bluuebunny/crossref_metadata_2025 huggingface dataset:
On the fractal dimensions of a root system
Authors: Eshel A.
Published: March 2003

Several attempts have been made to apply the principles of fractal geometry to the description of root systems. However, fractal analysis of a real plant root system that maintains its original three‐dimensional structure has not been performed to date. An intact root system of a dwarf tomato plant was embedded in gelatin and cut into 3 mm slices. Image analysis was used to collect the data required for determination of three‐dimensional and planar fractal dimensions. It was found that the root system has characteristics of a fractal object. The variation of the planar fractal dimension of horizontal and vertical planes intersecting the root system was shown, and their maxima were found to correspond with maximal root proliferation. These results open the way for further application of fractal analysis in root research.
Contrasting patterns of photosynthetic acclimation to the light environment are dependent on the differential expression of the responses to altered irradiance and spectral quality
Authors: Murchie E. H. , Horton P.
Published: March 2003

Chl, chlorophyll Chl a/b, ratio of chlorophyll a to chlorophyll b Cyt f, cytochrome f FR, far‐red light LFR, low irradiance, far‐red enriched growth light LHCII, light harvesting complex associated with PSII LW, low irradiance, white growth light MW, moderate irradiance, white growth light PAR, photosynthetically active radiation Pmax, light and CO2 saturated photosynthetic rate PSI, photosystem I PSII, photosystem II  Four plant species (Chamerion angustifolium, Digitalis purpurea, Brachypodium sylvaticum and Plantago lanceolata) which have previously been shown to demonstrate contrasting photosynthetic acclimatory responses to the light environment (Murchie & Horton 1997, Plant, Cell and Environment 20, pp. 438–448) were analysed at a biochemical level. Plants were grown under low irradiance with a shade‐type spectrum (LFR: 50μmol quanta m–2 s–1), moderately high white light (MW: 300μmol quanta m–2 s–1) and low irradiance white light (LW: 50μmol quanta m–2 s–1). The effects of light quality upon chlorophyll content and photosynthetic capacity were found to be species‐dependent. A far‐red dependent reduction in chlorophyll was found in three species, and an irradiance‐dependent reduction was found in B. sylvaticum, which showed the greatest alteration in the xanthophyll cycle pool size of all species tested under these conditions. Chlorophyll a/b ratios were sensitive to both light quality and quantity in C. angustifolium and D. purpurea, being highest in MW, lowest in LFR, and intermediate in LW, whilst the other species showed no response. Ratios of photosystem II to photosystem I (PSII and PSI) demonstrated a strong irradiance‐associated increase in all species except B. sylvaticum, whereas an increase in PSII/PSI in LFR compared to LW conditions was present in all species. A change in chlorophyll a/b was not always associated with a change in PSII/PSI, suggesting that the level of LHCII associated with each PSII varied in some species. Cytochrome f content showed an irradiance‐dependent effect only, indicating a relationship with the capacity of electron transport. It is concluded that differing strategies of acclimation to the light environment demonstrated by these species results from differing strengths of expression of a series of independently regulated changes in the levels of photosynthetic components.
Subcellular localization and stress responses of superoxide dismutase isoforms from leaves in the C3‐CAM intermediate halophyte Mesembryanthemum crystallinum L.
Authors: Miszalski Z. , Ślesak I. , Niewiadomska E. , Baczek‐Kwinta R. , Lüttge U. , Ratajczak R.
Published: March 2003

BSA, bovine serum albumin CAM, Crassulacean acid metabolism DTT, dithiothreitol EDTA, ethylenediaminetetraacetic acid FPLCfast protein liquid chromatography HEPES, N‐(2‐hydroxyethyl)piperazine‐Ń‐(ethanesulphonic acid) ME, β‐mercaptoethanol NBT, nitro blue tetrazolium PAGE, polyacrylamide gel electrophoresis SDS, sodium dodecyl sulphate SDS‐PAGE, sodium dodecyl sulphate polyacrylamide gel electrophoresis Rubisco, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (EC 4.1.1.39) SOD, superoxide dismutase (EC 1.15.1.1) TEMED, N,N,Ń,Ń‐tetramethylethylenediamine Tris, Tris (hydroxymethyl) aminomethane Tricine, N‐Tris(hydroxymethyl)methylglycine  Treatment of Mesembryanthemum crystallinum for several days with 0·4 kmol m–3 NaCl in the root medium, in parallel to an increase of the cell sap osmolarity enhances activity of important antioxidative enzymes, such as superoxide dismutases (SODs). M. crystallinum is equipped with three SOD isoforms. These isoforms were identified as Mn‐, Fe‐, and Cu/Zn‐SODs, respectively. Mn‐SOD was found in the mitochondrial fraction, Fe‐SOD in the chloroplast fraction, and Cu/Zn‐SOD is probably localized in the cytosol. The Fe‐SOD found in M. crystallinum is the first iron‐containing SOD enzyme to be characterized in the plant family Aizoaceae. Salt treatment increases the activity of this isoform earlier than the other SODs. Molecular masses of SOD isoforms were determined as 82, 48 and 34 kDa for Mn‐, Fe‐, Cu/Zn‐SODs, respectively. Native Mn‐SOD seems to be a tetramer, while Fe‐SOD and Cu/Zn‐SOD are dimers. All SOD isoforms show high thermal stability. Mn‐SOD is active even after short heating at 90 °C and Fe‐SOD at 70 °C. Moreover, high concentrations of β‐mercaptoethanol used as a reducing agent did not destroy the function of all isoforms. With the salinity treatment in M. crystallinum, Crassulacean acid metabolism (CAM) is induced. Build‐up of large stationary O2 concentrations in the leaf air spaces is associated with the photosynthetic CO2 reduction behind closed stomata in phase III of CAM. This illustrates why M. crystallinum may require higher antioxidative activities under NaCl stress and also explains earlier findings that CAM plants are more resistant than C3 plants to environmental stress as imposed by, for example, SO2 and O3.
A biophysical model of fruit growth: simulation of seasonal and diurnal dynamics of mass
Authors: Fishman S. , Génard M.
Published: March 2003

