bluuebunny/crossref_metadata_2025 huggingface dataset:
A facility for the large‐scale exposure of plants to gaseous atmospheric pollutants
Authors: RAFAREL C. R. , ASHENDEN T. W.
Published: April 2006

summary

A 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

summary

The 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

summary

Seeds 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

summary

Four 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.
Effects of dry‐deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter I. Changes in communities of fungal saprotrophs
Authors: NEWSHAM K. K. , FRANKLAND JULIET C. , BODDY LYNNE , INESON P.
Published: April 2006

summary

Comparisons of the saprotrophic fungi isolated from ash (Fraxinus excelsiorL.), birch (Betulaspp.), hazel (Corylus avellanaL.), pedunculate oak (Quercus roburL.), sessile oak [Q. petraea(Mattuschka) Liebl.] and sycamore (Acer pseudoplatanusL.) leaf litters from three woodlands exposed to low, medium and high levels (c. 0.0→ 0.060μl l−1) of sulphur dioxide (SO2) showed that the composition of the fungal communities differed between sites. Fumigation of angiosperm tree leaf litters from the least and the most polluted site with environmentally‐realistic concentrations (0.010–0.030 μl1) of SO2for 16–68 wk in an open‐air field‐fumigation experiment resulted in marked changes in the composition of the fungal communities in the leaf litters, comparable with differences found between the woodland sites.Cladosporiumspp.,Epicoccutn nigrumLink,Fitsariumspp. andPhoma exiguaDesm. were less commonly isolated from leaf litters exposed to SO2, whereasConiothyrium quercinumSacc. var.glandicolaGrove,Cylindrocarpon orthosporum(Sacc.) Wollenw. andPenicilliumspp. were more frequently isolated from fumigated litters. However, few differences could be detected in the response to SO2of the mycofloras of leaf litters originating from different woodland sites. In general, SO2did not affect the total extent of fungal occupancy of the microsites in the litter, as fungal species which decreased in abundance on exposure to the gas appeared to be replaced in the litter by other species more tolerant to the gas. SO2therefore appeared to be selectively toxic to saprotrophic fungi isolated from these litters.
Nitrate and ammonium uptake by maize: adaptation during relief from nitrogen suppression
Authors: JACKSON W. A. , VOLK R. J.
Published: April 2006

summary

Initial (0–1 h) net rates of nitrate and ammonium uptake from 200 μM NH4NO3 were progressively increased as 8‐d‐old maize (Zea mays L.) seedlings, grown on 5 mM nitrate, were exposed to nitrogen‐free solutions for up to 48 h. Further nitrogen deprivation to 72 h resulted in a decline in the nitrate uptake rate. Nitrate uptake rates of plants at all stages of nitrogen deprivation increased steadily during an 8 h exposure to 200 μM NH4NO3. The pattern of the response of ammonium uptake during the 8 h adaptation period was considerably different. In nitrogen‐replete plants the ammonium uptake rate increased steadily, but deprivation of nitrogen for 12 h and longer resulted in complex responses in which the initial rate was followed by a decline, a subsequent increase, and another decline.

The responses of the nitrate uptake system are considered to reflect a lifting of the suppressive effects of nitrate and a product of nitrate assimilation during nitrogen deprivation, a concomitant degradation of an induced component of the nitrate uptake system during that time, and reinduction of the uptake system during the adaptation period. The responses of the ammonium uptake system are considered to reflect the interplay of suppression by a product of ammonium assimilation, the accumulation of root ammonium and associated ammonium efflux, and a stimulation by ammonium of its own uptake. As a consequence of the differential responses of the two uptake systems, nitrate and ammonium uptake rates were positively correlated, largely independent, or negatively correlated as the plants progressed through the 8 h adaptation period.
Root endophytes of lupin and some other legumes in Northwestern USA
Authors: O'DELL T. E. , TRAPPE J. M.
Published: April 2006

summary

Roots of ten species ofLupinusand three other legumes collected from field soils were cleared, stained, and examined for fungal colonization. Three species were not colonized. Nine species were colonized by aseptate hyphae and vesicles attributable to vesicular‐arbuscular mycorrhizal fungi. Seven species were sometimes colonized by fungi with septate hyphae, which often formed intracellular sclerotia. The associations observed are compared with previous reports and discussed in relation to legume systematics.
Chlorophyll fluorescence decay profiles of O3‐exposed spruce needles as measured by time‐correlated single photon counting
Authors: EVANS E. H. , BROWN R. G. , WELLBURN A. R.
Published: April 2006

