bluuebunny/crossref_metadata_2025 huggingface dataset:
Elevated Atmosphere Partial Pressure of CO2 and Plant Growth. III. Interactions Between Triticum aestivum (C3) and Echinochloa frumentacea (C4) During Growth in Mixed Culture Under Different CO2, N Nutrition and Irradiance Treatments, With Emphasis on Below-Ground Responses Estimated Using the δ13C Value of Root Biomass
Authors: Wong SC , Osmond CB
Published: January 2006

Wheat (Triticum aestivum L.), a C3 species, and Japanese millet (Echinochloa frumentacea Link), a C4 species, were grown in pots in monoculture and mixed culture (2 C3 : 1 C4 and 1 C3:2 C4) at two ambient partial pressures of CO2 (320 and 640 μbar), two photosynthetic photon flux densities (PPFDs) (daily maximum 2000 and 500 �mol m-2 s-1) and two levels of nitrogen nutrition (12 mM and 2 mM NO3-). Growth of shoots of both components in mixed culture was measured by physical separation, and the proportions of root biomass due to each component were calculated from δ13C value of total root biomass. In air (320 μbar CO2) at high PPFD and with high root zone-N, the shoot biomass of C3 and C4 components at the first harvest (28 days) was in proportion to the sowing ratio. However, by the second harvest (36 days) the C4 component predominated in both mixtures. Under the same conditions, but with low PPFD, C3 plants predominated at the first harvest but C4 plants had over- taken them by the time of the second harvest.
Elevated atmospheric CO2 (640 μbar) stimulated shoot growth of Triticum in 15 of 16 treatment combinations and the stimulation was greatest in plants provided with low NO3-. Root growth of the C3 plants was generally stimulated by elevated CO2, but was only occasionally sensitive to the presence of C4 plants in mixed culture. However, growth of the C4 plants was often sensitive to the presence of C3 plants in mixed culture. In mixed cultures, elevated CO2 plants stimulated growth of C4 plants at high PPFD, high-N and in all low-N treatments but this was insufficient to offset a marked decline in shoot growth with increasing proportion of C3 plants in mixed cultures. The unexpected stimulation of growth of C4 plants by elevated CO2 was correlated with more negative δ13C values of C4 root biomass, suggesting a partial failure of the CO2 concentrating mechanism of C4 photosynthesis in Echinochloa under low-N. These experiments show that for these species nitrogen was more important than light or elevated pCO2 in determining the extent of competitive interactions in mixed culture.
Environmental Effects on the Relationship Between the Quantum Yields of Carbon Assimilation and in vivo PsII Electron Transport in Maize
Authors: Krall JP , Edwards GE
Published: January 2006

The partitioning of light energy absorbed by photosystem (PS) II in the C4 species maize was investigated under various photosynthetic photon flux densities (PPFD), temperatures, and intercellular CO2 concentrations. The relationship between the quantum yield of PSII electron transport (�e) and the quantum yield of CO2 assimilation (ΦCO2) was generally found to be linear, with similar slopes. This indicates that PSII electron transport is tightly coupled to CO2 assimilation such that measurements of �e may be used to estimate photosynthetic rates in maize. Coefficients of quenching of PSII chlorophyll fluorescence indicated that, under excessive PPFD or when CO2 assimilation was decreased due to suboptimal or supraoptimal temperature or low Ci, the energy in excess of that needed to drive the reduced rate of PSII electron transport was dissipated via a mechanism known to be correlated to the trans-thylakoid proton gradient (high energy quenching, qE) and a mechanism believed to arise in the PSII antenna chlorophyll (qN(slow)). At suboptimal temperature the energy dissipation was principally at the antenna level and qE was low, while at supraoptimal temperature the reverse was true. The results are discussed relative to coupling of PSII activity to CO2 fixation and mechanisms of energy dissipation in this C4 species.
Identification and Determination by Fast Atom Bombardment Mass Spectrometry of the Compatible Solute Choline-O-sulfate in Limonium Species and Other Halophytes
Authors: Hanson AD , Gage DA
Published: January 2006

A sensitive and specific method was developed for determining choline-O-sulfate by fast atom bombardment mass spectrometry, using a deuterium labelled choline-O-sulfate internal standard. This method was used to survey leaves or shoots of 30 native halophytic species from 14 families, collected from temperate and subtropical saline habitats. Twenty-three species had very little choline-O-sulfate (-1 dry wt) but Avicennia germinans contained 8 μmol g-1 dry wt, and all six members of the family Plumbaginaceae surveyed (Limonium spp. and Armeria maritima) accumulated > 100 μmol g-1 dry wt. Three cultivated Limonium species were also found to accumulate choline-O-sulfate when salinised with NaCl or with NaCl plus Na2SO4 under controlled environmental conditions. The identity of choline-O-sulfate in Limonium species was confirmed by high resolution and tandem mass spectrometry, by 1H nuclear magnetic resonance, and by analysis of hydrolysis products. Tests with Limonium leaf disks showed that the salt glands of this genus secrete very little sulfate. Possible roles for choline-O-sulfate in osmotic adjustment and sulfate detoxification are discussed.
Multiple Forms of 1,4- β -Glucanase in Ripening Tomato Fruits Include a Xyloglucanase Activatable by Xyloglucan Oligosaccharides
Authors: Maclachlan G , Brady C
Published: January 2006

