bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of the embryonic axis and phytohormones on proteolysis of the storage protein in buckwheat seed
Authors: Dunaevsky Yakov E. , Belozersky Mikhail A. 
Published: May 2006

The role of the embryonic axis in regulation of proteolysis of the main storage protein was studied in buckwheat (Fagopyrum esculentum) seed. Polyacrylamide gel electrophoresis (PAGE) analysis revealed that removal of the embryonic axis had no effect on the first stage of hydrolysis, that is proteolytic modification, of 13S globulin. This modification took place in the growing seedlings also in the presence of cycloheximide, i.e. it was due to an enzyme present in dry seed. However, in isolated cotyledons the 13S globulin was not degraded completely. Incubation of isolated cotyledons with cytokinins, gibberellic acid and indoleacetic acid could not replace the excised embryonic axis. At the same time, proteolysis of the 13S globulin in the growing seedlings was strongly inhibited by casein hydrolyzate. It is suggested that a complete proteolysis of the modified storage protein is regulated by the concentration of hydrolysis products at the site of hydrolysis. The embryonic axis serves, most probably, as a site of efflux of the products of protein hydrolysis in the cotyledons during seedling growth and thus regulates the course of proteolysis.Abscisic acid (10–100 μM) was without effect on modification of the 13S globulin, but suppressed the complete proteolysis of the protein by inhibiting, apparently, the synthesis of the cysteine proteinase in the growing seedlings.
Kinetic parameters of nitrate uptake by different catch crop species: effects of low temperatures or previous nitrate starvation
Authors: Lainé P. , Ourry A. , Macduff J. , Boucaud J. , Salette J. 
Published: May 2006

The pollution of aquifers by NO−3 in temperate environments is aggravated by farming practices that leave the ground bare during winter. The use of catch crops during this time may decrease nitrate loss from the soil. Nitrate uptake by several catch crop species (Brassica napus L., Sinapis alba L., Brassica rapa L., Raphanus sativus L., Trifolium alexandrinum L., Trifolium incarnatum L., Phacelia tanacetifolia Benth., Lolium perenne L., Lolium multiflorum Lam. and Secale cereale L.) was here studied in relation to transpiration rate and low temperatures applied to the whole plant or to roots only. The Michaelis constant (Km), maximum uptake rate (Vmax), time of induction and contributions of inducible and constitutive mechanisms were estimated from measurements of NO−3 depletion in the uptake medium. There were large differences between species, with Km (μM) values ranging between 5.12 ± 0.64 (Trifolium incarnatum) and 36.4 ± 1.97 (Lolium perenne). Maximum NO−3 uptake rates expressed per unit root weight were influenced by ageing, temperature and previous NO−3 nutrition. They were also closely correlated with water flow through the roots and with shoot/root ratio of these species. The combined results from all species and treatments showed that Vmax increased with shoot/root ratio, suggesting a regulatory role for the shoots in NO−3 uptake. Overall, the results showed a great diversity in NO−3uptake characteristics between species in terms of kinetic parameters, contribution of the constitutive system (100% of total uptake in ryegrass, nil in Fabaceae) and time of induction.
Xyloglucan oligosaccharides with at least two α‐d‐xylose residues act as acceptor substrates for xyloglucan endotransglycosylase and promote the depolymerisation of xyloglucan
Authors: Lorences Ester P. , Fry Stephen C. 
Published: May 2006

