bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Sodium Nutrition on Chlorophyll a/b Ratios in C4 Plants
Authors: Johnston M , Grof CPL , Brownell PF
Published: January 2006

Methods for the determination of chlorophyll were compared in Amaranthus tricolor, Kochia childsii and Chloris gayana. From sequential extraction data, 96% ethanol appeared to be more efficient than 80% acetone in extracting chlorophyll from these plants.
The chlorophyll a/b ratio was significantly lower in sodium-deficient compared to normal C4 plants. Of the group I elements, only sodium, irrespective of the salt supplied to deficient cultures, restored the chlorophyll a/b ratios to the value observed in normal plants. The concentration of sodium required to increase the chlorophyll a/b ratio in leaves of sodium-deficient plants was similar to that required to bring about the growth responses. The increase of the chlorophyll a/b ratio occurred at an early stage during recovery from sodium deficiency preceding the increase in chlorophyll concentration and the growth response. It is therefore likely that the low chlorophyll a/b ratio may be intrinsically associated with the condition of sodium deficiency.
Hydraulic Resistance of Plants. III. Effects of NaCl in Barley and Lupin
Authors: Munns R , Passioura JB
Published: January 2006

Barley (salt-tolerant) and white lupin (salt-sensitive) were grown in sand in pots designed to fit within a pressure chamber. The sand was irrigated with a nutrient solution to which increasing amounts of NaCl were added daily in increments of 10-25 mol m-3. For a range of transpiration rates (Q), the hydrostatic pressure of the leaf xylem sap of an intact plant was measured by applying sufficient air pressure (p) to the root system to raise the pressure of this sap to zero. The relation between p and Q was linear, i.e. of the form p = po + rQ. Po, the intercept on the p axis, reflects the difference in osmotic pressure across the root, and it is assumed that r, the slope of this relation, gives the hydraulic resistance of the plant.
In NaCl-treated barley, r remained constant as the NaCl in the soil solution was increased to 200 mol m-3 over 10 days, and differed little from that of the controls. Po increased by about the same amount as the increase in osmotic pressure of the soil solution. This indicates near-perfect osmotic behaviour by the roots, and consistent with this, osmotic pressure of sap expressed from the cut shoot base generally changed little with increasing NaCl, for a given transpiration rate.
In NaCl-treated lupin, by contrast, r increased continually from 25 to 150 mol m-3 NaCI, when it was four times that of the controls. Beyond 75 mol m-3, po increased less than increases in the osmotic pressure of the soil solution, which suggests that salts were then leaking into the root xylem. However, the osmotic pressure of the xylem sap flowing through the petiole did not start to increase until 3 days later when the external solution was over 120 mol m-3, suggesting that substantial amounts of NaCl were being removed from the xylem sap before it reached the petiole.
Plant Growth and Water Use With Limited Water Supply in High CO2 Concentrations. I. Leaf Area, Water Use and Transpiration
Authors: Morison JIL , Gifford RM
Published: January 2006

Plants of 16 agricultural and horticultural species were grown from seed in spaced pots in two glasshouses, one with normal and one with twice the present atmospheric CO2 concentration. Water use and leaf area development were measured while soil moisture content declined from field capacity to c. 6%. High CO2 increased leaf area in all but two species, the increase varying from 20 to 75%. However, the water loss per plant followed a similar time course to that of plants in control CO2 concentration because of the reduction of daily transpiration rate per unit leaf area (range 4-39%). Cowpea and sunflower plants rewatered after one soil drying cycle showed 9 and 5%, respectively, lower transpiration rate in high CO2 over a subsequent drying cycle than in the first cycle. Averaging across all species and soil moisture contents, transpiration rate was less reduced by high CO2 (21%) than was stomatal conductance (36%) and this is attributed to the increased leaf temperature caused by reduced stomatal conductance.
Studies of Mineral Reserves in Pea (Pisum sativum) Cotyledons Using Low-Water-Content Procedures
Authors: Lott JNA , Goodchild DJ , Craig S
Published: January 2006

Most of the phytin in pea (Pisum sativum) cotyledons is water soluble. In order to determine where K and P are located it was necessary to use anhydrous or low water content tissue preparation procedures to obtain samples suitable for energy dispersive X-ray analysis studies using a transmission electron microscope. While some protein bodies do contain electron-dense globoid crystals, most do not. Globoid crystals are more prevalent in the abaxial part of the cotyledon where the provascular network is located. When present, globoid crystals contain considerable Mg, and/or Ca along with P and K. Protein bodies that lack globoid crystals still contain considerable P and K with lesser amounts of elements such as S, Cl and Mg. This is consistent with these protein bodies containing K-phytate in the proteinaceous matrix. While there is a lot of K inside the protein bodies, K is widespread in pea cotyledon tissue and could be detected in starch grains, cell walls and the cytoplasmic matrix.
Effect of Prolonged Exposure to Nacl on the Osmotic Pressure of Leaf Xylem Sap From Intact, Transpiring Barley Plants
Authors: Munns R , Passioura JB
Published: January 2006