summary

Chlorophyll fluorescence decay profiles have been measured in the wavelength range 680–720 nm for needles from Norway spruce [Picea abies (L.) Karst] trees which have been exposed to ozone. All profiles required three exponential components of lifetime 100–150 ps, 400–600 ps and 3.5–5.0 ns to fit the experimental data. Compared to control samples, the ozone‐treated needles exhibited a greater amount of the longest‐lived chlorophyll fluorescence and a redistribution in intensity for both the other components from 720 + to 690 nm. These observations are interpreted in terms of disruption of energy transfer and break‐up of light‐harvesting complexes on exposure to ozone. The potential for use of the technique in monitoring forest decline is discussed.
Nuclear magnetic resonance (NMR) microimaging of raspberry fruit: further studies on the origin of the image
Authors: GOODMAN B. A. , WILLIAMSON B. , CHUDEK J. A.
Published: April 2006

summary

Nuclear magnetic resonance (NMR) micro‐images of mature red raspberry (Rubus idaeus L.) fruits and their separated components have been produced under a variety of experimental conditions with the objective of understanding factors which determine image quality in different types of tissue. By varying the delay time between image accumulation sequences it has been shown that water molecules in drupelet surface layers in contact with other drupelets, and in the vascular bundles and traces in the receptacle and drupelets have shorter relaxation times than those in other tissues of the fruit. By performing separate T1‐ > and T2‐weighted imaging sequences it was shown that the short relaxation times in the vascular tissue was primarily a T1 effect. This is probably caused by paramagnetic ions because electron paramagnetic resonance (EPR) spectroscopy showed significant amounts of the manganese(n) ion in a spectrum of an aqueous extract of receptacle tissue. The cause of the short relaxation times in the drupelet surface layers is less clear, but we suggest that epicuticular waxes or the suberized cuticular layer of the epidermis might be responsible.

The appearance of entire seeds, including the mature embryos, as featureless black regions in the images has been shown to be due to the lower concentration of mobile protons in these structures compared with that in the surrounding mesocarp, and not to differences in relaxation properties of the protons. Consequently, internal detail of the seeds could only be obtained by separating them from the fruit.
Exposure of spring wheat, Triticum aestivum L., cv. Drabant, to different concentrations of ozone in open‐top chambers: effects on the ultrastructure of flag leaf cells
Authors: OJANPERÄ K. , SUTINEN S. , PLEIJEL H. , SELLDÉN G.
Published: April 2006

summary

Spring wheat, Triticum aestivum L., cv. Drabant, was exposed to different concentrations of ozone in open‐top chambers for one growing season, at a site located in south‐west Sweden. The chambers were placed in a field of commercially grown spring wheat. The treatments were charcoal‐filtered air (CF), non‐filtered air (NF), non‐filtered air + 25 nl 1−1ozone (NF +) and non‐filtered air + 35 nl 1−1ozone (NF++). Ozone was added daily between 11.00 and 18.00 h, starting at anthesis. Fumigation with elevated concentrations of ozone caused chlorosis of the flag leaves. In the NF++ and NF+ treatments chlorosis appeared after 7 and 20 days of fumigation, respectively, and in the CF treatment after about 34 days, A progressive series of changes occurred in the mesophyll cells of the flag leaves after ozone fumigation. Starting at anthesis, the first changes occurred in the cytoplasm and involved a decrease in the amount of cytoplasm and an increase in the vacuolization of the cells. Subsequently the chloroplasts became affected decreasing in area and containing more plasto‐globuli. Finally vesicles were formed between the grana thylakoids and at the same time the plasma membrane came loose from the cell wall and convoluted. The mitochondria remained unaffected until only lipid droplets, oleosomes, were left in the cells. These changes were not specific for ozone as they occurred also in the CF treatment, although later in time. This indicates that ozone causes premature senescence in wheat flag leaves.
Long‐term effects of ozone and simulated acid rain on the foliage dynamics of slash pine (Pinus elliottii var. elliottii Engelm.)*
Authors: BYRES DAVID P. , DEAN THOMAS J. , JOHNSON JON D.
Published: April 2006

summary

Seedlings from four half‐sib families of Pinus elliottii var. elliottii Engelm. were planted in open‐top chambers, and exposed to ozone and simulated acidic precipitation. Treatments were applied for 11 months per year for 28 months. The ozone concentrations were: charcoal filtered air (CF), nonfiltered ambient air (1×), twice the nonfiltered level (2 ×) and three times the nonfiltered level (3 ×). Ozone exposures were computer controlled to follow natural diurnal fluctuations in ambient ozone concentrations. Simulated acid rain at pH 3.3, 4.3 or 5.3 was delivered weekly at the same volume as average weekly rainfall to all chambers.

