bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental effects of 24‐epibrassinolide in excised roots of tomato grown in vitro
Authors: Roddick James G. , Rijnenberg Anna L. , Ikekawa Nobuo
Published: May 2006

The effects of 1 pM–10 μM 24‐epibrassinolide presented to apical and basal regions of excised roots of tomato (Lycopersicon esculentum Mill. cv. Best of All) grown aseptically in a two‐well culture vessel have been investigated. Only inhibitory effects were observed and only at 0. 1 μM or greater. At 10 μM basally‐ and apically‐applied epibrassinolide inhibited growth in apical regions, but not in basal regions. Lower concentrations (1 and 0. 1 μM) also inhibited growth, again only in apical regions and usually only when presented directly to those regions. Cultured tomato roots therefore appear to transport epibrassinolide acropetally, but whether they do so basipetally is not yet clear. The reduced responsiveness to epibrassinolide observed in roots grown by this method is thought to be due to the larger inoculum used rather than the physiological age of the roots. There was some evidence that the sensitivity of cultured roots to epibrassinolide is directly related to growth rate
Inhibition of whole plant respiration by elevated CO2 as modified by growth temperature
Authors: Ziska Lewis H. , Bunce James A.
Published: May 2006

Plants of alfalfa (Medicago sativa) and orchard grass (Dactylus glomerata) were grown in controlled environment chambers at two CO2 concentrations (350 and 700 μmol mol‐1) and 4 constant day/night growth temperatures of 15, 20, 25 and 30°C for 50–90 days to determine changes in growth and whole plant CO2 efflux (dark respiration). To facilitate comparisons with other studies, respiration data were expressed on the basis of leaf area, dry weight and protein. Growth at elevated CO2 increased total plant biomass at all temperatures relative to ambient CO2, but the relative enhancement declined (P≤0.05) as temperature increased. Whole plant respiration (Rd) at elevated CO2 declined at 15 and 20°C in D. glomerata on an area, weight or protein basis and in M. sativa on a weight or protein basis when compared to ambient CO2. Separation of Rd into respiration required for growth (Rg) and maintenance (Rm) showed a significant effect of elevated CO2 on both components. Rm was reduced in both species but only at lower temperatures (15°C in M. sativa and 15 and 20°C in D. glomerata). The effect on Rm could not be accounted for by protein content in either species. Rg was also reduced with elevated CO2; however no particular effect of temperature was observed, i. e. Rg was reduced at 20, 25 and 30°C in M. sativa and at 15 and 25°C in D. glomerata. For the two perennial species used in the present study, the data suggest that both Rg and Rm can be reduced by anticipated increases in atmospheric CO2; however, CO2 inhibition of total plant respiration may decline as a function of increasing temperature
Purification and characterization of adenine phosphoribosyltransferase from Arabidopsis thaliana
Authors: Lee Diana , Moffatt Barbara A.
Published: May 2006

Adenine phosphoribosyltransferase (APRT; EC 2. 4,2. 7) from Arabidopsis thaliana was purified approximately 3800‐fold, to apparent homogeneity. The purification procedure involved subjecting a leaf extract to heat denaturation, (NH4)2SO4 precipitation, Sephadex G‐25 salt separation, ultracentrifugation and liquid chromatography on Diethylaminoethyl Sephacel, Phenyl Sepharose CL‐4B, Blue Sepharose CL‐6B and adenosine 5′‐monophosphate‐Agarose. The purified APRT was a homodimer of approximately 54 kDa and it had a specific activity of approximately 300 μmol (mg total protein)‐1 min‐1. Under standard assay conditions, the temperature optimum for APRT activity was 65°C and the pH optimum was temperature dependent. High enzyme activity was dependent upon the presence of divalent cations (Mn2+ or Mg2+). In the presence of MnCl2+ other divalent cations (Mg2+, Ca2+, Ba2+, Hg2+ and Cd2+) inhibited the APRT reaction. Kinetic studies indicated that 5‐phosphoribose‐1‐pyrophosphate (PRPP) caused substrate inhibition whereas adenine did not. The Km for adenine was 4.5±1.5 μM, the Km for PRPP was 0.29±0.06 mM and the Ki for PRPP was 1.96±0.45 mM. Assays using radiolabelled cytokinins showed that purified APRT can also catalyze the phosphoribosylation of isopentenyladenine and benzyladenine. The Km for benzyladenine was approximately 0.73±0.06 mM
Osmotic adjustment in Lycopersicon esculentum and L. Pennellii under NaCl and polyethylene glycol 6000 iso–osmotic stresses
Authors: Pérez‐Alfocea F. , Estañ M. T. , Caro M. , Guerrier G.
Published: May 2006

