bluuebunny/crossref_metadata_2025_split huggingface dataset:
Osmotic relations of the drought‐tolerant shrub Artemisia tridentata in response to water stress
Authors: EVANS R. D. , BLACK R. A. , LOESCHER W. H. , FELLOWS R. J. 
Published: April 2006

ABSTRACTTurgor maintenance, solute content and recovery from water stress were examined in the drought‐tolerant shrub Artemisia tridentata. Predawn water potentials of shrubs receiving supplemental water remained above −2 MPa throughout summer, while predawn water potentials of untreated shrubs decreased to −5 MPa. Osmotic potentials decreased in conjunction with water potentials maintaining turgor pressures above 0 MPa. The decreases in osmotic potentials were not the result of osmotic adjustment (i.e. solute accumulation). Leaf solute contents decreased during drought, but leaf water volumes decreased more than 75% from spring to summer, thereby passively concentrating solutes within the leaves. The maintenance of positive turgor pressures despite decreases in leaf water volumes is consistent with other studies of species with elastic cell walls. Inorganic ion, organic acid, and carbohydrate contents of leaves declined during drought. The only solutes accumulating in leaves of A. tridentata with water stress were proline and a cyclitol, both considered compatible solutes. Total and osmotic potentials recovered rapidly following rewatering of shrubs; solute contents did not change except for a decrease in proline. Maintaining turgor through the passive concentration of solutes may be advantageous compared to synthesis of new solutes for osmotic adjustment in arid environments.
Absorption of nitrate and ammonium ions by Lolium perenne from flowing solution cultures at low root temperatures
Authors: CLARKSON D. T. , JONES L. H. P. , PURVES J. V. 
Published: April 2006

ABSTRACT Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH4 or NO3 at 10 mmol m−3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze‐dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO3. The specific absorption rate (SAR) of NH+4 was greater at all temperatures than SAR‐NO3. In plants grown with NH+, 3–5% of the total N was recovered as NH+4, whereas in those grown with NO−3 the unassimilated NO−3 rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH+4 lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO−3‐grown plants. Plants grown with NH+4 had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO−3 grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH+4 or NO−3. The additional residual N (protein) in NH+4 grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient.
Non‐destructive analysis of root growth in porous media
Authors: GORDON D. C. , HETTIARATCHI D. R. P. , BENGOUGH A. G. , YOUNG I. M. 
Published: April 2006

ABSTRACTA technique is described for non‐destructive observations and analysis of root growth in granular media, using time‐lapse video in conjunction with a pressure cell. The pressure cell consists of one half of a traditional triaxial cell with a flat clear perspex front allowing growth of the root to be monitored using a video camera. The cell is connected to an external pressure supply, which is used to regulate precisely the confining pressure, and hence, the physical impedance to root growth. Preliminary results of the growth of root axes and the emergence of laterals of peas over a range of physical impedances are presented to illustrate the potential of this technique in studying root growth.
The cyanobacterium Synechococcus R‐2 (Anacystis nidulans, S. leopoliensis) PCC 7942 has a sodium‐dependent chloride transporter
Authors: RITCHIE R. J. 
Published: April 2006