A xyloglucan‐derived pentasaccharide. Xyl2‐Glc3, was shown by viscometry to promote the depolymerisation of xyloglucan by enzyme extracts from bean (Phaseolus vulgaris L. cv. Canadian Wonder) leaves and pea (Pisum sativum L. cv. Alaska) stems. Xyl2‐Glc3 was also shown by a radiochemical assay to act as an acceptor substrate for xyloglucan endotransglycosylase activity (XET: EC 2.4.1.—) present in the same extracts. In both these assays, a heptasaccharide (Xyl3‐Glc4) was more effective than Xyl2‐Glc3 whereas two isomeric tetrasaccharides (Xyl1‐Glc3) were essentially ineffective. The agreement in the structural requirements of the two assays suggests that they share a common basis; we therefore propose that the oligosaccharide‐sensitive enzyme that depolymerises xyloglucan is XET rather than cellulase (EC 3.2.1.4). In the viscometric assay, the penta‐ and heptasaccharides would, according to our interpretation, compete with high molecular weight xyloglucan molecules as acceptor substrates for XET, leading to a decrease in the weight‐average molecular weight of the xyloglucan and, therefore, to a decrease in viscosity.Our results indicate that oligosaccharides have to possess two α‐d‐xylose residues in order to act as acceptor substrates for XET. The non‐reducing end of a high‐molecular weight xyloglucan can also act as an acceptor substrate. Therefore, it is likely that exo‐hydrolysis by α‐d‐xylosidase would destroy the ability of a polysaccharide to act as an acceptor, even though α‐d‐xylosidase may remove only a single xylose residue from each polysaccharide molecule.
Salinity stress and cytoplasmic factors. A comparison of cell permeability and lipid partiality in salt sensitive and salt resistant cultivars and lines of Triticum aestivum and Hordeum vulgare
Authors: Magdy M. , Mansour F. , Lee‐Stadelmann OK Young , Stadelmann Eduard J. 
Published: May 2006

Salinity effects on the cell membranes of four lines of wheat (Triticum aestivum L.). and two cultivars of barley (Hordeum vulgare L.), differing in salt resistance were investigated. Plants were grown for 10 days in 1/4‐strength Hoagland solution and then for 5 more days in 1/4‐strength Hoagland with and without NaCl (100 mM) or (for Hordeum only) polyethylene glycol (PEG). Permeability to three non‐electrolytes (urea, methylurea and ethylurea) of subepidermal cells of leaf sheaths (Triticum) and coleoptiles (Hordeum) was determined and membrane partiality calculated, a parameter which numerically indicates the degree of lipophilicity of a membrane. Non‐electrolyte permeability significantly increased and membrane partiality decreased in the salt sensitive cultivars or lines under salt stress. Neither parameter changed significantly in the salt resistant lines and cultivar in a saline environment. Osmotic stress in Hordeum by PEG 10000 had no significant effect on permeability and thus membrane partiality neither in sensitive nor in resistant cultivars.The osmotic component of salinity stress did not seem to be a major factor causing injury, rather ion toxicity may be a cause of cell damage. The results indicate differences in the membrane between salt sensitive and salt resistant genotypes. Salt resistance seems to be controlled by genetic factors independent of external salinity levels.
The relationship between the activity of various iron‐containing and iron‐free enzymes and the presence of nicotianamine in tomato seedlings
Authors: Pich Axel , Scholz Günter 
Published: May 2006

The influence of nicotianamine (NA) and iron on the activities of 4 iron‐containing and two iron‐free enzymes in leaves and roots of the NA‐free tomato mutant chloronerva and its NA‐containing wild‐type (Lycopersicon esculentum Mill. cv. Bonner Beste) was investigated. Aconitase (EC 4.2.1.3) activity in both leaves and roots was much higher in the mutant under normal iron supply (10 μM FeEDTA) and in wild‐type under iron deficiency than in wild‐type supplied with 10 μM FeEDTA. Application of NA to chloronerva leaves led to a decrease of aconitase activity in leaves and roots. NA had no effect on the enzyme activity when added to the assay medium.Similar results were obtained for the iron‐containing enzymes catalase (EC 1.11.1.6), ascorbate‐dependent peroxidase (EC 1.11.1.11) and guaiacol‐dependent peroxidase (EC 1.11.1.7) in roots. NA treatment of the mutant leaves decreased enzyme activities in roots down to wild‐type values. In vivo NA application had no effect on enzyme activities in leaf extracts.The activities of the iron‐free enzymes NAD+‐malate dehydrogenase (EC 1.1.1.37) and phosphofructokinase (EC 2.7.1.11) in root and leaf extracts were not influenced by the iron supply to the plants.
Induction of elongation in maize coleoptiles by hexachloroiridate and its interrelation with auxin and fusicoccin action
Authors: Lüthen Hartwig , Böttger Michael 
Published: May 2006

