bluuebunny/crossref_metadata_2025_split huggingface dataset:
Virus movement proteins and other molecular probes of plasmodesmal function
Authors: WOLF S. , LUCAS W. J. 
Published: April 2006

ABSTRACTPlasmodesmata exist as supramolecular complexes that interconnect plant cells to form a symplasmic continuum. Microinjection (dye‐coupling) studies confirmed the validity of the symplasmic concept by establishing that molecules of up to 1 kDa can pass from cell to cell, via plasmodesmata. Thus, cells can exchange small molecules, such as metabolites and hormones, to coordinate biochemical and physiological processes occurring within tissues. Plasmodesmata also mediate in cell‐to‐cell transport of macromolecules, including proteins and nucleic acids. This new function was elucidated by studies on virus‐plasmodesmata interaction. Plant viruses encode for movement proteins (MPs) that are essential for cell‐to‐cell spread of infectious material. When expressed in transgenic plants, these MPs are targeted to plasmodesmata and induce a considerable increase in plasmodesmal size exclusion limit (SEL). Studies on mutant MPs confirmed that this increase in SEL is essential for viral infection. Microinjection of MP alone, or together with its conjugate infectious viral transcript, indicated that both the protein and the viral RNA (or DNA) move rapidly from cell to cell. These findings are consistent with the operation of an endogenous plasmodesmal macromolecular transport pathway. Control over this transport pathway has been probed using viral MPs, and the results support the hypothesis that plasmodesmata are involved in the creation of physiological and developmental domains. Elucidation of the molecular constituents involved in the formation and functioning of plasmodesmata will provide valuable insights into the integrated functioning of higher plants, as well as potentiating the development of new strategies for viral resistance.
Approaches to influence starch quantity and starch quality in transgenic plants
Authors: MÜLLER‐RÖBER B. , KOßMANN J. 
Published: April 2006

ABSTRACTStarch plays a major role as a transitory and long‐term storage compound in higher plants, and therefore is of prime importance for plant growth and development. Additionally, starch serves as a widely used material for a variety of industrial uses. The formation of starch can arbitrarily be divided into three types of event: (I) those leading to the supply of glucose‐1‐phosphate in the plastids; (II) the conversion of glucose‐1‐phosphate to ADP‐glucose catalysed by the enzyme ADP‐glucose pyrophosphorylase; and (III) the enzymatic reactions converting ADP‐glucose to long‐chain glucans (amylopectin, amylose). In recent years, numerous cDNA and genomic sequences encoding enzymes involved in starch metabolism have been identified. Some of these have been used to down‐regulate enzyme activities via the antisense RNA technique. Additionally, bacterial genes have been ectopically expressed in transgenic plants in order to increase corresponding enzyme activities. By modulating the activity of ADP‐glucose pyrophosphorylase in plastids, it was possible to decrease and increase, respectively, the starch content in source and sink organs of transgenic plants. In addition, down‐regulation of granule‐bound starch synthase (isoform I) resulted in the production of starch that was almost completely free of amylose. Further experiments aimed to modulate starch structure are currently underway and will briefly be discussed.
Approaches to improve stress tolerance using molecular genetics
Authors: BARTELS D. , NELSON D. 
Published: April 2006

ABSTRACTPlant productivity is greatly affected by environmental stress factors. In this review, we give an overview of molecular approaches that have been taken to study stress tolerance; in particular, we consider drought, salt and cold stress. Strategies and perspectives in using molecular biology to improve stress tolerance are outlined describing specific examples. Osmotic stress is associated with the synthesis of novel polypeptides and/or osmolytes. The spectrum and action of these different metabolites are summarized. A number of stress‐related genes have been characterized and several representatives are discussed. After transforming plants with these genes, the effect of the encoded proteins on altered stress behaviour is examined. If genes with enzymatic functions were chosen for these experiments, complete pathways may be altered and this can implement the production of novel metabolites conferring stress tolerance.
Studying plant development in mosses: the transgenic route
Authors: KNIGHT C. D. 
Published: April 2006

