bluuebunny/crossref_metadata_2025 huggingface dataset:
Dimorphic epidermal cell chloroplasts in the mesophyll‐less leaves of an extreme–shade tropical fern, Teratophyllum rotundifoliatum (R. Bonap.) Holtt.: a light and electron microscope study
Authors: NASRULHAQ‐BOYCE A. , DUCKETT J. G.
Published: April 2006

summary

This light and electron microscope study of the iridescent blue leaves of the fern Teratophyllum rotundifoliatum, reveals several novel anatomical and cytological features. In this extreme shade species [0.4—‐(3)–4 W m−2] of lowland tropical rainforest in peninsular Malaya, the greater part of the lamina between the simple collateral vascular bundles, consists only of epidermal cells. From 4–(6.9)–12 large chloroplasts 9.4–(17.9)–27 μm in diameter are located adjacent to the inner walls of the lens‐shaped upper epidermal cells. Those in the tessellated lower epidermal cells are smaller [5.0–(7.6)–19.5 μm], much more numerous [21–(53)–83] and regularly distributed around the periphery. They are identical in size and ultrastructure to the chloroplasts in the guard cells of the stomata. Whereas the upper epidermal chloroplasts and those in the stelar tissues contain very little starch, numerous starch grains occupy up to Sl‐9% of the volume of the lower epidermal chloroplasts. As in other extreme‐shade plants the epidermal chloroplasts in T. rotundifoliatum contain numerous large grana, with no preferred orientation, and integranal lamellae completely filling the stroma. The numbers of thylakoids per granum in the lower epidermal cells [9–(29.3)–84] are significantly smaller than those in the upper [22–(86)–28O]. The latter appear to be the largest yet recorded in land plants and this probably accounts for the remarkably low chlorophyll a: b ratio (1.8) in T. rotundifoliatum. Record amounts of chlorophyll per unit leaf fresh weight and per unit leaf area in T. rotundifoliatum reflect the high proportion of leaf cells containing chloroplasts. The unusual features of leaf anatomy and cytology in T. rotundifoliatum appear to be associated with maximizing the efficiency of absorption of very low diffuse radiation.
Rapidity of cellular changes induced by zinc in a zinc tolerant and non‐tolerant cultivar of Festuca rubra L.
Authors: DAVIES M. S. , FFRANCIS D. , THOMAS J. D.
Published: April 2006

summary

7 day‐old seedlings of a Zn‐tolerant cultivar (Merlin) and a non‐tolerant cultivar (S59) of Festuca rubra L. were transferred to aerated solution culture containing 3 concentrations of Zn (0, 80 and 120 μM). Roots were sampled at 0, 6, 12, 24, 48, 72 and 96 h following transfer. Zn markedly reduced root extension in S59; this inhibition was evident after only 12 h exposure. In contrast Zn stimulated the root extension of Merlin. The length of the apical meristem of S59 was reduced within 12 h after transfer to the Zn‐containing solutions, followed by a further reduction to 69 % and 61 % of that of control roots (0 μM Zn) after 96 h at 80 μM Zn and 120 μM Zn respectively. The meristem length of Merlin was much less affected by Zn. Treatment with 80 μM Zn resulted in a stimulation in the number of lateral root primordia in both cultivars but their formation was depressed relative to the control roots at 120 μM Zn in S59, though not in Merlin. The area of mitotic cells was reduced by 25 % after only 12 h exposure to 120 μM Zn in S59 and this reduction increased with duration of exposure. However, in Merlin, the area of mitotic cells increased with increasing length of exposure to Zn. The protein content of mitotic cells of S59 was reduced by 28 %, relative to that of roots grown in the control solutions, after 12 h exposure to 120 μM. Zn, culminating in a 50 % reduction after 96 h exposure. However, the cellular protein content of Merlin increased progressively with time of exposure to Zn. The sensitivity and rapidity of response of these cellular changes to Zn in S59 may make them useful early markers of metal toxicity in roots.
Population variation in Spartina anglica C. E. Hubbard
Authors: THOMPSON J. D. , McNEILLY T. , GAY A. J.
Published: April 2006

