bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of Senescence Induction by Silicone Oil
Authors: NAIM RAFI , NEUMANN PETER M. 
Published: April 2006

AbstractThe physiological basis for senescence symptoms induced by spraying attached primary leaves of bean plant (Phaseolus vulgaris L. cv. Brittlewax) with silicone oil emulsions was investigated. It was found that chlorophyll levels declined significantly between 24 and 48 h after spraying, whereas neither protein levels nor respiration rates were affected over a 7‐day period. Rates of photosynthesis and reducing sugar levels in silicone‐sprayed leaves were however significantly reduced after 1 and 24 h respectively. These responses were obtained using plants grown under low stress controlled environment conditions. By contrast, leaves on greenhouse plants did not senesce in response to silicone sprays. A possible mechanism of silicone oil action based on selective leaf penetration and inhibition of photosynthesis is postulated.
The Location of Cytokinins and Gibberellins in Wheat Seeds
Authors: THOMAS T. H. , KHAN A. A. , O'TOOLE DIANE F. 
Published: April 2006

AbstractWheat seeds (Triticum aestivum L. cvs. Yorkstar and Sirius) were cut transversely into embryoless and embryo‐containing (embryonated) halves and the content of endogenous cytokinins and gibberellins in both halves determined before and after the seeds imbibed water for 12–15 h at 22°C in the light. Dry seeds contained little ethyl acetate‐extractable gibberellin activity as measured by bioassay but n‐butanol‐soluble cytokinins were detected mainly in the embryoless halves. Dry, embryonated half‐seeds contained water‐soluble gibberellins which could be extracted into acidic ethyl acetate after treatment of the aqueous extract with either alkaline phosphatase, β‐glucosidase or a crude pectolytic enzyme preparation.When half‐seeds were allowed to imbibe water for 12 h and then extracted, cytokinin activity was largely lost from the embryoless halves and completely from the embryonated halves and water‐soluble gibberellins were also lost from the embryonated halves. However, ethyl acetate‐soluble gibberellins were present in the latter suggesting that “bound’ gibberellins were released during imbibition. The hormones present in normal and naturally embryoless dry grains of cv. Yorkstar were also determined. Both gibberellin and cytokinin activity was higher in normal grains suggesting that the presence of an embryo is essential for synthesis or accumulation of these hormones in the grain during development.
Properties of Invertases in Sugar Storage Tissues of Citrus Fruit and Changes in Their Activities during Maturation
Authors: KATO TADASHI , KUBOTA SHUJI 
Published: April 2006

AbstractBoth acid and alkaline invertases were present in immature juice sacs of satsuma mandarin (Citrus‘Unshu Marcovitch”) fruit, in which sugar content was low. Maturing and mature juice sacs, in which sugar content increased steadily with time, were characterized by the presence of alkaline invertase and the absence of acid invertase.When the immature juice sacs were homogenized with 0.2 M sodium phosphate‐citrate buffer (pH 8.0), almost all of the acid invertase activity was found in the solubilized fraction, whereas almost all of the alkaline invertase activity was present in the insoluble fraction. The distribution of alkaline invertase between the solubilized and insoluble fractions changed with the development of fruit.The acid invertase had a molecular weight of 69,000, optimum pH of 4.8–5.3, and Km value for sucrose of 7.3 mM. The alkaline invertase had a molecular weight of 200,000, pH optimum of 7.2–7.7, and Km value of 35.7 mM. The hydrolysing activities of both enzymes for raffinose were considerably less than those for sucrose. The alkaline invertase had lower activity for raffinose than the acid invertase.
Kinetic Measurements of Small Ethylene Changes in an Open System Designed for Plant Physiological Studies
Authors: DE GREEF J. A. , DE PROFT M. 
Published: April 2006

AbstractBased upon the method we developed to measure ethylene in very low concentrations (as low as 0.01 ppb in the ambient atmosphere) an experimental chamber was constructed and integrated in the measuring system for plant physiological studies. Parameters influencing the accuracy of the technique are evaluated. The pressure in the plant chamber increased 0.05 atm at a flow rate of 10 1/h during ethylene trapping. At this flow rate the ethylene production per seedling is independent of the number of seedlings used. The ethylene measured per seedling is directly proportional to the length of trapping time. Under standard conditions of chamber configuration and volume very small changes in ethylene content can be detected accurately in a very short time range. Our experimental arrangement allows kinetic studies of ethylene evolution by biological objects in a qualitative and quantitative manner. All methods used heretofore are more complicated and less accurate compared to the measuring system presented here. Its versatility is demonstrated for both in vitro and in vivo studies of ethylene production by bean seedlings. The application fields of the apparatus are discussed.
Light‐Induced Adaptive Responses under Greenhouse and Controlled Conditions in the Fern Pteris cretica var. ouvrardii
Authors: HARIRI M. , PRIOUL J. L. 
Published: April 2006

