bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Temperature During Grain Growth and Ripening of Barley on the Subsequent Response to Exogenous Gibberellic Acid
Authors: Nicholls PB
Published: January 2006

When endosperm halves taken from batches of Himalaya barley grown in the United Kingdom and in various years in the U.S.A. and from Clipper barley grown in South Australia were incubated in either the presence or absence of gibberellic acid, variability in the production of α-amylase was found between batches. Samples from selected batches were grown in glasshouse conditions in winter and in summer. The amount of α-amylase produced in either the presence or absence of gibberellic acid depended on the environmental conditions operating during grain filling and on drying temperature of ears harvested late in grain filling. Two reponse-types of endosperm were distinguished: type A had a strict requirement for exogenous gibberellic acid, whereas type B did not.
Himalaya ears grown at temperatures greater than 20°C in controlled environment conditions produced type B endosperm. Similar kinetics of production of °-amylase were found for both types. The notion that the high production of °-amylase in the absence of exogenous gibberellic acid by type B endosperm was induced by high amounts of endogenous gibberellin-like materials was not supported by experiments where either endosperm halves or stacks of endosperm slices of both types were incubated together.
Photophosphorylation in Chloroplasts With Varied Proton Motive Force (PMF): I. The PMF and Its Onset
Authors: Hope AB , Ranson D , Dixon PG
Published: January 2006

The transthylakoid pH difference (ΔpH) following shuttered periods of actinic light from 10 ms to 30 s duration was estimated from fluorescence quenching of N-(1-naphthyl)ethylenediamine or 9-aminoacridine in phosphorylating conditions, � valinomycin and � nigericin. ΔpH in controls varied from about 2 units after 10 ms to a maximum of 3.6 - 3.8 units in the steady state.
The transthylakoid potential difference (ΔV), defined as the average electric potential energy for protons moving from the intrathylakoid spaces to the outside, was estimated from the size of ΔA520-500 (the electrochromic shift) during similar light periods, with a correction for diffuse-double-layer potentials on the outside and inside of the thylakoids. A relation between ΔA520-500 and ΔV followed from the assumption that the former signal during a single-turnover flash represented 30 mV between the insides of the thylakoid surfaces. On this basis ΔV rose rapidly to about 80 mV at ~25 ms, and declined thereafter, to reach a steady-state level of ~13 mV at 10-30 s.
The total proton motive force (PMF) thus estimated rose to about 225 mV within 20 ms and remained constant (controls) or declined slowly (+nigericin). With added valinomycin + K+, the PMF rose from 120 mV at 10 ms to c. 190 mV in the steady state, corresponding to low values of ΔV throughout.
The findings are discussed in relation to present concepts of electron transport, proton translocation and charge accumulation in chloroplast thylakoids, especially on the millisecond timescale, and compared with other estimates of ΔpH and ΔV.
Photophosphorylation in Chloroplasts With Varied Proton Motive Force (PMF): II. Phosphorylation and the PMF
Authors: Hope AB , Ranson D , Dixon PG
Published: January 2006

Measurements of ATP (luciferase assay) formed by class C pea chloroplasts in illumination times varying from 10 ms to 30 s are reported for control, + valinomycin and + nigericin conditions. ATP was made at a constant rate in controls following a time lag of a few milliseconds which varied with the illumination. Valinomycin increased the time lag to ~100 ms after which therate approached controls. Nigericin caused a gradual decrease in rate of ATP synthesis over a period of ~1s . In the steady state the rate was a different function of the transthylakoid pH difference (ΔpH) with nigericin and with valinomycin, with thresholds at ΔpH = 2.9 and 3.5 respectively. The time lags and thresholds are shown to be consistent with a threshold proton motive force (PMF) of 140-190 mV in various experiments. It is argued that this PMF corresponds to that required to poise the phosphorylation reaction to the point of ATP net synthesis at the prevailing dark phosphorylation potential. The experiments could not decide between a stoichiometry of 2 or 3 protons per ATP.
Data suitable for use in constructing a kinetic model are briefly discussed. The findings generally are interpreted as showing a close correlation between phosphorylation and the PMF estimated as the mean potential energy of protons in the intrathylakoid spaces relative to the outside. It is concluded that Mitchellian coupling between bulk protons and the ATP synthetase is not yet to be discarded.
Purification and Properties of Phosphoenolpyruvate Carboxylase From Plants With Crassulacean Acid Metabolism
Authors: Nott DL , Osmond CB
Published: January 2006

Phosphoenolpyruvate (PEP) carboxylase was purified from three species of crassulacean acid metabolism (CAM) plants. There was no evidence for isoenzymes of PEP carboxylase in these plants and the purified protein was an active dimer of Mr 220 000-250 000 which dissociated to a monomer of Mr 110 000 after treatment with sodium dodecyl sulfate. Active, higher aggregates could be obtained on Sepharose 6B but the functional significance, if any, of these remains to be assessed. In the absence of effectors, normal Michaelis-Menten kinetics were obtamed with the substrates HCO3- and PEP. The purified enzyme shows a preference for HCO3-, rather than CO2, at pH 6.1 and 8.1, with a Km (HCO3-) of 10-20 �M. The Vmax was relatively independent of pH between pH 5.5 and 8.5, but the Km (PEP) (like most other kinetic properties) was pH dependent with a minimum of about 0.1 mM PEP at pH 6.8. Malate inhibition was more effective at pH 6.2 than at pH 8.2, and the inhibition evidently involved a slow binding of malate which increased the Km (PEP) and resulted in non-hyperbolic kinetics. The Km (PEP) was lowered about 5-10-fold by 1.0 mM glucose 6-phosphate which also overcame malate inhibition and restored hyperbolic kinetic relationships in the presence of malate. Possible roles for these properties in the regulation of CAM are discussed.
Water-Stress-Induced Changes in the Growth and Metabolism of Growing and Non-Growing Root Zones of Barley Seedlings
Authors: Prasad R , Singh PN , Khan AH
Published: January 2006

