bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toxicity symptoms caused by high expression of Tet represser in tomato (Lycopersicon esculentum Mill. L.) are alleviated by tetracycline
Authors: CORLETT J. E. , MYATT S. C. , THOMPSON A. J. 
Published: April 2006

ABSTRACTAs a first step towards transferring a tetracycline (Tc)‐inducible gene expression system to tomato, we have transformed tomato plants with the Tn10‐encoded tet repressor gene (tetR). Homozygous transformed plants with high expression of tetR mRNA show a deleterious phenotype, having reduced shoot dry weights and leaf chlorophyll content, an even more marked reduction in root dry weight and leaf size, and altered photosynthetic physiology. It appears that TetR protein exerts its toxicity only when expressed beyond a threshold level and by interacting with a process that is non‐limiting under slow growth conditions. The deleterious phenotype was almost completely reversed by the application of 1 mg dm−3 Tc to plants grown in sand. The possiblity is discussed that TetR causes these symptoms by binding to a specific DNA sequence functioning as a Tet operator.The effect of Tc on growth and physiology in wild‐type plants grown in sand or rockwool is described. Tc at 0.1 mg cm−3 had no effect. Tc at 1 mg dm−3 caused a small reduction in root growth, while 5 and 20 mg dm−3 Tc caused large reductions in growth and photosynthetic parameters.
Wetting of the upper needle surface of Abies grandis: influence of pH, wax chemistry and epiphyllic microflora on contact angles
Authors: SCHREIBER L. 
Published: April 2006

ABSTRACTWetting of the upper needle surface of Abies grandis Lindl. by aqueous solutions of different pH values was investigated. With increasing needle age, contact angles decreased significantly from about 75° on current‐year needles to values lower than 30° on 4‐year‐old needles. On older needles, contact angles were significantly lower, by more than 10°, when aqueous solutions of pH9‐0 were used compared with those of pH3‐0. On the surfaces of older needles, contact angle titrations were carried out, contact angles being measured with aqueous solutions covering a pH range from 3.0 to 11.0. Measured titration curves showed clear inflection points around pH 7.0, indicating the existence of ionizable carboxylie groups in the interface between needle surface and atmosphere. The evidence seems convincing that the pronounced pH dependence of wetting is mainly due to the presence and/or activity of epiphyllic micro‐organisms, whereas the cuticular wax composition of Abies grandis needles does not appear to contribute significantly to this phenomenon. Thus, the results presented here allow the general conclusion that changes of contact angles measured on leaf surfaces may not always be due to changes in the leaf surface chemistry and/or the fine structure of leaf surface waxes, but may also be due to increased amounts of epiphyllic micro‐organisms significantly altering the leaf surface wetting properties.
Phloem transport of abscisic acid in Ricinus communis L. seedlings
Authors: ZHONG W. , HARTUNG W. , KOMOR E. , SCHOBERT C. 
Published: April 2006

ABSTRACTSieve tube sap exuded from the cut hypocotyl of castor bean seedlings (Ricinus communis L.) was found to contain 0.2–0.5 mmol m−3abscisic acid (ABA). The ABA concentration in the sieve tube sap always exceeded that in root pressure exudate under a wide range of water supply. Exudation of sieve tube sap from the cut hypocotyls caused water loss, and this induced ‘water shortage’ in the cotyledons which resulted in the ABA concentration in the cotyledons increasing by 3‐fold and that in the sieve tube sap increasing by up to 50‐fold within 7h. The wounded surface of the cut hypocotyl was not responsible for the ABA increase.Incubation of the cotyledons of endosperm‐free seedlings in various ABA concentrations (up to 100 mmol m−3) increased the ABA concentration in sieve tube sap. The concomitant increase in ABA, both in cotyledons and in sieve tube sap, had no effect on the phloem loading of sucrose, K+ and Mg2+ within the experimental period, i.e. up to 10h.It can be concluded that (i) the phloem is an important transport path for ABA, (ii) water stress at the phloem loading sites elevates phloem‐mobile ABA, which may then serve as a water stress signal for sinks, for example stem and roots (not only for stomata), and (iii) the ABA concentration of cells next to or in the phloem is more important than the average ABA content in the whole cotyledon for determining the ABA concentration in sieve tube sap.
The effects of pH and dissolved inorganic carbon on external carbonic anhydrase activity in Chlorella saccharophila
Authors: WILLIAMS T. G. , COLMAN B. 
Published: April 2006

