bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficiency of C4 photosynthesis in Atriplex lentiformis under salinity stress
Authors: Meinzer Frederick C. , Zhu Jun
Published: January 2006

Photosynthetic gas exchange, carboxylase activities, and leaf tissue carbon
isotope discrimination (Δ) were measured in
Atriplex lentiformis (Torr.) Wats. (saltbush) plants
grown in a glasshouse at five levels of salinity ranging from 0 to 600 mM
NaCl. The net CO2 assimilation rate decreased by
64% from the lowest to the highest level of salinity imposed. The
quantum yield for CO2 uptake was maximal in plants grown
at 50 mM NaCl, and decreased sharply above and below this salinity level. The
ratio of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)
activity to that of phosphoenolpyruvate carboxylase
(PEPC) decreased from 0.96 in plants grown at 0 mM NaCl to 0.37 in plants
grown at 600 mM NaCl because PEPC activity on a leaf area basis increased
linearly with increasing salinity, while Rubisco activity remained relatively
constant. Compensatory changes in the leaf area/dry weight ratio and
area-based leaf N content with increasing salinity suggested that the linear
increase in PEPC activity was a passive response to increasing area-based leaf
N content, whereas Rubisco activity on a leaf N basis actually dropped
sharply. Relative leakage of CO2 from the bundle sheath,
calculated from measurements of gas exchange and foliar Δ values,
increased with increasing salinity in parallel with the decrease in the ratio
of C3 cycle activity relative to
C4 cycle activity. These results suggest that salinity
stress diminished the inherent efficiency of the C4
CO2 concentrating mechanism in addition to reducing net
CO2 uptake.
Effects on photosynthesis, carbohydrate accumulation and regrowth induced by temperature increase in maize genotypes with different sensitivity to low temperature
Authors: Pietrini F. , Iannelli M. A. , Battistelli A. , Moscatello S. , Loreto F. , Massacci A.
Published: January 2006

Photosynthesis and carbohydrate accumulation in maize genotypes
(Zea mays L.) VA-36 and A-619, ranked as possessing low
and high sensitivity to low temperature, were studied in relation to regrowth
after transfer from day/night temperatures of 16/12˚C to
25/20˚C. Plants were grown for 45 days at 25/20 or
16/12˚C, or transferred after 45 days from 16/12˚C to
25/20˚C for 27 days. Photosynthesis of both genotypes after a 45-day
growth at 16/12˚C was lower than at 25/20˚C. When the
photosynthesis of plants at 16/12˚C was measured at 25˚C it was
as high as the photosynthesis of plants at 25˚C in VA-36, while it
remained lower in A-619. A strong reduction of rubisco content was observed in
the sensitive genotype and is suggested as the cause of photosynthesis
limitation that was still observed after recovery at 25/20˚C. After a
45-day growth at 16/12˚C, a reduction of sucrose and, to a lesser
extent, starch content was observed. Biomass accumulation was also reduced in
both genotypes. Transfer from 16/12 to 25/20˚C increased
photosynthesis, partially restored sucrose but not starch content and induced
a rapid regrowth in VA-36. Conversely, photosynthesis, carbohydrate content
and regrowth remained low in A-619. It is suggested that for the two
genotypes, regrowth is dependent on the integrity of the photosynthetic
apparatus which contributes to sensitivity to low temperatures.
Increased C-gain by an endemic Australian pasture grass at elevated atmospheric CO2 concentration when supplied with non-labile inorganic phosphorus
Authors: Barrett Damian J. , Gifford Roger M.
Published: January 2006

Limited phosphorus (P) availability in Australia's highly weathered soils
may constrain an increase in terrestrial net primary productivity (NPP) with
the globally increasing atmospheric CO 2 concentration.
We examined whether an Australian temperate pasture grass
(Danthonia richardsonii) grown in sand culture and
supplied solely with virtually insoluble Al- and Fe-phosphate was able to
increase C-gain when exposed to elevated (731 µmol mol
−1 ) compared with ambient (379 µmol mol
−1 ) CO 2 concentrations.
When supplied with 8 mg kg −1 insoluble P
concentration, total citrate efflux by root systems (µmol h
−1 ), plant P uptake, shoot photosynthesis rates
and plant mass were all significantly greater at elevated than at ambient CO
2 after a growth period of between 55 and 63 days. In
this treatment, although the P concentration of the rooting medium limited
growth at ambient CO 2 , elevated CO
2 increased P-uptake from the non-labile source,
increased photosynthesis rates per unit shoot soluble-P and increased plant
mass. At P concentrations lower than 8 mg kg −1 ,
plant mass, specific citrate efflux and maximum leaf carboxylation rates were
limited by the amount of P available in the rooting medium and no CO
2 effect was observed. In all treatments, carbon supply
did not appear to limit citrate efflux. Where an increase in P uptake at
elevated CO 2 was achieved, it was due to an increase in
root mass (indicative of a potentially larger soil volume explored) rather
than to increased specific rates of citrate efflux. Above 8 mg kg
−1 , the supplied P concentration was sufficient
that minimal rates of specific citrate efflux alone solubilised enough P for
growth and a strong CO 2 effect on plant mass,
photosynthesis and P uptake was observed.
Changes in gene expression during development and thermogenesis in Arum
Authors: Chivasa Stephen , Berry James O. , ap Rees Tom , Carr John P.
Published: January 2006