Leaf area, bud number and fascicle survival were all highest in the CF chambers. Genetic differences between half‐sib families were apparent in both leaf area and the number of live buds. Leaf area and fascicle survival were reduced with every increase in ozone exposure from CF to 3 ×. Leaf litterfall increased significantly with increasing ozone exposure. Leaf growth, measured by mean leaf area and mean dry weight per needle, was not affected by ozone exposure or by acid rain. It was concluded that ozone reduced leaf area mainly by causing premature leaf senescence.

The only significant effect of acidic precipitation was enhanced leaf retention in trees irrigated with pH 3.3 solution. The results indicate that the increasing levels of trophospheric ozone may significantly reduce the growth of slash pine through foliage loss. The increased leaf retention caused by acid rain is unlikely to compensate for the detrimental effect of ozone.
Effects of nitrogen oxides on nitrate assimilation in bryophytes
Authors: MORGAN S. M. , LEE J. A. , ASHENDEN T. W.
Published: April 2006

summary

Nitrate assimilation and photosynthetic responses of Ctentdium mulluscum (Hedw.) Mitt. Homalothecium sericeum (Hedw.) Br.Eur. Pleurusium schreberi (Brid.) Mitt. Hylocomium splendens (Hedw.) Br.Eur. were studied during and after controlled exposures to 35 nl 1−1NO2 and 35 nl 1−1NO. NO2 induced nitrate reductase activity in all species 24 hours after the start of fumigation. The magnitude of the inductions varied between 23 and 89%. In contrast, exposure to NO caused a rapid decline in activity within 24 hours. After 21 days continuous exposure to each of the gases, the plants were supplied with a single application of 10 mM, NaNO3. Nitrate reductase activity was induced only in plants exposed to clean air. NO8exposure caused a loss of nitrate inducibility of NR. There were no marked effects on rates of oxygen evolution. After a three‐week pollution‐free period, the bryophytes regained the capacity for nitrate assimilation.
Isozymes in isolates of Suillus species from Pinus cembra L.
Authors: KELLER G.
Published: April 2006

summary

Isolates of Suillus plorans (Roll.) Sing., Suillus placidus (Bon.) Sing, and Suillus sibiricus Sing. obtained from basidiocarps collected in two sub‐alpine forest regions were subjected to analysis of isozyme expression by means of horizontal starch gel electrophoresis. Four unknown strains isolated from tuberculate mycorrhizas of Pinus cembra L. were included in this study. Isozymes, expressed as individual bands, were reproducibly detected in mycelial extracts of 20, 11, and 2 isolates of S. plorans, S. placidus, and S. sibiricus, respectively. Isozyme banding patterns were diagnostic for each species and consistent for each strain tested. Isozyme electrophoresis is suitable for characterizing and fingerprinting individual isolates of Suillus species ectomycorrhizal with Pinus cembra. Enzyme assays for distinguishing between these species are recommended. Isolates from tuberculate mycorrhizas gave isozyme patterns that were consistent with S. plorans. Cluster analyses based on calculated similarity values of isozyme data demonstrated that intraspecific variability exists among isolates of S. plorans and S. placidus. Isozyme variability‐ was quite different in isolates of S. plorans from two different forest regions.
DNA topoisomerases in Gloeothece (Nägeli) sp. ATCC 27152: a role in N2 fixation?
Authors: Page T.S. , Gallon J. R.
Published: April 2006

summary

Extracts from aerobically grown cultures of the unicellular cyanobacterium Gloeothece (Nägeli) sp. ATCC 27152 converted relaxed ColE1 plasmid cccDNA into a supercoiled form. They therefore contained a DNA gyrase. However, when DNA gyrase was inhibited, these same extracts catalyzed a net relaxation of ColE1 DNA, implying that they also contained an enzyme similar to DNA topoisomerase I. During the first 2 h after transfer of aerobically grown cultures of Gloeothece to an atmosphere of O2, the ability of extracts to generate supercoiled DNA was temporarily lost. Instead, extracts catalyzed net relaxation of ColE1 DNA during this period, which coincided with a transient inhibition of nitrogenase synthesis. O2 and some related compounds also inhibited DNA supercoiling by extracts of Gloeothece in vitro. As in other diazotrophs therefore, O2 may inhibit nitrogenase synthesis in Gloeothece by altering the relative activities of DNA gyrase and DNA topoisomerase I in such a way that relaxation of one or more of the nif genes may occur, with consequent inhibition of transcription. However, this effect is only transient. In contrast, addition of NH4+ to cultures of Gloeothece permanently inhibited nitrogenase synthesis and did not abolish the ability of extracts to catalyze net supercoiling of DNA. Moreover, NH4+ did not abolish DNA supercoiling in vitro. NH4+ therefore appears to inhibit nitrogenase synthesis in Gloeothece by a mechanism different from that of O2.
The late Quaternary vegetational history of northwest Greece
Authors: Willis K.J.
Published: April 2006

