bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of NADP-Malate Dehydrogenase in C4 Plants: Activity and Properties of Maize Thioredoxin M and the Significance of Non-Active Site Thiol Groups
Authors: Lunn JE , Agostino A , Hatch MD
Published: January 2006

Some unusual properties of purified maize leaf thioredoxin m were attributable to the presence of non-active site thiol groups, Unlike thioredoxins from other sources, maize leaf thioredoxin m was susceptible to inactivation by heating and this was associated with polymerisation of the molecule. Both these effects of heating were prevented or reversed by adding thiol compounds such as dithiothreitol. We concluded that, on heating, the free SH groups in the oxidised thioredoxin m molecule react with disulfide groups of other molecules to form polymeric complexes linked by disulfide bonds. We also observed the formation of a stable complex between the oxidised forms of thioredoxin m and NADP-malate dehydrogenase (NADP-MDH) under certain conditions. Evidence that in maize chloroplasts thioredoxin m and NADP-MDH occur in a 1: 1 molar ratio suggested that they may exist as a complex in vivo. However, ratios of thioredoxin rn to NADP-MDH varied widely in other species but always with thioredoxin m in excess. Furthermore, the complex we observed in vitro was shown to be the result of intermolecular disulfide bond formation and apparently occurred only with a non-physiological form of oxidised thioredoxin m. We could not demonstrate any non-covalent binding between thioredoxin m and NADP-MDH.
Plant Regeneration and Microprojectile-Mediated Gene Transfer in Embryonic Leaflets of Peanut (Arachis hypogaea L.)
Authors: Livingstone DM , Birch RG
Published: January 2006

Excised leaflets from mature embryos of peanut cultivars Robut, Gajah, McCubbin and NC-7 produced multiple shoot primordia via organogenesis on Murashige and Skoog medium supplemented with 3 mg L-1 BAP and 1 mg L-1 NAA. Plants were regenerated by elongation of shoot primordia on transfer to MS medium supplemented with 5 mg L-1 BAP. The regeneration frequency of five plants per embryonic leaflet was 10-40-fold higher than previously reported from seedling leaflets. Microprojectile bombardment parameters were optimised for high transient expression rates of the β-glucuronidase (uidA or gus) reporter gene in peanut embryos (> 2000 cells per bombardment) and in excised embryonic leaflets (> 1200 cells per bombardment). The firefly luciferase reporter gene (luc) allowed repeated non-toxic assays, revealing the transition from hundreds of transiently expressing cells soon after bombardment, to a few stably expressing regions in callus grown without selection for 8 weeks after bombardment of embryonic leaflets.
Modelling Canopy Production. II. From Single-Leaf Photosynthesis Parameters to Daily Canopy Photosynthesis
Authors: Sands PJ
Published: January 2006

This paper presents a simple algorithm for calculating daily canopy photosynthesis given parameters of the single-leaf light response, the canopy extinction coefficient, canopy leaf area index, daylength, daily solar irradiance and daily maximum and minimum temperatures. Analytical expressions are derived for total daily production by a canopy of leaves whose light response is either a rectangular hyperbola or a Blackman response. An expression which gives an excellent approximation to canopy photosynthesis for an arbitrary hyperbolic light response is then derived. These expressions assume photosynthetically active radiation (PAR) within the canopy follows Beer's law, light-saturated photosynthetic rate at any point in the canopy is proportional to the ratio of local PAR to full-sun PAR, diurnal variation of PAR is sinusoidal, and parameters of the single-leaf photosynthetic light response do not vary diurnally. It is shown how these expressions can be used to accommodate diurnal temperature variation of photosynthesis in a simple manner. The accuracy of the approximation to the basic integral of leaf photosynthesis over the canopy and over time is illustrated by applying the algorithm to compute the seasonal variation of daily canopy photosynthesis and comparing these data with corresponding values obtained by numerical integration.
Temporal and Spatial Regulation of Sucrose Accumulation in the Sugarcane Stem
Authors: Moore PH
Published: January 2006

Sucrose accumulation has been studied extensively in sugarcane-an example of a highly productive crop plant with the capacity for storing large quantities of sugar. Initial recognition and characterisation of the enzymes involved in sucrose synthesis and cleavage led to widely accepted models of how sucrose transport and accumulation occur. Studies on cells in culture and on isolated cellular fragments initially supported and strengthened these models but more recently have revealed weaknesses in them. Biophysical measurements and anatomical, histochemical, and tracer dye studies further eroded the older models. Molecular studies are beginning to reveal details at the gene and transcriptional levels of the enzymes involved in sucrose transport and metabolism. Collectively, results of recent research indicate the need for a new sucrose accumulation model. A dynamic model of rapid cycling and turnover of sucrose between the vacuole and metabolic and apoplastic compartments explains much of the data, but details of how the cycling is regulated remains to be discovered.
Effects of Pyridate on Chickpea
Authors: Gimeenez-Espinosa R , Jimenez-Diaz R , Prado RD
Published: January 2006

