bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐uniform stomatal closure induced by water stress causes putative non‐stomatal inhibition of photosynthesis
Authors: DOWNTON W. J. S. , LOVEYS B. R. , GRANT W. J. R.
Published: April 2006

summary

The partial pressure of intercellular CO2 derived from gas exchange data for water‐stressed grapevine (Vitis vinijera L.), oleander (Nerium oleander L.) and red‐flowering gum (Eucalyptus ficifolia F. Muell.) does not indicate the actual average intercellular CO2 of the leaf. This can be determined from chlorophyll fluorescence signals and modelled from conventional gas exchange information. Water stress increases endogenous levels of abscisic acid and the leaves respond in a similar manner to that observed when exogenous abscisic acid is applied. Autoradiograms show that water stress results in non‐uniform gas exchange over small areas of the leaf. Non‐uniform stomatal closure can account for the apparent non‐stomatal inhibition of photosynthesis in plants experiencing water stress.
Kinetics of inhibition of foliar gas exchange by exogenous ethylene: an ultrasensitive response*
Authors: GUNDERSON CARLA A. , TAYLOR GEORGE E.
Published: April 2006

summary

The objective of this study was to examine the inhibition of foliar gas exchange as a function of ethylene (C2H4) concentration in order to evaluate the potential role of stress C2H, in mediating changes in gas exchange in response to environmental stress. Net photosynthesis (PN) and stomatal conductance to H2O vapour (gs H2o) were measured in soybean (Glycine max (L.) Merr cv. Davis) seedings after a 4 h exposure to one of a range of exogenous C2H4 concentration (0–20μII−1)in a controlled environment system. Declines in both Ps and gs H2O shifted from first‐order (liner decline) to zero‐order (saturation response) with increasing C2H4 concentration. The response of gs H2O to C2H4, was more pronounced than the response of Ps, with maximal declines for gs H2O of 32–48%, and half‐maximal response at 0.15μII−1. Corresponding parameters for PN were 18–29%, inhibition and half‐maximal response at 0–35μII−1. Both response curves were similar to those documented for C2H4, binding and for hormonally mediated C2H4 actions. Kinetic analysis of the saturation patterns by the Hill equation showed both responses to be ultrasensitive, i.e. they provide a relatively large change in gas exchange for a small change in C2H4 concentration. Based on this ultrasensitivity, we propose that endogenous stress C2H4 mediates some of the responsiveness of gas exchange to environmental stresses of natural and anthropogenic origin.
Prediction of the probability of forest decline damage to Norway spruce using three simple site‐independent diagnostic parameters
Authors: MEHLHORN H. , FRANCIS B. J. , WELLBURN A. R.
Published: April 2006

summary

Survey data for Norway spruce (Picea abies I.) trees at 12 different forest sites across Europe have been analysed. Three variables (dry weight/fresh weight ratio differences between current and two‐year‐old needles, ethylene emissions and violaxanthin/antheraxanthin ratios) were found which together show a significant relationship to tree damage in areas affected by forest decline and which are independent of site effects (P < 0.001). Results are also presented that support the contention that atmospheric pollution, especially tropospheric ozone, is the major cause of this problem. After a four‐year fumigation experiment, 12‐year‐old Norway spruce trees showed similar cellular changes as those found in the 30‐to 40‐year‐old trees of the survey affected by forest decline. In the fumigation experiment, these changes were most pronounced in those plants exposed to a combination of treatments including ozone, sulphur dioxide and acid rain. The pollutant concentrations used in the four‐year study were representative of those experienced by trees growing in affected areas.
torphological and physiological changes in ectomycorrhizas of spruce [Picea excelsa (Lam.) Link] associated with ageing
Authors: AL ABRAS K. , BILGER I. , MARTIN F. , LE TACON F. , LAPEYRIE F.
Published: April 2006

summary

Ectomycorrhizas of four‐year‐old Picea excelsa (Lam.) Link seedlings, grown in nursery soil, are described. The main ectomycorrhiza type, occurring on 55–80% of the root apices, exhibited a normal sheath. The associated symbiotic fungus probably belonged to the Hebeloma genus. Behind these extomycorrhizal root lips, older ectomycorrhizas were observed and the apical ones presumably originated from those. One‐ and two‐year‐old ectomycorrhizas lacked sheaths, but a normal Hartig net could be observed in transverse sections. The metabolic‐activity of these older ectomycorrhizas, as measured by radiorespirometry of [14C]glucose, was reduced compared to the younger symbiotic organs. This glucose respiration was, however, still larger than the activity of non‐mycorrhizal exploratory roots. The mechanism of sheath loss and its significance as an ageing process are discussed.
The involvement of glutamate dehydrogenase and glutamine synthetase in ammonia assimilation by the rapidly growing ectomycorrhizal ascomycete, Cenococcum geophilum Fr.
Authors: MARTIN F. , STEWART G. R. , GENETET I. , MOUROT B.
Published: April 2006

