bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrogen Fixation by Nodulated Roots of Viminaria juncea (Schrad. & Wendl.) Hoffmans, (Fabaceae) When Submerged in Water
Authors: Walker BA , Pate JS , Kuo J
Published: January 2006

Nodulated seedlings of Viminaria juncea were raised in free-draining or flooded sand culture. Unflooded seedlings developed limited amounts of aerenchyma in lower stem, root and nodules, and responded to flooding by accelerated aerenchyma production and, after 10 days, by formation of pneumatophores from their near-surface lateral roots. Continuously flooded seedlings showed earlier and greater development of aerenchyma and pneumatophores, and had their nodules and roots restricted to the upper 10 cm of the rooting medium. Aerenchyma was developed from an inner cambium, distinct from the outer phellogen which subsequently developed on older parts of stem, root and nodules. Gas contents of plant parts varied from 4-8% for organs with little aerenchyma to over 30% for the aerenchyma-invested basal stem and root of continuously flooded seedlings.
A role of the sheaths of aerenchyma in gaseous exchange between aerial environment and nodulated root was demonstrated by gas injection experiments, in situ C2H2 reduction assays and 15N2 feeding experiments on intact plants with flooded roots. Samples of gas removed from the aerenchyma of plants exposed to C2H2 contained up to 14 times the amount of C2H2 and 4 times the amount of CO2 than in the atmosphere of the assay chamber, indicating that gas exchange for both N2 fixation and respiration occurred via the aerenchyma.
Previously unflooded, 12-week seedlings exposed to 14 days flooding gained as much dry matter and total N in the 2-week treatment as did control unflooded plants, but 21-week continuously flooded seedlings showed only half the dry matter and nitrogen gains of similarly aged unflooded seedlings. Observations on the seasonal growth, nodulation and pneumatophore development of natural populations of the species were discussed in relation to the above findings.
Effect of Temperature on Grain Growth and Protein Accumulation in Cultured Wheat Ears
Authors: Donovan GR , Lee JW , Longhurst TJ , Martin P
Published: January 2006

The growth of the grain and the non-grain parts of wheat ears grown in culture was more rapid at 25°C than at 21 or 15°C. The non-grain portion of the ear accounted for 40% of ear growth at 25°C over a 21-day period of culture while at 15°C it was 23%. The rate of grain growth was, however, higher at the higher temperature. Ear growth per unit weight of dry matter taken up from the culture medium was higher at 25°C than at lower temperatures. More soluble sugar accumulated in the bracts at high temperature but there was no corresponding increase in grain sugar. High temperature did not lead to increased grain nitrogen levels as has been observed for whole plants. The proportion of total ear nitrogen translocated to the grain was higher at 15 and 21°C than at 25°C.
Lectins as Cytochemical Probes of the Developing Wheat Grain. IV. Demonstration of Mucilage Containing L-Fucose Associated With Roots in Ungerminated Grain
Authors: Baldo BA , Reid AL , Boniface PA
Published: January 2006

Fluorescein-labelled lectins from Ulex europaeus and Lotus tetragonolobus, each with a specific binding affinity for L-fucose, reacted with carbohydrate material in the root cap and surrounding the roots in the embryos of developing wheat grains. The reactions were completely inhibited by preincubation of the lectins with L-fucose and were observed throughout development of the grain from 6 days post-anthesis to physiological maturity 29 days later. These findings provide the first demonstration of the location of L-fucose in the wheat grain. Although a lectin-reactive slime or mucilage containing L-fucose has been studied by others in the roots of germinated cereal grains, particularly maize, our results demonstrate that such a mucilage already occurs around the roots prior to germination.
Photoperiod, Photon Exposure and the Growth and Sucrose Content of the Wheat Shoot Apex
Authors: Mohapatra PK , Aspinall D , Jenner CF
Published: January 2006

Wheat cv. Warimba plants were grown in a controlled environment in either a long (16 h) or short (8 h) photoperiod. When the apices reached the stage of floret initiation in the long photoperiod, some plants were transferred to the short photoperiod at the same photon irradiance and others to a lower photon irradiance in the long photoperiod. The plants growing initially in the short photoperiod were transferred at a slightly earlier stage of development (lemma initiation) to either the high photon irradiance-long photoperiod environment or to the short photoperiod at the lower photon irradiance. Apices were divided into upper and lower portions and their dry weights and soluble sugar contents were determined.
Sucrose alone was found in most of the apices with trace amounts of glucose and fructose being found late in development in the apices of plants growing in the long photoperiod. There was always a higher sucrose concentration in the lower portion of the apex than in the upper. Transfer to a low photon irradiance reduced apical sucrose content, sucrose initially disappearing completely from the upper region of the apices growing in the long photoperiod. There was some subsequent recovery, however. Transfer to the alternative photoperiod also reduced apical sucrose content, although not as severely.
Responses to Brief Periods of Elevated Temperature in Ears and Grains of Wheat
Authors: Bhullar SS , Jenner CF
Published: January 2006

