bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of high carbohydrate content on the activity of plastidic and cytosolic isoenzyme pairs in photosynthetic tissues
Authors: KRAPP A. , STITT M.
Published: April 2006

The carbohydrate content of photosynthetic cells or tissues was increased by feeding glucose to autotrophic Chenopodium rubrum cell suspension cultures, by feeding glucose via the transpiration stream to detached spinach leaves, and by expressing yeast‐derived invertase in the apoplast of tobacco leaves. Extracts were prepared, and plastidic and cytosolic isoenzymes were separated by electrophoresis and assayed by in situ activity staining. In all three systems, compared to control treatments, accumulation of carbohydrate led to decreased activity of plastid starch phosphorylase and phosphoglucose mutase, but not of the corresponding cytosolic isoenzymes. It led to increased activity of cytosolic 6‐hosphogluconate dehydrogenase but not of the plastid isoenzyme. The activities of cytosolic and plastidic aldolase, triose‐phosphate isomerase, and phosphoglucose isomerase were unaltered. The transcript and activity of nitrate reductase and pyrophosphate:fructose‐6‐phosphate phosphotransferase (both cytosolic enzymes) increased. The transcript levels for the S‐gene of ADP‐glucose pyrophosphorylase (a plastid enzyme) increased, but the overall enzyme activity decreased slightly. It is concluded that high carbohydrate leads to a selective change in the enzyme complement of the plastid, retaining enzymes which are required for glycolysis and losing enzymes which are needed for photosynthesis or starch mobilization.
A gauge to measure the mass flow rate of water in trees
Authors: CHANDRA S. , LINDSEY P. A. , BASSUK N. L.
Published: April 2006

A gauge that measures the mass flow rate of water in a growing tree is described. The gauge consists of an electric band heater wrapped around a section of the stem, a temperature controller that switches the current to the heater on and off so as to maintain a constant temperature rise across the heated section, and a timer to record the total time for which the heater is switched on. An energy balance shows the mass flow of water to be proportional to the time of operation of the heater. The magnitude of measurement errors is estimated using dimensional analysis and a numerical model. Experimental measurements of the flow rate of water in a tree using the gauge agree well with its recorded loss of weight.
Winding threads around plant cells: a geometrical model for microfibril deposition
Authors: EMONS A. M. C.
Published: April 2006

In this paper, a geometrical model is put forward to account for the deposition orientation of plant cell wall microfibrils (CMFs). The model presupposes the insertion in the plasma membrane of CMF initiation complexes, which, once inserted, are moved through the fluid plane of the plasma membrane by the kinetic force of CMF synthesis, leaving CMFs in their wake. Deposition occurs in a limited space and the CMFs are linked to wall matrix molecules. CMF orientation is governed by the laws of geometry and, taking space‐limiting conditions into account, therefore depends on (1) cell geometry, (2) the other wall molecules linked to the CMFs, and (3) the number of CMF initiation complexes inserted into the plasma membrane. The model does not exclude the idea that cortical microtubules may determine initial CMF orientation after cell division by determining the cell elongation direction.
Relationship between photoinhibition of photosynthesis, D1 protein turnover and chloroplast structure: effects of protein synthesis inhibitors
Authors: SCHNETTGER B. , CRITCHLEY C. , SANTORE U. J. , GRAF M. , KRAUSE G. H.
Published: April 2006

Irradiation of Spinach oleracea intact leaf tissue and of mesophyll protoplasts of Valerianella locusta at 20° C with strong light resulted in severe (40–80%) inhibition of photosynthesis, measured as photosystem II electron transport activity in isolated thylakoids or as fluorescence parameter FV/FM on intact leaf disks. No net degradation of the D1 protein of photosystem II was seen under these conditions. However, in the presence of streptomycin, an inhibitor of chloroplast protein synthesis, net D1 degradation (up to about 80%) did occur with a half‐time of 4–6h, and photoinhibition was enhanced. Thylakoid ultrastructure remained stable during photoinhibition, even when substantial degradation of D1 took place in the presence of streptomycin. When leaf disks were irradiated at 2°C, streptomycin did not influence the degree of photoinhibition, and net Dl degradation did not occur. These results suggest that in excess (photoinhibitory) light at 20°C, turnover (coordinated degradation and synthesis) of D1 diminished the degree of photoinhibition. The observed photoinhibition is thought to be due to the accumulation of inactive photosystem II reaction centres still containing D1. In the presence of streptomycin, the Dl protein was degraded (probably in the previously inactivated centres), but restoration of active centres via D1 synthesis was blocked, leading to more severe photoinhibition. Low temperature (2°C), by restricting both degradation and resynthesis of D1, favoured the accumulation of inactive centres. Streptomycin and chloramphenicol (another inhibitor of chloroplast protein synthesis) were tested for side‐effects on photosynthesis. Strong inhibitory effects of chloramphenicol, but much less severe effects of streptomycin were observed.
The relationship between wound‐induced proteinase inhibitors and hydraulic signals in tomato seedlings
Authors: MALONE M. , PALUMBO L. , BOARI F. , MONTELEONE M. , JONES H. G.
Published: April 2006

