bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of atmospheric CO2 concentration on the protein, starch and mixing properties of wheat flour
Authors: Rogers G.S. , Gras P.W. , Batey I.L. , Milham P.J. , Payne L. , Conroy J.P.
Published: January 2006

Wheat (Triticum aestivum L.) cultivars Hartog and
Rosella were grown at CO2 concentrations of 280
µL L-1 (representing the
pre-industrial CO2 concentration), 350
µL L-1 (ambient) and 900
µL L-1 (an extreme projection of atmospheric
CO2 concentration). The plants were grown in naturally
lit glasshouses in 7 L pots containing soil to which basal nutrients had been
added and the pH adjusted to 6.5. Hartog yielded 2.4 g of grain per plant when
grown at 280 µL CO2
L-1. This yield was increased by 38% and
75% at CO2 concentrations of 350
µL L-1 and 900
µL L-1 respectively. These
changes were due to increases in both grain number and individual grain weight
as the level of CO2 was raised. The yield of Rosella was
unaffected by altering the CO2 concentration. Increasing
the CO2 concentration reduced grain protein
concentration of cv. Hartog from 17.4% at 280
µL CO2
L-1 to 16.5% and 16% at
CO2 concentrations of 350 µL
L-1 and 900 µL
L-1 respectively. The grain protein concentration of cv.
Rosella was reduced from 10.7% to 10.2% by increasing the
CO2 concentration from 280
µL L-1 to 350
µL L-1; however, an
additional increase in the CO2 concentration to 900
µL L-1 had no effect on
grain protein concentration. In Hartog flour, the highest proportion of
polymeric protein in the flour (7.7%) occurred at 280
µL CO2
L-1. This was reduced to 6.3% at 350
µL CO2
L-1 but then increased again to 7.0% at 900
µL CO2
L-1. These changes in concentration of polymeric protein
were correlated (r2=0.58)
with changes in mixing properties. The mixing time required to produce optimum
dough strength was greatest at 900 µL
CO2 L-1 (181 s), then 141 s and
151 s at 350 µL CO2
L-1 and 280 µL
CO2 L-1 respectively. These
changes in mixing time could not be explained by changes in grain protein
concentration. The proportion of ‘B’ starch granules (<10
m diameter) increased from 25% of total weight of
starch at 280 L CO2
L-1 to 30% at CO2
concentrations 350 and 900 µL
L-1. There were generally no effects of
CO2 concentration on dough mixing properties or starch
granule size distribution for Rosella.
Changes of Enzyme Activity During Pollen Germination in Maize, and Possible Evidence of Lignin Synthesis
Authors: Liu Zin-Huang , Ger Mang-Jye
Published: January 2006

During pollen germination in Zea mays L., the activity
of phenylalanine ammonia-lyase and peroxidases increased, accompanied by a
decline of phenolic compounds. Levels of IAA decreased dramatically as the
pollen germinated, and this decline was correlated with enhanced IAA oxidation
activity by IAA oxidase in the germinated pollen. The cationic peroxidase
isozymes (pI 9.0) with estimated molecular mass of 45 kDa may be involved in
lignin polymerisation in the pollen cell wall.
Instantaneous and Developmental Effects of Low Temperature on the Catalytic Properties of Antioxidant Enzymes in Two Zea Species
Authors: Hull Mark R. , Long Stephen P. , Jahnke Leland S.
Published: January 2006

When Zea mays cv. LG11 plants were grown 14˚C(close to the lower thermal limit for leaf expansion), three of the five enzymes of the active oxygen scavenging cycle (Halliwell-Asada Pathway) showed changes in total leaf activity compared with growth at 25˚C. Two of theseenzymes, ascorbate peroxidase (APX) and glutathione reductase (GTR), were selected for further investigation. The effects of assay temperature on threekinetic parameters (Vmax,Km,Vmax/Km) were determined inextracts from Z. mays and compared with extracts fromits low temperature tolerant relative, Z. diploperennisIltis, Doebley & Guzman. The kinetic power(Vmax/Km) was determinedbecause the Km alone may not be a useful predictor of anenzyme’s effectiveness in situ. The decrease inthe kinetic power of APX on lowering the temperature to 5ºC was muchsmaller in Z. diploperennis thaninZ. mays. This suggests that theZ. diploperennis APX is better able to removeH2O2 at severely reducedtemperatures than is APX from Z. mays.Z. diploperennis had a twofold greater ascorbate poolthan the chilling-susceptible Z. mays. Only minordifferences were seen in the kinetic properties of GTR and the size of theglutathione pool between the genotypes.
The Effect of CO2 Enrichment and Irradiance on the Growth, Morphology and Gas Exchange of a C3 (Panicum laxum) and a C4 (Panicum antidotale) Grass
Authors: Ghannoum Oula , Caemmerer Susanne von , Barlow Edward W. R. , Conroy Jann P.
Published: January 2006

