bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the potential to measure photosynthetic rates in C3 plants (Flaveria pringlei and Oryza sativa) by combining chlorophyll fluorescence analysis and a stomatal conductance model
Authors: HE D. , EDWARDS G. E.
Published: April 2006

The response curves of leaf photosynthesis to varying light, temperature and leaf‐to‐air vapour pressure deficit were measured in the C3 plants Flaveria pringlei and Oryza sativa in normal air with a computerized open infrared gas analysis (IRGA) system, and the photochemical efficiency of photosystem II, described as (1–F,/F′m) after Genty. Briantais & Baker (1989, Biochimica et Biophysica Acta 990, 87–92), was simultaneously measured with a modulated fluorometer. A model was written for rates of CO2 fixation as a function of the true rate of O2 evolution measured by fluorescene analysis (Jo2), mesophyll conductance and intercellular CO2 partial pressure. A second model was developed for rates of CO2 fixation as a function of Jo2, mesophyll conductance and stomatal conductance. In the latter case, leaf stomatal conductance was simulated using the stomatal model proposed by Leuning (1995, Plant, Cell and Environment18, 339–355). The rates of CO2 fixation predicted from the models were similar to rates measured by IRGA. The results indicate that there is potential to measure CO2 fixation in C3 plants by combining the non‐invasive measurement of Jo2 by chlorophyll fluorescence analysis with the stomatal conductance model.
Osmotic stress and abscisic acid reduce cytosolic calcium activities in roots of Arabidopsis thaliana*
Authors: CRAMER G. R. , JONES R. L.
Published: April 2006

Cytosolic Ca2+· ([Ca2+]i, and elongation growth were measured in the roots of Arabidopsis thaliana. Exposure of plant tissues to high NaCl and abscisic acid (ABA) concentrations results in a reduction in the rate of growth, but the mechanism by which growth is inhibited is not understood. Both NaCl and ABA treatments are known to influence [Ca2+]i, and in this study we measured the effects of salinity and ABA on [Ca2+]i in cells from the meristematic region of Arabidopsis roots. The Ca2+‐sensitive dye Fura‐2 and ratiometric techniques were used to measure [Ca2+]i in cells of the root meristem region. Resting [Ca2+]i was found to be between 100 and 200 μmol m−3 in roots of untreated plants. Resting [Ca2+]i changed in response to changes in the [Ca2+] surrounding growing roots. An increase of external [Ca2+] increased [Ca2+]i; conversely, a decrease of external [Ca2+] decreased [Ca2+]i. Exposure of roots to NaCl caused a rapid reduction of [Ca2+]i, a response that was proportional to the external NaCl concentration. Thus, as the NaCl concentration was increased, [Ca2+]i in root meristematic cells decreased. Root elongation was also inhibited in proportion to the external NaCl concentration, with maximal inhibition occurring at 120 mol m−3 NaCl. The [Ca2+]i of root meristem cells also changed in response to ABA, and the magnitude of the effect of ABA was dependent upon ABA concentration. Treatment with 0.2 mmol m−3 ABA caused a momentary increase in [Ca2+]i followed by a decrease after 15 min, but 10 mmol m−3 ABA caused an immediate decline in [Ca2+]i. There was a strong positive correlation between [Ca2+]i and root elongation rates. Experiments with the ABA‐deficient Arabidopsis mutant aba‐3 indicated that the reduction in [Ca2+]i brought about by NaCl was unlikely to be mediated via changes in endogenous ABA. Experiments with solutes such as sorbitol, KCl and NaNO3 indicated that the effects of NaCl could be mimicked by other solutes and was not specific for NaCl.
Sulphate transport in the cyanobacterium Synechococcus R‐2 (Anacystis nidulans, S. leopoliensis) PCC 7942
Authors: RITCHIE R. J.
Published: April 2006