summary

The mountainous region of northwest Greece has often been cited as a possible area for the existence of temperate tree taxa during the last glacial. This series of papers examines the vegetational history and sedimentary history of two small basins in the Pindus mountain range of northwest Greece. The two basins are 18 km apart but at contrasting heights of 285 and 1800 m. The present paper describes results from the lowland basin of Gramousti lake. Techniques of pollen analysis, plant macrofossil analysis, sediment chemistry, mineral magnetics and radiocarbon dating are employed to reconstruct both the vegetational and sedimentary history of the basin. The sequence extends c. 14000 bp to c. 1000 bp. Palaeobotanical studies suggest that, during the lateglacial, vegetation in this lowland region was dominated by herbaceous taxa indicative of an open environment. Of the trees, only Quercus and Pinus were present, in low numbers. The lateglacial/postglacial transition was represented by an expansion of oak woodland and a reduction in steppe vegetation. Quercus dominated woodland persisted throughout much of the postglacial and became more diverse at c. 7500 bp with the arrival and expansion of Carpinus orientalis/Ostrya carpinifolia. Anthropogenic intervention at c. 4500 bp was probably responsible for a reduction in the oak woodland and the formation of a vegetation type similar to present day which is dominated by herbaceous taxa and chew‐resistant shrubs such as Quercus coccifera and Paliurus spina‐christi.
The late Quaternary vegetational history of northwest Greece
Authors: WILLIS K.J.
Published: April 2006

summary

Gramousti lake and Rezina marsh are small basins, of similar size, 20 km apart but at contrasting heights of 285 and 1800 m. Comparison of the palaeoecological and sedimentary sequences from the two sites indicates that in the early postglacial, there was distinct altitudinal zonation of the vegetation. In the mountains, a dense mixed woodland containing at least sixteen different tree taxa became established whereas the lowland vegetation consisted of an open oak woodland which was much less diverse. It is suggested that the differences seen between the two sites is evidence for the existence of a montane refugium for temperate tree taxa during the lateglacial. The great contrast over such a small spatial distance suggests that refugia were probably small pockets of vegetation in micro‐environmentally favourable locations, for example, the more humid mountains. Throughout the first 5000 yr of the postglacial, the contrast in vegetation around the two sites persisted and it was not until c. 6000 BP that the ‘warm‐stage’ refugium in the mountains became reduced in diversity and density. Finally, the onset of anthropogenic disturbance at c. 4000 BP resulted in the total depletion of the montane forest and the dominance of a herbaceous vegetation at both sites.
Synonymy of the three apparent isoenzymes of 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate synthase in Pisum sativum L. with 3‐deoxy‐d‐manno‐octulosonate 8‐phosphate synthase and the DS‐Co/DS‐Mn isoenzyme pair
Authors: DOONG R. L. , JENSEN R. A.
Published: April 2006

summary

Three enzymes, capable of condensing phosphoenolpyruvate with erythrose 4‐phosphate, were separated by DEAE‐cellulose column chromatography of extracts from young leaves of Pisum sativum. One enzyme was identified as 3‐deoxy‐d‐manno‐octulosonate 8‐phosphate (KDOP) synthase (EC 4.1 .2.16). This novel plant enzyme mimicks 3‐deoxy‐D‐arabino‐heptulosonate 7‐phosphate synthase (EC 4.1 .2.15) in vitro by virtue of its substrate ambiguity. KDOP synthase used erythrose 4‐phosphate 28% as well as arabinose 5‐phosphate at high substrate concentrations. The pH optimum was 6.5 and divalent cations were neither required nor stimulatory. The remaining two enzymes possessed the distinctive properties of the DAHP synthase (DS) isoenzymes, DS‐Mn and DS‐Co, previously established in tobacco and spinach to be chloroplast‐ and cytosol‐localized isoenzymes, respectively. DS‐Mn was highly specific for its substrates, required dithiothreitol (a hysteretic activator) for activity, was stimulated 3.6‐fold by 0.5 mM Mn2+, and exhibited a pH optimum of 7.5. DS‐Co, by contrast, showed an extreme degree of substrate ambiguity (giving greater rates with glycolaldehyde and glyceraldehyde 3‐phosphate than with erythrose 4‐phosphate at saturating substrate concentrations), had an absolute requirement for a divalent metal, and exhibited a high pH optimum of 9.0 for catalysis.
Calcification and utilization of inorganic carbon by the coccolithophorid Emiliania huxleyi Lohmann
Authors: NIMER N. A. , MERRETT M. J.
Published: April 2006

