bluuebunny/crossref_metadata_2025 huggingface dataset:
Shoot Control of Supernodulation in a Number of Mutant Soybeans, Glycine max (L.) Merr
Authors: Delves AC , Higgins AV , Gresshoff PM
Published: January 2006

Seven supernodulation mutants of soybean (Glycine max) derived from the cultivar Bragg were investigated for shoot control of the supernodulation response. Reciprocal grafts showed that supernodulation in all lines tested was obtained only if the genotype of the shoot was homozygous for the mutant allele(s). In addition two lines of Korean origin (selected in the field for increased nitrate tolerance) were included in the grafting studies. Under our experimental conditions nitrate tolerance could not be demonstrated in the Korean cultivars. Grafts gave near-control levels of nodulation, suggesting that the genetic basis of nitrate tolerance and increased nodulation in the Korean lines is different from that seen in the induced mutants of Bragg. The data suggest that, contrary to earlier reports with pea (Pisum sativum) mutants, no root control of supernodulation could be demonstrated. Furthermore the results point to a possible novel regulatory system governing nodule numbers and patterning which involves an intertissue transfer of a chemical signal.
Light Response of CO2 Assimilation, Reduction Stage of Q and Radiationless Energy Dissipation in Intact Leaves
Authors: Demmig B , Winter K
Published: January 2006

Response curves of the rate of net CO2 uptake and of fluorescence quenching (photochemical, qp, and non-photochemical, qE) to photon irradiance were obtained for leaves of eight species. Their photosynthetic capacity varied greatly due to genetic (sun/shade species) and environmental factors (growth under different light and nutrient regimes). The two fluorescence parameters were studied in response to the proportion of excess light at each irradiance, which is given by 1 -Aa/Ap, where Aa is the actual and Ap the potential rate of photosynthesis (assuming that the high photon yield of CO2 uptake seen at low light occurred at all irradiances). All leaves exhibited a very similar response of either 1-qp or qE to 1 - Aa/Ap indicating that the differences in 1 - qp or qE among leaves at a given irradiance can be explained exclusively by differences in the balance between absorbed light and electron transport. In leaves of all species qE, which is primarily a reflection of radiationless dissipation of excitation energy, responded linearly to 1 -Aa/Ap, except for a component already present under conditions in which light is limiting (i.e. when Aa=Ap). By contrast, the reduction state of the primary electron acceptor of photosystem II, 1 - qp, when expressed as a function of 1 - Aa/Ap, increased in all leaves much less than expected if it were solely a reflection of the balance between light absorption and photochemistry. Radiationless energy dissipation is a process which has the potential to maintain Q in a low reduction state.
Spatial and Temporal Distribution of Photosynthesis and Transpiration by Single Leaves in a Rainforest Tree, Argyrodendron peralatum
Authors: Doley D , Unwin GL , Yates DJ
Published: January 2006

The light environments and rates of photosynthesis by leaves of Argyrodendron peralatum (F. M. Bailey) I.H. Boas were examined at eight positions within a natural rainforest canopy. Daily integrals of irradiance at leaf surfaces expressed as a percentage of that reaching a horizontal sensor in the open decreased from about 50% in the uppermost leaves to about 20% at a point 2 m below the top of the crown and to 10-15% in the lower crown and understory. Leaves in the upper crown had maximum instantaneous rates of apparent photosynthesis of 11.5 �mol CO2 m-2 s-1, whilst leaves in the lower crown of the same tree, and in understory saplings had maximum photosynthesis rates of 8.2 �mol m-2 s-1. These rates were not significantly different, and are within the range observed in a number of rainforest species characteristic of later successional stages. Under conditions of adequate water supply, photosynthetic rate was light-saturated by 500 �mol quanta m-2 s-1, irrespective of level in the canopy.
Photosynthetically Active Radiation Environment, Patch Dynamics and Architecture in a Tropical Rainforest in Sumatra
Authors: Torquebiau EF
Published: January 2006

The photosynthetically active radiation (PAR) environments of three sites within a tropical rainforest in Sumatra were characterised. The sites and sensor locations were chosen according to a previous study of forest dynamics based on forest mosaic maps and an analysis of forest architecture by means of detailed profile diagrams. Two sites were located in mature forest patches: one showed a layered architecture while the other had a continuous vertical distribution of foliage. A third site represented a 320 m� treefall gap.
Vertical gradients of PAR from above canopy to ground level were studied in the mature forest zones, while a horizontal gradient of PAR at ground level was studied across a gap-mature forest boundary.
Daily total PAR at ground level in the mature forest sites was 0.78% and 0.57% of incident radiation above the forest. The decrease of radiation from above canopy downwards was strikingly different between the sites: the layered site showed a 'PAR inversion' between successive layers, the amount of radiation under a given layer being less than at the top of the next lower layer. The non-layered site did not show such an inversion. The treefall gap radiation received was approximately 20% of the radiation recorded above the canopy.
The spatial distribution of PAR in the forest is highly variable but can be usefully analysed against a framework of forest dynamics and architecture. Temporal distribution of PAR is also highly variable, and both distributions need to be analysed to understand photosynthetic responses and growth rates of rainforest species.
Reduced Starch Content and Sucrose Synthase Activity in Developing Endosperm of Barley Plants Grown at Elevated Temperatures
Authors: MacLeod LC , Duffus CM
Published: January 2006