Extracts of ripening tomato (Lycopersicon esculentum L. var. Sunny) were tested for their capacity to hydrolyse carboxymethylcellulose (CMC) and seed xyloglucan (XG) at different pH values in the presence or absence of seed XG oligosaccharide subunits (7 to 9 sugar residues). CMC-ase activities were most active at pH 5 and 7 in locule extracts, whereas XG-ase activity was most active in the presence of XG oligosaccharides at pH 6 in pericarp extracts. The cation exchange FPLC column, Mono S, separated three zones of CMC-ase activity in pericarp extracts. One zone was most active at pH 5, and two at pH 7. The three CMC-ases had some XG-ase activity in the presence of oligosaccharide but, in addition, there were two regions of the eluate with XG-ase but no CMC-ase activity. The presence of XG-ase activity, separate from CMC-ases, was also observed after hydrophobic interaction chromatography, and in protein precipitated by lowering the salt content of extracts. During ripening, the CMC-ases and the oligosaccharide-activated XG-ases in pericarp extracts increased in total and specific activities, while endogenous XG-ase activity, that is in the absence of XG oligosaccharides, remained unchanged or declined. It is concluded that multiple, 1,4-β-glucanase activities develop in ripening tomato fruit, including, in pericarp tissue, a specific XG-ase which is latent and activated by XG oligosaccharides.
Effect of Soil Salinity on the Expression of Betaine Aldehyde Dehydrogenase in Leaves: Investigation of Hydraulic, Ionic and Biochemical Signals.
Authors: Mccue KF , Hanson AD
Published: January 2006

Betaine aldehyde dehydrogenase (BADH) catalyses the last step in glycine betaine synthesis. The levels of BADH enzyme and BADH mRNA have previously been shown to be increased several-fold by salt stress. To characterise this induction more thoroughly, BADH mRNA levels and enzyme activities were analysed in leaves of sugar beet plants (Beta vulgaris L.) subjected to different salinisation regimes. Following a salt shock (transfer from 0 to 400 mM NaCI) BADH enzyme activity rose slowly for several days. In contrast, BADH mRNA level first decreased for several hours, and then increased. When salt was leached from the rooting medium of salinised plants, BADH enzyme activity declined, with a half-life of more than 4 days. However, the level of BADH mRNA declined sharply with an apparent half-life of 2 h showing that transcription of the BADH gene or the stability of BADH mRNA in leaves can respond very dynamically to salinity changes around the root. In plants which had been gradually salinised and then held at various NaCl concentrations, the steady state level of enzyme rose continuously between 0 and 500 mM NaCl, whereas that of BADH mRNA reached a plateau at 100 mM NaCl. In general, the observed BADH mRNA fluctuations could not be satisfactorily explained by assuming them to be responses to hydraulic signals. This suggests the participation of a non-hydraulic signal or signals coming from the root. The non-hydraulic signal is unlikely to be NaCl, because leaf disks exposed to salt concentrations typical of the apoplast of salinised leaves did not accumulate BADH mRNA. A biochemical messenger is thus implied. Although abscisic acid application to leaf disks elicited significant increases in BADH mRNA level, these were several-fold smaller than those observed in leaves of intact salinised plants, suggesting the involvement of some other substance.
Water Relations in Cowpea and Pearl Millet Under Soil Water Deficits. I. Contrasting Leaf Water Relations
Authors: Petrie CL , Hall AE
Published: January 2006

Cowpea [Vigna unguiculata (L.) Walp.] can survive soil water deficits more effectively than pearl millet [Pennisetum americanum (L.) Leeke]. Cowpea and millet were grown in a glasshouse in different rooting media and different sizes of container, under wet and dry treatments, and as sole crops and intercrops to evaluate any differences in leaf water potential. Millet developed significantly lower predawn leaf water potentials (ΨL) than cowpea under the dry treatment of all of the rooting media and container sizes used, but both millet and cowpea maintained high predawn ΨL in the well-watered treatment. With the dry treatment, the same difference in predawn ΨL between cowpea and millet developed in plants grown either as sole crops or as intercrops in the same pot. These results suggest that plants grown as intercrops were somehow isolated from each other, even though their root systems may have overlapped, and that competition for water was probably not occurring. Differences in predawn ΨL between cowpea and millet were detected with either a pressure chamber or psychrometers, but values of ΨL varied with measurement method. Compared with psychrometer values, pressure chamber values became significantly lower in millet late in the dry treatment but were higher in cowpea. Agreement between the methods for measuring ΨL improved in cowpea when predawn xylem osmotic potential was added to the pressure chamber value. At the end of the experiments, leaf surface conductance to water vapour and leaf area were lower in millet than cowpea. Consequently, it is possible that the significantly lower predawn ΨL in millet was not due to greater water use by millet compared with cowpea.
Water Relations in Cowpea and Pearl Millet Under Soil Water Deficits. II. Water Use and Root Distribution
Authors: Petrie CL , Hall AE
Published: January 2006

