bluuebunny/crossref_metadata_2025 huggingface dataset:
The 15N natural abundance (δ15N) of ecosystem samples reflects measures of water availability
Authors: Handley L. L. , Austin A. T. , Stewart G. R. , Robinson D. , Scrimgeour C. M. , Raven J. A. , Heaton T. H. E. , Schmidt S.
Published: January 2006

We assembled a globally-derived data set for site-averaged foliar
δ15N, the δ15N of
whole surface mineral soil and corresponding site factors (mean annual
rainfall and temperature, latitude, altitude and soil pH). The
δ15N of whole soil was related to all of the site
variables (including foliar δ15 N) except altitude
and, when regressed on latitude and rainfall, provided the best model of these
data, accounting for 49% of the variation in whole soil
δ15N. As single linear regressions, site-averaged
foliar δ15N was more strongly related to rainfall
than was whole soil δ15N. A smaller data set
showed similar, negative correlations between whole soil
δ15N, site-averaged foliar
δ15N and soil moisture variations during a single
growing season. The negative correlation between water availability (measured
here by rainfall and temperature) and soil or plant
δ15N fails at the landscape scale, where wet spots
are δ15N-enriched relative to their drier
surroundings. Here we present global and seasonal data, postulate a proximate
mechanism for the overall relationship between water availability and
ecosystem δ15N and, newly, a mechanism accounting
for the highly δ15N-depleted values found in the
foliage and soils of many wet/cold ecosystems. These hypotheses are
complemented by documentation of the present gaps in knowledge, suggesting
lines of research which will provide new insights into terrestrial N-cycling.
Our conclusions are consistent with those of Austin and Vitousek (1998) that
foliar (and soil) δ15N appear to be related to the
residence time of whole ecosystem N.
Purification and Characterization of the Polygalacturonases of Tomato Fruits
Authors: Ali ZM , Brady CJ
Published: January 2006

Endopolygalacturonase [poly(1,4-α-D-galacturonide) glycanohydrolase, EC 3.2.1.15] was purified from ripening tomato fruits. The dominant enzyme in fruits at an early stage of ripening had a native molecular weight (Mr) of about 115 000, an isoelectric point (pI) of 8.6, and retained 50% of activity after 10 min at 70°C. Divalent metal ions enhanced the activity of this enzyme and ethylenediaminetetraacetate (EDTA) inhibited activity. In fully ripe fruits, two enzymes of Mr about 43 000 and 46 000 were most prominent. These enzymes each had a pI of 9.4; when a mixture of these two enzymes was heated for 10 min at 50°C, 50% of activity was lost. Antibodies raised against the smallest enzyme, Mr 43 000, reacted also with the larger enzymes. After denaturation in sodium dodecyl sulfate, the largest (Mr 115 000) and smallest (Mr 43 000) enzymes yielded polypeptides of identical size while the third enzyme (Mr 46 000) was slightly larger. All three enzymes were glycoproteins. From fully ripe fruits, enzyme preparations with specific activities of 1.7 �kat mg-1 were obtained. This specific activity exceeds those described previously for plant polygalacturonases.
Recovery From Water Stress in Five Sunflower (Helianthus annuus L.) Cultivars. II. The Development of Leaf Area
Authors: Rawson HM , Turner NC
Published: January 2006

Five cultivars of sunflower with different durations to anthesis were grown in the field either entirely on stored soil moisture (DRY), irrigated frequently throughout growth (WET), or transferred from the DRY to the WET regime at 44 days (REC 1) or at 54 days from sowing (REC 2). The expansion patterns of all leaves were followed with a view to determining which leaves responded when stress was relieved.
Cultivars differed in their ability to recommence leaf expansion after water was applied to DRY crops, but any differences were related to the stage of plant development reached when water was applied. Thus in the REC 1 treatment, no leaves of early cultivars equalled the areas achieved in equivalent leaves in the WET regime, whereas the latest cultivar generated individual leaves which were 60% larger than equivalent leaves in the WET treatment. In the REC 2 treatment, few leaves of the early cultivars reached significantly larger areas than equivalent leaves in the DRY while all leaves above node 12 in the latest cultivar exceeded those in the DRY regime.
Examining the data in terms of the age of leaves in the profile when the REC 1 and REC 2 treatments were applied showed that, regardless of cultivar, all leaves which were less than 15 days old (age 0 = leaf emergence) had some capacity for renewed expansion when water was applied. However, primordia which still had 15 days to go before they emerged as leaves had the greatest capacity for expansion to a potential size, and this capacity decreased progressively over their next 30 days of aging.
Leaf age profiles did not explain all the difference in renewed expansion potential among cultivars: a leaf position factor at the time of water application was almost as important. Thus, the closer that leaves were to the head, the less was their capacity for renewed expansion regardless of their age. In order to achieve larger areas when water was applied, old leaves increased their duration of expansion while young leaves increased their rate of expansion.
It is concluded that cultivars do not differ in their ability to 'recover' leaf area upon application of water except by virtue of their different durations to anthesis.
Growth and Osmotic Relations of the Mangrove Avicennia marina, as Influenced by Salinity
Authors: Downton WJS
Published: January 2006