Brief warming of wheat ears reduced total grain weight, due mainly to a reduction in individual grain weight but also to a small reduction (2.6-12.8%) in grain number.
Warming of ears reduced the water content of the grain, independently of humidity of the air with which the ears were warmed. Warming ears at high humidity accelerated the rate of dry matter accumulation as compared to warming at low humidity but both treatments resulted in a reduction of final weight per grain. The effect of temperature, and interaction with humidity, on grain dry matter accumulation are not due to changes in the water or osmotic potential of the grain.
Warming the ears reduced temporarily the amount of sucrose and other soluble sugars in the grain, but not in the rachis or the floral organs. It seems unlikely that the supply of sugars available for distribution to the grain is depressed by elevated temperature, nor were reduced rates of grain- filling at elevated temperature simpiy related to apparent concentrations of sucrose within the grain: ripening and senescence of the pericarp were hastened by warming the ears, and these responses were not accompanied by reductions in the levels of sugars in the grain.
Effect of Nitrogen Concentration on Endosperm DNA Content and Cell Number in Wheat Ears Grown in Liquid Culture
Authors: Donovan GR
Published: January 2006

Endosperms from grains from wheat ears grown in liquid culture at high N concentrations commencing at 7 days post-anthesis attained cell numbers within 90% of those obtained by grains from intact plants of comparable age. The endosperm DNA content of grains from cultured ears increased as the nitrogen concentration increased in the culture medium. Cell numbers, however, were only significantly affected when the cultured ears were deprived of exogenous nitrogen. The increase in endosperm DNA content as nitrogen concentration in the culture medium increased is explained by endoreduplication of nuclear DNA, a phenomenon previously observed in the aleurone of some other cereals.
Changes in Osmolarity and Solute Content of Pea Plants Exposed to Salinity and Abscisic Acid
Authors: Hasson E , Poljakoff-Mayber A
Published: January 2006

The response of pea plants (Pisum sativum L.) to the presence of 192 mM NaCl or of 10-5 abscisic acid (ABA) was similar: shoot growth was inhibited, internal osmolarity and the content of organic solutes increased, and proline accumulated. It appears that most but not all of the new proline synthesized due to stress is located in the cytoplasmic compartment. The responses of the plant to salinity and externally applied ABA differed, apparently, in the mechanism of adjustment of the internal osmolarity: mainly ion absorption in the first, mainly synthesis of organic osmotica in the second. Potassium might have a special role in controlling internal events in pea shoots. Increase in the internal ABA content may serve as a trigger for the changes in pea shoots, but the sequence of events in pea roots may be different; the trigger may be some mechanism other than ABA accumulation. In this study ABA had no effect on root growth.
Assimilate Supply and Floret Development Within the Spike of Wheat (Triticum aestivum L.)
Authors: Stockman YM , Fischer RA , Brittain EG
Published: January 2006

The effect of increased as well as reduced assimilate on floret growth and development in wheat (cv. Yecora) was investigated in a controlled environment. Plants from which all tillers were removed were grown at 21/10°C with a 14 h photoperiod. At flag leaf emergence, an additional light (15% above control) and two shading treatments (40 and 70% below control) were applied to the plants for an 8-day period, ending 6 days before anthesis.
The additional light and the 70% shade treatments had significant effects (+37%, -43% respectively), on the number of competent florets (as judged by anther appearance at anthesis) and subsequently similar effects on the number of kernels per spike at maturity. The changes in competent floret numbers were closely related to changes in spike dry weight at anthesis and in turn, during the treatment period. The heavy shading decreased grain yield significantly.
Within the spike, treatment effects on floret and kernel number were greater in basal spikelets than in distal and especially central spikelets, in both an absolute as well as relative sense. These effects were paralleled by greater changes in basal spikelet dry weight and water-soluble carbohydrate concentration. They may be related to the smaller size or later development of basal spikelets at the onset of treatment, and suggest that the base of the spike is normally a lower priority sink for assimilate at that time.
Physiological Reactions to an Imposed Drought by Macroptilium atropurpureum and Cenchrus ciliaris in a Mixed Sward
Authors: Sheriff DW , Ludlow MM
Published: January 2006

M. atropurpureum cv. Siratro and C. ciliaris cv. Biloela (buffel grass) plants in well-watered and droughted mixed swards were studied to investigate how the two species survive during periods of drought. Rates of photosynthesis and water use efficiencies were generally highest in well-watered buffel grass, whereas the conductance of the abaxial surfaces of leaves was highest in well-watered Siratro. The minimum and daily mean water potentials were consistently lower in well-watered buffel grass than in well-watered Siratro, indicating a lower hydraulic conductance in the soil-plant system of buffel grass. Gross photosynthesis and the conductance of the abaxial surfaces of leaves of both species fell with falling water potential, as did the water use efficiency of buffel grass. Droughted Siratro exhibited paraheliotropic leaf movement, and a reduction in stomatal aperture in the middle of the day. Despite its greater sensitivity to water deficits, Siratro remained physiologically active throughout at least a portion of the day even on the last day of a drying cycle when its leaf water potential ranged from -1 MPa at dawn to a minimum of -1.8 MPa, when the corresponding water potentials for buffel grass were about -4 MPa and about -5 MPa. Siratro had a higher water potential mainly because of the deeper penetration of its roots and its consequent access to water lower in the profile. However, the higher water potential was also due to stomatal opening, and therefore photosynthesis, in droughted Siratro occurring only at times of the day when evaporation, temperature and solar radiation were low. The conductance of the abaxial surfaces of droughted buffel grass leaves was generally steady, or declined gradually during the day. Buffel grass was able to survive drought because of its inherent desiccation tolerance, whereas Siratro was able to survive drought in a mixed sward because it did not compete with buffel grass for soil water.
Posidonia australis Growing in Altered Salinities: Leaf Growth, Regulation of Turgor and the Development of Osmotic Gradients
Authors: Tyerman SD , Hatcher AI , West RJ , Larkum AWD
Published: January 2006