Pearl millet [Pennisetum americanum (L.) Leeke] develops lower predawn leaf water potentials than cowpea [Vigna unguiculata (L.) Walp.] when plants are subjected to progressive soil dehydration. Water use and root distribution were studied as possible explanations for this difference using plants grown in pots and in tubes in a glasshouse. In experiments grown in pots, weights of each container were measured daily after initiation of the dry treatment to determine water use, and roots and soil were sampled at the end of the experiment to determine root length density and soil water content. In experiments conducted in 1 m long tubes, plants were grown in either Turface Plus or a Turface Plus/sand mixture which had a high water-holding capacity and could be easily separated from roots. Roots and rooting medium were sampled during the dry treatment. Water content and root length density in the same sample were measured, and root distributions at various depths were determined. Pearl millet (millet) did not use more bulk water than cowpea by the time the difference in predawn leaf water potential developed. Millet root length density was at least twice as great as cowpea, and the decline in predawn leaf water potential was greater in millet, even when its root system was more extensive than that of cowpea.
Transpiration Ratio and Plant Mineral Content Are Related Among Genotypes of a Range of Species
Authors: Masle J , Farquhar GD , Wong SC
Published: January 2006

The relationship between transpiration ratio (R, ratio of water transpired to carbon fixed) or cabon isotopic discrimination (Δ) and leaf dry-matter mineral content (m) was examined within several C3 species including monocot and dicotyledonous species (Triticum aestivum, Hordeum spontaneum, Helianthus annuus and Nicotiana tabacum) and the C4 species, Sorghum bicolor. In all species, whether grown in the glasshouse or in the field, m was positively correlated to R; consistently, m was positively correlated to Δ in the C3 species, and negatively in sorghum.
These genetic correlations between transpiration ratio and mineral content contrast with the absence of such a relationship when variations of R were environmentally induced by changes of atmospheric humidity or carbon dioxide concentration. In those circumstances, and consistent with earlier reports, ash content or its major constituents were remarkably stable and insensitive to a doubling or more of R.
The genetic relationships shown in the present study are to some extent brought about by variations in assimilation and transpiration rates per se (i.e. passive mineral uptake), but the data indicate that they involve other quantitatively more important mechanisms, some of which may be related to the control of leaf water content. With the exception of Hordeum spontaneum, potassium was the element contributing the most to the relationship between R, or Δ, and mineral content. Depending on the species other elements showed a significant correlation with R or Δ. Further experiments are needed to unravel the nature of the genetic association between R and m. Meanwhile plant mineral content may be a useful criterion in selection programs to improve transpiration efficiency since its correlation with R was not much lower than that of carbon isotope discrimination.
Effect of Leaf Senescence on Glyoxylate Cycle Enzyme Activities
Authors: Pistelli L , Perata P , Alpi A
Published: January 2006

In order to elucidate the metabolism of the peroxisomes during foliar senescence of leaf beet (Beta vulgaris L., var. cicla), peroxisomal activities have been determined at various stages of senescence. Catalase and hydroxypyruvate reductase activities decreased whereas those of the β-oxidation pathway and glyoxylate cycle enzymes increased at the same time. The increased activities of malate synthase, isocitrate lyase, malate dehydrogenase and citrate synthase indicate that the glyoxylate cycle might be activated during the foliar senescence of leaf beet.
Influence of Water Stress on Grapevines Growing in the Field: From Leaf to Whole-Plant Response
Authors: Winkel T , Rambal S
Published: January 2006

A comparative study of soil-plant water relations was conducted on three grapevine cultivars (Vitis vinifera L. cvv. carignane, merlot, shiraz) to investigate their adjustment to short-term and long-term water stress under field conditions. Adjustment was a function of the relative stability of the internal plant water status on diurnal and seasonal scales. On a diurnal scale, stomatal closure in response to water vapour pressure directly contributed to this stability. Indirect evidence suggested an influence of the soil water status on the diurnal stomatal activity. On a seasonal scale, sufficient leaf hydration required high whole-plant hydraulic conductance. This was achieved by either daily stomatal regulation or limitation of leaf area. Physiological adjustment to water stress through stomatal control was well developed in cv. carignane, which originated in a Mediterranean environment. However, cv. shiraz, which was of mesic origin, apparently adjusted to water stress by reducing leaf area. Our study demonstrates the utility of integrating data on stomatal conductance, leaf water potential and whole-plant hydraulic conductance to interpret whole plant adaptation to water stress, and elucidates two mechanisms by which genotypes differentially acclimate to water stress.
Elevated CO2 Improves the Growth of Wheat Under Salinity
Authors: Nicolas ME , Munns R , Samarakoon AB , Gifford RM
Published: January 2006

Wheat plants (Triticum aestivum cv. Matong and T. durum cv. Modoc) were grown at ambient and elevated CO2 (350 cm3 m-3 above ambient) in soil with or without 150 mol m-3 NaCl for 6 weeks. The increase in dry matter, leaf area and tillering under high CO2 was relatively greater under saline than non-saline conditions for both cultivars. Tillering was the primary component of growth affected by both salinity and high CO2. Salinity greatly reduced tillering and high CO2 partly reversed the effects of salinity. High CO2 increased dry matter accumulation of the salt-sensitive Modoc to a greater extent (+104%) than that of the more salt-tolerant Matong (+73%) in the salt treatment. Transpiration rates were greatly reduced by salinity for both cultivars. Under high CO2, increased leaf areas compensated for reduced transpiration rates per unit leaf area (i.e. greater stomatal closure), and total transpiration was little affected by CO2 level within each treatment. The more salt-tolerant Matong showed greater stomatal closure and higher transpiration efficiencies than the salt-sensitive Modoc under salinity. High CO2 reduced transpiration rate (per unit dry weight) by 40 to 50%, but did not significantly change the rate of sodium accumulation (per unit dry weight), indicating that salt uptake was largely independent of water uptake, and that high CO2 did not increase growth by reducing the salt load. Our results suggest that high CO2 increased growth by stimulating the development of tiller buds that would otherwise have been inhibited.
The Role of Auxin in the Polar Organisation of Apical Meristems
Authors: Sachs T
Published: January 2006

