bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stomatal and non‐stomatal contribution in the decline in leaf net CO2 uptake during rapid water stress
Authors: Cornic Gabriel , Prioul Jean‐Louis , Louason Geneviève 
Published: April 2006

A simple method is proposed for quantitative evaluation of Stomatal and non‐stomatal components of the decline in leaf CO2 uptake during rapid water stress. The changes in leaf conductance were measured during the stress and were used to calculate the photosynthetic rate which would be observed if Stomatal closure were the only cause of the decline in photosynthesis. Photosynthesis‐CO2 response curves, determined just before the stress, were used for this calculation. The difference between the calculated and the actual rate is a measure of the non‐stomatal effect of water stress.This analysis was tested on Sinapis alba submitted to rapid and severe water stress by excising leaves or roots. Experiments were performed at saturating light conditions under high (61 Pa), normal (34 Pa) or low (11 Pa) ambient CO2 pressure. The non‐stomatal effect on de‐rooted plants reaches a maximum at the beginning of the stress and is dependent on the CO2 pressure: after 45 min its influence is still about 100°, 70° and 8°, respectively, at high, normal and low CO2. In the excised leaf system in which desiccation was more rapid, the non‐stomatal effect accounted for nearly 100° of the assimilation decline whatever the CO2 pressure.
Localization of newly synthesized indoIe‐3‐methylglucosinolate (= glucobrassicin) in vacuoles from horseradish (Armoracia rusticana)
Authors: Helmlinger Jürgen , Rausch Thomas , Hilgenberg Willy 
Published: April 2006

The presence and concentration of indole‐3‐methylglucosinolate [= glucobrassicin; 0.49 μmol (g dry weight)‐1] and its 1‐methoxy derivative [0.38 umol (g dry weight)−1] in Armoracia rusticana P. Gärtner, B. Meyer and Scherb, storage roots were measured. The storage tissue contains L‐tryptophan [1.63 μmol (g dry weight)‐1], which is the common precursor amino acid of the indoleglucosinolates. Tissue cylinders convert [14C]‐l‐tryptophan efficiently to the indoleglucosinolates (25%) in vivo. The conversion of [14C]‐l‐tryptophan to indole‐3‐methylgluco‐sinolate shows biphasic kinetics.A fraction rich in vacuoles was prepared from tissue sections to which [14C]‐l‐tryp‐tophan had been fed and allowed to be metabolized. The predominantly vacuolar location of both L‐tryptophan and the indoleglucosinolates is demonstrated by correlation with the vacuolar marker acid phosphatase.The significance for the regulation of the indoleglucosinolate biosynthesis and the role of indole‐3‐methylglucosinolate as a potential auxin precursor are discussed.
Regulation of the activity of the alternative oxidase in callus forming discs from potato tubers
Authors: Linus H. W. , van der Plas  , Wagner Marijke J. 
Published: April 2006

Callus‐forming discs from potato tubers lose 80% of their starch during one month of incubation on nutrient medium containing either 0, 3 or 6% (w/v) sucrose. The content of soluble sugar in the discs varies from 5 mg (incubated without sucrose) to 22 mg (on 3% sucrose) and 40 mg (on 6% sucrose) per g fresh weight. The activity of the cytochrome pathway (Vcyt) increases during the first week of incubation on all media. Thereafter Vcyt decreases again on 0% sucrose medium, while it remains constant on 3 and 6% sucrose media. Alternative pathway capacity (Valt), absent in freshly sliced tissue, shows a sharp increase during the first days of incubation, independent of the sucrose concentration in the medium. This capacity further increases during prolonged incubation on 3 and 6% sucrose but decreases on 0% sucrose.The in vivo activity of the alternative pathway (the participation in uninhibited respiration, ϱValt) varies with the sucrose concentration and with the culture time. In tissue incubated for 2‐3 weeks on 6% sucrose as much as 45% of the electrons are transfered to oxygen via the alternative pathway. In this tissue the factor Q (the part of the alternative pathway capacity that is operative) is about 0.8, while in tissue incubated on 0 and 3% sucrose media p generally does not exceed 0.5.When chloramphenicol, an inhibitor of mitochondrial protein synthesis, is added to the medium together with 3% sucrose, the increase in Vyet does not occur, while the induction of Valt during the first week of incubation is the same as without chloramphenicol. A greater part of the alternative pathway capacity becomes operative in this tissue, leading to values of Q of almost 1 after prolonged incubation. Apparently, incubation on high sugar medium leads to extra participation in respiration of the energetically inefficient alternative oxidase pathway Excess sugar leads to wasteful respiration suggesting that the alternative oxidase functions as an ‘energy overflow’.
Induction of urease by urea analogues in Evernia prunastri thallus
Authors: Vicente C. , Nieto J. M. , Legaz María Estrella 
Published: April 2006

