bluuebunny/crossref_metadata_2025_split huggingface dataset:
Salinity‐dependent regulation of starch and glycerol metabolism in Dunaliella parva
Authors: GIMMLER HARTMUT , MÖLLER EVA‐MARIA 
Published: April 2006

Abstract. The glycerol and starch metabolism of synchronized Dunaliella parva cells as a function of the salinity of the medium has been investigated.The higher the salinity of the medium the higher is the rate of glycerol synthesis and the endogenous glycerol concentration, whereas starch content and salinity of the medium are inversely related. Upon transfer to a hyperosmotic NaCl‐medium cells respond by an immediate increase in glycerol synthesis and an inhibition of starch formation in the light. Under corresponding conditions in darkness, starch degradation is stimulated. In both light and darkness hyperosmotic shocks are followed by a rapid increase in the endogenous pool of inorganic phosphate (Pi). It is suggested that in the light the increase in the endogenous phosphate level inhibits the chloroplast ADPG‐pyrophosphorylase (E.G.2.7.7.27), and thereby starch synthesis, and promotes starch phosphorolysis. Photosynthetically produced triosephosphates and triosephosphates derived from starch degradation are converted to glycerol. Also, in the dark the increase in the Pi‐level stimulates phosphorolytic starch degradation and thereby synthesis of glycerol. Reasons for the salt stress induced increase in the endogenous Pi‐level are discussed.
Improvement of the heat pulse method for determining sap flow in trees
Authors: COHEN Y. , FUCHS M. , GREEN G. C. 
Published: April 2006

Abstract. The heat pulse method for determining sap flux in large woody sterns was modified for easier field operation. It uses the measurement of the time elapsed between heat pulse release by a line heater radially inserted in the stem, and the occurrence of maximum temperature 15 mm downstream of the heater. This spacing between heater and thermometer is critical to the reliability of the measurement. Calculations using uncorrected theory provide estimates of the sap flux density in stems with both uniform and non‐uniform cross‐sectional distribution of conducting tissues which are about 55% of the actual sap flux density. This factor results from insufficient thermal homogeneity between tissues where sap flow occurs and tissues where sap flow has been interrupted.Sap flow in trunks of citrus trees was inferred from measurements of the cross‐sectional distribution of sap flux density. Variability of sap flux density is specific to each trunk and is time‐dependent and imposes multiple radial and angular measurements. The method was checked in a citrus trunk ramified into three branches. Instantaneous determinations of the flow in the trunk and in the branches differed by less than 5.7%. The daily values agreed within 2.8%.
Leaf expansion of four sunflower (Helianthus annuus L) cultivars in relation to water deficits. I. Patterns during plant development
Authors: TAKAMI SHINICHI , TURNER NEIL C. , RAWSON HOWARD M. 
Published: April 2006

Abstract. The influence of a slow stress and recovery cycle on the pattern of leaf expansion in four diverse sunflower cultivars (Helianthus annuus L. cvs. Hysun 31, Havasupai, Hopi and Seneca) was studied in a glasshouse. Stress had no significant effect on the time of flower bud emergence and anthesis, or on final leaf number, but delayed the appearance of leaves at high insertions in all cultivars except Hysun 31.Leaf expansion was markedly reduced as the predawn leaf water potential decreased from −0.35 to −0.60 MPa, and the predawn turgor pressure decreased from 0.3 to 0.2 MPa, and expansion ceased at a predawn leaf water potential of about −1.0 MPa, i.e. when the predawn turgor pressure reached zero.The leaves most reduced in final size when water was withheld were those at the insertions which grew the most rapidly in unstressed plants. The maximum reduction in final leaf size of 25–35% was similar in all cultivars and was due to retardation of the rate of leaf expansion: the duration of leaf expansion was actually increased by stress. However, leaves that were initiated during stress, but emerged after rewatering, had final leaf areas at least equal to those in the unstressed plants: in the cultivar Seneca, the final size of leaves of high insertion was significantly greater in stressed than unstressed plants, whereas in the three other cultivars the final leaf sizes were similar in both treatments. All four cultivars examined adjusted osmotically to the same degree, but leaf water potentials in one, Seneca, increased more rapidly after rewatering than in the other three, and this may have contributed to the greater relative leaf size in the leaves of high insertion in this cultivar.
Photoperiodism and rhythmic response to light
Authors: KING R. W. , SCHÄFER E. , THOMAS B. , VINCE‐PRUE D. 
Published: April 2006