Thermogenesis in Arum species is induced by salicylic
acid (SA) and caused by activation of the alternative respiration pathway and
the alternative oxidase (AOX), resulting in heat production. The enzymes
phosphoenolpyruvate carboxylase (PEPCase) and
NAD-dependent malic enzyme (NAD-ME) also show dramatic increases in activity
during thermogenesis and are essential for heat generation. In this current
study, we characterized the timing and localization of changes in levels of
AOX, NAD-ME, and PEPCase polypeptide accumulation, and changes in
Ppc and Me mRNA accumulation, in
various Arum tissues during prethermogenic development
and during thermogenesis. In addition, changes in ribulose-1,5-bisphosphate
carboxylase/oxygenase (Rubisco) gene expression were analysed at the level
of rbcL protein and mRNA accumulation. AOX, PEPCase, and
NAD-ME all increased only in clubs during development, increasing
5–6-fold by the latest prethermogenic stage and remained at this level.
The induction of thermogenesis did not cause any changes in levels of AOX,
indicating that SA does not affect levels of the enzyme itself, but instead
must act to stimulate activity. Reported increases in NAD-ME activity during
club development correlated closely with mRNA and protein accumulation,
whereas PEPCase activity appears to be determined by post-transcriptional and
post-translational processes. Interestingly, Rubisco protein and mRNA were
found in relatively abundant amounts in clubs during early developmental
stages, and disappeared rapidly as the thermogenic enzymes began to increase
in abundance. The induction of thermogenesis by a synthetic inducer of plant
pathogen resistance, 2,6-dichloroisonicotinic acid, as well as the involvement
of SA and AOX in both processes, reinforces evidence for a link between
mechanisms controlling disease resistance in all plants and thermogenic
induction in Arum.
Organic acid concentration is little controlled by phosphoenolpyruvate carboxylase activity in peach fruit
Authors: Svanella L. , Gaudillère M. , Gaudillère J. P. , Moing A. , Monet R.
Published: January 2006

Changes in phosphoenolpyruvate carboxylase (PEPC)
activity were studied during the fruit development of two peach cultivars
(Prunus persica (L.) Batsch) with normal
(‘Fantasia’) and low (‘Jalousia’) organic acid
concentration. PEPC activities were measured in fruit mesocarp at two stages
of development, corresponding to malate accumulation and citrate accumulation
phases in ‘Fantasia’, respectively. In vitro
activity, measured under optimal conditions, was significantly higher in
‘Fantasia’ than in ‘Jalousia’ during the malate
accumulation phase but lower during the citrate accumulation phase.
In vivo activity was estimated using
14CO2 labelling. The total
incorporated radioactivity was higher in ‘Fantasia’ than in
‘Jalousia’ during the malate accumulation phase but lower during
the citrate accumulation phase. During the malate accumulation phase, the
partitioning of incorporated 14C into malate was
significantly reduced in ‘Jalousia’ compared to
‘Fantasia’ after 20 min labelling. During the citrate accumulation
phase, 14 C partitioning into malate was not significantly different between
varieties, but partitioning into citrate was significantly reduced in
‘Jalousia’ compared to ‘Fantasia’. Therefore, PEPC
activity does not seem to be the controlling step for the absence of organic
acid accumulation in ‘Jalousia’ fruit. The other metabolic causes
of the difference in organic acid accumulation are discussed; these may be
connected with vacuolar storage.
The Transport Behaviour of the Synthetic Auxin 2,4-Dichlorophenoxyacetic Acid in Decapitated Seedlings of Sunflower (Helianthus annuus L.)
Authors: Brown BT , Phillips JN
Published: January 2006

The transport behaviour of the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D), applied in aqueous solution to the cut stem surface of sunflower seedlings decapitated in the epicotyl, was studied using steam-ringing to differentiate between apoplastic and symplastic movement. Initially the 2,4-D moved in apoplastic tissue and was distributed rapidly throughout the plant, apparently as the result of a non-auxin-specific transport process. When an amount of 2,4-D sufficient to maintain apical dominance in the decapitated seedling was applied, the initially distributed material was subsequently redistributed acropetally in the stem apoplast and accumulated in the stump apex. When a lower level of 2,4-D, insufficient to maintain apical dominance, was applied, the initially distributed material was redistributed basipetally in the stem symplast, probably via the auxin polar transport system, and accumulated in the root. It is suggested that the 2,4-D loading capacity of the polar transport system is an important factor determining both the transport behaviour of the 2,4-D and its ability to maintain apical dominance in this system.
Biosynthesis of Arabinogalactan-Protein in Lolium multiflorum (Ryegrass) Endosperm Cells. II. In vitro Incorporation of Galactosyl Residues From UDPgalactose Into Polymeric Products
Authors: Mascara T , Fincher GB
Published: January 2006

When mixed-membrane fractions from suspension-cultured Lolium multiflorum endosperm cells are incubated in vitro with UDP-[14C]galactose, 66% ethanol-insoluble products of apparent molecular weight greater than 60 000 are labelled in both galactosyl and glucosyl residues, suggesting that an active UDPgalactose 4-epimerase is present on the membrane fraction. The epimerase can be inhibited with ADPribose, to produce polymeric material in which [14C]galactosyl residues pre-dominate. While some of these residues appear to be associated with glycoproteins, affinity chromatography of the products on mouse myeloma protein J539-Sepharose provides evidence that β-galactans containing 1,6-linkages are amongst the products.
Monosaccharide analyses and methylation data indicate that the mixed-membrane preparations contain associated polysaccharide of structure analogous to the 1,3;1,4-β-glucans, arabinoxylans and arabino-3,6-galactans normally found in cell walls or secreted into the medium.
Cell-Free Synthesis of Wheat Prolamins
Authors: Donovan GR , Lee JW , Longhurst TJ
Published: January 2006