The marine angiosperm Posidonia australis Hook f. is always submerged and the leaf cells are able to exchange ions, gases and water with the surrounding seawater. The base of the youngest lamina is surrounded by sheaths from older leaves and a gradient in cell osmotic pressure existed from the base of the lamina enclosed within the sheath to the emerged zone at the top of the sheath. For plants grown in seawater, the cells at the base of the lamina had an osmotic pressure of 1.34 MPa (seawater = 2.54 MPa); the osmotic pressure increased with distance along the lamina to the emerged lamina value of 3.09 MPa. The osmotic gradient was accounted for by cell concentration gradients of Na+ (73 mol m-3 increasing to 412 mol m-3), K+ (91 mol m-3 increasing to 279 mol m-3) and Cl- (62 mol m-3 increasing to 578 mol m-3). Gradients also existed in the cell concentrations of sucrose and amino acids. It is proposed that, within the solution enclosed by the sheath, a standing osmotic gradient is created by ion uptake from the sheath solution.
Leaf growth was unaffected by salinities from 13‰ to 57‰ and net photosynthesis was unaffected by reduction in salinity from 34‰ to 19‰. The cells of the leaves and rhizome adjusted their osmotic pressure by changes in Na+, K+ and Cl- concentrations such that turgor varied only between 0.67 and 1.52 MPa over a range in external osmotic pressures from 0.83 to 3.89 MPa. The tolerance of P. australis to changes in salinity in the absence of severe physical disturbance is due, largely, to the sheath and to the osmotic pressure gradient.
Translocation of Manganese in Subterranean Clover (Trifolium subterraneum L. Cv. Seaton Park). II. Effect of Leaf Senescence and of Restricting Supply of Manganese to Part of a Split Root System
Authors: Nable RO , Loneragan JF
Published: January 2006

Split root systems were used to examine the hypothesis that manganese is not mobile in the phloem of subterranean clover plants during vegetative growth. The effect of senescence on manganese mobility was also examined by shading mature leaves.
Plants given a luxury supply of radioactive manganese to one half of a split root system failed to translocate any more than a trace of manganese to the other half. Shading and subsequent senescence of a large number of leaves did not cause movement of manganese from them. Omitting an external supply of manganese depressed growth of roots but produced no visual abnormalities even though Mn concentrations decreased to 5 �g/g dry matter of root.
Association Between Loss of Leaf Turgor, Abscisic Acid Levels and Seed Set in Two Wheat Cultivars
Authors: Morgan JM , King RW
Published: January 2006

An increase in abscisic acid (ABA) content of the spike and a decrease in seed set of the spike resulted from the withholding of water from the wheat plant during pollen meiosis. The leaf was probably the source of this ABA since spike turgor was maintained whereas leaf turgor was lost. A change in elasticity of the leaf was associated with its loss of turgor (0-0.4 MPa leaf turgor). The correlation with ABA content points to this change in elasticity as a possible pressure-sensing mechanism regulating ABA synthesis at low or zero turgor. For the two cultivars examined, differences in seed set under well-watered conditions were associated with differences in ABA content of the spike. However, complete infertility was not observed and, also, all florets were affected to the same extent. Possibly pollen is sensitive to stress over a range of developmental stages and not solely during meiosis. Alternatively, the effects of stress may linger for some time after rewatering of the plants.
Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. II. Proton Deposition
Authors: Hope AB , Matthews DB
Published: January 2006

The deposition of protons in the inside spaces of pea class C chloroplasts was studied by means of the acidification of neutral red measured spectrophotometrically, with the outside space buffered.
Careful kinetic analysis of such signals revealed three components, during non-cyclic electron flow induced by single-turnover flashes. These components included a 'slow' phase not emphasized in previous studies. The half-times of these phases were: 'Fast', < 1 ms (not resolved); 'Intermediate', 13-25 ms with added electron acceptor or 4 ms without; and 'Slow', 70-90 ms.
Under conditions for cyclic electron flow only the I phase remained; it was the same magnitude as the I phase in non-cyclic flow, and its half-time was c. 3 ms. The F phase, which is usually attributed to protons from the oxidation of water, increased in average size with number of flashes (taken four flashes at a time) and was not fully patent until more than 20 flashes.
The size of the I phase, which is usually attributed to protons from the oxidation of plastohydroquinone, when measured in a sequence of flashes to dark-adapted suspensions under non- cyclic conditions, had a binary oscillation in phase with the oscillation in proton uptake reported previously. It was concluded that protons leave PQH2 two at a time on alternate flashes.
The S phase (average in 10 test flashes) was reduced by fast preflashes; an origin near photosystem II is suggested. The S phase may imply a small pool of proton-sequestering ability near the water oxidation site, or a number of other possibilities.
In steady-state conditions, the ratio of the protons from PQH2 to those from water was 1.0 under all conditions examined except in the absence of added electron acceptor, when it was as high as 1.6. This was the only condition apparently indicating a Q-cycle, with infrequent single-turnover flashes.
Effect of Sodium Nutrition and Light Upon the Concentrations of Alanine in Leaves of C4 Plants
Authors: Nable RO , Brownell PF
Published: January 2006

