bluuebunny/crossref_metadata_2025 huggingface dataset:
Endogenous Biosynthetic Precursors of (+)-Abscisic Acid. III. Incorporation of 2H from 2H2O and 18O from 18O2 into Precursors
Authors: Netting A. G. , Windsor M. L. , Milborrow B. V.
Published: August 2004

Deuterium from 2H2O was
incorporated into the methyl abscisate released from components of the
‘adduct’ (Netting, Willows and Milborrow,
Plant Growth Regulation11:
327–334, 1992) fraction and into the free abscisic acid in stressed
tomato seedlings. Incorporation of deuterium after 7 or 10 days of daily
wilt/recover cycles suggested that components of the adduct fraction could
be precursors of free abscisic acid. It was then found that when seedlings,
that had been through seven wilt/recover cycles in
2H2O were put through four wilt
and recover cycles in 1H2O, the
methyl abscisate released from the adduct components had significant
incorporation of protium, as did the free abscisic acid from the same plant
organs. The pattern of protium incorporation raised the possibility that some
of the adduct components were synthesised in the roots in response to stress
and were then transported to the shoot, where they broke down to liberate free
abscisic acid.
When tomato shoots were wilted in an
18O2 atmosphere they incorporated
18O into the methyl abscisate plus abscisic acid
released from the ‘ketone’ fraction of the adduct group of
compounds at a high level in mildly stressed plants. It was possible that
18O was similarly incorporated into the methyl abscisate
plus abscisic acid from the ‘enolate’ fraction of adduct when
plants were wilted to between 4% and 17% water loss. These
experiments led to the conclusion that components of the adduct fraction were
the endogenous precursors of stress-induced abscisic acid. It appeared that
they were produced from a precursor pool in response to stress and then
rapidly broke down to liberate abscisic acid (and methyl abscisate).
Water Stressed Nodal Roots of Wheat: Effects on Leaf Growth
Authors: Volkmar K. M.
Published: August 2004

This experiment as undertaken to determine the efects of soil drying around
the nodal and/or seminal root systems on the shoot growth of wheat
(Triticum aestivum L.). Two split-root experiments were
conducted, the first on newly emerged nodal roots of 18-day-old wheat plants,
the second on 25-day-old plants. In both experiments, nodal and seminal roots
were isolated from one another and water was withheld from either the nodal
root chamber, the seminal root chamber, or both, over 6 days. In the first
experiment, leaf growth was unaffected by withholding water from very short
nodal roots, even though leaf relative water content of the droughted plants
decreased. By comparison, both leaf elongation rate and relative water content
decreased by withholding water from the seminal roots. On plants that were 1
week older, leaf growth rate and leaf relative water content decreased when
nodal roots were drought-stressed. Leaf growth rate of seminal root droughted
plants was more impaired than their nodal root counterparts, even though leaf
relative water contents of the two treatments were the same. In both
experiments, drought stress applied to the nodal root system enhanced nodal
root growth more than seminal roots. These results suggest that seminal and
nodal roots perceive and respond to drought stress differently with respect to
the nature of the message conveyed to the shoots.
Observations of Bifurcation and Chaos in Plant Physiological Responses to Light
Authors: Shabala Sergey , Delbourgo Robert , Newman Ian
Published: August 2004

Although some theoretical predictions have been made, no experimental evidence
of chaotic behaviour in plant physiological responses has been reported. Here
we present observations of period- doubling and tripling in higher plants. For
leaf bioelectric and temperature responses of maize, tomato, and burweed
plants to rhythmical light, two different routes to chaos were found
experimentally. One was via successive period-doubling and the other via the
formation of intermittently chaotic oscillations from a subharmonic
synchronisation. Because these effects appeared in intact plants, under
conditions close to those found in nature, they may have wide significance,
including for plant phylogenesis.
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: August 2004

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.
Biochemical Responses of Suspension-cultured Sugarcane Cells to an Elicitor Derived from the Root Pathogen Pachymetra chaunorhiza
Authors: McGhie Tony K. , Masel Niall P. , Maclean Don , Croft Barry J. , Smith Grant R.
Published: August 2004

The fungus Pachymetra chaunorhiza Croft & Dickcauses a root rot in sugarcane (Saccharum interspecifichybrid). Suspension-cultured sugarcane cells prepared from cultivars Q114(P. chaunorhiza resistant) and Q90(P. chaunorhiza susceptible) were inoculated with aheat-derived elicitor preparation from P. chaunorhizaand the cellular responses monitored by measuring phenylalanine ammonia-lyase(PAL) and peroxidase (POD) activity and the production of additional phenoliccompounds.Introduction of the P. chaunorhiza elicitor inducedmarked changes in the biochemistry of both sugarcane cell lines. Both celllines produced additional phenolic compounds not present in untreated cellsand different compounds were produced by each cell line. Induced enzymeactivities also differed between the cell lines with Q90 (susceptible) showinga large and transitory increase in PAL activity that was far greater than thatobserved for Q114 (resistant). POD activity increased more in Q114 than inQ90, although the differences between the resistant and susceptible cell lineswere not as great as for PAL.
A Statistical Comparison of the Two-Source δ15N and 15N Isotope Dilution Methods for Estimating Plant N2-Fixation using Trifolium pratense and Lolium perenne
Authors: Brendel O. , Wheeler C. , Handley L.
Published: August 2004

