bluuebunny/crossref_metadata_2025 huggingface dataset:
The uptake of phenylalanine into suspension‐cultured cells of Atropa belladonna
Authors: Nyman Seija , Simola Liisa Kaarina
Published: May 2006

When suspension‐cultured cells of Atropa belladonna L. were in late growth phase, phenylalanine, one of the early precursors of atropine, was taken up mainly by diffusion without carrier but also actively via mediated transport. The uptake capacity of different callus lines varied from 0.4 to 1.9 μol (g fresh weight)−1 h−1 with an optimum pH at 4.5 or 5.0, depending on the callus line, 2,4‐Dinitrophenol (DNP) and KCN inhibited about 35–45% of the total uptake in all tested callus lines, so that a part of the uptke was dependent on metabolic energy.

The rate of phenylalanine uptake was fastest from 2 to 7 days after the start of the suspension culture. The increase was from 50 to 300%, depending on the cell line. The enhancement was mainly due to increased mediated uptake and could be inhibited by cycloheximide during the first days of the suspension culture. Glutamine, added to the nutrient medium, also prevented the increase. The inhibition caused by glutamine together with cycloheximide was not additive. Obviously, glutamine did not directly affect the carrier, but possibly repressed its synthesis. When cells entered the stationary phase, the total uptake began to decrease, and most of it was non‐mediated. The suspension cultures of A. belladonna had only limited capacity to regulate the transport of phenylalanine into the cells at this phase of growth.
Fusicoccin, an inhibitor of brassinosteroid‐induced ethylene production
Authors: Arteca Richard N. , Bachman Jeannette M. , Tsai De‐Sheng , Mandava N. Bushan
Published: May 2006

Fusicoccin was evaluated for its effects on brassinosteroid (BR), indole‐3‐acetic acid (IAA) and BR + IAA‐induced ethylene, 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and ACC‐synthase production by etiolated mung bean (Vigna radiata L. Rwilez cv. Berken) hypocotyl segments. Fusicoccin inhibition of ethylene and ACC production induced by 2 μM BR started at concentrations as low as 0.05 μM. Maximum inhibition occurred at a 1 μM concentration with no further inhibition at higher concentrations tested. Fusicoccin (1 μM) was effective in the inhibition of BR‐induced ethylene, ACC and ACC‐synthase production at low and high concentrations of BR.

Fusicoccin at concentrations as high as 2 μM had no effect on ethylene and ACC production promoted by low concentrations of IAA (1 to 10 μM). When higher concentrations (100–1000 μM) of IAA were used, fusicoccin (1 μM) had an inhibitory effect on ethylene and ACC production. Interestingly, fusicoccin (1 μM) had little or no effect on ACC‐synthase promoted by high concentrations of IAA (1000 μM).

When BR and IAA were used in combination, fusicoccin inhibited ethylene and ACC production at concentrations as low as 0.05 μM with maximum inhibition occurring at 0.5 μM. At a 1 μM concentration, fusicoccin was effective in inhibiting the synergistic stimulation of ACC‐synthase promoted by BR and IAA.
Characterization of the pyrophosphate‐dependent proton transport in microsomal membranes from maize roots
Authors: Chanson Alain , Pilet Paul‐Emile
Published: May 2006

Cleared maize (Zea mays L. cv. LG 11) root homogenates were prepared and layered on the top of sucrose step gradients (10, 35 and 45%). The ATP‐ and pyrophosphate (PPi)‐dependent proton‐pumping activities were recovered almost completely at the 10%/35% interface, corresponding to the microsomal fraction (Golgi, tonoplast and endoplasmic reticulum). The PPi‐dependent proton pump was characterized by the fluorescence quenching of quenching of quinacrine. The pH optimum was 7 to 8. The H+‐PPase was Mg2+‐dependent and the Km for PPi (in the presence of 3 mM MgSO4) was 28 μM. The pump was electrogenic, K+‐dependent and a permeant anion was necessary to dissipate the membrane potential (NO3−= I− >Br− > Cl−). No activity was detected in the presence of electroneutral proton inonophores or, when valinomycin was added, with electrogenic ionophores. The H+‐PPase was insensitive to vanadate, oligomycin and molybdate. ‐Diethylstilbestrol (DES) and N,N′‐dicyclohexylcarbodiimide (DCCD) were strongly inhibitory at 100 μM.
Potassium requirement of pyruvate kinase extracted from leaves of halophytes
Authors: Matoh Töru , Yasuoka Sumito , Ishikawa Takayuki , Takahashi Eiichi
Published: May 2006

Pyruvate kinase enzymes were partially purified from leaves of halophytes, Atriplex gmelini C. A. Mey., Chenopodium acuminatum Wild, and Spergularia salina J. et C. Presl., grown hydroponically in the presence of 250 mM NaCl in a greenhouse, to determine their Km values for potassium. The values were all ca 10−3M, as also reported for the glycophyte enzymes. However, the Km values were reduced by 60 to 70% by the addition of betaine to a concentration of 1 M.
Electrophysiological characteristics of the unicellular green algaMicrasterias torreyi
Authors: Vuorio Päivi , Lehtonen Juhani
Published: May 2006