Experiments were conducted on 7-day-old barley (Hordeurn vulgare L. cv. KN 16) seedlings using polyethylene glycol (PEG-6000) to induce water stress. Growth, amount of PEG absorbed, and glucose, sucrose, free proline and organic acid contents were measured in growing (non-vacuolated) and non-growing (vacuolated) root tissues and shoots. Relative water content (RWC) and water potential were used to indicate the degree of stress. Lowering of RWC reduced growth and decreased the root : shoot ratio. Sugar content of the non-growing root zone changed with a pattern almost the reverse of that occurring in the growing root zone. The glucose level changed much more than the sucrose level in both growing and non-growing roots and shoots. Stress-induced proline accumulation was greater in the growing than in the non-growing root zones. The citric and malic acid contents increased in growing roots only above stress levels of -0.6 MPa. In growing roots, citric and malic acid concentrations began to decrease at - 0.35 MPa and - 0.8 MPa or lower stress levels, respectively. High water potential (-0.35 MPa) caused a decrease in malic acid concentration but low water potential (- 0.80 to - 0.89 MPa) caused a decrease in citric acid concentration in shoots.
A Possible Role for Abscisic Acid in Coupling Stomatal Conductance and Photosynthetic Carbon Metabolism in Leaves
Authors: Cowan I.R , Raven J.A , Hartung W. , Farquhar G.D
Published: January 2006

Data on pH in free space, cytoplasm, chloroplasts and vacuoles in leaf tissue are used to calculate the distribution of abscisic acid (ABA) amongst these compartments, assuming that the intervening membranes are permeable to undissociated ABA only. Data on the permeability of membranes to ABA are used to calculate the time constant for equilibration between the free space and the other components. It is concluded that changes in pH in the chloroplast stroma due to irradiance, or other factors, will change the amount of ABA available to the guard cells via the free space, and that the time constant is similar to that for light-induced stomatal movement. The possibility that such changes play a role in modulating stomatal aperture is discussed.
Photosynthetic Oxygen Exchange in Attached Leaves of C4 Monocotyledons
Authors: Furbank RT , Badger MR
Published: January 2006

Photosynthetic O2 evolution, O2 uptake and CO2 uptake by intact leaves from plants of the three C4 decarboxylation types were examined using mass-spectrometric gas-exchange and stable isotope techniques. All species showed a relative insensitivity of O2 uptake to CO2 concentration. The uptake rates observed were between 0.2 and 1 nmol O2 cm-2 S-1 at the CO2 compensation point. At ambient external CO2, NADP-malic enzyme type species showed the lowest average O2 uptake, phosphoenolpyruvate carboxykinase types the highest values, and NAD-malic enzyme types showed intermediate values for O2 uptake. These results are discussed in relation to the contributions to O2 uptake of ribulosebisphosphate oxygenase and photoreduction of oxygen.
Ultrastructural and Compositional Changes in Chloroplast Thylakoids of Leaves of Borya nitida during Humidity-sensitive Degreening
Authors: Hethzerington SE , Hallam ND , Smillie RM
Published: January 2006

The leaves of the desiccation tolerant plant Borya nitida, when dehydrated at 96% relative humidity, lose chlorophyll but retain viability. During the first 14 h of dehydration thylakoid stacking increased, probably because of increasing salt concentrations within the chloroplast as the cells lost water. After 18 h of dehydration the chloroplasts were partly swollen and unstacking of the thylakoids was taking place. This apparent reversal of the effects of dehydration was attributed to the conversion of starch to sugar. Swelling of the chloroplast and unstacking of the thylakoids continued until 22 h of leaf dehydration. A progressive rise in leaf variable chlorophyll fluorescence between 14 and 22 h indicated that a block began to form in the electron transfer system after photosystem II. Leaf fluorescence declined after 22 h of dehydration and parallelled the loss of chlorophyll, P700, chloroplast proteins and the degradation of thylakoid membranes. By 37 h of dehydration the leaves were yellow and the chloroplasts contained little internal structure. In the dried yellow leaves, cytochrome f and cytochrome b-559HP were almost completely absent but cytochrome b6 and b-559LP were not, indicating that some thylakoid remnants were retained.
Lectins as Cytochemical Probes of the Developing Wheat Grain. I. Fluorescein-Labelled Lectins Covering a Range of Specificities With Emphasis on Those That Bind D-Galactose.
Authors: Baldo BA , Boniface PA , Simmonds DH
Published: January 2006