ABSTRACT Synechococcus R‐2 (PCC 7942) actively accumulated Cl− in the light and dark, under control conditions (BG‐11 media: pHo, 7·5; [Na+]o, 18 mol m−3; [Cl−]o, 0·508 molm−3). In BG‐11 medium [Cl−], was 17·2±0·848 mol m−3 (light), electrochemical potential of Cl− (ΔμCl−i,o) =+211±2mV; [Cl−]i= 1·24±0·11 mol m−3(dark), ΔμCl−i,o=+133±4mV. Cl− fluxes, but not permeabilities, were much higher in the light: ϕCl−i,o= 4·01±5·4 nmol m−2 s−1, PCl−i,o= 47±5pm s−1 (light); ϕCl−i,o= 0·395±0·071 nmol m−2 s−1, PCl−i,o= 69±14 pm s−1 (dark). Chloride fluxes are inhibited by acid pHo (pHo 5; ϕCl−i,o= 0·14±0·04 nmol m−2 s−1); optimal at pHo 7·5 and not strongly inhibited by alkaline pHo (pHo 10; ϕCl−1i,o= 1·7±0·14 nmol m−2 s−1). A Cl−in/2H+in coporter could not account for the accumulation of Cl− alkaline pHo. Permeability of Cl− is very low, below 100pm s−1 under all conditions used, and appears to be maximal at pHo 7·5 (50–70 pm s−1) and minimal in acid pHo (20pm s−1). DCCD (dicyclohexyl‐carbodiimide) inhibited ϕCl−i,o in the light about 75% and [Cl−]i fell to 2·2±0·26 (4) mol m−3. Valinomycin had no effect but monensin severely inhibited Cl− uptake ([Cl−]i= 1·02±0·32 mol m−3; ϕCl−i,o= 0·20±0·1 nmol m−2 s−1). Vanadate (200 mmol m−3) accelerated the Cl− flux (ϕCl−i,o= 5·28±0·64 nmol m−2 s−1) but slightly decreased accumulation of Cl− ([Cl−], = 13·9±1·3 mol m−3) in BG‐11 medium but had no significant effect in Na+‐free media. DCMU (dichlorophenyldimethylurea) did not reduce [Cl−], or ϕCl−i,o to that found in the dark ([Cl−]i= 8·41±0·76 mol m−3; ϕCl−i,o= 2·06±0·36 nmol m−2 s−1). Synechococcus also actively accumulated Cl− in Na+‐free media, [Cl−]i was lower but ΔΨi,o hyperpolarized in Na+‐free media and so the ΔμCl−i,o was little changed ([Cl−]i= 7·98±0·698 mol m−3; ΔμCl−i,o=+203±3 mV). Net Cl− uptake was stimulated by Na+; Li+ acted as a partial analogue for Na+. Synechococcus has a Na+ activated Cl− transporter which is probably a primary 2Cl−/ATP pump. The Cl− pump is voltage sensitive. ΔμCl−i,o is directly proportional to ΔΨi,o(P»0·01%): ΔμCl−i,o= ‐1·487 (±0·102) ×ΔΨi,o, r= ‐0·983, n= 31. The ΔμCl−i,o increased (more positive) as the Δμi,o became more negative. The ΔμCl−i,o has no known function, but might provide a driving force for the uptake of micronutrients.
Xylem ABA controls the stomatal conductance of field‐grown maize subjected to soil compaction or soil drying
Authors: TARDIEU F. , ZHANG J. , KATERJI N. , BETHENOD O. , PALMER S. , DAVIES W. J. 
Published: April 2006

ABSTRACTStomatal conductance of individual leaves was measured in a maize field, together with leaf water potential, leaf turgor, xylem ABA concentration and leaf ABA concentration in the same leaves. Stomatal conductance showed a tight relationship with xylem ABA, but not with the current leaf water status or with the concentration of ABA in the bulk leaf. The relationship between stomatal conductance and xylem [ABA] was common for variations in xylem [ABA] linked to the decline with time of the soil water reserve, to simultaneous differences between plants grown on compacted, non‐compacted and irrigated soil, and to plant‐to‐plant variability. Therefore, this relationship is unlikely to be fortuitous or due to synchronous variations. These results suggest that increased concentration of ABA in the xylem sap in response to stress can control the gas exchange of plants under field conditions.
ATP‐driven proton pumping in two species of Chara differing in salt tolerance
Authors: YAO X. , BISSON M. A. , BRZEZICKI L. J. 
Published: April 2006