ABSTRACTExternal carbonic anhydrase (CA) activity in Chlorella saccharophila is suppressed by growth at high dissolved inorganic carbon and at acid pH. External CA activity was shown to be suppressed by growth at pHs below 7.0, with total repression at pH5.0. Growth in the presence of the buffer 3‐[N‐Morpholino]propane‐sulphonic acid (MOPS) between pH 7 and 8 suppressed CA activity. Cells grown at pH8.0 aerated at 6 dm3 h−1 exhibited external CA activity of 5 units mg−1 Chl once the dissolved inorganic carbon (DIC) was reduced to 300 mmol m−3, and this increased to 30 units mg−1 Chl over a period of 3d while the DIC dropped to 30mmol m−3. Cells aerated at 180 dm3 h−1 showed a similar trend in CA activity, although the onset was delayed by 1 d and the DIC did not drop below 300 mmol m−3. Cells grown at pH 7.8 near an air equilibrium DIC of 300 mmol m−3had no detectable external CA activity. It is probable that it is the CO2 supply to the cell, and not total DIC or HCO−3 which controls external CA activity. Cells grown at pH 5.0 had no detectable activity, although they reduced the CO2 concentration to 0.6 mmol m−3. The loss of CA upon transfer of air‐grown cells to 10 mmol mol−1 CO2 took place over 48 h and was light dependent, while the loss upon transfer from alkaline pH to acid pH look place over 12 h and was independent of light. The effects of pH are independent of the response to CO2.
Evidence for a role for L‐proline as a salinity protectant in the cyanobacterium Nostoc muscorum
Authors: SINGH A. K. , CHAKRAVARTHY D. , SINGH T. P. K. , SINGH H. N. 
Published: April 2006

ABSTRACTNostoc muscorum required an active proline oxidase in order to assimilate exogenous proline as a source of fixed nitrogen. A mutant strain (Acr) resistant to growth inhibition by L‐azetidine‐2‐carboxylate (AC) was found to be deficient in proline oxidase activity, and to be a proline overaccumulator. Proline overaccumulation, resulting either from mutational acquisition of the Acr phenotype or from salinity‐inducible uptake of exogenous proline, conferred enhanced salinity tolerance in this cyanobacterium.
Effect of cytokinins supplied via the xylem at multiples of endogenous concentrations on transpiration and senescence in derooted seedlings of oat and wheat
Authors: BADENOCH‐JONES J. , PARKER C.W. , LETHAM D.S. , SINGH S. 
Published: April 2006

ABSTRACTThis study was conducted lo determine whether naturally occurring xylem cytokinins, when supplied to leaves via the xylem at approximately endogenous concentrations, increase transpiration and delay senescence in selected monocot species (oat and wheat). The concentrations of some of the major cytokinins (zeatin, dihydrozeatin, ciszeatin and their ribosides, the O‐glucosides and nucleotides) were determined in the xylem exudate of oat and wheat seedlings by radioimmunoassay. Evidence is presented that the small volume of exudate (4–5 mm3) collected per plant was xylem sap in transit at the time of shoot excision. Using the data on cytokinin levels, the individual bases and ribosides (and a base/riboside mixture), at multiples of concentrations determined in xylem sap, were tested in transpiration and senescence bioassays. The individual O‐glucosides (and mixtures of the O‐glucosides) were similarly tested at (i) multiples of the molar concentrations of the corresponding bases and ribosides, and/or at (ii) multiples of the endogenous concentrations. Similarly, zeatin and dihydrozeatin nucleotides were tested at multiples of the molar concentration of zeatin riboside and, in some instances, at multiples of endogenous concentrations.Our results suggest that, at least in oat and possibly in wheat, zeatin‐type bases, ribosides and O‐glucosides supplied to the leaf in xylem sap are likely to play a role in regulating transpiration in vivo. O‐glucosides in oat xylem sap may be important regulators of leaf senescence in the intact plant. The nucleotides were present in xylem sap at lower concentrations than most of the bases, ribosides and O‐glucosides. The nucleotides appear likely to play a lesser role than the bases, riboside and O‐glucosidcs in controlling transpiration and senescence in the intact plant.
Aphototropic mutants of the moss Ceratodon purpureus with spectrally normal and with spectrally dysfunctional phytochrome
Authors: LAMPARTER T. , ESCH H. , COVE D. , HUGHES J. , HARTMANN E. 
Published: April 2006

