bluuebunny/crossref_metadata_2025 huggingface dataset:
Transfer Cells in the Root Epidermis of Atriplex hastata L. As a Response to Salinity: a Comparative Cytological and X-Ray Microprobe Investigation
Authors: Kramer D , Anderson WP , Preston J
Published: January 2006

A cytological investigation has been made of the roots of the halophyte Atriplex hastata L. Transfer cells developed in the epidermis in response to salt treatment. They occurred only in a zone 1-3 mm behind the root apex and possessed a labyrinth only in their outer tangential walls (facing the root environment). When the epidermis was damaged, the adjacent exodermal cells then developed wall ingrowths in saline conditions. Ontogenetically this differentiation is correlated with the formation of the Casparian strip and the disintegration of the vessel contents. The X-ray microanalysis data on deep-frozen hydrated root specimens indicate that the epidermal transfer cells concentrate K+, and exclude Cl-, relative to the medium. It is concluded that the epidermal transfer cells function in selective uptake of K+ which is subsequently transported laterally into the stele and secreted into the vessels by the xylem parenchyma cells.
Influence of Nitrogen Source on Nitrogen Metabolism in Detached Wheat Heads
Authors: Lee JW
Published: January 2006

Detached wheat heads growing in liquid culture, with either ammonium nitrate or amino acids as the nitrogen source, were exposed to 14CO2 for 1, 2 or 3 h. Examination of the free amino acids in different parts of the heads showed the highest specific activities in glumes. Specific activities were higher in heads cultured on ammonium nitrate than in those cultured on a complete mixture of amino acids. Of the nine amino acids examined, serine had the highest specific activity in grain, glumes and rachis. Proline was present in glumes and rachis at relatively high concentrations but its specific activity was low. Results suggest that the glumes are a significant site of synthesis of carbon skeletons for amino acids in the grain in detached wheat heads.
Salt Stress and Comparative Physiology in the Gramineae. IV. Comparison of Salt Stress in Spartina × townsendii and Three Barley Cultivars
Authors: Jones RGW , Storey R
Published: January 2006

The possible significance of the compartmentation of major solutes between cytoplasm and vacuole is described. The barley cultivars appear to have a restricted ability, by comparison with S. × townsendii, to exploit Na+ and Cl- as major vacuolar ions and contributors to osmotic adjustment. They also appear less able to maintain a basal K- supply in the presence of Na+. The basal K+ supply to the shoot is interpreted as a requirement for a minimal cytoplasmic K+ concentration. The role of glycinebetaine and proline as cytoplasmic osmotic effectors is discussed. It is concluded that, in these hydroponic experiments, the synthesis of glycinebetaine and proline is not a limitation on the salt tolerance of these species.
Loading of Assimilates and Some Sugars Into the Translocation System of Cuscuta
Authors: Tsivion Y
Published: January 2006

Cuscuta species are holoparasitic plants which constitute a strong sink by draining a large proportion of the carbohydrates produced by the host plant. An experimental system has been constructed in order to study the loading of sugars into the translocation system of Cuscuta. Cuscuta campestris parasitizing alfalfa plants were trimmed to one fast-growing shoot on a host stem and allowed to accumulate label from 14C-labelled assimilates, [14C]sucrose, sucrose ([14C]glucose), [14C]glucose, or 3-O-[14C]methylglucose supplied to the host stem. Rates of label accumulation were measured and a higher level of sugar accumulated per time unit was interpreted as preferred loading of the sugar. As sucrose was the sugar most rapidly loaded into the translocation system of the parasite, an analogy between this loading mechanism and established cases of phloem loading into leaf veins is suggested.
Photosynthesis in the Aquatic Macrophyte Egeria densa. II. Effects of Inorganic Carbon Conditions on 14C Fixation
Authors: Browse JA , Brown JMA , Dromgoole FI
Published: January 2006

In short-term labelling experiments, tripling the concentration of total inorganic carbon (TIC) did not significantly increase the high rates of 14C fixation reported in an earlier paper [19.0 μmol C (g dry wt)-1 min-1 at pH 6.8, [TIC] = 1 mM]. However, either decreasing [TIC] or increasing the pH caused the fixation rate to fall markedly. Thus at pH 6.8, [TIC] = 38 μM and pH 10.2, [TIC] = 1.0 mM, photosynthesis was 2.3 and 1.3 μmol g-1 min-1, respectively.
Time courses of the distribution of photosynthetic intermediates indicated that the Calvin cycle remained the predominant pathway of carbon fixation, irrespective of the ambient conditions of TIC and pH. When the rate of photosynthesis was reduced by decreasing [TIC] or increasing pH, the proportion (but not the absolute amount) of label found in malate increased. At pH 6.8, [TIC] = 2.9 mM, μ-carboxylation accounted for only 2.7% of the total carbon fixed, compared with 9% at air levels of CO2 (pH 4.5, [TIC] = 13 μM).
Egeria does not appear to exhibit C4 photosynthesis under any of the conditions studied, but malate may be a significant product of photosynthesis whenever the fixation rate is reduced by carbon availability.
Coloured Components of Chloroplast Membranes as Intrinsic Membrane Probes for Monitoring the Development of Heat Injury in Intact Tissues
Authors: Smillie RM
Published: January 2006

