bluuebunny/crossref_metadata_2025 huggingface dataset:
Expression of the Rhizobium leguminosarum biovar phaseoli melA Gene in Other Rhizobia Does Not Require the Presence of the nifA Gene
Authors: Cubo Teresa , Romero Francisco , Vinardell Jose M. , Ruiz-Sainz Jose E.
Published: August 2004

Many different Rhizobium strains produce melanin
(Mel+) when grown on solid media supplemented with
L-tyrosine. The composition of the media and the culture conditions are of
great importance for pigment production. Previous reports showed that some
Rhizobium leguminosarum biovar
phaseoli strains that produce the pigment in complete
solid media (TY) failed to produce the pigment in minimal media (SY)
supplemented with L-tyrosine or in TY liquid media. In this paper we have
investigated different R. fredii,
R. meliloti, R. etli and
R. leguminosarum bv. trifolii and
phaseoli strains (all of them Mel+
in solid media) for their ability to produce the pigment in liquid media. All
Rhizobium species tested, except
Rhizobium etli, were Mel+ in
liquid media and in all cases the pigment yielded maximum absorption peaks at
280 and 315 nm. Melanin production by other bacteria (such as
Vibrio, Streptomyces or
Azospirillum) is enhanced by the presence of amino acids
other that tyrosine. In this paper we show that the addition of L-methionine,
which is not a precursor of rhizobial melanins, stimulated pigment production
by Rhizobium cultures supplemented with L-tyrosine. The
role of melanin production by Rhizobium strains is
unclear. One hypothesis is that the Rhizobium
tyrosinase, a bifunctional copper-containing enzyme that is essential for
melanin biosynthesis, could detoxify polyphenolic compounds which might
accumulate in senescing nodules. We show here that
R. etli and R. fredii bacteroids
produced melanin, which supports the idea that bacteroids contain the enzyme
tyrosinase. Previous reports showed that, in
R. leguminosarum bv. phaseoli
strain 8002, the expression of the tyrosinase gene
(melA) is dependent on the presence of
nifA, a regulatory gene that is located in the symbiotic
plasmid. However, transfer of R. leguminosarum bv.
phaseoli melA gene to pSym-cured derivatives of
R. leguminosarum bv. trifolii and
viciae, R. fredii and
Rhizobium sp. (Hedysarum) produced
Mel+ transconjugants. DNA-hybridisation experiments
showed that the pSym-cured strains did not contain any copy of
nifA. Therefore, in contrast to the results reported on
R. leguminosarum bv. phaseoli
strain 8002, the expression of the melA gene in other
rhizobia is not nifA-dependent.
Key words: Rhizobium, melanin.
The pattern of flowering, seed set, seed growth and ripening along the ear of Lolium perenne
Authors: Warringa J.W. , Struik P.C. , Visser R. de , Kreuzer A.D.H.
Published: August 2004

A greenhouse pot experiment was conducted to elucidate the pattern of
decreasing seed set and seed dry weight found from the basal to the upper
spikelet in Lolium perenne L. ears and—very
markedly—acropetally within a spikelet. The changes in fresh and dry
weight of the seed after anthesis were monitored for 12 positions within the
ear. To determine the duration of seed growth, the spatial and temporal
patterns of flowering and ripening along the ear were assessed. The proximal
florets of the central spikelets flowered first, and the upper spikelets in
the ear flowered before the basal spikelets, with flowering proceeding
acropetally within a spikelet. The upper spikelets ripened earlier than the
basal ones, and the seeds within a spikelet ripened simultaneously. These
patterns of flowering and ripening along the ear resulted in different
durations of seed growth along the ear. Thus from the proximal to the distal
seed within a spikelet the duration of growth decreased by 26%, the
rate of growth fell by 48% and seed set and seed dry weight also fell
sharply. Of the total variation in maximum, final seed dry weight within the
ear, 4% could be attributed to the difference in seed dry weight
between spikelets and 89% to differences in seed dry weight within
spikelets. Differences in duration and rate of seed growth and seed set were
also much smaller between spikelets than within spikelets. About 60% of
the differences in seed dry weight along the ear were attributable to
differences in growth rate and about 30% to differences in the duration
of seed growth. The relative growth rate did not differ between seeds in
different positions. The main factor determining seed growth rate was the dry
weight of the ovule at anthesis, which declined sharply from the proximal to
the distal floret within a spikelet. Analysis of the fructose, glucose,
sucrose and starch concentrations showed that seed growth was not limited by
the availability of sucrose nor by the ability of the seeds to convert sucrose
into starch. These conclusions were supported by results from a second
greenhouse experiment in which all ovules in 50% of the spikelets were
removed at anthesis. Dry weight of the remaining seeds increased by only
15%.
Effects of Nitrogen on the Photosynthetic Apparatus of Clematis vitalba Grown at Several Irradiances
Authors: Bungard Ralph A. , McNeil David , Morton James D.
Published: August 2004