Xylem sap was collected from the leaf tip of intact transpiring barley plants at low and high external [NaCI], by applying pressure to roots of plants growing in sand containing nutrient solution plus 0, 100, 150 or 200 mol m-3 NaCl. Transpiration rates during the collection period were manipulated by varying the light and humidity level around the shoot. The osmotic pressure of the xylem sap (πx) from the oldest leaf of plants without added NaCl increased hyperbolically with decreasing transpiration rate, and rose to values 2-3 times that of the nutrient solution at very low rates of transpiration. A similar pattern applied to plants exposed to high external [NaCl] for several days, except that πx was about 30% higher than that of plants without NaCl, for a given rate of transpiration. However, after a week or more at high external [NaCl], πx of the oldest leaf increased dramatically, and the leaf died a day or two after πx increased by 200-300 kPa. Growth of the youngest leaf was independent of these changes. Simultaneous collections of πx from leaves of all ages showed that πx was lowest in the youngest leaf. We suggest that ions in the transpiration stream build up in the cell walls when ion contents of the cells reach a maximum, and net uptake rates become zero. Such an accumulation would cause loss of turgor then dehydration of cells, and may be the primary cause of death of the old leaves.
Rates of Photosynthesis Relative to Activity of Photosynthetic Enzymes, Chlorophyll and Soluble Protein Content Among Ten C4 Species
Authors: Usuda H , Ku MSB , Edwards GE
Published: January 2006

Among 10 C4 species having a wide range in photosynthetic activity, the rates of photosynthesis/leaf area under high light were examined and compared with the chlorophyll and soluble protein content and the activities of several photosynthetic enzymes. The species examined were Digitaria sanguinalis, Echinochloa crus-galli, Microstegium vimineum, Panicum capillare, Panicum miliaceum, Paspalum dilatatum, Paspalum notatum, Pennisetum purpureum, Setaria lutescens, and Zea mays. The photosynthetic rates per unit leaf area ranged from 10 to 38 �mol CO2 fixed m-2 s-1.
Among the 10 species there was a high degree of correlation of rate of photosynthesis/leaf area with soluble protein (r = 0.88), ribulose 1,5-bisphosphate carboxylase (r = 0.88) and pyruvate,PI dikinase (r = 0.94), but a lower correlation of photosynthetic rate/leaf area with phosphoenolpyruvate carboxylase
(r = 0.74) and no significant correlation of photosynthetic rate/leaf area with chlorophyll content (r = 0.56). Among eight species of the NADP-malic enzyme C4 subgroup, there was a good correlation of photosynthetic ratelleaf area with NADP-malate dehydrogenase (r = 0.88) and NADP- malic enzyme
(r = 0.92). Extractable activities of both the ribulose 1,5-bisphosphate carboxylase and the dikinase were generally close to the rate of photosynthesis. When comparing the activity per unit leaf area of one enzyme with another, generally a high degree of correlation was found among the species. The results suggest that a given C4 species tends to maintain a balance in the activities of several photosynthetic enzymes and that there is potential to estimate capacity for C4 photosynthesis under high light through determining activity of certain photosynthetic enzymes.
Proton Motive Force and Phosphorylation Potential in Thylakoids
Authors: Hope AB , Doherty G , Stainer P
Published: January 2006

The relationship between phosphorylation potential and the transthylakoid pH difference (ΔpH) was explored in class C pea chloroplasts under two conditions: (a) in the light, in a steady state following photophosphorylation, where ΔpH was varied with addition of nigericin, and (b) in the dark after a light period in the presence of dithioerythritol to promote ΔTP-hydrolase activity. In experiments of type (b), the phosphorylation potential was varied through the concentrations of adenylates. In both conditions there was a correlation between the phosphorylation potential and ΔpH. The slope of the relationship between the two in the light was taken as giving the product n.q of the mechanistic stoichiometry, n with q, the degree of coupling of the ATP-synthetase reaction with the proton flux. This product was 1.9 � 0.1, implying n=2 if q=0.95, or n=3 if q=0.66. The data from both types of experiment required a transthylakoid potential difference of up to + 155 mV for the phosphorylation potential to be poised against the proton motive force as in a macrochemiosmotic theory.
Hydraulic Characteristics of Mountain Ash (Eucalyptus regnans F. Muell.) Derived From in situ Measurements of Stem Water Potential
Authors: Legge NJ , Connor DJ
Published: January 2006

An osmotic tensiometer has been successfully used for in situ measurements of stem water potential, Ψst, in mountain ash. During spring and early summer when soils were saturated, fluctuations in Ψst, at a given height in different trees were very similar. When Ψst, values were measured at different positions around the circumference of individual trees during late summer, considerable variation between the different positions was recorded. The data at this time also suggest that night temperatures above 17°C can lead to stomatal opening, but this was not confirmed by direct measurement. Possible reasons for apparent discrepancies between leaf and stem water potential measurements are discussed. The time lag between vapour pressure deficit and Ψst was around 2 h whenΨst values were high, but fell to 10 min or less for Ψst values below about - 1.2 MPa. Analysing this time lag in terms of a resistance-capacitance model of water flow made it possible to estimate the storage-to-vessel transfer resistance as 1.7 × 107 Pa s m3 kg-1.
Relating Water Potential Gradients in Mountain Ash (Eucalyptus regnans F. Muell.) To Transpiration Rate
Authors: Legge NJ
Published: January 2006