Assays for heat injury in intact leaves were investigated by heating leaf tissue at a rate of 1°C per minute and recording changes in chlorophyll fluorescence; chlorophyll absorbance; light-induced absorbance change at 518 nm of the bulk chloroplast pigments (chlorophylls and carotenoids); and photooxidation of chloroplast cytochrome-554 (cytochrome f ). Leaves of the golden passionfruit (Passiflora edulis forma flavicarpa were used as the experimental material.
Heat injury to the chloroplast thylakoid membranes began above 35°C as evidenced by abnormal changes in chlorophyll fluorescence and absorbance and inactivation of chloroplast membrane activities. Chlorophyll fluorescence increased and chlorophyll absorbance decreased above 35°C and the increase and decrease, respectively, were greatest at 52°C.
The measurements made on intact leaf tissue together with assays of photosystem 2 activity in isolated chloroplasts indicated the relative thermostabilities of several chloroplast membrane activities. Inactivation of photosystem 2 activity linked to oxygen evolution appeared to be associated with membrane changes occurring between 35 and 44°C. The 518-nm absorbance changes indicated that energy-dependent proton pumping and associated reactions were inactivated between 44 and 48°C. Photosystem-1-mediated photooxidation of cytochrome-554 became inactivated between 48 and 52°C.
These studies demonstrate that chlorophylls, carotenoids and cytochrome f may be used as intrinsic membrane probes for monitoring the development of heat injury in the chloroplast membrane system. The absorbance and fluorescence changes that these compounds undergo upon heating provide a basis for reliable and rapid methods applicable to intact tissue for determining heat sensitivity in green plants.
Male Sterility in Sorghum bicolor (L.) Moench Induced by Low Night Temperature. II. Genotypic Differences in Sensitivity
Authors: Brooking IR
Published: January 2006

Three genotypes of sorghum grown in controlled environments were compared for low temperature sensitivity during the leptotene stage of microsporogenesis. Treatment regimes imposed during this period were 21°C day and 14,11, 8 or 5°C night. A known sensitive hybrid (CK60 × Tx415) showed progressive reduction in pollen proline level, percentage starched pollen, and seed set with decreasing night temperature, indicating that sterility induction was a quantitative response to night temperature. The line 606, deveIoped at high altitudes in Mexico, was fertile under all treatment regimes. The hybrid CK60 × 606 was intermediate in response for pollen fertility, but pollen fertility was still sufficient to enable near complete seed set in all treatments. Factors considered important in breeding grain sorghums with low-temperature-tolerant microsporogenesis are discussed.
Growth Inhibition by Glyphosate and Reversal of Its Action by Phenylalanine and Tyrosine
Authors: Gresshoff PM
Published: January 2006

The broad spectrum herbicide glyphosate inhibited growth of a bacterium (E. coli), an alga (Chlamydomonas reinhardi), plant cell cultures (carrot and soybean) and roots of whole plants (Arabidopsis thaliana). Inhibition was transitory, except in plant roots, suggesting breakdown of the herbicide by the test organism. Phenylalanine and tyrosine acted synergistically to reverse the growth inhibition. Addition of these alone, other amino acids and/or divalent metal ions (Fe2+, Co2+ , Zn2+) had no effect. The data are discussed in relation to a possible mode of action of glyphosate.
Induction of Sensitivity to Gibberellic Acid in Developing Wheat Caryopses: Effect of Rate of Desiccation
Authors: Nicholls PB
Published: January 2006

No change in the total β-amylase activity, attributable to the presence of 10-6 M gibberellic acid (GA3) in the incubation medium, was found in freshly harvested, de-embryonated, immature (11-38 days post-anthesis) caryopses of wheat. Significant amounts of GA3-induced α-amylase activity was found in 26-h incubates of similar caryopses which had been allowed to dry out either in the ear or detached from the ear.
After 10 days of storage of detached immature caryopses in air of 99-100% relative humidity, de-embryonated half-caryopses responded to applied GA3 by producing α-amylase. More α-amylase was found in 26-h incubates if detached caryopses dried out slowly, but rapid desiccation led to little or no α-amylase being produced in the presence of GA3.
Caryopses taken from ears cultured on 0.4 or 4% sucrose for 10 days did not respond to applied GA3 whereas those from ears cultured on water did respond, although the amount produced in 26-h incubates was not as large as those from slowly dried ears.
Development of the ability to respond to GA3 by increasing α-amylase activity depended on the duration of desiccation or isolation from the plant. Changes in metabolism emanating from the interruption to the supply of sucrose to the caryopsis may be involved in the development of the ability of the aleurone to respond to GA3.
Growth and Yield of CO2-Enriched Wheat Under Water-Limited Conditions
Authors: Gifford RM
Published: January 2006

Wheat was grown at a density of 120 plants m-2 in deep pots of soil in two artificially illuminated growth cabinets. One cabinet was left at ambient CO2 levels and the other enriched by 250 volumes per million (vpm). Four levels of growth-restricting water supply were imposed. Responses by the two cultivars used (Gabo and WW15) did not differ appreciably in terms of the mature crop dry-weight parameters examined.
Comparison of the crop responses to water supply indicated sufficient correspondence between generalized field behaviour and cabinet behaviour to justify tentative interpretation of the results in terms of possible response of water-limited field wheat crop yields to the globally rising level of atmospheric CO2.
The less water made available to the crop the less was the absolute response of grain yield to CO2 enrichment, but the greater was the response relative to the control yield. Under extreme aridity (about 100-120 mm crop transpiration overall), the data implied infinite relative enhancement of yield due to CO2 enrichment, because it allowed some grain growth where none occurred without extra CO2. The absolute yield enhancement was equivalent to 5-13 kg ha-1 per 1.2 vpm increment of atmospheric CO2 concentration. The level of CO2 in the global atmosphere is currently rising by about 1.2 vpm year-1. The higher temperature at which the crops were grown (19°C), relative to average field conditions in many wheat areas, may influence this interpretation.
Solute Accumulation in the Apex and Leaves of Wheat During Water Stress
Authors: Munns R , Brady CJ , Barlow EWR
Published: January 2006