The effects of pyridate on 15 different chickpea (Cicer arietinum L.) genotypes have been investigated under controlled environmental conditions. Different degrees of tolerance to pyridate were detected. Pyridate applied at 2.0 and 4.0 kg active ingredient ha-1 inhibited the growth of two of the 15 genotypes. Chlorophyll fluorescence intensity showed high levels of inhibition 3 h after treatment in chickpea. For all the genotypes, photosynthetic activity was recovered 10 days after treatment. Fluorescence-induction curves revealed that pyridate inhibited photosynthetic electron transport in chickpea genotypes and Amaranthus blitoides faster than in Lolium rigidum. Photosynthesis in chickpea genotypes recovered more quickly than in Lolium rigidum, while Amaranthus blitoides died 3 days after treatment. Hill reaction assays concluded that CL9673 was the most phytotoxic pyridate metabolite. The order of phytotoxicity was CL9673 >> CL9673-N-Gly > CL9869 > pyridate > CL9673-O-Gly. These results support the idea that tolerance of chickpea to pyridate is due to degradation and detoxification of the herbicide.
Effects of Enhanced UV-B Radiation on the Drought Semi-deciduous Mediterranean Shrub Phlomis fruticosa under Field Conditions are Season-specific
Authors: Nikolopoulos D , Petropoulou Y , Kyparissis A , Manetas Y
Published: January 2006

The effects of enhanced UV-B radiation on Phlomis fruticosa L. were recorded during a 1- year field study. Plants received ambient or ambient plus supplemental UV-B radiation (simulating a 15% stratospheric ozone depletion over Patras, 38.3�N, 29.1�E) and only natural precipitation, i.e. they were simultaneously exposed to other natural stresses, particularly water stress during summer. Actual, biologically equivalent UV-B doses were 8.55 and 11.21 kJ m-2 day-1 during the summer maximum (14 July) and 0.85 and 1.12 kJ m-2 day-1 during the winter minimum (27 December) for control and W-B plants respectively, while intermediate values were received for the rest of the year. lho seasonally separated effects could be distinguished. The first was a growth response, observed at late spring, in the absence of any simultaneous stress and at the period most favourable for this shrub, during which it shows maximum photosynthetic performance. The effect was an inhibition of new leaf development and premature falling of old leaves, leading to lower leaf numbers and total leaf areas for the rest of the experimental period. The second effect coincided with the summer drought, during which net photosynthesis, chlorophyll content and photochemical efficiency of photosystem II decreased in the controls, but a trend towards a further decrease in W-B irradiated plants was also evident. Changes in total carotenoids were negligible, leading to higher carotenoid to chlorophyll ratios under enhanced W-B radiation. Photosynthetic parameters recovered to the same levels in control and UV-B irradiated plants after the first heavy rains in autumn. At final harvest, considerable decreases in total dry mass were evident for UV-B irradiated plants, while plant height, UV-B-absorbing compounds, relative water content and leaf specific mass were unaffected during the whole experimental period. UV-B effects may depend not only on co-occumng natural stresses, but on the specific sensitivity of individual developmental stages as well, i.e. they may be season-specific.
Osmotic Adjustment: Effect of Water Stress on Carbohydrates in Leaves, Stems and Roots of Apple
Authors: Wang Z , Quebedeaux B , Stutte GW
Published: January 2006

Potted apple (Malus domestica Borkh. cv. Jonathan) trees were subjected to water stress in a greenhouse. Midday leaf water potential (ΨW), osmotic potential (ΨS), soluble carbohydrates, and starch content of expanding and mature leaves, stems, and roots were measured to determine whether active osmotic adjustment occurred and if water stress affected carbohydrate metabolism. Mature leaves had the highest total soluble carbohydrate level (357 mM) and lowest Ψ (-1.85 MPa), followed by young leaves (278 mM, -1.58 MPa), stems (115 mM, -1.02 MPa), and roots (114 mM, -0.87 MPa). Sorbitol was the major component in all organs ranging from 53% of total soluble carbohydrate in young leaves to 73% in mature leaves. When ΨW decreased from -1.0 to -3.2 MPa, active osmotic adjustments of 0.3-0.4 MPa were observed in mature leaves, stems, and roots while a significantly higher adjustment of 1.0 MPa was detected in young leaves 5 days after the initiation of water stress. Sorbitol levels in leaves and stems gradually increased as ΨW decreased from -1.0 to -2.5 MPa, and then remained relatively stable or decreased slightly as ΨW decreased from -2.5 to -3.2 MPa. However, the percentage of soluble carbohydrate as sorbitol in roots decreased in response to water stress. Sucrose concentration decreased in mature leaves and stems, but increased in young leaves and roots as ΨW decreased. Starch concentrations in stems and roots also decreased as water stress developed. The sorbitol to sucrose ratios increased in mature leaves, but decreased in roots in response to water stress.
Relationship of Carbohydrate Sources and Indole-3-Butyric Acid in Olive Cuttings
Authors: Wiesman Z , Lavee S
Published: January 2006

Indole-3-butyric acid (IBA) treatment improves rooting of easy-to-root and moderate-rooting olive cultivars, but does not stimulate root formation in hard-to-root cultivars. The rate of root formation in olive cuttings is slow and a source of carbohydrates is required to maintain and improve the effect of IBA. Sucrose treatment applied together with IBA and several times thereafter improved all rooting parameters: rooting percentage, number of adventitious roots and root length. During rooting, photosynthesis in the cuttings is very low and has almost no effect on the carbohydrate content, so that starch appears to be the major source of carbohydrates. Amyloplast levels decline during rooting and IBA increases the rate of their disappearance. A significant percentage of rooted olive cuttings collapse during their hardening process, when no starch pool is available. Only photosynthesis of fully-expanded leaves can contribute to the source of the carbohydrates needed by the rooted plants. However, when the top growth is reduced, as often occurs in IBA-treated cuttings, the carbohydrate supply may not be enough to keep the rooted plants alive and to support their growth and development. The data suggest that carbohydrates have an important role in rooting and improve the stimulatory effect of IBA in this process. During the stages involved in the formation of adventitious roots the endogenous carbohydrate pool is the main source of carbohydrates, while in young rooted plants the main source comes directly from the photosynthesis.
X-Ray Microanalytical Studies on Two Modes of Strontium Binding in Fronds of Lemna minor
Authors: Steveninck RFMV , Fernando DR
Published: January 2006

