bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative ecophysiology of CAM and C3 bromeliads. V. Gas exchange and leaf structure of the C3 bromeliad Pitcairnia integrifolia
Authors: LÜTTGE U. , KLAUKE B. , GRIFFITHS H. , SMITH J. A. C. , STIMMEL K.‐H. 
Published: April 2006

Abstract Pitcairnia integrifolia is endemic to northern Trinidad and the Paria peninsula of Venezuela and is the only member of the bromeliad‐subfamily Pitcairnioideae in Trinidad. It is terrestrial with roots fully functional in water and solute uptake, grows on exposed steep rocky cliffs and can occur just above the spill zone of sea waves under continuous sea spray. Thus, it can be subject both to water stress, particularly during the dry season, and to salt stress.Gas exchange of P. integrifolia leaves was measured on a clear day in Trinidad. Uptake of CO2 and leaf conductance to diffusion of water vapour had two peaks during the light period, a larger one in the early morning and a smaller one in the late afternoon, which were separated by an extended midday depression of gas exchange. CO2 partial pressure in the leaf air‐spaces increased during the midday depression. Leaf temperatures reached a maximum of 51.6°C and leaf‐air water‐vapour‐concentration differences were also very high during the midday depression, when quantum fluxes were up to 2 mmol m−2 s−1 and higher. The midday depression is considered as a functional adaptation to temporary water stress.Although P. integrifolia is subject to sea‐spray, an internal osmotic pressure of only 0.91 MPa indicated that NaCl is not accumulated. Leaf epidermis cells are thick‐walled and have a prominent cuticle. The abaxial leaf surface with the trichomes is not wettable, and the trichomes apparently do not function in water and solute uptake. They cover the stomata densely and may create a favourable microenvironment around them. They also have a high reflectance. This does not prevent overheating of the leaves, but does reduce the photosynthetically active radiation penetrating to the mesophyll. The trichomes may thus contribute to the prevention of photoinhibition at high incident quantum flux.
Structural and metabolic properties of green tissue cultures from a CAM plant, Kalanchoë blossfeldiana hybr. Montezuma
Authors: KLUGE M. , HELL R. , PFEFFER A. , KRAMER D. 
Published: April 2006

Abstract Crassulacean acid metabolism (CAM) was studied in mixotrophic callus tissue cultures of Kalanchoë blossfeldiana hybr. Montezuma and compared with plants propagated from the calli.The ultrastructural properties of the green callus cells are similar to mesophyll cells of CAM plants except that occasionally abnormal mitochondria were observed. There was permanent net CO2 output by the calli in light and darkness, which was lower in darkness than in light. The calli exhibited a diurnal rhythm of malic acid, with accumulation during the night and depletion during the day. 14C previously incorporated by dark CO2 fixation into malate was transferred upon subsequent illumination into end products of photosynthesis. All these data indicate that CAM operates in the calli tissue. The results revealed that the capacity for CAM is obviously lower in the calli compared with plantlets developing from the calli, or with ‘adult’ plants. The data suggest also that CAM in the calli was not limited by the activities of CAM enzymes.
Amino acid uptake by Ricinus communis roots: characterization and physiological significance
Authors: SCHOBERT C. , KOMOR E. 
Published: April 2006

Abstract Roots of sterile‐grown, intact 6‐day‐old seedlings of Ricinus communis possess at least two independent active amino acid uptake systems, one for neutral and one for basic amino acids. The kinetics of uptake of L‐proline and L‐arginine, which were taken as representative substrates for the two systems, are biphasic. At low concentrations (0.01–0.5 mol m−3) Michaelis ‐Menten kinetics prevail, changing to a linear concentration dependence at higher substrate concentrations (1–50 mol m−3). L‐glutamate uptake velocity is linear over the whole substrate concentration range.For comparison the uptake kinetics of nitrate and ammonium were determined as well as interactions among the different nitrogen sources. The Km value for nitrate uptake was 0.4 mol m−3, and for ammonium 0.1 mol m−3. The uptake capacity for nitrate or ammonium was approximately the same as for amino acids. The interaction between the uptake systems for organic and inorganic nitrogen is small.Two hypotheses for the physiological significance of amino acid uptake by roots were considered:(i) Uptake of amino acids from the soil‐determination of amino acids in soil and in soil water indicates that they might contribute 15–25% to the nitrogen nutrition of the plant.(ii) Amino acid uptake systems of root cells serve primarily as retrieval of amino acids delivered from the phloem‐ it was found that 14C L‐glutamine, which was delivered to the cotyledon and transported to the root via the phloem, was not lost by the roots, whereas it appeared in the bathing medium if L‐glutamine was applied externally to the root to compete for the uptake sites; this suggests that an apoplastic pool of amino acids in the root exists due to their efflux from the phloem.
Thermal history regulates methylbutenol basal emission rate in Pinus ponderosa
Authors: GRAY DENNIS W. , GOLDSTEIN ALLEN H. , LERDAU MANUEL T. 
Published: April 2006

