bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultraviolet‐B‐induced DNA lesions and their removal in wheat (Triticum aestivum L.) leaves
Authors: TAYLOR R. M. , NIKAIDO O. , JORDAN B. R. , ROSAMOND J. , BRAY C. M. , TOBIN A. K. 
Published: April 2006

ABSTRACTMonoclonal antibodies were used in an enzyme‐linked immunosorbent assay (ELISA) to detect the induction and removal of cyclobutane pyrimidine dimers (CPDs) and (6‐4) photoproducts in DNA isolated from ultraviolet B (UV‐B)‐exposed primary wheat (Triticum aestivum L. cv. Chinese Spring) leaf tissue. The accumulation of lesions in the primary leaves of 6‐d‐old wheat seedlings was followed during the exposure of the leaf to an approximate dose of 3.6×10−1 W m−2 UV‐B (Caldwell weighting). Significant increases in the levels of both CPDs and (6‐4) photoproducts were detected in wheat leaves exposed to UV‐B in the absence of other light However, only an increase in (6‐4) photoproduct levels could be measured in wheat leaves exposed to the same UV‐B source in the presence of supplemental white light. The removal of CPD antibody binding sites in the DNA after irradiation was rapid under conditions of high light intensity in contrast to the removal of (6‐4) photoproduct antibody binding sites, which was significantly slower. The removal of CPDs appeared to be light dependent, this rate of removal decreasing with decreasing light fluences. The removal of (6‐4) photoproducts also appeared light dependent, but to a lesser extent than the removal of CPDs, under the conditions studied here. Gene expression in the primary wheat leaf was measured and showed an up‐regulation of chalcone synthase expression and a reduction in expression of chlorophyll a/b‐binding protein (cab) in response to supplementary UV‐B. No effect was seen on the expression of the other photosynthetic genes studied (the genes coding for the enzymes sedoheptu‐lose 1,7‐bisphosphatase and fructose 1,6‐bisphosphatase). Measurement of the levels of DNA lesions in this same tissue showed that the observed changes in gene expression accompanied the appearance of UV‐B induced lesions in the form of (6‐4) photoproducts in the wheat leaf genome.
Leaf gas exchange and carbon isotope composition responses to drought in a drought‐avoiding (Pinus pinaster) and a drought‐tolerant (Quercus petraea) species under present and elevated atmospheric CO2 concentrations
Authors: PICON C. , GUEHL J. M. , FERHI A. 
Published: April 2006

ABSTRACTThe responses of predawn leaf water potential (φwp), leaf conductance to water vapour diffusion (g), CO2 assimilation rate (A) and carbon isotope competition (δ13C) to a soil drying cycle were assessed in Pinus pinaster, a drought‐avoiding species with high stomatal sensitivity to drought, and Quercus petraea, a drought‐tolerant species with lower stomatal sensitivity to drought, under present (350 μmol−1) and elevated (700 μmol−1) atmospheric CO2 concentrations ([CO2]). In P. pinaster, decreasing A in response to drought was associated with increasing plant intrinsic water use efficiency (A/g) and with decreasing calculated intercellular [CO2] (C1), suggesting a stomatal limitation of A. In contrast, in Q. petraea, A/g declined and C1 increased during the drying cycle, which suggests a non‐stomatal origin for the decrease in A. In P. pinaster, a negative relationship was observed between the gas exchange‐derived values of Ci/Ca and δ13C, which conforms to the classical two‐step carbon isotope discrimination model. In Q. petraea, the relationship between C1/Ca and δ13C was positive. Possible causes of this discrepancy are discussed. Lower g values were observed under elevated [CO2] than under present [CO2] in Q. petraea, whereas g was unaffected in P. pinaster. A stimulation of A by elevated [CO2] was found in P. pinaster but not in Q. petraea. In both species, A/g was markedly higher under elevated than under present [CO2]. Whether the differences in the g response to elevated [CO2] found here can be generalized to other drought‐avoiding and non‐avoiding species remains to be assessed.
Differential effects of turgor on sucrose and potassium transport at the tonoplast and plasma membrane of sugar beet storage root tissue
Authors: BELL C. I. , LEIGH R. A. 
Published: April 2006