ABSTRACTThe current status of transgenic studies in mosses is reviewed with particular attention being given to the mosses Physcomitrella patens and Ceratodon purpureus. This paper reviews the advantages of using mosses as models for higher plants in the study of plant development, and includes developmental processes, already partially characterized at the genetic level by mutant analysis, for which transgenic studies may be applicable. The P. patens transformation process is being studied in this laboratory and details are given for a class of transformants which contain extrachromosomal plasmid DNA. Publications which present the nucleic acid and/or protein sequence for nuclear, chloroplast and mitochondrial genes are reviewed. Areas of research in which transgenic studies promise to complement existing cell biological and physiological approaches are discussed. These include the measurement of calcium levels in mutant and wild‐type transformants expressing the apoaequorin gene and a role for phytochrome gene expression in the establishment of polarity.
Suitability of Arabidopsis for studies on intracellular pH regulation: correlation between H+ pump activity, cytosolic pH and malate level in wild‐type and in a mutant partially insensitive to fusicoccin
Authors: BEFFAGNA N. , ROMANI G. 
Published: April 2006

ABSTRACTData are presented on the suitability of Arabidopsis thaliana seedlings for studies on intracellular pH regulation. In this material, grown in the dark in liquid medium, the determination of weak acid distribution at equilibrium provides an adequate method for calculating cytosolic pH values, in spite of the failure of benzylamine as a vacuolar pH probe. The stimulation of the H+ pump by K+ or K+ and fusicoccin (FC) is associated with a marked alkalinization of both cytosol and cell sap, and with a strong increase in malate level, whereas its inhibition by erythrosin B (EB) leads to the opposite effects. A good quantitative correlation is evident between the changes in net H+ extrusion and those in intracellular pH and malate content, in particular, with FC+K+. Cell sap buffer capacity is strongly influenced by the different treatments, its changes being substantially accounted for by changes in malate level. A comparison between the values of intracellular pH and malate level in wt and in the 5‐2 mutant shows that in the mutant the cytosolic pH is always more acidic, and the intracellular alkalinization induced by FC+K+ and also by K+ alone is significatively lower. These results support the view that the partial insensitivity of 5‐2 to FC is due to a reduced functionality of the H+‐extruding system on which FC acts, and that the depression of the H+ pump activity in the mutant does not depend on a possible regulation by constitutively higher cytosolic pH values.
Non‐uniform stomatal closure and the apparent convexity of the photosynthetic photon flux density response curve
Authors: OLSSON T. , LEVERENZ J. W. 
Published: April 2006

ABSTRACTThe photosynthetic response of leaves to photosynthetic photon flux density (PPFD) may be described by parameters for the rate of dark respiration (R), the initial slope (Ф), the PPFD‐saturated rate of net photosynthesis (AmQ) and the apparent convexity (θa). We tested the hypothesis that non‐uniformity in stomatal aperture across a leaf results in a clearly lower θa because PPFD saturation will occur at different irradiances in different regions of the leaf. A computer model was constructed to simulate the effects of bell‐shaped and other distributions of stomatal conductance for CO2 (gs) across a model leaf. In the model, Ф and AmQ decreased by up to 50% whereas θa decreased by at most 8%, essentially negating the hypothesis. The relationship between photosynthetic rate and gs determined the size of the responses of θa and Ф to non‐uniform gs. In support of the model, experiments on sunflower leaves showed that Ф and AmQ decreased by 32 and 52%, respectively, while no measurable change in θa occurred, when abscisic acid was used to induce patchiness in gs. Although not all possible patterns of non‐uniform stomatal conductance have been tested, it appears that if large variations in θa occur in nature they do not result from non‐uniform gs.
Low‐temperature pretreatment of the root system of Brassica rapa L. plants: effects on the xylem sap exudation and on the nitrate absorption rate
Authors: BIGOT J. , BOUCAUD J. 
Published: April 2006