Changes in leaf solute contents in response to saline (NaCl) and osmotic (polyethylene glycol, PEG, 6000) stresses were measured in three different salt tolerant cultivars of Lycopersicon esculentum (L.) Mill. (Pera, P‐73 and Volgogradskij), and its wild relative L. pennellii (Correll) D'Arcy accession PE‐47. Iso‐osmotic stresses (–0. 5 MPa) of NaCl (140 mM) and PEG 6000 (150 g l‐1) were applied to one‐month old plants for 3 weeks. Decreasing leaf dry weight was similar in L. pennellii or L. esculentum cv. P‐73 and Volgogradskij under both stresses, while leaf dry weight of L. esculentum cv. Pera decreased more under PEG stress than under NaCl stress. Water contents decreased in all the PEG treated populations, while their calculated solute potential (Ψs increased. Under osmotic stress, the total ion contents decreased in relation to control, whereas organic solutes (sugars, amino acids and organic acids) markedly increased in both tomato species, specially in the tomato cultivars, where these solutes represented 50% of the Ψ5 calculated. Soluble sugar increase was three times higher in leaves of L. esculentum than in the leaves of L. pennellii. Free proline increased under both stresses and its content was highest in L. esculentum and in L. pennellii, respectively, under NaCl and PEG stresses. Nevertheless, the contribution of this metabolite to Ψs did not exceed 5%, irrespective of treatment and species. The greater organic solute accumulation in L. esculentum than in L. pennellii– which was not reflected in their Ψ5 values – was not correlated with the tolerances of the two species to osmotic stress. Therefore, osmotic adjustment may not be the only process influencing salt and drought tolerances in tomato; the ability of plants to regulate their metabolic and physiological functions could also play an important role under these harmful conditions. The possible roles of inorganic solutes and metabolites in osmotic adjustment, energetic metabolism and redox regulation are discussed
Proteins accumulate in the apoplast of winter rye leaves during cold acclimation
Authors: Marentes Eduardo , Griffith Marilyn , Mlynarz Andrzej , Brush Ruth Anne
Published: May 2006

During cold acclimation, winter rye (Secale cerealeL.) plants develop the ability to tolerate freezing temperatures by forming ice in intercellular spaces and xylem vessels. In this study, proteins were extracted from the apoplast of rye leaves to determine their role in controlling extracellular ice formation. Several polypeptides in the 15 to 32 kDa range accumulated in the leaf apoplast during cold acclimation at 5°C and decreased during deacclimation at 20°C. A second group of polypeptides (63, 65 and 68 kDa) appeared only when the leaves were maximally frost tolerant. Ice nucleation activity, as well as the previously reported antifreeze activity, was higher in apoplastic extracts from cold‐acclimated than from nonacclimated rye leaves. These results indicate that apoplastic proteins exert a direct influence on the growth of ice. In addition, freezing injury was greater in extracted cold‐acclimated leaves than in unextracted cold‐acclimated leaves, which suggests that the proteins present in the apoplast are an important component of the mechanism by which winter rye leaves tolerate ice formation
Lipid composition of plasma membranes isolated from sunflower seedlings grown under water‐stress
Authors: Navari‐Izzo Flavia , Quartacci Mike Frank , Melfi Donato , Izzo Riccardo
Published: May 2006

Plasma membranes were isolated by aqueous two‐phase‐partitioning from sunflower (Helianthus annuus cv. Isabel) seedlings grown both under field irrigation and dryland conditions. Water‐stressed plants showed a decrease in the leaf water potential and in the osmotic potential at full turgor, with the turgor pressure remaining at positive values. Dryland conditions also induced a reduction in the bulk modulus of elasticity. Plasma membranes of irrigated plants were characterized by high contents of phospholipids (68% of total lipids), free sterols (15. 7%) and glycolipids (9. 1%), mainly glycosphingolipids and steryl glycosides. Diacylglycerols, triacylglycerols and free fatty acids were also present. The major phospholipids were phosphatidylcholine and phosphatidylethanolamine with smaller amounts of phosphatidylinositol and phosphatidylglycerol. Following water stress, the plasma membranes showed a reduction of about 24 and 31% in total lipids and phospholipids, respectively. Also the amounts of glycolipids and diacylglycerols decreased significantly upon water stress. There was no change in free fatty acids, however, and triacylglycerols and free sterols increased. As a consequence, the free sterol to phospholipid molar ratio increased from 0. 4 to 0. 7 under water deficit conditions. The ratio of phosphatidylcholine to phosphatidylethanolamine increased from 1. 1 (control plants) to 1. 6 (water‐stressed plants), while phosphatidic acid rose to 4% of total phospholipids. Dehydration did not result in any substantial change in the unsaturation level of the individual lipid classes, however. The results show that dryland conditions resulted in a marked alteration in the lipid composition of the sunflower leaf plasma membrane
Effect of chilling and subsequent storage at 20°C on electrolyte leakage and phospholipid fatty acid composition of tomato pericarp
Authors: Bergevin M. , L'Heureux G. P. , Thompson J. E. , Willemot C.
Published: May 2006