The electrophysiological characteristics of the unicellular green algaMicrasterias torreyiBail. are studied here for the first time using microelectrode techniques. The resting potential of the plasma membrane varied between –39.5 and –42.2 mV for different developmental stages of the dividing cell and was –41.7 mV (se= 3.2, n = 9) in the interphase cells. The resting potential of the chloroplast envelope was lower, –53.9 mV (se= 3.6, n = 15). Supraoptimal K+(20 mM) had no clear effects on the plasma membrane but caused a depolarization of 10 mV in the chloroplast. Additional external Ca2+(10 mM) depolarized the membrane potential quite strongly (by 23 mV). Low external pH did not affect the resting potential of the cell. There is a marked difference in the resting potential values between non‐vacuolated cells (about –40 mV), to whichMicrasteriasbelongs, and vacuolated plant cells (–100 to –250 mV). This indicates the participation of the tonoplast in the transport of ions and charged molecules in vacuolated cells. Na+and Cl−, which play an important role in ion metabolism in most plant cells, are not needed byMicrasterias.
Re‐evaluation of characteristics of a carrot cell line previously selected as aluminum‐tolerant cells
Authors: Koyama Hiroyuki , Okawara Ryoji , Ojima Kunihiko , Yamaya Tomoyuki
Published: May 2006

A carrot (Daucus carota L. cv. MS Yonsun) cell line previously selected to be tolerant to Al supply was re‐evaluated by culturing with hardly soluble or ionic Al. When insoluble Al‐phosphate (2.0 mM) was supplied as a sole source of phosphate at an initial pH of 5.6, the selected cell line, but not wild‐type cells, grew normally corresponding to the growth of the cells supplied with Na‐phosphate in the absence of Al Under these conditions, the selected cells excreted large amounts of citrate into the medium. Insoluble Fe‐phosphate could also be utilized as a phosphate source by the selected cells. Excretion of citrate was, however, not detected when the cells were cultured in the absence of insoluble phosphate. The selected cells were less tolerant against soluble. Al ions than the wild‐type cells.
Calcium ion transport through tissue discs of the cortical flesh of apple fruit
Authors: Harker F. R. , Ferguson I. B. , Dromgoole F. I.
Published: May 2006

Tissue discs cut from the cortical flesh of apple fruit (Malus domestica Borkh. ev. Granny Smith) were clamped between two chambers, and the transport of 45Ca2+ from one chamber to the other was followed. After initial transport associated with partial infiltration of air spaces by the Ca2+ ‐containing solution, steady‐state transport rates were achieved over several hours. Transprt was by diffusion through the apoplast, faciliated by exchange with binding sites on the cell walls. Cation competition was observed during Ca2+ loading, transport and unloading, suggesting that the presence of other cations and pH will be important in modifying Ca2+ transport through non‐vascular tissue and in xylem unloading. Modification of the extracellular volume of solution by vacuum infiltration increased Ca2+ transport at high concentrations, suggesting that diffusion is the prime motive force when Ca2+ is abundant. When low concentrations were infiltrated, there was little effect on Ca2+ transport, and exchange had a strong influence. Transport was reduced at 1°C but this could be accounted for by physical effects of low temperature on diffusion and viscosity. The results are discussed in relation to the nature of the apoplast and the transport of Ca2+ in non‐vascular plant tissue.
Calcium ion transport across discs of the cortical flesh of apple fruit in relation to fruit development
Authors: Harker F. R. , Ferguson I. B.
Published: May 2006

Transport of Ca2+ through discs of apple fruit tissue was examined in tissue taken at different stages of fruit development. Transport rates decreased with fruit development when cation exchange was the predominant influence on transport (with 10−6M45CaCl2 as the source solution). This decrease was associated with a reduction in relative cell wall surface area, cation exchange capacity and cell wall yield that occurred during fruit growth. When diffusion was the major transport force, and when transport was influenced by solution infiltration of the tissue disc (10−2M45CaCl2 in the source solution), transport rates increased during fruit growth. This increment was related to increases in air space of the tissue. Ca2+ transport through apple fruit tissue is influenced by the extent and nature of the cell wall, changing proportions of air space and Ca2+ concentration in the extracellular solution.
Effects of vesicular‐arbuscular mycorrhizal infection and phosphate on Plantago major ssp. pleiosperma in relation to the internal phosphate concentration
Authors: Bass Rob , Lambers Hans
Published: May 2006

Two experiments were carried out to study physiological effects of vesicular‐arbuseular mycorrhizal infection on Plantago major L., ssp. pleiosperma (Pilger). In the first experiment, infection by the Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe increased growth, shoot to root ratio, P concentrations in both shoot and roots and total uptake of P per plant. The percentages of dry matter in both shoot and roots were lower in mycorrhizal plants.

In the second experiment different P treatments were applied to both mycorrhizal and non‐mycorrhizal P. major plants to separate any effects of mycorrhizal infection from increased uptake of P. In addition to the effects found in the first experiment, mycorrhizal, P, and mycorrhizal x P interaction effects were found on root respiration rate and the concentration of soluble sugars in the roots. No clear effects on total dry weight, N and starch concentrations in shoot and roots and sugar concentraion in the shoot were found. Irrespective of the mycorrhizal treatment, increased P concentration in the shoot correlated with an increased shoot to root ratio and root respiration rate, and a decreased percentage dry matter and sugar concentration in the roots. However, the root respiration rate and the P concentration in the roots of mycorrhizal plants were enhanced more than expected from the increased P concentrations in the shoots of these plants.
Deaggregation and proteolytic modification of a galactosyltransferase of Poterioochromonas malhamensis
Authors: Brunner Georg , Kauss Heinrich
Published: May 2006

