bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Effects of Foliar Nitrogen, Temperature, and Humidity on Gas Exchange in Pinus radiata
Authors: Sheriff DW , Mattay JP
Published: January 2006

Seedlings of Pinus radiata were grown in a glasshouse in large pots with sand as the potting mix. They were kept well-watered and frequently supplied with nutrient solutions which contained different amounts of nitrogen for different treatments. Carbon assimilation and diffusive conductance of the foliage were measured under steady-state conditions at saturating light in all treatments. Experimental variables were leaf-air vapour pressure difference and leaf temperature at time of measurement. Data were fitted to a non-linear regression equation to examine responses of carbon assimilation, diffusive conductance, transpiration, assimilatory nitrogen-use efficiency, and assimilatory transpiration efficiency to foliar nitrogen concentration expressed on a leaf area basis ([N]), to leaf temperature, and to leaf-air vapour pressure (D). Parameters from the regression have been used to plot three-dimensional surfaces, so that simultaneous effects of experimental variables can be easily visualised. Carbon assimilation increased linearly with foliar [N], declined exponentially as D increased, and had a broad temperature optimum between c. 14 and 38�C. Diffusive conductance increased linearly with foliar [N], was related to the reciprocal of D, and declined as temperature increased. Using climatic vapour pressure deficit and air temperature data for Canberra, ACT, and for Mount Gambier, SA, and with the functions that had been fitted to experimental data, it was found that these regional climatic differences have potential for appreciably affecting carbon gain and water loss in the regions, which have P. radiata plantations. Predicted differences in carbon gain are of the order of reported differences in stem growth in the regions. This shows the need to take into account regional variation in climatic variables that strongly affect gas exchange when investigating regional differences in productivity.
The Use of Transgenic Plants to Study the Regulation of Plant Carbohydrate Metabolism
Authors: Stitt M
Published: January 2006

Transgenic plants with decreased expression of specific enzymes provide a powerful new tool to investigate metabolic regulation. Their use is discussed in the context of theories of metabolic regulation. It is argued that an enzyme is a key site for regulation, in the strict sense, when (i) natural mechanisms exist to alter the activity of the enzyme in vivo ('regulatability'), and (ii) a change in the activity of the enzyme is able to lead to a change in flux through the pathway ('regulatory capacity'). Previous approaches to the study of regulation allow the identification of enzymes with high 'regulatability', but they do not provide consistent or valid criteria to assess their 'regulatory capacity'. They therefore do not distinguish between enzymes which actually control metabolic fluxes, and enzymes which just respond to changes initiated elsewhere in the pathway. They may also underestimate the contribution of enzymes that catalyse reversible reactions. In contrast, mutants and transgenic plants can be used to directly test the importance of different aspects of an enzyme's regulatory properties in vivo. Even more importantly, they provide a method to determine flux control coefficients which provide a quantitative measure of an enzyme's 'regulatory capacity'. Recent results are surnrnarised, and potential practical problems in measuring control coefficients are reviewed.
The Biochemistry and Molecular Biology of Starch Synthesis in Cereals
Authors: Morell MK , Rahman S , Abrahams SL , Appels R
Published: January 2006

Starch is a key constituent of plant products finding utility as both a major component of a wide range of staple and processed foods, and as a feedstock for industrial processes. While there has traditionally been a focus on the quantity of starch production, starch quality is of increasing importance to the end-user as consumer demands become more sophisticated and as the range of industrial applications of starch broadens. Determinants of starch quality include the amylose to amylopectin ratio, the distribution of molecular structures within these fractions, and the packaging of the starch in granules. The biochemical processes involved in the transformation of the sucrose delivered to the endosperm cytosol to starch in the amyloplast are understood in broad outline. The importance of particular isoenzymes or processes to the production of starches of specific structures are, however, not well understood. This paper reviews aspects of the physiology, biochemistry and molecular biology of starch in plants, with an emphasis on the synthesis of starch in the cereal endosperm. Progress in understanding the linkages between the molecular events in starch synthesis and developing strategies for the manipulation of starch quantity and quality in cereals are discussed.
Evidence for Anoxic Zones in 2-3 mm Tips of Aerenchymatous Maize Roots Under Low O2 Supply
Authors: Gibbs J , Bruxelle GD , Armstrong W , Greenway H
Published: January 2006

Root elongation and the production of the end-products of anaerobic catabolism, ethanol, alanine and lactate, were measured in intact maize roots and excised tips exposed to a variety of oxygen regimes. Elongation was retarded by 56 and 44% respectively in intact aerenchymatous primary roots of maize incubated in 0.1% stagnant agar, or exposed to 0.06 mol m-3 external O2 in gas-sparged solution. This growth reduction was accompanied by a 3-5-fold increase in alanine as a percentage of total soluble amino acids in the 0-2 mm root tips. The increase in this value was not in response to ethylene or translocation of alanine from other parts of the root. Moreover, in excised tips exposed to 0.06 mol O2 m-3, net production of ethanol, alanine and lactate occurred. Even so, these root tips continued to elongate at 30% of the rate observed in aerated excised root tips. It appears that adaptation of maize to O2 deficiency may involve a combination of aerenchyma formation and tolerance to anoxia. We suggest that metabolic cooperation, in the form of symplastic transport of energy-rich compounds, might exist between cortical cells receiving adequate oxygen supply and cells in anoxic zones.
Allelopathic and Water Conserving Functions of Leaf Epicuticular Exudates in the Mediterranean Shrub Dittrichia viscosa
Authors: Stephanou M , Manetas Y
Published: January 2006