Accumulation of several low-molecular-weight solutes was measured in the developing floral apex, in an enclosed, elongating leaf, and in an expanded leaf of wheat plants during a 13-day period of water stress. In the apices and enclosed leaves, osmotic potential fell from - 1.2 to -4.0 MPa. The main contribution to the decline in osmotic potential during the first 3 days of stress was from an increase in the content of ethanol-soluble carbohydrate. Later, increases in the concentrations of both carbohydrates and amino acids made major contributions. Of the amino acids, the largest increases were in asparagine and proline. The enclosed tissues lost little water, although the water- to-dry matter ratio declined as a result of imported solutes. The ethanol-insoluble nitrogen content of apices remained high, and growth of apices and enclosed leaves recommenced when plants were watered after 13 days. In exposed leaves, increases in carbohydrate and amino acid contents were comparatively small, and the content of ethanol-insoluble nitrogen decreased by 50%. These leaves dehydrated within 6 days, and failed to recover when the plants were rewatered.
Influence of Temperature Between Floral Initiation and Flag Leaf Emergence on Grain Number in Wheat
Authors: Rawson HM , Bagga AK
Published: January 2006

Plants of Kalyansona, Condor and Janak semidwarf wheats, grown at a density of 130 plants m-2, were transferred every 4 days after floral initiation of the main shoot from temperature regimes of 27/22°C and 21/16°C to a regime of 15/10°C to determine if specific developmental stages of the ear are particularly important to the establishment of grain number. No stages between the appearance of double ridges and flag leaf emergence were significantly more sensitive to temperature changes than others, there being a progressive reduction in grain number per ear for every day that plants of Kalyansona and Condor remained at a higher temperature. Grain number of the main ear was closely correlated with the amount of dry matter in the stem, in the ear structure (chaff), and in the four uppermost leaves of the main shoot; the partial correlation coefficients demonstrated that leaf weight was best related to grain number. Thus large shoots with heavy ear structures had many grains and vice versa. It can be inferred from these results that the distribution of dry matter to the various plant organs before anthesis is in a strict proportionality irrespective of the availability of assimilates.
Photoperiodic Time Measurement and Effects of Temperature on Flowering in Chenopodium rubrum L
Authors: King RW
Published: January 2006

The critical dark period length (c. 8 h darkness) required for induction of flowering of C. rubrum is insensitive to temperature (Q10 c. 1.0) over the temperature range 10-25°C. However, the period of a rhythm controlling floral induction is shown to be temperature sensitive (Q10 c. 1.4) over the temperature range 9-22°C. The discrepancy in temperature dependence of these two parameters of photoperiodic time-measurement could reflect differences in their rates of adjustment after a temperature shift. By contrast, at least two other species (Pharbitis nil and Hyoscyamus niger) show marked temperature sensitivity of their critical daylength. Thus, there may be more than one time- keeper in the photoperiodic control of flowering.
C4 Photosynthesis in Sodium-Deficient Plants
Authors: Boag TS , Brownell PF
Published: January 2006

The C4 plants Kochia childsii Hort. and Chloris barbata Sw. showed symptoms characteristic of sodium deficiency. The δ13C value, CO2 compensation point and percentage of 14C label in C4 dicarboxylic acids in short-term photosynthesis were similar in sodium-deficient and normal plants. This is consistent with the operation of the C4 pathway.
Effect of Different CO2 Regimes on the Induction of Crassulacean Acid Metabolism in Mesembryanthemum crystallinum L
Authors: Winter K
Published: January 2006

Induction of crassulacean acid metabolism (CAM) in Mesembryanthemum crystallinum in response to high salinity was studied in plants grown in different CO2 regimes to determine whether the induction of CAM could be controlled by CO2 supply in the light and dark; a possible consequence of stomatal closure in response to water stress. The activity of extractable phosphoenolpyruvate carboxylase (EC 4.1.1.31) and the nocturnal change in malate content were followed at frequent intervals after onset of the treatments. The results suggest that the initial event during the induction of CAM is a change in the biochemical apparatus, indicated by the activity of phosphoenolpyruvate carboxylase, which then leads to the day/night fluctuations of malate synthesis typical of CAM. This initial step is not controlled by the availability of CO2 in the light or dark.
Regulation of C4 Photosynthesis: Factors Affecting Cold-Mediated Inactivation and Reactivation of Pyruvate, PI Dikinase
Authors: Hatch MD
Published: January 2006

