bluuebunny/crossref_metadata_2025 huggingface dataset:
Cytosolic ion exchange dynamics: insights into the mechanisms of component ion fluxes and their measurement
Authors: Britto Dev T. , Kronzucker Herbert J.
Published: August 2003

The quantification of cellular pool sizes of ions is essential for the understanding of the energetics of metabolic and membrane transport processes. No less important is the quantification of ion fluxes into, out of, and within cells. Of the variety of analytical methods available, only one, compartmental analysis by tracer efflux (CATE), can be used to simultaneously determine subcellular ion pool sizes and resolve ion fluxes. Thus, this methodology can be used to provide steady-state isotherms for major flux processes not amenable to direct measurement, such as effluxes or xylem fluxes, and to develop hypotheses about mechanisms underlying them. The exchange half-time for an ion in a cellular compartment emerges as a key CATE parameter that relates pool sizes with fluxes, and is a term that can be used to estimate errors in a wide range of findings in plant ion relations, and verify their plausibility. Case studies involving the flux and compartmentation of Ca2+, K+, and inorganic N are presented.
Photoacclimation involves modulation of the photosynthetic oxygen-evolving reactions in Dunaliella tertiolecta and Phaeodactylum tricornutum
Authors: Quigg Antonietta , Beardall John , Wydrzynski Tom
Published: August 2003

Net energy accumulation by marine microalgae at very low photon fluxes involves modulation of several attributes related to both the growth and photosynthetic physiology of these organisms. Here we studied flash-induced oscillatory patterns in oxygen evolution by previously dark-adapted cells of the green alga Dunaliella tertiolecta (Butcher) and the diatom Phaeodactylum tricornutum (Bohlin). The activity of the oxygen-evolving complex was found to be species-specific and influenced by photoacclimation. Results from measurements of oxygen flash yield obtained for these organisms grown under light-saturating conditions are directly comparable to those previously reported in the literature for other microalgae and higher plants. However, similar measurements on cells grown in low-light and/or light-starved conditions indicate an increased level of backward transitions (double misses) leading to the formation of super-reduced states (i.e. S–1 and S–2). Thus, in this communication, we present the first evidence that super-reduced states can be generated in vivo and speculate, on how they may be physiologically important.
Analysis of local and systemic spread of the crucifer-infecting TMV-Cg virus in tobacco and several Arabidopsis thaliana ecotypes
Authors: Arce-Johnson Patricio , Medina Consuelo , Padgett Hal S. , Huanca Wilson , Espinoza Carmen
Published: August 2003

The crucifer-infecting tobacco mosaic virus, TMV-Cg, infects Arabidopsis thaliana (L.) Heynh. efficiently without causing severe symptoms. The systemic spread of TMV-Cg in Arabidopsis was evaluated in 14�ecotypes. Five days after inoculation, TMV-Cg was detected in apical leaves of 8 out of 14 ecotypes. As expected, the spread of TMV-Cg in the ecotypes tested was considerably faster than that of tobacco mosaic virus (TMV-U1). To study the participation of viral proteins in the TMV-Cg-induced infection, a complete genomic cDNA of TMV-Cg was cloned. The role of TMV-Cg movement protein in systemic spread was tested with a hybrid virus, constructed from the TMV-U1 genome and the TMV-Cg movement protein gene. Contrary to expectations, the systemic spread of this hybrid in Arabidopsis was similar to that of TMV-U1. The failure of the hybrid virus to spread at rates similar to those of TMV-Cg was not due to restrictions in local movement. In tobacco (Nicotiana tabacum L.), the hybrid virus spread efficiently and induced systemic mosaic symptoms characteristic of TMV-U1. The TMV-Cg cDNA clone provides an attractive tool to study virus–host interactions.
Extension of a Farquhar model for limitations of leaf photosynthesis induced by light environment, phenology and leaf age in grapevines (Vitis vinifera L. cvv. White Riesling and Zinfandel)
Authors: Schultz Hans R.
Published: August 2003

Measurements of gas exchange and stomatal conductance were made on potted and field-grown grapevines (Vitis vinifera L.) on leaves from different light environments (sun and shade) at different phenological stages during the season to parameterise the Farquhar model. The model parameters for Rubisco activity (Vcmax), maximum electron transport rate (Jmax), and triose-phosphate utilisation (TPU) were estimated on the basis of a large data set (n = 105) of CO2 assimilation (A) versus internal CO2 pressure (Ci) curves. Leaf age was described with the leaf plastochron index (LPI). Stomatal coupling to photosynthesis was modelled with the Ball–Woodrow–Berry empirical model of stomatal conductance. Mature shade leaves had 35–40% lower values of Vcmax, Jmax and TPU than sun leaves. The difference between leaf types decreased at the end of the season. The ratio Jmax / Vcmax and values of day respiration (Rd) and CO2 compensation point in the absence of mitochondrial respiration (Γ*) varied little during the season and were independent of LPI. Validation of the model with independent diurnal data sets of measurements of gas exchange and stomatal conductance at ambient CO2 concentrations for three days between June and October, covering a large range of environmental conditions, showed good agreement between measured and simulated values.
Effects of UV-B radiation on plant growth, symbiotic function and concentration of metabolites in three tropical grain legumes
Authors: Chimphango Samson B. M. , Musil Charles F. , Dakora Felix D.
Published: August 2003

