bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth rate of potato tubers and endogenous contents of indolylacetic acid and abscisic acid
Authors: Marschner H. , Sattelmacher B. , Bangerth F.
Published: April 2006

Potato plants (Solanum tuberosum L. ev. Ostara) were grown in water culture and the growth rate of individual tubers was measured daily or at two day intervals. Tubers of different growth rate and/or different age (days after tuberization) were harvested and analysed for indolylacetic acid (IAA) and abscisic acid (ABA). Within individual tubers the IAA content decreases from the apical to the basal part of the tuber. Tuber age and corresponding fresh weight are negatively correlated with the endogenous IAA content. If, however, individual tubers of comparable age but different growth rates are compared, a significant positive correlation between growth rate and IAA content is revealed, while ABA showed a significant negative correlation with growth rate. Removal of all fast‐growing tubers from individual plants causes an increase in the growth rate of the remaining tubers within 3–4 days. This coincides with a particularly steep increase in IAA content. The data support the idea that endogenous IAA content may be one factor responsible for controlling the growth rate (“sink‐activity “) of individual tubers.
ATPase activity associated with vacuoles and tonoplast vesicles isolated from the CAM plant, Kalanchoë daigremontiana
Authors: Aoki Kunio , Nishida Kojiro
Published: April 2006

Intact vacuoles were isolated from leaves of the CAM plant, Kalanchoë daigremontiana Hamet et Perr. Both ATPase and acid phosphatase activities were found in the vacuoles. Purified tonoplast vesicles showed only ATPase activity with a pH optimum of 8.0. This activity was Mg2+‐dependent and KCI or NaCI caused a further stimulation. N,N′‐dicyclohexylcarbodiimide, diethylstilbestrol and quercetin inhibited the ATPase almost completely at concentrations well below 1 mM. NaVo3, 1‐ethyl‐3(3‐dimethylaminopropyl)carbodiimide, oligomycin and NaN3 had little or no effect. Carbonyl cyanide m‐chlorophenylhydrazone stimulated the ATPase about 40% at 5 × 10−4M. The Km for ATP was found to be 0.55 mM. These results indicate that the ATPase found in the tonoplast membrane of Kalanchoë daigremontiana is qualitatively similar to that of other plant species.
Influence of accelerated and natural aging on free radical levels in soybean seeds
Authors: Buchvarov P. , Gantcheff Ts.
Published: April 2006

Embryonic axes and cotyledons of three soybean (Glycine max L. cv. Gudzon) seed lots designated as “normal”, “naturally aged” and “acceleratedly aged” were analyzed for their organic free radical contents. No signals of free radicals were found in ESR spectra from cotyledonary material of the three samples investigated. High levels of organic free radicals were observed in the embryonic axes. There were significant differences in the free radical contents of the embryonic axes: the relative values of free radicals were 100, 190 and 170% for samples aged normally, naturally and in an accelerated manner, respectively. These results point to the physiological role of the embryonic axes during natural or accelerated aging of seeds, notwithstanding that the axis is a small part as compared to the cotyledons. It is suggested that lipid peroxidation in embryonic axes may play an important role in the seed deterioration during aging.
The effect of different media and culture techniques on plating efficiency of strawberry mesophyll cells in culture
Authors: Sarwar M.
Published: April 2006

Mesophyll cells of strawberry were isolated mechanically by a hand homogenizer, One g healthy, fully‐expanded leaves yielded 107 cells. The agar culture method was the only culture technique found suitable to obtain any quantitative data.
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.
Effects of Ni2+ on proton extrusion, dark CO2 fixation and malate synthesis in maize roots
Authors: Morgutti Silvia , Sacchi Gian Attilio , Cocucci Sergio M.
Published: April 2006

The presence of Ni2+ in the incubation medium of maize root segments (Zen mays L. cv. Dekalb XL 640) induces an early and significant enhancement of the rate of proton extrusion both in the absence and presence of fusicoccin; with time, an inhibition of proton extrusion and a leakage of K+ appear. The inhibition of proton extrusion is accompanied by a decrease in the dark CO2 fixation and by a decrease in the level of malate in the cells. Ni2+ inhibits in vitro phosphoenolpyruvale carboxylase activity of maize roots. The data indicate a correlation between the operativity of the proton pump and that of the malate‐pH stat mechanism for the homeostasis of cytoplasmic pH.
Protein and carbohydrate accumulation in normal and high‐lysine barley in spike culture
Authors: Mather Diane E. , Giese Henriette
Published: April 2006