Abstract. Seedlings of Pharhitis nil show a circadian rhythm in the capacity to flower in response to the timing of a second red light pulse given at various times after a first saturating exposure to red when this is given together with a benzyladeninc spray. There are also changes in the photon irradiance required for half maximum response to the second red pulse.The photochemical properties of phytochrome in the photoperiodically sensitive cotyledons were also shown to change rhythmically. Oscillations in both pr→ Pfr and Pfr→ Pr photoconversion characteristics persisted over at least two circadian cycles with a periodicity of about 12 h. There were, however, no significant oscillations in either Pfr peak absorbance or in Δ(ΔA). The changes in sensitivity for the photoconversion of Pr→ Pfr did not parallel the much larger changes in sensitivity of the flowering response to red light. The amplitude of the Pr→ Pfr rhythm was at least as great as that for Pr→ Pfr, but the flowering response to far‐red light was not rhythmic, nor was there any large change in sensitivity. The changes in photoconversion properties may reflect a basic biochemical oscillation which affects both photoreceptor properties and sensitivity to photoreceptor input.There was also a marked rhythm in the Pfr/P ratio that would be established by a saturating pulse of red light and this too may have affected the flowering response to such a pulse.Far‐red light inhibited flowering when given at any time during the inductive night. After 14 h in darkness, Pfr could still be measured in the cotyledons and it was concluded that far‐red light inhibited flowering by removing Pfr As red light also inhibited flowering at this time, there may be two pools of phytochrome with different kinetic properties.
The non‐osmotic volume of Commelina guard cells
Authors: WEYERS JONATHAN D. B. , FITZSIMONS PETER J. 
Published: April 2006

Abstract. The non‐osmotic volume (NOV) of Connnelina communis L. guard cells was estimated by observing the volumes of guard cell protoplasts incubated in mannitol solutions of different solute potential, and applying the Boyle‐van't Hoff relation to the results. NOV values of between 517 and 1782 μm3 were obtained for different batches of protoplasts. There was a negative correlation between NOV and apparent protoplast solute contents, and the NOV and solute content were observed to alter when pretreatments affecting stomatal aperture were given. H is hypothesized that changes in guard cell chloroplast starch levels could account for variation in NOV and solute content.For closed stomata, it is calculated that the NOV could reduce the proportion of the total guard cell volume which is osmotically active by over 40%. Serious inaccuracy may thus result if the NOV is not taken into account in the estimation of guard cell solute potential or solute concentration from measurements of solute levels per cell. The error is maximal at low stomatal apertures.
ATP‐dependent proton uptake inhibited by Cercospora beticola toxin in pea stem microsomal vesicles
Authors: MACRÌ F , DELL'ANTONE P. , VIANELLO A. 
Published: April 2006

Abstract. The effect of Cercospora beticola toxin (CBT) on ATP‐dependent and nigericin‐induced proton translocation, monitored by acridine orange uptake in pea stem microsomal vesicles, was studied. CBT inhibits ATP‐dependent proton translocation, but not the nigericin‐induced H+/K+ exchange. The inhibitory effect is dependent on CBT concentration, time of preincubation with CBT and protein concentration of the vesicle suspension.The previously observed effects of CBT on membrane transport phenomena, in the light of the present results, are in agreement with the hypothesis that the primary effect of the toxin is exerted on an ATPase of plasmalemma and/or tonoplast, acting as a proton pump.
The role of peristomatal transpiration in the mechanism of stomatal movement
Authors: MAIER‐MAERCKER UTA 
Published: April 2006