summary

The relationship between inorganic‐carbon dependent photosynthetic oxygen evolution and calcification was investigated in high‐ and low‐calcifying strains of Emiliania huxleyi showing a ten‐fold difference in calcification rate. Unlike the low‐calcifying strain calcifying cultures showed a four‐fold increase in inorganic carbon (1 mM) dependent photosynthetic oxygen over the pH range 5‐8.3 resulting in a 20 fold difference in photosynthetic rate between the two strains at pH 8.3. Calcifying cells have a high affinity for HCO3−, the concentration of dissolved inorganic carbon [DIC] required for half‐maximal rate of photosynthetic O2 evolution (K0.5[DIC]) being 200 μM at pH 8‐3. In mid‐exponential phase cultures the stoichiometry between 14CO2 fixation and calcification was 1 : 1 so it is likely that the high photosynthetic rate at pH 8.3 is sustained by 14CO2, released from H 14CO2 during calcification.

Measurement of bicarbonate transport by the silicone‐oil‐layer centrifugal filtering technique demonstrated a rapid uptake and achievement of equilibrium (less than 3 s) between the intracellular and external inorganic carbon concentrations in low and high‐calcifying cells. Subsequent metabolism of the 14C intracellular inorganic carbon pool did not occur in low‐calcifying cells suggesting the block in calcification occurs either in transport into or within the coccolith vesicle.
Partitioning of biomass and carbohydrates in field‐grown radish under ambient concentrations of ozone, and treated with the anti‐ozonant ethylene‐diurea (EDU)
Authors: KOSTKA‐RICK REINHARD , MANNING WILLIAM J.
Published: April 2006

summary

The use of an anti‐ozonant provides a potential way for assessing yield losses caused by oxidant air pollution, predominantly ozone (O3), in field‐grown crops without the need of enclosures like open‐top chambers. One major prerequisite for the soundness of this method is the absence of direct effects of the anti‐ozonant EDU (ethylenediurea) itself on plant growth at low concentrations of O3 pollution. This condition was tested for field‐grown cultivars of radish (Raphanus sativus L.) parallel with investigations on the influence of soil drench treatments with EDU on the partitioning of biomass and carbohydrates between shoot and sink organs, i.e. hypocotyl and fibrous root, under ambient amounts of atmospheric O3, pollution. During 9 staggered plantings in two years, radish cultivars of differential sensitivity to O3 were harvested at two‐day intervals from emergence until vegetative maturity. Mean relative growth rates (RGR) for both sink and shoot organs were compared between EDU‐treated and non‐treated plants.

When the relative deviation in RGR between EDU‐treatments was regressed vs. the O3 exposure of corresponding time intervals, linear relationships were highly significant for the sink organs of all three cultivars tested. Significant decreases in RGR attributable to O3 occurred above thresholds of O3 exposure equivalent to 52‐58 nl l−1O3 (daily 7‐h mean). No significant alterations of RGR of shoots were observed due to O3. Shoot growth rate of one variety was slightly increased by EDU as was RGR of sink organs in two of the cultivars at low‐levels of O3.

Amounts of soluble carbohydrates (TSC) increased with biomass accumulation of both shoot and sink organs, and starch content decreased. These patterns were more apparent in sink tissues than in shoots. No significant differences in carbohydrate partitioning between treatments or between cultivars were detected. The linear relationship between the sink‐to‐shoot ratios of biomass and total non‐structural carbohydrates (TNC) was highly significant. From the results it is suggested that sink‐to‐shoot patterns of TNC occur synchronously with or slightly precede the partitioning of biomass rather than lag behind it.
The influence of varied microbial substrate conditions on the growth and mycorrhizal colonization of little bluestem (Schizachyrium scoparium (Michx.) Nash]
Authors: MEREDITH J. A. , ANDERSON R. C.
Published: April 2006

summary

To determine the response of little bluestem [Schizachyrlum scoparium (Michx.) Nash] to vesicular‐arbuscular mycorrhizal (VAM) fungi, various microbial populations, and interactions between VAM fungi and other microbes, plants were grown in three substrates: autoclaved soil, autoclaved soil to which VAM fungal‐free sievings of non‐autoclaved soil were added, and non‐autoclaved soil. Mycorrhizal plants were established in autoclaved soil and in autoclaved soil receiving sievings by using little bluestem root pieces that were Clorox‐treated for 9 or 17 s as a source of VAM fungal inoculum. Exposure of root pieces to a 0‐5 % solution of sodium hypochlorite (Clorox) for 13–23 s, surface‐sterilizes the roots, but it does not destroy viable internal VAM fungi. Control plants were grown in substrates receiving autoclaved root pieces. Plants grown in the autoclaved substrates had greater total biomass than plants grown in non‐autoclaved soil. Inoculum type (autoclaved or surface sterilized root pieces) or addition of sievings had no effect on any growth parameter for plants grown in autoclaved soil. Mycorrhizal plants grown in the autoclaved substrate, not receiving sievings had higher tissue concentrations of P, Ca, S, Zn, Mn, and Fe than non‐mycorrhizal plants grown in the same substrate. However, mycorrhizal plants did not produce more biomass than non‐mycorrhizal plants in autoclaved substrates. Differences observed between plants grown in the autoclaved and non‐autoclaved substrates are most likely attributable to greater nutrient availability of autoclaved substrates. The type of inoculum used and substrate conditions had negligible effects on rhizoplane and soil microbial populations. These included rhizoplane fungi and bacteria and selected functional groups of rhizoplane microbes (cellulose, chitin, and protein decomposers).
Architectural analysis of plant root systems
Authors: FITTER A. H. , STICKLAND T. R.
Published: April 2006

