bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sensitivity to ethylene: the key factor in submergence‐induced shoot elongation of Rumex
Authors: BANGA M. , BLOM C.W.P.M. , VOESENEK L.A.C.J. 
Published: April 2006

ABSTRACTRosettes of flooding‐resistant Rumex palustris plants show a submergence‐induced stimulation of elongation, which is confined to the petioles of young leaves. This response increases the probability of survival. It is induced by ethylene that accumulates in submerged tissues. Flooding‐intolerant Rumex acetosella plants do not show this response. We investigated whether differences in shoot elongation between the species, between old and young leaves and between the petiole and leaf blade of a R. palustris plant result from differences in internal ethylene concentration or in sensitivity to the gas. Concentrations of free and conjugated ACC in petioles and leaf blades of R. palustris indicated that ethylene is synthesized throughout the submerged shoot, although production rates varied locally. Nevertheless, no differences in ethylene concentration were found between submerged leaves of various ages. In contrast, dose‐response curves showed that only elongation of young petioles of R. palustris was sensitive to ethylene. In R. acetosella, elongation of all leaves was insensitive to ethylene. We conclude that variation in ethylene sensitivity rather than content explains the differences in submergence‐induced shoot elongation between the two Rumex species and between leaves of R. palustris.
Effects of air temperature, photoperiod and leaf age on foliar senescence of western larch (Larix occidentalis Nutt.) in environmentally controlled chambers
Authors: ROSENTHAL S. I. , CAMM E. L. 
Published: April 2006

ABSTRACTWe induced foliar senescence in western larch (Larix occidentalis Nutt.) needles (100 to 400 d old) in chambers set to combinations of photoperiod (8 or 16 h) and air temperature (8 or 15°C). We used regression analysis to estimate the effects of air temperature, photoperiod, provenance and leaf age on the date of decline in chlorophyll, photosynthesis, and chlorophyll a/b ratio. Increased air temperature delayed the decline in chlorophyll and photosynthesis without affecting chlorophyll a/b: seedlings with 200‐d‐old needles placed under 8h days and 8°C lost chlorophyll, photosynthesis and chlorophyll a/b in 22, 37 and 63d, respectively, while those senescing under 15°C lost them in 54, 61 and 63d. Extended photoperiod delayed the decline in chlorophyll but not photosynthesis or chlorophyll a/b ratio: the 200‐d‐old needles placed in 8°C and 16 h photoperiod lost chlorophyll, photosynthesis, and chlorophyll a/b in 34, 37 and 63 d, compared with 22, 37 and 63 d for seedlings in 8 h days. Our analysis shows that it is possible to quantify the extent to which the timing and process of senescence vary with environmental conditions.
Determination of diffusion coefficients of octadecanoic acid in isolated cuticular waxes and their relationship to cuticular water permeabilities
Authors: SCHREIBER L. , RIEDERER M. 
Published: April 2006

ABSTRACTTransport properties of cuticular waxes from 40 different plant species were investigated by measuring desorption rates of 14C‐labelled octadecanoic acid from isolated and subsequently reconstituted wax. Diffusion coefficients (D) of octadecanoic acid in reconstituted waxes, calculated from the slopes of the regression lines fitted to the linearized portions of desorption kinetics, ranged from 1.2 × 10−19 m2 s−1 (Senecio kleinia leaf) to 2.9 × 10−17 m2 s−1 (Malus cf. domestica fruit). Cuticular water permeabilities (cuticular transpiration) measured with intact cuticular membranes isolated from 24 different species varied from 1.7 × 10−11 m s−1 (Vanilla planifolia leaf) up to 2.1 × 10−9 m s−1 (Malus cf. domestica fruit), thus covering a range of more than 2 orders of magnitude. Cuticular water permeabilities were highly correlated with diffusion coefficients of octadecanoic acid in isolated cuticular wax of the same species. It is therefore possible to estimate cuticular barrier properties of stomatous leaf surfaces or of leaves where isolation of the cuticle is impossible by measuring D of octadecanoic acid in isolated waxes of these leaves.
Acclimation of leaf carotenoid composition and ascorbate levels to gradients in the light environment within an Australian rainforest
Authors: LOGAN B. A. , BARKER D. H. , DEMMIG‐ADAMS B. , ADAMS W. W. 
Published: April 2006

