bluuebunny/crossref_metadata_2025 huggingface dataset:
Root geotropism and the role of growth regulators from the cap: a re‐examination
Authors: JACKSON MICHAEL B. , BARLOW P. W.
Published: April 2006

Abstract. It is widely believed that the root cap participates in geotropism by acting both as a sensor of the direction of gravity and as a source of at least one regulator of root growth, which may be abscisic acid (ABA). It has been suggested that this regulator accumulates within the prospective concave (or lower) half of the root and there causes a retardation of growth that brings about bending. A re‐examination of the evidence upon which this inhibitor hypothesis of geotropic control is based reveals that (1) it is derived almost entirely from microsurgical studies and the deductions from such experiments still require corro‐orations from analyses of inhibitor content and action; (2) the evidence that ABA is the inhibitor seems poor at present; (3) in maize and lentil, two well‐studied species, geocurvature is probably a consequence of accelerated growth within the prospective convex (or upper) half rather than inhibited growth within the concave (or lower) half; (4) the geotropic signal from the cap may be one that redirects a pre‐existing basipetal flow of inhibitor away from the upper
The role of the shoot apex in geotropism*
Authors: FIRN R. D. , DIGBY J. , HALL A.
Published: April 2006

Abstract. The belief that the shoot apex plays a special role in geotropism is shown to be erroneous and the implications of this widely held misconception are discussed.
The geotropic reaction and statolith movements following geostimulation of mung bean hypocotyls*
Authors: HEATHCOTE DAVID G.
Published: April 2006

Abstract. Characteristics of the geotropic response of de‐etiolated mung bean hypocotyls are presented. Geotropic sensitivity is not confined to the apical tissue but exists throughout the responding zone. The presentation time is estimated to lie between 0 and 30 s for this tissue. Anatomical features of the presumed geoperceptive tissues are described. Rapid sedimentation and cyclosis of statolith amyloplasts in living tissue are reported, which are fast enough not to preclude the possibility of receptor sites situated at or near the lateral wall of statocytes.
The dependence of auxin transport on cell length
Authors: WANGERMANN E. , MITCHISON G. J.
Published: April 2006

Abstract. Velocities of transport of IAA through long‐celled (dark‐grown) and short‐celled (light‐grown) coleoptile segments have been measured by the intercept method. Transport is faster through short‐celled segments, and the difference is highly significant. Calculations show that this finding is consistent with a model for polar auxin transport which postulates a pumping mechanism between cells and movement through the cell by diffusion.
Seed dormancy in Rumex species in response to environmental factors
Authors: ROBERTS E. H. , TOTTERDELL SUSAN
Published: April 2006

Abstract. Many Rumex species show similar seed dormancy characteristics but there is more information concerning R. crispus and R. obtusifolius than other species. These species respond positively to red or white light. Far‐red light applied for short periods may promote or inhibit germination depending on the timing of the irradiation in relation to temperature change; but long periods of far‐red inhibit germination. Seeds may also be stimulated to germinate in the dark by low‐temperature stratification at 15°C or less providing the temperature of the seeds is subsequently raised to a minimum of about 15°C. Seeds can, however, germinate at lower temperatures providing they have received other appropriate stimulatory treatment. Seeds also respond to alternating temperatures. In a diurnal cycle the minimum upper temperature required is about 15°C and the maximum lower temperature is about 25°C. The optimum period spent at the upper temperature is about 8 h when it is 15–25°C but the optimum period decreases as the upper temperature is increased above this range so that at 45°C, for example, it is only about 30 min. The period spent at the lower temperature in a diurnal cycle is not critical. Providing these criteria are met, the percentage germination increases with the number and amplitude of the cycles. The warming part of the cycle is necessary for the response but so far there is no convincing evidence that cooling itself is important. Secondary dormancy is induced at constant temperatures at a rate dependent on temperature, but apparently only in the presence of oxygen. This feature affects the optimum timing of a temperature change or exposure to light. Strong positive interactions are shown between stimulatory temperature treatments and white or red light. Unlike many other weed species the seeds respond only slightly to nitrate ions. The implications of these responses are discussed in relation to field behaviour.
Water permeability of plant cuticular membranes: the effects of humidity and temperature on the permeability of non‐isolated cuticles of onion bulb scales
Authors: SCHÖNHERR JÖRG , MÉRIDA TATIANA
Published: April 2006