The concentration of alanine in the leaves of representatives of each of the three types of C4 plants was found to be consistently greater in sodium-deficient than in sodium-sufficient plants. The sodium treatment, however, did not affect the alanine concentration in the leaves of tomato, a C3 plant or in the roots of Amaranthus tricolor, a C4 plant. The alanine concentration of leaves of A. tricolor decreased rapidly upon the addition of sodium to cultures of sodium-deficient plants. The concentration of sodium required to give this response was approximately 50 �M, which was similar to that needed for the growth response. When plants that had been previously illuminated were placed in the dark, the alanine concentration increased rapidly, but was lowered again to the original concentration on return to the light. These changes in the alanine concentrations of leaves of C4 plants in response to sodium and light treatments are discussed in relation to the C4 photosynthetic system.
Comparison of the Growth and Development of Two Selections of Guar, Cyamopsis tetragonoloba (L.) Taub., With Contrasting Branching Patterns
Authors: Beech DF , Charles-Edwards DA
Published: January 2006

Two selections of guar, C. tetragonoloba, with contrasting branching patterns were grown at two times of year at each of three plant densities. Although the efficiency with which they used intercepted light energy in the production of new dry matter did not differ between the two selections, or between the treatments, it did appear to increase during the ontogeny of the crops. The gross partitioning of new dry matter between leaves, stems and roots was similar between selections and across treatments, but there were large differences in the mean weights of stem associated with each internode, mean leaf weights and specific leaf areas of the two selections. The results of the analysis of dry matter production and partitioning are discussed in relation to the field performances of the two selections.
Germination of Australian Channel Millet (Echinochloa turnerana (Domin) J.M. Black) Seeds. I. Dormancy in Relation to Light and Water
Authors: Conover DG , Geiger DR
Published: January 2006

Channel millet, a native to inland Australia, is recognized as a promising forage and grain crop for arid regions. In its native habitat germination occurs after the flood plains are inundated. Newly harvested seeds were dormant, but germinated after several months of storage or after disruption of enclosing structures. Intact, after-ripened seeds did not germinate in the dark, but dehulled seeds achieved high percentage germination in the dark. Secondary dormancy was induced by imbibing intact seeds in the dark and was broken by subsequent dry storage or by disruption of enclosing structures. Intact, after-ripened seeds that were subjected to wetting-drying cycles in the light germinated faster during the final wetting than did untreated seeds. High final germination percentage values were attained by both leached and unleached seeds. The light requirement may restrict germination to the rapidly drying surface layers of the soil and consequently restrict germination in its natural habitat to periods of flooding or prolonged rains when the surface soil is kept moist for extended periods.
Germination of Australian Channel Millet (Echinochloa turnerana (Domin) J.M. Black) Seeds. II. Effects of Anaerobic Conditions, Continuous Flooding, and Low Water Potential
Authors: Conover DG , Geiger DR
Published: January 2006

Channel millet seeds require a period of substantial wetting (as occurs during flooding) before mass germination is attained in its native environment, while the remainder of the life cycle often occurs under arid conditions. Imbibing seeds in solutions of mannitol or NaCl ranging from 0 to -1.5 MPa slowed germination and seedling growth but, after 14 days of imbibition in the light at 30°C germination was about 50% even at levels of moisture availability as low as -1.0 MPa. High germination percentages were also attained in the light inside flasks flushed continuously with humidified air, humidified N2, or N2 followed by air. Seeds failed to germinate in the dark under any of the above treatments, but did so to a certain extent when subsequently exposed to light. In the absence of O2, seedlings were non-pigmented and without protruding radicles. Under conditions of continuous flooding in stagnant water to a depth of at least 10 cm, channel millet seeds germinated and produced plants which went on to flower within 3 months.
Changes in Water Relations, Water Flux, and Root Exudate Abscisic Acid Content With Cold Acclimation of Pinus sylvestris L
Authors: Smit-Spinks B , Swanson BT , Markhart AH Iii
Published: January 2006

Scotch pine seedlings (Pinus sylvestris L.) were subjected to 6 week photoperiod and thermoperiod treatments to induce different levels of cold acclimation. The water content, relative water content, xylem pressure potential, transpiration rate, root hydraulic conductance, and abscisic acid (ABA) content of root exudate were then measured.
Water content decreased in woody stems and needles with cold acclimation but not in the roots and green stems. There was a close correlation between relative water content and water content of woody stems and needles as well as a decrease in xylem pressure potentials of hardy needles, indicating that the reduction in water content was at least partially due to increased water deficit. The increased water deficit was not caused by increased water loss since transpiration rates decreased in hardy shoots. Water uptake was reduced by decreased root hydraulic conductance which could account for the shoot water deficits. Root hydraulic conductance and transpiration rate returned to non-acclimated levels after warm temperature exposure. ABA levels were highest in the root exudate collected in the morning from non-acclimated plants.
Exogenous Manganese as an Electron Source for Both Photosystem II and Radical Superoxides
Authors: Handley L , Hope AB , Matthews DB
Published: January 2006