summary

In order to determine significance of the glutamate dehydrogenase pathway and a glutamine synthetase/glutamate synthase cycle in NH4+ assimilation, we followed a number of different metabolikc parameters (nutrient uptake, free amino acid pools, NH4+‐induced glutamine accumulation) and 15N incorporation into amino acids of rapidly growing Cennoccum geophilum. Arginine was a major free amino acid in C. geophilum during its entire growth period. C. geophilum synthesized and accumulated very large amounts of glutamine at the beginning of the rapid phase of growth in low nitrogen medium, during the whole growth period in high nitrogen medium, and immediately after addition of NH4+. Therefore, the accumulation of a large amount of glutamine tool; place when the external ammonium concentration was high. The current data identify four pathways of N metabolism in rapidly growing C. geophilum: (1) glutamine synthesis, invoking transfer of N to both amino and amino moieties; (2) glutamate formation; (3) transamination with pyruvate to yield alanine; (4) transamination with oxaloacetate to yield asparate. The higher accumulation of glutamate and related amino acids (alanine and aspartate) in the presence of the glutamine synthetase inhibitor methionine sulphoximine indicates that glutamate, the precursor of glutamine, was formed by a pathway insensitive to methionine sulphoximine, the glutamate dehydrogenase pathway. Up to 40% of the assimilated 15N terminated in the amido‐N of glutamine. These data are consistent with a pivotal role for glutamine synthetase activity and indicates that the primary assimilation of NH4+ in rapidly growing C. geophilum is brought about by concurrent activity of the GDH and GS pathways. The pathway of primary assimilation of NH4+ by C. geophilunt in the rapid phase of growth therefore differs from those operating in the stationary phase of growth where N flax through GDH is higher than the flux through the GS pathway.
Recognition in flowering plants: A comparison of the Brassica self‐incompatibility system and plant pathogen interactions
Authors: HODGKIN T. , LYON G. D. , DICKINSON H. G.
Published: April 2006

summary

Morphological, genetic, and biochemical data on the sporophytic self‐incompatibility (SI) system of Brassica spp. are evaluated and compared with those from host‐pathogen (HP) interactions which conform to the gene‐for‐gene hypothesis and are characterized by the production of phytoalexins.

SI and HP systems have many features in common, reflecting similarities in the processes of discrimination, particularly with respect to the response to an incompatible recognition event. Thus, both recognition reactions involve cell surface components which are likely to be glycoproteins in at least one of the partners. Both incompatible responses are active processes requiring enzyme synthesis, are biostatic rather than biocidal with respect to pollen and pathogen, and are accompanied by the production of low molecular weight phytoalexin‐like compounds. Recent evidence also suggests that incompatible HP interactions may involve recognition of ‘self’ cell wall components. These similarities are distinguished from those, such as the production of cuticle and cell wall degrading enzymes, which may result only from the common requirement of pollen and pathogen to penetrate through the plant surface. The significance of the most obvious differences between the two systems, such as the evidence that SI may be mediated through the supply of water lo the pollen grain and the absence, in SI interactions, of cell necrosis or ‘cross protection’ reactions is also explored. It is suggested that some of the observed differences may result from ‘pre‐programming’ of the SI response.
The effects of zinc contamination from electricity pylons – evolution in a replicated situation
Authors: AL‐HIYALY S. A. , McNEILLY T. , BRADSHAW A. D.
Published: April 2006

summary

Most electricity pylons are zinc coated. It might be possible for this to cause zinc contamination of soil beneath the pylons sufficient to impose selective forces by which zinc‐tolerant populations would develop in a replicated manner. An investigation of Agrostis capilluris L. populations sampled under a series of pylons in North Wales shows that:

 Zinc concentrations are considerably greater in soils beneath pylons, particularly adjacent to pylon legs.

 Soils sampled under different pylons had mean zinc concentrations varying from 1250 ± 200 to 6500 ± 4000 μg−1 as total, and from 570 + 188 to 3000 ± 2000 μg g−1 as acetic acid extractable. In control soils, comparable values were from 170 ± 35 to 320 ± 90 μg g−1 total zinc, and 70±10 to 140 ± 30 μg g−1 acetic acid‐extraetable zinc.

 Zinc toxieity is found in such soils causing significant reduction in plant dry weight and tiller production of normal material of A. capillaris.

 The pattern of root growth response to increasing zinc concentration in solution culture of samples of adult plants collected from beneath pylons differed significantly.

 Some individuals had zinc tolerance equivalent to that of zinc mine plants; others had low but measurable tolerance; others differed little from plants from uncontaminated control sites.

These results clearly show that evolution of zinc tolerance has occurred rapidly, since the pylons sampled were all less than 30 years old, but the outcome is different under different pylons, almost certainly because of differing genetic constitutions of different founding populations.
A pollen diagram from Norwich Crag at Outney Common, Bungay, Suffolk
Authors: WEST R. G.
Published: April 2006

summary

A pollen diagram from Norwich Crag at Outney Common, Bungay, gives evidence of a stage with temperate forest, preceded by boreal forest. A tentative correlation of this temperate stage with the Bramertonian Stage is suggested.
The role of CO2uptake by roots and CAM in acquisition of inorganic C by plants of the isoetid life‐form: a review, with new data onEriocaulon decangulareL.
Authors: RAVEN JOHN A. , HANDLEY LINDA L. , MACFARLANE JEFFREY J. , MCINROY SHONA , MCKENZIE LEWIS , RICHARDS JENNIFER H. , SAMUELSSON GORAN
Published: April 2006

The isoetid life‐form was originally defined on morphological grounds; subsequent physiological investigations showed that all of the isoetids examined took up a large fraction of the inorganic C fixed in their leaves from the root medium under natural conditions, and that some of them carried out much of their assimilation of inorganic C via a CAM‐like mechanism. Root‐dominated uptake of inorganic C appeared to be unique to, and ubiquitous in, the isoetids. I However, a large capacity for CAM‐like metabolism in submerged vascular plants is not universal in isoetids, nor is it restricted to this life‐form, being also found inCrassulaa aquatica.