The demonstration of an auxin‐stimulated NADH‐oxidase in the plasma membrane (Brightman et al. 1988. Plant Physiol. 86: 1264–1269) has led to the suggestion that the plasma membrane redox system is involved in the mechanism of auxin action. To evaluate the relevance of this concept in vivo, the influence of micromolar concentrations of hexachloroiridate (IV), an impermeable electron acceptor for the plant plasma membrane redox system, on elongation growth of excised, abraded maize coleoptile (Zea mays L. cv. Golden Bantam) segments was studied. It was found that the substance induced a rapid growth response if the experiment was carried out in an unbuffered solution. This effect was entirely prevented by a 2 mM phosphate buffer. Nevertheless, the acid‐growth‐theory does not seem sufficient to explain this effect, since proton extrusion is induced without a lag, whereas increased growth rates commence after a lag phase of 40 min.If growth is stimulated by a pretreatment with fusicoccin or auxin, hexachloroiridate IV transiently inhibits growth. The kinetics of the response are then determined by the concentrations of hexachloroiridate and auxin or fusicoccin. These results are compatible with the view that the plasma membrane redox system is somehow involved in the control of elongation growth.
Accumulation of calcium, potassium and magnesium in apple fruits under various conditions of humidity
Authors: Tromp J. , Van Vuure J. 
Published: May 2006

In each of two experiments done under controlled conditions, starting at bloom, 4 humidity treatments were applied to potted trees of apple (Malus pumila Mill. cv. Cox's Orange Pippin), i. e. in experiment 1: (1) high humidity throughout, (2) low humidity throughout, (3) low humidity for 7 weeks followed by high humidity for 6‐7 weeks, and (4) the reverse (first high and then low humidity); in experiment 2: (1) day/night humidity high/high, (2) low/low, (3) low/high, and (4) high/low.In both experiments high humidity favoured shoot growth appreciably. Change from low to high humidity after 7 weeks resulted in some growth stimulation but in the reverse situation growth was markedly reduced. Shoot growth responded little to different night humidities. In the two experiments fruit growth was little affected by treatments. In experiment 2 irrespective of night humidity, water consumption was higher at low than at high day humidity. In the high/low humidity regime water use during the night was high and leaf water potential low, relatively; during the day water potential was little affected by treatments.At any time leaf Ca and Mg were clearly highest at low day humidity; night humidity had no effect. Leaf K did not respond to treatments. Fruit Ca at high humidity throughout was lower than at low humidity throughout. Increasing humidity later in the season was ineffective but a decrease at that time tended to reduce fruit Ca slightly. The clearly lowest Ca values occurred in the high/low day/night treatment. Fruit K and Mg were not or hardly affected by treatments.The findings are discussed in terms of humidity effects on transpiration, shoot and fruit growth, and xylem mineral concentration and ion exchange translocation along the xylem walls.
Inhibition of cell wall autolysis and auxin‐induced elongation of Cicer arietinum epicotyls by β‐galactosidase antibodies
Authors: Valero Pilar , Labrador Emilia 
Published: May 2006

Polyclonal antibodies were raised in response to βIII‐galactosidase purified from cell wall of Cicer arietinum epicotyls. The antibody preparation generated, bound to βIII protein giving a major protein band in the zone corresponding to Mr 45 000, the molecular mass previously estimated for βIII‐galactosidase. These antibodies clearly suppress autolytic reactions in isolated walls of Cicer arietinum epicotyl segments, while the preimmune serum had no effect on autolytic reaction. The results strongly support the idea that the autolytic degradation of the cell wall is carried out by the βIII‐galactosidase.The antibodies against β‐galactosidase were also able to inhibit cell wall hydrolysis mediated by both total cell wall protein extracted by LiCl and cell wall hydrolysis mediated by βIII‐galactosidase.Since autolysis is thought to be related to the process of cell wall loosening, the effects of the antibodies against the autolytic enzyme was also tested on epicotyl growth. β‐galactosidase antibodies consistently inhibited IAA‐induced elongation.
Synergistic activation of plasma membrane H+– ATPase in Arabidopsis thaliana cells by turgor decrease and by fusicoccin
Authors: Curti Giovanna , Massardi Ferdinando , Lado Piera 
Published: May 2006

