bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbon Dioxide Assimilation and Foliar Ion Concentrations in Leaves of Lemon (Citrus limon L.) Trees Irrigated With Nacl or Na2SO4
Authors: Walker RR , Blackmore DH , Sun Q
Published: January 2006

An attempt was made to differentiate between the possible effects of high Cl- or Na+ ions on lemon leaf photosynthesis by treating grafted (Citrus limon (L.) Burm. f. cv. 'Taylor') plants with either NaCl or Na2SO4 to establish different foliar concentrations of Cl- or Na+. The rootstocks, Rangpur lime (C. reticulata var. austera hybrid?) and rough lemon (C. jambhiri), were chosen because Rangpur lime is known to be a good Cl- 'excluder' and rough lemon to be a poor Cl- 'excluder'. The grafted plants were initially treated for 7 weeks with nutrient solution (control) or nutrient solution containing 50 mol m-3 NaCl or 25 mol m-3 Na2SO4, after which time there were only marginal reductions in both photosynthetic rates and shoot growth, with the exception of 'Taylor' lemon on rough lemon roostock treated with NaCl where growth was affected more severely than the other treatments. Salinity levels were then doubled to 100 mol m-3 NaCl and 50 mol m-3 Na2SO4 and the plants treated for a further 8 weeks, causing significant increases in leaf Na+ and/or Cl- concentrations. Mature, 3-4-month-old leaves of 'Taylor' lemon on Rangpur lime rootstock treated with Na2SO4 for this period, contained c. 105 mol m-3 Na+ and c. 10 mol m-3 Cl- and had photosynthetic rates 60% lower than controls. Similar reductions in assimilation rate were seen in leaves on rough lemon roostock treated with NaCl containing c. 195 mol m-3 Cl- and c. 35 mol m-3 Na+. Smaller (35%) but significant reductions in assimilation rate were observed for trees on rough lemon roostock treated with Na2SO4, where the tagged leaves contained c. 40 mol m-3 Na+ and 50 mol m-3 SO42-. Leaf nitrogen concentrations were significantly reduced by treatment of trees with NaCl or Na2SO4 but, apart from small reductions in chlorophyll concentrations, there were no visible symptoms of nitrogen deficiency. Leaf turgor was not adversely affected. The data indicate that both Cl- and Na+ can reduce assimilation rates in salt-stressed lemon leaves, possibly because of poor compartmentation within leaves of either ion. Increases in leaf Na+ and Cl- accounted for 54-96% of the reduction in osmotic potential in 'Taylor' lemon leaves on trees treated with NaCl, whereas increases in Na+ and SO42- accounted for 33-71% of the reduction in osmotic potential in leaves on trees irrigated with Na2SO4. The greater increase in Cl- compared with the net increase of [Na+ + K+] in 'Taylor' leaves on rough lemon rootstocks was offset (65%) by reductions in malic and succinic acids. Proline increased significantly only in 'Taylor' leaves on Rangpur lime roostock treated with Na2SO4.
Identification of the Main Osmotically Active Solutes in the Unstressed and Water-Stressed Root-Hemiparasitic Angiosperm Thesium humile and Its Host Triticum vulgare
Authors: Simier P , Fer A , Renaudin S
Published: January 2006

The root-hemiparasite Thesium humile Vahl (Santalaceae) causes important damage to cereal crops in Mediterranean countries. It maintains lower osmotic potentials than its host and the main osmotically active solutes involved are identified and measured in host and hemiparasite under well-watered conditions or water stress.
Mineral ions account for more than 50% of the osmolarity in the unstressed host (Triticum vulgare), K+ and Cl- playing the major role. Organic solutes contribute to a limited extent and, among these, free amino acids are present at higher concentration than carbohydrates (glucose, fructose, sucrose) or carboxylic acids (mainly as malate).
Inorganic ions (especially K+, Cl- and Na+) account for the greatest part of the osmolarity in unstressed Thesium. Organic solutes contribute to a lower extent; among them, carbohydrates (mainly as mannitol) and carboxylic acids (mainly as malate, ketoglutarate and citrate) are present at an higher concentration than free amino acids.
Host and parasite respond to water stress by decreasing their osmotic potentials through accumu- lation of species-specific sets of solutes. Increases in inorganic ion concentration in the stressed host result from water loss. Organic solutes are also strongly accumulated, mostly as carbohydrates (mainly fructose). Contents of free amino acids (compatible solutes) and carboxylic acids are about four times higher than under unstressed conditions. Thesium shows less dehydration under water deficits than does wheat and the mineral ion content is still slightly enhanced. Free amino acids and carbohydrates are present at about twice the concentration as under well-watered conditions. The increase in carboxylic acid content relates principally to an accumulation of citrate and glycerate.
Soluble carbohydrates, identified as oligofructans, may be also involved in the osmoregulation of both wheat and Thesium under stressed or unstressed conditions, but the extent of their contribution to osmolarity is unknown. Among carbohydrates, the compatible solute mannitol occurs in Thesium at highest concentration. The biosynthetic pathway of this polyol may be a possible biochemical target for chemical control of Thesium.
The Antioxidant Status of Soybean (Glycine max) Leaves Grown Under Natural CO2 Enrichment in the Field
Authors: Badiani M , D'annibale A , Paolacci AR , Miglietta F , Raschi A
Published: January 2006