Synechococcus R‐2 (PCC 1942) actively accumulates sulphate in the light and dark. Intracellular sulphate was 1.35 ± 0.23 mol m−3 (light) and 0.894 ± 0.152 mol m−3 (dark) under control conditions (BG‐11 media: pHo, 7.5; [SO42−]o, 0.304 mol m−3). The sulphate transporter is different from that found in higher plants: it appears to be an ATP‐driven pump transporting one SO42−/ATP [ΔμSO42−i,o=+ 27.7 ± 0.24 kJ mol−1 (light) and + 24 ± 0.34 kj mol−1 (dark)]. The rate of metabolism of SO42−at pHo, 7.5 was 150 ± 28 pmol m−2 s−1 (n = 185) in the light but only 12.8 ± 3.6 pmol m−2 s−1 (n = 61) in the dark. Light‐driven sulphate uptake is partially inhibited by DCMU and chloramphenicol. Sulphate uptake is not linked to potassium, proton, sodium or chloride transport. The alga has a constitutive over‐capacity for sulphate uptake [light (n= 105): Km= 0.3 ± 0.1 mmol m−3, Vmax, = 1.8 ± 0.6 nmol m−2 s−1; dark (n= 56): Km= 1.4 ± 0.4 mmol m−3, Vmax= 41 ± 22 pmol m−2 s−1]. Sulphite (SO32−) was a competitive inhibitor of sulphate uptake. Selenate (SeO42−) was an uncompetitive inhibitor.
Tree ring responses to elevated CO2 and increased N deposition in Picea abies
Authors: HÄTTENSCHWILER S. , SCHWEINGRUBER F. H. , KÖRNER Ch.
Published: April 2006

Four‐ to seven‐year‐old spruce trees (Picea abies) were exposed to three CO2 concentrations (280, 420 and 560 cm3 m−3) and three rates of wet N deposition (0, 30 and 90 kg ha−1 year−1) for 3 years in a simulated montane forest climate. Six trees from each of six clones were grown in competition in each of nine 100 × 70 × 36 cm model ecosystems with nutrient‐poor natural forest soil. Stem dises were analysed using X‐ray densitometry. The radial stem increment was not affected by [CO2] but increased with increasing rates of N deposition. Wood density was increased by [CO2], but decreased by N deposition. Wood‐starch concentration increased, and wood nitrogen concentration decreased with increasing [CO2], but neither was affected by N deposition. The lignin concentration in wood was affected by neither [CO2] nor N deposition. Our results suggest that, under natural growth conditions, rising atmospheric [CO2] will not lead to enhanced radial stem growth of spruce, but atmospheric N deposition will, and in some regions is probably already doing so. Elevated [CO2], however, will lead to denser wood unless this effect is compensated by massive atmospheric N deposition. If can be speculated that greater wood density under elevated [CO2] may alter the mechanical properties of wood, and higher ratios of C/N and lignin/N in wood grown at elevated [CO2] may affect nutrient cycles of forest ecosystems.
Phytochrome is required for the occurrence of time‐dependent phototropism in maize coleoptiles
Authors: LIU Y. J. , IINO M.
Published: April 2006

Time‐dependent phototropism (TDP), sometimes called second positive curvature, occurs when the duration of phototropic stimulation with blue light (B) exceeds a few minutes. TDP was characterized in maize (Zea mays L.) coleoptiles raised under continuous red light (R). Subsequently, coleoptiles adapted to darkness were used to investigate the effect of R on TDP. It was found that TDP, which is induced in R‐grown coleoptiles, does not occur in dark‐adapted coleoptiles and that dark‐adapted coleoptiles begin to show TDP after treatment with R. The TDP responsiveness became maximal 1–2 h after treatment with a R pulse and decreased during the next few hours. At least 10 min was required after a short pulse of R before the coleoptile began to respond to B for the induction of TDP. The effect of R in establishing the TDP responsiveness was totally suppressed by a pulse of far‐red light given immediately after an inductive pulse of R. It is concluded that the mechanism of TDP requires for its establishment a R signal perceived by phytochrome. The TDP of R‐grown and R‐pretreated coleoptiles showed relationships to stimulation times and fluence rates that are similar to those reported for oat coleoptiles, except that TDP of maize showed a sharp increase in its magnitude within a narrow range of stimulation times as short as 5–10 min.
Effects of turgor potentials of epidermal cells neighbouring guard cells on stomatal opening in detached leaf epidermis and intact leaflets of Vicia faba L. (faba bean)
Authors: KLEIN M. , CHENG G. , CHUNG M. , TALLMAN G.
Published: April 2006

Leaflets of Vicia faba L. (faba bean) were used to determine whether the mechanical forces resulting from the turgor potentials (Φp) of the larger epidermal cells neighbouring guard cells play a significant role in regulating stomatal aperture. When Φp, of epidermis and Φp of bulk leaflet tissue were compared at midday, Φp of epidermis were only 15–25% those of bulk leaflet tissue at all but the most negative leaflet water potentials (Φ). When plants were bagged to increase Φ by reducing vapour pressure differences between leaflets and air, Φp of bulk leaflet tissue increased to predawn values, but Φp, of epidermis increased to only = 20% of predawn values and stomata opened to their widest apertures. Stomatal apertures were positively correlated with Φp of bulk leaflet tissue but they were not correlated with Φp of epidermis. Reductions in epidermal Φp, began predawn, before stomata were open, and reached minimum values at midday, when stomata were open. We conclude that, in Vicia faba, (1) reduction of Φp of epidermal cells begins predawn, reducing the counterforce to stomatal opening that would exist if full epidermal turgor were maintained throughout the day, and (2) changes in Φp, of leaf epidermal cells do not play a significant role in regulating stomatal aperture.
Differential proton secretion in the apical elongation zone caused by gravistimulation is induced by a signal from the root cap
Authors: MONSHAUSEN G. B. , ZIESCHANG H. E. , SIEVERS A.
Published: April 2006

