bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of amino acid uptake by ectomycorrhizal roots
Authors: WALLENDA T. , READ D. J.
Published: March 2003

It is well established that ectomycorrhizal fungi can use amino acids as nitrogen and carbon sources, but data on the kinetic properties of amino acid uptake systems of ectomycorrhizal systems are scarce. Using 14C‐labelled compounds we have determined the kinetics of uptake of amino acids by excised ectomycorrhizal roots for a range of distinct mycorrhizal types from three tree species, beech, spruce, and pine. All mycorrhizal types examined took up amino acids via high‐affinity transport systems (KM values ranging from 19 to 233 mmol m–3). A comparative analysis of kinetic parameters for uptake of amino acids and the ammonium analogue methylammonium showed that ectomycorrhizal roots have similar or even higher affinities (lower KM values) for the amino acids, indicating that absorption of these organic forms of nitrogen (N) can contribute significantly to total N uptake by ectomycorrhizal plants. Analysis of amino acid uptake by ectomycorrhizal roots collected along a European north/south gradient of increasing mineral N pollution from northern Sweden to south Germany revealed no obvious trend in the uptake capabilities for amino acids by ectomycorrhizal roots in relation to the location of the sampling site on this gradient. Rather, the fungal species forming a particular morphotype was the factor determining uptake kinetics. It can therefore be deduced that the species composition of the fungal community will contribute significantly to the functional diversity of a population of mycorrhizal roots.
Postanthesis temperatures influence cytokinin accumulation and wheat kernel weight
Authors: BANOWETZ G. M. , AMMAR K. , CHEN D. D.
Published: March 2003

High temperatures during reproductive development alter kernel development and reduce yield and quality in wheat (Triticum aestivum L.). Understanding how temperature alters kernel formation will help the development of genetic approaches to enhance heat tolerance in this cereal. A relationship between kernel development and postanthesis cytokinin accumulation is well documented, but the effect of temperature on this relationship is not known. This study quantified the effects of a postanthesis temperature treatment (7 d at 35/25 °C day/night) on kernel development and cytokinin accumulation in a soft white winter wheat (c.v. Stephens). Kernels from control plants maintained at 25/15 °C accumulated zeatin, dihydrozeatin and their corresponding 9‐ribosides from 1 to 4 d postanthesis. Postanthesis kernel cytokinin accumulation was reduced by 50–80% by the temperature treatment. Kernel cytokinin content in control plants declined to baseline by 5 d postanthesis and remained at that level. Kernels from treated plants had a secondary peak of cytokinin accumulation 6–8 d after anthesis. This treatment significantly reduced kernel weight. The magnitude of the effect on kernel number was smaller than on kernel weight, but was statistically significant. Reduced kernel weight was accompanied by reduced cytokinin accumulation. Exogenous cytokinins did not mitigate the temperature effects on kernel weight, but at the highest concentrations, did reduce the effect on kernel number.
Oceanic sinks for atmospheric CO2
Authors: RAVEN J. A. , FALKOWSKI P. G.
Published: March 2003

There is approximately 50 times more inorganic carbon in the global ocean than in the atmosphere. On time scales of decades to millions of years, the interaction between these two geophysical fluids determines atmospheric CO2 levels. During glacial periods, for example, the ocean serves as the major sink for atmospheric CO2, while during glacial–interglacial transitions, it is a source of CO2 to the atmosphere. The mechanisms responsible for determining the sign of the net exchange of CO2 between the ocean and the atmosphere remain unresolved. There is evidence that during glacial periods, phytoplankton primary productivity increased, leading to an enhanced sedimentation of particulate organic carbon into the ocean interior. The stimulation of primary production in glacial episodes can be correlated with increased inputs of nutrients limiting productivity, especially aeolian iron. Iron directly enhances primary production in high nutrient (nitrate and phosphate) regions of the ocean, of which the Southern Ocean is the most important. This trace element can also enhance nitrogen fixation, and thereby indirectly stimulate primary production throughout the low nutrient regions of the central ocean basins. While the export flux of organic carbon to the ocean interior was enhanced during glacial periods, this process does not fully account for the sequestration of atmospheric CO2. Heterotrophic oxidation of the newly formed organic carbon, forming weak acids, would have hydrolyzed CaCO3 in the sediments, increasing thereby oceanic alkalinity which, in turn, would have promoted the drawdown of atmospheric CO2. This latter mechanism is consistent with the stable carbon isotope pattern derived from air trapped in ice cores. The oceans have also played a major role as a sink for up to 30% of the anthropogenic CO2 produced during the industrial revolution. In large part this is due to CO2 solution in the surface ocean; however, some, poorly quantified fraction is a result of increased new production due to anthropogenic inputs of combined N, P and Fe. Based on ‘circulation as usual’, models predict that future anthropogenic CO2 inputs to the atmosphere will, in part, continue to be sequestered in the ocean. Human intervention (large‐scale Fe fertilization; direct CO2 burial in the deep ocean) could increase carbon sequestration in the oceans, but could also result in unpredicted environmental perturbations. Changes in the oceanic thermohaline circulation as a result of global climate change would greatly alter the predictions of C sequestration that are possible on a ‘circulation as usual’ basis.
Estimation of path lengths for diffusion of organic compounds through leaf cuticles
Authors: BAUR P. , MARZOUK H. , SCHÖNHERR J.
Published: March 2003

