bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of electric and growth responses to excision in cucumber and pea seedlings. II. Long‐distance effects are caused by the release of xylem pressure
Authors: STAHLBERG R. , COSGROVE D. J. 
Published: April 2006

ABSTRACTExcision of a growing stem causes local wound responses, such as membrane depolarization and growth inhibition, as well as effects at larger distances from the cut. In this study, cucumber hypocotyls were excised 100mm below the hook, so that the growing region was beyond the reach of the wound‐induced depolarization (up to 40mm). Even at such a distance, the cut still caused a considerable and rapid drop in the hypocotyl growth rate. This growth response is not a direct wound response because it does not result from the cut‐induced depolarization and because it can be simulated by root pressure manipulation (using a pressure chamber). The results indicate that the growth response resulted from the rapid release of the xylem pressure upon excision. To test this conclusion we measured the xylem pressure by connecting a pressure probe to the cut surface of the stem. Xylem pressure (Px) was found to be +10 to +40kPa in cucumber hypocotyls and ‐5 to ‐10 kPa or lower in pea epicotyls. Excision of the cucumber hypocotyl base led to a rapid drop in Px to negative values, whereas excision in pea led to a rapid rise in Px to ambient (zero) pressure. These fast and opposite px changes parallel the excision‐induced changes in growth rate (GR): a decrease in cucumber and a rise in pea.The sign of the endogenous xylem pressure also determined whether excision induced a propagating depolarization in the form of a slow wave potential (SWP). Under normal circumstances pea seedlings generated an SWP upon excision whereas cucumber seedlings failed to do so. When the Px in cucumber hypocotyls was experimentally inverted to negative values by incubating the cumber roots in solutions of NaCN or n‐ethylmaleimide, excision caused a propagating depolarization (SWP). The experiment shows that only hydraulic signals in the form of positive Px steps are converted into propagating electric SWP signals. These propagating depolarizations might be causally linked to systemic ‘wound’ responses, which occur independently of the short‐distance or direct wound responses.
Limitation of net CO2 assimilation rate by internal resistances to CO2 transfer in the leaves of two tree species (Fagus sylvatica L. and Castanea sativa Mill.)
Authors: EPRON D. , GODARD D. , CORNIC G. , GENTY B. 
Published: April 2006

ABSTRACTUsing a combination of gas‐exchange and chlorophyll fluorescence measurements, low apparent CO2/O2 specificity factors (1300 mol mol−1) were estimated for the leaves of two deciduous tree species (Fagus sylvatica and Castanea sativa). These low values contrasted with those estimated for two herbaceous species and were ascribed to a drop in the CO2 mole fraction between the intercellular airspace (Ci) and the catalytic site of Rubisco (Cc) due to internal resistances to CO2 transfer. Cc. was calculated assuming a specificity of Rubisco value of 2560 mol mol−1. The drop between Ci and Cc was used to calculate the internal conductance for CO2 (gi). A good correlation between mean values of net CO2 assimilation rate (A) and gi was observed within a set of data obtained using 13 woody plant species, including our own data. We report that the relative limitation of A, which can be ascribed to internal resistances to CO2 transfer, was 24–30%. High internal resistances to CO2 transfer may explain the low apparent maximal rates of carboxylation and electron transport of some woody plant species calculated from A/Ci curves.
The phototropic response of Triticum aestivum coleoptiles under conditions of low gravity
Authors: HEATHCOTE D. G. , BROWN A. H. , CHAPMAN D. K. 
Published: April 2006

ABSTRACTWheat (Triticum aestivum L. cv Broom) coleoptiles were stimulated by unilateral blue light pulses, the duration of which varied between 3 s and 30 min, under microgravity conditions on the IML‐1 Spacelab mission and in ground controls. The stimuli covered first positive, indifferent and second positive response regions. When phototropic responses were observed under low‐gravity conditions, slightly fewer seedlings responded compared with 1 g conditions. The latent period was similar in flight and 1g treatments (10–20 min), except for the response to 300,μmol m−2 in the indifferent response region, where a positive response in flight plants followed a 130 min latent period, while no response was observed in 1 g plants. First positive responses at Og were slightly enhanced, both in magnitude and in duration, compared to the 1 g controls, but not to the extent predicted by clinostat studies. The response kinetics in the second positive region at 1g showed a plateau at 120 min, in contrast to the single maximum at Og. The fluence‐response relationship was similar in both flight and ground controls. Only the responses to 4 and 6μmolm‐2 showed significantly greater curvatures at 9g. This contrasts with previous clinostat studies, which reported substantial response enhancement at all fluence levels.
Effects of salinity on seed set in rice
Authors: KHATUN S. , FLOWERS T. J. 
Published: April 2006