The effect of CO2 enrichment and irradiance on the
growth and gas exchange of two tropical grasses,
Panicum laxum (C3) and
Panicum antidotale (C4) were
investigated. The two species were grown at either 350 (low) or 700 (high)
µL L-1 CO2 concentration,
under 40% (low) or 100% (high) of direct sunlight and supplied
with ample water and nutrition. Elevated CO2 enhanced
plant dry weight at both irradiances in the C3 species
(1.41-fold and 1.71-fold increase at low and high light, respectively) but
only at high light in the C4 species (1.28 fold
increase). CO2 enrichment had no effect on the dry
weight of P. antidotale, when stem development was
suppressed by growth under artificial lighting. When measured at the
CO2 concentration at which they were grown, assimilation
rates were similar in the low and high CO2 grown plants,
for both species. However, when measurements made at low
CO2 were compared, CO2
assimilation rates of the high light, high CO2 grown
C3 and C4 species were lower than
those of their low CO2 grown counterparts. High
CO2 strongly reduced the stomatal conductance of both
species, while it affected the Rubisco content (30% decrease) of the
high light C3 species only. This work shows clearly that
C4 species can respond to CO2
enrichment under favourable growth conditions, and that acclimation to
elevated CO2 in pasture grasses does not necessarily
involve accumulation of non-structural carbohydrates or reduction of total N
or soluble proteins in source leaves.
Germination in Photosensitive Seeds: Does Phytochrome Stimulate Metabolism of GA19 and GA20 to GA1?
Authors: Plummer Julie A. , McChesney Catherine J. , Bell David T.
Published: January 2006

The effect of light on gibberellic acid (GA) metabolism was investigated in
Asteraceae seeds. White light (80 mmol m-2
s-1 PAR) increased seed germination in
Craspedia sp.,
Erymophyllum ramosum and
Rhodanthe chlorocephala subsp.
splendida compared with darkness. In these taxa, red
light (R, 640 nm, 8 mmol m-2 s-1)
stimulated and far red light (FR, 720 nm, 4 mmol m-2
s-1) inhibited germination, indicating the involvement
of phytochrome. Paclobutrazol, a GA biosynthesis inhibitor, reduced
light-stimulated germination and this was overcome by exogenous
GA3. GA3 and
GA1 promoted germination in the dark, but
GA19 and GA20, which are
precursors to GA1, generally did not. GAs were applied
to paclobutrazol-treated seeds which were incubated under either R or FR. Very
few paclobutrazol-treated seeds germinated without GAs under FR, and exposure
to R only marginally improved germination. Application of
GA19 or GA20 to
paclobutrazol-treated seeds increased germination in
Rhodanthe chlorocephala subsp.
splendida under R, with no germination under FR. This
trend was observed in Craspedia sp., but not in
Erymophyllum ramosum or
Rhodanthe floribunda. CGA 163′935, a
3b-hydroxylation inhibitor, and R and FR were used to investigate
phytochrome-stimulated conversion of GA19 and
GA20 to GA1. It could not be shown
that R was required for 3b-hydroxylation in light stimulated germination of
these species.
Effect of Calcium and Calmodulin on Intrinsic Heat Tolerance in Relation to Antioxidant Systems in Maize Seedlings
Authors: Gong Ming , Chen Shan-Na , Song Yi-Qian , Li Zhong-Guan
Published: January 2006

Pretreatment of maize (Zea mays L.) seeds with
CaCl2 solution significantly raised calcium and
calmodulin levels and enhanced intrinsic heat tolerance in maize seedlings.
This enhancement is specific to Ca2+ and cannot be
substituted by Mg2+. In contrast, treatments with the
Ca2+ chelator EGTA or plasma membrane
Ca2+ channel blockers La3+ or
verapamil lowered the intrinsic heat tolerance. Concurrent treatment with
Ca2+ and Ca2+ -channel blockers
(La3+, verapamil) also decreased the
Ca2+ -enhanced heat tolerance. In addition, calmodulin
antagonists chlorpromazine or W7 treatment eliminated the
Ca2+ -enhanced heat tolerance, whilst W5, a less active
analogue of W7, had little effect on the Ca2+ -enhanced
heat tolerance. Measurement of antioxidant enzyme activities and lipid
peroxidation showed that heat stress induced an oxidative stress in maize
seedlings. External Ca2+ treatment enabled the seedlings
to keep relatively higher activities of superoxide dismutase (SOD), catalase
(CAT) and ascorbate peroxidase (APX) and lower levels of lipid peroxidation
than Ca2+ -deficient treatments; on the contrary, EGTA
treatment led to more rapid loss of SOD, CAT and APX activities and higher
levels of lipid peroxidation in the seedlings under heat stress. In addition,
concurrent Ca2+ and W7 treatment weakened the effects of
Ca2+ treatment on SOD, CAT and APX activities and caused
more severe lipid peroxidation. These results suggested that external
Ca2+ can enhance the intrinsic heat tolerance of maize
seedlings. This enhancement requires the entry of external
Ca2+ into cells across plasma membranes and the
mediation of intracellular calmodulin, and is associated with the increase of
antioxidant system activity.
Phosphate and slow vacuolar channels in Beta vulgaris
Authors: Dunlop James , Phung Thai
Published: January 2006

Movement of phosphate through slow vacuolar (SV) ion channels and the effects
of phosphate on SV currents were investigated using vacuoles from
Beta vulgaris L. When the vacuoles contained 50 mM
phosphate, the addition of phosphate to the bath shifted the apparent reversal
potential for whole vacuole currents to more positive values, suggesting an
outward rectifying current due to movement of phosphate ions out of the
vacuole. However absolute values for reversal potentials obtained from the
current-voltage curves and tail currents for whole vacuoles suggested that the
membranes were relatively impermeable to phosphate. Single-channel data showed
that the vacuole preparations contained more than one species of ion channel
and therefore the whole-vacuole data will not give definitive information
about individual species of ion channels. One of the channels had a single
channel reversal potential that indicated a permeability of
H2PO4- ions
relative to Cl- of 7. The probability of this outwardly
rectifying channel being open had a marked dependence on voltage and, in these
experiments, it was effectively closed for potentials negative of +20 mV.
The single-channel conductance was 19.4 ± 3.1 pS with 50 mM
KH2PO4 in the vacuole and 10 mM
total phosphate concentration in the bath. A channel with these
characteristics has not been reported previously.
In addition to the data identifying a phosphate channel, it was found that the
presence of phosphate in the bath solution slowed the rate of activation of
the SV currents. This effect was partially reversed when phosphate was removed
from the bath.
High vapour pressure deficit and low soil water availability enhance shoot growth responses of a C4 grass (Panicum coloratum cv. Bambatsi) to CO2 enrichment
Authors: Seneweera Saman P. , Ghannoum Oula , Conroy Jann
Published: January 2006