ABSTRACT Brassica rapa plants were exposed for a 52 h period (as pretreatment) to a differential temperature (DT) between roots (5°C) and shoots (20°C), while control plants were maintained with both shoot and roots at 20°C (warm grown = WG). Measured at 20°C, volume flow of xylem exudate from roots of DT plants was enhanced compared with that from WG plants, while transpiration flows were similar in pretreated and control plants. Both transpiration and exudation flows were dependent upon shoot/root ratio. Differences in the volume flow of exudate were principally related to increases in root hydraulic conductance. Anion fluxes (notably nitrate) into xylem exudate of DT plants were significantly greater than those into exudate of WG plants. This enhancement of nitrate flow from the pretreated roots was associated with a two‐fold increase in nitrate uptake rate. The relationship of the cold‐induced change in nitrate uptake capacity with shoot/root ratio is discussed in terms of control of nitrate absorption by shoot sink strength.
The sensitivity of C3photosynthesis to increasing CO2concentration: a theoretical analysis of its dependence on temperature and background CO2concentration
Authors: KIRSCHBAUM M. U. F. 
Published: April 2006

ABSTRACTThe atmospheric CO2concentration has increased from the pre‐industrial concentration of about 280 μmol mol−1to its present concentration of over 350 μmol mol−1, and continues to increase. As the rate of photosynthesis in C3plants is strongly dependent on CO2concentration, this should have a marked effect on photosynthesis, and hence on plant growth and productivity. The magnitude of photo‐synthetic responses can be calculated based on the well‐developed theory of photosynthetic response to intercellular CO2concentration. A simple biochemically based model of photosynthesis was coupled to a model of stomatal conductance to calculate photosynthetic responses to ambient CO2concentration. In the combined model, photosynthesis was much more responsive to CO2at high than at low temperatures. At 350 μmol mol−1, photosynthesis at 35°C reached 51% of the rate that would have been possible with non‐limiting CO2, whereas at 5°C, 77% of the CO2non‐limited rate was attained. Relative CO2sensitivity also became smaller at elevated CO2, as CO2concentration increased towards saturation. As photosynthesis was far from being saturated at the current ambient CO2concentration, considerable further gains in photosynthesis were predicted through continuing increases in CO2concentration. The strong interaction with temperature also leads to photosynthesis in different global regions experiencing very different sensitivities to increasing CO2concentrations.
Photosynthetic characteristics of the shade‐adapted C4grassMuhlenbergia sobolifera(Muhl.) Trin.: control of development of photorespiration by growth temperature
Authors: SMITH M. , WU Y. 
Published: April 2006

ABSTRACTMuhlenbergia sobolifera(Muhl.) Trin., a C4grass, occurs in understory habitats in the northeastern United States. Plants ofM. soboliferawere grown at 23 and 30°C at 150 and 700 μmol photons m−2s−1. The photosynthetic CO2compensation point, maximum CO2assimilation, dark respiration and the absorbed quantum use efficiency (QUE) were measured at 23 and 30°C at 2 and 20% O2. Photosynthetic CO2compensation points ranged from 4 to 14mm3dm−3CO2and showed limited O2sensitivity. The mean photosynthetic CO2compensation point of plants grown at 30°C (4·5 mm3dm−3) was 57% lower and 80% less inhibited by O2than that of plants grown at 23°C. Photosynthesis was similarly affected by growth temperature, with 70% more O2inhibition in plants grown at 23°C; suppression over all treatments ranging from 2 to 11%. Unlike typical C4species, plants ofM. soboliferafrom both temperature regimes exhibited higher CO2assimilation rates when grown at low light. Growth temperature and light also affected QUE; plants grown at low light and 23°C had the highest value (0·068 mol CO2/mol quanta). Measurement temperature and growth light regime significantly affected dark respiration; however, O2did not affect QUE or dark respiration under any growth or measurement conditions. The results indicate thatM. soboliferais adapted to low PPFD, and that complete suppression of photorespiration is dependent upon high growth temperature.
Developmental changes in the diurnal water budget of the grape berry exposed to water deficits
Authors: GREENSPAN M. D. , SHACKEL K. A. , MATTHEWS M. A. 
Published: April 2006

