bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hierarchy establishment among potentially similar buds
Authors: NOVOPLANSKY A. 
Published: April 2006

ABSTRACTA plant has a great excess of buds each with the potential of developing an entire shoot system. The general question tackled was to what extent shoot size and time of bud development are important for bud hierarchy. Pea seedlings with two shoots, which were either equal or unequal in size, were obtained by the early removal of the seminal shoot. When these two shoots were also removed, one of the two cotyledon buds next to the bases of the shoots developed into the new shoot system. The determination of which of the buds became dominant was studied as a function of the relative sizes of the two primary cotyledonary shoots, of differences in the timing of the removal of these shoots and of the size of the buds. The bud that became dominant was not necessarily the larger one, nor did it always emerge from the axil of the larger shoot. Instead, it was usually the bud that was inhibited for a shorter period by the shoot next to it. It is suggested that the fate of a bud is predominantly determined by developmental parameters, for example lime of release, which are correlated with its developmental status and not necessarily with its physical size or with the past development of its shoot.
Photoinhibition of photosynthesis on a coral reef
Authors: FRANKLIN L. A. , SEATON G. G. R. , LOVELOCK C. E. , LARKUM A. W. D. 
Published: April 2006

ABSTRACTPhotoinhibition of macroalgae in the epilithic algal community (KAC) of coral reefs was studied using chlorophyll fluorescence techniques at One Tree Island, Great Barrier Reef, Australia. Fv/Fm (variable to maximum fluorescence, darkened samples) of shallow macroalgae declined by 50% on fine summer and winter days, recovering in late afternoon. Within a species, thalli from low‐light habitats were more photoinhibited (2h at 1400μimol m−2 s−1) than those from high‐light habitats. The sensitivity of Lobophora variegata (Phacophyta) and Chlorodesmis fastigiata (Chlorophyta) increased with depth (1 versus 20 m). However, shallow Halimeda tuna (Chlorophyta) plants growing between corals were more photoinhibited than those from deep, open areas.Photoinhibition and recovery were depth‐ and species‐specific. Shallow Lobophora and Chlorodesmis maintained a greater degree of QA oxidation during photoinhibition. In deep thalli, reduced effective quantum yield of open photosystem II centres reflected lower proportions and excitation capture efficiencies of open centres. In Lobophora, zeaxanthin formation accompanied non‐photochemical fluorescence quenching (NPQ), but in Chlorodesmis NPQ was limited and no zeaxanthin or antherxanthin formed. Higher photosynthetic efficiency in the lower storey of the EAC may compensate for photoinhibition in the upper storey, thereby reconciling photoinhibition of individual thalli with previous observations of no net inhibition of community productivity.
Nitrate and ammonium influxes in soybean (Glycine max) roots: direct comparison of 13N and 15N tracing
Authors: CLARKSON D.T. , GOJON A. , SAKER L.R. , WIERSEMA P.K. , PURVES J.V. , TILLARD P. , ARNOLD G.M. , PAANS A.J.M. , VAALBURG W. , STULEN I. 
Published: April 2006

ABSTRACTWe compared influxes and internal transport in soybean plants (Glycine max cv. Kingsoy) of labelled N from external solutions where either ammonium or nitrate was labelled with the stable isotope15N and the radioactive isotope13N. The objective was to see whether mass spectrometric determinations of tissue 15N content were sufficiently sensitive to measure influxes accurately over short time periods. Our findings were as follows. (1) There was a close quantitative correspondence between estimates of N influx of individual plants using 15N or 13N measurements with either NO3/− or NH4+ at 4 or 2 mol−3, respectively in the external solution. (2) Transport to the shoot of N from NO3 absorbed over a 5–15 min period could be monitored when the external NO3− concentration ranged from 0–05 to 4 mol m−3. NH4+ as the N source labelled shoot tissue more slowly, and estimates of the transport between root and shoot could be made only with 13N. (3) Influx of NO3− into root tissue could be measured by 15N enrichment after 5–10 min at concentrations approaching the probable KM of the high‐affinity transport system. (4) There was some indication of isotope discrimination, especially with respect to the movement of labelled N to the shoot, when NO3− is the N source.For many purposes, 15N tracing can be used satisfactorily to estimate influxes of both NO3− and NH4+ in soybean roots. Use of the short‐lived radio nuclide 13N remains the method of choice for more refined measurements of internal distribution and assimilation.
Where does all the calcium go? Evidence of an important regulatory role for trichomes in two calcicoles
Authors: DE SILVA D.L.R. , HETHERINGTON A.M. , MANSFIELD T.A. 
Published: April 2006