summary

The techniques of architectural analysis were applied to the root systems of plants growing under field conditions, to determine their validity in this situation and to measure the extent and causes of plasticity and of interspecific differences in root architecture in co‐existing species. In a three‐year study of two species (Trifolium repensL. andPlantago lanceolataL.) on eleven different soils, large differences were found between species, soils and years; much of the variation in the root architecture ofT. repenscould be explained in terms of soil moisture concentration. On two woodland sites, the root architecture of five species was followed over a 15–month period, and at one a manipulative experiment involving irrigation and nitrogen and phosphorus addition was set up. There were large differences between species in root architecture and seasonal changes in some aspects (topology and exterior link length), which probably represent developmental patterns. Irrigation induced topological changes in one species (Galium aparineL.) which were consistent with the results of the three‐year study, but not apparently with an earlier model. In the case ofMercurialis perennisL., however, both irrigation and N and P addition brought about the predicted changes in root architecture, namely shorter interior links and lower topological index, though N had the opposite effect on exterior links. Interior link length differed widely between species, but showed little temporal variation, suggesting that it may be a valuable character for further studies. These results illustrate the validity and potential of architectural analysis for the study of root systems extracted from field soils.
Effect of boron on the growth and mineral economy of some halophytes and non‐halophytes
Authors: ROZEMA J. , DE BRUIN J. , BROEKMAN R. A.
Published: April 2006

summary

Growth of halophytes in nutrient solutions with increasing boron concentrations was less reduced than that of some non‐halophytes. Boron (B) concentrations occurring in sea water (0350 mol m−3B) depressed growth of glycophytic plant species strongly, while growth of halophytes did not significantly differ from that under control conditions (Hoagland's nutrient solution containing 0025 mol m−3B).

With increasing boron concentrations in the medium, the total boron concentrations in the shoot tissue increased up to 35 umol B B g−1d. wt (350 mg kg−1B d. wt basis) in the non‐halophytic species and were lower in most of the halophytic species examined. Sodium chloride (200 mol m−3) in the culture medium depressed the total B content of the shoot in the halophytic species. In most halophytic species, the water‐insoluble B fraction in the shoot and root tissue was higher than in the non‐halophytic species tested with the exception of Phaseolus vulgaris. When the plants were grown in culture solution containing 200 mol m−3NaCl, the ratio of insoluble: total B in shoot and root tissue increased. The resistance of halophytes to excess B and the possible detoxification of excess borate by complexation, either with cis‐diol groups of carboxyl groups in the cell walls or with dissolved compounds such as sorbitol in the halophytic Plantago maritima is discussed. The mechanism by which B tolerance in the halophytes might be accomplished is also discussed.
Role of calcium in aluminium toxicity
Authors: RENGEL ZDENKO
Published: April 2006

summary

Aluminium is the most important growth‐limiting factor in many acid soils throughout the world. Physiological effects of Al toxicity and mechanisms of tolerance are not well understood. An initial uptake of Al is confined to the apoplasm. Aluminium complexes (whose exact identification is beyond current experimental techniques) enter the cytosol slowly and only after prolonged exposure. Electrochemical properties of the cell wall Donnan free space as well as the plasma membrane of root cells are altered by the presence of Al ions that are polyvalent cations in acidic environments. The primary Al effects are very fast (taking only seconds to several minutes to develop) and may therefore occur while Al is still in the Donnan free space and on the apoplasmic side of the plasma membrane. Resumption of root growth upon removal of Al ions supports such a claim. Aluminium affects membrane permeability for both electrolytes and non‐electrolytes; it reduces accumulation of divalent cations (especially Ca and Mg) by interfering with the membrane transport. Aluminium alters the pattern of Ca2+ fluxes across the plasma membrane, thus supposedly disturbing symplasmic Ca2+ homeostasis. Supplemental Ca2+ can greatly alleviate deleterious Al effects. Frequently observed changes in the secretory activity of root cells exposed to Al are mediated through altered cell Ca2+ homeostasis; they result in cessation of cell wall growth and stoppage of root elongation. Involvement of calmodulin in the Al‐related phenomena is suggested to be indirect, at least in the initial stages of the Al treatment when Al is likely to be confined to the apoplasm. The role of growth substances, at least auxins and cytokinins, in the Al toxicity syndrome appears to be related to the Ca‐Al interactions that may alter the pattern of auxin transport as well as cytokinin biosynthesis and transport. Disturbance of the cell Ca2+ homeostasis appears to be an important feature of ion‐related environmental stresses in general (salt, heavy metals, aluminium).
Growth and maintenance respiration in leaves of Liriodendron tulipifera L. exposed to long‐term carbon dioxide enrichment in the field
Authors: WULLSCHLEGER S. D. , NORBY R. J. , GUNDERSON C. A.
Published: April 2006

