bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus and Carbon Economies of Ectomycorrhizal Seedlings of Eucalyptus pilularis Smith
Authors: Mulligan DR , Patrick JW
Published: January 2006

The distribution patterns of phosphorus and carbon in Eucalyptus pilularis Smith seedlings raised in phosphorus-deficient conditions for at least 4 months have been examined. These seedlings possessed well developed ectomycorrhizas and there was significant retention of phosphorus by the mycorrhizal roots at low levels of phosphorus supply. A high proportion of residue phosphorus (possibly polyphosphate) was found in mycorrhizal roots and also in foliage at a level of deficiency at which very little storage phosphorus would be expected to remain. There was evidence of a control mechanism, perhaps operating via this 'storage' pool, which guarded against any overstimulation of growth rate in response to periodic increases in soil phosphorus. This control acted by regulating the amount of phosphorus available for photosynthesis, especially in those leaves with the highest potential to export carbon for growth. It is proposed that the E. pilularis seedlings combine strategies which characterize fast-growing and slow-growing species, namely a responsiveness of photosynthesis to available phosphorus in the foliage and foliar storage of phosphorus when supply persists. Such flexibility may contribute to this species being able to compete successfully in a range of habitats of varying nutritional status.
Whole-Plant Carbon Balance During Osmotic Adjustment to Drought and Salinity Stress
Authors: Mccree KJ
Published: January 2006

The whole-plant daily carbon balance (the 24-h sum of photosynthetic input of substrate carbon per plant and loss of carbon through respiration) is the CO2 exchange measure that relates most closely to crop production rates. Water stress reduces the photosynthetic input, reducing both leaf area and photosynthetic rate per unit leaf area. Respiratory losses are reduced more or less proportionately. A less-than-proportional loss was observed during osmotic adjustment in sorghum (Sorghum bicolor (L) Moench): the metabolic cost of storing photosynthate and using it for osmotic adjustment was less than the cost of converting it to new biomass. A slightly increased metabolic cost is often found under salt stress but, in sorghum plants that were salinized and then water stressed, the adverse effects of salt were mitigated by decreased water loss rates and enhanced osmotic adjustment during water stress. More tests involving combined salt and water stress are needed.
Water Relations of Expanding Leaves
Authors: Barlow EWR
Published: January 2006

The reactivity of leaf growth to changes in plant water status has been analysed in terms of leaf development, water transport and turgor. The different growth patterns of monocotyledonous and dicotyledonous leaves result in fundamental differences in the water relations of expanding leaves. Most monocotyledonous leaf cells complete their expansion phase within the protective older leaf bases, while the majority of dicotyledonous leaf cells expand in an exposed evaporative environment. The consequence of this morphological difference is that expanding monocotyledonous leaves behave similarly to other enclosed tissue during water stress by exhibiting turgor maintenance through osmotic adjustment. Expanding dicotyledonous leaves do not exhibit this response. The maintenance of turgor in monocotyledons in the absence of leaf expansion suggests that growth is controlled by the yield threshold of the cell wall during episodes of water stress.
Whole-Plant Responses to Drought
Authors: Schulze ED
Published: January 2006

The partitioning of carbon and interactions which cause limitations on gas exchange and growth under conditions of a limited supply of water and nutrients are discussed. Possible mechanisms of effects of air humidity on stomatal functioning and carbon assimilation are described. Also, it is shown that stomata respond to a signal from the root when the soil dries out prior to leaf wilting. Stomatal conductance determines canopy transpiration if the aerodynamic boundary layer resistance is low, such as in trees. Water shortage significantly affects extension growth and the root-shoot ratio at the whole- plant level. But experiments with xylem-tapping mistletoes show that stem growth can also be promoted by the presence of the mistletoe even when there is no apparent signal from the subtending shoot except the flow in the stem xylem. It appears that the internal plant water status may not affect gas exchange and carbon partitioning unless the plant fails to maintain a flow of water through the leaf epidermis and root tip.
Salinity Resistance in Rice (Oryza sativa L.) And a Pyramiding Approach to Breeding Varieties for Saline Soils
Authors: Yeo AR , Flowers TJ
Published: January 2006

Varieties and breeding lines of rice (Oryza sativa L.) differ in their resistance to NaCl salinity and in their Na uptake. These varieties (which are not single homozygous lines) also show large variation between individuals. The gross uptake of Na+ is, however, poorly correlated with growth and survival because net transport interacts with vigour and degree of dwarfing and because NaCl is compartmentalized within the plant confounding any simple relationship between tissue concentration, growth reduction and toxicity symptoms. It is argued that resistance is conferred by no single factor, but is the sum of a number of contributory traits which include variation in (1) NaCl entry via membrane leakage or apoplastic pathways; (2) preferential accumulation of Na+ in the older leaves; and (3) tolerance of NaCl within the leaf tissue which may reflect differences in apoplastic salt load. It is suggested that the salt resistance of rice can be increased by selecting separately for such physiological traits and then pyramiding them together.
Changes in Some Carbohydrate Fractions and Some Related Enzymic Activities in Plump and Shrivelled Triticale and in Wheat Grains
Authors: Dhaliwal AS , Sharma HL
Published: January 2006

