the annual
Floerkea proserpinacoides. Total biomass, total leaf area and flower and seed production increased with increasing
temperature, water availability and light intensity. Total leaf area and total biomass were reduced in plants that
were stressed under drought. However, at high temperatures, this reduction was less pronounced when droughted
plants were partially shaded. At low temperatures, plants began to senesce after approximately 9 wk, whereas at
higher temperatures, signs of senescence appeared after only 7 wk of growth. Despite shorter longevity, total
biomass was approximately 1.5 times higher in the control water treatment at higher than at lower temperatures
as a result of greater above‐ground growth, and plants allocated a significantly greater proportion of mass gain to
seed production. Although F. proserpinacoides can tolerate low temperatures such as those typical of early spring, higher temperatures such as those of late spring/early summer are more favorable for growth and reproduction as long as water and light are not limiting. Spring ephemeral annuals might be rare because low temperatures reduce growth rate and extend the life cycle. An annual plant might not have time to reproduce before resource availability deteriorates with canopy closure unless reproduction begins early in the life cycle of the species.
Overwintering problems of newly established Miscanthus plantations can be overcome by identifying genotypes with improved rhizome cold tolerance
Authors: CLIFTON‐BROWN J. C. , LEWANDOWSKI I.
Published: March 2003

Miscanthus, a perennial rhizomatous C4 grass, is a potential biomass crop in Europe, mainly because of its high
yield potential and low demand for inputs. However, until recently only a single clone, M.×giganteus, was
available for the extensive field trials performed across Europe and this showed poor overwintering in the first year
after planting at some locations in Northern Europe. Therefore, field trials with five Miscanthus genotypes,
including two acquisitions of Miscanthus×giganteus, one of M. sacchariflorus and two hybrids of M. sinensis were
planted in early summer 1997 at four sites, in Sweden, Denmark, England and Germany. The field trials showed
that better overwintering of newly established plants at a site was not apparently connected with size or early
senescence. An artificial freezing test with rhizomes removed from the field in January 1998 showed that the lethal
temperature at which 50% were killed (LT50) for M.×giganteus and M. sacchariflorus genotypes was −3.4 °C.
However, LT50 in one of the M. sinensis hybrid genotypes tested was −6.5 °C and this genotype had the highest
survival rates in the field in Sweden and Denmark. Although the carbohydrate content of rhizomes, osmotic
potential of cell sap and mineral composition were not found to explain differences in frost tolerance adequately,
moisture contents correlated with frost hardiness (LT50) in most cases. The results obtained form a basis for
identifying suitable Miscanthus genotypes for biomass production in the differing climatic regions of Europe.
Modelling field emergence patterns in arable weeds
Authors: VLEESHOUWERS L. M. , KROPFF M. J.
Published: March 2003

A model was developed to simulate weed emergence patterns after soil cultivation. In the model, the consecutive processes of dormancy release, germination and pre‐emergence growth were modelled in separate modules. Input variables of the model were: date of soil cultivation, soil temperature and soil penetration resistance. Output variables of the model were: seedling density and timing of seedling emergence. The model was parameterized for Polygonum persicaria, Chenopodium album and Spergula arvensis with data from previous field and laboratory experiments. The model was evaluated with data from an experiment, in which emergence of P. persicaria, C. album and S. arvensis was monitored in field plots that were cultivated once only, at one of five dates in the spring. At the same time as the field observations on seedling emergence, seasonal changes in seed dormancy of the buried weed seeds were assessed by testing the germination of seed lots that were buried in envelopes. From a comparison between field observations and simulated data, it appeared that the model overestimated the rate of dormancy release in spring, whereas germination and pre‐emergence growth were simulated well. In general, therefore, both the numbers of emerging seedlings and the timing of emergence could be predicted accurately, when dormancy was not simulated but introduced from experimental data. Improvement of predictions of field emergence of weeds should mainly focus on increasing the precision of the simulation of dormancy release. Close correlations were found between seedbed temperature and both the extent and rate of seedling emergence, but analysis with the simulation model revealed that they were only partly based on causal relationships, so that they have limited predictive value.
Litter nutrients and retranslocation in a central African rain forest dominated by ectomycorrhizal trees
Authors: CHUYONG G. B. , NEWBERY D. M. , SONGWE N. C.
Published: March 2003

