bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of increasing rhizospheric calcium on the ability of Lupinus luteus L. to control water use efficiency
Authors: ATKINSON C. J. 
Published: April 2006

summaryThe stomatal behavior of Lupinus luteus L. was examined to determine the ability of a calcifuge to regulate water loss against a background of different rhizospheric Ca concentrations. A previous study had suggested that a cultivar of this species had limited stomatal sensitivity to ABA, and so the physiological events which enable L. luteus to adjust its water use efficiency (WUE) in response to changes in both atmospheric and soil water availability were explored in a number of ways. L. luteus did not lack the ability to control water loss and there was no evidence to suggest that ABA was unable to regulate stomatal behavior during water deficits, Stomatal closure was shown to occur in a linear manner when different concentrations of ABA were applied. The presence of different concentrations of Ca within xylem sap did not influence the degree to which stomata closed in response to applied ABA. The patterns of stomatal behavior in response to changes in atmospheric humidity, declining soil water potentials and applied ABA, were generally similar to those of other species.The presence of high rhizospheric Ca 8 mol m−3 did not apparently induce stomatal closure when gas exchange measurements were made at a δW of mmol mol−1, when compared with plants grown on 1 mol m−3 Ca. However, when measurements of gas exchange were made over a range of δW values, the relationship between assimilation and stomatal conductance suggested that the degree of coupling between these two variables was less pronounced with plants grown at 8 mol m−3 compared to those at 1 mol m−3 Ca. The effect of this on the regulation of leaf conductance was to perturb WUE.There was little evidence here to support a role for changes in the flux of xylem sap Ca as a means of root‐to‐shoot signaling.
Orientation of the lateral roots of trees
Authors: COUTTS M. P. , NICOLL B. C. 
Published: April 2006

summaryThe main lateral roots of some tree species grow close beneath the soil surface, even on irregular or sloping ground. Experiments were carried out to explore the origin and behavior of such surface roots. Pinus contorta Douglas ex Loudon and Picea sitchensis (Bong.) Carr. plants were grown under growth room and glasshouse conditions. Lateral roots were excavated and vertical and horizontal co‐ordinates measured. The liminal angles (0°= vertically downwards) of first‐order lateral roots of seedlings of both species decreased linearly with depth of origin on the taproot, Some of the roots of highest origin had liminal angles > 90° (ie they grew upwards). However, these roots deflected downwards on approaching the soil surface. If additional soil was added soon after germination the upper lateral roots grew further in an upward direction and then deflected beneath the elevated surface. Two‐year‐old Picea sitckensis transplants were planted centrally in large containers of soil and an elevated ridge of soil was made 160 mm to one side of the plants. Vigorous upwardly growing roots developed from the damaged and bent root systems that had been produced in the forest nursery. The upwardly oriented roots deflected horizontally when their tips arrived below the flat peat surface, but when they extended beneath the ridge they turned upwards within it. As they approached the top of the ridge they again deflected downwards.It is concluded that the direction of growth of surface roots is the result of two opposing influences. Certain of the main lateral roots are plagiogravitropic and grow obliquely upwards but as these roots approach the soil surface they respond to some signal from the environment that causes downward deflection. The nature of the signal was not determined but it was shown that downward deflection occurred whether or not the soil was exposed to light. The biological importance of this form of surface root orientation is discussed. The growth behavior described enables the main lateral roots to explore the nutrient‐rich surface layers of the soil while avoiding the injury to the root tip that would result from exposure.
Response of nitrogen metabolism in beans (Phaseolus vulgaris L.) after exposure to ozone and nitrogen dioxide, alone and in sequence
Authors: BENDER J. , WEIGEL H. J. , Jäger H. J. 
Published: April 2006