AbstractThe photosynthetic capabilities of the fern Pteris cretica var. ouvrardii were analysed by means of the light response curves of CO2 exchange. In control growth conditions (greenhouse, low‐light: 20–32 W m−2); photosynthesis was shown to be saturated for low irradiance (20–25 W m−2); the saturating photosynthetic rate, very low as compared to higher plants, was due to an extremely high intracellular resistance. When irradiance during the photosynthesis measurement was higher than 60–80 W m−2, a constant decline of net CO2 exchange as a function of time was observed.When irradiance during growth was enhanced, whether in greenhouse (20–250 W m−2) or controlled (62 W m−2) conditions, the first fronds that had developed in the new condition from the crosier stage exhibited decreased net maximal photosynthesis and a decreased efficiency in low light, but saturating irradiance was unmodified. However, the fronds whose entire differentiation (from meristem) occurred under these moderate irradiances (plants defoliated of all fronds and crosiers at the time of transfer), possessed more efficient photosynthetic characteristics than control plants. Pteris is able to grow under extreme shade conditions (4–8 W m−2); light saturating photosynthesis and efficiency are higher under extreme shade than under control conditions. These adaptive characteristics indicate that Pteris is a well‐adapted shade species.
Interactions between Symbiotic Nitrogen Fixation, Combined‐N Application, and Photosynthesis in Pisum sativum
Authors: BETHLENFALVAY GABOR J. , PHILLIPS DONALD A. 
Published: April 2006

AbstractThe effect of photosynthetic photon flux density (PPFD) on nitrogen utilization was determined in peas (Pisum sativum L. cv. Alaska) inoculated with Rhizobium leguminosarum and treated with nutrient solutions containing no combined nitrogen, 16 mM NO3−, or 16 mM NH4+. Plants were grown under controlled conditions at three PPFD values ranging from severely limiting to nearly saturating.Carboxylation efficiencies and CO2‐exchange rates were highest in the N2‐fixing plants and lowest in plants supplied with NH4+, and they generally increased with increasing PPFD. Photoefficiencies increased with PPFD but did not differ appreciably with the form of nitrogen applied. Nitrogen fixation, calculated from C2H2‐reduction and H2‐evolution data, was inhibited more by NH4+ than by NO3−application. Inhibition was counteracted by increasing PPFD. Percentage nitrogen decreased with increasing PPFD in plants treated with combined nitrogen and increased in the plants dependent on N2 fixation.The data reveal that photosynthetic efficiency and the capacity to fix N2 in peas are functions of PPFD and the availability of combined nitrogen and that these two factors are interrelated.
Levels of Sorbitol in Bleeding Sap and in Xylem Sap in Relation to Leaf Mass and Assimilate Demand in Apple Trees
Authors: HANSEN POUL , GRAUSLUND JØRGEN 
Published: April 2006

AbstractRemoval of fruits and treatment with SADH (succinic acid 2,2‐dimethylhydrazide) were used to change the balance between sources and sinks for photosynthates in Malus domestica‘Golden Delicious’. Sorbitol and sugar content were measured in bleeding sap, in xylem sap prepared by suction, and in 80% methanol extracts of the roots. Concentration as well as total amount of sorbitol in bleeding sap sampled in July and September were lower in fruiting than in defruited trees, and so was the total amount of sorbitol in xylem sap from the trunk. SADH treatment tended to reduce the sorbitol content. Sorbitol in root extracts, expressed as percentage of methanol (80%) insoluble root dry matter, was highest in fruiting trees; but root dry matter was here less than half of that in defruited trees. Sorbitol content in xylem sap as well as sorbitol + sugar percentage of roots showed a distinct maximum in late winter followed by a heavy decrease during spring. It is suggested that sorbitol in xylem sap during the growth season represents a return transport from the roots, and that the level of sorbitol in this return transport reflects, to a certain degree, the ratio between leaf area and assimilate demand by the tree.
Anatomy of Maize Tissue Cultures
Authors: MOTT R. L. , CURE W. W. 
Published: April 2006