Effects of nitrogen supply (N-supply) on the photosynthetic apparatus of
Clematis vitalba L. grown at several irradiances were
determined by measuring soluble protein content, rubisco activity,
photosynthetic pigment content and composition, and the photochemical
efficiency of photosystem II
(Fv/Fm).
Compared to low irradiance (3 and 10% full sunlight), leaves grown at
higher irradiance (up to full sunlight) had up to 5–6 times the soluble
protein content and rubisco activity, and up to 2–4 times the total
carotenoid content, on both a leaf area and a chlorophyll basis. On a leaf
area basis, decreased N-supply reduced soluble protein concentration, rubisco
activity and total carotenoid concentration to a greater extent at high
compared to low irradiance. On a chlorophyll basis, in contrast, soluble
protein and rubisco activity decreased by over 40% with increased
N-supply (1.0–0.1 mol m-3) at high irradiance but
N-supply did not influence the concentration of total carotenoids. Leaves
grown at high compared to low irradiance had a greater concentration of
xanthophyll cycle pigments (V+A+Z), β-carotene and lutein (but
not neoxanthin) on a chlorophyll basis, and a slightly lower
Fv/Fm.
Nitrogen- supply did not influence the composition of the photosynthetic
pigment pool,
Fv/Fm,
or the extent of de-epoxidation of the V+A+Z pool. The results
suggest that irradiance-acclimation of C. vitalba can
occur regardless of N-supply. Under N limitation at high irradiance, a balance
between light capture and photosynthetic capacity is important rather than an
increase in xanthophyll cycle-dependent energy dissipation. The importance of
lutein as a light-harvesting pigment is questioned. A rapid method for the
reversed phase-HPLC separation of carotenoids is described.
The Role of Sucrose-Phosphate Synthase in the Control of Photosynthate Partitioning in Zea mays Leaves
Authors: Lunn John E. , Hatch Marshall D.
Published: August 2004

The influence of light and leaf sucrose content on partitioning of
photosynthate and sucrose-phosphate synthase (SPS) activity in maize
(Zea mays L.) leaves was investigated. The ratio of
partitioning of photosynthate between sucrose and starch shifted from about
17:1 to 2:1 when the irradiance was increased from 180 to 1450 µmol
quanta m-2 s-1. Increasing the
sucrose content of the leaves had little effect on the partitioning ratio. SPS
from illuminated leaves had a higher affinity for its substrates, UDPGlc and
Fru6P, and was less inhibited by
Pi than the enzyme from darkened leaves but the
Vmax was unaffected. SPS was fully
light activated at an irradiance of 340 but not 180 µmol quanta
m-2 s-1. Increasing the sucrose
content of maize leaves more than 3-fold had little or no effect on the
activation state of SPS which, together with the partitioning data, suggests
that sucrose does not exert significant short-term feedback inhibition of its
own synthesis in this species.
Symbiotic Vesicular-Arbuscular Mycorrhizae Influence Maximum Rates of Photosynthesis in Tropical Tree Seedlings Grown Under Elevated CO2
Authors: Lovelock C. E. , Kyllo D. , Popp M. , Isopp H. , Virgo A. , Winter K.
Published: August 2004

To investigate the importance of phosphorus and carbohydrate concentrations in
influencing photosynthetic capacity of tropical forest tree seedlings under
elevated CO2, we grew seedlings of
Beilschmiedia pendula (Sw.) Hemsl. (Lauraceae) under
elevated CO2 concentrations either with or without
vesicular-arbuscular (VA) mycorrhizae. VA-mycorrhizae increased phosphorus
concentrations in all plant organs (leaves, stems and roots). Maximum rates of
photosynthesis (Amax) measured
under saturating levels of CO2 and light were correlated
with leaf phosphorus concentrations. VA-mycorrhizae also increased leaf
carbohydrate concentrations, particularly under elevated
CO2, but levels were low and within the range observed
in naturally occurring forest species. Root carbohydrate concentrations were
reduced in VA-mycorrhizal plants relative to non-mycorrhizal plants. These
results indicate an important role for VA-mycorrhizae in controlling
photosynthetic rates and sink strength in tropical trees, and thus in
determining their response to future increases in atmospheric
CO2 concentrations.
Photosynthetic Responses of Three Codominant Species from the North-western Sonoran Desert - a C3 Deciduous Sub-shrub, a C4 Deciduous Bunchgrass, and a CAM Evergreen Leaf Succulent
Authors: Nobel Park S. , Zhang Hehui
Published: August 2004

To investigate seasonal and annual influences of environmental conditions on
leaf net CO2 uptake (A), three
codominant species from the north-western Sonoran Desert differing in
photosynthetic pathway and leaf phenology were examined: the
C3 deciduous sub-shrub
Encelia farinosa, the C4 deciduous
bunchgrass Pleuraphis rigida, and the CAM evergreen leaf
succulent Agave deserti. To allow interspecific
comparisons and to predict field responses from 1974 through 1995, an
environmental productivity index (EPI) model previously developed for CAM
plants was used, which scaled the responses of A to
water, temperature, and photosynthetic photon flux (PPF) over 24-h periods to
individual dimensionless values. The net CO2 uptake
predicted using the EPI approach agreed well with field measurements.
Agave deserti was the most drought-tolerant and
E. farinosa was the least; the optimum day/night air
temperatures and the PPF requirement for A were highest
for P. rigida and lowest for
A. deserti. For 1974 through 1995, daily EPI averaged
over a year was highest for E. farinosa, indicating that
it operates closest to its photosynthetic optimum. However, the predicted
A was highest for P. rigida.
Variations in A were annually bimodal, with the greatest
differences among the three species in wet years. Afor
all three species increased linearly as annual rainfall increased. Leaf area
per plant for E. farinosa was highest in the winter and
early spring and did not respond appreciably to summer rainfall; leaf area for
P. rigida was also highest in the winter. For the
evergreen A. deserti, which based on ground cover is the
dominant species at the field site, new leaves unfolded in response to both
winter and summer rainfall but most photosynthetic area was contributed by
older leaves, leading to the highest annual plant net
CO2 uptake.
The Kinetics Associated with Phosphate Absorption by Arabidopsis and its Regulation by Phosphorus Status
Authors: Dunlop J. , Phung H.T. , Meeking R. , White D.W.R.
Published: August 2004