Twelve fluorescein-labelled lectins with combining sites that collectively recognize a range of sugars were used as specific cytochemical probes to study both plastic-embedded and frozen sections of developing wheat grain. Specific reactions, inhibited by preincubation of lectin with sugars complementary to the specific combining sites, were observed with all of the lectins except the L- fucose-binding agglutinins from Lotus tetragonolobus and Ulex europaeus, and the N-acetyl-D-glucosamine-binding lectin from U. europaeus. Lectins from Canavalia ensiformis, Pisum sativum and Bandeiraea simplicifolia reacted with the starch granules. Potato and wheat-germ agglutinins, both of which bind N-acetyl-D-glucosamine, stained protein bodies. The latter lectin also reacted strongly with the nucellar epidermis in the immature grain. Four D-galactose-binding lectins from Abrus precatorius, Arachis hypogaea, Bandeiraea simplicifolia and Glycine max reacted with the cell walls of both the nucellar epidermis and the nucellar projection. Fluorescent staining of the nucellar epidermis was most uniform and intense at about 14 days post-anthesis (p.a.) and declined thereafter until it had completely disappeared by 35 days p.a. However, staining of the nucellar projection persisted throughout the period of examination.
Lectins as Cytochemical Probes of the Developing Wheat Grain. Ii. Reaction of Wheat-Germ Lectin With the Nucellar Epidermis.
Authors: Baldo BA , Boniface PA , Simmonds DH
Published: January 2006

Fluorescein-labelled wheat-germ lectin, which has a specific binding affinity for N-acetyl-D-glucosamine, has been shown to react specifically with nucellar epidermal cell walls in frozen and JB-4-embedded sections of developing wheat grain. The reaction was completely inhibited by preincubation of the lectin with diacetylchitobiose or triacetylchitotriose, two sugars known to be good inhibitors of the wheat-germ lectin combining sites. Labelled lectins with different specificities, and labelled non-lectin proteins such as bovine serum albumin, failed to react. Reaction with the nucellar epidermis increased to a maximum at approximately 14 days post anthesis (p.a.) and then progressively declined. At 35 days p.a., clear fluorescence was visible only in the inner crease area. Labelled wheat-germ lectin did not stain the nucellar projection at any stage of the developmental period studied. Treatment of wheat grain sections with chitinase almost completely abolished reactivity between nucellar epidermal cell walls and the lectin. Reactivity was slightly diminished following treatment with cellulase, but hemicellulase and two preparations of �-N-acetyl-D-glucosaminidase had no effect. These observations indicate the probable presence of a chitin-like structure in nucellar epidermal cell walls, which may be an endogenous saccharide receptor for wheat-germ lectin in developing or germinating wheat grains.
Assessment of Leaf-Washing Techniques for Measuring Salt Secretion in Avicennia Marina (Forsk.) Vierh.
Authors: Boon PI , Allaway WG
Published: January 2006

Leaves of A. marina are unsuitable for measurements of salt secretion because the lower leaf surface, where most secretion occurs, is densely tomentose. Washing of leaves with distilled water, although effective in removing secreted salt, was followed by a period of apparently increased salt secretion. Washing of leaves with strong osmotica was not followed by such a large increase in the rate of salt secretion as was washing with distilled water, suggesting that this acceleration was due to an osmotic flow of water into the salt-gland complex from the washing liquid. The apparent overestimation of secretion rates over short periods was probably not due to incomplete removal of pre-secreted salt by the initial wash nor, on the basis of a comparison of leaf washings with salt contents of the leaf, to the leaching of salt from the leaf interior into the solution used to wash the leaf. Subtraction of the amount of salt secreted in the first 2 h from the total amount secreted over periods of up to 96 h resulted in roughly constant calculated rates of secretion, so that in this species the steady rate of salt secretion, not accelerated by washing with distilled water may be calculated by using a duplicate set of leaves to measure the salt secreted in the first 2 h, and subtracting this from the total secreted over a longer period. Rates of Cl- secretion, so corrected, were about 0.2 �mol m-� s-�. Unless this allowance is made, secretion rates based on washing with distilled water are overestimates, although the degree of overestimation is reduced as the length of secretion period is increased.
Distribution of 14c Label From Cotton Leaves: Consequences of Changed Water and Nitrogen Status.
Authors: Constable GA , Rawson HM
Published: January 2006

14CO2 was applied to individual cotton leaves and its distribution after 24 h was examined in plants of varying water and nitrogen status. Redistribution patterns as well as leaf net photosynthesis and leaf expansion patterns were also established.
Irrespective of growth conditions, phyllotaxis had a marked effect on distribution patterns. For example, fruit in vertical alignment with the labelled leaf received 2-4 times more label than fruit on the opposite side of the mainstem. Distance of a sink from the labelled source, as measured in number of nodes, was also of major importance in well watered plants, the relationship being logarithmic. However, during water stress or low nitrogen nutrition, proportionally more 14C moved to the roots. Furthermore, if plants were stressed slowly, the lower bolls received a greater share of the label than in well watered plants. Analysis of the distribution patterns indicated that empirical regression coefficients considering both phyllotaxis (angle) and distance between source and sink may be of use in simulations of plant performance. Using these regression coefficients and leaf photosynthesis data collected elsewhere, the distribution of total carbon within the cotton plant was calculated.
Differential Effects of Temperature on Floral Development and Sucrose Content of the Shoot Apex of Wheat
Authors: Mohapatra PK , Aspinall D , Jenner CF
Published: January 2006