Localized wounding is known to induce systemic proteinase inhibitors (PI) in seedlings of tomato (Lycopersicon esculentum L.). Inhibitors of elastase (EC 3.4.21.36) were shown here to be among those systemically induced by wounding, and a simple rapid assay for PI based on elastase was developed. Using this assay, the nature of the systemic signalling system (‘PIIF’) was investigated. Hydraulic signals were shown to be induced in tomato by localized wounds. These signals travelled throughout the plant well within the lag time before appearance of systemic wound‐induced PI. A number of correlations were drawn between the occurrence of the hydraulic signals and induction of systemic PI, suggesting that hydraulic signals might be the PIIF, or a component of it. It was shown that systemic hydraulic signals could be triggered, without significant wounding, by excision of a single leaflet through the submerged petiole. These hydraulic signals were similar in both kinetics and magnitude to those induced by localized wounding. However, they did not induce systemic PI. In addition, it was shown that systemic events almost as rapid as wound‐induced hydraulic signals could be induced without wounding, under certain environmental conditions. This indicates that rapid hydraulic signals do not provide a specific signal of wounding. These findings demonstrate that hydraulic signals per se are not the PIIF.
Requirement for carbonic anhydrase activity in processes other than photosynthetic Inorganic carbon assimilation
Authors: RAVEN J. A. , NEWMAN J. R.
Published: April 2006

A number of non‐green plant tissues have high rates of HCO3−‐consuming reactions in the cytosol, i.e. C4 dicarboxylic acid production preceding organic acid anion transport into dicarboxylate consuming compartments in N2‐fixing root nodules, in lipogenic tissues, and in thermogenic aroid spadices and, in the case of lipogenic tissues, in acetyl CoA incorporation into lipid in plastid stroma. Since inorganic C supply to the cytosol or stroma by decarboxylation reactions, and by transmembrane fluxes, involves only CO2, the HCO3− consumed in the rapid metabolic processes must originate from hydration (hydroxylation) of CO2. Computations based on the first‐order rate constant for uncatalysed conversion of CO2 to HCO3− and the most likely in vivo CO2 concentration show that the uncatalysed reaction is possibly adequate to supply the observed HCO3− requirement in the HCO3−‐consuming compartments. However, carbonic anhydrase activity is well established in legume root nodules, and also appears to occur in aroid spadices. In addition to coping with any heterogeneities in HCO3−, consumption in the cytosol, the root nodule activity may be involved in optimizing haemoglobin function. Further work is needed on carbonic anhydrase expression is tissues with rapid HCO3− consumption, especially in view of reports of negligible carbonic anhydrase activity in some non‐green plant tissues. Other possible roles of carbonic anhydrase in non‐green plant tissues are briefly discussed.
Temperature‐sensitivity of D1 protein metabolism in isolated Zea mays chloroplasts
Authors: BREDENKAMP G. J. , BAKER N. R.
Published: April 2006

The effects of low temperature on the synthesis and stability of the 32 kDa D1 protein of photosystem II were investigated in chloroplasts isolated from maize (Zea mays cv. LG11) leaves. The synthesis of D1 by intact chloroplasts in vitro was strongly dependent on temperature; the Q10 for the initial rate of incorporation of [35S]‐methionine into D1 was ca. 2.6 over the range 13–25°C. The synthesis of other thylakoid polypeptides exhibited a similar temperature dependence, whilst synthesis of stromal proteins was considerably less temperature‐dependent, with the exception of two polypeptides of ca. 56 and 59.5 kDa. The stability of newly‐synthesized D1 in the thylakoid membranes was dependent both on the temperature at which the plants were grown and on the temperature during the pulse‐labelling period when the protein was synthesized. In chloroplasts isolated from maize leaves grown at 25°C, D1 that was synthesized and assembled at 25 °C in vitro was rapidly degraded during the chase period. At lower chase temperatures the protein was more stable. When chloroplasts from 25°C‐grown leaves were pulse‐labelled at 13°C, the stability of D1 was markedly enhanced at all temperatures during the chase period. This effect was even more pronounced in chloroplasts isolated from plants grown at 14°C. The implications of these results are discussed with regard to the ability of maize to recover from photoinhibitory damage at low temperatures.
An open‐air system for exposing forest‐canopy branches to ozone pollution
Authors: TJOELKER M. G. , VOLIN J. C. , OLEKSYN J. , REICH P. B.
Published: April 2006

We developed a chamberless system to expose branches to elevated concentrations of ozone with little alteration of micro‐meteorological conditions. In a 35‐year‐old stand of sugar maple (Acer saccharumMarsh.), scaffolding and a platform (14 m in height) provided access to 10 branches and ten paired controls within the canopy. Ozone was delivered to the canopy through a manifold and an array of loops (38 cm in diameter) of teflon tubing individually fitted to each branch. Ozone‐enriched air was discharged through numerous small holes in each loop positioned beneath the exposed foliage. A sampling system controlled by a microcomputer monitored ozone concentrations for each loop by means of composite air samples from 12 leaves, drawn through small teflon tubes (1.65 mm diameter) attached to the petioles. On average, coefficients of variation for ozone concentrations for the sample points within each branch loop were less than 50%. Between 0900 and 1700 h for 68 d of exposure, the mean hourly ozone concentrations among the branches averaged 95nmol mol−1(±13SD), about twice the ambient mean. Frequency distributions of mean hourly concentrations during exposure were unimodal and approximately log‐normal, comparable to ambient ozone concentrations. The open‐air loop system enables exposure of branches to gaseous pollutants under relatively natural conditions.
A low‐cost psychrometer for field measurements of atmospheric humidity
Authors: ALLEN S. J. , BRENNER A. J. , GRACE J.
Published: April 2006