A model of fruit growth was developed, based on a biophysical representation of water and dry material transport, which is coupled with cell wall extension stimulated by turgor pressure. The fluxes of materials connect the growing fruit with the parent plant (by phloem and xylem transport) and with the ambient atmosphere (by respiration and transpiration). The sugars are transported from the phloem to the fruit mesocarp by mass flow, passive diffusion and an active (and/or facilitated) mechanism. The stages after cell division has ceased and when fruit growth is due mainly to cell enlargement were modelled. This enabled us to consider the fruit as a cell community with a constant number of cells and to apply directly the equation describing the effect of hydrostatic pressure on the irreversible cell wall expansion elaborated originally for a single cell. The model was applied to the peach [Prunus persica (L.) Batsch] fruit. Seasonal and diurnal fruit growth, expressed in terms of dry and fresh mass changes, was calculated for conditions of water stress with various crop loads. Simulation of the diurnal patterns of fruit fresh mass variation revealed, in agreement with observations, intensive growth by night and midday fruit shrinkage, which depend on plant water status and on crop load.
Ultraviolet‐B‐induced responses in Arabidopsis thaliana: role of salicylic acid and reactive oxygen species in the regulation of transcripts encoding photosynthetic and acidic pathogenesis‐related proteins
Authors: Surplus S. L. , Jordan B. R. , Murphy A. M. , Carr J. P. , Thomas B. , ‐Mackerness S. A.‐H.
Published: March 2003

Supplementary UV‐B was shown to lead to a decrease in transcripts encoding the photosynthetic genes Lhcb and psbA and a concomitant increase in transcripts encoding three acid‐type pathogenesis‐related proteins, PR‐1, PR‐2 and PR‐5, in Arabidopsis thaliana. UV‐B radiation has been reported to lead to the generation of reactive oxygen species (ROS). Here we report that ROS are required for UV‐B‐induced down‐regulation of the photosynthetic genes and up‐regulation of PR genes, as the addition of antioxidants before UV‐B treatment resulted in a marked reduction in the effect of UV‐B on both sets of genes. Rises in ROS are frequently accompanied by increases in salicylic acid (SA) accumulation. UV‐B treatment of transgenic NahG Arabidopsis plants, which are unable to accumulate SA, showed that the increase in PR transcripts, but not the decrease in photosynthetic transcripts, was dependent on the increase in SA. In addition, a 3 d exposure to UV‐B radiation resulted in a 7‐fold increase in SA levels. Oxidant treatment of NahG plants indicated that ROS could not up‐regulate PR genes in the absence of SA accumulation; however, the down‐regulation of photosynthetic transcripts was unchanged from that in wild‐type plants. The results indicate that the effects of UV‐B on the two sets of genes are mediated through two distinct signal tranduction pathways. One pathway is ROS‐dependent but SA‐independent and mediates the down‐regulation of photosynthetic genes. The other is SA‐ and ROS‐dependent and mediates the up‐regulation of the acidic‐type PR genes.
Acquisition and allocation of carbon and nitrogen by Danthonia richardsonii in response to restricted nitrogen supply and CO2 enrichment
Authors: Lutze J. L. , Gifford R. M.
Published: March 2003

Dry weight (DW) and nitrogen (N) accumulation and allocation were measured in isolated plants of Danthonia richardsonii (Wallaby Grass) for 37 d following seed imbibition. Plants were grown at ≈ 365 or 735 μL L–1 CO2 with N supply of 0·05, 0·2 or 0·5 mg N plant–1 d–1. Elevated CO2 increased DW accumulation by 28% (low‐N) to 103% (high‐N), following an initial stimulation of relative growth rate. Net assimilation rate and leaf nitrogen productivity were increased by elevated CO2, while N concentration was reduced. N uptake per unit root surface area was unaffected by CO2 enrichment. The ratio of leaf area to root surface area was decreased by CO2 enrichment. Allometric analysis revealed a decrease in the shoot‐N to root‐N ratio at elevated CO2, while the shoot‐DW to root‐DW ratio was unchanged. Allometric analysis showed leaf area was reduced, while root surface area was unchanged by elevated CO2, indicating a down‐regulation of total plant capacity for carbon gain rather than a stimulation of mineral nutrient acquisition capacity. Overall, growth in elevated CO2 resulted in changes in plant morphology and nitrogen use, other than those associated simply with changing plant size and non‐structural carbohydrate content.
Temperature‐induced bleaching of corals begins with impairment of the CO2 fixation mechanism in zooxanthellae
Authors: Jones R. J. , Hoegh‐Guldberg O. , Larkum A. W. D. , Schreiber U.
Published: March 2003