We isolated hybridomas that produced monoclonal antibodies specific for the UDP‐galactose:sn‐glycerol‐3‐phosphate α‐D‐galactosyltransferase (IFP synthase, EC 2.4.1.96), an enzyme involved in the volume regulation of Poterioochromonas malhamensis Peterfi. Western blotting of native gradient gels with the most reactive antibody S 162 revealed several immunoreactive proteins in crude homogenates suggesting the occurrence of multiple molecular mass species of the galactosyltransferase. The amount of the presumed enzyme monomer (64 kDa under native conditions) was strongly increased by a pH shift of crude homogenates from pH 8 to 6. During activation of the galactosyltransferase in the cell homogenate and also by shrinking the cells, the presumed enzyme monomer appeared to be proteolytically degraded generating stepwise products of 52 and 40 kDa. We assume that the proteolytically processed enzyme becomes highly active, but is very susceptible to further proteolytic degradation.
Partial purification and some biochemical properties of acid phosphatase in germinating chickpea (Cicer arietinum) seeds
Authors: Angosto T. , González F. , Matilla A.
Published: May 2006

An acid phosphatase (EC 3.1.3.2.) from the embryonic axes of chickpea seeds (Cicer arietinum L. cv. Castellana) was purified by ammonium sulphate precipitation, chromatography on Sephacryl S‐200 and polyacrylamide gel electrophoresis. The preparation has an apparent molecular weight of 39 kDa, pH optimum for p‐nitrophenylphosphate hydrolysis of 5.25, and Km of 0.57 mM. The enzyme hydrolyzed all the mono‐ and di‐phosphorylated sugars tested, but had no effect on ATP, ADP, AMP and phosphoenolpyruvate. Phosphate was a competitive inhibitor. Mg2+. Ca2+, Hg2+, Fe3+, arsenate, K+ and Zn2+ were inhibitory. Mn2+, dithiothreitol and EDTA had no effect, and polyamines were activators.
Homoglutathione: isolation, quantification and occurrence in legumes
Authors: Klapheck S.
Published: May 2006

Homoglutathione (hGSH: γ‐glutamyl‐eysteinyl‐β‐alanine) was purified from seeds of Phaseolus coccineus L. cv. Preisgewinner, using anion‐exchange chromatography and Cu2O precipitation. Quantitative and specific determination of this thiol is possible by high‐performance liquid chromatography (HPLC) after monobromobimane derivatization. The enzymatic recycling assay based on yeast glutathione reductase (EC 1.6.4.2) can also be applied, but only to samples containing either hGSH or glutathione (GSH), since enzyme reaction with hGSH is 2.7 times faster than with GSH. Using the very sensitive HPLC method, the thiol content of leaves, roots and seeds of several legumes was investigated. Although GSH and hGSH were found in all plants analysed, the GSH/hGSH ratio varied greatly within the different tribes as well as within the different organs of plants of one species. In seeds and leaves of Vicieae, only traces of hGSH were found beside the main thiol GSH, whereas in roots the hGSH content exceeded the GSH content. The Trifolieae contained both tripeptides and in the tribe Phaseoleae, hGSH predominated by far.
Pectic polysaccharides elicit chitinase accumulation in tobacco
Authors: Broekaert Willem F. , Peumans Willy J.
Published: May 2006

Upon infection of leaves of tobacco (Nicotiana tabacum L. ev. Havana) with Erwinia carotovora (Jones) Holl, strain 3912, a phytopathogenic bacterium that secretes pectinolytic enzymes, chitinase (EC 3.2.1.14) levels increased 12‐fold within 48 h. Heat‐killed E. carotovara cells did not induce this response. In young excised tobacco plants supplied with pectic polysaccharides, chitinase activity increased to about the same level as in leaves infected with E. carotovora. The amount of pectic polysaccharides required for half‐maximal induction was about 160 μg (g fresh weight)−1. Using in vivo labeling of plants with [35S]‐cysteine, it could be demonstrated that elicitormediated chitinase induction is due to enhanced de novo synthesis of the enzyme.
Nitrogenase activity decay and energy supply in Frankia after addition of ammonium to the host plant Alnus incana
Authors: Huss‐Danell Kerstin , Hahlin Ann‐Sofi
Published: May 2006

A clone of Alnus incana (L.) Moench was grown in symbiosis with a local source of Frankia or with Frankia Ar14. Seven to 9‐week‐old plants were given 20 mM NH4Cl (20 mM KCl = control) for 3 days. Nitrogenase activity of intact plants decreased gradually within the 3 days of treatment to about 10% of the initial rates. Hydrogen evolution in air and total nitrogenase activity responded similarly to the treatment. Relative efficiency of nitrogenase thus remained the same throughout the study period. Control plants were not affected. Measurements of nitrogenase activity in root nodule homogenates (in vitro measurements) indicated loss of active nitrogenase rather than shortage of energy for nitrogenase activity in Frankia from ammonium‐treated plants. Shoots were exposed to 14CO2 and translocation of 14C to Frankia vesicle clusters prepared from root nodules was studied. Frankia vesicle clusters from ammonium‐treated plants contained about half as much 14C as those of control plants during all 3 days studied. One explanation for the observed effects is that a reduced supply of carbon to Frankia vesicles in the root nodules caused a reduced metabolic rate, including reduced protein synthesis and synthesis of nitrogenase.
Separation of dense, polysaccharide‐containing vesicles from secreting, cultured oat cells. Characterization of a putative secretory vesicle fracton
Authors: Racusen Richard H.
Published: May 2006