Osmotic tensiometers recording in situ stem water potential, Ψst, were implanted at two heights in the trunks of mountain ash (Eucalyptus regnans) in mature and 1939 regrowth forests. Measurements over one summer showed that Ψst gradients, obtained from the mean Ψst values at each height, reached over 50 kPa/m, with the diurnal maxima generally occurring between 1500 and 1600 h. When Ψst gradients were averaged over 24 h it was found that, unless temperatures were extremely high or the foliage was wet, the average diurnal gradient was linearly related to the average vapour pressure deficit. From this relationship the average diurnal gradient during two earlier summers was estimated to be 23 kPa/m. The forest transpiration rate during this time was estimated to be 4.1 mm/day and when these data, together with sapwood area data, were put into a simple tree transpiration model, the relative conductivity of the sapwood was found to be approximately 7.9 × 10-12 m2.
Water Pathways in Wheat Leaves. I. The Division of Fluxes Between Different Vein Types
Authors: Altus DP , Canny MJ
Published: January 2006

This study concerns the pathway of water movement through the vascular system of the wheat leaf blades. These water pathways were followed using three kinds of markers dissolved in the transpiration stream by which the patterns of water reticulation were made visible. There was a partitioning of the total water flux between the veins of the different types. The lateral veins dominate the conduction of water along the leaf from the base, and also distribute water to the mesophyll in their immediate vicinity. The intermediate veins receive water from the lateral veins in the transverse direction, via the transverse veins. The intermediate veins are primarily involved in the distribution of water to the mesophyll in their vicinity. Since there are more intermediate veins than lateral veins across the leaf blade they are the more important distributors of water to the mesophyll. The transverse veins are the pathway by which water is moved transversely from the lateral veins to the intermediate veins. Water can also be conducted in both directions, or in either direction, from its point of entry into an intermediate vein from a transverse vein. This versatility enables the network of transverse and intermediate veins to act as alternative pathways for longitudinal water conduction in the event of damage to a lateral vein.
Low-Temperature-Induced GA3 Sensitivity of Wheat. III. Comparison of Low Temperature Effects on α-Amylase Production by Aleurone Tissue of Dwarf and Tall Wheat
Authors: Singh SP , Paleg LG
Published: January 2006

The low temperature effect on the gibberellic acid (GA3) sensitivity (measured as a-amylase production) of aleurone tissue or deembryonated seed of dwarf and tall wheat (F6 Rht 3/rht 3 isogenic lines) was studied. The results indicated that the low-temperature-induced increase in GA3 response is: quantitative and temporal; GA3 concentration-dependent; without effect on the lag-time of a-amylase production, and operative in the aleurone tissue of dwarf (Rht 3-containing) wheat. All these characteristics of the low temperature response of the Rht 3-containing aleurone tissue are similar to those reported earlier for Rht 1-containing and Rht 2-containing aleurone tissue. The present results support the hypothesis that low temperature exposure is able to cure or reverse the genetic lesions manifest in the aleurone tissue containing the Rht allele and that this may be mediated via an increase in GA3 receptor sites.
Low Temperature-Induced GA3 Sensitivity of Wheat. IV. Comparison of Low Temperature Effects on the Phospholipids of Aleurone Tissue of Dwarf and Tall Wheat
Authors: Singh SP , Paleg LG
Published: January 2006

Low temperature effects on the phospholipids of F6 Rht 3/rht 3 isogenic lines of wheat were studied. Significant low-temperature-induced (5°C) augmentation in the phospholipids of the dwarf selection were detected. More specifically, a 20 h-5°C preincubation enhanced considerably the levels of phosphatidylinositol, phosphatidylcholine and phosphatidylethanolamine in the aleurone tissue of the dwarf selection. In addition, these changes displayed a very close temporal relationship with the low- temperature-induced increase in gibberellic acid (GA3) sensitivity. In the case of the tall selection, only the imbibition of water was required to initiate the synthesis of major phospholipids of its aleurone tissue and low temperature preincubation had no effect on either the phospholipids or their fatty acid constituents. These results are discussed in the light of the hypotheses that GA3 receptor sites are membrane-based lipids and that the Rht gene causes an aberration in the phospholipid metabolism of the aleurone tissue which can be corrected by low temperature.
Release of Ferulic Acid Esters From Barley Aleurone. II. Characterization of the Feruloyl Compounds Released in Response to GA3
Authors: Gubler F , Ashford AE , Bacic A , Blakeney AB , Stone BA
Published: January 2006

Two major feruloyl-containing compounds are released into the incubation medium, when isolated aleurone layers are treated with gibberellic acid (GA3). These compounds were purified from 72 h, + GA3 incubation medium and analysed, using methylation analysis, various chromatographic techniques, including gas chromatography-mass spectroscopy, and nuclear magnetic resonance spectroscopy. The compounds were shown in each case to contain arabinose and xylose residues with molar ratios consistent with a feruloylated trisaccharide and tetrasaccharide, and indicating that they were hydrolysis products of feruloylated arabinoxylans. Three possible alternative structures are given for the tetrasaccharide, and the trisaccharide was identified as O-[5-O-feruloyl-L-arabinofuranosyl]- (1͛4 3)-O-D-xylopyranosyl-(1͛4 4)-D-xylopyranose, with the feruloyl residue in the trans form. The implication of the results in relation to wall structure and hydrolysis, and the removal of ferulic acid from the walls, during the GA3 response of barley aleurone is considered.
Ethylene and 1-Aminocyclopropane-1-Carboxylic Acid as Indicators of Chilling Sensitivity in Various Plant Species
Authors: Chen YZ , Patterson BD
Published: January 2006