The effects of phosphorus status on the kinetics of phosphate absorption by
3-day-old Arabidopsis thaliana (L.) Heynh. seedlings
were studied. Seeds were germinated for 3 days on agarose gel containing
different amounts of phosphate and the absorption of
32P-labelled phosphate by these seedlings was measured
at a range of phosphate concentrations. The absorption rates for seeds
germinated in the absence of phosphate were up to four times faster than for
seedlings germinated on gels containing 1, 5 or 10 mM phosphate. The kinetic
constants Km and Vmax were
determined by fitting the data to models with one and two mechanisms operating
in parallel. A model with two mechanisms was needed to provide a good fit to
the data for concentrations ranging from 0.5 µM to 5 mM. For the high
affinity mechanism, Km,1 (mean value 12.3 µM ) was
not affected as phosphorus status increased but Vmax,1
decreased. For the low affinity mechanism the values for both
Km,2 (5697–16547 µM) and
Vmax,2 increased with increasing phosphorus status.
Arsenate inhibited phosphate absorption but only moderately. Varying the pH
over the range 4.8 to 7.3 did not affect the rate of absorption. It is
concluded that a kinetic approach may not have sufficient resolution to
discriminate between different mechanisms unless there are large quantitative
differences in the constants Kmor
Vmax.
A Comparison of Scenarios for the Effect of Global Climate Change on Cotton Growth and Yield
Authors: Reddy K. Raja , Hodges Harry F. , McKinion James M.
Published: August 2004

If global surface temperatures change as projected because of radiative and
physiological effects of a changing environment, we should expect important
changes in crop production in the 21st Century. Experiments were conducted at
ambient and twice ambient atmospheric CO2 concentrations
at five temperatures. The 1995 temperature in Mississippi was used as a
reference with the other temperatures being 1995 minus 2˚C, and 1995 plus
2, 5 and 7˚C. Daily and seasonal variation and amplitudes were
maintained. Seedlings had 4–6 times as much leaf area and dry weight at
20 d after emergence when grown at 28˚C as at 23˚C (1995 ambient)
average temperature during that growth period. Number of days to first square,
flower, and open boll decreased as temperature increased. Double atmospheric
CO2 did not affect these developmental rates.
Temperatures above 28˚C, or 1995 average whole-season temperatures, were
detrimental to mid- and late-season boll retention and growth. No fruits were
retained to maturity at 1995 plus 5 or 7˚C. However, whole season
vegetative growth was not significantly reduced by temperature
5–7˚C above the 1995 ambient conditions. Twice ambient
CO2 caused about 40% increase in vegetative dry
matter accumulation across temperatures. In a separate experiment, similar
results were obtained on fruiting cotton grown at a range of temperatures
based on long-term average US Midsouth July temperatures. Therefore, if global
warming occurs as predicted, food and fibre production in such
high-temperature and humid environments may be more limited to vegetative
structures and the animals that consume vegetative structures.
Oxygen-sensitive Differences in the Relationship between Photosynthetic Electron Transport and CO2 Assimilation in C3 and C4 Plants during State Transitions
Authors: Andrews James R. , Baker Neil R.
Published: August 2004

Wheat (C3) and maize (C4) leaves
were exposed to light treatments that were limiting for
CO2 assimilation and which excite preferentially
photosystem I (PSI) or photosystem II (PSII) and induce State 1 or State 2,
respectively. In order to examine the relationships between linear electron
transport and CO2 in leaves during State transitions,
simultaneous measurements of CO2 assimilation,
chlorophyll fluorescence and absorbance at 820 nm were used to estimate the
quantum efficiencies of CO2 assimilation and PSII and
PSI photochemistry. In wheat leaves with photorespiratory activity, no
significant change in quantum efficiency of
CO2assimilation was observed during State transitions.
This was not the case when photorespiration was inhibited with either
2% O2 or 1000 ppm CO2 and
transition from State 2 to State 1 was accompanied by a large decrease
(c. 20%) in the quantum efficiency of
CO2 assimilation which was not associated with a
decrease in the quantum efficiency of electron transport through PSII.
Photorespiration appears to buffer the quantum efficiency of
CO2 assimilation from changes associated with decreases
in the rate of CO2 fixation resulting from imbalances in
PPFD absorption by PSI and PSII.
When maize leaves were subjected to similar State transitions, no significant
change in the quantum efficiency of CO2 assimilation was
observed on transition from State 2 to State 1, but on switching back to State
2 a very large decrease (c. 40%) was observed.
This decrease could be prevented if leaves were maintained in either 2%
O2 or 593 ppm CO2. The possible
occurrence of photorespiration in maize leaves on transition from State 1 to
State 2, which could result from an inhibition of the
CO2 concentrating mechanism, cannot account for the
decrease in the quantum efficiency of CO2 assimilation
since the relationship between PSII electron transport and
CO2 assimilation remained similar throughout the State
transitions. Also changes in the phosphorylation status of the
light-harvesting chlorophyll a/b protein associated with
PSII cannot be implicated in this phenomenon.
Molecular Evolution of C4 Phosphoenolpyruvate Carboxylase in the Genus Flaveria
Authors: Westhoff Peter , Svensson Per , Ernst Karin , Bläsing Oliver , Burscheidt Janet , Stockhaus Jörg
Published: August 2004