Seeds of the mangrove Avicennia marina were germinated and grown for up to 11 months on nutrient solution or nutrient solution containing 10, 25, 50, 75 or 100% natural seawater (500 mM sodium; 580 mM chloride). Early seedling development was most rapid in the absence of sodium chloride, but soon declined. As a result, biomass production in this treatment was poorest. The response was associated with the appearance of necrotic lesions. The growth optimum based on fresh or dry weight occurred on 10, 25 or 50% seawater. Plants receiving higher salinities, particularly full strength seawater, were slow to develop, and low in biomass, but healthy in appearance. Seeds taken from parent trees growing on tidal mudflats had osmotic potentials more negative than seawater, but contained little sodium or chloride, potassium being the most abundant inorganic ion. The osmotic potentials of the seedlings were more negative than those of the external watering solutions by at least 2 MPa in all of the treatments. Turgor pressures of approximately 0.8 MPa were evident for the salt-treated plants, but were much lower (0.2-0.3 MPa) for plants receiving only nutrient. Seedlings grown on nutrient alone accumulated mainly potassium (sodium and chloride being unavailable) and probably depended upon organic substances, in particular organic anions, to generate internal osmotic potential. Plants on 10-100% seawater treatments behaved as typical halophytes accumulating increasing levels of sodium and chloride as external salinity increased, even though the leaves can regulate steady-state ionic concentrations by means of salt glands. Sodium replaced potassium, but preferential potassium uptake was maintained over a wide range of external sodium concentrations. Chloride accumulation balanced approximately half of the cations present. The calculated osmotic contribution made by the cations (assuming complete charge balance by chloride) in the leaf extracts corresponded closely to measured osmotic potential.
The Growth of Banana Plants in Relation to Temperature
Authors: Turner DW , Lahav E
Published: January 2006

Bananas (cv. Williams) were grown for 12 weeks in sunlit growth chambers at day/night temperatures of 17/10, 21/14, 25/18, 29/22, 33/26 or 37/30°C. Humidity was not controlled. At 17/10°C, the plants showed chilling injury and heat injury occurred at 37/30°C. Total plant dry weight was greatest at 25/18°C while leaf area was greatest at 33/26°C. At high temperatures proportionately less dry matter was present in the roots and corm compared with plants at 25/18°C. High temperatures produced more horizontal leaves but, to compensate for this, the laminae folded more readily. Lamina folding was closely associated with relative water content of the laminae, except under cool conditions where laminae folded despite high (97-99%) leaf relative water contents. Unit leaf rate (increase in whole plant dry weight per unit leaf area per unit time) was greatest at 21/14°C (5.8 g m-2 day-1) and least at 37/30°C (1.7 g m-2 day-1.) and had a strong negative association with whole-plant leaf resistance. Leaf relative water content was more closely associated with vapour pressure deficit than temperature and even at 37/30°C was high at 94%.
Water Relations and Ion Concentrations of Leaves on Salt-Stressed Citrus Plants
Authors: Walker RR , Torokfalvy E , Grieve AM , Prior LD
Published: January 2006

Grafted plants of Valencia orange scion [Citrus sinensis (L.) Osbeck] on six different rootstocks were grown under glasshouse conditions and supplied with dilute nutrient solution containing either 0 or 75 mM NaCl. Salt treatment was increased to 150 mM NaCl after 49 days. Leaf water relations and leaf chloride, sodium and potassium concentrations were followed throughout the period of salt treatment until day 105, when salt treatment ceased, and thereafter until day 140. Seedlings of Rangpur lime (C. reticulata var. austera hybrid?), Cleopatra mandarin (C. reticulata) and sweet orange (C.sinensis) were treated similarly and leaf water relations and chloride concentrations were followed until salt treatment ceased on day 77.
All Valencia-rootstock combinations adjusted osmotically to the salt stress imposed and maintained turgor pressures at or above control values. Mature leaves on seedlings of sweet orange behaved similarly to Valencia orange leaves on sweet orange rootstocks by maintaining turgor pressures higher than control values. In contrast, mature leaves on seedlings of the genotypes Rangpur lime and Cleopatra mandarin tended to lose turgor during the period of treatment with 150 mM NaCl.
Leaf chloride analyses indicated that Rangpur lime and Cleopatra mandarin rootstocks restricted the uptake and/or transport of chloride to shoots. However, comparatively high concentrations of sodium (>approx. 200 mM, tissue water basis) were accumulated in mature leaves on all rootstocks during salt treatment. Leaf potassium concentrations remained similar to control values. The reduction in osmotic potential in mature Valencia leaves on rough lemon (C. jambhiri), Trifoliata (Poncirus trifoliata), Camzo citrange (C. sinensis × P. trifoliata) and sweet orange rootstocks on day 77 could be accounted for largely by the increase in sodium and chloride, whereas chloride (as NaCl) accounted for only approximately 50% of the reduction in osmotic potential in Valencia leaves on Rangpur lime and Cleopatra mandarin rootstocks.
Stomatal resistances in mature Valencia leaves on all rootstocks were increased by salt treatment and showed only partial recovery after the cessation of salt treatment. The incomplete recovery may have been associated with the retention in leaves of high concentrations of sodium.
Spatial Variation of the Electrical Properties of Chara australis. I Electrical Potentials and Membrane Conductance
Authors: Ogata K , Chilcott TC , Coster HGL
Published: January 2006