Total RNA, polyribosomes and polyribosomal RNA have been isolated from immature wheat grain and used to prime the wheat-germ cell-free protein synthesis system to produce storage protein. The synthesis of wheat prolamins, a major fraction of storage proteins, was mainly associated with membrane-bound polyribosomes. The ratio of bound to free polyribosomes increased from one at 8 days to approximately three at 32 days post-anthesis. SDS polyacrylamide gel electrophoresis and fluorography of the prolamins showed that the same components were being synthesized and accumulated from 12 days post-anthesis onward. Evidence is presented that prolamins within the molecular weight range 35 000-45 000 may be translated with a signal sequence attached. These signal sequences are rapidly removed during translation and further post-translational modifications may occur over longer periods.
Effect of Different Durations of Water Withholding on Regrowth Potential and Non-Structural Carbohydrate Content in Rhodes Grass (Chloris gayana Kunth)
Authors: Kigel J , Dotan A
Published: January 2006

The effect of water stress on the regrowth potential of Rhodes grass was studied in plants grown under controlled conditions at 27/22°C and 16-h photoperiods, and subjected to different periods of water withholding. After water was withheld, the levels of water-soluble carbohydrates (WSC) in the roots and basal parts of the leaves gradually increased from 2-4% to 8-9%, while the level of starch in the leaves remained stable below 1%. Regrowth and elongation of leaves that took place after cutting was increased markedly by withholding water for 6-10 days before cutting. A positive linear correlation was shown between initial leaf regrowth and the total amount of WSC present at cutting time. However, this initial advantage of the stressed plants gradually disappeared during the regrowth period, and no significant differences in leaf length and weight were found at later stages between the watered and stressed plants.
Polygalacturonase in Tomato Fruits and the Induction of Ripening
Authors: Brady CJ , Macalpine G , McGlasson WB , Veda Y
Published: January 2006

Endopolygalacturonase (EC 3.2.1.15) activity, endopolygalacturonase protein detected immunologically and water-soluble uronide were measured in tomato fruit samples (cv. Rutgers) at different stages of ripening. Endopolygalacturonase activity and endopolygalacturonase protein were only detected in samples in which ripening had been initiated for 2 or more days. Enzyme activity and enzyme protein increased during ripening and were highly correlated. A high molecular weight form of the enzyme appeared 2 or 3 days after ripening was initiated. Lower molecular weight forms of endopolygalacturonase appeared later and eventually accounted for most of the enzyme protein. The content of water-soluble uronide did not increase until fruit had been ripening for 4 or more days. It is concluded that endopolygalacturonase is not involved in the initiation of ripening.
Salt Tolerance of Trifolium alexandrinum L. III. Effects of Salt on Ultrastructure of Phloem and Xylem Transfer Cells in Petioles and Leaves
Authors: Winter E
Published: January 2006

The ultrastructure of vascular tissue of petioles, petiolules and major and minor leaf veins from T. alexandrinum plants grown with and without 50 mM NaCl in solution culture was examined at two stages of the salt treatment. Gradual destruction of the cell content in phloem transfer cells of major and minor veins in leaves of salt-treated plants was observed. This destruction was only found in these cells and preceded the development of leaf burn symptoms. First signs of disorganization are myelin-figures, final stages are coagulation of the cellular content and accumulation of large starch grains in the chloroplasts of the surrounding mesophyll tissue. The appearance of these symptoms coincides with the end of a period of increased Na+ inflow into the leaves. The obser- vations are discussed in relation to a hypothesis of intraveinal recycling of Na+ and Cl- in leaves as an integral part of the salt-tolerance mechanisms of T. alexandrinum.
Properties and Regulation of Adenylate Kinase From Zea mays Leaf Operating in C4 Pathway Photosynthesis
Authors: Hatch MD
Published: January 2006

Adenylate kinase from the mesophyll cells of Zea mays was partially purified and its kinetic and regulatory properties determined. Fractionation of mesophyll cell extracts by (NH4)2SO4 precipitation, filtration on Sephacryl S-200 and diethylaminoethylcellulose chromatography gave a fraction purified about 90-fold. For the reaction in the direction of ADP synthesis (forward reaction), activity was influenced by a complex interaction between Mg2+, ATP and pH. Optimal activity was observed with a Mg2+ to ATP ratio of about unity and the pH optimum under these conditions was about 8.0. With an excess of Mg2+, activity was reduced and the pH optimum was shifted to lower values. Varying ATP or AMP in a lower range of concentrations gave simple Michaelis- Menten responses. However, at higher concentrations there was a complex response to increasing ATP, and AMP became inhibitory. For the reverse reaction the Km (ADP) was about 70 �M and the pH optimum was between 8.0 and 8.5. AMP was a strong inhibitor of the reverse reaction (competitive with respect to ADP), the KI being about 40 �M. Several other metabolites tested had no effect on adenylate kinase activity. Adenylate kinase extracted from washed mesophyll chloroplasts had essentially identical properties.
Phytotropins. IV. Effect of Phytotropins on Cultured Plant Cells and Protoplasts
Authors: Larkin PJ , Scowcroft W , Geissler AE , Katekar GF
Published: January 2006