In field studies, 15N-enriched and
15N-natural abundance methods may yield similar mean
estimates for N2-fixation, but with no correlation of
the individual estimates. This study was designed as a glasshouse-based
microcosm and aimed to remove the landform and weather variables found in
previous field studies, while retaining other sources of variability such as
mineralisation of organic N and whatever slight variations of environment may
exist in the glasshouse.
The results showed little or no correspondence among the estimates of
N2-fixation at the three
15N-enrichment levels; however, estimates were
consistent within each 15N-enrichment level. There was
also no correlation between the results of acetylene reduction and those of
any of the isotopic enrichment treatments.
If the isotopic 15N-enrichment levels measured the same
processes with varying accuracies, then the general patterns of the replicated
results from each enrichment level should resemble each other against a
generally uniform background. They did not. Hence, we conclude that the
observed differences are due to unknown factors in addition to the varying
noise-to-signal ratio at different enrichment levels.
A Direct Method for Estimating the Average Sap Flux Density Using a Modified Granier Measuring System
Authors: Lu Ping
Published: August 2004

The Granier sap flow measuring system that normally uses one analogue input
channel of a datalogger for each sensor was modified to enable one channel to
measure the average value of signals from two or more sensors. The sap flux
density calculated from this average value of signals was very close
(difference < 6.0%) to the arithmetic mean of the sap flux densities
measured separately by means of individual sensors (using two or more input
channels). The dynamics of the sap flux density measured by the modified
method were similar to those measured by the original method. On a per-channel
basis, the modified method reduced the ‘estimation error’ of sap
flux density by 4–14-fold compared to the original method. By using the
modified Granier system, the error in sap flow measurement that is usually
associated with limited sampling can be substantially reduced without the need
for extra dataloggers, the greatest item of expense.
Endogenous Biosynthetic Precursors of (+)-Abscisic Acid. IV. Biosynthesis of ABA from [2Hn] Carotenoids by a Cell-free System from Avocado
Authors: Milborrow B. V. , Lee H-S.
Published: August 2004

The supernatant fraction (12 000 g) of a homogenate of
avocado mesocarp incorporated
3-R-[2-14C]mevalonate
(54 µCi/µmol, 0.9 µCi/5mL) into ABA and was used to
examine the incorporation of carotenoids into ABA.
[2Hn]carotenoids were
isolated by HPLC from mustard (Sinapis alba) seedlings
that had germinated in closed flasks in
2H2O (55 atom%). The
carotenoids were dissolved in Tween 80 and acetone (1:1 v/v; 100 µL)
and added to the cell-free system final vol. 5 mL, pH 7.1, together with
cofactors. After 16 h incubation in darkness the ABA was isolated by HPLC and
converted into the pentafluorobenzyl ester. The samples were analysed by
capillary gas–liquid chromatography and the CH4
chemical ionisation, negative ion mass spectra recorded. Deuterium-labelled
ABA was detected when [2H] carotenoids were
supplied.
‘Cold traps’ of unlabelled carotenoids added to the cell-free
system lowered the [14C]mevalonate
incorporated into ABA to 33% of the control value (1195 dpm)
(trans-viola, 33%;
trans-neo, 32%) but with 9´
-cis-neoxanthin the value fell to 29%. The
addition of naproxen (an inhibitor of lipoxygenases) hardly increased the
14C trapped in trans-viola- or
trans-neoxanthin but reduced the
14C in ABA to 17% of the control and raised the
14C trapped by the
9´-cis-neoxanthin by 179%. These changes
support earlier suggestions that it is
9´-cis-neoxanthin that is cleaved to give the
future ABA residue. Other metabolic inhibitors (bisulfite, AMO 1618,
tungstate, CO, piperonyl butoxide) affected the incorporation of
[14C]mevalonate into ABA by the cell-free
system and the incorporation of
[14C]mevalonolactone into ABA formed in slices
of avocado fruit in a closely similar way. This provides strong support for
ABA’s being biosynthesised in the cell-free system by the same reactions
as those by which it is made in vivo.
Studies of Cytokinin Action and Metabolism Using Tobacco Plants Expressing either the ipt or the GUS Gene Controlled by a Chalcone Synthase Promoter. IIipt and GUS Gene Expression, Cytokinin Levels and Metabolism
Authors: Wang Jian , Letham D. S. , Cornish Edwina , Wei K. , Hocart C. H. , Michael M. , Stevenson K. R.
Published: August 2004

The expression of GUS and ipt
genes under control of a chalcone synthase (chs)
promoter (PCHS) has been determined in tobacco
(Nicotiana tabacum L.) plants and related to the
development of plants expressing the chimaeric PCHS
-ipt gene. GUS gene expression,
which served as a model for the expression of the ipt
gene, was highest in the internal phloem tissue of stems, in mature leaf
laminae and in the upper part of corollas when fully open. Expression of the
PCHS -ipt gene was assessed by
quantifying the cytokinins produced, by determining incorporation of
[3H]adenine into cytokinins and by quantifying
ipt mRNA. Results from these studies were in general
agreement with those based on expression of the PCHS
-GUS gene. The chs promoter
controlled expression of the ipt gene with some degree
of tissue and temporal specificity. Expression of the
ipt gene markedly elevated the cytokinin level in mature
leaf laminae and the upper stems of flowering plants. The former was
associated with retardation of leaf senescence and increased rates of
transpiration due to changes in number, size and aperture of stomata, while
the latter was associated with development of lateral shoots. In shoot tip
cultures, 2-fold elevations in endogenous cytokinin level caused clear changes
in development and this is discussed in relation to current concepts
concerning the hormonal control of plant development.
Using the transgenic tobacco tissues, it was shown that
cis-zeatin is a substrate for cytokinin oxidase, that
cis-zeatin is not converted to
trans-zeatin in these tissues and that the endogenous
cytokinin level influences the level of cytokinin oxidase activity in tissue
and the rate of degradation of exogenous zeatin riboside to adenosine.
Identification and Characterisation of Two 1-Aminocyclopropane- 1-Carboxylate (ACC) Synthase cDNAs Expressed during Papaya (Carica papaya) Fruit Ripening
Authors: Mason Michael Glenn , Botella José Ramón
Published: August 2004

