bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of NaCl and KCl on Growth and Ionic Composition of the Halophytic C4 Succulent Chenopods Salsola kali, Suaeda monoica and Suaeda aegyptiaca
Authors: Eshel A
Published: January 2006

Salsola kali, Suaeda monoica and Suaeda aegyptiaca plants were grown in sand culture under controlled conditions and treated with half-strength Hoagland's nutrient solution (control), and control plus 150 mol m-3 KCl or NaCl.
Fresh weight of Salsola kali was doubled in the NaCl and KCl treatments, but the increase in dry matter as compared with the control was not significant. Ionic content in this species revealed high selectivity for K v. Na.
Fresh weight of Suaeda monoica and S. aegyptiaca was raised by NaCl 5 and 10 times respectively. Control and KCl-treated plants were poorly developed and plants of S. aegyptiaca exhibited sodium deficiency symptoms under these treatments. The two Suaeda species had lower selectivity of K v. Na than Salsola kali. Of the two annual species, Suaeda kali and S. aegyptiaca, S. kali flowered under all three treatments, whereas S. aegyptiaca flowered only under the Na treatment. In spite of the fact that all three species are inorganic ion accumulators and C4-succulent chenopods, they exhibit wide differences in their response to the two chloride salts.
Potassium, Sodium and Chloride Ion Concentrations in Leaves and Isolated Chloroplasts of the Halophyte Suaeda australis R. Br
Authors: Robinson SP , Downton WJS
Published: January 2006

Seedlings of S. australis were grown hydroponically in nutrient solutions with 0-600 mM NaCl added. The plants grew poorly in the absence of added NaCl and optimal growth, based on fresh or dry weight, occurred at 50-150 mM NaCl. Higher concentrations of NaCl decreased growth although the plants continued to grow even at 600 mM NaCl. The osmotic potential of the leaf sap decreased with increasing salinity and this was mostly the result of accumulation of NaCl in the leaves. Leaf K+ concentration decreased with increasing salinity while both Na+ and Cl- increased, reaching 800 and 500 mM, respectively, on a tissue water basis. Intact chloroplasts were isolated by mechanically disrupting the leaves and the chloroplasts were purified on a two-step Percoll gradient. The osmotic potential of the isolation medium was adjusted so as to be isotonic with the leaf sap in each case. The chloroplasts were generally more than 90% intact and exhibited rates of CO2-dependent oxygen evolution of 70-130 �mol (mg chlorophyll) -1 h-1. The concentration of K+ in the chloroplast decreased with increasing salinity and was similar to the concentration of K+ in the leaf as a whole. For plants grown without added NaCI, leaf Na+ and Cl- concentrations were low (less than 10 mM) but these ions were accumulated in the chloroplasts, which contained 70-140 mM Na+ and 80-120 mM Cl-. With increasing salinity, the concentration of Na+ and Cl- in the chloroplast did not increase despite the more than 70-fold increase in the concentration of these two ions in the leaf. The results suggest that the concentration of Na+ and Cl- in the chloroplasts of Suaeda australis is regulated, with these ions being accumulated in the chloroplast at low leaf levels and excluded from the chloroplast when leaf Na+ and Cl- are high.
Phosphorus and Carbon Budgets of Eucalyptus pilularis Smith Seedlings During Their Cotyledonary Phase of Growth
Authors: Mulligan DR , Patrick JW
Published: January 2006

The budgeting of phosphorus and carbon in Eucalyptus pilularis Smith seedlings raised in a phosphorus-deficient sandy podzol was examined for the first 35 days of seedling growth. During this period, the photosynthetic cotyledons were a major source of both phosphorus and carbon. At 7 days from sowing, the cotyledons were gross importers of assimilated phosphorus but switched to gross (day 15) and then net (day 20) export in response to the current rate of phosphorus acquisition and the phosphorus demand by other organs. However, the cotyledons retained the capacity to revert to phosphorus import. This strategy would permit the seedlings to take advantage of any favourable fluctuations that may occur in soil phosphorus supply. Initial cotyledonary phosphorus export was directed basipetally to the roots and soil. From 20 days after sowing the partitioning pattern altered, with exported phosphorus moving solely to the expanding leaves. Carbon exported from the cotyledons initially supplied all sinks although, once the first leaf pair was self-supportive for carbon, the roots and stem received a higher proportion of exported cotyledonary carbon.
The efficiency of phosphorus redistribution was considered to minimize the consequences of a rapidly depleted pool of readily available soil phosphorus on seedling growth. The seedlings also possessed a strategy of maximizing the investment of carbohydrate into dry matter by keeping respiratory losses to a minimum. A proposed link between the distribution of the limiting phosphate ion and carbon distribution may be a contributing factor to the success of E. pilularis in the phosphorus-deficient soil.
Metabolic Effects of Water and Salinity Stress in Relation to Expansion of the Leaf Surface
Authors: Aspinall D
Published: January 2006

Leaf expansion is comparatively sensitive to the onset of stress, and metabolic dysfunctions purported to contribute to the leaf expansion response can be judged against this sensitivity. Accumulated evidence does not support the proposition that leaf expansion is controlled primarily by the availability of basic metabolites during exposure to stress, nor is there evidence for the primacy of any specific metabolic lesion. Caution must be exercised in reaching such conclusions, however, as there is difficulty in separating cause and effect in the relationships between tissue physical status (water or salt), metabolic function and expansion. Certain metabolic consequences of stress, particularly those leading to the accumulation of specific organic solutes, are viewed as adaptive. Such responses must be viewed in the light of their metabolic cost and the possibility that they contribute more to survival than to continued growth and expansion. Recent information on the effects of water and salinity stress on plant metabolism is reviewed in this paper with respect to these various considerations.
Adaptation to Water Deficits: a Changing Perspective
Authors: Turner NC
Published: January 2006