The phytotropins l-(2'-carboxyphenyl)-3-phenylpropane-1,3-dione (CPP) and 5-(2-carboxyphenyl)- 3-phenylpyrazole (CPD) reduced the net efflux of radiolabel from suspension-cultured cells treated with [14C]2,4-dichlorophenoxyacetic acid when present at concentrations comparable to those that inhibit polar transport of auxins in bean petioles. These phytotropins stimulated division of protoplasts of both Nicotiana debneyi and Petunia hybrida at concentrations of exogenous auxins that were otherwise suboptimal for divisions. The results are consistent with the proposal that phytotropins interact with specific receptors to reduce auxin efflux, resulting in increased intracellular auxin concentrations.
Effect of Photoperiod, Night Temperature, and Frost Incidence on Development of Frost Hardiness in Pinus radiata
Authors: Greer DH , Warrington IJ
Published: January 2006

The role of photoperiod, night temperature, and frequency and severity of frosts on the development of frost hardiness in seedlings of Pinus radiata was studied using controlled environment treatments. In one experiment the specific effects of 9 and 14 h photoperiods and 5 and 15°C night temperatures were examined. In a second experiment, seedlings were sequentially hardened under two simulated early autumn to late winter climates, with the photoperiod and day/night temperatures progressively altered at 11 and 21 day intervals respectively. In addition, half of the seedlings raised in each simulated climate were exposed concurrently to a conditioning frost regime. Frost hardiness of the seedlings in each sequence was determined at regular intervals using a series of evaluation frosts. Frosts of between -3 and -5°C were the most effective factor in controlling the development of frost hardiness. Night temperatures as low as 1°C were also effective but not those above 5°C. A minimum photoperiod requirement of less than 11 h for up to 42 days exposure was required for low-temperature hardening. There appeared to be a response lag in the development of frost hardiness once the critical photoperiod and inductive night temperatures had been imposed.
Differences between nursery sites in frost hardiness of seedling stock were attributed to differences in their environments, particularly the incidence of frosts. The final maximum frost hardiness varied between the treatments from - 7.5 to -19°C indicating that Pinus radiata has a greater potential to develop frost hardiness than was previously thought from field observations.
Temperature-Induced Water Stress in Chilling-Sensitive Plants
Authors: Mcwilliam JR , Kramer PJ , Musser RL
Published: January 2006

Cotton (Gossypium hirsutum) and bean (Phaseolus vulgaris) seedlings wilted when entire plants or roots alone were chilled in the light. The water relations and gas exchange characteristics of these chilling-sensitive species have been compared with a chilling-resistant species, collard (Brassica oleracea), following exposure to a chilling temperature at 5°C.
Chilling either whole seedlings or roots alone had little or no effect on leaf water potentials or gas exchange of collard seedlings but induced a rapid response in cotton and bean. Leaf water potentials were reduced below - 1.5 MPa within 1-2 h; however, this response was reduced when seedlings were chilled in the dark or when leaves or roots of bean were pretreated with abscisic acid. Chilling also caused a rapid reduction in photosynthesis but a more gradual decline in transpiration over the first 2-4 h due to the slow closure of stomata.
These results suggest that water deficits in chilling-sensitive seedlings when exposed to low temperature in the light are caused by a reduction in the hydraulic conductivity of the root membranes and by the loss of stomatal control in the leaves. The reduced flow of water into the plant through the roots and continued transpiration, because of the slow closure of stomata, bring about a rapid decline in leaf water potential and wilting of primary leaves.
Intracellular Localization of Acid Peptide Hydrolases and Several Other Acid Hydrolases in the Leaf of Pea (Pisum sativum L.)
Authors: Noble ER , Dalling MJ
Published: January 2006

Protoplasts and vacuoles were prepared from pea (P. sativum L.) leaves to determine the acid-hydrolase content of the vacuole. The protoplasts and vacuoles were isolated on sucrose-sorbitol gradients. We conclude that the protoplast preparation was free of enzyme contamination arising from the digestion mixture, after comparing the specific activities of the crude extract and of the isolated protoplasts, and the response to the thiol inhibitor p-chloromercuribenzoate of the crude extract and protoplast acid proteinase with that of the Cellulysin enzyme. N-acetyl-β-D-glucosaminidase, α-mannosidase, acid carboxypeptidase and acid proteinase appeared to be located entirely in the vacuole. Approximately 60% of the acid-phosphatase and 27% of the phosphodiesterase activities were found in the vacuole. We conclude that the acid proteinase and the acid carboxypeptidase are separate enzymes in pea leaves, based on their different sensitivities to the inhibitors phenylmethylsulfonyl fluoride and p-chloromercuribenzoate.
Characterization of Dihydrophaseic Acid 4′-O- β -D-Glucopyranoside as a Major Metabolite of Abscisic Acid
Authors: Milborrow BV , Vaughan GT
Published: January 2006

(�)-[2-14C]abscisic acid (ABA) and [2-14C]dihydrophaseic acid (DPA) fed to tomato shoots were converted into an acidic, polar conjugate that was hydrolysed (1 M HCl, 100°C) to D-glucose and DPA. The tetraacetylmethyl ester of the metabolite was isolated by high performance liquid chromatography as colourless crystals (m.p. 81-84°). N.m.r. spectra showed the presence of a β-glucosidic linkage (J 7 Hz, CDCl3; 8 Hz, D5 pyridine) between C-4' of DPA and C-1 of glucose. Mass spectra of the 0-acetylmethyl ester of the conjugate, and also of material biosynthesized from [1'-18O]ABA, showed that the glucoside is at C-4' of DPA. The abbreviation 'DPAGS' is proposed.
Recovery From Water Stress in Five Sunflower (Helianthus annuus L.) Cultivars. I. Effects of the Timing of Water Application on Leaf Area and Seed Production
Authors: Rawson HM , Turner NC
Published: January 2006