Abstract.Peristomatal transpiration is defined as the relative high local rate of cuticular water loss from external and internal surfaces around the stomatal pore and its decisive role in the control of stomatal movement is re‐emphasized. As the resistance towards changes in air humidity is low in the pore surroundings, the state of turgor is particularly unsteady there. Due to the inherent instability the guard cell ‘senses’ fluctuations in the supply‐demand relationship of water and is thus the control unit proper. The environmental variables (supply and demand) are cross‐correlated within the subsidiary cell and the information is transmitted to the guard cell through the water potential gradient between the two cells. A conceptual segregation of a ‘humidity response’ by ‘passive’ stomatal movements is rejected.As ions always accumulate at the most distant point of the liquid path and as this point varies with pore width according to the prevailing water potential gradients, it is felt that the water stream is causing the characteristic pattern of ion distribution within the epidermis. Passive import of ions is attributed to local concentration gradients which are steepened by continuous supply and by water uptake into the guard cell in response to starch hydrolysis. A mechanistic model supplements the discussion.
Effects of external NaCI, and of changes in turgor pressure and volume, on K+ concentrations in Chlorella emersonii
Authors: GREENWAY H. , WATKIN ELIZABETH 
Published: April 2006

Summary. Soluble potassium concentrations were determined for the slightly vacuolated, unicellular, walled alga Chlorella emersonii. Sap of cells grown in 1 mol m−3 NaCI contained 140 mol m−3 K+ and sap of cells grown in 125, 200, and 335 mol m−3 NaCI contained 160‐180 mol m−3 K +.The possible regulation of K + concentrations by a system of lurgor and volume maintenance was investigated by supplying 3‐0‐methylglucose. This solute accumulates to 85‐230 mol m−3 in C. emersonii, but is not metabolized. Accumulation of 3‐0‐methylglucose increased the volume of cells grown at both low and high NaCI by about 10%. Furthermore, accumulation of 3‐0‐methylglucose also increased turgor pressures of cells grown in 1 and 125 mol m−3 NaCI by 0.3 and 0.2 MPa, respectively. (Similar measurements were not attempted for cells grown in 200 and 335 mol m−3 NaCI, because of the insensitivity of available methods to measure turgor pressure of cells exposed to high external osmotic pressures.)At all NaCI concentrations, the K + concentrations of cells which had accumulated 3‐0‐methylglucose were only 10‐20 mol m−3 lower than K+ in cells which had not been supplied with 3‐0‐methylglucose. In contrast, accumulation of 3‐0‐methylglucose greatly decreased concentrations of the endogenous osmotic solutes, proline and sucrose, which accumulated in cells grown in 125 mol m−3 and higher NaCI concentrations.It is concluded that K+ concentrations in Chlorella emersonii are not controlled by a system of turgor and volume maintenance.
The use of model‐fitting in the interpretation of ‘dual’ uptake isotherms
Authors: BORSTLAP A.C. 
Published: April 2006

Abstract. Published data of the concentration dependence of the uptake rate (uptake isotherms) of K+ Na+, Cl−, SO2−4, and L‐lysine in barley roots, and glucose and 3‐O‐methylglucose in potato tuber tissue, were re‐examined. In as much as these isotherms yield non‐linear, concave upward Eadie‐Hofstee plots, they might have been termed ‘dual’ isotherms. In addition, all these isotherms have been considered to display discontinuous transitions in gradient. The following models that yield continuous isotherms were fitted to the isotherms: (1) the sum of a Michaelis‐Menten term and a linear term; (2) the sum of two Michaelis‐Menten terms; (3) the sum of two Michaelis‐Menten terms and a linear one. Goodness of fit was judged from: (i) the weighted mean square of deviates; (ii) the standard errors of the kinetic parameters; (iii) the algebraic significance of the terms; (iv) a Rankits plot of the residuals; (v) a Runs test on the residuals.For the precise and detailed isotherms of SO2− uptake, only model (3) gave a fit that was satisfactory in all respects. There appeared to be no reason to consider these isotherms as multiphasic. The same conclusion was reached for the L‐lysine uptake isotherms. For the other isotherms the results were less conclusive. Thai for K+ and Na+ could, at any rate, be described satisfactorily by a continuous model, the best fit being obtained with model (2). The uptake isotherms of Cl− and 3‐0‐methylglucose could be best described by model (2), and that of glucose by model (3), only the result of the Runs test being unsatisfactory. It is concluded that there is hardly any evidence that the presumed ‘jumps’ or discontinuities or inflections in the gradient of uptake isotherms are not due to experimental error in the data. It is suggested that many uptake isotherms may be described by model (3), although the reason for this is still incompletely understood.
Effects of temperature on the development of Sinapis alba L. phytochrome‐control of nitrate reductase activity at 10°C
Authors: MOROZ S. M. , ALFORD E. A. , JOHNSON C. B. 
Published: April 2006