Abstract. Water permeability of cuticular membranes (CM) from the inner bulb scales of Allium cepa has been investigated. CM have a thickness ranging from 0.6 to 1.3 μm. They are composed of a thin (120–200 nm) lamellated cuticle proper and a thicker (300–900 nm) cuticular layer. Permeability coefficients for diffusion of water across these thin membranes are very low (4 × lO−10ms−10). There was no difference in permeability of CM from successive scales of the same onion. Extraction of soluble cuticular lipids (SCL) with chloroform increased permeability by a factor of 1350 to 2050. Preliminary data indicate that only 1 μg cm−10 of SCL are removed by this treatment, hydrocarbons being the main (75%) consistuent. Permeability coefficients of cuticular transpiration were little affected by relative humidity, showing that transport is limited by a hydrophobic barrier that lacks dipoles. However, following extraction, permeability of the membranes depended strongly on humidity due to the presence of polar functional groups in the polymer matrix. Soluble cuticular lipids undergo a phase transition around 47°C. Temperatures higher than that irreversibly increased water permeability.
Charge balance and acidity regulation during growth of sugar‐cane cell suspensions
Authors: KOMOR EWALD , THOM MARGARET , MARETZKI ANDREW
Published: April 2006

Abstract. An analysis of nutrient uptake by batch cultures of sugar‐cane cells was performed to gain information about the ionic balance during uptake of charged metabolites. Whereas younger cultures (up to 1 week old) have to compensate excess cation influx with proton efflux, older cultures show balanced cation–anion uptake.

Younger cells produce a small amount of carboxylic acids to furnish protons for charge compensation at the cytoplasmic membrane. Older cells synthesize organic acids more abundantly to generate protons necessary for the proton demand of nitrate and sulphate assimilation. Despite these assimilation reactions only a small percentage of carbon, which is taken up mainly as hexose, needs to be oxidized to carboxylic acids for that purpose. In contrast, younger cultures preferentially use the amino acids of the medium instead of assimilating nitrate. The use of amino acids as a nitrogen source does not require a significant part of metabolism for biochemical pH‐stability, whereas an efficient proton circulation on the cytoplasmic membrane seems to be of major importance.

A balance study of the main metabolized elements, carbon, nitrogen and sulphur was performed to get a quantitative impression of the fate of these nutrients during growth of cell cultures.
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.
Changes in phenylalanine ammonia‐lyase levels in excised potato tuber tissue: effects of the gaseous environment and desensitization to cinnamate repression by in situ pre‐incubation
Authors: SMITH B. G. , RUBERY P. H.
Published: April 2006

Abstract. The rise in phenylalanine ammonia‐lyase (PAL) activity following excision of potato tuber discs is antagonized by increasing partial pressures of CO2 This inhibition is potentiated by depleting the atmospheric ethylene level. We suggest that the previously observed suppression of PAL appearance by in situ incubation of excised discs in reassembled tubers may be related to an internal atmosphere relatively rich in CO2 and of low ethylene content. The transition to an oscillatory time course of PAL activity that follows transfer of discs from in situ incubation to air appears to be accompanied by the development of enzyme activity becoming desensitized to repression by exogenous cinnamate. The concentration dependence of cinnamate uptake is not significantly altered by in situ pre‐incubation of tuber discs.
Uptake of triphenyltin chloride by Enteromorpha intestinalis and Ulothrix pseudoflacca
Authors: MILLNER P. A. , EVANS L. V.
Published: April 2006

Abstract. The uptake of triphenyltin chloride by Enteromorpha intestinalis and Ulothrix pseudoflacca zoospores and vegetative tissue was examined under various conditions affecting the metabolic state of the chloroplast. A synthesis for [113Sn]‐triphenyltin chloride is presented. Results indicate that uptake of [113Sn]‐triphenyltin chloride by vegetative tissue (and probably zoospores) is a passive process. Differences in the uptake of [113Sn]‐triphenyltin chloride by zoospores of the two algae, in the dark and light, and by vegetative tissue of the two algae in the light, cannot be explained readily on the basis of surface area available for adsorption. Uptake studies suggest that differences in response to triphenyltin chloride exist between vegetative tissue and zoospores. Treatments which depress chloroplast membrane energization in vegetative tissue, e.g. lack of light, the presence of the uncoupler carbonyl cyanide m‐chlorophenyl hydrazone (CCP) or of DCMU prevent the exchange of triphenyltin chloride in pulse‐chase experiments.
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.
Information theory and plant growth substance analysis
Authors: SCOTT IAN M.
Published: April 2006