Starch accumulation is reduced when endosperms develop at elevated temperatures. Reduced starch deposition does not appear to be due to limiting assimilate levels during the grain filling period; on the contrary, endosperm sucrose may even be increased at the elevated temperature. Results indicate that elevated temperatures significantly reduce the activity of the sucrose cleavage enzyme UDPsucrose synthase (EC 2.4.1.13), found in the endosperm during grain development, and that these effects may be initiated by a relatively short period of thermal stress applied close to anthesis. It would appear that, when developing barley ears are exposed to elevated temperatures, there is an irreversible reduction in the capacity of the endosperm to convert sucrose to starch, caused by a decrease in the activity of at least one of the enzymes involved in this conversion pathway.
Nocturnal Transpiration in Wheat
Authors: Rawson HM , Clarke JM
Published: January 2006

Over the night, stomata of wheat leaves took several hours to reach their most closed position and began to open some hours before dawn. The pattern and amount of night transpiration was changed by current vapour pressure deficit (VPD) but not by VPD or transpiration during the previous day. Mean night transpiration per unit VPD was unchanged by current VPD. Night transpiration of whole plants increased linearly with VPD though genotypes differed significantly in amount. The most profligate genotype transpired at 50 g m-2 leaf h-1 at a VPD of 30 mbar which was twice the rate of the most thrifty genotype.
Attempts were made to estimate the proportion of night transpiration occurring through the stomata and the cuticle by three methods: comparisons of stressed and unstressed leaves, wilting patterns of detached leaves, and transpiration rates of detached leaves in ABA solutions. The methods gave equivalent rankings of the genotypes and similar absolute values for the 'cuticular component', which contributed 13-50% of total night transpiration. We conclude that transpiration could exceed 0.5 mm per night in unstressed crops, though this would be considerably reduced by selection of genotypes with both low cuticular and low stomatal transpiration.
Improved Extraction of Abscisic Acid From Plant Tissue
Authors: Loveys BR , van Dijk HM
Published: January 2006

Methods have been developed for the extraction of abscisic acid (ABA) from plant tissues using water as the extracting solvent. Abnormally high levels of ABA were extracted with water at room temperature from some tissues. This was attributed to enzymic hydrolysis of conjugated forms of ABA. This problem was overcome by briefly boiling the plant tissue in water before homogenisation. Subsequent analysis of ABA was by combined gas chromatography/mass spectrometry using deuterium-labelled ABA as an internal standard but it is suggested that the method may be particularly suited to assay procedures based on immunological techniques where solvent residues may be undesirable.
Salinity Tolerance in the Mangroves Aegiceras corniculatum and Avicennia marina. I. Water Use in Relation to Growth, Carbon Partitioning, and Salt Balance
Authors: Ball MC
Published: January 2006

The water use characteristics of two mangrove species, Aegiceras corniculatum and Avicennia marina, in salinities of 50, 250 and 500 mol m-3 NaCI and leaf-to-air vapour pressure differences of 6, 12 and 24 mbar were studied in relation to growth, carbon partitioning and salt balance. The net water use efficiency in A. corniculatum declined with increasing salinity and decreasing humidity. In contrast, water use was more conservative in A. marina, which maintained the net water use efficiency almost constant with variation in salinity. Aegiceras corniculatum maintained higher rates of water uptake and higher leaf area/plant mass ratios than A. marina. Growth of both species declined with increasing salinity, with A. corniculatum being the more sensitive species. Differences in growth rates between species and between treatments were consistent with differences in the assimilation rate and leaf areal plant mass ratio. Salt exclusion by both species increased from 90 to 97% with increase in salinity from 50 to 500 mol m-3 NaCl. The xylem Cl- concentrations increased with increase in salinity, but decreased with increase in shoot evaporation rates such that the salt flux to the leaves did not increase with increase in evaporation rates at a given salinity. Despite similarities in the salt fluxes to leaves, the transport of Cl- to the shoot per unit of shoot growth increased more with increasing salinity in A. corniculatum than in A. marina because the net water use efficiencies were lower in the former species. Thus, the amount of salt secreted per mole water transpired (and hence also per mole carbon gained) increased more with increasing salinity in A. corniculatum than in A. marina. These differences in salt balance may be associated with the greater sensitivity of A. corniculaturn to increasing salinity. The possible ecological significance of these findings is discussed.
The Xylem Sap of Maize Roots: Its Collection, Composition and Formation
Authors: Canny MJ , Mccully ME
Published: January 2006

Three methods of sampling xylem sap of maize roots were compared: sap bleeding from the stem cut just above the ground; sap bleeding from the cut tops of roots still undisturbed in the ground; and sap aspirated from excavated roots under reduced pressure. The bleeding saps were often unobtainable. When their composition was measured with time from cutting, the concentrations of the major solutes approximately doubled in 2 h. Aspirated sap was chosen as the most reliable sample of root xylem contents. Solute concentrations of the saps showed great variability between individual roots for all solutes, but on average the concentrations found (in �mol g-1 sap) were: total amino acids, 1.8; nitrate, 1.8; sugars (mainly sucrose), 5.4; total organic acids, 18.3. Individual amino acids also varied greatly between roots. Glutamine, aspartic acid and serine were generally most abundant. The principal organic acid found was malic, approximately 8 �mol g-1. From these analyses the ratios of carbon in the fractions (sugars : amino acids : organic acids) = (44 : 6 : 50). 14Carbon pulse fed to a leaf appeared in the root sap within 30 min, rose to a peak at 4-6 h, and declined slowly over a week. During all this time the neutral, cation and anion fractions were sensibly constant in the proportions 86 : 10 : 4. The 14C therefore did not move towards the equilibrium of 12C-compounds in the sap. It is argued that the results do not support a hypothesis of formation of amino carbon from recent assimilate and reduced nitrate in the roots and an export of this to the shoot in the transpiration stream.
Effects of Growing Wheat in Hypoxic Nutrient Solutions and of Subsequent Transfer to Aerated Solutions. I. Growth and Carbohydrate Status of Shoots and Roots
Authors: Barrett-Lennard EG , Leighton PD , Buwalda F , Gibbs J , Armstrong W , Thomson CJ , Greenway H
Published: January 2006