ABSTRACTMethylbutenol (MBO) is a 5‐carbon alcohol that is emitted by many pines in western North America, which may have important impacts on the tropospheric chemistry of this region. In this study, we document seasonal changes in basal MBO emission rates and test several models predicting these changes based on thermal history. These models represent extensions of the ISO G93 model that add a correction factor Cbasal, allowing MBO basal emission rates to change as a function of thermal history. These models also allow the calculation of a new emission parameter Estandard30, which represents the inherent capacity of a plant to produce MBO, independent of current or past environmental conditions. Most single‐component models exhibited large departures in early and late season, and predicted day‐to‐day changes in basal emission rate with temporal offsets of up to 3 d relative to measured basal emission rates. Adding a second variable describing thermal history at a longer time scale improved early and late season model performance while retaining the day‐to‐day performance of the parent single‐component model. Out of the models tested, the Tamb,Tmax7 model exhibited the best combination of day‐to‐day and seasonal predictions of basal MBO emission rates.
Spatial coordination of aluminium uptake, production of reactive oxygen species, callose production and wall rigidification in maize roots
Authors: JONES D. L. , BLANCAFLOR E. B. , KOCHIAN L. V. , GILROY S. 
Published: April 2006

ABSTRACTAluminium (Al) toxicity associated with acid soils represents one of the biggest limitations to crop production worldwide. Although Al specifically inhibits the elongation of root cells, the exact mechanism by which this growth reduction occurs remains controversial. The aim of this study was to investigate the spatial and temporal dynamics of Al migration into roots of maize (Zea mays L.) and the production of the stress response compound callose. Using the Al‐specific fluorescent probe morin, we demonstrate the gradual penetration of Al into roots. Al readily accumulates in the root’s epidermal and outer cortical cell layers but does not readily penetrate into the inner cortex. After prolonged exposure times (12–24 h), Al had entered all areas of the root apex. The spatial and temporal accumulation of Al within the root is similarly matched by the production of the cell wall polymer callose, which is also highly localized to the epidermis and outer cortical region. Exposure to Al induced the rapid production of reactive oxygen species and induced a significant rigidification of the cell wall. Our results suggest that Al‐induced root inhibition in maize occurs by rigidification of the epidermal layers.
Involvement of gibberellins in the stem elongation of sun and shade ecotypes of Stellaria longipes that is induced by low light irradiance
Authors: KUREPIN LEONID V. , PHARIS RICHARD P. , REID DAVID M. , CHINNAPPA C. C. 
Published: April 2006

ABSTRACTPlants from two ecotypes of Stellaria longipes, alpine (an open, sunny habitat) and prairie (where adjacent plants provide a shaded habitat), were grown under normal and reduced levels of photosynthetically active radiation (PAR). Growth under low PAR is significantly promoted in both ecotypes. When quantified by the stable isotope dilution method, endogenous gibberellins (GAs) (GA1, GA8, GA20, GA19) were significantly elevated under low PAR in both ‘sun’ and ‘shade’ ecotypes, as was GA53 in the shade ecotype. Changes in endogenous GA1 levels were significantly correlated with stem growth during a 28 d growth cycle and with relative growth rate (RGR) for height under low PAR for both ecotypes. Interestingly, under low irradiance PAR, changes (both increases and decreases) in GA8, the 2β‐hydroxylated ‘inactive’ catabolite of GA1, closely parallel bidaily stem growth changes for both ecotypes. Because the significantly greater stem elongation of both ecotypes in response to low irradiance PAR is associated with significant increases in the endogenous levels of five GAs (GA53, GA19, GA1, GA8) in the early 13‐hydroxylation GA biosynthesis pathway (measured at days 7, 14 and 21), we conclude that the low irradiance PAR has very likely induced an overall increase in GA biosynthesis.
The effect of gibberellic acid on the response of leaf extension to low temperature
Authors: FARRELL A. D. , OUGHAM H. J. , TOMOS A. D. 
Published: April 2006