AbstractTissue cultures of Zea mays L. derived from four different somatic sources all appeared to grow as callus. Microscopic examination, however, showed this growth to be merely an aberrant root‐like form.A continium in the degree of aberrant root behavior, ranging from cultures appearing very root‐like to those visibly indistinguishable from callus, was recognized. The continuum and ultimately the callus appearance resulted from increasing inhibition of root elongation coupled with strong enhancement of branch root initiation. This aberrant form of root growth was apparent in all cultures observed. Tissue source and growth regulator treatment interacted to shift the growth form within the extremes of the continuum but in no case was the root‐like mechanism of proliferation disrupted, even during extended subculture. Removal of exogenous growth regulators from the culture medium simply allowed outgrowth of existing root primordia as normal roots and this accounts for the characteristic ease of rhizogenesis from what has been called maize callus.
Physiological Changes in the Hemiparasite Rhinanthus serotinus before and after Attachment
Authors: KLAREN CHRISTINE H. , JANSSEN GREET 
Published: April 2006

AbstractGrowth of the hemiparasite Rhinanthus serotinus (Schönh.) Oborny was greatly stimulated after attachment of the parasite to the roots of the host plant, Hordeum vulgare L. In order to find the limiting factors for the growth of Rhinanthus without a host, unattached and attached Rhinanthus plants were compared. Within I day after attachment the contents of nitrogen, phosphorus, potassium, magnesium, and sodium increased considerably. Organic nitrogen and phosphorus compounds were rapidly synthesized in attached Rhinanthus. The accumulation of sugars in unattached Rhinanthus and the decrease in sugar content after attachment suggested that the main requirement from the host was not for carbohydrates.
Effects of Crude Oil and Aromatic Hydrocarbons on the Photosynthesis of the Diatom Nitzschia palea
Authors: KUSK KRESTEN OLE 
Published: April 2006

AbstractThe rate of light saturated photosynthesis of Nitzschia palea was reduced by crude oil, naphthalene and benzene. A decrease in the rate of photosynthesis at weak irradiance was also found with crude oil and naphthalene and high concentrations of benzene. On a mg/1 basis naphthalene decreased photosynthesis to a greater extent than did crude oil and crude oil to a greater extent than did benzene. A linear proportionality was found between the decrease in light saturated photosynthesis and the concentrations of aromatic hydrocarbons. The effects on photosynthesis were generally reversible, but a concentration of 700 mg benzene/1 stopped photosynthesis completely and irreversibly.
Photo‐oxidative Degradation of Chlorophyll‐a and Unsaturated Lipids in Liposomal Dispersions at Low‐Temperature
Authors: DE KOK LUIT J. , VAN HASSELT PHILIP R. , KUIPER PIETER J. C. 
Published: April 2006

AbstractLiposomal dispersions in water were used as a tool to study photo‐oxidation of chlorophyll‐a and photo‐oxidation of unsaturated lipids at 1 or 4°C. The presence of monogalactosyl diglyceride stimulated chlorophyll‐a degradation. In addition the level of linolenic acid was decreased in liposomal dispersions containing chlorophyll‐a, dipalmitoyl phosphatidyl choline, and monogalactosyl diglyceride, indicating that monogalactosyl diglyceride and chlorophyll‐a were coupled in the preparations. In liposomal dispersions containing equal (molar) quantities of a‐tocopherol, monogalactosyl diglyceride, and chlorophyll‐a, a‐tocopherol fully protected linolenic acid against photo‐oxidative degradation, while chlorophyll‐a degradation was only slightly reduced. In liposomal preparations containing a‐tocopherol, chlorophyll‐a and phosphatidyl choline, a‐tocopherol catalyzed degradation of chlorophyll‐a. Absorption spectra of the liposomal dispersions showed that the presence of a‐tocopherol caused increased absorption in red light, which was attributed to structural changes in the liposomal preparations and thus could explain the noted effects. Tocopherol itself was rapidly degraded in chlorophyll‐a containing liposomal preparations. Complex formation between chlorophyll‐a and monogalactosyl diglyceride in chloroplasts is suggested and protection by a‐tocopherol against photo‐oxidation in chilling‐sensitive plants; a suggestion which is founded on the similarities that exist between chloroplast preparations and liposomal preparations containing chlorophyll‐a and monogalactosyl diglyceride as regards photo‐oxidative degradation of chlorophyll‐a, a‐tocopherol and linolenic acid.
Adaptation of the Photosynthetic Apparatus of Scenedesmus obliquus to Strong and Weak Light Conditions
Authors: SENGER HORST , FLEISCHHACKER PH. 
Published: April 2006