The release of ethylene after warming leaves of plant species which had been stored at 0°C was found to be a good indicator of incipient chilling injury. Ethylene evolution was maximal around the onset of visible symptoms, and was prevented by serious chilling damage. The duration of chilling required to induce ethylene production varied from about 1 h in the very chilling-sensitive tropical herb Episcia reptans to days in cucumber and various species of tropical passionfruit. In a series of six passionfruit species, ranking for chilling sensitivity indicated by ethylene release agreed with their known relative sensitivity to chilling. The compound 1-aminocyclopropane-1-carboxylic acid (ACC), which is the immediate metabolic precursor of ethylene, was accumulated during the chilling treatment, and continued to accumulate after warming the leaves to 20°C. The rate of accumulation of ACC during chilling also depended on the sensitivity of the species to chilling, but was not reduced by severe chilling as was the release of ethylene.
The level of hydrogen peroxide, which could provide a source of oxidant for the breakdown of ACC to ethylene, did not change significantly during chilling. The results indicate that ethylene and ACC are sensitive indicators of chilling stress. ACC production suggests a possible method for the selection of chilling-resistant genotypes among crop plants.
Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. III. Conditions for the Operation of an Apparent Q-Cycle in Thylakoids
Authors: Hope AB , Handley L , Mathews DB
Published: January 2006

The proton-to-electron ratio in pea thylakoids, considering proton uptake with ferricyanide as electron acceptor, was reconfirmed as 1 in periods of single-turnover (<0.5 �s, 2-3 mJ) flashes delivered at 5-50 Hz and at pH values 6.4-8.3. Addition of valinomycin in the presence of K+ increased proton uptake in a way depending on [val], flash frequency and flash number.
A maximal stimulation by valinomycin of up to about 1.8× controls was observed in fresh preparations. Half-maximal stimulation was caused by c. 2 nM valinomycin at 10-20 Hz, at c. 3 Hz with 10 nM valinomycin, and after c. five flashes at 50 Hz with 10 nM valinomycin.
The results are discussed in terms of recent models for the Q-cycle. It is suggested that such a cycle operates in chloroplasts only when the intramembrane electric field induced in a series of flashes is kept small by the presence of valinomycin. Preliminary observations of 'P518', the thylakoid component probably indicating the electric field, are consistent with this idea. This field may control the transverse electron flow between the two cytochrome b6 molecules in the b/f complexes.
A Possible Role for Abscisic Acid in Controlling Dormancy in Jojoba Flower Buds
Authors: Benzioni A , Dunstone RL
Published: January 2006

Jojoba flower buds break dormancy in response to low temperatures in the presence of adequate water. The possibility that abscisic acid (ABA) is involved in the regulation of dormancy was examined by following endogenous ABA levels in flower buds and leaves and by applying synthetic (�)-ABA.
Under controlled conditions endogenous levels of ABA were high in dormant flower buds and decreased under conditions of low temperatue that led to flowering. Similar results were obtained in the field. Levels in the leaves were low and changes in response to environmental treatments were small.
Daily spraying of the plants with water containing 0.01% Tween enhanced flowering while water stress inhibited it. The application of (�)-ABA delayed flowering and reduced the percentage of flowers open at the end of the experiment.
An experiment aimed at distinguishing between the effects of temperature and of water status was inconclusive and part of the effect of temperature on ABA may be related to the effect of temperature on the water status of plant.
Low-temperature-induced GA3 Sensitivity of Wheat. V. Sterol Conversions in the Wheat Aleurone Tissue during Imbibition
Authors: Singh SP , Firn RD , Paleg LG
Published: January 2006

Sterol profiles during imbibition and low temperature preincubation of aleurone tissue from Kite (Rht 2) and F6 Rht 3/rht 3 lines were studied. There was a dramatic disappearance of sterol derivatives during imbibition and a coincident appearance of an equivalent increment of free sterols in all three aleurone tissues. None of the preincubation conditions had any effect on the sterol content or spectrum of either the Rht-containing aleurone tissue (Kite and dwarf selection) or the non-Rht-containing aleurone tissue (tall selection). The results indicate that the sterol derivatives of the wheat aleurone tissue may serve a storage role for free sterols.
Transport of Tritiated Water and 14C-Labelled Assimilate Into Grains of Wheat. II. Independence of Entry of 14c-Labelled Assimilate and THO
Authors: Jenner CF
Published: January 2006

The mechanism involved in the transport of assimilates through the stalk by which the grain is attached to the rachilla has been investigated. Based on the presumption of pressure-driven mass flow, treatments designed to inhibit the import of assimilates would be expected to inhibit also the entry of water into the grain. Detached ears were supplied with solutions of [14C]sucrose in tritiated water (THO), and ears attached to the plant were watered with THO and supplied with 14CO2. The rachilla was heated by contact with a hot wire, and the stalk by steam-girdling. In addition, dinitrophenol (DNP) was used as an inhibitor of metabolically linked transport mechanisms. Heating or treatment with DNP reduced the transport of [14C]sucrose or [14C]-labelled assimilate into the grain, but the entry of THO was not reduced even by treatments which abolished altogether the transport of 14C into the grain. These results cannot be reconciled with mass flow as the means of transporting assimilates through the stalk of the wheat grain during grain filling.
Regulation of Grain Number in Wheat: Genotypic Difference and Responses to Applied Abscisic Acid and to High Temperature
Authors: Zeng ZR , Morgan JM , King RW
Published: January 2006