The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tissues of a reef‐building coral were examined using pulse‐amplitude‐modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 °C for 4 h resulted in (1) the development of strong non‐photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (Fv/Fm) of photosystem II (PSII). Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensities were combined with elevated temperature (33 °C as opposed to 28 °C). qN collapsed in heat‐stressed samples when quenching analysis was conducted in the absence of oxygen. Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O2‐dependent electron flow through the Mehler‐Ascorbate‐Peroxidase cycle (MAP‐cycle) following the point at which the rate of light‐driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in S. pistillata is carboxylation within the Calvin cycle, as has been observed during heat damage in higher plants. Damage to PSII and a reduction in Fv/Fm (i.e. photoinhibition) are secondary effects following the overwhelming of photoprotective mechanisms by light. This secondary factor increases the effect of the primary variable, temperature. Potential restrictions of electron flow in heat‐stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the dinoflagellate Rubisco. Significant features of our model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, and (2) light plays a key secondary role in the initiation of the bleaching phenomena.
Control of stomatal conductance by leaf water potential in Hymenoclea salsola (T. & G.), a desert subshrub
Authors: Comstock J. , Mencuccini M.
Published: March 2003

The role of leaf water potential in controlling stomatal conductance (gs) was examined in the desert subshrub Hymenoclea salsola. For plants operating at high irradiance, stomatal closure in response to high leaf‐air humidity gradient (D) was largely reversed by soil pressurization. Stomatal re‐opening eliminated, on average, 89% of the closure normally induced by high D. Transpiration rates (E) reached under these conditions were far higher than maximal rates normally observed at any point of the D response. In situ stem psychrometry indicated that water flux at all times conformed to a simple Ohm’s‐law analogy. Under conditions of high D, E increased substantially in response to soil pressurization. Stomatal regulation did not constrain E during this treatment, but did result in nearly constant minimum leaf water potentials.
The nopaline synthase (nos) promoter is inducible by UV‐B radiation through a pathway dependent on reactive oxygen species
Authors: Yu G.‐H. , Sung S.‐K. , An G.
Published: March 2003

The molecular mechanism of plant response to UV‐B radiation was studied using the nopaline synthase (nos) promoter, which has been shown to be inducible by methyl jasmonate (MJ) and reactive oxygen species (ROS). In the leaves of transgenic tobacco (Nicotiana tabacum L.) plants that carried a fusion between the nos promoter and the chloramphenicol acetyltransferase (cat) gene, 2 h of UV‐B treatment resulted in a transient increase in the level of cat mRNA, a maximum being reached at 6 h after the UV‐B treatment. It was also found that MJ and UV‐B enhance nos promoter expression via separate pathways. Diethyldithiocarbamic acid, a potent inhibitor of jasmonate production, had little effect on UV‐B stimulation of the nos promoter. In contrast, antioxidants, such as dimethylthiourea, reduced glutathione, cysteine, N‐acetylcysteine and DTT, blocked UV‐B induction of the nos promoter, but did not affect MJ induction of the nos promoter. These results suggest that UV‐B induction of the nos promoter is mediated via a pathway that requires reactive oxygen species and is distinct from the jasmonate or MJ mediating pathway.
Effects of elevated CO2 concentrations on photosynthesis, growth and reproduction of branches of the tropical canopy tree species, Luehea seemannii Tr. & Planch.
Authors: LOVELOCK C. E. , VIRGO A. , POPP M. , WINTER K.
Published: March 2003

Mature trees have already experienced substantial increases in CO2 concentrations during their lifetimes, and will experience continuing increases in the future. Small open‐top chambers were used to enclose branchlets that were at a height of between 20 and 25 m in the canopy of the tree species Luehea seemannii Tr. & Planch. in a tropical forest in Panamá. Elevated concentrations of CO2 increased the rate of photosynthetic carbon fixation and decreased stomatal conductance of leaves, but did not influence the growth of leaf area per chamber, the production of flower buds and fruit nor the concentration of nonstructural carbohydrates within leaves. The production of flower buds was highly correlated with the leaf area produced in the second flush of leaves, indicating that the branchlets of mature trees of Luehea seemannii are autonomous to a considerable extent. Elevated levels of CO2 did increase the concentration of nonstructural carbohydrates in woody stem tissue. Elevated CO2 concentration also they increased the ratio of leaf area to total biomass of branchlets, and tended to reduce individual fruit weight. These data suggest that the biomass allocation patterns of mature trees may change under future elevated levels of CO2. Although there were no effects on growth during the experiment, the possibility of increased growth in the season following CO2 enrichment due to increased carbohydrate concentrations in woody tissue cannot be excluded.
Structure and chemical composition of endodermal and rhizodermal/hypodermal walls of several species
Authors: ZEIER J. , GOLL A. , YOKOYAMA M. , KARAHARA I. , SCHREIBER L.
Published: March 2003