ABSTRACTWhen turgor was increased, by decreasing the concentration of mannitol bathing discs of sugar beet storage root tissue, the rates of sucrose and potassium uptake into the vacuole were decreased. At all external mannitol concentrations the rate of sucrose and potassium uptake across the plasma membrane was an order of magnitude greater than the rate of quasi‐steady uptake into the vacuole, implying a very large efflux. Efflux of both sucrose and potassium was increased at high turgor. However, while increasing turgor decreased the rate of K+ uptake, the rate of sucrose uptake at the plasma membrane increased with time. Compartmental analysis of tracer exchange kinetics was used to determine unidirectional K+ fluxes. From these results, it was estimated that the increase in K+ efflux accompanying a 1.5 MPa increase in turgor could lead to a net increase of 140mol−3h−1 in the external potassium concentration. It is suggested that the turgor‐imposed increase in solute efflux is a means of regulating intracellular osmotic pressure and/or turgor in sugar beet storage roots, but that sucrose is preferentially retrieved from the apoplast, even under conditions of excessively high turgor. However, much of this sucrose is probably lost from the cell, implying a ‘futile’ sucrose transport cycle at the plasma membrane. The turgor‐stimulated leak of potassium could play a major role in the regulation of turgor pressure in sugar beet storage root tissue.
The effects of long‐term elevation of air temperature and CO on the frost hardiness of Scots pine
Authors: REPO T. , HÄNNINEN H. , KELLOMÄKI S. 
Published: April 2006

ABSTRACTThe frost hardiness of 20 to 25‐year‐old Scots pine (Pinus sylvestris L.) saplings was followed for 2 years in an experiment that attempted to simulate the predicted climatic conditions of the future, i.e. increased atmospheric CO2 concentration and/or elevated air temperature. Frost hardiness was determined by an electrolyte leakage method and visual damage scoring on needles. Elevated temperatures caused needles to harden later and deharden earlier than the controls. In the first year, elevated CO2 enhanced hardening at elevated temperatures, but this effect disappeared the next year. Dehardening was hastened by elevating CO2 in both springs. The frost hardiness was high (<−40 °C), even at elevated temperatures, in midwinter, at which time the electrolyte leakage method underestimated the frost hardiness compared with the visual scoring. In addition to the significant differences between treatments, there was also significant variation between trees in frost hardiness within treatments. These results suggest that the risks of frost damage are marked in the predicted climatic conditions in Finland, and, more specifically, they depend on how the occurrence of the frost episodes changes with respect to climatic warming during the annual cycle, especially in the autumn and spring. We also conclude that the conditions in midwinter are not critical for frost injury to trees in the future.
The effects of elevated temperature on the photosynthetic efficiency of zooxanthellae in hospite from four different species of reef coral: a novel approach
Authors: WARNER M. E. , FITT W. K. , SCHMIDT G. W. 
Published: April 2006

ABSTRACTBleaching of reef corals is a phenomenon linked to temperature stress which involves loss of the symbiotic algae of the coral, which are known as zooxanthellae, and/or loss of algal pigments. The photosynthetic efficiency of zooxanthellae within the corals Montastrea annularis, Agaricia lamarki, Agaricia agaricites and Siderastrea radians was examined by pulse‐amplitude modulation fluorometry (PAM) during exposure to elevated temperatures (30–36°C). Zooxanthellae within M. annularis and A. lamarki were found to be more sensitive to elevated temperature, virtually complete disruption of photosynthesis being noted during exposure to temperatures of 32 and 34°C. The photosynthetic efficiency of zooxanthellae within S. radians and A. agaricites decreased to a lesser extent. Differences in the loss of algal cells on an aerial basis and in the cellular chlorophyll concentration were also found between these species. By combining the non‐invasive PAM technique with whole‐cell fluorescence of freshly isolated zooxanthellae, we have identified fundamental differences in the physiology of the symbionts within different species of coral. Zooxanthellae within M. annularis appear to be more susceptible to heat‐induced damage at or near the reaction centre of Photosystem II, while zooxanthellae living in S. radians remain capable of dissipating excess excitation energy through non‐photochemical pathways, thereby protecting the photosystem from damage during heat exposure.
Light and stage of development influence the expression of desiccation‐induced genes in the resurrection plant Craterostigma plantagineum
Authors: ALAMILLO J. M. , BARTELS D. 
Published: April 2006

