bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of N metabolism and organic acid synthesis on the natural abundance of isotopes of carbon in plants
Authors: RAVEN JOHN A. , FARQUHAR GRAHAM D. 
Published: April 2006

SUMMARYThis paper relates the13C/12C ratio of C3plant material relative to that of source CO2to the N source for growth, the organic N content of the plant, and the extent of organic acid synthesis. The13C/12C ratio is quantified as Δ, defined as (δ13C substrate –δ13C product)/(1+δ13C product), where δ13C values of substrate or product (i.e. the samples) are defined as [13C/12C]sample]/[(13C/12C)standard]−1. The computation is performed by relating differences in plant composition as a function of N nutrition and acid synthesis to the fraction of plant C which is acquired via Rubisco and via other carboxylases. The fractional contribution of the different carboxylases to C gain is then related, using the known isotopic fractionations exhibited by these carboxylases, in a model to predict the final Δ of the plant (relative to atmospheric CO2). Application of this approach to a ‘typical’ C3land plant yields predictions of the decrease of Δ relative to a hypothetical case in which all C is fixed via Rubisco. The predicted decreases range from 0–24 %, for NH4+assimilation (which always occurs in the roots) to 2–80%, for NO3−assimilation in shoots with the organic acid salt which results from acid‐base balance, plus any additional organic acid salts plus free acids for a plant with a basal C:N molar ratio in organic material of 15. Intermediate values are predicted for symbiotic growth with N2, or where NO3−assimilation in root or shoot is accompanied by some acid‐base regulation via OH‐ loss to the root medium.Comparison with published data on the difference in Δ ofRicinus communiscultured with NH4+or NO3−shows that the measured influence of nitrogen source is in the right direction (NO3−grown plants with a smaller Δ, i.e. a larger deviation from the value predicted for the absence of non‐Rubisco carboxylations) to be explained by the observed difference in composition and hence fractional C contribution by the various carboxylases. However, the effect of N source on Δ is greater than that predicted by the model, i.e. a 2.1 % decrease as opposed to a 0.10 % decrease. It is likely that the major cause of the difference in δ13C of the plants grown on the two N sources is a change in the ratio of transport and biochemical conductances of leaf photosynthesis. Such a change is quantitatively consistent with the lower water use efficiency of NH4+‐grown plants.The predicted, and observed, changes in Δ as a function of N source are of the same magnitude as those found for C3terrestrial species grown at different temperatures or photon flux densities, or in environments yielding different water use efficiencies by changing root water supply relative to shoot evaporation potential. Variations in N source should be added to the factors which might alter δ of plants growing in the field.
Characteristics of pollen production in a population of New Zealand snow‐tussock grass (Chionochloa pallens Zotov)
Authors: MCKONE MARK J. 
Published: April 2006

SUMMARYIntraspecific variation in pollen production and pollen size were studied within a population of Chionochloa pallens, an alpine snow‐tussock grass of New Zealand. I sampled plants from two sites at the altitudinal extremes (1620 and 1070 m) of the distribution of C. pallens on Mt. Hutt, South Island. There was a highly skewed distribution of pollen production among plants; the largest 10% of plants produced over a third of the pollen. In contrast to some other species, pollen production in C. pallens can be accurately estimated by simple measures such as tussock area and number of flowering shoots. Other components of yield (number of spikelets per shoot, number of florets per spikelet, and average anther length) varied significantly among individuals, but these characteristics had a small impact on total pollen yield. There was continuous variation in pollen size among individuals; between the plants with the largest and the smallest pollen grains, there was a 21 % difference in pollen diameter and a 76% difference in pollen volume. Interplant differences in pollen size have been found in a number of plants, although the biological significance of this variation is unknown. There were few differences in pollen characteristics between sites. Plants at the low‐altitude site had slightly greater pollen yield because total plant size was greater.
The significance of changes in the red/far‐red ratio, associated with either neighbour plants or twilight, for tillering in Lolium multiflorum Lam.
Authors: CASAL J. J. , SANCHEZ R.A. , GIBSON DIANA 
Published: April 2006

