bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectral quality during pod development modulates soybean seed fatty acid desaturation
Authors: BRITZ S. J. , CAVINS J. F. 
Published: April 2006

ABSTRACTHigh‐density cropping of soybeans results in considerable mutual shading. Consequently, pods mature under a range of light conditions, with those lower in the canopy exposed to drastically altered spectral quality as well as lower irradiance. The influence of spectral quality on reproductive development and seed quality was investigated in soybeans raised to physiological maturity under either broad spectrum or blue‐deficient light sources. The absence of blue light had a large influence on vegetative morphology, but the timing of reproductive events was not affected. Total seed yield per plant, dry matter per seed, per cent protein and per cent oil were similar for all treatments. However, seeds harvested from plants matured under broad spectrum illumination contained high levels of oleic acid (18:1) and low linoleic acid (18:2) compared to seeds from plants grown under blue‐deficient conditions. In addition to the spectral quality effect, there was a smaller effect of pod position. Seeds from pods lower in the canopy contained less 18:1 and more 18:2 than seeds that matured closer to the top of the canopy. Considering both spectral quality and pod position, the ratio of 18:1 to 18:2 varied four‐fold between 0·35 and 1·43, indicative of a possible photoregulatory step in fatty acid desaturation. The spectral effects are consistent with the participation of a photomorphogenetic photoreceptor in the control of fatty acid metabolism during seed maturation and triglyceride accumulation.
Water relations of cotton flower petals and fruit
Authors: TROLINDER N. L. , McMICHAEL B. L. , UPCHURCH D. R. 
Published: April 2006

ABSTRACTWater needed for expansion is believed to enter plant tissue in response to a growth‐induced water potential gradient that occurs as turgor is reduced during relaxation of cell walls or in response to increased solutes. Under water stress, the cotton flower petal continues to expand when all leaves on the plant are wilted and new leaf expansion has ceased in the shoot tips. This study was undertaken to determine if water for expansion entered the petal in response to a gradient or to increased solutes. Water potentials of cotton petal, leaf, bract and fruit were determined pre‐dawn and midday in dryland and irrigated field plots. The mechanism by which petal expansion occurs appears not to be associated with a growth‐induced water potential gradient or to increased solutes because the gradient is reversed from that needed to drive expansion. The water potential of the petal tissues was consistently higher than that of the subtending leaves and bracts both during and after anthesis, and under different water stress conditions. How this reversal in water potential gradient is established and maintained should provide insight into mechanisms involved in growth during water stress.
Asymmetric patchy stomatal closure for the two surfaces of Xanthium strumarium L. leaves at low humidity
Authors: MOTT K. A. , CARDON Z. G. , BERRY J. A. 
Published: April 2006

ABSTRACTImages of chlorophyll fluorescence were used to demonstrate patchy stomatal closure at low humidities in leaves of well‐watered Xanthium strumarium plants. The pattern and extent of patchy stomatal closure were shown to be different for the two surfaces of amphistomatous leaves by taking images of leaves with CO2 available to only one leaf was exposed to low humidity, patchiness was more extensive on that surface. Gas‐exchange experiments were also conducted to determine the apparent photosynthetic capacity of the mesophyll (photosynthesis rate at constant ci when it was supplied with CO2 through both surfaces or through each surface alone. These experiments showed declines in the apparent photosynthetic capacity of the mesophyll at low humidities that were consistent with patchy stomatal closure on one or both surfaces. The results suggest that patchy stomatal closure can be a factor in the steady‐state reponses of stomata to humidity. In amphistomatous leaves this is further complicated by the fact that patches on one epidermis may not coincide with those of the other surface.
The differential role of mechanisms for drought resistance in a Mediterranean evergreen shrub: a simulation approach
Authors: RAMBAL S. 
Published: April 2006