The work described here shows that submerged specimens of the North AmericanEriocaulon decangularehave a high fraction of their dry weight in the root system, a trait characteristic of isoetids but uncommon in other submerged vascular plants.E. decangularehas vesicular‐arbuscular mycorrhizas, as do other flowering plant isoetids hut not, generally, submergedIsoetesspp. Under conditions of natural supply of inorganic C,E. decangulare, like other isoetids, takes up most of its inorganic C through its roots. Uptake of inorganic C by both roots and shoots involves CO2rather than HCO3: photosynthesis at high external pH values does not exceed the rate of uncatalysed HCO3‐to CO2conversion in the medium and there is no detectable extracellular carbonic anhydrase activity.

Measurements of titratable acidity and of malate content of leaves sampled at dawn and at dusk showed thatE. decangulare, growing and tested under either emersed or submersed conditions, did not exhibit CAM‐like behaviour. CAM was also absent from three non‐isoetid aquatic macrophytes(Amphibolic antarctica, Eeklonia radiataandVallisneria spiralis)which were examined.E. decangularethus resembles all other isoetids tested in acquiring much of its inorganic C via the root system.E. decangularealso resembles most of the isoetids which are not members of the Isoetaceae (e.g.)E. septangulare, Lobelia dortmannaandSubularia aquatica)but differs from submerged Isoetaceae andLittorella uniflorain lacking CAM.

The ecological significance of uptake of CO2via the roots and, where it occurs, of CAM in isoetids may be related to either inorganic C or, via improved N use efficiency, inorganic C as a limiting resource.

The isoetid life‐forms has evolved independently in at last five different families of vascular plants; it probably derived fairly immediately from terrestrial or amphibious ancestors with a similar rosette form. Emergent Isoetaceae with acquisition of CO2via roots and CAM probably evolved from submerged isoetids.

CONTENTSSummary123I.Introduction126II.Material and Methods127III.Results and Discussion129IV.Conclusions142Acknowledgements142References143
Effects of sulphur dioxide and nitrogen dioxide on the control of water loss by birch (Betula spp.)
Authors: NEIGHBOUR EMILY A. , COTTAM D. A. , MANSFIELD T. A.
Published: April 2006

The effects of SO2 and NO2 on the control of water loss by birch trees were investigated using clonal populations of both Betula pendula Roth, (silver birch) and Betula pubescens Khr. (downy birch). Plants were grown in controlled environments and were fumigated in a 2 × 2 factorial experiment with 65 nl l‐1 SO2 and/or NO2, or with equal concentrations of both SO2 and NO2 in four treatments, namely zero, 20, 40 and 60 nl l‐1.

Excised leaves showed in increased rate of water loss approximately corresponding to the concentration of pollutant to which they had been previously exposed. When petroleum jelly was applied to the abaxial epidermal surface of polluted leaves the increased rate of water loss was not found, strongly implying that the damage had occurred only at this site, and not on the adaxial epidermis, which is virtually devoid of stomata.

Measurements of gas exchange were made on B. pubescens exposed to the four doses of the mixture of the two gases. The rate of transpiration was approximately doubled as a result of the two higher pollution treatments, judging from measurements made later in clean air. When transpiration was measured in high and low CO2 concentrations, polluted plants had a slightly reduced and more variable response to the change in CO2 concentration.

Both clones were also exposed first to the four doses of the gas mixture, and then to drought. There was a more rapid onset of water stress, accompanied by an earlier decrease in effective leaf area in the polluted plants, when compared with the unpolluted plants.

The abaxial surface of frozen hydrated leaves of the Betula pubescens clone were examined at low temperature with a scanning electron microscope. Damaged epidermal cells were clearly visible on the polluted leaves and thought to be responsible for areas of wide open stomata.

It is concluded that leaves of these species are less efficient in the utilization of water after a period of exposure to pollution and are less able to restrict water loss in a time of shortage.
The influence of ozone on the winter hardiness of Norway spruce [Picea abies (L.) Karst.]
Authors: Barnes J. D. , Davison A. W.
Published: April 2006

Three‐year‐old clonal saplings of Picea abies (L.) Karst. were exposed in chambers to 240μg O3 m‐3 for 70 d, 6hd‐1 and then hardened for 14 d at 4°C day/night. The winter hardiness of trees was tested by subjecting excised shoots, bearing previous and current year's needles, to night temperatures of –6, –9, –12, –15 and – 18°C in a computer‐controlled freezer. No visible injury was observed during the fumigation, hardening period or on the current year's needles of any of the clones. However, during post‐freezing recovery in a mist spray unit four of the clones exposed to ozone developed extensive visible injury on the previous year's needles, in the form of severe, uniform necrosis. The affected needles began to fall prematurely. Induced chlorophyll fluorescence was significantly reduced by O3 in two of the clones that showed post‐freezing injury. This suggested that O3‐induced membrane injury increased the sensitivity of needles to freezing. One clone (no. 4076), which exhibited no effect of ozone on fluorescence kinetics, showed severe ozone‐induced injury of the previous year's needles, developing about 40 d after fumigation independent of temperature. Previous year's needles of O3‐treated plants of this clone showed significantly greater rates of euticular transpiration, so the O3 may have induced gradual desiccation of the needles. The restriction of damage to the older needles of certain clones of Norway spruce is consistent with symptoms of forest decline affecting high‐altitude forests on acid soils. Results indicate that O3 predisposes trees to freezing injury, winter desiccation and drought, and it is proposed that such interactions are important factors contributing to the decline of high‐altitude forests of Norway spruce in Europe.
Adaptation of grasses in the Netherlands to air pollution
Authors: DUECK TH. A. , DIL E. W. , PASMAN F. J. M.
Published: April 2006