Suspension cultured oat (Avena sativa L. cv. Garry) cells, which secrete polysaccharides into the medium, were used as starting material for analyses of Golgi‐derived vesicle membranes and plasma membranes isolated during cell fractionation. Vesicles collected by a procedure employing ultrafiltration followed by ultracentrifugation into a sucrose step gradient exhibited an equilibrium density of 1.27 g cm−3 when run on continuous sucrose gradients, a feature which is most likely attributable to the high concentration of enclosed polysaccharides. Brief sonication lowered the density of these vesicles to about 1.15 g cm−3, as judged from the coincidence of the protein peak and the marker enzymes for Golgi [Triton‐stimulated UDPase, cold‐storage IDPase (EC 3.6.1.6)] and plasma membrane [vanadate‐inhibited K+, Mg2+‐ATPase (EC 3.6.1.3)]. Sonication of these vesicles also greatly diminished the amount of detectable polysaccharide observed in a colorimetric assay for sugars. Fractionation of a plasma membrane‐enriched preparation from these cells on continuous sucrose gradients showed the major protein peak and the peak activity for the plasma membrane marker at 1.17 g cm−3, however, there was also significant overlap with a mitochondrial [cytochrome c oxidase (EC 1.9.3.1)] peak at 1.18 g cm−3, Smaller peaks of the Golgi markers were seen at 1.14 g cm−3. Analyses of marker enzymes for ER and mitochondria (EC 1.6.99.3) showed little contamination of the membranes of presumptive secretory vesicles from these sources, and the lack of significant vanadate‐insensitive ATPase activity in the density range from 1.13–1.18 g cm−3 in either fractionation scheme suggests that these membranes do not include material from the tonoplast. The coincidence of markers for Golgi and plasma membrane with from the tonoplast. The coincidence of markers for Golgi and plasma membrane with the membranes of sonicated, dense vesicles, at a density slightly lower than that of plasma membranes prepared from the same cells, supports the possibility that membranes en route to the plasma membrane are incompletely differentiated.
Substrate specificity and activities of glyoxylate and hydroxyypyruvate reductases from leaf extracts: differentiation by ammonium sulfate fractionation and by immunoprecipitation
Authors: Kleczkowski Leszek A. , Givan Curtis V. , Randall Douglas D. , Loboda Tadeusz
Published: May 2006

Leaf extracts from seven monocotyledonous and dicotyledonous species contained considerable levels of NADPH‐dependent glyoxylate‐ and hydroxypyruvate reductase activities. These activities ranged from 0.02 to 0.22 μmol (mg protein)−1 min−1. For all plants tested, the glyoxylate reductase (GR) activity, assayed with either NADPH or NADH, was sensitive to inhibition by acetohydroxamate, a glycine analogue. Hydroxypyruvate reductase (HPR) activities were unaffected by acetohydroxamate. Differential precipitation of soluble leaf proteins of spinach, pea and barley by ammonium sulfate (0–45% and 45–60% saturation) indicated the presence of at least three distinct reductases, which differed in their specificities for glyoxylate, hydroxypyruvate and NAD(P)H. For all species, the NADH‐dependent HPR‐activity was almost completely precipitated by low ammonium sulfate concentration (45%), while precipitation of the NADPH‐GR, NADH‐GR and, to some extent, NADPH‐HPR activities required 60% ammonium sulfate. The NADPH‐dependent GR and HPR activities had high affinity for glyoxylate and hydroxypyruvate, respectively, as indicated by low apparent Km values of 40–120 μM. The occurrence of at least three distinct reductases utilizing hydroxypyruvate and/or glyoxylate as substrate was supported by antibody‐precipitation studies using antibodies prepared against NADH(NADPH)‐HPR, the well‐known peroxisomal enzyme that also shows non‐specific GR activity. These data are discussed with respect to recent reports on the purification and characterization of NADPH(NADH)‐GR, and NADPH (NADH)‐HPR, two cytosolic reductases, and the role is assessed for these enzymes in reducing hydroxypyruvate and glyoxylate that may be leaked from peroxisomes.
Effects of UV‐C radiation on extension growth, H+‐extrusion and transmembrane electric potential in maize coleoptile segments
Authors: Karcz Waldemar , Stolarek Jan
Published: May 2006

The effect of 253.7 nm ultraviolet radiation on elongation growth, medium acidification and changes in electric potential difference between vacuole and external medium in cells of maize (Zea mays L.) coleoptile segments was investigated. It was found that irradiation with 390, 1170, 3900 and 5 850 J m−2 UV‐C (ultraviolet radiation 253.7 nm) inhibited elongation growth, whereas at 195 J m−2 stimulation of growth was observed. The administration of IAA (10−5M) to the incubation medium of coleoptile segments partially abolished the inhibitory effect of UV‐C. The pH of the incubation medium, measured simultaneously with growth, showed that the exposure of the segments to UV‐C caused inhibition of H+‐extrusion (or stimulation of H+ uptake). The presence of IAA (10−5M) in the incubation medium promoted (except after 5850 J m−2 irradiation) H+‐extrusion to a level comparable with that produced by IAA in non‐irradiated segments. In UV‐C irradiated segments the potential difference underwent significant alterations. Irradiation of coleoptile segments with 390 J m−2 caused a transient depolarization, which was fully reversible within 30 min, while at higher doses depolarization was irreversible. The hyperpolarization of the membrane potential (MP) in cells of maize coleoptile induced by IAA was completely nullified by subsequent irradiation with UV‐C. It is suggested that UV‐C inhibited IAA‐induced growth by a mechanism independent of cell wall acidification.
Nodule phosphoenolpyruvate carboxylase: a review
Authors: Deroche Marie‐Esther , Carrayol Elisa
Published: May 2006

