bluuebunny/crossref_metadata_2025_split huggingface dataset:
A feedback control system for the precise and continuous regulation of photosynthetic photon flux density
Authors: LIVINGSTON N. J. 
Published: April 2006

ABSTRACTA simple and inexpensive feedback control system that provides continuous and precise control of photosynthetic photon flux density (PPFD) in a whole plant cuvette is described. A ‘Plexiglass’ tank is interposed between a light source and cuvette and PPFD changed by varying the level of dyed liquid in the tank. The amount of liquid pumped into or drained from the tank is a function of the difference (error) between a defined set point value of PPFD and that measured in the cuvette. The set point can be varied as a function of time, can follow the output of a quantum sensor measuring ambient PPFD or can be driven by values of PPFD read from a data file. Within the 0.4 to 0.64 μm waveband, the dye acts as a neutral density filter so that there is no change in spectral distribution with PPFD. Photosynthetic photon flux density in the cuvette was controlled to better than 20 μmol m−2s−1 when the set point was varied from 200 to 1100 μmol m−2s−1 over 3 min. When the set point was held constant or changed less rapidly, errors did not exceed 5 μmol m−2s−1. Net photosynthesis of Western redcedar (Thuja plicata Donn.) seedlings held at 18 °C closely followed rapid changes in PPFD.
Symbiotic nitrogen‐fixing root nodules of Lathyrus maritimus (L.) Bigel (beach pea) from Newfoundland shore lines with special reference to oleosomes (lipid bodies)
Authors: BARIMAH‐ASARE J. , BAL A. K. 
Published: April 2006

ABSTRACT Lathyrus maritimus (L.) Bigel, commonly known as beach pea, grows along the shorelines of Newfoundland, Canada. Rhizobia have been isolated from the subterranean root nodules and the cultures were induced to nodulate seedlings raised in the laboratory. The nodules collected from the field were elongated and sometimes branched with proximal ends thickened. Histological characteristics revealed their indeterminate perennial form. Oleosomes (lipid bodies) were present in the nodule tissues. Morphometric analysis showed their presence in the nodule cortex cells throughout all developmental stages, but they were found in the infected cells only during the early stages of infection and symbiosis. It is suggested that oleosomes are utilized for membrane and rhizobial proliferation during establishment of symbiosis in the infected cells. The role of oleosomes in the cortical cells remains unclear.
Amino acid metabolism associated with N‐mobilization from the flag leaf of wheat (Triticum aestivum L.) during grain development
Authors: PEETERS K. M. U. , VAN LAERE A. J. 
Published: April 2006

ABSTRACTField‐grown winter wheat (Triticum aestivum L. cv. Castell) was used to study changes in the free amino acid pools of different plant parts and related enzyme activities in the flag leaf throughout the grain‐filling period in three consecutive growing seasons. Amino acid analysis data indicated that, during senescence, the nitrogen flow in the flag leaf was directed towards the synthesis of glutamine as a specific nitrogen transport form. Of the enzymes involved, total glutamine synthetase (GS; EC 6.3.1.2) and especially ferredoxin‐dependent glutamate synthase (Fd‐GOGAT; EC 1.4.7.1) activities declined continuously as senescence progressed. Unlike (chloroplastic) GS2, (cytosolic) GS1 was shown to be very persistent suggesting a special role for this isoenzyme in the N‐reallocation process. Glutamate‐oxaloacetate transaminase (GOT; EC 2.6.1.1), glutamate‐pyruvate transaminase (GPT; EC 2.6.1.2) and isocitrate dehydrogenase (IDH; EC 1.1.1.42) showed a characteristic biphasic activity profile after anthesis. It is proposed that these enzymes, for each of which at least two isoenzymes were demonstrated, are involved in glutamate synthesis at the later stages of leaf senescence. Ammonium levels were fairly constant throughout the flag leafs life span, an ultimate rise often following peak values of glutamate dehydrogenase (GDH; EC 1.4.1.4) activity. The enzymology of flag leaf amino acid metabolism during grain development is further discussed in relation to observations of NH3‐volatilization from naturally senescing wheat plants.
Compartmentation and transport of zinc in barley primary leaves as basic mechanisms involved in zinc tolerance
Authors: BRUNE A. , URBACH W. , DIETZ K.‐J. 
Published: April 2006