In three separate experiments, the response of three populations of Agrostis capillaris L., Nardus stricta L., and Lolium perenne L., from areas differing in ambient air pollution concentrations, were examined in experimental fumigations using SO2, O3, NO2 and NH3. Growth of A. capillaris generally increased following the fumigations, except at the highest pollutant concentrations (120 μg m‐3 O3, alone or combined with 150 μg m‐3 SO2 and 35 μg m‐3 NO2). Growth of each population of N. stricta was stimulated by the SO2 and NH3 combination, but was significantly increased only in the populations originating from the most heavily polluted of the three areas. The growth of L. perenne was not inhibited by any air pollutant or combination of pollutants. Despite a low growth rate in clean air and a large amount of within‐population variation, biomass production was significantly stimulated by the highest pollutant mixture.

The response of each species to the experimental treatments depended in part on the location from which it originated. This site‐dependent (population) response differed between species, suggesting that the selective processes induced by these air pollutant concentrations were insufficient for a clear‐cut adaptation to gaseous air pollutants.
The structure and function of the vegetative mycelium of ectomycorrhizal plants III. Ultrastructural and autoradiographic analysis of inter‐plant carbon distribution through intact mycelial systems
Authors: DUDDRIDGE J. A. , FINLAY R. D. , READ D. J. , SÖDERSTRÖM B.
Published: April 2006

Plants of Pinus sylvestris L. were grown in mycorrhizal association with Suillus bovinus (Fr.) O. Kuntze in observation chambers until an interconnecting mycelial network had developed between the seedlings. The shoot of an individual seedling was then scaled in a perspex cuvette and exposed to 14CO2. After incubation for 48 h, the‘donor’shoot was removed and components of the mycelial network and mycorrhizal roots of connected and unconnected‘receiver’seedlings were harvested, fixed, embedded and sectioned prior to being autoradiographed and examined by transmission electron microscopy. The patterns of distribution of 14C‐labelled material within the mycelial strands, the sheath and root tissues was examined. The results are discussed in relation to carbon metabolism of the fungus and of the interconnected host plant.
The mycorrhizal relationship of multinucleate rhizoctonias from non‐orchids with Microtis (Orchidaceae)
Authors: Milligan M. J. , Williams P. G.
Published: April 2006

Multinucleate rhizoctonias isolated from the roots of non‐orchid plants were used in symbiotic germination tests with seed of 18 orchid species from 10 genera. The rhizoctonias only stimulated germination of Microtis. Investigation of the natural mycosymbionts of adult Microtis failed to yield fungi similar to the original multinucleate rhizoctonias: 27 Microtis plants collected at seven sites in the Sydney region yielded 26 binucleate rhizoctonias tentatively identified as Tulasnella calospora (Boudier) Juel and one very slow growing multinucleate rhizoctonia tentatively identified as Sebacina vermifera Oberwinkler. Fungi closely resembling the original multinucleate rhizoctonias were isolated by baiting the soil with subterranean clover (Trifolium subterraneum L.) plants at three of the seven Microtis sites.
Effects of aluminium on fluoride uptake by plants
Authors: TAKMAZ‐NISANCIOGLU S. , DAVISON A. W.
Published: April 2006

SUMMABY

The effect of aluminium on the uptake and transport of fluoride by bean (Phaseolus vulgaris L.) was examined by means of water culture. Tomato (Lycopersicon esculentum Mill.) was used in one experiment. Exposing bean roots to NaF led to fluoride concentrations in the roots and first leaves of 47 and 17 times respectively those of controls. In contrast, the same concentration of F given as A1F3 gave concentrations 83 and 68 times respectively those of controls. Both roots and leaves showed an increase in concentration of 042 mol of F for each mol of Al in contrast to the 3:1 molar ratio of F to Al in the A1F., solution. Giving the Al (as A1C13) before NaF also led to significant increases in uptake and transport of F compared with controls. Fluoride was readily washed out of roots whether it was presented as NaF or A1F3. Analysis of xylem exudate of tomato given A1F3 showed that 44 % of the fluoride was associated with metals compared with 4.7% in controls. It was concluded that when F is presented as F−, it remains largely in the apoplast and that it enters the xylem by leaking past the endodermal barrier at the root tip or where laterals emerge. In complexing with Al, the negative charge on the F is neutralized, decreasing Donnan exclusion and therefore leading to a higher concentration of F in the apoplast. The formation of fluoride‐aluminium complexes in plant tissues would be expected to decrease the toxicity of both elements.
The structure and function of the vegetative mycelium of ectomycorrhizal plants IV. Qualitative analysis of carbohydrate contents of mycelium interconnecting host plants.
Authors: SÖDERSTRÖM B. , FINLAY R. D. , READ D. J.
Published: April 2006