A design for an aspirated wet and dry bulb psychrometer, suitable for continuous field measurement of atmospheric humidity, is described. The psychrometer is simple and cheap to make, with a material cost of UK £40 per unit. It is mainly constructed from ready‐made plastic plumbing parts, thus avoiding the need for expensive workshop facilities. The wet and dry bulb temperature sensors are suitable for direct connection to a solid‐state data‐logger. During extensive field use, it has proved reliable and easy to maintain. The accuracy of the device was assessed by intercomparison with an Assman psychrometer, a standard instrument for measuring atmospheric humidity. The test was conducted under high ambient saturation deficits (4.08 ± 1.22 kPa) and shortwave radiation fluxes in Niger, West Africa. Reasonable agreement between the two instruments was observed, with the low‐cost psychrometer giving a mean saturation deficit 0.12 ± 0.25 kPa higher than the Assman.
Effect of Ca2+ on the retention of glycerol and amino acids in Dunaliella tertiolecta
Authors: FUJII S.
Published: April 2006

When D. tertiolecta cells, previously incubated in a 0.5 kmol m−3 NaCl medium with 1mol m−3 Ca2+, were transferred to an isotonic NaCl medium without Ca2+, the intracellular glycerol, as well as intracellular amino acids, was transiently lost to the medium within 30 min. The transient leakage of glycerol and amino acids was enhanced by the addition of EGTA (1 mol m−3), while the addition of SrCl2 (1 mol m −3) or polyamines such as spermidine (5 mol m−3) and spermine (5 mol m−3) restrained the leakage caused by the lack of external Ca2+ of intracellular glycerol and amino acids.
Plant distribution and the temperature coefficient of metabolism
Authors: CRIDDLE R. S. , HOPKIN M. S. , McARTHUR E. D. , HANSEN L. D.
Published: April 2006

The spatial distribution of a plant species is limited by the range of climatic conditions to which the species can adapt. Temperature is one of the most significant determinants of plant distribution, but except for the effects of lethal limits, little is known about physiological changes in responses to differences in environmental temperature. In this study, temperature coefficients of non‐photosynthetic metabolism have been determined in the normal environmental temperature range for selected annual and perennial plants. Distinct differences were found in the temperature coefficient of metabolism of woody perennial plants from high latitudes and high elevations and closely related low‐latitude and low‐elevation plants. Low‐latitude and low‐elevation woody perennials have Arrhenius temperature coefficients for metabolism that are larger than those for congeneric high‐latitude and high‐elevation plants. The Arrhenius temperature coefficient is not rapidly adapted to new environments. A simple function was developed relating Arrhenius temperature coefficient to latitude and elevation for accessions of three, woody, perennial species complexes of plants collected from a wide geographic range but grown in common gardens. Within these taxa, plants that experience broader ranges of temperature during growth in their native habitat have smaller temperature coefficients. Temperature coefficients also varied with growth stage or season. No similar relationship was found for annuals and herbaceous perennials. For the plants tested, Arrhenius temperature coefficients are high during early spring growth, but shift to lower values later in the season. The shift in Arrhenius temperature coefficients occurs early in the season for southern and low‐elevation plants and progressively later for plants from further north or higher elevation. The changes in Arrhenius temperature coefficients result largely from increases in plant metabolic rates at lower temperatures while little change occurs in the rates at higher temperatures. Altering the temperature dependence of the control of metabolic rate is apparently an important means of response to climate change.
Differential stimulation of an arid‐environment winter ephemeral Dimorphotheca pluvialis (L.) Moench by ultraviolet‐B radiation under nutrient limitation
Authors: MUSIL C. F. , WAND S. J. E.
Published: April 2006

A South African winter ephemeral D. pluvialis was exposed, under low and high nutrient conditions, to four different daily doses of biologically effective UV‐B radiation. These simulated different depletions (range 0–30%) in the ozone layer at the southerly distribution limit (33° 56′S) of this species, and included daily UV‐B doses received at the northerly distribution limit (26° 38′S) without ozone depletion. Growth inhibition by increased UV‐B radiation was observed during early vegetative stages, but only under low nutrient conditions. Thereafter, net CO2 assimilation rate, growth and reproduction were stimulated by an increase in UV‐B radiation, though doses above those approximating a 20% ozone depletion appeared to be inhibitory. Differential stimulation occurred in the two nutrient treatments. Under high nutrient conditions, photosynthesis (specifically carboxylation efficiency), and numbers of leaves, inflorescences and diaspores per plant, and leaf areas increased, but leaf thickness decreased with increased UV‐B radiation. Under low nutrient conditions, dry masses of leaves, stems, inflorescences and diaspores, and total above‐ground dry masses increased with increased UV‐B radiation. Foliar organic carbon and nitrogen concentrations and foliar concentrations of UV‐B absorbing compounds were unaffected by increased UV‐B radiation, but foliar P concentrations declined. Diaspore viability declined with increased UV‐B radiation. The net effect was a 35 to 43% reduction in viable diaspore production under high nutrient conditions at UV‐B doses equivalent to those currently received at the northerly distribution limit during the reproductive phase. It is concluded that anticipated increases in UV‐B radiation could reduce regeneration success, and seedling survival in areas of low soil fertility, particularly at lower latitudes, and consequently increase the risk of localized population extinctions from stochastic causes.
Control of steady‐state photosynthesis in sunflowers growing in enhanced CO2
Authors: WOODROW I. E.
Published: April 2006

