bluuebunny/crossref_metadata_2025_split huggingface dataset:
Translocation of nitrogen in osmotically stressed wheat seedlings
Authors: LARSSON M. 
Published: April 2006

ABSTRACTWheat (Triticum aestivum L., cv. Drabant) seedlings were grown in a ‘split root’ system where either the whole root system or one root half was subjected to osmotic stress for 24 h, using 200 g polyethylene glycol (PEG, molecular weight 4000) dm−3 nutrient solution. 15N‐Labelled nitrate was fed to one of the root compartments and total N and 15N‐labelling were measured in plant material and xylem sap. Untreated plants translocated 87% of the N taken up to the shoot, and 10% of this was then retranslocated back to the root. Recalculated on a root nitrogen basis, 36% of the label recovered in the root after 24 h had passed through the shoot. Significant labelling of xylem sap collected from non‐labelled roots indicated cycling of organic N through the roots. PEG‐treatment of the whole root system caused significant water loss in both roots and shoots. Uptake of nitrate and retranslocation of N to roots were inhibited, whereas cycling of organic nitrogen through the root was still measurable. Treatment of half the root system with PEG had minor effects on shoot water content, but reduced the water content of the treated root part. The total uptake of nitrate by the root system was unaffected, and the effect on the treated root half was comparatively small. Nitrate reductase activity (NRA) declined in PEG‐treated roots even if high nitrate uptake rates were maintained. Shoot NRA was unaffected by osmotic stress. The data indicate that the reduction in water content of the root per se has only small effects on nitrate uptake. Major inhibition of nitrate uptake was observed only after treatment of a sufficiently large portion of the root system to given an effect on shoot water content.
Development correlations between roots in heterogeneous environments
Authors: GERSANI M. , SACHS T. 
Published: April 2006

ABSTRACTRoots are known to respond to favourable nutrient conditions by increased initiation and growth of lateral roots. The problem studied here was to what extent does this local developmental response depend on the environments of other roots on the same plant. Such dependence could allow for an optimal allocation of resources required for root growth in unpredictable, heterogeneous soils. Pea seedlings (Pisum sativum var. arvense cv. Dun) were pruned and grown to have two equal root systems, each in an individual container. As expected, these roots responded by increased development to a wide range of nutrient solution concentrations. The local development of these roots, expressed by their dry weight, was a function of the relative rather than the absolute conditions in which they were grown: roots in a given environment developed more rapidly if other roots on the same plant were in poorer than if they were in richer nutrient conditions. The number of lateral initials doubled within 3d after the roots were exposed to optimal nutrient conditions, before any dry weight differences could be detected. This rapid root initiation was also a function of the conditions other roots of the same plant were in. These results mean that root development, and especially lateral root initiation, depends on the integrated effects of the local environment and the internal correlative relations between the roots.
Hydraulic architecture of sugarcane in relation to patterns of water use during plant development*
Authors: MEINZER F. C. , GOLDSTEIN G. , NEUFELD H. S. , GRANTZ D. A. , CRISOSTO G. M. 
Published: April 2006

ABSTRACTHydraulic conductance was measured on leaf and stem segments excised from sugarcane plants at different stages of development. Maximum transpiration rates and leaf water potential (ΨL) associated with maximum transpiration were also measured in intact plants as a function of plant size. Leaf specific hydraulic conductivity (Lsc) and transpiration on a unit leaf area basis (E) were maximal in plants with approximately 0.2 m2 leaf area and decreased with increasing plant size. These changes in Fand Lsc were nearly parallel, which prevented φL in larger plants from decreasing to levels associated with substantial loss in xylem conductivity caused by embolism formation. Coordination of changes in E and leaf hydraulic properties was not mediated by declining leaf water status, since φL increased with plant size. Hydraulic constrictions were present at nodes and in the node‐leaf sheath‐leaf blade pathway. This pattern of constrictions is in accord with the idea of plant segmentation into regions differing in water transport efficiency and would tend to confine embolisms to the relatively expendable leaves at terminal positions in the pathway, thereby preserving water transport through the stem.
A theoretical model of hydraulic conductivity recovery from embolism with comparison to experimental data on Acer saccharum
Authors: YANG S. , TYREE M. T. 
Published: April 2006