The possible ecophysiological roles of the water soluble, epicuticular material accumulated on the leaves of Dittrichia viscosa (L.) W.Greuter (syn. Inula viscosa (L.) Aiton) (Asteraceae), were investigated in laboratory experiments. It was found that: (a) the material reduced cuticular transpiration; (b) it had a strong absorbance in the ultraviolet, apparently offering the leaves an ultraviolet-B radiation screen; (c) removal of this material, however, and exposure of the leaves to visible light supplemented with ultraviolet-B radiation had no effects on photosystem II photochemical efficiency or stomatal functions and caused no epidermal browning; and (d) the material was strongly inhibitory against germination of lettuce seeds and caused considerable decrease in the radicle length of Phlomis fruticosa L., a species often occupying the same habitat as D. viscosa. We infer from the above that D. viscosa leaves may be resistant to ultraviolet-B radiation damage and, accordingly, the water conservation and allelopathic functions of the epicuticular material may predominate over its potential to protect against ultraviolet-B radiation.
Short-term Photosynthetic Responses of the C3-CAM Epiphyte Guzmania monostachia var. monostachia to Tropical Seasonal Transitions Under Field Conditions
Authors: Maxwell C , Griffiths H , Borland AM , Young AJ , Broadmeadow MSJ , Fordham MC
Published: January 2006

A study was undertaken to investigate the rapid adaptation of photosynthesis which accompanies the tropical seasonal transition for the C3-CAM epiphyte Guzmania monostachia (L.) Rusby ex Mez var. monostachia. In the rainy season, exposed and semi-exposed plants exhibit C3 photosynthesis, together with sustained reductions in FvFm, dependent on incident light levels. At the onset of the dry season, an efficient photoprotective unit is induced within 5 days. CAM activity augments CO2 supply and maintains sinks for electron transport. Strongly expressed photoinhibition is associated with very high levels of zeaxanthin formation. As incident light increases, total chlorophyll will decrease by around 50% in 5 days. These photoprotective functions are reversible over the same period at the start of the rainy season. The integrated response maximises productivity in the favourable rainy season and maintains photosynthetic integrity through the short adverse dry season. Such a strategy optimises carbon gain for these slow growing plants where longevity is critical for survival in the resource limited, epiphytic niche.
The Major Proteins of Wheat Endosperm Starch Granules
Authors: Rahman S , Kosar-Hashemi B , Samuel MS , Hill A , Abbott DC , Skerritt JH , Preiss J , Appels R , Morell MK
Published: January 2006

Wheat starch contains two classes of associated proteins: proteins which are embedded within the granule and loosely associated surface proteins. The characterisation of the major proteins that are embedded in the granule are described. Gel electrophoresis on the basis of size resolved these proteins into five bands of molecular weights 60, 75, 85, 100 and 105 kDa. These polypeptides were demonstrated to be within the granule by their resistance to proteinase K digestion when granules were ungelatinised. The N-terminal sequences of these polypeptides are reported. The most prominent polypeptide is the 60 kDa granule-bound starch synthase. The N-terminal sequence obtained from the 75 kDa polypeptide shows homology to rice soluble starch synthase. The 85 kDa band was resolved into at least two types of polypeptides, one of which reacted with polyclonal antiserum to the maize branching enzyme IIb. The 100 and 105 kDa polypeptides were located only in the granule and are related, on the basis of N-terminal sequence similarity and cross-reactivity to monoclonal antibodies. SDS-PAGE and monoclonal antibody cross-reactivity experiments suggest that the 100 and 105 kDa polypeptides are absent from starch granules from all other species examined, including other cereals. It is speculated that all the major granule proteins are involved in starch biosynthesis.
Evidence That Glutamate Dehydrogenase Plays a Role in the Oxidative Deamination of Glutamate in Seedlings of Zea mays
Authors: Stewart GR , Shatilov VR , Turnbull MH , Robinson SA , Goodall R
Published: January 2006

In order to investigate the role of glutamate dehydrogenase we have compared the metabolism of [15N]glutamate in young seedlings of wild-type and a glutamate dehydrogenase-null mutant of Zea mays. The principal labelled products in roots of wild-type seedlings are the amide nitrogen of glutamine, glutamine-amino nitrogen and ammonium. The incorporation of label into glutamine-amide is markedly inhibited by methionine sulfoximine. In contrast, little or no labelling of glutamine-amide or ammonium occurs in roots of the GDH1-null mutant, the major labelled product is the amino group of asparagine. In shoots of the wild type, 15N is recovered in the amide of glutamine, ammonium, the amino group of asparagine and other amino acids. In mutant shoots, over 75% of the label is recovered in the asparagine-amino group and there is little labelling of glutamine-amide or ammonium. These major differences in glutamate metabolism of wild-type and mutant seedlings are consistent with glutamate dehydrogenase functioning in the direction of oxidative deamination and having a role in protein catabolism of germinating seeds.
Breeding for Salinity Resistance in Crop Plants: Where Next?
Authors: Flowers TJ , Yeo AR
Published: January 2006