This paper evaluates the effects of hypoxia (imposed by flushing N2 gas through the nutrient solution) on the growth and carbohydrate status of wheat (Triticum aestivum L.), and the reversibility of these effects once aeration is resumed.
Plants were transferred to hypoxic nutrient solutions (containing 0.003 mol O2 m-3) at the early tillering stage, when they had 3-4 leaves, well developed seminal roots, and a few crown roots. Hypoxia for 10-14 days had little adverse effect on shoot growth, whereas the seminal roots stopped growing, i.e. elongating and increasing in dry weight; in contrast, the crown roots elongated to a maximum of 9 cm and continued to increase in dry weight. Hypoxia increased the porosity of crown roots 2-3-fold compared with those grown under aerated conditions; in contrast, the porosity of seminal roots was unaffected.
Oxygen concentrations in the gas filled pores of hypoxic crown roots (65 mm or longer) were estimated from measurements of radial oxygen loss using cylindrical platinum electrodes. Oxygen concentrations in the root tips were substantially lower than the critical oxygen pressures required for maximum respiration. Further, both oxygen concentrations in root tips and rates of root elongation were higher in shorter than in longer roots.
Plants grown in hypoxic nutrient solutions had substantially higher sugar concentrations in shoots and roots than plants grown in aerated solutions. Sugars were not deficient in hypoxic roots since concentrations over a diurnal cycle remained higher than in aerated roots in both the bulk of the seminal and crown roots, and in the tips of the crown roots. Furthermore, tips of seminal roots had similar sugar concentrations when exposed to either aerated or hypoxic solutions.
Hypoxia presumably killed seminal root apices, since the seminal axes did not resume elongation once aeration was restored. In contrast, crown roots resumed elongation when aeration was resumed. Although seminal root tips were moribund, the bulk of the seminal root was still alive. Following the transfer to aerated solutions, there was a rapid increase in the dry weight of both crown and seminal roots, in the latter case due to the proliferation of laterals.
Organic Cosolutes Increase the Catalytic Efficiency of Phosphoenolpyruvate Carboxylase, From Cynodon Dactylon (L.) Pers., Apparently Through Self-Association of the Enzymic Protein
Authors: Stamatakis K , Gavalas NA , Manetas Y
Published: January 2006

Several organic cosolutes (glycerol, sorbitol, betaine, proline, polyethylene glycol, polyvinylpyrrolidone) increase, to a large extent and in a concentration-dependent manner, the apparent affinity of phosphoenolpyruvate carboxylase for phosphoenolpyruvate, whereas the maximum activity remains unaffected. In absence of cosolutes, a similar response is obtained as the concentration of the enzymic protein in the assay medium is increased. The effect of the organic additives does not depend on the osmotic potential or the viscosity of the medium and it could be best interpreted with the exclusion volume theory. It is inferred that the inclusion of an appropriate cosolute in the assay medium promotes the self-association of the enzymic protein and, therefore, mimics the intracellular situation, where the enzyme is much concentrated. In light of these results, it is suggested that the physiological relevance of past data concerning the non-saturating activity and the regulation of the enzyme in vivo should be reevaluated.
The Kinetics of Reactions in and Near the Cytochrome b/f Complex of Chloroplast Thylakoids. I. Proton Deposition
Authors: Hope AB , Liggins J , Matthews DB
Published: January 2006

The kinetics of proton deposition in the intrathylakoid spaces of pea chloroplasts were measured under a wide range of conditions. With duroquinol added to reduce the plastoquinone pool, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea added to inhibit photosystem II, but no ionophore present, the proton deposition, attributed to plastoquinol oxidation, was biphasic. About half the deposition had an apparent rate constant (k) of 150-200 s-1, the other half about 10 s-1. Valinomycin or nonactin (<0.1 �M) plus potassium ions made the deposition almost monophasic, with k = 140 s-1.
When the state of reduction of the plastoquinone pool was varied by the addition of varied concentrations of duroquinol, in the presence of 1 �M nonactin, k for proton deposition varied from about 20 (0.01 mM duroquinol) up to a maximum of 140 s-1 (0.5 mM duroquinol).
When temperature was varied between 4 and 23°C, with 1 �M nonactin, an Arrhenius plot of ln(k) for proton deposition was linear; the activation enthalpy was 67 kJ mol-1, the entropy of activation, 23 J K-1 mol-1.
The data are analysed in terms of a bimolecular reaction between a varying concentration of plastoquinol and a fixed concentration of oxidised Rieske centre. The results are consistent with a rate constant, for the first electron donation by plastoquinol, of 28 s-1 (the rate-limiting step), followed by a relatively fast second electron donation to cytochrome b563 (low potential), followed by deposition of two protons. The speed of the second proton deposition is dependent on the membrane potential difference.
NaCl Alters Contents of Nucleic Acids, Protein, Polyamines and the Activity of Agmatine Deiminase During Germination and Seedling Growth of Rice (Oryza sativa L.)
Authors: Prakash L , Dutt M , Prathapasenan G
Published: January 2006