ABSTRACTA theoretical model of bubble dissolution in xylem conduits of stems was designed using the finite differential method and iterative calculations via computer. The model was based on Fick's, Henry's and Charles' laws and the capillary equation. The model predicted the tempo of recovery from embolism in small diameter branches of woody plants with various xylem structures under different xylem water pressures. The model predicted the time required to recover conductivity in any position in the stem. Repeated iterative solution of the model for different situations yielded an empirical formula to calculate the time for complete recovery of conductivity in stems from a fully embolised initial state. The time, tp, is given by:

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where α is a temperature coefficient; D is the coefficient of diffusion of air in wood at 25°C; rcs is the ratio of the area of total conduit cross section to the stem cross section; Ψxp is the stem xylem pressure potential (Pa, where 0 Pa equals atmospheric pressure); τ is solution surface tension (0.072 N m−1); and Dc and Ds are diameters of the conduits and the stem, respectively (m). The equation is valid only when Ψxp > –4τ/Dc. The model predicts no recovery of conductivity when Ψxp≤–4τ/Dc. The model agreed with experiments.
Phosphate uptake, efflux and deficiency in the water fern, Azolla
Authors: BIELESKI R. L. , LÄUCHLI A. 
Published: April 2006

ABSTRACTHigh phosphorus status (High‐P) Azolla mexicana plants (P content 15.5 μmoles g fr wt−1, doubling time ca. 2.2 d) and Low‐P plants with early signs of P‐deficiency (P content 6.2 μmoles g fr wt−1, doubling time ca. 3.2 d) were used to study Pi uptake, efflux and deficiency. When High‐P plants were transferred to medium lacking Pi, uptake capacity increased 1.5‐fold within 12 h and before any detectable change in growth rate (24–48 h). When High‐P and Low‐P plants were compared, uptake rates from 0.3–10000 mmoles m−3 Pi were 2.6–1.7 times higher in Low‐P than High‐P plants (18–1150 vs 7–665 μmoles g fr wt−1 h−1). The relationship of uptake rate to concentration was interpreted as arising from a combined operation of a high‐ and a low‐affinity uptake system. Higher uptake in Low‐P plants involved a 3.4‐fold increase in Vmax (high affinity), no change in Km (high affinity), and a 1.5 to two‐fold increase in both Vmax (low affinity) and Km (low affinity). Rates of P efflux into 1–1000 mmoles m−3 Pi were 1.7 to two times higher from High‐P than Low‐P plants (12–22 vs 7–11 μmoles g fr wt−1 h−1). Below 1 mmole m−3 Pi, uptake and efflux rates were similar: the equilibrium concentration, at which net uptake was zero, was 0.22 mmoles m−3 for High‐P plants and 0.05 mmoles m−3 for Low‐P plants. Similar results were obtained with A. filiculoides. P transport characteristics of Azolla, a fern, are closely comparable with those of higher plants. Its high P requirement in the field arises from its ecological rather than physiological behaviour. We interpret the field behaviour by exploring the relationship between Azolla growth rate in the field, plant P concentration in the field, Pi transport rates required to support such growth, and Pi concentrations in pond waters. The transport characteristics which must operate in the field match those of Low‐P plants in the laboratory, not High‐P plants. Thus, Pi uptake in High‐P plants should be interpreted as repressed from the normal state, instead of that in Low‐P plants being induced.
Rapid calcium exchange for protons and potassium in cell walls of Chara
Authors: RYAN P. R. , NEWMAN I. A. , ARIF I. 
Published: April 2006

ABSTRACTNet fluxes of Ca2+, H+ and K+ were measured from intact Chara australis cells and from isolated cell walls, using ion‐selective microelectrodes. In both systems, a stimulation in Ca2+ efflux (up to 100 nmol m−2 s−1, from an influx of ∼40 nmol m−2 s−1) was detected as the H+ or K+ concentration was progressively increased in the bathing solution (pH 7.0 to 4.6 or K+ 0.2 to 10mol m−3, respectively). A Ca2+ influx of similar size occurred following the reverse changes. These fluxes decayed exponentially with a time constant of about 10 min. The threshold pH for Ca2+ efflux (pH 5.2) is similar to a reported pH threshold for acid‐induced wall extensibility in a closely related characean species. Application of NH4+ to intact cells caused prolonged H+ efflux and also transient Ca2+ efflux. We attribute all these net Ca2+ fluxes to exchange in the wall with H+ or K+. A theoretical treatment of the cell wall ion exchanges, using the ‘weak acid Donnan Manning’ (WADM) model, is given and it agrees well with the data. The role of Ca2+ in the cell wall and the effect of Ca2+ exchanges on the measured fluxes of other ions, including bathing medium acidification by H+ efflux, are discussed.
Evacuolation and enucleation of mesophyll protoplasts in self‐generating percoll gradients
Authors: WU F.‐S. , TSAI Y.‐Z. 
Published: April 2006