Plants of Pinus spp. were grown in observation chambers with the mycorrhizal fungi Suillus bovinus, Pisolithus tinctorius or Paxillus involutus. After interconnecting mycelial systems had developed between plants, individual hosts in some chambers of each species were fed with 14CO2. Mycelia from radioactively labelled and unlabelled chambers were harvested and their carbohydrates were extracted, separated chromatographically and identified. The major carbohydrates in all of the fungi were trehalose, mannitol and arabitol, their relative proportions differing in the different fungi. The results are discussed in relation both to carbon nutrition of the fungus and to carbon transfer between interconnected plants.
Nuclear DNA content in root cells of Lotus and Trifolium colonized by the VAM fungus, Glomus versiforme
Authors: Blair D. A. , Peterson R. L. , Bowley S. R.
Published: April 2006

Nuclear DNA content of root cortical cells of Lotus pedunculatus Cav., Lotus corniculatus L. and Trifolium pratense L. was determined using a microspectrophotometer. Infected and uninfected roots from plants which had been colonized with the fungus, Glomus versiforme (Daniels and Trappe) Berch and roots from non‐inoculated plants were compared. Relative DNA contents for cortical cell nuclei of the three hosts were within the 2–4C range for uninfected root cells. There was no evidence that the VAM fungus, G. versiforme, induced endoreduplication of cortical cell nuclei during infection of these forage legumes. Nuclear enlargement reported in other studies of VAM colonization is likely to involve mechanisms of nuclear enlargement other than DNA endoreduplication.
Comparative effectivity of three Fraxinus pennsylvanica Marsh, vesicular‐arbuscular mycorrhizal fungi in a high‐phosphorus nursery soil
Authors: LAMAR R. T. , DAVEY C. B.
Published: April 2006

Inoculation of seedlings of green ash (Fraxinus pennsylvanica Marsh.) with vesicular‐arbuscular (YA) mycorrhizal fungi, significantly increased seedling heights, root collar diameters, dry matter accumulations and phosphorus (P) nutrition relative to control seedlings. The ability of these YA mycorrhizal fungi, which were isolated from low‐P forest soils (5–7 mg kg−1), to enhance seedling growth in a high‐P (148 mg kg−1) nursery soil provides evidence for the occurrence of YA mycorrhizal fungi which may be effective under both high and low soil P conditions. There was a significant positive correlation between foliar P concentration and percentage infection. Despite significant differences in tissue P concentrations among seedlings receiving different inoculum treatments, the degree of growth enhancement was the same. Growth increases due to enhanced P nutrition in seedlings with higher concentrations of foliar P may have been offset by an increased drain on host photosynthate via production and maintenance of greater amounts of fungal bomass, or may have been limited by the low K fertility of the nursery soil.

Colonization percentages in roots of seedlings of green ash were high despite high soil P concentrations. The pattern of infection development was unique for each YA mycorrhizal fungal species. A modification of the grid‐line intercept technique was used to assess intensity of infection. Infection for all endophytes during the period of most rapid vegetative host growth was predominantly arbuscular. However, arbuscular intensity fluctuated during this period. Vesicles increased in number with time but always made up a small percentage of total infection.
A discrete probability model for polycyclic infection by soil–borne plant parasites
Authors: BRASSETT P. R. , GILLIGAN C. A.
Published: April 2006

A discrete, theoretical infection model is developed to describe the temporal progress of an epidemic of a soil‐borne pathogen. The model is based upon the probability of escape of host units, such as roots, seeds or entire plants from two sources of inoculum, a primary source, comprising randomly dispersed propagules in soil, and a secondary source derived from infected hosts. A polycyclic sequence of infection is modelled: thus infections derived from soil inoculum serve as sources of infection, giving rise to secondary infections which, in turn, give rise to tertiary infections and so on to the the cycle. The discrete, successive cyclical progression is generalized by the introduction of a parameter for survival of existing infections. The problem of a dynamically varying population of host units is discussed. A simplification of the model is obtained to give a continuous analogue, in which non‐integer values for time replace cycle number. Statistical methods of fitting the model to experimental data are discussed and illustrated by the fit to disease progress curves for the infection and damping–off of cress seedlings, Lepidium sativum L., by Pythium ultimum Trow.
The sensitivity of pollen from various coniferous and broad–leaved trees to combinations of acidity and trace metals
Authors: COX R. M.
Published: April 2006

The effects of acidic and trace element components of polluted rain on pollen germination and tube growth in vitro are described. The sensitivity of pollen to pH in vitro was related to the species' position in canopy and was different for conifers and broad‐leaved trees. Most pollen assayed revealed significant inhibition of germination and germ tube growth in response to pHs currently observed in rain samples in eastern Canada. Acer saccharum Marsh and Betula alleghaniensis Britt. pollen in vitro showed a high sensitivity to pH in combination with copper. The pollen of Populus tremuloides L, was shown to be highly sensitive to pH, and a synergism between pH and copper on pollen function in this species was also demonstrated. This was in contrast to the general antagonistic interaction of pH and copper noted in the other species tested in which copper by it self either did not affect pollen function or was stimulatory. Zinc has little or no effect, whereas lead at the concentrations used significantly inhibited both germination of Pinus strobus L. pollen at pH 5.6–3.6 and tube growth of both P. strobus and Pinus resinosa Ait. The increase in pollen mortality in response to air pollution at the time of pollination raises certain implications for reproduction and breeding. These implications are also discussed in the light of the significant genetic overlap between pollen and sporophytes of higher plants.
Absorption of atmospheric NO2 by several herbaceous species: estimation by the 15N dilution method
Authors: OKANO K. , MACHIDA T. , TOTSUKA T.
Published: April 2006

Absorption of nitrogen dioxide (NO2,) by eight herbaceous species was determined by the 15N dilution method. The plants were continuously exposed to NO2, at 0.5 μll−1 for 2 weeks. Susceptibility to NO2, was simultaneously examined in the tested species to see if this was correlated with the rate of absorption.