For sunflower (Helianthus annuus L.) plants grown at a density of 5 m-2, maximum leaf areas per plant ranging between 0.2 and 2.2 m2 resulted from using five cultivars of different maturity and imposing four different water treatments. Seed production increased with the number of irrigations supplied, and in the irrigated treatments it was positively correlated with time to anthesis: later cultivars yielded better. Lateness was no advantage in crops grown on stored soil moisture and the best yielding cultivar was one which ranked only third when it was irrigated. All cultivars showed a remarkable ability to produce leaf area whenever water was available. Moreover, seed production was positively correlated with the maximum leaf area achieved by crops: the relationship between leaf area and seed yield was curvilinear across cultivars and irrigations, though a linear regression provided a significant fit to the data. The highest oil percentages occurred in a recently released commercial cultivar, but this vatiety did not produce the moist oil per plant. In addition, the line which ranked highest for oil production varied with water availability.
It is concluded that, within the material studied, the longer duration lines were most suited to irrigation, since they permitted the establishment of more leaf area. The interaction between the effects of irrigation management and plant maturity on seed yield is discussed.
Salt Tolerance and Regulation of Enzymes of Starch Synthesis in Cassava (Manihot esculenta Crantz)
Authors: Hawker JS , Smith GM
Published: January 2006

The growth rate of cassava plants (Manihot esculenta cv. MAUS7) decreased with increasing concentrations of NaCl from 0 to 75 mM in nutrient solutions supplied regularly in a porous growth medium in a glasshouse. Tuber weight was reduced to one-half between 30 and 50 mM NaCl and there was some burning of apical leaves at 50 and 75 mM NaCl. By comparison with other plants, this cultivar of cassava can be considered to have medium sensitivity to salinity. Na+ and Cl- concentrations increased in all tissues with increasing concentrations of supplied NaCl, except that Na+ remained low in laminae until the 75 mM treatment. K+ levels decreased in tubers. Starch concentrations remained the same in tubers, and K+ stimulated starch bound ADPglucose starch synthase by 1 .5-fold. Leaves and tubers contained activities of ADPglucose pyrophosphorylase and ADPglucose-starch synthase similar to those found in leaves and storage organs of other starch synthesizing plants. ADPglucose pyrophosphorylase from leaves was stimulated 20-fold by 3-phosphoglyceric acid (3PGA) while the enzyme from tubers was almost completely dependent on 3PGA at pH 8.5. The A0.5 values for 3PGA (the concentration required for one-half maximal activation) for the leaf and tuber enzymes at pH 8.5 were 1.31 mM and 7.41 mM respectively. At pH 7.5 the leaf enzyme was stimulated 26-fold and the tuber enzyme was again almost completely dependent on 3PGA. The A0.5 values at pH 7.5 were 1.17 mM and 3.8 mM, respectively. The I0.5 values for PI (concentrations required to cause 50% inhibition) in the presence of 3PGA were 2 mM, 0.25 mM and 0.04 mM for leaf enzyme at pH 8.5 and tuber enzyme at pH 8.5 and 7.7 respectively. The results support the view that it is not possible to generalize about the magnitude of the control of ADPglucose synthesis in leaves as opposed to non-chlorophyllous tissues.
Variation in Endosperm Characteristics and Nitrogen Content in Six Wheat Lines
Authors: Gleadow RM , Dalling MJ , Halloran GM
Published: January 2006

Grain growth was studied in six wheat lines which represented a wide range of mature grain weights (18-56 mg). Endosperm cell number, measured by counting nuclei, was positively related to final grain weight, apparently by allowing a higher rate of grain growth. Those wheat lines with fewer endosperm cells also tended to have smaller cells. As a consequence, large grains contained larger numbers of starch granules per endosperm and per cell. The time after anthesis at which nitrogen in the flag leaves began to decline varied between wheat lines and appeared to be related to both the pattern of nitrogen storage in the grain and the duration of grain growth. However, once initiated, the rate of flag-leaf senescence exhibited similar kinetics in all wheat lines.
An Investigation of the Importance of Transpiration Gradients in the Control of Phototropic Curvature in Coleoptiles of Avena sativa
Authors: Franssen JM , Digby J , Firn RD
Published: January 2006

The coleoptiles of Avena sativa bend towards blue light whether they are submerged or in air. The pattern of differential growth causing curvature is similar in both cases. These measurements support previous observations and argue against a role for transpiration in phototropism.
Humidity-sensitive Degreening and Regreening of Leaves of Borya nitida Labill. As Followed by Changes in Chlorophyll Fluorescence
Authors: Hethzerington SE , Smillie RM
Published: January 2006