C4 plants are known to be of polyphyletic origin and
have evolved independently several times during the evolution of angiosperms.
We are interested in understanding the molecular changes that the
C4 genes have undergone as they were adapted to their
new functions in C4 photosynthesis and are using the
C4 phosphoenolpyruvate carboxylase
(PEPC) of the genus Flaveria as a model. The PEPCs of
F. trinervia (C4) and
F. pringlei (C3) are encoded by a
gene family that is composed of at least three different gene classes named
ppcA, ppcB and
ppcC. The C4 PEPC of
F. trinervia is encoded by the
ppcA gene class and is expressed at high levels only in
the mesophyll cells of the leaves. The nearest neighbour to the
ppcA gene class of F. trinervia is
found in F. pringlei. Comparisons of this pair of
orthologous gene classes are used to identify the C4
-specific differences between the enzymatic properties of the
ppcA PEPCs and the activities of the
ppcA promoters. The two ppcA PEPCs
are 96% identical, but differ in the Km for
phosphoenolpyruvate (PEP) and their inhibition by
malate. Chimerical PEPCs are presently constructed to map the differences in
the enzymatic properties of the C4 and
C3 PEPC isoforms. To investigate determinants for the
C4 specific expression pattern, the 5´ flanking
regions of the ppcA1 genes of
F. trinervia and F. pringlei were
fused to the uidA reporter gene encoding
ß-glucuronidase and transformed into the C4 plant
F. bidentis and the C3 species
tobacco. In F. bidentis, the
C4ppcA1 promoter drives a high
level of expression of the transgene only in the mesophyll cells, while the
C3ppcA1 promoter leads to low
levels of expression in leaves, stems and roots. Determinants for the
C4 specific expression of the
ppcA1 gene of F. trinervia must
therefore be located in the 5´-flanking region of this gene. Further
analyses showed that two regions, a proximal and a distal segment, are
sufficient to generate the C4 specific expression
pattern. In tobacco, the C4ppcA1
promoter is preferentially expressed in the palisade parenchyma cells of the
leaves. These results indicate that the major events during the evolution of
the C4ppcA promoter occurred at
the promoter level.
Resolving C4 Photosynthesis: Trials, Tribulations and Other Unpublished Stories
Authors: Hatch Marshall D.
Published: August 2004

In this lecture the author reminisced about three critical phases of research
on C4 photosynthesis.These case histories had their
origins in the very early studies of the process but then spanned most of the
intervening period.
The Activity of a Tobacco Basic Chitinase Promotor in Transgenic White Clover Provides Insights into Plant Development and Symbiosis
Authors: Pittock Christopher , Weinman Jeremy J. , Rolfe Barry G.
Published: August 2004

White clover was transformed with a tobacco basic chitinase promoter:GUS
fusion. Basic chitinase promoter activity was detected by histochemical
staining. Comparison of the spatial and temporal expression of the chitinase
promoter-driven GUS gene in tobacco to that in white clover indicates that
transcription from the promoter is induced by similar developmental and
environmental response programs in each species. Wound-responsiveness of the
white clover transgene was rapid and localised following mechanical and aphid
(Family Aphididae) wounding. Developmental expression of the transgene during
root morphogenesis reveals strong expression in tap and lateral root meristems
but expression in lateral root meristems was observed only after the emergence
through the tap root epidermis. No expression of the transgene was detected in
the pericycle or the dividing cells of the developing lateral root. The
expression of the tobacco basic chitinase promoter:GUS transgene in white
clover was then used as a marker to examine the differences between the early
developmental pathways leading to lateral root formation and those involoved
in nodule formation in response to Rhizobium
inoculation. Inoculation of the zone of emerging root hairs with a
nodulation-competent Rhizobium strain ANU845(pRI4003),
triggered transient transgene expression 2 to 4 h post-inoculation. No
transgene expression was detectable after inoculation with purified Nod factor
from strain ANU843. Our results suggest that lateral roots and nodules differ
both in some of the mechanisms required to initiate cell division, and in
their ongoing development after the emergence from the root epidermis.
Voltage Control of Calcium Influx in Intact Cells
Authors: Reid Robert J. , Tester Mark A. , Smith F. Andrew
Published: August 2004

This work describes quantitative measurements of membrane fluxes of
Ca2+ in intact cells of
Chara corallina Klein ex Will. em. R.D. Wood, in
relation to the control of Ca2+ uptake by membrane
voltage (PD). At the normal resting PD, 45Ca influx was
low but was stimulated up to 25-fold when the membrane was depolarised by
voltage clamping to values more positive than –100 mV . Similarly, in
cells in which the PD was varied by changing the concentration of
K+ in the external solution, influx was strongly
stimulated in the depolarised state. Transient depolarisation during action
potentials resulted in large influxes of 45Ca which,
when averaged over the duration of the action potential, yielded influxes of
up to 2000 times higher than the resting level. Thus, there appears to be a
large surplus of Ca2+ channels over that required for
adequate nutrition. The possible physiological role of voltage-dependent
Ca2+ channels is discussed in relation to the fact that,
under normal growth conditions, cells of Chara corallina
exist in the hyperpolarised state where these channels would not be activated.
Diverse Mechanisms Regulate the Expression of Genes Coding for C4 Enzymes
Authors: Taylor William C. , Rosche Elke , Marshall Jerry S. , Ali Shahjahan , Chastain Chris J. , Chitty Julie A.
Published: August 2004

