bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of pH on ammonium uptake byTypha latifoliaL.
Authors: DYHR‐JENSEN K. , BRIX H. 
Published: April 2006

ABSTRACTThe effects of solution pH on NH4+uptake kinetics and net H+extrusion byTypha latifoliaL. were studied during short‐term (days) and long‐term (weeks) exposure to pH in the range of pH 3.5–8.0. The NH4+uptake kinetics were estimated from depletion curves using a modified Michaelis‐Menten model.T. latifoliawas able to grow in solution culture with NH4+as the sole N source and to withstand a low medium pH for short periods (days). With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing. The solution pH affected NH4+uptake kinetics. The affinity for NH4+, as quantified by the half saturation constant (K1/2) andCmin(the NH4+concentration at which uptake ceases), decreased with pH.K1/2was increased from 7.1 to 19.2 mmol m−3andCminfrom 2.0 to 5.7 mmol m−3by lowering the pH in steps from 8.0 to 3.5.Vmaxwas, however, largely unaffected by pH (∼22 μmol h−1g−1root dry weight). Under prolonged exposure to constant pH, growth rates were highest at PH 5.0 and 6.5. At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped. NH4+uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH4+uptake almost completely stopped. The ratio between net H+extrusion and NH4+uptake decreased significantly at low pH. The adverse effects of low pH on NH4+uptake kinetics are probably a consequence of a reduced H+‐ATPase activity and/or an increased re‐entry of H+at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.
Salinity‐induced enhancement of L‐myo‐inositol 1‐phosphate synthase in rice (Oryza sativa L.)
Authors: RAYCHAUDHURI A. , MAJUMDER A. LAHIRI 
Published: April 2006

ABSTRACTThe salt‐tolerant varieties of rice (Oryza sativa L.) exhibit enhanced activity of the chloroplast form of L‐myo‐inositol 1‐phosphate synthase (EC 5.5.4.1) under NaCl treatment either during the seedling stage or in fully grown plants during field growth. The salt‐induced enhancement was noticeable only in chloroplasts from light‐grown plants. The effects of these treatments on the cytosolic inositol synthase activity were less pronounced. While the effect of salt on the activity of the two forms was marginal in the salt‐sensitive varieties during seedling growth, salinity affected the chloroplast inositol synthase activity adversely in these varieties during growth of the plants under field conditions. The salt‐enhanced activities of inositol synthase(s) in the highly salt‐tolerant varieties studied were found to be comparable to that observed in Porteresia coarctata, a halophytic wild rice species. The implications of these findings, which suggest a role of the inositol pathway in osmoregulation, are discussed.
1H‐NMR spin‐spin relaxation time assessment of the reflection coefficient of the Triticale seed cell wall–plasmalemma barrier to mannitol
Authors: MIEDZIEJKO E. M. , PLENZLER G. B. , NAPIERAŁA D. M. , NAROŻNA A. T. 
Published: April 2006

ABSTRACTThe 1H‐NMR spin‐spin relaxation time (T2) in Triticale seeds swelling in external osmotica, polyethylene glycol 8000 or mannitol can identify both bound and free water. At the same water content, the free water spin‐spin relaxation time increases for seeds imbibed with the mannitol solution, demonstrating inadequate water potential adjustment. The exchange rate of free/bound water molecules is apparently influenced by the driving force for water flow. The reciprocal lifetime of free water molecules, as a measure of water flow through the main cell barrier, was obtained. From a model of the seed as a resistance–capacitor network for water flow, a method was derived for calculating the reflection coefficient σ as a lifetime ratio of the free water molecules in seeds imbibed with two different osmotica (one penetrating across the main cell barrier and one not penetrating) at the same water potential. The 1H‐NMR method and the classical method based on volume rate changes yielded reflection coefficients for mannitol for the cell wall–plasmalemma barrier of 0.78 ± 0.08 and 0.68 ± 0.06, respectively.
Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina
Authors: MACHALEK K. M. , DAVISON I. R. , FALKOWSKI P. G. 
Published: April 2006

ABSTRACTThermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m−2 s−1. When measured at a standard temperature (17°C), rates of light‐saturated photosynthesis (Pmax) were higher in 5 °C‐grown algae (c. 3.0 μmol O2 m−2 s−1) than in 17 °C‐grown algae (c. 0.9 μmol O2 m‐2 s‐1). Concentrations of Rubisco were also 3‐fold higher (per unit protein) in 5 °C‐grown algae than in algae grown at 17 °C. Light‐limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low‐light algae absorbed c. 75% of incident light, whereas 5 °C high‐light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin‐Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low‐light‐grown algae was twice that of high‐light‐grown algae (c. 160.0 versus 80.0 nmol m−2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.
Accumulated effect of elevated ultraviolet‐B radiation over multiple generations of the arid‐environment annualDimorphotheca sinuataDC. (Asteraceae)
Authors: MUSIL C. F. 
Published: April 2006

ABSTRACTTwoD. sinuatapopulations, established from the same seed batch, were cultured concurrently under ambient (2.5–8.9 kj m−2d−1) and enhanced (4.7–11.4 kj m−2d−1) ultraviolet‐B radiation for two consecutive generations. The two populations, designated low‐ and high‐UV‐B cultivars, were each grown for an additional generation under both UV‐B fluences at different alignments. Differences in plant performance were examined between UV‐B treatments (immediate UV‐B effects), cultivars (accumulated UV‐B effects), alignments and their interactions. Accumulated UV‐B had a greater effect on plant performance than immediate UV‐B. The former induced earlier reproductive effort, substantial (up to 35%) reductions in dry mass (stems, leaves and reproductive organs), decreased stem and inflorescence production, and diminished steady‐state fluorescence yields, chlorophyllaconcentrations, pollen tube growth and germination of seeds set. The latter caused only diminished non‐photochemical quenching, reduced chlorophylla, soluble sugar and starch concentrations, decreased pollen germination, and increased carotenoid contents. Interactions between UV‐B fluence level and alignment occurred for all measured dry mass parameters, leaf area, photosynthetic pigment and soluble sugar concentrations, and germination success of seeds set. These results indicate altered DNA integrity rather than an indirect UV‐B effect of photomorphogenic origin.
The relationship between leaf growth and ABA accumulation in the grass leaf elongation zone
Authors: DODD I. C. , DAVIES W. J. 
Published: April 2006

ABSTRACTDetached barley (Hordeum vulgare L.) shoots, maintained at different air temperatures and VPDs, were fed ABA via the sub‐crown internode in a leaf elongation assay. Analysis of variance of leaf elongation rate (LER) showed significant effects of temperature (T), fed [ABA] and the interaction T × [ABA]. However, the interaction became non‐significant when LER was modelled against the [ABA] of the elongation zone, [EZ‐ABA]When detached barley shoots were fed sap from droughted maize (Zea mays L.) plants, sap [ABA] could not explain the growth inhibitory activity. Measurement of [EZ‐ABA] accounted for this ‘unexplained’ growth inhibition.The detached shoot experiments indicated that [EZ‐ABA], and not xylem sap [ABA], was an appropriate explanatory variable to measure in droughted plants. However, ABA accumulation in the elongation zone could not explain a 35% growth reduction in intact droughted plants; thus we considered an interaction of water status and ABA.Using a coleoptile growth assay, we applied mild osmotic stresses (ψ=0 to −0.06 MPa) and 10−4 mol m−3 ABA. Individually, these treatments did not inhibit growth. However, osmotic stress and ABA applied together significantly reduced growth. This interaction may be an important mechanism in explaining leaf growth inhibition of droughted plants.
Changes in photon flux can induce stomatal patchiness
Authors: ECKSTEIN J. , BEYSCHLAG W. , MOTT K. A. , RYEL R. J. 
Published: April 2006