The kinetics and other characteristics of cold-induced inactivation and subsequent reactivation of pyruvate, PI dikinase from Zea mays were examined in leaf extracts and with the partially purified enzyme. Significant inactivation occurred at about 10°C and the rate of inactivation increased as the temperature was reduced below 10°C. The rate of inactivation at 0°C varied with Mg2+ concentration; the half-time for inactivation was about 5 min with 2 mM Mg2+ compared with more than 60 min with 15 mM Mg2+. With 10 mM Mg2+, used routinely, the half-time for pyruvate,P*i dikinase isolated from a variety of species varied from less than 10 min to more than 40 min. Activity was rapidly recovered by rewarming to 25°C the kinetics of reactivation were second order. Cold-induced inactivation was completely prevented by both pyruvate and phosphoenolpyruvate at concentrations of about 2 mM and 0.1 mM, respectively. The molecular weight of cold-inactivated pyruvate,PI dikinase, assessed by mobility on Sepharose 6B, was about a quarter of the active enzyme; the tetrameric active enzyme apparently dissociates to monomers at 0°C. When illuminated leaves were exposed to lower temperature, pyruvate, Pi dikinase was partially inactivated. This activity was rapidly recovered by returning leaves to a temperature of 25°C, or by incubating extracts from the cold-treated leaves at 25°C. The dark-inactivated enzyme was apparently also modified by exposure to temperatures in the range 0-5°C.
Grain-Filling in Wheat Plants Shaded for Brief Periods After Anthesis
Authors: Jenner CF
Published: January 2006

Plants of wheat (grown in a controlled environment) were subjected to brief (5-10 days) periods of shading just after the ears showed the first signs of anthesis, and afterwards were grown to maturity in full illumination. Shading resulted in smaller grains, slower rates of accumulation of dry matter in the grains, and lower final grain weights.
Shading cut down contemporaneously the provision of sucrose to the developing grain but, soon after return to full illumination, the supply of sucrose was restored to levels observed in ears that had not been shaded. Moreover, the estimated concentrations of sucrose in the endosperm of grains that accumulated less dry matter as a result of shading were higher than in endosperm filling on the unshaded plants. Although shading resulted in lighter grains, the grains contained just as much protein as the unshaded ones. Trimming the ears (by removing some spikelets) of shaded plants did not influence grain weight.
These responses to shading are taken as evidence for the existence of a mechanism operating during the early stages of grain development, before grain-filling begins, which can influence the capacity of the endosperm to accumulate starch. Capacity to accumulate protein is evidently not subject to the same kind of control.
Physicochemical Studies of Conglutin γ, a Storage Globulin From Seeds of Lupinus angustifolius
Authors: Blagrove RJ , Gillespie JM , Lilley GG , Woods EF
Published: January 2006

Physicochemical studies are reported for conglutin �, the minor globulin isolated from seeds of L. angustifolius cv. Uniwhite. Isoelectric focusing of the native protein in polyacrylamide gel slabs resolved major and minor broad bands near pH 8.0 and 7.8 respectively. Following reduction of disulfide bonds with β-mercaptoethanol in 8 M urea, the smaller polypeptide chain of known sequence focused near pH 6.9 while the larger chain focused near pH 8.0. Sedimentation equilibrium studies showed that the major component in aqueous buffers at neutral pH is a hexamer of molecular weight 280 000 which dissociates to the monomer of molecular weight 47 000 at pH 4.8. The sequence molecular weight of the small subunit polypeptide is 16 517 [Elleman, T.C. (1977). Aust. J. Biol. Sci. 30, 33-45]. The molecular weights determined for the larger chain by sedimentation equilibrium or column chromatography in 6 M guanidine hydrochloride, and by dodecyl sulfate-polyacrylamide gel electrophoresis, were in the range 28 000-30 000. Optical rotatory dispersion and circular dichroism measurements have been used to establish the approximate proportions of α-helix (15%), β-structure (35%), β-turns (18%) and unordered regions (32%) in the native protein. The denaturation curve for guanidine hydrochloride and the proportions of α-helix (50%), β-turns (18%) and unordered regions (32%) in 80 % trifluoroethanol have been determined.
Aluminium Distribution in Freeze-Dried Roots of Cabbage, Lettuce and Kikuyu Grass by Energy-Dispersive X-Ray Analysis
Authors: Huett DO , Menary RC
Published: January 2006

The aluminium distribution in transverse sections of fractured and freeze-dried roots of cabbage, lettuce and kikuyu grass was studied by energy-dispersive X-ray analysis. The mean ratios of the integrated counts corresponding to Kα emission spectra for aluminium, phosphorus and silicon were recorded between aluminium and control treatments over three experiments. Peak-to-back- ground ratios (PA/B) were calculated and the aluminium ratios corrected for variations in the corresponding total silicon ratios.
Aluminium was found to be uniformly distributed along roots of the three species. The highest peaks (PA) and peak-to-background ratios, suggesting higher concentrations, were recorded in the epidermis followed by the cortex. Aluminium was recorded in the stele of all species and in the protoplasm of cortical cells, with smaller amounts in the protoplasm of xylem parenchyma cells for lettuce and kikuyu grass.
The distribution of aluminium supports the hypothesis that its entry to the stele can be achieved by transport both into meristematic cells and the symplasm via the cortex and hence bypassing the barrier at the endodermis. The latter evidence was supported by the presence of aluminium in the radial wall (and cytoplasm) of the endodermis for each species. There was a poor correlation between the distribution of aluminium and phosphorus.
Purification and Characterization of an Unusual Aminopeptidase From Pea Seeds
Authors: Caldwell JB , Sparrow LG
Published: January 2006

An aminopeptidase with specificity for N-terminal glutamic and aspartic acid residues has been purified to apparent homogeneity from pea seeds (Pisum sativum cv. Greenfeast). It also catalyses the hydrolysis of the glutaryl-phenylalanine bond of the synthetic chymotrypsin substrate glutaryl- L-phenylalanine p-nitroanilide. The native enzyme, which has a molecular weight of approximately 500 000, gives a single band on polyacrylamide gel electrophoresis but two major bands when subjected to electrophoresis in the presence of sodium dodecyl sulfate after reduction. Its behaviour with various inhibitors suggests that a sulfhydryl group is important for its activity.
Interaction of Slicing and Osmotic Stress on Proline Metabolism in Jerusalem Artichoke Tuber Tissue
Authors: Wrench P , Brady CJ , Hinde RW
Published: January 2006