The effects of high temperature on the growth and development of the shoot apex of wheat, cv. Warimba, growing in a short photoperiod (8 h) were examined. High temperature (30°C) from germination onwards delayed the initiation of double ridges on the apex in comparison to low temperature (20°C) but did not affect the subsequent rate of spikelet development to stamen initiation. The rate of primordium production on the apex was reduced at the higher temperature and there was a decrease in the final number of spikelets produced. The growth in dry weight of both the shoot and apex was reduced at the higher temperature, but the relative growth rate of the apex was unaffected after double-ridge initiation. The sucrose concentration in the shoot apex tended to be higher at the higher temperature and so it was concluded that the effects of exposure to high temperature on apex growth were not mediated through effects on assimilate supply.
Adaptation of Species of Centrosema to Water Stress
Authors: Ludlow MM , Chu ACP , Clements RJ , Kerslake RG
Published: January 2006

The responses to water stress of five accessions representing four species of the legume Centrosema from contrasting moisture environments were compared under controlled conditions with those of Macroptilium atropurpureum cv. Siratro, a species which avoids dehydration. Species of Centrosema
were able to tolerate leaf water potentials as low as -8 to -12 MPa, and all showed osmotic and stomatal adjustment. However, they differed in the tolerance of their leaves to water stress and in the leaf water potential at which stomata were effectively closed. There was a strong positive relationship between water stress tolerance of leaves and the leaf water potential for effective stomatal closure, among the Centrosema accessions and Siratro. The results are consistent with the natural ecological distribution of the species and their behaviour in different moisture environments in northern and north-eastern Australia.
Effect of Heat Stress During Floral Development on Pollen Tube Growth and Ovary Anatomy in Wheat (Triticum aestivum L.)
Authors: Saini HS , Sedgley M , Aspinall D
Published: January 2006

Wheat plants (cv. Gabo) otherwise grown at 20°C were subjected to a temperature of 30°C for 3 days at the onset of meiosis in the anthers. Control plants were maintained at 20°C throughout development. Serial sections through the heat-stressed ovaries just prior to anthesis showed that a third contained abnormal embryo sacs. Abnormalities ranged from the complete absence of an embryo sac accompanied by reduced nucellus development, to small embryo sacs that contained the full complement of cells. No abnormalities were observed in control ovaries.
Following pollination with fertile pollen, heat-stressed stigmas had similar numbers of germinated pollen grains to non-stressed controls but there were fewer tubes reaching the ovary. In 7% of the stressed pistils, no pollen tube reached the ovary. Callose was deposited in some of the inhibited pollen grains and tubes that showed abnormal growth.
It is concluded that heat stress during meiosis in wheat can reduce yield by causing abnormal ovary development, which results in reduced pollen tube growth and seed set.
Metabolite Oxidation and Transport in Mitochondria of Endosperm From Germinating Castor Bean
Authors: Millhouse J , Wiskich JT , Beevers H
Published: January 2006

Mitochondria from germinating castor bean endosperm were purified on linear sucrose-density gradients. It is shown that succinate and malate plus glutamate are oxidized rapidly; other substrates including malate (via malic enzyme) and external NADH are oxidized slowly. It is proposed that the oxidation of NADH produced during β-oxidation and the glyoxylate cycle occurs intramitochondrially via malate. Castor bean mitochondria are relatively impermeable to oxaloacetate and a malate-aspartate type shuttle is required. Metabolite transport and exchange properties support the operation of malatein (or succinatein)/2-oxoglutarateout and glutamatein/aspartateout shuttles. Not all the exchange systems were reversible. The results support proposed schemes for metabolite transfer between glyoxysomes and mitochondria of castor bean endosperm during germination.
Regulation of C4 Photosynthesis : Stability and Other Characteristics of the ADP-ATP-Dependent Inactivation of Pyruvate,PI Dikinase in Maize Chloroplast Extracts
Authors: Hatch MD , Burnell JN
Published: January 2006

Recovery of the capacity for the ADP plus ATP-dependent inactivation of pyruvate,PI dikinase in maize mesophyll chloroplast extracts was highly variable and the remaining enzyme inactivating activity was rapidly lost during subsequent storage at both 0°C and 25°C. Usually no more than 20% of the original activity remained after about 45 min at 25°C or 120 min at 0°C. These losses were largely or completely prevented by the addition of 0.4 mM orthophosphate or 0.1 mM ATP and probably also ADP. AMP or phosphoenolpyruvate at 0.1 mM had little or no effect. Following these studies an analysis of mesophyll cell extracts showed the protein catalysing inactivation of pyruvate,PI dikinase to be exclusively located in chloroplasts and an assay procedure was developed to allow the monitoring of this activity during fractionation.
Effects of Methionine Sulfoximine and Glycine on Nitrogen Metabolism of Maize Leaves in the Light
Authors: Berger MG , Fock HP
Published: January 2006