summaryBush bean (Phaseolus vulgaris L.) plants were exposed to low levels of ozone (O3) and/or nitrogen dioxide (NO2) in open‐top chambers during the growing seasons of 1988 and 1989. Treatments consisted of charcoal‐filtered (CF) air, and CF air enriched with either O3 (50–60 nll −1), NO2 (30–40 nll−1) or both gases. A daily sequential exposure, O2 followed by NO2, was used in each year in the combined treatment: O2 was added for 8 h d−1 from 08.00 h until 16.00 h, and NO2 for 16 h d−1 from 16.00 h until 08.00 h. Growth variables and key enzymes of N assimilation in leaves were investigated during vegetative growth and at anthesis. Pollutant effects varied between years. No significant effects were found in 1988. In 1989 NO2, alone or in sequential exposure with O3+, increased leaf dry weight and total biomass until anthesis. Moreover, there was a parallel increase in the extractable activity of both nitrate and nitrite reductase in the NO2 treatments during vegetative growth, while glutamine synthetase and glutamate dehydrogenase were only increased by sequential exposure to O3+ NO2. In contrast, during anthesis the activities of nitrite reductase and glutamine synthetase were lowest in leaves sequentially exposed to O3+ NO2. Ozone alone had very little effect on N metabolism but suppressed growth during anthesis. At pod maturity, the lowest leaf dry weight and leaf area occurred in plants exposed to the sequential combination of O3+ NO2, but yield (pod weight) was not significantly affected by any of the pollutant treatments. It is concluded that chronic exposure especially to the sequence O3−NO2 reduced the capacity of the plants for N assimilation. The observed shift in nitrogen metabolism during the plants' development may have contributed to the adverse effects of the sequential treatment O3+ NO2 on growth variables at the end of the exposure period.
Effects of salinity on severity of infection by Phytophthora parasitica Dast., ion concentrations and growth of tomato, Lycopersicon esculentum Mill.
Authors: SNAPP S. S. , SHENNAN C. , VAN BRUGGEN A. H. C. 
Published: April 2006

summaryThe response of tomato (Lycopersictm esculentum Mill., cv. UC82B) to salinity, alone and in combination with Phytophthora parasitica Dast. (a fungal pathogen causing root rot) was investigated in a field study. Three salinity regimes were established: 1) a low salinity control, 2 medium salinity, where 75 mm total salts (NaCl and CaCU in a 4:1 molar ratio of Na:Ca) were added to the irrigation water to give an electrical conductivity (EC) of approximately 8 dS m−1, and 3) high salinity, where ISO mM total salts (4:1 molar ratio of Na: Ca) gave an EC of approximately 16 dS m−1. Half of the plots were inoculated with P. parasitica. and the remainder were treated with a selective fungicide to inhibit the pathogen. Soil salinity markedly increased the incidence of Phytophthora root rot in both years of the study. The combination of salinity and enhanced disease severity led to significant reductions in fresh fruit yields, fruit size and, to a lesser extent, total above ground biomass. Fruit size was affected to the greatest extent and showed a strong interaction between the effects of disease and salinity, suggesting that the import of water by fruit was more sensitive than dry matter production to the combination of these stresses. Net root growth (0–50 cm depth) was greatly reduced (by 40–50%) in the presence of salinity, whereas P. parasitica had no discernable effect even when more than 50% of the root system showed severe root rot lesions. In spite of the reduced root system, leaf water potential was not affected by disease in the 1989 growing season. During the fruit‐fill period in 1988, however, leaf water potential was more negative in inoculated plots. A marked degree of leaf ion homeostasis was maintained even under high salt and root rot stress. Excessive build up of Cl or Na concentrations in the leaves did not contribute substantially to the observed reductions in plant growth and yield. The results suggest that a reduced root growth rate or an enhanced root death rate may be at least partially responsible for the increased disease severity at high salinity.
Variations in epidermal cell turgor of rust‐infected barley seedlings
Authors: BERRYMAN C. A. , EAMUS D. , FARRAR J. F. 
Published: April 2006