Urease activity in Evernia prunastri (L.) Ach. thallus is induced by incubation of lichen samples on 20 mM N,N‐dimethylformamide and 20 mM N‐formylurea or 40 mM thiourea although, in these two last cases, activity subsequently decreases again. The induction of enzyme activity is repressed by including 40 μM cycloheximide in the medium. Filtration through Sepharose 6B of cell‐free extracts from thalli incubated on 20 mM N,N‐dimethylformamide shows a main peak of urease activity which has a molecular weight of about 560000 dalton. However, those extracts from thalli floated on 20 mM N‐formylurea and 40 mM thiourea show several peaks of similar enzyme activity, which have molecular weights of about 1 100000, 670000, 260000 and 140000 dalton and 1 100000, 670000 and 140000 dalton respectively.A time‐course of urease activity could be related to the accumulation of lichen phenols in the thallus for samples incubated on N,N‐dimethylformamide and thiourea.
Inhibition of photosynthetic activity by UV‐B radiation in radish seedlings
Authors: Tevini M. , Iwanzik W. 
Published: April 2006

Inhibition of primary photosynthetic reactions by UV‐B radiation (280 nm‐320 nm) was demonstrated in radish leaves (Raphanus sativus cv. Saxa Treib). Detached radish cotyledons from 10‐day‐old seedlings were irradiated with continuous white light and increasing UV‐B irradiances using cut‐off filters with increasing transmission for shorter wavelengths (WG 360, WG 345, WG 320, WG 305, WG 295, WG 280). Photosynthetic activity measured in terms of chlorophyll fluorescence induction (Kautsky effect) after 2, 4, 6, 8 and 24 h irradiation decreased in a wavelength dependent way with increasing UV‐B irradiance and irradiation time.Radish seedlings grown for 10 days from the time of germination under the same UV‐B irradiation conditions exhibited similar reductions of the variable fluorescence as detached cotyledons irradiated for short time periods. They additionally had lower initial fluorescence at high UV‐B radiation levels, although the chlorophyll content per leaf area increased. In contrast to short term experiments, the plastoquinone and flavonoid content increased with increasing UV‐B irradiance when based on leaf area.
The effects of time of seed production on the germination response of Spergularia marina
Authors: Okusanya Olubukanla T. , Ungar Irwin A. 
Published: April 2006

Germination studies were carried out with seeds of Spergularia marina L. Griseb produced over an interval of six months (June‐November). The response of the seeds to light and dark, various constant and alternating temperature regimes, and salinity were determined. In addition, the effects of soil moisture status at the time of seed production on the subsequent germination response of seeds were also determined. Light was an absolute requirement for germination. While a constant temperature regime did not generally favour germination of seed of any month, alternating temperature greatly enhanced germination with an optimum at 5/15°C in all seeds. When imbibed in solutions of different salinities, seeds collected in July and October behaved like true halophyte seeds whereas those collected in June. August, September and November behaved like glycophyte seeds.High concentration of gibberellic acid (3 000 μM) stimulated dark germination in the June and November seed lots, but in light, low GA3 concentration (300 μM) stimulated germination most. The addition of kinetin (30 μM) plus gibberellic acid enhanced germination in the dark in contrast to GA3 alone; kinetin alone stimulated a very low percentage germination.The moisture status of the soil at the time seeds were produced did not affect the germination response of an early seed crop (July) but affected that of the later seeds (August).Judging from the different germination responses, it appears that the seeds belong to at least two physiological groups, one which appears to need either a dark‐wet or cold‐wet pretreatmem for high germination to occur; and the other group which does not need pretreatmem. The ecological significance of these varied responses is discussed in relation to the survival of the species in its habitat.
2,4‐Dichlorophenoxyacetic acid inhibition of potassium transport in barley seedlings
Authors: François Guido , Dewit Maria , Neirinckx Louis 
Published: April 2006