X-ray microprobe analysis of freeze-fractured Lemna fronds has shown that zinc (Zn) and cadmium (Cd) are not incorporated into oxalate crystals in idioblasts, whereas strontium (Sr) is readily incorporated as an alternative to calcium (Ca). Ca and Sr are uniformly distributed throughout the crystal bundle when both elements are present in the nutrient solution. However, in neighbouring, non-idioblast cells Sr (but not Ca) may also be incorporated into globular deposits of less than 1 �m diameter. These globules contain the mineral elements potassium and phosphorus and their composition appears to be identical to that of phytate globules which contain Zn or Cd under conditions of Zn or Cd toxicity.
A Model of Wheat Grain Growth and Its Applications to Different Temperature and Carbon Dioxide Levels
Authors: Wang YP , Gifford RM
Published: January 2006

Kernel growth after anthesis is simulated as a function of the potential kernel growth rate, current photosynthate production and mobilisation of stored reserves. The potential growth rate of the kernel is simulated as two temperature-sensitive processes, cell production and cell growth. The difference between the potential and actual growth rates of the kernel depends on the carbon supply to the free space of the kernel endosperm, while the carbon supply is itself affected by the actual kernel growth rate. Sensitivity analysis showed that the growth rate of the grain per plant is most sensitive to the potential growth rate of the kernel and number of kernels per plant. This model is able to simulate the observed rates of grain growth and leaf senescence from anthesis to physiological maturity for wheat plants grown in two CO2 concentrations. The simulated temperature response of grain growth agrees well with the experimenal observations.
The Influence of the Lignotuber on Hydraulic Conductance and Leaf Conductance in Eucalyptus behriana Seedlings
Authors: Myers BA
Published: January 2006

Hydraulic conductances of stem segments and stem-plus-lignotuber segments were estimated for 3-year-old seedlings of the mallee eucalypt Eucalyptus behriana F. Muell. Stems of seedlings were cut underwater and either above or below the lignotuber. Cutting the stem of intact seedlings underwater and above the lignotuber resulted in rapid increases in leaf water potential (Ψ); 1.1 MPa in 10-15 min with a concomitant decrease in leaf conductance. Cutting the stem below the lignotuber did not significantly affect leaf Ψ or leaf conductance. Transpirational flow through whole seedlings and segments of seedlings was about 10-9 m3 s-1. The hydraulic conductance of the lignotuber (2.27 × 10-9 m3 s-1 Mpa-1) was about half that of the stem. This work suggests that resistance to water flow through the lignotuber accounts, in part, for the persistently low dawn Ψ of the foliage of mature trees of E. behriana.
Carbon Fixation Profiles Do Reflect Light Absorption Profiles in Leaves
Authors: Evans JR
Published: January 2006

Bifacial leaves contain an array of chloroplasts which are aligned along cell walls adjacent to intercellular airspaces. Cells beneath the adaxial (upper) surface are generally cylindrical in shape, forming palisade tissue and contain chloroplasts that have characteristics associated with acclimation to high irradiance. Conversely, cells near the abaxial (lower) surface are irregular in shape, forming spongy tissue and contain chloroplasts that have characteristics associated with acclimation to low irradiance. This results in a gradient of declining photosynthetic capacity per unit chlorophyll with increasing depth into the leaf. Space irradiance declines dramatically through the leaf. The profile of light absorption through the leaf has yet to be measured, but should approximate the product of space irradiance and pigment profiles. Since pigment content is highest in the middle of the leaf, light absorption peaks about one quarter of the way through the leaf. The response of leaf photosynthetic rate to irradiance reflects the interaction between the profiles of light absorption and chloroplast characteristics. Quantum yield (mol CO2 mol-1 quanta absorbed) varies for different layers in the leaf because the profile of Rubisco content per unit chlorophyll is not as steep as the light absorption profile. This skews the profile of carbon fixation away from the light absorption profile, favouring greater fixation in deeper layers. Nishio, Sun and Vogelmann (1993, Plant Cell 5, 953-961) measured profiles of 14C fixation across spinach leaves and concluded that carbon fixation was disconnected from the light gradient. Reanalysis of their data shows that carbon fixation is remarkably consistent with light absorption obeying the Beer- Lambert law when allowance is made for chlorophyll and Rubisco profiles through the leaf. This interpretation is supported by chlorophyll fluorescence properties of adaxial and abaxial surfaces. An apparent extinction coefficient of about 1500 m2 (mol Chl)-1 could be derived from leaf data which compares with 2230 m2 (mol Chl)-1 for pigment-protein complexes in solution. A possible test for this analysis would be to measure the 14C fixation profile of leaves illuminated on their abaxial surface.
The Influence of Recovery Temperature on the Effects of a Brief Heat Shock on Wheat. I. Grain Growth
Authors: Stone PJ , Savin R , Wardlaw IF , Nicolas ME
Published: January 2006