The regulation of the H+‐ATPase of plasma membrane is a crucial point in the integration of transport processes at this membrane. In this work the regulation of H+‐ATPase activity induced by changes in turgor pressure was investigated and compared with the stimulating effect of fusicoccin (FC). The exposure of cultured cells of Arabidopsis thaliana L. (ecotype Landsberg 310–14‐2) to media containing mannitol (0. 15 or 0. 3 M) or polyethylene glycol 6000 (PEG) (15. 6% or 22% w/v) resulted in a decrease in the turgor pressure of the cells and in a strong stimulation of H+ extrusion in the incubation medium. The osmotica‐induced H+ extrusion was (1) inhibited by the inhibitor of plasma membrane H+‐ATPase, erythrosin B (EB), (2) dependent on the external K+ concentration, (3) associated with a net K+ influx, and (4) lead to an increase of cellular malate content. These results show that the reduction of external osmotic potential stimulates the activity of plasma membrane H+‐ATPaseThe effect of mannitol was only partially inhibited by treatments with cycloheximide (CH) and cordycepin, which block protein and mRNA synthesis, respectively. All the effects of osmotica were qualitatively and quantitatively similar to those induced by 5 μM FC. However, when FC and mannitol (or PEG) were fed together, their effects on H+ extrusion appeared synergistic, irrespective of whether FC was present at suboptimal or optimal concentrations. This behaviour suggests that the modes of action of FC and of the osmotica on H+‐ATPase activity differ at least in some step(s)
Response of seedlings of radish (Raphanus sativus) to osmotic shock and external hydrostatic pressure
Authors: Cocucci Sergio M. , Morgutti Silvia , Abruzzese Alessandro , Alisi Chiara , Yahye Asha H. , Espen Luca 
Published: May 2006

The effects of an osmotic shock (300 mM mannitol, –0. 67 MPa) or/and increased external hydrostatic pressure on seedlings (42‐h‐germinated seeds) of radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) were investigated. The osmotic shock did not inhibit H+ extrusion and net K‐ uptake, and did not affect the levels of malic acid, reducing sugars, sucrose or amino acids or of the energy charge (i. e. the synthesis of energy‐rich phosphate bonds), but inhibited the synthesis of proteins. RNA and DNA, measured as incorporation of labelled precursors. When the osmotic shock was applied together with an increased external hydrostatic pressure of the same magnitude (+0. 67 MPa), the same metabolic parameters and the inhibition of synthesis of RNA and DNA were not substantially affected, while the inhibition of protein synthesis was practically reversed and the energy charge decreased; the recovery of protein synthesis was not due to a change in labelled leucine uptake capability. Increased external hydrostatic pressure alone decreased the energy charge without affecting the other parameters considered.The possibility that protein synthesis activity is directly controlled by cell turgor pressure (internal hydrostatic pressure) is discussed.
Effects of osmotic preconditioning on nuclear replication activity in seeds of pepper (Capsicum annuum)
Authors: Lanteri Sergio , Kraak H. Lieke , De Vos C. H. Ric , Bino Raoul J. 
Published: May 2006

Flow cytometric determination of nuclear DNA contents in embryos of dry, fully matured pepper seeds revealed only 2C signals. Therefore, pepper belongs to those species in which the quiescent embryo arrests nuclear division in the presynthetic G1 phase. In whole seeds, two other peaks were observed which corresponded with the 3C and 6C DNA content and originated from the triploid endosperm. After 36 to 48 h of imbibition in water (48 to 60 h before visible germination), a rise in the 4C signal was observed in the root tip of the embryo.Osmotic preconditioning (priming) of pepper seeds for 7, 14 or 21 days in polyethylene glycol (PEG) or KNO3+ K3PO4 considerably reduced the time to 50%; germination (t50) and the mean germination time, and the effect was proportional to the duration of the priming treatments. An induction of the 4C signal was firstly observed after 10 days osmopriming in either PEG or KNO3+ K3PO4. For both priming methods, a positive correlation was found between the efficiency of the treatment to reduce the mean germination time, and the induction of DNA synthesis, measured as the amount of 4C versus 2C, at 12 h before radicle protrusion. Apart from the quantitative effect, there was also a temporal influence of priming on DNA synthetic activity. When primed seeds were subsequently imbibed in water, the induction of DNA synthesis started about 12 h earlier than in untreated seeds. This was also found for seeds primed for 7 days, when no induction of DNA synthesis had yet occurred. Apparently, during priming of pepper seeds there is a lag period of 9 days in which physiological processes other than DNA synthesis can take place. These processes sustain a rapid inception of nuclear replicative activity upon imbibition. By comparing the relative nuclear DNA contents of dry, imbibed and primed seeds, we provide information about the relation between the percentage of cells in seeds which have entered the replication stage of nuclear division, and germination performance.
Iron stress‐induced redox reactions in bean roots
Authors: Schmidt Wolfgang 
Published: May 2006