summary

Replicated clones from ten populations of Spartina anglica C. E. Hubbard were grown in a common garden experiment to determine whether the phenotypic variation previously observed in natural habitats was due to inherent differences between clones. For a range of morphological characters, mean differences between populations, and clonal repeatability, were very low. Different morphological forms were, however, evident from differences in character correlations. Thus, morphological variation appears to be dominated by phenotypic plasticity with a limited amount of possibly genetic differences distinguishing different morphological forms. No differences in the relative variability of morphological characters were recorded between populations sampled from successionally adjacent salt‐marsh zones, although the oldest population, from Poole Harbour, contained significantly less morphological variation than other populations. The pattern of (a) flowering during the first year of the experiment, (b) clone survival, and (c) clonal growth, showed that the vigour of clones sampled from four successionally mature populations was significantly less than that of the other populations. It is suggested that these consistent differences between populations are due to an age‐related decline in vigour of clonal material and, thus, due to somatic variation rather than to genetic differences between populations. The ecological implications of this interpretation are discussed in relation to the origin of S. anglica and the successional development and ‘die‐back’ of natural populations.
Leaf area compensation and nutrient interactions in CO2‐enriched seedlings of yellow‐poplar (Liriodendron tulipifera L.)
Authors: NORBY RICHARD J. , O'NEILL E. G.
Published: April 2006

summary

The responses of yellow‐poplar (Liriodendron tulipifera L.) seedlings to elevated levels of atmospheric CO2 were investigated to identify attributes governing growth and physiological responses to CO2. Based on the pattern of leaf initiation and nutrient requirements of the species, it was predicted that (1) CO2, enrichment would enhance growth of yellow‐poplar seedlings both through accelerated leaf area production and through higher rates of carbon assimilation per unit leaf area; and (2) growth enhancement of yellow‐poplar by CO2 enrichment would be reduced by nutrient limitations. The hypotheses were tested in an experiment in which yellow‐poplar plants were grown from seed for 24 weeks in controlled‐environment chambers. The experimental design comprised three atmospheric CO2 concentrations (371, 493, and 787 cm3m−3), two levels of mineral nutrients (unfertilized or weekly additions of complete nutrient solution), and three harvests (6, 12, and 24 weeks). Plant growth rate, water use, foliar gas exchange, component dry weights, and nutrient contents were measured.

Both hypotheses were rejected. Whole‐plant dry weight increased similarly with CO2, enrichment in plants provided with additional mineral nutrients and in unfertilized plants, although the fertilized plants grew 10‐fold larger. The increase in dry weight resulting from elevated CO2 occurred only in root systems. Although leaves were produced continuously during the experiment, leaf area was slightly reduced in elevated CO2, and the whole‐plant growth response was wholly attributable to an increase in carbon assimilation per unit leaf area. Although the compensation between photosynthesis and leaf area reduced the potential growth response to CO2, the reduction in leaf area ratio was associated with a significant increase in water‐use efficiency. This unexpected result demonstrated the importance of feedbacks and interactions between resources in shaping the response of a plant to CO2.
Atmospheric pollution and the sensitivity of stomata on barley leaves to abscisic acid and carbon dioxide
Authors: ATKINSON C. J. , WOOKEY P. A. , MANSFIELD T. A.
Published: April 2006

summary

Spring barley (Hordeum vulgare L. cv. Klaxon) plants were exposed to mixtures of SO2+ NO2 (at concentrations of 24–35 nl l−1of each gas, depending upon fumigation system), or to charcoal‐filtered, or unfiltered ambient air during the period in which the second, and subsequent, leaves were emerging. The ability of individual detached leaves to regulate water loss was then examined after terminating the pollutant treatment.

Observations of diurnal changes in stomatal resistance of well‐watered plants, using a viscous flow porometer, failed to indicate any major alterations which could be attributed to prior exposure to SO2+ NO2. By contrast, when an ABA solution (10−1mol m−3) was applied to detached leaves, the stomata of polluted plants were less responsive than plants previously exposed to control air. The dynamics of the observed responses strongly implicated impaired physiology of the guard cells rather than mechanical changes in the epidermis that might, for example, result from damage to the cuticle. Stomatal closure was considerably slower in polluted leaves compared with the controls. This decline in responsiveness to ABA was observed using leaves excised from well‐watered plants and in the absence of any externally visible injury.