Spikes of barley (Hordeum vulgare L.) cultivar Bomi and high‐lysine mutants Riso 1508 and Riso 56 were cultured on liquid media at varying N and sucrose levels. Bomi accumulated N in response to increasing N levels in the medium and a higher level was reached than in spikes of intact plants. The distribution of N in salt‐soluble, hordein, and non‐protein N fractions appeared to be normal. Endosperm dry weight and starch were lower than in intact plants and declined at higher N levels. A linear relationship was observed between starch content and the concentration of sucrose in the endosperm water. Uptake of culture medium by the spikes was affected by both N and sucrose concentration. The mutants had lower dry weights and starch contents, and higher sucrose contents than Bomi. At high N levels, the mutants accumulated less hordein, and more non‐protein N than Bomi.
Effect of the surface potential upon ion selectivity found in competitive inhibition of divalent cation uptake. A theoretical approach
Authors: Borst‐Pauwels G. W. F. H. , Severens P. P. J.
Published: April 2006

The sequence of inhibition of cation uptake caused by a series of cationic inhibitors may shift dramatically on varying the experimental conditions. This sequence depends upon the concentration of the inhibitory cation, the concentration of the substrate cation, the charge density of the cell membrane, the ionic strength of the medium and the affinity of the substrate cation for the negative groups located on the cell membrane. A shift in sequence between inhibitory cations can only occur if one of the inhibitory cations shows a greater affinity for the translocation site than the other, while the affinity for the negative groups on the cell membrane is lower.
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.
Salinity, growth and root respiration in the grey mangrove, Avicennia marina
Authors: Burchett M. D. , Field C. D. , Pulkownik A.
Published: April 2006

Relationships between growth parameters and root respiration under various conditions of salinity were investigated in seedlings of the grey mangrove Avicennia marina (Forsk.) Vierh. Growth, root/shoot ratios, leaf succulence and osmotic potential of leaves were measured for seedlings grown for 6–8 weeks in 100, 50, 25 and 0% seawater. Oxygen uptake of root segments, from distal to proximal ends of roots, was measured for all treatments. Total growth was maximal in 25% seawater, highest leaf succulence was obtained in 50% seawater, and highest leaf osmotic potential in 100% seawater. Oxygen uptake in distal root segments, as measured both by Clark oxygen electrode and Warburg manometry, showed a stimulation in the presence of salt that closely paralleled growth stimulation. The rates of respiration were highest in 25% seawater. The oxygen uptake was not stimulated by salt per se, since concentrations higher than 25% were associated with a decline in rate of oxygen uptake from the maximum. Values for the respiratory quotient approximated to one in all treatments. Avicennia marina has been reported to exclude from its roots about 90% of the salt in the surrounding medium. It might have been expected that increased concentrations of salt in the growth medium would be associated with a standard salt respiration response in the roots; however, this was not obtained.
Characteristics of ammonium absorption by excised root and leaf tissues of maize
Authors: Singh Rana P. , Mehta Pratima , Srivastava H. S.
Published: April 2006

Absorption of ammonium from solutions of ammonium chloride by maize (Zea mays L. cv. GS‐2) tissue was studied. In contrast to an initial rapid phase of absorption in root tissue, a one hour lag period was recorded in leaf tissue. The maximum rate of uptake was observed at 5–10 mM NH4Cl in both tissues. Roots had a Km value of 1.0 mM and Vmax of 24.3 μmol ammonium (g fresh weight)−1 h−1, whereas the leaf tissue had a higher Km (4.1 mM) and a lower Vmax (8.7 μmol). There was a concentration dependent increase in ethanol soluble and insoluble fractions of organic nitrogen during ammonium supply. The optimum pH for ammonium absorption for both tissues was 7.4. The optimal concentration of CaCl2 for ammonium absorption was 5 mM whereas that of KCl was only 1 mM. In both tissues, the absorption was inhibited substantially by DCMU, DNP, cycloheximide, lincomycin, sodium tungstate, sodium arsenate and to some extent also by the anions nitrate and sulfate. It is suggested that a carrier is involved in an active uptake of ammonium in the leaf tissues.
Calcium effects on ethylene and ethane production and 1‐aminocyclopropane‐1‐carboxylic acid content in potato disks
Authors: Evensen Kathleen B.
Published: April 2006

Potato (Solanum tuberosum L. cv. Katahdin) disks produce ethyline in increasing amounts from 6 to 24 h incubation in buffer at pH 4.0. Ethylene production is increased 2–3 times in the presence of 50 mM CaCl2. Levels of endogenous 1‐amino‐cyclopropane‐1‐carboxylic acid (ACC) increase in parallel with ethylene production, and ACC levels are 3–5 times higher in calcium‐treated disks than in controls. Most of the calcium‐induced stimulation of ethylene production can be accounted for by its effect on ACC production, indicating that the primary effect of calcium is on a step of ethylene biosynthesis preceeding ACC production. However, calcium may also have an effect on conversion of ACC to ethylene, since a consistent increase in ACC‐de‐pendent ethylene production was observed in the presence of calcium. Production of ethane, a marker of lipid peroxidation, was reduced by calcium, so it is possible that membrane stabilization by calcium could be involved in its effects on ethylene production.
Energy state of spring and winter wheat during cold hardening. Soluble sugars and adenine nucleotides
Authors: Perras Michel , Sarhan Fathey
Published: April 2006