summaryBarley [Hordeum distichum (L.) Lam.] seedlings were infected with uredmiospores of rust, Puccinia hordei Otth., 10 d after germination and the Zimmermann micro‐pressure probe was used to measure the turgor potential of individual epidermal and palisade cells, during disease development. Turgor potential was measured as a function of time and as a function of distance from the centre of the rust colony. When the centre of a rust colony was within 300 μm of probed cells, palisade cell turgor declined significantly on days 6, 7 and 9 after infection in comparison to control leaf palisade cells.Control leaf palisade cell turgor remained constant with time. On day 4 after infection, epidermal cell turgor of control and infected leaves did not differ. However, by day 6 when the uredinium was visible and approaching sporulation, epidermal cell turgor of infected leaves declined. The reduction was dependent upon the distance from the centre of the colony, thereby creating a gradient of turgor such that the lowest turgors were recorded at the centre of the colony and the highest at the colony boundary. By day 9 after infection, when ‘green island’ development had begun, this gradient was reversed. However, turgors of all epidermal cells in colony areas were significantly less than those in control leaves. These results are discussed in relation to die impact of rust infection upon leaf water relations in barley.
Uptake, accumulation and translocation of arsenate in arsenate‐tolerant and non‐tolerant Holcus lanatus L.
Authors: MEHARG ANDREW A. , MACNAIR MARK R. 
Published: April 2006

summaryUptake, translocation and accumulation of arsenate was determined in arsenate‐tolerant and non‐tolerant genotypes of Holcus lanatus L. Over a 6 h period of growth in 005 mol m−3arsenate, non‐tolerant genotypes accumulated arsenate to a much greater extent than tolerant plants. Tolerant plants transported a much greater proportion of As to their shoots compared with non‐tolerant plants. Phosphate at a concentration of either 0.05 or 0.5 mol m−3decreased arsenate uptake in both tolerant and non‐tolerant genotypes. When arsenate uptake was determined over 3 d at the same arsenate concentration, non‐tolerant plants grown in the presence of 0 and 0.05 mol m−3phosphate died, while those growing in 0.5 mol m−3phosphate survived and continued to take up arsenate. At all three phosphate levels tolerant plants survived. Over the 3 d period transport of arsenate to the shoots decreased. With increasing phosphate levels in solution transport of arsenate to the shoots increased in tolerant plants. The results from these experiments are discussed in terms of strategies for metal tolerance in this species.
Fungal decomposition of attached angiosperm twigs
Authors: GRIFFITH G. S. , BODDY LYNNE 
Published: April 2006

summaryExperimental investigations indicated that over wet periods the moisture content of dead attached ash twigs was very variable. Frequently they were subject to very rapid and large changes in moisture content, of the order of ± 40% in 24 h. Over wet periods drying of twigs was apparently due mainly to drainage, the rate of which was determined by a number of interrelated factors including density, diameter and degree of bark loss. Over dry periods the moisture content of twigs was less variable and drying was due mainly to evaporation. Water sorption isotherms were determined for twigs and the form of these isotherms was essentially similar to that recorded for sapwood of various trees by other authors. The form of the sorption isotherm was affected by density, a factor related to their state of decay. The sorption isotherms indicated that the pore size distribution within twigs was markedly different from that in typical branch sapwoods. The isotherms were used to estimate water potential variation in dead attached twigs in the field.
Lack of antagonism between the biocontrol agent Gliocladium virens* and vesicular arbuscular mycorrhizal fungi
Authors: PAULITZ T. C. , LINDERMAN R. G. 
Published: April 2006

summaryThe effect of the fungal biocontrol agent Gliocladium wrens Miller, Giddens & Foster on the colonization of cucumber by the VA mycorrhizal fungi Glomus etunicatum Becker & Gerdemann and Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe was investigated. Inoculum of G. virens, grown on wheat bran or peatmoss‐Czapek substrate, was added to soil artificially infested with Pythium ultimum Trow. Both damping‐off of cucumber and pathogen population density were reduced in treatments with G. virens. Inoculum of G. virens was also added to soils containing increasing propagule densities of Glomus etunicatum or Glomus mosseae. After one week of incubation, the soils were planted with cucumber seeds, and the percent mycorrhizal colonization of roots was determined after 12 d. When grown on wheat bran, G. virens was phytotoxic and increased mycorrhizal colonization by Glomus etunicatum. However, G. virens had no effect on Glomus etunicatum when added as peatmoss‐Czapek inoculum. Amendment of soil with peatmoss‐Czapek inoculum of G. virens reduced colonization by Glomus mosseae when compared to a non‐amended control. Inoculum colonized by other fungal biocontrol agents and sterilized with propylene oxide gave a similar reduction, suggesting that the substrate, not G. virens, was responsible for the reduction in VA mycorrhizal colonization. This evidence suggests that the fungal biocontrol agent G. virens does not have a detrimental impact on these VA mycorrhizal fungi, and would be compatible if applied as a dual‐inoculum.
Superoxide dismutase activity in needles of Scots pine and Norway spruce under field and chamber conditions: lack of ozone effects
Authors: POLLE ANDREA , RENNENBERG HEINZ 
Published: April 2006