Experiments are described with cells of Chara, using a water-film technique, to determine the dependence on position along the cells of the membrane conductance, electromotive force (e.m.f.) and noise spectrum. It was found that both the e.m.f. and the conductance were far from uniform along the cells. The e.m.f. showed distinct zoning patterns, regions of greater e.m.f. (acid zones) having potentials of up to 70 mV greater than the zones of minimum e.m.f. (alkaline zones). In the alkaline zones the conductance was ≈ 3.5 times larger than in the acid zones. The noise spectra of the membrane potential in both the acid and alkaline zones were similar, despite the differences in membrane conductance. The details of the results presented are consistent with the motion that in the acid zones the potential is hyperpolarized by the operation of an active H+ transport system, whilst in the alkaline zones the membrane is in a proton-permeable state (in which the conduction mechanism itself may be fluctuating).
Effects of Salinity on Ion Uptake and Growth of Mung Bean Plants (Vigna radiata L.)
Authors: Salim M , Pitman MG
Published: January 2006

Effects were compared of different concentrations in nutrient culture solutions of KCl alone and its mixture with NaCl on the growth of mung beans. At the same concentrations of Cl, growth was more reduced in KCl solutions alone than in mixtures of NaCl and KCl. Growth reduction in KCl solutions seemed to be related to higher (K + Na) and Cl contents of the shoots due to higher rates of net transport from roots to shoots.
Time Trends of Solute Accumulation and the Influence of Potassium Fertilizer on Osmotic Adjustment of Water-Stressed Leaves of Three Tropical Grasses
Authors: Wilson JR , Ludlow MM
Published: January 2006

Osmotic adjustment, calculated from the difference in concentrations of ions and sugars between stressed and unstressed leaves of green panic, buffel grass and speargrass given normal or high potassium supply in the field, was determined during a 37-day drying cycle and following rewatering. Pressure/volume (P/V) curves were used to characterize the water relations of buffel grass with normal K supply on eight occasions during the experiment, and of the remaining treatments only at the end of the drying cycle.
The maximum osmotic adjustment for the three grasses was 0.84-1.0 MPa calculated from chemical analyses of solutes and 0.5-0.7 MPa derived from the P/V analyses. High K supply did not enhance osmotic adjustment of water-stressed leaves.
Osmotic adjustment reached a plateau 22 days after watering ceased, and its relationship with leaf water potential (Ψ) was the same for all species. When midafternoon Ψ was c. -4.8 MPa and leaves were permanently wilted, osmotic adjustment was 90% of maximum, suggesting that osmotic adjustment ceased when growth and most physiological activity were curtailed by loss of turgor.
Osmotic adjustment delayed the onset of permanent wilting in water-stressed leaves by c. 4 days. Therefore, its contribution to the maintenance of leaf growth during water stress in these three grasses was small.
Macrozin, a Novel Storage Globulin From Seeds of Macrozamia communis L. Johnson
Authors: Blagrove RJ , Lilley GG , Higgins TJV
Published: January 2006

The isolation, characterization and amino acid composition are reported for macrozin, the major storage globulin found in seeds of Macrozamia communis. Electrophoresis of macrozin on cellulose acetate membranes at neutral pH resulted in a single broad band indicating limited charge heterogeneity. Isoelectric focusing under dissociating and reducing conditions showed this globulin to be composed of a family of polypeptide chains with apparent isoelectric points in the range pH 6.0-7.5. Sedimentation equilibrium studies showed that the main component purified by gel filtration in aqueous buffers at neutral pH has a molecular weight of 260 000 and a sedimentation coefficient S020.w = 10.9 S. This component dissociates in 8 M urea to yield subunits of molecular weight 126 000. Each subunit is composed of disulfide-bonded polypeptide chains of approximate molecular weight 44 000. The apparent molecular weights for the macrozin subunit and its constituent polypeptides were 130 000 and 46 000 from dodecyl sulfate-polyacrylamide gradient gel electrophoresis. The dimeric nature of the main oligomer in aqueous solution was confirmed by crosslinking the subunits with dithiobis(succinimidylpropionate); the presence of three polypeptide chains per subunit is inferred from the molecular weights. Optical rotatory dispersion and circular dichroism measurements suggest that macrozin is devoid of α-helix in its native conformation, but contains some 25% α-helix after incubation with sodium dodecyl sulfate.
Responses to Ambient CO2 Concentrations by Sodium-Deficient C4 Plants
Authors: Johnston M , Grof CPL , Brownell PF
Published: January 2006

The signs of sodium deficiency in the C4 species Amaranthus tricolor and Atriplex spongiosa were alleviated when the species were grown in conditions of high CO2 concentration (1 500 �l CO2 1-1). In experiments in which A. tricolor was grown in conditions of low CO2 concentration (15 �l CO2 1-1), the signs of sodium deficiency were accentuated. The sodium-deficient plants resembled the C3 species Atriplex hastata and tomato in their response to the CO2 treatments. Growth and chlorophyll concentrations increased in both the sodium-deficient C4 plants and the C3 plants when they were grown in conditions of increased CO2 concentration. Sodium-sufficient C4 plants were relatively unaffected by the CO2 treatments.
Plant Growth and Water Use With Limited Water Supply in High CO2 Concentrations. II. Plant Dry Weight, Partitioning and Water Use Efficiency
Authors: Morison JIL , Gifford RM
Published: January 2006