Soil salinity is widely reported to be a major agricultural problem, particularly in irrigated agriculture, and research on salinity in plants has produced a vast literature. However, there are only a handful of instances where cultivars have been developed which are resistant to saline soils. Reasons for the lack of success in developing salt-resistant genotypes, and for the low impact that plant physiological research has made, are explored. We conclude that soil salinity has not yet become a sufficient agricultural problem, other than on a local scale, to make salt resistance a high priority objective for plant breeders. The limited success of simple selection, where this has been practised in breeding programs, can be accounted for by the fact that research has consistently shown salt resistance is a complex character controlled by a number of genes or groups of genes and involves a number of component traits which are likely to be quantitative in nature. We also conclude that the results of physiological research have been poorly marketed by physiologists and, understandably, have failed to impress plant breeders. We anticipate that the importance of salinity as a breeding objective will increase in the future. Our assessment of reports of the degradation of irrigation systems, together with projections of the future demands of irrigated agriculture, is that enhancing the salt resistance of at least some crops will be necessary. Salinity resistance will both help provide stability of yield in subsistence agriculture and, through moderating inputs, help limit salinisation in irrigation systems with inadequate drainage. It is emphasised that plant improvement and drainage engineering should be seen as partners and not alternatives. We conclude with a personal view of one way forward for developing salt-resistant genotypes, through the pyramiding of physiological characters.
On the Relationship Between Electron Transport Rate and Photosynthesis in Leaves of the C4 Plant Sorghum bicolor Exposed to Water Stress, Temperature Changes and Carbon Metabolism Inhibition
Authors: Loreto F , Tricoli D , Marco GD
Published: January 2006

We examined the effect of carbon metabolism inhibition, temperature, and water stress on the relationship between the linear electron transport and photosynthetic CO2 assimilation in sweet sorghum, Sorghum bicolor (L.) Moench. Carbon metabolism was inhibited either by removing CO2 from the air or by feeding glyceraldehyde to the leaves. Irrespective of the method used, the linear electron transport and photosynthesis were coordinately inhibited. However, when photosynthesis was totally inhibited, a residual electron transport between 20 and 35 μmol m-2 s-1 could be measured. The residual electron transport increased with increasing leaf temperature up to 38�C and was higher in water-stressed leaves than in control leaves. Temperature affected photosynthesis in intact leaves. The optimal temperature for photosynthesis in control leaves was between 30 and 35�C. The ratio between linear electron transport and photosynthesis showed a temperature dependency similar to that of photosynthesis. As a consequence, the electrons required to fix one mole of CO2 were 5.5 at suboptimal temperatures but were 6.5 at 30�C. Our results indicate that the relationship between linear electron transport and photosynthesis is not perfectly steady in nature but is subject to transient changes. The observed changes in the linear electron transport were mostly related to changes in the efficiency of light trapping by open photosystem II (PSII) reaction centres, while the fractions of open PSII reaction centres were relatively constant during the experiment. Water stress severely reduced the photosynthetic CO2 assimilation of sweet sorghum leaves. The greater the water stress, the lower the temperature at which optimal photosynthesis was reached. The linear electron transport was coordinately inhibited by water stress but a residual electron transport was again found when photosynthesis was extremely reduced by water stress. Under water-stress conditions the fraction of PSII reaction centres in an open state was very low but constant, and the temperature dependent reduction of linear electron transport was caused by the reduction of the efficiency of energy capture of PSII reaction centres.
The Presence of Ubiquitin-Protein Conjugates in Plant Chloroplast Lysates Is Due to Cytosolic Contamination
Authors: Ramos PCR , Cordeiro ACF , Ferreira RMB , Ricardo CPP , Teixeira ARN
Published: January 2006

Chloroplasts were isolated by Percoll density gradient centrifugation from Lemna minor and Spinacia oleracea grown under normal conditions or from L. minor subjected to sulfur starvation, a condition that induces a dramatic increase in the rates of proteolysis, namely in the degradation of the chloroplast enzyme ribulosebisphosphate carboxylase. The presence of free ubiquitin or ubiquitin-protein conjugates was not immunologically detected in the purified chloroplast extracts under either of these conditions. Moreover, no ATP-dependent conjugation of 125I-labelled ubiquitin to endogenous proteins was detected in L. minor chloroplast lysates. Our results support the view that plant chloroplasts do not possess free ubiquitin or ubiquitin conjugating activity. Furthermore, treatment of the mechanically isolated chloroplasts with thermolysin suggests that the presence of ubiquitin-protein conjugates in some chloroplast preparations is due to cytosolic contamination.
Rates and Cardinal Temperatures for Processes of Development in Wheat: Effects of Temperature and Thermal Amplitude
Authors: Slafer GA , Rawson HM
Published: January 2006