Detached maize leaves with their cut bases in water or in solutions containing 15 mM [14C, 15N]glycine, 15 mM [14C]glutamate, 5 mM methionine sulfoximine (an inhibitor of glutamine synthetase) or the appropriate amino acid plus inhibitor, were incubated for up to 135 min in the light. The concentrations and the 15N content of ammonia and of amino acids involved in photorespiratory nitrogen cycling were determined. Incubation with methionine sulfoximine or glycine increased the ammonia content significantly, whereas glutamate showed no effect. The nitrogen of glycine was metabolized into serine and ammonia. Ammonia was first recycled into glutamine, and then into glutamate. The glycine carbon skeleton served as a precursor for serine. Based on the data for ammonia accumulation the minimum rate of photorespiratory CO2 evolution in maize leaves was estimated to be about 1% of the rate of CO2 assimilation.
Influence of Water Deficits on the Water Relations Characteristics and Productivity of Wild and Cultivated Sunflowers
Authors: Sobrado MA , Turner NC
Published: January 2006

The effects of water deficits on the water relations characteristics and yield of two cultivated Helianthus annuus L. lines, Hysun 31 and Seneca, and two wild Helianthus species, H. nuttallii and H. petiolaris, were compared. The study was conducted on frequently irrigated and unirrigated plants growing in the field during the summer. Predawn measurements of leaf water potential and relative water content showed that, in the uninigated plants, water deficits increased in all species during the first month after sowing (period I), were relieved by rain in the second month (period II), and then increased progressively in the final month (period III). The osmotic potential at full turgor of unirrigated plants, estimated by pressure-volume curves, decreased by 0.12-0.22 MPa during periods I and III in the cultivated sunflowers, but did not decrease significantly in the wild sunflowers. Except in the irrigated Hysun 31 and Seneca during period I, the apoplastic water content was about 20% in all species and treatments. During period I, the turgid weight: dry weight ratio decreased significantly with water stress, particularly in the cultivated sunflowers; the changes were less marked in the wild sunflowers and during period III. Additionally, the turgid weight: dry weight ratio in the imgated cultivated sunflowers decreased throughout the season. The volumetric modulus of elasticity was similar among species and did not change with water stress or plant age. Dry matter accumulation was smaller in the wild species than in the cultivated lines; water stress reduced shoot dry matter similarly in all species. However, water deficits significantly reduced the seed yield only in Hysun 31 and Seneca.
Culture of Detached Ears of Wheat in Liquid Culture: Modification and Extension of the Method
Authors: Singh BK , Jenner CF
Published: January 2006

The method of culturing detached ears of wheat in a liquid medium has been modified to provide for the culture of ears from anthesis to maturity. For prolonged culture of ears, the presence of the peduncular node was beneficial. Grains developing in ears cultured from 2 days after anthesis until they had ripened germinated normally. By comparison with ammonium or nitrate, glutamine was the better source of nitrogen particularly at low levels of sucrose in the medium; inorganic forms of nitrogen inhibited grain-filling. Setting of grains was apparently dependent upon the availability of carbohydrate and there was no evidence from treatments involving shading for a photomorphogenetic response to reduced light intensity. While grain-filling was sustained by the provision of sucrose supplied artificially, light did nevertheless affect the accumulation of dry matter in the grains.
Composition of Stigmatic Exudate, Nectar and Pistil of Watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai, Before and After Pollination
Authors: Hawker JS , Sedgley M , Loveys BR
Published: January 2006

The composition of stigmatic exudate, nectar, stigma tissue and style tissue was studied in watermelon flowers at 25/20°C (day/night) as the flowers aged after opening, and in unpollinated and pollinated flowers at 30/25°C. The stigmatic exudate contained fructose, glucose, sucrose, and polysaccharide which increased during ageing. Pollination also resulted in an increase in the secretion of these compounds by the stigma. Killed ethanol-extracted pollen was not as effective as live pollen, as less sugar and no polysaccharide was secreted. The fatty acid composition of stigma lipids did not change as a response to pollination. Linolenic acid was the major fatty acid in the lipids of stigmas, ovaries and pollen; high levels of lipids were present in pollen. The current results provide the quantitative composition of the stigmatic exudate which has been shown previously by microscopy to increase within minutes of pollination of watermelon flowers.
The Roles of Sink Size and Location in the Partitioning of Assimilates in Wheat Ears
Authors: Cook MG , Evans LT
Published: January 2006

Geometric factors influencing the partitioning of 14C-labelled photosynthate between two sinks were examined in wheat ears. An awn on one spikelet was the only source of current assimilate while grains in two other spikelets were the competing sinks. The number of grains in these and their distance and vascular connection to the source were varied, while access to stem reserves could be cut off by heat ringing.
Even this apparently simple experimental system presented a number of complications, such as a bias in favour of 14C movement to the upper spikelets within an ear and to the upper grains within a spikelet. These are considered before results on the effect of relative size, distance and vascular connection are described. The larger sink obtained more than its pro-rata share of 14C, usually more than the square of its size relative to the smaller sink. Partitioning between sinks of differing distance was in proportion to 1/d�, where d is the relative distance of the two sinks from the source. A sink on the opposite side of the ear received only one-tenth to one-thirtieth as much as a comparable sink on the same side as the source and the competing sink.
The Electrical Properties of Plant Cell Membranes: Cable Properties involving the Plasmalemma, Tonoplast and Cytoplasm in Chara
Authors: Smith JR
Published: January 2006