Plants of 18 species were grown from seed in two glasshouses, one with normal and one with twice the present atmospheric CO2 concentration. Plants were grown singly with a diminishing soil moisture content and were harvested either after the initial period of rapid growth and water use or after subsequent prolonged soil drying. Plant dry weight (DW) was increased substantially by high CO2 in all but two species (cotton and maize) at the first harvest (average increase of 65%, range from 26 to 132%). Over the whole period, increases in DW with high CO2 (average of 53%) were associated with increases in water use efficiency (WUE) of between 40 and 80% (average of 67% for all species). Cowpea and sunflower plants grown through two additional soil moisture drying cycles showed 26 and 21% increases, respectively, in the effect of high CO2 on WUE. Approximate calculations indicated that high CO2 increased the apparent efficiency of use of intercepted radiation by 11-49% (average of 27%) in C3 species but in C4 species there was no effect. The effect of high CO2 on the partitioning of DW varied between species and between harvests. During the first period, 14 species showed increased specific leaf weight of 10-40% in high CO2 and 16 species showed no effect of high CO2 on the root : shoot ratio. Over the whole experiment, eight species had lower leaf to total plant weight ratio in high CO2 attributable to increased non-leaf aerial tissues.
Sucrose and Starch Content of Plant Parts as a Possible Indicator for Salt Tolerance
Authors: Rathert G
Published: January 2006

The effects of NaCl on total root and leaf sucrose and on total foliar starch in crops of differing salt tolerance were investigated during the early stages of salinity stress. Leaf sucrose level increased most in bushbean (sensitive) but less in rice (moderately sensitive), whereas it decreased slightly in soybean (moderately tolerant) and more in cotton (tolerant). Initial root sucrose was lowest in bushbeans, but this sensitive species showed the biggest percentage increase after salination. Foliar starch increased in sensitive crops but decreased in tolerant crops. NaCl-induced carbohydrate change in roots and laminae was correlated with tolerance of the species independently of ion-regulation behaviour. Sucrose and starch contents may assist in the selection for salt tolerance within species.
Multiple Forms of Aminopeptidases in Representatives of the Tribe Vicieae (Leguminosae)
Authors: Murray DR , Waters SP
Published: January 2006

The distribution of aminopeptidases with activity against aminoacyl β-naphthylamide substrates has been studied in several close relatives of pea (Pisum sativum L.), a species known to possess two forms of aminopeptidase distinguished by their insensitivity (AP1) or complete sensitivity (AP2) to the chelator 1,10-phenanthroline. Leaf, cotyledon or embryo extracts exhibited one or two bands of aminoacyl β-naphthylamidase activity following electrophoresis, yet test-tube assays for enzyme activity conducted with the same extracts in the absence or presence of 5 mM phenanthroline suggested a distribution of isoenzymes similar to that of pea in every instance. Better resolution of isoenzymes was obtained by anion exchange chromatography with diethylaminoethyl-Sephadex A-50, using the fraction of protein precipitating between 35% and 55% of saturation with ammonium sulfate as a concentrated source of isoenzymes. When the phenanthroline-insensitive activity was inactivated by dialysis at pH 4.7, then two phenanthroline sensitive forms, AP2 and AP3, could be distinguished from cotyledons of sweet pea (Lathyrus odoratus L.) and broad bean (Vicia faba L.). Embryos of lentil (Lens culinaris Medik.) yielded single forms corresponding to AP1 and AP2 of pea; however, the AP1 from lentil showed partial sensitivity to phenanthroline, the degree of inhibition depending on the substrate employed.
Growth and Developmental Responses of Perennial Ryegrass Grown at Constant Temperature. II. Influence of Light and Temperature on Leaf, Tiller and Root Appearance
Authors: Hunt WF , Thomas VJ
Published: January 2006

Spaced plants of perennial ryegrass (Lolium perenne L. cv. Grasslands Ruanui) were grown in nutrient solution under six levels of irradiance at six temperatures (7-33°C). Response curves to light and temperature of leaf, tiller and root appearance rates were determined during the exponential growth phase. Appearance rate responses showed saturation-type kinetics with irradiance, the shape of the response curve being temperature dependent. Light-saturated appearance rates increased with temperature over the 7-17°C range, but were independent of temperature above 20°C. No apparent optimum temperature was found for leaf appearance, root appearance or tillering in the 7-33°C range. The ratios for both tillering/leaf appearance and root appearance/leaf appearance (light-saturated) were notable for their insensitivity to temperature.
The results indicate that light and temperature determined the rate of leaf appearance through effects on the rate of assimilate supply and utilization at the stem apex. Leaf appearance rates determined the potential rates for tiller and root axis production through determining the sites available. Low irradiance combined with high temperature reduced tillering below the potential but did not reduce root production.
Gas Movements in the Roots of Avicennia marina (Forsk.) Vierh
Authors: Curran M
Published: January 2006

Apparatus for the determination of the rates of oxygen diffusion through excised portions of the root system of Avicennia marina is described. The diffusive resistances of portions of the horizontal root system are measured and the results compared with the values predicted by simple formulations of Fick's first law of diffusion. Predictions of oxygen diffusion rates made without making allowance for respiration or tortuosity are in close agreement with the measured values and thus it is concluded that the horizontal root system is a highly efficient means of oxygen transport. The diffusive resistances of a selection of pneumatophores are also measured and the effect of epiphytic algae is assessed. Structural studies of both horizontal roots and pneumatophores help to explain the ease with which gas moves within the root system, which is compared in conceptual terms with a series of open tubes.
Stomatal Adjustment to Water Deficits in Three Tropical Grasses and a Tropical Legume Grown in Controlled Conditions and in the Field
Authors: Ludlow MM , Fisher MJ , Wilson JR
Published: January 2006