AbstractHomocontinuous cultures of the unicellular green alga Scenedesmus obliquus were grown under strong (28 W/m2∼28,000 lux) and weak (5 W/m2∼5000 lux) light conditions to simulate the conditions of ‘sun’ and ‘shade’ plants. As in higher plants the cells adapted to strong light had less chlorophyll but demonstrated a higher photosynthetic capacity and a higher respiration rate, so that their compensation point was reached at three times higher energy than in the cells grown under low light intensities. The CO2 fixation rate and the RuDP carboxylase activity under saturating light intensities were both higher in the cells grown in strong light. In spite of the differences in the pigment content and in the light saturated photosynthetic capacities for both cultures, the quantum yields of photosynthetic oxygen evolution were equal. As documented for some species of higher plants Scenedesmus is not genetically determined to be either a ‘sun’ or ‘shade’ organism but can adapt its photosynthetic apparatus to the different light intensities.
Adaptation of the Photosynthetic Apparatus of Scenedesmus obliquus to Strong and Weak Light Conditions
Authors: FLEISCHHACKER PH. , SENGER HORST 
Published: April 2006

AbstractSimulating ‘sun’ and ‘shade’ conditions of higher plants, homocontinuous cultures of Scenedesmus obliquus were grown under 28 W/m2 (∼28,000 lux) or 5 W/m2 (∼5000 lux). In the high light intensity grown culture the photosynthetic capacity per chlorophyll was three times higher than in the low light intensity grown cells. The activity of photosystem II changed parallel to the photosynthetic capacity, whereas photosystem I activity was influenced to a lesser amount by the light intensity under which Scenedesmus was grown. The molar concentration of all cytochromes and reactive plastoquinone were higher in cells grown under high light intensities. Since only plastoquinone activity represented changes equivalent to photosynthetic capacity, its activity is regarded as the rate limiting step. In spite of the changes in the photosystems and the electron transport chains, the size of the photosynthetic units is independent of the light intensity under which the cells are grown. The results reported for Scenedesmus represent a striking similarity to those published for higher plants grown under different light intensities.
Effects of Acetazolamide (Diamox), Ethoxzolamide and High Levels of CO2 on Carbonic Anhydrase, Photosystem Activity, and Oxygen Evolution in Euglena gracilis
Authors: LONERGAN THOMAS A. , SARGENT MALCOLM L. 
Published: April 2006

AbstractInvestigations using steady‐state culture conditions indicate that carbonic anhydrase activity is correlated to the photosynthetic rate in Euglena in some but not all circumstances. When cultures grown with 5% CO2 were changed to air growth, the photosynthetic rate was independent of the carbonic anhydrase activity.While experiments using the inhibitor acetazolamide indicated a close correlation between photosynthetic capacity and carbonic anhydrase activity, the inhibitor was found to be nonspecific. Acetazolamide altered photosystem activities directly as measured by the photoreduction of DCPIP in chloroplast preparations, whole‐cell fluorescence transients of chlorophyll a, and by whole chain photoelectron flow. Ethoxzolamide, another inhibitor of carbonic anhydrase, was also found to inhibit photosystem activities, i.e., the photoreduction of DCPIP, and in vivo photoelectron flow, at high concentrations.Cells grown in 5% CO2 were less sensitive to the effects of acetazolamide than cells exposed to air. The rate of electron flow in chloroplasts from cells grown with 5% CO2 and exposed to 10 mM acetazolamide was 2.5‐fold faster than that of chloroplasts from air‐grown cells exposed to the same concentration of inhibitor. The whole cell chlorophyll a fluorescence transients of cultures grown with high CO2 were completely different from those of air‐grown cells and also showed fewer effects on exposure to acetazolamide.These results suggest a reevaluation of the hypothesis that carbonic anhydrase activity regulates photosynthesis. It is also apparent that results from air‐grown and 5% CO2‐grown cultures cannot be directly compared in such studies.
Response of Substituted Indoleacetic Acids in the Indolo‐α‐pyrone Fluorescence Determination
Authors: BÖTTGER MICHAEL , ENGVILD KJELD C. , KAISER PETRA 
Published: April 2006