Floret infertility was induced by the application of abscisic acid ((�)-ABA) directly to the developing wheat spike, but only for applications over a 3-6-day period during pollen meiosis, not earlier or later. Yield components affected included loss of up to 20% of florets, senescence of the tip of the spike and the prevention of ear emergence. The major effect, however, was failure of grain in apparently competent florets. Cultivars differed in both their sensitivity to (�)-ABA and in the yield components affected. Also, for at least one cultivar (Triticum durum cv. Durati), the yield components affected changed over the 6-day period around pollen meiosis.
High temperature (27°C average) for 7 days over the period of meiosis also reduced grain set and in some cultivars florets were lost. The variety most sensitive to high temperature was also most sensitive to (�)-ABA but there were differences in the yield components affected. Direct action of (�)-ABA in the spike and a possible indirect effect on assimilate supply are discussed.
Effect of Photoperiod on Growth and Development of Cassava (Manihot esculenta Crantz)
Authors: Keating BA , Wilson GL , Evenson JP
Published: January 2006

Effects of photoperiod on growth and development of cassava were studied in controlled environments. Plants of cultivars M Aus 7 and M Aus 10 were grown under short (10-h) and long (16-h) photoperiods and harvested at approximately weekly intervals for a period of 13 weeks. Long photoperiods resulted in large increases in leaf area through increases in both number (both cultivars) and size of leaves (M Aus 7 only). The timing, extent and anatomical characteristics of storage root initiation were similar for both cultivars under 10-h and 16-h photoperiods but the subsequent balance between shoot and storage root growth strongly favoured shoot growth in long days. Dry matter partitioning followed a simple allometric pattern with the proportionality between the relative growth rate of shoots and the relative growth rate of storage roots remaining constant with time but being altered by photoperiod.
Distribution to storage roots was quantitatively reduced in another experiment using M Aus 10 with each additional 1-h increment from 10-h to 16-h photoperiods. A treatment consisting of a short day (10 h) plus a 1-h night break in the middle of the dark period produced growth similar to long day treatment. Differences in cultivar response (Ceiba, CMC 84 and M Aus 7) to a range of photoperiods (11, 12, 13 and 14 h) were detected in a third experiment. The possible mechanisms and significance of these responses are discussed.
Isotopic Fractionation During Reduction of Nitrate and Nitrite by Extracts of Spinach Leaves
Authors: Ledgard SF , Woo KC , Bergersen FJ
Published: January 2006

The isotopic fractionations of nitrogen during the reduction of NO3- and NO2- in a cytosolic fraction and in a chloroplast preparation from spinach (Spinacia oleracea L.) leaves were determined. The reduction of NO3- to NH3 was studied using a reconstituted system containing cytosolic extract and intact chloroplasts, while a chloroplast system was used for NO2- reduction. In the reconstituted systems the ratio of nitrate reductase activity to nitrite reductase activity had a large effect on the relative amounts of NO2- and NH3 formed. Ammonia predominated when the nitrate reductase to nitrite reductase activity ratio was 1 : 5 and this ratio was used in the isotopic fractionation studies. Significant isotopic fractionation of N was observed in the reconstituted system but not in the chloroplast system. This indicates that the observed isotopic fractionation was associated with the reduction of NO3- to NO2- by nitrate reductase. The isotopic fractionation (i.e. δ15Nproduct - δ15Nsubstrate) for this reaction was - 15‰.
A Test of a Model for Light Interception by Mixtures
Authors: Rimmington GM
Published: January 2006

Predicted and observed data for the amount of light energy intercepted by mixtures of clover and ryegrass are compared, in an additional test of a model which relates competition for light to crop dry matter production. The closeness of predicted and observed values for light interception implies that the optical properties of the component species do not change significantly when they are grown in mixtures. If this is true, then it should be possible to predict the growth of mixtures using information about their optical properties when they are grown in monocultures.
Resistance to Drought and Salinity: Avenues for Improvement
Authors: Passioura JB
Published: January 2006

Various techniques for improving the resistance of plants to drought or salinity are discussed in relation to a notional spectrum ranging from rationality to random search. The rational end of the spectrum is exemplified by the control of phenology so that flowering occurs at an optimal time; the random end by wide crosses, such as that between wheat and Elytrigia, which give the remote hope that the high yield-potential of one will combine with the toughness of the other. Most of the techniques occupy the middle ground and involve selecting for characters whose protagonists have strong, but often poorly articulated, hunches that the characters will confer resistance to drought or salinity on the plants possessing them. For drought resistance of grain crops, the possible worth of many of these characters is discussed in relation to their likely impact on improving a crop's ability to (a) extract water from the soil, (b) produce dry matter given a limited water supply, and (c) convert dry matter into grain.
Assimilation of Gaseous Ammonia by Sunflower Leaves during Photosynthesis
Authors: Brooks A
Published: January 2006

Illuminated (150 �mol m-2 s-1 PAR) sunflower (Helianthus annuus L.) leaves were exposed to 15N-labelled NH3 gas (30 or 300 �l NH3 l-1) or supplied with NH4Cl (2, 20 or 200 mM) through the cut leaf base for up to 1 h. The photosynthetic carbon dioxide uptake and the transpiration were continuously monitored. The leaves were extracted and the concentrations of ammonia, glutamine, glutamate, glycine, serine and alanine were determined as well as the patterns of 15N incorporation.
Although the rates of CO2 uptake and transpiration were unchanged in intact leaves, the ammonia level increased from 3 to 42 �mol g fresh wt-1 during feedings of 300 �l NH3 l-1 for 25 min. In contrast, NH4Cl (20 and 200 mM) inhibited photosynthesis immediately and increased the evaporation rate while the total ammonia level was still less than 10 �mol g fresh wt-1. The 15N-labelling pattern suggested that the NH3 assimilation proceeded via glutamine synthetase and glutamate synthase. 15N was transferred into glycine and serine presumably by the activity of glycollate pathway enzymes. The experiments demonstrate that the photosynthetic CO2 uptake and ammonia assimilation by intact sunflower leaves were not inhibited by NH3 concentrations orders of magnitudes above typical concentrations of this compound in the atmosphere. NH3 feedings through the gas phase provide a tool for the examination of nitrogen metabolism in intact leaves.
Respiration and Alanine Metabolism in Commelina Epidermis
Authors: Thorpe N , Milthorpe FL
Published: January 2006