ABSTRACTImages of chlorophyll fluorescence were used to detect the occurrence of stomatal patchiness in leaves from eight species under variable photon flux conditions. Pronounced stomatal patchiness was induced within 5–10 min after PFD was changed from intermediate (∼450 μmol quanta m−2 s−1) to low (∼150 μmol quanta m−2 s−1) levels. This effect was completely reversible by returning PFD to intermediate levels. The pattern of heterogeneous fluorescence for each leaf was usually similar during repeated applications of medium and low PFD. In three species, stomatal patchiness could only be induced in slightly water‐stressed plants. Leaves of more severely water‐stressed Xanthium strumarium plants in low air humidity exhibited oscillations in fluorescence that corresponded with oscillatory changes in leaf diffusion conductance for water vapour. Stomatal patchiness was also induced by illuminating dark‐adapted leaves with low PFD (below 200–300 μmol quanta m−2 s−1). Infiltration of leaves with distilled water showed that heterogeneous chlorophyll fluorescence was caused by changes in stomatal apertures.
Complete mechanical impedance increases the turgor of cells in the apex of pea roots
Authors: CLARK L.J. , WHALLEY W.R. , DEXTER A.R. , BARRACLOUGH P.B. , LEIGH R.A. 
Published: April 2006

ABSTRACTIn this paper we describe an experimental approach which allows turgor (p) in an impeded root to be measured without the need to remove the root from the impeding environment. The maximum axial growth pressure (σmax) generated by completely impeded pea (Pisum sativum L.) roots was measured using a novel apparatus incorporating a force transducer. The apparatus was designed so that it was possible to gain access to the impeded root with the microcapillary of a pressure probe and so obtain in situ measurements of P. Turgor in cells in the apical region of impeded roots was 0.78 MPa, compared with 0.55 MPa in unimpeded roots. In impeded roots, σmax was 0.52 MPa, showing that the pressure component resulting from cell wall tension (W, where W=P–σ) decreased from 0.55 to 0.26 MPa as the roots became impeded. When impeded roots were removed from the apparatus, there was no decrease in P over the following 90 min. Impedance did not cause P to change in the non‐elongating part of the roots further from the apex.
Acclimation to low water potential determines changes in membrane fatty acid composition and fluidity in potato cells
Authors: LEONE A. , COSTA A. , GRILLO S. , TUCCI M. , HORVATH I. , VIGH L. 
Published: April 2006

ABSTRACTPotato (Solanum tuberosum) cells were gradually acclimated to grow at low water potential created by addition of increasing concentrations of polyethylene glycol (PEG) 8000 to the nutrient medium. While growth of cells abruptly transferred into a medium containing 20% PEG was dramatically inhibited, under the same stress intensity gradually acclimated cells were able to sustain active growth similarly to control unstressed cells. Gradual acclimation allowed the maintenance of normal cellular and subcellular membrane structure at an osmotic potential of ‐2.3 MPa, which caused extended membrane disruption when applied to non‐acclimated control cells. Analysis of fatty acids (FAs) from control and acclimated cells revealed that the mol percentage composition of the major extra‐plastidial phospholipids (PLs) was basically unchanged, but both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were more saturated in acclimated cells. The decrease in unsaturation occurred primarily at the expense of linoleic acid (18:2) in the PE fraction. A significant increase in the percentage content of palmitic acid (16:0) of the PE fraction was also detected in acclimated cells. Membrane microviscosity, as determined by diphenyl‐hexatriene (DPH) labelling, was higher in PEG‐acclimated cells, as expected from the lower degree of unsaturation of membrane FAs found in acclimated cells. The steady‐state transcript levels of a Δ9‐stearoyl‐acyl carrier protein‐desaturase and a Δ12‐oleoyl‐desaturase gene decreased in acclimated cells, suggesting that the variation in the level of FA unsaturation was at least partially associated with down‐regulation of the expression of these genes.
Responses to elevated CO2 of Flaveria linearis plants having a reduced activity of cytosolic fructose‐1,6‐bisphosphatase
Authors: MICALLEF B. J. , VANDERVEER P. J. , SHARKEY T. D. 
Published: April 2006

