bluuebunny/crossref_metadata_2025 huggingface dataset:
Salt Stress and Comparative Physiology in the Gramineae. III. Effect of Salinity Upon Ion Relations and Glycinebetaine and Proline Levels in Spartina × townsendii
Authors: Storey R , Wyn Jones RG
Published: January 2006

S. × townsendii was grown at a number of salinity levels ranging from 0 to 800 mol m-3. Growth was suppressed by all salt treatments, but in particular, above 300-400 mol m-3. The osmotic pressure of the extracted shoot sap paralleled the rise in the osmotic pressure of the medium. Osmotic compensation was attributed to Na+ and Cl- accumulation at low salinities and to a lowered fresh weight : dry weight ratio at the higher salinities. In the shoots sf plants grown in 50-100 mol m-3 NaCl, Na+ accumulation exceeded the K+ decline. Root K+ was unaffected by all salt treatments. The shoot glycinebetaine content rose in response to external salinity and the accumulation of glycinebetaine was highly correlated (r = 0.99; P < 0.01) with the increase in sap osmotic pressure. Proline also accumulated in response to salt stress and was correlated with sap osmotic pressure (r = 0.98; P < 0.01). However, proline levels were much lower than those of glycinebetaine and became quantitatively significant only in shoots exposed to high inhibitory salinities.
Alteration in the Composition of β-Lectins Caused by Chemical and Enzymic Attack
Authors: Gleeson PA , Jermyn MA
Published: January 2006

Variation in the conditions of extraction of β-lectins from a number of seeds and plant tissues resulted in differences in the amino acid composition and the protein content of the isolated product. These differences may be due to differential extraction of the β-lectin, degradative losses of protein or carbohydrate components of the β-lectin, or a combination of these possibilities. Subtilisin treatment of the Alocasia macrorrhizos β-lectin removes 80% of the protein and the material remaining after enzymic treatment retains the capacity to bind to the Yariv artificial antigen. A number of β-lectins were treated with subtilisin and the amino acid compositions of the residual material were similar, with high contents of hydroxyproline, alanine and serine. The amino acid composition of the Phaseolus lunatus β-lectin was not altered by β-elimination. The capacity of the β-lectin to bind to the Yariv artificial antigens was eliminated by progressive acid hydrolysis under conditions where both glycosidic and peptide linkages may be labile.
Change of Flux of Orthophosphate Between Cellular Compartments in Ripening Tomato Fruits in Relation to Climacteric Rise in Respiration
Authors: Woodrow IE , Rowan KS
Published: January 2006

Slices cut from the pericarp of mature-green tomato fruit and incubated at 18°C in isotonic mannltol (0.25 M) containing 25 �M CaSO4 undergo changes in rate of respiration and in colour similar to whole ripening fruits. When fluxes of orthophosphate were analysed using washout techniques, the fluxes from vacuole to cytoplasm and from free space to cytoplasm increased markedly as the rate of respiration of the fruits from which they were cut increased. This is consistent with stimulation of the enzyme phosphofructokinase (previously identified as the point of regulation of respiration) by increasing concentration of orthophosphate at the enzyme site.
Photosynthesis and Partitioning of Dry Matter in Sunflower
Authors: English SD , Mcwilliam JR , Smith RCG , Davidson JL
Published: January 2006

Environmental and plant factors affecting photosynthesis in sunflower were studied in controlled environments and under field conditions. The response to temperature had a broad optimum around 27°C indicating that temperature is unlikely to limit photosynthesis of the crop under normal summer growing conditions. As found for most crops, carbon dioxide was the main factor limiting photosynthesis under optimum conditions of temperature and irradiance. Photosynthetic rates varied with the age and position of the leaf on the main stem. The maximum rate achieved by any leaf was obtained by fitting an exponential relationship of the form P = A(l -e-BI), which gave an adequate description of the light response curve. The photosynthetic rate of leaves increased to a maximum just prior to full leaf expansion and then declined. An increasing rate of photosynthesis was also characteristic of the leaf profile up the main stem, culminating in highest rates in the upper part of the leaf canopy.
These data indicate that the larger recently developed active leaves, which are produced on the upper part of the stem, have the greatest potential photosynthetic capacity and are most effective in supplying carbon assimilates at all stages during the development of the crop.
In the field, rates of photosynthesis for individual leaves were of the same order of magnitude and followed the same pattern as those recorded in controlled environments. Also, their diurnal patterns of photosynthesis and stomatal conductance were relatively unaffected by reduced water potentials as low as -2.0 to -2.5 MPa during the middle of the day.
The partitioning of dry matter in sunflower into the various above ground parts was characterized and at physiological maturity the seed represented 55% of the dry weight of the inflorescence but only 33% of the dry weight of the total plant. There was a linear increase with time in the oil content of the seed following fertilization, reaching a maximum at about 20-25 days, several weeks before the seed reached physiological maturity.
These data can provide the necessary response functions required for the photosynthetic submodel of a more comprehensive model to predict the yield and adaptation of sunflower under varying environmental conditions.
Growth, Maintenance and Nitrogen Fixation of Nodulated Plants of Subterranean Clover (Trifolium subterraneum L.)
Authors: Silsbury JH
Published: January 2006