Marked increases were found in the content of total soluble sugars, reducing sugars and ATP in winter wheat (Triticum aestivum L. cv. Frederick) during cold hardening. The changes in soluble sugars and ATP of spring wheat (T. aestivum L. cv. Glenlea) grown under similar conditions were less pronounced. The increase in ATP content during hardening of winter wheat was not associated with significant changes in the content of ADP or AMP. The adenylate energy charge did not change during hardening in either cultivar, but it was higher in the winter cultivar under both growth conditions. This difference could be related to the cold hardiness capacity of winter wheat.
Role of protein synthesis and light in the regulation of senescence in detached barley leaves
Authors: Cuello Juan , Quiles María J. , Sabater Bartolomé
Published: April 2006

The role of protein synthesis in senescence and in the inhibition of senescence by light and kinetin was studied in barley (Hordeum vulgare L. cv. Hassan) leaves with different inhibitors of protein synthesis. A comparison of the actions of D‐ and L‐chloramphenicol was made to compensate for the effects of D‐chloramphenicol not mediated by inhibition of protein synthesis. The involvement of phytochrome was also studied. The results suggest that: 1) cytoplasmic protein synthesis is required for senescence in the light and in the dark; 2) chloroplasts, in the dark, synthesize protein which accelerates senescence; 3) kinetin inhibits the synthesis by chloroplasts of senescence‐accelerating protein; 4) light changes the type of protein synthesized by chloroplasts from those accelerating to those retarding senescence; and 5) lightretar‐dation of senescence is mediated by phytochrome and, probably, by photophos‐phorylation.
Transcriptional activity of chromatin in developing and germinating triticale embryos
Authors: Weidner Stanislaw , Wielgat Bernard
Published: April 2006

Rythmical changes in the transcriptional activity of embryo chromatin during development and maturation of grain of triticale (cv. MT‐3) have been observed. The template availability and RNA polymerase (EC 2.7.7.6) 1 and II activities were high at the beginning of embryo development (20 to 30 days) and lowest at days 35 to 40 after anthesis, after which they increased to the end of maturation (60 days). Grains from three important periods of development (20, 40 and 60 days after anthesis; that is milk, wax and full ripeness, respectively) were used for germination, and chromatin was isolated from embryos and seedlings. A dramatic increase in the activity of both RNA polymerases and template availability was observed after 48 h of germination. The increase in template availability depended also on the ripeness stage of the grain used for germination.
Water and ion fluxes of abscisic acid‐treated root systems of pear, Pyrus communis
Authors: Andersen P. C. , Proebsting W. M.
Published: April 2006

Water and ion fluxes of intact root systems of Pyrus communis L. cv. Old Home × Farmingdale 97 immersed in a nutrient solution were determined at various pressures and temperatures. Water flux (Jv was normalized on the basis of initial flow rates of a root system after 30 min at 0.50 MPa and 25°C, expressed as the ratio Qv. Qv responded linearly to pressures between 0.20 and 0.62 MPa, implying a constant root hydraulic conductivity (Lp) within this range. Similarly Qv was linearly related to temperatures between 7 and 35°C; however, large, rapid temperature changes resulted in a break of the Arrhenius plot of Qv versus the reciprocal of temperature, Abscisic acid (ABA) from 2 × 10−6 to 10−4M, applied to intact root systems, increased Qv within 10–20 min, with the effect leveling off after 1.5 h. At a pressure of 0.50 MPa, ABA at 10‐4M enhanced Qv by 28%. The stimulation of Qv was not due to the ethanol solvent since 0.13 or 1.33% ethanol decreased Qv‐, The osmotic potential of the xylem fluid was determined and was used to calculate total normalized solute flux. The results suggest that ABA‐induced or ethano1‐induced changes in Qv were mainly due to changes in Lp and not to changes in ion transport to the xylem.
Carbon dioxide fixation in orchid aerial roots
Authors: Hew C. S. , Ng Y. W. , Wong S. C. , Yeoh H. H. , Ho K. K.
Published: April 2006

Acidity fluctuation, CO2 gas exchange, δ13C value, PEP carboxylase and RuBP carboxylase activities in aerial roots of selected thick‐leaved orchid hybrids (Arachnis and Aranthera) were studied. Both aerial roots and leaves showed acidity fluctuation over a 24 h period. Dark acidification in aerial roots was enhanced at low temperature (15°C). Aerial roots had δ13C values close to those of leaves which have been previously demonstrated to possess crassulacean acid metabolism. Variation in δ13C values along the length of the roots was observed; the root tip having a less negative δ13C value (—13.34%‰) than the older portions of the roots (—14.55%‰). There was no net CO2 fixation by aerial root, although 1432CO2 fixation was observed in light and in darkness. The pattern of fluctuation in activities of PEP carboxylase and RuBP carboxylase in aerial roots was similar to that obtained for the leaves. In both aerial roots and leaves, PEP carboxylase activity was several times higher than that of RuBP carboxylase.
Pathway and regulation of phosphate translocation to the pods of soybean explants
Authors: Neumann Peter M. , Noodén Larry D.
Published: April 2006