Auxin is a correlative signal, coordinating leaf development with vascular differentiation and other developmental processes throughout the plant. It has a unique influence on the orientation of the differentiation of the cambium and its products. The problem considered was whether auxin has similar correlative roles in the development of meristematic stems. Seedlings of Pisum sativum L. were decapitated and the buds in the axil of the lower bract were used in all experiments. The lower stem internodes of these buds were ≤ 2 mm long and grew to about 50 mm in 6 d. The elongation of a stem internode continued even in the absence of all young leaves. However, vascular differentiation and transverse parenchyma growth correlated with the presence of developing leaves. Auxin replaced leaf effects on all stem tissues. The influence of both leaves and auxin were limited to the direction of the roots and to the sectors of the stem below the point of auxin application. This polarity differed from that of more mature tissues in requiring a direct contact with the roots. Another characteristic of minute stem internodes was that changes of orientation, expressed by cell shape and the axis of vascular differentiation, did not occur readily. However, at a narrow competence window local hormone applications did cause the formation of new stem-like axes. It is concluded that auxin is a correlative signal even within shoot apices and that the information it carries has an essential directional com- ponent. This directionality has not been studied at the cellular level.
Aluminium and Hydrogen Ions Inhibit a Mechanosensory Calcium-Selective Cation Channel
Authors: Ding JP , Badot PM , Pickard BG
Published: January 2006

tension-dependent activity of mechanosensory calcium-selective cation channels in excised plasma- lemmal patches from onion bulb scale epidermis is modulated by pH in the physiologically meaningful range between 4.5 and 7.2. It is rapidly lowered by lowering pH and rapidly raised by raising pH. Channel activity is effectively inhibited by low levels of aluminium ions and activity can be partially restored by washing for a few minutes. We suggest that under normal conditions the sensitivity of the mechanosensory channels to pH of the wall free space plays important roles in regulation of plant activities such as growth. We further suggest that, when levels of acid and aluminium ions in the soil solution are high, they might inhibit similar sensory channels in cells of the root tip, thus contributing critically to the acid soil syndrome.
Root Growth, Water Uptake and Canopy Development in Eucalyptus viminalis Seedlings
Authors: Phillips JG , Riha SJ
Published: January 2006

A split-root experiment was conducted using Eucalyptus viminalis seedlings which were exposed to three watering regimes in order to investigate root growth and soil water extraction under conditions of a drying soil profile. Seedlings were grown in columns in which the soil was divided horizontally with a soft wax plate. Watering treatments were composed of (1) both upper and lower sections of the column well watered (W/W), (2) only the lower section well watered (D/W), and (3) water withheld completely from both upper and lower sections (D/D). Daily measurements included soil water potential (Ψs), column water loss and leaf elongation. Increase in above- and below-ground biomass was deter- mined from initial and final harvests after 25 days of treatment. Whole-column water loss and leaf extension were depressed as Ψs in the upper section of D/W and D/D decreased to -0.4 MPa over the first 8-10 days. However, water loss did not decrease significantly in the lower section of treatment D/W relative to the lower section of treatment W/W during this period. This indicated that water extraction by roots remaining in wet soil was not severely inhibited by the decrease in transpiration associated with the soil conditions in the upper profile. Root distribution at the end of the experiment indicated significant growth in the lower section of treatment D/W. There was evidence that hydraulic lifting of water between column sections may have occurred, as periodic increases in soil water potential of the unwatered upper section of D/W were observed.
Effect of Changes in Leaf Water Oxygen Isotopic Composition on Discrimination Against C18O16O During Photosynthetic Gas Exchange
Authors: Flanagan LB , Phillips SL , Ehleringer JR , Lloyd J , Farquhar GD
Published: January 2006

Photosynthetic gas exchange measurements were combined with measurements of the carbon and oxygen stable isotopic composition of CO2 after it passed over a leaf of Phaseolus vulgaris or Senecio spp. plants held in a controlled environment chamber. Calculations were then made of discrimination by the leaf against 13CO2 and C18O16O. Leaves were maintained at different vapour pressure gradients in order to generate a range of leaf water 18CO/16CO ratios. The 18CO content of leaf water increased when plants were exposed to higher vapour pressure deficits. The observed C18O16O discrimination values also increased with an increase in the leaf-air vapour pressure gradient and the associated change in leaf water 18/CO16CO values. In addition, the observed C18O16O discrimination values were strongly correlated with values predicted by a mechanistic model of isotopic fractionation.
Endogenous Biosynthetic Precursors of (+)-Abscisic Acid. II. Incorporation of Isotopes From ( Plus or Minus )-[2H]Abscisic Aldehyde, 18O2 and H218O
Authors: Netting AG , Milborrow BV
Published: January 2006