Vigna unguiculata (L.) Walp. (cowpea), Glycine max (L.) Merr (soybean) and Phaseolus vulgaris (L.) (common bean) plants were exposed to UV-B radiation at above- and below-ambient levels, and their effects on growth, symbiotic performance and root concentration of metabolites were assessed. Moderately and highly elevated UV-B exposures averaging 32 and 62% above ambient had no effect on plant total dry matter, nodule number, nodule mass, nodule size, N fixed or root concentration of flavonoids, anthocyanins, soluble sugars and starch in the three species studied. However, N concentrations were markedly reduced in roots of G. max and P.��vulgaris, and in leaves of P. vulgaris, which contrasted with the significant increase in stems and leaves of V.�unguiculata. Below-ambient UV-B exposures averaging 22% of ambient also altered growth and metabolism of these legumes. Total plant dry matter, nodule number, nodule dry mass, N fixed and root starch concentrations in V.�unguiculata decreased relative to both visible and UV-A radiation controls, whereas in G. max and P. vulgaris, these parameters were not altered. Root concentrations of flavonoids and anthocyanins in all species tested were also unchanged with below-ambient UV-B exposures. Taken together, growth and symbiotic function of these species remained unaltered with exposure to above-ambient UV-B, but differed in their response to below-ambient UV-B radiation.
A suite of novel promoters and terminators for plant biotechnology
Authors: Schünmann Petra H. D. , Llewellyn Danny J. , Surin Brian , Boevink Petra , Feyter Robert C. De , Waterhouse Peter M.
Published: August 2003

The gene regulation signals from subterranean clover stunt virus (SCSV) were investigated for their expression in dicot plants. The SCSV genome has at least eight circular DNA molecules. Each circular DNA component contains a promoter element, a single open reading frame and a terminator. The promoters from seven of the segments were examined for their strength and tissue specificity in transgenic tobacco (Nicotiana tabacum L.), potato (Solanum tuberosum L.) and cotton (Gossypium hirsutum L.) using a GUS reporter gene assay system. While the promoters of many of the segments were poorly expressed, promoters derived from segments 4 and 7 were shown to direct high levels of expression in various plant tissues and organs. The segment 1 promoter directs predominantly callus-specific expression and, when used to control a selectable marker gene, facilitated the transformation of all three species (tobacco, potato and cotton). From the results, a suite of plant expression vectors (pPLEX) derived from the SCSV genome were constructed and used here to produce herbicide- and insect-resistant cotton, demonstrating their utility in the expression of foreign genes in dicot crop species and their potential for use in agricultural biotechnology.
A suite of novel promoters and terminators for plant biotechnology. II. The pPLEX series for use in monocots
Authors: Schünmann Petra H.D. , Surin Brian , Waterhouse Peter M.
Published: August 2003

A suite of plant expression vectors (pPLEX), constructed from the gene regulation signals from subterranean clover stunt virus (SCSV) genome, has previously been used in dicot transformation for a variety of applications in plant biotechnology. To assess their use for the transformation of monocots, a number of modifications were made to the basic vector series and assessed in rice. In their unmodified forms, the SCSV promoters directed low levels of gene expression, however, insertion of an intron between the promoter and the transgene open reading frame (analogous to the rice actin and maize ubiquitin promoter systems) increased transgene expression 50-fold. The expression patterns from the intron-modified SCSV (segments 4 and 7) promoters were very similar to those directed by the actin or ubiquitin promoters. All promoter systems investigated directed expression that appeared to be constitutive within leaf tissue, and localised to the epidermal and vascular tissues of the root. The pPLEX vectors described here are an important counterpart to the dicot pPLEX series and have the potential to be useful in monocot research and biotechnology.
Dormancy release in Lolium rigidum seeds is a function of thermal after-ripening time and seed water content
Authors: Steadman Kathryn J. , Crawford Andrew D. , Gallagher Robert S.
Published: August 2003

Dormancy release in seeds of Lolium rigidum Gaud. (annual ryegrass) was investigated in relation to temperature and seed water content. Freshly matured seeds were collected from cropping fields at Wongan Hills and Merredin, Western Australia. Seeds from Wongan Hills were equilibrated to water contents between 6 and 18% dry weight and after-ripened at constant temperatures between 9 and 50°C for up to 23 weeks. Wongan Hills and Merredin seeds at water contents between 7 and 17% were also after-ripened in full sun or shade conditions. Dormancy was tested at regular intervals during after-ripening by germinating seeds on agar at 12-h alternating 15°C (dark) and 25°C (light) periods.Rate of dormancy release for Wongan Hills seeds was a positive linear function of after-ripening temperature above a base temperature (Tb) of 5.4°C. A thermal after-ripening time model for dormancy loss accounting for seed moisture in the range 6–18% was developed using germination data for Wongan Hills seeds after-ripened at constant temperatures. The model accurately predicted dormancy release for Wongan Hills seeds after-ripened under naturally fluctuating temperatures. Seeds from Merredin responded similarly but had lower dormancy at collection and a faster rate of dormancy release in seeds below 9% water content.
Partial rootzone drying: effects on growth and fruit quality of field-grown grapevines (Vitis vinifera)
Authors: Santos Tiago P. dos , Lopes Carlos M. , Rodrigues M. Lucília , Souza Claudia R. de , Maroco João P. , Pereira João S. , Silva Jorge R. , Chaves M. Manuela
Published: August 2003