We investigated the degree to which developing fruit compete directly with leaves for mineral nutrients, e.g. phosphate coming up from the roots. When soybean (Glycine max(L.) Merrill cv. Anoka) explants cut at mid‐late podfill were given a 15‐min pulse of32Pi via the cut stem and then transferred to distilled water, 75% of the32P accumulated in the leaves and 21% in stem and petiole during the first hour. The amount of32P entering the seeds was low (1%) initially, but thereafter increased to 30% in 48 h. An accumulation of32P in the seed coats preceded its entry into the embryos. Disruption (with hot steam) of the phloem between the leaf and the pods after pulse labelling indicated that more than 80% of the32Pi pulse moved to the leaf before redistribution to the pods. Increasing “sink” size by adjusting the pod load from 1 to 2–3 did not increase the32P accumulated by the pods proportionally. Conversely, excision of the seeds after pulse labelling did not prevent translocation of32P out of the leaves. These results suggest that the rate of transport of phosphate to the pods at mid‐late podfill is controlled primarily by factors in the leaves. The results are consistent with the observation that the relative size of the sink (pod load) does not regulate leaf senescence.
Appearance of a State 1 – State 2 transition during chloroplast development in the wheat leaf: Energetic and structural considerations
Authors: Webber Andrew N. , Baker Neil R. , Platt‐Aloia Kathryn , Thomson William W.
Published: April 2006

The ability of developing chloroplasts to dynamically regulate the distribution of excitation energy between photosystem 1 and photosystem 2, and thus perform a State 1 – State 2 transition, was examined from analyses of chlorophyll fluorescence kinetics in 4‐ and 8‐day‐oldTriticum aestivumL.cv.Maris Dove leaves grown under a diurnal light regime. Chloroplasts at all stages of development in the two leaf systems could undergo a State 1 – State 2 transition, except those found in the basal 0.5 cm of the 4‐day‐old leaf. The ability to physiologically modify the excitation energy distribution between the chlorophyll matrices of the two photosystems developed after the development of mature, fully photochemically competent photosystem 2 units and the appearance of excitation energy transfer between photosystem 2 and photosystem 1. Also, changes in the degree of energetic interaction between the two photosystems, in vivo rates of electron transport and the chlorophylla/bratio could not be correlated with the appearance of a State 1 – State 2 transition. Ultrastructural studies demonstrated a 32% increase in the degree of thylakoid appression in chloroplasts at the base of the 8‐day‐old leaf compared to the situation in the basal 0.5 cm of the 4‐day‐old leaf. This difference in thylakoid stacking can account for the differing abilities of these two tissues to perform a State 1 – State 2 transition when considered in the context of the distribution of the two photosystems within appressed and non‐appressed regions of thylakoid membranes.
Does the chloroplast envelope contain carotenoids and quinones in vivo?
Authors: Grumbach K. H.
Published: April 2006

Leaves, cotyledons, isolated chloroplasts and subplastid fractions (thylakoids and envelopes) of radish (Raphanus sativus L. cv. Saxa) and spinach (Spinacia oleracea L. cv. Matador) were assayed for their pigment and quinone content and composition. Evidence is presented suggesting that the chloroplast envelope does not contain carotenoids and quinones in vivo. Envelopes prepared by the method described contained very low amounts of chlorophyll a and b, violaxanthin and neoxanthin, but no β‐carotene, lutein, zeaxanthin and antheraxanthin. Among the quinones, trace amounts of plastoquinone and α‐tocopherol but no plastohydroquinone, α‐tocoquinone and phylloquinone were detected. The data presented suggest that, contrary to previous findings, carotenoids and quinones are not located in the chloroplast envelope.
Carbon dioxide‐independent and ‐dependent components of light inhibition of the conversion of 1‐aminocyclopropane‐1‐carboxylic acid to ethylene in oat leaves
Authors: Preger Ronit , Gepstein Shimon
Published: April 2006

Light inhibits while carbon dioxide enhances the conversion of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) to ethylene in oat (Avena sativa L. cv. Victory) leaf segments. The possibility that the light inhibition is mediated through changes of carbon dioxide has been investigated. The level of CO2 increases or decreases in the sealed incubation vial in darkness or in light, respectively, which can apparently account for the differences in ACC‐dependent ethylene production between the dark and light treatments. However, although the evolution of ethylene from ACC in the dark is reduced upon depletion of CO2, the difference between light and dark is still very noticeable. Moreover, the production of the ethylene in CO2‐free air in the dark was still higher than in the light, where the concentration of CO2 was 0.01%. It is proposed that the light effect on the conversion of ACC to ethylene is composed of two distinguishable components: one CO2‐mediated and the other CO2‐independent.
Effects of ultraviolet‐C radiation on net photosynthesis, transpiration and dark respiration of Spathiphyllum wallisii
Authors: Murali N. S. , Saxe Henrik
Published: April 2006