The ability of stomata to respond to a range of CO2 concentrations from 195–735 μmol mol−1was also examined using individual leaves, attached to the plant, in an environmentally controlled cuvette. Here the stomata of leaves which had been fumigated with SO2+ NO2 behaved in a similar manner to the non‐fumigated leaves, both showing closure in elevated CO2 concentrations.
A comparison of foliar wettability of red spruce and balsam fir* growing at high elevation
Authors: BOYCE RICHARD L. , McCUNE DELBERT C. , BERLYN GRAEME P.
Published: April 2006

summary

The contact angle method was used to determine the wettability of red spruce (Picea rubens Sarg.) and balsam fir [Abies balsamea (L.) Mill.] foliage in subalpine sites (1010–1400 m above sea level) at three locations in northern New England, USA (Camels Hump in Vermont and Mt. Moosilauke and Mt. Washington in New Hampshire).

The dependence of contact angle (θ) on foliage age (t, in months) could be expressed in the form θ=θ1+θ2 e−kt. The value of the decay constant (k) ranged from 0.02 to 0.12 (month−1), depending upon location, but was independent of elevation, canopy position, and, in most cases, species. The asymptotic value of the contact angle (θ1) i.e. that approached by very old foliage, did not differ between species at some sites but was greater in fir than in spruce at others. The value of θ1 decreased with elevation in both species and tended to increase with an increase in height within the canopy. The value of the component which affected contact angle variation with age (θ2) was always greater in fir than in spruce, but was unaffected by elevation; in fir, it appeared to increase with height in the canopy. Thus, the estimated value of the initial (t= 0) contact angle (θ1+θ2) was greater in fir, increased with height in the canopy, and decreased with elevation. The overall pattern found was that (1) young foliage of spruce is more wettable than young foliage of fir, but the difference becomes smaller in older age classes; (2) young foliage near the bottom of the canopy is more wettable than near the top; and (3) foliage from a given age class and species is more wettable at higher elevations.

The treatment of foliage with xylene to remove epicuticular wax decreased contact angles of fir but increased them in spruce. Scanning electron microscopy revealed that wax removal by xylene did not mimic natural wax removal. Contact angles obtained with acidified water did not vary significantly from those obtained with deionized water.
Absorption of atmospheric NO2 by spruce (Picea abies L. Karst.) trees
Authors: THOENE BARBARA , SCHRÖDER PETER , PAPEN HANS , EGGER ALFRED , RENNENBERG HEINZ
Published: April 2006

summary

When spruce (Picea abies L., Karst.) branches were exposed to 5.2–18.7 nl NO2 l−1the flux to the shoots increased linearly with increasing NO2 concentrations. At NO2 concentrations below 2.6 nl l−1uptake of NO2 by the shoots was not observed. The measured flux of NO2 to the shoots was found to be lower than the NO2 flux predicted from the shoot conductance to diffusion of H2O. These results are consistent with the existence of internal resistances for NO2 influx, e.g. production and emission of NO2 by the leaves. However, emission of NO2 was not observed. When the NO2 flux to the shoots was plotted versus transpiration rate, a linear increase was found with an y‐axis intercept. The intercept may be interpreted as the NO2 flux to the cuticle and the bark; its value increased with increasing atmospheric NO2 concentrations.

The flux of NO2 to the shoots showed diurnal variation with high levels in the light and low levels during darkness. NO2 flux to the branches was dependent on light intensity. This dependency can largely be explained by light dependent changes in shoot conductance. Daytime light intensity determined also the night‐time shoot conductance and, hence, the NO2 flux to the branches during the night. The ratio of NO2 flux to transpiration rate was higher in the dark than in the light. Whether this observation can be explained by a light dependency of internal resistances remains to be elucidated.

The absorption of NO2 by the shoots enhanced the in vitro NR activity of the needles, while NiR and GS activities were not increased significantly. One day after exposure to NO2 concentrations of 60 nl l−1, nitrate reductase (NR) activity was three times higher than that of untreated controls. However, after three days of NO2 exposure the NR activity declined to the level of untreated controls. Apparently, the increased in vitro NR activity upon NO2 fumigation is a transient phenomenon in spruce needles. The regulatory events that may modulate NR activity of the needles, when exposed to atmospheric NO2, are discussed.
The role of nitrogen concentration in determining the outcome of the interaction between Dactylorhiza incarnata (L.) Soó and Rhizoctonia sp.
Authors: BEYRLE H. , PENNINGSFELD F. , HOCKF B.
Published: April 2006

summary

Protocorms of Dactylorhiza incarnata (L.) Soó grown in shaking cultures were used for synthesis of mycorrhizas on agar plates in the presence of a Rhizoctonia strain. At low nitrogen (N) concentration [0.36 m++++m Ca (NO3)2.4H2O] normal mycorrhizas were formed, whereas the same concentration of carbon a higher concentration of N (3.6 mm) led to parasitism with low survival of protocorms. Carbon source did not influence the symbiotic interactions. Growth of mycorrhizal protocorms at low N concentrations increased with sucrose concentrations up to 58 mm, but in the absence of the fungus there was practically no growth.