The effect of waxes on the mobilities of organic solutes in isolated leaf cuticular membranes (CM) of six species was investigated using compounds with molar volumes ranging from 99 cm3 mol–1 (salicylic acid) to 349 cm3 mol–1 (cholesterol). When log(solute mobility) was plotted versus molar volumes straight lines were obtained for all plant species showing that the mobilities decreased exponentially with increasing molar volumes of solutes. The slopes of these graphs represent the size selectivity of the CM. Extracting waxes from the CM using chloroform–methanol had no effect on size selectivity, but absolute values of mobilities increased by 28‐fold (Citrus grandis L. and Camellia assamica L.) to 759‐fold (Ilex paraguariensis St.‐Hil). Since the removal of waxes did not affect size selectivity it is argued that extraction reduced the path lengths and these values are a measure for tortuosity, that is the ratio of path lengths in CM and MX. Mobilities in the polymer matrix of extracted cuticles did not differ much among species with the exception of C. assamica. Although the mobilities in CM of I. paraguariensis and C. assamica were similar, the mobilities in the polymer matrix of C. assamica were almost 40‐fold lower than in I. paraguariensis. Neither the mobilities in CM and MX nor the tortuosity were correlated with thickness of CM or amounts of wax.
Use of thermography for quantitative studies of spatial and temporal variation of stomatal conductance over leaf surfaces
Authors: Jones H. G.
Published: March 2003

This paper describes a new approach to the calibration of thermal infrared measurements of leaf temperature for the estimation of stomatal conductance and illustrates its application to thermal imaging of plant leaves. The approach is based on a simple reformulation of the leaf energy balance equation that makes use of temperature measurements on reference surfaces of known conductance to water vapour. The use of reference surfaces is an alternative to the accurate measurement of all components of the leaf energy balance and is of potentially wide application in studies of stomatal behaviour. The resolution of the technique when applied to thermal images is evaluated and some results of using the approach in the laboratory for the study of stomatal behaviour in leaves of Phaseolus vulgaris L. are presented. Conductances calculated from infrared measurements were well correlated with estimates obtained using a diffusion porometer.
Stress tolerance and reactive oxygen metabolism in the intertidal red seaweeds Mastocarpus stellatus and Chondrus crispus
Authors: Collén J. , Davison I. R.
Published: March 2003

Mastocarpus stellatus and Chondrus crispus are morphologically similar red seaweeds that co‐occur on rocky intertidal seashores in the Northern Atlantic. Mastocarpus stellatus grows higher on the shore and is more tolerant of environmental stress, caused by factors such as freezing and desiccation, than C. crispus. Here we report a correlation between reactive oxygen metabolism and stress tolerance, which suggests that reactive oxygen metabolism may play a role in stress tolerance of intertidal red seaweeds. Mastocarpus stellatus scavenged added H2O2 slightly faster, and was more resistant to oxidative stress induced by addition of H2O2 and Rose Bengal, than C. crispus. These data were consistent with higher levels of ascorbate and β‐carotene and higher activities of catalase and glutathione reductase, in M. stellatus. Tocopherol content and activities of superoxide dismutase and ascorbate peroxidase were similar in both species. Activities of reactive oxygen scavenging enzymes generally increased with tidal height in M. stellatus; this was, however, not a consistent trend in C. crispus.
An improvement of the method for calibrating measurements of photosynthetic CO2 flux
Authors: Hari P. , Keronen P. , Bäck J. , Altimir N. , Linkosalo T. , Pohja T. , Kulmala M. , Vesala T.
Published: March 2003

Measurements of rapid changes in concentrations and fluxes of gaseous compounds relating to photosynthetic gas exchange are commonly performed using flow‐through cuvettes in connection with infrared gas analysers. The accuracy and repeatability of these measurements relies ultimately upon the design of the system as a whole, rather than upon each of its components, and therefore the calibration and testing of the system should be performed keeping this in mind. We present here a simple and efficient method for the calibration of such a measurement system using a precisely determined CO2 flow. This method gives us the opportunity to take into account any disturbing effects caused by undesired properties of the chamber or tubing materials. With the proposed calibration method, the accuracy of the CO2 flux measurement is improved from 8% up to the level of 2%, determined mainly by the accuracy of the control gas used for calibration of the CO2 analyser.
Inter‐specific variation of the biochemical limitation to photosynthesis and related leaf traits of 30 species from mountain grassland ecosystems under different land use
Authors: Wohlfahrt G. , Bahn M. , Haubner E. , Horak I. , Michaeler W. , Rottmar K. , Tappeiner U. , Cernusca A.
Published: March 2003