This paper addresses three issues relating to development in wheat. Whether thermal amplitude changes rates of leaf appearance and phenological development, whether the responses of leaf appearance to a wide range of temperature can be acceptably described in terms of rates and cardinal (base and optimum) temperatures, and whether similar rates and cardinal temperatures can be applied to parallel processes of development. The two studies used a total of 22 naturally-lit growth chambers and 44 treatments, and the disparate wheat cultivars Sunset, Condor, Rosella and Cappelle Desprez. All plants were vemalised and then grown under photoperiods extended to 18 h. In the first study, thermal amplitudes varying between 0 and 14�C around a common mean of 19�C did not change rates of leaf appearance and had no consistent effect on phenological development at any stage to anthesis. Consequently, conclusions from data collected under one amplitude at this mean temperature can be extrapolated with confidence to another. In the second study, with six mean temperature regimes of 10-25�C, rate of leaf appearance was significantly increased progressively by increasing temperature up to 19�C. All cultivars had an optimum temperature for this process which approximated 22�C but they differed in their base temperatures which ranged from -5.7 to -1.9�C. Optimum and base values for the concurrent phase of phenological development ranged between similar extremes, but the rankings of base values amongst genotypes differed markedly for leaf appearance and phenology. For the process of culm extension, temperature significantly, but not linearly, affected final length but not internode number. Length was unchanged by temperatures between 10 and 16�C but was significantly reduced above 19�C. Cultivars differed in their respective optimum and base temperatures for rate of elongation, ranging from ca 19 to 21�C and from 2 to 5�C. The concurrent phenological process had a higher optimum of 22-25�C but again a similar range in base temperature with differing cultivar rankings. We conclude from the second study that cardinal temperatures for leaf appearance, culm elongation and phenology were different, and for each process there were cultivar differences.
Acclimation of Photosynthesis and Growth by Cotton to Elevated CO2: Interactions With Severe Phosphate Deficiency and Restricted Rooting Volume
Authors: Barrett DJ , Gifford RM
Published: January 2006

Acclimation of photosynthesis and growth at three CO2 concentrations (376, 652 and 935 μmol mol-1) was examined in cotton grown under three growth-limiting phosphate (P) supplies (2.1, 6.1 and 18.2 mg P plant-1) and where biomass allocation between roots and shoots was altered by pots of three different sizes (0.32 × 10-3, 0.72 × 10-3 and 1.56 × 10-3 m3 pot-1). Phosphate supplies were chosen such that carbon gain at ambient CO2 increased linearly with P supply. Relative growth rates of these plants were 5-10-times less and photosynthetic rates 3-16-times less than for cotton supplied with abundant nutrients. Pot sizes were chosen so that root biomass and root:shoot ratios decreased with a decrease in rooting volume. Maximum carboxylation rates per unit leaf area (Vcmax) were lower in leaves grown at two elevated CO2 concentrations, compared with ambient CO2 concentrations, under all P and pot size treatments indicating that acclimation of photosynthesis had occurred. The degree of photosynthetic acclimation to elevated CO2 was not related to the degree by which whole plant carbon gain was stimulated by elevated CO2 concentration at the different P supplies, or to the degree by which allocation to root and shoots was altered by pot size. Thus there is no simple relationship between photosynthetic and growth acclimation by cotton to elevated CO2. At ambient CO2, the maximum carboxylation rate increased linearly with an increase in leaf P per unit area (mg P m-2), but rates were lower at elevated CO2 for a given P content m-2. Vcmax also increased linearly with an increase in leaf P concentration (mg P g-1 structural dry weight). However, values of Vcmax were similar for plants grown at ambient and elevated CO2, for a given P concentration. Acclimation of photosynthesis at elevated CO2 was associated with an increase in leaf starch determined 5 h into the light period. However, increased starch concentration with an increase in P supply was not associated with any decline in Vcmax.
Regulation of Phosphoenolpyruvate Carboxylase in Zea mays by Protein Phosphorylation and Metabolites and Their Roles in Photosynthesis
Authors: Gao Y , Woo KC
Published: January 2006

The effects of metabolites, protein phosphorylation and malate inhibition on phosphoenolpyruvate carboxylase (PEPC) activity were investigated at pH 7.0 in partially purified enzyme from maize leaves. Glycine, glucose 6-phosphate or alanine stimulated the activity two- to three-fold. Glycine and glucose 6-phosphate increased the affinity for PEP by factors of eight and four respectively. These metabolites changed the response of the enzyme activity to pH. Activity increased between pH 6.8 and 8.0 by 10-fold in the absence and 26% in the presence of these metabolites. In vitro phosphorylation of PEPC increased the activity two-fold in the absence but not in the presence of these metabolites. Malate was a strong inhibitor of PEPC, the KI value being 0.25-0.5 mM. Protein phosphorylation and the above metabolites increased the Ki value by factors of three and 12 respectively, but they synergistically increased the Ki 50-fold, thus providing maximal protection against malate inhibition. In the crude extracts from light- and dark-adapted leaves in the presence of a physiological concentration of malate (20 mM), PEPC activity comparable to the photosynthetic rate was obtained only from the light-adapted leaves in the presence of metabolites indicating that both light-induced protein phosphorylation and metabolic activators were essential for PEPC activation during photosynthesis. We propose that both these factors act synergistically to modulate PEPC during photosynthesis in maize.
Water Use and Growth of Cotton in Response to Elevated CO2 in Wet and Drying Soil
Authors: Samarakoon AB , Gifford RM
Published: January 2006