The cloning and characterisation of two cDNAs (capacs1
and capacs2) encoding ACC synthase in papaya
(Carica papaya L.) is described.
capacs1 is 1104 bp long encoding 368 amino acids.
capacs2 is 1098 bp long encoding 366 amino acids. The
proteins encoded by both cDNAs contain the highly conserved active site of ACC
synthases as well as 10 (capacs1) or 11
(capacs2) of the 12 amino acid residues conserved in
most aminotransferases. Southern analyses indicate that capacs1 and capacs2
are present in the papaya genome as single copy genes. Both genes show very
different expression patterns during fruit ripening. capacs1 mRNA levels are
high in mature green fruits, decreasing steadily during ripening, whereas
capacs2 mRNA levels are undetectable in mature green fruits but experience a
dramatic increase with the onset of ripening and remain high throughout the
various stages of ripening.
The effect of duration of heat stress during grain filling on two wheat varieties differing in heat tolerance: grain growth and fractional protein accumulation
Authors: Stone P.J. , Nicolas M.E.
Published: August 2004

Two varieties of wheat differing in heat tolerance were exposed to very high
temperature (40/19°C day/night) for periods of 1–10 days
duration. Responses of grain dry matter, water and fractional protein
accumulation to high temperature were monitored throughout grain filling in
the heat- sensitive variety, and at maturity only in the heat-tolerant
variety. Results are compared with controls maintained at 21/16°C
day/night. As little as 1 day of heat treatment reduced kernel mass by
14% in the heat-sensitive variety (Oxley), but by only 5% in the
heat-tolerant variety (Egret). In both varieties, the reduction of individual
kernel mass due to high temperature increased linearly with increased duration
of heat treatment, such that after the first day of heat stress, each
additional day of treatment reduced mature individual kernel mass by a further
1.6%. For a given duration of heat treatment, the difference in
response of the two varieties was constant (9%), indicating that the
varietal difference in heat tolerance was maintained for both brief and
extended periods of very high temperature. Responses of grain water content
and fractional protein accumulation to duration of heat stress are discussed.
Photosynthetic Gene Expression in Amaranth, an NAD-ME Type C4 Dicot
Authors: Berry James O. , McCormac Dennis J. , Long John J. , Boinski Joseph , Corey Amy C.
Published: August 2004

Post-transcriptional regulation determines initial C4
gene expression patterns in developing leaves of
Amaranthus hypochondriacus, an NAD-ME type
C4 dicot. RuBPCase, PEPCase, and PPdK mRNAs are abundant
in meristems and in leaf primordia, but are utilised only during specific
developmental stages. While each enzyme shows independent patterns of initial
mRNA and polypeptide accumulation, cell-specific localisation of the
polypeptides occurs prior to cell-specific localisation of the mRNAs. In
mature three-coloured leaves of A. tricolor, loss of
photosynthetic activity correlates with reductions in the transcription rates
of some plastid-encoded genes, reduction and loss of coordination in the
translation of RuBPCase polypeptides, and loss of cell-specific accumulation
of RuBPCase mRNAs (but not the polypeptides). The mitochondrial NAD-dependent
malic enzyme (NAD-ME) provides an example of a basic metabolic enzyme that has
acquired specialised gene expression patterns allowing it to function in the
C4 pathway. NAD-ME occurs preferentially in
photosynthetic tissues, and is specific to bundle sheath cells throughout
development. NAD-ME synthesis is regulated by light and development at
transcriptional and post-transcriptional levels. The findings summarised here
indicate that C4 genes are independently regulated by
multiple control mechanisms in response to developmental, environmental, and
metabolic signals.
Post-illumination CO2 Exchange and Light-induced CO2 Bursts during C4 Photosynthesis
Authors: Laisk Agu , Edwards Gerald E.
Published: August 2004

Detailed kinetics of the post-illumination CO2 exchange,
and darklight transients following post-illumination exchange, were measured
in leaves of Sorghum bicolor, a NADP-malic enzyme
(NADP-ME), and Amaranthus cruentus, a NAD-malic enzyme
(NAD-ME) type C4 plant using a gas system that has a
full-response time of 3.5 s. The amount of CO2 fixed in
the dark (assimilatory charge, AC) was up to 200
µmol m-2 for A. cruentus and
350-450 µmol m-2 for
S. bicolor. AC was at its maximum
value at CO2 concentrations close to the inflection of
the CO2 response curve, and decreased when
photosynthesis was limited by low light intensity. The kinetics of
post-illumination CO2 fixation indicate that the rate of
carboxylation in the C4 cycle is limited by the supply
of phosphoenolpyruvate. In
A. cruentus, under saturating CO2
the post-illumination CO2 uptake was replaced by a burst
(68 µmol m-2). In S. bicolor, the dark-light
induction commenced with a rapid CO2 burst (less than 5
s) of 46 µmol m-2, followed by a gulp. The
observed CO2 transients show imbalances in the
C4 and C3 cycles. In
S. bicolor the lack of a post-illumination burst, and
the presence of the light- induced CO2 burst is taken as
evidence for strict coupling of malate decarboxylation to PGA reduction in
NADP-ME species; the opposite response in A. cruentus
indicates the lack of strict coupling between the C4 and
C3 cycle in NAD-ME species.
Structural Requirements for Phosphorylation of C4-Leaf Phosphoenolpyruvate Carboxylase by its Highly Regulated Protein-Serine Kinase. A Comparative Study with Synthetic-Peptide Substrates and Mutant Target Proteins
Authors: Li Bin , Pacquit Valérie , Jiao Jin-an , Duff Stephen M.G. , Maralihalli Gururaj B. , Sarath Gautam , Condon Shirley A. , Vidal Jean , Chollet Raymond
Published: August 2004