SUMMARY Lolium multiflorum Lam. plants were used to investigate whether phytochrome‐mediated tillering responses, anticipatory to competition: (a), are potentially disturbed by the twilight drop in the red to far‐red ratio (R:FR) of sunlight (caused by atmospheric factors), and (b), occur in densely‐sown (> 280 plants m−2) grass canopies, where competition is quickly established.Isolated plants grown under sunlight received natural low R: FR during twilight, but supplementary R provided simultaneously did not increase tillering. When a wide range of R: FR was provided at the end of natural or fluorescent light photoperiods, tillering was reduced only by very low R: FR (lower than natural twilight R: FR). Leaf sheath length followed a similar pattern of response.Single plants were grown in pots placed at various densities. High densities reduced the R:FR at plant bases and the number of tillers per plant before changes in dry weight and leaf number were found.Both very low R:FR provided at the end of the photoperiod, and increasing plant densities, caused more erectophile shoots.In densely‐sown canopies of Lolium multiflorum both R:FR signals caused by neighbours, and tillering responses occur well before strong competition is established. Tillering is not obviously affected by the twilight drop in R: FR.
Daily and seasonal courses of leaf conductance and abscisic acid in the xylem sap of almond trees [Prunus dulcis (Miller) D. A. Webb] under desert conditions
Authors: WARTINGER A. , HEILMEIER H. , HARTUNG W. , SCHULZE E.‐D. 
Published: April 2006

SUMMARYIndividual 1‐ to 4‐year‐old almond trees [Prunus dulcis (Miller) D. A. Webb] were grown in lysimeters of different volumes, filled with loess. Once per year, at the beginning of each growing season, the lysimeters were watered to field capacity, and consequently each tree experienced a seasonal drought in relation to the amount of available water depending on soil volume and tree age. Measurements of leaf conductance were performed on youngest fully expanded, sun‐exposed leaves in climatized cuvettes. Leaf water potential was measured with a pressure chamber, which was also used for collecting xylem sap. Abscisic acid concentration of the xylem sap was determined with ELISA.There was no consistent diurnal relationship between abscisic acid concentration in xylem sap and leaf conductance. During a drying cycle, however, there was an inverse relationship between maximum leaf conductance and daily average abscisic acid concentration in xylem sap. With soil drying, the concentration of abscisic acid in xylem sap initially increased to a maximum in summer but decreased again towards autumn. Thus, during the first part of the drying cycle the predawn water potential of the leaf was significantly correlated with abscisic acid concentration in xylem sap. As predawn water potential becomes more negative during the first part of the drying cycle, the decline in maximum leaf conductance correlates with an increase in concentration of abscisic acid in xylem sap. With further decrease in predawn water potential towards the end of the drying cycle, the stomata remained closed even though there was a decreasing concentration of abscisic acid in the xylem sap.We conclude that the concentration of abscisic acid in xylem sap is not related to leaf conductance during the course of a day from end of May to September. However, during the course of a drying cycle the range of maximum leaf conductance seems to be dependent on the concentration of abscisic acid in xylem sap.
A comparison of maturation drying, germination, and desiccation tolerance between developing seeds of Acer pseudoplatanus L. and Acer platanoides L
Authors: HONG T. D. , ELLIS R. H. 
Published: April 2006

SUMMARYDifferences in maturation drying and desiccation tolerance during seed development were detected between the two contrasting Acer spp., Norway maple (Acer platanoides L.), which shows orthodox seed storage behaviour, and sycamore (A. pseudoplatanus L.), which shows recalcitrant seed storage behaviour. In both species, the onset of germinability (150 d tests at 5 °C) occurred after percentage seed moisture content had begun to decline, but before net loss in seed moisture. The onset of germinability in Norway maple occurred 4 wk before physiological maturity (i.e. 4 wk before the end of the increase in seed dry matter), whereas in sycamore it occurred some ten weeks before physiological maturity when the seeds were only 60 % filled. Seeds of Norway maple were able to tolerate enforced rapid desiccation to 10% moisture content (f. wt) at physiological maturity, when maturation‐drying had reduced seed moisture content to 54 %. Between 2 and 4 wk later seed moisture content rapidly declined naturally to 25 %, at which value the fruits were shed. In contrast, a constant rate of maturation‐drying was observed in sycamore. The seeds were shed at 58 % moisture content and, in almost all cases, the seeds were intolerant of rapid desiccation to c. 10 % moisture content throughout seed development. A very small proportion of sycamore seeds did survive rapid desiccation when harvested between 6 September and 4 October, but no seeds survived desiccation to 5 % moisture content or below. A comparison of the germination of sycamore seeds harvested on four dates and dried to various moisture contents showed that the seeds tolerated greater desiccation as they matured between 12 July and 20 September, but there was no further change thereafter. The results are therefore compatible with previous classifications of seed storage behaviour in each species, and with the view that the initial decline in seed moisture content stimulates the developmental switch which results in the onset of germinability in both orthodox and recalcitrant seeds.
Water relations, thallus structure and photosynthesis in Negev Desert lichens
Authors: PALMER ROBERT J. , FRIEDMANN E. IMRE 
Published: April 2006