The extracellular proton activity along primary roots of Phelcum pratense L. was measured using proton‐selective microelectrodes. Removal of the root cap caused a reduction of the proton influx in the transitional region between the meristem and the apical elongation zone of the vertical root and inhibited the development of pH differences between the physically upper and lower flanks of the gravis‐stimulated root. Disruption of the actin filament system of the root with 5 mmol m−3 cytochalasin D did not result in an altered proton flux and pH pattern compared with untreated vertical control roots, but inhibited the gravity‐induced development of pH differences between the physically upper and lower root flanks as well as gravitropic curvature. These results provide evidence that pH changes following gravistimulation are induced by a signal transmitted from the root cap and that the actin filament system is involved in the gravity perception/transduction mechanism.
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

Rosettes 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

We 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

Transport 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

The 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

Experiments 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

The 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

We 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

In 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

The 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

The 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

The 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

We 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

The 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.
Sap flow in wheat under free‐air CO2 enrichment
Authors: SENOCK R. S. , HAM J. M. , LOUGHIN T. M. , KIMBALL B. A. , HUNSAKER D. J. , PINTER P. J. , WALL G. W. , GARCIA R. L. , LaMORTE R. L.
Published: April 2006

The effects of elevated carbon dioxide (CO2) concentration on plant water use are best evaluated on plants grown under field conditions and with measurement techniques that do not disturb the natural function of the plant. Heat balance sap flow gauges were used on individual main stems of wheat (Triticum aestivum L. cv Yecora rojo) grown under normal ambient conditions (control) and in a free‐air CO2 enrichment (FACE) system in Arizona with either high (control + high H2O = CW; FACE + high H2O = FW) or low (control + low H2O = CD; FACE + low H2O = FD) irrigation regimens. Over a 30d period (stem elongation to anthesis), combinations of treatments were monitored with,10–40 gauges per treatment. The effects of increased CO2 on tiller water use were inconsistent in both the diurnal patterns of sap flow and the statistical analyses of daily sap flow (Ftot). Initial results suggested that the reductions in Ftot, from CO2 enrichment were small (,0–10%) in relation to the H2O treatment effect (,20–30%). For a 3d period, Ftot of FW was,19–26% less than that of CW (P = 0.10). Examination of the different sources of variation in the study revealed that the location of gauges within the experimental plots influenced the variance of the sap flow measurements. This variation was probably related to positional variation in subsurface drip lines used to irrigate plots. A sampling design was proposed for use of sap flow gauges in FACE systems with subsurface irrigation that takes into account the main treatment effects of CO2 enrichment and the other sources of variation identified in this study. Despite the small and often statistically non‐significant differences in Ftot between the CW and FW treatments, cumulative water use of the FW treatment at the end of the first three test periods ranged from 7 to 23% lower than that of the CW treatment. Differences in sap flow between FW and CW compared well with treatment differences in evapotranspiration. The results of the study, based on the first reported sap flow measurements of wheat, suggest that irrigation requirements for wheat production, in the present climatic regimen of the south‐western US, may be predicted to decrease slightly because of increasing atmospheric CO2.
Contribution of intercellular reflectance to photosynthesis in shade leaves
Authors: DeLUCIA E. H. , NELSON K. , VOGELMANN T. C. , SMITH W. K.
Published: April 2006