Cotton (Gossypium hirsutum cv. Sicala 34) was grown at 352 ('low CO2') or 710 ('high CO2') μL L-1 atmospheric CO2 in continuously wet soil, or in drying soil, or in drying soil re-wetted after plant wilting. In wet soil, the approximately 15% reduction in transpiration per unit leaf area owing to high CO2 was only half that for other species, whereas effects on growth and leaf area were relatively larger. Consequently, water use per plant was 45-50% higher for high CO2 plants in contrast to other species for which the rate of water use is either the same or lower in high CO2. Greater plant water use early in a drying cycle caused the soil to dry faster under high CO2 than under low CO2. The addition of the consequential greater water stress at high CO2 in drying soil to the direct CO2 effect on stomata caused the transpiration rate of high CO2 plants to fall by up to 60% as the soil dried relative to plants drying at low CO2. After re-wetting the dry soil, the reduction in transpiration rate at high CO2 returned within hours to the value of 15% seen in wet soil. The results were inconsistent with the idea that water deficits increase the sensitivity of stomatal aperture to CO2. Other consequences of drier soil under high CO2 compared with low CO2 were: (a) unlike in many other species, in cotton, the relative growth enhancement by high CO2 is not higher under drying soil compared with wet soil owing to the opposite effect on soil water content; and (b) the increased water-use efficiency in drying soil relative to wet soil was greater in high CO2 plants than in low CO2. The confounding of indirect effects of soil water with the direct CO2 effects may explain the wide variability of literature reports about CO2 effects on stomatal conductance and water use.
Evidence for Polygenic Control of Fibre Differentiation in Spring Wheat and Its Relationship With the Gibberellin-Insensitivity Locus Rht1
Authors: Lev-Yadun S , Beharav A , Abbo S
Published: January 2006

The relationship between culm anatomy and the rht (reduced height) system of wheat was studied in rhtl (GA-sensitive, tall) and Rhtl (GA-insensitive, semidwarf) spring wheat F11 isolines. The experimental design allowed to distinguish between the effect of the major height-controlling gene (rhtl) and that of the genetic (polygenes) background. Counting the number of fibre cell files in the cortex of the first internode at heading time, we found no structural differences between the tall (rhtl) and the semidwarf (Rhtl) isolines. It appears that stem elongation and the determination of cell fate to fibres are regulated by two different mechanisms. However, a significant polygenic effect on the number of fibre cell files in the culm cortex was found. These data are consistent with the hypothesis that wheat lodging is not affected by the culm structure but mainly by root characteristics such as anchorage.
Genotypic Variation in Relative Growth Rate and Carbon Isotope Discrimination in Sunflower Is Related to Photosynthetic Capacity
Authors: Virgona JM , Farquhar DG
Published: January 2006

A previous study showed that carbon isotope discrimination (Δ) was negatively related to transpiration efficiency (W, the ratio of dry matter accumulation to transpiration) and biomass accumulation amongst sunflower (Helianthus annuus L.) genotypes. Three experiments which explore the physiological basis of relationships between Δ, relative growth rate (RGR) and leaf gas exchange characteristics are reported. Growth was analysed on seven genotypes during the early vegetative stage (up to 31 days after emergence). Carbon isotope discrimination, Δ, W, and photosynthetic CO2 assimilation rate per unit leaf area (A) at ambient concentration of CO2 were measured on plants that made up the final harvest. Six of the seven genotypes were also grown under a low nitrogen (N) regime and harvested at 30 days after emergence. Carbon isotope discrimination was negatively related to relative growth rate (RGR), net assimilation rate (NAR) and photosynthetic rate per unit area, which in turn, were all positively correlated with each other. Genotypic variation inA (51%) was greater than that in leaf conductance, g (32%) and there was no relationship between g and Δ. Under the low N regime, A and g declined by 33 and 12%, respectively, across all genotypes producing a significant rise in A of 1.10. In a second experiment, growth analysis on 13 cultivated forms of H. annuus, a wild accession and a H. argophyllus accession, also showed that there was a positive relationship between RGR and NAR, and that both growth indices were negatively related to Δ. In a further experiment, using 14 genotypes (including the wild accession) there was a highly significant negative correlation (r = -0.85, P < 0.001) between photosynthetic capacity, measured using an oxygen electrode, and Δ. These results indicate that variation in photosynthetic capacity can account for genotypic variation in both Δ and RGR during vegetative growth in sunflower. Hence, faster growing sunflower genotypes have higher rates of photosynthesis and use water more efficiently.
Sink Strength May Be the Key to Growth and Nitrogen Responses in N-Deficient Wheat at Elevated CO2
Authors: Rogers GS , Milham PJ , Gillings M , Conroy JP
Published: January 2006

The influence of elevated CO2 (350, 550 and 900 μL L-1) and N supplies ranging from deficient to excess (0-133 mg N kg-1 soil week-1) on the leaf N concentration and shoot growth of wheat (Triticum aestivum L.), cultivar Hartog, was investigated. Shoot growth was 30 % greater at 550 μL L-1 compared to ambient CO2 at all levels of N supply. When the CO2 concentration was increased to 900 μL L-1, there was no increase in shoot growth at low N supply but it more than doubled at high N supply (67 mg N kg-1 soil week-1). Growth effects were closely matched by changes in sink development, suggesting that sink strength, mediated through N supply controlled the shoot growth response to elevated CO2. The shoot N concentration was lower at each level of CO2 enrichment and the greatest effect (30% reduction) occurred at 900 μL CO2 L-1, 33 mg N kg-1 soil week-1. The effect of high CO2 on shoot N concentration diminished as N supply increased and, at the highest N addition rate, there was only a 7% reduction. Changes in foliar N concentration due to CO2 enrichment were closely correlated with lower soluble protein concentration, accounting for 58 % of the total leaf N reduction. Ribulose- IS-bisphosphate carboxylase/oxygenase (Rubisco) levels were also reduced at high CO2 and N was allocated away from Rubisco and into other soluble proteins at high CO2 when N supply was low. Non- structural carbohydrate concentration (dry weight basis) was greatest at 900 μL CO2 L-1 and low N supply and may have reduced Rubisco concentration via a feed-back response. Critical foliar N concentrations (N concentration at 90 % of maximum shoot growth) were reduced from 43 mg g-1 at ambient CO2 to 39 and 38 mg g-1 at 550 and 900 μL CO2 L-1, respectively. Elevated CO2, at N supplies of 0-17 mg N kg-1 soil week-1, reduced flour protein concentration by 9-13 %.
Correlations Between Carbon Isotope Discrimination and Climate of Native Habitats for Diverse Eucalypt Taxa Growing in a Common Garden
Authors: Anderson JE , Williams J , Kriedemann PE , Austin MP , Farquhar GD
Published: January 2006