The total amount of NO2‐nitrogen absorbed by a plant during the 2‐week exposure period primarily depended on the size of the plant. Among the tested species, sunflower showed the highest rate of NO2, absorption per unit leaf area, reaching as much as 0.55 mg N dm −2 d−1, which was about four times greater than that for sorghum which had the lowest rate. A highly significant correlation was observed between the rate of absorption and the stomatal conductance among the species. A proportion of the NO2‐nitrogen accumulated in the plant might be absorbed via the air‐soil‐root route.

Sunflower and radish which had higher rates of NO2 absorption than the other species were more susceptible to NO2. On the contrary, sorghum and maize which showed a lower rate of NO2, absorption were tolerant. Consequently, the higher susceptibility to NO2 of radish and sunflower is considered to be directly related to their superior ability to absorb NO2.
Genetic variation for tolerance to copper and zinc within and among populations of the moss, Funaria hygrometrica Hedw.
Authors: SHAW JONATHAN
Published: April 2006

Ten individuals from each of lour populations of the moss, Funaria hygrometrica Hedw., were grown on two copper and two zinc treatments and a control in order to assess tolerance to these metals. Tolerances of two life‐history stages (protonemal growth and stem production) showed significant variation among populations, and among individuals within all populations. Heritabilities for tolerance were high within three populations, but were close to zero within a population that originated on a copper mine. Phenotypic correlations among growth responses to the five experimental treatments were similar in the four populations, but this reflected a greater similarity among the environmental correlations than among the genotypic correlations. There was evidence of positive genetic correlations between growth on control medium and growth on media enriched with copper or zinc. This is in contrast to data from flowering plants and fungi, and raises the question of why tolerant individuals are restricted to contaminated sites in nature.
Vegetational history and land use: a radiocarbon‐dated pollen diagram from Machrie Moor, Arran, Scotland
Authors: ROBINSON DAVID E. , DICKSON JAMES H.
Published: April 2006

Pollen, plant macrofossil and charcoal analyses are presented from a radiocarbon‐dated sequence of peat deposits from Machrie Moor, Arran. The deposits began forming at the close of the late glacial and the sequence continued unbroken into recent times. During this period there was a transition at the site from rich to poor fen and finally to blanket mire communities. The major deciduous forest tree species were late in migrating to the island, probably as a consequence of the sea acting as a harrier to fruit dispersal. The development of the local terrestrial vegetation during the Flandrian period was also heavily influenced by human activity. There is evidence for mesolithic disturbances as early as 8500 B.P. and these almost certainly played a role in depressing tree pollen values. The first cereal pollen grain (ef. Hordeum) was found at a level dated to an estimated 5375 B.P. Later, agriculture was apparently of such an intensity that there were periods during the late Neolithic and at the transition between the Bronze and Iron Ages when it could no longer he sustained with the resources available. I he latter period coincided with the onset of blanket peat formation. A similar episode of reduced agricultural activity is evident in the Dark Ages. It was followed by a clear resurgence in Viking and early medieval times which apparently coincided with the improvement of the climate during the so‐called ‘little optimum’
Holocene pollen stratigraphy of central East Anglia, England, and comparison of pollen zones across the British Isles
Authors: BENNETT K. D.
Published: April 2006

Two new Holocene pollen diagrams are presented from central East Anglia. Using these sites and others from the same area, regional pollen assemblage‐zones for the area are formally defined. The regional pollen assemblage‐zones are then combined with zones from other well‐dated sequences in the British Isles to produce time/space diagrams for vegetation history along three transects across the islands. It is shown that pollen assemblage‐zones have only a limited extent in time and space. Forest vegetation has varied almost continually in time and space throughout the Holocene and over the whole of the British Isles.
Fructan biosynthesis in excised leaves of Lolium temulentum L.
Authors: CAIRNS A. J. , POLLOCK C. J.
Published: April 2006

Fructan oligosaccharides with degree of polymerization of 3–12 extracted from leaves of Lolium temulemtum L. were analyzed by normal‐phase thin‐layer chromatography. The pattern of oligosaccharides was more complex than that observed in tubers of Helianthus tuberosus L. and stem internodes of Hordeum vulgare L., indicating that fructans of multiple linkage types were present in this tissue.

On the basis of co‐chromatography with known standards and constituent hexose analysis, two trisaccharides, neokestose (6‐G fructosyl sucrose) and isokestose (1‐F fructosyl sucrose) were found to accumulate to high concentrations. A third trisaccharide, thought to be kestose (6‐F fructosyl sucrose) was present at much lower tissue concentrations. An abundant tetrasaccharide with a chromatographic mobility similar to that of nystose (1‐F difructosyl sucrose) also accumulated.

