bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined Transcript and Metabolite Profiling of Arabidopsis Leaves Reveals Fundamental Effects of the Thiol-Disulfide Status on Plant Metabolism
Authors: Kolbe Anna , Oliver Sandra N. , Fernie Alisdair R. , Stitt Mark , van Dongen Joost T. , Geigenberger Peter
Published: April 2006

In this study, we used gas chromatography-mass spectrometry analysis in combination with flux analysis and the Affymetrix ATH1 GeneChip to survey the metabolome and transcriptome of Arabidopsis (Arabidopsis thaliana) leaves in response to manipulation of the thiol-disulfide status. Feeding low concentrations of the sulfhydryl reagent dithiothreitol for 1 h at the end of the dark period led to posttranslational redox activation of ADP-glucose pyrophosphorylase and major alterations in leaf carbon partitioning, including an increased flux into major respiratory pathways, starch, cell wall, and amino acid synthesis, and a reduced flux to sucrose. This was accompanied by a decrease in the levels of hexose phosphates, while metabolites in the second half of the tricarboxylic acid cycle and various amino acids increased, indicating a stimulation of anaplerotic fluxes reliant on α-ketoglutarate. There was also an increase in shikimate as a precursor of secondary plant products and marked changes in the levels of the minor sugars involved in ascorbate synthesis and cell wall metabolism. Transcript profiling revealed a relatively small number of changes in the levels of transcripts coding for components of redox regulation, transport processes, and cell wall, protein, and amino acid metabolism, while there were no major alterations in transcript levels coding for enzymes involved in central metabolic pathways. These results provide a global picture of the effect of redox and reveal the utility of transcript and metabolite profiling as systemic strategies to uncover the occurrence of redox modulation in vivo.
Gene Expression Programs during Shoot, Root, and Callus Development in Arabidopsis Tissue Culture
Authors: Che Ping , Lall Sonia , Nettleton Dan , Howell Stephen H.
Published: April 2006

Shoots can be regenerated from Arabidopsis (Arabidopsisthaliana) root explants in tissue culture through a two-step process requiring preincubation on an auxin-rich callus induction medium. Regenerating tissues can be directed along different developmental pathways leading to the formation of shoots, new roots, or callus by transferring to the appropriate organ induction medium. Using gene-profiling methods, we identified groups of genes that serve as molecular signatures of the different developmental processes, i.e. genes that were specifically up- or down-regulated on one developmental pathway, but not on others. One transcription factor gene that was up-regulated during early shoot development was RAP2.6L (At5g13330), a member of the ERF (ethylene response factor) subfamily B-4 of the ERF/APETALA2 transcription factor gene family. RAP2.6L functions in shoot regeneration because T-DNA knockdown mutations in the gene reduced the efficiency of shoot formation in tissue culture, but not normal embryo or seedling development. RAP2.6L promoter:β-glucuronidase fusions demonstrated that the up-regulation of the gene during shoot regeneration was, at least in part, transcriptionally controlled. The promoter:β-glucuronidase fusions also demonstrated that RAP2.6L expression was localized to the shoot and emerging leaves, but expression declined in the leaf lamina as leaves expanded. T-DNA knockdown mutations in RAP2.6L reduced the expression of many genes that are normally up-regulated during shoot development including CUP-SHAPED COTYLEDON2 that is involved in shoot meristem specification. Thus, RAP2.6L appears to be part of a network involved in regulating the expression of many other genes in shoot regeneration.
Nitrogen nutrition of seedling grain legumes: some taxonomic, morphological and physiological constraints
Authors: SPRENT J. I. , THOMAS R. J.
Published: April 2006

Abstract The growth of young plants of the epigeal species Phaseolus vulgaris and Glycine max is compared with that of the hypogeal species Pisum sativum and Vicia faba, with particular reference to synchronization between the exhuastion of seed reserves of N and the availability of fixed N. It is argued that the N stress symptoms which occur when these two processes are not synchronized are more common and obvious in Phaseolus or Glycine than in Pisum or Vicia. This is primarily because in these species (a) the first fixed N is used for nodule growth rather than being exported to the shoot system and (b) the first foliage leaves have a much greater area and contain a larger proportion of N reserves from the seed.

It is further suggested that Phaseolus and Glycine may show the greater response to nitrogen fertilizer applied at sowing since (a) most of the applied nitrate is passed directly to the shoots (rather than being reduced in the roots as in Pisum or Vicia) and (b) in addition to being used for growth (following reduction), it may also be used prior to reduction as part of the osmotic force driving cell expansion.
Fluorescence microscopy of the endomembrane system of living plant cells
Authors: HARRIS N. , GATES P.
Published: April 2006

Abstract The fluorochrome Auramine O has been evaluated as a fluorescent probe for components of the endomembrane system of living plant cells. At 0.001% w/v the compound did not inhibit seedling growth or cytoplasmic streaming but stained the nuclear envelope, endoplasmic reticulum and Golgi apparatus. The three‐dimensional, structural interrelationships of these organelles in living tissues could be resolved after minimal tissue preparation. The method is also a valuable control treatment for use in conjunction with electron microscope fixation procedures. It provides a rapid means of examining dynamic changes in the endomembrane system associated with cell development and differentiation and could have application in monitoring the effects of applied physiological or chemical stress.
Responses of apple leaf stomata to environmental factors
Authors: WARRIT B. , LANDSBERG J. J. , THORPE M. R.
Published: April 2006

Abstract. Stomatal conductances (gs) were measured on the leaves of 3–4 year old Golden Delicious trees and of seedlings of two other cultivars. Measurements were made on container grown trees in the field with a diffusion porometer in 1975 and 1976, and in controlled conditions in a leaf chamber in the laboratory in 1976. Stomatal densities in the Golden Delicious leaves were assessed from scanning electron micrographs. Stomatal density on extension shoot leaves was higher than on other leaf types after June.