Control coefficients were used to describe the degree to which ribulose bisphosphate carboxylase/oxygenase (Rubisco) limits the steady‐state rate of CO2 assimilation in sunflower leaves from plants grown at high (800 μmol mol−1) and low (350 μmol mol−1) CO2. The magnitude of a control coefficient is approximately the percentage change in the flux that would result from a 1% rise in enzyme active site concentration. In plants grown at low CO2, leaves of different ages varied considerably in their photosynthetic capacities. In a saturating light flux and an ambient CO2 concentration of 350 μmol mol−1, the Rubisco control coefficient was about 0.7 in all leaves, indicating that Rubisco activity largely limited the assimilation flux. The Rubisco control coefficient for leaves grown at 350 μmol mol−1 CO2 dropped to about zero when the ambient CO2 concentration was raised to 800 μmol mol−1. In relatively young, fully expanded leaves of plants grown at high CO2, the Rubisco control coefficient was also about 0.7 at a saturating light flux and at the CO2 concentration at which the plants were grown (800 μmol mol−1). This apparently resulted from a decrease in the concentration of Rubisco active sites. In older leaves, however, the control coefficient was about 0.2. Because, on the whole, Rubisco activity still largely limits the assimilation flux in plants grown at high CO2, the kinetics of this enzyme can still be used to model photosynthesis under these conditions. The relatively high Rubisco control coefficient under enhanced CO2 indicates that the young sunflower leaves have the capacity to acclimate their photosynthetic biochemistry in a way consistent with an optimal use of protein resources.
Induction of PPi‐dependent phosphofructokinase by phosphate starvation in seedlings of Brassica nigra
Authors: THEODOROU M. E. , PLAXTON W. C.
Published: April 2006

Activity of PPi‐dependent phosphofructokinase (PFP) was monitored in Brassica nigra seedlings grown under nutrient‐sufficient or phosphate (Pi)‐starved conditions. Roots, stems and leaves of 50 d Pi‐deficient seedlings displayed 4.0‐, 3.7‐ and 2.3‐fold greater PFP activity, respectively, than did nutrient sufficient controls. This induction was based primarily upon an increased susceptibility of PFP from the Pi‐starved tissues to activation by fructose‐2,6‐bisphosphate. The ratio of PFP to ATP‐dependent phosphofructokinase (PFK) was approximately 2:1 and 1:1 in the various organs of 50 d Pi‐starved and Pi‐fed plants, respectively. Immunoblots probed with anti‐(potato PFP) immune serum revealed that the induction of PFP in Pi‐starved B. nigra was coincident with an elevation in the amount of PFP α‐subunit in the leaves as well as an increase in the α:β subunit ratio in the stems and roots. Induction of PFP in the various tissues was also accompanied by an appreciable decline in intracellular Pi level, decreased soluble protein content, and elevated phosphoenolpyruvate phosphatase activity. Time course studies revealed that these responses to Pi stress were significantly delayed in the leaves as compared to the roots and stems suggesting that Pi may be preferentially sequestered to the leaves during Pi starvation. These data also provide further evidence that B. nigra PFP is an adaptive enzyme that may function during Pi deprivation as: (1) a glycolytic bypass to PFK; and (2) a ‘Pi‐recycling system’ that converts esterified‐P to Pi that would be rapidly reassimilated into the metabolism of the Pi‐deficient cells.
The importance of the ratio UV‐B/photosynthetic active radiation (PAR) during leaf development as determining factor of plant sensitivity to increased UV‐B irradiance: effects on growth, gas exchange and pigmentation of bean plants (Phaseolus vulgaris cv. Label)
Authors: DECKMYN G. , MARTENS C. , IMPENS I.
Published: April 2006

To evaluate the effect of different naturally occurring irradiation conditions on the sensitivity of bean (Phaseolus vulgaris cv. Label) to increased UV‐B levels, plants were grown under six different light treatments. In the control series (at ambient levels of UV‐B), UV‐B and visible light were decreased in parallel, resulting in three different total irradiation treatments with the same UV‐B/PAR ratio. A second series with a 15% increase in UV‐B irradiation at each PAR level was used to investigate the effect of UV‐B under the varying total irradiance levels. The different total irradiance levels resulted in large differences in total dry weight, specific leaf weight, photosynthesis‐light response and pigment concentrations. Nevertheless, the 15% increase in UV‐B resulted in equal reductions in total dry weight (from 24.5 to 34.3%) and effective photosynthesis for all light levels. The accumulation of protective pigments in the primary bean leaves was strongly correlated to the total irradiance level (200% increase from the lowest to the highest light level), but was not influenced by increasing UV‐B levels. As the UV‐B/PAR ratio outside increases with decreasing total irradiance (when induced by cloud cover) this implies that low radiation levels are potentially dangerous to some plants, even though the UV‐B levels may seem negligible.
Growth cycle stage‐dependent NaCl induction of plasma membrane H+‐ATPase mRNA accumulation in de‐adapted tobacco cells
Authors: PEREZ‐PRAT E. , NARASIMHAN M. L. , NIU X. , BOTELLA M. A. , BRESSAN R. A. , VALPUESTA V. , HASEGAWA P. M. , BINZEL M. L.
Published: April 2006