ABSTRACT Craterostigma plantagineum is a representative of the resurrection plants, which are able to withstand complete dryness. During the dehydration process, many characteristic transcripts and proteins are induced; these have been isolated by molecular cloning. The expression of most of these gene products can also be triggered by ABA. Five representative desiccation‐related cDNA clones were selected. The effect of light and developmental stage on the expression of the transcripts and corresponding proteins was analysed during dehydration and ABA treatment. Desiccation and ABA treatment in the presence of light induced a marked increase in several of the transcripts, whereas light had the reverse effect on the levels of some proteins (relative to mRNA levels) localized in the chloroplast. Although very young plants have the capacity to resume full physiological activity after dehydration, some of the desiccation‐related gene products are still expressed at low levels.
Studies on the distribution, re‐translocation and homeostasis of inorganic phosphate in barley leaves
Authors: MIMURA T. , SAKANO K. , SHIMMEN T. 
Published: April 2006

ABSTRACTChanges in inorganic phosphate (Pi) concentrations in barley leaves during growth of plants with sufficient or deficient supplies of Pi were studied. Measurements of the Pi distribution from subcellular levels to the leaf tissue level under the same experimental conditions allowed us to analyse the relationship between the Pi homeostasis of various compartments and Pi re‐translocation in the whole plant. Under Pi deficiency, the finding of growth‐dependent changes in the Pi concentrations of whole leaves established that Pi was re‐translocated from the older leaves to the young leaves. Translocation of 32Pi was also confirmed with an ‘imaging plate’ system, which made it possible to follow Pi movement in the same plantlet. To analyse the mechanism of Pi re‐translocation, the Pi distribution amongst various compartments of the leaves was measured. Under Pi deficiency, the cytoplasmic Pi concentration of the first leaf remained constant until 16d after sowing, while vacuolar Pi was completely exhausted after 8 to 10d. Exhaustion of vacuolar Pi in the first leaf coincided with the appearance of the second leaf. The Pi concentration in the apoplast changed similarly to that of the whole leaf. However, the apoplastic Pi concentration was affected to some extent by the vacuolar Pi concentration and the growth of the younger leaf, because the main change in apoplastic Pi concentration coincided with the time of the disappearance of the vacuolar Pi and the appearance of the younger leaf. The Pi concentration in the apoplast was about 0.1 to I molm−3, even in the absence of Pi, which was much higher than that in the usual soil environment (a few mmolin−3). This suggests that the Pi absorbed by root cells is concentrated in the transport process from the root to the leaf apoplast. The content of Pi in the xylem exudate was constant irrespective of growth culture conditions. The root may be functioning as the constant Pi supplier to the above tissues.
Functional and molecular changes in the photosynthetic apparatus during senescence of flag leaves from field‐grown barley plants
Authors: HUMBECK K. , QUAST S. , KRUPINSKA K. 
Published: April 2006

ABSTRACTChanges in the function and composition of the photosynthetic apparatus were analysed during maturation and senescence of barley (Hordeum vulgare L.) flag leaves under field conditions. At about 8 d post‐antbesis. photo‐synthetic capacity, measured as oxygen evolution under light‐saturating conditions, and the D1 protein level started to decrease. At about 14 d post‐anthesis, the pigment content, photosystem II efficiency (Fv/Fm) and levels of cytochrome f and the large subunit of ribulose‐1,5‐bis‐phosphate carboxylase started to decline. The levels of cytochrome b559 and the small subunit of ribulose‐1,5‐bis‐phosphate carboxylase decreased later, at about 22 d post‐anthesis. High levels of the light‐harvesting complex of pliotosyslem II were still detectable at an even later stage of senescence, at 26 d post‐anthesis.There were also differences in the kinetics of the declines in the levels of transcripts coding for components of the photosynthetic apparatus. rbcS mKNA abundance had already decreased when flag leaves reached their final lengths, at about 4 d post‐unthesis, whereas levels of psbA and petC transcripts did not decrease until 16 d post‐anthesis. In contrast, a senescence‐related transcript, pHvS40 (Becker & Apel 1993), accumulated in the flag leaves 14 d post‐anthesis.Several senescence‐related processes which differ in their kinetics are described. The interrelationships among these processes and their regulation are discussed.
A mutant ofArabidopsisthaliana partially resistant to fusicoccin has reduced plasma membrane H+‐ATPase
Authors: DE MICHELIS M. I. , PUGLIARELLO M. C. , RASI‐CALDOGNO F. , SOAVE C. 
Published: April 2006