The maximum rate of carboxylation (Vcmax) and the potential rate of RuBP regeneration (Pml, which equals Jmax/4), as well as leaf nitrogen content (NL) and specific leaf area (SLA), were studied in sun leaves of 30 species from differently managed mountain grassland ecosystems (abandoned areas, pastures and meadows) at three study areas in the Eastern Alps. A significant correlation between Vcmax and Pml across the investigated species was observed. In comparison to a previous survey on the relationship between Pml and Vcmax, the investigated species were found to invest a proportionally smaller amount of available resources into Pml. Despite this close correlation between Vcmax and Pml, variation in the Vcmax–NL and Pml–NL relationships was large, indicating that the investigated species differed widely in their respective nitrogen use efficiencies. Among the investigated species, dwarf shrubs were characterized by significantly lower values of Vcmax, Pml and NL compared to graminoids and forbs, which did not differ significantly from each other. Species from abandoned areas were found to be lower with respect to Vcmax, Pml, NL and SLA than species from pastures and meadows, which were not significantly different from each other.
Inhibition of ethylene biosynthesis by antisense ACC oxidase RNA prevents chilling injury in Charentais cantaloupe melons
Authors: Ben‐Amor M. , Flores B. , Latché A. , Bouzayen M. , Pech J. C. , Fomojaro F.
Published: March 2003

Non‐freezing low temperature storage causes injury to melons and most other fruit and vegetables of tropical and subtropical origin. We demonstrate here that ethylene suppression through an antisense ACC oxidase (ACO) gene considerably reduced the sensitivity of Charentais cantaloupe melons to chilling injury. In contrast to wild‐type fruit, antisense ACO melons did not develop the characteristic chilling injury of pitting and browning of the rind neither when stored at low temperature (3 weeks at 2 °C) nor upon rewarming. Treating antisense melons with 10 p.p.m. ethylene for more than 1 d prior to cold storage resulted in the restoration of chilling sensitivity. When the ethylene treatment was performed after cold storage, the chilling injury symptoms did not appear. The tolerance to chilling was associated with a lower accumulation of ethanol and acetaldehyde, reduced membrane deterioration and higher capacity of the fruit to remove active oxygen species. The activities of catalase, superoxide dismutase and peroxidase were markedly increased in antisense ACO fruit in comparison with wild‐type fruit, particulary upon rewarming and post‐storage ethylene treatment. Severe chilling injury symptoms were correlated with a lower activity of activated oxygen scavenging enzymes. These results demonstrate that ethylene acts in conjunction with low temperature to induce metabolic shifts that participate in the development of chilling injury.
Leaf expansion – an integrating plant behaviour
Authors: Volkenburgh E. Van
Published: March 2003

Leaves expand to intercept light for photosynthesis, to take up carbon dioxide, and to transpire water for cooling and circulation. The extent to which they expand is determined partly by genetic constraints, and partly by environmental conditions signalling the plant to expand more or less leaf surface area. Leaves have evolved sophisticated sensory mechanisms for detecting these cues and responding with their own growth and function as well as influencing a variety of whole‐plant behaviours. Leaf expansion itself is an integrating behaviour that ultimately determines canopy development and function, allocation of materials determining relative shoot : root volume, and the onset of reproduction. To understand leaf development, and in particular, how leaf expansion is regulated, we must know at the molecular level which biochemical processes accomplish cell growth. Physiological experimentation focusing on ion fluxes across the plasmamembrane is providing new molecular information on how light stimulates cell expansion in some dicotyledonous species. Genetic analyses in Arabidopsis, corn, and other species are rapidly generating a list of mutations and enzyme activities associated with leaf development and expansion. Combination of these approaches, using informed physiological interpretations of phenotypic variation will allow us in the future to identify genes encoding both the processes causing cell expansion, and the regulators of these events.
AtSTP3, a green leaf‐specific, low affinity monosaccharide‐H+ symporter of Arabidopsis thaliana
Authors: Büttner M. , Truernit E. , Baier K. , Scholz‐Starke J. , Sontheim M. , Lauterbach C. , Huss V. A. R. , Sauer N.
Published: March 2003

This paper describes the expression analyses of the AtSTP3 gene of Arabidopsis thaliana, the functional characterization of the encoded protein as a new monosaccharide transporter, and introduces the AtSTP gene family. The kinetic properties of the AtSTP3 protein (for sugar transport protein 3) were studied in a hexose transport deficient mutant of Schizosaccharomyces pombe. AtSTP3 represents a new monosaccharide transporter that is composed of 514 amino acids and has a calculated molecular mass of 55·9 kDa. Kinetic analyses in yeast showed that AtSTP3 is a low affinity, energy‐dependent H+ symporter with a Km for D‐glucose of 2 mM. RNase protection analyses revealed that AtSTP3 is expressed in leaves and floral tissue of Arabidopsis. This expression pattern of the AtSTP3 gene was confirmed in AtSTP3 promoter‐β‐glucuronidase (GUS) plants showing AtSTP3‐driven GUS activity in green leaves, such as cotelydons, rosette and stalk leaves and sepals. Wounding caused an induction of GUS activity in the transgenic plants and an increase of AtSTP3 mRNA levels in Arabidopsis wild‐type plants. Polymerase chain reaction analyses with degenerate primers identified additional new AtSTP genes and revealed that AtSTP3 is the member of a large family of at least 14 homologous genes coding for putative monosaccharide‐H+ symporters (AtSTPs).
A possible optical role of the bundle sheath extensions of the heterobaric leaves ofVitis viniferaandQuercus coccifera
Authors: Karabourniotis G. , Bornman J. F. , Nikolopoulos D.
Published: March 2003