The hypothesis that shoot growth responses of C4 grasses
to elevated CO2 are dependent on shoot water relations
was tested using a C4 grass,
Panicum coloratum (NAD-ME subtype). Plants were grown
for 35 days at CO2 concentrations of 350 or 1000
µL CO2
L-1. Shoot water relations were altered by growing
plants in soil which was brought daily to 65, 80 or 100% field capacity
(FC) and by maintaining the vapour pressure deficit (VPD) at 0.9 or 2.1 kPa.
At 350 µL CO2
L-1, high VPD and lower soil water content depressed
shoot dry mass, which declined in parallel at each VPD with decreasing soil
water content. The growth depression at high VPD was associated with increased
shoot transpiration, whereas at low soil water, leaf water potential was
reduced. Elevated CO2 ameliorated the impact of both
stresses by decreasing transpiration rates and raising leaf water potential.
Consequently, high CO2 approximately doubled shoot mass
and leaf length at a VPD of 2.1 kPa and soil water contents of 65 and
80% FC but had no effect on unstressed plants. Water use efficiency was
enhanced by elevated CO2 under conditions of stress but
this was primarily due to increases in shoot mass. High
CO2 had a greater effect on leaf growth parameters than
on stem mass. Elevated CO2 increased specific leaf area
and leaf area ratio, the latter at high VPD only. We conclude that high
CO2 increases shoot growth of C4
grasses by ameliorating the effects of stress induced by either high VPD or
low soil moisture. Since these factors limit growth of field-grown
C4 grasses, it is likely that their biomass will be
enhanced by rising atmospheric CO2 concentrations.
Corrigendum to: A model of frost impacts on seasonal photosynthesis of Eucalyptus pauciflora
[volume 25, No.1 (1998), pp 27-37]
Authors: King David A. , Ball Marilyn C.
Published: January 2006

A model of the time course of frost impacts on seasonal photosynthesis of
Eucalyptus pauciflora Sieb. ex Spreng. was constructed,
incorporating seasonal shifts in frost hardiness and both short- and long-term
impacts on the initial slope and saturated level of the photosynthetic light
response curve. The approach is an extension of Sands’ model
(Australian Journal of Plant Physiology, 1995,
22, 603–614) which calculates daily canopy
photosynthesis as a function of daily irradiance and temperatures without the
impacts of cold nights. Modelled effects of frost on cumulative photosynthesis
over 8 months were highly nonlinear and rather sensitive to the temporal
sequence of minimum temperatures and extent of frost hardening. Most of the
effects were associated with long-term damage caused by a few severe or
unseasonal frosts. Shifting either plant sensitivity or minimum temperatures
by several degrees had large impacts on predicted outcomes. These results are
consistent with other observations that the increase in frost severity
associated with land clearing is impeding eucalypt regeneration in interior
Australia and may be applicable to other frost-prone areas.
Carbonic anhydrases in the C3 -plant leaf cell
Authors: Ignatova Lyudmila K. , Moskvin Oleg V. , Romanova Alla K. , Ivanov Boris N.
Published: January 2006

Carbonic anhydrase (CA) activities of the mesophyll protoplasts from
Pisum sativum L. leaves (plasmalemma CA), the
supernatant after thylakoid precipitation (soluble CA), and the washed
thylakoids (thylakoid CA) were studied. It was found that the
Km (CO2)
were 104 mM for the plasmalemma CA, 20 mM for the soluble CA, and 9 mM for the
thylakoid CA. The activity of the last differed from the first two in response
to the inhibitor acetazolamide by increasing at submicromolar concentrations
of inhibitor. pH-dependencies of
Km
(HCO3-) for soluble CA and
thylakoid CA differed in that the former increased as pH increasd from 7.0 to
8.0, while the latter slightly decreased over this pH change. A comparison of
the pH-dependencies of the soluble CA and thylakoid CA dehydrase activities
expressed in Wilbur-Andersen units demonstrated that, while the activity of
soluble CA was unchanged over pH range 6–8, the activity of thylakoid CA
had a distinct pH optimum at pH 6.8–7.0. The possible functions of the
three forms of CA in the leaf cell of C3 -plants are
briefly discussed.
Carbon Reduction and Photosystem II Deficiency in Leaves of C4 Plants
Authors: Osmond CB
Published: January 2006

The Hill reaction and photosystem I activity of chloroplasts isolated from mesophyll and bundle sheath cells of Atviplex spongiosa and Sorghum bicolov was measured using narrow-band, high-intensity illumination of 646, 712, and 730 nm. The photosystem I reactions (methylviologen Mehler reaction and diphenylcarbazone reduction) were equally active in 646 and 712 nm light, whereas Hill activity was reduced by 70% in 712 nm light relative to 646 nm. Intact leaves were illuminated with 646 nm light and exposed to a pulse of 14CO2. The pulse was followed by a chase in 646,712, or 730 nm light or in darkness. In A. spongiosa leaves the movement of carbon from C4 acids to carbohydrates during the chase period only occurred to a significant extent in 646 nm light. In S. bicolor leaves, 712 nm light was almost as effective as 646 nm light in inducing the movement of carbon from C4 acids to carbohydrate. Evidently in this species carbon reduction is not entirely dependent on concurrent photosystem I + II activity for the provision of reducing potential. The data are discussed in relation to the deficiency of photosystem II activity in bundle sheath cells of S. bicolor.
Free Space Characteristics of Barley Leaf Slices
Authors: Pitman MG , Luttge U , Kramer D , Ball E
Published: January 2006