ABSTRACT Chara corallina is an obligate freshwater alga, while C. buckellii can be grown in salt and freshwater culture. When grown in fresh water, C. buckellii has electrophysiological properties similar to C. corallina, but when cultured in salt water, it has a less negative membrane potential and has a higher conductance. We show in internally perfused, tonoplast‐free cells that the ATP‐dependence of the two species cultured in fresh water is similar, although C. buckellii hyperpolarizes at lower ATP concentrations. We determined the pump parameters in perfused and intact cells. Using both techniques, C. corallina and C. buckellii cultured in fresh water show similar values of Ep, Gp and Ip. However, there is a significant difference between the two techniques: Ep is more negative (–400 to –700 mV) in perfused cells than in intact cells (–220 to –260mV); Gp is lower (0·1–0·2 versus 0·3–0·9 S m−2); and Ip is higher (40–60 versus 10–18 mA m−2). Salt‐cultured C. buckellii was compared with freshwater C. buckellii using intact cells; Gp and Ep were similar, but Ip was much higher in salt‐cultured cells (60 versus 15mA m−2). This higher pump rate is due to the depolarization of the membrane of salt‐cultured algae, which is caused by a higher passive conductance. The significance of the less negative membrane potential and the higher rate of proton pumping is discussed with respect to the banding pattern and salt stress.
Effects of daytime carbon dioxide concentration on dark respiration in rice
Authors: BAKER J. T. , LAUGEL F. , BOOTE K. J. , ALLEN L. H. 
Published: April 2006

ABSTRACTRising atmospheric carbon dioxide concentration ([CO2]) has generated considerable interest in the response of agricultural crops to [CO2]. The objectives of this study were to determine the effects of a wide range of daytime [CO2] on dark respiration of rice (Oryza sativaL. cv. IR‐30). Rice plants were grown season‐long in naturally sunlit plant growth chambers in subambient (160 and 250), ambient (330), or super‐ambient (500, 660 and 900 μmol CO2mol−1air) [CO2] treatments. Canopy dark respiration, expressed on a ground area basis (Rd) increased with increasing [CO2] treatment from 160 to 500 μmol mol−1treatments and was very similar among the superambient treatments. The trends in Rdover time and in response to increasing daytime [CO2] treatment were associated with and similar to trends previously described for photosynthesis. Specific respiration rate (Rdw) decreased with time during the growing season and was higher in the subambient than the ambient and superambient [CO2] treatments. This greater Rdwin the subambient [CO2] treatments was attributed to a higher specific maintenance respiration rate and was associated with higher plant tissue nitrogen concentration.
Interactions of blue light and inorganic carbon supply in the control of light‐saturated photosynthesis in brown algae
Authors: FORSTER R. M. , DRING M. J. 
Published: April 2006

ABSTRACTPhotosynthetic capacities of five species of brown algae in red light were found to be strongly limited by the inorganic carbon supply of natural sea water. Under these conditions, pH 8·2 and dissolved inorganic carbon concentration (DIG) of 2·1 mol m−3, a short pulse of blue light was found to increase the subsequent rate of photosynthesis in saturating red light. The degree of blue light stimulation varied between species, ranging from an increase of over 200% of the original rate in Colpomenia peregrins to only 10% in Dictyota dichotoma. Increasing the DIG concentration of sea water by bicarbonate addition resulted in carbon saturation of photosynthesis in all five species. Blue light stimulation was greatly reduced at these higher DIG concentrations. The response in Laminaria digitata was examined in more detail by manipulation of pH and DIG to produce solutions with different concentrations of dissolved CO2. At a CO2 concentration typical of normal sea water (12·4 mmol m−3), blue light treatment increased photosynthetic rate by approximately 50%. Blue light stimulation was increased to over 150% at CO2 concentrations below that of sea water, whereas at concentrations above that of sea water, the effect was diminished. Therefore, the effect of blue light on photosynthetic capacity appears to involve an increase in the rate of supply of carbon dioxide to the plant.
Carbonate ions appear to neither inhibit nor stimulate use of bicarbonate ions in photosynthesis by Ulva lactuca
Authors: MABERLY S. C. 
Published: April 2006

ABSTRACTRates of photosynthesis by the marine macroalga Ulva lactuca were measured in a factorial experiment at five concentrations of HCO3− and CO32‐ between 0·20 and 1·26 mol m−3, but very low concentrations of CO2. The results demonstrated that HCO3− was available for use, but an analysis of variance showed that CO32‐ had neither an inhibiting nor a stimulating effect on rates of photosynthesis over this concentration range. Over the experiment, pH varied from 8·46 to 10·06 and this also had no significant effect on rates of photosynthesis. The lack of a stimulatory effect of high concentrations of CO32‐ on the rate of photosynthesis at low concentrations of HCO3− was taken as circumstantial evidence for direct uptake of HCO3− rather than proton extrusion and external production of CO2. In the rockpools in which U. lactuca grows, pH values up to 10·35 have been recorded, and for much of the time, CO32‐ was the major form of inorganic carbon available. The apparent lack of an ability to use CO32‐ under these conditions suggests that direct use of CO32‐ as a source of inorganic carbon for photosynthesis is unlikely to be widespread.
Intercellular communication in Chara: factors affecting transnodal electrical resistance and solute fluxes
Authors: REID R. J. , OVERALL R. L. 
Published: April 2006