summary

Specific respiration rate (SRR) was mathematically partitioned into its growth and maintenance components for leaves of yellow‐poplar (Liriodendron tulipifera L.) after 3 yr of CO2 enrichment in open‐top field chambers. Despite the absence of a CO2 effect on individual leaf expansion or specific growth rate (SGR), increasing the CO2 concentration to ambient +150 or +300 cm3 m−3 decreased SRR by 28 to 45% compared with ambient‐grown controls. These lower leaf respiration rates were correlated with reduced leaf nitrogen concentrations. As described by the two‐component model of growth and maintenance respiration, SRR was a linear function of SGR. Ambient‐grown leaves had a growth respiration coefficient of 704 mg CO2 g−1 dry mass compared with 572 and 570 mg CO2 g−1 for leaves grown at the two higher CO2 concentrations. Leaves from the elevated CO2 treatments had an average maintenance respiration coefficient of 88 mg CO2 g−1 dry mass d−1 compared with 135 mg CO2 g−1 d −1 for leaves from the ambient treatment. Incorporating these growth and maintenance coefficients into a leaf growth simulation model indicated that total respiration would be reduced by 21 to 26 % for a leaf exposed to + 150 or + 300 cm3 m−3 CO2 throughout its 50‐d lifespan compared with one grown at ambient CO2 conditions. Reductions in total respiration were dominated by a lower rate of maintenance respiration, while the contribution of a lower specific rate of growth respiration was largely offset by a greater dry mass for leaves grown at elevated CO2 concentrations. Although reductions in the respiratory loss of carbon could be beneficial, respiration is unlikely to decrease without a concomitant decrease in other metabolic processes. Whether these reductions are beneficial or detrimental to the long‐term growth of plants exposed to elevated CO2 remains unresolved.
In vitro germination of wheat pollen on raffinose medium
Authors: CHENG CANHONG , MCOMB J. A.
Published: April 2006

summary

Wheat pollen gave up to 81.7 % germination when cultured on a 0.7 % agar medium containing 100 mg 1−1 H3BO3, 300 mg 1−1 CaCl2.2H2O and 0.75 M raffinose. On this medium at 25°C, germination started within 5 min and tubes reached a mean maximum length of 200 μm after 1 h. Maltose supported 27.9% germination, while sucrose gave at most 6.8%. Pollen on media with fructose, galactose, dextrose or lactose failed to germinate.
Seedling growth and root morphology of plants with different life‐histories
Authors: GROSS KATHERINE L. , MARUCA DEBORAH , PREGITZER KURT S.
Published: April 2006

summary

Differences among plant species in morphology and patterns of growth are assumed to influence their ability to acquire resources and, consequently, their competitive ability. Despite the acknowledged importance of below‐ground resources for plant growth, our knowledge of species differences in root morphology of non‐agricultural plants is limited. Comparisons of root morphology, growth rate and topology of seedlings of 12 herbaceous plant species that occur in early to mid‐successional fields revealed significant differences among species that were largely related to life history. Annuals grew faster and produced longer and more branched roots than did biennials and perennials. Only among the annuals was there a positive correlation between seed mass and root growth. The grasses allocated proportionately more biomass to roots than the dicots, but did not differ in root length or branching pattern. As seedlings, all 12 species exhibited a herringbone topology; although after 10 d there were significant differences in topology between annuals and perennials indicating that the annuals had begun to develop a more dichotomously branched root system. The possible effects of early differences in root morphology among life‐history types in acquiring soil resources in heterogeneous and successional environments are discussed.
Water stress effects on successional populations of the dioecious herb, Rumex acetosella L.
Authors: HOUSSARD C. , ESCARRÉ J. , VARTANIAN N.
Published: April 2006