CWM, isolated cell wall material ECW, isolated endodermal cell walls G, guaiacyl monomer H, p‐hydroxyphenyl monomer HCW, isolated hypodermal cell walls RHCW, isolated rhizodermal and hypodermal cell walls S, syringyl monomer XV, isolated xylem vessels  Endodermal cell walls of the three dicotyledoneous species Pisum sativum L., Cicer arietinum L. and Ricinus communis L. were isolated enzymatically and analysed for the occurrence of the biopolymers lignin and suberin. From P. sativum, endodermal cell walls in their primary state of development (Casparian strips) were isolated. Related to the dry weight, these isolates contained equal amounts of suberin (2·5%) and lignin (2·7%). In contrast, the endodermal cell walls of C. arietinum and R. communis, which were nearly exclusively in their secondary state of development, contained significantly higher proportions of suberin (10–20%) and only traces of lignin (1–2%). The results of the chemical analyses were supported by a microscopic investigation of Sudan III‐stained root cross‐sections, showing a Casparian strip restricted to the radial walls of the endodermis of P. sativum and well‐pronounced red suberin lamellae in C. arietinum and R. communis roots. Compared with recently investigated monocotyledoneous species, higher amounts of suberin by one order of magnitude were detected with the secondary state of development of dicotyledoneous species. Furthermore, the carbohydrate and protein contents of primary (Clivia miniata Reg. and Monstera deliciosa Liebm.), secondary (C. arietinum and R. communis) and tertiary endodermal cell walls (Allium cepa L. and Iris germanica L.) were determined. The relative carbohydrate content of secondary endodermal cell walls was low (14–20%) compared with the content of primary (42–50%) and tertiary endodermal cell walls (60%), whereas the protein content of isolated endodermal cell walls was high in primary (13%) and secondary (8%) and low in tertiary endodermal cell walls (0·9–2%). The results presented here indicate that the quantitative chemical composition of primary, secondary, and tertiary endodermal cell walls varies significantly. Finally, cell wall proteins are described as an additional important constituent of endodermal cell walls, with the highest concentrations occurring in primary (Casparian strips) and secondary endodermal cell walls.
Interactions between increasing CO2 concentration and temperature on plant growth
Authors: MORISON J. I. L. , LAWLOR D. W.
Published: March 2003

The global environment is changing with increasing temperature and atmospheric carbon dioxide concentration, [CO2]. Because these two factors are concomitant, and the global [CO2] rise will affect all biomes across the full global range of temperatures, it is essential to review the theory and observations on effects of temperature and [CO2] interactions on plant carbon balance, growth, development, biomass accumulation and yield. Although there are sound theoretical reasons for expecting a larger stimulation of net CO2 assimilation rates by increased [CO2] at higher temperatures, this does not necessarily mean that the pattern of biomass and yield responses to increasing [CO2] and temperature is determined by this response. This paper reviews the interactions between the effects of [CO2] and temperature on plants. There is little unequivocal evidence for large differences in response to [CO2] at different temperatures, as studies are confounded by the different responses of species adapted and acclimated to different temperatures, and the interspecific differences in growth form and development pattern. We conclude by stressing the importance of initiation and expansion of meristems and organs and the balance between assimilate supply and sink activity in determining the growth response to increasing [CO2] and temperature.
A modified two‐compartment model of the root: response to a pressure clamp
Authors: Murphy R.
Published: March 2003

A, membrane area Cs, solute concentration LP, hydraulic conductivity P, pressure Π, osmotic pressure ω, solute permeability QV, volume flow rate Qs, solute flow rate Qs*, active solute flow rate, σ, reflection coefficient of apical root ‘membrane’ t, time τ, time constant Va, apical xylem volume superscript a, apical xylem superscript b, basal xylem superscript x, xylem (apical and basal) superscript o, external medium  Magnani et al. (Planta 199, 296–306, 1996) have described a model of the root in which apoplastic transport of water occurs in the older (basal) regions, and intercellular transport occurs in the younger (apical) regions. They tested this model by performing pressure‐clamp experiments on excised root systems, and found that their model gave a good fit to the data. In the present study, their model is extended to include solute transport across an apical root ‘membrane’, with reflection coefficient, σ. When σ = 1 (i.e. no apoplastic transport across the root membrane) the model yields solutions for the volume flow rate that are identical in form to those of Magnani et al. (1996). Hence, given that their solutions provide a good description of the data, it seems possible to explain these data without invoking apoplastic water transport in the apical zone. For σ < 1, the predicted behaviour is more complex. It is concluded that the analysis of Magnani et al. (1996) overestimates the apoplastic hydraulic conductance of the basal zone (which could, in principle, be zero), and underestimates the intercellular hydraulic conductance of the apical zone. The magnitude of these errors depends on the solute permeability of the apical root membrane. The analysis suggests that solute transport parameters should be included in models of water transport across plant roots, even when σ≈ 1. For the exosmotic pressure clamp, this is emphasized by considering the case where σ = 1, and the basal region is replaced with a chamber filled with water. Under this regime, the volume‐relaxation time constant does not depend on the membrane hydraulic conductance, but is determined by the solute permeability.
A model of isoprene emission based on energetic requirements for isoprene synthesis and leaf photosynthetic properties for Liquidambar and Quercus
Authors: Niinemets Ü. , Tenhunen J. D. , Harley P. C. , Steinbrecher R.
Published: March 2003