A cDNA clone encoding an isoform of the plasma membrane H+‐ATPase was isolated from Nicotiana tabacum. The steady‐state plasma membrane H+‐ATPase message levels were the same in unadapted tobacco cells and tobacco cells adapted to 428 mol m−3 NaCl. When cells adapted to 428 mol m−3 NaCl maintained in the absence of NaCl (deadapted) for an excess of 100 passages were exposed to 400 mol m−3 NaCl for 24 h, there was an increased accumulation of plasma membrane H+‐ATPase message. The NaCl responsiveness of the deadapted cells was dependent upon the growth cycle stage. Alterations in the levels of plasma membrane FT‐ATPase message during the growth cycle support a role for the H+‐ATPase in cell growth. These results document the induction by NaCl of plasma membrane FT‐ATPase message accumulation in tobacco cells, and suggest that enhanced expression of the plasma membrane FT‐ATPase has a role in the short term response of cells of NaCl, but is not necessarily involved in long‐term adaptation.
Starch metabolism in germinating soybean cotyledons is sensitive to clinorotation and centrifugation
Authors: BROWN C. S. , PIASTUCH W. C.
Published: April 2006

Soybean (Glycine max [L.] Merr. cv. McCall) seedlings germinated and grew for 6d under the altered gravity conditions of horizontal clinorotation and centrifugation. Both of these conditions resulted in decreased growth relative to the control (vertically rotated) plants. Starch concentration in the cotyledons was lower in the clinorotated plants and was higher in the centrifuged plants compared to the controls. The opposite relationship was noted for total lipid concentration. Of the six starch metabolic enzyme activities measured, only ADP glucose pyrophosphorylase was affected by the gravity treatments; being lower in the cotyledons of the horizontally rotated plants and higher in the cotyledons of the centrifuged plants relative to the control values.
Speculations on carbon dioxide starvation, Late Tertiary evolution of stomatal regulation and floristic modernization
Authors: ROBINSON J. M.
Published: April 2006

Ambient atmospheric CO2concentration ([CO2]a) has apparently declined from values above 200μmol mol−1to values below 200μmol mol−1within the last several million years. The lower end of this range is marginal for C3plants. I hypothesize that: (1) declining [CO2]aimposed a physiological strain on plants, and plant taxa evolving under declining [CO2]atended to develop compensating mechanisms, including increased stomatal efficiency; (2) angiosperms were better able to adjust to declining [CO2]athan were gymnosperms and pteridophytes; and (3) angiosperm adjustment has been uneven. Fast‐evolving taxa (e.g. grasses and herbs) have been better able to adapt to CO2starvation. If these propositions are true, stomatal adjustment mechanisms should show patterned variation, and a single pattern of stomatal regulation cannot be assumed.
A modelling analysis of the effects of climatic warming on the probability of spring frost damage to tree species in The Netherlands and Germany
Authors: KRAMER K.
Published: April 2006

Two studies presented in the literature (Murray, Canned & Smith 1989; Hanninen 1991) evaluate the effect of increasing winter temperature on the probability of spring frost damage to trees, but yield contradictory results. It is unclear whether the disparity can be ascribed to the fact that different models were used, or is the result of different climatic warming scenarios being used, or is because the tree species at the different locations do indeed respond differently to warmer winters. To evaluate the effects of climatic warming to tree species in The Netherlands and in Germany, both models were fitted to long series of observations on the date of leaf unfolding of eleven tree species. The impact of the two scenarios (uniformly and non‐uniformly changing winter temperature) on the date of leaf unfolding and on the probability of freezing temperature around that date was evaluated. To test the importance of adaptation to local climate, hypothetical provenance transfers were analysed. It was concluded that, for tree species in The Netherlands and Germany, the probability of spring frost damage will decrease. The contradictory results found in the literature could be ascribed to differences between provenances adapted to their local climate, and is not because different models and different climatic warming scenarios were used in these studies.
Water uptake regulation in peach trees with split‐root systems
Authors: SIMONNEAU T. , HABIB R.
Published: April 2006

The water uptake of 3‐ to 4‐year‐old peach trees ‘May‐crest/Prunus Damas’ grown in an aerated nutrient solution was studied using a split‐root system. Each container and the whole tree were weighed independently to measure water absorption by both parts of the root system and tree transpiration. Water potential of leaves was measured with a pressure chamber. Water potential of roots was estimated using root suckers sealed in plastic bags before the measurement. The nutrient solution was removed from one container so that half the root system was left in humid air for 48 h. Water potential of roots left in solution decreased, which (partly) maintained water absorption and thus transpiration. No modification of root hydraulic resistance was required to simulate the experimental results. Nevertheless, enhancement of absorption by the roots supplied with solution cannot compensate for the water loss by transpiration. Depletion of water from the plant essentially came from the non‐absorbing roots. This was demonstrated by substituting vegetable oil for nutrient solution around one half of the split‐root system, and by following the changes in root volume on the basis of Archimedes principle. Conflicting results in the literature about apparent changes in hydraulic resistance are discussed.
Reversing cavitation in tracheids of Pinus sylvestris L. under negative water potentials
Authors: EDWARDS W. R. N. , JARVIS P. G. , GRACE J. , MONCRIEFF J. B.
Published: April 2006