summary

The effects of water stress and rewatering on the water relations and biomass of male and female plants of the dioecious herb, Rumex acetosella L., have been examined. Plants were collected from two fields, 2 and 15 yr old respectively, and submitted to different water regimes. Male plants from both populations showed a similar response to water deficit, having a low transpiration rate and low consumption of soil water, whilst maintaining a high green leaf area. Females from the two populations differed from each other more than males, both in terms of their response to drought and survival capacity. Females from the young population, which had a small green‐leaf area and a small root biomass, had progressively lower water potentials and maintained higher levels of transpiration at the onset of the first drought period, indicating a progressive acclimation to water stress. They also recovered more rapidly and to a greater extent than all the others upon rewatering. Females from the old population, with a high root/shoot ratio, transpired the most prior to the onset of water stress. They maintained a high water potential throughout the stress period, having high stomatal resistances and removing more water as soil moisture declined. This is indicative of drought avoidance. Root development was, however, limited in the shallow pots, hence the water resource was depleted rapidly and mortality occurred to a greater extent in these old‐field females. These characteristics may be adaptative, given the selection pressures which operate on water balance characters along a successional gradient and the spatial segregation of sexes that has been previously observed in this dioecious species in the same old‐field succession, with the sex ratio becoming progressively male‐biased with time.
Measuring investment in carnivory: seasonal and individual variation in trap number and biomass in Utricularia vulgaris L.
Authors: FRIDAY LAURIE E.
Published: April 2006

The partitioning of biomass between traps and leaves is a measure of the investment in carnivory of Utricularia vulgaris and is dependent on the relative values of three attributes: trap size, trap number and leaf size.

Marked seasonal and individual variations in trap size, trap number and leaf size occur within a small population of U. vulgaris at Wicken Fen, Cambridgeshire, UK, with some plants consistently having fewer traps per leaf than others, and some smaller leaves than others, throughout the growing season. However, the three attributes vary independently, so that all combinations over the observed ranges of trap size, trap number and leaf size occur simultaneously in the population.

In spite of the variation in the three constituent factors, the proportion of biomass invested in traps is close to 50% in the majority of plants and throughout most of the growing season. The contribution of traps to total biomass cannot be predicted from the number of traps per leaf.

Although the proportion of biomass represented by traps is the most useful measure of a plant's investment in carnivory, the precise way in which the biomass is partitioned between a variable number of traps of different sizes may also be an important consideration in cost‐benefit analyses.
The clones of common lime (Tilia×vulgaris Hayne) planted in England during the seventeenth and eighteenth centuries
Authors: PIGOTT DONALD
Published: April 2006

Most avenues of limes planted in England and Wales during the late seventeenth and early eighteenth century contain two distinct clonal types of common lime (Tilia×vulgaris Hayne). They differ in many morphological characters.

Clonal group A has a fluted trunk with epicormic bosses or sprouts, a conical crown, scarlet, shining, ellipsoid overwintering buds, bright green leaves with obliquely asymmetric bases, long bracts narrowed to both ends and inflorescences normally of seven flowers. Clonal group B has a cylindrical trunk which is almost without epicormic buds or shoots, a hemispherical crown, crimson, pruinose, ovoid and sub‐acute buds, more or less cordate, dull green leaves, bracts narrowed to the stalk but broadly rounded at the distal end, and inflorescences with 3–5 flowers.

Clonal group A includes the Dutch clones ‘Pallida’ and ‘Koningslinde’. Clonal group B is closely related to, but not identical with, the Dutch clone ‘Svartelinde’.

Both clonal groups were probably originally imported from the Netherlands and were possibly derived from ancient village trees, which in the Netherlands are usually T. ×vulgaris.
Predicting plant responses to global environmental change
Authors: WOODWARD F. I.
Published: April 2006

Predicting the future responses of plants and ecosystems to further changes in the CO2 concentration of the atmosphere and to the possibility of global warming are important current concerns. Predictions have been most frequently attempted using short‐term, single‐factor experiments in controlled environments. However, these experiments have failed to indicate the outcome of field experiments at larger spatial and temporal scales. Some of this failure is due to ignorance of environmental conditions and interactions while some is due to the use of inappropriate short‐cuts, such as the addition of fertilizers for simulating enhanced mineralization, and some is due to ignorance of the processes involved in scaling‐up from individual plants to populations. Long‐term observations on plants in ecosystems nevertheless indicate that community‐scale experiments may provide a useful but imperfect capacity to predict ecosystem responses. Although difficult to implement in practice, it is concluded that catchment‐scale experiments offer the best opportunity to predict plant, community and ecosystem responses to environmental change.

CONTENTS

Summary
239

I.
Introduction
239

II.
CO2‐enrichment experiments
240

III.
Experiments with applied nitrogen fertilizer
243

IV.
Population ecophysiology
245

V.
Ecosystem predictions
248

Acknowledgements
249

References
250