ABSTRACTSalinity reduces fertility in rice (Oryza sativa L.), but little is known of the underlying cause(s). In order to determine the relative importance of pollen viability and stigmatic receptivity for seed setting, plants of the rice cultivar IR36 were treated with ‘artificial’ sea water (0,10, 25 or 5Omol−3 with respect to NaCl) from 1 month after germination until the main tiller flowered.An increase in the salinity in the medium resulted in a decrease in the number of fertile florets and in the viability of pollen as determined both by pollen germination and by pollen staining with the tetrazolium salt 3‐(4,5‐dimethyl‐ithyazolyl)‐2,5‐diphenyl monotetrazolium bromide.In order to assess the effects of salt on stigmas, seed production was measured for salt‐grown and non‐salt‐grown female plants pollinated with viable pollen (from plants grown in the absence of salt). The percentage of seed set was reduced by 38% when the female plants were grown in 1Omol m−3 Na and by 72% at 25mol m−3 Na: no seed setting was recorded for plants grown in 50mol m−3 Na. Comparisons between crosses involving male and female parents grown at different salinities indicated that effects on the female plants dominated those on pollinator plants. Mineral analysis of leaves of different ages showed that there was a gradient of K concentration from leaf to leaf which was opposite to that of Na and Cl at all levels of applied salinity: K was maximal in the flag leaf, where Na and Cl were minimal. Analysis also revealed that there was an increase in the concentrations of Na and Cl and a decrease in the concentration of K in the pollen grains and stigmas of plants subjected to saline conditions. Correlations between the concentration of Na and Cl in pollen and pollen staining and pollen germination in vitro suggest that Na and Cl perse were responsible for the poor viability. The change in ionic concentrations in pollen and stigmas was much larger than that in the younger leaves, and in particular very much larger than that in the lemmas and paleas.
Relations between vulnerability to xylem embolism and xylem conduit dimensions in young trees of Quercus corris
Authors: LO GULLO M. A. , SALLEO S. , PIACERI E. C. , ROSSO R. 
Published: April 2006

ABSTRACTMeasurements of xylem conduit length and width and the distribution of xylem conduit ends were made in inter‐nodes (I), nodes (N) and twig junctions (J) of 1‐, 2‐ and 3‐year‐old twigs of plants of Quercus cerris L. Parallel measurements were also made of the loss of hydraulic conductivity of twigs subjected to pressure differentials across conduit pit membranes, equalling the leaf water potential at the turgor loss point. The loss of theoretical hydraulic conductivity was calculated as the ratio of i esivr4 (where r is the conduit radius) of the non‐conducting conduits to that of all the conduits in the outermost wood ring of I, N and J. Stem zones such as 1‐year‐old nodes and junctions were localized with narrower and shorter xylem conduits and with higher percentages of conduit ends than internodes. Such ‘constricted zonesrsquo; were less vulnerable to embolism than internodes. Latewood conduits were consistently narrower, shorter and less vulnerable to embolism than earlywood ones. A positive relation therefore existed between conduit diameter and length and vulnerability to embolism. The overall vulnerability to embolism of Q. cerris plants is discussed in terms of xylem conduit width and length and of the distribution of conduit ends.
Shoots, roots and ectomycorrhiza formation of pine seedlings at elevated atmospheric carbon dioxide
Authors: INEICHEN K. , WIEMKEN V. , WIEMKEN A. 
Published: April 2006