A study to assess the effects of the Partial Rootzone Drying (PRD) irrigation strategy in comparison to other irrigation systems was carried out in southern Portugal in two field-grown grapevines varieties, Moscatel and Castelão. We addressed the question of whether by regulating growth and plant water use, the PRD system would enable an equilibrated vegetative development, leading to a favourable capture of solar radiation for photoassimilate production and, at the same time to provide an optimum environment for fruit maturation. Three irrigation schemes were applied in addition to the non-irrigated (NI) vines: partial root drying (PRD), 50% of crop evapotranspiration (ETc), supplied to only one side of the root system while the other one was allowed to dry, alternating sides every 15 days; deficit irrigated (DI), 50% ETc supplied, half to each side of the root system and full irrigated (FI, 100% ETc). During the whole season FI plants of both varieties exhibited a high leaf predawn water potential (ψpd , ca�–0.2�MPa) while a progressive decline was observed in NI plants, reaching ψpd values near –0.7 MPa at the end of August. PRD and DI presented intermediate values. PRD vines exhibited a stronger control over vegetative growth as compared with DI and FI plants. This was expressed by lower values of total leaf area at harvest, leaf layer number, canopy wideness and water shoots number, allowing a higher light interception at the cluster zone that induced an improvement in some berry quality characteristics. Watering had no significant effects on sugar accumulation in the berries but led to a favourable increase in the must titratable acidity, mainly in Castelão. Whereas in DI and FI treatments berry skin anthocyanins and phenols content were always lower than in NI, in PRD there was either no reduction or the reduction was much lower than in the other irrigation treatments. Water use efficiency (WUE) was increased by about 80% in PRD and DI when compared with FI, as a result of almost similar yields in the three treatments. Yield gains of irrigated plants in relation to NI were modest, explained by the rainy spring in both years.
Regulation of canopy conductance and transpiration and their modelling in irrigated grapevines
Authors: Lu Ping , Yunusa Isa A. M. , Walker Rob R. , Müller Warren J.
Published: August 2003

Whole-vine transpiration was estimated for well-watered nine-year-old Sultana grapevines (Vitis vinifera L. cv. Sultana) from xylem sap flow measured with Granier's heat-dissipation probes. Canopy conductance of the grapevine was calculated by inverting the Penman–Monteith equation. Transpiration from grapevine canopies was strongly controlled by the canopy conductance. Canopy conductance decreased exponentially with increasing vapour pressure deficit (VPD) except in the morning when solar radiation was less than 200 W m–2 and the canopy conductance was predominantly limited by the solar radiation. A non-linear model of canopy conductance as a function of the solar radiation and VPD explained > 90% of the variation observed in canopy conductance. Under contrasting VPD conditions (daytime maximum of 3 kPa vs 8 kPa), grapevines were able to regulate their canopy conductance from 0.006 to 0.001 m s–1 to maintain a near constant transpiration. Whole-canopy transpiration calculated from modelled canopy conductance using the Penman–Monteith equation was highly correlated with the measured transpiration (sap flow) values over the range of 0–0.20 mm h–1 (R2 > 0.85). Cross-validation shows that these mechanistic models based on solar radiation and VPD provide good predictions of canopy conductance and transpiration under the conditions of the study.
Loss of pod set caused by drought stress is associated with water status and ABA content of reproductive structures in soybean
Authors: Liu Fulai , Andersen Mathias N. , Jensen Christian R.
Published: August 2003

Drought stress occurring during flowering and early pod expansion decreases pod set in soybean (Glycine max L. Merr.). The failure of pod set may be associated with changes in water status and ABA content in soybean reproductive structures under drought stress. To test this, pot experiments in an environmentally-controlled greenhouse were conducted, in which soybeans were exposed to drought stress around anthesis. In a preliminary experiment (Expt. I), irrigation was withheld at –6 (D1), –4 (D2) and –2 (D3) to 11 days after anthesis (DAA), then the droughted plants were re-watered to control levels until physiological maturity. Pod set percentage, seed yield and yield components were recorded. In the main experiment (Expt. II), irrigation was withheld from –11 to 10�DAA. During the drying cycle, parts of the droughted plants were re-watered at 0, 3, 5, 7 and 10 DAA and kept well-watered until physiological maturity. In Expt. II, water status, ABA contents in xylem sap, leaves, flowers and pods were measured at 0, 3, 5, 7 and 10 DAA. The water potential in the flowers and pods was always lower than the leaf water potential. Turgor was decreased in leaves by drought 3 DAA, but remained at control levels in flowers and pods. Compared with well-watered plants, in severely droughted plants (10 DAA), xylem [ABA] increased about 60-fold; leaf [ABA] increased 9-fold; pod [ABA] increased 6-fold. During soil drying, flower and pod [ABA] was linearly correlated with xylem [ABA] and leaf [ABA], indicating that root-originated ABA and/or leaf ABA were the likely sources of ABA accumulated in the flowers and pods. In Expt. I, pod set and seed number per pod was unaffected by drought stress, while seed yield and individual seed weight was significantly decreased by drought. In Expt. II, significant reductions in pod set and seed yield were observed when re-watering the droughted plants at 3–5 DAA, re-watering the droughted plants later than this stage resulted in a similar pod set. Collectively, these results suggest that drought-induced decrease in water potential and increase in ABA content in flowers and pods at critical developmental stage (3–5 DAA) contribute to pod abortion in soybean.
A H2O2-forming peroxidase rather than a NAD(P)H-dependent O2• - synthase may be the major player in cell death responses controlled by the Pto - Fen complex following fenthion treatment
Authors: Biasi Margherita G. De , Astolfi Stefania , Acampora Andrea , Zuchi Sabrina , Fonzo Valentina , Santangelo Enrico , Caccia Riccardo , Badiani Maurizio , Soressi Gian Piero
Published: August 2003