ABSTRACTWide variation exists in the growth responses of C3 plants to elevated CO2 levels. To investigate the role of photosynthetic feedback in this phenomenon, photosynthetic parameters and growth were measured for lines of Flaveria linearis with low, intermediate or high cytosolic fructose‐1,6‐bisphosphatase (cytFBPase) activity when grown at either 35 or 65 Pa CO2. The effects of pot size on the responses of these lines to elevated CO2 were also examined. Photosynthesis and growth of plants with low cytFBPase activity were less responsive to elevated CO2, and these plants had a reduced maximum potential for photosynthesis and growth. Plants with intermediate cytFBPase activity also showed a lower relative growth enhancement when grown at 65 Pa CO2. There was a significant pot size effect on photosynthesis and growth for line 85‐1 (high cytFBPase). This effect was greatest for line 85‐1 when grown at 35 Pa CO2, since these plants showed the greatest downward acclimation of photosynthesis when grown in small pots. There was a minimal pot size effect for line 84‐9 (low cytFBPase), and this could be partly attributed to the reduced CO2 sensitivity of this line. It is proposed that the capacity for sucrose synthesis in C3, plants is partly responsible for their wide variation in CO2 responsiveness.
Photosynthetic performance and resistance to photoinhibition of Zea mays L. leaves grown at sub‐optimal temperature
Authors: HALDIMANN P. , FRACHEBOUD Y. , STAMP P. 
Published: April 2006

ABSTRACTThe performance of the photosynthetic apparatus was examined in the third leaves of Zea mays L. seedlings grown at near‐optimal (25 °C) or at suboptimal (15 °C) temperature by measuring chlorophyll (ChI) a fluorescence parameters and oxygen evolution in different temperature and light conditions. In leaf tissue grown at 25 and 15 °C, the quantum yield of PSII electron transport (ψPSII) and the rate of O2 evolution decreased with decreasing temperature (from 25 to 4 °C) at a photon flux density of 125 μmol m−2 s−1. In leaves grown at 25 °C, the decrease of ψPSII correlated with a decrease of photochemical ChI fluorescence quenching (qp), whereas in leaves crown at 15 °C qp was largely insensitive to the temperature decrease. Compared with leaves grown at 25 °C, leaves grown at 15 °C were also able to maintain a higher fraction of oxidized to reduced QA (greater qp) at high photon flux densities (up to 2000 μmol m−2 s−1), particularly when the measurements were performed at high temperature (25 °C). With decreasing temperature and/or increasing light intensity, leaves grown at 15 °C exhibited a substantial quenching of the dark level of fluorescence F0 (q0) whereas this type of quenching was virtually absent in leaves grown at 25 °C. Furthermore, leaves grown at 15 °C were able to recover faster from photo inhibition of photosynthesis after a photoinhibitory treatment (1200 μmol m−2 s−1 at 25, 15 or 6 °C for 8 h) than leaves grown at 25 °C. The results suggest that, in spite of having a low photosynthetic capacity, Z. mays leaves grown at sub optimal temperature possess efficient mechanisms of energy dissipation which enable them to cope better with photoinhibition than leaves grown at near‐optimal temperature. It is suggested that the resistance of Z. mays leaves grown at 15 °C to photoinhibition is related to the higher content of carotenoids of the xanthophyll cycle (violaxanthin + antheraxanthin + zeaxanthin) measured in these leaves than in leaves grown at 25 °C.
Stomatal conductance in relation to xylem sap abscisic acid concentrations in two tropical trees, Acacia confusa and Litsea glutinosa
Authors: LIANG J. , ZHANG J. , WONG M.H. 
Published: April 2006

ABSTRACTTwo tropical trees, Acacia confusa and Litsea glutinosa, were grown under controlled conditions with their roots subjected to soil drying and soil compaction treatments. In both species, a decline in stomatal conductance resulting from soil drying took place much earlier than the decline of leaf water potential. Soil compaction treatment also resulted in a substantial decrease in stomatal conductance but had little effect on leaf water potential. A rapid and substantial increase in xylem abscisic acid (ABA) concenation ([ABA]), rather than hulk leaf ABA, was closely related to soil drying and soil compaction. A significant relationship between stomatal conductance (gs) and xylem [ABA] was observed in both species. Artificially feeding ABA solutions to excised leaves of both species showed that the relationship bet ween gs and [ABA] was very similar to that obtained from the whole plant, i.e. the relationship between gs and xylem [ABA]. These results suggest that xylem ABA may act as a stress signal in the control of stomatal conductance.
Adaptation of pea to elevated atmospheric CO2: Rubisco, phosphoenolpyruvate carboxylase and chloroplast phosphate translocator at different levels of nitrogen and phosphorus nutrition
Authors: RIVIERE‐ROLLAND H. , CONTARD P. , BETSCHE T. 
Published: April 2006