Recent data concerning the fixation of CO2 and the functioning of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) in legume, nodules are reviewed. The activites of N2 fixation (acctylene reduction) and PEP carboxylase are correlated Activities of PEP carboxylase are always higher in nodules than in roots. PEP carboxylase is located in the cytosol of the plant part of the nodules. When nodules are fed with 14CO2, radioactivity appears predominantly in malate and aspartate. The resolution of isoenzymes of PEP carboxylase shows one more band in nodules than in related roots. The role of PEP carboxylase in nodule metabolism is discussed.
Physiological and biochemical characterization of a suspensionculture system for sustained exponential growth of Nicotiana silvestris
Authors: Bonner Carol A. , Kenyon Cathy , Jensen Roy A.
Published: May 2006

A strong approach to understanding the regulation of enzymes in metabolic pathways, such as those responsible for amino acid biosynthesis, is to follow enzyme levels throughout the growth curve of higher plant cells in suspension culture. The rise and fall of enzyme levels can be traced as a function of physiological stage of growth Subculturing, as typically carried out by low‐factor dilution of stationary phase cells, yields a system suitable for the study of changes in enzyme and metabolite levels that accompany the transition from stationary‐phase physiology to exponential‐phase physiology. However, the short duration of exponential growth in such subculture protocols is inadequate to avoid carryover effects from previous stationary‐phase physiology. Suspension cultures of Nicotiana silvestris Speg, et Comes (2N = 24) were used to demonstrate substantial carryover levels of acid phosphatase, alkaline phosphatase and protease activities. A subculture routine is described for maintaining cell populations in exponential phase indefinitely. About 10 generations of sustained exponential growth is required to approach a true balanced state of exponential growth. Such exponential phase populations consist of cells termed EE cells. EE‐cell populations were similar to cells that have been in exponential phase for only a few generations (E cells), with respect to doubling time (about 40 h) and to minimal density of diluted populations able to resume growth (about 500 cells ml−1). EE cells possess a high content of soluble protein; they are smaller and more aggregated than are E cells. Upon dilution into fresh medium, EE cells resume exponential growth without a lag. In contrast to E cells, EE cells exhibit properties of balanced growth, since proportionate increases in cell number, dry weight, wet weight and packed‐cell volume were observed. E cells, sampled at different elapsed times of growth, are likely to differ in metabolite, enzyme and cell properties, whereas EE cells exhibit near‐constant properties.
Substrate stabilization of lysophosphatidylcholine‐solubilized plasma membrane H+‐ATPase from oat roots
Authors: Palmgren Michael Gjedde , Sommarin Marianne , Jørgensen Peter Leth
Published: May 2006

Plasma membrane vesicles with H+‐ATPase activity were purified from 8‐day‐old oat (Avena sativa L. cv. Brighton) roots using an aqueous polymer two‐phase system. Of several detergents tested, only lysophosphatidylcholine solubilized the H+‐ATPase in an active form. Solubilization of the H+‐ATPase with lysophosphatidylcholine was possible in the absence of glycerol, but the ATPase activity decreased about 4–5 times as rapidly in the absence as in the presence of 30% (w/v) glycerol. The solubilized enzyme was further stabilized by ATP and protons. Addition of 1 mM ATP to the plasma membranes halted inactivation of the H+‐ATPase. Even in the absence of polyol compounds and ATP, the enzyme was stable for hours at relatively low pH with an optimum around pH 6.7 at room temperature. The curve for the stability of soluble H+‐ATPase as a function of pH closely resembles the pH curve for the activity of the H+‐ATPase. This suggests that binding of protons to transport sites may stabilize the soluble H+‐ATPase in an enzymatically active form.
Protection by the epidermis of photosynthesis against UV‐C radiation estimated by chorophyll a fluorescence
Authors: Shimazaki Ken‐ichiro , Igarashi Tetsuya , Kondo Noriaki
Published: May 2006

The epidermis of Argenteum mutant of Pisum sativum L. and Vicia faba L. was shown to be effective in protecting mesophyll photosynthesis from UV‐C irradiation (peak 254 nm; 1.5 W m−2). These plants were chosen because it is easy to peel the epidermis from both sides of the leaf in Argenteum and the abaxial side in Vicia. Chlorophyll a fluorescence induction was decreased to the same extent by UV‐C radiation in both leaf sides when the epidermis was removed. The fluorescence from the leaf with the epidermis inact was not affected. With irradiation of leaves with higher intensity (3.4 W m−2) of UV‐C, the variable fluorescence was decreased by UV‐C impinging on the abaxial side, but not the adaxial side in either of the plant species. A methanol extract from the mutant Pisum epidermis had a high absorbance in the UV region, and the absorbance was more than two‐fold larger in adaxial epidermis than in abaxial epidermis. These results indicate that the epidermal layer, which contains substances that have high UV absorbance, protects mesophyll photosynthesis against UV radiation.
Effect of rootstock on photoperiodic control of elongation growth in grafted ecotypes of Salix
Authors: Junttila Olavi
Published: May 2006

Scions of a southern (59° 40’N Lat.) and a northern (69° 39’N Lat.) ecotype of Salix pentandra L. were grafted on clonal rootstocks of the same ecotypes. Effects of photoperiod on elongation growth of the 4 combinations (south/south, south/north, north/south and north/north) were studied in a phytotron at 18° and 15°C. The photoperiodic response was primarily dependent on the ecotype of the scion, but this response was significantly modified by the rootstock. Cessation of apical growth was advanced by a northern clone and delayed by a southern clone as a rootstock. The results indicate that the critical photoperiod for cessation of apical growth could be slightly decreased by a northern and increased by a southern rootstock.
Effects of hardening and freezing stress on membrane lipids and CO2 fixation of Ceratodon purpureus protonemata
Authors: Aro Eva‐Mari , Karunen Pirjo
Published: May 2006