SUMMARYThe role of lichen thallus structure in water relations and photosynthesis was studied in Ramalina maciformis (Del.) Bory and Teloschistes lacunosus (Rupr.) Sav. Water‐vapour adsorption and photosynthesis are dependent upon thallus integrity and are significantly lower in crushed thalli. Cultured phycobiont (Trebouxia sp.) cells are capable of photosynthesis over the same relative humidity range (> 80 % RH) as are intact lichens. Thus, water‐vapour adsorption by the thallus and physiological adaptation of the phycobiont contribute to the ability of these lichens to photosynthesize in an arid environment. Despite differences in their anatomical structure and water‐uptake characteristics, their CO2 incorporation is similar. The two lichens use liquid water differently and they occupy different niches.
Ecophysiology of microcolonial fungi and lichens on rocks in northeastern Oregon
Authors: PALMER F. E. , STALEY J. T. , RYAN B. 
Published: April 2006

SUMMARYIn this study of rocks in eastern Oregon, air and rock temperatures and moisture were monitored, along with the abundance and distribution of micro‐colonial fungi (MCF) and lichens, for 2 yr. Conditions were suitable for MCF growth during all but the winter months with the most favorable conditions occurring in spring and autumn. In these seasons moisture was frequent and the absorption of solar irradiation by rocks increased the surface temperatures considerably above the very cool air temperatures.Distributions of MCF and lichens were studied in detail on ten granite rocks at one site. While MCF were most numerous on southern rock exposures, this appeared to be because this exposure was least favorable for lichen growth. MCF appeared to precede lichens in colonizing recently fractured, exposed rock surfaces. The ability of the MCF to grow in the dark as well as the light may be an important factor favouring growth of MCF relative to lichens, especially in the summer when daytime air and rock temperatures were too high to permit growth. However, conditions on some areas of the rocks were especially favourable for lichen growth and in these places lichens effectively dominated the MCF for surface area. A list of lichen species observed at this and nearby locations is provided. 14CO2 release from [14C]acetate was used as a measure of MCF activity at 10–12 °C and 25 °C under different conditions of moisture. Moderate respiration was found at 10–12 °C and respiration occurred with a 2 h period of air drying. In contrast, MCF on rocks air dried for several weeks and subsequently dried for 18 h over H2SO4 did not become active during incubation for 2 h following wetting.
Effect of degree of soil disturbance on mycorrhizal colonization and phosphorus absorption by maize in growth chamber and field experiments
Authors: McGONIGLE T. P. , EVANS D. G. , MILLER M. H. 
Published: April 2006

SUMMARYPrior studies have established that phosphorus absorption by maize from undisturbed soil is greater than from soil which has been disturbed since the previous period of growth. Those experiments were conducted under controlled conditions and with only two disturbance treatments, namely disturbance of the soil by hand sufficient that it will pass a 5 mm sieve, and no disturbance at all. We present here two experiments in which additional treatments of intermediate degrees of disturbance are included.In a growth chamber experiment, cutting the soil into 1, 2 or 4 cm cubes reduced the phosphorus absorption and shoot dry matter, but the reduction was not as great as that after hand disturbance of the soil. In a field experiment, the phosphorus absorption and shoot dry matter found in a conventional tillage and no‐till treatments were less than in hand‐planted no‐till plots, but greater than with severe soil disturbance. In both experiments increases in shoot dry mass and shoot phosphorus concentration in the less disturbed treatments were not accompanied by an increase in mycorrhizal colonization. This is inconsistent with earlier studies in which colonization was greater in undisturbed soil.Since it has now been demonstrated that increased colonization is not a necessary component in the process whereby lack of disturbance results in improved plant performance, the role of mycorrhizas in this effect should be reconsidered. If mycorrhizas are important in this respect then this can only be by means of changes in the external mycelium. However, without experimental confirmation this interpretation is speculative.
Direct and indirect effects of VA mycorrhizal fungi and rhizosphere microorganisms on acquisition of mineral nutrients by maize (Zea maysL.) in a calcareous soil
Authors: KOTHARI S. K. , MARSCHNER H. , RÖMHELD V. 
Published: April 2006