ABSTRACTFollowing UV mutagenesis of protonemal tissue of the moss Ceratodon purpureus we have isolated different aphototropic mutant lines that can be divided into two distinct classes. One class, represented by the line ptr1, shows characteristic features of phytochrome chromophore deficiency. ptrl shows negligible photoreversibility (<5% of wild type), whereas immunoblots show normal apoprotein levels. The aphototropic phenotype could be partially restored with biliverdin, a precursor of the phytochrome chromophore. It was found that, whereas in wild type formation of Pfr leads to suppression of gravitropism, there is no such suppression ptrl. In addition, ptr1 shows lower chlorophyll levels than the wild type. These findings indicate that, as expected for a chromophore‐deficient mutant, multiple phytochrome effects are lost. The other class of mutants, represented by the line ptr103, shows more specific effects. In this mutant, only phototropism is affected. Suppression of gravitropism, the content of chlorophyll and photoreversibility of phytochrome were similar to those of the wild type.
Short‐term regulation of cytosolic Ca2+, cytosolic pH and vacuolar pH under NaCl stress in the charophyte alga Nitellopsis obtusa
Authors: OKAZAKI Y. , KIKUYAMA M. , HIRAMOTO Y. , IWASAKI N. 
Published: April 2006

ABSTRACTIsolated characean internodal cells of Nitellopsis obtusa can be stored in artificial pond water for many days, but they cannot survive in 100mol m−3 NaCl solution unless more than several mol m−3 Ca2+ is added. Short‐term effects of NaCl stress on the cytosolic concentration of Ca2+ ([Ca2+]c), cytosolic pH (pHc) and vacuolar pH (pHv) were studied in relation to the external concentration of Ca2+ ([Ca2+]e). Changes in [Ca2+]c were measured with light emission from a Ca2+‐sensitive photoprotein, semisynthetic fch‐aequorin which had been injected into the cytosol. Both pHc and pHv were measured with double‐barrelled pH‐sensitive microelectrodes. When internodal cells were treated with 100 mol m−3 NaCl (0–1 mol m−3 NaCl (0.1 mol m−3 [Ca2+]e), [Ca2+]c increased and then recovered to the original level within 60 min. The time course of the transient change in [Ca2+]c was not influenced by the level of [Ca2+]c (0.1 and 10 mol m−3). In some cases, the transient increase in [Ca2+]c was induced only by increasing external osmotic pressure with sorbitol. In response to treatment with 100 mol m−3 NaCl (0.1 mol m−3 [Ca2+]c), pHc decreased by 0.1–0.2 units after 10min but recovered after 30–60 min, while pHv increased by 0.4–0.5 units after 2–50 min and tended to recover after 60 min. The initial changes in both pHc and pHv were suppressed when [Ca2+]e was raised from 0.1 to 10mol m−3. These results show that the charophyte alga Nitellopsis can regulate [Ca2+]c, pHc and pHv under NaCl stress in the short term and that the protective effect of Ca2+ on salinity stress is apparently unrelated to perturbation of Ca2+ and pH homeostasis.
Immunogold localization of nodule‐enhanced phosphoenolpyruvate carboxylase in alfalfa
Authors: Robinson D. L. , Pathiran S. M. , Gantt J. S. , Vance C. P. 
Published: April 2006

ABSTRACTPhosphoenolpyruvate carboxylase (PEPC; EC 4‐1‐1‐31) plays a paramount role in providing carbon for synthesis of malate and aspartate in alfalfa (Medicago sativa L.) root nodules. PEPC protein and activity levels are highly enhanced in N2‐fixing alfalfa nodules. To ascertain the relationship between the cellular location of PEPC and root nodule metabolism, enzyme localization was evaluated by immunogold cytochemistry using alfalfa nodule PEPC antibodies. Gold labelling patterns in effective nodules showed that PEPC is a cytosolic enzyme and is distributed relatively equally in infected and uninfected cells of the nodule symbiotic zone. A high amount of labelling was also observed in pericycle cells of the nodule vascular system. Labelling was also detected within inner cortical cells, but the density was reduced by 60%. When Lotus corniculatus was transformed with a chimeric gene consisting of the 5′‐upstream region of the PEPC gene fused to β‐glucuronidase (GUS), GUS staining in nodules was consistent with immunogold localization patterns. The occurrence of PEPC in both infected and uninfected cells of the symbiotic zone of effective nodules coupled to the reduced amounts in ineffective nodules suggests a direct role for this enzyme in supporting N2‐fixation. PEPC localization in the uninfected, interstitial cells of the symbiotic zone indicates that these cells may also have a role in nodule carbon metabolism. Moreover, the association of PEPC with the nodule vascular system implies a role for the enzyme in the transport of assimilates to and from the shoot.
From epiphyte to tree: differences in leaf structure and leaf water relations associated with the transition in growth form in eight species of hemiepiphytes
Authors: HOLBROOK N. M. , Putz F. E. 
Published: April 2006