Abstract. Reeve & Crozier (1980) have recently proposed a method of evaluating the accuracy of a plant growth substance analysis by using information theory to estimate whether the analysis would distinguish the growth substance from all other components of the sample. In the present article, it is argued that their method requires knowledge of the relevant analytical characteristics of all potential components of the sample, and hence is not applicable to plant extracts. Instead, the identity of a growth substance in a plant extract can only be conclusively established using techniques which yield information on its chemical structure.
Regional growth patterns in the hypocotyls of etiolated and green cress seedlings in light and darkness
Authors: GORDON DENNIS C. , MACDONALD IAN R. , HART JAMES W.
Published: April 2006

Abstract. A system is described whereby seedling development can be analysed in terms of growth rates of specific 1 mm regions of the hypocotyl. The technique involves time‐lapse photography of marked hypocotyls in a specially designed chamber which accommodates seedlings in various orientations with respect to gravity, and under irradiation regimes differing in light quality, quantity and direction. The results of a preliminary study of the upward growth of etiolated or green cress seedlings in darkness or overhead while light are reported. Highest growth rates in etiolated seedlings were observed in zones in the upper one‐third of ihe hypocotyl. In green seedlings, growth was more prominent within the subapical zones. Light further restricted growth of the median and basal zones in both types of seedling. However, in their immediate responses to the onset of irradiation, green and etiolated seedlings differed markedly. In etiolated seedlings, recovery of growth at the apex was accompanied by the development of inhibition in the median‐basal regions; green seedlings showed a transient inhibition of growth in the apical zone together with a strong immediate inhibition in the median‐basal regions.
Cation‐stimulated H+ efflux by intact roots of barley
Authors: GLASS ANTHONY D. M. , SIDDIQI M. YAEESH
Published: April 2006

Abstract. Rates of proton extrusion and potassium (86Rb) influx by intact roots of barley (Hordeum vulgare cvs. Fergus, Conquest and Betzes) plants were simultaneously measured in short‐term (15min) experiments. The nature and extent of apparent coupling between these ion fluxes was explored by manipulating conditions of temperature, pH and cation composition and concentration during flux determinations. In addition, the influence of salt status upon these fluxes was examined. At low K+ concentrations (0.01 to 1 mol m−3), H+ efflux and K+ influx were strongly correlated in both low‐ and high‐K+ roots, although K+: H+ exchange stoichiometries were almost consistently greater than 2:1. At higher concentrations (1 to 5 mol m−3), H+ efflux was either reduced or remained unchanged while K+ influxes increased. In the presence of Na2SO4, rates of H+ extrusion demonstrated similar cation dependence, although below 10 mol m−3 Na2SO4, H+ fluxes were generally 50% lower than in equivalent concentrations of K2SO4. These observations are considered in the context of current hypotheses regarding the mechanisms of k+/H+ exchange.
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.
Effects of accumulation of 3‐O‐methylglucose on levels of endogenous osmotic solutes in Chlorella emersonii
Authors: GREENWAY H. , MUNNS RANA , GIBBS JANE
Published: April 2006

Abstract. Regulation of the concentration of osmotic solutes was studied in Chlorella emersonii grown at external osmotic pressures (II) ranging between 0.08 and 1.64MPa. NaCl was used as osmoticum. The total solute content of the cells was manipulated by applying 2 mol m−3 3‐O‐methylglucose (MG), which was not metabolized, and accumulated at concentrations ranging between 60 and 230 mol m−3 within 4 h after its addition to the medium. Methylglucose uptake resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high external II. The responses were consistent with the hypothesis that proline and sucrose concentrations are controlled by a system of osmotic regulation, with turgor and/or volume as a primary signal. Short‐term experiments showed that even very small increases in turgor and/or volume, due to accumulation of methylglucose, resulted in large decreases in proline and sucrose. Over the first 30‐60 min the total solute concentration in the cells increased by at most 15 osmol m−3 which would represent an increase in turgor pressure of at most 0.04 M Pa. Yet, the decreases in proline and sucrose were as fast as those in cells exposed to a sudden decrease of 0.25 MPa in external II, when the turgor pressure would have increased by at least 0.15 MPa. High concentrations of methylglucose in cells grown at high II did not affect the rapid synthesis of proline and sucrose which started when the cells were transferred to yet higher II. Thus, methylglucose had no direct effects on proline and sucrose metabolism, and it has been assumed that it acted solely as an inert osmotic solute within the cell.
Effects of accumulation of 3‐O‐methylglucose on growth and osmotic regulation in Chlorella emersonii
Authors: MUNNS RANA , GREENWAY H. , PRIOR LYNDA
Published: April 2006