The effects of progressively higher CO2 levels on the foliar antioxidant status were studied by growing soybean (Glycine max Merrill cv. Cresir) plants at decreasing distances from natural CO2 sources of geothermal origin in central Italy. When compared with neighbouring controls grown under normal CO2 concentration (C), soybean leaves grown at 2 × C, 7 × C and more than 20 × C showed a substantial reduction in the size of ascorbate pool and in the activity of Cu,Zn-superoxide dismutase; both the content of ascorbic acid and the activity of ascorbate peroxidase declined at 2 × C and 7 × C and recovered to the control values at 20 × C. The foliar titre of glutathione disulfide and the activities of glutathione disulfide reductase and Mn-superoxide dismutase progressively increased as CO2 concentration increased in ambient air. The results obtained suggest that the immanent risk of dioxygen toxicity associated with photosynthetic electron flow could be reduced in the presence of high CO2 levels. On the other hand, depending on both the CO2 exposure regimes and the cell compartment considered, high CO2 could promote oxidative processes which cause GSH oxidation and require an enhanced cellular ability to scavenge superoxide anion and hydrogen peroxide.
Responses of Detached Rice Leaves (Oryza sativa L.) To Moderate Supplementary Ultraviolet-B Radiation Allow Early Screening for Relative Sensitivity to Ultraviolet-B Irradiation
Authors: Huang LK , He J , Chow WS , Whitecross MI , Anderson JM
Published: January 2006

Responses to short-term supplementary ultraviolet-B (UV-B) radiation were studied in detached leaves of two indica rice cultivars (Er Bai Ai and Lemont) to evaluate whether this might be an initial method for screening for UV-B susceptibility. Leaf tissue from plants grown in a greenhouse (28�C day/ 20�C night, with a maximum irradiance of 800-1000 μmol photons m-2 s-1) was placed under moderate supplementary UV-B radiation for 20 h. The effects of this short-term treatment were measured by determining the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm), quantum yield of photosynthetic O2 exchange, chlorophyll content, maximum Rubisco activity as well as the concentrations of total soluble protein and Rubisco protein. All the above parameters showed considerable declines, which were always greater in cv. Er Bai Ai than in cv. Lemont. The in vivo activation of Rubisco was markedly increased in detached leaves treated with supplementary UV-B compared with control leaves; the increase was greater in cv. Er Bai Ai than in cv. Lemont. The photosynthetic responses invoked in the detached rice leaves are remarkably similar to those observed previously [He et al. (1993). Aust. J. Plant Physiol. 20, 129-42] in intact rice plants which had a longer-term supplementary UV-B exposure of comparable cumulative biologically effective UV-B dosage. We conclude that rapid short-term responses of detached leaves allow early screening of relative sensitivity of rice cultivars to UV-B.
Influence of Light on Assimilate Partitioning in White Clover (Trifolium repens L.)
Authors: Pasumarty SV , Fountain DW
Published: January 2006

In order to identify factors which might contribute to the premature abortion of young inflorescences of white clover Trifolium repens L. in low irradiances, a study was made of the possible role of limiting photosynthetic assimilates to the developing inflorescence.
The relationship between the irradiance and distribution pattern of assimilates in the clover plant under different irradiances was determined. Besides driving the photosynthetic supply of sucrose, light seems to play an indirect role in controlling partitioning of photoassimilates. Under low irradiance, the growing tip of the shoot and roots were major sinks and negligible amounts of 14C-labelled assimilates were supplied to the inflorescence. In medium and high irradiances, the inflorescence competes for assimilates with stolon apex and roots.
The Synthesis of [14C]Starch From [14C]Sucrose in Isolated Wheat Grains Is Dependent Upon the Activity of Soluble Starch Synthase
Authors: Jenner CF , Siwek K , Hawker JS
Published: January 2006

Soluble starch synthase activity decreased in isolated wheat grains heated in vials at temperatures between 31 and 40�C; a decrease of more than 50% occurred at 35�C within 30 min. Sucrose synthase activity was not significantly affected by heating and ADPglucose pyrophosphorylase decreased to a lesser extent and more slowly than soluble starch synthase. Wheat grains which were heated for 1 h at 35�C and allowed to recover at 20�C exhibited partial recovery of soluble starch synthase activity within 4 h. These responses in isolated grains to heating resembled effects reported elsewhere in intact ears.
Isolated grains were exposed to a range of temperatures for 1 h prior to incubation in [14C]sucrose at 20�C. Within the range 20-40�C, the effect of pretreatment temperature on the activity of soluble starch synthase was highly correlated with the incorporation of 14C into starch. Control coefficients close to unity indicated that the activity of soluble starch synthase imposed a high degree of control on the rate of starch synthesis in this system. These results with isolated grains support a previous suggestion that the activity of soluble starch synthase at elevated temperature in wheat is an important factor limiting the accumulation of dry matter through effects on the synthesis of starch.
Ash, Carbon Isotope Discrimination, and Silicon as Estimators of Transpiration Efficiency in Crested Wheatgrass
Authors: Mayland HF , Johnson DA , Asay KH , Read JJ
Published: January 2006