A family of synthetic peptides modelled after the highly conserved,
N-terminal phosphorylation domain of
C4 phosphoenolpyruvate carboxylase
(PEPC) and a complementary set of recombinant mutant target proteins were
exploited to investigate the local structural requirements for phosphorylation
of this cytosolic C4 enzyme by its
Ca2+-independent protein kinase. The only peptide
homolog examined that was significantly phosphorylated by maize
(Zea mays L.) leaf PEPC-kinase spanned the P−5
through P+16 region surrounding the target serine residue in maize PEPC (fifth
through sixteenth residues on the N- and
C-terminal sides, respectively, of the phosphorylatable
serine at position ‘P’). However, its apparent
Km value was 200-times that of intact
C4 PEPC. The results from the related site-directed
mutagenesis experiments with the recombinant sorghum
(Sorghum vulgare) C4 -enzyme
indicated that alteration of several highly conserved residues flanking the
target serine with non-conservative Ala substitutions at the P−4,
P−3, and P+10 positions had only modest effects, if any, on its
in-vitro phosphorylation by maize PEPC-kinase. These
collective findings implicate a secondary site(s) of interaction in
C4 PEPC, removed from the
N-terminal phosphorylation domain, that is also an
important recognition element for its low abundance, highly regulated
protein-serine/threonine kinase.
Responses to water stress of enzyme activities and metabolite levels in relation to sucrose and starch synthesis, the Calvin cycle and the C4 pathway in sugarcane (Saccharum sp.) leaves
Authors: Du Y.-C. , Nose A. , Wasano K. , Uchida Y.
Published: August 2004

During a slowly induced water stress, almost all measured activities of
enzymes, including the important enzymes associated with the Calvin cycle, the
C4 pathway, and sucrose and starch synthesis, and the
pool sizes of metabolites, including hexose phosphates, 3-phosphoglycerate,
triose phosphates, malate, pyruvate and PEP, in leaves of sugarcane
(Saccharum sp. cv. NiF4) were not or only moderately
reduced by mild water stress (above –0.9 MPa leaf water potential
(Ψw)), and the magnitudes of reductions in those
parameters were less than the reductions in photosynthetic rates. We conclude
that the biochemical processes of sucrose and starch synthesis, the Calvin
cycle and the C4 pathway in sugarcane leaves were not
seriously affected by mild water stress, and the changes in those processes
were not the cause for the decline in photosynthesis; mild water stress
induced decline in photosynthesis is caused by stomatal closure. Under severe
water stress (–1.2 MPa leaf Ψw), most
metabolite levels and enzyme activities decreased significantly compared with
those under mild water stress. But the enzyme activities and metabolite levels
relating to sucrose and starch synthesis, and the Calvin cycle still remained
at high levels compared with the corresponding photosynthetic rate. PPDK
activity and pyruvate content decreased to very low levels. It is suggested
that PPDK is a possible limiting enzyme for photosynthesis in leaves of
sugarcane under severe water stress.
Pathogenesis-Related Proteins in Trifolium subterraneum: A General Survey and Subsequent Characterisation of a Protein Inducible by Ethephon and Redlegged Earth Mite Attack
Authors: Broderick Kevin , Pittock Christopher , Arioli Tony , Creaser Ernest H. , Weinman Jeremy J. , Rolfe Barry G.
Published: August 2004

One of the chief predators of subterranean clover
(Trifolium subterraneum) pastures is redlegged earth
mite (Halotydeus destructor; RLEM). Subterranean clover
pathogenesis-related (PR) proteins induced by RLEM attack and ethephon
treatment were surveyed, and PR proteins with peroxidase, β-1,3-glucanase
and chitinase activities were detected. A protein co-migrating with a
chitinase activity, induced by RLEM predation and treatment with ethephon, was
isolated. It was purified and the N-terminal amino acid
sequence determined. Using a degenerate oligonucleotide primer designed from
this sequence, a corresponding cDNA fragment was amplified by reverse
transcriptase-PCR, then cloned, and used as a probe to screen a subterranean
clover cv. Karridale genomic library. The cDNA and a 97% homologous
genomic clone were sequenced and the deduced amino acid sequence revealed an
open reading frame of 157 amino acids capable of encoding a peptide of 16 478
Da. Significant homology (80%) was found between this protein and an
abscisic acid (ABA)-responsive protein from
Pisum sativum of unknown function which is an
intracellular pathogenesis-related (IPR) protein. The gene encoding this
protein also has homology to pea ‘disease response resistance
genes’ and to proteins from other plant species in the PR-10 family. The
induced protein was designated TsPR-10a due to its
homology to other PR-10 proteins. Genomic Southern analysis indicates that the
gene encoding this protein, designated Ypr10a, is a
member of a multigene family with at least three members. Northern blot
analysis indicates that the subterranean clover Ypr10a
mRNA, or homologous transcript, level is strongly induced by ethephon
treatment in both root and aerial tissues of 3 week old plants. The rapid
induction kinetics of Ypr10a mRNA under ethephon
treatment, its correlation with a putative chitinase activity, and homology to
other PR-protein genes, suggests a pathogenesis-related role for
TsPR-10a protein in subterranean clover.
Effect of soil type on nitrate uptake by wheat shoots characterized using 15N-labelled NH4 NO3-fertilizer and in vitro, leaf nitrate reductase activity
Authors: Hannachi Lynda , Bousser Agnès , Deléens Eliane
Published: August 2004