Tomato shoots that had been (a) fed (�)-[2H9]abscisic aldehyde via the xylem or (b) fed H218O together with (�)-[2H9]abscisic aldehyde via the xylem or (c) exposed to 18O2 and fed (�)-[2H9]abscisic aldehyde, were then wilted. The abscisic acid present was isolated, methylated and resolved into (+)- and (-)- methyl abscisate. These methyl abscisate samples were then examined by negative ion chemical ionisation (methane) gas chromatography/mass spectrometry. The undeuteriated (+)-abscisic acid contained no 180 from H218O but did contain one 18O from 18O2. No 18O from either of these sources was present in the undeuteriated (-)-abscisic acid. It was not possible to discount the xanthophyll hypothesis for the origin of stress-induced abscisic acid on the basis of these experiments. Both (+)- and (-)- multiply deuteriated abscisic acid contained one and two 18O atoms from H218O but none from 18O2. It is postulated that this multiply deuteriated (�)-abscisic acid is formed by a separate enzyme system from that which forms endogenous stress-induced (+)-abscisic acid. On the basis of the low incor- poration of abscisic aldehyde into abscisic acid, it is suggested that the endogenous precursor of stress- induced abscisic acid is an as yet unidentified structure and that abscisic aldehyde competes with it.
Drought Enhances Stomatal Closure in Response to Shading in Sorghum (Sorghum bicolor) and in Millet (Pennisetum americanum)
Authors: Jones HG , Hall DO , Corlett JE , Massacci A
Published: January 2006

When field-grown sorghum (Sorghum bicolor (L.) Moench) and millet (Pennisetum americanum (L.) Leeke) plants are subjected to drought, the speed of stomatal closure in response to darkness is enhanced in comparison with the speed observed in well-irrigated control plants. This shade-induced closure is most apparent at early stages of desiccation and is not rapidly reversible. These results need to be considered when developing protocols for the measurement of photosynthetic light response curves in the field. The sensitivity to crop water status of this stomatal closure response potentially provides a very valuable means for detection of the early stages of soil drying, and may also provide opportunities for screening different varieties for their adaptation to drought conditions.
Effect of Carbonic Anhydrase Inhibition on Photosynthesis by Leaf Pieces of C3 and C4 Plants
Authors: Badger MR , Pfanz H
Published: January 2006

The role of carbonic anhydrase (CA) in the photosynthesis of C3 and C4 plants was investigated by use of the effects of the CA inhibitor ethoxyzolamide on peeled and vacuum infiltrated leaf pieces. Two C4(Zea mays and Amaranthus edulis) and three C3 (Spinacea oleracea, Nicotiana rustica and Hordeum vulgare) species were studied. The results clearly showed that photosynthesis at limiting inorganic carbon was more severely inhibited in the C4 species compared with the C3 species. However, the degree of inhibition in the C4 species was less than might have been expected based on the rate limitation which the conversion of CO2 to HCO3- would impose on the provision of substrate to PEP carboxylase. The reasons for this lower than expected inhibition is discussed in terms of the lack of penetration of ethoxyzolamide, the diffusion of HCO3- through plasmodesmata and the possible existence of a plasma membrane CA activity.
Chilling Temperatures and the Xanthophyll Cycle. A Comparison of Warm-Grown and Overwintering Spinach
Authors: Adams WW Iii , Hoehn A , Demmig-Adams B
Published: January 2006

Photoprotective energy dissipation activity, that was largely associated with the de-epoxidation of the xanthophyll cycle, was examined in spinach leaves grown outside during the winter versus leaves that had developed at moderate temperatures in a glasshouse. On a leaf area basis the rates of photosynthesis were higher in leaves from the field at all temperatures examined, but were similar in both sets of leaves on a chlorophyll basis. The rate at which energy dissipation activity increased upon sudden exposure to high light was similar for the warm-grown leaves and those growing outside. This rate was futhermore similar to that of the rate of antheraxanthin and zeaxanthin formation, and was similar throughout the winter as long as the pre-dawn level of photosystem II (PSII) efficiency was at a normal high level. Whereas energy dissipation activity developed more rapidly at higher temperatures, the final extent of energy dissipation activity was greater at lower temperatures, where the rate of energy utilisation through photosynthetic electron transport was much lower. On colder days leaves collected pre-dawn from plants growing outside exhibited sustained decreases in PSII efficiency, which were associated with sustained decreases in both maximal and minimal levels of fluorescence. Such characteristics suggest that the leaves exposed to high light on colder days during the winter exhibited sustained energy dissipation activity that remained engaged throughout the night. It is likely that the xanthophyll cycle was involved in this response, as the sustained high levels of energy dissipation activity were found to be associated with sustained high levels, and thus the retention of, zeaxanthin and antheraxanthin overnight.
Acclimation of Pineapples to Nightlength.
Authors: Olesen TD , Bailey GJ
Published: January 2006

The leaves of pineapples conditioned to 6:6 h light:dark (L:D) cycles, with 32:24�C L:D temperatures, had lower chlorophyll concentrations, lower malate concentrations at the beginning of the light period, and higher malate concentrations at the end of the light period than the leaves of pineapples conditioned to 6:18 h L:D cycles, with 32:24�C L:D temperatures. These results are consistent with a nightlength acclimation that involves the specific crassulacean acid metabolism pathways.
Single Ion Channel Current Data from the Plasmalemma of Cytoplasmic Fragments of the Green Alga, Hydrodictyon africanum
Authors: Findlay N , Findlay GP
Published: January 2006