Distributions of common species of Eucalyptus in south-eastem Australia are related to gradients in temperature and rainfall. To determine whether intrinsic water-use efficiency (as indexed by carbon isotope discrimination, Δ) or other leaf attributes were related to climate of native habitats, we sampled 17 populations representing 14 species of Eucalyptus growing in a common garden in south- central New South Wales. Phreatophytes were clearly distinguished from populations that are totally dependent upon soil moisture derived from rainfall by having higher Δ at a particular level of rainfall. Among 12 non-phreatophytic populations (11 species), Δ was positively correlated with mean annual precipitation (r = 0.75, P = 0.005), December-March precipitation (r = 0.79, P = 0.002), an index of annual soil moisture (r = 0.81, P = 0.001) and seasonality of precipitation (r = 0.85, P < 0.001). There were similarly strong but negative correlations between Δ and potential evaporation during the summer months, but Δ was not correlated with annual potential evaporation of the source sites. Leaf mass per unit area (ρe) was negatively correlated with indices of water availability, positively correlated with nitrogen per unit leaf area (r = 0.90, P < 0.001), and negatively correlated with Δ (r = -0.73, P = 0.007). A was negatively correlated with area-based leaf nitrogen (r = -0.79, P = 0.002). These complementary correlations among Δ, ρe, and nitrogen per unit leaf area indicate that variation in Δ may stem largely from variation in photosynthetic capacity. The results provide strong evidence that variation in Δ and ρe reflect genetic adaptations to native habitats.
Protein Synthesis During Oxygen Deprivation in Cotton
Authors: Millar AA , Dennis ES
Published: January 2006

The alteration of protein synthesis induced by oxygen deprivation has been examined in the root tips of cotton (Gossypium hirsutum cv. Siokra), a plant that is intolerant to anoxia. Using [35S]methionine labelling and two-dimensional gel electrophoresis it was demonstrated that 14 major polypeptides are being selectively synthesised during oxygen deprivation. These polypeptides have been designated the cotton anaerobic polypeptides (ANPs), and have estimated molecular masses that correspond to molecular masses of ANPs from other plant species. However, compared to maize, several of the major molecular weight classes are absent, suggesting that the response to oxygen deprivation in cotton is simpler than that of maize. Alcohol dehydrogenase (ADH) activity is induced by oxygen deprivation. Using western analysis we have determined that this increase in activity is correlated with the accumulation of the ADH polypeptide and that three of the major cotton ANPs are ADH, including the most intensely labelled ANP, demonstrating that the synthesis of ADH constitutes a major part of the response in cotton.
Voltage-Dependence of Extracellular Ca2+-Induced Modification in Properties of the Inward Rectifying K+ Channels in the Plasma Membrane of Mesophyll Protoplasts of Avena sativa
Authors: Kourie J
Published: January 2006

Data obtained using the whole-celi configuration of the patch-clamp technique reveal that characteristics of the inward rectifying K+ current across the plasma membrane of protoplasts isolated from mesophyll cells of leaves of oat (Avena sativa) are modified by increasing concentrations or removing the extracellular Ca2+.
The whole-cell membrane current reveals two components. The first component an initial current II* which is the sum of two currents: (a) a linear ohmic leak current passing through non-gated channels, liNGC, and (b) a rectifying inward K+ current passing through inward rectifying gated K+ channels, IKi, that are instantaneously open. The second component of the membrane current at the steady state Iss is a time-dependent K+ current IKss defined as Iss-IiNGC and passes through inward rectifying gated K+ channels. The tail K+ current, IKT, is also defined as IT-IiNGC.
Raising external calcium concentration, [Ca2+]o, from 0.1 mM to 10 mM blocked the inward rectifying currents IKi, IKss and IKT. The voltage-dependence of the activation time constant (τa) for time-dependent KC current IKss was not altered significantly by increasing [Ca2+]o whereas the deactivation time constant (τd) of the IKT increased from 16 ms to 30 ms at a Vm of -100 mV.
Removal of [Ca2+]o increased the amplitude and altered the characteristics of the inward rectifying K+ current. Ten minutes after the removal of [Ca2+]o the increase in IKi was 3.5-fold larger than the increase in IKss. Furthermore, removing [Ca2+]o hastened the activation of IKss and the deactivation of IKT. However, the deactivation time constant (Td) remained dependent on membrane voltage (Vm).
Extracellular Ca2+ may modulate the function of mesophyll cells by regulating K+ transport through the inward rectifying K+ channels and this may have significant implications for photosynthesis and cell expansion.
Metabolite Regulation of Phosphenolpyruvate Carboxylase in Legume Root Nodules
Authors: Woo KC , Xu S
Published: January 2006