ABSTRACTThe diurnal water budget of developing grape (Vitis vinifera L.) berries was evaluated before and after the onset of fruit ripening (veraison). The diameter of individual berries of potted ‘Zinfandel’ and ‘Cabernet Sauvignon’ grapevines was measured continuously with electronic displacement transducers over 24 h periods under controlled environmental conditions, and leaf water status was determined by the pressure chamber technique. For well‐watered vines, daytime contraction was much less during ripening (after veraison) than before ripening. Daytime contraction was reduced by restricting berry or shoot transpiration, with the larger effect being shoot transpiration pre‐veraison and berry transpiration post‐veraison. The contributions of the pedicel xylem and phloem as well as berry transpiration to the net diurnal water budget of the fruit were estimated by eliminating phloem or phloem and xylem pathways. Berry transpiration was significant and comprised the bulk of water outflow for the berry both before and after veraison. A nearly exclusive role for the xylem in water transport into the berry was evident during pre‐veraison development, but the phloem was clearly dominant in the post‐veraison water budget. Daytime contraction was very sensitive to plant water status before veraison but was remarkably insensitive to changes in plant water status after veraison. This transition is attributed to an increased phloem inflow and a partial discontinuity in berry xylem during ripening.
The effect of growth at elevated CO2 concentrations on photosynthesis in wheat
Authors: McKEE I. F. , WOODWARD F. I. 
Published: April 2006

ABSTRACTRising levels of atmospheric CO2 will have profound, direct effects on plant carbon metabolism. In this study we used gas exchange measurements, models describing the instantaneous response of leaf net CO2 assimilation rate (A) to intercellular CO2 partial pressure (Ci), in vitro enzyme activity assay, and carbohydrate assay in order to investigate the photosynthetic responses of wheat (Triticum aestivum L., cv. Wembley) to growth under elevated partial pressures of atmospheric CO2 (Ca). At flag leaf ligule emergence, the modelled, in vivo, maximum carboxylation velocity for RuBisCO was significantly lower in plants grown at elevated Ca than in plants grown at ambient Ca (70 Pa compared with 40 Pa). By 12 d after ligule emergence, no significant difference in this parameter was detectable. At ligule emergence, plants grown at elevated Ca exhibited reduced in vitro initial activities and activation states of RuBisCO. At their respective growth Ci values, the photosynthesis of 40‐Pa‐grown plants was sensitive to p(O2) and to p(CO2) whereas that of 70‐Pa‐grown plants was insensitive. Both sucrose and starch accumulated more rapidly in the leaves of plants grown at 70 Pa. At flag leaf ligule emergence, modelled non‐photorespiratory respiration in the light (Rd) was significantly higher in 70‐Pa‐grown plants than in 40‐Pa‐grown plants. By 12 d after ligule emergence no significant differences in Rd were detectable.
A critical comparison of the pressure‐probe and pressure‐chamber techniques for estimating leaf‐ceil turgor pressure in Kalanchoë daigremontiana
Authors: MURPHY R. , SMITH J. A. C. 
Published: April 2006

ABSTRACTThe aim of the present study was to test the accuracy of the pressure‐chamber technique as a method for estimating leaf‐cell turgor pressures. To this end, pressure‐probe measurements of cell turgor pressure (Pcell) were made on mesophyll cells of intact, attached leaves of Kalanchoë daigremontiana. Immediately following these measurements, leaves were excised and placed in a pressure chamber for the determination of balance pressure (Pbal). Cell‐sap osmotic pressure (?cell) and xylem‐sap osmotic pressure (?xyl) were also measured, and an average cell turgor pressure calculated as Pcell=?cell–?xyl–Pbal. The apparent value of Pbal was positively correlated with the rate of increase of chamber pressure, and there was also a time‐dependent increase associated with water loss. On expressing sap from the xylem, ?xyl fell to a plateau value that was positively correlated with ?cell. Correcting for these effects yielded estimates of Pbal and ?xyl at the time of leaf excision. On average, the values of Pcell obtained with the two techniques agreed to within ±002 MPa (errors are approximate 95% confidence limits). If ?xyl were ignored, however, the calculated turgor pressures would exceed the measured values by an average of 0.074 ± 0.012MPa, or 48% at the mean measured pressure of 0.155 MPa. We conclude that the pressure‐chamber technique allows a good estimate to be made of turgor pressure in mesophyll cells of K. daigremontiana, provided that ?xyl is included in the determination. The 1:1 relationship between the measured and calculated turgor pressures also implies that the weighted‐average reflection coefficient for the mesophyll cell membranes is close to unity.
Isotopic heterogeneity of water in transpiring leaves: identification of the component that controls the δ18O of atmospheric O2 and CO2
Authors: YAKIR D. , BERRY J. A. , GILES L. , OSMOND C. B. 
Published: April 2006