Electric arc welding was suspected to have damaged about 25000 potted Spathiphyllum wallisii plants in a commercial greenhouse. Therefore, the effects of UV‐C radiation, phytotoxic gases and smoke particles on some basic physiological processes and on growth of Spathiphyllum plants were investigated in a controlled environment. The phytotoxic gases (NO, NO2, O3), separately and in combination, were harmless at exposure concentrations (2 mg m−3) well above incident levels, for several hours. The smoke particles, mainly ZnO, Fe2O3 and MnO, did not disturb the root environment and plant growth, even at 25 g m−2, which is approximately 400 times the calculated dose after the adverse incident. UV‐C radiation from electric welding significantly reduced photosynthesis and transpiration shortly after exposure at 1 m (80 μW cm−2 nm−1 at 254 nm), while dark respiration was significantly increased. Effects at 3 m were less pronounced. The effect persisted for 2–4 days, after which recovery was complete. Further experiments with continuous measurement of gas exchange in whole plants confirmed that short‐term UV‐C radiation (Philips 30W germicidal tubes) dramatically affects photosynthesis, dark respiration and transpiration. Plants irradiated with more than 10 μW cm−2 nm−1 at 254 nm did not recover completely within the week of the experiments. The immediate effects of UV‐C on photosynthesis is caused by stomatal closure. However, most effects are transient, and electric are welding does not appear to have caused the investigated damage.
Development of phosphogluco‐isomerase isozymes in perennial ryegrass (Lolium perenne)
Authors: Jones Thomas W. A.
Published: April 2006

The development of isozymes of phosphogluco‐isomerase (PGI; D‐glucose‐6‐phosphate ketol isomerase EC 5.3.1.9.) in perennial ryegrasses was followed from dry seed through to leaf senescence using starch gel electrophoretic separations. Root isozymes were also examined. Two forms of the enzyme were found, one (PGI/2) being present in all tissues and at all stages of the life cycle. The other (PGI/1) had two zones of activity, one of which was detected only in light‐exposed tissue. Normal development of this form could be inhibited by growing seedlings on distilled water. Some alleles of PGI/2 not previously reported for ryegrasses are also described.
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.
Rhizobium strain effects on yield and bleeding sap amino compounds in Pisum sativum
Authors: Rosendahl Lis
Published: April 2006

Bleeding sap composition, dry matter production and nitrogen distribution in pea (Pisum sativum L. cv. ‘Bodil’) grown with and without nitrate and nodulated with either Rhizobium leguminosarum strain 128c53 or strain 1044 were compared. Nitrate increased the total dry matter production of both symbioses, but decreased both the proportions of below‐ground dry matter to total dry matter production and nodule dry matter to total below‐ground dry matter production. The total dry matter yield and N‐accumulation was greater in the symbiosis with strain 1044, whereas the accumulation of N in the roots plus nodules relative to the total N‐accumulation was greater with strain 128c53 due to a higher production of nodule tissue. The root bleeding sap of the symbiosis with the greater yield (strain 1044) contained high levels of asparagine and aspartic acid. In the 128c53 symbiosis, glutamine plus bomoserine accounted for a higher percentage of the organic solutes transporting newly assimilated nitrogen from the root system than in the association with 1044. The Rhizobium strain effect on amino compound composition of the bleeding sap may indicate an influence of the bacteroids on either the N‐assimilatory enzyme system in the plant cytosol, or on the pools of the Krebs cycle intermediates or related compounds in the nodules.
The senescence of cut carnations: A phasic phenomenon
Authors: Trippi Vittorio , Paulin André
Published: April 2006

Senescence in carnations (Dianthus caryophyllus L. cv. Scania) comprises two phases. The first phase is characterized by active proteolysis and a moderate exudation of electrolytes. These changes are apparently reversible. Exogeneous glucose prolongs this phase. The second phase is preceded by a burst of ethylene, and rapidly leads to death. The changes observed, primarly in membrane permeability and proteolysis, are under the control of a process whose mechanism remains unknown, but which is marked at the cellular level by a lack of energy. Some phenomena of the senescence syndrome can be detected at the time of flower opening, so that withering is only the last phase of an aging process that begins very early.
The physiological basis of seed dormancy in Avena fatua III. Action of nitrogenous compounds
Authors: Adkins Stephen W. , Simpson Graham M. , Naylor James M.
Published: April 2006