Fast and slow chlorophyll fluorescence induction kinetics were used to follow changes in photosynthetic activity during humidity-sensitive degreening and regreening of leaves of Borya nidita Labill. During dry periods the leaves of this desiccation-tolerant plant lose chlorophyll, becoming yellow-brown and upon rehydration turn green again. This degreening process can be simulated in detached leaves by slow dehydration at 96% relative humidity. Under these conditions changes in chlorophyll fluorescence in vivo and the activities of photosystems I and II in chloroplasts isolated from dehydrated leaves indicated that degreening was accompanied initially by a stimulation of photosystem II activity and a gradual decrease in photosystem I-mediated electron transfer, while at advanced stages of degreening both photosystems were lost. Control leaves detached and kept at 100% relative humidity remained green and showed little change in chlorophyll fluorescence kinetics. During the rehydration and subsequent regreening of dry yellow leaves, photosystem I activity appeared to recover faster than photosystem II. The ability of the leaves to recover and regreen from the dried state, either on the plant or after detachment, depended upon the physiological age of the leaves at the time of dehydration.
Potential Photosynthesis in Trellis-Type Orchard Canopies.
Authors: Denholm JV , Connor DJ
Published: January 2006

The choice of fork angle in orchards of the Tatura trellis design is investigated through simulations of the light relations and resultant photosynthetic response of a variety of structural alternatives. Computations consider a treatment of the penetration of direct solar beam on which is superimposed either a simplified or a complex treatment of the diffuse radiation climate within the orchard canopy. Computations show that, at any leaf area index, the potential seasonal photosynthesis of a flat canopy (fork angle = 180�) sets the upper limit to the productivity of all canopies of lesser fork angle. The diffuse component of radiation has a significant influence on expected absolute harvest yields, reducing the relative differences in yields between canopies of various fork angles which result from the strong interaction between solar trace and canopy geometry. The commonly selected fork angle of 60� cannot be defended on the basis of maximum seasonal potential photosynthetic productivity.
15n Moved to the Grain of Winter Wheat When Applied as Nitrate to Senescing Flag Leaves.
Authors: Blacklow WM
Published: January 2006

Flag leaves of wheat in the field took up a solution containing 30 mM K15NO3 through their cut tips. Treatment was applied 37 days after anthesis and uptake was allowed to continue for intervals up to 76 h by which time about 0.6 mg of 15N nitrate nitrogen was taken up. At the time of treatment, the flag leaves from plants grown under two levels of nitrogen nutrition had lost half of their nitrogen content and were exporting it at about 0.2 mg per day. Despite this state of senescence the flag leaves were able to reduce the nitrate and 30-40% of that taken up was translocated to the grain within 3 days. No nitrate accumulated in the leaves or grain. Emission spectrometry was sufficiently sensitive to detect 15N which increased from 0.02 to 1.18% of grain nitrogen during the 76 h of accumulation.
Lectins as Cytochemical Probes of the Developing Wheat Grain. Iii. Reaction of Potato and Wheat-Germ Lectins With Wheat Protein Bodies.
Authors: Baldo BA , Boniface PA , Simmonds DH
Published: January 2006

Fluorescein-labelled lectins from the potato tuber and from wheat germ stained endosperm protein bodies in JB-4-embedded transverse sections cut from developing wheat grains. With potato lectin the reaction was observed in sections cut from grains at all stages between 10 and 35 days post-anthesis (p.a.). With wheat-germ lectin, staining was far less intense and the reaction was seen clearly only at 25-35 days p.a. Protein bodies isolated from wheat endosperm between 14 and 21 days p.a., and thin sections of dough prepared from mature wheat flour, also reacted with potato lectin. Intense fluorescence of aleurone granules was observed following treatment of JB-4-embedded sections with labelled potato lectin. The specificity of the reactions was further investigated by inhibition studies with monosaccharides, N,N'-diacetylchitobiose, N,N',N"-triacetylchitotriose, and some glycoproteins. We hypothesize that these reactions are mediated through specific sugar residues covalently attached to the storage proteins present in the protein bodies. Hydrophobic interactions may also be involved in the lectin binding. Experiments designed to investigate the existence of a wheat reserve glycoprotein(s) are therefore an important research priority. Potato lectin in particular should prove to be a valuable cytochemical probe in ultrastructural studies designed to examine the cytoplasmic origin and mode of transport of storage proteins to the vacuoles in the developing wheat endosperm.
Assimilate Movement in Lolium and Sorghum Leaves. Iii. Carbon Dioxide Concentration Effects on the Metabolism and Translocation of Photosynthate.
Authors: Wardlaw IF
Published: January 2006

Raising the CO2 concentration of air to 720 �l I-� increased the rate of net CO2 uptake by the leaf of Lolium temulentum, a C*3 species, more than in Sorghum sudanense, a C*4 species. In Lolium, but not in Sorghum, high CO2 over a 6 h period resulted in relatively more of the additional leaf photosynthate being partitioned into storage rather than to translocation. Removing CO2 from the air passing over a 5 cm length of leaf before and after a pulse application of 14CO2 resulted in a reduced labelling of sucrose and a slower rate of export of 14C-labelled photosynthate in both species. With the fall in net CO2 exchange by the leaf section deprived of CO2 there was a compensating increase within this section in retention of photosynthate derived from the distal part of the leaf. Evidence provided by 14CO2 pulse chase experiments and CO2 exchange studies confirmed the relative enhancement of photorespiration under low CO2 concentrations in Lolium, but not in Sorghum. The CO2 depletion experiments provide a useful base for comparison with the effect of low light and water stress on photosynthate metabolism and translocation in that both these conditions reduce CO2 uptake. There is support for the suggestion that the change in photosynthate metabolism under water stress in C*3 species may result from reduced CO2 entry into the leaf due to stomatal closure.
Photosynthesis and Transpiration of Pinus Radiata D. Don Under Plantation Conditions in Southern Australia. I. Response to Irrigation With Waste Water.
Authors: Attiwill PM , Cromer RN
Published: January 2006