Abstract. An analysis of three biochemical parameters during growth of white mustard in continuous white light (WL) has been undertaken at 10°, 15° and 20°C. The time required for anthocyanin and chlorophyll content and nitrate reductase [E.C. 1661 NAD(P)H: nitrate oxidoreductase] activity (NRA) to reach a peak in the cotyledons is shown to be temperature dependent, the rise in chlorophyll content being delayed to a much greater extent than anthocyanin content. In addition, with NRA, there is a significant increase in the level of the peaks with a lowering of temperature.The NRA in dark‐grown plants has been investigated in detail at 10°C. The pre‐competence time for this response is increased to 20–24 h, compared with 14 h in seeds grown at 25°C. Other responses are affected far more by the lower temperature; for example, time for 50% loss of photoreversibility of a red (R) pulse in 48‐h‐old seeds is approximately 13 h, compared with 8 min in seeds grown at 25°C. At 25°C, light treatments during precompetence have been found to increase significantly the effectiveness of a subsequent R pulse on NRA; at 10°C, this effect appears to be almost entirely absent.
Photosynthesis and wood structure in Pinus radiata D. Don during dehydration and immediately after rewatering
Authors: SHERIFF D. W. , WHITEHEAD D. 
Published: April 2006

Abstract. Experiments were carried out on Pinus radiata (D. Don) trees grown as cuttings from clonal parent stock. Some of these trees were about 0.4 m high while others were about 5 m high; all were grown in containers. The stem diameters at the tops and at the bottoms of the large trees, rates of photosynthesis, and needle water potentials were measured both when the trees were well watered and as they dehydrated after water was withheld. The water potentials of well‐watered plants was highest in the small trees and lowest at the top of the large trees. When water was withheld, photosynthesis was in most cases unaffected by a small reduction in water potential, but the rate of photosynthesis fell as water potentials declined further. The stems of the large trees expanded at a constant rate when the trees were well watered and for part of the dehydration period, while subsequent stem shrinkage and the fall in photosynthesis both occurred at approximately the same time.Water potentials increased little in the 24 h after rewatering, and significant rates of photosynthesis were not measured until 2 or 3 d later while renewed stem expansion was not measured until 2 d after rewatering.Water deficits reduced the lumen diameter of newly matured stem tracheids, but increased the thickness of their walls. After 1 month of water potentials of about −2.4 MPa, tracheid lumen diameter and wall thickness were both much reduced, and this reduction continued in tracheids maturing shortly after rewatering.
Sensitivity to phytohormones determined by outer‐inner polarity of higher plants: An overall model for phytohormone action
Authors: LIU SI‐JIU , TILLBERG ELISABETH 
Published: April 2006

Abstract A generalized model of the higher plant body is proposed in order to assemble the discrete knowledge of the actions, and sites of biosynthesis, of phytohormones. In this model, we attempt to explain the differential sensitivities of different tissues. With this model most effects of plant hormones appear to be reasonable, and even expected. The model is based on a new anatomical and physiological classification of plant tissue. In higher plants the integration of an outer‐inner polarity and an upper‐lower polarity plays a major role in phytohormone behaviour.Plant tissues and organs which are derived from the cortex of paleophytes (the bud, the mesophyll of the leaf, the cortex of the stem, and the root cap) are classified as the outer pole of the plant. On the other hand, tissues and organs which are derived from the stele of paleophytes (the root, the stele of the shoot, and the vein of the leaf), are classified as the inner pole. It is suggested that tissue sensitivities to phytohormones are mainly determined by the outer‐inner polarity. Phytohormones which are synthesized from one pole act on the other, whereas they exert either much less or no effect, or an inverse effect on their own pole. This is shown for both promoters and inhibitors of the phytohormones for both cortical and stelar vegetative tissues of plants.
Comparison between two methods of generating pressure—volume curves
Authors: RITCHIE G. A. , RODEN J. R. 
Published: April 2006