Xylem cavitation is a frequent event, but since resistance to flow does not generally increase in vivo, reversal must also occur even under negative potentials. We demonstrated that this can occur in excised wood. Our results suggest that refilling of cavitated tracheids at negative water potentials may result from a change in equilibrium between gas concentrations, water potential and surface tension at the embolism interface. Excised branch‐wood specimens from small trees of Pinus sylvestris were dried on the bench to a range of relative water contents and then rehydrated in a permeability apparatus using ultra‐filtered, de‐aerated water as permeant. Water inflow and outflow were measured gravimetrically by recording the gain or loss from two reservoirs held on balances. Flow was induced through the specimen by holding the balances at different levels, while an overall negative water potential could be imposed by raising the specimen above the inflow/outflow reservoirs. Changes in water content of the specimen were calculated as the difference between inflow and outflow. The time‐course data for both relative water content and permeability were fitted to an exponential function to give initial and final estimates and a time constant. Rehydration occurred at all imposed water potentials, but the speed of recovery was affected at lower potentials. Where drying of the specimen was more protracted, permeability was initially lower but also recovered during permeation. Both flow and de‐aeration were necessary for complete rehydration. A model requiring new information on gas concentrations and transport coefficients is suggested.
The influence of elevated CO2 on non‐structural carbohydrate distribution and fructan accumulation in wheat canopies
Authors: SMART D. R. , CHATTERTON N. J. , BUGBEE B.
Published: April 2006

We grew 2.4 m2 wheat canopies in a large growth chamber under high photosynthetic photon flux (1000 μmol m−2 s−1) and using two CO2 concentrations, 360 and 1200 μmol mol−1. Photosynthetically active radiation (400–700 nm) was attenuated slightly faster through canopies grown in 360μmol mol−1 than through canopies grown in 1200μmol mol−1, even though high‐CO2 canopies attained larger leaf area indices. Tissue fractions were sampled from each 5‐cm layer of the canopies. Leaf tissue sampled from the tops of canopies grown in 1200μmol mol−1 accumulated significantly more total non‐structural carbohydrate, starch, fructan, sucrose, and glucose (p≤ 0.05) than for canopies grown in 360μmol mol−1. Non‐structural carbohydrate did not significantly increase in the lower canopy layers of the elevated CO2 treatment. Elevated CO2 induced fructan synthesis in all leaf tissue fractions, but fructan formation was greatest in the uppermost leaf area. A moderate temperature reduction of 10 °C over 5d increased starch, fructan and glucose levels in canopies grown in 1200μmol mol−1, but concentrations of sucrose and fructose decreased slightly or remained unchanged. Those results may correspond with the use of fructosyl‐residues and release of glucose when sucrose is consumed in fructan synthesis.
Root elongation rate is accounted for by intercepted PPFD and source‐sink relations in field and laboratory‐grown sunflower
Authors: AGUIRREZABAL L. A. N. , DELEENS E. , TARDIEU F.
Published: April 2006

The existence of relationships between intercepted photo‐synthetic photon flux density (PPFD) and growth of individual organs is somewhat controversial. We have tested whether such relationships could account for the natural variability in elongation rates of taproot and secondary roots of sunflower (from 2 to 135 mm d−1), in field and laboratory conditions. Elongation of taproot and secondary roots was recorded daily through windows in the field. A range of PPFD was obtained by following day‐to‐day natural fluctuation for three contrasting growing periods, and by shading part of the plants under study. A parallel experiment was carried out in a growth chamber with contrasting light intensities and with a 14CO2 labelling experiment. After the two‐leaf stage, i.e. when the contribution of photosynthetic carbon became appreciable in root growth, daily root elongation rate was closely linked to the PPFD intercepted from 36 to 12 h before the measurement of root elongation. Curvilinear relationships applied to plants grown in the field as well as in a growth chamber, and to shaded plants as well as to plants subjected to day‐to‐day changes in intercepted PPFD. For a given intercepted PPFD, the taproot elongated faster than secondary roots, and secondary roots originating near the base of the taproot elongated faster than those originating near the apex. The elongation rate of any secondary root apex was accounted for (r= 0.77) by the ratio of intercepted PPFD to the distance between the apex and the base of the taproot. No relationships between intercepted PPFD and elongation rate were observed before the two‐leaf stage, when the CO2 labelling experiment suggests that carbon essentially originates from the seed. Therefore, this study suggests a role for source‐sink relations in the distribution of elongation between apices and a role for carbon nutrition in day‐to‐day variations of root elongation rate. Precise mechanisms explaining this behaviour remain to be investigated.
Redox characteristics of normal and habituated cell lines of sugarbeet
Authors: CARRIÉ B. , GASPAR T.H. , GREPPIN H. , PENEL C.
Published: April 2006