Activities of α-amylase (EC 3.2.1.1), β-amylase (EC 3.2.1.2), soluble ADPglucose-starch synthase (EC 2.4.1.21), starch phosphorylase (EC 2.4.1.1), sucrose synthase (EC 2.4.1.13) and invertase (EC 3.2.1.26), and amounts of reducing sugars, total soluble sugars and starch, were studied in the developing grains of wheat and triticale lines. A triticale line (TL1) with shrivelled grains contained a low starch content, increased reducing and total soluble sugars during the final grain-filling period as well as a higher moisture at maturity than wheat and a plump-grain triticale line (TL2). The overall activities of soluble ADPglucose-starch synthase and starch phosphorylase remained lower and that of α- and β-amylases higher in TL1 than wheat and TL2 throughout grain development. The higher amylolytic activity retained during the final maturation period appears to be at least partly due to the higher moisture content of the grain in the triticale line TL1 with shrivelled grains.
Regulation of Grain Number in Wheat: Changes in Endogenous Levels of Abscisic Acid
Authors: Zeng ZR , King RW
Published: January 2006

An association between abscisic acid (ABA) content and fertility is demonstrated in the wheat spike. ABA contents are significantly higher and the rate of ABA degradation is almost halved in male sterile spikes from the chromosomal mutant, Cornerstone. On a dry weight basis the anther contains disproportionately more ABA than the rest of the spike. Spike ABA is high before pollen meiosis and drops within 3-6 days (2 to 20-fold) both in the Cornerstone material and in a normal cultivar.
Effects of Environmental Conditions on Expression of the 'Gigas' Characters in Wheat
Authors: Atsmon D , Bush MG , Evans LT
Published: January 2006

Two lines of 'gigas' wheat, the uniculm 492 and oligoculm 380, were compared with a normal cultivar of comparable duration to anthesis, Yaqui 50 or its dwarf isogenic line 50E, under a range of temperatures, daylengths and irradiances in the Canberra phytotron in order to define the conditions under which gigas characteristics are expressed.
In the gigas lines the characteristics of large ears with many grains were expressed most strongly at low temperatures and were associated with fewer, heavier shoots than in Yaqui 50E. At higher temperatures both gigas lines had more tillers and ears, not fewer as in Yaqui 50E and most cultivars, and yielded more grain per plant than Yaqui.
Both gigas lines were sensitive to daylength, the oligoculm showing the greater reduction in time to anthesis, the uniculm the greater increase in stunting and reduction in tillering with longer days. However, long days were not detrimental to the full expression of the gigas characteristics in the oligoculm.
Grain number and weight per shoot increased with increasing irradiance in the order: uniculm > oligoculm> Yaqui 50. However in terms of yield per plant or per unit area this order was reversed, reflecting the different capacities for tiller and ear production of the three genotypes.
Gigas ears were larger throughout their development. The flowering gradient along each spikelet was similar in gigas and Yaqui ears, but the initial lag in growth of the upper floret grains was shorter in the oligoculm, resulting in more synchronous grain growth, which was also more prolonged in the gigas ears. Partial removal of grains from gigas ears led to a fall in photosynthetic rate of the flag leaf and to its earlier senescence, whereas removal of the lower leaves resulted in faster photosynthesis and delayed senescence. Thus even when supporting gigas ears, flag leaf photosynthetic rate was not maximal, nor was the mobilisation of reserves. Maximum harvest index was no higher in the gigas lines than in Yaqui 50E or in modern wheat varieties. The gigas characteristics appear to derive from the capacity to utilise the savings from restricted tillering for both greater leaf and ear growth per shoot.
Low-Temperature-Induced GA3 Sensitivity of Wheat. VI. Effect of Inhibitors of Lipid Biosynthesis on α-Amylase Production by Dwarf (Rht3) and Tall (Rht) Wheat, and on Lipid Metabolism of Tall Wheat Aleurone Tissue
Authors: Singh SP , Paleg LG
Published: January 2006

The effects of six inhibitors, gammexane, diclofop-methyl, chlorpromazine, trifluoperazine, BASF 13-338 and SK&F 7997-A3, known to be involved in the inhibition of lipid biosynthesis, on the α-amylase response and lipid metabolism of the dwarf and tall wheats were examined. The results are discussed in the light of the proposed relationship between the rht alleles, phospholipid synthesis and gibberellic acid-sensitivity.
Understanding the Control of Plant Development and the Role of Growth Substances
Authors: Trewavas A
Published: January 2006

The control of development is often viewed as a simple process which can be approached experimentally in an equally simple fashion. However metabolism, cells, tissues and indeed whole plants form networks with a great density of connections. The control of complicated networks is little understood and their
behaviour on perturbation is usually counter-intuitive. The notions of 'limiting factors' and 'cause and effect' are commonly used to conceptualise developmental control by growth substances. This article shows that these concepts are incompatible with metabolic network behaviour and it suggests how both can be modified to bring them into line with modern understanding.
Shoot and Root Responses to Water Deficits in Rainfed Lowland Rice
Authors: Cruz RT , O'Toole JC , Dingkuhn M , Yambao EB , Thangaraj M , De Datta SK
Published: January 2006

A field study was conducted to determine the response of the rice cultivar IR54 to a gradient of soil moisture conditions imposed for 19 days at the vegetative stage using a line source sprinkler system. A mild plant water stress at the vegetative growth stage decreased tiller number, leaf area index (LAI), apparent canopy photosynthetic rates, leaf nitrogen per unit land area, shoot and total root dry mass, and total root length density. After complete stress relief by reflooding, LAI and crop growth remained below that of unstressed plants. The lower cumulative assimilation per unit land area in the stressed treatments resulted in reduced shoot and root dry matter yields and lower grain yields.
Water stress increased the ratio of shoot dry mass to root dry mass, and the ratio of leaf area to total root length. The decrease in root length was attributed to increased soil mechanical impedance.
Relationship Between Steady-State Gas Exchange, in vivo Ribulose Bisphosphate Carboxylase Activity and Some Carbon Reduction Cycle Intermediates in Raphanus sativus
Authors: Caemmerer SV , Edmondson DL
Published: January 2006