AbstractThe method of indolo‐α‐pyrone fluorescence‐determination of indoleacetic acid was investigated to study possible interference from 4‐chloro‐indoleacetic acid and 5‐hydroxyindoleacetic acid, which occur naturally. Both compounds show about 40% of the fluorescence of indoleacetic acid after conversion into their a‐pyrones. Other halogenated indoleacetic acids show between zero and 60% of the fluorescence of indoleacetic acid.It is concluded that the concentration of indoleacetic acid cannot be determined in crude extracts in the presence of 4‐chloro‐ or 5‐hydroxy‐indoleacetic acid, because separate determinations of each of these compounds are not possible by changing the excitation or fluorescence wave‐lengths of the testing equipment.
Attenuation of the Petal Movement Rhythm in Kalanchoë with Light Pulses
Authors: ENGELMANN WOLFGANG , JOHNSSON ANDERS , KARLSSON H. G. , KOBLER R. , SCHIMMEL M.‐L. 
Published: April 2006

AbstractThe circadian petal movement rhythm of Kalanchoë flowers has been studied. The amplitude of the rhythm can be drastically reduced by an appropriate stimulus of a light pulse. It has also been shown that it is possible to stop the rhythm permanently by administering a single light pulse to the flowers. This is interpreted to indicate that the light pulse has sent the circadian rhythm into a stable state of singularity.The conditions which attenuate the rhythm have been investigated both theoretically (on the basis of a previously published model for circadian rhythms) and experimentally. 120 min red light of 230 μW · cm−2, starting briefly before the second petal closure about 30 h after transfer to constant safe light conditions is optimal in inducing rhythm‐damping. Damping requires the same duration when the light is given at the corresponding phase during the third or fourth cycle of the rhythm. However, in the first cycle 240 min red light of 230 μW · cm−2 is required to get optimal damping of the rhythm.Conditions to achieve damping for other irradiances are investigated. Individual recordings are presented which show the behaviour of the rhythm when perturbed by light stimuli close to its singularity.
Cytokinin Activity in Lupinus albus
Authors: DAVEY J. E. , VAN STADEN J. 
Published: April 2006

AbstractThe cytokinin activity of the root exudate, the leaves, and the apices of vegetative and flowering white lupin plants (Lupinus albus L.) was investigated. The level of cytokinin activity in the root exudate decreased over the 11‐week experimental period. Four peaks of cytokinin activity were recorded in the root exudate of 8‐week‐old plants after fractionation on Sephadex LH‐20. Two of these peaks co‐eluted with zeatin and zeatin riboside. It is suggested that the remaining peaks represent nucleotide and glucoside cytokinins. The cytokinin levels in extracts of the mature leaves fluctuated slightly over the experimental period. Three peaks of activity co‐eluting with zeatin, zeatin riboside and the glucoside cytokinins were recorded in extracts of mature leaves of 8‐week‐old plants. In the apices cytokinin activity could only be detected in the inflorescences of flowering plants. It would appear that cytokinins produced by the roots accumulate in the fully expanded mature leaves, but are utilized in the rapidly growing apical region and in young expanding leaves.
The Effect of Activated Charcoal on Tissue Cultures: Adsorption of Metabolites Inhibiting Morphogenesis
Authors: FRIDBORG GUNNAR , PEDERSÉN MARIANNE , LANDSTRÖM LARS‐ERIK , ERIKSSON TAGE 
Published: April 2006

AbstractCell suspensions of Daucus carota and Haplopappus gracilis and callus suspensions of Allum cepa var. proliferum were grown in media with and without activated charcoal. Differentiation occurred in those Daucus and Allium cultures that contained charcoal. It was shown by mass spectrometry that the media without charcoal contained high amounts of phenylacetic acid and p‐OH‐benzoic acid (Daucus), 2,6‐OH‐benzoic acid (Allium) and benzoic acid, pelargonic acid and caprylic acid (Haplopappus), whereas the media with activated charcoal did not. It was also shown that p‐OH‐benzoic acid had inhibitory effects on the embryogenesis in Daucus cultures.