Most of the enzymes of the C4 pathway of photosynthesis
are compartmentalised in either mesophyll or bundle sheath cells. We have
begun to dissect the mechanisms controlling the cell-specific expression of
genes coding for C4 enzymes by locating the regulatory
DNA sequences from two genes in the transformable C4
dicot, Flaveria bidentis. We show that chloroplast and
cytosolic forms of pyruvate,orthophosphate dikinase are encoded by a single
gene, Pdk. By fusing selected regions of the
Pdk gene, to the gusA reporter
gene we were able to infer promoter activities from measurements of GUS enzyme
activity in transgenic F. bidentis plants. We show that
the 5´ end of the Pdk gene contains sequences
controlling high-level, mesophyll-specific expression of the
C4 form of the enzyme. The promoter controlling
low-level expression of the cytosolic form was located in the large intron.
The C4 isoform of NADP-malic enzyme is encoded by the
Me1 gene. Analyses of a series of reporter gene fusions
showed that sequences at the 5´ end of the gene control bundle sheath
expression but that sequences located near the 3´ end are necessary for
high-level expression. The mechanisms regulating the expression of both genes
are clearly different and suggest that there is no universal mechanism
controlling the expression of genes coding for C4
enzymes.
Carbon Isotope Discrimination during C4 Photosynthesis: Insights from Transgenic Plants
Authors: Caemmerer Susanne von , Ludwig Martha , Millgate Anthony , Farquhar Graham D. , Price Dean , Badger Murray , Furbank Robert T.
Published: August 2004

We have measured the discrimination against 13C during
CO2 assimilation in
Flaveria bidentis wild type plants and in transgenic
Flaveria bidentis plants transformed
(1) with an antisense RNA construct targeted to the
nuclear encoded gene for the small subunit of Rubisco—these plants had
reduced amounts of Rubisco, decreased CO2 assimilation
rates and increased carbon isotope discrimination, which was also evident in
the carbon isotope discrimination of leaf dry matter; and
(2) transformed with the mature coding region of
carbonic anhydrase, CA, from tobacco (Nicotiana tabacum)
in the sense direction under the control of the cauliflower mosaic virus 35S
promoter—these plants had slightly increased CA activity in the
mesophyll as well as a 2–4-fold increase in CA activity in the
bundle-sheath cells. The introduction of tobacco CA manifested itself by a
reduction in CO2 assimilation rate and an increase in
carbon isotope discrimination. We suggest that the increased carbon isotope
discrimination is a result of increased bicarbonate leakage out of the bundle
sheath.
C4 Photosynthesis: Thirty or Forty Years On
Authors: Osmond C. B.
Published: August 2004

The C4 pathway has served as a rallying point for so
many creative contributions, a focus for attention from so many outstanding
researchers, that any attempt to set the context 30 or 40 years on is doomed
to offend the majority of one’s colleagues. However, there is one
colleague whose personal research has set the standards to which we all
aspire, and rarely attain; whose achievements have been applauded for more
than a quarter of a century. Hal Hatch has brought great distinction to
Australian plant science.
This preamble deals with what is perhaps Australia’s most significant
contribution to modern plant sciences research. It is certainly one of the
main reasons why plant sciences research over the last decade or so has had
more influence internationally (measured by relative citation impact), than
any other field of biological research in Australia (Bourke and Butler 1994;
Osmond 1995). Although we may take pride in this quantitative evidence, I
believe we share a deeper sense of achievement in C4
pathway photosynthetic carbon metabolism. This deeper sense is reflected in
the neatness, the comprehensiveness, that accompanied the unfolding of our
understanding in this field. We can identify with Medewar (1968) that, above
all else, researchers value discoveries first for their explanatory value,
second for their clarifying power
‘the degree to which they resolve what has hitherto been perplexing’
and third, for the feat of originality involved,
‘the surprisingness of the solution to which it led’.
Thirty or 40 years on, it is good to reflect on where we have come from, what
has been achieved and, as this Symposium has defined, where we will go next.
One acknowledged starting point is an incidental observation and an inspired
guess of Haberlandt (1884), whose anatomical insight provoked a more
comprehensive understanding of photosynthetic carbon metabolism in all its
forms. There is no question that the insights and the confidence gained
through progress in C4 photosynthesis research led to a
mature view of photosynthetic carbon metabolism in C3
and CAM plants as well. Our perception of leaf photosynthesis has been refined
through the integrative philosophy, and growth of research capability, that
accompanied the unfolding of the C4 pathway. We are now
presented with a plethora of well-defined new problems that tax our creativity
in fields of gene expression, cell biology, ecophysiology and evolutionary
biology, all arising from a desire to understand this remarkable pathway.
In a musical contribution to an early C4 pathway
conference, it was heralded that Roger Slack wanted a ‘C-through
plant’ (Hatch et al. 1971). After 30 or 40 years,
the essence of the C4 pathway is so transparent that it
gives insight into some of the big questions in plant biology with the promise
of more to come. Looking back, it seems natural to deal with the growth of
research in C4 photosynthesis as phases of a generalised
biological growth cycle.
Growth and Nitrogen Uptake by Agropyron desertorum and Pseudoroegneria spicata when Exposed to Nitrate Pulses of Different Duration
Authors: Cui M. , Caldwell M. M.
Published: August 2004

Plant growth and nitrate uptake were measured for two Great Basin perennial
grasses, Agropyron desertorum and
Pseudoroegneria spicata, in sand-filled pots in either
monoculture or mixed culture (2 plants/pot). All plants were supplied with
the same initial amount of nitrate but delivered in five different pulse
durations ranging from 0.5 to 72 h. The pulse duration was controlled by
flushing the pots with water at different times after applying the nitrate
pulse. The same concentration of nitrate was used in all pulse treatments.
Increasing the pulse duration led to significantly increased plant biomass
production for both species in both mono- and mixed cultures, and to reduced
root/shoot biomass ratio. Biomass and root/shoot ratio were greater
for Agropyron in mixed culture than in monoculture. To
assess root nitrate uptake capacity, a 30-min tracer pulse was applied to all
plants. Plants that had been exposed to longer pulses acquired significantly
more nitrate than those that had been exposed to shorter pulses for both total
plant acquisition and acquisition per unit root length. With greater
root/shoot ratio than Pseudoroegneria, total nitrate
acquisition by Agropyron was significantly greater at
most pulse durations. Root nitrate uptake per unit mass was also greater for
Agropyron than for
Pseudoroegneria, indicating that
Agropyron is more responsive to nitrate pulsing.
Generation of transgenic Eucalyptus globulus plantlets through Agrobacterium tumefaciens mediated transformation
Authors: Moralejo M. , Rochange F. , Boudet A.M. , Teuliéres C.
Published: August 2004