Mature green tomato fruit (Lycopersicon esculentum cv. Caruso) were stored at 1°C or 20°C and analyzed on day 0, 18 and 22 for electrolyte leakage, ripening‐associated changes in pigmentation and phospholipid fatty acid composition. Chilled fruit were also analyzed 4 days after they were returned to 20°C. Fruit did not ripen significantly during chilling and subsequent storage at 20°C, and showed visible chilling injury symptoms only at 20°C. Electrolyte leakage increased in control and chilled fruit, indicating enhanced membrane permeability during both ripening and chilling. Returning the fruit to ambient temperature gave an apparent decrease in electrolyte leakage. Phospholipid and linolenic acid content and double bond index decreased during ripening at 20°C. The small changes in phospholipid fatty acid composition during chilling cannot account for the enhanced membrane permeability. The significant decrease in percentage of linolenic acid and in double bond index in the total lipids, but not in the phospholipids, upon returning the fruit to 20°C suggests loss of galactolipid polyunsaturated fatty acids
Effect of osmotic stress on the growth of epicotyls of Cicer arietinum in relation to changes in the autolytic process and glycanhydrolytic cell wall enzymes
Authors: Muñoz Francisco José , Labrador Emilia , Dopico Berta
Published: May 2006

Simulation of drought by polyethylene glycol (PEG) inhibited elongation of epicotyls of Cicer arietinum L. cv. Castellana but had no effect on growth capacity since growth was restored once the inhibitory condition had been removed. The amount of proteins in the cell wall was correlated with the elongation of the epicotyls and decreased when elongation was inhibited. PEG‐induced inhibition of elongation had different effects on the various glycanhydrolytic cell wall enzymes. Only α‐galactosidase (EC 3. 2. 1. 22) seemed related to the lack of elongation, increasing its activity when elongation was inhibited. The β‐galactosidase (EC 3. 2. 1. 23) and β‐glucosidase (EC 3. 2. 1. 21) studied did not show changes in their specific activities during the inhibition of elongation. β‐Galactosidase is responsible for the autolytic process in Cicer arietinum. This enzyme hydrolyzes specified linkages in the cell wall, releasing sugar constituents. Our present results show that β‐galactosidase is not directly related with elongation because no changes could be observed during inhibition of elongation. The autolytic process is related with chemical processes taking place in the cell wall and preceding elongation of the epicotyls, i. e. the loosening process. Cell wall loosening is necessary for elongation to take place but elongation does not necessarily follow loosening if the osmotic conditions are unfavorable
Effect of osmotic stress on the growth of epicotyls of Cicer arietinum in relation to changes in cell wall composition
Authors: Muñoz Francisco José , Dopico Berta , Labrador Emilia
Published: May 2006

The inhibition of growth by polyethlene glycol (PEG)‐induced osmotic stress led to modifications in the changes taking place in cell wall composition during normal growth of epicotyls of Cicer arietinum L. cv. Castellana. Epicotyls growing under normal conditions showed a decrease in the amount of pectic fractions and an increase in the hemicellulosic fractions and α‐cellulose that led to an increase in the rigidity and a loss in growth capacity. Among the hemicellulosic fractions, the KI‐2 fraction (insoluble fraction of 10% KOH‐extracted hemicelluloses) seemed to be the only one related to the elongation process and subsequent rigidity. During normal growth a decrease was observed in the total amount of galactose, mainly from the pectic fractions. The inhibition of elongation led to an increase in the amount of the cell walls, due to inhibition of cellular elongation. PEG prevented the increase in the hemicelluloses and the α‐cellulose, indicating that these changes were related to elongation. Thus, during the inhibition of elongation there is probably an inhibition of new synthesis that prevents cell wall rigidity and maintains cell wall growth capacity. Changes in the pectic fractions during growth were not affected by the inhibition of elongation, showing that these fractions are related to cell wall loosening rather than to elongation. Study of the cell wall composition confirms the idea that the autolytic process is regulated by changes in the cell wall structure during epicotyl growth
What is in the intercellular spaces of roots? Evidence from the cryo‐analytical‐scanning electron microscope
Authors: Canny M. J. , Huang C. X.
Published: May 2006