ABSTRACTTwo direct but independent approaches were developed to identify the average δ18O value of the water fraction in the chloroplasts of transpiring leaves. In the first approach, we used the δ18O value of CO2 in isotopic equilibrium with leaf water to reconstruct the δ18O value of water in the chloroplasts. This method was based on the idea that the enzyme carbonic anhydrase facilitates isotopic equilibrium between CO2 and H2O predominantly in the chloroplasts, at a rate that is several orders of magnitude faster than the non‐catalysed exchange in other leaf water fractions. In the second approach, we measured the δ18O value of O2 from photosynthetic water oxidation in the chloroplasts of intact leaves. Since O2 is produced from chloroplast water irreversibly and without discrimination, the δ18O value of the O2 should be identical to that of chloroplast water. In intact, transpiring leaves of sunflower (Helianthus annuus cv. giant mammoth) under the experimental conditions used, the average δ18O value of chloroplasts water was displaced by 3—10 % (depending on relative humidity and atmospheric composition) below the value predicted by the conventional Craig & Gordon model. Furthermore, this δ18O value was always lower than the δ18O value that was measured for bulk leaf water. Our results have implications for a variety of environmental studies since it is the δ18O value of water in the chloroplasts that is the relevant quantity in considering terrestrial plants influence on the δ18O values of atmospheric CO2 and O2, as well as in influencing the δ18O of plant organic matter.
Accumulation of glycinebetaine during cold acclimation and freezing tolerance in leaves of winter and spring barley plants
Authors: KISHITANI S. , WATANABE K. , YASUDA S. , ARAKAWA K. , TAKABE T. 
Published: April 2006

ABSTRACTA study was performed to examine whether or not betaine (glycinebetaine), a compatible solute, is accumulated in response to cold stress and is involved in mechanisms that protect plants from freezing injury. For this purpose, we used near‐isogenic lines of barley, with each line differing only in a single gene for the spring type of growth habit; the various lines were produced by back‐crosses to a recurrent cultivar of the winter type. The winter type of growth habit requires a low temperature for triggering of flower development (vernalization), whereas the spring type does not. Betaine was accumulated to five times the basal level over the course of 3 weeks at low temperature (5 °C) in the winter‐type cultivar and in a spring‐sh line having the sh gene for the spring‐type growth habit, but the level was only doubled in the spring‐Sh3 line, which carried the Sh3 gene for the spring‐type growth habit. Among near‐isogenic lines of the same cultivar, the levels of betaine accumulated in leaves at low temperature were well correlated with the percentages (on a dry weight basis) of green leaves that survived freezing injury (‐5 °C). This observation indicates the possibility, separate from the recognized role of betaine in the response to salinity and/or drought, that betaine accumulates in response to cold stress and that the accumulation of betaine during cold acclimation is associated to some extent with freezing tolerance in leaves of barley plants.
A system for imaging transverse distribution of scattered light and chlorophyll fluorescence in intact rice leaves
Authors: TAKAHASHI K. , MINEUCHI K. , NAKAMURA T. , KOIZUMI M. , KANO H. 
Published: April 2006

ABSTRACTIn order to examine the transverse distribution of scattered light and chlorophyll fluorescence in intact rice leaves, a micro‐fluorescence imaging system was devised using a microscope, a CCD camera with an image intensifier, an Ar and a He‐Ne laser light source, an image processor, and a microcomputer. A laser light was projected vertically on to the surface of a rice leaf segment at a cut‐edge, and scattered light and induced fluorescence were observed at the cut‐section from a 90° angle to the axis of the laser beam. The intensity of scattered light showed a maximum at several micrometres depth from the leaf surface and a steep gradient afterwards. Fluorescence reached a maximum crossing with the decline curve of the scattered light. The maximum of fluorescence measured at 741 nm was observed at a greater depth from the leaf surface than that at 687 nm, suggesting that part of the fluorescence of the longer wavelength was emitted due to absorption of fluorescence of the shorter wavelength. Profiles of the scattered light and the chlorophyll fluorescence depended on leaf anatomy.