The potential contribution of intercellular light reflectance to photosynthesis was investigated by infiltrating shade leaves with mineral oil. Infiltration of leaves of Hydrophyllum canadense and Asarum canadense with mineral oil decreased adaxial leaf reflectance but increased transmittance. As a result of the large increase in transmittance, infiltration caused a decrease in absorptance of 25% and 30% at 550 and 750 nm, respectively. Thus, intercellular reflectance increased absorptance in these species by this amount. In a comparison of sun and shade leaves of Acer saccharum and Parthenocissus quinquefolia, oil infiltration decreased absorptance more in shade than in sun leaves. This difference suggests that the higher proportion of spongy mesophyll in shade leaves may increase internal light scattering and thus absorptance. The importance of the spongy mesophyll in increasing internal reflectance was also evident in comparisons of the optics of Populus leaves and in the fluorescence yield of oil‐infiltrated leaves of several sun and shade species. Oil infiltration decreased the quantum yield of fluorescence (Fo) by 39–52% for shade leaves but only 21–25% for sun leaves. We conclude that the greater proportion of spongy parenchyma in shade leaves increased intercellular light scattering and thus absorptance. Direct measurements with fibre‐optic light probes of the distribution of light inside leaves of Hydrophyllum canadense confirmed that oil infiltration decreased the amount of back‐scattered light and that most of the light scattering for this species occurred from the middle of the palisade layer to the middle of the spongy mesophyll. We were not, however, able to assess the potential contribution of reflectance from the internal abaxial epidermis to total internal light scattering in these experiments. Using a mathematical model to compare the response of net photosynthesis (O2, flux) to incident irradiance for control leaves of H. canadense and theoretical leaves with no intercellular reflectance, we calculated that intercellular reflectance caused a 1.97‐fold increase in photosynthesis at 20 μmol m−2s−1 (incident photon flux density). This enhancement of absorption and photosynthesis by inter‐cellular reflectance, without additional production and maintenance of photosynthetic pigments, may maintain shade leaves above the photosynthetic light compensation point between sunflecks and maintain the light induction state during protracted periods of low diffuse light.
The water relations of the root–soil interface
Authors: STIRZAKER R. J. , PASSIOURA J. B.
Published: April 2006

The difference in hydrostatic pressure between the xylem of the leaf and the soil depends, for a given transpiration rate, on the series of hydraulic resistances encountered along this pathway. Many studies have shown that the sum of the resistances in the plant and the soil is too small to account for the fall in water pressure between the leaf xylem and the soil, especially when plants are growing in sandy soils, which are prone to dry rapidly. A resistance at the root–soil interface, caused possibly by poor contact between the roots and the soil, has been proposed to account for the discrepancy. We explored the resistance in the pathway from soil to leaf using a technique that allows precise and continuous non‐destructive measurement of the hydrostatic pressure in the leaf xylem. When the soil was leached with water, the fall in leaf water status as the soil dried was reasonably well described by a simple physical model without the need to invoke an interfacial resistance. However, when the soil was flushed with a nutrient solution with an osmotic pressure of 70kPa, the hydrostatic pressure in the leaf xylem fell several times faster than that in the soil. We suggest that solutes accumulated either in the root or just outside it, creating large osmotic pressures, which gave the appearance of an interfacial resistance.
Effect of environment on the early steps of ear initiation in maize (Zea mays L.)
Authors: LEJEUNE P. , BERNIER G.
Published: April 2006

The effects of environmental conditions on ear‐shoot initiation have been investigated in three inbred genotypes of Zea mays L. which are used for seed production. Scanning electron microscopy (SEM) and binocular examination during the vegetative phase showed that axillary meristems are initiated at the same rate as the leaf primordia on the apical meristem, but with a delay of 5.6–7.0 plastochrons, depending on the genotype. Furthermore, the topmost axillary meristem is initiated on the same day as the tassel, whatever the genotype. One of the inbreds (B22) used in this study has been reported to exhibit, in field conditions, a reproductive failure affecting car initiation, causing the topmost car to be replaced at maturity by a sterile, leaf‐like, structure. Scanning electron microscopic study of the formation of the abnormal axillary buds indicated that ear failure resulted from the early collapse of the axillary meristem followed by elongation of the prophyll or of the meristem itself. Using controlled environments, ear abortion was mimicked by a chilling treatment (10°C), given just before tassel initiation. Other factors, such as high irradiance and flooding, enhanced the abortive response. The critical stage for the main car was just before the initiation of the topmost axillary meristem which also corresponded to tassel initiation. Chilling the plants before or after tassel initiation either induced an acclimation response or had no effect. The three inbreds showed differential responses to the stress treatment, indicating that a genetic factor is implicated as well. It is suggested that chilling causes a perturbation of apical dominance which, in the responsive genotypes, represses axillary meristem development. The use of a stress‐sensitive inbred such as B22 as a model system could yield some interesting clues to the mechanism of endogenous control of ear initiation in maize.
Measurement of short‐term nutrient uptake rates in cranberry by aeroponics
Authors: BARAK P. , SMITH J. D. , KRUEGER A. R. , PETERSON L. A.
Published: April 2006