We present a physiological model of isoprene (2‐methyl‐1,3‐butadiene) emission which considers the cost for isoprene synthesis, and the production of reductive equivalents in reactions of photosynthetic electron transport for Liquidambar styraciflua L. and for North American and European deciduous temperate Quercus species. In the model, we differentiate between leaf morphology (leaf dry mass per area, MA, g m−2) altering the content of enzymes of isoprene synthesis pathway per unit leaf area, and biochemical potentials of average leaf cells determining their capacity for isoprene emission. Isoprene emission rate per unit leaf area (μmol m−2 s−1) is calculated as the product of MA, the fraction of total electron flow used for isoprene synthesis (ɛ, mol mol−1), the rate of photosynthetic electron transport (J) per unit leaf dry mass (Jm, μmol g−1 s−1), and the reciprocal of the electron cost of isoprene synthesis [mol isoprene (mol electrons−1)]. The initial estimate of electron cost of isoprene synthesis is calculated according to the 1‐deoxy‐
D‐xylulose‐5‐phosphate pathway recently discovered in the chloroplasts, and is further modified to account for extra electron requirements because of photorespiration. The rate of photosynthetic electron transport is calculated by a process‐based leaf photosynthesis model. A satisfactory fit to the light‐dependence of isoprene emission is obtained using the light response curve of J, and a single value of ɛ, that is dependent on the isoprene synthase activity in the leaves. Temperature dependence of isoprene emission is obtained by combining the temperature response curves of photosynthetic electron transport, the shape of which is related to long‐term temperature during leaf growth and development, and the specific activity of isoprene synthase, which is considered as essentially constant for all plants. The results of simulations demonstrate that the variety of temperature responses of isoprene emission observed within and among the species in previous studies may be explained by different optimum temperatures of J and/or limited maximum fraction of electrons used for isoprene synthesis. The model provides good fits to diurnal courses of field measurements of isoprene emission, and is also able to describe the changes in isoprene emission under stress conditions, for example, the decline in isoprene emission in water‐stressed leaves.
Growth in elevated CO2 protects photosynthesis against high‐temperature damage
Authors: Taub Daniel R. , Seemann Jeffrey R. , Coleman James S.
Published: March 2003

We present evidence that plant growth at elevated atmospheric CO2 increases the high‐temperature tolerance of photosynthesis in a wide variety of plant species under both greenhouse and field conditions. We grew plants at ambient CO2 (~ 360 μmol mol−1) and elevated CO2 (550–1000 μmol mol−1) in three separate growth facilities, including the Nevada Desert Free‐Air Carbon Dioxide Enrichment (FACE) facility. Excised leaves from both the ambient and elevated CO2 treatments were exposed to temperatures ranging from 28 to 48 °C. In more than half the species examined (4 of 7, 3 of 5, and 3 of 5 species in the three facilities), leaves from elevated CO2‐grown plants maintained PSII efficiency (Fv/Fm) to significantly higher temperatures than ambient‐grown leaves. This enhanced PSII thermotolerance was found in both woody and herbaceous species and in both monocots and dicots. Detailed experiments conducted with Cucumis sativus showed that the greater Fv/Fm in elevated versus ambient CO2‐grown leaves following heat stress was due to both a higher Fm and a lower Fo, and that Fv/Fm differences between elevated and ambient CO2‐grown leaves persisted for at least 20 h following heat shock. Cucumis sativus leaves from elevated CO2‐grown plants had a critical temperature for the rapid rise in Fo that averaged 2·9 °C higher than leaves from ambient CO2‐grown plants, and maintained a higher maximal rate of net CO2 assimilation following heat shock. Given that photosynthesis is considered to be the physiological process most sensitive to high‐temperature damage and that rising atmospheric CO2 content will drive temperature increases in many already stressful environments, this CO2‐induced increase in plant high‐temperature tolerance may have a substantial impact on both the productivity and distribution of many plant species in the 21st century.
Ground monitoring the light–shadow windows of a tree canopy to yield canopy light interception and morphological traits
Authors: Giuliani Rita , Magnanini Eugenio , Fragassa Cristiano , Nerozzi Fabrizio
Published: March 2003

Monitoring the light–shadow windows of a tree via a grid system on the ground was performed on sunny summer days at high spatial resolution using a custom‐built, inexpensive scanner. The measurements were taken with two goals: (1) to quickly and remotely quantify the overall, short‐wave solar radiation (300–1100 nm) intercepted by the tree canopy, and (2) to yield such crown geometric traits as shape, size and the number of theoretical canopy leaf layers (leaf layer index, LLI) in relation to the section orthogonal to sunbeam direction (sun window). The ground readings at each measurement over the day were used to project a digitized shadow image. Image processing was applied and the intercepted radiation was calculated as the difference from the corresponding incoming radiation above the canopy. Tree‐crown size and shape were profiled via computer imaging by analysing the different shadow images acquired at the various solar positions during the day. It is notable that these combined images yielded the crown features without having to parameterize such canopy characteristics as foliage extension and spatial distribution.
The growth response of C4 plants to rising atmospheric CO2 partial pressure: a reassessment
Authors: Ghannoum O. , Caemmerer S. Von , Ziska L. H. , Conroy J. P.
Published: March 2003