Plants were grown in a nitrogen-free medium in pots to form a closed canopy. Over a 50-day period, the net CO2 exchange of the pot was measured; nitrogen fixation was estimated by acetylene reduction assay; chemical analyses were performed; and dry matter was determined. Growth and maintenance requirements were estimated in terms of CO2. Dry matter growth rate was almost constant with time, the value half-way through the experiment agreeing with an estimate calculated from the daily CO2-exchange rate and 37.4% carbon in the biomass. Nitrogen accumulation rate was nearly constant. The total daytime CO2 influx for thirteen successive pots during the experiment was almost the same. By contrast, the total dark CO2 efflux increased with time. After partitioning into growth and maintenance components, the increase was due to increase in maintenance. The proportion of the dark efflux attributed to growth was constant with increase in biomass over the range 200-600 gm-2 but the maintenance coefficient may have decreased slightly over this range. Nitrogen fixation rate was constant during the growth period and reproducible between pots: 2.86 moles acetylene were concluded to be equivalent to each mole of nitrogen fixed. As CO2 efflux decreased to the maintenance level in a dark period longer than the usual 12 h, acetylene reduction decreased to near zero. This suggests a close association between growth rate and the rate of nitrogen fixation.
Proteolysis in Cotyledon Cells of Phaseolus vulgaris L.: Changes in Multiple Hydrolase Activities Following Germination
Authors: Crump JA , Murray DR
Published: January 2006

Changes in activity of several hydrolytic enzymes were measured in extracts prepared from the cotyledons following germination of bean seeds (Phaseolus vulgaris cv. Hawkesbury Wonder). Aminopeptidase AP2 (phenanthroline-sensitive leucyl β-naphthylamidase), N-carbobenzoxy-L- tyrosine-p-nitrophenol ester (N-CBZ-L-Tyr-pNP) hydrolase, N-benzoyl-L-tyrosineethyl ester (BTEE) hydrolase and acid phosphatase all increased in activity per cotyledon, reaching maximum values after 4, 6, 10 and 10 days respectively. By comparison, aminopeptidase AP1 (phenanthrolineinsensitive leucyl β-naphthylamidase) showed maximum activity after 2 days and declined immediately. α-N-benzoyl-D,L-arginine-p-nitroanilide hydrolase activity was maintained at a maximum value between days 2 and 10 before declining. Differences in maximum activity per cotyledon, initial presence or absence, and timing of both increase and decrease of N-CBZ-L-Tyr-pNP and BTEE hydrolase activities suggest that at least two enzymes contribute to these activities, and that neither activity indicates the presence of a chymotrypsin-like endopeptidase.
Effect of Photoperiod and Temperature on Flowering in Pea (Pisum sativum L.)
Authors: Berry GJ , Aitken Y
Published: January 2006

Six pea varieties, early to late flowering, were grown in 16 environments made up of all combinations of four mean daily temperatures (6, 12, 18 or 24°C) and four photoperiods (8, 12, 16 or 24 h). For the earliest variety, days from sowing to first flower was inversely proportional to temperature, and independent of photoperiod. Sensitivity to photoperiod in the other five varieties was temperature-dependent. At 24°C, all were photoperiod-sensitive, but at 6°C only the latest three varieties were sensitive. Flowering was most rapid at 24°C in 24-h photoperiod. However, the lowest node of first flower occurred in 24 h photoperiod, irrespective of temperature. The duration of the period from floral initiation to first flower was independent of variety and photoperiod. Thus, any differences in flowering between varieties arose prior to floral initiation.
These differences are explained by three factors: different times to floral initiation in 24 h photoperiod, a photoperiod response in low temperature, and a photoperiod-temperature interaction. These factors are related to the flowering genes Lf, Sn and Hr and the 'units of maturity genotype'. The likely genotypes of the varieties are deduced from the reported action of these genes. Vernalization is interpreted in terms of high-temperature inhibition of flowering in short photoperiods. The effect of temperature on the relationship between node of first flower and days from sowing to floral initiation, and the influence of genotype and growing season on flowering time, are also discussed.
Analytical Approach to the Study of Circadian Leaf Oscillations in Clover. I. Recording and Spectral Analyses of Leaf Oscillations
Authors: Robinson GR , Rust TSO , Scott BIH
Published: January 2006

Problems in the spectral analysis of short oscillatory data records such as are obtained in circadian studies are discussed. The advantages and limitations of Fourier analysis are described and possible errors in parameter estimates are considered. These techniques are applied to a study of the degree of entrainment of the clover leaf (Trifolium repens L.) oscillation by sinusoidally varying white light. The results indicate that entrainment is not an all-or-none response but that frequency components due to both the natural and forcing oscillations may contribute to the leaf movement. A means of automatically recording leaf angle in a form suitable for computer processing is also described.
Effect of Leaf Position, Expansion and Age on Photosynthesis, Transpiration and Water Use Efficiency of Cotton
Authors: Constable GA , Rawson HM
Published: January 2006