This paper briefly reviews the current developments on the role of leaf hydration on leaf growth and photosynthesis and concludes that changes in growth and stomatal action are not always closely correlated with changes in leaf hydration. A case is developed for soil and root water relations affecting leaf growth and stomatal function, and a role for plant growth regulators is postulated. The influence of this changed perspective on the adaptation of plants to water deficits is discussed. In particular, the importance of the adaptation of roots to water deficits is highlighted and the need for more studies on the interaction between the shoot and the root is emphasized.
Regulation of C4 Photosynthesis A Role for Pyruvate in Regulating Pyruvate,Pi Dikinase Activity in vivo
Authors: Burnell JN , Jenkins CLD , Hatch MD
Published: January 2006

Results are presented in support of the view that pyruvate levels are critical in the light-dark regulation of pyruvate,PI dikinase in vivo. In an in vitro system containing purified Zea mays pyruvate,PI dikinase, increasing pyruvate reduced both the initial rate and the final extent of ADP-mediated inactivation of the enzyme. Pyruvate also reversed the inhibitory effect of ADP on the initial rate of PI-mediated activation of pyruvate,P*i dikinase. With intact Zea mays leaves, inactivation of pyruvate,PI dikinase in darkened leaves was prevented by anaerobic conditions or reduced temperature; both treatments resulted in elevated steady-state levels of pyruvate. Added pyruvate was shown to substantially increase the level of active pyruvate,PI dikinase in chloroplasts incubated with PI in the dark but not in the light. The likely physiological significance of these results is discussed.
Photosynthetic Enzyme Activities in the C3-C4 Intermediate Neurachne minor S. T . Blake (Poaceae)
Authors: Hattersley PW , Stone NE
Published: January 2006

The activities of eight key photosynthetic enzymes were measured in leaf blade extracts of the C3-C4 intermediate Neurachne minor S. T. Blake, its C3 and C4 relatives, C3-C4 Panicum milioides Nees ex Trin., and controls (all Poaceae). Phosphoenolpyruvate (PEP) carboxylase (PEPC) activity in N. minor (5.46 �mol mg Chl-1 min-1) is higher than previously reported for any other C3-C3 plant, and the ratio of ribulose-1,5-bisphosphate carboxylase activity to PEPC activity is lower than for P. milioides or C3 species. Activity of pyruvate,PI dikinase (up to 0.88 �mol mg Chl-1 min-1) is 3-5 times higher than in P. milioides. Assays of NADP-malic enzyme (NADP-ME), NAD-malic enzyme (NAD-ME) and PEP carboxykinase (PCK) show Paraneurachne muelleri (Hack.) S. T. Blake and Neurachne munroi (F. Muell.) F. Muell., N. minor's two close C4 relatives, to be NADP-ME type, as predicted from leaf anatomy. Aspartate and alanine aminotransferase activities in these species are higher than expected, however. N. minor (C3-C4) exhibits higher C4 acid decarboxylase activity than C3 species or P. milioides, for NADP-ME only (up to 1.07 �mol mg Chl-1 min-1). Our results suggest that N. minor possesses a limited C4 acid cycle, and that it is the most C4-like C3-C4 intermediate grass currently identified, comparable with some of the known C3-C4 Flaveria (Asteraceae) species.
Physiological Reactions to an Imposed Drought by Two Twining Pasture Legumes: Macroptilium atropurpureum (Desiccation Sensitive) and Galactia striata (Desiccation Insensitive)
Authors: Sheriff DW , Fisher MJ , Rusitzka G , Ford CW
Published: January 2006

Macroptilium atropurpureum cv. Siratro and Galactia striata were grown in both well-watered and droughted swards to allow comparisons between plants with similar form but different physiological responses to desiccation. Siratro maintained leaf water potentials (�Ψl) above c. -2.2 MPa, while in G. striata they fell to c. -6.7 MPa. G. striata exhibited osmotic adjustment of up to 2.3 MPa and considerable desiccation tolerance, with relative water contents in live leaves as low as c. 25%. In Siratro, osmotic adjustment was less than 0.26 MPa and its relative water content was always above c. 65%. Leaves of droughted G. striata accumulated pinitol and proline, while Siratro did not accumulate substantial amounts either. Despite having consistently higher positive (calculated) turgor pressure, leaf expansion was limited by drought more in Siratro than in G. striata.
Well-watered plants of both species had similar abaxial conductance (g) and gross photosynthesis (P). However, as the drought progressed ΨI, g, and P fell more in G. striata than in Siratro due to a less effective extraction of soil water, which we attribute to shallower rooting habit in G. striata. The active mechanism of paraheliotropic leaf movement in Siratro reduced light interception at higher ΨI than did the passive rolling and drooping of leaves in G. striata. Both mechanisms reduced the mean daily integral of intercepted radiation, but leaf temperatures of droughted G. striata were sometimes considerably higher than those of Siratro. Rooting depth and the hydraulic conductance of the plant-soil system appear to be as important in determining plant responses to drought as are the physiological responses of their leaves.
Effects of Temperature on the Conversion of Sucrose to Starch in the Developing Wheat Endosperm
Authors: Bhullar SS , Jenner CF
Published: January 2006

