bluuebunny/crossref_metadata_2025_split huggingface dataset:
Water relations and growth of tomato fruit pericarp tissue
Authors: GRANGE R. I. 
Published: April 2006

ABSTRACTThe water relations of young tomato fruit pericarp tissue were examined and related to tissue expansion. The relationship between bulk turgor pressure and tissue expansion (as change in fresh mass or length of tissue) was determined in slices of pericarp cut from young, growing fruit by incubation in different osmotic concentrations of polyethylene glycol 6000 or mannitol. The bulk turgor of this tissue was low (about 0.2 MPa), even in fruit from plants that were otherwise fully turgid, whether measured psychrometrically or by length change in osmotic solutions. The rate of tissue growth at maximum turgor was less than that at moderate turgor unless calcium was added to the incubation medium. However, added calcium also decreased the rate of growth at lower turgor pressures. Yield turgor was < 0.1 MPa, but it was increased by the addition of calcium ions. Electrolyte leakage from tissue was greatest at maximum turgor pressure but was decreased by the addition of calcium ions or osmoticum. Tissue growth was unaffected by a range of plant growth regulators (IAA, abscisic acid, benzyladenine and GA3) but was inhibited, particularly at high turgor, by low concentrations of malic or citric acid. The low turgor pressure of pericarp tissue could be due to the presence of apoplastic solutes within the pericarp, and evidence for this is discussed. Thus, fruit tissue may be able to maintain optimal expansion rates only at moderate turgor and low calcium concentration.
Proton flux measurements from tissues in buffered solution
Authors: ARIF I. , NEWMAN I. A. , KEENLYSIDE N. 
Published: April 2006

ABSTRACTProton movement across plant cell membranes is part of many important physiological processes. The net proton flux to or from tissues can be determined non‐invasively by measuring the proton electrochemical potential gradient in the adjacent solution. In buffered solution, some of the protons crossing the tissue boundary diffuse as proto‐nated buffer whose flux is not included in the flux calculated from the proton (hydrogen ion) electrochemical gradient. In this theoretical paper, it is shown how experimenters can calculate the protonated buffer flux from the measured proton flux in solution. The ratio of these two components of total proton flux depends on the pH of the solution and on the concentration and pK of the buffer. For a given concentration of a buffer which has a single pK, the flux ratio rises with pH when the solution pH is lower than the buffer pK. The slope is about 2 on a log10 scale. As the pH increases above the pK, the flux ratio levels off to approach its maximum. With mixed buffers, or one having two or more pK values, the flux ratios are additive: each buffer acts independently based on its concentration and its pK value. Unbuffered solutions always have the buffering effects of water itself and also of carbonates due to carbon dioxide dissolved from the atmosphere. In unbuffered solutions at pH 6, the flux carried by water and carbonate is about 1 % of the measured proton flux. This validates measurements of proton flux from tissues, made by a number of workers, in unbuffered solutions below pH 6.
Effects of aluminium on nitrate uptake and assimilation
Authors: RUFTY T. W. , MacKOWN C. T. , LAZOF D. B. , CARTER T. E. 
Published: April 2006

ABSTRACTA study was conducted to examine the hypothesis that the effects of external Al on NO3− uptake and assimilation depend upon the concentration of Al present. Young soybean seedlings [Glycine max (L.) Merrill, cv. Essex], growing under moderate acidity stress at pH 4‐2, were exposed to a range of {A13+} in solution for 3d, and to labelled 99 atom %15NO3− during the final hour of Al exposure. Uptake of 15NO3−g−1 root dry weight was increased by about 28% in the presence of Al at {A13+} below 10 mmolm−3, and NO3− uptake was decreased by about 12% when the {A13+} increased to 44mmoln−3. The stimulation phase closely paralleled stimulation of root elongation. At higher {A13+}, the inhibition of root elongation was much more severe than that of NO3− uptake. There was no indication of a separate effect of Al on root 15NO3− reduction in situ, as the accumulation of reduced 15N in the root remained a similar percentage of 15NO3− uptake at all {A13+}. At higher {A13+}, the atom %15N enrichment of the insoluble reduced‐N (protein) fraction of root tips increased. This suggests that the Al inhibition of root elongation did not result from disruption of the N supply to the root apex.
The impact of mycorrhizal colonization upon nitrogen source utilization and metabolism in seedlings of Eucalyptus grandis Hill ex Maiden and Eucalyptus maculata Hook
Authors: TURNBULL M. H. , GOODALL R. , STEWART G. R. 
Published: April 2006