ABSTRACTMesophyll protoplasts from Brassica oleracea, B. napus, Nicotiana tobaccum and Solanum tuberosum were isolated and subjected to uttracentrifugation at 65000g for 30 min in percoll solutions containing various strengths of salt and osmotic stabilizing agents. After centrifugation, the self‐generated percoll gradients were evaluated for their effectiveness in protoplast evacuolation and enucleation. The vacuoles, cell debris, evacuolated protoplasts and enucleated protoplasts were separated. Factors that affected evacuolation and enucleation in the percoll gradients were described. Mesophyll protoplasts produced by epidermis peeling and short enzyme incubation periods were more easily evacuolated and enucleated than those produced by leaf‐slicing and long incubation periods. Lower centrifugal force at 25000g for 80 min was also successful in evacuolating and enucleating the mesophyll protoplasts. A green band that contained nearly pure evacuolated protoplasts, of which 45% were enucleated protoplasts, was obtained from the self‐generated percoll gradient. Rhodamine 123 staining of mitochondria indicated that the evacuolated protoplasts were metabolically active and were capable of regenerating the vacuole and cell wall. Cell divisions were also observed when the evacuolated protoplasts were cultured.
Dirunal leaf movement, chlorophyll fluorescence and carbon assimilation in soybean grown under different nitrogen and water availabilities
Authors: KAO W.‐Y. , FORSETH I. N. 
Published: April 2006

ABSTRACTDiurnal heliotropic leaf movements, photosynthetic gas exchange, and the ratio of variable fluorescence to maximum fluorescence (Fv/Fm) of unrestrained and horizontally restrained leaves from soybean (Glycine max cv. Cumberland) plants grown in two different water and two different nitrogen treatments were measured. Leaves of plants grown in low water or low nitrogen availability treatments displayed more pronounced diaheliotropism (solar tracking) in the afternoon and a longer period of paraheliotropism (light avoiding) at midday relative to those of well‐watered, high‐nitrogen‐grown plants. Photosaturated photosynthetic rates and the photon flux required to saturate photosynthesis were reduced by water stress and nitrogen deficiency. Compared to horizontal leaves, irradiance on orienting leaves was nearer to the breakpoint of the photosynthetic light response curve, where photosynthesis is co‐limited by ribulose biphosphate regeneration and carboxylation. This would increase the carbon return on investments of nitrogen into photosynthesis. A positive linear relationship between Fv/Fm and quantum yield of photosynthesis was measured. Leaves of low‐nitrogen‐grown plants had earlier and more prolonged reductions in Fv/Fm at midday compared to leaves of high nitrogen grown plants of the same water treatment. Within the same water and nitrogen treatment, horizontally restrained leaves had lower midday Fv/Fm in relation to orienting leaves. Nitrogen deficiency and water stress enhanced this difference such that horizontally restrained leaves of low water and low nitrogen grown plants had earlier and longer midday depressions in Fv/Fm.
Comparison of salt tolerance and osmotic adjustment of low‐sodium and high‐sodium subspecies of the C4 halophyte, Atriplex canescens
Authors: GLENN E. P. , WATSON M. C. , O'LEARY J. W. , AXELSON R. D. 
Published: April 2006