The decrease in growth of rice caused by NaCl salinity is accompanied by a decrease in the contents of DNA, RNA and protein in the embryo axis. As was in the case of seedling growth the levels of polyamines (putrescine, spermidine and spermine) and the activity of agmatine deiminase (EC 3.5.3.12), an enzyme involved in the biosynthesis of polyamines, in endosperm and embryo axis also were markedly lowered by salt. These biochemical changes induced by NaCl are discussed with respect to growth and development of rice seedlings.
Heritability and Genotype × Environment Interactions of Carbon Isotope Discrimination and Transpiration Efficiency in Peanut (Arachis hypogaea L.)
Authors: Hubick KT , Shorter R , Farquhar GD
Published: January 2006

The discrimination, Δ, against 13C in carbon accumulation by different genotypes of peanut was investigated by looking at changes in composition of isotopes of CO2 during CO2 assimilation and at the 13C/12C ratio in dry matter. The short term (minutes) discrimination, which was measured as CO2 passed over leaves in a gas exchange cuvette, was positively related to pi/pa, the ratio of the pressure of CO2 inside the leaves to the pressure of CO2 around the leaves, which is independently related to transpiration efficiency, W. Heritability of Δ was studied in plants grown in pots and in the field. Crosses were made of cultivars with contrasting Δ and W. For these genotypes, small Δ (and large W) seemed to be dominant in the F1 progeny. Severe drought stress slightly decreased Δ and W in F2 plants but, for parental genotypes in another experiment, Δ decreased but W increased when they were less severely stressed. A strong negative phenotypic correlation (r = -0.78) was found between W (g DM/ kg water used) and Δ in the leaves of well-watered potted plants of F2 progeny from a cross between two cultivars with contrasting W and Δ. Transpiration efficiency varied significantly among cultivars of peanut irrespective of whether plants were drought-stressed or well-watered. Transpiration efficiency in the potted F2 plants had a heritability of 34% while Δ had a heritability of 53%. The broad sense heritability of Δ in fieid-grown cultivars was 81% and there was no significant genotype × environment interaction for Δ. The high heritability of Δ and its strong genetic correlation with W indicates that Δ is a suitable selection criterion for W in peanut breeding programs.
Cell Walls in Plant-Microorganism Associations
Authors: Stone BA
Published: January 2006

In this review the surface structures of plants and microorganisms are briefly compared, the role of plant walls in recognition and communication events in pathogenesis and the changes occurring in walls as part of the plant's defence mechanisms are considered. Pathogenesis-related proteins with hydrolytic action on pathogen walls and the callose response are briefly discussed. Finally, wall-related phenomena in non-pathogenic associations between plants and microbial symbionts, exemplified by Rhizobium-root hair and mycorrhizal fungus-root associations are described.
Lectin and Antibody Labelling of Surface Components of Spores of Phytophthora cinnamomi
Authors: Hardham AR
Published: January 2006

Molecules on the surface of zoospores and cysts of soilborne fungi such as Phytophthora cinnamomi are important mediators in the early stages of infection of host plants. Surface components of P. cinnamomi cells have been analysed ultrastructurally and at the molecular level using lectins and monoclonal antibodies, with a view to localising and characterising molecules involved in the infection process.
Staining with ruthenium red and the lectin, concanavalin A, indicates the presence of a glycocalyx over the surface of the zoospores. Localised antibody binding also reveals that the zoospore surface is subdivided into at least three distinct molecular domains.
During encystment, the spectrum of molecules on the cell surface changes dramatically with the secretion of material which is rich in N-acetyl-D-galactosamine and which bonds the cells to any adjacent structure. lmmunolabelling shows that this material is stored in small peripheral vesicles and is secreted 1-3 min after encystment is induced. Encystment can be triggered by the binding of a monoclonal antibody to the flagella, suggesting that specific receptors may be localised there.
Surface components on the fungal cells display a variety of taxonomic specificities including those for species and genus. Monoclonal antibodies which bind to these components promise to be valuable tools for diagnostic use.
The Host-Haustorium Interface in Powdery Mildews
Authors: Manners JM
Published: January 2006

The powdery mildew fungi have proven to be a useful model system for studies of the host-parasite interface in biotrophic parasitism. Investigation of the interface has requrred the development of novel experimental approaches, for example the isolation of populations of haustoria in association with other interface components and the chemical and physical manipulation of living isolated epidermal strips infected wth powdery mildew fungi. These experimental approaches have provided information on the nature of metabolites transferred from host to pathogen at the interface and on the underlymg mechanisms. Studies of incompatible interactions with powdery mildew fungi have indicated that the establishment of a functional host-haustorial interface is critical for successful infection. In future, the application of recombinant DNA and monoclonal antibody technologies to the host-haustorium interface of powdery mildews should lead to a more detailed molecular analysis of the interface, and thus provide new insights into its structure and function.
A Reassessment of Polyphosphate Granule Composition in the Ectomycorrhizal Fungus Pisolithus tinctorius
Authors: Orlovich DA , Ashford AE , Cox GC
Published: January 2006