Measurements are described of free space content of barley leaf slices. It is shown that the leaf slices contain a Donnan free space of about 3 µ-equiv/g fresh weight of tissue at a concentration of 300 mN, together with a water free space occupying 0.21 ml/g fresh weight. The Donnan free space is shown to be located in cell walls, as in other tissues (beet discs, barley roots) but the water free space is largely due to cut or damaged cells, injected intercellular spaces, and surface films of solution. The results are discussed in relation to free space of intact leaves.
Control of Fruit Ripening in Peach, Prunus persica: Action of Succinic Acid-2,2-Dimethylhydrazide and (2-Chloroethyl)Phosphonic Acid
Authors: Looney NE , Mcglasson WB , Coombe BG
Published: January 2006

Fruits of Halehaven and Fragar peaches (mid- and late season respectively) were sampled and examined weekly during one complete growing season. The period of rapid growth following anthesis (stage I) was characterized by relatively high respiration and ethylene production rates. Fruits of both cultivars entered the subsequent period of slow growth (stage II) together. Ethylene production was low and respiration declined throughout stage II. Sprays of (2-chloroethyl)phosphonic acid (ethephon), but not succinic acid-2,2-dimethylhydrazide (SADH), resulted in increased ethylene evolution by stage II fruits. Neither chemical altered respiration or the duration of stage II. Both chemicals, however, advanced commercial harvest and promoted ripening of fruits sampled throughout the final rapid growth period (stage III). All fruits sampled during stage III showed a climacteric-like increase in respiration and ethylene production. The horticultural effectiveness of SADH and ethephon appears to be due to a promotion of physiological activity in stage III. Abscisic acid in peach pericarp increased just before and during stage III. Possible roles for abscisic acid and ethylene in regulating the stage II-stage III transition in peaches and other fruits are discussed.
Chemical Regulation of Plastid Development. II.* Effect of CPTA on the Ultrastructure and Carotenoid Composition of Chromoplasts of Capsicum annuum Cultivars
Authors: Simpson DJ , Rayman FMM , Buckle KA , Lee TH
Published: January 2006

Electron microscopy of the fruit of three C. annuum cultivars, two with red fruit and one with yellow, showed that the chromoplasts of each cultivar contained fibrils, although carotenoid distribution of the red cultivars differed greatly from that of the yellow cultivar. The fibrils had a microfibrillar ultrastructure. The chloroplast-chromoplast transformation in C. annuum fruit as well as the carotenoid distribution were affected by 2-(4-chlorophenylthio)ethyldiethylammonium chloride (CPTA). The synthesis of capsanthin and capsorubin, which are responsible for the colour of the red cultivars, was inhibited. The level of β-carotene was reduced in all three cultivars, accompanied by the accumulation of lycopene, γ-carotene and neurosporene. Chromoplasts of CPTA-treated fruit lacked fibrils but contained plastoglobuli. The inhibition of fibril formation at an early stage was interpreted as evidence for the genesis of fibrils from plastoglobuli. It seems likely that fibril formation is under separate genetic control, independent of carotenoid synthesis. * Part I, Aust. J. Plant Physiol., 1974, 1, 119–33.
Can Externally Applied Atp Supply Energy to Active Ion Uptake Mechanisms of Intact Plant Cells?
Authors: Lüttge U , Schöch EV , Ball E
Published: January 2006

ATP applied in the external medium of leaf slices and bundle-sheath preparations at concentrations between 1.0 and 2.5 mM apparently enhances K+ uptake. However, this effect depends on the presence of Ca2+ or Mg2+ in the medium. ATP is shown to release a Ca2+ or Mg2+ inhibition of K+ uptake. If the Ca2+ or Mg2+ content of the medium is varied and EDTA used to mimic the effect of ATP, it can be demonstrated that the observed effect of ATP is entirely explicable by its chelation of divalent cations. Externally applied ATP has similar relative effects on K+ uptake under control conditions and under conditions where metabolism is inhibited, and although it apparently fully releases metabolic inhibition, these experiments reveal ambiguities which are discussed. It is con- cluded that apparent effects of externally applied ATP may often be indirect. The possibility of specific, i.e. energy-providing, effects can nevertheless not be ruled out in principle, but more sophisti- cated experimentation than found hitherto in the literature is required to demonstrate such effects.
Structure, Carbon Dioxide Fixation and Metabolism of Stomata
Authors: Pearson CJ , Milthorpe FL
Published: January 2006