Heterobaric leaves are characterized by transparent regions in their lamina, due to the occurrence of bundle sheath extensions. Fused silica fibre‐optic microprobes were used to monitor light gradients and part of the spectral regime along the bundle sheath extensions, as well as along the mesophyll in the heterobaric leaves of two representative plants, one mesomorphic (Vitis viniferaL.) and one xeromorphic (Quercus cocciferaL.). It was found that the attenuation of collimated visible light by the bundle sheath extensions of both plants was weaker than the attenuation by the photosynthetic parenchyma layers. However, only a small portion of the amount of light that strikes the leaf surface is transmitted through these structures. The adaxial epidermis covering the bundle sheath extensions, as well as the mesophyll, afforded similar effective protection against UV radiation in both tissues. The relative amount of the forward‐scattered visible light inside the bundle sheath extensions approached that detected by the microprobe at the adaxial illuminated leaf surface. Moreover, light transmitted through the bundle sheath extensions was enriched mainly in the blue and red regions, compared to light transmitted through the photosynthetic tissue. The time course of photosynthetic starch formation in the leaves ofV. viniferadetected by iodine staining showed that the accumulation of starch during the first minutes of illumination was high within photosynthetic parenchyma cells adjacent to the bundle sheath extensions. The data showed that bundle sheath extensions act as transparent ‘windows’ which enrich the neighbouring mesophyll areas with high levels of photosynthetically active radiation (400–700 nm). The phenomenon was more pronounced in the thick and compact sclerophyllous leaves ofQ. cocciferaby virtue of the greater abundance of bundle sheath extensions as compared to that inV. vinifera.The enhancement of the light micro‐environment within the deep internal layers of the mesophyll may affect the photosynthetic performance of such leaves, giving adaptive advantages.
Nitrate reductase in Zea mays L. under salinity
Authors: Baki G. K. Abd‐El , Siefritz F. , Man H.‐M. , Weiner H. , Kaldenhoff R. , Kaiser W. M.
Published: March 2003

Young maize seedlings (Zea mays L. cv.Giza 2) were exposed to moderate salinity in hydroponic culture. NADH‐nitrate reductase (NR) activity (E.C. 1·6.6·1), NR activation state, NR‐mRNA‐steady state levels and major solute contents in leaves and roots were investigated. With increasing external salt concentration, Na+, Cl−, sugars, amino acids and quarternary ammonium compounds accumulated in leaves and roots, with concentrations in leaves exceeding those in roots. The nitrate content of leaves decreased, but increased in roots. The diurnal pattern of NR activity and of NR‐mRNA was also changed under salinity, but the NR activation state was not affected. In the first light phase, maximum NR activity increased rapidly in leaves of control plants, but was much slower in leaves from salinized plants. Thus, integrated over the whole day, the NR activity of salt‐stressed plants was lower than in control plants. NR transcript levels of control plants were low in the early night phase, started to increase in the second night phase, followed by a distinct peak at 2 h into the light period. This large ‘early morning peak’ of NR‐mRNA was hardly affected by salinity, whereas the initial slow increase of m‐RNA levels in the early night phase was almost absent in salinized plants. This is considered as one reason for the low NR activity of salinized plants in the first half of the day. It is also suggested that nitrate is a major signal affecting NR expression and activity under salinity. Sugars and amino acids appeared less important.
The role of genes influencing the corolla in pollination of Antirrhinum majus
Authors: Comba L. , Corbet S. A. , Hunt H. , Outram S. , Parker J. S. , Glover B. J.
Published: March 2003

Studies of pollination ecology have been hindered by an absence of biochemical information about the basis of polymorphism. Using model plants and mutant lines described by molecular genetics may circumvent this difficulty. Mutation of genes controlling petal colour and petal epidermal cell shape in Antirrhinum majus was previously shown to influence fruit set. White flowers set less fruit than magenta flowers and mutants with flat petal epidermal cells set less fruit than flowers with conical cells. Here we analyse the causal pathway underlying this phenomenon through a study of floral characteristics and bee behaviour. Results indicate that bees recognized plants with magenta conical‐celled flowers at a distance and did not approach white flowers or magenta flat‐celled flowers so frequently. Petal cell shape interacted with colour in determining whether an approaching bee landed on a flower within a plot and whether a bee landing on a flower would probe it. The intrafloral temperature of flowers with conical petal cells was shown to increase with solar irradiance, unlike the intrafloral temperature of flowers with flat petal cells. The difference in fruit set may reflect pollinator discrimination between genotypes as a consequence of the effect of intrafloral temperature on nectar quality and quantity.
Olive phenology as a sensitive indicator of future climatic warming in the Mediterranean
Authors: Osborne C. P. , Chuine I. , Viner D. , Woodward F. I.
Published: March 2003