ABSTRACTAnalysis of soil solution from forest sites dominated by Eucalyptus grandis and Eucalyptus maculata indicates that soluble forms of organic nitrogen (amino acids and protein) are present in concentrations similar to those of mineral nitrogen (nitrate and ammonium). Experiments were conducted to determine the extent to which mycorrhizal associations might broaden nitrogen source utilization in Eucalyptus seedlings to include organic nitrogen. In isolation, species of ectomycorrhizal fungi from northern Australia show varying abilities to utilize mineral and organic forms of nitrogen as sole sources. Pisolithus sp. displayed strongest growth on NH4+, glutamine and asparagine, but grew poorly on protein, while Amanita sp. grew well both on mineral sources and on a range of organic sources (e.g. arginine, asparagine, glutamine and protein). In sterile culture, non‐mycorrhizal seedlings of Eucalyptus grandis and Eucalyptus maculata grew well on mineral sources of nitrogen, but showed no ability to grow on sources of organic nitrogen other than glutamine. In contrast, mycorrhizal seedlings grew well on a range of organic nitrogen sources. These observations indicate that mycorrhizal associations confer on species of Eucalyptus the ability to broaden their resource base substantially with respect to nitrogen. This ability to utilize organic nitrogen was not directly related to that of the fungal symbiont in isolation. Seedlings mycorrhizal with Pisolithus sp. were able to assimilate sources of nitrogen (in particular histidine and protein) on which the fungus in pure culture appeared to grow weakly. Experiments in which plants were fed 15N‐labelled ammonium were undertaken in order to investigate the influence of mycorrhizal colonization on the pathway of nitrogen metabolism. In roots and shoots of all seedlings, 15N was incorporated into the amide group of glutamine, and label was also found in the amino groups of glutamine, glutamic acid, γ‐aminobutyric acid and alanine. Mycorrhizal colonization appeared to have no effect on the assimilation pathway and metabolism of [15N]H4+; labelling data were consistent with the operation of the glutamate synthase cycle in plants infected with either Pisolithus sp. (which in isolation assimilates via the glutamate synthase cycle) or Elaphomyces sp. (which assimilates via glutamate dehydrogenase). It is likely that the control of carbon supply to the mycorrhizal fungus from the host may have a profound effect on both the assimilatory pathway and the range of nitrogen sources that can be utilized by the association.
Evidence that photoperiodic, dark time measurement in Pharbitis nil involves a circadian rather than a semidian rhythm
Authors: LUMSDEN P. J. , YOUNGS J. A. , THOMAS B. , VINCE‐PRUE D. 
Published: April 2006

ABSTRACTExperiments were carried out to determine whether a semidian (12 h) rhythm in flowering response operates in Pharbitis nil as the basis for photoperiodic time measurement. The effect of 5 min far‐red light followed by 85 min dark (FRD) given 4, 8,14 and 22 h before the end of a 48 h photoperiod on night‐break timing and critical night length was determined. When given 4 h before the end of a 48 h photoperiod, an interruption with FRD advanced the phase of the circadian rhythm in the night‐break inhibition of flowering. In contrast, earlier interruptions of the photoperiod had no effect on the phase of the rhythm. The critical night length was modified by FRD given 4 h (shortened) or 8 h (lengthened) before the end of the photo‐period; when given at other times FRD did not alter the critical night length. The results are discussed in relation to the basis for photoperiodic timekeeping, with particular reference to suggestions for the involvement of a semidian rhythm. A circadian model based on the concept of limit cycles is described.
Diurnal variations in growth rate and growth substrate levels of spinach (Spinacia oleracea L.) under nitrogen‐limiting conditions
Authors: BUYSSE J. , MERCKX R. 
Published: April 2006