Abstract. The effect of accumulation of 3‐O‐methylglucose (MG) on growth and steady‐stale concentrations of the endogenous osmotic solutes proline and sucrose was studied in Chlorella emersonii grown at external osmotic pressure (II) of 0.08‐1.64 MPa. NaCL was used as osmoticum. The total solute content of the cells was manipulated by supplying 2 mol m−3 MG for 4 and 48 h. MG accumulated to 50–230 mol m−3 within 4h and was not metabolized. Uptake of MG resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high II. After 4 or 48 h growth in the presence of MG, the decreases in concentration of proline and sucrose were as predicted from the contribution of MG to the total solute content of the cell.
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.
Water‐relation parameters of giant and normal cells of Capsicum annuum pericarp
Authors: RYGOL J. , LÜTTGE U.
Published: April 2006

Abstract. Measurements of the water‐relation parameters of the giant subepidermal cells (volume, V= 0.119 to 1.658 mm3; = 0.53±0.35 mm3, SD, n= 23) and the smaller mesocarp parenchyma cells (V= 0.10 to 0.79×10−3 mm3; = 0.36±0.27×10−3 mm3, SD, n= 6) of the inner pericarp surface of Capsicum annuum L. were made using the Jülich pressure probe. The volumetric elastic modulus ɛ for the large cells was between 1.5 and 27 MPa for a pressure range of 0.09 to 0.41 MPa. For the small cells ɛ was 0.1 to 0.6 MPa for a pressure range of 0.22 to 0.39 MPa. The turgor pressure P, the half‐time of water exchange T1/2, and the hydraulic conductivity Lp were as follows, with SD and number of replicates: large cells, P= 0.27±0.06 MPa (23), T1/2=2.7±2.2 s (46), Lp=5.8±3.7 pm s−1 Pa− (46); small cells, P= 0.33±0.07 MPa (6), T1/2= 33±10s (12), Lp=0.21±0.07 pm s−1 Pa−1 (12). The determination of these basic water‐relation parameters is considered as a prerequisite for future ecotoxicological and phytopathological studies. The differences between the large and the small cells are discussed in relation to a desirable biophysical definition of succulence. Further, for the large cells a pressure and volume dependence of ɛ was demonstrated.
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.
Interactions between growth, uptake of Cl− and Na+, and water relations of plants in saline environments. II. Highly vacuolated cells
Authors: GREENWAY H , MUNNS RANA
Published: April 2006

Abstract. In a highly saline environment high rates of ion uptake are required to generate sufficient osmotic pressure to maintain the turgor that is needed for the continued growth of plants. We estimate the rates of net uptake of Cl− and Na+ required by growing cells to sustain cell expansion at an external NaCl concentration of 500 mol m−3. We also estimate the ion fluxes required to regulate turgor of expanding and fully expanded cells during diurnal changes in transpiration. Passive fluxes could contribute significantly to osmotic regulation, but active fluxes are still essential and would consume a substantial amount of energy. We discuss whether a limitation to growth at high salinity would arise from lack of energy, or from insufficient capacity for ion uptake. There is insufficient evidence to choose between these possibilities.
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.
Analysis of growth during geotropic curvature in seedling hypocotyls
Authors: MACDONALD IAN R. , HART JAMES W. , GORDON DENNIS C.
Published: April 2006

Abstract. The patterns of growth in organs curving under the influence of gravity were analysed by time‐lapse photography of cress and cucumber hypocotyls which were delimited into 1 mm zones by ion‐exchange beads. Geotropic curvature resulted from changes in growth rate on both sides of the organ. Growth inhibition of varying degrees of intensity occurred in all the previously growing zones of the upper (concave) side. An absolute reduction in length due to compression frequently occurred in some zones. Also, in both species growth stimulation was observed on the lower (convex) side. The disparity in growth rate between the upper and lower surfaces varied with time, being more apparent in the subapical region in the first hour of curvature. A later promotion of growth rate on the lower surface subsequently increased the curvature of the more basal zones. Autotropic straightening occurred as a consequence of growth changes, both inhibitory and stimulatory, in the apical zones. These events indicate a polarity of response in which apical zones have precedence over basal zones.
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.
The site of action of abscisic acid at the guard cell plasmalemma of Valerianella locusta
Authors: HARTUNG WOLFRAM
Published: April 2006