ABSTRACTIn previous studies of the calcicoles Centaurea scabiosa and Leontodon hispidus, the stomata on isolated epidermis closed partially when the concentration of calcium in the medium was above 1 mol m−3. This is a much smaller concentration than that believed to be delivered into the leaves in xylem sap when the plants are growing in a calcium‐rich medium, and hence the mechanism for ‘protecting’ stomata from excessive exposure to free calcium is thought to be of great physiological significance. It is shown here that, in the leaves of both species, a substantial amount of the calcium they contain is located within meso‐phyll cells, and virtually all of that which does enter the epidermis is contained within trichomes, probably as calcium oxalate. The amounts of calcium in the vicinity of the stomata thus remain small despite high concentrations elsewhere, ensuring that the essential role of Ca2+ in intra‐cellular signalling in guard cells can continue to be performed without disturbance.
Stable carbon isotopes as indicators of increased water use efficiency and productivity in white spruce (Picea glauca (Moench) Voss) seedlings
Authors: SUN Z. J. , LIVINGSTON N. J. , GUY R. D. , ETHIER G. J. 
Published: April 2006

ABSTRACTThe relationship among water use efficiency (WUE), productivity and carbon isotopic composition (δ13C) in white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings representing 10 controlled crosses were planted in the field in individual buried sand‐filled cylinders. The soil water content in the cylinders was measured using time domain reflectometry over two growing seasons and seedling water use determined by water balance. Two watering treatments were imposed: irrigation and dry land. There was significant (1.6–2.0%c) genetic variation in needle δ13C. Ranking of crosses in terms of δ13C was generally maintained over watering treatments and there was not a significant genetic versus environmental interaction. There was a positive correlation between δ13C and both intrinsic and long‐term WUE (more positive δ13C with increased WUE) and between δ13C and productivity, suggesting a correlation due to variation in photosynthetic capacity. Root to shoot ratios did not increase in water‐stressed plants, indicating that responses to drought were primarily at the level of gas exchange, rather than through morphological changes. Our results indicate that it should be possible to use δ13C as a surrogate for WUE and to select white spruce genotypes for high WUE without compromising yield.
Antisense inhibition of the sucrose transporter in potato: effects on amount and activity
Authors: LEMOINE R. , KÜHN C. , THIELE N. , DELROT S. , FROMMER W.B. 
Published: April 2006

ABSTRACTThe sucrose proton‐cotransporter gene from potato (StSUT1) is mainly expressed in the phloem of mature, exporting leaves. To study the in vivo role of the protein, potato plants were transformed with antisense constructs of the sucrose transporter cDNA under control of the CaMV35S and the rolC promoters, respectively. Both types of transgenic plant develop symptoms characteristic of an inhibition of phloem loading. To determine the level of inhibition, immunological and transport studies were performed. Purified antibodies directed against a peptide from the central loop of SUT1 recognized a transporter with an apparent molecular mass of 47 kDa in leaf plasma membrane vesicles. Antisense repression under control of the non‐specific CaMV35S promoter led to a strong reduction in SUT1 protein, whereas no such reduction could be detected when the companion cell‐specific rolC promoter was used. Similarily. sucrose uptake in plasma membrane vesicles was reduced by 50–75% in CaMV35S but not in rolC plants. These data suggest that, unlike the rolC promoter, the sucrose transporter is expressed not only in the companion cells but also in other leaf cells. However, inhibition of the transporter by rolC‐controlled antisense repression is sufficient to impair phloem loading.
Water availability – a physiological constraint on nitrate utilization in plants of Australian semi‐arid muiga woodlands
Authors: ERSKINE P.D. , STEWART G.R. , SCHMIDT S. , TURNBULL M.H. , UNKOVICH M. , PATE J.S. 
Published: April 2006