Exogenous manganese acts as an electron source for both photosystem I1 (PS 11) and radical superoxides formed after PS I. This conclusion is supported by measurements of external acidification when chloroplasts containing exogenous manganese and methyl viologen are illuminated. The acidification and increased oxygen consumption when manganese was added shows two moles of protons to be produced per mole of oxygen consumed. Reactions for manganese oxidation preceding PS I1 and following PS I are given with the net result:
2H2O + Mn2+ + O2 ͛4 MnO2 + H2O2 + 2H+
This reaction was shown to reverse in the dark and to have a chlorophyll dependency for both the rate of the forward photoreaction and reverse dark reaction. The pH-dependency shows manganese can compete with water as an electron source for PS II only under alkaline conditions and the electrochemical potentials for the competition are discussed in terms of the half reactions involved.
Temperature Dependence of Whole-Leaf Photosynthesis in Eucalyptus pauciflora Sieb. Ex Spreng
Authors: Kirschbaum MUF , Farquhar GD
Published: January 2006

The temperature dependence of net photosynthetic assimilation of CO2 by snowgum (Eucalyptus pauciflora Sieb. ex Spreng.) was investigated. CO2 assimilation was divided into its component processes, stomatal and biochemical. The biochemical limitation was investigated with gas-exchange techniques and found to conform well to a recent model of C3 photosynthesis. In line with the model, net assimilation was further divided into ribulose 1,5-bisphosphate (RuP2) regeneration or electron-transport/photophosphorylation limitation, limitation by RuP2 carboxylase/oxygenase (Rubisco; EC 4.1.1.39) activity, together with loss of CO2 in non-photorespiratory respiration. The estimated temperature dependence of electron transport agreed well with one published for uncoupled electron transport, while the estimated temperature dependence of the catalytic activity of Rubisco was slightly less than that reported from biochemical determinations. The estimated rate of non-photorespiratory respiration was about 0.6 times the rate of respiration at night and appeared to have the same temperature dependence. With this information the temperature dependence of the biochemical limitation was modelled. Stomatal conductance was assumed to follow the theory of constant marginal water cost of carbon assimilation (δE/δA) and net assimilation rate at ambient concentration of CO2 was predicted. It was concluded that, for a given Rubisco activity and RuP2-regeneration capacity, both temperature optimum and net assimilation rate at the optimum temperature increased with increasing stomatal conductance.
Isotopic Composition of Plant Carbon Correlates With Water-Use Efficiency of Wheat Genotypes
Authors: Farquhar GD , Richards RA
Published: January 2006

Variation in carbon-isotope composition among and between wheat genotypes was correlated with variation in water-use efficiency in separate pot experiments conducted in spring-summer and in winter. In the main, winter experiment, the water-use efficiencies ranged from 2.0 to 3.7 mmolC/mol H2O (means of four replicates) while the corresponding isotope effects for leaf material ranged from 1.0225 to 1.0194. 13C was more abundant in grain than in leaves and stems. It is suggested that carbon-isotope analysis may be a useful tool in selection for improved water-use efficiency in breeding programmes for C3 species.
Effects of Drought and High Temperature on Grain Growth in Wheat
Authors: Nicolas ME , Gleadow RM , Dalling MJ
Published: January 2006

The effects of two levels of temperature and of water supply on grain development of wheat (cv. Warigal) were studied by imposing treatments during the early or late period of cell division. High temperature (28°C day/20°C night) accelerated development of the grain. Dry matter accumulation and cell division proceeded at a higher rate but had a shorter duration in the high temperature treatments. Maximum cell number, final cell size and the number of large starch granules per cell were not significantly reduced by high temperature. Drought and drought × high temperature reduced the storage capacity of the grain, with a decrease in number of cells and starch granules in the endosperm. Cell size was also reduced when treatments were imposed late during cell division. Duration of dry matter accumulation and cell division was reduced in the drought and drought × high temperature treatments. The combined effects of drought and high temperature were much more severe than those of each separate treatment. The amount of sucrose per cell was similar in all treatments. It appears unlikely that the supply of sucrose to the endosperm cells is the main limiting factor of dry matter accumulation in both drought and high temperature treatments.
Adsorption of Amines to Thylakoid Surfaces and Estimations of ΔpH
Authors: Hope AB , Matthews DB
Published: January 2006

The adsorption of the fluorescent, weak amine ΔpH indicators 9-aminoacridine and N-(1-naphthyl)ethylenediamine to thylakoids of pea chloroplasts in the dark was measured as a function of amine concentration, at several pH's between 8 and 5, and with varied MgCl2 concentration. It was concluded that it was the protonated form of the amine that was adsorbed. Maximum amounts adsorbed, saturation occurring at about 1 mM amine concentration in the presence of 5 mM KCl and 10 mM MgCl2, were up to 1 mol (mol Chl)-1. This was calculated as exceeding the number of available surface negative charges (0.26 for a charge density of 0.025 C m-2). An apparent binding constant of 400-500 μM (concentration for half saturation) was noted for both amines under the above conditions.
A model was developed that enabled the estimation of the relative amounts of amine bound to the inside and outside thylakoid surfaces in the steady state, in the light. By this means corrections to the apparent ΔpH calculated from fluorescence quenching of the amines could be established. These corrections amounted to about 1 pH unit for the diamine and more for 9-aminoacridine. The predictions of the model were in good agreement with experimental relations between estimated, light-induced ΔpH values and amine concentration.
The implications of a lower ΔpH for earlier estimations of proton motive force in relation to photophosphorylation are briefly considered.
Some Effects of Temperature and Light on Floral Initiation and Development in Acacia pycnantha
Authors: Sedgley M
Published: January 2006