summarySpruce [Picea abies (L.) Karst.] and pine (Pinus sylvestris L.) trees were exposed to various ozone regimes ranging from short‐term fumigation of twigs for some hours up to long‐term exposures of young plants for 20 wk in environmental chambers. At the end of the experimental treatments needles of spruce trees exposed to episodes with moderate ozone mixing rations (10–150 nl l−1) showed no visible symptoms of injury; needles exposed to high ozone mixing ratios (300 and 600 nl l−1) were bleached. None of the treatments affected the soluble protein content and superoxide dismutase activity. When the same stocks used in the chamber experiments were exposed in pots at a forest site to ambient conditions with an average of 30 nl l−1ozone, the specific superoxide dismutase activities were increased by factors ranging from 1–4 to 3–7. The needles of old field‐grown pine and spruce trees contained 1.5‐ to 60‐fold higher specific superoxide dismutase activities than the needles of young plants kept under chamber conditions. Mature trees with decline symptoms were also investigated. Current year's bleached needles of field‐grown spruce did not contain increased superoxide dismutase activities. Only in older needle age classes of damaged spruce orpine trees were moderate increases (1.2‐ to 1.3‐fold) of superoxide dismutase activities observed, as compared to needles from healthy trees. The results indicate that superoxide dismutase activity in needles of spruce and pine growing outdoors responds to factors different from ozone.
A facility for the large‐scale exposure of plants to gaseous atmospheric pollutants
Authors: RAFAREL C. R. , ASHENDEN T. W. 
Published: April 2006

summaryA large‐scale fumigation system is described for studying the effects of low concentrations of SO2, NO2, and O3 on herbaceous plants and small shrubs. The system is based on a commercially available small hemispherical glasshouse which can be adapted to provide a closed chamber with forced air ventilation. It is a scaled down version of earlier ‘Solardome’ designs and benefits from easier and less expensive control of pollutant gases. SO2 and NO2 are supplied from cylinders of diluted gases (∼1 %) while O3 is produced from oxygen using an ozone generator of the electric discharge type. Good control of gas flows and efficient air/gas mixing ensures high uniformity of pollutant gas concentrations. The good air circulation within the chambers maintains the temperatures in the domes near to ambient.
The cell cycle in plant development
Authors: FRANCIS DENNIS 
Published: April 2006

summaryThe aim of this review is to discuss the molecular controls of the cell cycle in relation to higher plant development. An analysis is made of the current models of the cell cycle based on the biochemistry and genetics of the budding yeast, Saccharomyces cerevisiae and the fission yeast, Schizosaccharomyces pombe. What emerges are universal mechanisms observed in a wide range of taxonomic groups involving a group of protein kinases which regulate the transition from both post‐synthetic interphase (G2) to mitosis and from pre‐synthetic interphase (G1) to DNA synthetic‐(S) phase. The data are consistent in showing the activity of protein kinase complexes operating in conjunction with at least one dephosphorylating enzyme. The natural substrate(s) for the key cell division cycle gene product, p34cdc 2, has yet to be resolved although the nuclear lamins and microtubular apparatus are strong candidates. These models serve as a basis for assessing the cell cycle in higher plants. Mitosis and various stages of nuclear DNA replication are considered in relation to the presumed initiation and termination factors that regulate these events. In order to make a link between the cell cycle and plant development special consideration has been given to plant meristems. In particular, the activity of the cell cycle in cells that have the capacity to regenerate whole tissue systems (‘stem cells’) within the meristem is discussed. In the root meristem, the quiescent centre cells conform to a stem cell population; a non‐cycling stem cell may be immune to the morphogenetic signals that cause cycling cells to arrest and differentiate. The pericycle may act as a vestigial stem cell population. The shoot apex is also discussed in relation to both vegetative and floral growth. Although gradients of cell division exist in shoot meristems it is far less obvious where ‘stem’, or founder, cells reside in the apex. The way in which the cell cycle shortens on transition to floral growth is considered critical for identifying when the meristem becomes florally determined. Temperature and toxic metals are given special attention where it is emphasized that G1 phase becomes protracted when plants are stressed. Species that can tolerate stressful environments may have meristems in which a greater number of cells are competent for division. Finally, the cell cycle in vitro is discussed in relation to rapid changes in gene expression which are linked to the transition from G1 to S phase. The latter emerges as a key cell cycle transition for plant meristems both in vivo and in vitro.