The relationships between CO2 assimilation rate, RuP2 carboxylase activity and sizes of the pools of ribulose 1,5-bisphosphate (RuP2) and 3-phosphoglyceric acid (PGA) were examined using a freeze clamp device to rapidly freeze sections of attached leaves of R. sativus which previously had gas-exchange measurements made on them.
At high irradiance and ambient partial pressures of CO2 and O2, RuP2 carboxylase was fully active in vivo. Activity was less at very low CO2 pressures and at high CO2 pressures, particularly when combined with low O2 pressures. In vivo RuP2 carboxylase activity and both RuP2 and PGA pool sizes increased with increasing irradiance. RuP2 pool sizes were high at low CO2 pressures and decreased at high CO2 pressures. PGA pool sizes, on the other hand, were low at low CO2 and high at high CO2 pressures.
A model of RuP2 carboxylase-oxygenase (Rubisco) kinetics is used to examine the quantitative relationship between in vivo RuP2 carboxylase activity, CO2 assimilation rate and RuP2 and PGA pools. The model predictions fit in vivo data, except at high CO2 pressures, if it is assumed that RuP2 does not bind tightly to the inactive enzyme form in vivo. It is shown that a large fraction of the RuP2 and PGA pools may be chelated by magnesium in the stroma and that the high RuP2 pools (e.g. at low irradiance) may represent an optimal concentration rather than be truly saturating. We conclude that RuP2 pool sizes above Rubisco site concentration do not necessarily indicate a Rubisco limitation of photosynthetic rate.
N2-Fixation in Field Settings: Estimations Based on Natural 15N Abundance
Authors: Shearer G , Kohl DH
Published: January 2006

This paper reviews a growing body of literature on the use of variations in the natural abundance of 15N to estimate the fractional contribution of N2-fixation to N2-fixing systems. This method is based on the small difference in 15NN abundance which frequently occurs between N derived from N2-fixation and N derived from other sources. The requirement of the method is that this difference be significant. Whether this requirement is met is site specific and must be empirically established at each site of interest. Advantages and disadvantages of this method are compared with those of more conventional methods. Sources of error, including heterogeneity of 15NN abundance of non-atmospheric N sources are considered. Tests of the method, under both greenhouse and field conditions, are described. Estimates based on this method compare favourably with other methods for field evaluation of N2-fixation, provided that the site and the sampling strategy are appropriate for application of the method. Applications of the method in several ecosystems are described.
Na+ and Cl- Transport in the Phloem from Leaves of NaCl-treated Barley
Authors: Munns R , Fisher DB , Tonnet ML:
Published: January 2006

Sieve tube sap was collected from fully expanded leaves of NaCl-treated barley plants through aphid stylets. The sap was analysed for Na+, CI-, K+, phosphate, sucrose and osmolality. Na+ and Cl- appeared in the sap within a day of NaCl being added to the nutrient solution. When plants were exposed to various NaCl concentrations for 1-2 weeks, the sap contained about 15 mol m-3 Na+ and 25 mol m-3 Cl+, irrespective of whether the external NaCl concentration was 25, 100 or 200 mol m-3. When plants were kept for more than 2 weeks at 200 mol m-3 NaCl, the Cl- concentration in the sap increased but the Na+ concentration remained the same. Na+ and Cl- in the sap decreased very slowly when NaCl was removed from the nutrient solution. The calculated efflux of Na+ and Cl- in the phloem from the leaves was only 10% of the influx in the xylem, so the phloem can play little part in controlling the NaCl content of the leaves of these plants.
Photosynthetic Responses of Pisum sativum to an Increase in Irradiance During Growth. I. Photosynthetic Activities
Authors: Chow WS , Anderson JM
Published: January 2006

The extent and time course of changes in photosynthetic activities of leaves and isolated chloroplasts was followed in pea plants which were adapted to low light (60 �mol photons m-2 s-1, 400-700 nm, 16 h light/ 8 h dark cycles), and subsequently transferred to higher light (390 �mol photons m-2 s-1). The photosynthetic rates of leaves in CO2-saturating conditions, measured at light saturation or subsaturation, increased with no noticeable lag, doubling within 1 week after transfer to high light. In contrast, the increase of in vitro ribulose-1,5-bisphosphate carboxylase activity (~ 130%) and photosystem II electron transport capacity (~ 60%) occurred with an apparent lag of - 1 day after transfer to high light. The capacity for uncoupled whole-chain electron transport also increased slowly (~ 70%). Whilst the total chlorophyll (Chl) per unit leaf area remained steady, the Chl a/Chl b ratio increased with no apparent lag phase from 2.7 in low irradiance to 3.2 in high irradiance within 1 week. The results demonstrate that, following an increase of growth irradiance, pea leaves readily increase the capacity for utilising high light effectively, even when the total chlorophyll per unit leaf area remained constant. However, a better understanding of the time course of response requires measurements of other chloroplast parameters.
Photosynthetic Responses of Pisum sativum to an Increase in Irradiance During Growth. II. Thylakoid Membrane Components
Authors: Chow WS , Anderson JM
Published: January 2006