ABSTRACTThe effect of cooling on leaf extension rate (LER) and on relative elemental growth rate (REGR) was measured in both gibberellic acid (GA)‐responsive dwarf barley and in the same barley variety treated with GA. Seedlings were maintained at 20 °C while their leaf extension zone (LEZ) temperature was reduced either in steps to −6 °C in short‐term cooling experiments, or to 10 °C for 48 h in long‐term cooling experiments. Short‐term cooling resulted in a biphasic response in LER, with a clear inflection point identified. Below this point, the activation energy for leaf extension becomes higher. The short‐term response of LER to cooling was altered by the application of GA, which resulted in a lower base temperature (Tb), inflection point temperature and activation energy for leaf extension. Both GA‐treated and untreated seedlings were less sensitive to cooling maintained for a prolonged period, with LER making a partial recover over the initial 5 h. Although long‐term cooling reduced maximum REGR, it resulted in a longer LEZ and an increase in the length of mature interstomatal cells in GA‐treated and untreated seedlings. These changes in overall physiology appear to enhance the ability of the leaves to continue expansion at suboptimal temperatures. In both GA‐treated and cold‐acclimated tissue, the occurrence of a longer LEZ was associated with a lower temperature sensitivity in LER.
Environmental and developmental effects on the biosynthesis of UV‐B screening pigments in Scots pine (Pinus sylvestris L.) needles
Authors: KAFFARNIK FLORIAN , SEIDLITZ HARALD K. , OBERMAIER JOSEF , SANDERMANN HEINRICH , HELLER WERNER 
Published: April 2006

ABSTRACTThe major UV‐B screening pigments of the epidermal layer of Scots pine (Pinus sylvestris) needles are flavonol 3‐o‐glycosides (F3Gs) esterified with hydroxycinnamic acids at positions 3′′ and 6′′. Acylation is the last step in biosynthesis and is catalysed by position‐specific hydroxycinnamoyl transferases (3′′ and 6′′HCT). The UV‐B dependence of these enzyme activities was studied in primary needles of Scots pine seedlings grown under different UV‐B conditions in environmentally controlled sun simulators. 6′′HCT activity was induced upon UV‐B irradiation while 3′′HCT activity was not induced but showed high constitutive values. To investigate the biosynthesis of diacylated F3Gs during needle development under natural conditions, the HCT activities and metabolite contents were analysed in needles of field‐grown mature pine trees. Accumulation of diacylated compounds as well as of 6′′HCT activity occurred transiently in the first year of needle development only. In contrast, 3′′HCT activity exhibited broad maxima in two consecutive years during needle growth. The data suggest that acylated F3Gs are first formed as soluble compounds which are then translocated into the cell wall to be bound by their hydroxycinnamoyl residues.
Response of Chlorella to Scandium and Potassium at Various pH
Authors: HOROVITZ C. T. , WEGMANN K. 
Published: April 2006

AbstractThe response of Chlorella pyrenoidosa cells to moderate potassium deficiency and to the addition of various scandium amounts in the nutrient solution were studied at different pH. The effects on growth, chlorophyll content, oxygen consumption, and the 14CO2 incorporation in photosynthesizing cells were measured. Considerable metabolic changes inside the cells were registered under the given nutrient conditions. The separated 14C‐labelled compounds showed, at acid and neutral pH in complete nutrient solution, an increase in the relative content of sugar phosphates and a decrease in the relative content of sucrose, caused by increasing scandium concentrations. Moderate potassium deficiency caused a diminution of the relative content of sugar phosphates. The relative content of amino acids was increased by scandium added to complete nutrient solution, but it decreased under potassium deficiency.
The ATP Levels Obtained in Photophosphorylation, Glycolysis and Oxidative Phosphorylation in Scenedesmus Titrated with Desaspidin
Authors: OKKEH ASSAD , KYLIN ANDERS 
Published: April 2006