Increases in nitrogen concentration can thus lead to change from a mycorrhizal to a parasitic interaction. The effects of nitrogen on the interaction between fungus and orchid provided an experimental system which was subsequently used to investigate hormone production in the different types of symbiosis by enzyme immunoassays. Phytohormone levels remained low under asymbiotic conditions. The presence of the fungus led to a large increase in phytohormone concentration, which was correlated with a growth stimulation in mycorrhizal protocorms. In parasitized protocorms auxin and to a lesser extent cytokinins remained at higher concentrations for longer than in mycorrhizal protocorms. It is thought that the phytohormones are derived mainly from the mycorrhizal fungus.
In vitro synthesis of ectomycorrhizas on Casuarinaceae with a range of mycorrhizal fungi
Authors: THEODOROU COSTAS , REDDELL PAUL
Published: April 2006

summary

Eleven species of mycorrhizal fungi, selected from stands of either Eucalyptus spp., Allocasuarina spp. or Pinus radiata D. Don were tested in an aseptic system for their abilities to initiate ectomycorrhiza with Allocasuarina littoralis (Salisb.) L. Johnson, Casuarina equisetifolia ssp. equiselifolia L. and C. cunninghamiana Miq. Elaphamyces sp., Hysterangium sp., Laccaria laccata (Scop ex Fr.) Bk. & Br., Pisolithus tinctorius (Pers.) Coker & Couch, Scleroderma sp. and Thelephora terrestris (Ehrh.) Fr. formed ectomycorrhizas on all three hosts. Amanita sp. formed ectomycorrhizas on A. littoralis and C. cunninghamiana but not on C. equisetifolia. Paxillus involutus (Batch ex Fr.) Fr. formed ectomycorrhizas on A. littoralis only. P. tinctorius also formed ectomycorrhizas with C. obesa Miq. Rhizapogon luteolus Fr. & Nord, Suillus granulatus (L. ex Fr.) Kuntze and S. piperatus (Bull ex Fr.) O. Kuntze colonized the rhizosphere of Casuarinaceae but did not form ectomycorrhizas.

The comparative intensity of ectomycorrhizal infection by P. tinctorius and L. laccata was assessed on four host species. Infection intensity ranged from 13 to 70%, of laterals infected and decreased for both fungal species in the order: A. littoralis > Eucalyptus pilularis Smith > C. equisetifolia > C. cunninghamiana.

An exogenous supply of glucose induced greater and sometimes earlier, ectomycorrhizal infection of A. littoralis, C. equisetifolia and C. cunninghamiana by P. tinctorius and L. laccata than that in the absence of glucose. The optimum glucose level for these fungi and hosts in this synthesis system was 750 μg glucose (g soil)−1.
Root factors stimulate 32P uptake and plasmalemma ATPase activity in vesicular‐arbuscular mycorrhizal fungus, Gigaspora margarita
Authors: LEI J. , BÉARD G. , CATFORD J. G. , PICHÉ Y.
Published: April 2006

summary

Root‐inducing (Ri) T‐DNA transformed roots of carrot were used as the plant partner in a study of 32P absorption and plasmalemma ATPase activity in the hyphae of the vesicular‐arbuscular mycorrhizal fungus Gigaspora margarita Becker & Hall. Hyphae from germinating spores were grown in the presence or absence of root exudates and volatiles. In the presence of these root factors, 32P isotope labelling occurred in hyphae, auxiliary cells and spores, while in the absence of these factors, the labelling only occurred in fungal spores. Similarly, ATPase activity appeared on the fungal plasmalemma only in the presence of root factors. The use of the ATPase inhibitor, diethylstilbestrol, demonstrated the importance of plasmalemma ATPase in the stimulation of hyphal growth of this obligately biotrophic fungus.
Application of the diffusion equation for modelling splash dispersal of point‐source pathogens
Authors: YANG XIUSHENG , MADDEN LAURENCE V. , BRAZEE ROSS D.
Published: April 2006