ABSTRACTThe influence of the growth photon flux density (PFD) on the size and composition of the carotenoid pool and the size of the reduced ascorbate pool was determined across a light gradient from the forest floor to the canopy and the forest edge of a sub‐tropical rainforest in New South Wales, Australia. Nineteen plant species (most collected from multiple sites) representing a broad taxonomic range consistently possessed larger total carotenoid pools when found growing in more exposed sites. There was a significant positive correlation between β‐carotene content and growth PFD and a significant negative correlation between α‐carotene content and growth PFD. Neoxanthin content exhibited no significant trend while the trend in lutein content varied with mode of expression. The pigments of the xanthophyll cycle (violaxanthin, antheraxanthin and zeaxanthin) exhibited the most pronounced response to growth PFD; they comprised a much greater portion of the total carotenoid pool in high light‐acclimated plants. The pool of reduced ascorbate was also several‐fold greater in high light‐acclimated plants. These acclimatory changes in carotenoid and ascorbate content are consistent with a need for a greater capacity to dissipate excessive absorbed light energy in high light‐acclimated plants.
Hydraulic control of stomatal conductance in Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and alder [Alnus rubra (Bong)] seedlings
Authors: FUCHS E. E. , LIVINGSTON N. J. 
Published: April 2006

ABSTRACTExperiments were conducted on 1‐year‐old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] and 2‐ to 3‐month‐old alder [Alnus rubra (Bong)] seedlings growing in drying soils to determine the relative influence of root and leaf water status on stomatal conductance (gc). The water status of shoots was manipulated independently of that of the roots using a pressure chamber that enclosed the root system. Pressurizing the chamber increases the turgor of cells in the shoot but not in the roots. Seedling shoots were enclosed in a whole‐plant cuvette and transpiration and net photosynthesis rates measured continuously. In both species, stomatal closure in response to soil drying was progressively reversed with increasing pressurization. Responses occurred within minutes of pressurization and measurements almost immediately returned to pre‐pressurization levels when the pressure was released. Even in wet soils there was a significant increase in gc with pressurization. In Douglas fir, the stomatal response to pressurization was the same for seedlings grown in dry soils for up to 120 d as for those subjected to drought stress over 40 to 60 d. The stomatal conductance of both Douglas fir and alder seedlings was less sensitive to root chamber pressure at higher vapour pressure deficits (D), and stomatal closure in response to increasing D from 1.04 to 2.06 kPa was only partially reversed by pressurization. Our results are in contrast to those of other studies on herbaceous species, even though we followed the same experimental approach. They suggest that it is not always appropriate to invoke a ‘feedforward’ model of short‐term stomatal response to soil drying, whereby chemical messengers from the roots bring about stomatal closure.
Plasma membrane fluidity and hydraulic conductance in wheat roots: interactions between root temperature and nitrate or phosphate deprivation
Authors: CARVAJAL M. , COOKE D. T. , CLARKSON D. T. 
Published: April 2006

ABSTRACTThe hypothesis was tested that the negative effect of mineral nutrient deprivation (–N and –P) on the hydraulic conductance (L0) of wheat roots may be relieved by increasing the fluidity of plasma membrane (PM) lipids through elevated temperature. An increase in root temperature from 20 to 30°C increased the sap flow, Jv, from the excised roots of nutrient‐deprived plants for 4 h, with a corresponding increase in L0. In the same period, there was a decline in the flux of osmotically active solutes (Js > to the xylem. As the duration of the period at 30°C increased, it was clear that the differential in L0 between control and nutrient‐deprived roots was maintained, even though Lu was significantly greater than the initial (20 °C) value after 48h. The lipid order parameter, determined by fluorescence polarization of 1, 6 diphenyl‐ 1, 3, 5‐hexatriene (DPH), decreased markedly in two‐phase purified PMs in the first 4 h of treatment at 30°C, but thereafter remained steady. The differential between control and nutrient‐deprived roots was maintained throughout the 48h period. The correlation between lowered L0 in nutrient‐deprived roots and increased PM lipid ordering remained unchanged in conditions where the overall membrane fluidity was increased by elevated temperature.
Genetic and physiological characterization of Flaveria linearis plants having a reduced activity of cytosolic fructose‐1.6‐bisphosphatase
Authors: MICALLEF B. J. , SHARKEY T. D. 
Published: April 2006