Following the transfer of pea plants grown at low irradiance (60 �mol photons m-2 s-1, 16 h light/8 h dark cycles) to high irradiance (390 �mol photons m-2 s-1), the extents and time courses of the increase in the concentrations of thylakoid membrane components on a chlorophyll basis have been determined. The increase in cytochrome f (~ 70%) and plastoquinone (~ 50%) contents occurred with no noticeable lag phase. The increase in photosystem Il reaction centres (PS II, ~ 35%) and ATP synthetase (~ 90%) occurred possibly with a lag period of 1-2 days. In contrast, there was no significant increase in the concentration of P700 (reaction centre) of PS I complex.
The concentration of PS II reaction centres measured by atrazine-binding exceeded that from the O2 yield per single-turnover flash by a factor of 1.17 (compared with the expected value of 1.14); this contrasts with the factor of 1.8 obtained by P. A. Jursinic and R. Dennenberg [Arch. Biochem. Biophys. (1985) 241, 540-9]. It is suggested that both methods are equivalent for the determination of PS II reaction centres in active chloroplasts.
The stoichiometry of PS II : cyt f: PS I was highly flexible, and not fixed at 1 : 1 : 1. We obtained the stoichiometries of 1.25 : 0.7 : 1.0 for low-light pea chloroplasts and 1.7 : 1.25 : 1.0 for chloroplasts in pea plants that had been transferred to high light for about 10 days, demonstrating the dynamic nature of thylakoid composition and function.
In the first 2 days after transferring low light pea plants to high light, the time course of the increase in CO2- and light-saturated rate of leaf photosynthesis corresponded better with that of cyt f and plastoquinone than that of other chloroplast components examined. This suggests that, during the transition period, the relatively prompt increase of cyt b/f and plastoquinone plays a part in enhancing the CO2- and light-saturated rate of leaf photosynthesis.
Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. IV. Effects of Cytochrome b/f Complex Inhibitors on Proton Uptake and Cytochrome b6 Turnover
Authors: Hope AB , Birch S , Matthews DB
Published: January 2006

The effects of the substances 2-n-heptyl- and 2-n-nonyl-4-hydroxyquinoline N-oxide (HQNO, NQNO), and antimycin A (AMA) on proton uptake stimulated by a 10-20 Hz train of single-turnover flashes given to pea thylakoids were investigated. Electron transport was from H2O to ferricyanide ('oxidising conditions') and the pH indicator of proton uptake was phenol red. All three of HQNO, NQNO and AMA inhibited proton uptake in control conditions, with concentrations (c½) for half-maximum effect of 1.7, 0.1 and 5 �M, respectively. The valinomycin-stimulated proton uptake, which has been attributed to Q-cycle activity in thylakoids, was more sensitive to HQNO and NQNO, with c½ of 0.6 and < 0.05 �M respectively. AMA had the same or less relative effect on proton uptake in the presence of valinomycin as in its absence.
In oxidising conditions the maximum extent of flash-induced cytochrome (cyt) b6 reduction was 7-9% of the total present (which was 2 molecules/620 chlorophylls), as an average during 10 flashes, valinomycin being always added to reduce interference from the electrochromic effect. The average half- time for this reduction was 3.4 ms, while that for oxidation was 420 ms. The amount of cyt b6 reduced was increased by NQNO to a maximum of 14-19%, the c½ being 0.05 �M. Reduction and oxidation rates were both diminished by NQNO.
In reducing conditions [electrons from duroquinol to methyl viologen, 3-(3,4-dichlorophenyl)-l,l- dimethylurea added to inhibit photosystem II], the cytochrome b6 was 12-16% reduced during flashes at 0.5-1 Hz, with half-times of 3.1 and 21 ms for reduction and oxidation, respectively. NQNO increased the percentage reduced to a maximum of 34-45, with a c½ of 0.05 �M. The diminution of the oxidation rate of cyt b6 was similarly related to [NQNO] but that of the reduction rate had a c½ of -1 �M.
The findings on proton uptake are seen as consistent with HQNO and NQNO inhibiting at the Qc sites on cyt b/f complexes, at QB sites near photosystem II with less specificity and possibly at Q2 sites during the first few turnovers. Data for AMA indicated that it does not inhibit at Qc. Electron transport from H2O to methyl purple was more sensitive to NQNO for the first few turnovers (c½ 0.1 �M) than in the steady state (c½ - 1 �M).
Effects of Nitrogen Nutrition on Electron Transport Components and Photosynthesis in Spinach
Authors: Evans JR , Terashima I
Published: January 2006

Spinach plants (Spinacia oleracea L.) were grown in hydroponic culture in a glasshouse under full sunlight. They were supplied with different concentrations of nitrate nitrogen in solution, ranging from 1 to 12 mM, in order to produce leaves with different nitrogen contents. Oxygen evolution at CO2 saturation was measured as a function of absorbed irradiance in leaf discs with an oxygen electrode. Electron transport activities, reaction centre densities, cytochrome f and plastoquinone contents, RuP2 carboxylase and coupling factor activities and soluble protein content were measured in similar material. Although nitrogen and chlorophyll contents per unit leaf area were reduced by 60% by nitrogen deficiency, when expressed on a chlorophyll basis, thylakoid components, electron transport activities and the rate of oxygen evolution at CO2 saturation were similar between nitrogen treatments. In contrast, the content of soluble protein and RuP2 carboxylase expressed on a chlorophyll basis was greater the greater the nitrogen content per unit leaf area. Therefore the ratio of RuP2 carboxylase activity to electron transport activity increased in leaves having greater nitrogen content.
Potassium Flux Studies in Intact Portions of the Roots of Oryza sativa
Authors: Aramrattana P , Scott BIH
Published: January 2006