Comparison of the elemental composition of freeze-substituted and conventionally fixed phosphorus-containing granules of the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch, using energy dispersive X-ray microanalysis, shows that the cation composition is altered appreciably by the method of specimen preparation. Following conventional chemical fixation, the major cation detected in the granules together with phosphorus was calcium, while freeze-substituted granules most frequently contained phosphorus, potassium and sodium. We conclude that chemical fixation causes serious loss or redistribution of ions. The occurrence of monovalent cations in polyphosphate granules has not previously been demonstrated for mycorrhizal fungi and their presence should be considered in determining the role of the granules in mycorrhizas.
Ericoid Mycorrhizas of Styphelieae: Intensity of Infection and Nutrition of the Symbionts
Authors: Reed ML
Published: January 2006

Soil and leaf total nitrogen and intensity of ericoid mycorrhizal infection were measured in Leucopogon juniperinus R.Br. growing under forest in four different soils. Leaf nitrogen varied from 1.1 to 1.9%, which was correlated with soil nitrogen (0.17-0.32%) but was not related to intensity of infection. Maximal infection occurred in March and the cold months. Five vegetative types of endophytes were isolated from roots of L. juniperinus. Three produced ericoid mycorrhizas in pot cultures of Vaccinium. A fungus isolated from a decaying endocarp of Styphelia tubiflora Sm. produced an infection in Vaccinium which was similar to ericoid mycorrhizas.
Photoinhibition of Photosynthesis and Its Recovery in Two Maize Hybrids Varying in Low Temperature Tolerance
Authors: Greer DH , Hardacre AK
Published: January 2006

Photoinhibition of photosynthesis was induced in intact leaves of two maize hybrids that differed in low temperature tolerance by exposing the leaves to a photon irradiance (PI) of 1500 �mol m-2s-1 at temperatures of 10, 15 and 20°C. Hybrid A665 × H99 (CBD) is adapted to the U.S.A. Corn Belt and is intolerant of cool conditions, while NZlA × 5-113 (CT) is of high-altitude tropical origin and tolerant of low temperatures. Each hybrid was grown at two temperature regimes of 22/18 and 16/14°C at a PI of 700 �mol m-2s-1. Recovery from photoinhibition was followed at the same temperatures and at a PI of 20�mol m-2s-1. In either case the time-courses of photoinhibition and recovery were monitored by measuring chlorophyll fluorescence at 692 nm and 77K and the photon yield of photosynthetic O2 evolution.
Chronic photoinhibition resulting from growth at the moderate PI and at 16/ 14°C was apparent in both hybrids but was more severe in the CBD hybrid. Additional photoinhibition, induced by subsequent exposure to high light, was highly temperature-dependent with increasing severity at lower temperatures. The CT hybrid was more susceptible to this photoinhibition but photoinhibition in the CBD hybrid was more temperature-dependent than in the CT hybrid. Susceptibility to photoinhibition was, therefore, not apparently related to the degree of low temperature tolerance in these maize hybrids.
Induced photoinhibition was readily reversible though recovery was temperature-dependent with the most recovery at the higher temperature. Recovery in these hybrids was not impeded by temperatures as low as 10°C as it is in other species and there was no difference between the hybrids in their ability to recover. However, differences in chronic rather than induced photoinhibition conformed to a greater extent with the ability of these maize hybrids to tolerate low temperature.
Submergence of Rice. II. Adverse Effects of Low CO2 Concentrations
Authors: Setter TL , Greenway H , Kupkanchanakul T
Published: January 2006

Submergence of rice in water at low CO2 concentrations was studied in phytotron experiments using plants in the 3rd to 4th leaf stage. Cultivars known to differ in tolerance to complete submergence were adversely affected by the same mechanisms but to a different degree. Submergence for 4-12 days either reduced dry weight production of the whole plant by 6 to 10 fold or even resulted in a loss of dry weight. Nevertheless, the emerging leaf elongated, and both ethanol insoluble material and protein content increased with time. These increases were associated with translocation of dry matter and nitrogen from expanded to expanding leaves.
Submergence also reduced concentrations of soluble sugars and starch in all plant parts by 4 to 12 fold. In contrast, concentrations of potassium and free amino acids in shoots were either the same or, in the case of the emerging leaf, higher than in plants which were not submerged. These results indicate (i) these solutes were not limiting growth and (ii) the tissues retained their semipermeability to these solutes during submergence.
Insufficient capacity of root metabolism in submerged plants was indicated by low rates of respiration, which persisted in the presence of glucose, and by a low ability to consume ethanol.
A model is presented on the adverse effects of submergence of rice which considers possible interactions between CO2, low O2 and high ethylene concentrations.
Maximising Photosynthetic Activity and Cell Integrity in Isolated Bundle Sheath Cell Strands From C4 Species
Authors: Agostino A , Furbank RT , Hatch MD
Published: January 2006