Stomatal conductance (g) and leaf photosynthetic rate (P) of many species in the field are often less sensitive to water deficits than when grown in small pots under controlled conditions. This may result from stomatal adjustment in field-grown plants in response to water deficits that develop slowly, whereas adjustment does not occur under the rapid drying experienced by plants in small pots. To test this hypothesis we studied the response to water potential (Ψl) of g and P in three tropical C4 grasses, green panic (Panicum maximum var. trichoglume), buffel grass (Cenchrus ciliaris) and spear grass (Heteropogon contortus) and a tropical legume, Siratro (Macroptilium atropurpureum), grown under controlled conditions and in the field.
Field experiments clearly showed that stomatal adjustment occurred so that g and P were progressively less sensitive to the decline in Ψl as water deficits increased during a long soil drying cycle. For example in one experiment, the Ψl at which P approached zero fell from - 1.9, -2.0 and -2.4 MPa to -4.0, -4.0 and -3.3 MPa for green panic, spear grass and buffel grass, respectively. This stomatal adjustment was reversed within 10 days after rewatering to the well watered condition. Little stomatal adjustment occurred in plants grown under controlled conditions in small pots in which both soil water and Ψl fell rapidly. However, if plants were grown in similar conditions but in large pots of soil so that soil water and Ψl decreased slowly, stomatal adjustment comparable with field-grown plants was observed.
Siratro showed much less stomatal adjustment than the grasses and Ψl at which P approached zero only fell from - 1.2 to - 1-5 MPa.
Biochemical Characterization of Chlorophyll-Free Mitochondria From Pea Leaves
Authors: Day DA , Neuburger M , Douce R
Published: January 2006

Mitochondria from pea leaves were purified by centrifugation on a self-generated Percoll gradient which contained a linear gradient of polyvinylpyrrolidone-25 (0-10%, w/v). The chlorophyll content of the purified mitochondria was less than 1 �g per mg protein. All substrates were rapidly oxidized by these
mitochondria, the rate of glycine oxidation being between 200 and 300 nmol O2 min-1 mg-1 protein, depending on the age of the leaves used. These rates did not vary significantly over a period of 20 h, provided NAD+ was supplied exogenously, when the mitochondria were stored on ice. Respiratory control, ADP/O ratios and outer membrane integrity (always more than 95%) were also maintained during storage. The phospholipid composition of the membranes from the leaf mitochondria was virtually identical to that of mitochondria from non-photosynthetic tissues although their lipid to protein ratio was slightly lower. The polypeptide pattern of the membranes from green leaf mitochondria and those from etiolated leaves and hypocotyls were also similar, but marked differences were observed between the matrix proteins from the different tissues. In particular, intensely stained bands at 94, 51,41 and 15.5 kDa which were present in the matrix of green leaf mitochondria were missing or present in much smaller quantities in the non-photosynthetic tissues. This difference was correlated with the ability of the mitochondria to oxidize glycine, suggesting that the four polypeptides may be associated with the glycine decarboxylase complex.
Effect of NAD and Rotenone on the Partitioning of Malate Oxidation Between Malate Dehydrogenase and Malic Enzyme in Isolated Plant Mitochondria
Authors: Bryce JH , Wiskich JT
Published: January 2006

Our aim was to determine whether there is a specific link between NAD-malic enzyme and the rotenone- insensitive bypass of electron transport. Mitochondria were isolated from fresh beetroot tissue, aged beetroot slices, and turnips. Oxygen uptake and pyruvate production were measured in reactions where these mitochondria were metabolizing malate at pH 6.8 in the presence of glutamate, to facilitate the removal of oxaloacetate, and in its absence. In the absence of glutamate there was substantial activity of malic enzyme. NAD+ (577 �M) prevented a fall in oxygen uptake by stimulating malic enzyme. Rotenone (19 �M) reduced oxygen uptake. This inhibited rate was stimulated by NAD+ due, in particular, to a stimulation of malic enzyme. We conclude that the stimulation of malate metabolism by NAD+ is accounted for by malic enzyme due to the unfavourable equilibrium of malate dehydrogenase for malate oxidation and the resultant accumulation of oxaloacetate, and not to any specific link between malic enzyme and the rotenone-insensitive bypass. In the presence of glutamate, malate dehydrogenase was the predominant malate metabolizing enzyme. Oxygen uptake and malic enzyme were stimulated and inhibited by NAD+ and rotenone, respectively. In the presence of rotenone, NAD+ stimulated oxygen uptake and increased the percentage due to malic enzyme. This stimulation is accounted for by the higher Kin of the rotenone-insensitive dehydrogenase for NADH and the unfavourable equilibrium position of malate dehydrogenase resulting in activation of malic enzyme only. We conclude that malic enzyme is not specifically linked to the rotenone-insensitive pathway of electron transport. This has important implications for the regulation of energy metabolism in plants.
An Empirical Model of Net Photosynthesis and Leaf Conductance for the Simulation of Diurnal Courses of CO2 and H2O Exchange
Authors: Kuppers M , Schulze ED
Published: January 2006

