bluuebunny/crossref_metadata_2025_split huggingface dataset:
Induction of crown galls by Agrobacterium tumefaciens (strain C58) reverses assimilate translocation and accumulation in Kalanchoë daigremontiana
Authors: MALSY S. , BEL VAN , KLUGE M. , HARTUNG W. , ULLRICH C. I. 
Published: April 2006

ABSTRACTThe mechanism of hormone‐enhanced solute accumulation was investigated in crown galls of Kalanchoë diagremontiana, induced by Agrobacterium tumefaciens (C58). Electrophysiological, cytological staining, and 14CO2‐tracer techniques were used. Intracellular auxin and zeatinriboside concentration increased in tumours by three and five times, respectively, compared with the mesophyll. In contrast, the electrical membrane potential difference, in particular the energy‐dependent component across the plasma membrane of tumours was at least 60 mV smaller than that of mesophyll cells. The detection of functional sieve tubes, metabolically active companion cells and also developed xylem vessels correlated well with evidence for reversed, long‐distance, 14C‐labelled assimilate flow from CAM–performing mesophyll to sugar and potassium‐accumulating tumours. The change in hormone production, encoded by the iaaM, iaaH and ipt T‐DNA genes, apparently induced functioning vascular bundles and established a strong sink. From a comparison with tobacco suspension cells (SR1 and SR1‐C58), the changes in the amino acid pattern in the mesophyll/tumour complex can be attributed to the enzymatic activities incited by the nos encoding gene. Differences in sugar and inorganic ion content were not apparent in the transformed suspension cells, indicating that the increase in extracellular concentration by enhanced phloem unloading may be the crucial factor for the pathological solute accumulation in the tumours.
Stomatal conductance, photosynthesis and respiration of temperate deciduous tree seedlings grown outdoors at an elevated concentration of carbon dioxide
Authors: BUNCE J. A. 
Published: April 2006

ABSTRACTSeedlings of temperate deciduous tree species were grown outdoors at ambient and at an elevated concentration of carbon dioxide to examine how aspects of their gas exchange would be altered by growth at elevated carbon dioxide concentration. Leaf conductances to water vapour and net carbon dioxide exchange rates were determined periodically near midday. Whole‐plant carbon dioxide efflux rates in darkness were also determined. The stomatal conductance of leaves of plants grown and measured at 700 cm3 m−3 carbon dioxide did not differ from that of plants grown and measured at 350 cm3 m−3 in Malus domestica, Quercus prinus and Quercus robur at any measurement time. In Acer saccharinum, lower conductances occurred for plants grown and measured at elevated carbon dioxide concentration only at measurement temperatures above 33°C. Photo‐synthetic adjustment to elevated carbon dioxide concentration was evident only in Q. robur. All species examined had lower rates of dark respiration per unit of mass when grown and measured at elevated carbon dioxide concentration.
Photosynthesis in flashing light in soybean leaves grown in different conditions. I. Photosynthetic induction state and regulation of ribulose‐1,5‐bisphosphate carboxylase activity
Authors: PONS T. L. , PEARCY R. W. , SEEMANN J. R. 
Published: April 2006

ABSTRACTThe photosynthetic induction state under conditions of different lightfleck frequencies or durations, or different shade periods was studied in soybean leaves in order to examine how it might limit utilization of sunflecks in leaf canopies. Induction following an increase in photon flux density (PFD) from strongly limiting to saturating PFDs exhibited two phases; a fast‐inducing one, requiring about 1 min and a slow one, requiring up to 60 min for completion. Transfer of fully induced leaves to low light resulted in a rapid decrease in the fast‐inducing component, a slower decrease in the slow‐inducing component and an even slower decrease in stomatal conductance. Therefore, the decreases in extent of induction appeared to be due to biochemical factors and not to stomatal closure. Under flashing light regimes consisting of 1‐s lightflecks given at different frequencies for long periods, a constant induction state was achieved, the measure of induction state increased with the frequency of the lightflecks. This constant induction state also depended on the growth conditions, with shade leaves having a higher value than those grown at high light at any particular lightfleck frequency. The measure of induction state was mostly lower in flashing light as compared to constant light of the same mean PFD, particularly in leaves with a low light saturation point and in short lightflecks. Initial activities of ribulose‐1,5‐bisphosphate carboxylase (rubisco) were also higher in continuous light and were highly correlated with the measure of induction state. The rapid decrease in extent of induction of soybean leaves during shade periods is an important limitation to the ability of the leaves to respond to light increases similar to those occurring with sunflecks. At least part of the limitation on carbon assimilation during sunflecks due to photosynthetic induction is based on regulation of rubisco activity.
Photosynthesis in flashing light in soybean leaves grown in different conditions. II. Lightfleck utilization efficiency
Authors: PONS T. L. , PEARCY R. W. 
Published: April 2006