summary

A model of splash dispersal of point‐source pathogens is developed and parameterized from experimental data of Colletotrichum acutatum, the cause of strawberry anthracnose. Starting with analysis on a probability density function of a sum of random displacement vectors, the model turned out to be the fundamental solution of the classic diffusion equation. Model parameters were determined for three ground covers (plastic, soil, and straw) and two rain intensities (15 and 30 mm h−1). The nonlinear coefficient of determination varied from 0.80 to 0.96, indicating that the application of the diffusion equation is promising in modelling of splash dispersal processes from a point source over a homogeneous ground cover.
The action spectrum of far‐red light in interaction with orange light on orientation of chloroplasts in Mougeotia
Authors: LECHOWSKI Z. , BIAŁCZYK J.
Published: April 2006

summary

Chloroplast rotation from profile to face position in Mougeotia can be controlled by an interaction of far‐red and orange light during dichromatic irradiation. In experiments to determine the action spectrum in the far‐red light range during dichromatic irradiation, light conditions prevented the formation of a gradient of the far‐red‐absorbing form of phytochrome in the cell. Linearly polarized monochromatic light of 620 nm vibrating parallel to the cell axis or unpolarized far‐red light (700 run to 900 nm) when given alone had no effect on chloroplast reorientation to the face position. Unpolarized far‐red light in the range from 700 nm to 775 nm was active in an interaction with 620 nm monochromatic light and had its maximum effect on face chloroplast orientation at 710 nm. Wavelengths above 775 nm were ineffective. In this kind of chloroplast photoorientation in Mougeotia, high irradiance of both kinds of light together with prolonged exposure were necessary to obtain the full response. The time‐course response showed three phases: lag, movement and steady‐state. At the saturating dose of both kinds of light there was a 10–15 min lag period between the first detectable change in chloroplast position. Then the response was linear (movement phase) until after approximately 30 min when all the chloroplasts had become reorientated. Simultaneous irradiation of Mougeotia cells with green and far‐red light did not change the maximum activity in far‐red light. The effect was similar when treatment with one kind of light e.g. orange or far‐red light, was followed by the other. The photo responses of Mougeotia chloroplasts are typical of the high irradiance reactions that control many photomorphogenetic processes.
Concurrent exposure to SO2 and/or NO2 alters growth and yield responses of wheat and barley to low concentrations of O3
Authors: ADAROS G. , WEIGEL H. J. , JÄGER H. J.
Published: April 2006

summary

During 1988 and 1989, single and interactive effects of low concentrations of O3, SOS and NO2 (6–44, 9–63 and 10–43 μm−a as 24 h daily means) on two varieties of spring barley (Hordeum vulgare L., ‘Arena’ and ‘Alexis’) and spring wheat (Triticum aestivum L., ‘Turbo’ and ‘Star’) were investigated in factorial experiments using open‐top chambers. Potted plants were exposed during the whole growing season to either charcoal‐filtered air (CF; control) or CF supplemented with one (SO2, NO2) or two (O3) concentrations of the pollutants. While SO2 was applied continuously, fumigation with O3 and NO2 occurred every day sequentially from 8.00 to 16.00 and from 16.00 to 8.00 h, respectively. Analysis of variance indicated that from the main treatments O3 caused the most detrimental effects on growth and yield parameters. Depending on season and on variety, yield of wheat was reduced by O3 between 20% and 40% compared with the control treatment; a significant reduction of yield of barley (−15%) was only registered for ‘Arena’ (1988), while ‘Alexis’ appeared to be insensitive towards this gas. SO2 did not affect yield of barley significantly, while yield of wheat was either decreased (−7% for ‘Turbo’ in 1988) or increased (+11% for ‘Star’). NO2 did not alter yield of wheat significantly but it increased yield of barley (‘Arena’) by 15% in 1988. Significant interactive effects between the pollutants were observed only for a few parameters. Among these the most sensitive ones were the length of ears, the 1000‐grain weight and the weight of straw. The interaction between the pollutants was mostly antagonistic, i.e. positive or negative effects of a single gas were cancelled or mitigated by the presence of other pollutants. However, a clear tendency towards a synergism was found for wheat in 1988: detrimental effects of O3 on yield (e.g, –26%;‘Turbo’) were aggravated by the addition of either SO2 (−38%) or, partially, NO3 (−31%) or both pollutants together (−44%). Before the plants were fully mature, visible symptoms were only observed on wheat after exposure to the highest O3 concentrations. The results showed that although effects of O3 dominated, these responses were strongly modified by the presence of one or both of the other gases. It is evident that yield losses of O3‐sensitive crop species may be enhanced under certain circumstances by low concentrations of other pollutants. Therefore, estimations of yield losses from open‐top chamber experiments should consider interactive effects between those pollutants which are relevant to ambient air.
Unusual patterns in the distribution of calcium oxalate in spruce needles and their possible relationships to the impact of pollutants
Authors: FINK SIEGFRIED
Published: April 2006