Four tomato (Lycopersicon esculentum Mill.) near-isogenic lines were treated by foliar spraying with the insecticide fenthion. Two, Riogrande and Rimone, differed from each other only for the presence in the latter of the Fen gene, conferring propensity to develop foliar symptoms upon exposure to fenthion. The other two, namely RC332 and RC131, were the transgenic versions of Riogrande and Rimone, respectively, harbouring the Gox gene encoding for glucose oxidase of Aspergillus niger. The production of H2O2 as well as the activities of H+-ATPase, NAD(P)H-dependent superoxide synthase, catalase, peroxidase, and Cu,Zn-superoxide dismutase were evaluated in the foliar tissues up to 24 h after exposure to fenthion. The Fen gene conferred sensitivity to fenthion, regardless of the expression of a Gox transgene. A prolonged accumulation of H2O2 was observed in the leaves of Rimone and of RC131, which was instead transient in Riogrande and in RC332. In all the tomato lines, exposure to fenthion induced rapid but transient changes in the activities of most enzymes. The only exception was peroxidase activity in the leaves of Rimone and of RC131, which steadily increased until the end of the sampling period. It is suggested that the sensitivity of Rimone to fenthion might be due to the sustained activity of a H2O2-forming peroxidase.
The effect of leaf removal and canopy height on whole-vine gas exchange and fruit development of Vitis vinifera L. Sauvignon Blanc
Authors: Petrie Paul R. , Trought Michael C. T. , Howell G. Stanley , Buchan Graeme D.
Published: August 2003

Canopy topping and leaf removal are management practices commonly used in New Zealand vineyards to increase light and pesticide penetration to the fruit zone, thus, reducing disease incidence. Previous research has suggested that an increase in photosynthesis occurs when leaves are removed, and this may compensate for the reduced leaf area. However, it is difficult to extrapolate single-leaf photosynthesis measurements to a whole-plant scale. Therefore the extent of the compensation is unknown. To evaluate the impact of leaf removal and canopy height on whole-vine photosynthesis, treatments were imposed during the lag phase of berry growth. Leaves were removed from the lower quarter of the canopy, or vines were topped to three quarters of the height of control plants, in a two-by-two-factorial design. Both topping and leaf removal caused a decrease in whole-vine photosynthesis immediately after the treatments were imposed. Leaf removal, but not topping height, reduced photosynthesis on a per unit leaf area basis. This suggests that the lower portion of the canopy contributes more than the upper portion of the canopy to whole-vine photosynthesis. When measurements were made again approximately two months later, tall vines without leaf removal had a higher photosynthesis rate than the other treatments. Fruit yield, sugar content, vine carbohydrate reserves and pruning weights followed trends similar to those observed for photosynthesis, suggesting that although some photosynthetic compensation occurred, the defoliation treatments had a negative effect on vine growth.
Artificial infection by endophytes affects growth and mycorrhizal colonisation of Lolium perenne
Authors: Müller Joachim
Published: August 2003

Fungal endophytes of the Clavicipitaceae live in aboveground parts of many grasses of temperate regions. Seedlings of two different cultivars of perennial ryegrass, Lolium perenne L., were artificially infected with one of two endophytes, Epichloë typhina and Neotyphodium lolii, or mock infected. The seedlings were then grown in a mixture of vermiculite and sand in the presence or absence of an inoculum of an arbuscular mycorrhizal fungus (Sclerocystis sp.). Ten weeks later, the plants were harvested and analysed with respect to mycorrhizal colonisation and shoot and root biomass. Endophyte-infected plants showed a significant decrease of mycorrhizal colonisation. This decrease was in some cases correlated with alterations of growth. Depending on the endophyte strains and on the mycorrhizal status, shoot–root biomass ratios were significantly affected. For both L. perenne cultivars, arbuscular mycorrhiza formation led to a higher shoot–root biomass ratio in N. lolii-infected plants and, conversely, to a lower shoot–root ratio in E. typhina-infected plants. These results indicate that effects of endophytes may be enhanced or counterbalanced in the presence of arbuscular mycorrhizal fungi.
Cold-induced photoinhibition and winter leaf-loss in the broad-leaved tree Aristotelia serrata (Elaeocarpaceae)
Authors: Dungan Roger J. , Whitehead David , McGlone Matt , Duncan Richard P. , Allen Robert B.
Published: August 2003