ABSTRACTLeaves of soybean plants grown in contrasting light and nutrient availability conditions were exposed to constant and to flashing light regimes with lightflecks of different frequencies, durations and photon flux density (PFD). The lightfleck characteristics were selected to be representative of the range of variation found for sunflecks in a soybean canopy. CO2 fixation rates were measured using a fast‐response gas‐exchange apparatus. The net CO2 fixation due to 1‐s‐duration lightflecks was 1·3 times higher than predicted from steady‐state measurements in constant light at the lightfleck and background PFD. This lightfleck utilization efficiency (LUE) was somewhat higher at a high than at a low frequency of one second lightflecks. LUE in flashing light with very short lightflecks (0·2s) and single 1 s lightflecks was as high as 2, but decreased sharply with increasing duration of lightflecks. This decrease occurred because CO2 fixation rates during lightflecks were constrained by carbon metabolism and induction limitations, and because the contribution of post‐illumination CO2 fixation to total CO2 fixation decreased with increased duration of lightflecks. LUE increased with increased PFD during the lightflecks, particularly in leaves from plants grown in high‐light, high‐nutrient conditions. Saturation PFDs were much higher in flashing light than in constant light. Only small differences in LUE were apparent between leaves from the three growth conditions.
X‐ray microanalytical (EDX) investigation of potassium distributions in mesophyll cells of non‐acclimated and cold‐acclimated rye leaves
Authors: PIHAKASKI‐MAUNSBACH K. , HARVEY D. M. R. 
Published: April 2006

ABSTRACTElectron probe X‐ray microanalysis was used to analyse the effects of sub‐zero temperatures on K+ distribution in compartments within non‐acclimated and cold acclimated rye (Secale cereale L. cv Voima) leaf cells and to evaluate membrane leakage of ions caused by freezing‐injury. The specimens were rapidly frozen from growing temperatures and from two different sub‐zero temperatures (LT50 and LT100) to which the leaves had already been slowly cooled. Measurements were made in the cytoplasm, vacuole and cell walls in freeze‐substituted mesophyll cells. At ambient temperatures, the mean K+ concentration in the cytoplasm (100 mol m−3) differed significantly from that of the vacuole (49 mol m−3) in the non‐acclimated (NA) cells, while in cold acclimated (A) cells, the concentrations were similar (109 vs 93 mol m−3, respectively). At LT50 temperatures, the K+ concentration in NA‐cells decreased significantly in the cytoplasm (59 mol m−3) but increased in the cell walls. In the A‐cells, on the other hand, the mean K+ concentration increased significantly (about three‐fold) in all major compartments. At LT100 temperatures, K+ concentrations in the cytoplasm and cell walls decreased when compared with corresponding LT50 values in the A‐cells but increased in the NA‐cells. The increased potassium concentration in the cytoplasm of A‐cells at LT50 temperature is compatible with the observed cell shrinkage and an absence of plasma membrane damage. The decreased potassium concentration in the cytoplasm of NA‐cells at LT50 temperature is compatible with the slight cell shrinkage and suggests that the plasma membrane in these cells shows increased permeability due to freeze injury.
The influence of elevated CO2 and temperature on biomass production of continuously defoliated white clover
Authors: RYLE G. J. A. , POWELL C. E. 
Published: April 2006