When carbohydrate‐depleted leaves were excised and continuously illuminated, total water‐soluble carbohydrate accumulation was linear with respect to time at a rate of 1–8 mg g‐1 fresh mass over a 30 h period. In the first 6h sucrose accumulated to lOmgg1, at which time fructan biosynthesis was detected. Isokestose appeared first, followed by neokestose and subsequently kestose and longer oligo‐ and polyfructosides. Changes in the concentrations of these compounds, and their radioactivity following feeding of 14CO2, was consistent with precursor‐product relationships between sucrose and trisaccharides, and between trisaccharides and oligo‐ and polyfructans.
Enzymology of ammonium assimilation in three green flagellates
Authors: AHMAD IFTIKHAR , HELLEBUST JOHAN A.
Published: April 2006

The relationship between assimilation of nitrogen and animating activities of glutamine synthetase (GS), NADH‐glutamate dehydrogenase (GDH) and NADPH‐GDH in ammonium‐grown Chlamydomonas pulsatilla Wollen‐weber and ammonium‐ and nitrate‐grown Brachiomonas submarina Bohlin and Tetraselmis succica (Kylin) Butcher was investigated. The three flagellates show minor changes (15–60%) in enzyme activities when ammonium is replaced by nitrate as the nitrogen source or the concentration of nitrogen is lowered from 2 to 0·2 mM. The activities of NADH‐GDH and NADPH‐GDH in the three flagellates do not appear to be high enough to make a significant contribution to ammonium assimilation in the presence of a highly active GS. Fast protein liquid chromatography (FPLC) of GS revealed the presence of two distinct molecular forms, designated as GS1 and GS2, in C. pulsatilla and T. suecica, whereas only a single GS peak designated as GS2 was detected in B. submarina. Both GS1 and GS2 are stabilized by sorbitol and glycinebetaine in media employed for enzyme extraction and FPLC fractionation. The presence of thiol reagents is essential for GS2 stability, but inhibits GS1 activity. GS2 is by far the more active of the two isoenzymes in C. pulsatilla and T. suecica. This isoenzyme, therefore, appears to be the major port of entry of ammonium in all three flagellates.
Ectomycorrhizal rain‐forest legumes and soil phosphorus in Korup National Park, Cameroon
Authors: NEWBERY D. M. , ALEXANDER I. J. , THOMAS D. W. , GARTLAN J. S.
Published: April 2006

The mycorrhizal status of a group of caesalpinioid legumes in lowland rain‐forest in Korup National Park, SW Cameroon, was examined. Species in ten genera, Anthonotha, Aphanocalyx, Berlinia, Didelotia, Gilbertiodendron, Julbernardia, Microberlinia, Monopetalanthus, Tetraberlinia(tribe Amherstieae) and Afzelia(tribe Detarieae) were ectomycorrhizal. These species were not uniformly distributed in the forest, and three large emergent species Microberlinia bisulcata A. Chev., Tetraberlinia bifoliolata(Harms) Hauman, and T. moreliana Aubr. in particular appear to form groves c. 600 m across. This type of distribution may be related to the ectomycorrhizal habit.

A previous large scale enumeration and soil survey on four 5 km transects of plots in the forest, carried out during the wet season, had revealed an association between these ectomycorrhizal legumes and low concentrations ( 5 μg g‐1) of extractable phosphorus in the mineral soil. In the current study part of one of the original transects in a low phosphorus area of the forest, where ectomycorrhizal trees comprise 29 % of the basal area, was resampled at the subplot level during the dry season. Whereas in the wet season soil phosphorus had been lower (2·8 μg g‐1) within the ectomycorrhizal groves than without (3·8 μg g‐1), in the dry season the situation was reversed and the overall concentrations were higher (12·3 and 7·9 μg g‐1 respectively). Ordination analysis re‐affirmed the association of the three Microberlina/Tetraberlinia species with relatively low concentrations of extractable phosphorus in the wet season but relatively high ones in the dry season. The groves are characterized by high inputs of leaf litter in the dry season, extensive colonization of surface organic matter by ectomycorrhizas and hyphal strands, and high carbon: extractable inorganic phosphorus ratios in the mineral soil in the wet season. These features are discussed in relation to the presumed ability of ectomycorrhizas to utilize organic phosphorus.
Growth response to and morphology of mycorrhizas of Thysanotus (Anthericaceae Monocotyledonae)
Authors: McGee P. A.
Published: April 2006

Seedlings of Thysanotus were inoculated in pot culture with fungi that form vesicular‐arbuscular or ectomycorrhizas on other hosts. Mycorrhizas formed by both fungi were similar in morphology to each other and to mycorrhizas observed in field‐collected plants. Hyphae of mycorrhizal fungi penetrated between epidermal cells and ramified between the cortex and epidermis. Spread of mycorrhizas in pot‐cultured T. tenellus Endl. occurred only in the presence of a companion plant. In soils with low levels of nutrients, mycorrhizal plants of T. tenellus grew faster than non‐mycorrhizal plants, with roots of infected plants growing relatively faster than shoots.
The effect of shoot spacing on the growth and branch development of the moss Rhytidiadelphus triquetrus
Authors: BATES J. W.
Published: April 2006

The effects of a range of shoot spacings (5, 10, 20, 50 mm) on the growth and development of the moss Rhytidiadelphus triquetrus (Hedw.) Warnst. within artificial colonies were studied under conditions of intermittent moisture supply. Growth of the main axis was promoted by decreased spacings of the shoots, probably due to increased resistance to evaporation and prolongation of the period of metabolic activity. Etiolation of shoots occurred at close spacings but no self‐thinning was observed. The growth of determinate lateral branches was also stimulated by decreasing shoot spacings but the closest plantings led to inhibited branch growth for shoots in the centres of the colonies. Marginal shoots generally showed less growth of the main axis and branches than central shoots except at the 5 mm spacing.

The numbers of offshoots of indeterminate growth produced at each shoot spacing were low and only a slight trend of increasing offshoot production with increasing spacing was observed over the range 5–20 mm.