Abstract. Pressure—volume (P—V) curves were generated on roots and shoots of coastal Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings using two procedures. In the first (Method A), samples were dehydrated inside a pressure chamber. Exuded stem sap was collected and weighed at successive pressure increases to derive the P—V curve. In the second method (Method B). excised samples were allowed to dry outside the pressure chamber by evapotranspiration. They were weighed periodically to determine sap loss and their corresponding balance pressures were determined in a pressure chamber in order to derive the P—V curve.Estimates of volume averaged osmotic potential at full turgor and water potential at zero turgor which were derived graphically from the P—V curves, were different for each method. In general, estimates were more negative in Method A, by as much as 1.5 MPa in one case. Also, Method B did not record an osmotic adjustment in seedlings which were subjected to severe water stress while Method A did.
Compatible solutes and their effects on phosphoenolpyruvate carboxylase of C4‐halophytes
Authors: MANETAS Y. , PETROPOULOU Y. , KARABOURNIOTIS G. 
Published: April 2006

Abstract Phosphoenolpyruvate carboxylase (PEPCase), extracted from two Poaceae (Cynodon dactylon and Sporobolus pungens) grown on saline soil, was affected physiologically by betaine and proline. Its affinity for phosphoenolpyruvate (PEP) was increased and full protection against NaCl inhibition was observed; enzymic activity was also stabilized when assayed at low PEP levels. Betaine has the same effects on PEPCase extracted from a Chenopodiaceae (Salsola soda), whereas proline behaves as a competitive inhibitor, i.e. it does not protect the enzyme against NaCl and it accelerates inactivation at low PEP levels. Betaine was only compatible with PEPCase extracted from Saisola kali, without any effect on activity, protection or stabilization, but proline was again inhibitory.The levels of free proline in the two salt‐stressed Poaceae were high, whereas in the Chenopodiaceae the free proline was low, as in non‐stressed plants. The above data indicate that osmoregulators could not only be compatible with cytoplasmic enzymes, but they could either promote or inhibit enzyme activity, depending on the source of enzyme. Coevolution of PEPCase with the osmolyte selected for, could also be inferred.
Comparative ecophysiology of CAM and C3 bromeliads. II. Field measurements of gas exchange of CAM bromeliads in the humid tropics
Authors: LÜTTGE U. , STIMMEL K.‐H. , SMITH J. A. C. , GRIFFITHS H. 
Published: April 2006

Abstract The results described represent the first detailed measurements of gas exchange of epiphytic plants with crassulacean acid metabolism (CAM) in the humid tropics. A portable steady‐state CO2 and H2O porometer was used to measure net exchange rates of CO2 and H2O vapour (JCO2, JH2O), leaf temperature (T1), air temperature (TA), air relative humidity (RH) and photosynthetically active radiation (PAR) for bromeliads in the field during the dry season in February and March 1983 on the tropical island of Trinidad. Different lengths of tubing (up to 25 m) were used so that the gas exchange could be measured of bromeliads in situ in their epiphytic habitats. Derived parameters such as leaf‐air water‐vapour‐concentration difference (Δw), water‐vapour conductance of leaves (g) and internal CO2 partial pressure (piCO2) could be calculated.The particular problems of making such measurements in the humid tropics due to high relative humidities and high dew‐point temperatures are discussed. The long and often broad, strap‐like leaves of bromeliads are well suited for measurements with the steady‐state porometer. It is shown that CAM activity varies along the length of individual leaves, and variability between different leaves is also demonstrated.The major phases of CAM, i.e. nocturnal stomalal opening, CO2 uptake and dark fixation as malic acid (Phase I), daytime stomatal closure and light‐dependent assimilation of CO2 derived from decarboxylation of the malic acid (Phase III), and late‐afternoon stomatal opening with direct light‐dependent assimilation of atmospheric CO2 (Phase IV) were all clearly shown by CAM bromeliads in situ. Their expression and magnitude depended on the environmental conditions. An early‐morning peak of CO2 uptake as is characteristic of Phase II of CAM was not detected during the night‐day transition. A bromeliad intermediate between C3 and CAM, Guzmania monostachia, showed substantial net CO2 uptake in the early morning but no net uptake integrated over the whole of the night.