ABSTRACTThe heavy metal zinc was administered to barley seedlings by increasing its concentration in the hydroponic medium. The most dramatic effect was a severe inhibition of root elongation with little effect on root biomass production. The growth of primary leaves was little affected although the zinc content of the primary leaves increased several‐fold. A detailed compartment analysis was performed for 10‐d‐old barley primary leaves. Under low zinc nutrition (2mmol m −3), highest zinc contents were observed in the cytoplasm of mesophyll protoplasts. At inhibitory zinc concentrations in the hydroponic medium (400 μmol m −3), zinc levels dramatically and preferentially increased in the apoplastic space. Elevated zinc levels were also observed in the epidermal cells, and to a lesser extent, in mesophyll vacuoles. The cytoplasmic content of mesophyll protoplasts was unchanged, indicating perfect zinc homeostasis within the leaf. In order to understand the transport mechanisms underlying the steady‐state distribution profile, we used 65Zn to conduct uptake experiments with leaves whose lower epidermis had been stripped. The leaves were placed on zinc solutions of varying concentrations containing 65Zn for 5 min to 6 h. After the incubation, the leaves were fractionated into mesophyll and epidermis protoplasts and residue, the latter mainly representing cell wall. Adsorption of Zn to the extracellular matrix was 100 times faster than Zn uptake into the cells. By far the largest portion taken up into the mesophyll protoplasts rapidly appeared in the vacuolar compartment. These results demonstrate the importance of compartmentation and transport as homeostatic mechanisms within the leaves to handle high, possibly toxic, zinc levels in the shoot.
Behaviour of plasma membrane, cortical ER and plasmodesmata during plasmolysis of onion epidermal cells
Authors: OPARKA K. J. , PRIOR D. A. M. , CRAWFORD J. W. 
Published: April 2006

ABSTRACTDuring plasmolysis of onion epidermal cells, the contracting protoplast remains connected to the cell wall by an intricate, branched system of plasma membrane (PM) ‘Hechtian strands’ which stain strongly with the fluorescent probe DiOC6. In addition, extensive regions of the cortical endoplasmic reticulum (ER) network remain anchored to the cell wall during plasmolysis and do not become incorporated into the contracting protoplast with the other cell organelles. These ER profiles become tightly encased by the PM as the latter contracts towards the centre of the cell. Thus, although the cortical ER is left outside the main protoplast body, it is nonetheless still bound by the PM of the cell. As well as being anchored to the wall, the cortical ER remains intimately linked with plasmodesmata and retains continuity between cells via the central desmotubules which become distended during plasmolysis. The PM also remains in close contact with the plasmodesmatal pore following plasmolysis. It is suggested that plasmodesmata, although sealed, may not be broken during plasmolysis, their substructure being preserved by continuity of both ER and PM through the plasmodesmatal pore. A structural model is presented which links the behaviour of PM, ER and plasmodesmata during plasmolysis.
Carbon isotope discrimination and water‐use efficiency of six crops grown under wet and dryland conditions
Authors: KNIGHT J. D. , LIVINGSTON N. J. , VAN KESSEL C. 
Published: April 2006

ABSTRACTMustard (Sinapis alba L.), Argentine canola (Brassica napus L. cv. Westar), Polish canola (Brassica campestris L. cv. Tobin), pea (Pisum sativum L.), durum wheat (Triticum durum L. cv. Kyle) and soft wheat (Triticum aestivum L. cv. Fielder) were grown at Outlook, Saskatchewan, Canada, under irrigated and dryland conditions. Carbon isotope discrimination (Δ) and water‐use efficiency (W), defined as grams of above ground dry matter produced per kilogram water used, were negatively correlated in the six field‐grown crops. In irrigated plants Δ remained relatively constant (20–21‰) throughout the growing season. However, in dryland plants, Δ declined in response to the progressive depletion of stored soil water (Polish canola, 20‐2‐18‐8‰; mustard, 19.9–18 5‰; pea, 19.9–17 2‰ durum wheat, 19.7–16.4‰; Argentine canola, 19.4–17.6‰; soft wheat, 19.0–17.4‰). Although there were genetic differences in Δ among the species, water availability was the major factor controlling Δ.
Expansion rate of young tomato fruit growing on plants at positive water potential
Authors: GRANGE R. I. , ANDREWS J. 
Published: April 2006