Relationships between cold-induced photoinhibition of photosynthesis and winter leaf-loss were investigated for leaves of a wineberry (Aristotelia serrata J. R. Forst. and G. Forst.) tree. Previous work identified consistent differences in leaf loss between shaded and exposed parts of wineberry trees, possibly related to the adverse effects of cold temperatures and high irradiance during winter frosts. Differences in leaf temperature and irradiance between shaded and exposed parts of a wineberry canopy were quantified, together with their relationships to decline and recovery of cold-induced photoinhibition of photosynthesis (measured by the ratio of variable to maximal chlorophyll fluorescence; Fv / Fm). These data, together with measurements of leaf loss from selected shoots, were used to test the hypothesis that leaf loss is greater from open than from shaded parts of wineberry canopies, and increases with decreases in Fv / Fm following winter frosts. Fv / Fm of leaves on exposed shoots was always significantly (P<0.001) lower than leaves on shaded shoots. The absolute difference in Fv / Fm ranged from 0.11 to 0.57. Fv / Fm declined markedly following periods of freezing leaf temperatures (Tl), but recovered after several days of non-freezing Tl. A multiple regression model, including terms for integrated irradiance (Qi), minimum Tl, Tl at the time of Fv / Fm measurements, and the value of Fv / Fm, on the previous day explained 95% of the variability in daily Fv / Fm. Leaf loss was greater from exposed shoots (0.22 leaves shoot–1 d–1) than from shaded shoots (0.07 leaves shoot–1 d–1; P<0.001) and increased following frost-induced decreases in the value of Fv / Fm. Measured rates of leaf loss from exposed shoots were significantly related to Fv / Fm measured 14�d previously (r2=0.89, P<0.01), supporting our hypothesis.
Whole-plant transpiration efficiency of Sultana grapevine grown under saline conditions is increased through the use of a Cl - -excluding rootstock
Authors: Gibberd Mark R. , Walker Rob R. , Condon Anthony G.
Published: August 2003

The aim of this study was to test the influence of salinity (1, 20, 40 and 80 mol m–3) on the transpiration efficiency (W = biomass / water transpired), lamina gas exchange and carbon isotope discrimination (Δ) of grapevine (Vitis vinifera L. cv. Sultana) grown on own roots or grafted to a Cl–-excluding rootstock (Ramsey; Vitis champini�L.). Growth of own-rooted and Ramsey-rooted vines irrigated with a salinity of 40 mol m–3 was reduced by 55 and 12%, respectively, compared with vines irrigated with 1 mol m–3. At 1 mol m–3 W of Ramsey-rooted vines was 1.3-fold higher than own-rooted vines (3.9 and 3.0 g L–1, respectively). Salinity resulted in a decrease in W of own-rooted vines (31% reduction at both 40 and 80 mol m–3). In contrast, W of Ramsey-rooted vines increased by up to 1.25-fold under saline conditions. Consequently, at 80 mol m–3 W of Ramsey-rooted vines was 2-fold higher than own-rooted vines. To our knowledge this is the first demonstration of the potential of a rootstock to increase W of a crop species under saline conditions. The rootstock-dependent differences in grapevine W under saline conditions were not determined by differences in lamina gas exchange. Differences in W associated with rootstock may be attributed to differences in ion uptake and the energy requirements associated with ion partitioning and the formation of compatible solutes.
Screening methods for waterlogging tolerance in lucerne: comparative analysis of waterlogging effects on chlorophyll fluorescence, photosynthesis, biomass and chlorophyll content
Authors: Smethurst Christiane F. , Shabala Sergey
Published: August 2003

Waterlogging is a serious environmental stress on lucerne (Medicago sativa) affecting its agronomic performance. To facilitate the breeding process, efficient tools to screen a population of lucerne cultivars are needed. In this study, a comparative analysis of waterlogging effects on leaf photosynthesis, pigment composition, PSII photochemistry, and plant growth characteristics was undertaken using four different lucerne cultivars (Aurora, Hunter River, L153 and Sequel HR). Two-month-old plants, grown in half-strength Hoagland nutrient solution, were waterlogged for 16 days, and plant physiological characteristics were monitored at regular intervals (every few days). All cultivars had significantly reduced fresh and dry weight for both shoots and roots after 16 days of waterlogging. Root biomass showed a greater percentage of reduction than did shoot biomass. As waterlogging stress developed, chlorophyll content, CO2 assimilation rate, transpiration rate, stomatal conductance and maximal quantum efficiency of PSII (Fv/Fm) decreased significantly. Chlorophyll a and b content gradually decreased over the time of the experiment in the stressed cultivars, and leaf chlorosis became increasingly evident. Although most of the parameters showed significant changes as waterlogging progressed, limitations render some of them inapplicable for screening. It is concluded that for practical screening purposes, the Fv/Fm ratio is the most appropriate. A significant difference between control and waterlogged plants became evident as early as day 7. Possible physiological mechanisms involved are discussed.
Steady-state water relations of soybean seedling roots
Authors: Murphy Ricardo
Published: August 2003

A previous four-compartment steady-state model of the root is extended to include the following: gradients of pressure (P) and osmotic pressure (Π) in the rooting medium, cortical apoplast and xylem; unloading of solutes to the xylem from internal stores; and apoplastic water flow across the endodermis. The model is tested by determining the steady-state relationship between applied pressure (Po) and volume flow rate (Qv) for excised roots of 4-day-old soybean seedlings under various conditions (vermiculite- versus water-cultured plants, different salt concentrations, permeant versus impermeant solutes). It is concluded that apoplastic volume flow across the endodermis is negligible. It is also argued that external or apoplastic gradients of P and Π tend to reduce the magnitude of the anomalous offset often observed in Po–Qv curves. The trans-root difference in water potential (ΔΨ) is shown to be a linear function of Qv at low Qv , but both ΔΨ(Qv) and Po(Qv) become nonlinear at high Qv . This unusual behavior may result from a nonlinear dependence of apoplastic pressure gradients and / or symplastic solute-concentration gradients on Qv . Alternatively, it might reflect saturation of water transport in plasmodesmata or aquaporins. The ΔΨ associated with growth-induced water uptake is shown to be negligible compared with the growth-induced water potentials measured in the stem elongation zone.
Tissue stresses and resistance to water flow conspire to uncouple the water potential of the epidermis from that of the xylem in elongating plant stems
Authors: Passioura John B. , Boyer John S.
Published: August 2003