Bundle sheath cells prepared from C4 leaves have a variety of experimental applications because of their high permeability to metabolites. We determined the factors affecting the physical and metabolic integrity of Panicum miliaceum bundle sheath cell strands immediately following isolation and during subsequent storage. Cell integrity was monitored by determining chloroplast intactness (as ferricyanidedependent O2 evolution) and photosynthetic activity (usually as HCO3-, 3-phosphoglycerate- or C4 acid-dependent O2 evolution). In freshly isolated cell preparations, at least 85-90% of the chloroplasts were apparently intact and there was no significant decline in this value during storage for up to 5 h. With the best extraction conditions, light-dependent O2 evolution in response to adding HCO3- or C4 acids ranged between 3 and 6 �mol min-1 mg-1 chlorophyll. Preillumination of leaves was critical for good isolated cell photosynthetic activity and the activity due to C4 acids in particular was increased substantially by including EDTA. During storage for up to 5 h at 0°C as much as 80% of the capacity for HCO3-- or C4 acid-dependent O2 evolution was lost; this loss was very largely prevented by storing the cells with EDTA. Large kinetic lags (induction phase) also developed during storage of cells. Both the loss of photosynthetic activity and the kinetic lags were reduced or eliminated by including photosynthetic intermediates such as dihydroxyacetone phosphate or ribose 5-phosphate in the storage medium. Under the best conditions, bundle sheath cell preparations could be stored for at least 3 h with little apparent change in cell integrity or metabolic capacity.
Leaf Gas Exchange and Water Relations of Lupins and Wheat. III. Abscisic Acid and Drought-Induced Stomatal Closure
Authors: Henson IE , Jensen CR , Turner NC
Published: January 2006

Changes in the content of endogenous abscisic acid (ABA) were followed in glasshouse experiments during stomatal closure induced by drought in leaves of lupin (Lupinus cosentinii Guss. cv. Eregulla) and wheat (Triticum aestivum L. cvv. Gamenya and Warigal), species which differ in stomatal sensitivity to changes in leaf water potential. Increases in bulk leaf ABA concentration were closely correlated with decreases in leaf conductance in both species. In lupin, substantial increases in ABA and decreases in conductance occurred over a very narrow range of leaf water potential. ABA concentrations in wheat leaves were highly negatively correlated with bulk leaf turgor, but there was no significant relationship between ABA and turgor in lupin. However, ABA accumulated progressively in the leaves of both species as soil water content decreased.
Stomatal closure in lupin could be induced by supplying exogenous ABA to detached leaves via the transpiration stream at concentrations of 10-4 to 10-2 mol m-3 of (+)-ABA. Abaxial stomata closed more readily than those on the adaxial surface in response to both drought and applied ABA. Stomatal response to ABA was not affected by the presence of the cytokinin zeatin, and zeatin by itself had no effect on conductance. When treatments designed to reduce endogenous cytokinin concentrations were imposed (prolonged leaf detachment or prior drought), stomatal response to low concentrations of ABA was enhanced. However, such treatments did not significantly change the stomatal response to high ABA concentrations, nor affect the stomatal conductance of leaves supplied with water alone. It is concluded that drought-induced stomatal closure could be mediated by ABA in both wheat and lupin, despite the initially small change in leaf water status in the latter species.
Evidence Does Not Support Ethylene as a Cue for Synthesis of Alcohol Dehydrogenase and Pyruvate Decarboxylase During Exposure to Hypoxia
Authors: Morrell S , Greenway H
Published: January 2006

Low O2 concentrations increased the activity of alcohol dehydrogenase (ADH; EC 1.1.1.1) and pyruvate decarboxylase (PDC; EC 4.1.1.1), but exogenously applied ethylene did not reproduce this effect in either maize roots or rice coleoptiles. However, ethylene was clearly exerting its known effects on the maize roots, since it inhibited root extension, and promoted aerenchyma formation. Furthermore, treatment with silver nitrate, an antagonist of ethylene action, failed to inhibit the rise in ADH activity in O2-deficient maize roots. We conclude that ethylene causes morphological adaptations to O2-deficiency, but is not involved in concurrent increases in activities of ADH and PDC. Alternative causes for the increases in enzyme activity are proposed.
Modelling Photosynthesis in Monocultures and Mixtures
Authors: Johnson IR , Parsons AJ , Ludlow MM
Published: January 2006

A comparison is made between two models of canopy photosynthesis for monocultures that differ in their treatment of the variation of the rate of single-leaf photosynthesis in response to the irradiance in which the leaves have grown. Both are shown to be deficient, and a simple modification to one that results in a much improved performance is presented. The theory uses the non-rectangular hyperbola for the rate of single-leaf photosynthesis and incorporates the Monsi-Saeki approach for the light-intercepting characteristics of the canopy. The model is then extended to describe the photosynthesis of mixed canopies, which requires knowledge of the relative position of each leaf-area component within the sward. Analytical expressions can be derived for the case where the leaf-area components are homogeneously distributed relative to each other through the depth of the canopy. This is shown to be a good representation of leaf-area distributions in continuously grazed temperate grass-clover swards as well as frequently cut tropical grass-legume swards, and so is an important special case.
C4 Photosynthesis: Quantum Requirement, C4 and Overcycling and Q-Cycle Involvement
Authors: Furbank RT , Jenkins CLD , Hatch MD
Published: January 2006