Abstract. Abscisic acid (ABA) is taken up by guard cells of isolated epidermata of Valerianella locusta only at low external pH values. At pH 8.0, when nearly all ABA molecules are present as the union of ABA (ABA−), no uptake can be observed. ABA‐dependent movement of stomata was tested at external pH values between 5.0 and 8.0. Independent of the external pH, ABA induced stomatal closure at all tested ABA concentrations. It is concluded that ABA need not be taken up into the cytosol of the guard cells in order to induce slomatal closure. The primary site of ABA action at the guard cell plasmalemma must be located either at the outer surface of the plasmalemma or at least be easily accessible from outside. ABA− is as effective as undissociated ABA (ABAH).
Plant cell extension: structural implications for the origin of the plasma membrane
Authors: QUAITE ELSIE , PARKER R. E. , STEER M. W.
Published: April 2006

Abstract. The proposal that rapidly elongating plant cells cannot maintain plasma membrane synthesis by means of the normal endomembrane system has been examined in elongating segments of Avena sativa coleoptiles. Segments were sampled and fixed for electron microscopy, before and after elongation on auxin solutions. Mean cell extensions, cytoplasmic volumes, dictyosomc numbers, and vesicle sizes and numbers were determined. It was shown that there are sufficient dictyosomes present to sustain the vesicle production necessary for the observed plasma membrane extension.
Endogenous ethylene does not initiate but may modify geobending–A role for ethylene in autotropism
Authors: CLIFFORD P. E. , REID D. M. , PHARIS R. P.
Published: April 2006

Abstract. Ethylene production during geostimulation was examined in peduncles of dandelion (Taraxacum officinale). Significant amounts of ethylene were evolved from geostimulated peduncles compared with vertical controls only after geostimulation of 2 h or longer and the extra ethylene arose mainly from the lower portion of geostimulated peduncles. Reduction of the ethylene produced from geostimulated peduncles by pretreatment with ethylene‐synthesis inhibitors did not affect or enhanced subsequent geobending. It is proposed that ethylene may control the later stages of geobending and influence the straightening process of autotropism.
An integrating sphere leaf chamber
Authors: IDLE D. B. , PROCTOR C. W.
Published: April 2006

Abstract. A combination of an optical integrating sphere and leaf chamber is described, and some principles of its design are given. It is shown that the number of quanta absorbed by the leaf inside the sphere can be found from measurements of the quantum flux density inside the sphere with and without the leaf present, when certain constant parameters of the sphere are known. Methods for finding these are given. It is not necessary to know leaf area or absorptivity for the quantum yield for photosynthesis to be derived from additional measurement of CO2, fixation.
Direct and indirect effects of light on stomata II. InCommelina communisL.
Authors: MORISON J. I. L. , JARVIS P. G.
Published: April 2006

Abstract.Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO2assimilation rate, and intercellular CO2concentration (Ci), using whole shoots ofCommelina communisL. In the first, conductance increased with decreasing Ci, at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or Ci, In the second, conductance increased hyperbolically with increasing quantum flux density while Ciwas held constant at 466, 302, and 46 μmiolmol−1, and the response differed at each Ci. In neither experiment was conductance consistently related to net CO2assimilation rate in the mesophyll. In both experiments high Cisuppressed the response of conductance to light, while there was a large response of conductance to light at low Ci, indicating an interaction between the effects of light and CO2on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO2concentrations, and not that stomata maintain a ‘constant Ci’.
Optimal water‐use efficiency in a California shrub
Authors: WILLIAMS WILLIAM E.
Published: April 2006

Abstract.The stomatal behaviour of a California chaparral shrub was compared with that predicted by a model of optimal water‐use efficiency (Cowan & Farquhar, 1977). The daily courses of stomatal conductance, evaporation, and assimilation were calculated as was the derivative of evaporation with respect to assimilation (∂E/∂A). The derivative ∂E/∂Awas not constant, and the measured courses of conductance were not optimal, but daily courses of evaporation and assimilation were usually very close to what would have been predicted had ∂E/∂Abeen constant. This discrepancy arises because evaporation and assimilation are sometimes so severely constrained by the microenvironment that stomatal conductance has almost no effect on them.
Spine influences on PAR interception, stem temperature, and nocturnal acid accumulation by cacti
Authors: NOBEL P. S.
Published: April 2006