The response to irradiance shown by both the porometer and the leaf chamber results could be described by a rectangular hyperbola:
image

where gmax is maximum conductance and β indicates the sensitivity of gs to photon influx density (Qp). The values of β were in the range 60–90 μmol m−2 s−1.

There was no evidence that apple stomata are sensitive to temperature per se, but gs was reduced by increasing leaf to air vapour pressure deficits (D). There was a linear relationship between gs and D which was not attributable to feed‐back to leaf water potential (ψL) as the latter did not affect gs until a threshold of about −2.0 to −2.5 MPa was reached. Conductance generally declined with increasing ambient CO2 concentration.
Stomatal response to humidity: implications for transpiration
Authors: LANDSBERG J. J. , BUTLER D. R.
Published: April 2006

Abstract.Transpiration rates from apple leaves are analysed in terms of the ratio of latent heat flux (λE) to leaf net radiation (Q1) and the climatological resistance (ri). Increases in stomatal resistance with increasing leaf to air vapour pressure gradient (D), described by an empirical model, are incorporated in the analysis. This humidity effect causes the proportion of energy dissipated as latent heat to fall asQ1increases, so that leaf transpiration rates in high energy environments are likely to be similar to those in lower energy environments. Boundary layer resistance (ra) exerts an increasingly important effect on transpiration rates asQ1increases. At constantQ1stomatal closure in response to increasingDresults in very small changes in leaf temperature (T1) across a wide range of ambient vapour pressure deficits (δe);rais then the major factor determiningT1. The implications of these results are discussed.
The cytological effects of the gametocides Ethrel and RH‐531 on microsporogenesis in barley (Hordeum vulgare L)
Authors: COLHOUN CHARLES W. , STEER MARTIN W.
Published: April 2006

Abstract. Barley plants (Hordeum vulgare L. cv. Midas) raised under controlled environmental conditions were sprayed with either of the gametocides Ethrel and RH‐531. At various times after spraying the anthers were fixed for light and electron microscopy. Abortion of sporogenous cells occurred in plants sprayed at both pre‐ and post‐meiotic stages of microsporogenesis. In contrast, cells of the tapetum were insensitive to the immediate effects of gametocides. The cytological effects of the gametocides are similar to those induced by male sterile genes in a variety of plants. These range from the induction of additional mitotic divisions in the pollen mother cells to exine malformations on developing microspores. These observations are discussed in terms of the control mechanisms operating during microsporogenesis.
The uptake and release of water vapour by the foam seal of a diffusion porometer as a source of bias
Authors: HACK H. R. B.
Published: April 2006

Abstract. The apparent resistance to diffusion of water vapour presented by a set of holes in a calibration plate when measured by a commercial porometer depended on materials previously measured in the sensor head of the instrument. The data reported show the variation in apparent resistance of a set of holes with a specified value of 13.7 s cm−1 after a leaf of small resistance, a set of holes with a specified resistance of 3.75 s cm−1, or a hydrophobic membrane had been in the sensor head and the effect of covering the foam seal around the mouth of the cup with aluminium foil. It was concluded that the results were profoundly affected by the history of water vapour accumulation and release from the foam seal which could give rise to biased readings both during calibration and in measurements of leaf resistance and might also explain much of the scatter when calibration data obtained at different times were pooled for the calculation of a calibration equation. Reliable estimates of resistance over the effective range of the instrument cannot be expected unless this transfer of water vapour between the seal and the cup is prevented.
Copper tolerance in the green alga, Chlorella vulgaris
Authors: BUTLER MICHAEL , HASKEW ANTHONY E. J. , YOUNG MARSALI M.
Published: April 2006

Abstract. The effect of sub‐lethal concentrations of copper upon tolerant and non‐tolerant strains of Chlorella vulgaris was investigated. Copper concentrations of 0.2 and 0.4 mg dm−3 increased the lag phase of both strains, the effect being greater in the non‐tolerant strain. No difference was observed in the toxicity of copper to the photosynthetic rates of the isolated chloroplasts of either strain. However, significant differences were shown at the whole cell level.

Lower copper uptake was shown by the tolerant cells. In both strains initial uptake of copper was followed by a phase of desorption before cell division occurred. In cultures of both strains the concentration of ionic copper was decreased by complexation with extracellular organic material. Over a 14 day growth period more organic material was produced by the tolerant cells. The organic material produced by the tolerant cell formed organo‐copper complexes which had a higher conditional stability constant.