To measure, by patch clamping, electric current through ion channels in the plasmalemma of plant cells, access to the membrane surface is required. In higher plants, this access is gained by the preparation of protoplasts by enzymic methods. In plants such as the freshwater alga Hydrodictyon africanum, which have large cells, the preparation of protoplasts by enzymic methods is not possible. In this paper we describe a non-enzymic method for gaining access to the plasmalemma of Hydrodictyon. Our initial attempts to gain access to the plasmalemma of these cells by first plasmolysing the cells, and then cutting a window in the wall, so exposing the plasmalemma, were not successful. It was possible, however, after drying the cells in air, to cut them open and obtain fragments of the cytoplasm which maintain their original curvature. Standard patch clamping methods were then used to measure currents through single ion channels in the membrane, presumed to be the plasmalemma, bounding the outer surface of the fragments, although the success rate was low. Two types of channels were observed: (a) a multistate channel whose ion specificity was not established, and which in attached patches behaved as an outward current rectifier, and in a detached patch, as both inward and outward rectifier; and (b) a Cl- channel.
Non-Destructive Collection of Apoplast Fluid From Developing Tomato Fruit Using a Pressure Dehydration Procedure
Authors: Ruan YL , Mate C , Patrick JW , Brady CJ
Published: January 2006

Pressure dehydration techniques were evaluated for the collection of samples of apoplast fluid from the outer pericarp tissues of developing tomato fruit. Sap was expelled under pressure through a cannula inserted into the selected tissue of a fruit sealed in a Scholander pressure bomb. Osmolality and concentrations of K+ and hexoses were significantly lower and pH higher in sap exudates than in bulk fruit tissues. After infusion of fruit with trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate as an apoplastic marker, the dye was confined to the same fruit compartment as that which yielded sap under pressure. During extended periods of sap exudation at 24�C under 1.4 MPa or more, the initial 100 μL of exuded sap was obtained without contamination from protoplasmic contents followed by a proportionate increase in sap osmolality with the aggregate volume. However, when the exuded sap was collected at 4�C under the applied pressure of 0.6-1.0 MPa, the composition of the sap remained constant with time and was independent of the applied pressure. This permits the collection of a relatively large volume of exuded fluid, up to about 500 μL sap per 70 g fruit, at an initial flow rate of 100-150 μL h-1. We conclude that the pressure dehydration technique under the described conditions allows the collection of uncontaminated apoplastic fluid from the pericarp of intact developing tomato fruit.
Photosynthetic Characteristics of Sun Versus Shade Plants of Encelia farinosa as Affected by Photosynthetic Photon Flux Density, Intercellular CO2 Concentration, Leaf Water Potential, and Leaf Temperature
Authors: Zhang Hehui , Sharifi MR , Nobel PS
Published: January 2006

Limitations to photosynthesis were examined for Encelia farinosa Toney et A.Gray, a common C3 sub-shrub in arid regions of south-westem United States, for plants grown in full sunlight and those shaded to 40% of full sunlight. The initial slopes of CO2 assimilation (A) versus intercellular CO2 concentration curves were similar for sun and shade plants at low photosynthetic photon flux density (PPFD) but higher for sun plants as the PPFD increased, indicating a greater limitation by carboxylation capacity in shade plants. Sun plants had higher electron transport rates but a lower ratio of electron transport capacity to carboxylation capacity (Vmax); the ratio was inversely proportional to mesophyll conductance for both sun and shade plants. Dark respiration decreased with decreasing leaf water potential (Ψ1) in sun plants but remained unchanged in shade plants; day respiration was little affected by PPFD for both sun and shade plants. Stomatal conductance (gs) was similar for sun and shade plants under high soil-moisture conditions but higher in sun plants as Ψ1 decreased; for all data considered together, changes in the leaf-air vapour pressure difference accounted for 71% of the variation in gs. The lower A for shade plants of E. farinosa apparently resulted from a lower Vmax, as well as a lower gs when plants were under water stress.
Comparison of Sudden Heat Stress With Gradual Exposure to High Temperature During Grain Filling in Two Wheat Varieties Differing in Heat Tolerance. I. Grain Growth
Authors: Stone PJ , Nicolas ME
Published: January 2006

Two wheat varieties differing in heat tolerance were exposed to four heat treatments in order to determine if a sudden rise from ca 20-40�C caused a greater reduction of individual kernel mass than a gradual (6�C h-1) rise over the same temperature range. For the heat sensitive variety (Oxley), the reduction of individual kernel mass following sudden heat stress (26%) was greater than that resulting from a gradual heat stress of equivalent thermal time (13%) or equal days of treatment (18%). By contrast, for the heat tolerant variety (Egret), the reduction of individual kernel mass following rapid exposure to heat stress (12%) was not significantly greater than that caused by a gradual treatment of equal days duration (10%). Nevertheless, for Egret, sudden heat stress significantly reduced mature kernel mass compared with high temperature treatment of equivalent thermal time (6%). We conclude that heat acclimation may help to mitigate wheat yield losses due to high temperature and that the ability to acclimate to high temperature varies between wheat genotypes. Comparison of wheat varieties for yield tolerance to high temperature should therefore occur under conditions that allow gradual acclimation to elevated temperature.
Effect of Subsoil Compaction and Three Densities of Simulated Root Channels in the Subsoil on Growth, Carbon Gain and Water Uptake of Pinus radiata
Authors: Sheriff DW , Nambiar EKS
Published: January 2006