SUMMARYMaize (Zea maysL.) was grown in a fertilized calcareous soil in pots which were separated by 30 μm nylon nets into three compartments, a central one for root growth and two outer ones for hyphal growth. The treatments comprised of sterilised soil, either inoculated with rhizosphere microorganisms together withGlomus mosseae(Nicol. & Gerd.) Gerdemann & Trappe, with rhizosphere microorganisms alone, or non‐inoculated (sterile control).In the mycorrhizal treatment concentrations of P and Zn were increased in shoot and roots, as was uptake of P and Zn per unit root dry weight or per unit root length. Copper concentration in roots of mycorrhizal plants, and total uptake and uptake per unit root dry weight or per unit root length of Cu was also increased. The higher acquisition of P, Zn and Cu in the mycorrhizal plants is ascribed to VA mycorrhizaper se(hyphal uptake and translocation to the host). Besides these direct effects, VA mycorrhizal fungi and rhizosphere microorganisms affected the acquisition of other nutrients mostly through alteration of root morphology. In both mycorrhizal and sterile treatments, the decreased concentrations of Ca and Si in the shoot but increased concentrations in the roots seem to be related to restricted apoplasmic solute transport across the endodermal barrier due to decreased number of lateral roots.The concentration of K in both shoot and roots, and Fe in shoot were lower in mycorrhizal plants due to reduced root length. Manganese concentration was also distinctly lower in both shoot and roots in mycorrhizal and sterile treatments, an effect which is attributed to the decrease in Mn reduction in the rhizosphere. Irrespective of nutrient, the uptake per unit root length was higher in mycorrhizal plants, probably due to hyphal contribution and increased supply of nutrients to the root surface by mass flow. Soil analysis indicates hyphal translocation of K but not Mg.The results demonstrate that effects of VA mycorrhizal infection on root morphology and rhizosphere microorganisms have to be considered in interpretations of mycorrhizal effects on mineral nutrient acquisition.
Field use of 32P to measure phosphate uptake by birch mycorrhizas
Authors: DIGHTON JOHN , MASON PHILIP A. , POSKITT JAN M. 
Published: April 2006

SUMMARY 32P was used to determine phosphorus uptake by different mycorrhizas of birch in the field. Time of year and location of the application of 32P were the dominant variables influencing uptake into the canopy. There was evidence of differential uptake by the three mycorrhizal types selected. Where Hebeloma mycorrhizas were more frequent, a significantly greater rate of phosphorus uptake per unit leaf weight occurred than where Laccaria or Lactarius were more frequent. The method shows potential for field evaluation of efficiency of nutrient uptake by mycorrhizas, although a number of factors need to be taken into account in determining uptake. In locating areas for 32P injection, it was found that the distribution of mycorrhizal types on roots did not always reflect the distribution of the corresponding fruitbodies.
Root colonization by four closely related genotypes of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton – comparative studies using electron microscopy
Authors: WONG KEN K. Y. , MONTPETIT DIANE , PICHÉ YVES , LEI JIYU 
Published: April 2006