It is proposed that the cell wall acts as a barrier to copper in the tolerant cells and prevents copper from affecting cell metabolism. Organo‐copper complexation occurs at this barrier and this complex is then released into the medium.
Gravity induces fast electrical field change in soybean hypocotyls
Authors: TANADA TAKUMA , VINTEN‐JOHANSEN CHRISTIAN
Published: April 2006

Abstract. Measurement of the electrical field along soybean hypocotyls shows the development of a positive electrical potential in the lower side approximately 1 min after horizontal placement. The time is as fast or faster than the geotropic presentation time of soybean seedlings. The maximum positive electrical field potential is produced in a zone 1–2 cm below the hook, which is the region showing the geotropic curvature.
The effects of O2 on net photosynthesis at low temperature (5°C)
Authors: CORNIC GABRIEL , LOUASON GENEVIÈVE
Published: April 2006

Abstract. It has been shown that atmospheric O2 can either depress or stimulate the rate of apparent photosynthesis of white mustard depending on the environmental conditions: CO2 concentration, light intensity and temperature. Stimulation by O2 was observed only under high photon fluence rate and at high CO2 concentrations. The critical CO2 concentration below which O2 was inhibiting and above which it was stimulating was dependent on the temperature of the assay: for plants grown at 12°C the critical CO2 concentration was 13.35 mmol at 5° C and 21.92 mmol at 10° C. Stimulation by O2 depended also on the growth temperature: for measurements at 26.31 mmol m−3 CO2, O2 was stimulating at temperatures less than 12°C for plants grown at 12°C and less than 19°C for plants grown at 27°C. The efficiency of the O2‐dependent stimulation of net photosynthesis was maximum at 9.21 mol m−3 O2 at 26.31 mmol m−3 CO2.

Oxygen‐stimulation of net photosynthesis was detected in Nicotiana tabacum L. var Samsun, Lycopersicum esculentum L. and Chenopodium album L. At 5°C and under high photon fluence rate, O2 increased the carboxylation capacity of the photosynthetic apparatus of mustard and decreased its affinity for CO2. The O2 inhibition of the net CO2 uptake observed at low CO2 concentrations was the result of a decrease in the affinity for carbon dioxide. The nature of the mechanism which causes the stimulation of photosynthesis is discussed.
Modifications of chloroplasts of flax cotyledons treated with monuron: myelinoid figures formed under low light conditions
Authors: PALLETT K. E. , DODGE A. D.
Published: April 2006

Abstract. Monuron treatment of flax cotyledons in the dark and at a low light intensity of 0.2 Wm−2 caused a retardation of chlorophyll breakdown. With low light, carotenoid breakdown occurred more rapidly, suggesting a possible overloading of the carotenoid protective system, but in darkness chlorophyll loss was first. The ultrastructure of treated leaves was markedly altered. In the dark, monuron caused a swelling of the chloroplasts and a subsequent disruption of the thyl‐akoids resulting in a concentric membrane formation in the stroma. Following envelope rupture the thylak‐oid system was visible as a myelinoid figure in the cytoplasm.
Research strategy in the plant sciences
Authors: THORNLEY J. H. M.
Published: April 2006

Abstract The nature of science and of scientific progress is discussed, with special reference to the role of mathematics, and the existence in biology of hierarchical organization and levels of description. A distinction is made between a description of a phenomenon, and an understanding of that phenomenon; if mathematics is applicable, this is reflected in the use of an empirical or a mechanistic model. Reductionism is considered in relation to alternative viewpoints, and some examples from cell biology and plant physiology of problems where reductionism alone may be leading to difficulties, are discussed. A possibly more effective research strategy is suggested.
Alfalfa water status and cold hardiness as influenced by cold acclimation and water stress
Authors: STOUT DARRYL G.
Published: April 2006

Abstract Water stress at a nonacclimating temperature (18–20°C) increased the cold hardiness of Medicagosativa L. (alfalfa) plants. This increased cold hardiness was retained when the previously water‐stressed plants were cold acclimated (2–9°C) in the absence of water stress. Water stress during cold acclimation also increased cold hardiness. Alfalfa was demonstrated to suffer injury, measured as decreased growth following freezing, at sub‐lethal temperatures. During cold acclimation the turgor potential (ψ) of watered plants increased, whereas the solute potential and the water content per unit dry weight decreased. The large positive psgrdap of acclimated plants indicates that the decreased water content per unit dry weight is related to an increased proportion of tissue dry matter rather than to tissue dehydration.
Effects of organic acids on the germination of seeds and growth of seedlings
Authors: LYNCH J. M.
Published: April 2006

Abstract A range of aliphatic, aromatic and amino acids at a concentration of 5 mol m‐3 inhibited the extension of roots of barley seedlings. Acetic acid is one of the least toxic but its action has the greatest ecological significance because it can be formed in phytotoxic concentrations by micro‐organisms in soil. Its uptake and toxicity were greatest at low pH. Of the plant species which were examined, those most affected were barley, wheat and maize, followed by rape and clover. In aerobic conditions, microbial breakdown of the acid decreased its activity, but in atmospheres containing small concentrations of oxygen the acid prevented the germination of seeds. The toxicity could be partially alleviated by calcium carbonate applied as ground chalk to seeds.
Photosynthetic efficiency during ontogenesis of leaves ofBetula pendula
Authors: ÖQUIST G. , BRUNES L. , HÄLLGREN J‐E.
Published: April 2006

Abstract.Net photosynthesis, photosynthetic electron transport, and leaf area density of photosynthetic units have been studied in developing, mature, and old leaves of seedlings ofBetula pendula. The photosynthetic quantum yield under light‐limiting conditions and the leaf area related rale of light‐saturated net photosynthesis were lower in developing than in mature and old leaves. Developing leaves also had more oxygen inhibition of photosynthesis, a lower pool size of plastoquinone in the electron transport chain, a lower chlorophyll content and a lower leaf area density of photosynthetic units than mature and old leaves. The photosynthetic properties of The oldest leaves resulted partly from acclimation to shade and partly from a different ontogeny to that of younger leaves.
Protective mechanisms and acclimation to solar ultraviolet‐B radiation in Oenothera stricta
Authors: ROBBERECHT RONALD , CALDWELL MARTYN M.
Published: April 2006