Breeding and selection for higher transpiration efficiency (W) has been hampered by tedious and costly methodology. Rapid and less costly methods are needed for screening W in plant improvement programmes. We report the relationship of ash, silicon (Si) concentration, and Si uptake to W in crested wheatgrass (Agropyron desertorum Fischer ex Link] Schultes), an important C3 range grass in western North America. Clones of crested wheatgrass were grown under three water levels in a field rainout shelter and as potted plants under two water levels in the field and greenhouse. Ash and Si concentrations were compared to previously determined values of shoot mass, transpiration, W, and carbon isotope discrimination (Δ). Ash and Si concentrations were not consistently related to Δ and W across all environments; however, ash concentration was positively correlated with Δ (r=0.69**, df= 22) and negatively correlated with W (r= -0.61**, df =22) in the well-watered field environment. Across all environments and studies, the ranges in the coefficients of variation (CV, %) for clonal means were: W, 4-15; Δ, 1-4; ash concentration, 6-14; Si concentration, 13-30; and Si uptake, 21-33. The generally lower CV for W, Δ, and ash concentration suggest that these traits were more repeatable than Si concentration or uptake. Although a consistent relationship was not observed between Si and W and between ash and W, the correlations of ash and W from the well-watered field environment were encouraging. In view of the low cost for ash analysis, we conclude that further research is needed to evaluate the potential of ash as a criterion in selecting for improved W, particularly during the early phases of a breeding programme when large populations are usually involved. Later selections could be based on the more precise and accurate, but costly, Δ analysis.
Blue Light-Induced Phosphorylation of a Plasma Membrane Protein in Pea: a Step in the Signal Transduction Chain for Phototropism
Authors: Warpeha KMF , Briggs WR
Published: January 2006

A 117 kDa polypeptide associated with the plasma membrane isolated from the growing zones of etiolated pea epicotyls is phosphorylated upon a brief exposure to blue light. The literature pertaining to this photosensitive system to date is briefly summarised prior to a short experimental section. In the experimental work the polypeptide has been studied in its non-denatured and denatured state in order to investigate its possible role in blue light-induced signal transduction. The polypeptide has a molecular weight near 117 kDa. Under non-denaturing conditions, following solubilisation in non-ionic detergent, and after electrophoresis, a complex migrating at approximately '335 kDa' still retains the ability to perceive the blue light signal and undergo phosphorylation. This complex is resolved into a phosphorylated protein of approximate molecular mass of 117 kDa by second dimensional analysis on denaturing polyacrylamide gels. It is not at present possible to determine whether this protein is the only one involved or whether two or more different proteins are required for the light-inducible phosphorylation. This reaction has been established elsewhere by genetic and physiological criteria to be an early step in the signal transduction pathway for phototropism. Two other reactions that are inducible in vitro in isolated plasma membranes from etiolated seedings - activation of GTPase activity and reduction of a b-type cytochrome-are almost certainly independent pathways unrelated to the phosphorylation reaction or to each other. Neither has as yet been associated definitively with a known physiological response.
Involvement of Abscisic Acid in Controlling Plant Growth in Soil of Low Water Potential
Authors: Munns R , Sharp RE
Published: January 2006

Hormones appear to be important in controlling plant growth in soils of low water potential, particularly in changing the root:shoot ratio as the soil dries or becomes saline, and in communicating soil conditions to the leaves. This review has necessarily focused on abscisic acid (ABA), as there is little information about the role of other hormones in controlling growth in dry or saline soils. ABA is partly responsible for the differential response of root and shoot growth to dry soils. In dry soil it maintains root growth and inhibits shoot growth. However, when applied to well-watered plants, it usually inhibits root and shoot growth, showing that plants in dry soil respond quite differently from well-watered plants. ABA affects the rate of cell expansion in plants in dry soils: it maintains cell expansion in roots and inhibits that in leaves. It may also affect the rate of cell production, but little is known about this. The role of ABA as a long-distance signal in controlling growth by root-to-shoot communication is unclear: the concentrations found in xylem sap can affect stomatal conductance, but seem too low to affect leaf expansion. Yet drought and salinity generally affect leaf expansion before they affect leaf conductance. A possible solution to this puzzle is that ABA is transported in xylem sap in a complexed form, or that another compound in xylem sap stimulates the synthesis or activity of ABA in leaves, or affects leaf expansion independently of ABA.
The Route, Control and Compartmentation of Auxin Synthesis
Authors: Nonhebel HM , Cooney TP , Simpson R
Published: January 2006

The study of indole-3-acetic acid synthesis has undergone something of a revival recently in an attempt to understand the control of IAA levels. Results are, however, contradictory with three separate hypotheses emerging. Our own work supports older evidence for L-tryptophan as the IAA precursor and appears to simplify the metabolism of tryptophan to IAA. Work comparing incorporation of 2H from 2H2O into IAA, tryptophan, tryptamine and indole-3-pyruvate in tomato shoots showed that the indole-3-pyruvate became labelled at a rate compatible with it being the sole intermediate between tryptophan and indole-3-acetaldehyde. Results also showed that tryptamine was not involved in IAA synthesis although it was present. Indole-3-acetaldoxime was not detected in tomato shoots. An aromatic aminotransferase able to catalyse the synthesis of indole-3-pyruvate has been purified from mung beans. This enzyme was separated from aspartate aminotransferase and is fairly specific for aromatic L-amino acids. Other work, however, has implicated D-tryptophan as a more direct precursor than the L-enantiomer. A D-tryptophan aminotransferase has been isolated from dark grown pea seedlings. Finally, other recent work has indicated the existence of an alternative biosynthetic route to IAA which does not involve tryptophan. These results are reviewed in this paper and the apparent contradictions between them discussed.
Mechanisms of Auxin Regulation of Structural and Physiological Polarity in Plants, Tissues, Cells and Embryos
Authors: Warren Wilson J , Warren Wilson PM
Published: January 2006