Studies were made of the structure and rates of CO2 fixation of epidermis and of changes in organic metabolites in Commelina cyanea during transition to light and dark in both normal and CO2-free air. Guard cells of C. cyanea and Vicia faba contain numerous highly developed mitochondria and starch-forming chloroplasts (mitochondria: chloroplast ratios of 3 : 1) in comparison to other epidermal cells with few mitochondria and rudimentary plastids without starch. Their rates of photosynthesis per chloroplast appeared to be at least as high as those of the mesophyll, but circumstantial evidence suggested that about half of current photosynthate was respired. The rate of CO2 fixation in the dark was about 0.2–0.4% of that in the light. Illumination caused an increase, and darkening a decrease, of aperture, malate, and organic acid 1% within the epidermis of C. cyanea. Darkening in CO2-free air was accompanied by only slight decreases in aperture and malate. There were close positive correlations between aperture and concentration of malate and between aperture and organic acid 14C. During opening, the rise in organic acid 14C was associated with a decline in amino acid 14C. It is suggested that organic acids may be formed through aspartate and possibly also from sugars and other amino acids entering the tricarboxylic acid cycle. Concentrations of sugars were not related to aperture although they increased on illumination and declined about 2 h after darkening. Polysaccharide concentrations in the epidermis of darkened leaves were similar to those in illuminated leaves.
Some Aspects of Protein Metabolism in Tamarix tetragyna Roots Grown in a Saline Substrate
Authors: Bar-Nun N , Polyakoff-Mayber A
Published: January 2006

Various aspects of protein metabolism were studied in T. tetragyna roots grown at various levels of salinity. Salinity in the growth medium as well as salinity present in the reaction mixture interfered with uptake and incorporation of L-[14C]leucine into a fraction insoluble in trichloroacetic acid. Uptake did not appear to limit incorporation, although both processes were affected by salinity. Growing the roots in – 3 atm NaCl increased their ability for uptake and incorporation of the externally supplied amino acid. Salinity during growth resulted in both quantitative and qualitative changes in the natural amino acid composition of the fraction insoluble in trichloroacetic acid. The amount of proline and hydroxyproline increased considerably, while valine and methionine decreased. Methionine sulphoxide and another unidentified substance were found only in the proteins of roots grown in the presence of high levels of salinity. Salinity also induced an increase in the hydroxyproline content of the cell wall fraction and modified the metabolism of exogenously supplied labelled proline. The results are compared with the effects of salinity on protein metabolism of pea roots, and the differences noted.
Some Chemical and Morphological Changes Induced by Gibberellic Acid in Embryo-free Wheat Grain
Authors: Fincher GB , Stone BA
Published: January 2006

Chemical changes which occur in components of the cell walls of wheat endosperm have been followed during gibberellic acid induced modification of embryo-free wheat grain. Water-soluble polysaccharides, which are mainly arabinoxylans, increased approximately threefold in yield during 3 days treatment with gibberellic acid while their molecular weights decreased progressively. The changes in arabinogalactan-peptide were obscured by the large increases in low-molecular-weight arabinoxylan but were probably slight. Parallel morphological studies using the scanning electron microscope showed that degradative changes occurred initially in the subaleurone endosperm and progressed towards the central endosperm. Between 1 and 2 days modification, cell walls in the subaleurone endosperm were pariially degraded and there was a rapid disappearance of matrix protein. Erosion of starch granules became apparent later. The results show that under conditions simulating germination, arabinoxylan depolymerizing enzymes are operating in addition to starch and protein hydrolases. Their action is manifest at a very early stage and the pattern of erosion of cell walls is consistent with the progressive liberation of arabinoxylan hydrolases from the aleurone or alternatively to the progressive activation or release from inhibition of a latent form of the enzyme in the endosperm.
An Electron Microscope Study of the Outer Layers of Barley Leaves Infected with Rhynchosporium secalis
Authors: Ryan CC , Grivell CJ
Published: January 2006

An electron microscopic examination was made of barley leaves before and after infection by R. secalis. Ruthenium red was used as an electron-opaque stain for pectic material. In uninfected leaves the adaxial surface consisted of wax, cuticle, pectic and inner and outer layer of the epidermal cell wall. Following penetration, infecting hyphae grew between the pectic layer and outer layer of the epidermal wall. The pectic and cuticular layers remained largely intact in leaf lesions until conidia were produced, whereas the cell wall was degraded and replaced by hyphae.
Changes in RNA-Synthesizing Activity and Template Activity in Nuclei From Cotyledons of Developing Pea Seeds
Authors: Millerd A , Spencer D
Published: January 2006

Using Pisum sativum grown under controlled conditions, the pattern of cotyledon development has been defined in terms of fresh and dry weight, number of cells, and content of chlorophyll, starch, DNA, RNA and protein. The onset of storage-protein synthesis has been determined using antibodies to purified vicilin and legumin. During growth by cell expansion, DNA per nucleus of the parenchymatous cotyledon cells increases to an average of 50 C. Measurements of the endogenous RNA polymerase activity of nuclei and the template activity of chromatin isolated at various stages during seed development, suggest that the DNA beyond 2 C level does not contribute in a major way to RNA synthesis, although its template activity per unit of DNA is not diminished.
Activity, Location and Role of NAD Malic Enzyme in Leaves With C4-Pathway Photosynthesis
Authors: Hatch MD , Kagawa T
Published: January 2006

C4 acid decarboxylation in many C4-pathway species is accounted for either by an NADP-specific malic enzyme or phosphoenolpyruvate carboxykinase but a major group lack these enzymes. The present paper provides evidence for the mediation of C4 acid decarboxylation in this group by an NAD malic enzyme located in bundle sheath mitochondria. This enzyme was most active with NAD and Mn2+ and, depending upon its source, activity was stimulated 5- to 15-fold by low con- centrations of CoA or acetyl-CoA. The activity in leaf extracts was 20-50 times that found in other groups of C4 species or in C3 species and was commensurate with the enzyme having an integral function in photosynthesis.
For most species showing high NAD malic enzyme activity there was little activity when Mg2+ replaced Mn2+ and the low activity recorded with NADP was not activated by CoA or acetyl-CoA. In others there was an activator-dependent rate with NADP equivalent to 25-30% of the rate with NAD. Evidence for the location of the NAD malic enzyme in bundle sheath mitochondria is provided. On the basis of these and earlier studies a detailed scheme is proposed to account for decarboxylation of aspartate derived from mesophyll cells.
Carbon Dioxide and Water Vapour Exchange Parameters of Photosynthesis in a Crassulacean Plant, Kalanchoe daigremontiana
Authors: Allaway WG , Austin B , Slatyer RO
Published: January 2006