Abstract Mechanisms of plant protection and acclimation to potentially damaging solar ultraviolet‐B (UV‐B, 280–320 nm) radiation incident on the Earth's surface were examined in Oenothera stricta. Attenuation of this radiation in the upper leaf epidermis reduces the penetration of UV‐B radiation to the mesophyll where damage to physiologically sensitive targets can occur. The epidermis is a highly selective radiation filter that can attenuate up to 95% of the incident UV‐B radiation and yet transmit between 70% and 80% of the visible radiation. Exposure to UV‐B radiation significantly reduced the degree of epidermal UV‐B transmittance by as much as 33%. No significant reduction in epidermal transmittance of visible radiation was observed as a result of UV‐B exposure. The plasticity in epidermal UV‐B transmittance results from production of flavonoid and related phenolic compounds in the tissue. Absorbance of UV‐B radiation in llavonoid extract solutions from epidermal and mesophyll tissues significantly increased by as much as 100% and 35%, respectively, after exposure to UV‐B radiation. Photosynthetic rates of leaves exposed to UV‐B radiation were not significantly reduced at dose rates representative of the radiation flux found in the habitat of this species, but significant photosynthetic depression was observed at dose rates that exceed the field UV‐B flux. The phenotypic plasticity in epidermal UV‐B transmittance resulting in decreased penetration of damaging UV‐B radiation to the mesophyll may reduce the rate of damage to a level where repair mechanisms can keep pace with reduced injury.
Accumulation and conversion of sugars by developing wheat grains. 4. Effects of phosphate and potassium ions in endosperm slices
Authors: RIJVEN A. H. G. C. , GIFFORD R. M.
Published: April 2006

Abstract. Transverse slices through developing grains of Triticum aestivum cv. SUN 9E 16 d after anthesis were incubated in simple defined media with various radioactive labels. In some enzymic assays slices were pretreated with 2.5% Triton X‐100 or with 5% butanol to remove cellular membranes and endogenous substrates.

Endogenous potassium leaked from endosperm slices into 30mol m−3 sucrose while sucrose was converted partly into starch. Exogenous alkali‐ions, except Li+, stimulated conversion of sucrose to insoluble matter, specifically to starch with K+. Starch synthetase activity of Triton‐pretreated slices was stimulated by K+ at both high and low substrate ADPG concentration, but was not affected by phosphate (25 mol m−3).

Phosphate in the medium had no effect on incorporation of sucrose or glucose into alcohol‐insoluble material or starch in fresh slices (internal inorganic phosphate (P,) concentration was about 11 mol m−3). Three‐ to four‐fold contrasts in internal Pi level, achieved by prolonged preincubations in different media, did not show an inhibition of starch synthesis by Pi. However, phosphate (25mol m−3) inhibited starch synthesis, that was mediated by ADPG pyrophosphorylase in butanol‐pretreated endosperm slices by 15–18%.

It is concluded that starch synthesis in wheat endosperm is not regulated directly by apoplastic Pi; level.
Phytochrome control mechanisms in leaf expansion ofPhaseolus vulgariscv. Limburg.
Authors: HOREMANS S. , VAN ONCKELEN H. A. , DE GREEF J. A.
Published: April 2006

Abstract.The effectiveness of a red‐light pulse acting through phytochrome in inducing primary leaf expansion in 9‐d‐old etiolated bean (Phaseolus vulgarisL. ev. Limburg) seedlings is strongly increased by a continuous far‐red light (CFR) pretreatment. This increase in effectiveness of a red pulse is positively correlated with the time and the fluence rate of the CFR pretreatment. Escape from photoreversibility of this red pulse after the CFR pretreatment is extremely slow (more than 3 d). When a dark period is interposed between the end of the CFR pretreatment and the inductive red pulse the photoreversible part of the response to this pulse is highly dependent upon the photostationary state of phytochrome at the onset of the dark period.

The results give strong evidence for the synergistic activity of two components of phytochrome action during leaf growth induction, one of them acting via a very stable Pfr fraction.
The fusicoccin‐stimulated phosphorylation of a 33 KDa polypeptide in cells of Acer pseudoplatanus as influenced by extracellular and intracellular pH
Authors: TOGNOLI L. , BASSO BARBARA
Published: April 2006

Abstract In a previous study, it was shown that the fungal toxin fusicoccin (FC) is able to stimulate the in vivo phosphorylation of a 33 KDalton polypeptide (33 KP) independently of protein synthesis. Here we show that the stimulation by FC of both proton efflux and 33 KP phosphorylation are strongly enhanced when the external medium contains K+ or Na+, suggesting that the two phenomena are related. The stimulatory effect of FC is higher in unbuffered than in buffered media; moreover, in the absence of FC, 33 KP is more phosphorylated at an acidic than at a basic pH of the medium, suggesting that the effect of FC may depend, to a certain extent, on the acidification of the free space caused by FC‐promoted proton efflux.