ABSTRACTThe effect of elevated atmospheric CO2 concentration on the growth of shoots, roots, mycorrhizas and extraradical mycorrhizal mycelia of pine (Pinus silvestris L.) was examined. Two and a half‐month‐old seedlings were inoculated axenically with the mycorrhizal fungus Pisolithus tincto‐rius (Pers.) by a method allowing rapid mycorrhiza formation in Petri dishes. The plants were then cultivated for 3 months in growth chambers with daily concentrations of 350 and 600 μmol mol−1 CO2 during the day. Whereas plants harvested after 1 and 2 months did not differ appreciably between ambient and increased CO2 concentrations, after 3 months they developed a considerably higher root biomass (%57%) at elevated CO2, but did not increase significantly in root length. The mycorrhizal fungus Pisolithus tinctorius, which depended entirely on the plant assimilates in the model system, grew much faster at increased CO2: 3 times more mycorrhizal root clusters were formed and the extraradical mycelium produced had twice the biomass at elevated as at ambient CO2. No difference in shoot biomass was found between the two treatments after 91 d. However, since the total water consumption of seedlings was similar in the two treatments, the water use efficiency was appreciably higher for the seedlings at increased CO2 because of the higher below‐ground biomass.
Phytochrome A, phytochrome B and HY4 are involved in hypocotyl growth responses to natural radiation in Arabidopsis: weak de‐etiolation of the phyA mutant under dense canopies
Authors: YANOVSKY M. J. , CASAL J. J. , WHITELAM G. C. 
Published: April 2006

ABSTRACTThe roles of phytochrome A (phyA), phytochrome B (phyB) and a putative blue‐light (BL) photoreceptor (HY4) in the control of hypocotyl growth by natural radiation were investigated using phyA, phyB and hy4 mutants of Arabidopsis thaliana. Full sunlight inhibited hypocotyl growth to a larger extent in wild‐type (WT) than in phyA, phyB and, particularly, hy4 seedlings. In WT seedlings, hypocotyl growth was promoted by selectively lowering BL irradiance, lowering red‐light (R) plus far‐red‐light (FR) irradiance or lowering the R/FR ratio (which was achieved either by increasing FR or by reducing R). The effects of lowering BL were reduced in hy4 and exaggerated in phyA seedlings. The effects of lowering R+FR were reduced in phyA and exaggerated in hy4 seedlings. Neither phyB nor hy4 mutants responded to low R/FR ratios. Neighbouring plants reflecting FR without shading caused subtle reductions of the R/FR ratio. This signal promoted hypocotyl growth in WT but not in phyA, phyB or hy4 seedlings. Intermediate canopy shade produced similar effects in all genotypes. Under deep shade, de‐etiolation was severely impaired in phyA seedlings, which died prematurely. Thus, the FR ‘high‐irradiance reaction’ mediated by phyA could be important for seedling survival under dense canopies.
Guard cell pressure/aperture characteristics measured with the pressure probe
Authors: FRANKS P. J. , COWAN I. R. , TYERMAN S. D. , CLEARY A. L. , LLOYD J. , FARQUHAR G. D. 
Published: April 2006

ABSTRACTPressure within guard cells in strips of intact epidermis of Tradescantia virginiana was controlled with a pressure probe apparatus after the guard cells had been filled with silicone oil. Pressure was increased and decreased incrementally between 0.0 and 4.1 MPa to cause inflation and deflation of the guard cells. At steady‐state guard cell pressures, the width of the stomatal pore was recorded and plotted against pressure. The pressure required for near‐maximum aperture was 4.1 MPa. Aperture as a function of pressure was sigmoidal.
Two proteins regulate the cell wall extensibility and the yield threshold in glycerinated hollow cylinders of cowpea hypocotyl
Authors: OKAMOTO A. , OKAMOTO H. 
Published: April 2006

ABSTRACTGlycerinated hollow cylinders of hypocotyl segments excised from the elongation region of cowpea seedlings were heated for 15s in 50% glycerol at 70, 80 or 90°C. Their in vitro yield threshold tension (y) and extensibility (φ) were determined by stress‐strain experiments under the perfusion of solutions of pH 4·0 or 6·2. The decrement in y and the increment in φ with acidification were extinguished at 80 and 90°C, respectively. Moreover, such changes in φ and y with acidification were prevented by proteinase treatment for 6 and 10 h, respectively. These results suggest that these two cell wall mechanical properties are controlled, respectively, by two functional proteins activated by acid.
Photosynthetic inorganic carbon uptake and accumulation in two marine diatoms
Authors: COLMAN B. , ROTATORE C. 
Published: April 2006