Sodium nitrate and nitrite (50–100 mM) induced germination in three out of four genetically pure dormant lines of Avena fatua L. The sensitivity to these treatments was low immediately ater harvest and increased markedly after six months of dry after‐ripening. The observation that a fourth dormant line failed to respond suggests at least two metabolic blocks may be involved in expression of dormancy. An inhibitor of gibberellin biosynthesis, 2‐chloroethyl trimethylammonium chloride, completely inhibited the dormancy‐breaking effect by nitrate and nitrite, indicating a requirement for gibberellin biosynthesis. Among reduced nitrogenous compounds, ammonium chloride and urea failed to break dormancy in all partly after‐ripened lines, suggesting that nitrate and nitrite may induce germination through their ability to act as electron acceptors. The sensitivity to all nitrogenous compounds tested increased with the length of after‐ripening indicating that the depth of the second dormancy block amy decrease with the time of after‐ripening. Other reduced nitrogenous compounds, thiourea and hydroxylamine hydrochloride, promoted some germination in the least dormant, partially after‐ripened lines. The function of these compounds as electron acceptors and their similarity in activity to the cytochrome oxidase inhibitor, sodium azide, is discussed with reference to dormancy and the possible involvement of the alternative pathway of respiration.
Photosynthate partitioning in diploid and autotetraploid barley (Hordeum vulgare)
Authors: Sicher Richard C. , Kremer Diane F. , Harris William G. , Baenziger P. Stephen
Published: April 2006

Net rates of carbon assimilation per unit leaf area by fully expanded, vegetative leaves of diploid (2x) and autotetraploid (4x) barley (Hordeum vulgare L. cultivars OAC‐21 and Brant) were not significantly different (90% level) when measured under controlled environment conditions with air levels of CO2 and either 2 or 20% O2. Leaf thickness increased with ploidy so that net photosynthetic rates measured on single leaves were lower for 4x than 2x barley varieties when compared on a dry or fresh weight basis. Rates of 14CO2 fixation by isolated mesophyll protoplasts prepared from seedlings were also lower for 4x than 2x varieties [about 108 and 125 μmol (mg ChI)−1 h−1, respectively]. Carbohydrate accumulation in leaves of 5‐weekold plants averaged 28% (2x) and 47% (4x) of the total photosynthetic weight gain during the first 9 h of the light period. Estimated photoassimilate export from leaves was 15% (OAC‐21) and 38% (Brant) lower for 4x compared to 2x isolines. The sucrose and oligofructan content of 4x compared to 2x leaves increased as a result of decreased photosynthate transport.

Total tiller dry weight of plants raised in a glasshouse was greater for 4x than 2x barley varieties at ear emergence, but tiller height decreased with increasing ploidy. The nonstructural carbohydrate content of the inflorescence, leaves and lower stem organs was significantly (P≤ 0.01) higher in 4x than in 2x lines at this sampling. During the first 15 days of grain development total tiller dry weight increased by 46% (2x) compared to 8% (4x) when the results of both varieties were averaged together. The dry weight gain of the ear during this period was about 60 to 80% lower for 4x compared to 2x isolines. The nonstructural carbohydrate content of the inflorescence was also about 24% (Brant) and 51% (OAC‐21) lower for 4x as compared to 2x plants 15 days post ear emergence. The above results suggested that photosynthate partitioning in autotetraploid barley was sink‐limited.
Isolation and properties of β‐glucan synthetase from the aquatic fungus, Aphanomyces astaci
Authors: Cerenius Lage , Söderhäll Kenneth
Published: April 2006

A β‐glucan synthetase was isolated from a membrane fraction of the crayfish parasitic fungus Aphanomyces astaci Schikora, strain Si. [14C]‐UDP‐glucose was incorporated linearly for about 1 h at 30°C into an acid insoluble product. The apparent Km for UDP‐glucose was found to be approximately 4.5 mM and the apparent Ki for UDP, a competitive inhibitor of the reaction, was 1 mM. The acid insoluble product obtained after incubating this glucan synthetase with[14C]‐UDP‐glucose was partially characterized by glucanase treatment. This product mainly consisted of β‐1,3‐linked glucosyl units. Synthetase activity was not stimulated by MgCl2, but cellobiose as well as GTP and EDTA in combination or ATP alone enhanced enzyme activity. A high proportion of the A. astaci synthetase was probably already activated during preparation and not accessible to further stimulation by nucleotide additions as found for glucan synthetase of Saccharomyces cerevisiae and Candida albicans. No synthetase activity or any factors affecting this enzyme was present in the cytosol. An exudate prepared from the cuticle of the crayfish host, did not inhibit glucan synthetase activity in vitro.
Light‐induced linear dichroism in photoreversibly photochromic sensor pigments. – IV. Lack of chromophore rotation in phycochrome b immobilized in vitro
Authors: Björn Gunvor S. , Ekelund Nils , Björn Lars Olof
Published: April 2006

In photochromic pigments, immobilized on Sepharose beads to prevent reorientation of the molecules, linear absorption dichroism can be induced with plane‐polarized light. This phenomenon was used to study the relation between the carrier protein and the chromophore in the photochromic cyanobacterial pigment, phycochrome b, from Tolypothrix distorta var. symplocoides Hansgirg, strain UTEX 424 (formerly IUCC 424). It was found that the transition moment of the chromophore has the same direction with respect to the protein in the long‐wavelength and the short‐wavelength forms of phycochrome b. This contrasts to earlier results for phytochrome in higher plants, in which the transition moment was found to rotate 32° (or 180°—32°) when the long‐wavelength form was converted to the short‐wavelength form or vice versa.
Tentoxin stops the processing of polyphenol oxidase into an active protein
Authors: Vaughn Kevin C. , Duke Stephen O.
Published: April 2006