A plantation of P. radiata growing on sandy soil responded by greatly increased growth to applications of waste water over 3 years. Foliar concentrations of phosphorus and potassium increased following imgation but, although the waste water contained sodium up to 200 mg l-�, the concentration of sodium in the foliage remained low. Maximum rates of photosynthesis of branches within the canopy were 1 .8 �mol m-� s-� (imgated trees) and 0.7 �mol m-� s-� (unimgated trees). Needle conductance (g,) in imgated trees was 20-50 mmol m-� s-� and, in unimgated trees, less than 10 mmol m-2 s-�. Greater rates of photosynthesis in imgated trees might be explained by greater values of g*l; variations in the rate of photosynthesis during the course of a day did not, however, always follow variations in g*l particularly in irrigated trees. Needle water potential (�*p) of imgated trees reached a minimum of -2.0 MPa during the day, indicating a large internal resistance to the transport of water through the tree. Minimum �*p of unirrigated trees was -2.6 MPa; substantial rainfall during the measurement period did not reduce the difference in �*p between imgated and unimgated trees.
Photosynthetic Responses of the Citrus Varieties Rangpur Lime and Etrog Citron to Salt Treatment
Authors: Walker RR , Torokfalvy E , Downton WJS
Published: January 2006

Seedlings of Rangpur lime (Citrus reticulata var. austera hyb.?) and Etrog citron (C. medica L.), which differ markedly in ability for salt exclusion (i.e. the ability to restrict the uptake and/or transport of salt between roots and shoots), were grown under glasshouse conditions and supplied with dilute nutrient solution containing either 0 or 50 mM NaCl. Photosynthetic response to salt treatment and subsequent recovery were followed for 105 days for Etrog citron and for 119 days for Rangpur lime. Photosynthesis in mature leaves of both varieties was progressively reduced by salt treatment irrespective of ability for salt exclusion. The photosynthetic decline in each case was related to increases in stomatal and internal resistances. The reduction in photosynthetic capacity in Etrog citron leaves was associated with high leaf chloride concentrations while in Rangpur lime, a salt excluder, it could be related to a loss of leaf turgor. Leaf sodium concentrations were not markedly increased by salt treatment in either variety.
Cessation of salt treatment led to a progressive recovery of photosynthesis for both varieties accompanied by a reduction in both stomatal and internal resistances. Recovery in Etrog citron leaves occurred despite little change in leaf chloride concentrations. These leaves tolerated up to 350 mM chloride (leaf water basis) under glasshouse conditions without sustaining a permanent reduction in photosynthetic capacity.
Time Trends for Change in Osmotic Adjustment and Water Relations of Leaves of Cenchrus ciliaris During and After Water Stress
Authors: Wilson JR , Ludlow MM
Published: January 2006

Buffel grass was subjected to a soil drying cycle for 5 weeks in a semi-arid environment. As water stress developed, the leaf water relations characteristics of these plants (Dry treatment) were compared with those of irrigated plants (Wet treatment). Leaf water potential (Ψ) of the Dry treatment measured at 1400 h decreased to a minimum of -6.9 MPa.
The stressed leaves adjusted osmotically, with the osmotic potential at full turgor (Ψπ100) decreasing (becoming more negative) linearly with time (0.017 MPa day-1) and with decreasing water potential measured at 1400 h (0.11 MPa per 1 MPa decrease in Ψ). Maximum osmotic adjustment (Ψπ100 Wet -Ψπ100 Dry) was 0.66 MPa, and this change together with lower cell wall elasticity decreased by 1.03 MPa the water potential (Ψ0) at which the stressed leaves lost turgor. Differences between the stress- acclimated Dry leaves and the Wet leaves in bound water, turgid weight:dry weight ratio and the relative water content at which they reached zero turgor were small and inconsistent. At 18 days after rewatering, the Ψπ100 value of acclimated leaves was still 0.18 MPa lower than that of the control leaves.
The substantial shift in Ψ0 gained the stress-acclimated leaves only one extra day before they lost turgor at 1400 h, and only 2.5 extra days before being permanently wilted. This small gain in time and the rapid cessation of leaf growth even before positive turgor was completely lost suggests that osmotic adjustment may not contribute greatly to continued leaf growth in water-stressed plants of buffel grass.
Light, Leaf Expansion and Seed Yield in Sunflower
Authors: Rawson HM , Hindmarsh JH
Published: January 2006

Two sunflower hybrids, Hysun 31 and Suncross 150, were grown in the field with adequate irrigation and given three light treatments throughout their life cycle. The treatments were 100, 50 and 20% sun (high, medium and low light); during the vegetative period the high light treatment averaged more than 20 MJ m-2 day-1 total short-wave radiation.
The two cultivars, although differing in many of the leaf and plant growth parameters measured, followed the same trends with respect to light. A reduction from 100 to 50% light delayed the appearance of leaves slightly but had no effect on patterns of leaf-area expansion such as the rate and duration of expansion of individual leaves and the distribution of leaf area among nodes. A further reduction in light, however, significantly reduced the size of all leaves through effects on the rates at which leaves expanded. There was no effect of light level on the period for which leaves expanded.
Whilst leaf expansion remained unaffected by a reduction from high to medium light, specific leaf weight was significantly reduced to 76% of control levels. The lowest light regime further reduced specific leaf weight to only 59% of control levels.
Total plant weights declined to 89% (not significant) at the medium light level and significantly to 47% at the low level and as harvest index was marginally, though not significantly, decreased by a reduction in light, these values translated into significant reductions in seed production (86 and 44% of controls).
Longitudinal Transport of Sucrose and Amino Acids in the Wheat Grain
Authors: Donovan GR , Jenner CF , Lee JW , Martin P
Published: January 2006