ABSTRACTSome physiological characteristics of photosynthetic inorganic carbon uptake have been examined in the marine diatoms Phaeodactylum tricornutum and Cyclotella sp. Both species demonstrated a high affinity for inorganic carbon in photosynthesis at pH7.5, having K1/2(CO2) in the range 1.0 to 4.0mmol m−3 and O2− and temperature‐insensitive CO2 compensation concentrations in the range 10.8 to 17.6 cm3 m−3. Intracellular accumulation of inorganic carbon was found to occur in the light; at an external pH of 7.5 the concentration in P. tricornutum was twice, and that in Cyclotella 3.5 times, the concentration in the suspending medium. Carbonic anhydrase (CA) was detected in intact Cyclotella cells but not in P. tricornutum, although internal CA was detected in both species. The rates of photosynthesis at pH 8.0 of P. tricornutum cells and Cyclotella cells treated with 0.1 mol m−3 acetazolamide, a CA inhibitor, were 1.5‐ to 5‐fold the rate of CO2 supply, indicating that both species have the capacity to take up HCO3− as a source of substrate for photosynthesis. No Na+ dependence for HCO3− could be detected in either species. These results indicate that these two marine diatoms have the capacity to accumulate inorganic carbon in the light as a consequence, in part, of the active uptake of bicarbonate.
Gravity perception in plants: a multiplicity of systems derived by evolution?
Authors: BARLOW P. W. 
Published: April 2006

ABSTRACTThe origin and subsequent evolution of life on Earth have taken place within an environment where a 1g gravitational field is omnipresent. Living organisms, at whatever stage in their evolution, have accommodated this variable in both their structure and their function. Systems have also evolved whereby gravitational accelerations are perceived by gravisensors and these, in turn, have led to responses that give particular spatial orientations to living processes. It is proposed that, the higher the evolutionary status of an organism, the more likely it is that it will possess multiple systems for gravisensing because evolution discards little that assists fitness and hence supplements with new gravisensing systems those which already existed within evolutionary older, less complex organisms. Moreover, in comparison with a single gravisensing system, a multiplicity of systems permits gravity to participate in a wider range of developmental programmes, such as taxes, morphisms and tropisms, through the action of different sensory mechanisms coupled to distinct signalling and response pathways. Whatever the precise mechanism of graviperception in any given set of conditions, all may transduce the g‐forcc by means of a membrane system. Transduction may involve the endoplasmic rcticulum and thence the plasma membrane.
Above‐ground nitrogen dynamics following the complete pruning of a nodulated woody legume in humid tropical field conditions
Authors: NYGREN P. 
Published: April 2006

ABSTRACTAbove‐ground nitrogen fluxes following a complete pruning of the neotropical agroforestry tree Erythrina poeppi‐giana (Walpers) O.F. Cook (Leguminosae: Phaseoleae) were studied during pruning intervals of 26 and 23 weeks in the humid tropics of Costa Rica. The experiment included four clones and a half‐sib family of the species. The leaf‐level N fluxes were modelled as a function of leaf age, and were scaled to the canopy level on the basis of the leaf age distribution. The N content of young leaves increased exponentially, followed by relatively small changes at maturity. Slight net N retranslocation started at the middle of leaf life span, but a major N efflux occurred only a few days before leaf shedding. It was estimated that, depending on the tree source, 29‐44& of the total N accumulation in the above‐ground biomass occurred during 11 weeks after pruning (WAP), before initiation of nodulation. The nodule biomass peaked at the time leaf shedding started (15–17 WAP). Considerable rapid N efflux from the foliage was observed at this time, suggesting regulation of nodulation by a feedback from the foliage. The implications of the N economy of E. poep‐pigiana on its management in agroforestry systems are discussed.
Stomatal behaviour in a beech canopy: an analysis of Bowen ratio measurements compared with porometer data
Authors: HERBST M. 
Published: April 2006

ABSTRACTOn the basis of measurements or stand transpiration and microclimate, the bulk stomatal or bulk leaf conductance (gL) of a beech forest in northern Germany was calculated for periods in which leaves were fully expanded and the canopy was dry. This conductance depends strongly on light and humidity conditions above the forest. During periods with photosynthetic photon flux densities Q > 1200 μmol m−2s−1, gL was reduced from 1500mmol m−2s−1 at a vapour pressure deficit D= 0.5kPa to 500 mmol m−2s−1 at D= 2kPa. Light saturation of gL was not reached until Q= 1200 μmol m−2s−1 at low D, or until even higher Q at higher D. The dependence of gL, on Q and D was described mathematically by a non‐linear equation that requires two empirical parameters. Values for gL as simulated by this equation provided a satisfactory agreement with independent porometer data collected on single leaves and scaled up to the canopy. A comparison of stomatal and aerodynamic conductances showed a strong coupling between the forest canopy and the atmosphere, indicating that transpiration of the beech forest is controlled mainly by the stomata.
Scaling processes and problems
Authors: JARVIS P. G. 
Published: April 2006