A procedure for genetic transformation of
Eucalyptus globulus Labill. using
Agrobacterium tumefaciens is described. Young seedlings
obtained from mature seeds were chosen as target material. The most important
factors affecting transformation efficiency were the nature of the
A. tumefaciens strain, precultivation of the seedlings
and wounding of the tissues. The optimised procedure allowed us to obtain the
first transgenic plants for E. globulus. On selective
medium, 1.2% of the inoculated seedlings regenerated shoots resistant
to kanamycin and expressing the gusA gene. Molecular
evidence for the presence of stably integrated T-DNA is provided for two
plants.
Photosynthetic Rate, Stomatal Conductance and Leaf Area in Two Cotton Species (Gossypium barbadense and Gossypium hirsutum) and their Relation with Heat Resistance and Yield
Authors: Lu Zhenmin , Chen Jiwei , Percy Richard G. , Zeiger Eduardo
Published: August 2004

Gossypium barbadense L. (Pima) and
Gossypium hirsutum L. (upland) cottons are the two major
fibre producing species grown in the south-western United States, where lint
yields are adversely affected by high temperatures. In these environments,
heat-adapted upland cultivars show higher yields and heat resistance than
advanced Pima cultivars. Recent studies with an historical series of
commercial Pima cultivars have shown that increases in lint yield and heat
resistance are tightly coupled to increases in stomatal conductance and
photosynthetic rate, and to decreases in leaf area. In the present study, Pima
S-6 and Pima S-7 (advanced Pima cultivars) and Deltapine 90 (advanced upland
cultivar) were compared under field and laboratory conditions to determine
whether the physiological and morphological gradients found in the Pima
historical series extrapolate to upland cotton. In the field, Deltapine 90
showed 25–35% higher stomatal conductance, 35–50%
higher photosynthetic rate and 45% smaller leaf area than Pima S-6. The
higher photosynthetic rate and stomatal conductance of Deltapine 90 leaves
were partially related to their sun-tracking ability. In gas exchange
experiments that prevented sun-tracking, the two cultivars had comparable
photosynthetic rate as a function of incident radiation, while stomatal
conductance was higher in upland cotton. In the 25–35°C range,
photosynthetic rate as a function of temperature remained nearly constant in
both cultivars, and was higher in upland cotton at all temperatures. Stomatal
conductance showed a strong temperature-dependence, and conductance value and
the slope of the stomatal response to temperature were higher in Deltapine 90.
In progeny from a cross between Deltapine 90 and Pima S-7, the segregation of
stomatal conductance in F1 and F2
populations showed a clear genetic component. These results indicate that the
differences in photosynthetic rate, stomatal conductance and leaf area
associated with increases in lint yield and heat resistance in the Pima
historical series are also evident in a comparison between advanced cultivars
of upland and Pima cotton. Upland cotton could be used as a source of genetic
variation for high stomatal conductance in Pima breeding programs.
Kinetics of Rubisco Activation as Determined from Gas-exchange Measurements in Antisense Plants of Arabidopsis thaliana Containing Reduced Levels of Rubisco Activase
Authors: Mott Keith A. , Snyder Gordon W. , Woodrow Ian E.
Published: August 2004

The kinetics of the increase in photosynthesis rate following an increase in
PFD were determined in wildtype Arabidopsis thaliana
plants and in two antisense plants that contained reduced levels of Rubisco
activase. Experiments were conducted over a range of intercellular
CO2 mole fractions
(ci). The rate at which
photosynthesis approached steady-state following an increase in PFD was
similar for wildtype and transformed plants at low values of
ci. At higher values of
ci, however, wildtype plants
approached steady state more rapidly than did the antisense plants.
Photosynthesis time courses were used to calculate Rubisco activation rates
for the three types of plants, and Rubisco activation rate was found to be
proportional to activase content at a
ci of 280 µmol
mol-1. These data are discussed in the context of
proposed mechanisms for Rubisco activase in the activation of Rubisco.
Effect of high temperature during grain filling on starch synthesis in the developing barley grain
Authors: Wallwork M. A. B. , Logue S. J. , MacLeod L. C. , Jenner C. F.
Published: August 2004

Plants of malting barley variety Schooner were exposed to 5 days of high
temperatures (up to 35°C) during mid grain filling under controlled
environment conditions. Grains from heat treated plants accumulated
c. 30% less starch than grains from control
plants (21/16°C; 14 h day). Reduced starch deposition was not limited
by assimilate levels in heat treated grains, but high temperature reduced the
conversion of sucrose to starch. The reduction in starch synthesis appeared to
result from the effects of diminished catalytic activity of a number of
enzymes in the committed pathway of starch synthesis, and/or delayed
recovery of enzyme activity in the cooler recovery conditions. Reductions of
11–75% in the activity of the enzymes under investigation
followed high temperature exposure. In addition, ADPglucose pyrophosphorylase,
branching enzyme and granule bound starch synthase showed increased activity
during exposure to moderate temperatures (28–32°C), but reduced
activity at high temperatures, while soluble starch synthase showed an
immediate loss of activity, even at moderate temperatures. Sucrose synthase
and UDPglucose pyrophosphorylase showed the greatest reduction in catalytic
activity after plants were returned to cooler conditions. Individual enzymes
showed variation in the level of recovery under the cooler temperature
conditions which followed the heating period.
Dynamics of zinc and manganese movement in developing wheat grains
Authors: Pearson J.N. , Rengel Z. , Jenner C.F. , Graham R.D.
Published: August 2004