In the strongly seasonal, but annually very wet, parts of the tropics, low‐water availability in the short dry season leads to a semi‐deciduous forest, one which is also highly susceptible to nutrient loss from leaching in the long wet season. Patterns in litterfall were compared between forest with low (LEM) and high (HEM) abundances of ectomycorrhizal trees in Korup National Park, Cameroon, over 26 months in 1990–92. Leaf litter was sorted into 26 abundant species which included six ectomycorrhizal species, and of these three were the large grove‐forming trees Microberlinia bisulcata, Tetraberlinia bifoliolata and Tetraberlinia moreliana. Larger‐tree species shed their leaves with pronounced peaks in the dry season, whereas other species had either weaker dependence, showed several peaks per year, or were wet‐season shedders. Although total annual litterfall differed little between forest types, in the HEM forest (dominated by M. bisulcata) the dry‐season peak was more pronounced and earlier than that in the LEMforest. Species differed greatly in their mean leaf litterfall nutrient concentrations, with an approx. twofold range for nitrogen and phosphorus, and 2.5–3.5‐fold for potassium, magnesium and calcium. In the dry season, LEM and HEM litter showed similar declines in P and N concentration, and increases in K and Mg; some species, especially M. bisculcata, showed strong dry‐wet season differences. The concentration of P (but not N) was higher in the leaf litter of ectomycorrhizal than nonectomycorrhizal species. Retranslocation of N and P was lower among the ectomycorrhizal than nonectomycorrhizal species by approx. twofold. It is suggested that, within ectomycorrhizal groves on this soil low in P, a fast decomposition rate with minimal loss of mineralized P is possible due to the relatively high litter P not limiting the cycle at this stage, combined with an efficient recapture of released P by the surface organic layer of ectomycorrhizas and fine roots. This points to a feedback between two essential controlling steps (retranslocation and mineralization) in a tropical rain forest ecosystem dominated by ectomycorrhizal trees.
Responses of two Sphagnum moss species and Eriophorum vaginatum to enhanced UV‐B in a summer of low UV intensity
Authors: Niemi Riikka , Martikainen Pertti J. , Silvola Jouko , Sonninen Eloni , Wulff Anu , Holopainen Toini
Published: March 2003

•   The flux of ultraviolet (UV)‐B radiation to the Earth's surface is increasing, particularly in high latitudes. We studied the sensitivity of some dominant plant species of boreal and subarctic peatlands to this increase.

•   Intact peat monoliths with the mosses Sphagnum balticum and Sphagnum papillosum, and cotton grass (Eriophorum vaginatum) were exposed to ambient solar UV‐B or ambient solar UV‐B supplemented by 30% in a field experiment in central Finland.

•   Although the UV‐B dose was low during the growing season, owing to frequent cloudiness, both Sphagnum species showed significantly higher membrane permeability under enhanced UV‐B. In S. balticum, UV‐B tended to decrease the capitulum dry mass and induced a 30–40% increase in the concentration of chlorophyll and carotenoid pigments. Enhanced UV‐B had no effects on leaf morphology, chlorophyll fluorescence or stomatal functioning in E. vaginatum.