The experiment investigates effects of subsoil compaction, of three densities of simulated root channels through the compacted layer, and of fertiliser addition on growth, carbon gain and water relations of Pinus radiata. Treatments were designed to simulate subsoil compaction produced by a previous tree crop and access to depth through the compacted layer via old root channels. Comparisons were also made of diurnal carbon assimilation, micro-climate, water potential, and mineral nutrition of well-exposed foliage. Subsoil compaction was negatively associated with growth, plant water potential, foliar nutrient concentration, water uptake and diurnal carbon gain per unit foliage area. All treatments with compacted subsoil grew more slowly than controls, and an interaction between root access to depth and nutrition is indicated. Diurnal carbon gain per unit foliage area of trees growing on unperforated, compacted subsoil was about 0.78 that of controls, while stem growth was about 0.56 that of controls. Root growth of trees on compacted subsoil with the largest number of root channels showed an effect of fertilisation on growth. Fertilised trees in this compaction treatment had a significantly greater fine root biomass in the upper 0.3 m of the profile, greater access to water at depth, higher plant water potential, higher soil water content below the compacted subsoil layer, and greater growth than unfertilised trees in the same soil compaction treatment.
Mitochondrial Respiration in Relation to Photosynthetic C4 Acid Decarboxylation in C4 Species
Authors: Agostino A , Heldt HW , Hatch MD
Published: January 2006

Certain respiratory features of bundle sheath cells isolated from the C4 species Urochloa panicoides (phosphoenolpyruvate carboxykinase (PCK)-type)), Panicum miliaceum (NAD malic enzyme (NAD-ME)-type) and Zea mays (NADP malic enzyme (NADP-ME)-type) were examined in relation to the requirements of the C4 acid decarboxylation step of C4 photosynthesis. Cells from both PCK-type and NAD-ME-type species showed high rates of malate-dependent respiration; with ADP or uncoupler the rates were in the range 2-3 μatom O min-1 mg-1 chlorophyll, about 5-10-times the rates with other respiratory substrates. Studies with inhibitors of cytochrome oxidase and the alternative oxidase indicated negligible alternative oxidase-mediated malate respiration in cells from Z. mays, a minor contribution in U. panicoides cells, but possibly a major role for this oxidase in the respiration of P. miliaceum cells. These differences were related to the different roles of respiration in photosynthetic C4 acid decarboxylation. Oxaloacetate strongly suppressed malate-dependent respiration in P. miliaceum bundle sheath cells but not in U. panicoides cells. This difference in the response to oxaloacetate was not due to different kinetic features of the mitochondrial malate dehydrogenase but was apparently largely due to the much lower activity of the enzyme in U. panicoides bundle sheath mitochondria. We propose that insensitivity of respiration to oxaloacetate in bundle sheath cells of PCK-type species may be essential for maintaining the C4 acid decarboxylation process. The reverse may be true for NAD-ME- type species.
Evaluating the Contribution of Glutamate Dehydrogenase and the Glutamate Synthase Cycle to Ammonia Assimilation by Four Ectomycorrhizal Fungal Isolates
Authors: Turnbull MH , Goodall R , Stewart GR
Published: January 2006

Combined gas chromatography-mass spectrometry were used to evaluate the contributions of glutamate dehydrogenase (GDH) and the glutamate synthase cycle in 15N-labelled ammonium assimilation by four ectomycorrhizal fungal isolates. In all four species (Elaphomyces, Amanita, Pisolithus and Gautieria), glutamine was the major product accumulated following transfer of 14-day-old nitrogen-limited cultures to fresh medium. Label was rapidly assimilated into fungal tissue, with rates of 733 nmol g-1 FW h-1 in Pisolithus, 972 nmol g-1 FW h-1 in Amanita, 2760 nmol g-1 FW h-1 in Gautieria and 6756 nmol g-1 FW h-1 in Elaphomyces sp in the first 4 h of incubation. Incorporation of [15N]ammonium was sensitive to the inhibitory effects of both methionine sulfoximine (MSX, an inhibitor of glutamine synthetase (GS)) and albizziin (an inhibitor of glutamate synthase (GOGAT)) in three species (Amanita, Gautieria and Pisolithus) and labelling patterns were consistent with the action of the glutamate synthase cycle in ammonium assimilation. In all three species glutamine synthesis was almost totally blocked by MSX and there was no continued incorporation of 15N into glutamate. Elaphomyces displayed high levels of total incorporation of labelled ammonium in mycelium even in the presence of MSX, although incorporation into glutamine was reduced by 88%. This inhibition of GS by MSX, in addition to its partial inhibition by albizziin suggests strongly the action of glutamate synthase cycle in ammonium assimilation. The reduction in label entering glutamate under the influence of albizziin is direct evidence for the inhibition of GOGAT activity. However, MSX treatment had the effect of increasing significantly the quantity of label recovered in both glutamate and alanine. In the absence of GS inhibition there is clearly competition for ammonium which under normal physiological conditions results in assimilation through the glutamate synthase cycle. However, when GS is blocked by MSX label is able to cycle through the GDH pathway.

