bluuebunny/crossref_metadata_2025_split huggingface dataset:
Circadian rhythms and the induction of flowering in the long‐day grass Lolium temulentum L.
Authors: PÉRILLEUX C. , BERNIER G. , KINET J.‐M. 
Published: April 2006

ABSTRACTPlants of Lolium temulentum L. strain Ceres were grown in 8‐h short day (SD) for 45 d before being exposed either to a single long day (LD) or to a single 8‐h SD given during an extended dark period. For LD induction, the critical photoperiod was between 12 and 14 h, and more than 16 h were needed for a maximal flowering response. During exposure to a single 24‐h LD, the translocation of the floral stimulus began between the fourteenth and the sixteenth hours after the start of the light period, and was completed by the twenty‐fourth hour. Full flowering was also induced by one 8‐h SD beginning 4 or 28 h after the start of a 40‐h dark period, i.e. by shifting 12 h forward or beyond the usual SD. The effectiveness of a so‐called ‘displaced short day’ (DSD) was not affected by light quality and light intensity. With a mixture of incandescent and fluorescent lights at a total photosynthetic photon flux density of 400 μmol m−2 s−1, a 4‐h light exposure beginning 4 h after the start of a 40‐h dark period was sufficient to induce 100% flowering. The flower‐inducing effect of a single 8‐h DSD was also assessed during a 64‐h dark period. Results revealed two maxima at a 20‐h interval. This fluctuation in light sensitivity suggests that a circadian rhythm is involved in the control of flowering of L. temulentum.
Chloroplast ultrastructure changes in Pisum sativum associated with supplementary ultraviolet (UV‐B) radiation
Authors: HE J. , HUANG L.‐K. , WHITECROSS M.I. 
Published: April 2006

ABSTRACTPea plants (Pisum sativum L. cv. Greenfeast) were grown and exposed to supplementary UV‐B radiation from day 17 after planting under growth cabinet conditions. The effects of this exposure on the ultrastructure of chloroplasts and the total soluble sugar and starch concentrations were estimated. Supplementary UV‐B radiation was shown to damage the structure of chloroplasts, as manifested by dilation of thylakoid membranes, a progressive disruption of the thylakoid structure and disintegration of the double membrane envelope surrounding the chloroplast, accompanied by the accumulation of large starch grains. Diurnal changes observed in starch concentration suggest that the higher concentration of starch in supplementary UV‐B‐treated leaves is due to its immobilization, rather than to any increase in starch synthesis: soluble sugars accumulated and remained at a higher level and then later declined.
Plant defence systems induced by ozone
Authors: KANGASJÄRVI J. , TALVINEN J. , UTRIAINEN M. , KARJALAINEN R. 
Published: April 2006

ABSTRACTRecent advances in the understanding of the molecular basis of plant response to ozone attack are reviewed. Plants grown in elevated atmospheric ozone are known to undergo several biochemical changes before any actual damage can be detected. These reactions include increases in the activities of enzymes associated with general plant defence mechanisms. Ozone exposure often causes a surge in the production of the plant hormone ethylene, as well as changes in polyamine metabolism and increases in the activities of several phenylpropanoid and flavonoid pathway enzymes. The activities of superoxide dismutase and peroxidases that protect cells from the oxidative damage caused by hydroxyl radicals, H2O2 and superoxides also increase. However, ozone‐induced changes in plant cells at the gene level are almost unknown. The limited data available suggest close similarities between ozone‐induced and pathogen‐induced defence responses in plants. Several general defence genes that have been cloned in other studies will soon be applied to studies of gene expression in ozone‐exposed plants. The use of molecular biological tools in ozone research should enable the development of highly specific and sensitive molecular markers for biomonitoring ozone‐induced injuries in plants.
Within‐season variability in mycorrhizal benefit to reproduction in Abutilon theophrasti Medic.
Authors: SHUMWAY D. L. , KOIDE R. T. 
Published: April 2006