Overall growth of shoots was optimal at or near to the closest spacing. Calculated productivity was, therefore, greatest for the densest colonies (1000 shoots dm a) indicating that the advantage of reduced water loss, conferred by dense packing of shoots, greatly outweighs the disadvantage of reduced irradiance.
Modelling of the root cap of Zea mays L in relation to temperature
Authors: CLOWES F. A. L. , WADEKAR R.
Published: April 2006

Rates of mitosis in each of the four tiers of the cap meristem of primary roots of Zea mays L. were measured at uniform root length by a stathmokinetic method and compared with rates for other regions of the apices in seedlings growing at between 15 and 35 °C. The highest elemental rate of cap cell production in the proximal tier and in the cap meristem as a whole occurs at 26 °C and the proportion of cells supplied by the proximal tier rises from 48%, at 15 °C to 90% at 35 °C. The number of cells in the whole cap and in its meristem decreases with increasing temperature. This is due to the general reduction in the width of root apices with age and growth in length being faster at the higher temperatures. The slimming of the apex is effected by a decline in the proportion of divisions that are longitudinal to the files of cells at the quiescent centre. This is enhanced by a slight but continuous increase in the rate of mitosis in the quiescent centre the higher the temperature (in contrast with the rest of the root whose maximal rate is at 2S °C). The decline results in an increase in the elemental rate for longitudinal divisions in the cap initials from 0.02 to 0.17 cells per cell per day between 15 and 35 °C and a consequent change in the cell pattern in the cap.
Different strategies of drought resistance in three Mediterranean sclerophyllous trees growing in the same environmental conditions
Authors: LO GULLO M. A. , SALLEO S.
Published: April 2006

Measurements have been made of leaf conductance to water vapour, relative water content and water potential inOlea oleasterHoffmgg et Link,Ceratonia siliquaL. andLaurus nobilisL., three evergreen sclerophyllous trees growing in Sicily at sea level. Measurements were made hourly in May and September 1986. Although all the three species are regarded as components of a homogeneous group (sclerophylls) and they all showed a high degree of sclerophylly, the strategies they adopted to withstand drought were completely different.Olea oleasterbehaved as a ‘drought‐tolerating’ species. Drought was ‘avoided’ byCeratonia siliquaby a ‘water‐spending’ strategy and byLaurus nobilisby a ‘water‐saving’ strategy combined with the capability of recovering even minimal water losses by dropping leaf water potential drastically. Such differences in drought resistance are discussed in terms of differences in the bulk elastic modulus of leaf cells and wood anatomy.
A comparative study of Geum rivale L. and G. urbanum L. to determine those factors controlling their altitudinal distribution II. Photosynthesis and respiration
Authors: GRAVES J. D. , TAYLOR K.
Published: April 2006

Geum urbanum and G. rivale are a sympatric interfertile pair of species with contrasting distributions. Geum rivale occurs at higher altitudes and more northerly latitudes than G. urbanum. As part of a study to determine the factors responsible for this difference in distribution, a comparison of the carbon economy of the two species was made. The light and temperature dependence of photosynthesis was assessed for plants of both species grown in contrasting light and temperature regimes. Acclimation to the prevailing environmental conditions was more pronounced in G. urbanum. Amongst populations of the two species originating from different altitudes the temperature optimum for photosynthesis was similar. When grown at 25/16 °C, higher rates of respiration were measured he roots of G. rivale at all temperatures, when pretreated at 8/5 °C there was a smaller increase in the rate of respiration in the roots of G. rivale. It is proposed that these differences in root respiration account for observed higher root growth rates at low temperatures in G. rivale. It is concluded that whilst carbon assimilation is not a critical factor determining the upper altitudinal limit of G. urbanum, the pattern of carbon utilization may be important. The greater phenotypic plasticity observed in G. urbanum, may be of value for survival in the herb layer of deciduous woodland where it is most commonly found.
Mycorrhizal growth responses: interactions between photon irradiance and phosphorus nutrition
Authors: SON C. L. , SMITH S. E.
Published: April 2006

The effects of photon irradiance, phosphorus (P) supply and mycorrhizal infection [Glomus mosseae (Nicol. and Gerd) Gerdemann and Trappe] on growth and P uptake by Allium cepa L. were measured. Two experiments were carried out, one in a naturally‐lit glasshouse and the other in a growth cabinet. Shade cloth was used to provide ‘high’ irradiance (600 and 550 μmol m−2s−1 in glasshouse and growth cabinet respectively) and ‘low’ irradiance (250 μmol m−2s−1). Growth at high irradiance was associated with increases in total dry weight, root: shoot dry weight ratio and total root length and with decreases in shoot fresh weight: dry weight ratio. Mycorrhizal growth responses were lower at low irradiance and depressions were observed at high P supply and high irradiance, as well as at low irradiance. Mycorrhizal plants generally had higher shoot fresh weight: dry weight ratios than those of equivalent non‐mycorrhizal plants. Mycorrhizal infection was lower in the presence of additional P in both experiments. In the glasshouse there was an interaction between low irradiance and high P, leading to very low values of fractional infection. This effect was not apparent in the growth cabinet. At high irradiance mycorrhizal plants had higher inflows than those of equivalent non‐mycorrhizal plants at all levels of P, regardless of the growth response. Low irradiance had little effect on inflow into non‐mycorrhizal plants, but depressed inflow into mycorrhizal plants. This reduction in inflow can be attributed in part to lower levels of infection, but an effect on P uptake by hyphae or on transport between the symbionts is also likely.