ABSTRACTChanges in tomato fruit expansion rate and carbohydrate content have been assessed during treatments designed to alter the carbon import rate. Because fruit expansion is sensitive to plant water status, the relationship with carbon import is difficult to assess, and thus, the diameter growth rate of young fruit was measured on plants maintained at positive water potentials. The detached top metre of a tomato plant was supplied with water, through the cut stem base, at a pressure of 0.08 MPa. Developing fruit on the stem continued to grow at high rates for up to 2 d. Fruit diameter growth rate after plant detachment was directly proportional to temperature. Plants acclimated to different continuous irradiances for 5 d before detachment gave fruit growth rates after plant detachment which were directly proportional to the irradiance up to 7 MJ m−2d−1 photosynthetically active radiation (PAR). In continuous darkness, fruit growth rate remained unchanged for 20 h and then declined to less than 40% of the original rate over the following 30 h. On re‐exposure to light, about 5 h elapsed before fruit growth rate increased but the growth rate stabilized at approximately 50% of the rate in continuously illuminated plants. During darkness, both fruit starch and hexose content decreased in comparison to illuminated controls, but on re‐illumination, carbohydrate content increased before carbon was allocated to structural growth. Heat‐killing the phloem of the fruit pedicel caused an immediate, but temporary, cessation of growth. After a partial recovery, expansion growth continued, but more slowly than in untreated fruit and at steadily declining rates. Starch and hexose sugars were not used to provide substrates for growth and starch synthesis was maintained. Continuing cell expansion was assumed to have been supported by water import via the xylem. Thus, fruit expansion may be related to carbon accumulation in most circumstances, but the changing allocation of imported carbon to storage and cell expansion may modify this relationship.
Elevated atmospheric CO2 alters stomatal responses to variable sunlight in a C4 grass
Authors: KNAPP A. K. , FAHNESTOCK J. T. , OWENSBY C. E. 
Published: April 2006

ABSTRACTNative tallgrass prairie in NE Kansas was exposed to elevated (twice ambient) or ambient atmospheric CO2 levels in open‐top chambers. Within chambers or in adjacent unchambered plots, the dominant C4 grass, Andropogon gerardii, was subjected to fluctuations in sunlight similar to that produced by clouds or within canopy shading (full sun > 1500 μmol m−2 s−1 versus 350 μmol m−2 s−1 shade) and responses in gas exchange were measured. These field experiments demonstrated that stomatal conductance in A. gerardii achieved new steady state levels more rapidly after abrupt changes in sunlight at elevated CO2 when compared to plants at ambient CO2. This was due primarily to the 50% reduction in stomatal conductance at elevated CO2, but was also a result of more rapid stomatal responses. Time constants describing stomatal responses were significantly reduced (29–33%) at elevated CO2. As a result, water loss was decreased by as much as 57% (6.5% due to more rapid stomatal responses). Concurrent increases in leaf xylem pressure potential during periods of sunlight variability provided additional evidence that more rapid stomatal responses at elevated CO2 enhanced plant water status. CO2‐induced alterations in the kinetics of stomatal responses to variable sunlight will likely enhance direct effects of elevated CO2 on plant water relations in all ecosystems.
Respiration rates predict differences in growth of coast redwood
Authors: ANEKONDA T. S. , CRIDDLE R. S. , LIBBY W. J. , BREIDENBACH R. W. , HANSEN L. D. 
Published: April 2006

ABSTRACTThe relation between growth rate traits (height, basal diameter, stem volume and branch diameter) and two measures of respiration rate [metabolic heat rate (q) and CO2 production rate (Rco2)] and their ratio (q/Rco2) was examined on a collection of 192 different genotypes of coast redwoods [Sequoia sempervirens (D.Don) Endl.]. Branch diameter was not correlated with any of the respiratory measures, but the other three growth traits gave highly significant (P < 0.001) correlations with positive slopes. Combining the four growth traits and the three respiratory variables (q, RCo2 and q/Rco2) to give two canonical variates, one representing growth and one representing respiration, gives an even stronger linear correlation (r= 0–85). These data suggest that simultaneous assay of multiple respiratory measures on juvenile trees can be used to predict their longer‐term growth rates.
The cellular pathway of photosynthate transfer in the developing wheat grain. I. Delineation of a potential transfer pathway using fluorescent dyes
Authors: WANG H. L. , OFFLER C. E. , PATRICK J. W. , UGALDE T. D. 
Published: April 2006