The electrical 'cable' properties associated with the two membranes (plasmalemma and tonoplast) and the conductive cytoplasm present in plant cells are analysed for a cylindrical radially symmetric geometry. Calculations indicate that the interpretation of measurements made via vacuolar electrodes on the charophytes Chara and Nitella will not usually be significantly in error if the presence of a longitudinally conductive cytoplasm is neglected. However because of their different conductances, the individual cable properties of the plasmalemma and tonoplast will normally differ. Thus if current is injected into the vacuole at only a single point, the ratio of the consequent potential differences developed across the plasmalemma and tonoplast will vary with longitudinal position on the cell surface, and consequently caution should be exercised in calculating the resistances of the plasmalemma and tonoplast in long cylindrical cells which are not space-clamped. It is also shown that the presence of a longitudinally conductive cytoplasm will ensure that any current leakage around a cytoplasmic electrode will not significantly alter the interpretation of measurements.
Spatial Variation of the Electrical Properties of Chara australis. II. Membrane Capacitance and Conductance as a Function of Frequency
Authors: Chilcott TC , Coster HGL , Ogata K , Smith JR
Published: January 2006

The water-film technique has been used to measure the frequency dependence of the membrane capacitance and conductance as a function of position along illuminated cells of C. australis. At low frequencies (< 1 Hz) the behaviour of the membrane capacitance was found to be strongly dependent upon both frequency and position. A complicated oscillatory pattern was observed which is possibly linked to interference effects between the impressed alternating current and the current normally circulating between alternate acid and alkaline zones. The area-specific membrane conductance was always higher in the alkaline zones than in the acid zones and at low frequencies was 0.45 - 1.3 S m-2 and 2.9 - 3.6 S m-2 respectively. The temperature dependence of the variation of the capacitance and conductance with frequency was also different in the acid and alkaline zones. The observed spatial and frequency dependence of the membrane electrical parameters is clearly associated with the dynamic homeostatis of the cell, and has consequences for the construction of realistic electrical models for the membrane of C. australis.
Carbon Isotope Composition of the Halophyte Disphyma clavellatum (Haw.) Chinnock (Aizoaceae), as Affected by Salinity
Authors: Neales TF , Fraser MS , Roksandic Z
Published: January 2006

The δ13C values of the leaves of Disphyma clavellatum (Aizoaceae) systematically became less negative as the salinity in the root environment increased from 0 to 500 mol m-3 NaCl. The maximum shift of δ13C was from -26.1‰ to -20.0‰. Similar increases in salinity did not, however, result either in a change in the diurnal pattern of net CO2 assimilation or in an appreciable increase in the fluctuations of titratable acidity. It is suggested that salinity induced the observed shift in δ13C values, not by effecting change in the mode of carboxylation towards that of crassulacean acid metabolism (CAM), but by affecting the degree of limitation of CO2 assimilation by diffusion processes. It is concluded therefore that, in D. clavellatum, CAM is not induced by salinity, as it is in Mesembryanthemum crystallinum.
Photorespiratory Characteristics of Isolated Bundle Sheath Strands of C4 Monocotyledons
Authors: Furbank RT , Badger MR
Published: January 2006

Bundle sheath strands (free of mesophyll tissue) were isolated from leaves of Zea mays L., Panicum miliaceum L. and Chloris gayana L. The response of oxygen exchange to CO2 and O2 concentration in these strands was examined using 18O2 and mass spectrometry. Bundle sheath strands from all these species showed considerable O2 uptake at low CO2, 40-80 �mol (mg Chl)-1 h-1. This O2 uptake was stimulated by O2 in the range 60-300 �M and was suppressed 60-70% by 5 mM NaHCO3. The remaining light-dependent O2 uptake was similarly sensitive to increasing O2 concentration. These results are interpreted in terns of the CO2 concentrating function of C4 photosynthesis and the low apparent rates of photorespiration observed in C4 plants in vivo.
Morphology of the Crease Region in Relation to Assimilate Uptake and Water Loss During Caryopsis Development in Barley and Wheat
Authors: Cochrane MP
Published: January 2006

Changes take place about 35 'days' after anthesis in the wall structure of the chalazal cells in caryopses of barley cv. Midas and wheat cv. Sicco grown in conditions where the number of 'days' from anthesis to harvest-ripeness is 60. The primary wall becomes lignified and is separated from the symplast by a layer of suberin. Massive deposits of electron-lucent wall material are laid down between the primary wall and the plasma membrane. From 15 'days' after anthesis increasing amounts of phenolic substances are found in the chalazal cell contents. Xylem parenchyma cells in the crease have some of the characteristics of gland cells and it is suggested that they may function in the control of the water content of the endospem. The cell wall modifications in the chalaza are interpreted as providing a means whereby, during the later stages of grain-filling, water loss from the endosperm can take place without interrupting the supply of assimilates to starchy endospem cells.
Translocation of Photosynthate in Bulbing Onions
Authors: Mann JD
Published: January 2006

[14C]urea was injected into the leaf lumens of growing onion plants (Allium cepa L.) and the redistribution of photosynthate was investigated after 24 h. Injections were into either an older mature leaf or into a younger recently enlarged leaf.
Most of the photosynthate was retained either in the green blade of the treated leaf or in the enlarged leaf base (scale) of that leaf. Of the relatively little photosynthate exported, most went to the innermost scales, especially during bulb enlargement. The innermost (younger) scales acquired photosynthate from both the nearby leaves and from the more remote older leaves. Relatively small levels of radioactivity were found in other leaf blades. Roots obtained small amounts of photosynthate from the oldest leaves.
No label was exported to scales of outer leaves. This pattern was modified, however, by excising photosynthetic area of such leaves. Scales of intermediate age, when deprived of a local supply of photosynthate, acquired translocated material from both older and younger scales. This alteration in source of photosynthate took less than 24 h to develop.
Cytokinin-Induced Mitosis in Cultured Explants of Helianthus tuberosus L. Tuber Tissue
Authors: Palmer MV , Gunning BES
Published: January 2006