Elevated temperature during grain filling resulted in reduced single grain weight due largely to an effect of temperature on the accumulation of starch in the endosperm. Wheat endosperm was cultured in vitro on solutions of [14C]sucrose and the responses to variation in temperature within the range 15-35°C were evaluated in terms of the absorption of radioactive sugar, the evolution of 14CO2, and the incorporation of radioactivity into starch.
At 35°C the level of 14C in the intracellular pool of soluble carbohydrate was higher than it was at 30°C, and the average Q,10 for 14CO2 production was 2.1. Incorporation of 14C into starch was greater at 30°C than at 25°C, but at 35°C only half as much [14C]starch was produced compared with that at 30°C.
Residual effects of exposure of ears to brief episodes of elevated temperature were investigated by culturing endosperm isolated from such ears on [14C]sucrose at a standard temperature (25°C). Two days of exposure resulted in greater amounts of [14C]starch produced, due to accelerated starch depo- sition, but longer periods (4-6 days) at elevated temperature resulted in substantial reductions in [14C]starch deposition. Exposure to elevated temperature also hastened the onset of chlorophyll degradation in the pericarp of the grain.
Two types of response to temperature appear to be involved: a comparatively low temperature optimum for starch synthesis, and an irreversible reduction in the capacity of the endosperm to convert sucrose to starch resulting from exposure of the ears, or the grains themselves, to elevated temperature.
Apoplastic and Symplastic Pathways in Avicennia marina (Forsk.) Vierh. Roots Revealed by Fluorescent Tracer Dyes
Authors: Moon GJ , Clough BF , Peterson CA , Allaway WG
Published: January 2006

The apoplastic permeability of Avicennia marina (Forsk.) Vierh. (grey mangrove) roots was investigated by examining the composition of xylem sap collected under pressure from root systems immersed in 25% seawater containing 0.01% trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS), a mobile fluorescent dye which is confined to ihe apoplast. Xylem sap from intact root systems contained between 3 and 18% of the NaCl, and less than 0.2% of the PTS concentrations present in the external bathing medium. The low levels of PTS in the xylem sap indicate that apoplastic transport was minimal. By contrast, xylem sap from disturbed roots that had been removed from the sand in which they were growing and transferred to the PTS treatment solution contained an average of 57% of the NaCl and 12% of the PTS concentrations present in the external solution, demonstrating the importance of using undisturbed root systems for such studies. Using Cellufluor, an apoplastic fluorescent dye which binds to cellulose, an apoplastic barrier was located at the periderm of mature roots, and at the exodermis and endodermis of progressively younger regions of fine roots. Uranin, a symplastic tracer dye, was taken up only by cells of the distal 17 mm of fine roots, the region of the root where the periderm had not yet developed. These results suggest that the uptake of ions and water in intact roots of A. marina occurs mainly via the symplast of younger regions of the third-order and fourth-order roots.
Mechanism of Paraquat Resistance in Hordeum glaucum. I. Studies With Isolated Organelles and Enzymes
Authors: Powles SB , Cornic G
Published: January 2006

The mechanism of resistance to paraquat was studied in a biotype of the important and widespread weed, Hordeum glaucum Steud. (barley grass). Experiments with isolated chloroplasts and protoplasts from resistant and susceptible plants established that resistance is not due to any change in the active site of paraquat binding. No difference was found in the permeability of paraquat through the plasmalemma or chloroplast envelope membranes. As paraquat catalyses the production of excited oxygen states, the capacity of varying enzymic means of detoxifying these destructive species was examined. No differences between leaf tissue of resistant and susceptible plants were found in the activities of superoxide dismutase, catalase or peroxidases. These experiments establish that, if paraquat enters the symplast of the resistant biotype, it will exert its herbicidal effect in the normal way. Thus the resistant plants must have the ability to prevent paraquat from entering the symplast.
New Structural/Biochemical Associations in Leaf Blades of C4 Grasses (Poaceae)
Authors: Prendergast HDV , Hattersley PW , Stone NE
Published: January 2006

Forty-three previously uninvestigated, mainly Australian, grass species (Poaceae) were assayed for activities of C4 acid decarboxylating enzymes (NADP-malic enzyme, NADP-ME; NAD-malic enzyme, NAD-ME; PEP carboxykinase, PCK). Twenty-five species exhibit long-established ('classical') associations between C4 type and structural features of leaf blade vascular bundles. However, Panicum virgatum and Triraphis mollis are NAD-ME species with structure like that of 'classical' PCK species. Seven Enneapogon species and Triodia scariosa are NAD-ME but are structurally intermediate between 'classical' NAD-ME and PCK species. Alloteropsis semialata (R.Br.) Hitch. is PCK, the first recorded non-NADP-ME XyMS - species, and Pheidochloa gracilis S.T. Blake and five Eriachne species are the first known XyMS+ NADP-ME species, with either centripetal or centrifugal/peripheral PCR (photosynthetic carbon reduction, or Kranz) cell chloroplasts. A suberised lamella is absent from the PCR cell walls of all species with an even PCR bundle sheath outline, irrespective of C4 type, as well as from NADP-ME Aristida, Eriachne and Pheidochloa; it is present in all other species with an uneven outline and centrifugal/peripheral chloroplasts. Pheidochloa gracilis and Eriachne spp. have unusually well-developed grana in PCR cell chloroplasts for NADP-ME species. This new-found structural/biochemical diversity is discussed in relation to high [CO2] maintenance in PCR cells.
Identification and Quantification of Cytokinins in the Xylem Sap of Mistletoes and Their Hosts in Relation to Leaf Mimicry
Authors: Hall PJ , Badenoch-Jones J , Parker CW , Letham DS , Barlow BA
Published: January 2006