•   The various UV‐B responses in the Sphagnum species under investigation indicate that they may be sensitive even to small increases in solar UV‐B radiation. By contrast, E. vaginatum appeared to tolerate the UV‐B fluxes of the experiment.
Sources of family income and expenditure on children's private, after‐school education in Korea
Authors: Chung Young Sook , Choe Minja Kim
Published: March 2003

This paper examines the relationship between sources of family income and household expenditure on private, after‐school education for children in secondary schools in Korea in the context of educational ‘credentialism’, which values evidence of college education highly. Data from a survey of 514 parents of secondary school students are used. Estimated ordinary least squares coefficients indicate that the wife's income, but not the husband's, was positively associated with the amount of spending on children's education at private, after‐school programmes. This finding suggests that some married women with children in Korea seek employment in order to earn the money needed for their children's private, after‐school education.
An investigation into the availability and economic accessibility of food items in rural and urban areas of Northern Ireland
Authors: Furey Sinead , Farley Heather , Strugnell Christopher
Published: March 2003

The question of access to food has three components: physical access to food, financial access to food and access to information about food. This study explores the issue of financial access to food. The affordability of food is a major consideration for consumers, an important marketing tool for retailers and a principal theme in food policy. Research methods included a comparative shopping exercise (shopping basket analysis) in 109 stores across four towns (two urban and two rural) in Northern Ireland. Store type included multiples (major supermarket chains) and symbol group stores (those stores operating under a franchise from one main buying group). Results indicate that in the main it is cheaper to buy from the multiples, shopping from a symbol group store can incur cost penalties of up to 39.4% above the multiples’ prices. Price disparities, analysed using z‐scores, were apparent between towns and across store types. Similarly, an availability audit of foodstuffs portrayed the multiples as the most comprehensive from which to shop, whereas symbol group stores fared poorly in the availability of fresh green vegetables, carcass meat and wholemeal breads. This is an important issue because it plays an integral part in the health inequality debate and also relates to social exclusion. Fundamentally, financial access to food impinges upon the whole question of food‐purchasing behaviour in terms of accessibility, affordability and availability. Therefore, economic access to food can be used as a useful precursor to a comprehensive analysis of food access in its entirety. It is also useful as an indicator of social exclusion. This study seeks to inform and influence the food policy debate.
Cooking, recipe use and food habits of college students and nutrition educators
Authors: Hertzler Ann A. , Bruce F.A.
Published: March 2003

The purpose of this study was to revisit Lewin's gatekeeper theory to observe current food role patterns (cooking experience, recipe sources, and both daily food consumption choices and eating out) with contemporary groups of college students (n = 292) and of nutrition educators (n = 26). Male college students equalled female students in cooking ability, use of family as a prime recipe source, and frequency of eating out, while exhibiting different food consumption excesses and deficiencies. Package labels and the Internet were most frequently identified as recipe sources by college students. Nutritionists surpassed both male and female college students in most attributes.
Estimation of income elasticities from Lorenz concentration curves: application to Canadian micro‐data
Authors: Abdel‐Ghany Mohamed , Gehlken Amy , Silver J. Lew
Published: March 2003

This study uses a method of estimating income elasticities of major Canadian expenditure groups. The technique is based on the implicit Engel functions derived from the Lorenz curve of permanent income and concentration curves of group‐specific expenditures. The methodology is applied to The 1996 Canadian Family Expenditure Survey. Results indicate that income elasticities for the majority of the broad expenditure categories considered in the study are inelastic and they increase monotonically with income.
Shopping orientation segments: exploring differences in store patronage and attitudes toward retail store environments among female apparel consumers
Authors: Moye Letecia N. , Kincade Doris H.
Published: March 2003

The purpose of this study was to identify shopping orientation segments for US female consumers. The sample included 151 women, aged 18 years and over. This research examined differences in the segments relative to store patronage preferences (i.e. department, discount, specialty), attitude toward the environment of the store selected as first choice when shopping for a specific apparel item (i.e. a dress), and demographic characteristics. Cluster analysis revealed that four shopping segments described the female consumers. The segments were named Decisive Apparel Shopper, Confident Apparel Shopper, Highly Involved Apparel Shopper, and Extremely Involved Apparel Shopper, based on several shopping factors. Differences were found among the shopping orientation segments for store of first choice, attitude and household income. Implications and future research directions are discussed.