Net photosynthesis, dark respiration and the response to photon flux density were measured on cotton leaves grown in a glasshouse. Leaves at four positions on the plant were examined from their unfolding until 70 days later. Photosynthesis and transpiration per unit of leaf area were unaffected by leaf position and, in all leaves, peak photosynthesis of about 110 ng CO2 cm-2 s-1 was attained 13-15 days after leaf unfolding, when the leaf was 75-90% of maximum area. Photosynthesis was maintained at this rate for only 12 days before declining linearly to values 20% of the maximum when leaves were 70 days old. Transpiration followed a similar pattern reaching a maximum of about 13 �g H2O cm-2 s-1 at 2 kPa vapour pressure deficit (VPD) at 13 days. Stomatal and internal conductances changed in parallel as leaves aged, with the consequence that internal CO2 concentration and water use efficiency remainedessentially constant at 220�ll-1 and 16.8 ng CO2 (�g H2O kPa VPD-1)-1 respectively.
Youngest and oldest leaves saturated at lowest light levels (400-800 pE m-2 s-1) while 16-18- day-old leaves had light saturation at 1100 �E m-2 s-1. The initial slope of the light response curves increased as leaves expanded up to 10 days age then remained constant at 0.25 ng CO2 cm-2 (pE m-2)-1. Dark respiration reached a maximum of 1.5 ng CO2 mg-1 s-1 5 days after leaf unfolding, when leaf dry weight was increasing most rapidly.
The relationship between the consistent pattern of gas exchange with age and the pattern of morphological development is discussed, along with internal factors associated with age-dependent photosynthesis.
Effects of photoperiod and paclobutrazol on growth dynamics of petioles in strawberry (Fragaria × ananassa)
Authors: Wiseman Nadine J. , Turnbull Colin G. N.
Published: January 2006

Petiole elongation of strawberry plants (Fragaria
× ananassa) is modified by photoperiod, and
gibberellins may mediate this response. To test the relationship further, we
measured petiole growth dynamics under short and long days, in comparison with
responses to paclobutrazol, which reduces gibberellin biosynthesis. Growth
rate in short days was lower after 2 days, and at its maximum was 60%
of long-day controls. Petiole length at maturity was 75%, and was
accounted for primarily by decreased cell length. Subsequent leaves showed
similar patterns, but in the third leaf, cell number was also reduced. Petiole
growth rate after treatment with paclobutrazol (5 mg
plant–1) was maximal at 2 days, 44% of the
control maximum at day 7. Mature length was 30% of controls, again due
to reduced cell length. Second leaves had even more severely reduced growth
rates. Increasing paclobutrazol concentration over the range 0.025–1.0
mg progressively reduced growth, but a gibberellin-independent component
accounted for 20% of elongation. Effects of combined paclobutrazol and
photoperiod treatments were additive. The normal short-day response therefore
occurred in paclobutrazol-treated plants with already slowed growth and
reduced capacity for gibberellin synthesis. We conclude that assessment of the
function of gibberellins requires direct measurement of gibberellins in
petioles during growth.
Osmotic Adjustment in Expanding and Fully Expanded Leaves of Sunflower in Response to Water Deficits
Authors: Jones MM , Turner NC
Published: January 2006

Sunflower plants were grown in large volumes of soil and slowly water-stressed by withholding water. The tissue water relationships of leaves at various stages of stress and of leaves of equivalent well watered controls were studied by the pressure chamber technique. Plants were stressed either when leaf 17 was expanding or when it was fully expanded. When expanding leaves reached a moderate level of stress (predawn leaf water potential of -0.9 MPa), the osmotic potentials at full turgor and zero turgor were lower than the control values by 0.1 MPa and 0.2 MPa, respectively. When fully expanded leaves were stressed to a similar degree (predawn leaf water potential of - 1.1 MPa), the osmotic potentials at full turgor and zero turgor were lower than the control values by 0.2 MPa and 0.3 MPa, respectively. The development of more severe stress in the fully expanded leaves was not accompanied by any further osmotic adjustment. However, when the expanding leaves reached a predawn leaf water potential of -2.3 MPa, the values of leaf osmotic potential at full turgor and zero turgor were lower than the values for the well watered plants by 0.4 MPa and 0.6 MPa, respectively. In expanding leaves prestressed to a predawn leaf water potential of -2.3 MPa, the osmotic potential at full turgor was significantly less than the control values for at least 7 days after rewatering. Stress had no effect on the bulk modulus of elasticity. It is concluded that both expanding and fully expanded sunflower leaves show osmotic adjustment.
Effect of Tiller Removal and Shading on Spikelet Development and Yield Components of the Main Shoot of Wheat and on the Sugar Concentration of the Ear and Flag Leaf
Authors: Kemp DR , Whingwiri EE
Published: January 2006

Continuous removal of tillers from wheat plants (cv. Gamenya) in an irrigated field crop resulted in an 86% increase in grain yield of the ear on the main shoot due, principally, to more kernels per fertile spikelet. On detillered plants 99% of spikelets were fertile with an average of 3.8 kernels per fertile spikelet compared with 91% and 2.4 for the control. Tiller removal increased spikelet numbers by 1 to a mean of 21.4 but did not affect the rate of production of spikelet primordia. The concentration of sugars (glucose, fructose, sucrose) in leaf bases at terminal spikelet formation and in leaf bases and ears just before ear emergence were the same in control and detillered plants. It was considered unlikely that tillers compete with the main shoot for carbohydrates thus limiting ear development and grain yields of the main shoot; instead, competition for reduced nitrogen may be involved.
Shading plants to 20% of full sunlight, especially during floret development, reduced grain yields per ear by 50% due to fewer kernels per fertile spikelet (2.2) plus a 32% decline in kernel weight. Tiller numbers and shoot size were reduced by shading while spikelet numbers were reduced by two compared with controls due to a reduced rate of production of spikelet primordia. Shading also reduced sugar concentrations relative to controls in leaf bases at terminal spikelet formation and in ears just prior to emergence. The supply of carbohydrates under shading was limited, affecting growth and grain yields.
A tryptophan residue involved in the inhibition of plant vacuolar H+-ATPase by 2-hydroxy-5-nitrobenzyl bromide
Authors: Kuo Soong Yu , Lin May Whei , Jiang Shih Sheng , Hung Shu Hsien , Tzeng Chi Meng , Pan Rong Long
Published: January 2006