The schizogenous intercellular spaces (i. e. those small spaces formed by cell walls coming apart) in the cortex of the roots of field‐grown maize (Zea mays L.) were studied in planed transverse faces of frozen tissue, very lightly etched and coated with Al. The spaces were mostly filled with either fluid or, in the drier roots, with a flaky deposit. This deposit may have been left behind when water was withdrawn, or may have been debris dislodged by the planing. Even in roots with mostly dry spaces, some wet, fluid‐filled spaces remained. X‐ray microanalysis of the wet spaces revealed that the fluid contained K (average concentration 230 mM, range 50–750 mM) and Ca (average concentration 100 mM, range 15 to 550 mM), and occasionally small amounts of S, P or Cl. No other balancing inorganic anions were detected. Concentrations in the wet intercellular spaces showed considerable variation between one space and the next, and were often quite different from those in the vacuoles of adjacent cells. However, overall the vacuoles of the cells surrounding the spaces showed mean concentrations, and distributions of concentrations, indistinguishable from those of the wet spaces. Analyses of the deposits in the dry spaces were less reliable because of their uneven surface, but the same ions in about the same amounts were found there. The contents of the spaces showed no correlation with either the time of collection of the roots, or with distance from the root tip. Nor was there any change in concentration of these ions in the spaces when the roots were grown for 19 h in distilled water mist. Experiments and evidence are presented suggesting that the observed distribution of ions is probably not an artefact. Pilot experiments showed similar distributions of extracellular ions in roots of barley, Sudan grass and soybean
Carrier‐mediated uptake of glyphosate in broad bean (Vicia faba) via a phosphate transporter
Authors: Denis Marie‐Hélène , Delrot Serge
Published: May 2006

The possibility that the herbicide glyphosate (N‐phosphonomethylglycine) may be taken up in plant cells via a phosphate transporter of the plasma membrane was investigated using protoplasts of broad bean leaves (Vicia fabaL.). Phosphonoformic acid, a powerful inhibitor of phosphate transport in animal cells, was first demonstrated to be a competitive inhibitor of phosphate uptake inbroad bean protoplasts. Glyphosate was able to inhibit phosphate uptake into the protoplasts, and to protect partially the phosphate transporter from inhibition by phosphonoformic acid. Concentration dependence studies showed that glyphosate uptake exhibited a saturable phase at low glyphosate concentrations (0. 5 to 3 μM), superimposed by a linear uptake at higher concentrations (up to 100 μM). Inhibition of glyphosate uptake by para‐chloromercuribenzene sulphonic acid, sodium azide and carbonyl‐cyanide‐m‐chlorophenylhydrazone was much stronger at 1 than at 100 μM glyphosate. Kinetics indicated that the saturable component of glyphosate transport was competitively inhibited by either phosphate or phosphonoformic acid. It is concluded that glyphosate can be absorbed via a phosphate transporter of the plasma membrane
Evidence for phosphorylation of tubulin in carrot suspension cells
Authors: Koontz Deborah A. , Choi Jung H.
Published: May 2006

Two‐dimensional gels of phosphoproteins from carrot (Daucus carota L. var. Juwarot) suspension cells labeled in vivo or in vitro revealed phosphoproteins that comigrate with carrot tubulin. A polyclonal antiserum to hibiscus tubulin immunoprecipitated an in vivo labeled phosphoprotein of 50 kDa. Cell‐free extracts of carrot suspension cells phosphorylated both purified carrot and bovine brain tubulins in the presence of gamma‐labeled adenosine triphosphate. This tubulin phosphorylating activity was reduced 2‐fold in extracts from globular stage embryos and approximately 10‐fold in extracts from heart/torpedo stage embryos. These data suggest that carrot cells phosphorylate tubulin, and that tubulin phosphorylating activity may be developmentally regulated
Benzyladenine‐induced changes in the translatable mRNA population in excised cucumber cotyledons
Authors: Teramoto Haruhiko , Momotani Eiki , Tsuji Hideo
Published: May 2006

Benzyladenine‐induced changes in the translatable mRNA population in excised cucumber cotyledons were studied. Poly (A)+ RNA was prepared from etiolated cotyledons incubated with or without benzyladenine (BA) for various periods in the dark. Using nonequilibrium pH gradient electrophoresis‐SDS polyacrylamide gel electrophoresis and isoelectric focusing‐SDS polyacrylamide gel electrophoresis, both basic and neutral proteins translated in vitro were separated. About 240 spots were detected and 16 of them changed within 6 h after BA application. Some spots changed quickly (within 1–2 h). Among them, three were repressed markedly
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+‐ATPase