ABSTRACTNitrate was found to be the predominant form of available nitrogen in mulga soils. Nitrate reductase activities on a fresh mass basis of a range of plants from eastern (Queensland) mulga ecosystems 2 weeks after partial relief from drought were uniformly low for both herbaceous species (165 ± 25 pkat g−1) and woody perennials (77 ± 14 pkat g−1). Supply of nitrate for 24 h to cut transpiring shoots of woody species or application of nitrate solution to the rooting zone of herbaceous species promoted little further increase in mean shoot nitrate reductase activities. Most species exhibited high tissue nitrate concentrations during water stress and soluble organic N profiles were in many cases dominated by the osmoprotective compounds, proline or glycine betaine. Species with low levels of proline or glycine betaine showed high foliar concentrations of other compatible osmotica such as polyols or sugars. Effects of relieving water stress on nitrate reductase activity, proline, glycine betaine and nitrate levels were followed over, 3d of irrigation. Available soil nitrate rose 10‐fold immediately and, following rapid restoration of leaf water status of the eight study species, a 4‐fold increase occurred in mean nitrate reductase activity together with progressive decreases in mean tissue concentrations of nitrate, proline and glycine betaine over the 3 d period. Similar changes in soil nitrate, nitrate reductase activity, proline and tissue nitrate were observed in the same ecosystem following a natural rainfall event and in western (S.W. Australia) mulga following irrigation. It is concluded that, although nitrate nitrogen is present at high concentrations and is the predominant inorganic nitrogen source in soils of the mulga biogeographic region, its assimilation by perennial and ephemeral vegetation is limited primarily by water availability. A scheme is presented depicting interrelated physiological and biochemical events in typical mulga species following a rain event and subsequent drying out of the habitat.
Buder revisited: cell and organ polarity during phototropism*
Authors: NICK P. , FURUYA M. 
Published: April 2006

ABSTRACTThe induction of a radial polarity by environmental stimuli was studied at the cellular and organ levels, with phototropism chosen as a model. The light gradient acting on the whole coleoptile was opposed to the light direction acting upon individual cells in the classical Buder experiment, irradiating from the inside out. Alternatively, the stimulus was administered to the coleoptile tip with a microbeam‐irradiation device. Tropistic curvature was assayed as a marker for the response of the whole organ, whereas cell elongation and the orientation of cortical microtubules were taken as markers for the responses of individual cells. Upon tip irradiation, signals much faster than basipetal auxin transport migrate towards the base. The data are discussed in terms of an organ polarity that is the primary result of the asymmetric light signal and affects, in a second step, an endogenous radial polarity of epidermal cells.
Long‐ and short‐term effects of decreased sink demand on carbohydrate levels and photosynthesis in wheat leaves
Authors: MORCUENDE R. , PÉEREZ P. , MARTÍNEZ‐CARRASCO R. , MARTIN DEL MOLING I. , SANCHEZ DE LA PUENTE L. 
Published: April 2006

ABSTRACTWheat (Triticum aestivum L.) ears were removed to investigate long‐term regulation of photosynthesis by sink demand at ambient CO2 and 22 °C. The CO2 level was also increased to 660 μmol mol−1 and temperature was lowered to 5 °C to examine short‐term responses of photosynthesis to low sink demand. Sink removal inhibited photosynthesis and increased leaf levels of glucose, fructose and ribulose‐1, 5‐bisphosphate (RuBP), and the glucose‐6‐phosphate (G6P)/fructose‐6‐phosphate (F6P) and RuBP/3‐phosphoglycerate (PGA) ratios under growth conditions, but had no effect on the activity and activation state of ribulose‐1, 5‐bisphosphate carboxylase oxygenase (Rubisco) either under growth or short‐term conditions, suggesting an inhibition of photosynthesis by decreased in vivo catalysis of Rubisco. Photosynthesis increased similarly in eared and earless shoots after a rise in CO2 concentration, and the ratio of triose‐phosphates (glyceraldehyde 3‐phosphate and dihydroxyacetone phosphate, TP) to PGA was similar or higher for removed than intact ears, suggesting that feedback inhibition of photosynthesis was not caused by a limitation of ATP synthesis in chloroplasts. Under short‐term conditions (660 μmol mol−1 CO2, 5 °C), TP and RuBP levels and the TP/PGA and TP/RuBP ratios were increased by sink removal, indicating an additional limitation of photosynthesis by the rate of RuBP regeneration.
EcoCELLs: tools for mesocosm scale measurements of gas exchange
Authors: GRIFFIN K. L. , ROSS P. D. , SIMS D.A. , LUO Y. , SEEMANN J. R. , FOX C. A. , BALL J. T. 
Published: April 2006