New experiments and insights extend current concepts to yield four integrated hypotheses on polarization. (1) In tissues that lack polarity, as in meristems and proliferating callus, short-distance diffusive movement of auxin between spatially separate sources and sinks can gradually induce polar transport of auxin and associated proton currents in the direction of the initially diffusive movement. (2) The formation of auxin at the shoot tip, on which maintenance of the plant's polarity depends, occurs by hydrolysis of auxin precursors such as IAA-myo-inositol, which readily hydrolyses (even non-enzymically) at rates that increase with pH, so that higher pHs arising in leaf primordia through auxin-proton cotransport can promote local formation of auxin. (3) The long axes of cells and the secondary wall banding of tracheary elements tend respectively to develop parallel and perpendicular to the direction of polar transport of auxin through tissue, especially vascular tissue; these orientations are mediated by the bioelectric current associated with polar auxin transport, through orientation of cortical microtubules transverse to the current. (4) Initiation of polarity in zygotic embryos is controlled by the direction of auxin movement in the surrounding parental tissues; in lower plants the exoscopic embryo's polarity is similar to that of the surrounding tissues, but in seed plants the endoscopic embryo's polarity is inverted as a result of physiological isolation, localised auxin breakdown, and suspensor formation.
In vivo Photoaffinity Labelling of Gibberellin-Binding Proteins in Avena fatua Aleurone
Authors: Hooley R , Smith SJ , Beale MH , Walker RP
Published: January 2006

It is generally accepted that specific recognition between plant hormones and proteins involved in their biosynthesis, metabolism, transport and perception are of profound importance in the hormonal regulation of plant growth and development. The identification and detailed characterisation of hormone-binding proteins which perform these functions is an important component of research that aims to understand plant hormone action. In this report the development of photoaffinity reagents for gibberellin (GA)-binding proteins is reviewed, and their use as probes with which to identify and characterise GA-binding proteins in Avena fatua aleurone is described. In vivo GA-photoaffinity labelling of aleurone layers, using the new photoaffinity probe GA4-17-sulfoxyethyl-p-azido-[125I]-iodosalicylate, leads to the covalent attachment of this reagent to numerous aleurone polypeptides. Biologically active and inactive GAs used as competitors during in vivo GA-photoaffinity labelling help discriminate between specific and non-specific binding. The biologically active GA4 and GA4-17-yl-1′- (1′-thia)propan-3′-ol-4-azido-5-iodosalicylate compete for photoaffinity labelling of a 60 kDa aleurone polypeptide, while the inactive GAs does not. These GA-photoaffinity labelling characteristics suggest that the 60 kDa aleurone polypeptide may interact specifically with active GAS. This is the first report to identify a specific GA-binding protein in aleurone.
We suggest that this specific interaction observed in vivo, under conditions where the aleurone cells are responding to the GA-photoaffinity probe by expressing α-amylase genes, may be of significance in the perception and action of GA in this tissue.
The Role of Cytokinin in Organised Differentiation of Vascular Tissues
Authors: Aloni R
Published: January 2006

The role of cytokinin as a limiting and controlling factor in the differentiation of vascular tissues in the plant body is discussed. Cytokinin controls the early stages of fibre differentiation in Helianthus stems and the regeneration of vessels and sieve tubes around a wound in Coleus internodes. The influence of cytokinin on cell differentiation in the vascular tissues varies according to its physiological levels and the levels of auxin. Cytokinin induces an acropetal polar pattern of vessel regeneration around a wound in internodes of Coleus. Similarly, adventitious roots induce acropetal polar patterns of vessel maturation in hypocotyls of Cucurbita. Cytokinin increases the sensitivity of the vascular cambium to the auxin stimulation, resulting in the highest ratio of phloem/xylem under the optimal level of cytokinin. High levels of cytokinin promote callose production on sieve plates. Studies of transgenic plants with altered levels of cytokinin (overexpressing the ipt gene) confirm the involvement of cytokinin in vascular differentiation.
Cytokinins in Plant Pathogenic Bacteria and Developing Cereal Grains
Authors: Morris RO , Blevins DG , Dietrich JT , Durley RC , Gelvin SB , Gray J , Hommes NG , Kaminek M , Mathews LJ , Meilan R , Reinbott TM , Sayavedra-Soto L
Published: January 2006

Cytokinin analysis by immunoaffinity chromatography (IAC), high-performance liquid chromatography (HPLC) and radioimmunoassay (RIA) or enzyme-linked immunosorption assay (ELISA) has been used to study two separate topics: the role of tRNA in bacterial cytokinin biosynthesis and the changes in cytokinin concentration which occur during cereal grain development. Transfer RNA isopentenylation in the gall-forming plant pathogen Agrobacterium tumefaciens is encoded by the chromosomal miaA locus. Mutation of miaA reduces tRNA isopentenylation significantly and preliminary data suggest that turnover of isopentenylated tRNA is responsible for low level secretion of free N6-isopentenyladenine (iP) by the bacteria. However, the major route of cytokinin biosynthesis by gall-forming plant patho- genic bacteria is not via tRNA turnover but by direct biosynthesis mediated by dimethylallylpyro- phosphate: 5'-AMP transferase (DMAPP :AMP transferase) encoded by such genes as ipt, tzs (from A, tumefaciens) or ptz (from Pseudomonas savastanoi). Analysis of cytokinin levels in developing wheat and rice grains in the period immediately following pollination showed large transient increases in zeatin (Z) and zeatin riboside (ZR) which coincided with the period of maximum endosperm cell division reported by others. Detailed analyses of maize kernels, where development can be staged readily, showed that Z and ZR concentrations peaked 9 days after pollination (DAP). During the period 8-10 DAP, cytokinin oxidase underwent a significant increase in specific activity, indicating that cytokinin catabolism was enhanced as endosperm cell division ended.
Interactive Effects of High Temperature and Light Quality on Floral Bud Development in Cowpea
Authors: Ahmed FE , Mutters RG , Hall AE
Published: January 2006