Wheat plants grown in a greenhouse in containers filled with chalky (CP) or
loamy (LP) soil were fertilized with
NH415NO3 or
15NH4 NO3 (5
atom% 15N), initial soil nitrate levels being
lower in chalky soil. Both the total amount of nitrate and the proportion
derived from fertilizer were higher in leaves of plants grown on chalky soil,
however, increased inorganic N was not paralleled by a higher organic N
content in the CP leaves. In vitro NR activity of the
youngest fully expanded leaves confirmed that NO3 flux
into the shoot was higher for CP than for LP. The ratio of the
‘proportion of fertilizer in the flag leaf NO3
pool divided by the proportion of fertilizer in the soil total N pool’
reached a maximum (0.8) at the onset of the flag leaves for CP but decreased
to 0.5 at the time of flowering because stored NO3 from
fertilizer was predominantly re-used to feed other parts of the plants. In LP,
NO3 was not remobilized and the ratio remained at 0.8.
Higher in vitro NR activity in the CP flag leaf
confirmed that release and re-use of stored nitrate occurred and that plants
grown on chalky soils appear to have an enhanced ability to utilise nitrate.
Leaf Bioelectric Responses to Rhythmical Light: Identification of the Contributions from Stomatal and Mesophyll Cells
Authors: Shabala Sergey N.
Published: August 2004

Bioelectric responses of plant leaves to rhythmical variation of irradiance
were measured using an extracellular electrophysiological technique. The 20
species studied differed in their metabolism, morphology and anatomy. They
included C3 or C4 photosynthesis,
mono- or dicotyledon, cultivated and weed species. For corn, 15 different
lines and hybrids were studied. All of them responded in a frequency-dependent
manner to rhythmical light. Using a resonant analysis approach, three resonant
modes were identified. The resonant response with the greatest amplitude was
observed for light/dark periods of about 40 min. It was associated with
stomatal movements and originated from ion exchange of the guard cells.
Another resonant mode was at a period about 8 min. It seems to reflect the
feedback interaction involving the membrane potential and the cytosolic pH in
mesophyll cells. The third resonant mode, of about 1.5 min period, may link
with thylakoid-related processes. The general feedback model of these leaf
responses to light is proposed and analysed, and the possible contribution of
its components is discussed. It is concluded that the resonant analysis
approach may be used to distinguish between the contributions of stomatal and
mesophyll cells to the composite bioelectric response measured on the leaf
surface. Stomatal cells are the major contributors in a frequency range of
tens of minutes; the mesophyll components have smaller time constants and
their contribution is substantial at higher frequencies.
Possible Participation of β-Cyanoalanine Synthase in Increasing the Amino Acid Pool of Cocklebur Seeds in Response to Ethylene during the Pre-germination Period
Authors: Maruyama Akiko , Yoshiyama Makoto , Adachi Yasuhiro , Nanba Hiroshi , Hasegawa Ryo , Esashi Yohji
Published: August 2004

The amino acid content in cocklebur
(Xanthium pennsylvanicum Wallr.) seeds was increased by
ethylene, which stimulated their germination, regardless of whether they were
non-dormant or secondarily dormant. This increase in amino acid content
coincided with the increased activities of β-cyanoalanine synthase (CAS,
EC 4.4.1.9) in response to ethylene. KCN and/or cysteine, the substrates
of CAS, also increased the amino acid content in both non-dormant and
secondarily dormant cocklebur seeds. The degrees of the increased amino acid
content corresponded roughly to the germination rates of the seeds reported
previously. The actual involvement of CAS in the germination process in
cocklebur seeds was demonstrated by incorporation into asparagine and
aspartate from 14CN which was fed to the cotyledon
segments of both non-dormant and secondarily dormant cocklebur seeds. In this
case, the incorporation of 14CN was augmented by
ethylene, and incorporated more abundantly in the cotyledons of secondarily
dormant seeds. Moreover, ethylene decreased the cysteine + cystine content in
both the axial and cotyledon tissues, but increased asparagine and aspartate
regardless of whether they were non-dormant or secondarily dormant. This
suggests that CAS responsiveness to ethylene participates in supplying
asparagine and aspartate and in increasing the amino acid pool of cocklebur
seeds during the pre-germination period.
Modelling Site Productivity of Eucalyptus globulus in Response to Climatic and Site Factors
Authors: Battaglia Michael , Sands Peter
Published: August 2004