The effects of metabolic activators and inhibitors on phosphoenolpyruvate carboxylase (PEPC) activity were examined at pH 7 in partially purified enzyme from nodules of soybean (Glycine max (L.) Merr.), Psophocarpus tetragonolobus DC. and Vigna unguiculata ssp. sesquipedalis (L.) Verdc. Glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate, fructose 1-phosphate, fructose 1,6- bisphosphate and phosphoglycerate stimulated the activity about 2-fold at low (0.5 mM) but not saturating (2.5 mM) PEP concentration. Glc 6-P and fru 6-P were the most effective activators and they increased the affinity of the enzyme for PEP by 2-4-fold. The dicarboxylates, malate, succinate, malonate, 2-oxoglutarate and aspartate inhibited PEPC activity. Malate was the most inhibitory, and strongly inhibited PEPC activity even at saturating PEP concentration. The Ki values for malate were 0.3-0.4 mM for soybean and P. tetragonolobus. However, glc 6-P and fru 6-P alleviated maiate inhibition and increased the Ki values by 11- to 28-fold in these two species. We propose that glc 6-P (fru 6-P) activates PEPC in a feedforward regulation and protects it against feedback inhibition by malate and thus coordinates the supply of photosynthate availability with malate synthesis required by the bacteroids to support symbiotic nitrogen fixation in nodules.
Construction of a YAC Contig of 2 Megabases Around the MS1 Gene in Arabidopsis thaliana
Authors: Chapple RM , Chaudhury AM , Blomer KC , Farrell LB , Dennis ES
Published: January 2006

The ms1 mutation of Arabidopsis thaliana causes male sterility by preventing the development of normal microspores in the developing anther. The gene is located on a region of chromosome 5 containing the RFLP markers g4111, g4560 and g21503. Using yeast artificial chromosome (YAC) libraries, we have constructed a contig of 38 YACs spanning approximately 2.1 megabases (approximately 2% of the genome) around MS1 and redefined the order of these RFLP markers. Chimeric YACs and repetitive DNA caused problems in chromosome 'walking'. A method for cloning YAC right ends by plasmid rescue was applied to arabidopsis. One YAC end contained a portion of the A. thaliana sucrose synthase gene ASUSI, hence locating this gene on chromosome 5 near MS1. Using recombinant plant populations containing ms1 and flanking markers, MS1 was localised to a 200 kb region within the YAC contig. In this contig the relationship between physical and genetic distance varied from less than 100 kb to 720 kb per centimorgan.
Acclimation of Stomatal Conductance to a CO2-Enriched Atmosphere and Elevated Temperature in Chenopodium album
Authors: Santrucek J , Sage RF
Published: January 2006

Acclimation of stomatal conductance to different CO2 and temperature regimes was determined in Chenopodium album L. plants grown at one of three treatment conditions: 23�C and 350 μmol CO2 mol-1 air; 34�C and 350 μmol mol-1; and 34�C and 750 μmol mol-1. Stomatal conductance (gs) as a function of intercellular CO2 (Ci) was determined for each treatment at 25 and 35�C, and these data were used to estimate gains of the feedback loops linking changes in intercellular CO2 with stomatal conductance and net CO2 assimilation. Growth temperature affected the sensitivity of stomata to measurement temperature in a pattern that was influenced by intercellular CO2. Stomatal conductance more than doubled at intercellular CO2 varying between 200 and 600 μmol mol-1 as leaf temperature increased from 25 to 35�C for plants grown at 23�C. In contrast, stomatal conductance was almost unaffected by measurement temperature in plants grown at 34�C. Elevated growth CO2 attenuated the response of stomatal conductance to CO2, but growth temperature did not. Stomatal sensitivity to Ci was extended to higher Ci in plants grown in elevated CO2. As a result, plants grown at 750 μmol mol-1 CO2 had higher Ci/Ca at ambient CO2 values between 300 and 1200 �mol mol-1 than plants grown at 350 �mol mol-1 CO2. The gain of the stomatal loop was reduced in plants grown at elevated CO2 or at lower temperature when compared to plants grown at 350 μmol mol-1 and 34°C. Both photosynthetic and stomatal loop gains acclimated to elevated CO2 in proportion so that their ratio, integrated over the range of Ci in which the plant operates, remained constant. Water use efficiency (WUE) more than doubled after a short-term doubling of ambient CO2. However, the WUE of plant grown and measured at elevated CO2 was only about 1.5 times that of plant transiently exposed to elevated CO2, due to stomatal acclimation. An optimal strategy of water use was maintained for all growth treatments.
Effects of Nppb and Niflumic Acid on Outward K+ and Cl- Currents Across the Plasma Membrane of Wheat Root Protoplasts
Authors: Garrill A , Tyerman SD , Findlay GP , Ryan PR
Published: January 2006