summary

The patterns of distribution of calcium oxalate crystals in spruce needles have been investigated in healthy needles and those subjected to either acid precipitation (ph 2.5) or various ozone fumigations. In the acid treatment, deposits of Ca oxalate were lacking in the outer walls of the epidermal cells. Under the impact of ozone, unusual complexes of Ca oxalate crystals embedded in a matrix of callose and cellulose projected from the walls inwards into the cells, filling the lumina of epidermal and hypodermal cells completely. In mesophyll cells, the complexes projected more or less from the walls into the vacuoles. In other cases, crystals appeared within the vacuoles of mesophyll cells. In dead cells, precipitates of Ca oxalate or phosphate apparently indicate destruction of the cytoplasm after a major influx of Ca2+. It is speculated, that the physiological significance of enhanced calcium leaching has been overestimated. With regard to ozone impact, it seems that the major problem of thereby enhanced membrane permeabilities may not be an increased efflux of mineral elements, but rather an increased influx of Ca into the symplast and subsequent disturbances in metabolism.
Uptake of NOxby mycorrhizal and non‐mycorrhizal Scots pine seedlings: quantities and effects on amino acid and protein concentrations
Authors: NÄSHOLM TORGNY , HÖGBERG Peter , EDFAST ANN‐BRITT
Published: April 2006

summary

Scots pine seedlings were grown from sterilized seeds in oven sterilized sand. Half of the seedlings were inoculated with the mycorrhizal fungusPisolithus arhizus(Pers.) Rausch (syn.Pisolithus tinctorius)while the rest were not. Seedlings were raised in a growth chamber for 61 d and supplied with a complete nutrient solution with NH4Cl as the nitrogen source. To measure uptake of NO2by the15N dilution method, nitrogen in the nutrient solution was enriched with 5.00 atom %15N. After 61 d pretreatment, all seedlings were transferred to cuvettes, and exposed to either 20–30 ppb NOxor carbon‐filtered air for 39 d. Seedlings harvested just prior to, and after 19 and 39 d exposure were analysed for growth and concentrations of total nitrogen and atom %15N in roots and shoots and free amino acids and total protein in shoots. As a measure of mycorrhizal infection the concentration of ergosterol in roots was determined.

Exposure of seedlings; to low concentrations of NOxhad no effect on growth, total nitrogen concentration, ergosterol concentration or total protein concentration. The atom %15N of seedlings increased and asymptotically approached that of the nutrient solution. Because differences in uptake of nitrogen from soil resulted in various values on atom %15N irrespective of exposure, quantification of uptake of NOxwas not possible with the formula previously used for this purpose. By calculating the atom %15N of the nitrogen taken up by plants between two harvests, and comparing this value for exposed and non‐exposed seedlings, uptake of nitrogen from NOxcould be quantified. The uptake of nitrogen from 20–30 ppb NOxthus calculated amounted IO, on average 1.4% of the total uptake of nitrogen by seedlings during exposure. After 19 d exposure nitrogen derived from NOxwas found in both shoots and roots indicating transport of nitrogen from shoots to roots. After 39 d exposure, negative values of uptake of NOxwere found in roots. This might be explained as an effect of decreased transport of NO, derived nitrogen from shoots and roots and/or decreased transport of soil derived nitrogen from roots to shoots. Glutamine, arginine and GABA+ proline were the most abundant amino acids detected in the seedlings. Exposure to NOx. resulted in lower concentrations of GABA+ proline but had no significant effect on concentrations of glutamine and arginine. Higher concentrations of glycine were found in exposed seedlings but this represented only a small fraction of the total amount of amino acids in the shoots. Inoculated seedlings were smaller and had significantly higher concentrations of glutamine and arginine compared with those that were not inoculated.