ABSTRACTClonal plants of white clover (Trifolium repens L.), grown singly in pots of Perlite and solely dependent for nitrogen on root nodule N2 fixation, were maintained in controlled environments which provided four environments: 18/13 °C day/night temperature at 340 and 680 μmol mol−1 CO2 and 20·5/15·5°C day/night temperature at 340 and 680 μmol mol−1 CO2. The daylength was 12 h and the photon flux density 500±25 μmol m−2 s−1 (PFD). All plants were defoliated for about 80d, nominally every alternate day, to leave the youngest expanded leaf intact on 50% of stolons, plus expanding leaves (simulated grazing). Elevated CO2 increased the yield of biomass removed at defoliation by a constant 45% during the second 40d of the experiment and by a varying amount in the first half of the experiment. Elevated temperature had little effect on biomass yield. Nitrogen, as a proportion of the harvested biomass, was only fractionally affected by elevated CO2 or temperature. In contrast, N2 fixation increased in concert with the promoting effect of elevated CO2 on biomass production. The increased yield of biomass harvested in 680 μmol mol−1 CO2 was primarily due to the early development and continued maintenance of more stolons. However, the stolons of plants grown in elevated CO2 also developed leaves which were heavier and slightly larger in area than their counterparts in ambient CO2. The conclusion is that, when white clover plants are maintained at constant mass by simulated grazing, they continue to respond to elevated CO2 in terms of a sustained increase in biomass production.
Do phospholipids and sucrose determine membrane phase transitions in dehydrating pollen species?
Authors: HOEKSTRA F. A. , CROWE J. H. , CROWE L. M. , VAN ROEKEL T. , VERMEER E. 
Published: April 2006

ABSTRACTGel‐to‐liquid crystalline transition temperatures (Tm) of phospholipids of five desiccation tolerant pollen species in vivo were compared at various levels of dehydration. In an attempt to explain chemically the differences in Tm between these species, phospholipids and soluble carbohydrate contents were examined. We observed a negative correlation between the number of double bonds per phospholipid and Tm values for the intact pollen. This negative correlation also applied to Tm and the relative amount of linolenic acid. For the purpose of comparing Tm values of pollen and of unsaturated PCs (from the literature), the relative amounts and degree of unsaturation of pollen PCs were determined. A discrepancy between Tm values of individual PCs and intact pollen is discussed. Sucrose is the major soluble carbohydrate in 15 pollen species tested, generally making up a considerable part of the dry weight. A positive correlation between sucrose content (either as a percentage of the dry weight or as grams sucrose per grams phospholipid) and Tm was established. This unexpected result was explained in terms of alternative adaptive strategies. We suggest that, for desiccation tolerance, pollen either has to contain sucrose for the protection of its phospholipids, or have a high degree of fatty acid unsaturation in its phospholipids. The advantages and disadvantages of the two options are discussed.
Effect of a pretreatment of seed coats with a low‐osmolality solution on subsequent [14C] sucrose transport into attached empty ovules of pea
Authors: WOLSWINKEL P. , KOERSELMAN‐KOOIJ J. W. 
Published: April 2006

ABSTRACTThis paper discusses the question as to whether or not the seed coat tissues can‘adapt’to a treatment with a solution containing a low osmoticum concentration, representing an environment which is sub‐optimal for assimilate transport into attached surgically modified ovules. Before the start of a pulse‐labelling procedure, in experiments on [14C] sucrose transport into fruits of pea (Pisum sativum) with four empty ovules, two empty ovules were filled with a low‐osmolality solution (a 200 mol m−3 mannitol medium or a solution without mannitol) and the other two ovules were filled with a 400 mol m−3 mannitol medium. Pretreatment with a low‐osmolality medium, during a period of 2–3 h, enhanced subsequent transport of [14C] sucrose into empty ovules filled with a low‐osmolality medium, in comparison with [14C] sucrose transport into empty ovules filled with a 400mol m−3 mannitol medium during the pretreatment period. This partial recovery of sink strength of attached empty ovules can be explained as the result of a stimulation of solute efflux from seed coat cells at high cell turgor.
The use of natural abundance of nitrogen isotopes in plant physiology and ecology
Authors: HANDLEY L. L. , RAVEN J. A. 
Published: April 2006