Floral bud development of cowpea (Vigna unguiculata (L.) Walp.) is arrested by high night temperature and long days under natural sunlight, but not under all types of artificial lighting systems. The objective of this study was to determine whether floral bud development at high night temperature is influenced by the red/far red (R/FR) ratio during the day. Cowpea plants were grown in glasshouses with natural sunlight, and growth chambers having either metal halide-based (MH) or fluorescent-based (EL) lighting systems. Plants were subjected to R/FR ratios of 1.3, 1.6, or 1.9 with both lighting systems. Floral bud development was arrested by high night temperature under natural sunlight with R/FR ratio of 1.2, and under MH and FL lighting systems when the R/FR ratio was 1.3 or 1.6. High night temperature did not affect floral bud development of plants grown under MH or FL light with a R/FR ratio of 1.9 and the plants produced flowers, but pod set was inhibited at this temperature. Floral bud development and pod set of a heat-tolerant cowpea genotype were normal under high night temperature and not influenced by light quality or lighting system. Apparently, the degree to which high temperatures injure floral bud development depends on the R/FR ratio during the day, and values of 1.3 to 1.6 are required to elicit the same responses as those that occur in sunlight.
Radiation Effects on Rate of Development in Wheat Grown Under Different Photoperiods and High and Low Temperatures
Authors: Rawson HM
Published: January 2006

This study was designed to examine whether development rate of wheat might be changed by radiation at high temperature and more generally whether development might be varied by changed source: sink ratio. In the genotype studied, when temperature was high (27/22�C) and especially when the photoperiod was short (9 h), leaf primordia were produced more slowly under low than high natural radiation, and this slowing was reflected in lower final spikelet numbers and in fewer grains per ear. Under the higher source: sink condition of low temperature (17/7�C), and under either short or long photoperiod, rates of primordia production were not measurably changed by radiation, but more light did result in more spikelets. The lengthening of plastochron intervals (thermal time between the appearance of leaf primordia) associated with low radiation did not translate into significantly increased phyllochron intervals (thermal time between emergence of leaves). However, phyllochron intervals were responsive to both photoperiod and temperature.
Under short photoperiod, source limitation associated with high temperature extended the thermal time to ear emergence. Thus, an increase in temperature from 17/7�C to 27/22�C doubled the thermal time to heading from 1241 to 2571 �Cd. Source limitation associated with low radiation also increased thermal time to heading by up to 400 �Cd and calendar time by up to 17 days. Under long photoperiod, where development was rapid, radiation did not change the timing of developmental stages. It is concluded that although development in wheat is generally not source-limited in the traditional environments for cultivation, under high temperatures and shorter photoperiods development may be slowed by limiting source:sink ratios.
Assimilation, Stomatal Conductance, Specific Leaf Area and Chlorophyll Responses to Elevated CO2 of Maranthes corymbosa, a Tropical Monsoon Rain Forest Species
Authors: Eamus D , Berryman CA , Duff GA
Published: January 2006

Seeds of Maranthes corymbosa Blume, a monsoon rain forest species of northern Australia, were sown under ambient or elevated CO2 concentrations in tropical Australia. Seedlings were grown under conditions of photon flux density, temperature and atmospheric vapour pressure deficit which followed ambient variations as closely as possible. Specific leaf area, chlorophyll, stomatal density, stomatal conductance and assimilation responses to photon flux density were measured after 30 weeks growth. Gas exchange characteristics were divided into morning and afternoon data sets and analysed separately. Stomatal density decreased and leaf area:dry weight ratio decreased in response to elevated CO2. In contrast there was no effect of elevated CO2 upon chlorophyll (total or ratio of a:b). Apparent quantum yield and rates of light saturated assimilation (Amax) increased in response to elevated CO2. There was a significant decline in apparent quantum yield for both treatments between morning and afternoon. Stomatal conductance (gs) declined in response to elevated CO2. There was no significant difference in gs between morning and afternoon for ambient grown trees, but gs declined significantly between morning and afternoon for elevated CO2 grown trees. Instantaneous transpiration efficiency (ITE) was higher for elevated CO2 grown trees compared with control trees. There was a significant increase in ITE between morning and afternoon data for ambient grown trees; in contrast a significant decline in ITE was observed for elevated CO2 grown trees between morning anf afternoon data sets. The slope of the regression between assimilation rate and stomatal conductance increased for plants grown under elevated CO2. These data are discussed and compared with the responses of plants adapting to different photon flux densities.
Photosynthetic Mechanisms of Weeds in Taiwan
Authors: Lin CH , Tai YS , Liu DJ , Ku MSB
Published: January 2006