Methods have been developed for studying ion kinetics in a portion of an intact root in its normal growth medium. Based on a simplified mathematical model, the amounts of a substance in the tissue compartments and the unidirectional fluxes between them and to and from the external medium and the xylem can be determined. The methods are applied in an electrochemical analysis of the stte of potassium in a portion of the root of an intact rice seedling. Potassium is shown to be pumped inwardly at the root's surface and to the xylem. There is also an indication that potassium may be actively exported from the vacuoles of cells in very young roots. 86Rb is shown to be suitable as a tracer for potassium in transport studies in rice but not for accumulation to cellular vacuoles.
Characterization of Multiple Acid Phosphatases in Salt-Stressed Spinach Leaves
Authors: Pan SM
Published: January 2006

Incremental salt stress brought about a clear enhancement of the activity of acid phosphatases in hydroponically grown spinach (Spinacia oleracea L.) leaves. Sephacryl S-200 chromatography of the enzyme fraction revealed multiple forms of acid phosphatases of high (300 000), intermediate (100 000), and low (35 000) molecular weight in control and salt-stressed spinach leaves. A similar zymogram of acid phosphatases, showing at least six bands in polyacrylamide disc gel electrophoresis, was observed for control and stressed leaves. However, promotive effects of incremental salt stress on the activity of acid phosphatases were more pronounced in high molecular weight acid phosphatases. Substrate specificity and differential effects of some ions on the multiple acid phosphatases were also examined for control and salt-stressed leaves.
The Relationship Between Electron Transport Components and Photosynthetic Capacity in Pea Leaves Grown at Different Irradiances
Authors: Evans JR
Published: January 2006

Pea plants (Pisum sativum) were grown under different irradiances and the photosynthetic characteristics and chloroplast properties were determined on young, fully expanded leaves. The light-saturated rate of oxygen evolution for leaf discs, measured in 1% CO2, correlated closely with the uncoupled whole- chain electron transport activity by the thylakoid membranes. When expressed on a chlorophyll basis, the photosynthetic rate was proportional to both the cytochrome f content and the coupling factor activity. The ratio of coupling factor activity to cytochrome f content was constant across all the growth irradiance treatments. The content of photosystem II reaction centres, determined by [14C]atrazine binding, varied to a small extent while the content of photosystem I reaction centres was unaltered by growth irradiance. Reaction centres do not seem to limit the rate of non-cyclic electron transport.
Analysis of the CO2 response curves suggested that the ratio of electron transport capacity to RuP2 carboxylation capacity was greater for plants grown at higher irradiances than for plants grown at lower irradiances. Within any irradiance treatment, the ratio of the two capacities was approximately constant. The proportion of leaf nitrogen allocated to thylakoid proteins (27%) was independent of growth irradiance. Adaptation to low irradiance was associated with a reduction in the electron transport components and an increase in the light-harvesting chlorophyll a/b protein such that the amount of chlorophyll per unit of thylakoid protein nitrogen increased. By contrast, adaptation to high irradiance was associated with an increase in the electron transport capacity per unit of chlorophyll such that the electron transport rate per unit of thylakoid nitrogen was increased.
Response of Droughted Wheat to Mid-Season Water Application: Recovery in Leaf Area and Its Effect on Grain Yield
Authors: Aggarwal PK , Sinha SK
Published: January 2006

Three varieties of wheat contrasting in drought resistance were sown in the field at two levels of soil moisture and water was applied on three occasions by the cumulative application of 75 mm or less water with a line-source sprinkler system. Application of water resulted in recovery of mean maximum leaf area index (LAI) from 0.5 to 3.0. Variety C306, known for its drought resistance, maintained maximum LAI around anthesis relative to other varieties. Since LAI was directly related to grain yield irrespective of the variety, we conclude that maintenance of high LAI at anthesis is desirable for obtain- ing high yield in stressed plants.
Mid-season water application resulted in the recovery of flag leaf area (FLA) of the main shoot and the first tiller in all the varieties. However, only in C306 did FLA equal that of its irrigated control. The recovery of FLA resulted in a proportionately greater increase in the grain yield of the main shoot. By comparison, in the first tiller, increase in grain yield was much lower though its flag leaf area had considerably recovered.
Grain yields of varieties did not differ in two drought situations - where all water was available at sowing or where 56% of the total water was available before sowing and the rest was supplied during vegetative growth. Among the varieties, only C306 showed a significant (30%) improvement in grain yield in the latter situation compared to the former.
Sources of Variation in Specific Leaf Area in Wheat Grown at High Temperature
Authors: Rawson HM , Gardner PA , Long MJ
Published: January 2006