Freshly excised explants of H. tuberosus tuber parenchyma tissue were cultured for up to 42 h in aqueous solutions of 0.6 �M indole-3-acetic acid (IAA; 0.6 �M) or one of four different cytokinins (0.4 or 2.0 �M) in the absence of IAA. All phytohormone treatments were effective in inducing partially synchronous mitosis, but mitosis was not observed in control explants cultured in water alone. IAA induced mitosis earlier and in a greater proportion of cells than did any cytokinin treatment. In most cases, cytokinins were more effective at the higher concentration. The relative effectiveness of the different cytokinins appeared to be benzyladenine > zeatin ≥ kinetin > zeatin riboside. Microdensitometric measurements of relative nuclear DNA levels indicated that DNA synthesis had not occurred in control explants, but was induced by both IAA and cytokinins before the mitotic activity that was observed in the later stages of culture. These responses of freshly excised explants were compared to the effect of zeatin on IAA-induced mitosis in prewashed explants, in which zeatin increased the synchrony of IAA-induced mitosis but not the proportion of cells undergoing mitosis.
Effect of Photoperiod at Different Growth Stages on the Initiation of Spikelet Primordia in Wheat
Authors: Pinthus MJ , Nerson H
Published: January 2006

Leaf and spikelet initiation of wheat (Triticum aestivum L.) was studied on plants grown in cabinets under a range of constant photoperiod regimes and on plants transferred, at different growth stages, between these regimes. The existence of genotypically specific limits to the effects of short photoperiods on the delay in floral initiation and on the increase in the number of spikelets was demonstrated.
A long photoperiod applied after the onset of apex elongation, but not earlier, induced the differentiation of spikelets in the axils of already existing primordia, which under a short photoperiod would have developed into leaves. The initiation of the terminal spikelet was induced by a long photoperiod applied not later than the double ridge stage. The final number of spikelets had been determined by the time of swelling of the spikelet primordia in the central portion of the spike.
Translocation of Manganese in Subterranean Clover (Trifolium subterraneum L. Cv. Seaton Park) I. Redistribution During Vegetative Growth
Authors: Nable RO , Loneragan JF
Published: January 2006

The mobility of manganese from old leaves and cotyledons during vegetative growth has been examined by following manganese content and radioactive manganese redistribution in parts of subterranean clover plants grown into manganese deficiency.
In plants transferred from nutrient solutions with 1 �M Mn2+ to solutions without Mn2+, the amount of manganese in the roots decreased markedly. During the same period there was no net loss of manganese from cotyledons and old leaves, although plants developed severe manganese deficiency symptoms in young leaves.
Old leaves of plants given an early supply of 54Mn lost no 54Mn when the plants were transferred to non-radioactive solutions without manganese for 14 days. Silicon, which is known to influence the distribution of manganese within leaves of some plants, had no effect on the loss of total manganese or 54Mn from old leaves.
Detached green, mature leaves lost 40% of their manganese within 24 h when aerated in water. If leaching by rain removes substantial amounts of manganese from leaves of plants grown in the field, this may account for reports of manganese mobility in plant phloem. The present results establish that manganese is not mobile in the phloem of subterranean clover plants during vegetative growth.
Proton Motive Potential Difference Across the Plasma Membrane of Plant Cells: a Comparison of Cultured Cells and Protoplasts From Italian Ryegrass (Lolium multiflorum Lam.) Endosperm
Authors: Henry RJ , Schibeci A , Stone BA
Published: January 2006

The electrochemical proton gradient (ΔμH+) was measured across the plasma membranes of ryegrass (Lolium multiflorum Lam.) endosperm cells grown in suspension culture. The pH gradient (ΔpH) and the transmembrane electrical potential (ΔΨ) of cells and protoplasts were compared. The pH gradient (ΔpH) was measured from the distribution of acetylsalicylic acid and 5,5-dimethyloxazolidine and the membrane potential (ΔΨ) was calculated from the distribution of the lipophilic tetraphenylphosphonium cation (TPP+) between the cells and medium. The protoplasts and cells maintained a similar ΔpH. At the external pH of the growth medium (pH 5.5), the cytoplasmic pH was about 7. Under these conditions the ΔΨ was -60 mV (negative inside) for cells and -46 mV for protoplasts. ΔpH and ΔΨ have values which vary reciprocally depending on the external pH. The main contributor to ΔμH+ at pH 4.0 is ΔpH whereas, at pH 7.0, ΔΨ is the main component. The external K+ concentration influences the cytoplasmic pH significantly only at the higher external pH values.
Cytokinin Accumulation in the Culture Medium of Vinca rosea L. Crown-Gall Tissue: a Time-Course Study
Authors: Palni LMS
Published: January 2006