ABSTRACTMycorrhizal infection of Abutilon theophrasti Medic, increased seed quality and resultant offspring performance, but the improvement varied significantly with the timing of seed production. In general, offspring from mycorrhizal plants were superior to offspring from non‐mycorrhizal plants, but the difference was greatest for the early cohort of seeds. Because increased seed size and quality can affect subsequent offspring competitive ability, increased variability in seed size and quality due to mycorrhizal infection may have an important impact on population dynamics of A. theophrasti.
An osmotic hypothesis for the regulation of oxygen permeability in soybean nodules
Authors: PURCELL L. C. , SINCLAIR T. R. 
Published: April 2006

ABSTRACTNodule permeability (P) controls the amount of O2 entering the nodule, and thereby the rates of both nodule respiration and N2 fixation. P may be regulated by changes in the effective thickness of a water‐filled diffusion barrier in the nodule cortex. Regulation of diffusion barrier thickness was hypothesized to result from changes in the water content of intercellular spaces. Modulation of intercellular water would be a response to osmotic potential gradients in the tissue. To test this hypothesis, preliminary experiments examined three classes of solutes (soluble sugars, free amino acids, and ureides) in nodules of intact plants exposed to 10 or 21 kPa O2 for 24 h. Neither soluble sugars nor free amino acids in nodules were responsive to O2 treatments. However, nodule ureides accumulated after exposure to 10kPa O2 for 24 h. A symplastic increase in nodule ureides under the 10kPa O2 treatment compared to the 21 kPa O2 treatment may have removed water from intercellular spaces in the nodule cortex and increased P. In addition, the nodule cortex of intact plants was infiltrated with water, polyethylene glycol (PEG), KC1, or Na‐succinate solutions to determine the effect of intercellular water and osmoticants on dinitrogenase activity and P. Results from infiltrating the apoplast of the nodule cortex with osmotic solutions indicated that both increases in intercellular water and decreases in the apoplastic water potential decrease dinitrogenase activity and P. Furthermore, the inability to recover dinitrogenase activity and P following the infiltration of the cortex with PEG compared to either KCl or Na‐succinate treatments may indicate that recovery was dependent upon removal of the solute from the apoplast.
Abscisic acid in apoplastic sap can account for the restriction in leaf conductance of white lupins during moderate soil drying and after rewatering
Authors: CORREIA M. J. , PEREIRA J. S. 
Published: April 2006

ABSTRACTWe studied the effects of drought on leaf conductance (g) and on the concentration of abscisic acid (ABA) in the apoplastic sap of Lupinus albus L. leaves. Withholding watering for 5d resulted in complete stomatal closure and in severe leaf water deficit. Leaf water potential fully recovered immediately after rewatering, but the aftereffect of drought on stomata persisted for 2d. ABA and sucrose were quantified in pressurized leaf xylem extrudates. We assumed that the xylem sucrose concentration is negligible and hence that the presence of sucrose in leaf extrudates indicated that they were contaminated by phloem. To eliminate this interference, the concentration of ABA in leaf apoplast was estimated by extrapolation to zero sucrose concentration, using the regression between ABA and sucrose concentrations. The estimated apoplastic ABA concentration increased by 100‐fold with soil drying and did not return to pre‐stress values immediately following rewatering. g was closely related to the concentration of ABA in leaf apoplast. Furthermore, the feeding of exogenous ABA to leaves detached from well‐watered plants brought about the same degree of depression in g as resulted from the drought‐induced increase in ABA concentration. We therefore conclude that the observed changes in the concentration of ABA in leaf apoplast were quantitatively adequate to explain drought‐induced stomatal closure and the delay in stomatal reopening following rewatering.
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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTIn 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

ABSTRACTIrradiation 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

ABSTRACTLocalized 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTWe 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

ABSTRACTA 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

ABSTRACTWhen 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.