Zinc and Mn accumulate in the pericarp of the developing wheat grain during
the middle stages of the grain-development period. The dynamics of Zn and Mn
loading into, and retranslocation within, wheat grain during different
development stages, as well as the role of the crease phloem and the pericarp
vascular system in distribution of Zn and Mn in various grain tissues, are not
known. This study showed that most 65Zn and
54Mn were distributed within the grain via the crease
phloem, while 65Zn could be transported to the embryo
via a phloem-only strand originating in the grain stalk. Neither Zn nor Mn was
transported circumferentially from the crease to the dorsal pericarp tissues.
After 24-h pulse- labelling of detached ears on day 15 post-anthesis,
accumulation of 65Zn and 54Mn in
the grain increased rapidly for 5 days but declined thereafter. The relatively
largest amounts of 65Zn and 54Mn
were located in the crease/inner pericarp tissues (>60%),
followed by the endosperm. The outer pericarp contained only small amounts of
65Zn, but relatively large amounts of
54Mn. Little 65Zn and
54Mn was found in the embryo. Pulse-labelling ears with
65Zn and 54Mn at various stages of
grain development showed that they are mostly transported to the
crease/inner pericarp tissues, but increasingly more to the endosperm and
the embryo as the grain matures. Retranslocation of Mn from the
crease/inner pericarp and outer pericarp tissues was coincident with an
increased accumulation of 54Mn in the embryo. It is
concluded that the rates of transport of Zn and Mn into, and retranslocation
within, wheat grains change during grain development.
Expression of heat shock protein genes in apple fruit in the field
Authors: Ferguson I.B. , Snelgar W. , Lay-Yee M. , Watkins C.B. , Bowen J.H.
Published: August 2004

Temperatures in the flesh of apple fruit
(Malus domestica Borkh., cv. Braeburn), during diurnal
cycles in summer conditions, were measured continuously using thermocouples.
Flesh temperatures on the exposed side of fruit in direct sunlight reached as
much as 15°C above air temperatures, even when the latter never exceeded
30°C. An increase in expression of heat shock protein (hsp) mRNA and
protein synthesis was associated with these high daily flesh temperatures.
Elevated levels of hsp transcripts were maintained over the night period, but
rapidly dropped after the onset of daytime. There appears to be a diurnal
cycle of hsp gene expression which underlies the heat-induced increases. High
internal temperatures, even under temperate climatic conditions, are likely to
be common in bulky tissues such as fruit, and the ability to withstand such
temperatures is a normal homeostatic response.
A model of frost impacts on seasonal photosynthesis of Eucalyptus pauciflora
Authors: King David A. , Ball Marilyn C.
Published: August 2004

A model of the time course of frost impacts on seasonal photosynthesis of
Eucalyptus pauciflora Sieb. ex Spreng. was constructed,
incorporating seasonal shifts in frost hardiness and both short- and long-term
impacts on the initial slope and saturated level of the photosynthetic light
response curve. The approach is an extension of Sands’ model
(Australian Journal of Plant Physiology, 1995,
22, 603–614) which calculates daily canopy
photosynthesis as a function of daily irradiance and temperatures without the
impacts of cold nights. Modelled effects of frost on cumulative photosynthesis
over 8 months were highly nonlinear and rather sensitive to the temporal
sequence of minimum temperatures and extent of frost hardening. Most of the
effects were associated with long-term damage caused by a few severe or
unseasonal frosts. Shifting either plant sensitivity or minimum temperatures
by several degrees had large impacts on predicted outcomes. These results are
consistent with other observations that the increase in frost severity
associated with land clearing is impeding eucalypt regeneration in interior
Australia and may be applicable to other frost-prone areas.
Transport of 1-aminocyclopropane-1-carboxylic acid (ACC) in the transpiration stream of tomato (Lycopersicon esculentum) in relation to foliar ethylene production and petiole epinasty
Authors: Else Mark A. , Jackson Michael B.
Published: August 2004

We investigated the concentration and delivery of
1-aminocyclopropane-1-carboxylic acid (ACC) in the transpiration stream of
flooded and well-drained 1-month-old tomato plants
(Lycopersicon esculentum Mill. cv. Ailsa Craig) over
time in parallel with foliar ethylene production and petiole epinasty. ACC was
measured by gas chromatography using a nitrogen–phosphorus detector.
Before analysis, roots of freshly detopped plants were pressurised
pneumatically to make xylem sap flow at rates similar to those of whole plant
transpiration. Delivery of ACC from roots to shoots of well-drained plants was
sufficient to support basal ethylene production in shoots of unstressed
plants. Delivery from flooded, oxygen-deficient, roots increased after 6 h and
coincided with the onset of epinastic leaf curvature. Further increases in ACC
delivery and epinastic curvature occurred later in the photoperiod. After 24 h
flooding, ACC delivery in xylem sap was 28 times more than in well-drained
plants. This increased export of ACC from flooded roots was more than
sufficient to account for the extra ethylene production in the shoots and
coincided with ACC accumulation in the leaves. Removing the shoot before
flooding did not reduce ACC export from oxygen-deficient roots indicating that
the ACC originated in roots and not the shoot. Increased ethylene production
in petioles of flooded plants lagged 18 h behind epinasty.
Photochemistry and xanthophyll cycle-dependent energy dissipation in differently oriented cladodes of Opuntia stricta during the winter
Authors: Barker David H. , Logan Barry A. , III William W. Adams , Demmig-Adams Barbara
Published: August 2004