ABSTRACTStranglers must undergo a transformation in growth form from epiphyte to tree to become reproductive mature and thus require developmental and/or physiological plasticity to cope with radical changes in their rooting environment. Differences in leaf structure and water relations between epiphytic‐phase and free‐standing individuals were marked in the five Ficus species examined. Epiphytic Ficus had several‐fold higher specific leaf area (cm2 g−1) and 2‐ to 4‐fold lower stomatal densities than conspecific trees. Osmotic potentials at full saturation were, on average, 0‐6 MPa higher (less negative) and the bulk modulus of elasticity approximately 50% lower in epiphytic plants than in conspecific trees. This resulted in leaves of epiphytic and tree individuals losing turgor at approximately the same relative water content, hut at a substantially higher leaf water potential in the epiphytic plants. In contrast, differences in leaf structure and water relations between epiphytes and trees of Clusia minor and Coussapoa villosa were small. In greenhouse experiments, alteration of the water and nutrient supply to epiphytic F. tuerckheimmii plants did not lead to significant changes in leaf structure.
Long‐term exposure to elevated [CO2] in a natural Quercus ilex L. community: net photosynthesis and photochemical efficiency of PSII at different levels of water stress
Authors: SCARASCIA‐MUGNOZZA G. , DE ANGELIS P. , MATTEUCCI G. , VALENTINI R. 
Published: April 2006

ABSTRACTNaturally grown trees of Mediterranean evergreen oak (Quercus ilex L.), representing the climax species of the region, were enclosed in six large open‐top chambers and exposed to ambient and elevated CO2 concentrations during a 3 year period. Maximum daily net photosynthetic rates measured at the two different CO2 concentrations were from 30 to 100% higher in elevated than in ambient [CO2] throughout the experimental period. The increase in maximum daily photosynthesis was also accompanied by a 93% rise in the apparent quantum yield of CO2 assimilation, measured during periods of optimum soil moisture conditions. Hence, no clear evidence of down‐regulation of net photosynthetic activity was found. Interactions between atmospheric CO2 concentration and plant water stress were studied by following the natural evolution of drought in different seasons and years. At each level of water stress, the maximum rate of carbon assimilation was higher in elevated than in ambient [CO2] by up to 100%.Analysis of in vivo chlorophyll fluorescence parameters in normal (21%) and low (2%) oxygen concentrations provided useful insights into the functioning and stability of the photosynthetic processes. The photochemical efficiency of PSII (Fv/Fm) progressively decreased as drought conditions became more evident; this trend was accentuated under elevated [CO2]. Thermal de‐excitation processes were possibly more significant under elevated than under ambient [CO2], in a combination of environmental stresses.This research suggests two possible conclusions: (i) a ‘positive’ interaction between elevated [CO2] and carbon metabolism can be obtained through relief of water stress limitation in the summer months, and (ii) elevated [CO2], under drought conditions, may also enhance the significance of slow‐relaxing quenching.
CAM induction in Clusia minor L. during the transition from wet to dry season in Trinidad: the role of organic acid speciation and decarboxylation
Authors: BORLAND A. M. , GRIFFITHS H. , MAXWELL C. , FORDHAM M. C. , BROADMEADOW M. S. J. 
Published: April 2006

ABSTRACTThe interrelationships between the induction of CAM and the turnover of malate and citrate in the dicotyledenous tree Clusia minor were compared with seasonal changes in rainfall, leaf water status, PFD and photoinhibitory responses during the transition from wet to dry season in Trinidad. Over a period of 8 weeks, as rainfall declined from a maximum observed around week 3, leaf xylem tensions measured at dusk and dawn reflected the concurrent reduction in day‐time carbon gain and an increase in the diel turnover of malate (exposed leaves) and citrate (shaded leaves). Clear seasonal trends were observed in the turnover of malate and citrate during the transition from wet to dry season. In contrast to the declining back‐ground concentrations of citrate during the wet‐dry season transition, malate accumulation was markedly enhanced and the ratio of malalc:citrate accumulated overnight increased as the dry season advanced. Photo‐inhibitory responses, assessed by chlorophyll fluorescence, indicated that photochemistry was largely determined by the diurnal course of PFD incident on leaves, regardless of the magnitude of internal CO2 release from malate and citrate decarboxylation. In the long term, photochemical efficiency in both shaded and exposed leaves appeared to decline as the dry season progressed. Although there was a clear linear relationship between integrated PFD and overnight accumulation of malate, no such correlation was found for citrate. However, citrate breakdown during the day showed a much closer correlation with PFD as compared to malate, with levels of citrate measured at dusk declining in response to higher daily light intensities. Moreover, enhanced citrate decarboxylation during the day was strongly correlated with increased CAM and overnight accumulation of both malate and citrate.
Marcescence and senescence in a submediterranean oak (Quercus subpyrenaica E.H. del Villar): photosynthetic characteristics and nutrient composition
Authors: ABADíA A. , GIL E. , MORALES F. , MONTAÑÉS L. , MONTSERRAT G. , ABADÍA J. 
Published: April 2006