Treatment of the vacuolar H+ -ATPase from mung bean
seedlings (Vigna radiata L.) with the tryptophan
modifying agent 2-hydroxyl-5-nitrobenzyl bromide (HNBB), caused a progressive
decline of the ATP hydrolysis activity and proton translocation in a time- and
concentration-dependent manner. Dithiothreitol could not restore the
inhibition of H+ -ATPase by HNBB, indicating possible
involvement tryptophan, and not cysteine residues. Protection studies
suggested that modified sites might not locate in the active domain. Kinetic
analysis shows that Vmax but not
Km of H+
-ATPase was changed by HNBB. The reaction order of inactivation by HNBB was
calculated as 0.98, implying that at least one tryptophan was labelled. The
steady-state dissociation constant
(Ki) and the pesudo-first-order
rate constant of inhibition (k2)
were determined as 1.61 mM and 0.22 min-1, respectively.
Furthermore, stoichiometry experiments indicated that 8 mol tryptophan/mol
ATPase were modified, when the enzyme activity was completely inhibited.
However, a Tsou analysis showed that only one out of these modified
tryptophans was crucial to the enzymatic activity. In addition, modification
of the vacuolar H+ -ATPase by HNBB led to a decrease in
intrinsic fluorescence, suggesting a possible conformational change of the
enzyme. Taken together, our data indicate that the tryptophan residue is
indispensable to vacuolar H+ -ATPase and the
modification of this residue may induce a significant conformational change,
consequently resulting in the loss of enzymatic activity.
Carbon dependency of the hemiparasite Striga hermonthica on Sorghum bicolor determined by carbon isotopic and gas exchange analyses
Authors: Pageau K. , Simier P. , Naulet N. , Robins R. , Fer A.
Published: January 2006

The development of autotrophy in Striga hermonthica
(Del.) Benth. parasitic on Sorghum bicolor L. was
quantitatively determined by
13C/12C isotope ratio analysis
and related to the photosynthetic capacity of the parasite. Net carbon
assimilation by the parasite was achieved within 4–5 days after
emergence and thereafter the photosynthetic capacity remained 3- to 5-fold in
excess of the respiratory rate. Nearly 40% of the dry matter of the
aerial parts of the parasite was derived from autotrophic assimilation after
only 7 days. While the development of the aerial parts continued to be
favoured, 65% of aerial dry matter being of autotrophic origin at 42
days, there was a shift towards the use of autotrophic photosynthate for root
development around the onset of flowering. When host aerial parts were cut off
50 days after emergence, the parasite exhibited reduced further growth, but
completed its life cycle autotrophically. As the
δ13C values in these plants were lower than in
plants that remain in association, we deduce that
S. hermonthica continues to benefit from heterotrophic
assimilation to the end of its life cycle.
Root phenolic accumulation and loss of autoregulation of root nodule formation in Bambara groundnut (Vigna subterranea) following boron nutrition and cotyledon excision
Authors: Muofhe Mmboneni L. , Dakora Felix D.
Published: January 2006

Effects of boron nutrition and cotyledon removal on nodulation and N
2 fixation were investigated on Bambara groundnut
(Vigna subterranea L. Verdc.) grown in the glasshouse.
Nodule number was siginificantly lower in boron-deprived plants relative to
those receiving 90 µM boron. As a result, the amount of N fixed was
markedly reduced in the zero-boron control plants. Phenolic content, measured
relative to the molar concentration of daidzein, an active phenolic nod gene
inducer from this species, was significantly lower in roots of boron-deprived
plants. However, with provision of 90 µM boron, plants significantly
increased root accumulation of total phenolics by 37%. HPLC analysis of
root extracts showed that the increase in phenolics was due to greater tissue
accumulation of the nod-gene-inducing daidzein, following the supply of 90
µM boron. The correlation between nodulation performance and increase in
tissue phenolics, especially daidzein, suggests that the increase in
nodulation and N 2 fixation with boron supply (90
µM) to intact plants was triggered by the greater accumulation of the
inducer molecule as a result of improved boron nutrition. However, removal of
seedling cotyledons also affected the number of nodules formed per plant.
Excision of cotyledons resulted in significantly reduced photosynthetic leaf
area, followed by a marked increase in the number of nodules per plant due to
loss of autoregulation of nodule formation. Boron supply and cotyledon removal
both increased nodule formation in Bambara groundnut plants, but via different
mechanisms.
An in vitro Assay of Sucrose Uptake by Developing Bean Cotyledons
Authors: Patrick JW
Published: January 2006

An in vitro procedure, based on net rates of sucrose uptake from [14C]sucrose solutions, was developed to determine the in vivo sucrose uptake rates of French bean (Phaseolus vulgaris L.) cotyledons. Net rates of in vitro sucrose uptake exhibited saturation kinetics and temperature dependency with Q10 values in the range 1.5-2.0. Optimal rates of net sucrose uptake were obtained in unbuffered media containing sucrose alone. Under sink-limited growth conditions, where in vivo free-space sucrose concentrations saturated (i.e. 90-145 mM) the sucrose uptake process, the in vitro procedure could account for in vivo gains of sucrose by the cotyledons.
An Analysis of the Effects of Repeated Short-Term Soil Water Deficits on Stomatal Conductance to Carbon Dioxide and Leaf Photosynthesis by the Legume Macroptilium atropurpureum Cv. Siratro
Authors: Fisher MJ , Charles-Edwards DA , Ludlow MM
Published: January 2006