ABSTRACTPlants have the ability to dampen the effects of variability in water resources. Various mechanisms contribute to these properties: reduction of leaf area, increased rooting depth and stomatal conductance. To evaluate the differential roles and interactions of these mechanisms, we have built a model and simulated flows of water in Mediterranean evergreen scrub. The essential concept of this model is that the water status of the canopy is governed by the water lost by transpiration, the availability of soil water and the hydraulic resistances to water flow in soil and plant. The amount of water supplied by the roots is related to changes in water potential between the soil and the leaf. The amount of water lost to the atmosphere is regulated by an interaction between atmospheric demand and canopy water potential. Water uptake by plant is assumed equal to plant water loss. Leaf area appears to affect largely the annual water balance. The critical leaf water potential required to reduce the maximum stomatal conductance by half has a dominant effect on annual leaf water potential. Reducing rooting depth induces a new functional equilibrium for the plant. This new equilibrium is reached by decreasing leaf area and the critical leaf water potential. Our results show the complexity of interactions of these mechanisms and highlight the importance of the coordination between them. Finally, we suggest a reconsideration of these mechanisms in a context of the survival and long‐term persistence of the plant.
Field investigations of ammonia exchange between barley plants and the atmosphere. I. Concentration profiles and flux densities of ammonia
Authors: SCHJOERRING J. K. , KYLLINGSBAEK A. , MORTENSEN J. V. , BYSKOV‐NIELSEN S. 
Published: April 2006

ABSTRACTThe exchange of ammonia between the atmosphere and the canopy of spring barley crops growing at three levels of nitrogen application (medium N, high N and excessive N) was studied over two consecutive growing seasons by use of micrometeorological techniques. In most cases, ammonia was emitted from the canopy to the atmosphere. The emission started around 2 weeks before anthesis, and peaked about or shortly after anthesis. The volatilization of ammonia only took place in the daytime. During the night‐time, atmospheric ammonia was frequently aborbed by the canopy. Occasionally, plants in the medium and high N treatments also absorbed ammonia from the atmosphere during the daytime. Daytime absorption of ammonia never occurred in the excessive N canopy. The loss of ammonia from the canopy amounted in both years to 0.5–1.5 kg NH3‐N ha−1 and increased with the N status of the canopy. In agreement with the small losses of ammonia, the content of 15N‐labelled nitrogen in the plants did not decline during the grain‐filling period. The experimental years were characterized by very favourable conditions for grain dry matter formation, and for re‐utilization of nitrogen mobilized from leaves and stems. Consequently, a very high part of the nitrogen in the mature plants was located in grain dry matter (80–84% in 1989; 74–80% in 1990). The efficient re‐utilization of nitrogen may have reduced the volatilization of ammonia.
Fructan contents and dry matter deposition in different tissues of the wheat grain during development
Authors: SCHNYDER H. , GILLENBERG C. , HINZ J. 
Published: April 2006

ABSTRACTThe role of fructan metabolism in the assimilate relations of the grain of wheat (Triticum aestivum L.) was investigated by determination of the dry matter and fructan content of grain components at short intervals during grain filling. During the initial phase of rapid expansion, most of the assimilates entering the grain were partitioned to the outer pericarp. A large fraction of these assimilates were used for the synthesis of fructan. Dry matter deposition and fructan synthesis in the outer pericarp ceased at about 5d after anthesis. At the same time, the endosperm and the inner pericarp and testa started to accumulate dry matter at a fast rate. This was also associated with significant fructan synthesis in the latter tissues. The outer pericarp lost about 45% of its former maximum dry weight between 9 and 19 d after anthesis. This loss was due almost entirely to the near complete disappearance of water‐soluble carbohydrates, most of which was fructan. The inner pericarp and testa accumulated dry matter until about mid‐grain filling. The fructan contents of the inner pericarp and testa and the endosperm decreased slowly towards the end of grain filling. Most of the fructans in the inner pericarp and testa and the endosperm had a low molecular weight, whereas higher molecular weight fructans predominated in the outer pericarp. The embryo did not contain fructan. The presence of low molecular weight fructans in the endosperm cavity at mid‐grain filling was confirmed. It is suggested that fructan synthesis is closely linked to growth‐related water deposition in the different tissues of the wheat grain and serves to sequester the surplus of imported sucrose.
Relationships between the kinetics of NH4+ and NO3− absorption and growth in the cultivated tomato (Lycopersicon esculentum Mill, cv T‐5)
Authors: SMART* D. R. , BLOOM A. J. 
Published: April 2006