The responses of wheat yield to moderately high (20-32�C) and very high temperatures (> 32�C) have been studied separately in the literature, but not in combination, despite the fact that this is usually how elevated temperatures occur in the field. In this study, controlled environment conditions were used in order to examine the interaction of moderately high and very high temperatures during grain filling and their effect on wheat yield. Specifically, we wished to test the hypothesis that cooler conditions would facilitate greater recovery of grain growth following a brief exposure to very high temperature. To this end, wheat was exposed to either 21/16 or 40/16�C (day/night) from 15-19 days after anthesis and subsequently grown under one of three moderately high temperature regimes until maturity: 21/16, 27/22 or 30/25�C. For all moderately high temperature treatments, a brief 'heat shock' significantly reduced mature individual kernel mass by 17%, on average. In the absence of 'heat shock', increasing moderately high temperature progressively reduced mature individual kernel mass by ca 2.5% for each 1�C increase in average daily temperature. After a 'heat shock' event, however, there was not a progressive decline in mature individual kernel mass with increasing moderately high temperature. A short period of very high temperature applied early in grain filling therefore reduced the response of wheat to subsequent moderately high temperatures. We conclude that the reduction in yield caused by 'heat shock' is not alleviated by cool post-shock conditions.
Membrane Transport in Anoxic Rice Coleoptiles and Storage Tissues of Beetroot
Authors: Zhang Qisen , Greenway H
Published: January 2006

Rice coleoptiles and aged storage tissues of beetroot are both tolerant to anoxia. Both types of tissues retain their membrane integrity over several days of anoxia and take up glucose and sucrose from 0.5 mol m-3 external concentrations at 40-65% of the rate of the aerated tissues. However, these tissues show substantial differences in other membrane properties under anoxia. Anoxic rice coleoptiles had membrane potentials generated by electrogenic ion transport, i.e. these tissues retained, at least partially, their ATP-dependent H+ extrusion. This conclusion is based on the following evidence: (1) The membrane potentials under aeration were between -120 and -130 mV and these depolarised to between -75 and -98 mV immediately upon exposure to anoxia, but repolarised to between -109 and -122 mV after 1 h. (2) Addition of carboxy-cyanide m-chlorophenylhydrazone (CCCP) and iodoacetamide during anoxia depolarised the membranes from -120 mV to -68 and -86 mV, respectively. (3) Transient membrane depolarisations following addition of sugars and amino acids, ranging between 10 and 35 mV, were similar during anoxia and aeration. In contrast to the rice coleoptiles, cell membranes of anoxic storage tissues of beetroot were, at most, weakly energised since they depolarised from between -156 and -159 mV in aerated tissues to -97 mV upon transfer to anoxia and this membrane potential was retained for at least 72 h of anoxia (longest time measured). Another difference between the two types of tissues was for Cl- uptake from 0.25 mol m-3 external Cl-. The anoxic rice coleoptiles took up Cl- at 10-15% of the rates during aeration, while there was no detectable Cl- uptake by the anoxic storage tissues of beetroot. The persistence of membrane potentials generated by electrogenic ion transport in anoxic rice coleoptiles, but not in anoxic storage tissues of beetroot, may be associated with higher rates of alcohol fermentation, and therefore of glycolysis and ATP synthesis, in the rice coleoptiles than in the storage tissues of beetroot.

Extra keywords: rice coleoptiles, beetroot, anoxia, membrane transport, membrane potential.
Pectinesterases From Mature, Unripe Peach Fruit Bind Strongly to Pectic Polysaccharides
Authors: Glover H , Brady CJ
Published: January 2006

Contrary to previous findings, the level of the pectin de-esterifying enzyme, pectinesterase (PE; EC 3.1 .1. 11), is shown to be much higher in mature, green peach fruit than in ripe fruit. Aqueous buffers readily extracted three pectinesterase isoforms from ripe fruit but only a portion of the activity from mature, green fruit. In mature, green fruit extracts the enzyme precipitated when the ionic strength was lowered; consequently isoforms could not be recovered by ion exchange chromatography. In extraction residues from mature, green fruit, residual PE could be measured as active enzyme and, when denatured, could be detected by immunological techniques. Extraction of the enzyme was enhanced after digestion of the tissue with pectin lyase. The extracted enzyme fractionated as a large molecular weight complex rich in uronic acid, rhamnose, galactose and arabinose. After further digestion with endo-β-1,4- galactanase, the enzyme was in two fractions of smaller size but with residual carbohydrate. When mature, green and ripe fruit tissue were co-extracted, the recovered activity was as predicted from independently extracted tissues demonstrating that enzyme activity was not influenced by inhibitors contributed by either tissue type. Isoforms known to be present in the ripe fruit were recovered from extracts of the mixed tissues. It is concluded that PE in extracts of mature, green fruit has a strong association with pectic polymers and this has lead to its underestimation in previous studies. It is suggested that such an association with pectin polymers in vivo may regulate enzyme activity and enzyme turnover.
Gas Exchange of Field-Grown Pinus radiata - Relationships With Foliar Nutrition and Water Potential, and With Climatic Variables
Authors: Sheriff DW
Published: January 2006