Iron stress‐induced and constitutive redox activity of bean (Phaseolus vulgaris L. cv. Delinel) roots was measured on intact plants using FeEDTA and ferricyanide as electron acceptors. The presence of the translation inhibitor cycloheximide caused a decrease in the reduction of both oxidants. However, a differential decline in the reduction rates of FeEDTA and ferricyanide was observed, suggesting enzyme heterogeneity. In the presence of the H+ ‐ATPase inhibitor vanadate, the reduction of FeEDTA was nearly completely suppressed in both Fe‐deficient (–Fe) and Fe‐sufficient (+Fe) plants, providing evidence for an involvement of plasma membrane‐bound ATPase activity in the regulation of the reduction process. The inhibition of the ferricyanide reduction by vanadate was restricted to –Fe plants.The data are interpreted in terms of simultaneous operation of distinct redox systems in roots of iron‐deficient bean plants. The role of proton extrusion in iron stress‐induced electron transfer is discussed.
The quantitative role of ammonia/ammonium transport and metabolism by plants in the global nitrogen cycle
Authors: Raven J. A. , Wollenweber B. , Handley L. L. 
Published: May 2006

Estimate of global yearly N assimilation by photolithotrophs are 417 Tmol N in the oceans and 167 Tmol on land and in freshwater, of which diazotrophy contributes 1 (sea) and 10 (land plus freshwater) Tmol N. More than half of the combined N assimilated (416 and 157 Tmol N year−1 in the sea and on land plus freshwater, respectively) is due to reduced N, i. e. organic N and, mainly, NH3/NH+4. Assimilation of reduced N amounts to up to 334 Tmol N year−1 in the oceans and at least 79 Tmol N year−1 in freshwater and on land.Reassimilation of NH3/NH+4 within the plant which is related to photorespiration is at least as great as primary NH3/NH+4 assimilation in the sea, and 8 times greater on land. The less frequently considered reassimilation of NH3/NH+4 that is related to phenyl‐propanoid (mainly lignin) synthesis in land plants is similar (111 Tmol N) to the primary assimilation of NH3/NH+4 on land each year.Shoots of terrestrial plants have higher NH3 compensation partial pressures than most natural soils, and especially than have ocean‐surface biota. However, gaseous transfer of NH3/NH+4 from land to the oceans is a negligible component of the global N cycle. Consideration of area‐based N assimilation rates, diffusion distances and diffusion coefficients can rationalise why steady‐state NH3/NH+4 concentrations in the sea are lower than in the soil solution.The possibility that photolithotrophs can catalyse the oxidation of NH3/NH+4, or organic N at the same redox level, to N2, N2O, NO, –NO2, NO−, 2, NO2 or NO4+, is critically assessed. The tentative conclusions are that such oxidation probably occurs, but is not a major component of the global conversion of reduced N to N2 and more oxidized N species. More work is needed, especially to determine if NO generated from reduced N (conversion of arginine to citrulline plus NO) has a regulatory role in plants analogous to that established in metazoa.Relative to NO3− (or N2) as N sources, growth using NH3/NH+4 as N source has a number of potential advantages in terms of cost of other resources. Mechanistically predicted economies for NH+4 as N source are: (1) lower cost of photons used and, in transpiring plants, (2) less water lost per unit C assimilated, and (3) lower costs of catalytic Fe, Mn and Mo (unit C assimilated)−1 s−1, as well as (4) a higher maximum growth rate. The lower photon costs are frequently borne out by experimentation and the predicted higher maximum growth rates sometimes occur, while the predicted lower water costs are invariably contradicted. Few data are available for the cost of Fe, Mn or Mo as a function N source.