In the belief that specific leaf area (SLA, cm2 g1 dry weight) may be correlated with plant growth rate under certain conditions, and thus may be used in selecting genotypes for high growth rates, studies were commenced to examine the main sources of variation in SLA. In most studies, wheat plants were grown in controlled environments with high mean temperature and vapour pressure deficit and with varying radiation regimes. All environmental variables followed cosine patterns which in amplitude mimicked field conditions.
Specific leaf area varied depending on: (1) location along a leaf: it decreased from tip to base by some 35%; (2) leaf age: SLA declined between leaf appearance and 10-12 days later then, after a plateau of varying length, it rose again; (3) leaf insertion: SLA of the flag leaf was the most stable with leaf age; (4) plant density: in canopies the final rise in SLA with leaf age occurred earlier than in spaced plants; (5) radiation: SLA declined at approximately
4 cm2 g-1 for each mol quanta m-2 day-1 increase in radiation; (6) genotype: SLA differed among genotypes and the ranking was unchanged by changes in radiation.
In two genotypes studied in detail, higher SLA equated with faster leaf area production and larger leaves, but not with chlorophyll content per unit area, stornatal frequency or net CO2 exchange rate per unit area (CER), though it was noted that both SLA and CER changed inversely with leaf aging after the leaf was fully expanded.
The importance of SLA in active (positive and negative) and passive roles in plant growth is discussed.
The Influence of Temperature on the Contribution of Awns to Yield in Wheat
Authors: Olugbemi LB , Bush MG
Published: January 2006

The effect of temperature during grain set and grain growth on the contribution of awns to yield in wheat was examined in the Canberra phytotron.
For eight pairs of awned and awnless near-isogenic lines, the mean advantage of the awned lines in grain dry weight per ear was greatest when plants were held at 21/16°C during grain development, less at 27/22°C and least at 15/10°C where grain weight per ear was highest. One pair, G16 (awned) and G18 (awnless), examined more closely, showed the same response with the yield advantage of the awned line tending to decline from 21/16°C to 33/28°C.
There were no significant differences between G16 and G18 in photosynthetic rates of the flag leaves, but the presence of awns increased photosynthetic rates of the ears by up to 1.2 mg CO2 h-1 per ear. During the linear grain growth phase. the relative net contributions per hour by awns and flag leaf, neither of which were much affected by temperature, were about 1 : 10 in all treatments.
It appeared probable that under well-watered conditions awns had an effect on yield only when assimilate supply was limiting. Awns did not always increase yield significantly in supra-optimal temperatures.
Nitrogenous Compatible Solutes in Native South Australian Plants
Authors: Poljakoff-Mayber A , Symon DE , Jones GP , Naidu BP , Paleg LG
Published: January 2006

Australian native flora was examined with nuclear magnetic resonance (n.m.r.) techniques for its content of nitrogenous compatible solutes. Plants were sampled from four habitats: two arid, one subhumid, and one saline estuarine marsh. Eight and two of the 15 plants in the subhumid area accumulated proline and glycinebetaine, respectively, whereas many of the plants in the two arid habitats accumulated these solutes. With only two exceptions plants in the saline marsh could be described as either proline accumulators (six species) or glycinebetaine accumulators (eight species). Attempts to correlate the glycinebetaine and proline contents with the relative water content (RWC) were not successful. Some plants accumulate compounds other than, or in addition to, proline or glycinebetaine, such as trans- 4-hydroxy-N-methyl-L-proline, which was accumulated in Melaleuca lanceolata. Exocarpos aphyllus accumulated an as yet unidentified compound.
Salinity-Induced Potassium Deficiency Causes Loss of Functional Photosystem II in Leaves of the Grey Mangrove, Avicennia marina, Through Depletion of the Atrazine-Binding Polypeptide
Authors: Ball MC , Chow WS , Anderson JM
Published: January 2006

Photosynthetic properties were studied in relation to the ionic composition of leaves of Avicennia marina grown in low and high salinity (i.e. 50 and 500 mol m-3 NaCl) nutrient solution containing either 0.01 or 10 mol m-3 K+. Leaves accumulated high concentrations of NaCl, but changes in photosynthesis were associated with changes in leaf K+ concentrations. The effects occurred at two levels. (1) With decrease in leaf K+ from 379 to 167 mol m-3, a 21% decline in light and CO2 saturated rates of oxygen evolution per leaf area was consistent with a 24% decrease in chlorophyll content. (2) Leaves containing only 103 mol m-3 K+ showed drastic loss of light and CO2 saturated photosynthetic capacity (42%) and photochemical dysfunctioning under limiting light conditions as manifest in a 38% decrease in quantum yield. Thylakoids isolated from these low K+ leaves showed no decrease in per chlorophyll concen- trations of photosystem I, cytochrome f/b complex and ATPase, but had 37% fewer atrazine-binding sites (corresponding to photosystem II reaction centres) than those from leaves with higher K+ concentrations. The decline in atrazine-binding sites in isolated thylakoids was sufficient to account for the loss of quantum yield in intact leaves. These results identify the atrazine-binding polypeptide of photosystem II as one site of sensitivity to salinity-induced K+ deficiency.
Non-Steady-State Water Flow for Three Desert Perennials With Different Capacitances
Authors: Hunt ER , Nobel PS
Published: January 2006

Non-steady-state water flow through plants was modelled using an electric circuit analog incorporating capacitance (change in water volume per unit change in water potential). Predictions of leaf water potential agreed with measurements for a C4 grass with a small capacitance, Hilaria rigida, and for a C3 shrub with an intermediate capacitance, Encelia farinosa. Predictions differed from measured stem water potentials for a stem succulent having crassulacean acid metabolism and a large capacitance, Ferocactus acanthodes, presumably because of daily variations in osmotic pressure. As capacitance increased, minimum shoot water potential and the maximum water uptake rate by the roots lagged further behind maximum transpiration rate. Predicted daily water uptake by roots was equal to daily water loss for H. rigida and E. farinosa, but not for F. acanthodes for which capacitance effects were particularly important. Because tissue volumes were large, water flow for F. acanthodes would be expected to reach the steady state only if conditions were constant for about 2 days, hence steady-state flow is not expected in the field. For all three species, capacitance was largely determined by total water volume rather than by the bulk elastic modulus.
Calmodulin Levels Are Not Responsible for Aluminium Tolerance in Wheat
Authors: Larkin PJ
Published: January 2006