ABSTRACTWe have studied some characteristics of marcescent leaves (withered retained leaves) and senescent leaves in Quercus subpyrenaica, a tree species that plays a major role in the climatic transition forests between temperate and mediterranean environments in north‐eastern Spain. Leaves were taken from the upper and lower halves of the tree crown, both in the south‐ and north‐exposed parts of the tree. Leaves receiving low photosynthetic photon flux density (PPFD) undergo autumnal senescence, which is associated with decreases in photosynthetic pigments and decreases in the chlorophyll a to chlorophyll b ratio. Leaves receiving higher PPFD underwent senescence at a later date. Leaves situated in the upper, south‐exposed part of the tree, which receive the highest PPFD, showed no signs of senescence and remained photosynthetically active for a longer period of time, marcescence occurring suddenly at the end of the season. Marcescence is unlikely to cause an improvement in nutrient recycling, since the removal of nutrients proceeded similarly in marcescent and senescent leaves. Marcescence may increase the time‐span of the assimilation capacity for a significant period of time during September and October, when high light intensities and mild temperatures occur. The phenomena triggering marcescence may be related to low temperatures.
Control of sodium influx by calcium and turgor in two charophytes differing in salinity tolerance
Authors: DAVENPORT R. , REID R. J. , SMITH F. A. 
Published: April 2006

ABSTRACTThe effects of Ca2+ and cell turgor on Na+ influx were examined in two charophytes, lamprothamnium papulo‐SUM (salt‐tolerant) and Chara corallina (salt‐sensitive), to try to identify causes of salinity toxicity. Mortality was associated with Na+ influx, with the two species showing similar sensitivities to high Na+ influx. In Lamprothamnium, toxic influxes of Na+ occurred at much higher external Na+ concentrations than in Chara. The differences in Na+ influx at the same Na+ concentration were not due to different responses to external Ca2+. Lamprothamnium adjusts its turgor in response to increasing NaCl whereas Chara cannot. In solutions of KC1 up to at least 200 mol m‐3, however, Chara regulated turgor, and when KC1 was subsequently replaced with NaCl, Na+ influx was low and similar to that in Lamprothamnium at the same Na* concentration. Chara cells which were not turgor‐adjusted in KCI had Na+ influxes 2‐5‐fold higher than the turgid cells. Thus, it appears that turgor is a major determinant of Na+ influx, and therefore of cell survival. We found no evidence that the mechanism of Na+ influx in Chara is different from that in Lamprothamnium. Higher susceptibility of Chara to NaCl seems to result from inability to regulate turgor, in turn leading to toxic Na+ influx.
Carbon isotope fractionation in tree ring early and late wood in relation to intra‐growing season water balance
Authors: LIVINGSTON N. J. , SPITTLEHOUSE D. L. 
Published: April 2006

ABSTRACTWe determined the stable carbon isotope composition (δ1.3C) of cellulose extracted from early and late wood in Douglas fir [Pseudotsuga menziexii (Mirb.) Franco] tree rings. Data were obtained for the period 1962 to 1981, at the start of which the trees were 20 years old. A water balance model was used to calculate daily stand transpiration and water deficit. The model incorporates site factors (soil water availability, slope and aspect) and environmental variables (solar radiation, air temperature and rainfall). There was far greater variability in late wood than in early wood δ1.3C. In wet years, late wood δ1.3C was significantly lighter (by as much as 2δ) than early wood δ1.3C but in dry years this difference was reversed. Differences between spring and summer cumulative transpiration accounted for almost 60δ of the variability in differences between early and late wood δ1.3C. We found excellent correspondence between summer cumulative transpiration and late wood δ1.3C, with estimates of transpiration accounting for up to 93% of the variability in δ1.3C. Correlations between early wood δ1.3C and spring transpiration were generally poor (r2<0.4), but we were able to identify those exceptional years in which there had been a very dry spring. Our results indicate that, while tree ring δ1.3C correlates reasonably well with basal area increment, it is a far better indicator of inter‐ and intra‐annual variability in water availability than radial growth.