In 16-h days and under a 26/19°C day/night temperature regime, leaves of K. daigvemontiana took up CO2 in the daytime as well as at night. Daytime net CO2 uptake was in two periods: an initial one about 5 h long, in which net uptake rose to a maximum and then fell to near zero; and, after a period in which stomata were closed and CO2 exchange did not take place, a second period of
net uptake. In this second period net uptake rose rapidly to a steady rate which was maintained for
about 8 h until the end of the day. In this period, mean rate of light-saturated photosynthesis in
normal air was 25 ng cm-2 s-1; maximum obtainable photosynthesis rate averaged 87 ng cm-2 s-1
at this time. These values are considerably lower than those to be expected for C3 plants. The
internal resistance to CO2 uptake averaged about 8 s cm-l. In normal air, leaf resistance to water
vapour diffusion averaged about 8.5 s cm-1 in the steady period of photosynthesis. Both these
resistances are higher than those often reported for C3 plants, and may explain the low photosynthetic
rates. The CO2 compensation point during the period of steady photosynthesis was about 51 μ 1/1 (92 ng cm-3). This value, together with some biochemical evidence from pulse-chase experiments, suggests that photosynthesis in the last 8 h of the light period follows a C3-type pathway.
Translocation of Photosynthetic Assimilate From Grass Leaves, as Influenced by Environment and Species
Authors: Lush WM , Evans LT
Published: January 2006

The export of 14C-labelled photosynthate from leaves of two grasses with Calvin cycle (C*3) photosynthesis, and five grasses with the C4 dicarboxylic acid pathway, was followed by continuous monitoring through the hours in light immediately after assimilation of 14CO2 and also through the subsequent dark period.
The proportion of activity exported in the first few hours was much greater in all C4 grasses than in the C3 species, being greatest in the C4 grasses best adapted to growth at cool temperatures. Large differences between species were also apparent in their rates of assimilate export per unit leaf area, but there was no consistent relation between these rates and the cross-sectional area of phloem serving a given catchment leaf area. The rate of assimilate transfer per unit phloem area in Lolium temulentum was comparable to rates previously recorded for other C3 plants, but the rates for all C4 grasses except Digitaria sanguinalis were considerably faster.
The rate of export in Paspalum dilatatum increased progressively up to the highest light intensity used, giving no evidence of saturation of translocation capacity. It was greater in plants grown under higher light intensities, and increased with increasing sink demand, but was not increased by darkening or removing the leaf blade distal to the area exposed to 14CO2 in Lolium temulentum.
Most of the photosynthate not exported within 6 h was stored as polysaccharide in Panicum maximum, and was subsequently mobilized over a brief period during the following night. 14C assimilated at the end of the light period was mobilized first, while that assimilated at the beginning of the day was mobilized only at the end of the following night. However, the rate of mobilization could be increased by partial defoliation or by other treatments which increased the demand for assimilates from the leaf. The time to mobilization was unaffected by night temperature in Lolium temulentum, but increased markedly at temperatures below 15°C in the C4 grasses Panicum maximum and Paspalum dilatatum.
The adaptive value and some possible explanations of the differences between C3 and C4 grasses in their translocation of assimilates are considered.
Longitudinal Translocation of 14C-Labelled Assimilates in Leaf Blades of Lolium temulentum
Authors: Lush WM , Evans LT
Published: January 2006

The distribution of 14C activity in leaf blades of L. temulentum following application of 14CO2 to a small area near the middle of the blades was studied over periods of up to 6 h. The profiles of 14C activity towards the leaf base comprised several regions. The very steep logarithmic profiles within a few centimetres of the area exposed to 14CO2, and symmetrical about it, were shown to be probably due to diffusion of gaseous 14CO2 within the leaves prior to its photosynthetic fixation.
The major profile region represented the movement of a pulse of 14C activity, in the hour following exposure to 14CO2, down the leaf at speeds of 40-84 cm/h. The activity in this pulse was attenuated along the pathway, the attenuation decreasing with increase in distance moved. In leaves harvested more than 1 h after exposure to 14CO2, there was an irregular transition zone between these two logarithmic profile regions which may represent a later or slower-moving component of translocation. In leaves harvested less than 30 min after exposure to 14CO2, there was an increase in slope at the profile front which was not attributable to changes in phloem cross-section relative to leaf catchment area.
No steady acropetal movement of 14C activity was detected, but some activity was found in the distal areas of even the earliest-harvested leaves. Long, parallel-veined leaves of grasses may well provide suitable systems for more detailed analysis of translocation profiles.
Pathways of CO2 Fixation in the CAM Plant Kalanchoe daigremontiana. I Patterns of 14CO2 Fixation in the Light
Authors: Osmond CB , Allaway WG
Published: January 2006