The 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)
Patterns of protein synthesis in the cambial region of Scots pine shoots during reactivation
Authors: Sitbon F. , Eklöf S. , Riding R. T. , Sandberg G. , Olsson O. , Little C. H. A.
Published: May 2006

Changes in protein synthesis in cambial region cells were monitored in 1‐year‐old cuttings of Scots pine (Pinus sylvestris L.) collected in November, when the cambium was dormant, and subjected to environmental conditions that promoted or inhibited cambial growth. The proteins were labelled in vivo with L‐[35S]‐methionine and separated using 2‐dimensional polyacrylamide gel electrophoresis. In budded cuttings cultured under environmental conditions favoring cambial reactivation, there was a reproducible quantitative change in 55 proteins (33 induced and 22 repressed), a less certain increase or decrease in 40 proteins, and no apparent change in about 150 proteins. Under the same conditions, 8 proteins were induced and 6 others were repressed in debudded cuttings treated apically with 1 mg indole‐3‐acetic acid (IAA) in 1 g lanolin, in which cambial reactivation occurred, compared with debudded cuttings treated with plain lanolin in which the cambium did not reactivate. Three of the proteins induced in the IAA‐reated cuttings only appeared after cambial cell division and derivative differentiation actually began, and the same proteins were found in budded cuttings after their cambium had become reactivated. In contrast, protein expression in cuttings exposed to environmental conditions that prevented cambial reactivation was similar at the beginning and end of the experimental period. These results indicate that the cambium was in the quiescence stage of dormancy at the start of the experiment, that quiescent cambial region cells can synthesize proteins as soon as exposed to environmental conditions favoring reactivation, and that only 3 of the approximately 250 proteins detected were specifically involved in cambial growth
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.
The identity of the water oxidizing enzyme in photosystem II is still controversial
Authors: Pistorius Elfriede K.
Published: May 2006

In recent years great advances in the understanding of photosystem II have been achieved. The process of photochemical charge separation seems to be fairly well understood, while the identity of the water oxidizing enzyme in photosystem II has remained uncertain. In the first part of the paper a brief review on structural and functional aspects of photosystem II is given, and in the second part the nature of the elusive water oxidizing enzyme is considered. Two models are discussed. The first model, favoured by the majority of groups working in this area, suggests that the reaction center polypeptide D1 (in association with other known photosystem II polypeptides) is the site of water oxidation. The second model, mainly based on our results with cyanobacteria, predicts that the water oxidizing enzyme is a separate polypeptide in the 30 kDa region, distinct from D1 and D2, in addition to the seven polypeptides so far recognized in minimal O2 evolving photosystem II complexes
Pine xyloglucan. Occurrence, localization and interaction with cellulose
Authors: Acebes José Luis , Lorences Ester P. , Revilla Gloria , Zarra Ignacio
Published: May 2006

The occurrence, localization, and properties of xyloglucan in the cell walls of growing regions of Pinus pinaster hypocotyls have been studied. Xyloglucan was released from the cell wall with alkali solutions, the concentration increasing from 4 through 35%; KOH. In vitro experiments showed that xyloglucan and cellulose can interact, forming a macromolecular complex. Electron microscope observations showed that the cell wall material extracted with 35%; KOH, which contained some amount of xyloglucan, was enough to cover and join the cellulose microfibrils.
An endogenous growth inhibitor, 3‐hydroxy‐β‐ionone. II. Changes in its levels associated with the light‐induced growth inhibition of hypocotyls of Phaseolus vulgaris
Authors: Kato‐Noguchi Hisashi
Published: May 2006

Dark‐grown, 4‐day‐old seedlings of dwarf bean (Phuseolus vulgaris L. cv. Morocco) and tall bean (cv. Kentucky Wonder) were transferred to conditions of continuous light at various fluence rates, and the resulting changes in growth rates and concentration of 3‐hydroxy‐β‐ionone, a novel endogenous growth inhibitor, were monitored. The light‐induced inhibition of growth and the levels of the inhibitor concentration were dependent on the fluence rate of light applied. The growth rate of hypocotyls of both cultivars decreased rapidly and reached a plateau 18 h after the onset of light. However, the more noticeable changes were the marked inhibition of growth of the hypocotyls of the dwarf cultivar. The concentration of 3‐hydroxy‐β‐ionone in the hypocotyls of both cultivars increased after a 20‐min lag and reached plateau values after 12 h. The concentration of the inhibitor in the hypocotyls of the dwarf cultivar increased to about 4 to 8 times the level in the nonirradiated controls, while that in the hypocotyls of the tall cultivar increased only about 2‐ to 3‐fold under the same conditions. The high concentration of 3‐hydroxy‐β‐ionone in the dwarf cultivar under steady‐state conditions in continuous light, as compared with that in the tall cultivar, may determine the growth habit of these cultivars.
Effect of salinity on growth, ion content and CO2 assimilation rate in lemon varieties on different rootstocks
Authors: García‐Legaz M. F. , Ortiz J. M. , Garcí‐Lidón A. , Cerdá A.
Published: May 2006