Extra keywords: ectomycorrhiza, ammonium assimilation, glutamate synthase cycle, glutamate dehydrogenase, amino acid metabolism.
Morphological and Physiological Comparisons of Clonal Lines of Eucalyptus camaldulensis. II. Responses to Waterlogging/Salinity and Alkalinity
Authors: Farrell RCC , Bell DT , Akilan K , Marshall JK
Published: January 2006

Eucalyptus camaldulensis Dehnh. has previously been shown to survive and grow in waterlogged, highly saline and highly alkaline soils. The ability of six clones from five provenances of E. camaldulensis to produce biomass and utilise water, and the processes of stomatal conductance and gas exchange under stress conditions was examined under controlled conditions in a glasshouse. A clone originally from Wooramel, Western Australia (M80) produced the largest total plant biomass, the greatest total leaf area and greatest total root dry weight under conditions of waterlogging and gradually increasing salinity. A second clone from Wooramel (M16), however, tended to be among the least productive of the clones under this stress, indicating the wide potential variation in stress tolerance of trees from a single provenance.
The response of clones to alkalinity stress was comparable to that measured under waterlogging/salinity stress. Water use was closely related to biomass production. Leaves produced while under salinity and alkalinity stress were comparable in ion content to those produced prior to the test conditions. An ability to control uptake by roots or limit ion transport to leaf tissues were hypothesised as controlling physiological functions resulting in tolerance to severe soil ion imbalances in this species. The impact of solution conductivity on stomatal conductance and water use, secondarily affected photosynthetic rates in these clones of E. camaldulensis. Tolerance of extreme conditions provides the opportunity to use these genotypes to reclaim damaged agricultural landscapes and mine spoils of high soil solution ion concentrations.
Photosynthetic Activity of Leaves of Pinus radiata and Nothofagus fusca After 1 Year of Growth at Elevated CO2
Authors: Hogan KP , Whitehead D , Kallarackal J , Buwalda JG , Meekings J , Rogers GND
Published: January 2006

Radiata pine (Pinus radiata D.Don) and red beech (Nothofagus fusca (Hook. f.) Oerst.) were grown for over 1 year at elevated (ELEV, 64 Pa) and ambient (AMB, 38 Pa) CO2 partial pressure in open-top chambers. Springtime measurements of overwintering leaves showed that light- and CO2-saturated photosynthetic rates (Amax) of pine leaves were similar for the two treatments (AMB: 6.7 � 1.08 μmol m-2 s-1, mean � 1 s.e.; ELEV: 6.6 � 0.47) but, for beech leaves, Amax was greater for AMB plants (8.8 � 0.90 μmol m-2 s-1) than for ELEV plants (6.10 � 0.71). Summertime measurements of leaves grown that spring showed that for pine, Amax was similar in the two CO2 treatments (AMB 14.9 μmol m-2 s-1 � 0.80; ELEV: 13.5 � 1.9) while, for beech, Amax was higher in AMB plants (21.0 � 1.1) than in ELEV plants (17.2 � 1.9), although the difference was not statistically significant. These results indicate downregulation of photosynthetic capacity of beech but not pine. Vcmax did not differ between treatments within species, suggesting that there was no acclimation of rubisco activity. Triose phosphate utilisation limitation may have contributed to the downregulation of Amax in beech. For pine, photosynthesis at treatment CO2 partial pressures was greater in ELEV plants in both spring and summer. For beech measured at treatment CO2 partial pressures, photosynthesis was greater in ELEV plants in summer, but was similar between treatments in the springtime.
Chlorophyll and Carotenoid Composition in Leaves of Euonymus kiautschovicus Acclimated to Different Degrees of Light Stress in the Field
Authors: Demmig-Adams B , Adams WW Iii
Published: January 2006

The response of carotenoid and chlorophyll composition to the actual degree of excess light experienced in the natural environment was examined in differently angled leaves of the sclerophyllous shrub Euonymus kiautschovicus. Increasing light stress caused a greater conversion of the xanthophyll cycle to zeaxanthin and antheraxanthin as well as thermal dissipation of a greater fraction of the absorbed light. Increasing light stress was also associated with increasing chlorophyll alb ratios and increases in the pool size of the xanthophyll cycle. The response of all other carotenoids to light stress was less pronounced than that of the xanthophyll cycle pool. While the ratio of β-carotene or lutein to chlorophyll increased with increasing light stress, the ratio of neoxanthin to chlorophyll remained constant. Only the (taxonomically restricted) carotenoids lactucaxanthin and �-carotene decreased relative to chlorophyll with increasing light stress. These findings are consistent with an increased emphasis on energy dissipation over light collection with increasing light stress, afforded presumably by a decreased ratio of major, peripheral (bulk chlorophyll-binding) to minor, proximal (xanthophyll cycle-rich) light-harvesting complexes of photosystem II. These responses to light stress within a single species could not be extrapolated to comparisons among different groups of species.
The effects of anion sorption on sorption and leaching of cadmium
Authors: Bolan N. S. , Khan M. A. R. , Tillman R. W. , Naidu R. , Syers J. K.
Published: January 2006

The effect of chloride, sulfate, nitrate, and phosphate anions on the sorption
and leaching of cadmium was examined in 2 soils (Manawatu silt loam and Egmont
clay loam) which differ in their variable charge components. There was a
larger sorption of cadmium in the presence of phosphate than in the presence
of sulfate, nitrate, and chloride, and the difference was more pronounced in
the Egmont soil. In soils, specific sorption of phosphate increases the
negative charge. The increase in negative charge per unit amount of phosphate
sorbed decreased with increasing phosphate sorption. The sorption of cadmium
increased in response to phosphate sorption. The phosphate-induced cadmium
sorption resulted from the increase in negative charge due to phosphate
sorption. Column studies indicated that cadmium was less susceptible to
leaching in the presence of phosphate than in the presence of nitrate.