Circumstantial evidence has suggested that the protein calmodulin may be the primary target of aluminium toxicity in plants. Experiments were carried out to test the hypothesis that genetic differences in aluminium tolerance in wheat (Triticum aestivum L.) are the consequence of different levels of calmodulin. The tolerant wheat, selection Waalt, differed from cv. Warigal by a single dominant gene for aluminium tolerance as indicated by analysis of the F2. The tolerance of cv. Carazinho also is reported to be genetically simple. Crosses between the two tolerant wheats, Carazinho and Waalt, showed that they have linked or allelic genes for aluminium tolerance.
Calmodulin was extracted from the whole roots and from root tips alone, either after 3 days exposure to aluminium, or without aluminium treatment. Calmodulin levels were measured using a radioimmunoassay. No significant differences were observed between Carazinho (tolerant) and Sunstar (sensitive). Additionally the four genotypes (Waalt, Carazinho, Warigal and Sunstar) showed no consistent differences in sensitivity, as measured by seedling root growth, to three calmodulin antagonists, trifluoperazine, chlorpromazine and calmidizolium.
Thus it appears that the different aluminium tolerances in these wheats are not due to different calmodulin levels.
Gas Exchange, Water Relations and Ion Concentrations of Leaves of Salt Stressed 'Valencia' Orange, Citrus sinensis (L.) Osbeck
Authors: Lloyd J , Kriedemann PE , Syvertsen JP
Published: January 2006

'Valencia' orange [Citrus sinensis (L.) Osbeck] scions grafted on sweet orange [C. sinensis (L.) Osbeck cv. Parramatta sweet orange] rootstock were grown in soil culture under controlled environmental conditions. Salt stress was imposed by adding NaCl to the nutrient solution in increments of 5 mol m-3 per day to a final concentration of 50 mol m-3. Leaf gas exchange, water relations and sodium, chloride and potassium concentrations were monitored until 89 days after commencement of salt treatment.
Initial CO2 assimilation rates were relatively low (2.8-4.4 �mol CO2 m-2 s-1) and were stimulated by 72-86% when ambient oxygen partial pressure was reduced from 210 mbar to 21 mbar. After 14 days salt treatment, there was an increase in assimilation rate of approximately 20% associated with a decrease in osmotic potential (π) of 0.6 MPa. Reduction in � occurred without foliar ion accumulation. Assimilation rates gradually declined thereafter, averaging less than 1 �mol CO2m-2 s-1 at day 89. Lower CO2 assimilation rates were not a consequence of increased photorespiration as no change in the extent of oxygen inhibition of CO2 assimilation or CO2 compensation point occurred with salinisation. Stomatal conductance appeared less sensitive to salt treatment than intrinsic photosynthesis, resulting in higher intercellular partial pressures of CO2 in salt stressed leaves (291 cf. 259 pbar for controls at day 89). Water use efficiency was accordingly lower in salt affected leaves.
Salinised leaves had consistently more negative osmotic potentials than control leaves; turgor potential was thus maintained at or above control levels for a given bulk-leaf water potential. Since leaf turgor was maintained via osmotic adjustment and uptake of sodium and chloride, lower assimilation rates were attributed to a toxic ion effect.
Is Phloem Transport Due to a Hydrostatic Pressure Gradient? Supporting Evidence From Pressure Chamber Experiments
Authors: Minchin PEH , Thorpe MR
Published: January 2006

A pressure chamber was used to increase suddenly the hydrostatic pressure in the upper shoot of a Phaseolus vulgaris plant while observing phloem transport of 11C-labelled photoassimilate. Phloem transport in the stem towards the chamber stopped immediately when pressure was applied and then recovered within about 5 min. If the pressure was then released, flow increased again. The results support the hypothesis that flow of photoassimilate in the stem phloem was driven by a hydrostatic pressure gradient.
Kinetics of Peptide Hydrolase Activity in Crude Wheat Leaf Extracts
Authors: French R , Paleg LG
Published: January 2006

The protein present in crude wheat leaf extracts causes serious deviations from simple Michaelis-Menten kinetics for soluble peptide hydrolases. A theoretical analysis indicated that the usual approach, of adjusting activities observed at various substrate concentrations for the activity observed in the absence of added substrate, gave erroneous estimates of kinetic parameters. The size of the error depends on the concentration of endogenous protein and the Km for its degradation. A technique is suggested to allow an estimate to be made of the true values of the kinetic parameters. The method also allows estimation of the Km for the degradation of the endogenous protein.
The Km for haemoglobin degradation by crude extracts of wheat primary leaves at pH 4.5 was 0.802 mg ml-1 and at pH 6.5 was 3.35 mg ml-1. The Km for endogenous protein degradation at pH 4.5 was 2.24 mg ml-1 and at pH 6.5 was 1.49 mg ml-1. The implications of these findings for the possible role of soluble peptide hydrolases in intracellular protein degradation is discussed.
Chloride Partitioning in Leaves of Salt-Stressed Sorghum, Maize, Wheat and Barley
Authors: Boursier P , Lynch J , Lauchli A , Epstein E
Published: January 2006