AbstractThe ATP levels in photophosphorylation, glycolysis and oxidative phosphorylation, in the unicellular green alga Scenedesmus obtusiusculus, were titrated with narrow concentration intervals of desaspidin in the presence of different concentrations of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), which allows the differentiation between non‐cyclic, pseudocyclic and true cyclic photophosphorylation. The data on photophosphorylative ATP levels were compared with earlier data on total binding of phosphate. In the true cyclic process, both parameters are equally sensitive towards desaspidin. Under pseudocyclic conditions and in non‐cyclic photophosphorylation, the level of ATP is more sensitive towards desaspidin than is total binding of phosphate. This suggests a structural difference between the cyclic and the two non‐cyclic (one of which is also pseudocyclic) sites. The non‐cyclic ATP level is more sensitive towards desaspidin than is pseudocyclic. This may be connected with the higher ATP level under pseudocyclic as compared to non‐cyclic conditions.
Volatilization of Mercury by Algae
Authors: BEN‐BASSAT D. , MAYER A. M. 
Published: April 2006

AbstractThe presence of Chlorella cells in a medium containing HgCl2 causes a rapid decrease of the mercury content in the algal suspension. The rate of decrease depends on the inoculum concentration. The presence of Hg in the medium induces a lag in the growth, whose length depends on the initial concentration of Hg and of the inoculum. Binding and/or uptake of mercury by the cells is not dependent on temperature. The mercury content per cell declines somewhat at the time at which the culture resumes growth at a rate similar to that of the controls without mercury.
Manganese Absorption and Transport in Rice
Authors: RAMANI SARADHA , KANNAN SESHADRI 
Published: April 2006

AbstractThe absorptive patterns of Mn2+ in excised rice roots, leaf tissues and intact plants, were studied. The rates of absorption of Mn2+ followed different patterns in the roots and the leaf tissues. The uptake from 0.1 and 5 mM MnSO4 was found to be sensitive to metabolic inhibitors. The time course of uptake from 0.1 mM and 5 mM MnSO4 followed a biphasic pattern which represented only the metabolic component of absorption. A secondary biphasic pattern of uptake at 5 mM MnSO4 (one at 20 min and another at 80 min) appears quite anomalous and is probably related to structural virations or cellular compartments. When absorption and transport of Mn2+ were measured in intact rice and wheat plants, it was found that Mn2+ was easily translocated to shoot from roots and the transport of Mn2+ was comparable to that of K+.
The Formation of Coremia in Ceratocystis piceae Induced by Hexanal
Authors: FRIES NILS 
Published: April 2006

AbstractHexanal, and to a lesser degree nonanal, added in gaseous form induce coremia formation in the blue stain fungus Ceratocystis piceae (Münch) Bakshi grown in axenic agar culture. The optimum initial concentration of hexanal in the gas phase proved to be c. 2 mg/1 (2 × 10−5M). Possible ecological implications are discussed.
Bolting Susceptibility of Sugar Beet (Beta vulgaris) in Relation to Contents of Sulfhydryls and Disulfides and to Protein Composition of Membranes
Authors: LEXANDER KERSTIN 
Published: April 2006

AbstractThe aim of the investigation was to correlate the sensitivity to low temperature that leads to bolting of sugar beet with a property of seedlings or seeds, analyzable without cold treatment. Populations or inbred lines were investigated, the bolting percentages of which had been determined in field trials. Sulfhydryls (—SH) and disulfide sulphur (‐S‐) were analyzed by amperometric titration with silver nitrate. Disulfides were broken with sulphite, and proteins were unfolded with urea.Negative correlations were found between the bolting percentage and (‐SH + ‐S‐) per leaf fresh or dry weight unit and per leaf protein nitrogen, with urea at the titrations. Positive correlations were obtained between the bolting percentage and the ratio of (‐SH + ‐S‐) titratable in the absence of urea to that titratable in the presence of urea, when leaf homogenates or leaf or seed protein precipitates were examined. Centrifugation experiments showed that membrane proteins were responsible for the correlation. By polyacrylamide gel electrophoresis of the membrane proteins it was found that the proportion between some of these proteins was correlated with the bolting percentage.From these results and such from analyses of beet plants during and after cold treatment a hypothesis was constructed: Low bolting susceptibility, i.e., low sensitivity to low temperature, is caused by a high proportion of a hydrophobic membrane protein, rich in ‐SH or ‐S‐. This protein interferes with the reactivity of the plants to gibberellins resulting from low temperatures or long days.
Biosynthesis of Abscisic Acid under Osmotic Stress: Studies Based on a Dual Labelling Technique
Authors: LOVEYS B. R. , BRIEN C. J. , KRIEDEMANN P. E. 
Published: April 2006