ABSTRACTResource allocation in high CO2 was studied with respect to plant nutrition. Pea (Pisum sativum) was grown in CO2‐enriched air (1000 cm 3 m3 CO2) during the entire vegetative phase, or grown in ambient air (340 cm3 m3 CO2), with different levels of nitrogen or phosphorus supply. Rubisco specific activity, abundance and small subunit transcript levels were unaltered at high N but declined at reduced N depending upon the degree of N deprivation. It is proposed that (a) a threshold value for the N status occurs in pea above which Rubisco is not down‐regulated by high CO2 and (b) a high leaf level of soluble carbohydrates is not a sufficient condition to downregulate Rubisco in high CO2. Phosphoenolpyruvate (PEP) carboxylase decreased, and chloroplast phosphate (P)‐translocator increased, in high CO2. In contrast to Rubisco, down‐regulation of PEP carboxylase was alleviated by low N and enhanced by low P. The increase in the P‐translocator was little affected by N but was accentuated by low P. The increase in the P‐translocator is considered to be one way of alleviating low P conditions in the chloroplast and thus rebalancing carbon partitioning between starch and soluble carbohydrates and amino acids. It is proposed that acclimation of PEP carboxylase and P‐translocator reflects adaptation to metabolic perturbations caused by high CO2.
The influence of water content and leaf anatomy on carbon isotope discrimination and photosynthesis in Sphagnum
Authors: RICE S. K. , GILES L. 
Published: April 2006

ABSTRACTThe relative effect of diffusional resistance due to water films (rwf) and leaf anatomy (rp) on rates of net photosynthesis and on‐line measures of carbon isotope discrimination (Δ=Δδ13C) was investigated in Sphagnum. Sphagnum species differ in the exposure of photosynthetic cells at the leaf surface. In S. affine, photosynthetic cells are widely exposed at the surface, whereas in S. magellanicum, photo‐synthetic cells are enclosed within water‐filled hyaline cells. This difference is expected to lead to variation in diffusive resistance within leaves (rp). Net photosynthesis and on‐line Δ were measured at two water contents: greenhouse water content (wet) and blotted dry (dry). Without correcting for respiration, on‐line Δ values differed significantly between wet (23.7%o) and dry (30.9%o) plants. However, there was no significant difference between species means and no species × water content interaction. Corrections for respiration lowered Δ values by approximately 8.1%o and reduced the mean difference to 3.1%o, but did not alter the rank order of treatments. Net photosynthesis also decreased by 16% in wet plants, but there was no significant difference between the two species. In addition, five populations of S. affine and S. magellanicum grown in a common garden were analysed for their organic matter carbon isotope composition (δ13C). These values varied more within each species (0.9–1.2%o) than between the two species (0.6%o). Therefore, we conclude that variation in surface water films leads to a greater difference in resistance to CO2 uptake and carbon isotope discrimination than that due to variation in leaf anatomical properties in Sphagnum.
Antioxidant composition of selected high alpine plant species from different altitudes
Authors: WILDI B. , LÜTZ C. 
Published: April 2006

ABSTRACTSelected high alpine plant species were collected from different elevations in the Obergurgl/Ötztal subnival and nival regions in Austria to investigate the content of antioxidants in plants growing under the particular in vivo conditions experienced in this area (e.g. chilling stress, short vegetation period and high irradiation). The contents of antioxidants (ascorbic acid, tocopherol and glutathionc) and photosynthetic pigments were measured throughout the day. The contents of most compounds were found to follow a diurnal rhythm, with the maximum occurring at midday and the minimum during the night. It was not clear whether these fluctuations were temperature‐dependent or light‐dependent.Analyses of the antioxidant spectrum in the same plant species at different altitudes (and thus under different environmental conditions: as altitude increases, for example, day temperature decreases and light intensity increases) revealed that the total amount of antioxidants increases as altitude increases. This enhancement was mainly due to ascorbic acid contents. Each plant species displayed a specific reaction to the increase in stress that accompanies an increase in altitude, resulting in a broad adaptation spectrum for these plants. The present study suggests that the combined effect of lower temperature and higher light intensity induces higher antioxidant contents.