The relationship between overcycling of the C4 acid cycle in C4 photosynthesis (due to CO2 leakage) and the quantum yield of photosynthesis is considered. From a comparison of theoretical and measured quantum yields we suggest that the high efficiency of light utilisation by most C4 plants can only be explained by the mandatory involvement of both the Q-cycle and cyclic or pseudocyclic electron transport in the proton partitioning process. The existence of the Q-cycle mechanism may have been a prerequisite for the evolution of the C4 pathway.
Dry Matter Partitioning and Vegetative Growth of Young Peach Trees Under Water Stress
Authors: Steinberg SL , Miller JC , Mcfarland MJ
Published: January 2006

Water stress affected the growth and dry matter partitioning of young peach trees grown in pots in a greenhouse. When the trees were subjected to four watering treatments, 100, 75, 50 and 25% of full water, total dry matter production was reduced with each incremental decrease in applied water. Despite large differences in biomass production, the difference in midday leaf water potential between the wettest and driest treatment was not greater than 0.6 MPa. This was partially attributed to lower leaf conductance in the drier treatments.
A reduction or halting of lateral branching and new leaf production was observed soon after water stress was imposed, and these two factors were the major contributors to differences in tree biomass production. Root production was maintained at similar levels in all but the severest stress treatment. As a result, the root fraction of total biomass increased from 0.4 to 0.6 as the level of stress increased from 75 to 50% of full water.
Currently growing leaves and internodes of the drier treatments reached maturity at a smaller size. In contrast to internode lengthening, leaf area expansion slowed in the final growth phase. This correlated well with leaf unfolding.
The Acquisition and Maintenance of Thermotolerance in Australian Wheats
Authors: Blumenthal C , Bekes F , Wrigley CW , Barlow EWR
Published: January 2006

The exposure of wheat (Triticum aestivum) coleoptiles to a transient high temperature stress results in the synthesis of a group of proteins known as the heat shock proteins (hsps). The appearance of these proteins is associated with a concomitant reduction in normal protein synthesis and has been correlated with the acquisition of thermotolerance (assessed as growth of coleoptiles). Pretreatment with a sublethal heat shock confers protection to a subsequent heat shock that would otherwise have been lethal. In addition, we find that increasing the time interval between the sublethal heat treatment and the subsequent heat shock from 0 to 72 h reduces the protective effect of the sublethal heat treatment considerably. The five cultivars examined (Sunelg, Sunco, Hartog, Vulcan, Halberd) showed differences in the degree of protection acquired, and in the length of time for which protection was maintained. Hartog was found to be the most thermotolerant, and acquired the greatest degree of protection from exposure to a sublethal heat treatment, but the duration of this acquired protection was shorter than in the remaining cultivars. Sunelg was most susceptible to a heat shock but the duration of acquired protection was the greatest.
Turgor Pressure in Mechanically Impeded Lupin Roots
Authors: Atwell BJ , Newsome JC
Published: January 2006

Seedlings of lupin (Lupinus angustifolius cv. 75A-258) were grown in cores of sandy loam which was compacted to bulk densities of 1.6 and 1.8 Mg m-3 . There was a substantial decrease in root elongation rate at the higher bulk density. After 4-7 d, roots were rinsed free of soil and clamped loosely in a Perspex block for measurement of turgor pressure (P) using a pressure probe. Measurements were made at 3-4 positions on each root, each estimation taking 2 min. Turgor pressures in the terminal 15 mm of the axes ranged between 0.213 and 0.530 at 1.6 Mg m-3 and 0.210 and 0.570 MPa at 1.8 Mg m-3; mean P values were 0.365 and 0.351 MPa in roots growing at 1.6 and 1.8 Mg m-3, respectively. These measurements were made on roots removed from the soil; P could have been greater in roots still growing in compact soil.
Anatomical studies showed that the distal boundary of the zone of cell expansion was 2-4 mm nearer the apex in roots growing at 1.8 than at 1.6 Mg m-3. Using this information, we showed that the mean P of expanding tissue was the same in roots of the two treatments. The apparent rise in P near the apex of roots at 1.8 Mg m-3 was not statistically significant.
Primary roots growing against high mechanical impedance had a 34% lower rate of elongation and a 22% greater diameter, resulting in nearly identical rates of volume expansion (35.1 and 34.9 mm3 d-1 at 1.6 and 1.8 Mg m-3 respectively). Furthermore, the rate of O2 uptake was the same in 10 mm root apices from both treatments so that there was no evidence that the carbohydrate requirement for respiration was enhanced by high soil strength. Moreover, while mechanical impedance decreased root elongation, it did not significantly affect our estimate of P. We believe that P in lupin roots changes in response to mechanical impedance only when volume expansion or utilization of solutes are affected.
Degrees of crassulacean acid metabolism in tropical epiphytic and lithophytic ferns
Authors: Holtum Joseph A.M. , Winter Klaus
Published: January 2006