ABSTRACTWe describe the use of a unique plant growth facility, which has as its centerpiece four ‘EcoCELLs’, or 5x7 m mesocosms designed as open‐flow, mass‐balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifically to bridge the gap between measurement scales during long‐term experiments examining the function and development of model ecosystems. There are several advantages to using EcoCELLs, including (i) the same theory of operation as leaf level gas exchange systems, but with continuous operation at a much larger scale: (ii) the ability to independently evaluate canopy‐level and ecosystem models; (iii) simultaneous manipulation of environmental factors and measurement of system‐level responses, and (iv) maximum access to, and manipulation of, a large rooting volume.In addition to discussing the theory, construction and relative merits of EcoCELLs, we describe the calibration and use of the EcoCELLs during a ‘proof of concept’ experiment. This experiment involved growing soybeans under two ambient CO2 concentrations (−360 and 710μmol mol−1. During this experiment, we asked ‘How accurate is the simplest model that can be used to scale from leaf‐level to canopy‐level responses?’ in order to illustrate the utility of the EcoCELLs in validating canopy‐scale models.
Modelling the soil‐plant‐atmosphere continuum in a Quercus–Acer stand at Harvard Forest: the regulation of stomatal conductance by light, nitrogen and soil/plant hydraulic properties
Authors: WILLIAMS M. , RASTETTER E. B. , FERNANDES D. N. , GOULDEN M. L. , WOFSY S. C. , SHAVER G. R. , MELILLO J. M. , MUNGER J. W. , FAN S.‐M. , NADELHOFFER K. J. 
Published: April 2006

ABSTRACTOur objective is to describe a multi‐layer model of C3‐canopy processes that effectively simulates hourly CO2 and latent energy (LE) fluxes in a mixed deciduous Quercus‐Acer (oak–maple) stand in central Massachusetts, USA. The key hypothesis governing the biological component of the model is that stomatal conductance (gs) is varied so that daily carbon uptake per unit of foliar nitrogen is maximized within the limitations of canopy water availability. The hydraulic system is modelled as an analogue to simple electrical circuits in parallel, including a separate soil hydraulic resistance, plant resistance and plant capacitance for each canopy layer. Stomatal opening is initially controlled to conserve plant water stores and delay the onset of water stress. Stomatal closure at a threshold minimum leaf water potential prevents xylem cavitation and controls the maximum rate of water flux through the hydraulic system. We show a strong correlation between predicted hourly CO2 exchange rate (r2= 0.86) and LE (r2= 0.87) with independent whole‐forest measurements made by the eddy correlation method during the summer of 1992. Our theoretical derivation shows that observed relationships between CO2 assimilation and LE flux can be explained on the basis of stomatal behaviour optimizing carbon gain, and provides an explicit link between canopy structure, soil properties, atmospheric conditions and stomatal conductance.
Developmental patterns of above‐ground hydraulic conductance in a Scots pine (Pinus sylvestris L.) age sequence
Authors: MENCUCCINI M. , GRACE J. 
Published: April 2006

ABSTRACTHydraulic resistance to water flow was measured in branches and stems of Scots pine trees ranging from 7 to 59 years of age in Thetford (East Anglia, UK). On the basis of these measurements, tree above‐ground conductance was calculated and related to the amount of leaf area sustained by each tree. Branches at the crown bottom had a lower proportion of sapwood area and a lower total hydraulic conductance than branches of the same diameter at the tree top. Within branches, most of the hydraulic resistance was located near the needles. Tree above‐ground conductance was positively related to tree diameter and inversely related to tree height. Compared with young trees, mature trees had about 4 times less above‐ground conductance per unit of leaf area. Apparently, the increase in pathway length associated with tree height growth could be only partially compensated for by the increase in conductive capacities resulting from diameter growth. We argue that this reduction may account for reported decreases of stomatal conductance with tree age. It is suggested that the increase in branchiness associated with tree maturation may represent a compensation mechanism to reduce the overall resistance to water flow in the crowns.
The effect of Albugo Candida (white blister rust) on the photosynthetic and carbohydrate metabolism of leaves of Arabidopsis thaliana
Authors: TANG X. , ROLFE S. A. , SCHOLES J.D. 
Published: April 2006