[U-14C]alanine offered to epidermal peels was readily metabolized, mostly via pyruvate and the tricarboxylic acid cycle. Some two-thirds of the radioactivity absorbed was respired and some 2-4% converted to sucrose and ethanol-insoluble compounds. Nevertheless, the calculated amounts of alanine respired were much less than expected. Despite a large degree of deamination and reamination, the fate of the imported amino acid groups is unknown but we believe they are re-exported to the mesophyll, possibly as aspartate during stomatal closing.
Carbon Isotope Discrimination measured Concurrently with Gas Exchange to Investigate CO2 Diffusion in Leaves of Higher Plants
Authors: Evans JR , Sharkey TD , Berry JA , Farquhar GD
Published: January 2006

Conventional gas-exchange techniques that measure the stomatal conductance and rate of CO2 assimilation of leaves were combined with measurements of the carbon isotope composition of CO2 in air passing over a leaf. Isotopic discrimination during uptake was determined from the difference in the carbon isotope composition of air entering and leaving the leaf chamber. Isotopic discrimination measured over the short term correlated strongly with that determined from combusted leaf material. Environmental conditions were manipulated to alter the relative influences of stomatal conductance and carboxylation on the discrimination of carbon isotopes by intact leaves. With C3 plants, discrimination increased as the gradient in partial pressure of CO2 across the stomata decreased. For C4 plants there was little change in discrimination despite substantial changes in the diffusion gradient across the sto- mata. These results are consistent with, and provide the first direct experimental support for, theoretical equations describing discrimination during photosynthesis.
Despite uncertainties about various processes affecting carbon isotope composition, the resistance to the transfer of CO2 from the intercellular airspaces to the sites of carboxylation in the mesophyll chloroplasts was estimated using this technique. For wheat the estimated resistance was 1.2-2.4 m2 s bar mol -1.
Sodium Exclusion and Potassium-Sodium Selectivity in Salt-Treated Trifoliate Orange (Poncirus trifoliata) and Cleopatra Mandarin (Citrus reticulata) Plants
Authors: Walker RR
Published: January 2006

Seedlings of trifoliate orange (Poncirus trifoliata (L.) Raf.) and Cleopatra mandarin (Citrus reticulata Blanco) were grown under glasshouse conditions and supplied with dilute nutrient solution containing 0, 25, 50 or 100 mM NaCl. Trifoliate orange plants grown at 25 or 50 mM NaCl possessed an ability to restrict the accumulation of sodium in leaves. This ability was lost at 100 mM NaCl. For plants treated with 50mM NaCl, uptake of both sodium and chloride per unit root weight was higher for trifoliate orange than for Cleopatra mandarin. Root to leaf transport of chloride was also higher for trifoliate orange, whereas root to leaf transport of sodium was significantly lower. This ability to exclude sodium was unrelated to the flux of water (water flux) per plant, which was similar between the genotypes. Trifoliate orange appeared to possess a greater ability to withdraw sodium from the xylem in the proximal root and basal stem and to sequester it in both the wood and the bark of these regions. This was accompanied by a significant reduction in the concentration of potassium in these tissues, suggesting sodium-potassium exchange. Release of potassium into the xylem in exchange for sodium is implied by the significant increase in leaf potassium concentrations. This ability for sodium exclusion at low to moderate salinities (Ͱ4 50 mM NaCl) enabled trifoliate orange to maintain a relatively constant sodium : potassium ratio in leaves. Salt-treated Cleopatra mandarin plants, on the other hand, tended to show a marginal decrease in leaf potassium concentration and a substantial increase in leaf sodium : potassium ratio.
Reducing the mean water flux in trifoliate orange from 38 to 26 �mol s-1 per plant by partial defoliation did not affect root to leaf transport of chloride. However, there was a marked reduction in root to leaf transport of sodium, suggesting an enhanced withdrawal of sodium from the xylem at lower water fluxes.
Morphological Variation between Seedling Progenies of Viminaria juncea (Schrad. & Wendl.) Hoffmans. (Fabaceae) and its Physiological Significance
Authors: Walker BA , Pate JS
Published: January 2006