Gas exchange measurements were conducted on Pinus radiata to investigate relationships between these and leaf-air vapour pressure deficit, photosynthetic photon flux density, and foliar temperature, water potential and nutrition in the field. Multiple non-linear regressions indicated strong relationships between gas exchange and foliar [P] (but of no other nutrient), leaf-air vapour pressure deficit, photosynthetic photon flux density, foliar water potential and temperature. The final regression produced for relationships between gas exchange and these variables explained 81% of the variance in the data. Micro-climate and foliar data from another site were used to predict gas exchange using the regressions and calculated parameters. Good agreement was obtained between the predicted values and carbon assimilation measured at that site. The relationship was poorer for leaf conductance.
Resistance to Acetyl-Coenzyme a Carboxylase-Inhibiting Herbicides Endowed by a Single Major Gene Encoding a Resistant Target Site in a Biotype of Lolium rigidum
Authors: Tardif FJ , Preston C , Holtum JAM , Powles SB
Published: January 2006

The mechanism and mode of inheritance of resistance to acetyl-coenzyme A carboxylase (ACCase)-inhibiting herbicides was investigated in a biotype of Lolium rigidum that has evolved resistance following selection with diclofop-methyl for 10 consecutive years. ACCase extracted from the resistant biotype is > 6.9 times more resistant to inhibition by diclofop than enzyme from a susceptible biotype. Similar or greater levels of resistance were found to other related herbicides. There is no difference in absorption or metabolism of diclofop-methyl or haloxyfop-methyl between the resistant and susceptible biotypes, hence differential absorption or metabolism of these herbicides does not contribute to resistance. F1 families from reciprocal crosses between the resistant biotype and a susceptible biotype respond similarly to the herbicide and are nearly as resistant as the resistant parent, indicating that the resistance trait is nuclearly located and has incomplete dominance over susceptibility. F2 families treated with 26 and 208 g ai ha-1 of haloxyfop-ethoxyethyl reveal only two phenotypes: resistant plants showing no injury and susceptible plants showing no growth. At both rates of haloxyfop-ethoxyethyl, the segregation of resistance to susceptibility follows a ratio of 3:1 (R:S) that fits the predicted ratio for a single nuclear gene with high dominance. From the F1 and F2 data, it is concluded that resistance to haloxyfop in this resistant biotype of L. rigidum is inherited as a single nuclear incompletely dominant gene coding for a resistant form of the target enzyme ACCase.
The Influence of Nitrogen on the Elevated CO2 Response in Field-Grown Rice
Authors: Ziska LH , Weerakoon W , Namuco OS , Pamplona R
Published: January 2006

Rice (Oryza sativa L. cv. IR72) was grown in the tropics at ambient (345 μL L-1) or twice ambient (elevated, 700 μL L-1) CO2, concentration at three levels of supplemental nitrogen (N) (no additional N (N0), 90 kg ha-1 (N1) and 200 kg ha-1 (N2)) in open-top chambers under irrigated field conditions from seeding until flowering. The primary objective of the study was to determine if N supply alters the sensitivity of growth and photosynthesis of field-grown rice to enriched CO2. A second objective was to determine the influence of elevated CO2 on N uptake and tissue concentrations. Although photosynthesis was initially stimulated at the leaf and canopy level with elevated CO2 regardless of supplemental N supply, with time the photosynthetic response became highly dependent on the level of supplemental N, increasing proportionally as N availability increased. Similarly, a synergistic effect was noted between CO2 and N with respect to above-ground biomass with no effect of elevated CO2 observed for the No treatment. Most of the increase in above-ground biomass with increasing CO2 and N was associated with increased tiller and, to a lesser extent, root production. The concentration of above-ground N decreased at elevated CO2 regardless of N treatment; however, total above-ground N did not change for the N1 and N2 treatments because of the greater amount of biomass associated with elevated CO2. For rice, the photosynthetic and growth response to elevated CO2 may be highly dependent on the supply of N. If additional CO2 is given and N is not available, lack of sinks for excess carbon (e.g. tillers) may limit the photosynthetic and growth response.
Rhizobium Inoculation Induces Condition-Dependent Changes in the Flavonoid Composition of Root Exudates From Trifolium subterraneum
Authors: Lawson CGR , Rolfe BG , Djordjevic MA
Published: January 2006

Rapid induction of chalcone synthase (predominantly CHSS) gene expression occurs within 6 h following the inoculation of Rhizobium leguminosarum bv. trifolii strain ANU843 on Trifolium subterraneum or wounding of plants (C. G. R. Lawson, M. A. Djordjevic, J. J. Weinman and B. G. Rolfe. 1994. Molecular Plant-Microbe Interactions 7, 498-507). Experiments were conducted under the same conditions to examine the time of onset of synthesis and excretion of flavonoids that might result from this early CHS expression. Flavonoids in root tissues and root exudates were examined by HPLC analysis and the ability of fractionated and unfractionated material to induce nodulation gene expression in Rhizobium measured. There were no detectable changes in nod-gene-inducing activity of individual HPLC fractions of root exudates of 1 day dark-grown roots after Rhizobium inoculation. In contrast, after 3 days exposure to Rhizobium, analysis of specific HPLC fractions showed the presence of an additional nod-gene-inducing compound which the data indicate was 4′,7-dihydroxyflavone. A different and additional nod gene inducer was found in inoculated 5 day samples of root exudate of light-grown plants indicating that light exposure changes the HPLC profiles as well as the nod-gene-inducing compound(s). Exudates collected from wounded plants were considerably different from those from Rhizobium-inoculated and uninoculated plants and contained no detectable nod gene inducers. The late detection (at day 3) of Rhizobium-induced flavonoid excretion may occur too late to be directly correlated with the observed expression of CHS 6 h after inoculation. In addition, the data suggest that although the CHS5 promotor responds to both wounding and Rhizobium inoculation, the biochemical consequences of CHS5 induction resulting from these treatments are different.
Interactions Between Rising CO2 Concentration and Nitrogen Supply in Cotton. I. Growth and Leaf Nitrogen Concentration
Authors: Rogers GS , Milham PJ , Thibaud MC , Conroy JP
Published: January 2006