Growth, potassium uptake and translocation as well as transpiration rates were measured in intact low‐salt barley seedlings (Hordeum vulgare L. cv. Union) in the presence of different 2,4‐D concentrations at pH 6.5. Growth was only affected at 10‐3M.Above 10‐7M 2,4‐D both uptake by the roots and transport to the shoots were inhibited. The inhibition at 10‐5M remained constant for at least 24 h. Furthermore inhibition of uptake was measurable within 1 h. Excised roots and roots of intact plants showed the same uptake pattern.It is suggested that the observed effects were caused by 2,4‐D‐induced changes in uptake and translocation systems in the roots. Pre‐treatment with 10‐5M 2,4‐D had no effect upon subsequent potassium uptake. Transpiration was reduced within 1 h in 10‐4 or 10‐3M 2,4‐D, probably due to changes in water transport or root permeability.
Photochromic pigments in akinetes and pigment characteristics of akinetes in comparison with vegetative cells of Anabaena variabilis
Authors: Björn Gunvor Solveig , Braune Wolfram , Björn Lars Olof 
Published: April 2006

Since akinete germination is triggered by light and the action spectrum for this process has features in common with the spectra of the two photochromic pigments, phycochromes b and d, a search was made for the presence of these phycochromes in akinetes of the blue‐green alga. Anabaena variabilis Kützing. Allophycocyanin‐B was also looked for, since the action spectrum for akinete germination points to a possible participation of this pigment too. Isoelectric focusing was used for purification of the pigments. The different fractions were investigated for phycochromes b and d by measuring the absorbance difference spectra: for phycochrome b. 500 nm irradiated minus 570 nm irradiated, and for phycochrome d, 650 nm irradiated minus 610 nm irradiated. For determination of allophycocyanin‐B. fourth derivative analysis of absorption spectra was made for some of the fractions from the isoelectric focusing column. Phycochrome b was also assayed for by measuring in vivo absorption difference spectra. The assays were positive for all three pigments.The complete photosynthetic pigment systems were also studied by in vivo fluorescence measurements on both akinetes and vegetative cells of Anabaena variabilis. Fluorescence emission and excitation spectra at selected emission wavelengths were measured at room temperature and liquid nitrogen temperature. The energy transfer from phycoerythrocyanin to phycocyanin is very efficient under all conditions, as is the energy transfer from phycocyanin to allophycocyanin at room temperature. At low temperature, however, phycocyanin is partly decoupled from allophycocyanin, particularly in the akinetes; the energy transfer from allophycocyanin to chlorophyll a is less efficient at low temperature in both types of cells, but especially in akinetes. Delayed light emission was measured for both types of cells and found to be very weak in akinetes compared to vegetative cells. From this study it would seem that akinetes lack an active photosystem II, although the 691 nm peak in the 570 nm excited low temperature fluorescence emission spectrum proves the presence of photosystem II chlorophyll, and also its energetic connection to the phycobilisomes.
Cinétique de la rhizogenèse adaptative à la sécheresse. Relation avec I'évolution des paramètres hydriques et morphologiques chez leSinapis alba, à deux niveaux d'énergie lumineuse
Authors: Sabatier G. , Vartanian N. 
Published: April 2006

Kinetics of adaptive drought rhizogenesis, as related to growth and water deficits inSinapis alba, attwo irradiance levels.The rhizogenic activity inSinapis albaL., subjected to progressively increasing water deficit during growth, shows a sigmoidal pattern of kinetics with three phases: initiation or latent phase, rapid exponential increase, and stationary phase. This pattern remains unchanged if the level of irradiance during growth is reduced. The same number of short tuberized roots is obtained as under high irradiance, although initiation of rhizogenesis appears to be delayed by a few days. However, this delay is not observed if the rhizogenesis is analyzed as a function of the water potential of aerial organs or as a function of the soil water deficit. Since the rate of dehydration depends upon the evaporative demand, which is modulated by high or low irradiance, drought rhizogenesis seems to be directly related to water deficits in the soil‐plant system. The onset of drought rhizogenesis, starting at the end of the growth period of the aerial organs, appears concomitant with the transpiration decline which is induced by water stress at both irradiance levels.
Role of cell wall in freezing tolerance of cultured potato cells and their protoplasts
Authors: Tao Dali , Li P. H. , Carter J. V. 
Published: April 2006