A simple model, PROMOD, predicts the growth of a forest following canopy
closure, i.e. under conditions in which the foliage biomass has attained a
steady state. The principal output from PROMOD is peak mean annual increment.
However, additional output available includes the closed-canopy leaf area
index, evapotranspiration and water use efficiency. In addition, an indication
of biomass partitioning around the time of peak MAI and the relative effects
different environmental factors play in limiting production can be obtained.
PROMOD is based on a generalisation of a simple forest growth model which
predicts biomass production and partitioning at the stand level with a daily
or annual time step. The minimum level of inputs required by PROMOD are of a
quality and quantity that forest managers can readily and cheaply obtain for
screening prospective plantation sites: the latitude, longitude, altitude,
slope and aspect of the site and a classification of the soil depth, texture,
stoniness, drainage and a rating of site fertility. However, PROMOD can be run
using daily inputs of weather data and hence predict the seasonal variation of
production. The closed-canopy leaf area index is calculated from the mean
annual rainfall and temperature at the site, and a simple rating of site
fertility. Annual production is calculated as the sum of daily production and
takes diurnal temperature variation and possible seasonal photosynthetic
acclimation into account. A simple soil water balance model is included in
which water use is based on a crop factor which is a function of soil water
content and a water use efficiency which is a function of vapour pressure
deficit. The model was developed on the basis of data from nine plots of
Eucalyptus globulus in south-eastern Tasmania and in
Western Australia, and was validated using data from 19 plots in northern
Tasmania.
Photoperiod alters partitioning of newly-fixed 14C and reserve carbon into sorbitol, sucrose and starch in apple leaves, stems, and roots
Authors: Wang Z. , Yuan Z. , Quebedeaux B.
Published: August 2004

The experiment was designed to determine how photoperiod duration affected the
partitioning of newly-fixed 14C and reserve carbon into
sorbitol, sucrose, and starch in apple source leaves, young sink leaves,
stems, and roots. Apple plants (Malus domestica Borkh.
cv. Gala), 1-year-old, were grown in environmental growth chambers and
received five different photoperiod treatments of 1, 4, 7, 10 and 14 h for 8
d. On the eighth day of the light treatments, plants were exposed to
14CO2 for 15 min and harvested at
0, 2, 6, 12 and 24 h after labelling for carbohydrate and
14C-carbohydrate analyses. Sorbitol and starch
concentrations in leaves, stems, and roots increased as photoperiod increased,
and peaked near 10-h photoperiod. Sucrose concentrations, however, either did
not change in mature leaves or decreased slightly in stems as photoperiod
increased from 1 to 14 h. At 24 h after 14
CO2 labelling, plants grown in longer photoperiods had
less [14C]sucrose,
[14C]sorbitol and
14C-total soluble fraction remaining in mature leaves,
but more 14C activities in stems and roots than those
grown in shorter photoperiods. We suggest that the increases in
14C-carbohydrates in stems and roots under longer
photoperiods are due to increased carbon export from mature source leaves.
Nitrogen status affects UV-B sensitivity of cucumber
Authors: Hunt J.E. , McNeil D.L.
Published: August 2004

The effects of an increase in ultraviolet-B radiation (UV-B, 280–320 nm)
on growth, photosynthesis and photoinhibition of a UV-B sensitive variety of
cucumber (Cucumis sativus L. cv. Poinsett) were
investigated at four levels of applied nitrogen (N, 0.5, 2.0, 5.0 and 10.0 mol
m-3). Plants were grown for 33 days in a UV-B
transparent greenhouse at ambient and ambient +25% biologically
effective UV-B radiation (UV-BBE). A modulated lamp
system controlled supplemental UV-B levels; average doses of
UV-BBE were 2.5 ± 0.8 (ambient) and 3.1 ±
1.0 (ambient +25%) kJ m-2
d-1. The doses are comparable to the expected change in
UV-BBE between 1979 and 1999 under similar weather
conditions at this latitude. Plant biomass, height, and leaf N, chlorophyll
and leaf carbon content increased with increasing amounts of applied N. At the
highest level of N application, supplemental levels of UV-B caused a near
identical decrease in leaf area (20%), height (28%) and total
biomass (20%) compared with plants grown under ambient UV-B conditions.
There was no such effect when N stress was imposed. Apparent quantum yield
(?app), dark respiration and photosynthetic rate
were unaffected by the supplemental UV-B and photodestruction of reaction
centres was not evident. However, there was a significant increase in
photoinhibition at midday in the N-replete plants. In leaves with N content
Two members of the Bet v 1 gene family encoding birch pathogenesis-related proteins display different patterns of root expression and wound-inducibility
Authors: Poupard Pascal , Strullu Désiré-Georges , Simoneau Philippe
Published: August 2004

Bet v 1-SC genes constitute a subset of a multigene
family in birch (Betula pendula Roth) that includes the
gene for the major pollen allergen and encode proteins belonging to a new
family of intracellular pathogenesis-related proteins. We have investigated
the expression in birch roots of the Bet v 1-SC1 and
Bet v 1-SC3 genes by northern and
reverse-transcription-polymerase chain reaction analyses. Only
Bet v 1-SC3 was found to be highly expressed in roots
under basal conditions but this gene was not wound-inducible. Conversely the
expression of the Bet v 1-SC1 gene was markedly
transiently induced 8 to 9 h after the stress. Immunoblotting with polyclonal
antiserum raised against the major birch pollen allergen confirmed that Bet v
1-related polypeptides are present in root extracts. This first report of
Bet v 1-SC gene expression and wound-inducibility in
birch roots suggests a possible function of proteins encoded by these genes in
plant defense and/or root organogenesis.
Photosynthesis, carbon partitioning and metabolite content during drought stress in peach seedlings
Authors: Escobar-Gutiérrez A. J. , Zipperlin B. , Carbonne F. , Moing A. , Gaudillére J.P.
Published: August 2004