Cytokinins present in the xylem saps of two species of Amyema mistletoes and three species of Eucalyptus hosts have been measured using radioimmunoassays employing antibodies elicited against zeatin riboside, dihydrozeatin riboside and isopentenyladenosine. The radioimmunoassays, when used in combination with enzymatic treatments and chromatographic separation techniques, allowed the detection of a wide variety of cytokinin bases, ribosides, O-glucosides and nucleotides. Column chromatography over paraffin-coated silica gel was used to separate cytokinins from contaminating polar plant compounds. Results demonstrated a closer relationship between the types and concentrations of cytokinins in the xylem saps of mistletoes and their hosts in a mimicking situation (A. miquelii on E. polyanthemos) than in a non-mimicking situation (A. pendulum on E. cinerea).
Inorganic Phosphate Concentration in the Stroma of Isolated Chloroplasts and Its Influence on Photosynthesis
Authors: Robinson SP , Giersch C
Published: January 2006

The concentration of inorganic orthophosphate (Pi) was determined in the stroma of isolated chloroplasts during photosynthesis under Pi-saturated and Pi-limited conditions. Pi was determined calorimetrically or by high performance liquid chromatography of extracts of chloroplasts labelled with 32Pi. When chloroplasts were illuminated in the absence of added Pi, photosynthesis soon declined due to Pi-depletion. After 5 min in the light, photosynthesis had declined to 2% of the maximum rate. At this point, stromal Pi was estimated to be 1.4 mM by the colorimetric method and 0.2 mM by 32P chromatography. Using the colorimetric method, Pi equivalent to approximately 1 mM in the stroma was found to be associated with thylakoid membranes isolated from chloroplasts, irrespective of the Pi content of the intact chloroplasts. This was considered to be a non-metabolic pool of Pi. During steady- state photosynthesis with optimal concentrations of Pi added to the reaction medium, the stromal Pi concentration was estimated to be 2.6 mM and 1.6 mM with the colorimetric and 32P methods, respectively. Measurement of stromal 32Pi in chloroplasts illuminated with varying concentrations of 32Pi in the reaction medium suggested that photosynthesis was saturated at stromal Pi concentrations above 2.0-2.5 mM. Photophosphorylation by thylakoid membranes was saturated at Pi concentrations above 1.2-1.5 mM. It is concluded that, during photosynthesis in isolated chloroplasts in the presence of an optimal supply of Pi from the reaction medium, the stromal Pi concentration is just above that required to saturate photophosphorylation. Any decrease in the supply of Pi from the medium results in a rapid decrease in stromal Pi to the point where photophosphorylation may become Pi-limited, decreasing the rate of CO2 fixation.
The Occurrence and Metabolism of the 1',4'-Diols of Abscisic Acid
Authors: Vaughan GT , Milborrow BV
Published: January 2006

The 1',4'-cis- and the 1',4'-trans-diols of abscisic acid (ABA) were produced when R,S-[2-14C]ABA was supplied to avocado fruit and broad bean shoots. The trans-diol was also a metabolite of R,S-ABA in peas but not in tomatoes. The diols were derived from both R- and S-ABA with the R- enantiomer predominating. The 1',4'-cis- and 1',4'-trans-diol were found to be endogenous constituents of avocado (14.5 ng/g and 93 ng/g respectively) and the trans-diol was found in pea shoots (5.2 ng/g). At low concentrations, exogenous 1',4'-cis- and 1',4'-trans-diols were metabolised by tomatoes, mainly to dihydrophaseic acid-4'-O-β-D-glucopyranoside. As the concentrations of the diols supplied to tomato shoots increased, a greater proportion was conjugated to form their 4'-glucosides and glucose esters.
When the 1',4'-[2-14C, 4'-2H]trans-diol of ABA was supplied to tomato shoots the deuterium atom was lost from the 4'- position during conversion into the 4'-glucoside of DPA. This suggests that the trans-diol is converted into DPA via enzymic oxidation to ABA.
Maintenance of Leaf Temperature and the Optimisation of Carbon Gain in Relation to Water Loss in a Tropical Mangrove Forest
Authors: Ball MC , Cowan IR , Farquhar GD
Published: January 2006

Properties and display of foliage were studied in relation to gas exchange characteristics of tropical mangrove species. Rates of assimilation of CO2 were maximal at leaf temperatures of approximately 30°C. The species operated with higher water use efficiencies than do most C3 species, and water-use characteristics became increasingly conservative with increase in the salinity tolerance of the species. Changes in three properties of leaves, i.e. inclination, area, and succulence, contributed to maintenance of leaf temperatures near air temperatures with minimal evaporative cooling. Interspecific differences in water-use characteristics, and their relationship to the maintenance of favourable leaf temperatures, could affect the competitive abilities of mangroves and the structure of mangrove forests.
Intercellular pH of Peach and Apricot Mesocarp
Authors: Ugalde TD , Jerie PH , Chalmers DJ
Published: January 2006