Information was sought to explain the changes with time and with osmotic stress in the rate of 14C transfer from added L-[U-14Carginine to proline in slices of tubers from Jerusalem artichoke (Helianthus tuberosus14 L.). Using osmotically stressed tubers, the transfer rates were shown to be independent of the size of the free proline pool, and of the net rate of proline accumulation. In osmotically stressed and in turgid slices, the rates of transfer increased after slicing, but decreased after 24 h. Only in freshly cut slices were the rates higher for stressed slices. Proline and hydroxy- proline in protein increased with time from slicing in both turgid and stressed slices, and proline and hydroxyproline in protein were labelled when L-[U-14C]arginine was added. However, no correlation could be shown between 14C in protein-bound proline plus hydroxyproline, and the net increase in these with time. It is concluded that externally added arginine donates carbon to proline in reactions whose rates do not determine the net rate of proline accumulation or the net rate of synthesis of proline destined for protein.
The metabolism of L-[U-14C]glutamate added to discs was also studied. [14C]proline was a minor product of glutamate metabolism at all times.
Phenylalanine Ammonia-Lyase and the Phenylalanine Ammonia-Lyase Inactivating System: Effects of Light, Temperature and Mineral Deficiencies
Authors: Tan SC
Published: January 2006

In constant light, whole apples (cv. Red Spy) that received alternating 6/25°C treatment accumulated more phenylalanine ammonia-lyase (PAL) and anthocyanin than those receiving constant 25° throughout the course of experiment. The stimulatory effect of low temperature (6°) on the activity of PAL and synthesis of anthocyanin was also observed in the alternating light and dark experiment when low temperature was applied in the dark period. In constant light, the activity of phenylalanine ammonia-lyase inactivating system (PAL-IS) was lower in the apples that had received alternating 6/25° treatment than that in apples that had received constant 25°. When the apples were incubated in constant darkness, no accumulation of PAL and anthocyanin occurred but the level of PAL-IS increased steadily throughout the course of incubation.
Nitrogen and potassium deficiency increased PAL accumulation and decreased accumulation of PAL-IS in the leaves of greenhouse-grown apple trees. PAL activity was found to be negatively correlated with activity of PAL-IS.
It is therefore concluded that low temperature reduces the level of PAL-IS and increases the accumulation of PAL which in turn increase anthocyanin accumulation in the skin of whole apples, and that nitrogen and potassium deficiencies reduce the level of PAL-IS and hence increase the accumulation of PAL in apple leaves.
Accumulation of Solutes in Leaves of Sorghum and Sunflower in Response to Water Deficits
Authors: Jones MM , Osmond CB , Turner NC
Published: January 2006

The influence of water deficits on the concentrations of major solutes in fully expanded sorghum leaves and fully expanded and partly expanded sunflower leaves was studied in order to assess their contribution to osmotic adjustment. The decreased osmotic potential at full turgor in fully expanded sorghum leaves at a moderate level of stress (predawn leaf water potential of -0.85 MPa) was fully accounted for by increases in sugars, potassium and chloride. The contributions of total inorganic ions and sugars (glucose and sucrose) were approximately equal.
In fully expanded sunflower leaves stressed to a predawn leaf water potential of - 1.4 MPa, only half of the decrease in leaf osmotic potential was accounted for by changes in the concentrations of the solutes studied: increases in the concentrations of the inorganic ions, potassium, magnesium, calcium and nitrate, together with free amino acids were approximately equal to the decrease in leaf osmotic potential at full turgor, but the contributions of these solutes were offset by a decrease in the concentration of total carboxylic acids. Sugars did not contribute to the decrease in leaf osmotic potential at full turgor in fully expanded sunflower leaves.
The major solutes responsible for the changes in leaf osmotic potential at full turgor in partly expanded sunflower leaves exposed to severe stress treatment (predawn leaf water potential of -2.3 MPa) were the inorganic anions, chloride and nitrate, and to a lesser extent carboxylic acids (principally aconitate). Free amino acids made a significant contribution (18%) to the decrease in leaf osmotic potential at full turgor, but there was a decrease in the level of soluble sugars.
Effects of Protein Synthesis Inhibitors on Acetylene Reduction Activity of Lupin Root Nodules
Authors: Sutton WD
Published: January 2006

Rifampicin and D-threo-chloramphenicol inhibited the incorporation of [35S]methionine into purified bacteroid suspensions, and into the bacteroid fraction but not the plant cytoplasmic fraction of cultured nodules. Cycloheximide and anisomycin inhibited [35S]methionine incorporation into the plant cytoplasmic fraction of cultured nodules; at early times they inhibited incorporation into the bacteroid fraction, but at later times this effect was reversed. Chloramphenicol, rifampicin, spectinomycin, cycloheximide and anisomycin all prevented the induction of acetylene reduction activity in immature nodules; spectinomycin did not prevent induction in nodules containing a spectinomycin-resistant Rhizobium. Neither rifampicin nor chloramphenicol inhibited the acetylene reduction activity of mature nodules, but cycloheximide and anisomycin caused rapid loss of activity. Cycloheximide did not inhibit the acetylene reduction activity of Rhizobium strain 32H1 in pure cultures.
The results suggest that both plant cytoplasmic protein synthesis and bacteroid protein synthesis are needed for the induction of nitrogenase activity in developing lupin nodules, and that plant cytoplasmic protein synthesis but not bacteroid protein synthesis is needed for the maintenance of nitrogenase activity at high levels.
Significance of Photosynthate Produced at Different Stages of Growth as Carbon Source for Fruit Filling and Seed Reserve Accumulation in Lupinus angustifolius L
Authors: Pate JS , Atkins CA , Perry MW
Published: January 2006