Photosynthesis, metabolic carbon partitioning and the contribution of sorbitol
to the osmotic potential of mature peach (Prunus persica
(L.) Batsch) leaves and phloem sap were examined in plants undergoing two
levels of a short term drought stress. The relationship between osmotic
potential at full turgor and water potential showed that neither mild nor
severe drought stress induced a significant active osmotic adjustment in
mature leaves. The osmotic potential of leaves at full turgor was -1.9 MPa;
sorbitol was the major organic component (20%). Leaf sucrose and starch
contents were significantly reduced by drought. The partitioning of
newly-fixed carbon was also affected by stress. These changes appeared to
originate from the inhibition of photosynthesis induced by drought stress. At
low photosynthetic rates, the turnover of organic ions was low, and sorbitol
synthesis was favoured over that of sucrose. Water stress did not affect the
in vitro activity of sucrose phosphate synthase (EC
2.4.1.14), the key enzyme in sucrose synthesis. The
in vitro activity of aldose-6-phosphate reductase (EC
1.1.1.200), the key enzyme in sorbitol synthesis, tended to increase linearly
in response to drought stress. It is concluded that, contrary to some other
polyol-synthesising species, peach did not seem to benefit from sorbitol
synthesis during short term drought stress for active osmotic adjustment in
mature leaves. However, in phloem sap, increases in sucrose and especially
sorbitol concentration were observed in stressed plants.
Hormonal control of ear abortion in a stress-sensitive maize (Zea mays) inbred
Authors: Lejeune Pierre , Prinsen Els , Onckelen Henry Van , Bernier Georges
Published: August 2004

A cold-sensitive maize (Zea mays L.) inbred was used as
a model for investigating the interactions between growth regulators,
reproductive development, and environmental stress. In this genotype, a
chilling treatment given just before floral transition caused the topmost ear
to abort and be replaced at maturity by a sterile, leaf-like, structure.
Exogenous applications of the synthetic auxin 2,4-dichlorophenoxyacetic acid
or of the cytokinin benzyladenine respectively mimicked or prevented the
abortive response caused by chilling. Chilling also induced a moderate
decrease in the content of endogenous indoleacetic acid (IAA) in the apical
shoot tissues. By contrast, zeatin-type cytokinins decreased dramatically
(5–8 fold), both in the apical shoot tissues and in the xylem exudate of
chilled plants. Overall, the ratio of free-IAA to zeatin-cytokinins was
increased in the apical shoot of chilled plants. Our results suggest that: (1)
ear abortion induced by chilling might be related to an altered cytokinin
content; (2) the number of developing ears may be limited by the endogenous
levels of cytokinins just before floral transition; and (3) cytokinins may
have a potential for increasing yield in maize.
Relationship between the inhibition of leaf respiration by light and enhancement of leaf dark respiration following light treatment
Authors: Atkin Owen K. , Evans John R. , Siebke Katharina
Published: August 2004

Respiration (R, non-photorespiratory mitochondrial
CO2 release) in leaves is inhibited by light. However,
exposure to darkness after a period of illumination can also result in
R being temporarily stimulated (termed ‘light
enhanced dark respiration’, LEDR). We used a fast-response
CO2 exchange system to investigate these observations in
tobacco leaves. After switching off the light, there were two peaks of
CO2 release, the first at 15–20 s (the
photorespiratory post-illumination burst) and the second at 180–250 s
(LEDR). LEDR occurred in all post-illumination experiments, independent of
O2 or CO2 concentration. However,
LEDR increased with increasing irradiance during the pre-dark period,
suggesting some dependency on prior photosynthesis. We investigated the
inhibition of R by light at low
CO2 concentrations (?*):
?* is the intercellular CO2
concentration at which net CO2 release represents R in
the light. The inhibition of R in the light took about 50 s and was even
evident at 3 mmol photons m-2 s-1,
regardless of the light quality (red, blue or white). The inhibition of
R by light showed similar dependency on irradiance as
LEDR, such that the degree of inhibition was positively correlated with the
level of LEDR. In the light, switching from 350 ppm to a low
CO2 concentration that resulted in the intercellular
CO2 concentration being at ?*,
resulted in R initially increasing and then stabilising.
Maintaining the leaf at ?* did not, therefore, lead
to an underestimation of R. Our data suggest that a
common mechanism may be responsible for both the inhibition of
R by light and LEDR.
Separation of sugars, polyols, proline analogues, and betaines in stressed plant extracts by high performance liquid chromatography and quantification by ultra violet detection
Authors: Naidu Bodapati P.
Published: August 2004

Osmoprotectants such as (i) sugars and sugar alcohols
(polyols), (ii) proline and its analogues, and (iii) a
number of quaternary ammonium compounds (betaines) play a significant role in
plant adaptation to environmental stresses. Lack of a simple and rapid
technique for the extraction and simultaneous determination of these
osmoprotectant solutes from a large number of samples originating from plant
breeding populations and agronomic trials, led to the development of this
method.
Osmoprotectants were extracted using methanol-chloroform-water. Extracts were
partially purified, where required, by treating with ion exchange resins.
Solutes were separated using a high performance liquid chromatograph fitted
with a Sugarpak-1 column and 5 mg L-1 Ca-EDTA solution
as the mobile phase. The eluted solutes were quantified by ultra violet
detection at 195 nm. This technique measures sugars/polyols, proline
analogues, and betaines in a variety of plant species such as peanut,
Melaleuca uncinata, and cotton, respectively. Pinitol
levels in peanut estimated using this method correlated significantly with the
determinations obtained by HPLC-refractive index determination
(R2 = 0.983,
P<0.001). Glycinebetaine determinations in cotton
using this method were significantly correlated with determinations achieved
by 1H NMR spectroscopy
(R2 = 0.989,
P<0.001). Cotton leaf extracts spiked with a range of
authentic glycinebetaine levels were also precisely measured using this
technique (R2 =0.999,
P<0.001). The described method is simple, rapid,
sensitive, cost effective and simultaneously measures more than one class of
osmoprotectants from a single chromatographic run.
A modified assay method shows leaf sucrose-phosphate synthase activity is correlated with leaf sucrose content across a range of sugarcane varieties
Authors: Grof Christopher P.L. , Knight Deon P. , McNeil Scott D. , Lunn John E. , Campbell James A.
Published: August 2004