The idea that sucrose and amino acids are transported along the furrow of the grain by dissimilar mechanisms has been tested by culturing detached ears of wheat on mixtures of [14C]sucrose and [3H]-labelled amino acid for short periods. The grain was cut transversely into slices 1 mm thick and radioactivity in the soluble fraction was measured. After 4-12 min of transport there was a steep downward gradient of radioactivity from the proximal to the distal end of the grain; and the logarithm of the amounts of both isotopes in the slices was related to distance from the proximal end. Apart from differences in the steepness of the gradients among the amino acids, and between sucrose and some amino acids, qualitative features of the distribution of sucrose and amino acids were indistinguishable from each other. Sucrose was not metabolized during its movement along the grain, but amino acids were metabolized before and/or after they reached the grain.
We conclude: (1) there is no substantive evidence for the operation of different mechanisms for the transport of sucrose and amino acids along the furrow; (2) both classes of solute are transported in the phloem; (3) metabolism of amino acids occurs before and/or after transport in the phloem; (4) differences among the slopes of the profiles of radioactivity may be attributable to variation in diffusion coefficient of the transported solutes.
Changes in Peroxidase in Isolated Aleurone Layers in Response to Gibberellic Acid
Authors: Gubler F , Ashford AE
Published: January 2006

The effect of gibberellic acid (GA3) on peroxidase activity and isoenzyme complement was followed in isolated aleurone layers of barley (Hordeurn vulgare L.) over a 48-h period. A high level of peroxidase activity was initially present in freshly isolated aleurone layers. Disc electrophoresis resolved nine peroxidase isoenzymes. By 36 h incubation, total peroxidase activity had doubled in response to GA3 and two new peroxidase isoenzymes were observed. Peroxidase release from isolated aleurone layers was also greatly stimulated by GA3 and more isoenzymes were found in the medium. The time course of release was similar to that for α-amylase. Peroxidase activity in endosperm of whole germinating grains began to increase after 2 days, peaked at 4 days and subsequently declined.
On the Nature of Carbon Isotope Discrimination in C4 Species
Authors: Farquhar GD
Published: January 2006

Theory is developed to explain the carbon isotopic composition of plants with the dicarboxylic acid (C4) pathway of carbon fixation. It is shown how leakage of inorganic carbon from the bundle sheath cells to the mesophyll cells can affect carbon isotopic discrimination. It is suggested that different types of C4 pathways will show variation in the degree of leakiness, reflecting variations in anatomy, and in the requirements for oxygen egress from the bundle sheath cells. It is also suggested that quantum yields may reflect these variations. A simplified expression is developed relating discrimination to leakiness and the ratio of intercellular and atmospheric partial pressures of CO2.
Influence of Environmental Factors on the Light Activation of Pyruvate, PI Dikinase and NADP-Malate Dehydrogenase in Maize
Authors: Nakamoto H , Edwards GE
Published: January 2006

The interaction among several environmental factors on the degree of light activation of NADP- malate dehydrogenase (MDH, EC 1.1.1.82) and pyruvate,PI dikinase (EC 2.7.9.1) in the C4 plant maize was determined. At 25°C under limiting light (50 �E m-2 s-1), there was a several-fold stimulation in the degree of activation of both enzymes when CO2 was removed from the atmosphere. Under high light (1000 �E m-2 s-1), CO2 did not influence the degree of activation of the enzymes.
At 25°C under limiting light in the absence of CO2, the degree of activation of NADP-MDH increased as O2 was reduced below 21% with maximum activation occurring under anaerobic conditions. O2 had little or no effect on the degree of activation of NADP-MDH under high light. In contrast, with pyruvate,PI dikinase at 25°C and in the absence of CO2, anaerobic conditions strongly inhibited the degree of activation of the enzyme under low or high light, while under aerobic conditions the enzyme was activated to the same extent under 2 or 21% O2. The inhibition of activation of the dikinase under anaerobic conditions was partially relieved by addition of atmospheric levels (0.03%) of CO2. In contrast to the results at 25°C, the presence or absence of CO2 or O2 at 10°C under low light had little or no effect on the activation of the two enzymes.
The results are evaluated in relation to previous in vitro studies which suggest activation of NADP- MDH by reduction of disulfide bonds on the enzyme and activation of pyruvate,PI dikinase by changes in adenine nucleotides.
Diurnal and Spatial Variation in Leaf Water Potential and Leaf Conductance of Irrigated Peach Trees
Authors: Olsson KA , Milthorpe FL
Published: January 2006

Leaf water potential, conductance and relative water content were measured in three layers of the canopy of large peach trees during imgation cycles. In the top layer, leaf water potential decreased from early morning until the early afternoon reaching values ranging from about -1.8 MPa soon after irrigation to -2 5 MPa at the end of a drying cycle; leaf conductance (mean about 0.42 cm s-1) decreased slightly during this period but did not appear to be influenced by water potential at values higher than about - 1 .9 MPa. From early afternoon to late evening, leaf conductance continued to decrease and water potential increased. Similar cycles were noted in the middle and lower layers except that water potential was always higher and conductance lower. A high degree of exposure of leaves to insolation appeared to result in low potentials and high conductances. The adequacy of current imgation recommendations for high productivity is discussed.