ABSTRACTWe investigated the genetic control of cytosolic fructose‐1,6‐bisphosphatase (cytFBPase) activity, and the relationships between sucrose synthesis capacity and photosynthesis, growth, flowering and whole‐plant carbon partitioning in Flaveria linearis Lag. F1; F2, and selfed lines generated from plants with low or high cytFBPase activity were used. CytFBPase activity was controlled by one gene and inherited co‐dominantly, giving three classes of activity (low, intermediate and high). Reversed O2 sensitivity of photosynthesis, which indicates an end‐product limitation on photosynthesis, was controlled by one gene and co‐segregated with low cytFBPase activity. A low activity of cytFBPase decreased the growth rate. A recessive day‐neutral flowering trait in Flaveria linearis did not co‐segregate with cytFBPase activity. Plants with low cytFBPase activity had an increased shoot‐to‐root ratio, and flowering caused an additional shift in carbon partitioning to shoots only in plants with low cytFBPase activity. These data indicate that altering sucrose synthesis can affect photosynthesis and plant growth and development.
Differential effects of Na+, Mg2+, K+, Ca2+ and osmotic stress on the wild type and the NaCl‐tolerant mutants stl1 and stl2 of Ceratopteris richardii
Authors: VOGELIEN D. L. , HICKOK L. G. , WARNE T. R. 
Published: April 2006

ABSTRACTIn order to identify physiological components that contribute to salinity tolerance, we compared the effects of Na+, Mg2+ and K+ salts (NaCl, Na2SO4, MgCl2, MgSO4, KCl and K2SO4), Ca2+ (CaSO4), mannitol and melibiose on the wild type and the single‐gene NaCl‐tolerant mutants stl1 and stl2 of Ceratopteris richardii. Compared with gametophytic growth of the wild type, stl2 showed a low level of tolerance that was restricted to Na+ salts and osmotic stress. stl2 exhibited high tolerance to both Na+ and Mg2+ salts, as well as to osmotic stress. In response to short‐term exposure (3 d) to NaCl, accumulation of K+ and Na+ was similar in the wild type and stl1. In contrast, stl2 accumulated higher levels of K+ and lower levels of Na+. Ca2+ supplementation (1.0 mol m−3) ameliorated growth inhibition by Na+ and Mg2+ stress in wild type and stll, but not in stl2. In addition, under Na+ stress (175 mol m−3) wild‐type, stll and stl2 gametopbytes maintained higher tissue levels of K+ and lower levels of Na+ when supplemented with Ca2+ (1.0 mol m−3). stl2 gametophytes were extremely sensitive to K+ supplementation. Growth of stl2 was greater than or equal to that of the wild type at trace concentrations of K+ but decreased substantially with increasing K+ concentration. Supplementation with K+ from 0 to 1.85 mol m−3 alleviated some of the inhibition by 75 mol m−3 NaCl in the wild type and in stl1. In stl2, growth at 75 mol m−3 NaCl was similar at 0 and 1.85 mol m−3 K+ supplementation. Although K+ supplementation above 1.85 mol m−3 did not alleviate inhibition of growth by Na+ in any genotype, stl2 maintained greater relative tolerance to NaCl at all K+ concentrations tested.
High salinity tolerance in the stl2 mutation of Ceratopteris richardii is associated with enhanced K+ influx and loss
Authors: WARNE T. R. , HICKOK L. G. , KINRAIDE T. B. , VOGELIEN D. L. 
Published: April 2006