ABSTRACTThe relationship between Na+ accumulation and salt tolerance was tested by comparing subspecies of the halophyte, Atriplex canescens (fourwing saltbush), that differed markedly in Na+ content and Na:K ratios. Above ground tissues of one low‐sodium and two high‐sodium subspecies were compared with respect to cation accumulation, osmotic adjustment and growth along a salinity gradient in greenhouse trials. Plants of each subspecies were grown for 80 d on 2.2, 180, 540 and 720 mol m−3 NaCl. At harvest, A. canescens ssp. canescens had significantly lower Na+ levels, higher K+ levels and lower Na:K ratios in leaf and stem tissues than A. canescens ssp. macropoda and linearis over the salinity range (P < 0.05 or 0.01). Na:K ratios in leaves of the latter two, high‐sodium, subspecies were approximately 2 on the lowest salinity treatment and ranged from 5 to 10 on the more saline solutions. By contrast, Na:K ratios in leaves of the low‐sodium subspecies canescens, were only 0.4 on the lowest salinity and ranged narrowly from 1.7 to 2.3 at higher salinities. However, despite different patterns of Na+ and K+ accumulation, all three subspecies exhibited equally high salt tolerance and had similar osmotic pressures in their leaves or stems over the salinity range. Contrary to expectations, high salt tolerance was not necessarily dependent on high levels of Na+ accumulation in this species.
Evidence supporting a non‐phloem source of water for export of solutes in the xylem of soybean root nodules
Authors: STREETER J. G. , SALMINEN S. O. 
Published: April 2006

ABSTRACTThe vascular anatomy of soybean nodules [Glycine max (L.) Merr.] suggests that export of solutes in the xylem should be dependent on influx of water in the phloem. However, after severing of stem xylem and phloem by shoot decapitation, export of ureides from nodules continued at an approximately linear rate for 5h. This result was obtained with decapitated roots remaining in the sand medium, but when roots were disturbed by removal from the rooting medium prior to shoot decapitation, export of ureides from nodules was greatly reduced. Stem exudate could not be collected from disturbed roots, indicating that flow in the root xylem had ceased. Thus, ureide export from nodules appeared to be dependent on a continuation of flow in the root xylem. When seedlings were fed a mixture of 3H2O and 14C‐inulin for periods of 14–21 min, nodules had higher 3H/14C ratios than roots from which they were detached. The combined results are not consistent with the proposal that export of nitrogenous compounds from nodules is dependent on import of water via the phloem. The results do support the view that a portion of the water required for xylem export from soybean nodules is supplied via a symplastic route from root cortex to nodule cortex to the nodule vascular apoplast.
Photophysiology of turion germination in Spirodela polyrhiza (L.) Schleiden. X. Role of nitrate in the phytochrome‐mediated response
Authors: APPENROTH K.‐J. , AUGSTEN H. , MOHR H. 
Published: April 2006

ABSTRACTIt was shown previously that light‐dependent germination of turions of Spirodela polyrhiza (Lemnaceae) is mediated by the photoreceptor phytochrome [Appenroth & Augsten (1990) Photochemistry and Photobiology 52, 61–65]. In the present study, we found that this photoresponse depends on nitrate in the surrounding medium both during after‐ripening (under natural conditions occurring in winter) and during germination after light‐induction (in spring). The action of nitrate in the germination response is neither related to the induction of nitrate reductase nor to the rate of uptake of 15NO3−. Moreover, two‐factor analysis (phytochrome, nitrate) revealed a multiplicative coaction, i.e. independent action of both factors in mediation of germination. The notion that nitrate is a nutritional prerequisite in phytochrome‐mediated germination of turions, is supported by the following facts: (1) Nitrate‐requirement during germination was strongly increased by nitrate starvation during after‐ripening prior to germination. (2) Ammonium could substitute for nitrate. (3) Nitrate uptake by the turions was unaffected by phytochrome and very pronounced even at low concentrations (0.07 mol m−3) in the medium. With regard to the phytochrome‐induced chain of events, it is concluded that nitrate is a prerequisite during a specific developmental phase. Nitrate is not a regulatory element within the chain. In an ecological sense, however, nitrate contents of the aquatic system regulate the germination of turions.
Response of plant roots to elevated atmospheric carbon dioxide
Authors: ROGERS H. H. , PETERSON C. M. , McCRIMMON J. N. , CURE J. D. 
Published: April 2006

ABSTRACTPlant root response to atmospheric CO2 enrichment can be great. Results from this controlled environment investigation demonstrate substantial effects on root system architecture, micromorphology and physiology. The most pronounced effects were an increase in root length (110%) and root dry weight (143%). Root diameter, stele diameter, cortex width, root/shoot and root weight ratios all increased; root numbers did not increase. The long‐term implications for belowground processes could be enormous.
Effects of elevated carbon dioxide concentration on photosynthesis and growth of small birch plants (Betula pendula Roth.) at optimal nutrition
Authors: PETTERSSON R. , McDONALD A. J. S. 
Published: April 2006