The response was measured of stomatal conductance and leaf photosynthesis to changing leaf water potential in the legume siratro subjected to a sequence of I-week cycles of increasing soil water deficit followed by watering. The response of stomatal conductance was described using a continuous mathematical function, which is more robust and accurate than the usual discontinuous linear function used to analyse such data.
After seven successive cycles of water deficit, there was no apparent adjustment of the short-term response of leaf conductance to leaf water potential.
Effects of Chronic Ozone Exposure on the Growth of Trifolium subterraneum and Trifolium repens
Authors: Horsman DC , Nicholls AO , Calder DM
Published: January 2006

Plants of Trifolium subterraneum and T. repens were exposed to 9 parts per hundred million ozone for 4 h per day, 5 days per week for 5 weeks. Leaf necrosis was apparent after the first week of exposure and this was followed by the death of some leaves and stems. At the end of the exposure, significant reductions were found in total dry weight (30-40%), plant part dry weight and leaf area (ͭ6 30%). Ozone caused a rapid decline in relative growth rate which was related to a reduction in net assimilation rate.
Glycine metabolism by plant roots and its occurrence in Australian plant communities
Authors: Schmidt S. , Stewart G. R.
Published: January 2006

Soluble organic nitrogen, including protein and amino acids, was found to be a
ubiquitous form of soil N in diverse Australian environments. Fine roots of
species representative of these environments were found to be active in the
metabolism of glycine. The ability to incorporate
[15N]glycine was widespread among plant
species from subantarctic to tropical communities. In species from
subantarctic herbfield, subtropical coral cay, subtropical rainforest and wet
heathland, [15N]glycine incorporation ranged
from 26 to 45 % of
15NH4+
incorporation and was 2- to 3-fold greater than
15NO3-
incorporation. Most semiarid mulga and tropical savanna woodland species
incorporated [15N]glycine and
15NO3- in
similar amounts, 18–26 % of
15NH4+
incorporation. We conclude that the potential to utilise amino acids as N
sources is of widespread occurrence in plant communities and is not restricted
to those from low temperature regimes or where N mineralisation is limited.
Seedlings of Hakea (Proteaceae) were shown to metabolise
glycine, with a rapid transfer of 15N from glycine to
serine and other amino compounds. The ability to take up and metabolise
glycine was unaffected by the presence of equimolar concentrations of
NO3- and
NH4+. Isonicotinic acid
hydrazide (INH) did not inhibit the transfer of 15N-
label from glycine to serine indicating that serine hydroxymethyltransferase
was not active in glycine catabolism. In contrast aminooxyacetate (AOA)
strongly inhibited transfer of 15N from glycine to
serine and labelling of other amino compounds, suggesting that glycine is
metabolised in roots and cluster roots of Hakea via an
aminotransferase.
Kinetic response of photosystem II photochemistry in the cyanobacterium Spirulina platensis to high salinity is characterized by two distinct phases
Authors: Lu Congming , Torzillo Giuseppe , Vonshak Avigad
Published: January 2006

The kinetic response of photosystem II (PS II) photochemistry in
Spirulina platensis(Norstedt M2 )
to high salinity (0.75 M NaCl) was found to consist of two phases. The first
phase, which was independent of light, was characterized by a rapid decrease
(15–50%) in the maximal efficiency of PS II photochemistry
(Fv
/Fm), the efficiency of
excitation energy capture by open PS II reaction centres
(Fv′/Fm′),
photochemical quenching (qp) and
the quantum yield of PS II electron transport (Φ
PS II) in the first 15 min, followed by a recovery up to
about 80–92% of their initial levels within the next 2 h. The
second phase took place after 4 h, in which further decline in above
parameters occurred. Such a decline occurred only when the cells were
incubated in the light, reaching levels as low as 45–70% of their
initial levels after 12 h. At the same time, non-photochemical quenching
(qN) and Q
B -non-reducing PS II reaction centres increased
significantly in the first 15 min and then recovered to the initial level
during the first phase but increased again in the light in the second phase.
The changes in the probability of electron transfer beyond
QA (ψo)
and the yield of electron transport beyond
QA (φ
Eo), the absorption flux (ABS/RC) and the trapping
flux (TRo /RC) per PS II reaction centre also
displayed two different phases. The causes responsible for the decreased
quantum yield of PS II electron transport during the two phases are discussed.
Effect of elevated [CO2] on photosynthesis and growth of snow gum (Eucalyptus pauciflora) seedlings during winter and spring
Authors: Roden John S. , Egerton John J. G. , Ball Marilyn C.
Published: January 2006