Floral initiation and development in Acacia pycnantha were studied under three environments. Two had ambient southern Australian temperatures of warm summer (mean max. 32°C, mean min. 16°C) and cool winter (mean max. 19°C, mean min. 8°C), one with full sunlight (outside) and the other with 30% light intensity (shadehouse). The other environment (glasshouse) had slightly lower than normal light intensity and a relatively constant year round temperature of mean 28°C maximum and 16°C minimum. Plants were scored for microscopic and macroscopic evidence of floral initiation and development.
Floral primordia were initiated all year round under all environments. Floral development proceeded normally under ambient conditions of temperature and light, and anthesis occurred between August and October. Under low light intensity, floral development did not progress beyond a very early stage and macroscopically visible racemes were rare. Under the constant temperatures, floral development proceeded normally up to the stage of microsporogenesis and megasporogenesis. Meiosis did not occur and inflorescence buds ceased growth and were shed from the plant. Plants were transferred between the outside and glasshouse conditions in June, at around the stage of meiosis. Those transferred from outside to the glasshouse did not flower whereas some of those transferred from the glasshouse to outside flowered, but later and for a shorter period than plants maintained outside throughout.
It appears that a 70% reduction in sunlight inhibits floral development at an early stage and that temperatures of approximately mean maximum 19°C and minimum 8°C are required for meiosis in Acacia pycnantha.
Interactions Between Glycine Decarboxylase, the Tricarboxylic Acid Cycle and the Respiratory Chain in Pea Leaf Mitochondria
Authors: Day DA , Neuberger M , Douce R
Published: January 2006

In pea leaf and potato mitochondria, external NADH oxidation was inhibited by concurrent oxidation of endogenous NADH and succinate. Succinate oxidation was also inhibited by concurrent oxidation of external NADH, but oxidation of endogenous NADH was not. NAD+-depletion studies suggested that glycine decarboxylase and other NAD-linked enzymes competed for available NAD+ within the matrix. However, at both high and low NAD+ levels, only the tricarboxylic acid cycle enzymes and malic enzyme were inhibited during concurrent oxidation with glycine. Measurements of the oxidation-reduction state of matrix NADH suggested that most of the mitochondria in the preparations contained both glycine decarboxylase and the tricarboxylic acid cycle enzymes and that steady-state levels of NADH were maximal with glycine alone as substrate. That is, there was no evidence for two populations of mitochondria being present. Nonetheless, malate stimulated state 4 and rotenone-inhibited O2 uptake in the presence of glycine. We conclude from these results that the priority glycine has as a substrate for leaf mitochondria is due to a priority that electrons from respiratory complex I have over those from complex II and the external NADH dehydrogenase, and the ability of glycine decarboxylase to compete favourably with tricarboxylic acid cycle enzymes for NAD+ in the matrix. Glycine may inhibit oxidation of other NAD-linked substrates by maintaining high matrix NADH/ NAD+ ratios. However, malate plus pyruvate appear to have access to some electron transport that is not accessible to glycine, at least under ADP-limiting conditions.
Diaheliotropic Responses of Leaves of Macroptilium atropurpureum cv. Siratro
Authors: Sheriff DW , Ludlow MM
Published: January 2006

Diaheliotropic movements in Macroptilium atropurpureum cv. Siratro caused the adaxial surfaces of leaflets to orient towards a light by the flexing of secondary pulvini at the base of the leaflets, and to a lesser extent by petiole bending and flexing of the primary pulvinus at the base of the petiole. Secondary pulvini flexed more in response to light than did primary pulvini. This flexing was in response to blue light such that the illuminated side of the pulvinus contracted, and the leaflet reoriented with its adaxial surface facing the light. This response was enhanced by the following: a light gradient along the length of the illuminated surface of the pulvinus, the presence of additional low-intensity diffuse light, a photon irradiance greater than 0.5 mmol m-2 s-1, and a change of photon irradiance. The abaxial surface of a pulvinus was more sensitive to light than was its adaxial surface.
The stimulus for movement was transmitted from an illuminated primary pulvinus to the shaded secondary pulvini of the same leaf, and this caused re-orientation of both individual leaflets and the whole leaf. Similarly, a stimulus was transmitted to the primary pulvinus from secondary pulvini (or from the adjacent petiole) when illuminated, resulting in a deflection of the petiole by the primary pulvinus and re-orientation of the adaxial surface of the whole leaf towards the light.
Secondary pulvini have the ability to move individual leaflets in three dimensions because the plane of the leaflet is at right angles, in two dimensions, to the axis of the distal end of the pulvinus. Terminal leaflets showed a greater three-dimensional movement than did lateral leaflets.
Movement of a light through large angles resulted in leaflet re-orientation proportional to, but less than, the change in angle of the light. On the other hand, secondary pulvini caused leaflets to track, though imperfectly, a light source that simulated the movement of the sun. A circumnutational circadian rhythm is partly responsible for the diaheliotropic movements of Siratro leaves outdoors, and the ability of an individual leaflet to track the sun depends upon its orientation with respect to the sun.
Water Pathways in Wheat Leaves. II. Water-Conducting Capacities and Vessel Diameters of Different Vein Types, and the Behaviour of the Integrated Vein Network
Authors: Altus DP , Canny MJ , Blackmann DR
Published: January 2006