ABSTRACTSpinach plants were grown in hydroponic culture provided with variable limiting amounts of N. During a complete diurnal cycle, growth of the root and shoot parts, as well as levels of soluble and insoluble sugars and of free amino acids, were monitored. No clear relationship could be detected between the level of N feeding and the levels of free sugars and amino acids. Analysis of variance revealed that the variances in the relative growth rates of plant root and shoot could be correlated with the levels of sugars and amino acids. Root amino acid concentration could be correlated with shoot amino acid concentration and root sugar concentration. No relationship was found between the variances in root and shoot free sugar concentrations.
Sodium transport measured in plasma membrane vesicles isolated from wheat genotypes with differing K+/Na+ discrimination traits
Authors: ALLEN G. J. , WYN JONES R. G. , LEIGH R. A. 
Published: April 2006

ABSTRACTRight‐side‐out plasma membrane vesicles were isolated from wheat roots using an aqueous polymer two‐phase system. The purity and orientation of the vesicles were confirmed by marker enzyme analysis. Membrane potential (Ψ)‐dependent 22Na+ influx and sodium/proton (Na+/ H+) antiport‐mediated efflux across the plasma membrane were studied using these vesicles. Membrane potentials were imposed on the vesicles using either K+ gradients in the presence of valinomycin or H+ gradients. The ΔΨ was quantified by the uptake of the lipophilic cation tetraphenylphosphonium. Uptake of Na+ into the vesicles was stimulated by a negative ΔΨ and had a Km for extrav‐esicular Na+ of 34.8 ± 5.9 mol m3. The ΔΨ‐dependent uptake of Na+ was similar in vesicles from roots of hexaploid (cv. Troy) and tetraploid (cv. Langdon) wheat differing in a K+/Na+ discrimination trait, and was also unaffected by growth in 50 mol m−3 NaCl. Inhibition of ΔΨ‐dependent Na+ uptake by Ca2+ was greater in the hexaploid than in the tetraploid.Sodium/proton antiport was measured as Na+‐dependent, amiloride‐inhibited pH gradient formation in the vesicles. Acidification of the vesicle interior was measured by the uptake of 14C‐methylamine. The Na+/H+ antiport had a Km, for intravesicular Na+ of between 13 and 19 mol m−3. In the hexaploid, Na+/H+ antiport activity was greater when roots were grown in the presence of 50 mol m−3NaCl, and was also greater than the activity in salt‐grown tetraploid wheat roots. Antiport activity was not increased in a Langdon 4D chromosome substitution line which carries a trait for K+/Na+ discrimination. It is concluded that neither of the transport processes measured is responsible for the Na+/K+ discrimination trait located on the 4D chromosome of wheat.
The xanthophyll cycle and sustained thermal energy dissipation activity in Vinca minor and Euonymus kiautschovicus in winter
Authors: ADAMS W. W. , DEMMIG‐ADAMS B. 
Published: April 2006

ABSTRACTThe influence of low temperature on the operation of the xanthophyll cycle and energy dissipation activity, as ascertained through measurements of chlorophyll fluorescence, was examined in two broad‐leaved evergreen species, Vinca minor L. and Euonymus kiautschovicus Loessner. In leaves examined under laboratory conditions, energy dissipation activity developed more slowly at lower leaf temperatures, but the final, steady‐state level of such activity was greater at lower temperatures where the rate of energy utilization (through photosynthetic electron transport) was much lower. The rate at which energy dissipation activity increased was similar to that of the de‐epoxidation of violaxanthin to antheraxanthin and zea‐xanthin at different temperatures. However, leaves in the field examined prior to sunrise on mornings following cold days and nights exhibited a retention of antheraxanthin and zeaxanthin that was associated with sustained decreases in photosystem II efficiency. We therefore suggest that this phenomenon of ‘photoinhibition’ in response to light and cold temperatures during the winter results from sustained photoprotective thermal energy dissipation associated with the xanthophyll cycle. Such retention of the de‐epoxidized components of the xanthophyll cycle responded to day‐to‐day changes in temperature, being greatest on the coldest mornings (when photoprotective energy dissipation might be most required) and less on warmer mornings when photosynthesis could presumably proceed at higher rates.
The role of calcium in turgor regulation in Chara longifolia
Authors: BISSON M. A. , KIEGLE E. , BLACK D. , KIYOSAWA K. , GERBER N. 
Published: April 2006