ABSTRACTTomato growth was examined in solution culture under constant pH and low levels of NH4+ or NO3−. There were five nitrogen treatments: 20 mmoles m−3 NH4+, 50 mmoles m−3 NO3−, 100 mmoles m−3 NH4+ 200 mmoles m−3 NO3−, and 20 mmoles m−3 NH4++ 50 mmoles m−3 NO3−. The lower concentrations (20 mmoles m−3 NH4+ and 50 mmoles m−3 NO3−) were near the apparent Km for net NH4+ and NO3− uptake; the higher concentrations (100 mmoles m−3 NH4+ and 200 mmoles m−3 NO3−) were near levels at which the net uptake of NH4+ or NO3− saturate. Although organic nitrogen contents for the higher NO3− and the NH4++ NO3− treatments were 22.2–30.3% greater than those for the lower NO3− treatment, relative growth rates were initially only 10–15% faster. After 24 d, relative growth rates were similar among those treatments. These results indicate that growth may be only slightly nitrogen limited when NH4+ or NO3− concentrations are held constant over the root surface at near the apparent Km concentration. Relative growth rates for the two NH4+ treatments were much higher than have been previously reported for tomatoes growing with NH4+ as the sole nitrogen source. Initial growth rates under NH4+ nutrition did not differ significantly (P≥ 0.05) from those under NO3− or under combined NH4++ NO3−. Growth rates slowed after 10–15 d for the NH4+ treatments, whereas they remained more constant for the NO3− and mixed NH4++ NO3− treatments over the entire observation period of 24–33 d. The decline in growth rate under NH4+ nutrition may have resulted from a reduction in Ca2+, K+, and/or Mg2+ absorption.
NMR imaging of root water distribution in intact Vicia faba L plants in elevated atmospheric CO2
Authors: BOTTOMLEY P. A. , ROGERS H. H. , PRIOR S. A. 
Published: April 2006

ABSTRACTThe effect of elevated atmospheric CO2 on water distribution in the intact roots of Vicia faba L. bean seedlings grown in natural soil was studied noninvasively with proton (1H) nuclear magnetic resonance (NMR) imaging. Exposure of 24‐d‐old plants to atmospheric CO2‐enriched air at 650 cm3 m−3 produced significant increases in water imaged in upper roots, hypogeal cotyledons and lower stems in response to a short‐term drying‐stress cycle. Above ground, drying produced negligible stem shrinkage and stomatal resistance was unchanged. In contrast, the same drying cycle caused significant depletion of water imaged in the same upper root structures in control plants subject to ambient CO2 (350 m3 m−3), and stem shrinkage and increased stomatal resistance. The results suggest that inhibition of transpiration caused by elevated CO2 does not necessarily result in attenuation of water transport from lower root structures. Inhibition of water loss from upper roots and lower stem in elevated CO2 environments may be a mitigating factor in assessing deleterious effects of greenhouse changes on crops during periods of dry climate.
Characteristics of inorganic nitrogen assimilation of plants in fire‐prone Mediterranean‐type vegetation
Authors: STEWART G. R. , PATE J. S. , UNKOVICH M. 
Published: April 2006

ABSTRACTA range of approaches was used to investigate how species within a fire‐prone Banksia woodland in South West Australia exploited inorganic soil nitrogen sources and how this changes through the development of the fire chronosequence. Nitrate and ammonium were present in soil solution throughout the chronosequence but nitrate predominated in recently burnt sites. Mean shoot nitrate reductase activities were high for all species in recently burnt sites and showed little increase when nitrate was supplied via the transpiration stream. Nitrate reductase of shoots of most species was low at sites not burnt for several years, but following transpirational induction with nitrate, developed activities similar to those at recently burnt sites. The principal amino compounds transported in the xylem were species specific, including asparagine, glutamine and citrulline‐dominated species, and changed little in relative composition across the chronosequence. Species most active in leaf nitrate reduction transported the largest amounts of nitrate in their xylem sap and proportional amounts of nitrate in xylem tended to be greatest in recently burnt sites. Most of the species examined appeared to be shoot rather than root nitrate assimilators, but marked differences were recorded in potential of leafy shoots of different species to reduce nitrate. As a general rule, shallow‐rooted herbaceous, non‐mycorrhizal or VAM‐positive species had the highest capacity to reduce nitrate, whereas woody species with ericoid mycorrhizae or combined vesicular arbuscular/ectomycorrhizal associations exhibited little capacity to reduce nitrate in roots or shoots. It seems likely that this latter group utilize ammonium or even organic forms of nitrogen rather than nitrate. Some putative nitrogen‐fixing species were active in reducing and transporting nitrate, others were virtually inactive in these respects.
Changing sensitivity to light and nitrate but not to gibberellins regulates seasonal dormancy patterns in Sisymbrium officinale seeds
Authors: DERKX M. P. M. , KARSSEN C. M. 
Published: April 2006