Citrus rootstocks as well as lemon scions differ in their ability to restrict sodium and chloride ions and in their sensitivity to saline stress. To determine the behaviour of different rootstock‐scion combinations, 3 lemon cultivars on 3 different rootstocks were grown in containers in a greenhouse and irrigated with 5, 25 and 50 mM NaCl. Growth of the plants and foliar contents of sodium and chloride as well as physiological parameters including transpiration rate, gas exchange, stomatal conductance and chlorophyll content were evaluated. Shoot length of the plants on sour orange and on C. volkameriana showed a greater reduction with salinity than those on C. macrophylla. Accumulation of salt in the leaves was also scion dependent, cv. ‘Eureka’ having higher concentrations of sodium and chloride than the others. Assimilation rate of CO2 and stomatal conductance were greatly reduced by salinity in the leaves of Verna and Eureka on sour orange. Gas exchange in the leaves was highly correlated with chloride and sodium contents in all lemon‐rootstock combinations. C. macrophylla showed a higher resistance to salinity than C. volkameriana and sour orange. Inferences on the mechanisms of action of salt on lemon trees are 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.
Water relations and osmotic adjustment in Lycopersicon esculentum and L. pennellii during short‐term salt exposure and recovery
Authors: Alarcón J. J. , Sánchez‐Blanco M. J. , Bolarín M. C. , Torrecillas A.
Published: May 2006

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P‐73 and its wild salt‐tolerant relative L. pennellii (Correll) D'Arcy accession PE‐47 growing on silica sand in a growth chamber were exposed to 0, 70, 140 and 210 mM NaCl nutrient solutions 35 days after sowing. The saline treatments were imposed for 4 days, after which the plants were rinsed with distilled water. Salinity in L. esculentum reduced leaf area and leaf and shoot dry weights. The reductions were more pronounced when sodium chloride was removed from the root medium. Reduction in leaf area and weight in L. pennellii was only observed after the recovery period. In both genotypes salinity induced a progressive reduction in leaf water potential and leaf conductance. During the recovery period leaf water potential (ψ1) and leaf conductance (g1) reached levels similar to those of control plants in wild and cultivated species, respectively. Leaf osmotic potential at full turgor (ψos) decreased in the salt treated plants of both genotypes, whereas the bulk modulus of elasticity was not affected by salinity. Leaf water potential at turgor loss point (ψtlp) and relative water content at turgor loss point (RWCtlp) appeared to be controlled by leaf osmotic potential at full turgor (ψos) and by bulk modulus of elasticity, respectively. At lowest salinity, the wild species carried out the osmotic adjustment based almost exclusively on Cl− and Na+, with a marked energy savings. Under highest salinity, this species accommodate the stress through a higher expenditure of energy due to the contribution of organic solutes to the osmotic adjustment. The domesticated species carried out the osmotic adjustment based always on an important contribution of organic solutes.
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.
Metabolite effectors for short‐term nitrogen‐dependent enhancement of phosphoenolpyruvate carboxylase activity and decrease of net sucrose synthesis in wheat leaves
Authors: Manh Cao Thi , Bismuth Evelyne , Boutin Jean‐Pierre , Provot Madeleine , Champigny Marie‐Louise
Published: May 2006