Membrane lipids and steady‐state CO2 fixation rates were studied in moss protonemata in order to evaluate separately the effects of growth temperature, freezing stress and the achievement of frost hardiness. Protonemata of Ceratodon purpureus (Hedw.) Brid, were grown at 20 and 4°C and parts of both materials were then hardened. The low growth temperature increased the content and unsaturation level of membrane lipids significantly. This did not, however, cause a noticeable increase in the frost hardiness. Nor was the achievement of frost hardiness in this material accompanied by further changes in the amount or unsaturtion level of any membrane lipid class. Cytoplasmic membranes were abundant in both unhardened and hardened materials grown at 4°C, which agreed with the high phospholipid content of these protonemata. The only significant difference in membrane lipids between unhardened and hardened materials was a 50% lower level of trans 16:1 fatty acid in the phosphatidylglycerol fraction of hardened protonemata.

In hardened protonemata monogalactosyldiacylglycerol (MGDG) was the membrane lipid most liable to decrease during the freeze‐thaw cycle. The loss of MGDG was accompanied by partial inhibition of CO2 fixation. Provided the content of phospholipids remained unchanged (freeze‐thaw cycle with – 10°C in hardened protonemata), this inhibition was mostly reversible. If loss of the phospholipids also had occurred during the freeze‐thaw cycle, as was the case in unhardened material at or below ‐10°C, CO2 fixation was severely and nearly irreversibly inhibited after thawing.
Respiration and soluble sugar metabolism in sugar pine embryos
Authors: Murphy J. Brad , Hammer Mark F.
Published: May 2006

Embroys excised from dormant seeds of sugar pine (Pinus lambertiana Dougl.) incubated at 25°C (non‐dormancy‐breaking) or stratified at 5°C (dormancy‐breaking) were analyzed to determine temperature effects on the relative activities of respiration and fermentative metabolism, the levels of soluble sugers and the activities of the hydrolytic enzymes, invertase and sucrose synthase, as related to the release of dormancy and germinatio. At 25°C, despite a sharp drop in embryo oxygen uptake after 48 h, a simultaneous decline in acetaldehyde and ethanol concentrations indicated that there was not a shift to fermentative metabolism. The concentrations of soluble sugars showed no treatment effects. Embryo invertase (EC 3.2.1.26) activity changed only slightly at either temperature, while stratification was accompanied by a 4‐fold increase in sucrose synthase (EC 2.4.1.13) activity (cleavage direction). Upon transfer of stratified seeds to 25°C, embryo sucrose synthase activity rapidly increased almost 10‐fold, with the increase beginning prior to germination, while mvertase activity increased 20‐fold, concomitant with germination.
Influence of red light on the activity of phosphofructokinase in Chlorella kessleri
Authors: Kowallik Wolfgang , Grotjohann Norbert
Published: May 2006

In crude extracts of the unicellular green alga Chlorella kessleri Fott et Novákóva grown in red light the activity of the glycolytic enzyme phosphofructokinase (PFK, EC 2.7.1.11) is about 40% higher compared to white light conditions giving the same dry matter production. Application of cycloheximide and density labelling with D2O indicate that this increase depends on the de novo synthesis of the enzyme: Twelve h of illumination at a fluence rate of 7 × 1018 quanta m−2 s−1 (11.6 μmol m−2 s−1) suffice to saturate the effect. In autotrophically grown algae maximal increase in enzyme saturate the effect. In autotrophically grown algae maximal increase in enzyme activity is reached in light of 680 nm, while in 3‐(3,4‐dichlorophenyl)‐1,1‐dimethyl urea (DCMU)‐poisoned, glucose‐fed cells, light of wavelengths around 727 nm is most effective. Involvement of a phytochrome‐like photoreceptor is discussed.
Effect of air and soil temperature on water balance of jojoba growing under controlled conditions
Authors: Benzioni A. , Dunstone R. L.
Published: May 2006

Jojoba [Simmondsia chinensis (Link) Schneider] cuttings were grown in pots under constant light intensity and vapour pressure deficit at wir temperatures of 18 and 27°C in climate‐controlled cabinets. Leaf conductance and transpiration rate decreased exponentially as the xylen water potential (Ψx) decreased concurrently with the drying out of the soil. At high Ψx’leaf conductance and transpiration rate were much higher at the higher air temperature, and as Ψx declined both parameters decreased more rapidly at 27°C than at 18°C. When soil temperatures were decreased from 27 to 13°C, leaf water potential was not affected at either air temperatures, but transpiration rate was reduced. A linear negative correlation was found between transpiration rates and soil temperatures. It is suggested that the low soil temperature may restrict reducion of water flux in turn reduces stomatal conductance and transpiration without affecting the water potential in the shoot. The releavance of the response to changes in soil or air temperature to the performance of the plant in its semi‐arid habitat is discussed.
Uptake and metabolism of benzyladenine in the early stage of flower bud development in vitro in tobacco
Authors: Van der Krieken W. M. , Croes A. F. , Barendse G. W. M. , Wullems G. J.
Published: May 2006