Intercellular pH of developing peach (Prunus persica (L.) Batsch) and apricot (Prunus armeniaca L.) mesocarp was estimated from the pH of small volumes of water in contact with washed cut surfaces. In both fruits, the pH changed from neutral to acidic as the rate of growth changed from slow and declining to rapid. In peaches, the changes in intercellular pH and growth rate occurred gradually over a 4-week period, while in apricots these changes were more rapid. Studies on the mechanism of the pH change showed the measured pH values to be a reasonable and adequate estimate of intercellular pH in vivo. We propose that intercellular acidity influences mesocarp development in at least two ways. It allows high rates of assimilate utilisation by inducing activity in existing intercellular invertase, and it predisposes the tissue to ripening.
Growth and Development in NaCl-Treated Plants. II. Do Na+ or Cl- Concentrations in Dividing or Expanding Tissues Determine Growth in Barley?
Authors: Munns R , Gardner PA , Tonnet ML , Rawson HM
Published: January 2006

Plants of barley (Hordeum vulgare cv. Clipper) were grown in solutions containing 0, 100 or 175 mol m-3 NaCl from leaf 3 emergence until anthesis. Na+ and Cl- concentrations in various growing tissues of the shoot were measured concurrently with increases in dry weight. The tissues on which the study focused were the basal 30 mm of leaves 4 and 7 (mainly expanding cells), and the primordial stage of leaf 7 and the floral apex (mainly dividing cells). Although leaf growth was reduced by the higher NaCl treatments, apex growth was initially increased. Na+ and Cl- concentrations were high in the expanding tissues (150 mol m-3), but there was no consistent relation between the concentrations and the growth rate. Na+ and particularly Cl- concentrations were much lower in the dividing tissues, and again did not correlate with the rate of development of the tissue, or the final size of the organ. These data strongly indicate that the growth of the shoot is not directly controlled by local concentrations of Na+ or Cl- of the growing tissues, but by some influence originating elsewhere in the plant.
Identification and Stability of Aminopeptidases in Extracts From Bean Seeds
Authors: Blattler R , Feller U
Published: January 2006

Extract from ungerminated bean seeds (Phaseolus vulgaris L. cv. Saxa) was fractionated by gel chromatography on Sephacryl S-200 and by anion exchange chromatography on diethylaminoethyl- Sephacel. Aminopeptidase activities were measured with the following amino acid-p-nitroanilides: phenylalanine, leucine, methionine, proline, alanine, lysine, arginine and glycine. Four forms differing in their substrate specificities were identified: form 1 (liberating alanine, lysine and arginine), form 2 (liberating leucine, methionine, phenylalanine and perhaps also proline), form 3 (liberating glycine) and form 4 (liberating phenylalanine). Form 1 was highly sensitive to 1,10-phenanthroline, while the same concentration of this chelator caused no major effects on the other forms. All aminopeptidases were relatively stable at pH 5.5 in extracts from ungerminated seeds, but the inactivation was accelerated by the addition of cotyledon extract from 8-day-old seedlings. Under such conditions form 3 was most rapidly inactivated followed by forms 1 and 2, while form 4 was less susceptible. The inactivation of the various forms was affected differently by high concentrations of free amino acids. L-Arginine accelerated the inactivation of form 2 and stabilised simultaneously form 3. All forms were protected by L-alanine. Forms 1, 2 and 4 were stabilised by L-serine and by L-proline. Glycine delayed the inactivation of forms 2, 3 and 4.
Nutrient Transfer and the Fungus-Root Interface
Authors: Ashford AE , Allaway CA , Peterson CA , Cairney JWG
Published: January 2006

Ectomycorrhizas synthesised in growth pouches between Eucalyptus pilularis and Pisolithus tinctorius show low permeability to the tracer Cellufluor in the apoplast of their sheath. This is attributed to the properties of an intracellular matrix, primarily of carbohydrate, in the sheath interhyphal spaces. A similar result has also been obtained with Pisonia grandis mycorrhizas and it is proposed that this may be a general phenomenon in ectomycorrhizas, effectively isolating the symbiont exchange interface from the soil. Materials travelling across the sheath would be required to travel in the fungal symplast, a mechanism which would place uptake under fungal control, and give it a high degree of selectivity. In eucalypt mycorrhizas the cell layer beneath the Hartig net zone is a fully differentiated state II exodermis, with a well developed suberised lamella in the walls of most cells The apoplast below the Hartig net is therefore also likely to be blocked. The effect of these two apoplastlc blockages, in the sheath and in the exodermis, is to produce a distinct apoplastic compartment at the exchange interface of finite volume and sealed off both internally and externally. Exchange between symbionts must involve an apoplastlc step and isolation of thls part of the apoplast would provide an exchange compartment in which the overall composition and the accumulation of molecules could be controlled by membrane transport processes of the adjoining cells, either fungal or higher plant. Isolation of apoplast would in this way enhance the efficiency of transfer. It would also prevent loss of materlal by back diffusion and its assimilation by competing organisms The concept of a sealed apoplast at the symbiont interface is extended to other symbiotic associations including endomycorrhizas and pathogenic associations and it is proposed that it may be a universal phenomenon in symbioses, necessary for the functional efficiency of the transfer system.
Evaluation of Maize Inbreds for Vegetative Nitrate Uptake and Assimilation
Authors: Weiland RT
Published: January 2006