Growth and reproductive phenology of field-grown, non-irrigated L. angustifolius (cv. Unicrop) were studied by periodic sampling of plants. Anthesis occurred when plant carbon content was only 15% of its final maximum. Flowering and the main periods of pod growth and seed filling took place, respectively, 0-6, 5-9 and 8-12 weeks after anthesis. Over 80% of the plant's gain of carbon in dry matter occurred 0-8 weeks after anthesis, after which drought-induced defoliation curtailed dry matter accumulation.
14CO2 was fed to selected plants at weekly intervals over the period 0-12 weeks after anthesis and time courses of transfer of 14C-labelled assimilates to fruits were assayed non-destructively by periodic sampling of phloem sap from fruits. Average specific radioactivity of carbon of phloem sap samples from primary, secondary and tertiary fruits of each feeding treatment were compared with specific 14C activities of the respective fruits harvested at maturity. The agreement between data was very close with times of 14CO2 feeding up to 8 weeks after anthesis. With later times of feeding, average specific radioactivity of phloem sap was higher than that of fruits as labelled sap was collected for only the latter part of the life of the fruit and before the fruit had accumulated unlabelled carbon.
Carbon from photosynthate fed before or during flowering contributed mainly to protein of the seed, that from photosynthate formed during fruiting mainly to non-protein seed components. Distribution of 14C between amino and non-amino compounds of fruit phloem sap of plants fed 14CO2 at anthesis or in late fruiting reflected this effect. Estimates of contributions of carbon of photosynthate to fruits suggested that only 2% of the fruit's carbon came from photosynthesis before flowering and only 3 % from photosynthesis 0-3 weeks after anthesis, while 18, 28 and 23% came from photosynthate formed respectively 3-6, 6-9 and 9-12 weeks after anthesis.
Structural Aspects of Protein Accumulation in Developing Pea Cotyledons. III. Immunocytochemical Localization of Legumin and Vicilin Using Antibodies Shown to Be Specific by the Enzyme-Linked Immunosorbent Assay (ELISA)
Authors: Craig S , Millerd A , Goodchild DJ
Published: January 2006

The site of sequestration of the storage proteins legumin and vicilin during development of cotyledons from pea (Pisum sativum L.) has been determined using improved immunocytochemical techniques. Antibodies to legumin and vicilin were made monospecific by affinity chromatography. They were allowed to react on sections of glycol methacrylate-embedded cotyledon tissue and detected by indirect immunocytochemical localization using rhodamine-labelled antibodies. The enzyme-linked immunosorbent assay (ELISA) technique was adapted to verify antibody specificity at a sensitivity up to 300 times greater than that of immunodiffusion.
Legumin and vicilin 4 are localized in small peripheral deposits within large vacuoles as early as day 8 after flowering. As the vacuoles fragment during development the storage proteins continue to be localized in the vacuolar deposits until, at day 16, they entirely fill vacuoles, now termed protein bodies. Thereafter, the protein bodies become more densely packed and retain a similar form from day 22 to maturity. Wherever the same vacuolar deposit of protein body could be observed in adjacent sections, antilegumin and antivicilin 4 labelled both deposits, clearly indicating that both storage proteins are sequestered into the same area of protein.
Carbon Dioxide Assimilation by Pineapple Plants, Ananas comosus (L.) Merr. I. Effects of Daily Irradiance
Authors: Sale PJM , Neales TF
Published: January 2006

Net carbon exchange over 24-h cycles was measured in well watered pineapple plants, using a 'minicrop' in field assimilation chambers and single leaves in a growth cabinet. Whole plants under natural light and a standard 30°C day/15°C night regime showed crassulacean acid metabolism, nearly all assimilation occurring in the dark period, with a net efflux of CO2 in the day. Assimilation, as measured by both CO2 exchange and changes in titratable acidity in the leaf tissue, was markedly dependent on the total photosynthetically active radiation incident in the previous photoperiod. The molar ratio of the maximum acidity change to maximum net nocturnal CO2 influx was 1.8 : 1. The rate of deacidification depended on the irradiance in the current photoperiod. Efflux in the photoperiod was largely independent of irradiance, but was greater at very low irradiances.
Maximum rates of CO2 assimilation in the minicrop were about 15 ng cm-2 (leaf area) s-1 in the dark at the standard temperature regime, and 22 ng-2 s-1 when photoperiod assimilation was induced by a 20°C day/30°C night regime. Similar rates were recorded in the single-leaf experiments, and are higher than those previously found for pineapple. Over a 24-h period, mean rates of about 6 ng cm-2 (leaf area) s-1 were recorded, in good agreement with measured dry weight changes over an extended period. These data help to explain earlier discrepancies in the literature between measured rates of CO2 assimilation and of crop growth rates in pineapples.
Carbon Dioxide Assimilation by Pineapple Plants, Ananas comosus (L.) Merr. II. Effects of Variation of the Day/Night Temperature Regime
Authors: Neales TF , Sale PJM , Meyer CP
Published: January 2006