ABSTRACTThe salt‐tolerant alga Chara longifolia (Robinson) is capable of regulating its turgor in response to hypotonic stress resulting from a decrease in the osmotic pressure of the medium. This regulatory process takes only 40 min in small cells (length ≤ 10 mm), but requires 3d in large cells (length ≥30mm). Turgor regulation in small cells is comprised of two phases, a fast phase reducing the increased turgor by about 25% in the First 5 min, and a second phase reducing the turgor to near the original value within 40 min. The second phase is inhibited by reducing the concentration of Ca2+ in the external medium from 4.6 to 0.01 mol m−3; the first phase is less affected by the reduction of Ca2+. In the first 5 min of stress, the membrane depolarizes in a voltage‐dependent fashion, electrical conductance of the membrane increases transiently and cytoplasmic streaming is inhibited. When the external Ca2+ concentration is lowered, conductance does not increase and streaming continues unaffected. In a low ionic strength medium, Ca2+ is not required in the medium for turgor regulation.To test the hypothesis that there is increased Ca2+ entry from the medium during turgor regulation, we measured the influx of 45Ca2+ into the cell. We found an increased influx of Ca2+, from 18 to 36 nmol m−2 s−1 during the first 30 to 90 s following osmotic stress. This increase was evident only in cells below about 7 mm in length, and was more marked in smaller cells.
Effects of soil fertility and mycorrhizal infection on pollen production and pollen grain size of Cucurbita pepo (Cucurbitaceae)
Authors: LAU T.‐C. , LU X. , KOIDE R. T. , STEPHENSON A. G. 
Published: April 2006

ABSTRACTThe effects of soil fertility (two levels of soil nitrogen and two levels of soil phosphorus) and mycorrhizal infection on pollen production and pollen grain size were studied in two cultivars of the common zucchini (Cucurbita pepo). Overall, soil fertility and mycorrhizal infection had significant effects on traits affecting the male function of plants (staminate flower production, pollen production per flower and pollen grain size). There were also differences between the cultivars for these male traits in all three experiments. In addition, pollen grain size decreased toward the end of the growing season. In the mycorrhiza experiment, both phosphate concentration per pollen grain and total phosphate content per anther were greater but not significantly greater in the mycorrhizal plants than in the non‐mycorrhizal plants. A significant negative relationship between pollen production and pollen grain size was found in the mycorrhiza and soil phosphorus experiments, indicating that there was a trade‐off between pollen production and pollen size. This study is the first to show that mycorrhizal infection has an effect on male function (pollen production and size) in addition to the well‐documented effects on female function (fruit/seed production and size).
The mechanism of water‐stress‐induced embolism in two species of chaparral shrubs
Authors: JARBEAU J. A. , EWERS F. W. , DAVIS S. D. 
Published: April 2006

ABSTRACTThe mechanism of water‐stress‐induced embolism of xylem was investigated in Malosma laurina and Heteromeles arbutifolia, two chaparral shrub species of southern California. We tested the hypothesis that the primary cause of xylem dysfunction in these species during dehydration was the pulling of air through the pores in the cell walls of vessels (pores in pit membranes) as a result of high tensions on xylem water. First, we constructed vulnerability‐to‐embolism curves for (i) excised branches that were increasingly dehydrated in the laboratory and (ii) hydrated branches exposed to increasing levels of external air pressure. Branches of M. laurina that were dehydrated became 50% embolized at a xylem pressure potential of ‐1.6 MPa, which is equal in magnitude but opposite in sign to the +1.6 MPa of external air pressure that caused 50% embolism in hydrated stems. Dehydrated and pressurized branches of H. arbutifolia reached a 50% level of embolism at ‐6.0 and +6.4 MPa, respectively. Secondly, polystyrene spheres ranging in diameter from 20 to 149 nm were perfused through hydrated stem segments to estimate the pore size in the vessel cell walls (pit membranes) of the two species. A 50% or greater reduction in hydraulic conductivity occurred in M. laurina at perfusions of 30, 42, 64 and 82 nm spheres and in H. arbutifolia at perfusions of 20 and 30 nm spheres. Application of the capillary equation to these pore diameters predicted 50% embolism at xylem tensions of ‐2.2 MPa for M. laurina and ‐6.7 MPa for H. arbutifolia, which are within 0.7 MPa of the actual values. Our results suggest that the size of pores in pit membranes may be a factor in determining both xylem efficiency and vulnerability to embolism in some chaparral species. H. arbutifolia, with smaller pores and narrower vessels, withstands lower water potentials but has lower transport efficiency. M. laurina, with wider pores and wider vessels, has a greater transport efficiency but requires a deeper root system to help avoid catastro‐phically low water potentials.
Ethylene and carbon dioxide: regulation of oat mesocotyl growth
Authors: NISHIZAWA T. , SUGE H. 
Published: April 2006