ABSTRACTA potential cellular pathway for photosynthate transfer between the crease phloem and the starchy endosperm of the developing wheat grain has been delineated using fluorescent dyes. Membrane permeable and impermeable dyes have been introduced into the grain through the crease phloem, the endosperm cavity or the dorsal surface of the starchy endosperm. The movement of the symplastic tracer 5‐(6)‐6‐carboxyfluorescein (CF) derived from 5‐(6)‐6‐carboxyfluorescein diacetate (CFDA), from either direction between the crease phloem and the endosperm cavity, indicated that the symplastic pathway was operative from the crease phloem to the nucellar projection. Furthermore, the inward movement of apoplastic tracer trisodium, 3‐hydroxy‐5,8,10‐pyrentrisulphonate (PTS) from the endosperm cavity and that of CF following plasmolysis showed that there was a high resistance to solute transfer within the apoplast of the pigment strand. All dyes entered the modified aleurone and adjacent sub‐aleurone bordering the endosperm cavity. Subsequent movement of the symplastic tracers CF and sulphorhodamine G (SRG) into and through the endosperm was rapid. However, the movement of apoplastic tracers PTS and Calcofluor White (CFW) was relatively slow and with tissue plasmolysis, CF was confined to the cytoplasm of the modified aleurone and subaleurone cells. Together, these results demonstrate that there is a high resistance to solute movement within the apoplast of the cells bordering the endosperm cavity. We propose that photosynthate transfer is via the symplast to the nucellar projection where membrane exchange to the endosperm cavity occurs. Uptake from the cavity is by the modified aleurone and small endosperm cells prior to transfer through the symplast to and through the starchy endosperm.
The effects of UV‐B radiation on loblolly pine. 3. Interaction with CO2 enhancement
Authors: SULLIVAN J. H. , TERAMURA A. H. 
Published: April 2006

ABSTRACTProjected depletions in the stratospheric ozone layer will result in increases in solar ultraviolet‐B radiation (290–320 nm) reaching the earth's surface, These increases will likely occur in concert with other environmental changes such as increases in atmospheric carbon dioxide concentrations. Currently very little information is available on the effectiveness of UV‐B radiation within a CO2‐enriched atmosphere, and this is especially true for trees. Loblolly pine (Pinus taeda L.) seedlings were grown in a factorial experiment at the Duke University Phytotron with either 0, 8.8 or 13.8 kJ m−2 of biologically effective UV‐B radiation (UV‐BBE). The CO2 concentrations used were 350 and 650 μmol mol−1. Measurements of chlorophyll fluorescence were made at 5‐week intervals and photosynthetic oxygen evolution and leaf pigments were measured after 22 weeks, prior to harvest. The results of this study demonstrated a clear growth response to CO2 enrichment but neither photosynthetic capacity nor quantum efficiency were altered by CO2. The higher UV‐B irradiance reduced total biomass by about 12% at both CO2 levels but biomass partitioning was altered by the interaction of CO2 and UV‐B radiation. Dry matter was preferentially allocated to shoot components by UV‐B radiation at 350 μmol mol−1 CO2 and towards root components at 650 μmol mol−1 CO2. These subtle effects on biomass allocation could be important in the future to seedling establishment and competitive interactions in natural as well as agricultural communities.
Stomatal responses to sodium ions inAster tripolium: a new hypothesis to explain salinity regulation in above‐ground tissues
Authors: PERERA L. K. R. R. , MANSFIELD T. A. , MALLOCH A. J. C. 
Published: April 2006

ABSTRACTA study has been made of the ionic relations of stomata ofAster tripoliumL., a maritime halophyte which colonizes coastal saltmarshes. The results obtained allow us to add this species to the growing list for which an involvement of K+transport in stomatal movements has been demonstrated. However, an additional and ecologically important characteristic was found: there was a suppression of stomatal opening by increasing NaCl concentrations. A new hypothesis is offered of the mechanism for controlling salt and water relations inA. tripolium, a species which does not possess glands or other means of excreting salt. It is suggested that when the capacity of the tissues to accumulate salt in cell vacuoles is exceeded, the concentration of Na+ions in the apoplast around the guard cells begins to rise. This causes partial stomatal closure, reduces transpiration and increases water‐use‐efficiency. Therefore, the flow of salt into the leaves is reduced but growth (and the manufacture of the new photosynthates required to support it) can continue.Aster tripoliumcan be added to the small list of known species which readily yield isolated epidermis suitable for detailed stomatal studies. Throughout this study, we have compared its stomatal physiology withC. communis, which has been thoroughly investigated in the past.
Influence of stem lacunar structure on gas transport: relation to the oxygen transport potential of submersed vascular plants
Authors: SCHUETTE J. L. , KLUG M. J. , KLOMPARENS K. L. 
Published: April 2006