ABSTRACTSmall birch plants (Betula pendula Roth.) were grown from seed for periods of up to 70d in a climate chamber at optimal nutrition and at present (350 μmol mol−1) or elevated (700 μmol mol−1) concentrations of atmospheric CO2. Nutrients were sprayed over the roots in Ingestad‐type units. Relative growth rate and net assimilation rate were slightly higher at elevated CO2, whereas leaf area ratio was slightly lower. Smaller leaf area ratio was associated with lower values of specific leaf area. Leaves grown at elevated CO2 had higher starch concentrations (dry weight basis) than leaves grown at present levels of CO2. Biomass allocation showed no change with CO2, and no large effects on stem height, number of side shoots and number of leaves were found. However, the specific root length of fine roots was higher at elevated CO2. No large difference in the response of carbon assimilation to intercellular CO2 concentration (A/Ci curves) were found between CO2 treatments. When measured at the growth environments, the rates of photosynthesis were higher in plants grown at elevated CO2 than in plants grown at present CO2. Water use efficiency of single leaves was higher in the elevated treatment. This was mainly attributable to higher carbon assimilation rate at elevated CO2. The difference in water use efficiency diminished with leaf age. The small treatment difference in relative growth rate was maintained throughout the experiment, which meant that the difference in plant size became progressively greater. Thus, where plant nutrition is sufficient to maintain maximum growth, small birch plants may potentially increase in size more rapidly at elevated CO2.
Ultraviolet‐B and visible light penetration into needles of two species of subalpine conifers during foliar development
Authors: DeLUCIA E. H. , DAY T. A. , VOGELMAN T. C. 
Published: April 2006

ABSTRACTThe depth of penetration of Ultraviolet‐B (UV‐B, 300 and 320 nm) and visible (680 nm) light was measured in foliage of Abies lasiocarpa and Picea engelmannii using a fibre‐optic microprobe. Measurements were made on foliage at four times during development: needles were sampled from within expanding buds (in bud); within 72 h of emergence from the bud scales (emergent); from elongating branches (elongating); and from foliage that emerged the previous summer (mature). Light attenuation in pre‐emergent needles of both species was steep and showed strong wavelength dependence. Short wavelength 300‐nm light was attenuated strongly in the developing epidermal layer, but a significant proportion of this potentially damaging UV‐B radiation penetrated into the mesophyll. For A. lasiocarpa and P. engelmannii, 99% attenuation of 300‐nm light occurred at 51 and 96 μm, respectively, well within the mesophyll. At this stage, however, the bud scales were opaque to light below 400nm. As the epidermal cell walls and cuticle continued to develop and chlorophyll accumulated following emergence from the bud scales, light attenuation, particularly of UV‐B radiation, increased. Although no UV‐B is transmitted through the epidermis‐hypodermis of mature needles, small but measurable quantities of 300‐ and 320‐nm light were measured in the photosynthetic mesophyll of post‐emergent and elongating needles. Thus, shortly after emergence from the bud scales in mid‐June to mid‐July, when incident UV doses are highest, absorption of UV‐B radiation by potentially sensitive chromophores in the mesophyll may disrupt physiological and developmental processes in these species. Soluble UV‐absorbing pigments accumulated during needle maturation for P. engelmannii but not A. lasiocarpa, suggesting that, for A. lasiocarpa at least, the development of effective UV screening properties in the epidermis may not be related to the induction of soluble flavonoids.
Water relations of the tomato during fruit growth
Authors: JOHNSON R. W. , DIXON M. A. , LEE D. R. 
Published: April 2006

ABSTRACTFruit and stem water potentials of tomato plants were measured continuously for several days using automated psychrometers. A linear voltage displacement transducer was used to simultaneously measure diameter changes on an adjacent fruit. A strong correlation was observed between the water potential gradient of the fruit and stem, and changes in fruit diameter. Fruit diameter increased when the apoplasmic water potential gradient favoured solution flow into the fruit and fruit shrinkage occurred only when the water potential gradient was inverted. Based on our data and other published data (Ehret & Ho 1986; Lee 1989a) on phloem transport in tomato, we have concluded that low stem water potentials have an immediate and direct effect on phloem turgor; reducing the driving force for sap flow into the fruit. Since fruit water potential remained relatively constant, the diurnal variation in stem water potential was sufficient to account for the correlation with changes in fruit diameter. There are consequences with respect to predicting the accumulation of dry matter in tomato fruit.