Cultured potato (Solanum tuberosum L., cv. Red Pontiac) cells suspended in PEG 1000 solutions of 0.6 and O.S osmol exhibited significantly different freezing tolerance from the same cells when suspended in PEG 6000 solutions of the same osmolalities. Cells suspended in PEG 6000 showed cytorhysis instead of plasmolysis. Cells in 0.2 and 0.4 osmol PEG 1000 had LT50(1 of −2.5°C, but the LT50 decreased to −7.50C as the osmolality increased to 0.8 osmol. In PEG 6000 the LT50 remained at −2.50C for all osmolalities used, up to and including 0.8 osmol.Released protoplasts suspended in 0.5 M sucrose had LT50 of −21.5°C, compared to −12°C for whole cells suspended in the same medium. These results lend credence to an involvement of the cell wall in freezing injury of cultured potato cells, and are interpreted in terms of the generation of a mechanical stress between cell wall and plasma membrane during the freeze‐thaw cycle.
Release of ethane from immobilised plant cell protoplasts in response to chemical treatment
Authors: Schnabl H. , Elbert Chr. , Youngman R. J. 
Published: April 2006

In isolated protoplasts ofVicia fabaL. (cv. Weißkernige Hangdown) which were immobilised in a cross‐linked alginate matrix, ethane production and ribulose bisphosphate carboxylase (RuBP carboxylase) aetivity were determined after treatment of the alginate strips with various chemical substances.The stimulation of ethane formation and the inhibition of RuBP carboxylase activity by the toxic materials might provide the basis for a simple, rapid and sensitive system for the determination of chemicals in the environment.
The subcellular distribution of carotenoids in light‐grown Verticillium agaricinum
Authors: Hsiao Ke‐cheng , Møller Ian M. 
Published: April 2006

Hyphae of light‐grown V. agaricinum (Link) Corda contain many lipid bodies. The hypae were disrupted and the membranes immediately pelleted by a 48 000 g spin for 30 min. The major part (90%) of the carotenoids was found in a lipid layer on top of the supernatant. Carotenoids extracted from the lipid layer in diethyl ether had an absorption maximum at 488 nm. On the basis of spectra in different organic solvents the main component was tentatively. Thin layer chromatography of extracted and saponified carotenoids revealed the presence of one major and one minor component.The 48 000 g pellet contained 80% of the NAD+‐dependent malate dehydrogenase (marker for mitrochondria), 25% of the antimycin‐resistant NADH‐cytochrome c reductase (marker for mitochodria and endoplasmic reticulum) and 10% of the proteins and the carotenoids. The latter were different from the carotenoids in the lipid layer in that the absorption maximum was at 471 nm in diethyl ether.Further fractionation of the 48 000 g pellet showed the presence of carotenoids in both mitochondria and endoplasmic reticulum (ER) all with an absorption maximum at 471 nm. On a thin layer plate these carotenoids migrated in one band coinciding with the minor band of the lipid layer. On a continous Percoll gradient two main areas of mitochodrial activity (1.068 and 1.063 g ml−1) were clearly separated from the ER (1.059 g ml−1). The carotenoid content was about 0.6 and 0.7–1.0 μg (mg protein)−1 for mitochondria and ER, respectively, equivalent to 1–2 carotenoid molecules per 1000 lipid molecules. The possible role of these membrane‐bound carotenoid molecules is discussed.
Citrate synthases from germinating castor bean seeds – II. Time course of synthesis and immunochemical comparison
Authors: Zehler Heinz , Schnarrenberger Claus 
Published: April 2006

The time course of total citrate synthase activity in castor bean (Ricinus communis L., type Sanzibariensis) endosperm showed a 7‐fold increase during the initial 5 days of germination and a decrease thereafter. All citrate synthase activity in the ungerminated seeds was due to the mitochondrial isoenzyme. After two days of germination the glyoxysomal isoenzyme began to appear. After 5 days the glyoxysomal citrate synthase represented 50 to 55% of the total activity and the mitochondrial enzyme the remainder. This was estimated from (a) inactivation of the glyoxysomal citrate synthase by 5,5′‐dithiobis(2‐nitrobenzoic acid); (b) solid phase adsorption of the glyoxysomal synthase by a specific antiserum; (c) separation of isoenzymes by (NH4)2SO4 gradient solubilization.The increase of both citrate synthases during the initial 4 days of germination could be prevented by 10 μg cycloheximide ml−1, but not by 40 or 400 μg chloramphenicol ml−1, indicating a synthesis on 80 S ribosomes. Actinomycin D completely inhibited the appearance of the glyoxysomal enzyme while the mitochondrial enzyme was not affected. Antisera against the two isoenzymes revealed major structural differences between two citrate synthases, however, also some common determinants. No cross‐reaction was observed with the citrate synthase from pig heart or E. coli.
Influence of light and darkness and the experimental design on kinetics of K+ (86Rb) influx in roots of intact spring wheat
Authors: Jensén Paul , Pettersson Sune 
Published: April 2006