Treatments reported to alter the intracellular pH influence 33 KP phosphorylation even more strongly than the external pH does. The acidifying agents isobutyric acid and trimethylacetic acid decrease 33 KP phosphorylation, while the alkalinizing agents, ammonia and procaine, increase it. FC partially counteracts the inhibition by the weak acids, whereas the stimulatory effect of FC is not additive with that of the weak bases.

The results indicate that 33 KP phosphorylation senses both the external and internal pH. The stimulatory effect of cytoplasm‐alkalinizing treatments, which mimics that of FC, agrees with the reported capacity of FC to cause cytoplasmic alkalinization, following activation of the plasmalemma proton pump.
Sucrose efflux and export from the maize scutellum*
Authors: HUMPHREYS T. E.
Published: April 2006

Abstract During incubation of maize scutellum slices in fructose, there was an efflux of sucrose. Efflux was constant for at least 4 h at fructose concentrations of 70 or 100 mol m−3. Efflux was increased by EDTA, and decreased by Ca2+. Efflux was independent of pH after EDTA treatment, but increased from untreated slices when the pH was lowered from 7 to 4. Uranyl ion and PCMBS (p‐chloro‐mercuribenzenesulfonic acid) abolished sucrose uptake, but were only weak inhibitors of sucrose efflux. These results are consistent with efflux occurring by simple diffusion through aqueous pores, but they do not rule out facilitated diffusion. Rates of sucrose export from the scutellum to the root shoot axis were estimated from measurements of axis respiration and dry weight gain. Sucrose efflux from scutellum slices was only 14‐22% of the export rate. Sucrose efflux from the whole scutellum was only 3‐4% of the export rate. It is concluded that the observed efflux is from leaky cells and does not represent sucrose on the way to the phloem along a path that includes the apoplast. These results support the idea that the path for sucrose from parenchyma cell to sieve tube in the maize scutellum is entirely symplastic.
Some characteristics of photosynthetic inorganic carbon uptake of a marine macrophytic red alga
Authors: COOK C M. , COLMAN B.
Published: April 2006

AbstractSome characteristics of photosynthetic inorganic carbon uptake byPalmaria palmata, a marine red macroalga, have been measured under physiological conditions in artificial seawater. The apparent affinity of thallus for CO2[K1/2(CO2)] at pH 8.0 and 15°C was 21.4±3.0mmol m−3CO2under air, and 25.7±70mmol m−3CO2under N2. The corresponding values ofVmaxwere 2.98 ± 0.42 and 3.65±0.87 mmol O2evolved g Chr−1s−l. The apparent Km(CO2) of isolated ribulose bisphosphate carboxylase was determined at pH 8.0 and 30 °C to be 30.2 mmol m−3CO2, and the corresponding value of Vmaxwas 19.67 μniol CO2g protein−1s−1. The CO2compensation points of the thallus were measured in artificial seawater at pH 8.0 under air and N2, using a gas‐chromatographic method. The values were relatively low, rising from 10 cm3m−3at 15°C, to 35 cm3m−3at 25°C, but were not affected by the O2concentration. The lack of an effect of O2on photosynthesis and on compensation point indicates that there is little photorespiratory CO2loss in this macroalga. The high affinity of the thallus for CO2, and the low CO2compensation concentrations, are consistent with the occurrence of bicarbonate uptake in this alga.
Chemical basis of host‐plant resistance to aphids
Authors: DREYER D. L. , CAMPBELL B. C.
Published: April 2006

Abstract The importance of host‐plant resistance of crop plants in the biological control of aphids and the formation of aphid biotypes is discussed. The rapid response of plant breeders to the formation of new aphid biotypes requires detailed knowledge on the mechanism of host‐plant resistance. Current knowledge on the chemical basis of host‐plant resistance to aphids is summarized. Of central importance to this relationship is the aphid‐pectinase plant‐pectin interdependence. Parallels between the mechanism of aphid‐plant and pathogen‐plant attack are pointed out and how aphid bacterial endo‐symbiotes play a central role in host‐plant selection.
A field portable system for the measurement of gas exchange of leaves under natural and controlled conditions: examples with field‐grown Eucalyptus pauciflora Sieb. ex Spreng. ssp. pauciflora, E. behriana F. Muell. and Pinus radiata R. Don.
Authors: KÜPPERS M. , SWAN A. G. , TOMPKINS D. , GABRIEL W. C. L. , KÜPPERS B. I. L. , LINDER S.
Published: April 2006

Abstract A field portable system is described which measures the response of gas exchange of one leaf to changes in environmental parameters under controlled conditions, and which simultaneously measures the gas exchange of another leaf as the climatic parameters vary naturally. The system consists of two independently operating cuvettes. It enables detailed studies of photosynthesis and stomata/transpiration of leaves attached to the plant in their natural position. It provides control of temperature, humidity, CO2 and oxygen concentration (or, alternatively, of other gases) as well as of light. Infrared gas analyzers for CO2 and H2O are used which allow similar time constants for the measurement of the two gases.

Examples of a diurnal course of gas exchange of a leaf in its natural exposition and of experiments with steady‐state responses of gas exchange are presented. In Eucalyptus pauciflora Sieb. ex Spreng. ssp. pauciflora, a set of response curves of CO, assimilation (A) to CO2, as measured at various leaf temperatures and light levels, shows carboxylation efficiency to be light saturated at the lower photon irradiances the lower the leaf temperature is. Carboxylation efficiency is maximal at 25°C. At ambient CO, partial pressure stomata open in a way that CO2 assimilation occurs at a rate found within the curvature region of the CO2 response function of A. The light‐independent CO2 compensation point as a function of temperature is presented.