ABSTRACTNitrogen stable isotope (15N, 14N) natural abundance has been much less used than carbon isotopes (13C, 12C) in plant physiology and ecology. Analytical problems, the lower fractional abundance of 15N than of 13C in the biosphere, the greater complexity of the N cycle relative to the C cycle, and smaller expressed discriminations in nature, are contributing factors. The major N pools, globally, have different isotope signatures: atmospheric N2 is 15N‐depleted relative to organic N (including sedimentary N), a situation resulting from a greater expressed discrimination in the organic N to N2 (via denitrification) reaction than of diazotrophy during accumulation of the reduced N. Essentially all of the enzymes except nitrogenase which transform N compounds show discrimination against 15N, although for glutamine synthetase, and the amination of 2‐oxoglutarate and pyruvate, this is only seen in terms of NH4+ rather than the true substrate, NH3. Discrimination is expressed in various N interconversions within plants, leading to substantial differences in δ15N (up to 12‰) among N compounds and macroscopic plant parts. N isotope fractionation during assimilation of exogenous combined N is often much lower than that expected from studies of isolated enzymes due to processes which show very little discrimination, such as limitation by transport through aqueous solution and membranes. Application of 15N/14N discrimination studies to plant ecology have concentrated largely on distinguishing diazotrophy from N supplied from combined N, based on the lower 15N/14N in diazotrophs due to the higher 15N/14N of combined N sources not being offset by fractionation during uptake. While potentially very useful, a number of pitfalls are discussed in its ecological use in both terrestrial and aquatic systems. N isotope discrimination is also useful in tracking N through food webs, and hence, back to combined N sources for plants.
Carbon: terrestrial C4 plants
Authors: PEISKER M. , HENDERSON S. A. 
Published: April 2006

ABSTRACTThe carbon isotope composition of terrestrial C4 plants depends on the primary carboxylation of phosphoenolpyruvate (PEP) and on the diffusion of CO2 to the carboxylation sites, but is also influenced by the final carboxylation of ribulose‐1,5‐bisphosphate (RuBP). Several models have been used for reproducing this complex situation. In the present review, a particular model is applied as a means to interpret the effects of environmental and genetically determined factors on carbon isotope discrimination during C4 photosynthesis. As a new feature, the model considers four types of limitation of the overall CO2 assimilation rate. Both carboxylation reactions are assumed to be limited by either maximum enzyme activity or maximum substrate regeneration rate. The model is applied to experimental data on the effects of CO2, irradiance and water stress on short‐term discrimination by leaves of several C4 species measured simultaneously with CO2 gas exchange characteristics. In particular, different patterns of the influence of low irradiances on carbon isotope discrimination are interpreted as due to variations in that irradiance at which a transition from limitation by PEP regeneration rate and RuBP carboxylase activity to limitation by the regeneration rates of both substrates occurs. After discussing literature data on the effects of environmental conditions on carbon isotope discrimination by C4 plants seasonal and developmental changes in carbon isotope composition, studies on the systematic and geographic distribution of C4 plants, evolutionary and genetical aspects, and some ecological implications are reviewed.
Carbon: freshwater plants
Authors: KEELEY J. E. , SANDQUIST D. R. 
Published: April 2006

ABSTRACTδ13C values for freshwater aquatic plant matter varies from −11 to −50‰ and is not a clear indicator of photosynthetic pathway as in terrestrial plants. Several factors affect δ13C of aquatic plant matter. These include: (1) The δ13C signature of the source carbon has been observed to range from +1‰ for HCO3− derived from limestone to −30‰ for CO2 derived from respiration. (2) Some plants assimilate HCO3−, which is –7 to –11‰ less negative than CO2. (3) C3, C4, and CAM photosynthetic pathways are present in aquatic plants. (4) Diffusional resistances are orders of magnitude greater in the aquatic environment than in the aerial environment. The greater viscosity of water acts to reduce mixing of the carbon pool in the boundary layer with that of the bulk solution. In effect, many aquatic plants draw from a finite carbon pool, and as in terrestrial plants growing in a closed system, biochemical discrimination is reduced. In standing water, this factor results in most aquatic plants having a δ13C value similar to the source carbon. Using Farquhar's equation and other physiological data, it is possible to use δ13C values to evaluate various parameters affecting photosynthesis, such as limitations imposed by CO2 diffusion and carbon source.
Site‐specific natural isotope fractionation of hydrogen in plant products studied by nuclear magnetic resonance
Authors: MARTIN G. J. , MARTIN M. L. , ZHANG B.‐L. 
Published: April 2006