Seedlings of spring wheat (Triticum aestivum L. cv. Svenno) were cultivated at 20°C in continuous light or darkness with the roots in nutrient solutions for six days. The plants were starved for K+ during different periods of time to produce plants with various K+ status. In one cultivation light‐grown plants were pretreated in darkness, and vice versa, before the uptake experiment. In all experiments, roots were put in a complete nutrient medium containing 2.0 mM K+ radiolabelled with 86Rb. The uptake time was varied (5, 60 or 120 min).The K+ concentration in the roots, [K+]root, increased during the course of the uptake experiments, especially in light and at initially low [K+]root, At the same time K+ (86Rb) influx in the roots decreased. The simoidal relationship obtained between K+ (86Rb) influx and [K+]root was affected by these changes, and Hill plots gave various Hill coefficients, nH, depending on the duration of the uptake experiments. nH from three apparently straight line segments of the same plot, in different [K+]root ‐ intervals, indicated a falling degree of interaction between the binding sites as [K+]root increased. For the dark‐grown plants negative cooperativity could not be demonstrated.
Function of polyphenol oxidase in higher plants
Authors: Vaughn Kevin C. , Duke Stephen O. 
Published: April 2006

Recent evidence has supported the folllowing views:1. Polyphenol oxidase (PPO) is a plastidic enzyme that is unclear‐coded, but is inactive until incorporated into the plastid.2. In healthy green tissues PPO exists in a latent form on the thylakoid membrane and is not involved in synthesis of phenolic compounds. In leucoplasts, proplastids, or amyloplasts PPO is often present in a latent form in rudimentary thylakoids.3. PPO normally functions as a phenol oxidase in vivo only in sencent or damaged cells.4. In the functional chloroplast, PPO may be involved in some aspect of oxygen chemistry – pherhaps mediation of pseudocyclic photophosphorylation.
Operation of the glycolate pathway in isolated bundle sheath strands of maize and Panicum maximum
Authors: Farineau Jack , Morot‐Gaudry Jean‐François , Lelandais Maud 
Published: April 2006

Operation of the glycolate pathway in isolated bundle sheath (BS) strands of two C4 species was demonstrated from 14C incorporation into two intermediates, glycine and serine, under conditions favourable for photorespiratory activity. Isolated BS strands fixing 14CO2 under light at physiological rates incorporate respectively 3% (Zea mays L., cv. INRA 258) and 7% (Panicum maximum Jacq.) of total 14C fixed into glycine + serine, at low bicarbonate levels (less than the Km for CO2 fixation, 0.8 mM). Higher bicarbonate concentrations depressed the percentage of incorporation into the two amino acids. No labelling was observed in the absence of added glutamate. Oxygen was required for glycine + serine labelling, since 14C incorporation into glycine was largely depressed by argon flushing, and labelling of the two amino acids was nearly suppressed by the addition of the strong reductant, dithionite, especially in maize. Two inhibitors of the glycolate pathway were tested. With α‐hydroxypyridine‐methanesulfonic acid, an inhibitor of glycolate oxidase, labelling of glycine and serine remained minimal whereas glycolate was accumulated. Isoniazid, an inhibitor of the transformation of glycine to serine induced a 50% increased labelling of glycine in maize BS, and a large decrease in serine labelling. In Panicum, the increase in [14C]‐glycine was 90%. These results suggest that the pathway glycolate → glycine → serine operates in these plants. However, leakage of metabolites occurs in BS cells, especially in maize and a large part of newly formed glycolate, glycine and serine is exported out of the cells.Operation of ribulose‐1,5‐bisphosphate oxygenase activity in competition with ribulose‐1,5‐bisphosphate carboxylase is demonstrated by the lowering of total 14CO2 fixation when O2 is increased at low bicarbonate concentration. An interesting feature observed in maize BS, at low bicarbonate concentration, was an increase in ribulose‐1,5‐bisphosphate labelling when the O2 level was decreased. This was accompanied by an increase in CO2 fixation. This could indicate an increased rate in synthesis of ribulose‐1,5‐bisphosphate (which accumulated) due to a stimulation of ATP synthesis by cyclic photophosphorylation under anaerobic conditions.