Cytokinin activity was detected in the culture medium of Vinca rosea (Catharanthus roseus (L.) G. Don) crown-gall tumour tissue 1 week after subculture. Activity increased with time, reaching a plateau at 5-6 weeks. The cytokinin activity from extracts of staled culture medium after 1 and 2 weeks culture cochromatographed with zeatin, zeatin riboside and their dihydro derivatives. An additional slow-moving peak of cytokinin glucoside-like activity was observed from 3 weeks after subculture, and was detectable even at the end of a 10-week culture period.
When [U-14C]adenine was supplied to V. rosea crown-gall tissue, analysis of radioactivity remaining in the medium showed incorporation of label into zeatin and zeatin riboside (trans-isomers only) after only 1 h of incubation. Radioactivity in these compounds increased with time; peaking at 8 h, and was still detectable 125 h after incubation. At no time was radioactivity detected in dihydrozeatin, isopentenyladenine or their ribosides. At the end of 125 h incubation, less than 0.2% of radioactivity supplied initially was still present as adenine in the medium.
Significant inhibition of tissue growth occurred when it was cultured on medium supplemented with a synthetic or naturally occumng cytokinin.
Changes in Ribosome Organization and Messenger RNA Abundance in Ripening Tomato Fruits
Authors: Spiers J , Brady CJ , Grierson D , Lee E
Published: January 2006

The involvement of RNA and protein synthesis in fruit ripening was investigated. Mature-green tomato fruits were found to contain about 30% of their ribosomal RNA in polyribosomes. At the 'breaker' or early ripening stage, about 50% of rRNA was in polyribosomes and this distribution of rRNA was maintained until fruits were fully ripe. The continued presence of polyribosomes is consistent with active protein synthesis persisting through and beyond the climacteric period when the wall-hydrolysing enzyme polygalacturonase accumulates and fruits soften, synthesize lycopene and undergo other ripening related changes. Poly(A)-containing RNA purified from polyribosomes extracted from individual fruits was used to prime the synthesis of [35S]methionine-labelled polypeptides by a wheat germ in vitro translation system. The pattern of polypeptides synthesized in response to RNA from mature-green fruits differed from that given by RNA from ripening fruits. The majority of changes were found to occur within approximately 48 h of the increase of ethylene synthesis and were apparent in all fruits with any pink or red colour. Similar results were obtained by translating total cellular RNA and total polyribosomal RNA indicating that the major RNA species shown in this study to change in abundance during ripening are polyadenylated, and hence most probably cytoplasmic, and do not accumulate as 'stored messages' outside of the polyribosomes.
The differences between green and ripening fruits in polyribosome profiles were demonstrated in two cultivars of tomato. Differences in mRNA populations between green and ripe fruits were found in three cultivars.
Vascular Control of Photosynthate Transfer From the Flag Leaf to the Ear of Wheat
Authors: Patrick JW , Wardlaw IF
Published: January 2006

The movement of 14C-labelled photosynthate from the flag leaf to the ear in wheat was followed when the path of transport was restricted by heat ringing the stem at selected positions and when the demand for photosynthate by the ear was reduced by grain removal. The effect of reducing the temperature of the nodal transfer zone from 21°C to 1.5°C was also examined as a guide to the operation of metabolic controls over movement of 14C-labelled photosynthate. The data provide evidence that the transfer of photosynthate from the flag leaf to the stem traces linked to the ear occurs at the flag node. Furthermore, this transfer does not involve metabolically controlled cell-to-cell movement and probably occurs via open phloem connections. However, there is greater resistance to this lateral transfer between vascular traces at the flag node than at the node below, and reducing the demand by the ear for photosynthate results in movement to the penultimate node before lateral transfer and upward movement to the ear. This pattern of movement is consistent with the vascular anatomy of the wheat culm.
Development Anatomy in Wheat of Male Sterility Induced by Heat Stress, Water Deficit or Abscisic Acid
Authors: Saini HS , Sedgley M , Aspinall D
Published: January 2006

Well watered wheat (Triticum aestivum L. cv. Gabo) plants grown at 20°C were subjected to heat stress (30°C for 3 days), water stress (leaf water potential -2.54 MPa) or exogenous application of abscisic acid (ABA, 3 × 10-5 M) during meiosis in the pollen mother cells. All these treatments caused male sterility. The developmental anatomy of abortive anthers and pollen grains was studied using light microscopy.
The anatomical events leading to pollen abortion in response to heat stress, water stress, and abscisic acid were generally similar. Three developmental sequences leading to sterility were identified. Type 1 was observed in response to heat stress and ABA. Premature tapetal degeneration resulted in periplasmodial invasion of the locule at meiosis and resulted in total sterility. Type 2 was observed in response to water stress when the microspores lost contact with the tapetum at first pollen grain mitosis (PGM I) and the filament degenerated. This also resulted in total sterility. Type 3 was observed in response to all three stresses and led to partial sterility. The microspores completed PGM 1 but a proportion became disoriented from the tapetum and developed no further.
Each stress treatment resulted in two groups of abnormal anther locules, one completely sterile and the other partially sterile. Heat stress and ABA resulted in very similar abnormal development which differed only in the proportion of the two types (1 and 3). Water stress produced partial sterility through the same developmental pattern as heat stress and ABA (type 3). The sequence leading to total sterility in water stress affected anthers (type 2) was similar to that resulting in partial sterility (type 3). The results do not support the hypothesis that ABA is the single primary controlling agent in water stress induced sterility and the question of whether similar mechanisms lead to male sterility in response to the three treatments remains unanswered.