Previous studies in our laboratory have indicated that polyphenol oxidase (PPO), as measured by its activity, is not present in tentoxin‐treated plants. In the present study, immunochemical techniques were used as a sensitive probe of tentoxin effects on PPO. Immunocytochemistry of PPO with peroxidase‐antiperoxidase labelling techniques, revealed that in control Vicia faba L. chloroplasts, PPO was associated mainly with the thylakoids. Cytochemical staining of PPO activity using DL‐dihydroxyphenylalanine (DOPA) as substrate was also localized only on the thylakoids in the control chloroplasts. In tentoxin‐treated plants all of the immunologically‐recognizable PPO accumulated at the plastid envelope although no PPO was detected by cytochemical methods. SDS polyacrylamide gels of extracts from control and tentoxin‐treated Vicia leaves were blotted onto nitrocellulose and reacted with rabbit anti‐PPO. Secondary labelling of the blots with goat‐antirabbit IgG labelled with peroxidase revealed a 40 kdalton protein in both extracts. However, only the PPO from the control extract had DOPA oxidase activity. These data suggest that PPO accumulates in the plastid envelope membranes in tentoxin‐affected cells and that PPO in these treated plants is not processed to an active protein.
Arginase activity in the cotyledons of soybean seedlings
Authors: Matsubara Shyuichiro , Suzuki Yonezo
Published: April 2006

The germination of soybean (Glycine max L. cv. Akita) seeds is accompanied by increased arginase activity in the cotyledons, and the enzyme is predominantly (84% for 5‐day‐old seedlings) recovered in the mitochondrial fraction (co‐purifies with succinate dehydrogenase) where it is located inside the inner membrane. When dry cotyledons from which the axis and testa have been removed surgically are imbibed for 6 h in water and maintained on filter paper during the subsequent incubation, there is little increase in mitochondrial arginase activity. However, if similar dry cotyledons are rinsed for 1 min after the sterilization of 3 min and maintained on filter paper from the beginning, the increase in enzyme activity is similar to that in the intact seedling. Thus the embryonic axis is not essential for the development of arginase in soybean cotyledon although the enzyme development was enhanced by the presence of the axis under the same conditions of incubation.

The addition of actinomycin D, 6‐methylpurine and cycloheximide early in the incubation period strongly inhibits the development of mitochondrial arginase activity in the cotyledons, but chloramphenicol does not. However, actinomycin D and 6‐methylpurine had little effect on enzyme development when added after 2 days of incubation. These results suggest that arginase is synthesized in the cytosol and then transported into the mitochondria, while mRNA for arginase synthesis is produced for a limited time only during early germination.
Site of light perception and motor cells in a sun‐tracking lupine (Lupinus succulentus)
Authors: Vogelmann Thomas C.
Published: April 2006

From the results of shading experiments and irradiation of leaves from different directions, the pulvinus has been identified as the site of light perception in leaves of the sun‐tracker Lupinus succulentus Dougl. Within the pulvinus, the light‐sensitive region is located on the adaxial surface of the base of each leaflet. This is coincident with the site of the motor cells which are located in the peripheral four cell layers. Motor cells were visualized by microscopy and undergo dramatic changes in cell volume as leaflets incline to orient perpendicular to an oblique beam of light. Communication between leaflets appears to be minimal because each leaflet has the capacity to perceive and orient towards a light beam independently of the others. Hypotheses for the mechanism of directional light perception are discussed.
Identification of proprionylcholine in higher plants
Authors: Miura George A. , Shih Tsung‐Ming
Published: April 2006

Propionylcholine, a novel analogue of acetylcholine, was identified in green plants by gas chromatography/mass spectrometry. Propionylcholine was found in the leaves of the following species previously shown to contain acetylcholine and cholinesterase activity: Codiaeum variegatum Blume, Phaseolus aureus Roxb. cv. Berken, Plantago rugelli Decne., Populus grandidentata Michx., and Betula pendula Roth. The quantities of propionylcholine ranged from a high of 2.3 nmol (g fresh weight)−1 in C. variegatum to a low of 0.11 nmol (g fresh weight)−1 in P. rugelli. These amounts represented 6 to 8% of the levels of acetylcholine. In contrast to animal tissues which rarely synthesize propionylcholine, this compound was found in all species examined which represented five families of flowering plants.
Oxygen‐quenched chlorophyll a fluorescence and electron transport in barley during greening
Authors: Popovic R. , Fraser D. , Vidaver W. , Colbow K.
Published: April 2006