AbstractSterile liquid suspension cultures from grape pericarp tissue incorporate label from mevalonic acid into abscisic acid (ABA), some of which is subsequently released into the surrounding medium. The addition of mannitol to the culture medium caused plasmolysis of individual cells and increased ABA generation and release. Levels in the medium increased up to 30 fold over a period of 8 h in the presence of mannitol (720 milliosmol).A dual labelling technique using 14C and 3H mevalonic acid was developed to distinguish between labelled compounds produced by turgid tissue and those specifically associated with the substantial increase in ABA synthesis following mannitol treatment.
Aminotransferase Activity in Relation to Floral Differentiation in Wheat Plants
Authors: SRIVASTAVA G. C. , SIROHI G. S. 
Published: April 2006

AbstractThe present investigation was carried out to study the transamination reaction in relation to floral differentiation in wheat (cv. NP 876) under three photoperiodic conditions. Three selected aminotransferases namely glutamic‐glyoxylate, glutamic‐pyruvate, and alanine‐glyoxylate were studied in the top young leaves at various growth and developmental stages. The activity of all the three systems increased progressively during the vegetative phase till the plants produced reproductive buds. When flower primordia started differentiating, there was a sharp decrease in the aminotransferase activity followed by an increase during anthesis period. Photoperiodic treatments clearly show that even when the vegetative period of the plant is shortened considerably by long day or extended by short day, the aminotransferase activity remains closely associated with different developmental processes.
Morphogenesis in Tissue Cultures of Different Organs of Nigella sativa
Authors: BANERJEE S. , GUPTA S. 
Published: April 2006

AbstractCalli were isolated from root, stem and leaf segments of Nigella sativa (Fam. Ranunculaceae) on White's medium containing napthaleneacetic acid and coconut milk. From all the three types of calli, roots were differentiated. Shoot development occurred in stem and leaf calli only after the omission of first coconut milk and then of auxin from the basal medium and also in IAA (2.0 mg/ml) and coconut milk (15 % v/v) in the medium. Frequency of organ formation and the maintenance of this capacity depend upon the nature as well as the age of the callus tissue.
Quelques Modifications Physico‐chimiques et Physiologiques liées à la Sénescence des Feuilles
Authors: VIGNES DOMINIQUE , CALMÉS JEAN 
Published: April 2006

AbstractDuring the senescence of the leaves of Parthenocissus tricuspidata Planchon, the high level of Ca2+ ions liberated from pectic membranes in the aqueous medium of the blade causes a decrease in photophosphorylation and chlorophyll regeneration, while carboxylation and diffusion resistances increase. After the hydrolysis of its carbohydrate and protein reserves, the leaf blade can no longer contribute to the nutrition of the plant and abscission is prepared.
Influence de la 6‐benzylaminopurine sur la différenciation plastidiale dans les cotylédons de concombre
Authors: FARINEAU NICOLE , ROUSSAUX JEAN 
Published: April 2006

AbstractTreatment with 6‐benzylaminopurine (6‐BAP; 10−5 g/ml) accelerates the growth of detached cucumber cotyledons (Cucumis sativas L.), primarily through an increased water uptake by the tissues. A comparative study of pigment composition and ultrastructure in 6‐BAP treated and untreated cotyledons shows that cytokinin, in the presence of light, accelerates the transformation of etioplasts into chloroplasts. 6‐BAP also enhances the synthesis of membrane precursors as indicated by the formation of a dense prolamellar body and by the persistence of a pseudo‐cristalline structure in 6‐BAP treated material. Stimulation of biosynthetic activity by cytokinin leads simultaneously to an increase in the rate of the pigment synthesis and to an acceleration in the building of the lamellar system. Furthermore, chloroplasts of 6‐BAP treated cotyledons show abnormal features such as a striking increase in the number of thylacoids per granum and a poor development of the intergranal system.