Thus, 40 d exposure to 20–30 ppb NO, had no effect on seedling growth, mycorrhizal infection or total nitrogen concentration, but resulted in a significant uptake of NOxand measurable changes in amino‐acid composition.
Fluxes of carbon and phosphorus between symbionts in willow ectomycorrhizas and their changes with time
Authors: JONES MELANIE D. , DURALL D. M. , TINKER P. B.
Published: April 2006

summary

One way of viewing a mycorrhizal symbiosis is as a balance between the nutritional ‘benefits’ and carbon ‘costs’ to the phytobiont. Phosphorus acquisition efficiency (the amount of phosphorus taken up per unit of carbon allocated belowground) can be used as an indicator of this balance. In this study, phosphorus uptake and belowground carbon allocation were measured using ectomycorrhizal (M) (Thelephora terrestris (Ehrh.) Fr.) and non‐mycorrhizal (NM) Salix viminalis L. cv. Bowles Hybrid. Following 50, 60, 85 or 98 d of growth in a gamma‐irradiated soil/sand mixture containing 4 mg bicarbunate‐extractable P kg−1, seven randomly‐selected cuttings of each treatment were harvested and their P contents determined. Nine d prior to each harvest, the three median plants from the group of seven were pulse labelled with 14C to determine the relative allocation of C aboveground and belowground. Mycorrhizal colonization of willow caused a two‐fold increase in growth owing to substantially higher P uptake. Phosphorus inflow rates were almost three times as high for M root systems as for NM root systems over the interval up to the first harvest (3.2 × 10 −12 and 1.2 × 1012 mol m−1 s–1, respectively). Over the interval from 50 to 98 d, inflows into M plants were 50% higher than into NM plants (1.4 × 1012 and 0.9 × 10−13 mol m−1 s−1 respectively). The M plants allocated about 25 times as much carbon belowground as the NM plants for both periods. The P acquisition efficiency was higher in M than in NM plants during the first interval (16% and 40% higher using two different calculation methods), whereas during the second interval it was higher in NM than in M plants (33% and 44% higher using the two different methods). Thus, ectomycorrhizas can be very effective in supplying P to their hosts even at an early stage of infection. Furthermore, it is suggested that a temporal separation exists in the maximal fluxes of P and C between the fungus and the host of the mycorrhizal association. The results are discussed in the context of the nutrient requirements and carbon economies of field‐grown woody plants.
Fructan composition in adventitious tuberous roots of Viguiera discolor Baker (Asteraceae) as influenced by daylength
Authors: ISEJIMA E. M. , FIGUEIREDO‐RRIEIRO R. C. L. , ZAIDAN L. B. P.
Published: April 2006

summary

Short (8–10h) photoperiods stimulated branching, flowering and enlargement of adventitious tuberous roots of Viguiera discolor Baker, a native plant of the Brazilian cerrado. Inulin was mostly accumulated in parenchyma cells associated with secondary xylem of tuberous roots. Accumulation was greater in plants grown under conditions that induce flowering (1) than in plants grown under conditions that do not induce flowering (NI) (photoperiods longer than 12 h), Although total fructan concentration was similar in both conditions [approx. 460 mg (g dry mass)−1], the amount of inulin in I was 10 times that of oligosaccharides, whereas in NI it was 6 times greater. In addition, the relative molecular mass of inulin was slightly lower in NI 16600) than in I (18600), but considerably higher than those reported for other Asteraceae (approx. 5500). The results suggest that flower‐inductive conditions affect fructan metabolism in Viguiera discolor without altering the total fructose.
The influence of increasing rhizospheric calcium on the ability of Lupinus luteus L. to control water use efficiency
Authors: ATKINSON C. J.
Published: April 2006

summary

The stomatal behavior of Lupinus luteus L. was examined to determine the ability of a calcifuge to regulate water loss against a background of different rhizospheric Ca concentrations. A previous study had suggested that a cultivar of this species had limited stomatal sensitivity to ABA, and so the physiological events which enable L. luteus to adjust its water use efficiency (WUE) in response to changes in both atmospheric and soil water availability were explored in a number of ways.