Despite mounting evidence showing that C4 plants can accumulate more biomass at elevated CO2 partial pressure (p(CO2)), the underlying mechanisms of this response are still largely unclear. In this paper, we review the current state of knowledge regarding the response of C4 plants to elevated p(CO2) and discuss the likely mechanisms. We identify two main routes through which elevated p(CO2) can stimulate the growth of both well‐watered and water‐stressed C4 plants. First, through enhanced leaf CO2 assimilation rates due to increased intercellular p(CO2). Second, through reduced stomatal conductance and subsequently leaf transpiration rates. Reduced transpiration rates can stimulate leaf CO2 assimilation and growth rates by conserving soil water, improving shoot water relations and increasing leaf temperature. We argue that bundle sheath leakiness, direct CO2 fixation in the bundle sheath or the presence of C3‐like photosynthesis in young C4 leaves are unlikely explanations for the high CO2‐responsiveness of C4 photosynthesis. The interactions between elevated p(CO2), leaf temperature and shoot water relations on the growth and photosynthesis of C4 plants are identified as key areas needing urgent research.
Diurnal and developmental changes in levels of nucleotide compounds in developing maize endosperms
Authors: Scott M. P.
Published: March 2003

Maize endosperm is dependent on source tissues to supply the energy and carbon required for development. This supply varies during the course of each day and also throughout development. The impact of these variations on the metabolism of developing endosperm was examined by determining the energy status of the endosperm throughout the course of a day. The adenylate energy charge decreased as the tissue matured, and exhibited a distinct diurnal pattern, reaching a minimum in the afternoon, when the flux of photosynthate is the highest. The minimum value observed was similar to the adenylate energy charge in tissues under mild stress. As the endosperm matured, the adenylate energy charge decreased steadily. The levels of the polysaccharide precursors ADP‐glucose and UDP‐glucose did not reflect the daily fluctuations in adenylate energy charge, but did exhibit similar long‐term behaviour in the latter half of development, decreasing steadily after 21 d after pollination. Similarities in the metabolic patterns of adenylate and uridylate nucleotide levels are discussed in terms of the analogous roles of these compounds in starch and cellulose biosynthesis, respectively. These data provide insight into the metabolic rhythms occurring during endosperm development, and provide a framework for efforts directed toward metabolic engineering.
Regulatory roles of benzyl adenine and sucrose during wound response of the ribosomal protein gene, rpL34
Authors: Yu G.‐H. , An G.
Published: March 2003

We previously reported that a large subunit ribosomal protein gene, rpL34, was wound‐inducible in tobacco leaves, and that benzyl adenine (BA) enhanced the wound‐inducible expression of the gene. Here we report that the wound‐inducible expression of the rpL34 gene is enhanced by sucrose. The regulatory roles of BA and sucrose in wound‐signalling pathways were investigated using transgenic plants expressing a fusion molecule between the rpL34 promoter and the chloramphenicol acetyltransferase (cat) gene. Wounding caused a progressive increase in CAT activity; BA and sucrose enhanced the response. This indicates that regulation occurs at the transcriptional level. Diethyldithiocarbamic acid (DIECA) and other potent inhibitors of the octadecanoid pathway inhibited the rpL34 promoter, and also reduced BA inducibility of that wound response. However, inhibitors of the octadecanoid pathway did not affect the sucrose response. Protein kinase inhibitors increased BA enhancement while decreasing the sucrose effect, suggesting that protein kinases differentially regulate BA‐ and sucrose‐signalling in the promoter's wound response. Taken together, BA and sucrose enhanced the wound response of the rpL34 promoter via different signalling pathways, although they exerted overlapping effects on wound‐induction of the promoter.
Discrimination of nitrogen isotopes during absorption of ammonium and nitrate at different nitrogen concentrations by rice (Oryza sativa L.) plants
Authors: Yoneyama T. , Matsumaru T. , Usui K. , Engelaar W. M. H. G.
Published: March 2003

Studies of uptake of ionic sources of N by two hydroponically grown rice (Oryza sativa L.) cultivars (paddy‐field‐adapted Koshihikari and dryland‐adapted Kanto 168) showed that the magnitude of the nitrogen isotope fractionation (ɛ) for uptake of NH4+ depended on the concentrations of NH4+ and cultivar (averaging –6·1‰ for Koshihikari and –12·0‰ for Kanto 168 at concentrations from 40 to 200 mmol m−3 and, respectively, –13·4 and –28·9‰ for the two cultivars at concentrations from 0·5 to 4 mol m−3). In contrast, the ɛ for uptake of NO3− in similar experiments was almost insensitive to the N concentration, falling within a much narrower range (+3·2‰ to –0·9‰ for Koshihikari and –0·9‰ to –5·1‰ for Kanto 168 over NO3− concentrations from 0·04 to 2 mol m−3). From longer term experiments in which Norin 8 and its nitrate‐reductase deficient mutant M819 were grown with 2 or 8 mol m−3 NO3− for 30 d, it was concluded that the small concentration‐independent isotopic fractionation during absorption of this ion was not related to nitrate reductase activity.
Maturation of integrated functions during development. I. Modifications of the regulatory network during transition periods in Sorghum bicolor
Authors: Amzallag G. N.
Published: March 2003