Considerable evidence exists that, in elongating dicot stems such as soybean hypocotyls: (1) the elongation rate is controlled largely by the mechanical properties of the epidermal cell walls; (2) the inner tissue is under compression in the sense that the turgor pressure of the cells is not fully borne by their cell walls; (3) the surplus turgor pressure in this inner tissue generates a force that is transmitted to the epidermis, where it drives irreversible elongation of the cell walls; and (4) the radial flow of water from the xylem to the rest of the tissue, needed to fill the expanding cells, is driven by gradients in water potential. On the basis of these propositions, this paper develops a mathematical description of the biophysical control of elongation rate and the radial distribution of water potential in the growing plant stem. Additional simplifying assumptions are that the osmotic pressure of the cells and their elastic modulus are constant throughout, and that the proportion of the tensile force that is borne by the walls of the inner cells is also constant. We assume, further, that the epidermal cell walls yield plastically in response to the tensile force they experience, as in the Lockhart model of cell expansion. The analysis gives expressions for the strain rate and the radial distribution of water potential as functions of the water potential of the xylem and of various parameters. These parameters include diffusivity of water in the tissue, the radii of the stem and of the cylindrical band of xylem within it, and the extensibility and yield threshold of the Lockhart equation. A�remarkable feature of the water relations of the elongating soybean hypocotyl is that changes in the water potential of the xylem, while they rapidly affect elongation rate, cause little or no change in the water potential of the epidermis, at least for many hours. The analysis shows how such an uncoupling can occur, and, further, predicts that low diffusivity would result in the water potential of the epidermis falling when that of the xylem is raised.
Effects of high temperature on grain growth and on the metabolites and enzymes in the starch-synthesis pathway in the grains of two wheat cultivars differing in their responses to temperature
Authors: Zahedi Morteza , Sharma Rajinder , Jenner Colin F.
Published: August 2003

The effects of a sustained period of moderately high temperature were evaluated on the availability of substrate and the activity of starch synthase (ADP-glucose: 1,4-α-D-glucan 4-α-D-glucosyltransferase, EC 2.4.1.21) in the developing grains of two wheat Triticum aestivum L. cultivars differing in their tolerance to high temperature. Final grain weight was reduced by 33% in the least sensitive (cv. Kavko) and by 40% in the most sensitive (cv. Lyallpur) cultivar as post-anthesis temperature was raised from 20/15°C (day/night) to 30/25°C. The difference in the response of the two cultivars was mainly due to changes in the rate of grain filling at high temperature. The response of the rate of grain filling at high temperature, and the differential effects on the two cultivars, did not seem to be explained by an effect of temperature on the supply of assimilate (sucrose) or on the availability of the substrate for starch synthesis (ADP-glucose) in the grains. In vitro, but not in vivo, the differential responses of the efficiency (Vmax/Km) of soluble starch synthase in the two cultivars to an increase in temperature were associated with differences in the temperature sensitivity of grain filling. In vivo, the most remarkable difference between the two varieties was in the absolute values of the efficiency of soluble starch synthase, with the most tolerant cultivar having the highest efficiency.
Endoxylanase expressed during papaya fruit ripening: purification, cloning and characterization
Authors: Chen Nancy Jung , Paull Robert E.
Published: August 2003

Papaya (Carica papaya L.) softening during fruit ripening is correlated with the activities of an endoxylanase (EC 3.2.1.8). A 32.5-kDa xylanase (CpaEXY1) from ripening fruit mesocarp was purified 45 871-fold on enzymatic activity and to homogeneity by SDS electrophoresis. The enzyme had endo- and not exo-xylanase activity, a pH optimum of 5–7 and was inhibited by Ca2+, Co2+, and Zn2+. Degenerate primers were constructed from five peptides obtained from the purified enzyme, and a full-length cDNA clone (AY138968) was isolated from a library constructed from ripening mesocarp. CpaEXY1 coded for a 64.96-kDa protein that had up to 61% identity with the 12 predicted Arabidopsis Family 10 endoxylanase-like sequences and 40% to the barley aleurone xylanase. The peptide sequences, obtained from the trypsin-digested purified protein, were all found between amino acid 267�and 426 out of the predicted 584 amino acids. The N-terminal 27 amino acids were hydrophobic and formed a predicted secretory signal peptide. A predicted carbohydrate-binding module was located between amino acids 60�and 182, distinct from the C-terminal endoxylanase catalytic center. CpaEXY1 was developmentally expressed during fruit ripening and the expression correlated with the variation in softening patterns of different varieties. The findings are consistent with the hypothesis that CpaEXY1 was expressed during fruit ripening; the expression was correlated with softening and was modified by post-translational proteolysis. This modification may take place in the cell wall, and regulate enzyme activity and cell-wall-microdomain-specific hydrolysis.
Calcium-accumulating cells in the meristematic region of grapevine root apices
Authors: Storey Richard , Wyn Jones R. Gareth , Schachtman Daniel P. , Treeby Michael T.
Published: August 2003