Leaves of K. daigremontiana from plants grown under controlled conditions were exposed to 14CO2
in the light for 15 s followed by a chase in 12CO2. During steady-state photosynthesis in the late light
period the pulsechase labelling of photosynthetic intermediates was very similar to that observed in
the C3 plant Atriplex patula subsp. hastata. Labelling of C4 acids and the distribution of 14C within
[14C]malate isolated from leaves of K. daigremontiana in these experiments suggest that these acids
arise by a secondary carboxylation of labelled phosphoenolpyruvate. During the initial burst of
photosynthesis following the night period, pulse-chase labelling of photosynthetic intermediates was
quite similar to that observed in A. spongiosa, a C4 species. Degradation of labelled malate suggests
that the C4 acids are formed largely by the primary carboxylation of phosphoenolpyruvate during the
initial burst of photosynthesis and that these intermediates mix with the pool of malate formed in
previous dark fixation. Growth conditions which substantially alter the proportion of CO2 fixed
during the clay and night did not alter the pulse-chase behaviour of photosynthetic intermediates.
Rapid Translocation in the Phloem of Wheat Roots
Authors: Passioura JB , Ashford AE
Published: January 2006

When wheat seedlings are forced to grow with only one seminal root, very high rates of mass transfer occur in the phloem of the root base. This transfer is many times faster than any reported in phloem from other tissue, and is too fast to be explained by either motile or electro-osmotic mechanisms. However, it does not conflict with the M�nch hypothesis providing the usual assumption is made that the sieve pores are not blocked. Despite the unusually rapid transfer, the growth of the roots appears to be in no way limited by the ability of the phloem to transport assimilates to the growing points.
Some Observations on Salinity-induced Crassulacean Acid Metabolism in Mesembryanthemum crystallinum: Effect of Ouabain
Authors: Van Zyl J , Pallaghy CK , Connor DJ
Published: January 2006

Plants grown in uncovered pots and watered daily with either 350 mM KCl or NaCl showed a net
uptake of CO2 during the day followed by CO2 release during the night, whereas plants grown under
identical conditions, but in polyethylene-covered soil (covered pots) showed net CO2 accumulation
and acidification during the night phase (CAM expression). Spraying the tops of plants with 5 mM
ouabain either induced CAM in the case of plants grown in uncovered pots or enhanced CAM in
plants grown in covered pots. This effect of ouabain and some aspects of the gross ion relations of
M. crystallinum are discussed.
Plasmalemma and Tonoplast Influxes of Potassium in Barley Roots, and Interpretation of the Absorption Isotherm at High Concentrations
Authors: Robinson JB , Laties GG
Published: January 2006

Estimates of plasmalemma influx and steady-state vacuolar influx of potassium in low-salt barley roots have been obtained in the concentration range 10-80 mM by the use of controlled loading and washing times. Both fluxes are reduced by preloading the tissue in solutions containing potassium. When the experimental temperature is increased from 20 to 30°C, an apparent increase in the steady-state vacuolar influx occurs; separation of this flux from the apparent plasmalemma influx is not possible. The data support the hypothesis that the kinetics of potassium exchange in barley root tissue may be confounded by both loading time and temperature, and thus interpretation of the influx isotherm in the high concentration range is difficult. Where experiments are carried out at 20-25°C the steady- state vacuolar influx is measured unless closely defined experimental conditions obtain. At higher temperatures the plasmalemma influx may be measured.
Effect of Light Intensity and Temperature on Photosynthetic Rate, Leaf Starch Content and Ultrastructure of Paspalum dilatatum
Authors: Forde BJ , Whitehead HCM , Rowley JA
Published: January 2006

;Paspalum dilatatum plants were grown in growth cabinets under two light intensities (224 and 90 W m-2) at day/night temperatures of 27.5/20.0, 20.0/12.5, 17.5/12.5 and 15.0/10.0°C. Additional plants were grown in the glasshouse and outside.
Relative growth rate was closely correlated with the mean hourly photosynthetic rate of the plant during the day.
Starch varied from 0.8 to 5.3 % of the leaf dry weight at the end of the night and from 3.0 to 11.6% at the end of the day. Photosynthetic rate of cabinet-grown plants remained constant during the day as starch accumulated. The rate declined for plants from outside, although their leaf starch levels were no higher than those of cabinet-grown plants. No evidence was found of feedback repression of photosynthetic rate caused by assimilate accumulation.
There was only minor variation in mesophyll chloroplast structure between plants grown at different light intensities at the same temperature. A decline in temperature below 20.0/12.5°C increased swelling of mesophyll chloroplasts, as well as reducing development of the peripheral reticulum. The structure of bundle sheath chloroplasts was little affected by the environment apart from its effect on starch accumulation.
While growth rate increased rapidly as temperature increased, there was much less effect of temperature on accumulation of starch during the day. It was concluded that photosynthesis and the accumulation of starch are less sensitive to temperature than is overall plant growth.
Effects of Killing by Heat or Desiccation on Membrane Structure in Pea Roots
Authors: Buttrose MS , Swift JG
Published: January 2006

Radicles of dry pea seeds were killed by heating at temperatures up to 160°C, and root tips excised from pea seedlings were killed by desiccation. The effect of these treatments on the appearance of membranes was studied in the electron microscope after fixation and thin-sectioning and after freeze- fracturing, After fixation, membranes from dead tissue appeared modified in various ways compared with membranes from control tissue, whereas after freeze-fracturing they appeared unchanged. It is argued that heating and desiccation denature or disorganize structural protein in membranes but that they do not affect the lipid structure of the membrane.
Faris Banding in Panicoid Grasses
Authors: Taylor AO , Halligan G , Rowley JA
Published: January 2006