ABSTRACT Albugo candida (pers.) O. Kuntze (white blister rust) is a biotrophic fungus which infects cruciferous plants including Arabidopsis thaliana (L) Heynh. We report the effect of this pathogen on the photosynthetic and carbohydrate metabolism of A. thaliana. As infection progressed A. Candida caused a reduction in the rate of photosynthesis when measured at either ambient or saturating concentrations of CO2. These data suggested that both chlorophyll and Rubisco were lost from regions of infected leaves, and measurements of chlorophyll, Rubisco content and activity supported these observations. The reduction in the rate of photosynthesis was not caused by closure of stomata as transpiration was unaffected by the disease. Infected leaves accumulated both soluble carbohydrates and starch. The activities of sucrose‐phosphate synthase, sucrose synthase and ADP glucose pyrophosphorylase did not change in response to infection. However, the activities of both the wall‐bound and soluble acid invertases were higher in infected leaves than in controls; a new soluble invertase isoform with a pl of 5‐1 appeared in infected leaves. The possible origin of the increase in wall‐bound and soluble invertase activities and its effect on the carbohydrate and photosynthetic metabolism of the leaf are discussed.
Long‐ and short‐term responses of leaf carbohydrate levels and photosynthesis to decreased sink demand in soybean
Authors: MORCUENDE R. , PÉREZ P. , MARTÍNEZ‐CARRASCO R. , MARTÍN DEL MOLINO I. , SÁNCHEZ DE LA PUENTE L. 
Published: April 2006

ABSTRACTAxillary buds and the apical portion of shoots of soybean [Glycine max (L.) Merr. cultivar Turchina] plants were trimmed to investigate long‐term regulation of photosynthesis by sink demand at ambient CO2 and 22 °C. Also, in intact and trimmed shoots, the CO2 level was increased to 660 μmol mol−1 and temperature was lowered to 5°C to examine the superimposed short‐term responses of photosynthesis to low sink demand. Under growth conditions, trimming the shoots increased leaf photosynthesis and the levels of sucrose, glucose‐6‐phosphate (G6P) and 3‐phosphoglycerate (PGA), as well as the G6P/fructose‐6‐phosphate (F6P) and sucrose/starch ratios, while it decreased the level of starch and the triose‐phosphate (glyceraldehyde 3‐phosphate and dihydroxyacetone phosphate, TP)/PGA ratio. Photosynthesis enhancement was accompanied by increased chlorophyll contents and ribulose‐l,5‐bisphosphate carboxylase oxygenase (Rubisco) activity. Sink removal consistently increased photosynthesis measured under a variety of conditions (growth CO2 or a short‐term change to 660 μmol mol‐1 CO2; growth temperature or a short‐term change to 5 °C), except when low temperature was combined with ambient CO2; the increase in photosynthesis was higher under short‐term elevated CO2 than at ambient CO2. In contrast with its effect at ambient CO2, shoot trimming increased the levels of TP and ribulose‐1,5‐bisphosphate (RuBP) and the TP/PGA ratio under high‐CO2 conditions.
A comparison of the composite and repeat pressurization methods of pressure–volume analysis for shoots of four North American conifer species
Authors: PARKER W. C. , COLOMBO S. J. 
Published: April 2006

ABSTRACTSignificantly different water relations attributes were derived for temperate conifers measured using the repeat pressurization (RP) and composite (CM) pressure–volume (PV) procedures. In the RP method, single shoots were measured 10–20 times for xylem water potential and mass during air‐drying to produce each PV curve. In contrast, for CM PV curves 25–30 shoots were air‐dried to relative water contents (R) ranging from 1.0 to 0.5 before being pressurized once. Aggregation of these 25–30 paired values produced single PV curves. Pinus banksiana, P. resinosa and Picea mariana, but not Pinus strobus, had lower full turgor osmotic potential, shallower slope of the linear segment of the PV curves and higher symplast fraction with the CM method. Data points along the linear segment of PV curves were obtained to lower R using the CM method. Reanalysis using similar R ranges eliminated differences between PV methods for Picea mariana but not Pinus banksiana and P. resinosa.