Redox properties of cells of normal hormone‐requiring (N) and habituated (H) sugarbeet calli have been investigated. It was found that H cells at all ages reduced exogenous ferricyanide at a much higher rate than N cells, but they exhibited a lower chemiluminescence either alone or in presence of luminol. The plasma membrane NADH:fer‐ricyanide oxidoreductase measured in vitro was almost identical for the two cell types. This could indicate that the higher reducing power of H cells had an intracellular origin. Among the enzyme activities which could provide electrons, malate dehydrogenase activity was found to be a good candidate, being more active in H cells. The results are discussed in relation to the abnormal structure of the cell wall of habituated cells.
Scaling sun and shade photosynthetic acclimation ofAlocasia macrorrhizato whole‐plant performance – II. Simulation of carbon balance and growth at different photon flux densities
Authors: SIMS D.A. , GEBAUER R.L.E. , PEARCY R.W.
Published: April 2006

A whole‐plant carbon balance model incorporating a light acclimation response was developed forAlocasia macrorrhizabased on empirical data and the current understanding of light acclimation in this species. The model was used to predict the relative growth rate (RGR) for plants that acclimated to photon flux density (PFD) by changing their leaf type, and for plants that produced only sun or shade leaves regardless of PFD. The predicted RGR was substantially higher for plants with shade leaves than for those with sun leaves at low PFD. However, the predicted RGR was not higher, and in fact was slightly lower, for plants with sun leaves than for those with shade leaves at high PFD. The decreased leaf area ratios (LARs) of the plants with sun leaves counteracted their higher photosynthetic capacities per unit leaf area (Amax). The model was manipulated by changing parameters to examine the sensitivity of RGR to variation in single factors. Overall, RGR was most sensitive to LAR and showed relatively little sensitivity to variation inAmaxor maintenance respiration. Similarly, RGR was relatively insensitive to increases in leaf life‐span beyond those observed. Respiration affected RGR only at low PFD, whereasAmaxwas moderately important only at high PFD.
Gamma‐ray‐induced changes in the synthesis of tomato pericarp protein
Authors: FERULLO J.‐M. , NESPOULOUS L. , TRIANTAPHYLIDÈS C.
Published: April 2006

The application of massive doses of gamma rays (1–8 kGy) to mature green cherry‐tomato fruits led to a transient fall in pericarp tissue protein metabolism within 6h. A separate 3 kGy treatment resulted in the appearance of certain transcripts and proteins, and a reduction in the abundance of others. At the same dose, protein synthesis regained the control level within 24 h, and in addition a new set of proteins was induced. Gamma‐induced proteins (referred to as GIPs) were divided into three groups, depending on the time‐course of their induction. Group 1 GIPs were synthesized only during the first few hours following treatment, whereas group 2 GIPs were synthesized for at least 48 h. Group 3 GIPs were progressively induced when the control level of synthesis was restored. These results demonstrated that, despite its deleterious effects on DNA and cell structures, irradiation induced an active response in plant tissue. Comparative experiments suggest that the majority of group 1 GIPs might belong to the heat shock protein family. GIPs might play a role in the protection and repair of cellular structures, or may be implicated in physiological disorders triggered by irradiation.
Regulation of the expression of photosynthetic nuclear genes by CO2 is mimicked by regulation by carbohydrates: a mechanism for the acclimation of photosynthesis to high CO2?
Authors: VAN OOSTEN J.‐J. , WILKINS D. , BESFORD R. T.
Published: April 2006

The abundance of transcripts of cab‐7 and cab‐3C, which code for the chlorophyll a/b binding proteins of the light‐harvesting complexes I and II, respectively, and the abundance of transcripts of Rca, which encodes Rubisco activase, were reduced in tomato plants exposed to high CO2 for up to 9d, whereas the abundance of mRNA from psa A–psa B and psb A, which encode the proteins of the core complex of PSI and the D1 protein of PSII, respectively, and the abundance of glycolate oxidase, which is involved in photorespiration, were not affected. However, the abundance of the transcript for the B subunit of ADP‐glucose pyrophosphorylase was increased after 1 d at elevated CO2. The chlorophyll a/b ratio decreased significantly over 9 d of exposure to elevated CO2. The responses of the nuclear genes to high CO2 were enhanced when leaves were detached so as to deprive them of any major sink. The responses of these transcripts to high CO2 were mimicked when sucrose or glucose was supplied to the leaf tissue, whereas acetate or sorbitol had no effect. Carbohydrate analyses of leaves grown in high CO2 or supplied with sucrose revealed that major increases occurred in the amount of glucose and fructose.