We have shown that feeding 40 mM NO−3 in the light to N‐limited detached leaves from wheat (Triticum aestivum L. cv Fidel) results in the short‐term, in the enhancement of light‐dependent phosphoenolpyruvate carboxylase (PEPcase) activation and the decrease of net sucrose synthesis. The aim of the research was to determine specifically the N metabolite(s) responsible for this modulation. Detached leaves from wheat were fed for 90 min in the light with (1) NO−3, NH+4, glutamine, glutamate, alanine or aspartate; or (2) NO−3 supplemented with sodium tungstate, methionine sulfoximine, azaserine or amino oxyacetate in order to inhibit specifically nitrate reductase, glutamine synthetase, glutamate synthase or amino transferases. Changes in phosphoenol‐pyruvate carboxylase activity and net sucrose synthesis were measured at the end of each treatment. Both sodium tungstate and methionine sulfoximine which inhibit reduction of NO−3 and assimilation of NH+4 respectively, suppressed the NO−3‐dependent activation of phosphenolpyruvate carboxylase. Tungstate restored the rate of sucrose synthesis to the level of the control (absence of nitrate), while methionine sulfoximine enhanced it. Whatever way the glutamine level was increased in tissues (feeding the leaves with glutamine or with azaserine which inhibits glutamate synthase), enhancement of the light‐dependent activation of phosphoenolpyruvate carboxylase and reduction of sucrose synthesis were observed similar to feeding the leaves with NO−3. In contrast, glutamate and aspartate suppressed light dependent phosphoenolpyruvate carboxylase activation. These results indicate that glutamine is the most likely effector for controlling the N‐dependent activation of phosphoenolpyruvate carboxylase, and that the glutamine/glutamate ratio might regulate phosphoenolpyruvate carboxylase activation and the rate of sucrose synthesis in wheat leaves. Glutamine and glutamate were shown to be positive and negative effectors respectively of in vitro PEPcase‐protein kinase. In addition glutamine and glutamate were shown to control PEPcase by induction and repression of RNA synthesis respectively. Thus, two aspects of PEPcase modulation by these metabolites must be considered, (1) control of the PEPcase gene expression and (2) regulation of the PEPcase‐protein kinase.
Hormonal control of lipase activity in oilseed rape germinants
Authors: Imeson Helena C. , Rood Stewart B. , Weselake Randall J. , Zanewich Karen P. , Bullock Blake A. , Stobbs Kathleen E. , Kocsis Michael G.
Published: May 2006

In oilseeds, storage lipids provide the respiratory fuel for seedling growth. The enzyme responsible for their initial hydrolysis is lipase (triacylglycerol acylhydrolase; EC 3.1.1.3). We investigated the possibility that lipase is regulated by gibberellins (GAs). In four oilseed rape cultivars of Brassica napus and B. rapa, seed imbibition in 10−6 to 10−3M GA3 increased lipase activity 1.5‐ to 7‐fold over control levels. Conversely, imbibition in 10−7 to 10−5M abscisic acid or 10−6 to 10−4M paclobutrazol, an inhibitor of GA biosynthesis, markedly decreased lipase activity. While lipase activity in B. napus cv. Parkland increased during the first 5 days following imbibition, concentrations of endogenous GA1, GA8 and GA19 (as measured by GC‐selected ion monitoring using [2H2]GA internal standards) were relatively constant and GA20, a precursor of GA1, decreased. Levels of endogenous GA3 were apparently variable. Thus, lipase activity was not correlated with GA1 concentration, but the inverse correlation with GA20 concentration suggests that GA turnover could be positively correlated with lipase activity. Lipase activity was also examined in three genotypes of rapid cycling B. rapa that vary in endogenous GA content: rosette, a GA‐deficient dwarf, a normal line and elongated internode, a tall mutant with high GA content. The three genotypes showed similar patterns of lipase activity during the first 4 days following imbibition and the subcellular distribution of lipase activity was also similar in the three genotypes. Although GA may be involved in the regulation of lipase in oilseed rape germinants, it is not the sole regulatory factor.
Abscisic acid and gibberellic acid‐regulated responses of embryos and aleurone layers isolated from dormant and nondormant barley grains
Authors: van Beckum Joke M. M. , Libbenga Kees R. , Wang Mei
Published: May 2006

Dormant and nondormant isogenic barley grains were obtained by maturing grains under short day (SD) or long day (LD) growth conditions, respectively. Hormonal responses of isolated embryos and aleurone layers from these grains were studied. Addition of abscisic acid (ABA) reduced germination rate and percentage of embryos, and induced Rab (ABA‐responsive) mRNA in aleurone layers from both types of grain. Embryos and aleurone layers from dormant grains responded stronger to ABA than those from nondormant grains. Gibberellic acid (GA3) increased the germination rate and percentage of embryos from dormant grains and counteracted the ABA‐induced inhibition of embryo germination. GA3 did not affect the amount of Rab mRNA in aleurone layers, suggesting that expression of the Rab gene has no direct correlation with germination. The stronger response of embryos and aleurone layers from dormant grains to ABA may not be explained by higher endogenous ABA levels, but might be due to differences in hormone signal transduction. Aleurone protoplasts from dormant grains had a higher cytosolic pH than those from nondormant grains. To inhibit the ABA‐induced Rab mRNA, a much higher concentration of weak acid was required for aleurone layers from dormant grains than for those from nondormant grains. A possible difference in ABA signal transduction between dormant and nondormant grains is discussed.
Tissue specificity and induction of class I, II and III chitinases in barley (Hordeum vulgare)
Authors: Kragh K. M. , Jacobsen S. , Mikkelsen J. D. , Nielsen K. A.
Published: May 2006