Twelve maize (Zea mays L.) inbred lines were cultured under hydroponic conditions in a controlled environment room for evaluation of NO3--N uptake, subsequent translocation patterns and utilisation. Prior to harvest (8-10-leaf stage), inbred roots were exposed to 24 h of 10 atom % 15NO3--N. Differences for N contents and biomass were determined. Root dry weight (RDW) was significantly correlated (r = 0.93) with root surface area. Significant inbred differences were found when N content in the plant was based on RDW.
When based on 15N during the 24 h, the amount of N absorbed varied between 30 and 71 mg per plant for the inbreds. Uptake rates ranged between 8.7 and 14.4 mg g-1 day-1 RDW. Nitrogen uptake over the 24 h based on RDW and total plant-N contents based on RDW were significantly (P< 0.001) correlated, implying that uptake rates were constant up to mid-vegetative stages for these genotypes. Of the 15N absorbed, between 30 and 61% was reduced by the inbreds and the amount reduced varied with plant tissue. The total amount reduced ranged between 0.72 and 1.25 mg g-1 dry weight.
Partitioning of Nitrogen Between and Within Leaves Grown Under Different Irradiances
Authors: Evans JR
Published: January 2006

The distribution of nitrogen between leaves on individual plants of Phaseolus vulgaris and Cucumis sativus which were grown under different irradiances was examined. For Phaseolus, shading treatments were imposed on individual leaflets when they had reached one-third of full expansion. Adjacent leaflets were either grown under the same irradiance or had different irradiances imposed on them. The nitrogen content of leaves depended on their growth irradiance and not on the growth irradiance of adjacent leaflets, with more nitrogen being found in leaves grown under higher irradiance compared to those grown in shade. For Cucumis, the nitrogen contents of the leaves changed following the imposition of shading treatments. The experiment was repeated four times with different nitrate nutrient treatments, twice in combination with a pretreatment growth irradiance of 40% sunlight. The relative changes in leaf nitrogen content for each irradiance treatment were independent of changes to the leaf nitrogen content of the plant and of the growth irradiance prior to the shading treatments. Again, nitrogen contents were highest in leaves grown at high irradiance.
Acclimation of individual leaves to their irradiance treatment was seen for both Phaseolus and Cucumis. Growth under shade resulted in lower rates of oxygen evolution per unit of chlorophyll, when measured at high irradiance, and increased partitioning of nitrogen into pigment-protein complexes. These two changes working in opposition to each other meant that for Cucumis, the relationship between photosynthetic capacity and nitrogen content was similar between irradiance treatments. For Phaseolus, the increased partitioning of nitrogen into pigment-protein complexes at low irradiance was not as great as the reduction in photosynthetic rate per unit of chlorophyll, so that the photosynthetic rate per unit leaf nitrogen was less for leaves grown under low irradiance compared to those grown under high irradiance. It is shown that acclimation to lower irradiance can increase the potential daily photosynthesis for a given leaf nitrogen content.
Diurnal and Developmental Changes in Canopy Gas Exchange in Relation to Growth in Transplanted and Direct-Seeded Flooded Rice
Authors: Dingkuhn M , Schnier HF , Datta SKD , Wijangco E , Dorffling K
Published: January 2006

Transplanted and direct-seeded flooded rice were compared in a field experiment using identical planting density and geometry. Leaf area index (LAI), plant dry weight, and tiller number were determined at 7-14 d intervals from seeding to maturity. Canopy CO2 and H2O exchange were measured using a mobile depletion-chamber system which requires 1-1.5 minutes per measurement. The canopy CO2 assimilation rates confirmed the plant dry matter accumulation observed. Diurnal measurements of net CO2 assimilation and night respiration indicated a mild midday/afternoon depression that depended on the atmospheric vapour pressure deficit (VPD). Light response of canopy CO2 assimilation exhibited light saturation at full daylight when LAI was lower than 1. No light saturation was observed at higher LAI. Transplanting shock in transplanted rice reduced net assimilation rates and delayed foliage expansion and tillering by 15 days. Crop development was retarded by 7 days. Uninhibited growth of direct-seeded rice during the vegetative stage led to superior biological yield and tiller number at maturity while grain yield was equal to that of transplanted rice. Potential yield increase in direct-seeded flooded rice is discussed on the basis of growth kinetics and assimilate source/sink relationships.
Persistence of Non-Crease Protophloem Strands in the Developing Wheat Grain
Authors: Fisher DB
Published: January 2006

The two protophloem strands in the lateral ovary walls of the developing wheat grain, previously reported to be obliterated during grain elongation, are shown to persist through about half, or somewhat longer, of the grain filling period. During the latter part of their functional life, they appear to be involved in the absorption of solutes produced during degeneration of the middle pericarp. During the final stages of pericarp degeneration, the protophloem strands show a basipetal progression of degeneration and adherence to the remaining inner and outer pericarp layers.
Substrate Gradients and Regional Patterns of Dry Matter Deposition Within Developing Wheat Endosperm. I. Carbohydrates
Authors: Ugalde TD , Jenner CF
Published: January 2006