Aeroponics, a soil‐less plant culture system in which fresh nutrient solutions are intermittently or continuously misted on to plant roots, is capable of sustaining plant growth for extended periods of time while maintaining a constantly refreshed nutrient solution. Although used relatively extensively in commercial installations and in root physiology research, use of aeroponics in nutrient studies is rare. The object of this study was to examine whether nutrient uptake rates could be calculated for aeroponic systems by difference using measurements of concentrations and volumes of input and efflux solutions. Data were collected from an experiment with cranberry plants (Vaccinium macrocarpon Ait. cv. Stevens) cultured aeroponically with nutrient solutions containing various concentrations of ammonium‐N and isotopically labelled nitrate‐N. Validation of the calculated uptake rates was sought by: (1) evaluating charge balance of the solutions and total ion uptake (including proton efflux) and (2) comparison with N‐isotope measurements. Charge balance and proton efflux calculations required use of chemical modelling of the solutions to determine speciation of dissolved phosphate and acid‐neutralizing capacity (ANC). The results show that charge balance requirements were acceptably satisfied for individual solution analyses and for total ion uptake when proton efflux was included. Relative rates of nitrate/ammonium uptake determined by difference were in agreement with those determined by isotopic techniques. Additional information was easily obtained from this experimental technique, including evidence of diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship between ion concentration and uptake. Use of aeroponic systems for non‐destructive measurement of water and ion uptake rates for numerous other species and nutrients appears promising.
Expression of cold‐inducible genes and frost hardiness in the crown meristem of young barley (Hordeum vulgare L. cv. Igri) plants grown in different environments
Authors: PEARCE R. S. , DUNN M. A. , RIXON J. E. , HARRISON P. , HUGHES M. A.
Published: April 2006

The purpose of this work was to examine environmental control of expression, at the mRNA level, of cold‐inducible genes and to test the relationship of the expression of the genes to cold acclimation. Barley plants (Hordeum vulgare L. cv. Igri) at the three‐ to four‐leaf stage were (a) grown in different temperature environments between 20/15°C and +4/‐4°C or (b) transferred between 20/15°C and 6/2°C or (c) grown under drought or nutrient stress conditions. Frost hardiness (using a regrowth method) and mRNA levels for three cold‐induced genes, blt4‐9, blt14 and blt101, from meristematic crown tissue (vegetative shoot meristem plus subtending stem and associated root initials) were measured. Hardiness and levels of blt4‐9, blt14 and blt101 mRNAs increased with lower growth temperatures, below a maximum inductive temperature. Prior temperature environment and plant age affected the rate of change in mRNA levels of these genes in response to a change of temperature environment. Hardiness was strongly correlated with mRNA levels of these genes in plants grown in different temperature environments. This correlation did not extend to plants exposed to drought or nutrient stresses. Implications are drawn for plant responses to a warmer climate.
Antioxidants in the apoplast and symplast of beech (Fagus sylvatica L.) leaves: seasonal variations and responses to changing ozone concentrations in air
Authors: LUWE M.
Published: April 2006

Concentrations of the antioxidants ascorbate and glutathione were measured in the apoplast of beech (Fagus sylvatica L.) leaves and in leaf tissue. During early leaf development, reduced ascorbate (ASC) was almost absent from the apoplast, whereas levels of oxidized ascorbate (DHA) were high. Less than 20% of the apoplastic ascorbate was reduced. ASC increased towards midsummer, reaching top levels of about 4molm−3 apoplast volume in July and August. Reduction increased to 60–75% in summer. Neither DHA reductase nor glutathione was detected in the apoplast of beech leaves. Levels of apoplastic ascorbate were compared with ambient concentrations of ozone in air. Statistical analysis indicated a significant interrelation between atmospheric ozone and apoplastic ascorbate. In midsummer of 1993, contents of DHA were increased in the apoplast when ozone concentrations were high. Apoplastic ASC was also positively correlated with ambient ozone concentrations, but with a delay of 3 to 7d. In leaf tissue, levels of ascorbate were between 17 and 21 μmolg−1 FW in summer. Except for late April and November, more than 95% of the intracellular ascorbate was reduced. Glutathione contents were lowest during the summer. Oxidation was increased in spring and autumn, when apoplastic ascorbate was also largely oxidized. Usually, 80 to 90% of the glutathione was reduced. During the summer, intracellular concentrations of oxidized glutathione (GSSG) were increased, with a delay of about 1d following periods of high ambient ozone concentrations. The transitory accumulation of GSSG may be explained by slow enzymatic regeneration of glutathione.