Barley (Hordeum vulgare L.) chitinases (EC 3.2.1.14) were found to be distributed and induced in highly tissue specific patterns. Out of 6 chitinases investigated 3 were present in leaves and only a class II chitinase (molecular mass 24 846 ± 5 Da, pI≥9.8) was markedly induced in leaves heavily infected with powdery mildew (Erysiphe graminis f. sp. hordei). The class II chitinase and a novel class III chitinase (molecular mass 30 kDa, pI≥9.8) were found in intercellular washing fluid of leaves, suggesting extracellular deposition. Neither of these two proteins were induced after infiltration of sodium salicylate (2 mM, pH 6.5) or nickel chloride (2 mM). The class III chitinase showed exochitinase activity in addition to endochitinase activity. No grain specific chitinases were found in leaves after any of the stresses applied. In contrast, 3 grain specific chitinases and one of the leaf chitinases were found in in vitro cultures.
Loss of ionic and osmotic regulation in Chara internodal cells in concentrated KCl solutions
Authors: Kiyosawa Keitaro
Published: May 2006

Intact internodal cells of Chara are known to maintain their osmotic pressures at constant levels in artificial pond water at room temperature. Cell fragments with osmotic pressures higher and those cell fragments with osmotic pressures lower than the original, both of which are prepared from intact internodal cells using transcellular osmosis and ligation with threads, can also return their osmotic pressures to the original level within a week in artificial pond water. These regulatory phenomena are realized mainly by extrusion of K+ and Cl− in the cytoplasm and/or vacuole or by absorption of K+ and Cl− from the external solution. According to the electrochemical potential difference calculated for K+ between the vacuole and the external solution, the cells should be able to maintain these regulatory functions even in 50–100 mM KCl+ 1 mM CaCl2 solutions. However, novel phenomena were observed when they were immersed in such concentrated KCl solutions. To maintain electroneutrality, their osmotic pressures increased up to ca l MPa in 2 days due to absorption of K+ and Cl− and many gradually died over time. Ionic and osmotic reguratory functions of Chara cells were lost when they were immersed in 50–100 mM K‐salt solutions containing 1 mM Ca2+.
Constitutive and inducible aspects of nitrate‐nitrogen uptake by Chlamydomonas reinhardtii
Authors: Watt Derek A. , Amory Alan M. , Cresswell Christopher F.
Published: May 2006

Similarly to higher plant root systems, Chlamydomonas reinhardtii Dangeard (UTEX 90) cells exhibited biphasic NO3− uptake kinetics. The uptake pattern was similar in cells cultured in 10 mM NO3− (NO3−‐grown), 0.25 mM NO3− (N‐limited) or 10 mM NO3− followed by an 18‐h period of N‐deprivation (N‐starved). In all cell types there was an apparent phase transition in uptake at 1.1 mM NO3−, although there were variations in the uptake Vmax of both isotherms. The rate of uptake via isotherm 0 ([NO3−]<1.1 mM) in N‐limited cells was higher than that of either NO3−‐grown or N‐starved cells. In contrast, NO3−‐grown and N‐limited cells exhibited comparable Vmax values when supplied with 1.1 to 1.8 mM NO3− (isotherm 1). When supplied with 1.6 mM NO3−, both N‐limited and N‐starved cells exhibited enhanced linear uptake after 60 min of incubation. We ascribed this to an induction phenomenon. This trend was not observed when NO3−‐grown cells were supplied with 1.6 mM NO3−, or when N‐limited and N‐starved cells were supplied with 0.6 mM NO3−. The ‘inducible’ aspect of uptake by N‐limited cells was blocked by cycloheximide (10 mg l−1), but not by actinomycin D (5 mg l−1), thus indicating the involvement of a translational or post‐translational event. To investigate this phenomenon further, we analysed the cell proteins of N‐limited cells supplied with either 0.6 or 1.6 mM NO3− for 90 min, using two‐dimensional gel electrophoresis. Comparison of protein profiles enabled the identification of a single cell membrane‐associated polypeptide (21 kDa, pI ca 5.5) and ten soluble fraction polypeptides (17–73 kDa, pI ca 5.0 to 7.1) unique to the high NO3− treatment. We propose that the ‘inducible’ portion of NO3− uptake may provide the means by which C. reinhardtii cells regulate uptake in accordance with assimilatory capacity.
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.