Starch and protein content of wheat endosperm are important factors determining yield and grain
quality. Experiments were conducted using microsectioning, HPLC, analysis, and radiotracer techniques
to describe regional patterns of deposition of starch and protein throughout wheat endosperm, and to
test whether these patterns of deposition could be due to regional patterns of substrate supply. This
paper describes the distribution patterns of starch and soluble carbohydrates.
Carbohydrate entered the grain as sucrose. It was transported to and through the endosperm mostly
as sucrose, even though sucrose accounted for only 40-45% (w/w) of the total soluble carbohydrates
in the endosperm cavity and endosperm. The concentration of hexose was low, equivalent to only 1.6%
and 7% (w/w) of the amount of sucrose in the endosperm cavity and endosperm respectively.
The endosperm cavity and endosperm contained appreciable amounts of a glucose disaccharide,
appearing in a number of tests as maltose. These regions also contained oligosaccharides appearing
as a fructan series. There was no evidence for ribose or raffinose. Other soluble carbohydrates were
identified.
Turnover of sucrose in the grain is rapid. Sucrose in the endosperm and endosperm cavity was
equivalent to only 3.1 h and 1.0 h of starch deposition respectively.
Starch was deposited evenly from the endosperm cavity to the endosperm periphery on the dorsal
side except for a decrease in the outermost section. Any gradient of protein percentage across the
endosperm is not due to changes in the concentration of starch. There was a 2-fold gradient of
sucrose across the same region, decreasing in an outward direction. The gradient was steepest near the
endosperm cavity. The pattern of starch deposition throughout wheat endosperm cannot be attributed
to a regional pattern of sucrose concentration. We conclude that transport of sucrose across the
endosperm is not a factor regulating the distribution of starch.
Involvement of a Novel Peptide in the Heat Shock Response of Australian Wheats
Authors: Blumenthal CS , Batey IL , Wrigley CW , Barlow EWR
Published: January 2006

A low molecular weight peptide, induced by exposure of coleoptiles to heat stress at 41°C, has been detected by reversed-phase high performance liquid chromatography of extracts from coleoptiles of five wheat (Triticum aestivum) cultivars. This component is detected within 1 h of a 41°C heat shock, is not detected 48 h after cessation of the heat shock, and remains present during a continuous 24 h heat treatment. The appearance of this component is also induced by exposure of the coleoptile to 0.1 M sodium arsenite or 10% ethanol. When other species such as barley (Hordeum vulgare), soybean (Glycine max), sorghum (Sorghum bicolor), maize (Zea mays), mungbean (Vigna radiata), or rice (Oryza sativa) were examined for the presence of a component eluting in the same position, it was only detected in maize. The amino acid sequence for the heat-induced peptide from wheat was determined to be: V-L-V-P-V-P-Q-L-Q-P-Q-N-Q-P/Q. The sequence of 12 of these amino acids is the same as the N-terminal sequence of α- and β gliadins (wheat endosperm storage proteins). The production of this heat-induced peptide in aneuploids of Chinese spring wheat indicated that the peptide gene was located on the same chromosome arm as one of the gliadin genes. The presence of this gliadin-like peptide in heat-stressed coleoptiles may be due to the presence of five heat shock elements in the gene sequence of gliadins. The potential heat inducibility of the gliadin gene has important implications for end-use quality of wheat. The results also imply that seed proteins may have a function other than storage of nitrogen.
Growth and Biomass Partitioning in Eucalyptus grandis Seedlings in Response to Nitrogen Supply
Authors: Cromer RN , Jarvis PG
Published: January 2006

Seedlings of Eucalyptus grandis were grown using an aeroponic culture technique in which continuously circulating solution was sprayed over seedling roots. Nutrient solutions, made up so that nitrogen was the element limiting growth, were added hourly at relative addition rates between 0.04 and 0.12 d-1. This technique enabled stable seedling nitrogen concentrations and relative growth rates to be maintained during experimental periods of 40-80 days in most treatments.
Once steady state growth was established, allocation of dry matter to stems compared with foliage increased with ontogeny and the allometric relationship was not influenced by plant nitrogen status or genotype. In contast, the intercept of the allometric relationship between root mass and foliage mass was dependent on plant nitrogen concentration, but the slope was equal to unity at all nitrogen concentrations.
Our data indicate that nitrogen-induced changes in allocation of dry matter between foliage and root components, together with changes in specific leaf area, had a larger influence on seedling growth rate than did changes in net rate of carbon gain per unit leaf area.
Wood Density and Above-Ground Growth in High and Low Wood Density Clones of Pinus radiata D. Don
Authors: Sheriff DW , Rook DA
Published: January 2006

In Pinus radiata a negative relationship has usually been found between stem volume and wood density. Clones previously found to produce wood of high or low density were used to investigate interrelationships between above-ground partitioning coefficients, carbon gain, and wood density. Cuttings had been propagated c. 5 years earlier, and were 5 m high when the experiment started. Potential carbon gain of the tree was manipulated by using two light environments; one with a light level c. 1.5 times the other.
Measurements were of changes in stem, branch, and needle biomass during the 305-day experiment, of rates of photosynthesis, and of wood density by β-ray densitometry and microscopy; densities determined by the two techniques were the same. For all but two trees, wood densities of a stem and its branches were the same; for the other two, stem density was 13% less than that of their branches.
Trees in the high light treatment accumulated more above-ground biomass, but there was no simple relationship between wood density and either above-ground growth or photosynthesis. With one exception, partitioning of photosynthate to stem was constant. In most cases, proportionately less photosynthate (30-80%) was allocated to below-ground biomass in the low light treatment than in the high light treatment (60-80%).
Final grain weight in wheat as affected by short periods of high temperature during pre- and post-anthesis under field conditions
Authors: Savin Roxana , Calderini Daniel F. , Slafer Gustavo A. , Abeledo Leonor G.
Published: January 2006