Gibberellin (GA) and cytokinin (CK) were exogenously supplied at different periods of the vegetative development in Sorghum bicolor. Growth response to these hormonal treatments differed according to the developmental stage. This reveals the existence of discrete phenophases, each one characterized by a specific sensitivity to plant growth regulations (PGRs). Developmental changes in sensitivity were less accentuated in plants grown in optimal conditions than in plants exposed to 150 mM NaCl. Variations in organ connectance (the level of coordination in growth of the shoot, adventitious roots and seminal root) were analysed during vegetative growth of salt‐treated plants. This analysis shows a temporary decrease in connectance during the transition period between phenophases. From the effect of hormonal treatments on connectance, it was concluded that (i) the transition period coincides with a partial dismantling of the initial regulatory network followed by the emergence of a new network coordinating growth of the different organs; (ii) GA is involved in the process of emergence of a transition period; and (iii) duration of the transition period is considerably enlarged for plants exposed to NaCl stress. This dynamics of alternance of phenophase and transition periods enables the integration of the two modes of action of the PGRs (dose–response and change in sensitivity) within a unified framework.
RATP: a model for simulating the spatial distribution of radiation absorption, transpiration and photosynthesis within canopies: application to an isolated tree crown
Authors: Sinoquet H. , Le Roux X. , Adam B. , Ameglio T. , Daudet F. A.
Published: March 2003

The model RATP (radiation absorption, transpiration and photosynthesis) is presented. The model was designed to simulate the spatial distribution of radiation and leaf‐gas exchanges within vegetation canopies as a function of canopy structure, canopy microclimate within the canopy and physical and physiological leaf properties. The model uses a three‐dimensional (3D) representation of the canopy (i.e. an array of 3D cells, each characterized by a leaf area density). Radiation transfer is computed by a turbid medium analogy, transpiration by the leaf energy budget approach, and photosynthesis by the Farquhar model, each applied for sunlit and shaded leaves at the individual 3D cell‐scale. The model typically operates at a 20–30 min time step. The RATP model was applied to an isolated, 20‐year‐old walnut tree grown in the field. The spatial distribution of wind speed, stomatal response to environmental variables, and light acclimation of leaf photosynthetic properties were taken into account. Model outputs were compared with data acquired in the field. The model was shown to simulate satisfactorily the intracrown distribution of radiation regime, transpiration and photosynthetic rates, at shoot or branch scales.
Effects of high‐temperature stress on microsporogenesis in heat‐sensitive and heat‐tolerant genotypes of Phaseolus vulgaris
Authors: Porch T. G. , Jahn M.
Published: March 2003

High ambient temperature (32/27 °C, day/night, 12 h photoperiod) applied prior to anthesis to Phaseolus vulgaris plants results in abnormal pollen and anther development during microsporogenesis. Scanning and transmission electron microscopy were used to examine anther and pollen morphology and pollen wall architecture after heat stress was applied to two genotypes that differ with respect to yield potential under high‐temperature field conditions: one, a heat‐sensitive, Mesoamerican genotype, A55, the second, a heat‐tolerant, Andean genotype, G122. High‐temperature treatment of both genotypes was applied 1–13 d before anthesis. Under heat stress, the heat‐tolerant genotype showed anther and pollen characteristics that were generally similar to the low temperature controls. In contrast, after 9 d of heat treatment before anthesis, the anthers of the heat‐sensitive genotype were indehiscent and contained abnormal pollen. Pollen wall architecture was also affected in the 12 and 13 d treatments. In addition to the morphological changes, the heat‐sensitive genotype also experienced reduced pollen viability and reduced yield in high‐temperature experiments conducted in both the greenhouse and field.
The effect of nitrogen and phosphorus deficiency on flavonol accumulation in plant tissues
Authors: Stewart A. J. , Chapman W. , Jenkins G. I. , Graham I. , Martin T. , Crozier A.
Published: March 2003

The flavonol content of Arabidopsis thaliana and tomato seedlings was assessed in conditions of reduced nitrogen or phosphorus availability. In both systems, a significant inverse relationship was observed between nutrient availability and flavonol accumulation, with nitrogen limitation promoting the greatest increase in flavonols. A trial was established to determine the effects of decreased nitrogen and phosphorus availability on the flavonol content of leaf and fruit tissues of tomato plants (Lycopersicon esculentum cv. Chaser) in a commercial situation. Nutrients were supplied by a hydroponic system with nutrient regimes designed to provide the highest and lowest nitrogen and phosphorus levels with which it is possible to support plant growth and fruit set. Fruiting was abundant and tomato fruits were harvested at mature green, breaker and red stages of ripening; leaves were also harvested from the tops of the plants. All tissues were analysed for flavonol content using reversed‐phase high‐performance liquid chromatography. Flavonol accumulation in the leaves of mature tomato plants was found to increase significantly in response to nitrogen stress, whereas phosphorus deficiency did not elicit this response. Reduced nitrogen availability had no consistent effect on the flavonol content of tomato fruits. Phosphorus deficiency elicited an increase in flavonol content in early stages of ripening. Effects of nutrient stress on the flavonol content of tomato fruits were lost as ripening progressed. The findings suggest that nutrient status may be employed to manipulate the flavonol content of vegetative tissues but cannot be used to elevate the flavonol content of tomato fruit.
Molecular and genetic aspects of plant responses to osmotic stress
Authors: Xiong L. , Zhu J.‐K.
Published: March 2003