Snow gum (Eucalyptus pauciflora Sieb. ex Spreng.)
seedlings were grown from autumn through spring in open top chambers located
in a pasture naturally subject to freezing temperatures in either ambient or
elevated (350 µL L-1 above ambient)
CO2 concentrations. Sustained reduction in quantum
efficiency, as measured by chlorophyll fluorescence
(Fv/Fm),
in over-wintering leaves may be related to seasonal down-regulation of
photosynthesis, combined with cumulative effects of freeze- induced damage to
the photosynthetic apparatus, with the effect being greater in leaves grown
under elevated [CO2]. Down-regulation of
photosynthesis apparently occurred in response to seasonal limitations to
growth which were not overcome by elevation of
[CO2] despite temperatures being favorable for
photosynthesis during most of the photoperiod. Elevated
[CO2] had no effect on growth of
over-wintering seedlings, but enhanced growth in spring when minimum
temperatures rose consistently above freezing. As there were no effects of
elevated [CO2] on allocation, the stimulation
of growth in spring was attributable to increase in net assimilation rates.
Thus seasonal differences in photoinhibition were consistent with seasonal
differences in the capacity for growth, with plants grown under elevated
[CO2] having to dissipate more excess
excitation energy over-winter.
Effect of elevated carbon dioxide concentration at night on the growth and gas exchange of selected C4 species
Authors: Ziska Lewis H. , Bunce James A.
Published: January 2006

Biomass of certain C4 species is increased when plants
are grown at elevated CO2 concentrations. Experiments
using four C4 species
(Amaranthus retroflexus L.,
Amaranthus hypochondriacus L.,
Sorghum bicolor (L.) Moench and
Zea mays L.) exposed both day and night from sowing to
carbon dioxide concentrations of 370 (ambient) or 700 µmol
mol-1 (elevated) or to 370 µmol
mol-1 during the day and 700 µmol
mol-1 at night, determined whether any biomass increase
at elevated CO2 concentrations was related to a
reduction in the night-time rate of CO2 efflux at high
night-time CO2 concentrations. Of the four species
tested, only A. retroflexus significantly increased both
CO2 assimilation (+13%) and plant biomass
(+21%) at continuous elevated relative to continuous ambient
concentrations of CO2. This increase was not associated
with improvement in leaf water potential during dark or light periods. In
contrast, high CO2 only during the night significantly
reduced plant biomass compared to the 24 h ambient CO2
treatment for both A. retroflexus and
Z. mays. This indicates that the observed increase in
biomass at elevated CO2 for
A. retroflexus was not caused by a reduction of carbon
loss at night (i.e. increased carbon conservation), but rather a direct
stimulation of daytime CO2 assimilation, independent of
any improvement in leaf water potential.
Association of Glutenin Subunits With Gliadin Composition and Grain Quality in Wheat
Authors: Wrigley CW , Lawrence GJ , Shepherd KW
Published: January 2006

The composition of high-molecular-weight (HMW) glutenin subunits was determined by sodium dodecyl sulfate (SDS) gel electrophoresis of grain proteins from a set of 98 wheats from many countries (17 from Australia) and a set of 78 wheats (mainly Australian) and one rye cultivar. Such SDS gel electrophoresis was shown to be a useful back-up to gel electrophoresis of the gliadin fraction for identifying Australian wheats. Associations between the glutenin subunits revealed by numerical analysis were interpreted to indicate genetic relationships between them. Associations were much stronger amongst glutenins or amongst gliadins than between members of the two protein classes. The HMW glutenin-subunit compositions of the Australian wheats were more strongly related to grain hardness than to dough strength, but both these relationships were mainly based on pedigree associations. Compared to the HMW glutenins, the composition of the gliadins was more closely related to dough strength, and this relationship was largely independent of pedigree.
Effects of Water Deficit on Endosperm Starch Granules and on Grain Physiology of Wheat and Barley.
Authors: Brooks A , Jenner CF , Aspinall D
Published: January 2006

Wheat (cv. Sun 9E) and barley (cv. Clipper) plants were subjected to water deficit after anthesis. In both species grain dry matter accumulation was initially unaffected by water deficit but terminated earlier in stressed plants than in controls. Water deficit did not affect endosperm cell number. In water stressed wheat plants the number of B-type starch granules per endosperm and the size of the largest A-type granules were significantly less than in control plants but A-type granule number was unaffected.
Water potentials of wheat flag leaves and bracts were reduced by water deficit but this treatment did not affect grain water potential or osmotic potential during the first 29 days after anthesis. During these 29 days, neither grain nor bract water potential of barley was affected by stress and the water potential of bracts was relatively low even in control plants. Maturing grains eventually lost water and endosperm volume declined. This water loss occurred earlier in stressed plants.
Stress significantly reduced the amount of sucrose per wheat grain but not the amount of sucrose per unit of grain dry matter or water content. In barley grains, stress did not reduce the relative or absolute sucrose contents. It was considered unlikely that the earlier cessation of grain growth on stressed plants was caused by insufficient assimilate. Although protein as a proportion of grain dry weight was higher in stressed plants than in controls, protein and amino acid content per grain were unaffected by water deficit.
Sterility in Wheat (Triticum aestivum L.) Induced by Water Deficit or High Temperature: Possible Mediation by Abscisic Acid
Authors: Saini HS , Aspinall D
Published: January 2006

The application of abscisic acid solution to developing spikes of wheat (cv. Gabo) via wicks threaded through peduncles at the stage of meiosis in pollen mother cells caused pollen sterility without affecting female fertility. The concentration of abscisic acid measured in the spikelets of plants treated in this manner was close to that induced by water stress, which produced a similar level of pollen sterility. After pollen mother cell meiosis, treatment with abscisic acid had no effect on pollen fertility, as has been shown previously with water stress. Abscisic acid applied immediately before meiosis reduced fertility, in contrast to the effect of water stress, but this may have been due to persistence of the hormone in the plant. High temperature during pollen mother cell meiosis had no effect on the endogenous abscisic acid content of the spikelets, even where the treatment caused a complete inhibition of grain set.
Gibberellic Acid-Induced Alpha -Amylase Synthesis in Wheat Aleurone Layers: a Distinction Between Site Saturation and Lag Times.
Authors: Gibson RA , Paleg LG
Published: January 2006