Experimental and modelling work suggests a strong dependence of olive flowering date on spring temperatures. Since airborne pollen concentrations reflect the flowering phenology of olive populations within a radius of 50 km, they may be a sensitive regional indicator of climatic warming. We assessed this potential sensitivity with phenology models fitted to flowering dates inferred from maximum airborne pollen data. Of four models tested, a thermal time model gave the best fit for Montpellier, France, and was the most effective at the regional scale, providing reasonable predictions for 10 sites in the western Mediterranean. This model was forced with replicated future temperature simulations for the western Mediterranean from a coupled ocean‐atmosphere general circulation model (GCM). The GCM temperatures rose by 4·5 °C between 1990 and 2099 with a 1% per year increase in greenhouse gases, and modelled flowering date advanced at a rate of 6·2 d per °C. The results indicated that this long‐term regional trend in phenology might be statistically significant as early as 2030, but with marked spatial variation in magnitude, with the calculated flowering date between the 1990s and 2030s advancing by 3–23 d. Future monitoring of airborne olive pollen may therefore provide an early biological indicator of climatic warming in the Mediterranean.
Cell wall pectin content modulates aluminium sensitivity of Zea mays (L.) cells grown in suspension culture
Authors: Schmohl N. , Horst W. J.
Published: March 2003

The pectin content of the cell walls of maize suspension cells was modified to investigate its role in the expression of aluminium (Al) toxicity. Long‐term adaptation to NaCl or to the cellulose synthesis inhibitor 2,6‐dichlorbenzonitirle (DCB) increased the pectin content by 31 and 86%, respectively. Subculturing salt‐adapted cells for up to 3 weeks without NaCl supply or treatment of cells with pectolyase for up to 15 min reduced pectin contents by up to 46%. Such pre‐cultured cells were incubated for 2 h in presence of Al. There was a close positive correlation between pectin and both total and BaCl2 non‐exchangeable Al contents. Aluminium‐induced callose formation as an indicator of Al injury was closely positively correlated to the loss of cell viability. In NaCl‐adapted and pectolyase‐treated cells, Al‐induced callose formation was reduced when compared with normal cells. However, there was a close positive relationship between pectin contents and relative callose induction (digitonin‐induced callose formation, reflecting the different capabilities of cells to synthesize callose set to 100%) indicating that cells with higher pectin contents are more Al‐sensitive. The results presented support our view that the binding of Al to the cell wall pectin‐matrix represents an important step in the expression of Al toxicity.
Photosynthetic performance at low temperature ofBouteloua gracilisLag., a high‐altitude C4grass from the Rocky Mountains, USA
Authors: Pittermann J. , Sage R. F.
Published: March 2003

The mechanisms controlling the photosynthetic performance of C4plants at low temperature were investigated using ecotypes ofBouteloua gracilisLag. from high (3000 m) and low (1500 m) elevation sites in the Rocky Mountains of Colorado. Plants were grown in controlled‐environment cabinets at a photon flux density of 700μmol m−2s−1and day/night temperatures of 26/16 °C or 14/7 °C. The thermal response of the net CO2assimilation rate (A) was evaluated using leaf gas‐exchange analysis and activity assays of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase) and pyruvate,orthophosphate dikinase (PPDK). In both ecotypes, a reduction in measurement temperature caused the CO2‐saturated rate of photosynthesis to decline to a greater degree than the initial slope ofAversus the intercellular CO2response, thereby reducing the photosynthetic CO2saturation point. As a consequence,Ain normal air was CO2‐saturated at sub‐optimal temperatures. Ecotypic variation was low when grown at 26/16 °C, with the major difference between the ecotypes being that the low‐elevation plants had higherA;however, the ecotypes responded differently when grown at cool temperature. At temperatures below the thermal optimum,Ain high‐elevation plants grown at 14/7 °C was enhanced relative to plants grown at 26/16 °C, whileAin low‐elevation plants grown at 14/7 °C was reduced compared to 26/16 °C‐grown plants. Photoinhibition at low growth temperature was minor in both ecotypes as indicated by small reductions in dark‐adaptedFv/Fm. In both ecotypes, the activity of Rubisco was equivalent toAbelow 17 °C but well in excess ofAabove 25 °C. Activities of PEPCase and PPDK responded to temperature in a similar proportion relative to Rubisco, and showed no evidence for dissociation that would cause them to become principal limitations at low temperature. Because of the similar temperature response of Rubisco andA, we propose that Rubisco is a major limitation on C4photosynthesis inB. gracilisbelow 17 °C. Based on these results and for theoretical reasons associated with how C4plants use Rubisco, we further suggest that Rubisco capacity may be a widespread limitation upon C4photosynthesis at low temperature.
The effects of moisture and temperature on the ageing kinetics of pollen: interpretation based on cytoplasmic mobility
Authors: Buitink J. , Leprince O. , Hemminga M. A. , Hoekstra F. A.
Published: March 2003