ABSTRACTDeuterium NMR at the natural abundance was used to determine the site‐specific isotope ratios (D/H)i of the non‐equivalent isotopomers of various chemical species which exist in plant products. The deuterium distribution in glucose, galactose and mannitol samples from different botanical and compartmental origins is discussed in terms of the influence of plant metabolism and environmental factors. Particular emphasis is given to the potential versatility of deuterium NMR in the study of natural isotopic distribution in pro‐chiral situations. Typical examples of chiral recognition are given in the field of glycolysis metabolites (ethanol, amino‐acids) and of monoterpene biosynthesis.
Carbon isotope discrimination and the integration of carbon assimilation pathways in terrestrial CAM plants
Authors: GRIFFITHS H. 
Published: April 2006

ABSTRACTMeasurement of carbon isotope discrimination (Δ) of organic plant material integrates the combination of C4 and C3 carboxylation processes during the phases of CAM through dark and light periods. These processes are tempered by environmental conditions which regulate CAM activity at the molecular, biochemical and ecological level. The factors contributing to short‐term changes in Δ are discussed in terms of the day‐night changes in metabolite pools and integration via on‐line, instantaneous discrimination techniques. Thus, the isotope signature of newly fixed carbon in malic acid reflects the balance between diffusion and carboxylation limitation together with direct and indirect effects of respiratory metabolism. Leakage of CO2 during decarboxylation leads to greater discrimination being expressed than is predicted from existing models. Over the timescales of seasonal growth and productivity, most constitutive CAM and C3‐CAM intermediate plants show little variation in Δ (2–4‰). The changes induced by developmental and environmental signals and genetic regulation of CAM are compared for stem and leaf succulents. The role of CAM as a potentially highly productive photosynthetic pathway is contrasted with the induction of CAM as a maintenance mechanism in response to environmental stresses. Analyses of Δ have already contributed much to our understanding of the distribution and regulation of CAM, and in turn can also be used to analyse phylogenetic relationships and the origins of CAM as determined from palaoecological evidence.
Carbon isotope discrimination in C3‐C4 intermediates
Authors: von CAEMMERER S. 
Published: April 2006

ABSTRACTCarbon isotope discrimination in C3–C4 intermediates is determined by fractionations during diffusion and the biochemical fractionations occurring during CO2 fixation. These biochemical fractionations in turn depend on the fractionation by Rubisco in the mesophyll, the amount of CO2 fixation. These biochemical fractionations in turn depend on the fractionation by Rubisco in the mesophyll, the amount of CO2 fixation occurring in the bundle sheath, the extent of bundle‐sheath leakiness and the contribution which C4‐cycle activity makes to the CO2 pool there. In most instances, carbon isotope discrimination in C3–C4 intermediates is C3‐like because only a small fraction of the total carbon fixed is fixed in the bundle sheath. In particular, this must be the case for Flaveria intermediates which initially fix substantial amounts of CO2 into C4‐acids. In C3–C4 intermediates that refix photorespiratory CO2 alone, it is possible for carbon isotope discrimination to be greater than in C3‐species, particularly at low CO2 pressures or at high leaf temperatures. Short‐term measurements of carbon isotope discrimination and gas exchange of leaves can be used to study the photosynthetic pathways of C3‐C4 intermediates and their hybrids as has recently been done for C3 and C4 species.
Water uptake by plants: perspectives from stable isotope composition
Authors: EHLERINGER J. R. , DAWSON T. E. 
Published: April 2006

ABSTRACTStable isotope studies of hydrogen and oxygen stable isotope ratios of water within plants are providing new information on water sources, competitive interactions and water use patterns under natural conditions. Variation in the utilization of summer rain by aridland species and limited use of stream water by mature riparian trees are two examples of how stable isotope studies have modified our understanding of plant water relations. Analyses of xylem sap and tree rings have the potential of providing both short‐term and long‐term information on plant water use patterns.