We have tested the effects of the reported Cl- channel blockers NPPB (5-nitro-2-(3- phenylpropylamino)benzoic acid) and niflumic acid (trifluoromethyl-3-phenylamino-2-nicotinic acid) on the slow-activating K+ (IKK.out) and fast-activating Cl- (IClCl.out) outward rectifying currents across the plasma membrane of wheat root protoplasts. Both compounds display a greater potency against IKK.out(half maximal inhibition (IC50) values of 8.7 μM for NPPB and 5.3 μM for niflumic acid with [K+]o= 10 mM) than against IClCl.out(IC50 values of 150 and 100 μM respectively). Single-channel studies using detached patches show that these blockers reduce the percentage of time that IKK.out out channels are in their open state. The data show that caution is necessary when using these compounds on intact cells to ascribe physiological functions to anion channels in plant membranes.
Organ-Specific Expression of Three Peroxidase-Encoding Cdnas From Lucerne (Medicago sativa)
Authors: Abrahams S , Hayes CM , Watson JM
Published: January 2006

Three putative peroxidase-encoding cDNA clones have been isolated from lucerne
(Medicago sativa) using an oligonucleotide probe based on the conserved FHDCFV amino acid
sequence domain of peroxidase proteins. The pxdA, pxdC and pxdD genes are specifically expressed in
leaf, root or stem tissue, respectively. The stem-specific gene, pxdD, is shown by tissue print
hybridisation analysis to be expressed in the phloem and collenchyma cells of lucerne tissue.
The Acceleration of Primordium Initiation as a Component of Floral Evocation in Lolium temulentum L
Authors: Evans LT , Blundell C
Published: January 2006

An acceleration of leaf primordium initiation by the shoot apex frequently follows floral evocation, but after varying intervals. The purpose of the experiments reported here was to define more closely the relation between this reduction of the plastochron and floral evocation, using the long day (LD) plant Lolium temulentum grown under closely controlled conditions.The acceleration begins at floral evocation, on the day after the first LD exposure, and increases after exposure to additional LDs. However, plants too young to be florally evoked by one LD nevertheless manifested an acceleration of primordium initiation, so the acceleration alone is not sufficient for evocation. Single applications of highly florigenic gibberellins (GAs), such as GA5, also accelerate the initiation of primordia and floral development, more so than does the weakly florigenic GA1. By contrast, single applications of the growth retardant Trinexapac-ethyl (CGA 163'935) to plants given one LD largely prevented the acceleration of primordium initiation but without inhibiting floral development. Thus, although the acceleration of primordium initiation by LD or by GA application is the first external sign of floral evocation in L. temulentum, it is neither a sufficient nor an essential component of it.
The Optimal Allocation of Nitrogen Within the C3 Photosynthetic System at Elevated CO2
Authors: Medlyn BE
Published: January 2006

The distribution of nitrogen among compounds involved in photosynthesis varies in response to changes in environmental conditions such as photon flux density. However, the extent to which the nitrogen distribution within leaves adjusts in response to increased atmospheric CO2 is unclear.
A model was used to determine the nitrogen distribution which maximises photosynthesis under realistic light regimes at both current and elevated levels of CO2, and a comparison was made with observed leaf nitrogen distributions reported in the literature.
The model accurately predicted the distribution of nitrogen within the photosynthetic system for leaves grown at current levels of CO2, except at very high leaf nitrogen contents. The model predicted that, under a doubling of CO2 concentration from its current level, the ratio of electron transport capacity to Rubisco activity (Jmax : Vcmax) should increase by 40%. In contrast, measurements of Jmax : Vcmax taken from the literature show a slight but non-significant increase in response to an increase in CO2. The discrepancy between predicted and observed Jmax : Vcmax suggests that leaf nitrogen distribution does not acclimate optimally to elevated CO2. Alternatively, the discrepancy may be due to effects of CO2 which the model fails to take into account, such as a possible decrease in the conductance to CO2 transfer between the intercellular spaces and the sites of carboxylation at elevated CO2.
Relationship Between Photosynthetic Carbon Exchange Rate, Specific Leaf Mass and Other Leaf Characteristics in Chickpea Genotypes
Authors: Mythili JB , Nair TVR
Published: January 2006

Thirteen chickpea (Cicer arietinum L.) genotypes, raised in the field, were screened for carbon exchange rate (CER), related leaf characters and dry matter production throughout the season. Seasonal pattern of the CER and related characters were similar in all genotypes. CER showed two peaks, one at the late vegetative phase and the other at the peak pod filling phase. Stomatal resistance (rs) and specific leaf mass (SLM) increased in the successively formed leaves while nitrogen concentration tended to decline, especially in later-formed leaves. Nitrogen (N) content per unit area, however, remained relatively constant throughout the season. Significant genotypic variabilities were observed in CER and related characters as well as in total dry matter accumulated at harvest. Seasonal means of CER ranged from 12.5 in HG 1765B to 18.4 μmol CO2 m-2 s-1 in BG 315, SLM from 5.1 in HG 1765 to 6.5 mg dry weight cm-2 in BG 315, rs from 1.31 in BG 315 to 1.92 s cm-1 in Hyb 16-3, leaf N content from 122.6 in HG 1765B to 172.1 mmol m-2 in BG 315 and total dry matter at final harvest from 9.9 in HG 17658 to 34.9 g plant-1 in K4. Seasonal means of CER were positively correlated with SLM, N content per unit area and final harvest dry matter. Stomatal resistance was negatively correlated with CER and final harvest dry matter. The results indicate that although CER is the best selection criterion for higher dry matter production in chickpea, it is possible to use SLM as an indirect selection criterion for CER in this crop. However, such a selection based on SLM involves the risk of elimination of high N-use efficiency genotypes.