We have examined a number of parameters relating to the gibberellic acid (GA3) requirement for the induction process which leads to the formation of �-amylase in wheat aleurone tissue. (1) Over a wide range of hormone concentrations, aleurone tissue was found to produce less �-amylase after hormone withdrawal by washing at a time soon after GA*3 application. (2) The approximate length of this washing-sensitive period was found to vary inversely to the applied GA*3 concentration. (3) Following this early period, a time was found when the response could not be lowered by this same washing procedure which had earlier lowered the response. (4) Separate experiments determined that these results could not be accounted for by variation in the lag/latent period, since the lag period was about the same for a wide range of GA*3 concentrations. To help explain these results we have suggested the term 'site saturation time' which is separate from but intimately involved with the lagllatent period. This term is defined as the time required for the saturation and activation of all sites which ultimately lead to the production of �-amylase. It is suggested that site saturation time must be taken into account when the early events of �-amylase induction are examined.
Effects of Various Solutes on the Thermostability of Isocitrate Dehydrogenase and Malate Dehydrogenase of Isolated Plant Mitochondria.
Authors: Nash D , Wiskich JT
Published: January 2006

Proline and betaine increased the thermostability of NAD-isocitrate dehydrogenase (EC 1.1.1.41) and of NAD-malate dehydrogenase (EC 1.1.1.37) when mitochondria isolated from pea leaves (Pisum sativum L.), wheat leaves (Triticum aestivum L.) and cauliflower buds (Brassica oleracea L.) were heated. Potassium chloride and choline chloride also increased the thermostability of isocitrate dehydrogenase in the three species, but their effects on malate dehydrogenase varied. Protection was found with both intact and disrupted mitochondria, indicating that it was not dependent on an osmotic effect. Proline and KCl also prolonged membrane integrity, as measured by impermeability to NAD+, during heating of pea leaf and cauliflower bud mitochondria. Phenylalanine reduced the thermostability of isocitrate dehydrogenase, indicating that protection is not a general solute effect.
Naturally Occurring Cytokinins in Mango (Mangifera indica L.) Fruit
Authors: Ram S , Sirohi SC , Rathore VS
Published: January 2006

The fruit of mango (Mangifera indica L.) contained cytokinins in both pericarp and seed. During the single period of rapid growth in fruit and seed (7-42 days after pollination), cytokinin concentration increased rapidly at two times. The first preceded the period of rapid cell division and cell enlargement and the second coincided with the period of rapid cell enlargement only. Deficiency of cytokinin in the fruit appears to favour fruit drop and cessation of fruit growth. Eleven cytokinin fractions were isolated by ion-exchange column and paper chromatography from immature mango fruits. These fractions were termed Mf1 to Mf11, on the basis of their RF values and spectral properties. Two of these, Mf9 and Mf10, could be tentatively identified as zeatin riboside and zeatin, respectively.
Water Relations and Composition of Wheat Ears Grown in Liquid Culture: Effect of Carbon and Nitrogen
Authors: Barlow EWR , Donovan GR , Lee JW
Published: January 2006

Detached wheat ears were grown, under lighted controlled conditions, in liquid culture media containing different concentrations of sucrose and amino acid. Higher levels of sucrose in the culture medium resulted in decreased transpiration, with large accumulations of soluble sugar in the bracts. The sugar accumulations led to decreased total and osmotic potentials of the bracts, but turgor was maintained or increased. The concentration of sucrose or nitrogen in the culture medium had no significant effect on the water or osmotic potentials of the grain. Soluble sugar concentrations in the grain were not affected by increasing the sucrose concentration in the culture medium. Increasing the nitrogen level in the culture medium led to increased concentrations of total nitrogen and non- protein nitrogen in the grain. Higher protein levels in the grain resulted in increased water content but no significant changes in the water potential of the grain. The grain was the strongest nitrogen sink within the ear and, within the grain, starch and protein synthesis were independent of each other. Proline accumulated in the bracts and to a lesser extent in the rachis in response to the accumulation of soluble sugars and nitrogen rather than to the low osmotic or total water potentials. Little proline accumulated in the grain and this was presumed to be due to translocation from other parts of the ear rather than to in situ synthesis.
Changes in Leaf Photosynthesis With Plant Ontogeny and Relationships With Yield Per Ear in Wheat Cultivars and 120 Progeny
Authors: Rawson HM , Hindmarsh JH , Fischer RA , Stockman YM
Published: January 2006

Six wheat cultivars, and 120 random progeny derived from composite crosses among these cultivars and 10 others, were grown in a glasshouse and changes in photosynthesis of the main-shoot leaves determined throughout ontogeny. Photosynthetic rates for each leaf generally showed a short-term rise after ligule emergence, a plateau, and then a linear decline as the leaf aged. Both peak photosynthesis, and the rates of reduction in photosynthesis with aging, increased with successive leaves, and then either stabilized or declined in the upper leaf positions. Leaves also increased in area in a power progression with plant ontogeny. The combined effect of these factors was that successive leaves fixed progressively more carbon during their lives.
Leaf emergence was essentially linear with time. Fast leaf emergence was linked with small leaves and a greater final leaf number. Whilst there was a negative correlation between area per leaf and photosynthetic rate, in terms of carbon fixation per leaf the benefits of larger leaves far outweighed the negative effects of reduced rates.
Rates of aging of leaves and areas of leaves accounted for the major differences in carbon fixation per leaf among cultivars. There was no correlation between peak photosynthetic rates of leaf 3 and the flag leaf so that any screening for high rates could not be done on seedling leaves. In any event, this could be of doubtful benefit because yield per ear was unrelated to peak photosynthetic rates of the flag leaf. However, yield per ear was correlated with flag leaf area (P<0.05), rate of decline of flag leaf photosynthesis with age (P<0.001, inverse), and most closely with cumulative carbon production by the flag leaf during its life (P<0.001).
Cellular Structures, Plasma Membrane Surface Areas and Plasmodesmatal Frequencies of Seed Coats of Phaseolus vulgaris L. In Relation to Photosynthate Transfer
Authors: Offler CE , Patrick JW
Published: January 2006