One hundred and one species (in 36 families) of weeds on cultivated land in Taiwan were investigated for the occurrence of Kranz leaf anatomy and activities of key enzymes of C4 photosynthesis to determine their photosynthetic mechanisms. Based on the anatomical and biochemical analyses, 75 species were found to possess the C3 and 26 species the C4 pathway of photosynthetic CO2 fixation. Among the 26 C4 species, 15 species are in Gramineae, 6 in Cyperaceae, 2 each in Euphorbiaceae and Amaranthaceae, and 1 in Portulacaceae. Two C4 species in the Gramineae, namely Digitaria radicosa (Presl) Miq. and Sporobolus fertilis (Steud.) Clayton, were recorded as C4 plants for the first time. The biochemical subdivisions of these C4 weeds were also determined. As in the natural C4 populations, the NADP-malic enzyme subtype of C4 photosynthesis dominates the list of C4 weeds on this island (62%), while the PEP carboxykinase subtype is relatively rare (12%). NAD-malic enzyme subtype has an intermediate representation (26%). The high proportion of weeds in Taiwan being C3 plants is noteworthy, and it may be accounted for by the high precipitation in this subtropical island.
Caution on the Use of the Generally Accepted Methanol Precipitation Technique for the Assay of Soluble Starch Synthase in Crude Extracts of Plant Tissues
Authors: Jenner CF , Denyer K , Hawker JS
Published: January 2006

The 14C-labelled glucan synthesised by soluble starch synthase (ADP glucose : 1,4-α-D-glucan-4-glucosyl transferase, EC 2.4.1.21) is partially degraded to glucose and maltose in assays of crude extracts of some plant organs. As these degradation products are not precipitated by treatment with aqueous methanol-KCl (75% v/v: 1% w/v), the conventional means by which the product of the starch synthase reaction is separated from the substrate, ADP[U-14C]glucose, the activity of the enzyme can be seriously underestimated. An alternative procedure involving the absorption of unreacted ADP[U-14C]glucose with anion exchange resin provides a more accurate estimate of the activity.
Drought and Pot Size Effects on Transpiration Efficiency and Carbon Isotope Discrimination of Cowpea Accessions and Hybrids
Authors: Ismail AM , Hall AE , Bray EA
Published: January 2006

Carbon isotope discrimination (Δ) has been proposed as a selection criterion for improving adaptation to water-limited environments because it provides a measure of seasonal transpiration efficiency ( WUE). In cowpea (Vigna unguiculata (L.) Walp.), consistent genotypic and drought-induced differences in Δ and WUE have been observed which were correlated as expected based on theory. Values of Δ and WUE for reciprocal hybrids grown under field conditions indicated nuclear inheritance for both characters. High WUE and low Δ were partially dominant under dry field pot conditions, whereas high Δ was partially dominant under natural wet soil conditions. Studies were conducted to test whether differences in rooting environment and xylem ABA levels are responsible for this change in dominance relations. Cowpea accessions and hybrids were grown in the field and subjected to wet or dry treatments with three different pot sizes. The experiment was conducted twice, giving similar results. The dry treatment resulted in decreases in Δ, and increases in WUE and ABA concentration in the xylem sap. Under drought, genotypes with higher WUE had higher xylem ABA, and the hybrids exhibited greater increases in ABA concentration in response to the dry treatment than either parent. Partial confounding was present in that the hybrids had substantial leaf area and water-use rate, and may have experienced greater soil drought in some conditions than some parents, with interacting effects of pot size. Plants in larger pots produced more biomass and leaf area but with no changes in xylem ABA. Concentration of ABA in the xylem sap was correlated with Δ and WUE for genotypic and drought treatment effects but not for pot size effects. Hybrids tended to have higher Δ and lower WUE in relation to mid-parent means when grown in large wet pots than in small dry ones. Changes in hybrid performance with respect to Δ and WUE were more consistent with changes in xylem ABA for drought treatment effects than for pot size effects. Another chemical signal might be involved in mediating pot size effects.
Accumulation of the Compatible Solute 3-Dimethylsulfoniopropionate in Sugarcane and Its Relatives, but Not Other Gramineous Crops
Authors: Paquet L , Rathinasabapathi B , Saini H , Zamir L , Gage DA , Huang ZH , Hanson AD
Published: January 2006

The tertiary sulfonium compound 3-dimethylsulfoniopropionate (DMSP) is found at high levels in many marine algae, but among higher plants it has been reported to accumulate only in Spartina (Gramineae) and one other genus. Cultivated and wild species from 23 genera of Gramineae were tested for DMSP accumulation in leaves of non-stressed plants, using an indirect gas chromatographic assay. Sugarcanes and closely related species accumulated up to 6 μmol g-1 fresh wt; other species contained no more than 0.3 #956;mol g-1 fresh wt. In sugarcanes, mature leaves had higher levels of DMSP than expanding leaves, immature internodes and mature internodes. The identity of DMSP was confirmed by a novel gas chromatography-mass spectrometry method, by fast atom bombardment mass spectrometry and by 1H nuclear magnetic resonance. Mass spectral evidence indicated that DMSP levels in leaves were at least ten-fold higher than glycine betaine levels, suggesting that DMSP may have replaced glycine betaine as a compatible osmolyte in sugarcane. Consistent with this possibility, DMSP was as effective as glycine betaine in relieving osmotic inhibition of bacterial growth, and was accumulated to concen- trations above 1 M by osmotically stressed bacterial cells. Because DMSP is the biological precursor of dimethylsulfide, sugarcane fields may be sources of dimethylsulfide emissions.
Distribution of Charasomes in Chara: Re-establishment and Loss in Darkness and Correlation with Banding and Inorganic Carbon Uptake
Authors: Chau R , Bisson MA , Siegel A , Elkin G , Klim P , Straubinger RM
Published: January 2006