The influence of sink development on the response of shoot growth in cotton (Gossypium hirsutum L. cv. Siokra BT1-4) was investigated by growing plants at three levels of CO2=2 concentration: 350 (ambient), 550 and 900 μL L-1 and six levels of nitrogen (N) supply ranging from deficient to excess (0-133 mg N kg-1 soil week-1). Changes in leaf N concentration were also investigated. At 59 days after sowing, there was an average 63% increase in shoot growth at 550 μL CO2 L-1 compared with ambient CO2-grown plants, with no significant growth increase at 900 μL CO2 L-1 and, this response was closely matched by sink development (flower number and stem weight). Low N supply restricted the responses of both sink development and shoot growth to high CO2. At elevated CO2, leaf N concentration was reduced by an average 27% at low to adequate N supply. The high CO2-induced reduction in leaf N concentration, however, disappeared when the N supply was increased to a high level of 133 mg N kg-1 soil week-1. These CO2 effects on leaf N concentration were smaller when N was expressed per unit leaf area, apparently due to a combination of the effects of elevated CO2 or high N supply reducing specific leaf area and, to an N uptake limitation at low to moderate levels of N supply. The critical foliar N concentrations (leaf N concentration at 90% of maximum shoot growth) were reduced from 42 to 38 and 36 mg g-1 when CO2 concentrations were increased from 350 to 550 and 900 μL L-1 respectively, indicating that changes in fertiliser management may be required under changing CO2 concentrations.
Mechanism of Action of C2H4 in Promoting the Germination of Cocklebur Seeds. II. The Role of C2H4 in the Enhancement of Priming Effects
Authors: Yoshiyama M , Yajima H , Atsumi T , Esashi Y
Published: January 2006

In cocklebur (Xanthium pennsylvanicum Wallr.) seeds, the pre-exposure to water stress imposed by polyethylene glycol or mannitol (seed priming) increased osmotic pressure (OP) in cell saps and water extracts. Carbohydrates were the major components and soluble proteins also played a partial role as an osmoregulator in the primed seeds. C2H4, which was effective in stimulating the growth of both axial and cotyledonary tissues even under water-stressed conditions, changed the amino acid pool size regardless of water stress. This C2H4-induced amino acid accumulation also occurred under anoxic conditions. CO2 was capable of stimulating growth of axial tissues but it did not increase OP values or carbohydrate and amino acid contents. The effectiveness of seed primlng gradually declined with increasing duration of presoaking, but C2H4 prevented the reduction of the priming effect by effectively maintaining the amino acid levels. Thus, it is likely that C2H4 contributes to the enhancement of the priming effect by abundantly supplying amino acids.
Possibility of Increasing Yield Potential of Rice by Reducing Panicle Height in the Canopy. II. Canopy Photosynthesis and Yield of Isogenic Lines
Authors: Setter TL , Conocono EA , Egdane JA
Published: January 2006

Reduced panicle height in a rice crop canopy may have beneficial effects of increasing yield potential through reduced shading of leaves leading to greater canopy photosynthesis. Effects of different panicle height in the canopy were evaluated in glasshouse and field experiments using isogenic lines with elongated upper internodes (EUI lines) from two cultivars. Isogenic lines of IR36 and IR50 with elongated upper internodes (IR36EUI and IR50EUI) had panicle heights at the top of the canopy of 96-100% of canopy height, while lines with low panicle heights had panicles which were 74 and 82% of canopy height respectively. Lines with low panicle height had about 10% more of the total leaf area index (LAI) above panicles and this resulted in up to 35% greater light interception by leaves above panicles relative to high panicle height plants. At 5 days before flowering IR36 and IR36EUI had equal canopy photosynthesis, while at flowering, lines had equal shoot nitrogen percentage and LAI. At maturity spikelets per mainstem were not significantly different. At 0, 7, 14 and 21 days after flowering (DAF), IR36, with low panicle height, had 10-30% greater canopy photosynthesis than IR36EUI; greater canopy photosynthesis was observed for IR50 relative to IR50EUI. These beneficial effects of low panicle height on canopy photosynthesis occurred even though the maximum single leaf photosynthesis and respiration rates were similar in both isogenic lines during grain filling. In the field and in a glasshouse experiment where plants were arranged into canopies, IR36, with low panicle heights had 15-40% greater yields than the isogenic line IR36EUI with high panicle heights; greater yields also occurred for IR50 than IR50EUI.
Occurrence of Proteoyltic and Lectin-Degrading Activities in the Bark of Robinia pseudoacacia
Authors: Tazaki K
Published: January 2006

Various endo- and exopeptidase activities were examined in an extract of the bark of Robinia pseudoacacia L. The crude extract hydrolysed azocasein, gelatin and benzyloxycarbonyl-Phe-Ala (Z-Phe-Ala) at acidic pH and leucine p-nitroanilide (LPA), alanine p-nitroanilide (APA) and N-benzoyl-arginine ρ-nitroanilide (BAPA) at neutral to weakly alkaline pH. The extract also hydrolysed lectin, which is one of the predominant bark proteins, to smaller polypeptides at acidic pH. The proteolytic activities against azocasein and Z-Phe-Ala remained at relatively high levels during the season when the amount of lectin in the bark decreased rapidly.
Molecular Forms and Kinetic Properties of Pyruvate, PI Dikinase From Two Populations of Barnyard Grass (Echinochloa crus-galli) From Sites of Contrasting Climates
Authors: Simon JP
Published: January 2006