ABSTRACT5‐2is a mutant ofArabidopsis thalianawhich is partially resistant to fusicoccinin vivo. We have analysed fusicoccin binding and the activity and amount of H+‐ATPase in plasma membrane isolated from mature leaves of the wild type and of mutant5‐2. Fusicoccin binding was similar in plasma membrane from the two genotypes, while H+‐ATPase activity was markedly (c. 50%) lower in plasma membrane from mutant5‐2than in that from the wild type. The H+‐ATPase of mutant5‐2was activated by fusicoccin as much as that of the wild type. In plasma membrane from mutant5‐2, the amount of immunodetectable H+‐ATPase, quantified by densitometry of Western blots, was about half that in the wild type. These results indicate that the major defect of mutant5‐2detectable at the plasma membrane level is a reduction in the amount of H+‐ATPase.
Influence of carbon supply on the circadian rhythmicity of photosynthesis and its stimulation by blue light in Ectocarpus siliculosus: clues to the mechanism of inorganic carbon acquisition in lower brown algae
Authors: SCHMID R. , DRING M. J. 
Published: April 2006

ABSTRACTStimulation or light‐saturated rates of photosynthesis in Ectocarpus siliculosus (Dillwyn) Lyngb. by blue light was eliminated by increasing dissolved inorganic carbon (DIC) or by lowering pH in natural seawater. The amplitude of the circadian rhythm of photosynthesis was also diminished under these conditions, and the pH compensation points in a closed system were higher in the presence of blue light and during the circadian day. These observations suggest that blue light and the circadian clock regulate the activity of a carbon acquisition system in these plants. The inhibitor of external carbonic anhydrase, acetazolamide, reduced overall rates of photosynthesis by only about 30%, but ethoxyzolamide suppressed the circadian rhythm of photosynthesis almost completely and markedly reduced the duration of responses to blue light pulses. Similar patterns were obtained when photosynthesis was measured in strongly limiting DIC concentrations (0–0.5 mol m−3). Since blue light stimulated photosynthesis under these conditions of strong carbon limitation, we suggest that blue light activates the release of CO2 from an internal CO2 store. We propose a metabolic pathway with similarities to that of CAM plants. Non‐photosynthetic fixation leads to the accumulation of a storage metabolite. The circadian clock and blue light control the mobilization of CO2 at the site of decarboxylation of this metabolite. In the presence of continuous blue light the pathway is proposed to cycle and act as a pump for CO2 into the chloroplasts. This hypothesis helps to explain a number of previously reported peculiarities of brown algal photosynthesis.
Influence of carbon supply on the stimulation of light‐saturated photosynthesis by blue light in Laminaria saccharina: implications for the mechanism of carbon acquisition in higher brown algae
Authors: SCHMID R. , MILLS J. A. , DRING M. J. 
Published: April 2006

ABSTRACTIn saturating irradiances of red light, photosynthesis of Laminaria saccharina (L.) Lamouroux was stimulated by low irradiances of continuous blue light only when the supply of dissolved inorganic carbon (DIC) was limiting. The degree of this stimulation was inversely proportional to the logarithm of the concentration of free CO2, whether this was adjusted by varying the total DIC or the pH at a given DIC concentration. The final pH reached in a closed system was higher in blue light than in red light. Both acetazolamide and ethoxyzolamide suppressed the responses to blue light almost completely, but reduced photosynthesis in red light by only 30%. Buffering the pH of the seawater also suppressed the stimulation of photosynthesis by blue light without affecting the photosynthetic rate in red light. The transient stimulation of O2 evolution by a blue light pulse was not accompanied by a corresponding increase in CO2 consumption. These observations could be explained if, in analogy to the mechanism proposed for Ectocarpus (Schmid, Mills & Dring 1996, Plant Cell and Environment 19,373–382, this issue, accompanying paper), photosynthesis was supported by a blue‐light‐activated release of CO2 from an internal store. We suggest that the store is located in the vacuoles of the cortical tissue of the blades. The main photosynthetic tissue, however, is in the overlying meristoderm, and blue‐light‐activated mobilization of the store could stimulate O2 evolution only if periplasmic carbonic anhydrase was available to facilitate CO2 uptake from the cortex.
Interactive effects of mycorrhization and elevated atmospheric CO2 on sulphur nutrition of young pedunculate oak (Quercus robur L.) trees
Authors: SEEGMÜLLER S. , SCHULTE M. , HERSCHBACH C. , RENNENBERG H. 
Published: April 2006