ABSTRACTEither ethylene or carbon dioxide stimulated the growth of oat mesocotyls in darkness, although the effect was much greater for carbon dioxide. Maximum elongation was obtained in the presence of both gases. Ethylene also induced lateral expansion of the mesocotyl: the volume of the mesocotyl was increased more in air with added ethylene than in air depleted of ethylene. Ethylene also stimulated mesocotyl growth under red light. Gibberellin only slightly increased mesocotyl length under red light and acted cooperatively with ethylene in the promotion of growth. The oat mesocotyl is a unique organ in terrestrial plants because ethylene simultaneously stimulates not only longitudinal growth but also lateral expansion. The ecological significance of oat mesocotyl growth in relation to the response to ethylene and carbon dioxide is discussed.
Phenotypic plasticity of the phenology of seven European tree species in relation to climatic warming
Authors: KRAMER K. 
Published: April 2006

ABSTRACTTo evaluate the potential responses of individual trees to climatic warming, phenological observations of clones of Larix decidua (Mill.), Betula pubescens (Ehrh.), Tilia cor‐data (Mill.), Populus canescens (Ait.), Quercus robur (L.), Fagus sylvatica (L.) and Picea abies (L.) relocated over a large latitudinal range in Europe were analysed. The magnitude of the response of the clone was compared to that of genetically different trees of the same species in part of the latitudinal range, which were assumed to have adapted to their local climates. It was found that the responses of the date of leaf unfolding and the date of leaf fall in the clones to temperature were similar in magnitude to those in the genetically different trees. This demonstrates that trees possess considerable plasticity and are able to respond phenotypically to a major change in their local climate.For the clones of Larix decidua and Quercus robur the duration of the growing season may decrease with increasing temperature, because leaf fall is advanced more than leaf unfolding. In Betula pubescens and Populus canescens, leaf unfolding and leaf fall are advanced equally, whereas in Tilia cordata and Fagus sylvatica the date of leaf fall seems to be unaltered but the date of leaf unfolding advances with increasing temperature. These differences in the duration of the growing season at increased temperature may alter the competitive balance between the species.Descriptive dynamic models showed that most of the variance in the date of leaf unfolding can be accounted for by temperature. However, a generally applicable model of leaf fall based on temperature and/or photoperiod could not improved the null model, i.e. the mean date of leaf fall, because of variability in other environmental factors.The lowest temperatures around the dates of leaf unfolding and leaf fall differed among the clones. The hypothesis that the survival of the clones is curtailed by spring frosts was supported. Thus, these lowest temper‐tures around leaf unfolding may represent thresholds below which the species cannot survive. It is argued that these thresholds may be a particularly sensitive means to evaluate the impact of climatic warming on the geographical distribution of tree species.
The effects of SO2 and O3 on the foliar nutrition of Scots pine, Norway spruce and Sitka spruce in the Liphook open‐air fumigation experiment
Authors: SHAW P. J. A. , McLEOD A. R. 
Published: April 2006

ABSTRACTFoliar elements were analysed in Scots pine, Sitka spruce and Norway spruce over a 6 year period before and during continuous exposure to SO2 and O3 in an open‐air fumigation experiment. Sulphur dioxide treatment elevated foliar sulphur concentration in all species, and there were increases in foliar nitrogen in the two spruce species but not in pine. The concentrations of cations were frequently increased by SO2 treatment, but there was no correlation between the sulphur concentration of needles and their total cation charge. SO2‐related elevations of foliar magnesium were correlated with the concentration of this element in soil solution, but the mechanism by which other cations were enhanced remains unclear. The only consistent effects on nutrient ratios were for SO2 treatments to increase sulphur/cation ratios.