Crassulacean acid metabolism (CAM) was observed in three species of tropical
ferns, the epiphytes Microsorium punctatum and
Polypodium crassifolium and the lithophyte
Platycerium veitchii.
Polypodium crassifolium and
P. veitchii exhibited characteristics of weak CAM.
Although no net nocturnal CO2 uptake was observed, the
presence of CAM was inferred from nocturnal increases in titratable acidity of
4.7 and 4.1 µequiv (g fr wt)–1 respectively,
a reduction in the rates of net CO2 evolution during the
first half of the dark period, and the presence of a CAM-like decrease in net
CO2 uptake during the early light period. In
M. punctatum net CO2 uptake during
the first half of the dark period was accompanied by an increase in titratable
acidity of 39.2 µequiv (g fr wt)–1 and a
pronounced reduction in net CO2 uptake during the early
light period. When water was withheld from
P. crassifolium and M. punctatum,
net CO2 uptake during the light was reduced markedly but
there was no change in the extent or patterns of CO2
exhange in the dark. As a consequence, the proportion of carbon gained due to
CO2 fixation in the dark increased from 2.8 and
10% to 63.5 and 49.3%, respectively (100% being net
CO2 uptake during the light plus the estimated
CO2 uptake during the dark). After 9 days without added
water, dark CO2 uptake was responsible for the
maintenance of a net 24 h carbon gain in
P. crassifolium.
Platycerium veitchii,
P. crassifolium and M. punctatum
exhibited carbon isotope ratios of between –25.9 and –22.6‰
indicating that carbon isotope ratios may not, by themselves, be sufficient
for the identification of weak CAM. We suggest that CAM may be more prevalent
in tropical epiphytic and lithophytic ferns than currently envisaged.
The Effect of Leaf Nitrogen and Temperature on the CO2 Response of Photosynthesis in the C3 Dicot MChenopodium album L
Authors: Sage RF , Sharkey TD , Pearcy RW
Published: January 2006

The CO2 response of photosynthesis was studied in the C3 annual, Chenopodium album L. Both the initial slope of the photosynthetic CO2 response and the CO2 saturated rate of photosynthesis were linearly dependent on organic leaf nitrogen content. As leaf nitrogen increased or leaf temperature declined, the CO2 saturation point of photosynthesis declined. Increasing leaf temperature from 15 to 34°C stimulated the CO2-saturated rate of photosynthesis but had little effect on the initial slope of the photosynthetic CO2 response. According to the photosynthesis model of Sharkey (1985 Bot. Rev. 51: 53-105), these results indicate that as leaf nitrogen increased, the capacity for RuP2 carboxylase and RuP2 regeneration increased to a greater extent than the capacity of starch and sucrose synthesis to regenerate orthophosphate. As a result, in high nitrogen leaves, photosynthesis appeared to be limited by the capacity to regenerate phosphate at lower CO2 partial pressures than in low nitrogen leaves. In high nitrogen leaves, increasing temperature appeared to enhance the phosphate regeneration capacity to a greater extent than the capacity of RuP2 carboxylase. Consequently, while under cool conditions (<20°C), CO2 assimilation in normal atmospheric air appeared to be limited by the phosphate regeneration capacity, under warm conditions (34°C), RuP2 carboxylase capacity appeared to limit CO2 assimilation.
Associations Between Productivity, Root Growth and Carbon Isotope Discrimination in Phaseolus vulgaris Under Water Deficit
Authors: White JW , Castillo JA , Ehleringer J
Published: January 2006

Recent theoretical and empirical studies have indicated that isotopic discrimination against 13C (Δ) during photosynthesis in C3 plants reflects variation in intercellular CO2 concentration (ci). Under water deficit, cultivar differences in Δ may indicate differences in leaf gas exchange characteristics. Cultivar differences in Δ may also result indirectly from genetic variation in root characteristics affecting the level of water stress experienced by the canopy. Differences in root growth affecting the degree of dehydration postponement could prolong gas exchange activity and the maintenance of relatively high ci and Δ.
To evaluate relations between root growth, productivity and Δ in common bean (Phaseolus vulgaris L.), Δ and crop growth parameters, including biomass production, grain yield and root length density, were determined for ten bean genotypes grown under rainfed conditions at two sites in Colombia which differed primarily in soil fertility and effective rooting depth. The 10 genotypes were also grown under irrigation at the more fertile site. Under rainfed conditions, root length density was positively correlated with Δ in the fertile Mollisol at Palmira, and was also positively correlated with Δ in the infertile Oxisol at Quilichao if one possibly abberent genotype was excluded. At Palmira, reduced crop growth and seed yield were associated with low Δ values. At Quilichao, intermediate Δ values were associated with the greatest growth and yield. Under irrigation at Palmira there was no association between growth or yield and Δ.
Effects of Nitrogen Source and Concentration on the Free Amino Acid Composition of Developing Wheat Grains
Authors: Blumenthal C , Lee JW , Barlow EWR , Batey IL
Published: January 2006

Detached wheat heads (7 days post-anthesis) were grown in liquid culture containing nitrogen concentrations of 0.025% or 0.1% in the form of glutamine, ammonium nitrate or asparagine. With each form of the nitrogen, increasing the concentrations of nitrogen in the culture medium led to increases in the total nitrogen and the non-protein nitrogen in the grain. Protein contents (N × 5.7) were approximately 16% and 21% on a dry weight basis in the low and high treatments respectively for all nitrogen sources. Amino acids from the endosperm cavity, the ethanol-soluble extract of the grain, and the grain protein were analysed by HPLC techniques to define the site of transfer between amino acid forms. The results indicated that amino nitrogen from glutamine, ammonium nitrate, or asparagine enters the grain and is found in the endosperm cavity fluid mainly in the form of glutamine, alanine and, to a lesser extent, aspartate (including asparagine). These amino acids are then converted into the various other amino acids required for protein synthesis, as is demonstrated by the increases found in the others in the ethanol-soluble free amino acid fraction with different nitrogen regimes. These variations in the composition of the free amino acids occurred without altering the amino acid composition of the protein component of the grain.