ABSTRACTThe permeability of plasmodesmata in the nodal complex of branch cells of Chara corallina was examined by measuring both the transnodal electrical resistance and transnodal fluxes of 36CI and 14C‐buty‐rate. Under normal circumstances, the resistance across the node was low, but increased rapidly in response to metabolic inhibition, pressure gradients across the node or excision of one of the cells. For each of these treatments, there was a substantial reduction in solute transport between the cells. Acidification of the cytoplasm by weak acids or alkalinization by amines did not affect either the electrical resistance or the flux of solutes through the node between whorl cells. The transnodal resistance was significantly higher in older cell pairs, but was unaffected by large transnodal voltage differences or by the passage of action potentials. There was no evidence that short‐term increases in cytoplasmic calcium have any effect on plasmodesmatal permeability.
Stomatal response to drying soil in relation to changes in the xylem sap composition of Helianthus annuus. I. The concentration of cations, anions, amino acids in, and pH of, the xylem sap
Authors: GOLLAN T. , SCHURR U. , SCHULZE E.‐D. 
Published: April 2006

ABSTRACTSunflower plants (Helianthus annuus L.) were subjected to soil drying with their shoots either kept fully turgid using a Passioura‐type pressure chamber or allowed to decrease in water potential. Whether the shoots were kept turgid or not, leaf conductance decreased below a certain soil water content. During the soil drying, xylem sap samples were taken from individual intact and transpiring plants. Xylem sap concentrations of nitrate and phosphate decreased with soil water content, whereas the concentrations of the other anions (SO42 and Cl−) remained unaltered. Calcium concentrations also decreased. Potassium, magnesium, manganese and sodium concentrations stayed constant during soil drying. In contrast, the pH, the buffering capacity at a pH below 5 and the cation/anion ratio increased after soil water content was lowered below a certain threshold. Amino acid concentration of the xylem sap increased with decreasing soil water content. The effect of changes in ion concentrations in the xylem sap on leaf conductance is discussed.
Stomatal response to drying soil in relation to changes in the xylem sap composition of Helianthus annuus. II. Stomatal sensitivity to abscisic acid imported from the xylem sap
Authors: SCHURR U. , GOLLAN T. , SCHULZE E.‐D. 
Published: April 2006

ABSTRACTSunflower plants [Helianthus annuus L.) were subjected to soil drought. Leaf conductance declined with soil water content even when the shoot was kept turgid throughout the drying period. The concentration of abscisic acid in the xylem sap increased with decreasing soil water content. No general relation could be established between abscisic acid concentration in the xylem sap and leaf conductance due to marked differences in the sensitivity of leaf conductance of individual plants to abscisic acid from the xylem sap. The combination of these results with data from Gollan, Schurr & Schulze (1992, see pp. 551–559, this issue) reveals close connection of the effectiveness of abscisic acid as a root to shoot signal to the nutritional status of the plant.
The relationship between vascular differentiation and the distribution of ice within Forsythia flower buds
Authors: ASHWORTH E. N. , WILLARD T. J. , MALONE S. R. 
Published: April 2006

ABSTRACTThe relationship between vascular development and the distribution of ice within overwintering forsythia flower buds was examined. Previous experiments demonstrated that ice formed in dormant buds within the bud scales, sepals, and in the peduncle and lower portions of the developing flower. The current study demonstrated that these tissues contained columns of primary xylem forming a continuous network with the subtending stem tissues. The vascular traces within the developing petals, anther filaments and pistil were not fully differentiated. Xylem vessels were not present and only procambial cells were observed. Large ice crystals did not accumulate in these tissues. When vascular development resumed in the spring, coincident changes in the distribution of ice within buds were noted. Observations were consistent with the hypothesis that ice propagates into buds via the vascular system, and that the segregation of ice within bud tissues reflects the distribution of xylem.
Photoadaptation, photoinhibition and productivity in the blue‐green alga, Spirulina platensis grown outdoors
Authors: VONSHAK A. , GUY R. 
Published: April 2006