Seed of Viminaria juncea was collected from single plants in a range of habitats throughout SW. Australia and the resulting seedling progenies grown in sand culture in a glasshouse. Each set of seedlings displayed highly uniform shoot morphology regardless of growth conditions, but differed markedly from other progenies in branching habit and timing of the transition from juvenile spathulate and trifoliolate leaves to adult phyllodineous foliage. Root flooding inhibited growth of progenies of squat phyllodineous habit more than tall leafy types. Seedling growth responded linearly to increased phosphate supply (0.6-16.0 mg P/I). Percentage plant dry weight as nodules increased 2-3-fold with increasing phosphate but proportional mass as cluster (proteoid) roots declined sharply. Statistically significant differences between progenies in nodulation and cluster root production were evident in certain phosphate treatments. Extreme early phyllodineous and prolonged leafy morphotypes were selected from a mixed population of seedlings (parent seed pooled from 70 habitats) and their growth and water use recorded under continuous root flooding, mesic, or drought-simulating conditions. Leafy morphotypes outgrew phyllodineous counterparts in flooded or mesic conditions, but shed their leaflets when droughted and thereafter behaved as phyllodineous morphotypes. Water-use efficiencies were similar between morphotypes and treatments (range 2.58-2.74 g dry matter gain/l water used), except for flooded phyllodineous seedlings for which 2.16 g/l was recorded. The genecological significance of the data is discussed.
Soil Water Status Affects the Stomata1
Authors: Gollan T , Richards RA , Rawson HM , Passioura JB , Johnson DA , Munns R
Published: January 2006

Wheat and sunflower were grown in pots that could be enclosed in a pressure chamber, with the shoot in a cuvette. Applying an appropriate pneumatic pressure to the roots enabled the leaves to be kept fully turgid despite any drying of the soil. The leaf conductance of plants was followed while the soil dried. Remarkably, this conductance fell with falling soil water content no matter whether the leaves were kept fully turgid or not. It is concluded that the roots sensed the drying of the soil and sent a message to the leaves which induced stomatal closure.
Differential Effects of K+ and Na+ on Oxygen Evolution Activity of Photosynthetic Membranes from Two Halophytes and Spinach
Authors: Preston C , Critchley C
Published: January 2006

KCl reduced oxygen evolution by Sarcocornia quinqueflora thylakoids to well below the level of activity in the presence of NaCI. This inhibition occurred at both high and low pH. On the other hand, both KCl and NaCl induced almost indistinguishable effects on oxygen evolution in spinach thylakoids. Photosystem (PS) Il membranes from Avicennia marina showed a similar inhibition of oxygen evolution by KCl to S. quinqueflora thylakoids, but spinach PS Il particles were not inhibited by KCl. The KCl inhibition of oxygen evolution of halophytic thylakoids was localised to the oxygen-evolving complex and required little KCl, as significant inhibition occurred with only 25 mM. K2SO4 was also inhibitory, but Na2SO4 was not, indicating that K+ was the inhibitory ion. Na2SO4 was partly able to reverse this inhibition caused by KCl, suggesting the inhibition to be a function of the K+ /Na+ ratio. These results have implications concerning the ionic relations of the leaf cells of halophytes.
Effects of Water Stress on Nitrogen Nutrition of Grain Sorghum
Authors: Rego TJ , Grundon NJ , Asher CJ , Edwards DG
Published: January 2006

A solution culture experiment was conducted to study the effects of solution osmotic potential and nitrogen (N) supply on growth and N content of grain sorghum cv. Texas 610SR. Polyethylene glycol-6000 was used to impose solution osmotic potentials of -0.1, -0.4, -0.8, and - 1.1 MPa during the fourth week of growth. Plants were harvested at 6 weeks.
Dry matter yields, total plant N content and mean rate of N uptake per unit root weight were significantly decreased by decreases in solution osmotic potential and N supply. Numbers of leaves expanded after imposition of the solution osmotic potential treatments were also reduced significantly by decreasing solution osmotic potential and decreasing N supply. Decreasing solution osmotic potential decreased mean N concentrations in leaves, had no effect on mean N concentrations in roots, and increased N concentrations in stems plus immature leaves, and in whole tops.
The form of relationships between leaf N concentration and yield prevented the calculation of critical N concentrations at any level of solution osmotic potential.
Use of Concentrated Macronutrient Solutions to Separate Osmotic from NaCl-specific Effects on Plant Growth
Authors: Termaat A , Munns R
Published: January 2006

The aim was to distinguish between osmotic and ion-specific effects of NaCl on plant growth and ion uptake by comparing plants grown in isosmotic solutions with and without NaCI. Preliminary experiments showed that polyethylene glycol 4000 and mannitol were unsuitable for even very-short-term studies because they caused immediate reductions in leaf elongation rate when plants were transferred from NaCl to isosmotic solutions of these compounds. However, concentrated solutions of macronutrients (modified Hoagland's nutrients) did not change the elongation rate.
Barley, wheat, Egyptian clover and white clover were grown in NaCl and concentrated macronutrient solutions of matching osmotic pressures. After 14 days, plants grown in concentrated macronutrients were smaller than controls (plants in normal strength nutrient solution) but had similar root : shoot ratios. NaCl-grown plants were less than half the size of plants in concentrated macronutrients, and had higher root : shoot ratios. NaCl-induced phosphate uptake did not cause this additional reduction in shoot growth. For barley, net transport of K+, Mg2+, Ca2+ and total nitrogen from the roots (per g root dry wt) was lower in NaCl-grown plants than in controls, but uptake by the shoot (per g shoot dry wt) of these minerals was similar. By contrast, both transport and uptake of these minerals in concentrated macronutrient-grown plants resembled control plants. NaCl-grown barley and wheat plants had higher osmotic pressures in both growing and mature tissue than did controls and macronutrient-grown plants, but a lower rate of uptake of solutes generating this osmotic pressure. We raise the possibility that growth in NaCl may be limited by a reduced rate of transport of an essential nutrient to the shoot.
Water Use, Grain Yield, and Osmoregulation in Wheat
Authors: Morgan JM , Condon AG
Published: January 2006