An empirical model of CO2 uptake and water loss of leaves is established using steady-state responses of gas exchange to climatic factors as input. From the model the response surface of net CO2 assimilation and leaf conductance to climate can be derived. The model consists of two submodels, one describing the response of CO2 uptake to light and temperature, the other describing the response of leaf conductance to temperature and humidity. Both submodels are joined via the linear relationship between CO2 uptake and leaf conductance at short-term (minutes) variation of irradiance. From the humidity response of leaf conductance and the 'demand function' (Raschke 1979) of CO2 uptake in the mesophyll, the effect of stomata on the diffusion of CO2 between leaf and air is determined. The model is tested by comparing measured and calculated diurnal courses of gas exchange for two plants of Pinus silvestris, differing in photosynthetic capacity due to different levels of magnesium nutrition. Applications and limitations of the model are discussed.
The National and International Importance of Drought and Salinity Effects on Agricultural Production
Authors: McWilliam JR
Published: January 2006

This review examines the impact of drought and salinity on agricultural production in both the semi- arid and humid regions of the world. The frequency and nature of drought events and some recent approaches to drought prediction are discussed along with the distribution of salinity and the various factors leading to its occurrence under both irrigated and dryland conditions. Strategies to minimize the impact of drought and salinity on the rural community and on the stability of land resources have been developed largely in high-income countries. However, because of the high cost, little has been done in the developing world where extensive areas of valuable land are deteriorating, representing a serious threat to food security.
Effects of Phosphorus Nutrition on Ribulose-1,5-Bisphosphate Carboxylase Activation, Photosynthetic Quantum Yield and Amounts of Some Calvin-Cycle Metabolites in Spinach Leaves
Authors: Brooks A
Published: January 2006

When spinach plants were transferred to nutrient solutions without phosphorus, the photosynthetic rate per unit leaf area gradually declined. Stomatal conductance also decreased but was not the sole cause of the decreased photosynthetic rate because the partial pressure of CO2 in the intercellular spaces (CI) was unaltered. Measurements of the photosynthetic rate as a function of CI indicated reductions in both ribulosebisphosphate (RuP2) carboxylase activity and RuP2 regeneration capacity. From assays of RuP2 carboxylase activity in vitro and 'percentage activation', it was concluded that low-P leaves had less enzyme per unit area than controls and that the enzyme was also less activated. The photosynthetic quantum yield was reduced by phosphorus deficiency with no effect on leaf absorptance or chlorophyll content. The reduced quantum yield was accompanied by changes in chlorophyll fluorescence of photosystems I and II measured at 77K. However, since phosphorus deficiency did not affect the uncoupled rate of whole-chain electron transport in vitro, some factor(s) other than photoinhibition probably contributed to the reduced quantum yield. The lack of effect on this electron-transport rate also indicates that the maximal RuP2 regeneration rate in low-P leaves was not limited by the amount of electon-transport components. At ambient [CO2], low-P leaves had significantly less RuP2 and 3-phosphoglycerate (PGA) than controls and the response of photosynthesis to low [O2] was similar to control leaves. Therefore photosynthesis did not appear to be limited by triose-phosphate utilization. The low concentrations of RuP2 and PGA (and presumably other Calvin-cycle intermediates) might have reduced the rate of the Calvin cycle. After returning low-P plants to nutrient solutions with PO4, the percentage activation of RuP2 carboxylase, amounts of RuP2 and PGA, quantum yield and maximal RuP2 regeneration rate increased within 24 h. The quantum yield and photosynthetic rate at higher irradiance also increased when leaf discs from low-P plants were floated on 10 mM PO4 solutions for 2 h.
Genetic Evidence for an Osmoregulatory Function of Glycinebetaine Accumulation in Barley
Authors: Grumet R , Hanson AD
Published: January 2006

Betaine (glycinebetaine) accumulates in several plant families in response to salt or water stress. Although betaine is hypothesised to be central to cellular osmoregulation, there is little direct evidence for this. Betaine level in barley was therefore altered genetically by creating two F4 isopopulations with different mean betaine levels, and the osmoregulatory behaviour of these populations and of their parents was examined under saline conditions. To minimise linkage effects, the isopopulation procedure included several parents and two rounds of crossing. Mean betaine levels of the two populations in unstressed conditions were 23 and 32 μmol g-1 dry weight; measurements of various morphological and developmental characters indicated that the populations were otherwise genetically comparable.
Salinising with 300 mM NaCl caused a decline of 0.5 MPa in solute potential (Ψs) and an 8- to 10-fold increase in betaine level in both isopopulations. The absolute difference in betaine level between the two populations remained constant as salt concentration was raised to 300 mM. Although selected only for differing betaine level, the parents and isopopulations differed also for Ψs; the high-betaine genotypes maintained a Ψs 0.1 MPa lower than the low-betaine genotypes at all salt levels. Furthermore, in both populations and parents, betaine level was linearly related to Ψs (r2 Ͱ4; 0.97). These observations are consistent with coordinated genetic control of betaine level and Ψs and imply that betaine accumulation is a mandatory component of osmoregulation in barley.
The Role of Leaf Area Development and Photosynthetic Capacity in Determining Growth of Kenaf under Moderate Salt Stress
Authors: Curtis PS , Lauchli A
Published: January 2006