Eight different commercial and breeding varieties of sugarcane
(Saccharum spp.) grown in controlled conditions were
assayed for leaf sucrose-phosphate synthase (SPS) (EC 2.1.4.14) activity and
leaf sucrose content. Leaf SPS activity measured at 25˚C ranged between
0.06 and 0.14 nmol sucrose formed mg protein -1
min-1. The cross-varietal average for leaf SPS activity
was 0.10 nmol µg protein-1
min-1 (equivalent to 63.4 µmol
h-1 g FW-1 or 17.6 nkat g
FW-1) which is consistent with previously published leaf
SPS activities for sugarcane; however, previous studies have assayed leaf SPS
activity at either 30 or 37˚C. The range of leaf sucrose content across
varieties (5.5–18.0 mg sucrose g FW-1, average
11.3 mg g FW-1) was consistent with all but one of four
previously published reports. Leaf SPS activity and leaf sucrose content were
significantly correlated across the eight varieties examined
(r2 =0.877, d.f.
=7,P<0.001). Whilst previous reports have
indicated a co-relationship between leaf SPS activity and leaf sucrose content
in single sugarcane varieties both diurnally and with different nutrient
regimes, this study shows, for the first time, that this co-relationship also
holds true across a range of sugarcane varieties.
Cloning and characterisation of ripening-induced ethylene biosynthetic genes from non-climacteric pineapple (Ananas comosus) fruits
Authors: Cazzonelli Christopher Ian , Cavallaro Antonino Salvatore , Botella José Ramón
Published: August 2004

To gain a better understanding of non-climacteric fruit ripening, pineapple
was used as a model system to clone and characterise two ripening-inducible
cDNAs coding for two enzymes of the ethylene biosynthetic pathway,
1-aminocyclopropane-1-carboxylate (ACC) synthase
(acacc-1) and 1-aminocyclo-propane- 1-carboxylate
oxidase (acaco-1) respectively. Due to the extreme
acidity and high polyphenolic content of pineapple fruits, a method was
optimised for the extraction of high quality RNA from fruit tissue.
acacc-1 is a 1080 bp ACC synthase cDNA fragment encoding
360 amino acids including 10 of the 12 amino acid residues conserved in all
aminotransferases. Comparison of the deduced amino acid sequence with
previously reported ACC synthases shows between 52 and 67% similarity
at the protein level. Southern analysis suggests the presence of only one copy
of acacc-1 in the pineapple genome. Although some
acacc-1 expression is detected in green fruits, there is
a 16-fold increase in the level of acacc-1 in ripe fruit
tissue. acaco-1 is a partial length cDNA clone of 611 bp
which codes for 203 amino acids representing approximately 66% of the
ACC oxidase open reading frame. Southern analysis suggests the presence of one
or two copies of the gene in the pineapple genome. Northern analysis shows the
expression of acaco-1 to be highly induced in wounded
leaf tissue and to a lesser extent in ripening fruit tissue. The accumulation
of ACC-synthase and ACC oxidase mRNAs during pineapple fruit ripening raises
new questions about the putative role of ethylene during non-climacteric fruit
ripening.
Effects of elevated CO2 on development and morphology of spring wheat grown in cooled and non-cooled open-top chambers
Authors: Oijen M. van , Schapendonk A.H.C.M. , Jansen M.J.H. , Pot C.S. , Kleef J. van , Goudriaan J.
Published: August 2004

Facilities for studying effects of elevated CO2 on crops
affect the microclimate in the crop. Open-top chambers may increase
temperature by 1–3˚C compared to ambient conditions.
This paper describes a newly developed cooling system for open-top chambers.
In 1995 and 1996, experiments were carried out to test the system and analyse
the effects of temperature on crop phenological and morphological response to
elevated CO2. Spring wheat
(Triticum aestivum L. cv. Minaret) was subjected to
ambient and doubled CO2 concentration in both cooled and
non-cooled chambers.
The cooling system reduced temperature by 1.6–2.4˚C, and this
delayed maturity by 10 days. In contrast, elevated CO2
did not affect phenological development. Elevated CO2
reduced tiller density, green leaf number per tiller and specific leaf area,
thereby reducing the capacity for light interception of the crop. Crop height
growth before anthesis mainly responded to temperature, but after anthesis it
was only affected by CO2, indicating a shift from sink-
to source-limited growth. For none of the parameters studied, a significant
statistical interaction of CO2 and temperature was
found.
The cooling system proved effective. Atemperature difference of about 2˚C
affected crop development and morphology more strongly than
CO2 doubling. However, the absence of
CO2-temperature interaction suggests that
CO2 effects may validly be investigated even without a
cooling system.