Abstract.The influence of spines on nocturnal acid accumulation was examined for two Crassulacean acid metabolism plants, the barrel cactusFerocactus acanthodes(Lemaire) Britton & Rose var.lecontei(Engelm.) Lindsay and thecylindropuntia Opuntia bigeloviiEngelm. var.bigelovii.The ambient photo‐synthetically active radiation (PAR) required for 90% saturation of nocturnal acid accumulation byO. bigeloviiwas 23 mol m−2d−1for stems that were 32% shaded by spines and 16 mol m−2d−1when the spines were removed. ForF. acanthodes, 90% saturation occurred for an ambient PAR of 45 mol m−2d−1where the stem was 78% shaded by spines and 21 mol m−2d−1when the spines were removed. For comparison, the ambient PAR averaged 21 mol m−2d−1at various times of the year and stem positions forO. bigeloviifully exposed to solar irradiation. Although spines can reflect some PAR toward the stem surface, their presence decreases the PAR incident on the stem surface, thereby decreasing the nocturnal acid accumulation. ForO. bigelovii, periodically removing the spines led to a 60% greater increase in stem volume over 21/2years. The effect of variation in spine‐shading on stem surface temperature was determined forF. acanthodesusing computer simulations and an energy budget model. A substantial reduction in daytime stem temperatures and a smaller increase in night‐time temperatures as the spine‐shading increased had very little influence on nocturnal acid accumulation for both winter and summer days. Thus, the main effect of spines on the metabolism of cacti is apparently to reduce the PAR incident on the stem surface and thereby to reduce productivity.
An apparatus for pulse and pulse‐chase experiments with 14CO2 on attached leaves with known, steady‐state rates of photosynthesis
Authors: JONES D. ALAN , SMITH ALISON M. , WOOLHOUSE HAROLD W.
Published: April 2006

Abstract. An apparatus is described to carry out pulse and pulse‐chase experiments with 14CO2 on intact, attached leaves with known, steady‐state rates of photosynthesis under defined conditions of temperature, vapour pressure deficit and photon flux density. Data are presented which show that the pattern of distribution of 14C between compounds in extracts of such leaves is a true reflection of the pathways of photosynthetic carbon metabolism in the leaf during steady‐state photosynthesis.
Responsivity amplification by light in phytochrome‐mediated induction of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase (NADP‐dependent, EC 1.2.1.13) in the shoot of milo (Sorghum vulgare Pers.)
Authors: OELMÜLLER RALF , MOHR HANS
Published: April 2006

Abstract. A prolonged light treatment strongly increases responsivity to Pfr in many instances of phytochrome‐controlled biogenesis of flavone or cyanidin glycosides. The present investigation deals with the question of whether light also leads to a corresponding increase of responsivity towards Pfr in such photoresponses which are not related to synthesis of flavonoid pigments in outer tissue layers of seedlings. Phytochrome‐mediated accumulation of the chloroplast GPD (glyceraldehyde‐3‐phosphate dehydrogenase, EC 1.2.1.13) was chosen as a response and the milo shoot (Sorghum vulgare Pers. cv. Weider, hybrid) as an appropriate subject. It was found that responsivity towards Pfr is extremely weak in a dark‐grown shoot while prolonged light pretreatments lead to a dramatic increase in responsivity. Blue and UV light are far more effective than red light in eliciting this effect within a few hours. High responsivity is only maintained in the light. When the seedlings are placed in darkness the level of responsivity drops rapidly with a half‐life of the order of 2 h. The data allow more complete explanations for intriguing phenomena of plant life under natural light/dark conditions such as shade detection or sensing of light → dark transitions.
The effect of red and far‐red light in the high irradiance reaction of phytochrome (hypocotyl growth in dark‐grown Sinapis alba L.)
Authors: HEIM BRIGITTE , SCHÄFER EBERHARD
Published: April 2006

Abstract. Fluence‐rate response curves were determined for the inhibition of hypocotyl growth in 54‐h‐old dark‐grown Sinapis alba L. seedlings by continuous or hourly 5 min far‐red light irradiation (24 h). Just as in red light (Heim & Schäfer, 1982), a fluence‐rate dependence was observed for both kinds of irradiations, even if only 35% of the continuous light effect could be substituted for by hourly far‐red pulses. The same total fluence was used for the two different light regimes. Measurements of Pfr and Pfr/Ptot showed a strong fluence‐rate dependence under continuous light which only partially paralleled the fluence‐rate response curves for the inhibition of the hypocotyl growth. It was concluded that neither spectrophotometrically determined levels of Pfr nor Pfr/Ptot can be the only light‐dependent factor controlling hypocotyl lengthening under continuous irradiation.
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.