Growth, net CO2 exchange rate and plant water relations were analysed in kenaf (Hibiscus cannabinus) cv. Cuba-108, a stem fibre crop, grown at 1, 37 and 75 mM NaCl. Dry weight was reduced only at 75 mM NaCl although leaf area was affected at both 37 and 75 mM NaCl. Growth analysis following nine serial harvests over 40 days showed a significant decline in leaf area ratio with salt stress but no decrease in net assimilation rate. CO2 exchange rate, measured on recently expanded leaves by infrared gas analysis, increased in plants grown at 37 mM NaCl and was unchanged at 75 mM NaCl. Pressure-volume analysis of plant water relations showed an osmotic adjustment of 0.15 MPa in plants grown at 75 mM but no adjustment at 37 mM NaCl. Turgor potential declined in plants grown at either salt level and fell to near zero during midday. We conclude that growth in kenaf under moderate salt stress is affected primarily through a reduction in expansive growth and leaf area development rather than a decline in photosynthetic capacity.
The Stoichiometries of Supramolecular Complexes in Thylakoid Membranes From Spinach Chloroplasts
Authors: Chow WS , Hope AB
Published: January 2006

The concentrations of photosystem II (PS II), photosystem I (PS I) and cytochrome b/f complexes on a chlorophyll basis have been determined for chloroplasts of spinach grown under three irradiances in a glasshouse. Assaying PS II by atrazine binding gave concentrations that exceeded the estimates from flash-induced O2 or H+ yield by a factor of 1.21 � 0.04 (23). Since part of this factor (1.14) is expected to arise from missed turnovers in excited reaction centres, it is concluded that both methods are valid to determine [PS II] in gently isolated chloroplasts. The agreement between the methods also suggests that atrazine does not bind to additional sites of quenchers such as 'Q400', contrary to the suggestion of R. J. Dennenberg and P. A. Jursinic [Biochim. Biophys. Acta 808 (1985), 192-200].
Whilst [PS I] was independent of growth irradiances, [PS II] and [cyt f ] increased with irradiance, as did the latent ATPase activity, a measure of the concentration of coupling factor 1. If [PS I] is taken as constant at 1.65 mmol (mol Chl)-1, the mean stoichiometries of PS II : cyt b/f complex : PS I obtained at the minimum and maximum irradiances were 1.2 : 0.7 : 1 and 1.6 : 1.0 : 1 respectively, PS II being determined by atrazine binding.
The Slow Phase of the Electrochromic Shift in Relation to the Q-Cycle in Thylakoids
Authors: Hope AB , Matthews DB
Published: January 2006

The electrochromic signal in oxidising conditions with whole-chain electron transport from water to ferricyanide or methyl viologen was compared with that under reducing conditions with electron transport from duroquinol to methyl viologen. Under oxidising conditions, in a train of flashes at 10 Hz, the slow phase in the growth of the electrochromic signal was not apparent after a few flashes whilst under reducing conditions it persisted.
The slow phase of the electrochromic signal was also examined particularly under conditions favouring the operation of an apparent Q-cycle, namely oxidising conditions plus the addition of low concentrations of valinomycin and flashes given at 5-10 Hz. The slow phase was retained in the presence of valinomycin at flash rates up to 10 Hz and its decay was accelerated.
The half-time for the slow phase was 18-20 ms (whole-chain), or 3-5 ms (reducing conditions, duroquinol/methyl viologen). There was a lag of 3 ms before the rise of the slow phase with ferricyanide. The onset was accelerated by valinomycin under oxidising conditions.
The slow phase was sharply inhibited by 2-n-heptyl- and 2-n-nonyl-4-hydroxyquinoline N-oxide (HQNO and NQNO) to at least half its maximum extent by 0.1 �M (HQNO) or 0.05 �M (NQNO); further inhibition took place in the micromolar range.
The slow phase is discussed in terms of probable electrogenic events in the cytochrome b/f complexes and their kinetics. We support the hypothesis that its basic cause is the transverse, intramembrane passage of electrons and show that this passage is controlled by the prevailing intramembrane potential difference, an estimated 85-140 mV sufficing for half inhibition of the slow phase.
Changes in the Concentration and Composition of Peduncle Sieve Tube Sap During Grain Filling in Normal and Phosphate-Deficient Wheat Plants
Authors: Fisher DB
Published: January 2006

Exuding aphid stylets were used to sample the contents of peduncle sieve tubes over 24-h periods at approximately weekly intervals during grain filling in normal and phosphate-deficient wheat plants. Samples were assayed for sucrose, total amino acids and potassium and for total solute concentration (osmolality). Sieve tube sap osmolality typically increased for about 2-4 h following illumination and then slowly declined. However, the response to illumination eventually disappeared in phosphate-deficient plants as grain filling progressed. These daily changes were superimposed on a progressive increase in sieve tube sap concentration by about 500 milliosmolal units during grain fill in both normal and deficient plants. Sieve tube sap concentration was always greater in phosphate-deficient plants. These results suggest that transport into the grains takes place via a developmentally controlled pathway of steadily increasing resistance.
The molar ratio of sucrose to total amino acids declined substantially in the 2-week period after anthesis and then remained constant at about 2 : 1. The proportion of potassium in the exudate also declined markedly during the same period. Relative proportions of sucrose, amino acids and potassium were very similar in normal versus phosphate-deficient plants of comparable ages. There were no evident differences between normal and phosphate-deficient plants in exudate amino acid composition. Only minor changes occurred during grain filling, except during the last week when glutamine, the predominant amino acid at all times, increased even more in relative importance. In general, the results are characterised by the absence of any simple relationship between grain development or growth rates and sieve tube sap concentration or composition.
The composition of the sieve tube sap may be used to calculate values of overall grain composition (N and K as a percentage of dry matter) which are in good agreement with reported values for wheat grains.
Salt Sensitivity of Chickpea During Vegetative Growth and at Different Humidities
Authors: Lauter DJ , Munns DN
Published: January 2006