Genotypic differences in turgor maintenance in wheat were shown to be associated with differences in grain yield in the field at both high and Low water deficits. High water deficits were produced by growing plants in field plots using water stored in the soil at sowing, and excluding rain with a rain cover. At low water deficits plants received rainfall, and irrigation was supplied before and immediately after sowing, at tillering, at jointing, at ear emergence, and during grain filling. Yield differences were analysed in terms of harvest index, water use, and water use efficiency. Water use was calculated from changes in soil water contents. At high water deficits all three factors were associated with differences in turgor maintenance. However, only the variations in water use and harvest index could be logically associated with differences in turgor maintenance. Analysis of the soil water extraction data showed that the differences in water use efficiency were due solely to differences in water use at depth while surface water losses were the same, i.e. the ratio of transpiration to soil evaporation would have been higher in low-osmoregulating genotypes. At low water deficits, no differences were observed in harvest index, though there were non-significant correlations between turgor maintenance and total water use efficiency or total water use. A similar result was obtained when the water use and yield data were related to osmoregulation measurements made in the glasshouse. It is therefore concluded that effects of turgor maintenance or osmoregulation on grain yield were primarily associated with differences in water use which were, in turn, due to differences in water extraction at soil depths between 25 and 150 cm.
Ion Regulation in the Organs of Casuarina Species Differing in Salt Tolerance
Authors: Aswathappa N , Bachelard EP
Published: January 2006

Distribution of Na+, Cl-, K+, Ca2+ and Mg2+ was studied in individual organs of two highly tolerant and one moderately tolerant species of Casuarina. The highly tolerant species (C. equisetifolia and C. glauca) accumulated little Na+ and Cl- in their shoots and the concentrations of Na+ and Cl- decreased from old to young growing needles. The concentrations of Na+ and Cl- were much higher in shoots of the moderately tolerant species (C. cunninghamiana) and a concentration gradient between old and young needles was not observed. The same pattern of distribution of Cl- in C. equisetifolia was found in seedlings exposed to both short term (13 days at 100 mol m-3 NaCl in solution culture), and long term (6 months at 250 mol m-3 NaCl in sand culture) salinisation. The three species showed little difference in their root ion concentrations. A time sequence experiment of Cl- uptake indicated that the better exclusion of Cl- from the shoots of C. equisetifolia than C. cunninghamiana was due to a lower rate of Cl- uptake and lower net transport into the shoot rather than to its retention in the roots, or reabsorption at the proximal root or hypocotyl.
Reduction by GA3 of Nacl-Induced Inhibition of Growth and Development in Suaeda ussuriensis
Authors: Zhao KF , Li ML , Liu JY
Published: January 2006

Seedlings of Suaeda ussuriensis were grown in soil with NaCl concentrations of 0.5, 1.0, 2.0 and 3.0% on a dry weight basis. The optimum salt concentration for growth and development was 1.0%. At 3.0% all seedlings died. Treatment with 10*5 �g/litre GA3 counteracted partly the growth inhibition, and the dry weight of plants increased 21.6, 2.2 and 19.4%, respectively, for soils with salt concentrations of 0.5, 1.0 and 2.0%. GA*3 increased the numbers of plants coming to flower in soil of salt concentration of 0.5 and 2.0%, by 40 and 20%, respectively, but had no effect on plant growth in a salt concentration of 1.0%.
Factors Influencing the Inactivation of Chloroplastic Fructose-1,6-Bisphosphatase
Authors: Kobza J , Edwards GE
Published: January 2006

The activity of chloroplastic fructose-1,6-bisphosphatase was found to be stable in the crude leaf homogenates of wheat and rye for an hour or more if stored at 2°C (on ice). If the homogenate was gel filtered over Sephadex G-25 and subsequently stored on ice, there was a time-dependent loss of the light-activated component of fructose-1,6-bisphosphatase activity. A similar response was found for the enzyme purified from spinach and activated by reduced thioredoxin or by dithioerythritol alone. The lost activity could be recovered if the purified enzyme was allowed to warm to room temperatures. Attempts to stabilise the enzyme in gel-filtered crude extracts by the inclusion of substrate, several other metabolites, or alteration of the ionic strength of the extraction medium were unsuccessful. A reduction in the extraction pH for fructose-1,6-bisphosphatase below 8.3, by 1-2 pH units, resulted in a moderate stabilisation of enzyme activity after gel filtration and cold storage. Sucrose density gradient ultracentrifugation revealed a dissociation of the tetrameric form of the enzyme into its dimer component after gel filtration and cold storage. As was the case for inactivation, depolymerisation was more prevalent at the higher pH levels. We hypothesise that the cold instability of fructose-1,6-bisphosphatase which is induced by gel filtration over Sephadex G-25 is a result of depolymerisation of the tetrameric enzyme. The mechanism by which gel filtration induces the cold lability of this enzyme is unclear although it is apparently not due to removal of free low-molecular-weight substances from the medium.
Estimates of Solutes Accumulating in Plants by 1H Nuclear Magnetic Resonance Spectroscopy
Authors: Jones GP , Naidu BP , Starr RK , Paleg LG
Published: January 2006

A method is described for the estimation of betaines and proline in plant extracts using 1H nuclear magnetic resonance. After partial purification of the crude extract on a simple cation-exchange column the technique enables the simultaneous determination of glycinebetaine, choline and other N-methylammonium-containing compounds as well as proline. The method is simple and the results obtained compare favourably with those determined by other methods.