ABSTRACTSeeds of Sisymbrium officinale (L.) Scop, that are buried under natural conditions in soil pass annually through a seasonal pattern of changes in dormancy. Dormancy is broken in autumn‐winter and re‐induced in summer. To elucidate dormancy regulation in this species under natural conditions, a detailed analysis of the changes in sensitivity to some relevant germination factors was carried out Germination data fitted as logistic dose response curves showed that sensitivity to light and nitrate, both indispensable stimuli for germination of this species, varied with the seasons. Patterns of shifts in requirement for light and nitrate were remarkably similar. Sensitivity increased when both primary and secondary dormancy were alleviated, and it was reversed during induction of secondary dormancy. During alleviation of primary dormancy in spring 1991, the fluence response curves exhibited a biphasic character with responses occurring both in the very‐low‐fluence‐range and in the low‐fluence‐range. The nitrate dose response data could all be fitted as monophasic curves, although responses might have occurred in two distinct ranges as well. From interpretation of curve parameters, it is postulated that dormancy is regulated by changes in the number of phytochrome and nitrate receptors, in shifts in the binding characteristics of the receptors and/or in shifts in the response chain initiated by the ligand‐receptor interaction. Somewhere in this response chain, biosynthesis of gibberellins (GAs) is stimulated. By use of the GA biosynthesis inhibitor tetcyclasis, it was indirectly proven that the capacity to synthesize GAs indeed varied with the seasons. Sensitivity to GAs gradually increased from burial onwards and was not particularly related to changes in dormancy. Thus, except for the first few months of burial, GA sensitivity may not be regarded as a limiting factor in controlling dormancy in this species.
Interpretation of the electrical potential on the surface of plant roots
Authors: DUE G. 
Published: April 2006

ABSTRACTThe electrical potential difference (p.d.) between two points on the surface of a plant root is shown to be a measure of the difference between the transmembrane potentials at those two points. More precisely, it is shown that axial differences in electrical potential on the surface of the root, or within several tenths of millimeters of it in the rhizosphere, are primarily a result of axial differences in p.d. across the plasmalemma of cells in the cortex, with an additional small effect from axial differences in p.d. across the plasmalemma of cells in the stele. This conclusion results from a model of the root as a three‐conductor electrical transmission line. The model requires the solution of a set of differential equations, but simple algebraic approximations are found to apply over a range of model parameters derived from published data. Given the predictions of the model, it follows that, for many research purposes, microelectrode measurements could be replaced with measurements of p.d. on the surface of the root. Such measurements offer substantial advantages over microelectrode measurements: they are non‐invasive; they do not include the potential difference across the tonoplast; they measure a spatial average of many cells, not just a single cell; and the measurement is physically robust. Surface potential measurements do not, however, measure trans‐membrane potential at one point, but measure differences in trans‐membrane potential.
Rapid appearance of 13C in biogenic isoprene when 13CO2 is fed to intact leaves
Authors: DELWICHE C. F. , SHARKEY T. D. 
Published: April 2006