Apical roots of grapevines were examined by cryo-SEM (scanning electron microscopy) and the intracellular distribution of Ca was demonstrated by X-ray microanalysis in different regions of the primary root. We show that large amounts of Ca are accumulated as raphide crystals in the vacuoles of specialised cortical cells (idioblast cells) of the root apex. These crystal idioblast cells appeared to form a discontinuous cone of cells in the outer region of the root meristem. The raphide crystals within these cells were less apparent in older regions of the root, 10–12 mm basipetal to the root tip. We suggest that the raphide crystals could initially act as another Ca sink involved in the regulation of Ca levels in root apices. In older regions of the root these cells are spaced at intervals around the periphery of the cortex and the subsequent disappearance of the raphides may be indicative of remobilisation, perhaps in the zone of elongation where cell wall synthesis occurs and Ca demand is high. Calcium-accumulating cells were also observed in the older regions of the root, forming endodermal protrusions extending into the cortex. These cells may play a part in regulating Ca delivery to the xylem stream by sequestration of Ca from the radial flow of water at the endodermis. The observed distribution of Ca in root apices was different from the other major cations (e.g. K) and anions (e.g. Cl) because high concentrations were localised to specific cells. We interpret the results in the context of a model of the dynamics of grapevine root growth and cell differentiation, and the temporal balance of solute supply from the protophloem and the external medium.
Epidermal cell division and cell elongation in two Aegilops species with contrasting leaf elongation rates
Authors: Bultynck Lieve , Fiorani Fabio , Volkenburgh Elizabeth Van , Lambers Hans
Published: August 2003

The 2-fold difference in final length of leaf number three on the main stem between the fast-growing Aegilops tauschii L. and the slow-growing Aegilops caudata L. is correlated with a difference in leaf elongation rate (LER), and not in duration of leaf elongation. In this paper the cellular basis of inherent differences in LER between these species was investigated.The dynamics of abaxial epidermal cells along the growth zone of leaf number three on the main stem of both species was analysed by means of a kinematic analysis. The faster LER of Ae. tauschii compared with that of Ae.�caudata was associated with (i) a larger leaf basal meristem and cell elongation-only zone, and (ii) a faster cell production rate owing to a larger number of dividing cells. Cell division rate, mature cell size and cell elongation rate did not differ between the two species. The lack of variation in cell expansion rate between the species was supported by a similar capacity of both species to extend their isolated cell walls upon acidification.These data suggest that differences in the number of dividing cells can bring about differences in the number of simultaneously elongating cells, and hence in LER.
An ultrastructural study using anhydrous fixation of Eragrostis nindensis, a resurrection grass with both desiccation-tolerant and -sensitive tissues
Authors: Willigen Clare Vander , Pammenter Norman W. , Jaffer Mohamed A. , Mundree Sagadevan G. , Farrant Jill M.
Published: August 2003

The ability of tissues to survive desiccation is common in seeds but rare in vegetative tissues. In this study the ultrastructure of hydrated and dehydrated tissues were examined at different stages of the life cycle of the resurrection grass, Eragrostis nindensis Ficalho & Hiern. Conventional fixation techniques are unsuitable for dry tissues as rehydration occurs during fixation in aqueous fixatives. Thus a cryofixation and freeze-substitution method was developed. As a result of the improved fixation methods, it was possible to identify the stage and nature of the damage in the desiccation-sensitive tissues. E. nindensis has desiccation-tolerant orthodox seeds, but the young seedlings are not tolerant to extreme water loss. However, like the seeds, most of the leaves of the adult plant are tolerant to desiccation (only the oldest outermost leaf on a tiller are not). Desiccation-induced damage in these outer leaves was observed in the later stage of dehydration, dominated by the appearance of abundant cell wall fractures (1 wall fracture per 50 μm2). Unlike the outer leaves, the leaves of seedlings appeared similar to those of the hydrated ones upon desiccation. Irreparable damage occurred on rehydration of these tissues possibly as a result of the absence of protection mechanisms observed during desiccation of the inner desiccation-tolerant leaves of the mature plants. The mesophyll tissues of these leaves become compact with extensive cell wall folding on drying. The bundle sheath cells maintained their shape with desiccation but became packed with small vacuoles.
Modelling the seasonal dynamics of the soil water balance of vineyards
Authors: Lebon Eric , Dumas Vincent , Pieri Philippe , Schultz Hans R.
Published: August 2003

A geometrical canopy model describing radiation absorption (Riou et al. 1989, Agronomie 9, 441–450) and partitioning between grapevines (Vitis vinifera L.) and soil was coupled to a soil water balance routine describing a bilinear change in relative transpiration rate as a function of the fraction of soil transpirable water (FTSW). The model was amended to account for changes in soil evaporation after precipitation events and subsequent dry-down of the top soil layer. It was tested on two experimental vineyards in the Alsace region, France, varying in soil type, water-holding capacity and rooting depth. Simulations were run over four seasons (1992–1993, 1995–1996) and compared with measurements of FTSW conducted with a neutron probe. For three out of four years, the model simulated the dynamics in seasonal soil water balance adequately. For the 1996 season soil water content was overestimated for one vineyard and underestimated for the other. Sensitivity analyses revealed that the model responded strongly to changes in canopy parameters, and that soil evaporation was particularly sensitive to water storage of the top soil layer after rainfall. We found a close relationship between field-average soil water storage and pre-dawn water potential, a relationship which could be used to couple physiological models of growth and / or photosynthesis to the soil water dynamics.
Root-derived trans-zeatin riboside and abscisic acid in drought-stressed and rewatered sunflower plants: interaction in the control of leaf diffusive resistance?
Authors: Hansen Hauke , Dörffling Karl
Published: August 2003