The water-conducting capacity of the lateral veins of the wheat leaf, measured by the velocity of movement of a dye marker, decreases with distance along the leaf towards the tip. The laterals contain a number of small (up to 10 �m) diameter vessels as well as two or three relatively large (up to 45 �m) diameter vessels. The largest vessel in each decreases in diameter with distance along the leaf towards the tip, resulting in the decreased velocity of conduction. The large vessels represent physical spaces through which laminar flow can occur; however, the flow rate is slower than that predicted by the Hagen-Poiseuille law for pipes of equivalent diameter. The intermediate veins contain only several 7-10 �m diameter vessels, and the diameter of the largest vessel in these veins does not change along the length of the leaf. The number of 7-10 �m diameter vessels per vein also remains unchanged. The water- conducting capacity of an intermediate vein is therefore constant along the length of the leaf. The transverse veins that cross-connect neighbouring longitudinal veins all have similar water-conducting capacity regardless of location in the leaf. These measurements support the view that the lateral veins serve to supply water from the base of the leaf to the tip, while the intermediate and transverse veins form a distribution network carrying the water across the leaf to the mesophyll cells. A theoretical analysis is made of the behaviour of the network as an integrated system. Assumed transpiration rates are imposed on the model to find what the pressure gradient along the leaf blade is, what pressures would be produced at the nodes of the network, and what fluxes would result through the vein elements of it. The model predicts movements of water in the intermediate veins very similar to those observed in a previous paper and suggests that the network responds to changes in supply or demand by producing minima of similar pressure in the distributing veins at different distances from the supplying longitudinal veins.
Effect of Brassinolide and other Growth Regulators on the Germination and Growth of Pollen Tubes of Prunus avium using a Multiple Hanging-drop Assay
Authors: Hewitt FR , Hough T , O'Neill P , Sasse JM , Williams EG , Rowan KS
Published: January 2006

A new multiple hanging-drop assay has been tested with a growth inhibitor, cycloheximide, and a growth-promoter, fusicoccin. This assay has been used to examine the growth-response of pollen-tubes of Prunus avium to brassinolide, a naturally occurring promoter of plant growth. This response is compared with that of indol-3-ylacetic acid, gibberellic acid, and kinetin. Pollen tubes responded to brassinolide and fusicoccin at 1 nM and above, a concentration one order of magnitude lower than that for indol-3-ylacetic acid and gibberellic acid. Kinetin did not stimulate growth of the pollen tubes.
Short-Day Cycle Requirements for Floral Initiation of Stylosanthes guianensis (Aublet) Sw. var. guianensis
Authors: Ison RL
Published: January 2006

Mature plants of the tropical legume Stylosanthes guianensis var. guianensis cv. Schofield required 20 short-day (SD) cycles (of 10-h days) for irrevocable commitment to floral initiation when returned to natural long days (LD), although the morphological changes associated with floral initiation were evident after 12-18 SD cycles. Commitment to flowering and spike production were favoured by 20 or more SD cycles. Floret number per spike and percentage seed set were not affected by return to LD. Within individual plants, sections of terminal and branch apices revealed a range of development stages. Terminal apices of well developed lateral branches were able to initiate as soon as, or sooner than, terminal apices of the main branch in this usually determinate plant; this points to individual branches having some autonomy for floral initiation, but suggests dissections made from well developed lateral branches would be a feasible method for determining floral initiation where plant replication is limited.
Release of Ferulic Acid Esters From Barley Aleurone. I. Time Course of Gibberellic-Acid-Induced Release From Isolated Layers
Authors: Gubler F , Ashford AE
Published: January 2006

Removal of ferulic acid from barley aleurone cell walls is closely correlated with wall hydrolysis. The ferulic acid content of isolated aleurone layers (Hordeum vulgare L. cv. Himalaya) falls progressively during incubation with gibberellic acid (GA3), to about one-third of the original content, by 72 h. At the same time an equivalent amount accumulates in the incubation medium, not as the free acid but still esterified to other components. The data show that there is no modification of the feruloyl group, or hydrolysis of the ester linkage prior to removal from the tissue, and therefore the GA3-induced aleurone peroxidases and esterases are not directly involved.
Characteristics of Glycine and Malate Oxidation by Pea Leaf Mitochondria: Evidence of Differential Access to NAD and Respiratory Chains
Authors: Dry IB , Wiskich JT
Published: January 2006