Chloride distribution in the blade, sheath and midrib of leaves was determined for several grasses in salinised field plots and in nutrient solutions at various NaCl levels in the greenhouse.
Chloride preferentially accumulated in the sheaths relative to the blades in all grass species and varieties examined when Cl- concentrations were expressed on a dry weight basis, although to varying degrees. Substantial levels of Cl- sheath partitioning were obtained only for sorghum when Cl- con- centrations were expressed on a fresh weight basis. Partitioning of Cl- in sorghum leaves was found to be ion specific and resulted from a combination of the ability of sheath tissue to accumulate Cl- to high concentrations and blade tissue to regulate Cl- concentrations at moderate levels.
Photosynthesis in Phosphoenolpyruvate Carboxykinase-Type C4 Species: Properties of Nad-Malic Enzyme From Urochloa panicoides
Authors: Burnell JN
Published: January 2006

NAD-malic enzyme (EC 1.1.1.39) was purified from bundle sheath strands of Urochloa panicoides (a phosphoenolpyruvate carboxykinase-type C4 plant) and its kinetic and regulatory properties were investigated. The native enzyme has a molecular weight of about 470 000 and is an octomer composed of two slightly different monomers which occur in a 1 : 1 ratio. The enzyme has an absolute requirement for Mn2+, is stimulated by CoA, acetyl CoA, fructose 1,6-bisphosphate and SO42- and is inhibited by HCO3, oxaloacetate, 2-oxoglutarate and pyruvate. The enzyme is shown to be localised in the mito- chondria. The purified NAD-malic enzyme is unable to catalyse the carboxylation of pyruvate according to the reverse reaction. These findings are discussed in relation to the C4 photosynthetic pathway and its possible role in PEP carboxykinase-type C4 plants.
Nodule Physiology of a Supernodulating Soybean (Glyine max) Mutant
Authors: Day AD , Price GD , Schuller KA , Gresshoff PM
Published: January 2006

The nodule physiology of a supernodulating, nitrate tolerant symbiosis soybean (Glycine max (L.) Merr.) mutant (nts382) was compared to that of its wild-type parent, cv. Bragg. Nodule number and mass were greater in nts382 than cv. Bragg and individual nodule mass, bacteroid and haem content, and acetylene reduction activity per g nodule were less. Acetylene reduction activity expressed per mg bacteroid protein was the same in the two genotypes. In median sections, the ratio of infected to total nodule area was smaller in nts382, infected cell size was smaller and there were fewer bacteroids per peribacteroid envelope. When inoculum dose was decreased from 109 to 103 viable cells per pot, nodule number on nts382 decreased approximately to that on cv. Bragg; nodule size, bacteroid and haem contents increased as did nodule acetylene reduction activity.
Application of moderate levels of nitrate, which did not significantly affect symbiotic parameters of cv. Bragg or high inoculum nts382, stimulated nodule growth and nitrogenase activity of low inoculum nts382. A combination of nitrate and low inoculum levels enhanced nodule parameters of nts382 to the level usually seen with cv. Bragg. When supernodulated, plant dry weight of nts382 was less than that of Bragg; decreasing inoculum dose had no significant effect but nitrate application increased plant growth; nitrate plus low inoculum induced similar plant growth to that of cv. Bragg. Nodule carbohydrate content was similar in both genotypes but nodule and xylem sap ureide contents were higher in nts382.
In general, nodules of supernodulated nts382 resembled under-developed cv. Bragg nodules; when supernodulation was avoided by using low inoculum doses, ,nts382 nodules resembled those of cv. Bragg. Nitrogen metabolism in the mutant seems to be disturbed, resulting in ureide accumulation.
Salinity Effects of Leaf Water Relations and Gas Exchange of 'Valencia' Orange, Citrus sinensis (L.) Osbeck, on Rootstocks With Different Salt Exclusion Characteristics
Authors: Lloyd J , Syvertsen JP , Kriedemann PE
Published: January 2006

Valencia orange [Citrus sinensis (L.) Osbeck] scions were grafted to rootstocks with different sodium and chloride excluding characteristics, viz. Trifoliata [Poncirus trifoliata (L.) Raf. and Cleopatra mandarin (Citrus reticulata Blanco). Grafted trees were grown at either 175 or 650 �mol m-2 s-1 photosynthetically active radiation and watered with nutrient solution with 0, 50 or 100 mol m-3 NaCl. Foliage of scions grafted to Trifoliata had higher levels of chloride but lower levels of sodium compared to foliage of scions grafted to Cleopatra mandarin.
Although leaf water potential declined with salinisation, salt accumulation in leaves on both root- stocks contributed to more negative osmotic pressures and subsequent maintenance of turgor at or above levels in control leaves. Despite turgor maintenance, CO2 assimilation rate (A) was reduced by salinity. Inhibition occurred to a greater degree for leaves on Cleopatra mandarin than those on Trifoliata. Reductions in CO2 assimilation and stomatal conductance were usually in step with each other. This correlation was paralleled by little change in intercellular partial pressures of CO2 (pI) despite large changes in gas exchange.
The response of A to pi was affected by salinity in such a way that impact of salt on CO2 assimilation was expressed to a greater degree at high pI. The extent of photosynthetic response to salt at high pI was independent of light level during growth. Room temperature chlorophyll a fluorescence induction kinetics remained unaltered.
Scions grafted to Trifoliata showed slower onset of photosynthetic dysfunction following salinisation than corresponding foliage of scions on Cleopatra mandarin. Moreover, photosynthetic sensitivity to increased leaf chloride also appeared to diminish on Trifoliata. This rootstock effect on scion performance was attributed to a superior capacity in Trifoliata for exclusion of sodium ions from Valencia scions.