ABSTRACTThe influence of stem lacunar structure on the potential of diffusion and mass flow to meet estimated root O2 demands was evaluated and compared in four submersed aquatic plant species. Internodal lacunae formed large continuous gas canals which were constricted at the nodes by thin, perforated diaphragms. Gas transport studies showed that nodes had little effect on diffusion, but significantly reduced mass flow. Measured diffusive resistances approximated those predicted by Fick's first law, ranged from 203 to 5107 × 108 s m−4 and increased as lacunar area decreased in Potamogeton praelongus, two Myriophyllum species and Elodea canadensis. Our analysis suggested that diffusion could satisfy estimated root O2 demands given the development of relatively steep O2 gradients (0.15–0.35 mol O2 mor−1 per 0.5 m stem) between shoots and roots. Plants with high resistances (e.g. > 750 × 108 s m−4) and long lacunar pathlengths may be unable, even during active photosynthesis, to support the O2 demands of a large root system by diffusion alone. Measured nodal resistances to mass flow approximated those predicted by Hagen‐Poiseuille law and ranged from 46 to 2029 × 108 Pa s m−3. Our analysis suggested that these resistances were quite low and that relatively small pressure differentials (< 150 Pa per 0.5 m stem) could drive mass flow at rates which would support root O2 demands. Possible mechanisms whereby plant architecture may serve to maintain these pressure differentials are proposed.
Carbon and nitrogen content of congeneric annual and perennial grass species: relationships with growth
Authors: GARNIER E. , VANCAEYZEELE S. 
Published: April 2006

ABSTRACTSeven annual‐perennial pairs of grass species (six congeneric and one pair taken at random) were grown under productive conditions in the laboratory in order to investigate which plant characters were responsible for the higher relative growth rate (RGR) of annuals as compared to perennials under these conditions. The nitrogen and carbon concentrations of shoot organs and of the whole plant were higher in annuals than in perennials. This was also the case for the specific absorption rate for nitrate and nitrogen productivity (on whole plant and leaf basis). The range of RGR displayed by the 14 species was large enough (0.15–0.33d−1) to examine the general relationships between RGR and the various parameters measured in the present study. RGR was positively related to plant, leaf blade and sheath nitrogen concentrations, but there was no relationship between RGR and any of the carbon concentrations. RGR also strongly correlated with specific absorption rate for nitrate and with nitrogen productivity. A new factorization of this latter parameter led to the definition of the ‘leaf nitrogen productivity’ (NLP), which is likely to depend on photosynthetic nitrogen use efficiency. RGR was shown to be strongly correlated with NLP, but not with the second term of the factorization, namely the proportion of plant nitrogen allocated to the leaves.
Overexpression of oat phytochrome A gene differentially affects stem growth responses to red/far‐red ratio signals characteristic of sparse or dense canopies
Authors: CASAL J. J. , SÁNCHEZ R. A. 
Published: April 2006

ABSTRACTThe effects of overexpression of oat phytochrome A on neighbour detection and on stem‐growth responses to changes in red light (R), far‐red light (FR) and blue light (B) simulating neighbours were investigated in transgenic tobacco seedlings grown under natural radiation. In wild‐type (WT) seedlings, stem extension growth was promoted: (1) by lowering the R:FR by means of daytime supplementary FR, end‐of‐day FR, neighbours reflecting FR, or selective light filters placed around the base of the shoot to reduce R without affecting FR; and (2) by lowering phytochrome‐absorbable radiation (R+FR) reaching the stem. Transgenic seedlings only responded to reductions in R:FR involving no significant changes in FR irra‐diance, i.e. end‐of‐day FR and filters placed around the stem to reduce R. Neither daytime supplementary R nor selective filters placed around the stem to reduce B affected stem growth in any genotype. In growing canopies, WT seedlings responded to the reduction of R:FR caused by FR reflected in neighbour plants. Transgenic seedlings responded to plant density about a week later, when mutual plant shading reduced R and (to a lesser extent) FR below sunlight levels. Overexpression of phytochrome A impaired early neighbour detection.