Seedlings of barley (Hordeum vulgare L. cv. Conquest) were dark‐grown for 7 days and then transferred to light. The time courses of chlorophyll a fluorescence induction underwent changes during greening periods of from 3 to 48 h. Yields of variable fluorescence during greening correlated with electron transport capacity via photosystem II (PS II) except at the early stage from 3 to 6 h. The discrepancy may result from there being only a small amount of light harvesting complex associated with PSII for 3 to 6 h greening. Oxygen quenching effects were interpreted as indicating the development of the electron transport system and the organization of light harvesting complex associated with PSII. The most intensive O2 quenching of relative fluorescence is found during the early stage of greening when the ratio of the primary quinone electron acceptor (Q) to chlorophyll is high.
Photosynthesis and carbon metabolism in photoautotrophic cell suspensions of Chenopodium rubrum from different phases of batch growth
Authors: Hüsemann Wolfgang , Herzbeck Hildegard , Robenek Horst
Published: April 2006

Rapidly dividing photoautotrophic cell suspensions from Chenopodium rubrum L. assimilated about 85 μmol CO2 (mg chlorophyll)−1 h−1. During the late stationary phase of culture growth, CO2 fixation rate was reduced to about 60 μmol CO2 (mg chlorophyll)−1 h−1. Actively dividing cells characteristically incorporated a smaller proportion of 14C into starch than cells from non‐dividing stationary phases. In rapidly dividing cells, [14C]‐turnover from free sugars, sugar‐phosphates, organic and amino acids was substantially higher compared to non‐dividing cells from stationary growth phase. Higher proportions of photosynthetically fixed carbon were channelled into proteins, lipids and structural components in actively dividing cells than in non‐dividing cells. In the latter. 14C was preferentially channeled into starch, and a striking increase in starch accumulation was observed. The transfer of non‐dividing, stationary growth‐phase cells into fresh culture medium resulted in an increase in the maximum extractable activities of some enzymes involved in the glycolytic and dark respiratory pathways and in the citric acid cycle. In contrast, the maximum extractable activities of the chloroplastic enzymes, ribulose‐1,5‐bisphosphate carboxylase (EC 4.1.1.38) and NADP+‐glyceraldehyde‐3‐phosphate dehydrogenase (EC 1.2.1.13) were highest after the cells had reached the stationary growth phase.
Effects of the embryonic axis and exogenous growth regulators on sunflower cotyledon storage protein mobilization
Authors: Allen Randy D. , Arnott Howard J. , Nessler Craig L.
Published: April 2006

Cotyledons of sunflower seedlings (Helianthus annuus L. cv. Giant gray stripe) expand and their protein content first rises then begins to decrease during the first three days of growth. Storage protein structures, which are visible with scanning electron microscopy, undergo modification that leads to storage protein disappearance by day 4 post‐imbibition. Expansion of cotyledons detached from seeds prior to imbibition is greatly reduced, total protein levels remain high, and storage protein structures remain visible in cells of these cotyledons. Incubation of excised cotyledons in 1.0 μM benzyladenine or kinetin increases the rates of cotyledon expansion and storage protein loss to levels higher than in intact seedling cotyledons, Incubation in 10 μM indole‐3‐acetic acid inhibits cotyledon expansion and protein mobilization. More rapid hydrolysis of storage proteins in cotyledons of intact seedlings or detached cotyledons treated with cytokinin is further indicated in day 2 specimens by SDS‐polyacrylamide gel electrophoresis. These results suggest a possible mechanism for regulation of cotyledon development by interactions of the promotive effects of cytokinin and inhibitory effects of auxin.
Effects of ultraviolet‐B radiation on plants during mild water stress. IV. The insensitivity of soybean internal water relations to ultraviolet‐B radiation
Authors: Teramura Alan H. , Forseth Irwin N. , Lydon John
Published: April 2006

The combined effects of ultraviolet‐B (UV‐B, 280–320 nm) radiation and water stress were investigated on the water relations of greenhouse grown soybean [Glycine max (L.) Merr. cv. Essex]. On a weighted (Caldwell 1971), total daily dose basis, plants received either 0 or 3 000 effective J m2 UV‐BBE supplied by filtered FS‐40 sunlamps. The latter dose simulated the solar UV‐B radiation anticipated at College Park, Maryland, U.S.A. (39°N latitude) in the event that the global stratospheric ozone column is reduced by 25%. Plants were either well‐watered or preconditioned by drought stress cycles. Diurnal measurements of water potential and stomatal conductance were made on the youngest fully expanded leaf. Various internal water relations parameters were determined for detached leaves. Plants were monitored before, during and after water stress. There were no significant differences in leaf water potential or stomatal conductance between treatments before plants were preconditioned to water stress. However, drought stress resulted in significantly lower midday and afternoon leaf water potentials and lower leaf conductances as compared to well‐watered plants. UV‐B radiation had no additional effect on leaf water potential; however, UV did result in lower leaf conductances in plants preconditioned to water stress. Turgid weight:dry weight ratio, elastic modulus, bound water and relative water content were unaffected by UV‐B radiation. Osmotic potentials at full and zero turgor were significantly lower in the drought stressed treatments as compared to well‐watered plants.