This study shows that characterization of the molecular mobility in the cytoplasm of pollen provides a new understanding of the effects of moisture and temperature on ageing rates. Using EPR spectroscopy, we determined the rotational motion of the polar spin probe, 3‐carboxy‐proxyl, in the cytoplasm of Typha latifolia pollen, under different temperature and moisture content conditions. Increasing the temperature resulted in faster rotational motion, analogous to faster ageing rates. With decreasing moisture content, rotational motion first decreased until a minimum was reached, after which rotational motion slightly increased again. The moisture content at which this minimal rotational motion was observed increased with decreasing temperature, comparable to the pattern of ageing rate. A significant linear relationship was found between ageing rates and rotational motion in the cytoplasm, suggesting that these parameters are causally linked. Upon melting of the intracellular glass, a twofold increase in activation energy of rotational motion and ageing rate was observed. In contrast, melting of the sucrose glass resulted in an increase in rotational motion of five orders of magnitude. The difference in rotational motion upon melting glasses of pollen or sucrose suggests that other molecules beside sugars play a role in intracellular glass formation in pollen.
Tolerance of pea (Pisum sativum L.) to long‐term salt stress is associated with induction of antioxidant defences
Authors: Hernández J. A. , Jiménez A. , Mullineaux P. , Sevilia F.
Published: March 2003

Using two cultivars of Pisum sativum L. with different sensitivity to NaCl, the effect of long‐term (15 d) NaCl (70 m
M) treatments on the activity and expression of the foliar ascorbate–glutathione cycle enzymes, superoxide dismutase isozymes and their mRNAs was evaluated and related to their ascorbate and glutathione contents. High‐speed supernatant (soluble) fractions, enriched for cytosolic components of the antioxidant system, were used. In this fraction from the NaCl‐tolerant variety (cv Granada), the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), Mn‐superoxide dismutase (Mn‐SOD) and dehydroascorbate reductase (DHAR) increased, while CuZn‐SOD activity remained constant. In the NaCl‐sensitive plants (cv Challis), salinity did not produce significant changes in APX, MDHAR and GR activities. Only DHAR activity was induced in cv Challis, whereas soluble CuZn‐SOD activity decreased by about 35%. Total ascorbate and glutathione contents decreased in both cultivars, but the decline was greater in NaCl‐sensitive plants. This difference between the two cultivars was more pronounced when the transcript levels of some these enzymes were examined. Transcript levels for mitochondrial Mn‐SOD, chloroplastic CuZn‐SOD and phospholipid hydroperoxide glutathione peroxidase (PHGPX), cytosolic GR and APX were strongly induced in the NaCl‐tolerant variety but not in the NaCl‐sensitive variety. These data strongly suggest that induction of antioxidant defences is at least one component of the tolerance mechanism of peas to long‐term salt‐stress.
Influence of nutrient versus water supply on hydraulic architecture and water balance in Pinus taeda
Authors: Ewers B. E. , Oren R. , Sperry J. S.
Published: March 2003

We investigated the hydraulic consequences of a major decrease in root‐to‐leaf area ratio (AR:AL) caused by nutrient amendments to 15‐year‐old Pinus taeda L. stands on sandy soil. In theory, such a reduction in AR:AL should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (GS) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower GS in F was associated with 50% reduction in leaf‐specific hydraulic conductance (KL) compared with other treatments. The lower KL in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower AR:AL in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower AR:AL in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought‐induced dieback compared with non‐fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld.
Plasticity in relative growth rate and its components following a change in irradiance
Authors: Shipley B.
Published: March 2003

A total of 244 plants from two species, Lythrum salicaria and Epilobium glandulosum, were grown individually in hydroponic sand culture from seed for 36 d. Until day 27 all plants experienced an irradiance of 550 μmol m−2 s−1 PFD and on day 27 half of the plants were subjected to a neutral shade treatment in which irradiance was reduced to 100 μmol m−2 s−1 photon fluy density (PFD). Measures of relative growth rate, net assimilation rate, specific leaf area, biomass partitioning to leaves, roots, structural tissues (i.e. stems, petioles and inflorescences) and tissue density were obtained from intensive harvests three or four times per day. The shade treatment caused an immediate decrease in relative growth rate and net assimilation rate. Within hours the specific leaf area of the shaded plants increased and leaf tissue density decreased, thus partially offsetting the decrease in relative growth rate. Biomass partitioning was not affected.
Metabolic regulation and gene expression of root phosphoenolpyruvate carboxylase by different nitrogen sources
Authors: Pasqualini S. , Ederli L. , Piccioni C. , Batini P. , Bellucci M. , Arcioni S. , Antonielli M.
Published: March 2003

Alfalfa (Medicago sativaL.) N‐sufficient plants were fed 1·5 mMN in the form of NO3−, NH4+or NO3−in conjunction with NH4+, or were N‐deprived for 2 weeks. The specific activity of phosphoenolpyruvate carboxylase (PEPC) from the non‐nodulated roots of N‐sufficient plants was increased in comparison with that of N‐deprived plants. The PEPC value was highest with NO3−nutrition, lowest with NH4+and intermediate in plants that were fed mixed salts. The protein was more abundant in NO3−‐fed plants than in either NH4+‐ or N mixed‐fed plants. Nitrogen starvation decreased the level of PEPC mRNA, and nitrate was the N form that most stimulated PEPC gene expression. The malate content was significantly lower in NO3−‐deprived than in NO3−‐sufficient plants. Root malate accumulation was high in NO3−‐fed plants, but decreased significantly in plants that were fed with NH4+. The effect of malate on the desalted enzyme was also investigated. Root PEPC was not very sensitive to malate and PEPC activity was inhibited only by very high concentrations of malate. Asparagine and glutamine enhanced PEPC activity markedly in NO3−‐fed plants, but failed to affect plants that were either treated with other N types or N starved. Glutamate and citrate inhibited PEPC activity only at optimal pH. N‐nutrition also influenced root nitrate and ammonium accumulation. Nitrate accumulated in the roots of NO3−‐ and (NO3−+ NH4+)‐fed plants, but was undetectable in those administered NH4+. Both the nitrate and the ammonium contents were significantly reduced in NO3−‐ and (NO3−+ NH4+)‐starved plants. Root accumulation of free amino acids was strongly influenced by the type of N administered. It was highest in NH4+‐fed plants and the most abundant amides were asparagine and glutamine. It was concluded that root PEPC from alfalfa plants is N regulated and that nitrate exerts a strong influence on the PEPC enzyme by enhancing both PEPC gene expression and activity.
The differential expression of a heat shock promoter in floral and reproductive tissues
Authors: Crone D. , Rueda J. , Martin K. L. , Hamilton D. A. , Mascarenhas J. P.
Published: March 2003