CONTENTS

Summary
1

I.
Introduction
2

II.
The cell division cycle (cdc) genes
2

III.
The plant cell cycle
5

IV.
Meristems
9

V.
Effects of external stress on the cell cycle in plant meristems
14

VI.
The plant cell cycle in vitro
15

VII.
Conclusions
15

Acknowledgements
16

References
16
Yield stimulation of a commonly grown cultivar of Phaseolus vulgaris L. at near‐ambient ozone concentrations
Authors: SANDERS G. E. , ROBINSON A. D. , GEISSLER P. A. , COLLS J. J. 
Published: April 2006

summarySeeds of Phaseolus vulgaris L. ev. Nerina were hand‐sown inside open‐top chambers (OTCs) in which the plants were exposed to charcoal‐filtered air (CF treatment), ambient air (NF), or ambient air with added 6, 12, 18, 25 or 30 nl 1−1 of ozone (NF6, NF12, NF18, NF25 and NF30 treatments, respectively). Exposure commenced as the crop emerged and continued on a daily basis until the end of the season. Ozone (O3) was added between 10.00 and 18.00 h GMT. The seasonal 7 h mean O3 concentrations ranged from 10 nl l−1 in the CF treatment to 50 nl l−1 in the NF30 treatment.The growth and yield of P. vulgaris ev. Nerina demonstrated two distinct responses to O3 depending upon concentration. At seasonal 7 h means of 20, 26 and 32 nl l−1 (NF, NF6 and NF12 treatments respectively), the yield increased relative to that of the CF treatment. The increase in yield peaked at 48% in the NF6 treatment (P < 0.05), and was associated with a 55 % increase in the maximum leaf number, longer retention of the canopy, and a 45 % increase in the number of pods present at the final harvest. In contrast, seasonal 7 h mean O3 concentrations of 38, 45 and 50 nl l−1 (NF18, NF25 and NF30 treatments) caused 26–42 % reductions in the yield of P. vulgaris. The leaves of such plants developed extensive symptoms of O3 injury and were prematurely abscised from the plants. The reductions in yield were due to a decrease in the numbers of seeds per pod and in the weights of individual seeds.
Seasonal response of slash pine (Pinus elliottiivar.elliottiiEngelm.) photosynthesis to long‐term exposure to ozone and acidic precipitation*
Authors: BYRES DAVID P. , JOHNSON JON D. , DEAN THOMAS J. 
Published: April 2006

summaryFour half‐sib families of slash pine (Pinus elliottiivar.elliottii) were planted in open‐top chambers and exposed to ozone and simulated acidic precipitation (3: 7 molar ratio of nitric and sulphuric acids). The 4 ozone treatments were (1) charcoal‐filtered air, (2) unfiltered ambient air, (3) twice ambient and (4) three times ambient ozone, with treatments applied 12 h per day, 11 months per year for 28 months. Seedlings were irrigated weekly with one of three rain acidities: pH 33, 4.3 or 5.3 at a total rainfall equivalent of 133 cm per year. Photosynthetic rates were measured approximately every 10 weeks, on the most recently emerged branches each year. In 1988 the 3rd flush was measured, and in 1989 and 1990 the 1st flush of each year was measured.Elevated ozone concentrations generally reduced photosynthetic rates, especially during the summer months, but there was no evidence of either a threshold dose or a simple linear relationship between photosynthesis and ozone exposure. There was a seasonal drop in photosynthetic rates from March to September each year. An ontogenetic decrease in photosynthesis was also evident as trees matured. Stomatal conductance also decreased as the needles aged. Seedlings irrigated with pH 3.3 solution typically exhibited the highest photosynthetic rates, presumably due to a fertilizer effect.