Applying a combined heat/low humidity pulse (15 or 60 min) on leaves of Eucalyptus behriana F. Muell. or Pinus radiata R. Don, respectively, leads to a lower level of intercellular carbon dioxide partial pressure (Ci) during the decline in A and leaf conductance to water vapour (g). A lower Ci level is maintained during recovery of A and g, A almost reaching the pre‐pulse level but not g. The existence of an after‐effect indicates that the response to the combined high temperature/low humidity pulse is a multi‐step process.
The cells shed by the root cap of Zea: their origin and some structural and physiological properties
Authors: GUINEL F. C. , McCULLY M. E.
Published: April 2006

Abstract Two populations of living detached cap cells are found within the drop of mucilage at the root tip of a 3‐d‐old corn seedling. Axial cells, which pass through the length of the columella, are shed at the apex of the cap and lateral cells, which have spent less time or no time within the columella, are detached from the cap flanks. The two types of cells differ in shape, size and internal structure. Whereas the axial cells are more or less spherical and have a projected surface area of 1300μm2, the lateral cells are elongated and possess a projected surface area of 2000μm2. The axial cells are further distinguished by the association with a polyhedric net thought to be remnants of undigested middle lamellar material from the columellar tissue. Both populations of cells arc metabolically active and can be plasmolysed, but no evidence was found that they secrete mucilage after detachment. The lateral cells have been cultured on solid nutrient media and on nutrient‐free agar. In both cases, they did not divide; however, they enlarged by one‐third in their projected surface area over 15 d.
Cyclamen coiling—the migration of a growth response
Authors: MACDONALD I. R. , GORDON D. C. , HART J. W.
Published: April 2006

Abstract Image analysis of suitably demarcated fruiting pedicels of Cyclamen hederifolium has revealed that the coiling of the pedicel subtending the fruiting body involves a resumption of growth in the mature organ. The distribution of resurgent growth is highly selective, both spatially and temporally, and involves a polar migration down the convex side of the organ, while the corresponding region on the concave side undergoes compression. The nature of the response is considered in relation to other plant movements.
Relationships between sap flow and water potential in woody or perennial plants on islands of the Great Barrier Reef
Authors: ALLAWAY W. G. , PITMAN M. G. , STOREY R. , TYERMAN S.
Published: April 2006

Abstract. This paper describes studies on trees of Pisonia grandis, bushes of Argusia argentea, and the perennial herb Melanthera biflora, growing on One Tree Island, a coral cay of the Great Barrier Reef with ‘soil’ of coarse coral rubble. Water potential (Ψb, measured on small shoots with a pressure chamber), sap flow, stomatal conductance, vapour pressure deficit and photon flux density were monitored over day/night cycles. Sap flow and Ψb responded to changes in light and humidity. From these experiments good linear correlations were found between sap flow in a shoot and Ψb of similar adjacent shoots. The linearity suggests that the resistance to sap flow is constant as Ψb varies. The correlation, however, does not indicate a causal relationship between Ψb of an individual shoot on the plant and its sap flow. Ψb was only slightly different in shaded shoots from those in sunshine, although sap flow would be expected to differ between them. Enclosing shoots and so reducing their transpiration and sap flow to very low rates resulted in only small changes in Ψb of the enclosed shoots; Tb of such enclosed shoots should closely approximate that of the xylem at the point of shoot attachment. From these results it is suggested that the resistance to water flow in shoot and leaf xylem is small compared to the resistance further down the plant, in the root or at the root/soil interface. Shoot xylem water potential would be similar for all parts of the plant, and in such plants the water potential of shoots in the shade would be determined by the overall water use of the plant.
The effect of nutrients on adenine nucleotide levels and the adenylate energy charge ratio in Spartina alterniflora and Spartina patens
Authors: MENDELSSOHN I. A. , McKEE K. L.
Published: April 2006

Abstract. The response of the adenylate energy charge (AEC) ratio and the adenine nucleotide pools to nutrients was studied in two perennial marsh plant species. Adenine nucleotide levels and the AEC ratio were measured in Spartina patens (Alton) Muhl. plants which were grown in the greenhouse at various nutrient levels as well as in Spartina alterniflora Loisel. transplants removed from the field but maintained in marsh soil amended with different nutrient supplements. In addition, adenine nucleotide concentrations were measured in both species in their natural environment and compared with that of the same species grown in the greenhouse with a complement of nutrients.

The addition of nutrients stimulated an increase in the individual and total adenylate pools and the AEC ratio. Low nutrient levels resulted in extremely reduced adenylate pools. The AEC ratio was significantly affected in some instances, but did not decrease proportionately with the adenine nucleotide level and was typically maintained at values above 0.60. The adenine nucleotide concentrations measured in the leaves of both species were significantly higher in greenhouse‐grown plants compared to field plants, but the AEC ratios were not significantly different.