The effects of variation of day/night temperature regime on the diurnal patterns of CO2 assimilation of pineapple plants were examined using single leaf and field enclosure methods.
At day temperatures of 30°C, increasing night temperatures from 20 to 35°C reduced the total assimilation of CO2 per daily light/dark cycle from 6.5 to 1.3 g CO2 m-2 (leaf area) day-1, and also reduced the proportion of total CO2 assimilation that occurred at night from c. 90% to c. 40%.
Decreasing day temperatures (30 to 10°C) had little effect on total daily CO2 assimilation in warm (25°C) nights, but reduced it in cooler (15°C) nights. At day temperatures of <152C, CO2 assimilation took place predominantly (60-100%) in the photoperiod. In cool (10°C) days, the normal inverted stomatal rhythm of CAM plants was reversed; leaf conductance was high (c. 1.0 mm s-1) throughout the photoperiod and a large CO2 efflux was observed, lasting c. 2 h, at the beginning of the dark period.
Leaf conductance of pineapples, by day and by night, is strongly influenced by ambient temperatures, with cool conditions favouring stomatal opening.
Factors Limiting the Rate of Dry Matter Accumulation in the Grain of Wheat Grown at High Temperature
Authors: Wardlaw IF , Sofield I , Cartwright PM
Published: January 2006

Increasing temperatures from 21/16°C to 30/25°C, during the period of development from anthesis to maturity, substantially reduced grain dry weight in wheat. Although this was associated with a shorter duration of grain development, the failure to obtain any compensating increase in the rate of dry matter accumulation, as occurs in the lower temperature ranges, was also considered important. There was no evidence that night temperatures were more important than day temperatures. Analysis of the movement of 14C-labelled photosynthate from the flag leaf to the ear indicated a faster rate of import of photosynthate by the grain at the higher temperature. However carbon lost through respiration is a component of the ear demand for photosynthate and it appears that increase in movement of photosynthate was balanced by greater respiratory losses. This additional carbon lost through enhanced respiration at high temperature could, however, only account at the most for 25% of the reduction in grain dry weight that occurred with the temperature increase from 21/16°C to 30/25°C. Altering either the demand for photosynthate by grain removal, or the supply of photosynthate by a defoliation and shading treatment, did not prevent the reduction in grain dry weight due to high temperature and this is a further indication that the temperature effect occurred mainly within, or close to, the grain itself, and did not result from an effect on the availability of photosynthate.
The Role of Water Distribution in Plant Tropisms.
Authors: Mcintyre GI
Published: January 2006

Dark-grown seedlings of Helianthus annuus, Pisum sativum and Phaseolus vulgaris all showed twofold to threefold increases in the rate of shoot elongation when the relative humidity was increased from 50% to 100%. In experiments with H. annuus, the lower half of the geostimulated hypocotyl had a higher water content and dry weight than the upper half, while the shaded side of hypocotyls subjected to phototropic stimulation had a higher water content and dry weight than the side towards the light. These differences occurred even when tropic curvatures were physically prevented. It was therefore postulated that water is normally the limiting factor in shoot elongation and that changes in its lateral distribution are primarily responsible for the differential growth induced by geotropic and phototropic stimulation. Experiments with P. sativum and Zea mays, which showed that root growth was inhibited by immersion of the root apex in water, lent support to the hypothesis that O2 is normally the limiting factor in root growth and that the positive geotropism of roots is caused by a gravity-induced increase in the water content of the lower half of the apex which inhibits growth in this region by reducing the O2 supply.
Penetration of Photosynthetically Active Radiation Into Tobacco Crops
Authors: Whitfield DM , Connor DJ
Published: January 2006

The spatial distribution of photosynthetically active radiation (PAR) was measured on several occasions during the growth of a tobacco crop. The data describe the penetration of PAR into the crop.
Penetration was influenced by crop size, row structure, time of day and conditions of incident irradiance. At solar elevations greater than 15° on clear days, there were few regions in the crop with flux densities between 0.1I0 and 0.9I0, where I0 is the flux density of PAR above the canopy. Frequency distributions of flux densities were therefore bimodal. At lower elevations, the direct- beam component was attentuated and frequency distributions were unimodal with few flux densities above 0.6I0. Under diffuse irradiance, the bimodal response was attentuated to give a relatively uniform distribution of flux densities on the transects.
These data were used to appraise two estimates of the penetration of PAR into the canopy. The first was based on a physical representation of the display of leaf surfaces in the canopy. Alternative estimates were derived from a mathematical model of the display of foliage of single plants which was extended here to account for the effect of neighbouring plants on the penetration of PAR into the crop.
Carbon Dioxide Exchange in Response to Change of Environment and to Defoliation in a Tobacco Crop
Authors: Whitfield DM , Connor DJ , Sale PJM
Published: January 2006

Rates of carbon dioxide exchange of field-grown tobacco crops at early flowering and maturity were measured using a pair of large closed-system field chambers. Photosynthetic responses to irradiance and temperature were investigated on both occasions. Rate of dark respiration and its response to temperature were measured during the night.
Defoliation treatments were employed to disrupt the correlation between leaf age and light environment in the canopy. In these experiments, the short-term photosynthetic response to irradiance was determined for crops that were progressively defoliated upwards or downwards. Long- term effects of varying intensities of downward defoliation were also investigated.
Maximum photosynthetic rates of 3.7 g CO2 m-2 h-1 were achieved at early flowering. These had fallen to 1.9 g CO2 m-2 h-1at maturity. Maximum rates occurred at an irradiance of approximately 700 W m-2. Short-term shifts in temperature in the range 10-32°C had little effect during the day, but dark respiration was strongly dependent on temperature. Defoliation experiments demonstrated that lower leaves retained a significant potential for photosynthesis but their contri- bution to the total exchange of CO2 of mature crops was only small. This was attributed in part to the poorer light regime in the lower canopy.
Results are discussed in the context of the development of yield and quality in flue-cured tobacco.
Carbon Production of Sunflower Cultivars in Field and Controlled Environment. II. Leaf Growth
Authors: Rawson HM , Constable GA , Howe GN
Published: January 2006