ABSTRACTPedunculate oak (Quercus robur L.) was germinated and grown at ambient CO2 concentration and 650 μmol mol−1 CO2 in the presence and absence of the ectomycorrhizal fungus Laccaria laccata for a total of 22 weeks under nonlimiting nutrient conditions. Sulphate uptake, xylem loading and exudation were analysed in excised roots. Despite a relatively high affinity for sulphate (KM= 1.6 mmol m−3), the rates of sulphate uptake by excised lateral roots of mycorrhizal oak trees were low as compared to herbaceous plants. Rates of sulphate uptake were similar in mycorrhizal and non‐mycorrhizal roots and were not affected by growth of the trees at elevated CO2. However, the total uptake of sulphate per plant was enhanced by elevated CO2 and further enhanced by elevated CO2 and mycorrhization. Sulphate uptake seemed to be closely correlated with biomass accumulation under the conditions applied.The percentage of the sulphate taken up by mycorrhizal oak roots that was loaded into the xylem was an order of magnitude lower than previously observed for herbaceous plants. The rate of xylem loading was enhanced by mycorrhization and, in roots of mycorrhizal trees only, by growth at elevated CO2. On a whole‐plant basis this increase in xylem loading could only partially be explained by the increased growth of the trees. Elevated CO2 and mycorrhization appeared to increase greatly the sulphate supply of the shoot at the level of xylem loading. For all treatments, calculated rates of sulphate exudation were significantly lower than the corresponding rates of xylem loading of sulphate. Radiolabelled sulphate loaded into the xylem therefore seems to be readily diluted by unlabelled sulphate during xylem transport.Allocation of reduced sulphur from oak leaves was studied by flap‐feeding radiolabelled GSH to mature oak leaves. The rate of export of radioactivity from the fed leaves was 4–5 times higher in mycorrhizal oak trees grown at elevated CO2 than in those grown at ambient CO2. Export of radiolabel proceeded almost exclusively in a basipetal direction to the roots. From these experiments it can be concluded that, in mycorrhizal oak trees grown at elevated CO2, the transport of sulphate to the shoot is increased at the level of xylem loading to enable increased sulphate reduction in the leaves. Increased sulphate reduction seems to be required for the enhanced allocation of reduced sulphur to the roots which is observed in trees grown at elevated CO2. These changes in sulphate and reduced sulphur allocation may be a prerequisite for the positive effect of elevated CO2 on growth of oak trees previously observed.
New evidence for large negative xylem pressures and their measurement by the pressure chamber method
Authors: SPERRY J. S. , SALIENDRA N. Z. , POCKMAN W. T. , COCHARD H. , CRUIZIAT P. , DAVIS S. D. , EWERS F. W. , TYREE M. T. 
Published: April 2006

ABSTRACTPressure probe measurements have been interpreted as showing that xylem pressures below c. –0.4 MPa do not exist and that pressure chamber measurements of lower negative pressures are invalid. We present new evidence supporting the pressure chamber technique and the existence of xylem pressures well below –0.4 MPa. We deduced xylem pressures in water‐stressed stem xylem from the following experiment: (1) loss of hydraulic conductivity in hydrated stem xylem (xylem pressure = atmospheric pressure) was induced by forcing compressed air into intact xylem conduits; (2) loss of hydraulic conductivity from cavitation and embolism in dehydrating stems was measured, and (3) the xylem pressure in dehydrated stems was deduced as being equal and opposite to the air pressure causing the same loss of hydraulic conductivity in hydrated stems. Pressures determined in this way are only valid if cavitation was caused by air entering the xylem conduits (air‐seeding). Deduced xylem pressure showed a one‐to‐one correspondence with pressure chamber measurements for 12 species (woody angiosperms and gymnosperms); data extended to c. –10 MPa. The same correspondence was obtained under field conditions in Betula occidentalis Hook., where pressure differences between air‐ and water‐filled conduits were induced by a combination of in situ xylem water pressure and applied positive air pressure. It is difficult to explain these results if xylem pressures were above –0.4 MPa, if the pressure chamber was inaccurate, and if cavitation occurred by some mechanism other than air‐seeding. A probable reason why the pressure probe does not register large negative pressures is that, just as cavitation within the probe limits its calibration to pressures above c. –0.5 MPa, cavitation limits its measurement range in situ.