Because the AEC ratio in plants can be significantly affected by nutrient level. AEC response in field investigations should be planned with attention to the potential effect of dissimilar nutrient levels among study sites.
Peroxidase involvement in lignification in water‐impermeable seed coats of weedy leguminous and malvaceous species
Authors: EGLEY G. H. , PAUL R. N. , DUKE S. O. , VAUGHN K. C.
Published: April 2006

Abstract. The development of water impermeable seed coats of two members each of the leguminoseae family [Crotalaria spectabilis Roth, Sesbania exaltata (Raf) Cory] and the malvaceae family [Anoda cristata (L.) Schlecht, Abutilon theophrasti Medic.] was investigated. Highest peroxidase (POD) activity of Anoda and Abutilon seed coat extracts was highly correlated with the developmental stages when soluble phenolics were maximally converted into lignin. Although extensive lignification occurred during seed coat development in both legumes, the patterns of POD activity, soluble phenolic levels and time of lignification were different from those of the malvaceous species. POD activity levels in developing coats of the malvaceous seeds increased as phenolics decreased. Both POD activity and phenolic levels decreased during seed coat development of the legumes. POD was immunocytochemically and immunochemically detected in seed coats of all four species; however, results for polyphenol oxidase were negative. The results confirmed POD involvement in lignification of leguminous and malvaecous species and support and extend our earlier view that POD is involved in lignin formation during development of impermeable seed coats.
Salt tolerance in the halophyte Suaeda maritima (L.) Dum. The influence of the salinity of the culture solution on leaf starch and phosphate content
Authors: HAJIBAGHERI M. A. , FLOWERS T. J.
Published: April 2006

Abstract. The starch concentration in mature leaves of the halophyte Suaeda maritima increased from 4.7 to 7.3 mg mg−1 chlorophyll when sodium chloride (680 mol M−3) was added to the solution in which the plants were grown. This effect of salinity on the starch: chlorophyll ratio was greater in young than in old leaves. Electron micrographs showed the starch to be in the chloroplasts and this was confirmed by measurements on isolated chloroplasts. Total phosphorus concentration (mg mg−1 chlorophyll) in leaves of all ages from plants of S. maritima decreased on salinization of the growth medium suggesting an inverse relationship between phosphorus and starch concentrations. However, although leaf starch concentration varied with leaf age, phosphorus concentration did not. The cause of starch accumulation in chloroplasts at salinities which are optimal for growth (340 mol m−3) remains unclear.
Stomatal mechanics. III. Geometric interpretation of the mechanical advantage*
Authors: WU H. , SHARPE P. J. H. , SPENCE R. D.
Published: April 2006

Abstract. Previous mathematical analyses of stomatal mechanics have demonstrated, and experimental measurements have confirmed, that the turgor‐generated force of the epidermal cells dominates that of the guard cells in determining aperture. DcMichele & Sharpe (1973) termed the phenomenon the mechanical advantage of the epidermal cells, while Cooke et al. (1976) expressed it as an antagonism ratio. Both of these formulations, however, have theoretical or practical limitations. This study presents a biophysical analysis demonstrating that the effective forces in the stomatal system may be studied in terms of simple stomatal geometry. From this analysis, the mechanical advantage can be redefined and interpreted based upon simple geometric relationships calculated from measurable anatomical dimensions.
Loading of assimilates in wheat leaves. II. The path from chloroplast to vein
Authors: ALTUS D. I. , CANNY M. J.
Published: April 2006

Abstract. An improved method is described for micro‐autoradiography of water‐soluble substances alter freeze‐substitution of plant tissue in which water is rigorously excluded. Resin sections are cut and flattened dry, and dry photographic emulsion is mounted on them. When the location of 14C in wheat leaves after assimilation of 14CO2 was studied with this method, it was found that 14C entered the intermediate veins before the laterals and entered both types of veins along the flanks of the veins adjacent to the phloem. High concentrations of 14C were found in small spaces in the cells of mesophyll and vein parenchyma; these spaces coincide with the nuclei. The concentration of 14C in these nucleus‐associated spaces was as high as that reached at later times in the sieve tubes. Water washed the 14C out of these spaces of the sections and the label in the washings was predominantly in sucrose. The high 14C concentrations of the nucleus‐associated spaces were particularly easily leached. It is concluded that the raising of the sugar concentration to the high levels found in sieve tubes can take place in these leaves in a special space in each mesophyll cell not, or not only, at the boundary of the sieve tubes.
Probing the events of photoinhibition by altering electron‐transport activity and light‐harvesting capacity in chloroplast thylakoids
Authors: CLELAND R. E. , MELIS A.
Published: April 2006

Abstract. The effect of photoinhibition on the activity of photosystem II (PSII) in spinach chloroplasts was investigated. Direct light‐induced absorbance change measurements at 320 nm (ΔA320) provided a measure of the PSII charge separation reaction and revealed that photoinhibition prevented the stable photoreduction of the primary quinone acceptor QA. Sensitivity to photoinhibition was substantially enhanced by treatment of thylakoids with NH2OH which extracts manganese from the H2O‐splitting enzyme and prevents electron donation to the reaction centre. Incubation with 3‐(3,4,‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) during light exposure did not affect the extent of photoinhibitory damage. The chlorophyll (Chl) b‐less chlorina (2 mutant of barley displayed a significantly smaller light‐harvesting antenna size of PSII (about 20% of that in wild type chloroplasts) and, simultaneously, a lower sensitivity to photoinhibition. These observations suggest that photoinhibition depends on the amount of light absorbed by PSII and that the process of photoinhibition is accelerated when electron donation to the reaction centre is prevented. It is postulated that the probability of photoinhibition is greater when excitation energy is trapped by P680+, the oxidized form of the PSII reaction centre. The results are discussed in terms of the D1/D2 heterodimer which contains the functional PSII components P680, pheophytin, QA and QB.
Changes in sodium and potassium in Nitellopsis cells treated with transient salt stress
Authors: KATSUHARA M. , TAZAWA M.
Published: April 2006