Benzyladenine (BA) was found to regulate the number of flower buds regenerated in vitro from pedicel tissue of tobacco. Flower bud induction was particularly sensitive to BA levels in the range of 0.45 to 1.0 μM, where a two‐fold increase in concentration caused a threefold rise in the number of buds. When tissues were fed radioactive BA for 24h, only 9–12% of the counts were recovered in the original compound. The rest was present in metabolites, tentatively identified as the mono‐, di‐ and triribotides, 7‐ and 9‐glucosides and 9‐riboside of BA. The amount of growth regulator taken up and the quantities of BA and its metabolites in the explants were all linearly related to the concentration of the medium. The internal BA concentration was ca 60% of the level in the medium after 24 h. When the concentration in the medium was raised, relatively more BA remained in the non‐conjugated form. However, this change in the equilibrium between BA and the conjugates is too small to account for the steep rise in the curve representing concentration vs effect between 0.45 and 1.0 μM.
Leaf senescence in Festuca pratensis: accumulation of lipofuscinlike compounds
Authors: Düggelin Theres , Bortlik Karlheinz , Gut Hans , Matile Philippe , Thomas Howard
Published: May 2006

Fluorescent compounds (FCs) with spectral properties comparable to those of lipofuscin‐like compounds are present in aqueous methanolic extracts of senescent meadow fescue, Festuca pratensis Huds., leaves. An HPLC system for the separation of FC from other fluorescent materials was developed. The chromatograms suggest that the FC‐fraction consists of a large number of chemically related compounds. FCs are accumulated during senescence in leaves of a yellowing genotype, cv. Rossa. In leaves of a non‐yellowing genotype, Bf 993, only traces of FCs appear at advanced stages of senescence.

FCs are regarded as final products of lipid peroxidation. Since both yellowing and non‐yellowing genotypes are competent with regard to the degradation of galactolipids (the potential sources of polyunsaturated fatty acids) as well as regarding lipoxygenase (EC 1.13.11.12; a key enzyme of lipid peroxidation), and since incompentence to degrade chlorophyll is associated with lack of FC accumulation in the mutant genotype, it is hypothesized that the polar FCs present in senescent F. pratensis leaves represent catabolites of chlorophyll.
Can a limitation in pholem supply to nodules account for the inhibitory effect of nitrate on nitrogenase activity in soybean?
Authors: Vessey J. Kevin , Walsh Kerry B. , Layzell David B.
Published: May 2006

Within 48 h of exposure of nodulated soybean [Glycine max (L.) Merr. cv. Harosoy 63 x Bradyrhizobium japonicum USDA 16] to 10 mM NO3, significant decreases were observed in nodule‐specific nitrogenase (EC 1.7.99.2) activity and CO2 evolution and in the proportion of [14C]‐labeled photosynthate partitioned to nodule biomass and respiration. These trends continued over the subsequent 3 days of the study period. Concomitant with these events was an 137% increase in the relative growth rate of the whole plant and a cessation in nodule growth. Although the concentration of total soluble sugar in nodules was not affected by NO3 treatment, the concentration of starch declined to 13% of the control level after 2 days exposure to NO3−. In contrast to the effects of NO3−, nodules in which nitrogenase activity was partially inhibited by a 30 min exposure to 100% O2, showed a 52% increase over control in the starch pool over a 72 h period.

The results were compared with recent studies of NO3− inhibition of nitrogenase activity in legumes, and in contrast to these studies it was concluded that the inhibitory effects of NO3− could be accounted for by alterations in photosynthate partitioning to nodules. A hypothesis is proposed which attempts to account for the recent observation (J. K. Vessey, K. B. Walsh, and D. B. Layzell 1988. Physiol. Plant. 73: 113–121) that nitrogenase activity in phloem‐limited and nitrate‐inhibited nodules is limited by O2 diffusion. This hypothesis separates the concepts of photosynthate partitioning and phloem supply from that of carbohydrate deprivation and related effects on the size of the carbohydrate pools in nodules.
The Glycine‐Glomus‐Bradyhizobium symbiosis. VIII. Phosphorususe efficiency of CO2 and N2 fixation in mycorrhizal soybean
Authors: Brown Milford S. , Thamsurakul Supaporn , Bethlenfalvay Gabor J.
Published: May 2006

Soybean [Glycine max (L.) Merr. cv. Hobbit] plants nodulated by Bradyhizobium japonicum strain USDA 110 were grown in pot cultures in severely P‐ and N‐deficient soil and either colonized by the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe or fertilized with a high (HP) or low (LP) level of KH2PO4 (0.6 or 0.3 mM, respectively), After 7 weeks of growth, nodule and chloroplast activities (C2H2 reduction and CO2 exchange rate) were determined. Photosynthetic P‐use efficiency of CO2 fixation was significantly higher in VAM than in HP plants, while that of nitrogenase activity was lower. The LP plants were intermediate in both respects. The ratio of nodule to chloroplast activity [mol C2H2 reduced (mol CO2 fixed)−1] was highest in HP and lowest in VAM plants. Root colonization by the VAM fungus significantly increased nodule number and dry weight and reduced nodule specific mass and activity in comparison to HP plants. In spite of lower nodule activity, VAM plants were significantly larger and had higher N concentrations than the HP plants. The results suggest nonnutritional. VAM‐elicited and host‐mediated effects on the symbiotic functions of the legume association.
Circular dichroism of phytochrome intermediates
Authors: Eilfeld Petra H. , Eilfeld Peter G.
Published: May 2006

Phototransformation Ptto Pfrwas investigated with 124‐kDa phytochrome from etiolated oat seedlings (Avena sativaL. cv. Pirol) using circular dichroism spectroscopy at ‐110°C to +30°C. Using absorption spectra of the intermediates formed at the respective temperatures, circular dichroism spectra (300–800 nm) of pure intermediates were calculated.