ABSTRACTA personal view is presented of current approaches to scaling processes and variables in the context of better understanding ecosystem function and predicting the consequences of global environmental change. Issues considered include spatial and temporal scales of interest, the scaling process, scaling strategy, scaling problems, heterogeneity, patchiness and non‐linearity, aggregation methodology and feedbacks.Knowledge of processes in plants and vegetation is largely at small scales. The transfer of this knowledge up to larger spatial and longer temporal scales is an open‐ended process with potential errors arising from heterogeneity and patchiness in the distribution of processes and non‐linearities in the functional relationships between processes and environmental variables. Scaling now covers several orders of magnitude with respect to spatial and temporal scales with attendant risks of propagating errors.At larger scales the wide diversity of vegetation classes poses a problem, and it is suggested that this can be countered by classifying classes of vegetation (not species) into a small number of ‘functional types’ of vegetation. Scaling through summation of component processes and through derivation of appropriately averaged parameters is considered. However, the increasing role of feedbacks at larger spatial and longer temporal scales is an essential feature of the scaling process. Thus, understanding the feedbacks and including them in upscaling schemes is a major priority.A scaling strategy is outlined to minimize the propagation of errors. Because the scaling process is open‐ended it is essential that good models are used and tested at each increase in scale.
The role of nitrogen in a simple scheme to scale up photosynthesis from leaf to canopy
Authors: KULL O. , JARVIS P. G. 
Published: April 2006

ABSTRACTA simple analytical scheme, involving the distribution of nitrogen, to scale up photosynthesis from leaf to canopy is proposed. The scheme is based on the assumption that there are two pools of nitrogen in leaves: nitrogen in photosynthetic, degradable structures (Np) and nitrogen in non‐photosynthetic and non‐degradable structures (Ns). The rate of photon‐saturated photosynthesis, Fm, is assumed to be proportional to Np and is distributed inside the canopy similarly to photon flux density (PFD). Prior assumptions of an optimum distribution of nitrogen are not a prerequisite. Calculations made with the scheme lead to development of the hypothesis that the canopy can be treated as a ‘big leaf’ on the time scales involved in acclimation of photosynthesis to PFD. Simulations using parameters for tree species with different requirements for PFD show that shade‐tolerant species may have denser canopies than sun‐demanding species because of smaller amounts of non‐photosynthetic structural nitrogen and/or supporting tissue in their leaves.
Identification of amino compounds synthesized and translocated in symbiotic Parasponia
Authors: BAKER A. , DODD C. D. , PARSONS R. 
Published: April 2006

ABSTRACTWe investigated the synthesis and translocation of amino compounds in Parasponia, a genus of the Ulmaceae that represents the only non‐legumes known to form a root nodule symbiosis with rhizohia. In the xylem sap of P. andersonii we identified asparagine. aspartate. glutamine, glutamated significant quantities of a non‐protein amino acid. 4‐methylglutamte(2‐amino‐4‐methylpentanedioic acid). This identification was confirmed by two methods, capillary gas chromatography (GC) electron ionization (El) mass spectrometry (MS) and reverse phase high pressure liquid chromatography (HPLC) analysis of derivatized compounds. In leaf, root and nodule samples from P. andersonii and P. parviflora we also identified the related compounds 4‐methyleneglutamate and 4‐methyleneglulamine. Using 15N2 labelling and GC‐Ms analysis of root nodule extracts we followed N2 fixation and ammonia assimilation in P. andersonii root nodules and observed Label initially in glutamine and subsequently in glutamate, suggesting operation of the glutamine synthetase/glutamine:2‐oxoglutarate aminotransferase (GS/GOGAT) pathway. Importantly, we observed the incorporation of significant quantities of 15N into 4‐methylglutamate in nodules, demonstrating the de nova synthesis of this non protein amino acid and suggesting a role in the translation of N in symbioticParasponia.