SUMMARYElectron microscopy was used to compare four closely related genotypes of Laccaria bicolor (Maire) Orton (the two sib‐monokaryons m4 and m10 having been crossed twice to give the two dikaryons d1 and d2) which showed substantially different ectomycorrhizal structures on roots of Pinus banksiana Lamb. All four strains incorporated into mucilage on long roots but only the most compatible strain dl formed thick mantles with closely packed hyphae at surfaces of both long and short roots. At the inner Hartig net found in short roots, hyphae of dl showed a highly convoluted morphology whereas other strains formed roundish hyphal cross sections. The rare Hartig nets formed by m4 occasionally showed highly distorted root cell walls adjacent to hyphae. The occurrence of extracellular glycofibrils during initial hypha‐root contact was rare for all four fungal strains whereas substantial tannin‐like deposits were frequently found in root cortical cells.
Comparative ozone sensitivity of old and modern Greek cultivars of spring wheat
Authors: BARNES J. D. , VELISSARIOU D. , DAVISON A. W. , HOLEVAS C. D. 
Published: April 2006

SUMMARYTen cultivars of spring wheat, bred and introduced in Greece between 1932 and 1980, were exposed to ozone (180 μg m−3) or to charcoal‐filtered air (< 4 μg O3 m−3) for 21 d. Ozone sensitivity was assessed by recording the extent of visible injury, effects on mean relative growth rate (R̄) and changes in fast fluorescence kinetics. Ozone significantly (P < 0.01) depressed the mean relative growth rate (R̄) and there were significant (P < 0.01) differences in response between cultivars. Moreover, there was a highly significant (P < 0.002) negative relationship between the reduction in R̄ and the year of introduction; the more modern the cultivar the greater its sensitivity to ozone. Ozone reduced root growth relative to the shoot, but the effect varied with cultivar. Although all varieties developed typical visible symptoms of ozone damage, there was little relationship between the extent of this damage and effects on growth, or changes in fluorescence.After 18 d fumigation there were significant (P < 0.001) changes in fast fluorescence kinetics in leaves that had not developed visible symptoms of injury. The ozone‐induced reduction in t1/2 was closely related (r= 0.92, P < 0.002) to the depression in R̄, indicating that a fluorescence assay based upon changes in the rise in fluorescence between Fo and Fm can be used to distinguish between genotypes of contrasting ozone sensitivity. It is concluded from this study that inadvertent selection by plant breeders may have resulted in modern varieties of some crop plants that are considerably more sensitive to ozone than their predecessors. Possible explanations for this phenomenon are discussed.
Rapid‐cycling Brassica species: anther culture potential of B. campestris L. and B. napus L.
Authors: ASLAM FERRE N. , MACDONALD MARY V. , INGRAM D. S. 
Published: April 2006

summaryA study was made of the production of embryoids by cultured anthers of rapid‐cycling populations of Brassica campestris L. and Brassica napus L. In the case of B. campestris, best results were obtained when anther donors were grown at 24 °C with continuous light; anthers were excised from 1.6–2.00 mm buds with the pollen at the mid‐uninucleate stage of development and were cultured on a solidifed Brassica anther culture medium of Keller & Armstrong (K), and when incubation was at 35 °C for 1 day, followed by 30 °C for 1 day and then continuous incubation at 25 °C. The response to anther culture of B. napus was generally very poor compared with that of B. campestris but the best results were obtained when anther donors were grown at 18 °C with continuous light; anthers were excised from 2.1–2.5 mm long buds with the pollen at the mid‐uninucleate stage of development, were cultured on a liquid formulation of K medium, and incubation was at 35 °C for 1 day, followed by 30 °C for 6 days and then continuous incubation at 25 °C.
The discrete root epidermis of floating plants
Authors: CLOWES F. A. L. 
Published: April 2006

summaryThe reason why roots of some floating plants have a discrete epidermal meristem was investigated by comparing rates of anticlinal and periclinal division in shells of tissue during early development of lateral primordia of Pistia stratiotes L., which has such an epidermis, with those of Eichhornia crassipes (C. F. P. Martius) Solms‐Laub., which has not. The main factor involved is the timing and extent of the expansion of the primordium in relation to the availability of cells that can switch their divisions to anticlinal planes conformably with the growth of contiguous cells. The greater growth rate of the primordia of Pistia at the critical early stage forces the proximal cells of the endodermis‐derived tissue to divide only anticlinally immediately after their initiation by periclinal divisions and until the pole of the root forms a quiescent centre. It thus creates a monostromatic shell between the root cap and the pericycle‐derived tissue.