Charasomes are complex structures found in the plasmalemma of the internodal and branchlet cells of the algal genus Chara. They are lost when internodes are stored in the dark for prolonged periods. Prolonged darkness results in the loss of the ability of internodes to form spatially separated bands of low and high pH. Rates for the uptake of inorganic carbon by the internodal cells are also diminished. The ability to band is re-established 8 h after the reintroduction of a light regime. Rates for the uptake of inorganic carbon begin to increase from 24 h. Charasomes reform over the period of 1-15 days after light, beginning as a simple cytoplasmic evagination and progressing toward a typical complex morphology. The re-establishment of charasomes is correlated with an increase in the uptake of inorganic carbon from bicarbonate-containing solutions.
Gene-Expression Following T-DNA Transfer Into Plant Cells Is Aphidicolin-Sensitive
Authors: Chaudhury AM , Dennis ES , Brettell RIS
Published: January 2006

A transient assay for gene-expression was used to study the early events of T-DNA transfer. Particularly, it was asked if gene expression following T-DNA transfer required DNA replication in the host cell. A β-glucuronidase gene, linked to a CaMV 35S promoter (35S-GUS, engineered so that it was inactive in Agrobacterium tumefaciens) was introduced into Nicotiana plumbaginifolia protoplasts via a disarmed supervirulent strain of Agrobacterium tumefaciens. High β-glucuronidase activity appeared after 3 days of co-cultivation. The activity required the presence of the vir functions of agrobacteria. The activity was drastically reduced if the plant cells were treated with aphidicolin, an inhibitor of DNA replication in eukaryotic cells. While double-stranded (ds) 35S-GUS DNA, introduced by electroporation, showed undiminished expression in the presence of aphidicolin, gene expression from single-stranded (ss) 35S-GUS DNA was inhibited by aphidicolin. These results suggest that DNA replication in host cells is not required for gene expression if ds-DNA is introduced by electroporation, but is required if ss-DNA is introduced by electroporation, or if DNA is transferred via A. tumefaciens. The findings are consistent with a model of T-DNA transfer in which ss-DNA molecules, once introduced into plant cells, must pass through an aphidicolin sensitive step before they can be transcribed. The simplest interpretation is that the ss-DNA is replicated by the host cell's aphidicolin-sensitive DNA polymerase before being integrated into the host genome.
Use of 13C and 15N Plant Label Near Natural Abundance for Monitoring Carbon and Nitrogen Partitioning
Authors: Deleens E , Cliquet JB , Prioul JL
Published: January 2006

Tracing with stable isotopes by using naturally or weakly labelled compounds has become a reliable approach in metabolic studies due to the high precision of isotope measurement by mass spectrometers fitted for natural range. Rapid and numerous isotope ratio determinations are now possible due to the recent automation of analyses. Three methods of analysis of carbon and nitrogen partitioning are reviewed from experiments on maize plants: (a) use of natural differences in organ isotope composition; (b) labelling with industrial CO2 naturally depleted in 13C; (c) double C and N labelling with CO2 and NO3 slightly enriched in 13C and 15N. For method (c) which is the most precise, the obtaining of plant matter with 13C and 15N label near their natural isotope abundance (1.1% for C and 0.36% for N) as well the principles of exposure and apparatus for feeding plants are described. Calculations of distribution parameters (relative specific allocation, RSA, and partitioning, %P) are presented and compared with their use in high-enrichment experiments. The precision of parameters and the theoretical or practical limitations of the methods are discussed. We show that the use of stable isotopes near their naturally occurring concentrations allows the tracing of new C or N input with precision, and is suitable for monitoring long-term partitioning. The significant advantages of this method with respect to precision, security and cost of handling compared with high abundance or radioactive tracing are discussed.
Characterisation of CO2 and HCO3- Uptake during Steady-state Photosynthesis in the Cyanobacterium Synechococcus PCC7942
Steady-state Photosynthesis in the
Cyanobacterium Synechococcus PCC7942
Authors: Yu J , Price GD , Badger MR
Published: January 2006

We have recently developed a mass spectrometric disequilibrium technique to measure CO2 and HCO3- uptake during steady-state photosynthesis in cyanobacteria and microalgae (Badger et al. 1993). Using this technique, we have found differences between the characteristics of Ci uptake in Synechococcus PCC7942 under steady- and non-steady state photosynthesis. Both low- and high-Ci cells have the capacity to transport CO2 and HCO3-. In contrast to reported results obtained under non-steady-state conditions, the activity of HCO3- uptake is higher than that of CO2 uptake, even in high-Ci cells. Dramatic increases in the affinity of the CI transport system for CO2 and HCO3- but not in maximal transport activities were found when high-Ci cells were induced under low-Ci conditions. These changes in affinity occurred within about 4 h. The affinity for HCO3- but not CO2 also increased when uptake activities were measured at a lower pH (pH 7.5 compared to pH 8.5), especially in high-Ci cells. HCO3- uptake was also more sensitive to LiCl inhibition than CO2 uptake. LiCl inhibition was partially relieved in the presence of NaCI. The carbonic anhydrase inhibitor ethoxyzolamide inhibited both CO2 and HCO3- uptake to about the same extent, consistent with the view that both transports might share a common 'carbonic anhydrase-like' component. The results are discussed in relation to previous results obtained under non-steady-state conditions.
Carbon Isotope Discrimination and Photosynthetic Gas Exchange in Coffee Hedgerows During Canopy Development
Authors: Gutierrez MV , Meinzer FC
Published: January 2006