The photosynthetic and energy dissipation responses of four differently
oriented photosynthetic surfaces (cladodes) from the cactus
Opuntia stricta (Haw.) Haw. were studied in the field
during the winter in Australia. Even under very low PFD (i.e. -2 s-1) all surfaces
experienced a dramatic decline in photosystem II (PSII) efficiency during the
morning period when temperatures were below freezing. However, light energy
absorbed during the warmer afternoon period was more efficiently utilised for
photochemistry with less diversion through the thermal energy dissipation
pathway. Low temperature presumably reduced the proportion of excitation
energy that could be utilised photosynthetically, resulting in a high rate of
energy dissipation with a concomitant decline in PSII efficiency. A lag in the
diurnal de-acidification of malic acid, and therefore the availability of
endogenous CO2, may have also contributed to the low
rate of photochemistry during the morning period. We interpret the increase in
energy dissipation and decline in PSII efficiency as a controlled response of
PSII that is dependent upon the de-epoxidised components of the xanthophyll
cycle under conditions when the absorption of light exceeds the capacity of
the photosynthetic apparatus to process the excitation energy through
photochemistry.
Carbon and nitrogen isotope discrimination and nitrogen nutrition of trees along a rainfall gradient in northern Australia
Authors: Schulze E.-D. , Williams R.J. , Farquhar G.D. , Schulze W. , Langridge J. , Miller J.M. , Walker B.H.
Published: August 2004

Carbon isotope discrimination (Δ) and nitrogen isotope ratios,
N-concentrations and specific leaf area of 50 tree species were investigated
along a continental-scale transect through northern Australia over which
annual rainfall varied from 1800 mm to 216 mm rainfall. Average specific leaf
area (SLA, m2 kg-1) of leaves
ranged from 10.7 ± 1.7 (av. ± s.d.) in N2
fixing deciduous trees to 0.8 ± 0.4 in spinescent sclerophylls shrubs.
SLA generally decreased with increasing aridity. N2
fixing species had higher leaf N concentration (average N-concentration 20.1
± 3.7 mgN g-1) than non- N2
fixing (10.8 ± 3.3) or spinescent species (7.05 ± 1.8).
Community-averaged Δ was approximately constant at rainfalls above 475
mm (average Δ = 19.4 ± 1.2‰). Where rainfall was
less than 475 mm, Δ decreased from 19‰ to 17‰ at 220 mm.
Δ was positively correlated with SLA. Δ of deciduous
N2 fixing species and spinescent species were 1‰
and 2.4‰ lower than in evergreen sclerophyllous species. Δ in
the N2 fixing Allocasuarina was
1.2‰ lower than in non- N2 fixing sclerophyllous
species. The δ15N-values indicated
N2 fixation only at high rainfall. Burning of the field
layer in a Eucalyptus forest had no effect on all
measured tree parameters including δ15N, but
δ15N increased under grazing conditions to
>5‰.
The constant value of community averaged Δ between 1800 and 450 mm may
be the result of replacement of functional types and species. The decline in
Δ in the more arid section may be a function of both low species
diversity, and a highly aseasonal and unpredictable rainfall regime.
Fluxes of carbon dioxide and water vapour over a C4 pasture in southwestern Amazonia (Brazil)
Authors: Grace John , Lloyd Jon , Miranda Antonio Carlos , Miranda Heloisa , Gash J.H.C.
Published: August 2004

In Brazil, pastures for cattle ranching are being established in areas that
were previously forested. To investigate some consequences of this change in
land use we measured fluxes of CO2 and water vapour over
a typical pasture, dominated by the introduced C4 grass
Brachiaria brizantha. In addition, we compared the
CO2, water vapour fluxes and canopy stomatal
conductances observed with those obtained simultaneously over a nearby
undisturbed rain forest. Measurements were made near the end of the wet season
under conditions of ample soil moisture. Leaf area index of the pasture was
3.9.
The pasture had a lower canopy stomatal conductance than the forest (typically
0.2–0.3 mol m-2 s-1 versus
0.4–0.9 mol m-2 s-1 at high
photon irradiance) and was less responsive to the canopy-to-air vapour
pressure difference. As a consequence of these lower canopy stomatal
conductances, the pasture used much less water than the forest with average
values over the period examined being 153 mol H2O
m-2 d-1 and 249 mol
H2O m-2 d-1
for pasture and forest respectively (2.74 and 4.48 mm
d-1 respectively). This was also reflected by differing
fractions of the absorbed energy being dissipated as evaporation. This
proportion was typically 0.56 for the pasture and 0.74 for the forest.
After allowing for soil and plant respiration, average daily photosynthetic
rates were 0.67 mol C m-2 d-1 for
the pasture and 0.57 mol C m-2
d-1for the forest (8.0 and 6.8 g C
m-2 d-1, respectively). Thus,
despite an appreciably lower rate of water use the pasture assimilated more
carbon on a daily basis. Nevertheless, Brachiaria
displayed a somewhat lower rate of photosynthesis than expected for a
C4 grass, perhaps because of a low nutrient status.
Indeed, at low and medium photon irradiance the pasture and forest showed
remarkably similar photosynthetic performance. There was, however, less
tendency for CO2 assimilation rates of the pasture
canopy to saturate at high photon irradiance. The respiratory fluxes from the
two ecosystems at night were quite similar, 6–8 µmol
m-2 s-1.
The ratio of intercellular CO2 concentration to ambient
CO2 concentration was usually 0.4 to 0.6 for the
pasture, a range which is higher than that often reported for
C4 plants but possibly not unusual for tropical grasses
in their natural environment.