A detailed histochemical analysis of the expression of the soybean small heat shock protein gene promoter, GmHSP 17·5E, fused to the GUS reporter gene, has been made in all organs and tissues of the flower as a function of stage of development and heat stress. This promoter is not uniformly expressed after a heat shock in all floral tissues and organs. Expression is seen at all stages of development in the sepals but not in the petals. The expression pattern in the pistil and in anthers is complex. Heat stress‐induced GUS staining is seen in the style and upper portion of the ovary, but not in the stigmatic papillae or in the lower part of the ovary or in ovules. In stamens the heat shock response is seen in the filament and in the extension of the vascular tissue from the filament into the anther. No induction is seen in other tissues of the anther or in microspores or pollen at any stage of development. Vegetative organs in contrast are more uniform in the heat shock inducibility of GUS activity. Based on evidence from transient assays after microprojectile particle bombardment of the GmHSP 17·5E/GUS construct into pollen, it is likely that the gene is transcriptionally in an inactive configuration in pollen nuclei in stably transformed transgenic plants. These results are discussed with reference to other information in the literature.
Direct evidence for non‐enzymatic fragmentation of chloroplastic glutamine synthetase by a reactive oxygen species
Authors: Ishida H. , Anzawa D. , Kokubun N. , Makino A. , Mae T.
Published: March 2003

Chloroplastic glutamine synthetase (GS: EC 6·3·1·2), the octamer of the 44 kDa subunit, is rapidly degraded under photo‐oxidative stress conditions in leaves, chloroplasts, and chloroplast lysates. Recent studies have suggested that chloroplastic GS might be cleaved by the hydroxyl radical under such conditions (Thoenen & Feller 1998; Australian Journal of Plant Physiology 25, 279–286; Palatnik, Carrillo & Valle 1999, Plant Physiology 121, 471–478). Herein, we present evidence which supports the above hypothesis. When the purified GS from wheat (Triticum aestivum L.) chloroplasts was exposed to the hydroxyl radical‐generating system comprising H2O2–FeSO4–ascorbic acid or FeCl3–ascorbic acid, the GS subunit was degraded into four distinct fragments having apparent molecular masses of 39, 35, 32 and 28 kDa. The apparent molecular masses and isoelectric points of these fragments were identical to those of the respective fragments found in the illuminated lysates of chloroplasts. In addition, the appearance of the GS fragments was completely suppressed in the presence of the scavenger for the hydroxyl radical, n‐propyl gallate, in the illuminated lysates of chloroplasts. These results strongly support the hypothesis that the primary cleavage of GS is directly driven by the hydroxyl radical, formed by Fenton reaction under photo‐oxidative stress conditions in chloroplasts.
Photo‐inhibition and seasonal photosynthetic performance of the seaweed Laminaria saccharina during a simulated tidal cycle: chlorophyll fluorescence measurements and pigment analysis
Authors: Gevaert F. , Creach A. , Davoult D. , Holl A.‐C. , Seuront L. , Lemoine Y.
Published: March 2003

Laminaria saccharina (Lamouroux) form the largest, most abundant and conspicuous seaweed populations along the French coast of the eastern English Channel. As they are located in the intertidal zone, they are exposed to considerable irradiance variations, mainly related to tidal cycles. The response of these macro‐algae to light variations over a simulated daily tidal cycle was investigated in the laboratory during spring, autumn and winter using chlorophyll fluorescence and pigment analysis. The maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm) and the operating PSII efficiency (ΦPSII) showed clear daily cycles according to the irradiance variation throughout the 12 h simulated tidal cycle, whereas the pattern of the relative photosynthetic electron transport rate (rETR) was not so obvious. The algae reacted to the light increase by developing photoprotective mechanisms able to dissipate the excess energy reaching PSII by the de‐epoxidation of violaxanthin into zeaxanthin. Because of their better acclimation to strong irradiance, spring populations were less affected by this light treatment than were winter populations. In particular, L. saccharina showed more pigments of the xanthophyll cycle in spring to cope with strong irradiance exposure. Alternatively, they developed their antenna complexes in winter to harvest a maximum of light.
Genetic parameters and QTL analysis of δ13C and ring width in maritime pine
Authors: Brendel O. , Pot D. , Plomion C. , Rozenberg P. , Guehl J.‐M.
Published: March 2003