In the developing ovule of P. vulgaris, the rapid lateral dissemination of photosynthates throughout the seed coat occurs within a reticulate vasculature of uniform sized veins embedded in a parenchymatous layer. Radial movement of photosynthate from the sieve elements to the cotyledonary apoplast is through vascular, ground and branch parenchyma, epidermis and residual endosperm. For this cellular pathway, there appears to be no barrier within the apoplast to photosynthate transfer and symplastic continuity exists from the sieve elements to the branch parenchyma-epidermal boundary. However, based on estimates of possible sucrose fluxes through the apoplastic and symplastic routes, it seems likely that photosynthates move symplastically from the sieve elements, through the vascular parenchyma to either the adjoining ground parenchyma or inner band of branch parenchyma where membrane transfer to the apoplast occurs. The resemblance of the ultrastructure of the branch parenchyma to that of known secretory cells favours this tissue as the main site of photosynthate exchange to the apoplast. The significance of these findings is discussed in relation to photosynthate transfer within the developing ovule.
Hydraulic Resistance of Plants. II. Effects of Rooting Medium, and Time of Day, in Barley and Lupin
Authors: Passioura JB , Munns R
Published: January 2006

Barley and lupin plants were grown in pots designed to fit inside a pressure chamber. The pots contained sand, soil, or nutrient solution. Transpiration rates were varied over a wide range. At a given transpiration rate, Q, the balancing pressure, p, of a plant was determined; p is the pneumatic pressure that must be applied to the roots in the pressure chamber to have a cut in the xylem of the shoot on the verge of bleeding. The relation between p and Q, p(Q), was non-linear and hysteretic for solution- grown plants, but was remarkably linear for plants grown in sand or soil, i.e. the data for a given plant on a given occasion conformed closely to the equation p =po + rQ, where po and r were constants. Even though p(Q) was linear for the plants grown in sand or soil, po was often much larger than Δπ, the difference in osmotic pressure between the external solution and the xylem of the root, so that the apparent hydraulic resistance of the plants, i.e. (p-Δπ)/Q, depended strongly on Q. Furthermore, po changed diurnally and was typically 100-200 kPa higher in the afternoon than in the morning. These results are discussed in relation to the equations that are commonly used to describe water flow through plants. It is postulated that r represents the true hydraulic resistance of the plant, which is independent of Q in the plants grown in soil or sand but may vary diurnally, and that the discrepancy between po and Δπ represents either an additional and hitherto unrecognized difference in osmotic pressure across the membranes of the root that intercept the transpiration stream, or a pressure required to open valves through which the water has to pass, with the valves possibly being located in the plasmodesmata.
Effects on Casuarina and Allocasuarina Species of Increasing Sodium Chloride Concentrations in Solution Culture
Authors: Luard EJ , El-Lakany MH
Published: January 2006

Ten species of Casuarina and Allocasuarina were exposed to increasing levels of NaCl (max 550 mM) in solution culture over a period of 5 months. Na+ and Cl- ion concentrations increased in the tissues of all species as the salinity increased and K+ was selectively accumulated. Those species which ultimately survived to the highest salinities tested had lower concentrations of Na+ and Cl- in both shoot and roots and lower Na+/K+ ratios than the more sensitive species at low external salinities. Osmotic adjustment of the Casuarina species was principally accounted for by Na+ and Cl- in the shoots. Turgor pressure was not lost until the plants were close to death, so that inhibition of height growth by NaCl was probably due to the high cellular ion concentrations. Plants were more sensitive to osmotic shock than to a gradual increase in salinity.
Specific Mass Transfer and Sink-Controlled Phloem Translocation in Castor Bean
Authors: Kallarackal J , Milburn JA
Published: January 2006

The specific mass transfer (SMT) into the fruits of Ricinus communis was measured in three different systems: (1) the intact truss, (2) fruit-thinned truss (all but one fruit removed), and (3) exuding peduncle. We found that the SMT in an intact system accords well with values reported in previous studies. But in the single-fruit and exuding systems the values were 2 and 18 times higher than the intact system, respectively. The inability of a single fruit to achieve a much higher SMT value shows that the assimilate unloading is sink-controlled. The high SMT value of the exuding system demonstrates the capacity of the sieve tubes to transport large volumes of phloem sap when turgor pressure in the sieve tubes at the sink ceases to be a limiting factor. This can be contrasted with the single-fruit system where the sink probably exerts a 'back pressure' while the assimilate supply is unlimited. The twofold increase in SMT shown by a single-fruit system is probably caused by hormone-stimulated assimilate unloading. SMT values have been used also to calculate the velocity of sap flow in the sieve tubes.