Abstract. Nitellopsis cells grown in fresh water have a relatively low cytoplasmic Na+ (11 mol m−3) and high cytoplasmic K+ (90 mol m−3) content. A 30‐min treatment with 100 mol m−3 external NaCl resulted in a high [Na+]c (90 mol m−3) and a low [K+]c (33 mol m−3), Subsequent addition of external Ca2+ (10 mol m−3) prevented Na+ influx and then [Na+]c decreased slowly. Changes in [K+]c were opposite to [Na+]c. During the recovery time vacuolar Na+ increased, while vacuolar K+ decreased. Since all these processes proceeded also under ice‐cold conditions, the restoration of original cytoplasmic ion compositions is suggested to be a passive nature. The notion that the passive movement of ions across the tonoplast can act as an effective and economic mechanism of salt tolerance under transient or under mild salt stress conditions is discussed.
Observed and modelled stomatal responses to dynamic light environments in the shade plant Alocasia macrorrhiza
Authors: KIRSCHBAUM M. U. F. , GROSS L. J. , PEARCY R. W.
Published: April 2006

Abstract. Dynamic responses of stomatal conductance to lightflecks (15 s to 5 min) were observed in the tropical understory plant Alocasia macrorrhiza. Brief observations were also made on step changes in light, flashing light and short low‐light periods (darkflecks) after stomata had reached steady state conductances in high light. Stomata opened substantially even in response to very short lightflecks, with maximal opening being reached about 20 min after the end of the lightfleck. These responses are compared to those of a semi‐mechanistic stomatal model consisting of three steps in series: a biochemical signal which responds directly to light, producing osmotic changes within the guard cells which, in turn, drive the movement of water into the guard cells. The rate of change of each component was assumed to be given by the difference between the current state of that component and the state of the previous component in the series divided by a characteristic time constant for each step. This model allowed excellent description of observed responses to lightflecks, including the fleck‐length dependence of stomatal opening, the lag between the end of the lightfleck and the time of maximal stomatal conductance and the response to multiple flecks. However, agreement with predicted responses to flashing light and darkflecks was poor. Good agreement could be restored by using different time constants for the initial biochemical step, suggesting that the speed of the initial biochemical response is not constant but dependent on the current physiological state of the stomata. For leaves experiencing predominantly low light, punctuated by relatively short and infrequent periods of high light, this model allows good description of the dynamic changes in stomatal conductance.
Mechanism of detecting light direction in first positive phototropism in Zea mays L.
Authors: PIENING C. J. , POFF K. L.
Published: April 2006

Abstract. The carotenoid content of corn seedlings was reduced by 80–90% with the herbicide SAN 9789 or by using carotenoidless mutants. This caused a decrease in ‘first positive’ phototropism by about 50% without affecting geotropism. This reduction in phototropism is attributed to the decreased light gradient across the albino shoot. Decreased screening should increase the response if a focusing mechanism is used to measure the light gradient, but should decrease the response if a screening mechanism is used. Thus, these data support the hypothesis that screening establishes the light gradient used to measure light direction in ‘first positive’ phototropism.
Invalidity of the multiphasic concept of ion absorption in plants
Authors: BORSTLAP A. C.
Published: April 2006

Abstract. According to the multiphasic concept uptake isotherms consist of a number of successive Michaelis‐Menten phases separated by discontinuous transitions. In this paper evidence is provided that the concept is most probably due to an erroneous interpretation of continuous uptake isotherms that yield non‐linear, concave downward Lineweaver‐Burk plots. With reference to the isotherm of sulphate uptake in barley roots (Nissen, 1971) uptake isotherms were simulated in which the uptake rates, computed from the sum of two Michaelis‐Menten terms and a linear term, contained a 4% (or 5%) random error. The same arguments that have been adduced in support of the multiphasic concept would also lead to a multiphasic interpretation of the simulated isotherms. The conclusions concerning a multiplicity of transition points and the multiphasic concept follow from the particular form of statistical test that had been applied rather than from the set of data itself. Characteristics that have been noted in multiphasic uptake appear to follow simply from the multiphasic interpretation of uptake isotherms that yield non‐linear, concave downward Lineweaver–Burk plots.
Analysing partitioning in plants
Authors: LANG ALEXANDER , THORPE M. R.
Published: April 2006

Abstract. Our understanding of the control of partitioning in plants and crops is confounded by unsatisfactory and incomplete description of the phenomenon. This paper attempts to improve upon this state of affairs by taking a fresh look at the concepts and the terms we use.

While the continued usefulness in general discussion of the popular concepts of source, path and sink and of limitation is recognized, for analysing carbon flows we propose a separate, more practicable and higher level form of description based on a pool: process concept. This is similar to those used to describe the flows of other things in nature. In our analysis of competition between pools, the constant properties pool permeance and pool potential determine partitioning which is a function of the single variable plant potential. A simple phenomenological model embodying them is developed. Because our scheme is less demanding of experimental technique than some, its wide application seems feasible, extending even to the analysis of conventional crop growth measurements. The paper concludes by indicating briefly the sorts of physiological factors which could give rise to these phenomenological properties.