Plants from two populations of the C4 barnyard grass (Echinochloa crus-galli (L.) Beauv.) from Qu�bec (QUE) and Mississippi (MISS) were acclimated under controlled conditions to 26/20 and 14/8�C daylnight. The apparent energy of activation (Ea, Km for pyruvate, Vmax/Km ratios, Kcat (substrate turnover number) and specific activity of pyruvate, PI dikinase (PPDK, EC 2.7.9.1) were analysed from partially purified Sephadex G-25 extracts of PPDK from leaves and from highly purified PPDK. PPDK from both populations consisted of one isomorph with the same electrophoretic mobility in polyacrylamide gels and similar molecular weights for the native enzyme (385 kDa) and for the subunit of the tetramer (94.8 kDa). No significant differences were observed for any of the kinetic properties of partially purified or purified PPDK or for the specific activity per mg protein of purified PPDK extracted from plants of the two populations and acclimated to the two thermoperiods. Net photosynthetic rates (Ps) were positively correlated with PPDK activity levels (E) but ElPs ratios were lower than 1.0, ranging from 0.43 to 0.67. Results indicate that differences in activity levels, thermal properties and in the kinetics of light activation and dark inactivation of PPDK extracted from cold-acclimated MISS and QUE plants, as reported in earlier studies, are due to causes other than kinetic properties or electrophoretic characteristics of PPDK.
Effects of Short Periods of Drought and High Temperature on Grain Growth and Starch Accumulation of Two Malting Barley Cultivars
Authors: Savin R , Nicolas ME
Published: January 2006

Short periods (3-5 days) of high maximum temperature (>35�C), often accompanied by drought, commonly occur during grain filling of cereals. Short periods of high temperature have been shown to reduce grain weight and baking quality in wheat, but little is known about their effects on barley. Consequently, we examined the effects of high temperature and drought, alone or combined, on grain growth for two barley cultivars, Schooner and Franklin. Treatments started 15 days after anthesis and consisted of the factorial combination of three temperatures and three water regimes. The high temperature (maximum 40�C for 6 h day-1) and drought treatments were maintained for 5 or 10 days. Drought reduced individual grain weight much more (ca 20%) than high temperature (ca 5%) for both cultivars. Franklin appeared to be more sensitive to heat stress than Schooner. The reduction in individual grain weight was greatest when both stresses were combimed (ca 30%). The reduction in mature grain weight under high temperature was due to a reduction in duration of grain growth for Schooner and to a reduction in both rate and duration of grain growth for Franklin (8-12%). The reduction in duration of grain growth was the most important cause of reduced grain weight at maturity under drought alone (12-25%) or combined with high temperature (25-33%). Nitrogen content per grain was quite high and similar for all treatments, and nitrogen percentage increased when stress was severe enough to reduce starch accumulation, confirming that starch accumulation is more sensitive to post- anthesis stress than nitrogen accumulation. We conclude that drought, particularly when combined with high temperature, is more likely than heat stress to cause large reductions in grain weight of barley under field conditions.
Anatomy of the Legume Nodule Cortex: Species Survey of Suberisation and Intercellular Glycoprotein
Authors: Brown SM , Walsh KB
Published: January 2006

Nodules of 29 species from 23 legume genera were examined for suberisation and glycoprotein deposits. Extensive suberisation of the nodule outer cortex to form a peridem was considered a primitive feature, common to non-legume and caesalpinioid nodules. The periderm was less extensive in nodules of Mimosoideae and Papilionoideae. Vascular bundles within the nodule were always surrounded by a vascular endodermis, defined by the presence of suberin on radial walls. Suberisation of the tangential walls of this endodermis was considered to be a primitive feature (present in all species examined of Caesalpinioideae and Mimosoideae, and in 10 out of 21 Papilionoideae) which may limit solute import to and export from the nodule. Glycoprotein was observed in the apoplast of the cortex in the three papilionoid species examined, but was absent in the caesalpinioid species examined. The common endodermis was recognised as an advanced feature, present only in certain species of the subfamily Papilionoideae (5 of 7, and 11 of 15 species of indeterminate and determinate nodule growth respectively). A membrane impermeant dye (lucifer yellow-CH), supplied in the rhizosphere under a mild vacuum, was observed to infiltrate through the cortex and into the infected zone in caesalpinioid nodules, and as far as the inner cortex in mimosoid and papilionoid nodules. Thus the common endodermis does not serve as an apoplastic barrier, and is unlikely to serve as a significant oxygen 'diffusion barrier'.
Partitioning of [14C]Glucose Into Sorbitol and Other Carbohydrates in Apple Under Water Stress
Authors: Wang Z , Quebedeaux B , Stutte GW
Published: January 2006