L. luteus did not lack the ability to control water loss and there was no evidence to suggest that ABA was unable to regulate stomatal behavior during water deficits, Stomatal closure was shown to occur in a linear manner when different concentrations of ABA were applied. The presence of different concentrations of Ca within xylem sap did not influence the degree to which stomata closed in response to applied ABA. The patterns of stomatal behavior in response to changes in atmospheric humidity, declining soil water potentials and applied ABA, were generally similar to those of other species.

The presence of high rhizospheric Ca 8 mol m−3 did not apparently induce stomatal closure when gas exchange measurements were made at a δW of mmol mol−1, when compared with plants grown on 1 mol m−3 Ca. However, when measurements of gas exchange were made over a range of δW values, the relationship between assimilation and stomatal conductance suggested that the degree of coupling between these two variables was less pronounced with plants grown at 8 mol m−3 compared to those at 1 mol m−3 Ca. The effect of this on the regulation of leaf conductance was to perturb WUE.

There was little evidence here to support a role for changes in the flux of xylem sap Ca as a means of root‐to‐shoot signaling.
Orientation of the lateral roots of trees
Authors: COUTTS M. P. , NICOLL B. C.
Published: April 2006

summary

The main lateral roots of some tree species grow close beneath the soil surface, even on irregular or sloping ground. Experiments were carried out to explore the origin and behavior of such surface roots. Pinus contorta Douglas ex Loudon and Picea sitchensis (Bong.) Carr. plants were grown under growth room and glasshouse conditions. Lateral roots were excavated and vertical and horizontal co‐ordinates measured. The liminal angles (0°= vertically downwards) of first‐order lateral roots of seedlings of both species decreased linearly with depth of origin on the taproot, Some of the roots of highest origin had liminal angles > 90° (ie they grew upwards). However, these roots deflected downwards on approaching the soil surface. If additional soil was added soon after germination the upper lateral roots grew further in an upward direction and then deflected beneath the elevated surface. Two‐year‐old Picea sitckensis transplants were planted centrally in large containers of soil and an elevated ridge of soil was made 160 mm to one side of the plants. Vigorous upwardly growing roots developed from the damaged and bent root systems that had been produced in the forest nursery. The upwardly oriented roots deflected horizontally when their tips arrived below the flat peat surface, but when they extended beneath the ridge they turned upwards within it. As they approached the top of the ridge they again deflected downwards.

It is concluded that the direction of growth of surface roots is the result of two opposing influences. Certain of the main lateral roots are plagiogravitropic and grow obliquely upwards but as these roots approach the soil surface they respond to some signal from the environment that causes downward deflection. The nature of the signal was not determined but it was shown that downward deflection occurred whether or not the soil was exposed to light. The biological importance of this form of surface root orientation is discussed. The growth behavior described enables the main lateral roots to explore the nutrient‐rich surface layers of the soil while avoiding the injury to the root tip that would result from exposure.
Response of nitrogen metabolism in beans (Phaseolus vulgaris L.) after exposure to ozone and nitrogen dioxide, alone and in sequence
Authors: BENDER J. , WEIGEL H. J. , Jäger H. J.
Published: April 2006

summary

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

summary

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

summary

Barley [Hordeum distichum (L.) Lam.] seedlings were infected with uredmiospores of rust, Puccinia hordei Otth., 10 d after germination and the Zimmermann micro‐pressure probe was used to measure the turgor potential of individual epidermal and palisade cells, during disease development. Turgor potential was measured as a function of time and as a function of distance from the centre of the rust colony. When the centre of a rust colony was within 300 μm of probed cells, palisade cell turgor declined significantly on days 6, 7 and 9 after infection in comparison to control leaf palisade cells.

Control leaf palisade cell turgor remained constant with time. On day 4 after infection, epidermal cell turgor of control and infected leaves did not differ. However, by day 6 when the uredinium was visible and approaching sporulation, epidermal cell turgor of infected leaves declined. The reduction was dependent upon the distance from the centre of the colony, thereby creating a gradient of turgor such that the lowest turgors were recorded at the centre of the colony and the highest at the colony boundary. By day 9 after infection, when ‘green island’ development had begun, this gradient was reversed. However, turgors of all epidermal cells in colony areas were significantly less than those in control leaves. These results are discussed in relation to die impact of rust infection upon leaf water relations in barley.
Uptake, accumulation and translocation of arsenate in arsenate‐tolerant and non‐tolerant Holcus lanatus L.
Authors: MEHARG ANDREW A. , MACNAIR MARK R.
Published: April 2006

summary

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

summary

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

summary

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

summary

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