Transverse chlorotic lesions (Faris bands) develop on the leaves of some panicoid grasses after exposure to low night temperatures. Generally, the higher the day temperature and the lower the night temperature, the greater the number and intensity of the bands which are formed. Most plants, when maintained continuously under conditions which initially produced bands, ceased producing them after only a few days, which suggests that some adaptation process occurs.
Amongst the panicoid grasses there was a wide between-plant, between-species and between-genus variation in banding sensitivity; plants which produced fewest bands or required the lowest temperatures to produce bands frequently showed better growth at low temperatures. However, as there are some wide departures from this general rule, banding sensitivity would appear to be a poor selection criterion for low-temperature hardiness.
An Equilibrium Model of Leaf Water Potentials Which Separates Intra- and Extracellular Potentials
Authors: Acock B
Published: January 2006

A model is proposed which makes it possible to estimate the intracellular turgor pressure potential, intracellular osmotic plus matric potential, and intra- and extracellular soIution fractions of water in leaf tissue at any water content. The model requires only the data normally collected with a thermocouple psychrometer: total water potential of live and dead (cells ruptured) tissue at various known water contents. The major assumptions are that (1) the total potential of water in the solution fraction in any part of the tissue multiplied by the volume of water is constant; (2) extracellular water experiences no pressure potential; (3) matrix-bound water is held only by matric forces and contains no solute; (4) the solution fraction of the intracellular water is constant at high water content; and (5) matrix-bound water content is constant over the range of leaf water contents normally examined.
The models developed to deal with pressure bomb data are examined critically and doubts are cast on the validity of some of their assumptions.
Growth, Water Relations and Yield of Wheat
Authors: Connor DJ
Published: January 2006

Two crops of Sherpa wheat grown in successive years, but under contrasting seasonal conditions, were subjected to comprehensive environmental and biological measurement. An analysis is made of the changing state of water in the soil-plant system and of the consequent growth and the development of grain yield. The early pattern of growth was strongly influenced by moderate restriction in the availability of soil water (> - 200 J kg -1) and was associated with a marked shift in the allocation of growth resources in favour of root development. In both years, but more so in the second, grain filling proceeded under rapidly increasing plant water stress and senescence of productive photosynthesizing area. An analysis of the quantitative consistency of the biological and environmental data is attempted by the application of a published model of crop growth to the experimental data.
Translocation of Boron to Plant Fruits
Authors: Campbell LC , Miller MH , Loneragan JF
Published: January 2006

Fruit of peanut (Arachis hypogaea L.) and burrs of subterranean clover (Trifolium subterraneaum L.) were shown to develop in white siliceous sand which was low in boron. Fruit and seed production and yield did not vary with the boron nutrition given to the medium in which seeds developed.
The results suggest that for the development of their fruits, peanut and subterranean clover translocate boron in their phloem.
A Class of Lectins Present in the Tissues of Seed Plants
Authors: Jermyn MA , Yeow YM , Woods EF
Published: January 2006

The seeds of both angiosperms and gymnosperms (91 of 104 families tested) contain a specific glycoprotein lectin, which gel-diffusion experiments suggest to be widely present in plant tissues. This lectin will form an insoluble complex with tris-(4-glycosyloxyphenylazo)phloroglucinol where glycosyl = �-D-gluco-, D-galacto-, D-xylo-, malto-, lacto- or cellobiopyranosyl. In legume seeds the major part of the lectin is concentrated in the intercellular spaces as distinct globular bodies. The purification and analysis of the glycoprotein from a selection of species is described. Both protein and carbohydrate composition show little variation over the range. Hydroxyproline and glucosamine are present and the major sugars are galactose and arabinose. From ultracentrifugation studies the weight-average molecular weight of the Brassica napus lectin is 126 000. Since the carbohydrate:protein ratio is c. 8: 1, the protein moiety has a molecular weight of approx. 15 000. The sole N-terminal amino acid detected in the very similar Allium porrum lectin is tyrosine, suggesting that a single type of peptide chain is present. Neither the function of the lectin nor the reasons for its extraordinary evolutionary stability are known.
Influence of Water Stress on Water Relations and Growth of a Tropical (C4) Grass, Panicum maximum var. trichoglume
Authors: Ng TT , Wilson JR , Ludlow MM
Published: January 2006

The effects of recurring cycles of short-term water stress on the water relations and growth of P. maximum var. trichoglume in pots of soil were investigated under controlled conditions. As soil water content decreased there was an increase in the resistance to water movement in the soil-plant system. Leaf stomatal resistance increased and concomitantly transpiration rate decreased when soil water content fell below 37 % (soil water potential of - 1 .0 bars) and leaf water potentials were less than - 6 bars. The leaf water potential at wilting (- 8 to - 10 bars) and the relation between leaf water potential and relative water content changed with leaf position on the tiller.
The death of early-formed leaves on the plants was accelerated by water stress but, in contrast, the later-formed leaves died more rapidly in the control (unstressed) treatment so that finally the control plants had a higher proportion of dead leaves. Plant growth was reduced at soil water contents above the permanent wilting point. Reduction in net assimilation rate was the main determinant of lower relative growth rate of stressed plants over the initial cycles of stress but subsequently, as leaf area expansion was reduced, leaf area ratio also had a significant influence.
Water stress influenced growth directly, and also indirectly via its effect on plant development (ontogeny). Two techniques were used to separate the direct from the indirect effects on relative growth rate Some published data which suggest a stimulation of growth rate after the relief of stress are re-interpreted and the effect is shown to be due mainly to differences in ontogeny between stressed and control treatments