Two experiments were designed to determine whether salt stress of the salt-sensitive legume Cicer arietinum L. was associated with water stress or with ion excess.
In the first experiment, shoot growth and the concentration of inorganic ions in cultivars L-550 and UC-5 were monitored for 26 days. In greenhouse solution cultures, 8-day-old plants received either no salt or 15 mM NaCl plus 7.5 mM Na2SO4 (- 0.115 MPa) and were then sampled 9 times over the 26-day growth period. Salt treatments and time period were factorially combined with two cultivars, in three replications.
Control and salt-treated plants remained nearly identical in growth rate and shoot weight until about 10 days after the addition of salt. Then the relative growth rate of stressed plants declined to a steady low value. The decline corresponded with changes in shoot sodium and chloride concentrations, and not with the changes in shoot water potential and osmotic potential that occurred soon after the addition of Na salts. The shoot Na and CI concentrations gradually increased until the growth rate of the salt treated plants diverged from the controls near day 10.
In the second experiment parameters of water status, ion accumulation, and ion distribution were correlated with growth of cultivars L-550 and E-100 at different humidities and salt levels. Plants grew for 6 weeks in four different growth chambers at relative humidities of 55, 75, 88 and 95%. The four salt levels were 0, 12, 24 and 36 mM Na added as sulfate and chloride in equal proportion on an equivalent basis.
The lowest humidity (55%) resulted in the death of several salt-treated plants. At high humidity (95%) cv. E-100 was slightly more salt-sensitive than cv. L-550; but at low humidity (75%) cv. E-100 was the less sensitive cultivar and had the lower shoot Na concentration. Despite the confounding effects of three independent variables - salt level, cultivar, and humidity - shoot dry weight correlated closely with leaf and shoot Na concentration. None of the other measured parameters - shoot Cl, shoot water potential, or transpiration rate - correlated well with growth. Low humidity impaired growth only when it led to high shoot Na.
Data from the two experiments suggest that salt primarily inhibits growth through accumulation of Na into the shoots.
Proline Analogues in Melaleuca Species: Response of Melaleuca lanceolata and M. uncinata to Water Stress and Salinity
Authors: Naidu BP , Jones GP , Paleg LG , Poljakoff-Mayber A
Published: January 2006

Fifteen species of Melaleuca and two species of Callistemon from the field were examined to determine whether they accumulated nitrogen-containing compatible solutes and, if so, which. In addition to L-proline, N-methyl-L-proline (MP) (isolated for the first time from plants), trans-4-hydroxy-N-methyl- L-proline (MHP), and N, N'-dimethyl-trans-4-hydroxy-L-proline (DHP) were found in various combinations in the 15 Melaleuca species.
M. lanceolata seedlings were subjected to water or salinity stress and M. uncinata to water stress under laboratory conditions. In both species significant reductions in leaf water potential (Ψw), osmotic potential (Ψs), turgor potential (Ψp), and relative water content (RWC) were observed in response to water stress. Salinised M. lanceolata plants showed considerable osmotic adjustment and maintained Ψp comparable to that of control plants; salinity, however, decreased RWC. In response to the imposed stresses under laboratory conditions, proline and MHP levels in M. lanceolata, and MHP and DHP levels in M. uncinata, increased.
In addition to possible protective or osmotic roles in vivo, these proline analogues may be useful in chemotaxonomic investigations of Melaleuca species.
C4 Acid Decarboxylation Enzymes and Anatomy in Sedges (Cyperaceae): First Record of NAD-Malic Enzyme Species
Authors: Bruhl JJ , Stone NE , Hattersley PW
Published: January 2006

The activities of C4 acid decarboxylation enzymes (NAD-malic enzyme, NADP-malic enzyme, and phosphoenolpyruvate carboxykinase), and the anatomy of photosynthetic organs (leaves, culms, bracts) were investigated in 30 species from 12 C3, C4, and mixed (C3+C4) genera of sedges. The sample incorporated representatives of the three previously known C4 anatomical types in the family (fimbristyloid, chlorocyperoid, and rhynchosporoid), and of six genera previously uninvestigated biochemically, including Eleocharis (six species). Eleocharis is variable for photosynthetic pathway: three species proved to be C3, two C4 (E. caespitosissima Baker and E. retroflexa (Poir.) Urban), and one (E. pusilla R. Br.) may be a C3-C4 intermediate. The C4 Eleocharis spp. exhibit a C4 anatomy ('eleocharoid') hitherto undescribed, and are NAD-ME type, in contrast to species of the other three C4 anatomical types examined in this and previous studies, which are all NADP-ME type. The PCK type remains unrecorded in the family.