Classical quantitative genetics and quantitative trait dissection analysis (QTL) approaches were used in order to investigate the genetic determinism of wood cellulose carbon isotope composition (δ13C, a time integrated estimate of water use efficiency) and of diameter growth and their relationship on adult trees (15 years) of a forest tree species (maritime pine). A half diallel experimental set‐up was used to (1) estimate heritabilities for δ13C and ring width and (2) to decompose the phenotypic δ13C/growth correlation into its genetic and environmental components. Considerable variation was found for δ13C (range of over 3‰) and for ring width (range of over 5 mm) and significant heritabilities (narrow sense 0·17/0·19 for δ13C and ring width, respectively, 100% additivity). The significant phenotypic correlation between δ13C and ring width was not determined by the genetic component, but was attributable to environmental components. Using a genetic linkage map of a full‐sib family, four significant and four suggestive QTLs were detected for δ13C, the first for δ13C in a forest tree species, as far as known to the authors. Two significant and four suggestive QTLs were found for ring width. No co‐location of QTLs was found between δ13C and growth.
Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings
Authors: Davy De Virville J. , Cantrel C. , Bousquet A.‐L. , Hoffelt M. , Tenreiro A.‐M. , Vaz Pinto V. , Arrabaça J. D. , Caiveau O. , Moreau F. , Zachowski A.
Published: March 2003

The present study investigated whether the cold‐sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35 °C), mitochondrial membranes were characterized by a higher phosphatidylcholine : phosphatidylethanolamine ratio and a lower content in 18 : 3 fatty acid. After a reduction of temperature (from 25 to 18 °C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35 °C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18 °C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35 °C, but not at 18 °C despite changes in lipid composition, in accordance with the cold‐sensitive character of the plant.
Modelling stomatal conductanceof field‐grown sunflower under varying soil water content and leafenvironment: comparison of three models of stomatal response toleaf environment and coupling with an abscisic acid‐based modelof stomatal response to soil drying
Authors: Gutschick V. P. , Simonneau T.
Published: March 2003

Stomatal conductance, gs, responds both tothe immediate or local environment of the leaf, such as CO2 partialpressure and irradiance, and to root‐sourced signals of water stress,particularly abscisic acid (ABA). Two models for the combined controlof gs were formulated and tested in sunflower(Helianthus annuus). First, several empirical models weretested for the local control, demonstrating that the Ball–Berrymodel [Ball, Woodrow & Berry (in Progress in PhotosynthesisResearch Vol. 4, pp. 5.221–5.224: M. Nijhoff,Dordrecht, The Netherlands) 1987] is consistently amongthe most accurate. A problem of statistical non‐independence inthis model is shown to be minor. The model offers regularity ofparameter values among most species and, despite an oversimplicationin representing known humidity‐response mechanisms, it incorporates othersignalling loops from CO2 and assimilation. In the firstcombined model, ABA as its concentration in xylem sap, [ABA]xy,down‐regulates the slope, m, in the Ball–Berry modelby the factor gfac = exp(– β[ABA]xy).The ABA‐induced reduction in gs decreases CO2 assimilation andsurface humidity, thus appearing to induce the local‐control mechanismto amplify the ABA‐induced stomatal closure. In the second combinedmodel, gs is estimated as the minimum of the local(Ball–Berry) response and the product gfac gs,max,with gs,max as a maximal unstressed conductance.Both models can predict gs from the external environmentalvariables with good accuracy (r2 near 0·8 over20‐fold variations in gs). Further analyses showthat gs responds to humidity almost quadraticallyrather than linearly. It also responds to assimilation as a powerlaw with an exponent that is significantly less than 1. These limitations,shared by other models, suggest more research into biochemical signalling.
Water‐deficit‐induced translational control in Nicotiana tabacum
Authors: KAWAGUCHI R. , WILLIAMS A. J. , BRAY E. A. , BAILEY‐SERRES J.
Published: March 2003

The effect of prolonged water deficit on mRNA translation was quantitatively analysed in apical and basal leaves of whole tobacco (Nicotiana tabacum) plants. The level of large polysomes (six or more ribosomes per mRNA) was significantly higher in apical than basal leaves under well‐watered conditions. In both young and old leaves, water deficit caused a progressive reduction in levels of polysomes with concomitant increases in 80S monosomes, indicative of reduced initiation of translation. Despite the global reduction in polysome formation over 144 h of water deficit, the water‐deficit‐induced putative lipid transfer protein (ltp) mRNA was associated with large polysomes and LTP content increased. Osmotin (osm) mRNA, another water‐deficit‐induced transcript, also remained associated with large polysomes during prolonged water deficit. In contrast, mRNAs encoding the non‐stress proteins ribulose bisphosphate carboxylase/oxygenase small subunit (rbcS) and eukaryotic initiation factor 4A (eIF4A) decreased in abundance and shifted to small polysomes and non‐polysomal complexes, indicating that initiation of translation of these mRNAs was impaired by water deficit. These results show that translational regulation is a component of the water‐deficit response and the differential translation of individual mRNAs is distinct in leaves of different age.