Four-week-old potted sunflower plants (Helianthus annuus L.) were exposed to drought for up to two days by withholding irrigation. During the stress treatment and after rewatering, xylem sap was collected from decapitated hypocotyls by pressurising the root system. The water potential (Ψw) of the hypocotyl, the diffusive resistance of the second leaf pair, total transpiration and the concentration and flux rates of ABA and trans-zeatin riboside (ZR), identified by combined gas chromatography–mass spectrometry (GC–MS) as the dominant cytokinin in xylem sap, were determined. ABA contents were also analysed in root and leaf tissue. When Ψw of the hypocotyl decreased, the concentration and flux rate of ZR decreased drastically after a transient rise. A significant rise in ABA concentration and flux rate in xylem sap as well as a parallel rise in leaf diffusive resistance occurred as soon as Ψw reached values of –0.4 MPa and lower. Root ABA concentration began to rise at the same water potential parallel to the rise in xylem sap, whereas the ABA concentration in leaves began to rise only at Ψw values lower than –0.6�MPa. Treatment of the root system with norflurazon prior to drought stress suppressed the increase in the ABA concentration in xylem sap and caused higher transpiration rates. Watering the drought-stressed plants led to a rapid decrease in ABA content of the xylem sap within three hours, whereas the decrease in leaf diffusive resistance was somewhat slower. The ZR concentration in the xylem sap rose continuously after rewatering, reaching a 60-fold increase after five hours, and declined again afterwards. Studies in which ZR and ABA were applied to cut shoots in concentrations similar to those in xylem sap of well-watered plants (ZR) and drought-stressed plants (ABA) showed that ZR, even in very low concentrations, antagonised the effect of ABA on transpiration. The results are discussed with regard to a possible antagonistic interaction of ZR and ABA as non-hydraulic root-to-shoot signals, and with regard to their interplay with hydraulic signalling.
The operation of the lutein epoxide cycle correlates with energy dissipation
Authors: García-Plazaola José I. , Hernández Antonio , Olano José M. , Becerril José M.
Published: August 2003

A new xanthophyll cycle involving de-epoxidation of lutein epoxide (Lx) into lutein in the light and epoxidation back in the dark has been recently described in parasitic plants and in trees from the genus Quercus. To explore the role of the Lx cycle in photoprotection, shade leaves of red oak (Q. rubra), with a relatively high Lx pool, were exposed to different light intensities. Both violaxanthin and Lx were de-epoxidised to the same extent, although the initial kinetics differed, with a rate proportional to the light intensity. De-epoxidation of violaxanthin and Lx was inhibited by dithiothreitol, suggesting that the same enzyme, violaxanthin de-epoxidase (VDE), catalyses both reactions. Dark recovery lagged in the case of Lx, and after 5 h in darkness, the Lx cycle was much more de-epoxidised than the violaxanthin cycle. The different rates of epoxidation of the violaxanthin and Lx cycles were used to study the role of the Lx cycle in photoprotection. Statistical approaches (partial correlation and multiple regression) indicate that in these leaves, maximal photochemical efficiency of PSII (Fv/Fm) and non-photochemical quenching are correlated with the level of Lx de-epoxidation. The potential implications of this finding for the understanding of the photosynthetic process in shaded and understorey leaves are discussed.
Exposed red (anthocyanic) leaves of Quercus coccifera display shade characteristics
Authors: Manetas Yiannis , Petropoulou Yiola , Psaras George K. , Drinia Antonia
Published: August 2003

Young leaves in some plants are transiently red due to the presence of anthocyanins, which disappear upon maturation. We investigated the hypothesis that light attenuation by anthocyanins may lead to a shade acclimation of the photosynthetic machinery in red leaves. We took advantage of the intra-species variation in anthocyanin levels of young, exposed leaves of Quercus coccifera. Thus, photosynthetic and photoprotective characteristics were compared in young green and red leaves of the same age, sampled from the corresponding phenotypes occupying the same habitat. Red leaves displayed several shade attributes like thinner laminae, lower Chl a/b ratios and lower levels of the xanthophyll cycle components and β-carotene. In addition, although both leaf kinds had the same area based levels of chlorophylls, these pigments were excluded from the sub-epidermic anthocyanic cell layers, leading to a further reduction of effective mesophyll thickness and an increase in chlorophyll density. Accordingly, red leaves had higher absolute chlorophyll fluorescence signals. In spite of these apparent shade characters, red leaves were less prone to photoinhibition under mild laboratory conditions and displayed slightly but significantly higher PS II photochemical efficiencies at pre-dawn in the field. No differences in all the above measured parameters were found in mature green leaves of the two phenotypes. The results confirm the light acclimation hypothesis and are also compatible with a photoprotective function of anthocyanins.