In field studies of several cultivars of sunflower grown on stored soil moisture or with irrigation, yield was positively related to leaf area at anthesis. The regression which described this relationship stated that 1370 kg seed ha-1 were associated with a unit increment in leaf area index.
Cultivars differed in final leaf number, rate of leaf appearance, and in the vertical distribution of leaf area in the profiles. Final leaf number of plants grown on stored moisture remained the same as in irrigated plants, but the period for which each leaf grew was reduced from 19 to 16 days while the average growth rate was reduced from 13 to 6 cm2 day-1. These changes reduced the final leaf area from 5700 to 1900 cm2 per plant. As water stress increased, the period when leaves grew fastest became progressively earlier, from approximately 35% Amax to when leaves were less than 5 cm2.
Water stress increased stomatal frequencies but reduced the area of individual stomata so that the area of the stomatal apparatus per unit leaf area was unchanged. This may partially explain the constancy of peak gas exchange per unit leaf area of sunflower grown under different water regimes. There was evidence that leaves could recommence growth when the stress was alleviated.
Stomatal Behaviour of Kenaf and Sorghum in a Semiarid Tropical Environment. I. During the Night
Authors: Muchow RC , Ludlow MM , Fisher MJ , Myers RJK
Published: January 2006

The extent of night-time stomatal opening in field-grown kenaf (Hibiscus cannabinus L.), a C3 dicotyledon, and sorghum [Sorghum bicolor (L.) Moench], a C4 grass, and the factors controlling the opening were studied at high and low soil water status. Since saturation deficit (δe) and temperature varied together in the field, the response of stomatal conductance (gs) to these individual factors was determined under controlled environment conditions in a leaf chamber apparatus.
At both high and low soil water status, the stomata of sorghum were closed from sunset to sunrise, whereas with kenaf partial stomatal opening was observed throughout the night. Initiation of night opening occurred in response to decreasing temperature, but the degree of opening was determined by plant water status. The importance of night-time stomatal opening on the water relations of the crop is discussed.
Photosynthetic Inhibitors From Capsicum annuum L.: Extraction and Bioassay
Authors: Kriedemann PE , Loveys BR , Dijk HMV
Published: January 2006

Photosynthesis of leaf slices from Capsicum annuum L. was inhibited by specific fractions from high-performance liquid chromatographic separations of extracts from those same plants. Two regions were apparent-a rapidly eluting discrete zone of high potency and a second more diffuse zone of lower activity which would have included phaseic acid. Equivalent fractions derived from solvent blanks were devoid of inhibitory activity.
Suggestions by T. Sharkey and K. Raschke (Plant Physiol., 1980, 65, 291-7) that our earlier demonstration (Aust. J. Plant Physiol., 1975, 2, 553-67) of inhibitory activity in plant extracts containing phaseic acid was due entirely to solvent residues is not substantiated. Nevertheless, their case against our proposal that phaseic acid acts as an endogenous regulator of photosynthesis is acknowledged. Present findings do, however, confirm the existence of photosynthetic inhibitors of biological origin.
Pathway of Carbon Transport Within Developing Ovules of Phaseolus vulgaris L
Authors: Patrick JW , Mcdonald R
Published: January 2006

14C-labelled photosynthates, on reaching developing ovules of Phaseolus vulgaris plants, were transported rapidly and evenly throughout the highly vascularized seed coats. Apoplastic transfer of 14C-labelled photosynthates from the seed coats to the developing embryos occurred over the entire inner surface of the seed coats. Further lateral transfer of the photosynthate through the cotyledons exhibited characteristics consistent with a diffusional process. The 14C-labelled photosynthates transported from the seed coat to cotyledon symplasts were principally composed of sucrose. The free space of the cotyledons was fully permeated by photosynthates at concentrations in the range of 100-200 mM sucrose equivalents. This pool of photosynthates was continuously maintained by transfer from the seed coats. Furthermore, initial rates of depletion of the free-space pool of photosynthates, following removal of the seed coats, accounted for cotyledon growth rates. These observations are consistent with photosynthate movement being largely restricted to the apoplast of the cotyledons.
Environmental Effects on Peppermint (Mentha piperita L.). II. Effects of Temperature on Photosynthesis, Photorespiration and Dark Respiration in Peppermint With Reference to Oil Composition
Authors: Clark RJ , Menary RC
Published: January 2006

Net CO2 exchange was investigated at several photon flux densities and day temperatures in both 21% and 2% O2. Light saturation occurred between 400 and 500 �Em-2, s-1 in attached, fully expanded leaves of peppermint. Maximum rates of 'apparent' photosynthesis occurred at 20°C. The important determinants of 'apparent' photosynthesis were an increase in 'true' photosynthesis when temperature was increased to 25°C, a steady increase in dark respiration with increased temperature and a rapid increase in photorespiration between 15 and 30°C. Such net CO2 exchange characteristics of peppermint support the photosynthate model proposed to explain environmental effects on oil composition.