The addition of glycine to pea leaf mitochondria oxidizing malate in either state 3 or state 4 led to a marked increase in the rate of O2 uptake. Malate was also found to stimulate the state 3 and state 4 rates of O2 uptake with glycine. The increases in state 4 rates were not due to increases in the rate of O2 uptake via the alternative pathway, as the state 4 rate in the presence of malate or glycine, or both, was not limited by the rate of electron flow between ubiquinone and O2.
The rotenone-insensitive state 3 rates of O2 uptake in the presence of malate or glycine, in freshly isolated mitochondria, could be stimulated by the addition of NAD. However, these NAD-limited, rotenone-insensitive, rates could also be stimulated by the addition of a second NAD-linked substrate. Mitochondria could be further depleted of NAD such that the rotenone-insensitive state 3 rate of glycine oxidation was stimulated threefold by added NAD. Even in these NAD-depleted mitochondria, the rate of O2 uptake in the presence of glycine was found to be markedly stimulated by malate, indicating that the malate-oxidizing enzymes had access to NAD, within these mitochondria, which was unavailable to glycine decarboxylase. These results are not consistent with a uniform distribution of enzymes within mitochondria with access to a common pool of NAD, and suggest that glycine decarboxylase and the malate-oxidizing enzymes may have differential access, both in terms of size and location, to NAD within pea leaf mitochondria.
Effect of Temperature on the Synthesis of Jojoba Wax
Authors: Dunstone RL , Benzioni A , Tonnet ML , Milthorpe P , Shani A
Published: January 2006

Seed was collected from jojoba [Simmondsia chinensis (Link) Schneider] plants growing at three field sites in two years. The wax percentage was determined by nuclear magnetic resonance and the compositions of the wax and the ethanolysis products (one site only) were determined by gas chromatography.
The mean wax concentration varied from 49.2 to 55.1% over all sites and years. The percentage of long-chain wax esters (>C40) decreased linearly with increase in mean maximum temperature during the period of linear seed growth (r� = 0.93). The decrease in long-chain esters was associated with a decrease in the C22 and C24 fatty acids and alcohols.
Data from controlled environment studies and from field studies were used to assess the effect of temperature on the percentage elongation, reduction and esterification of acyl-CoAs of carbon lengths 18-22. High temperature lowered the specificity for elongation of C20-C22 and of C22-C,24 and increased the specificity for reduction of the C20 acid to its corresponding alcohol.
The amount of C42 wax ester was greater than would be expected by random association of the alkoxy-acyl groups but this preference was not as great at high temperatures.
The Electrical Properties of Plant Cell Membranes. IV. The Effects of the Nodal Conductance upon the Cable Properties and Measured Membrane Conductance of Charophytes
Authors: Smith JR
Published: January 2006

A theoretical treatment of the electrical 'cable' properties of cylindrical, radially symmetric, plant cells with two concentric membranes is presented, in which the effects of additional conductance elements located at the nodes (ends) of the cell are considered. It is shown that the measured 'membrane' conductance is effectively independent of the conductance between the vacuole and exterior at the nodes, providing the nodes are at least a cable-length distant from the point of current injection. However any 'leakage' between the cytoplasm and the cell exterior at the nodes (as might occur via unsealed plasmodesmata) can drastically affect measurements made with cytoplasmic electrodes remote from the point of current injection. It is shown that isolating the nodes of the cell with insulating external barriers of a suitable width can effectively remove any error due to the electrical properties of the nodes.
Gas Penetration of Pit Membranes in the Xylem of Rhododendron as the Cause of Acoustically Detectable Sap Cavitation
Authors: Crombie DS , Hipkins MF , Milburn JA
Published: January 2006

The gas pressure required to force sap from Rhododendron stems was investigated. Sap was expressed from stems, and stem permeability to gas increased, at pressures of 1.3-3.5 MPa. We interpret the changing of permeability as a removal of water films in the pores of the pit membranes which normally limit the length of xylem conduits. Similar pressure differences exist across the pit membranes separating gas and sap-filled conduits when cavitation occurs in Rhododendron. It is suggested that cavitation in detached leaves and shoots of Rhododendron occurs when gas penetrates the pit membranes. The increase in the gas permeability of xylem subjected to high gas pressures was reversed by a soaking in water. It could not therefore have been a consequence of mechanical damage, caused when xylem conduits are subjected to high gas pressures, because such structural damage would be irreversible.
Transport of Tritiated Water and 14c-Labelled Assimilate Into Grains of Wheat. III. Diffusion of Tho Through the Stalk
Authors: Jenner CF
Published: January 2006

Measuring the rate at which tritiated water is transported by diffusion through the stalk of the wheat grain is the main purpose of this paper. Diffusion of THO through the stalk is much slower than expected on the basis of the self-diffusion of THO in water, demonstrating that there are substantial resistances to diffusion of water in the stalk.
Entry of THO into the grain by physical processes alone (diffusion), as measured in assemblies in which the grain (stripped of its bracts) is sealed into an impermeable capsule, is fast enough to account for the observed rate of transport of THO into normally functioning grains. Metabolically linked transport of water through the stalk is not detectable. Either the volume of water involved in mass flow through the stalk is too low to be detectable - which would require the concentration of sucrose to be about 2 M, or the entry of assimilate is not accompanied by water. Short-distance transfer of solute (only) from the plant's vascular system to a separate system servicing the grain seems the simplest explanation on the basis of the available evidence.