ABSTRACTThe roles of K+ uptake and loss in the salinity response of the wild type and the salt‐tolerant mutant stl2 of Ceratopteris richardii were studied by measuring Rb+ influx and loss and the effects of Na+, Mg2+, Ca2+ and K+‐transport inhibitors. In addition, electrophysiological responses were measured for both K+ and Rb+ and for the effects of Na+ and NH4+ on subsequent K+‐induced depolarizations. stl2 had a 26–40% higher uptake rate for Rb+ than the wild type at 0.5–10 mol m−3 RbCl. Similarly, membrane depolarizations induced by both RbCl and KCl were consistently greater in stl2. In the presence of 0–180 mol m−3 NaCl, stl2 maintained a consistently greater Rb+ influx than the wild type. stl2 retained a greater capacity for subsequent KCl‐induced depolarization following exposure to NaCl. Five mol m−3 Mg2+ decreased Rb+ uptake in stl2; however, additional Mg2+ up to 40 mol m−3 did not affect Rb+ uptake further. Ca2+ supplementation resulted in a very minor decrease of Rb+ uptake that was similar in the two genotypes. Tetraethylammonium chloride and CsCl gave similar inhibition of Rb+ uptake in both genotypes, but NH4Cl gave substantially greater inhibition in the wild type than in stl2. NH4Cl resulted in a greater membrane depolarization in the wild type and the capacity for subsequent depolarization by KCl was markedly reduced. stl2 exhibited a higher Independent loss of Rb+ than the wild type, but, in the absence of external K+, loss of Rb+ was equivalent in the two genotypes. Since constitutive K+ contents are nearly identical, we conclude that high K+ influx and loss exact a metabolic cost that is reflected in the inhibition of gametophytic growth. Growth inhibition can be alleviated by reduced supplemental K+ or by treatments that slightly reduce K+ influx, such as moderate concentrations of Na+ or Mg2+. We propose that high throughput of K+ allows maintenance of cytosolic K+ under salt stress and that a high uptake rate for K+ results in a reduced capacity for the entrance and accumulation of alternative cations such as Na+ in the cytosol.
Periodicity in the development of the root system of young rubber trees (Hevea brasiliensisMüell. Arg.): relationship with shoot development
Authors: THALER P. , PAGES L. 
Published: April 2006

ABSTRACTThe growth pattern of the root system of young rubber trees (Hevea brasiliensis) was studied in relation to shoot development over a period of 3 months. Temporal and spatial variations in elongation and branching processes were examined for the different root types, by means of root observation boxes. Shoot growth was typically rhythmic. Root development was periodic and related to leaf expansion. Root elongation was depressed during leaf growth, whereas branching was enhanced. Consequently, highly branched areas with vigorous secondary roots alternated along the taproot with poorly branched areas with shorter roots. Root types were not affected to the same degree by shoot competition: during leaf expansion, taproot growth was just depressed but remained continuous, the emergence and elongation rates of secondary roots were significantly affected and the elongation rates of tertiary roots fell to zero. These results were consistent with the hypothesis that root growth is related to competition for assimilates and to the sink strength of the different root types, whereas root branching appeared to be promoted by leaf development.
Stomatal control by fed or endogenous xylem ABA in sunflower: interpretation of correlations between leaf water potential and stomatal conductance in anisohydric species
Authors: TARDIEU F. , LAFARGE T. , SIMONNEAU Th. 
Published: April 2006

ABSTRACTThe stomatal conductance of several anisohydric plant species, including field‐grown sunflower, frequently correlates with leaf water potential (φ1), suggesting that chemical messages travelling from roots to shoots may not play an important role in stomatal control. We have performed a series of experiments in which evaporative demand, soil water status and ABA origin (endogenous or artificial) were varied in order to analyse stomatal control. Sunflower plants were subjected to a range of soil water potentials under contrasting air vapour pressure deficits (VPD, from 0.5 to 2.5 kPa) in the field, in the glasshouse or in a humid chamber. Sunflower plants were also fed through the xylem with varying concentrations of artificial ABA, in the glasshouse and in the field. Finally, detached leaves were fed directly with varying concentrations of ABA under three contrasting VPDs. A unique relationship between stomatal conductance (gs) and the concentration of ABA in the xylem sap (xylem [ABA]) was observed in all cases. In contrast, the relationship between φ1 and gs varied substantially among experiments. Its slope was positive for droughted plants and negative for ABA‐fed whole plants or detached leaves, and also varied appreciably with air VPD. All observed relationships could be modelled on the basis of the assumption that φ1 had no controlling effect on gs. We conclude that stomatal control depended only on the concentration of ABA in the xylem sap, and that φ1 was controlled by water flux through the plant (itself controlled by stomatal conductance). The possibility is also raised that differences in stomatal ‘strategy’ between isohydric plants (such as maize, where daytime φ1 does not vary appreciably with soil water status) and anisohydric plants (such as sunflower) may be accounted for by the degree of influence of φ1 on stomatal control, for a given level of xylem [ABA]. We propose that statistical relationships between φ1 and gs are only observed when φ1 has no controlling action on stomatal behaviour.
Changes in growth and pigment concentrations with leaf age in pea under modulated UV‐B radiation field treatments
Authors: DAY T. A. , HOWELLS B. W. , RUHLAND C. T. 
Published: April 2006