Based on these and other published data, a molecular model involving the repression or activation of the transcription of nuclear genes coding for chloroplast proteins by photosynthetic end‐products is proposed to account for photosynthetic acclimation to high CO2 in tomato plants and other species.
Anaerobiosis‐mediated early transcriptional and translational responses in rice (Oryza sativa L.) coleoptiles and roots
Authors: BREVIARIO D. , GIANÍ S. , MORELLO L. , CORAGGIO I.
Published: April 2006

To study the transcriptional and translational responses that occur in rice (Oryza sativa L., cv. Arborio) coleoptiles and roots during the first hours of anoxia, we analysed the patterns of in vitro translational products and in vivo labelled newly synthesized proteins obtained from both organs grown in the presence or absence of O2. Analysis of the protein pattern obtained from nuclear‐enriched sub‐cellular fractions showed the enhancement of the synthesis of several proteins with molecular weights of 67–62, 54 and 34 kD. In the cytoplasmic‐enriched subcellular fractions, we found that the synthesis of polypeptides of relatively low molecular weight (13–16 kD) was strongly induced by anaerobiosis. In vitro translation analysis showed that this enhancement was mainly due to a rapid increase in the level of the corresponding mRNA species. These low‐molecular‐weight translational products were already detected after 1h of anoxia in both rice roots and rice coleoptiles, but remained undetectable in aerobically grown organs. Additional anaerobic‐specific transcriptional and translational changes were also observed. In particular, a specific reduction in the level of mRNAs coding for polypeptides of 38 kD occurred in both roots and coleoptiles after only 1 h of anoxia.
Decreased ribulose‐1,5‐bisphosphate carboxylase/oxygenase in transgenic tobacco transformed with ‘antisense’rbcS.VIII. Impact on photosynthesis and growth in tobacco growing under extreme high irradiance and high temperature
Authors: KRAPP A. , CHAVES M. M. , DAVID M. M. , RODRIQUES M. L. , PEREIRA J. S. , STITT M.
Published: April 2006

Wild‐type and antisense rbcS tobacco (Nicotiana tabacum) plants were grown in a glasshouse in midsummer in Portugal with an irradiance of 1500–2000 μmol m−2s−1 and daytime temperatures of 30–35 °C. The Rubisco content of the transformants was lower by 35, 80 and over 90% than that of the wild‐type. Gas exchange was measured over three separate days. There was a near‐linear relation between Rubisco content and photosynthetic rate during the period of high irradiance, allowing a flux control coefficient of 0.83–0.89 to be estimated. The relation deviated slightly from linearity, because the internal CO2 concentration (c;) was higher in the transformants than in the wild‐type (190 and 275 μmol mol−1 in plants with 35 and 80% less Rubisco, respectively, compared with 175 μmol mol−1 for wild‐type), compensating to some extent for the decreased Rubisco content. This increase in ci occurred because the stomatal conductance (g) remained unaltered or was even higher in plants with decreased Rubisco, despite the lower rate of CO2 assimilation. As a consequence, water use efficiency declined. The decreased rate of photosynthesis was not accompanied by a stoichiometric decrease in apparent growth rate. These results are discussed in relation to earlier studies of the plant set in growth cabinets. It is concluded that tobacco can adjust over a wide range of growth conditions to avoid a onesided limitation by Rubisco, but that in extreme environmental conditions this capacity to adapt is exhausted.
The pH‐dependent yield threshold of the cell wall in a glycerinated hollow cylinder (in vitro system) of cowpea hypocotyl
Authors: OKAMOTO H. , OKAMOTO A.
Published: April 2006

In order to determine whether the pH‐dependent yield threshold of the cell wall still exists in an in vitro system, an extensometer was devised to enable the perfusion of any experimental solution through the hollow cylinder of a hypocotyl segment excised from a cowpea seedling. Stress‐strain experiments on glycerinated hollow cylinders revealed the existence of a definite yield threshold (y) of the cell wall in this in vitro system. The y value decreased reversibly with acidification (pH 4) to the same extent as the decrease of the yield threshold obtained in vivo (Y) with auxin‐induced growth acceleration of hypocotyl segments. Heat treatment of the glycerinated hollow cylinder completely inhibited the decrease in y with acidification. The increase in the extensibility of the cell wall with acidification was inhibited significantly but not completely by heat treatment. These results support strongly the ‘acid growth’ theory and provide evidence that the acid‐induced decrement of the yield threshold is mediated by an enzymatic reaction of a wall‐binding protein. The combination of in vitro and in vivo studies presented here provides a basis for the establishment of a molecular theory on the nature of the growth parameters Y and Ф which control the yielding of the cell wall.
Root xylem transport of amino acids in the root hemiparasitic shrub Olax phyllanthi (Labill) R.Br. (Olacaceaea) and its multiple hosts
Authors: PATE J. S. , WOODALL G. , JESCHKE W. D. , STEWART G. R.
Published: April 2006

The amino acid compositions of the root xylem saps of Olax phyllanthi and a range of its common hosts were examined in native coastal heath in Western Australia and in pot cultures of Olax reliant on single hosts. When hosts specializing in the xylem transport of one major solute (asparagine, glutamine, histidine, arginine or proline) were exploited, the endophytic tissue of haustoria and the xylem sap of Olax showed much lower proportions of this than of other solutes, suggesting pronounced metabolic transformation prior to xylem loading by the parasite. However, the xylem sap of Olax did partly reflect the compositions of its hosts; for example, djenkolic acid and pipecolic acid were present when Olax was parasitic on species of Acacia, and levels of citrulline and aspartic acid were higher than normal when it exploited hosts transporting large amounts of these compounds. Back‐flow of S‐ethenyl cysteine, a novel amino acid specific to Olax, was observed to another root hemiparasite (Exocarpos sparteus) in native habitat and to certain non‐parasitic hosts in water‐stressed pot cultures. Haustoria exhibited high levels of glutamine synthetase but showed appreciable in vivo nitrate reductase activity only when on hosts with high xylem levels of nitrate.