Sorbitol plays an important role in osmotic adjustment in mature apple leaves under water stress. This study was conducted to determine whether water stress increases the conversion of glucose to sorbitol in mature apple leaves. A solution of [14C]glucose or [14C]sorbitol was introduced into the cut end of detached apple (Malus domestica Borkh. 'Red Jonathan') shoots which had previously experienced either water stress or no stress. The cut shoots were then placed in sterile deionised water to maintain well-watered conditions or in no water to continue water-stressed conditions. When shoots were labelled with [14C]glucose, 38% of [14C]glucose was recovered as glucose in the leaves at a leaf water potential (Ψw) of -1.0 MPa following a 30-min labelling. The remaining [14C]glucose was converted to sucrose (24%), fructose (21%), and sorbitol (17%). Water stress altered the partitioning of [14C]glucose between sorbitol and sucrose, increasing the ratio from 0.8 at Ψw = -1.0 to 1.7 at Ψw = -3.0 MPa. When shoots were supplied with [14C]sorbitol, <10% of [14C]sorbitol was converted to other soluble carbohydrates. Water stress inhibited the conversion of both [14C]glucose and [14C]sorbitol into starch. The results suggest that sorbitol accumulation may result from the preferential conversion of glucose to sorbitol rather than to sucrose and starch.
Defective Infection and Nodulation of Clovers by Exopolysaccharide Mutants of Rhizobium leguminosarum bv. trifolii
Authors: Rolfe BG , Carlson RW , Ridge RW , Dazzo FB , Mateos PF , Pankhurst CE
Published: January 2006

The biological and symbiotic properties of two types of exopolysaccharide deficient (Exo- phenotype) mutants of Rhizobium leguminosarum were investigated. One mutant, a pss1 derivative (ANU437) of R. l. bv. trifolii, produces very low levels of acidic exopolysaccharide (EPS) and of the acidic oligosaccharide (AOS) repeating unit lacking its O-acetyl substituent. The second strain, originally a R. I. bv. viciae derivative, but containing a clover pSym plasmid (Exo-1 mutant ANU54(pBRIAN)), did not produce any EPS polymer or detectable oligosaccharide repeating unit. The Exo- mutants formed no capsules and their growth in laboratory media was comparable to their parent strains but was inhibited by the addition of the phytoalexins medicarpin and kievitone, but not by the phytoalexin pisatin. Both Exo- mutants were slow to induce clover root hair curling (Hac+), and formed growing infection threads (Inf-) only on white clovers. However, the extent of these early symbiotic defects depended on the plant growth conditions used. Both mutants induced small non-nitrogen-fixing (Fix-) nodules on white and subterranean clovers. Within the white clover nodules induced by mutant ANU437, bacteria were released into plant cells. On white clovers at elevated light and temperature conditions, the Exo-1 mutant ANU54(pBRIAN) usually failed to initiate infection threads and thus formed empty nodules which do not contain any bacteria. In addition, this mutant formed only empty nodules without infection threads on subterranean clovers under all growth conditions tested. The outermost layers of plant cells in these empty nodules had thickened cell walls and deposited materials. These experiments show that EPS synthesis is essential for the induction of rapid root hair curling, proper infection thread formation and the ability to sustain the growth of induced nodules on various clovers.
Modulation of the Cytochrome b6/f Complex and Photosystem I Under Growth-Limiting Light in Amaranthus hypochondriacus, an NAD-ME C4 Plant
Authors: Sailaja MV , Das VSR
Published: January 2006

Highly characteristic responses of thylakoid membranes were observed in function and composition when fully developed plants of Amaranthus hypochondriacus L. grown under light sufficient (2000 μmol m-2 s-1) conditions were transferred to light limited conditions (650 μmol m-2 s-1 and 200 μmol m-2 s-1). The whole-chain, photosystem I and photosystem II electron transport rates were depressed in both bundle sheath and mesophyll thylakoids with remarkable differences between them in variation of rates under limiting light. The reduction in PSI electron transport in the mesophyll could be attributed to reduced PSI centres, while in the bundle sheath, a modulation of cytochrome b6/f complex regulated the rates of PSI electron transport. The requirement for an unaltered number of PSI centres under limiting light in the bundle sheath is ascribed to operation of an energy-consuming C4 pump.
Effect of Drought Stress on Photosynthetic Characteristics, Growth and Sugar Accumulation of Field-Grown Sweet Sorghum
Authors: Massacci A , Battistelli A , Loreto F
Published: January 2006

We studied the effect of drought on photosynthesis, growth, and sugar accumulation in field-grown sweet sorghum (Sorghum bicolor (L.) Moench). Stomata closed when drought stress developed during the day. As a consequence, photosynthesis was reduced. The water use efficiency of drought-stressed leaves was slightly lower than that of controls and this reduction was more pronounced early in the morning and in the evening. This suggested that not only stomata limit photosynthesis under drought: photosynthesis at high CO2 was lower in drought-stressed than in control leaves, suggesting that carbon metabolism was inhibited. Electron transport was also reduced, but an increased number of electrons appeared necessary to fix CO2 under drought. Before anthesis, growth was not affected by drought but, after anthesis, elongation of the last internodes was greater in controls than in drought- stressed plants. Both controls and drought-stressed plants accumulated sucrose and starch in the stem after anthesis. The accumulation was low and ceased early in the stem apex. It is likely that seeds in the panicle compete with the apex for carbon. During panicle maturation sucrose and starch content was higher in drought-stressed than in control stems. At the end of our experiments, however, the sucrose content per plant was similar in all samples. We conclude that sugar accumulation is less sensitive to drought than photosynthesis. Irrespective of drought conditions, (i) before anthesis growth is the predominant sink for photosynthates; (ii) after anthesis sugar accumulation in the stem becomes the preferential sink at the expense of growth of apical internodes.