ABSTRACTWe assessed whether growth of garden pea (Pisum sativum mutant Argenteum) was reduced under ecologically relevant enhancements of ultraviolet‐B radiation (UV‐B, 280–320 nm) by employing modulated field lampbanks which simulated 0, 16 or 24% ozone depiction. In addition, we determined whether enhanced UV‐B altered the concentration and distribution of chlorophyll and UV‐B‐absorbing compounds in leaves, and whether this was dependent on leaf age. There were no significant UV‐B effects on the four whole‐plant parameters we examined (height, above‐ground biomass, total leaflet area or average leaflet area). Of the 12 leaf‐level parameters we examined, UV‐B had a significant effect (P < 0.05) on only one parameter: the ratio of UV‐B‐absorbing compounds to chlorophyll, which was greatest at the highest UV‐B level. Total chlorophyll concentrations tended to be lower under enhanced UV‐B (P= 0.11), while the proportion of UV‐B‐absorbing compounds in the adaxial epidermis tended to be higher (P= 0.11). Total leaf concentrations of UV‐B‐absorbing compounds were unaffected by UV‐B level. Cooler, suboptimal growing conditions during this late summer/early autumn experiment may have masked some potential UV‐B effects. In contrast to the UV‐B effects, we found strong leaf‐age effects on nearly all parameters that we assessed. On an area basis, concentrations of total chlorophyll and UV‐B‐absorbing compounds increased with leaf age, while Chlorophyll a/b) ratios decreased. One of the few parameters unaffected by leaf age was the ratio of UV‐B‐absorbing compounds to total chlorophyll, which remained constant within a given UV‐B treatment. Pea was much less sensitive to enhanced UV‐B than in previous growth‐chamber and greenhouse studies, and in nearly all cases UV‐B treatment effects were overshadowed by leaf‐age effects. In view of the large effect leaf age had on concentrations of UV‐B‐absorbing compounds, as well as their distribution within leaves, researchers may need to consider leaf age in UV‐B experimental designs.
A meta‐analysis of leaf gas exchange and nitrogen in trees grown under elevated carbon dioxide
Authors: CURTIS P. S. 
Published: April 2006

ABSTRACTThe response of trees to rising atmospheric CO2 concentration ([CO2]) is of concern to forest ecologists and global carbon modellers and is the focus of an increasing body of research work. I review studies published up to May 1994, and several unpublished works, which reported at least one of the following: net CO2 assimilation (A), stomatal conductance (gs), leaf dark respiration (Rd) leaf nitrogen or specific leaf area (SLA) in woody plants grown at <400 μmol mol−1 CO2 or at 600–800 μmol mol−1 CO2. The resulting data from 41 species were categorized according to growth conditions (unstressed versus stressed), length of CO2 exposure, pot size and exposure facility [growth chamber (GC), greenhouse (GH), or open‐top chamber (OTC)] and interpreted using meta‐analytic methods. Overall, A showed a large and significant increase at elevated [CO2] but length of CO2 exposure and the exposure facility were important modifiers of this response. Plants exposed for < 50 d had a significantly greater response, and those from GCs had a significantly lower response than plants from longer exposures or from OTC studies. Negative acclimation of A was significant and general among stressed plants, but in unstressed plants was influenced by length of CO2 exposure, the exposure facility and/or pot size. Growth at elevated [CO2] resulted in moderate reductions in gs in unstressed plants, but there was no significant effect of CO2 on gs in stressed plants. Leaf dark respiration (mass or area basis) was reduced strongly by growth at high [CO2] > while leaf N was reduced only when expressed on a mass basis. This review is the first meta‐analysis of elevated CO2 studies and provides statistical confirmation of several general responses of trees to elevated [CO2]. It also highlights important areas of continued uncertainty in our understanding of these responses.