ABSTRACTTwo Spirulina platensis strains, SP‐G and SP‐RB, resistant and sensitive to photoinhibition of photosynthesis, respectively, were grown outdoors in dense cultures and under different photon fluxes provided by shading. Cultures of both strains grown under full sunlight were more resistant to photoinhibition than those grown under nets with 15–50% decreases in the incident photon flux. Cultures grown outdoors were more resistant to photoinhibition than the laboratory ones. At noon, the photosynthetic activity, as expressed by O2 evolution, was higher for cultures grown under 50% shade, as compared with unshaded cultures. Productivity of the shaded cultures, in terms of biomass produced per day, was always higher when the cultures were protected from photoinhibition.
Variations in the natural abundance of oxygen‐18 and deuterium in plant carbohydrates
Authors: YAKIR D. 
Published: April 2006

ABSTRACTVariations in the natural abundance of 18O and 2H in plant cellulose are influenced by the isotopic composition of the water directly involved in metabolism—the metabolic water fraction. The isotopic distinction between the metabolic source water and total tissue water must reflect the formation of isotopic gradients within the tissue that are influenced by the rate of water turnover, by properties of the water conducting system and by environmental conditions. It seems that the 18O abundance in the metabolic water is conserved in cellulose with a relatively constant isotope effect. The relationship of the 2H abundance between metabolic water and cellulose is more complex. Hydrogen incorporated into photosynthetic products during primary reduction steps is highly depleted in 2H. However, a large proportion of these hydrogens are subsequently replaced by exchange with water, leading to 2H enrichment during heterotrophic metabolism. Deciphering the oxygen isotope ratio of cellulose could help in providing insights into the carbon and oxygen fluxes exchanged between plants and the atmosphere. This is because the 18O abundance in cellulose records the 18O abundance in the metabolic water, which in turn, controls the oxygen isotopic signatures of the CO2 and O2 released by plants into the atmosphere. The hydrogen isotope effects associated with carbohydrate metabolism provide insights into the autotrophic state of a plant tissue. This is because the hydrogen isotope ratio of carbohydrates must reflect the net effects of the two opposing isotope effects associated with photosynthesis and heterotrophic metabolism.
Present and potential uses of the natural abundance of stable isotopes in plant science, with illustrations from the marine environment
Authors: RAVEN J. A. 
Published: April 2006

ABSTRACTThe use of stable isotope natural abundance measurements in plant ecophysiological research is discussed in the context of studies of 13C/12C ratios in marine plants, with emphasis on the uniqueness of the information given by natural abundance measurements and of the importance of complementary data obtained by other techniques in making full use of the natural abundance data. (1) Inorganic C acquisition and assimilation in marine plants can involve diffusive entry of CO2, or the occurrence of a CO2‐concentrating mechanism frequently involving active HCO3− influx. For diffusive CO2 entry, the δ13C measurements can give unique information on the fractional limitation of photosynthesis by CO2 transport which, with photosynthetic rate measurements, can be used to compute transport conductances. For active HCO3−, influx, the δ13C values uniquely permit computation of the ratio of the bidirection fluxes (influx/efflux) which, with photon yield data, can be used to given information on the mechanism of the efflux. The analyses are absolutely dependent on external (non‐δ13C) data distinguishing between diffusive CO2 entry and the occurrence of a CO2 concentrating mechanism. (2) δ13C measurements on marine photolithotrophs and on members of other trophic levels collected from the sea can give unique data on food webs, with measurements of δ values for other isotopes and compositional data adding precision to the interpretations. (3) Measurements of in situδ13C values for extant marine photolithotrophs, compared with δ13C values for ancient atmospheric CO2, can give unique information on the mechanism of atmospheric CO2 draw‐down at the start of glacials; other information permits more concrete conclusions to be drawn.