Individual grain weight is an important source of variation for grain yield in
wheat. The aim of this study was to investigate the effect of short periods of
high temperature immediately pre-anthesis, or during post-anthesis, on grain
weight under field conditions. Thus, two wheat cultivars of different grain
weight potential were sown on four different sowing dates to provide different
temperature conditions during the pre- and post-anthesis periods. In addition,
for two sowings, acrylic boxes were installed to increase spike temperature
either immediately before anthesis, or during the lineal phase of the
grain-filling period. Final grain weight was significantly affected by sowing
date, genotype and grain position on the spike. Grain weight showed a clear
relationship with the average temperature of the grain filling period, but
this relationship was either linear or curvilinear, depending on the cultivar.
Both high temperature treatments, i.e. at pre- or post-anthesis, significantly
diminished final grain weight, and their effect was similar with the exception
of heavier grains, which were unresponsive to the high temperature treatment
at pre-anthesis. Finally, a better understanding of final grain weight was
reached when temperatures from the pre-anthesis period were included in the
analysis of grain weight response to temperature.
Expression patterns of the genes that encode lectin or lectin-related polypeptides in Robinia pseudoacacia
Authors: Yoshida Kazumasa , Tazaki Kiyoshi
Published: January 2006

Three genomic clones (Rplec2,
Rplec5 and Rplec6) and a cDNA
clone (LECRPA4) that encoded lectin or lectin-related polypeptides were
isolated from Robinia pseudoacacia L. A comparison of
the nucleotide sequences of Rplec2 and a previously
reported cDNA for the subunit indicated that Rplec2
encoded the 29 kDa subunit of the inner-bark lectin RPbAI.
Rplec5 encoded a polypeptide whose deduced amino acid
sequence was 96.1% identical to that of a subunit of seed lectin. The
amino acid sequence deduced from the open reading frame of
Rplec6 showed 61.1% identity to that encoded by
Rplec5. LECRPA4 was isolated from an inner bark cDNA
library and appeared to encode the 26 kDa subunit of inner-bark lectin RPbAII.
The expression patterns of the various genes in tissues were examined by the
reverse transcriptase-polymerase chain reaction (RT-PCR) with appropriate
primers. Rplec2 transcripts were detected in the inner
bark and roots. Rplec5 transcripts were detected in the
inner bark, seeds and roots. No Rplec6 transcripts were
detected in all tissues examined. LECRPA4 transcripts were found in leaves and
in the inner bark. The level of expression of Rplec2 in
the inner bark appeared to be similar in samples collected in different years
and from different trees, whereas levels of expression of
Rplec5 and LECRPA4 varied. These results suggest the
differential regulation of expression of members of the lectin gene family in
tissues of R. pseudoacacia.

The nucleotide sequence data reported herein will appear in the DDBJ, EMBL and
GenBank Nucleotide Sequence Databases under the accession numbers AB 012632
(Rplec2), AB012633 (Rplec5),
AB012634 (Rplec6) and AB012635 (LECRPA4).
Confocal microscopy of thylakoid autofluorescence in relation to origin of grana and phylogeny in the green algae
Authors: Gunning B. E. S. , Schwartz O. M.
Published: January 2006

Confocal microscopy was used to examine heterogeneity of chlorophyll
fluorescence in chloroplasts of selected green algae, in the light of evidence
that the technique reveals the distribution of photosystem II (PSII). Three
levels of complexity were seen: (1) uniform fluorescence
(Codium) or intergrading zones of bright and less bright
fluorescence in genera known from electron microscopy to have irregular areas
of thylakoid appression (e.g. Chlamydomonas — in
which Bertos and Gibbs (J. Phycol.,
34, 1009, 1998) have found absence of segregation of
photosystem I (PSI) and PSII, Ulothrix,
Stigeoclonium, Draparnaldia); (2)
a pattern of 1–2 µm patches of fluorescence on a less bright
uniform background, in taxa where more organized thylakoid stacking (but not
grana sensu higher plants) is seen by electron
microscopy (Ulva, Oedogonium); and
(3) Discrete 0.5–2 µm spots of fluorescence in a relatively
fluorescence-free background, closely resembling higher plant grana
(Cladophorophyceae, Zygnematales, Coleochaete,
Nitella). Further investigation of these states may
illuminate the evolution of higher plant thylakoid systems, where PSII is
segregated into grana, and may provide clues concerning the adaptive
advantages of grana. Association of putative PSII fluorescence with pyrenoids
was found in most taxa, although fluorescence of trans-pyrenoid thylakoids was
seen in one case only. The association prevails whether or not there is a
starch sheath around the pyrenoids, and is persistent in pyrenoids isolated
from Spirogyra. We speculate that this fluorescence may
represent a subset of PSII that functions with thylakoid carbonic anhydrase to
provide locally high concentrations of CO2 to the
Rubisco in the pyrenoid core, as predicted by Raven
(Plant, Cell and Environment,
20, 147, 1997).