In evergreen species, leaf carbon isotope discrimination (Δ) integrates phenological rhythms in gas exchange as well as seasonal changes in environmental conditions. However, few reports on long term variations in Δ of woody plants are available. We measured Δ, gas exchange, nitrogen content, and photosynthetic nitrogen-use efficiency (PNUE) in coffee hedgerows at different stages of canopy development encompassing a range of leaf area index (LAI) from 0.7 to 7.5. Assimilation was highest in sun leaves, but stomatal conductance was highest in shaded leaves. This resulted in a high correlation between assimilation and stomatal conductance in sun, but not in shaded leaves. Δ was about 20 lower in sun than in shaded leaves, and varied by 2.30 among leaves at different positions along two-year- old branches. These differences in Δ were the result of changes in carbon isotope composition that occurred in mature, fully expanded leaves as they became shaded during subsequent canopy growth. Results from a mass balance model based on leaf gas exchange characteristics and measured foliar Δ values suggested that about 50% of the carbon originally fixed during leaf development in the sun may have subsequently been turned over in the shade. Δ of sun leaves from the upper canopy decreased by about 20 with increasing LAI, indicating that intrinsic water-use efficiency (WUE) of this canopy layer increased during canopy development. In contrast, instantaneous WUE, estimated as assimilation divided by canopy transpiration obtained from sap flow measurements, seemed to decrease with increasing LAI. PNUE of upper canopy sun leaves decreased with increasing LAI, suggesting a physiological compromise between WUE and PNUE mediated by stomatal conductance, which also decreased with increasing LAI. A strong negative correlation obtained between leaf Δ and N content was consistent with a trade-off between intrinsic water- and N-use efficiency.
Influence of Elevated CO2 and Phosphorus Nutrition on the Growth and Yield of a Short-Duration Rice (Oryza sativa L. Cv. Jarrah)
Authors: Seneweera S , Milham P , Conroy J
Published: January 2006

The growth and development of a short-duration rice cultivar (Oryza sativa L. cv. Jarrah), grown in flooded soil with a range of phosphorus (P) levels and exposed to atmospheric CO2 concentrations of either 350 or 700 μL L-1 was followed for 146 days after planting (DAP). Development (estimated by rate of tiller production and time to flowering) was faster with higher soil P levels and CO2 enrichment, the effect being more pronounced with CO2 enrichment. During the early vegetative phase (up to 35 DAP), when rates of tiller production were low, shoot growth and rates of leaf expansion were faster at elevated CO2 concentrations and high soil P levels. Rates of tiller production were greater with these treatments during the 35-56 DAP period, when tillering was at a maximum. Shoot elongation was reduced at elevated CO2 levels and at high soil P levels during this period. By 146 DAP leaf weight was greater at high P levels, but CO2 enrichment accelerated tiller production to such an extent that final leaf weight was lower at high CO2, probably because there were fewer, and smaller, leaves on each tiller. Despite this, grain yield was increased by up to 58% by CO2 enrichment, with increases occurring even at low soil P levels. This was due mainly to an increase in grain number per panicle, although panicle number also increased. Higher soil P levels also increased grain number and yield. The P concentration in the foliage was unaffected by the CO2 treatments and the concentration required to produce maximum yield was 0.18% (dry wt basis) at both CO2 levels. Greater starch accumulation in the stems of high-CO2-grown plants may have accounted for the higher number of grains in each panicle.
Endogenous Biosynthetic Precursors of (+)-Abscisic Acid. I. Incorporation of Isotopes From 2H2O, 18O2 and [5-18O]Mevalonic Acid
Authors: Willows RD , Netting AG , Milborrow BV
Published: January 2006

RS-[5-18O]mevalonolactone has been synthesised and fed as the free acid via the transpiration stream or through the roots to tomato seedlings, to avocado fruit just prior to the climacteric, to cultures of the hyphomycete, Cercospora rosicola, to excised barley embryos and to an excised barley embryo cell-free system. Small amounts of 18O from [5-18O] mevalonolactone were detected in the abscisic acid from tomato plants and from the barley cell-free system but the mechanism involved is unclear. No 18O was detected in abscisic acid from the other tissues.
Mass spectrometry of the pentafluorobenzyl derivative of abscisic acid extracted from tomato plants that had been waterlogged in 2H2O (55 atom %) for 8 or 9 days showed that 40-47% was unlabelled or contained just one 2H atom. The remainder was seen as an envelope of peaks containing from two to 17 2H atoms. When plants waterlogged in 2H2O were subsequently wilted in an atmosphere, 80-90% of the multiply deuteriated abscisic acid was also labelled with 18O while only 43% of the mono/undeuteriated abscisic acid was so labelled. By saponification and re-analysis it was shown that most of the 18O, in the multiply deuteriated category of abscisic acid, was present in the carboxyl group. In the mono/undeuteriated abscisic acid a maximum of 50% was labelled with an 18O atom in the carboxyl group. These experiments led to the conclusion that there were two precursor pools involved in abscisic acid biosynthesis and that neither of these pools consisted of carotenoids.