Drought, high salinity and freezing impose osmotic stress on plants. Plants respond to the stress in part by modulating gene expression, which eventually leads to the restoration of cellular homeostasis, detoxification of toxins and recovery of growth. The signal transduction pathways mediating these adaptations can be dissected by combining forward and reverse genetic approaches with molecular, biochemical and physiological studies. Arabidopsis is a useful genetic model system for this purpose and its relatives including the halophyte Thellungiella halophila, can serve as valuable complementary genetic model systems.
Co‐action of temperature and phosphate in inducing turion formation in Spirodela polyrhiza (Great duckweed)*
Authors: Appenroth K.‐J.
Published: March 2003

Increased phosphate concentration, higher temperature and addition of glucose all increased the number of fronds and turions of the duckweed Spirodela polyrhiza formed under in vitro conditions. Increasing the number of turions by increasing the plant biomass does not mean that the developmental process (switch of the programme of the primordia from vegetative fronds toward resting turions) has been specifically influenced. The specific turion yield (STY; number of turions formed by one frond) and the time of onset of turion formation have been used as more specific measures of turion induction. At more than 30 µm initial phosphate the STY was increased by lower temperature (15 °C) and became independent of the phosphate concentration. Between 10 and 30 µm and at higher temperatures (25  °C) the STY was increased by lower phosphate levels. The stimulatory effect of lower temperature was more pronounced than that of lower phosphate concentrations. Decreased phosphate concentration highly accelerated the formation of the first turions. The influence of low temperature was small at lower phosphate concentration but became dominant at higher concentrations (especially in autotrophic cultures). Low phosphate levels (e.g. 10 µm) and low temperatures (e.g. 15 °C) both represent specific turion‐inducing factors having significant interactive effects. In S. polyrhiza, these signals may replace the interactive effects of photoperiods and low temperature known from other hydrophytes in turion induction under natural conditions.
Temperature response of parameters of a biochemically based model of photosynthesis. I. Seasonal changes in mature maritime pine (Pinus pinaster Ait.)
Authors: Medlyn B. E. , Loustau D. , Delzon S.
Published: March 2003

Responses of plant processes to temperature may vary according to the time scale on which they are measured. In this study, both short‐term and seasonal responses of photosynthesis to temperature were examined. A field study of seasonal changes in the temperature response of photosynthesis was conducted on two provenances, French and Moroccan, of mature maritime pine (Pinus pinaster Ait.). Measurements were made every 2 months over a 1‐year period and used to parameterize a mechanistic model of photosynthesis. Temperature responses of maximum Rubisco activity, Vcmax, and potential electron transport rate, Jmax, were obtained for each measurement period, as was the response of stomatal conductance, gs, to water vapour pressure deficit (VPD). Absolute values of Vcmax and Jmax at 25 °C were related to needle nitrogen content, Narea.Narea, and thus Vcmax and Jmax, were negatively correlated with the mean minimum temperature in the month preceding measurements. The ratio of Jmax : Vcmax at 25 °C varied between 1 and 1·7 but did not show any seasonal trend. Nor was there any seasonal trend in the relative temperature response of Vcmax, which had an activation energy Ha of approximately 57 kJ mol−1 throughout the experiment. The activation energy of Jmax was also close to constant throughout the experiment, averaging 39 kJ mol−1. For the French provenance, the optimal temperature of Jmax was positively correlated with the maximum temperature of the previous day, but no such correlation was found for the Moroccan provenance. The response of gs to VPD also varied seasonally, with much stronger stomatal closure in winter months. Taken together, these results implied a translational shift downwards of the photosynthetic temperature response curve with increasing Tprev, and a shift in the temperature optimum of photosynthesis of 5–10 °C between summer and winter. These results illustrate that the short‐term temperature response of photosynthesis varies significantly on a seasonal basis.
Hydraulic and photosynthetic co‐ordination in seasonally dry tropical forest trees
Authors: Brodribb T. J. , Holbrook N. M. , Gutiérrez M. V.
Published: March 2003

In the present study the linkage between hydraulic, photosynthetic and phenological properties of tropical dry forest trees were investigated. Seasonal patterns of stem‐specific conductivity (KSP) described from 12 species, including deciduous, brevi‐deciduous and evergreen species, indicated that only evergreen species were consistent in their response to a dry‐to‐wet season transition. In contrast, KSP in deciduous and brevi‐deciduous species encompassed a range of responses, from an insignificant increase in KSP following rains in some species, to a nine‐fold increase in others. Amongst deciduous species, the minimum KSP during the dry season ranged from 6 to 56% of wet season KSP, indicating in the latter case that a significant portion of the xylem remained functional during the dry season. In all species and all seasons, leaf‐specific stem conductivity (KL) was strongly related to the photosynthetic capacity of the supported foliage, although leaf photosynthesis became saturated in species with high KL. The strength of this correlation was surprising given that much of the whole‐plant resistance appears to be in the leaves. Hydraulic capacity, defined as the product of KL and the soil–leaf water potential difference, was strongly correlated with the photosynthetic rate of foliage in the dry season, but only weakly correlated in the wet season.