The sign of the circular dichroic absorption bands changed upon formation of lumi‐R, the primary photoproduct of Pr. This would be compatible with a Z→E isomerization taking place at this reaction step. The subsequent intermediates (meta‐Raand meta‐Rc) as well as Pfrshowed only small circular dichroism. Their absorption spectra were drastically shifted, but had similar spectral shapes. The results are discussed in terms of conformational changes of the phytochrome chromophore presumably taking place at the early steps of phototransformation Prto Pfr.
Determination of xanthoxin by immunoassay
Authors: Feyerabend Martin , Weiler Elmar W.
Published: May 2006

2‐Cis(‐)xanthoxin (XA) was linked to bovine serum albumin through a Schiff's base and the adduct stabilized by sodium borohydride reduction. The conjugate (molar coupling ratio: 3 mol XA per mol protein) was highly immunogenic in rabbits. Antisera contained antibodies binding XA with high affinity (Ka= 1.8 × 108M−1). [3H]‐XA (2.2 × 1014 Bq mol−1) was synthesized by oxidation of [3H]‐XA alcohol with MnO2 and used to set up a radioimmunoassay [RIA, detection limit, 1 pmol; measuring range, 1 to 200 pmol (0.3 to 60 ng) XA]. The sera were also suitable for enzyme‐linked‐immunosorbent assay (ELISA) using XA‐alkaline phosphatase conjugates. The technique was more sensitive [detection limit, 0.1 pmol; measuring range, 0.1 to 50 pmol (0.05 to 15 ng) XA] than the radioimmunoassay, but less precise.
Histone variants and high mobility group non‐histone chromosomal proteins of higher plants: Their potential for forming a chromatin structure that is either poised for transcription or transcriptionally inert
Authors: Spiker Steven
Published: May 2006

In order for the genes of higher plants to be transcribed, they must be in a transcriptionally poised chromatin structure – a structure that allows access of RNA polymerases and transcription factors to the DNA. The structural features of transcriptionally poised chromatin and what distinguishes it from transcriptionally incrt chromatin are as yet unknown. There are, however, two groups of proteins that have been implicated as determinants of such divergent chromatin structures – the high mobility group (HMG) non‐histone chromatin proteins and histone variants. In this paper I discuss what is known of these two groups of proteins in higher plants against the background of their suspected roles in chromatin structure in animal systems. Plants have a number of histone variants (particularly of the H2A and H2B histones) which have the potential to be the basis of nucleosome heterogeneity in divergent chromatin structures. There is a large body of evidence from animal systems suggesting that HMG proteins are structural proteins of transcriptionally poised chromatin. Plants have non‐histone chromosomal proteins that can be defined as HMG proteins based on operational criteria. That is, they are extracted from purified chromatin with 0.35 M NaCl, are soluble in 2% trichloroacetie acid and are very highly charged proteins with their charges being about evenly split between basic and acidic amino acid residues. Characterization of the plant HMG proteins by overall amino acid composition, peptide mapping, partial sequencing and immunological cross reactivity indicates that the plant HMG proteins are very different from their putative animal counterparts. Nevertheless, plant HMG proteins bind to monoucleosomes in the same manner as animal HMG proteins; they are released from chromatin by mild DNase I (EC 3.1.4.5) digestion under conditions that lead to preferential digestion of transcriptionally active sequences; and when chromatin is separated into fractions enriched or depleted in transcribed DNA sequences, the plant HMG proteins are found in the fraction enriched in transcribed sequences.
Nitrate reductase and its role in nitrate assimilation in plants
Authors: Campbell Wilbur H.
Published: May 2006

Nitrate reductase (EC 1.6.6.1) is an enzyme found in most higher plants and appears to be a key regulator of nitrate assimilation as a result of enzyme induction by nitrate. The biochemistry of nitrate reductase has been elucidated to a great extent and the role that nitrate reductase plays in regulation of nitrate assimilation is becoming understood.
Detection and identification of gibberellins in extracts of Begonia leaves by bioassay, radioimmunoassay and gas chromatography – mass spectrometry
Authors: Odén Per Christer , Heide Ola M.
Published: May 2006

Gibberellins A1 (GA1), GA4, GA9, GA19, and GA20 were identified in extracts of leaves of Begonia x cheimantha Everett cv. Nova (Christmas or Lorraine Begonia). GA‐like substances were purified by reverse phase and normal phase high performance liquid chromatography (HPLC) and detected by Tan‐ginbozu dwarf rice bioassay and binding to antibodies raised against GA1, GA4 and GA9. The final identifications were made by gas chromatography—mass spectrometry (GC‐MS).
Gas exchange and nutrition patterns during the life cycle of an artificial wheat crop
Authors: Gerbaud Alain , Andreè Marcel , Richaud Christiane
Published: May 2006

The growth, mineral and shoot and root CO2 exchange of wheat plants (Triticum aestivum L. cv. Courtot) cultivated in growth chambers have been studied during the complete life cycle. The life cycle could be divided into 4 periods according to the patterns of CO2 exchange: exponential increase, linear increase, stabilization and decline of photosynthesis. These patterns are analysed in relation to light interception, tillering, competition between plants and ageing of the leaves, all of which constitute successive limiting factors. Root metabolism seemed to be subordinated to the demand of the shoot for minerals. Ion uptake from the nutrient solution was particularly pronounced in young plants, which were higher in minerals and nitrogen than older ones. The ratios of K and P uptake varied with plant age, and the charge balance in ion exchange was equlibrated by H uptake. Rhythmic patterns appeared in all exchanges and varied with plant age. The highest amplitude of rhythm was found in root respiration. After taking the losses due to respiration and photorespiration into account, the maximum rate of photosynthesis approached the theoretical value calculated from the light energy absorbed.