ABSTRACTBiogenic isoprene substantially affects atmospheric chemistry, but it is not known how or why many plants, especially trees, make isoprene. We fed 13CO2 to leaves of Quercus rubra and monitored the incorporation of 13C into isoprene by mass spectrometry. After feeding 13CO2 for 9 min we found all possible labelling patterns from completely unlabelled to fully labelled isoprene. By 18 min, 84% of the carbon atoms in isoprene were 13C. Labelling of the last 20% of the carbon atoms was much slower than labelling of the first 80%. The rate of labelling of isoprene was similar to that reported for phosphoglyceric acid indicating that there is a close linkage between the carbon source for isoprene synthesis and the photosynthetic carbon reduction pathway.
The use of transgenic and naturally occurring mutants to understand and manipulate tomato fruit ripening
Authors: GRAY J. E. , PICTON S. , GIOVANNONI J. J. , GRIERSON D. 
Published: April 2006

ABSTRACTIn the years since we last reviewed the use of mutants to study tomato fruit ripening (Grierson et al. 1987), considerable information has been gained by the cloning, sequencing and identification of many mRNAs implicated in this developmental process. Genes involved in cell wall degradation, colour change and ethylene synthesis have been cloned, and antisense techniques have been developed and used to produce genetically engineered mutant fruit deficient in these aspects of ripening (see Gray et al. 1992). Recently, a previously cloned ripening gene has been used to complement a naturally occurring fruit colour mutant, yellow flesh (Fray & Grierson 1993a), and a ripening impaired mutant, ripening inhibitor, has been used to identify several new ripening‐related mRNAs (Picton et al. 1993b). The chromosomal region bearing the ripening inhibitor mutation has been subjected to high‐resolution mapping (Churchill, Giovannoni & Tanksley 1993) and chromosome walking experiments are in progress to identify this gene.
Action and function of phytochrome family members revealed through the study of mutant and transgenic plants
Authors: WHITELAM G. C. , HARBERD N. P. 
Published: April 2006

ABSTRACTThe adaptation of plant growth and development to changes in the light environment is dependent upon photoperception by information transducing photoreceptors. The red/far‐red light‐absorbing phytochromes are perhaps the best characterized of these regulatory photoreceptors. Higher plants possess multiple, discrete phytochromes, the apoprotein components of which are the products of a small, divergent gene family. Different phytochromes have different biochemical and physiological properties, and are differentially expressed in the growing plant. This has led to the proposal that different phytochromes have different physiological roles. Mutations that disrupt the normal perception of light signals have proved to be a valuable resource in assigning physiological roles to different phytochromes as well as in identifying residues/domains critical for phytochrome function and in attempting to elucidate the signal transduction pathway(s) downstream of phytochromes. This article reviews some recent progress in these areas from the study of conventional and transgenic photomorphogenic mutants.
Inhibition of photosynthesis by osmotic stress in pea (Pisum sativum) mesophyll protoplasts is intensified by chilling or photoinhibitory light; intriguing responses of respiration
Authors: SARADADEVI K. , RAGHAVENDRA A. S. 
Published: April 2006

ABSTRACTThe effects of reduced osmotic potential on photosynthesis and respiration were studied in mesophyll protoplasts of pea (Pisum sativum). Osmotic stress was induced by increasing the sorbitol concentration in the medium from 0·4 kmol m−3 (‐1·3 MPa) to 1·0 kmol m−3 (‐3·1 MPa). Protoplasts lost up to 35% of the maximum capacity of photo‐synthetic carbon assimilation (but not PS II mediated activity) soon after exposure to 1·0 kmol m−3 sorbitol. The response of protoplast respiration to osmotic stress was intriguing. Respiration was stimulated if stress was induced at 25°C, but was inhibited when protoplasts were subjected to osmotic stress at 0°C. Photosynthesis was also much more sensitive to osmotic stress at 0°C than at 25°C. The inhibitory effects of osmotic stress on photosynthesis as well as respiration were amplified by not only chilling but also photoinhibitory light. The photosynthetic or respiratory activities of protoplasts recovered remarkably when they were transferred from hyperosmotic (1·0 kmol m−3 sorbitol) back to iso‐osmotic medium (0·4 kmol m−3 sorbitol), demonstrating the reversibility of osmotic‐stress‐induced changes in protoplasts. Respiration was more resistant to osmotic stress and was quicker to recover than photosynthesis. We suggest that the experimental system of protoplasts can be useful in studying the effects of osmotic stress on plant tissues.