bluuebunny/crossref_metadata_2025 huggingface dataset:
13C Labeling kinetics of sucrose in glumes indicates significant refixation of respiratory CO2 in the wheat ear
Authors: Gebbing Thomas , Schnyder Hans
Published: September 2002

Photosynthesis by the vegetative structures of the ear (i.e. glumes) of wheat
(Triticum aestivum L.) may draw on two sources of
CO2: atmospheric CO2 and
CO2 originating from respiration within the ear. We
exposed wheat plants to a changed C isotope composition (δ) of one of
the two sources, atmospheric CO2, to assess the
contributions of atmospheric and respiratory CO2 to ear
photosynthesis by following the labeling kinetics of water-soluble
carbohydrates (WSC; fructose, glucose, sucrose, fructan) in glumes.
Experiments included sampling during diurnal cycles and after extended
exposures (7 and 14 d). The labeling kinetics of sucrose in the flag leaf and
grains was also determined. Significant diurnal changes in sucrose content
(depletion during dark and accumulation during light periods) were observed in
flag leaves and in glumes. In flag leaves (but not in glumes) the sucrose
accumulating during the light period had a d that was close to the value
expected if atmospheric CO2 (with changed δ) was
the sole source of CO2 for photosynthesis. The δ
of sucrose in glumes did not saturate after extended exposure to the labeling
CO2 indicating the utilization of unlabeled
(respiratory) CO2 for photosynthesis (i.e. refixation).
Short-term labeling indicated that 73% of the sucrose accumulating in
glumes after the start of labeling came from fixation of respiratory
CO2. Stable C isotope discrimination during glume
photosynthesis is discussed.
1H-Nuclear magnetic resonance imaging of ripening 'Kensington Pride' mango fruit
Authors: Joyce Daryl C. , Hockings Paul D. , Mazucco Roy A. , Shorter Anthony J.
Published: September 2002

Physicochemical gradients occur in mango mesocarp tissue during ripening. These gradients are reflected in water activity, which is non-uniform throughout the mesocarp. Signal intensity in proton magnetic resonance images (first echo, proton density and T2) for green-mature `Kensington Pride' mesocarp tissue was highest near the endocarp and lowest near the exocarp. Relative signal intensity increased in the middle mesocarp as ripening proceeded, but remained relatively low in the outer mesocarp. T2 relaxation times for inner and middle mesocarp regions fell during ripening. The data suggest that water activity in the mesocarp tissue increased in an outward-moving flux as ripening progressed. This change in water activity was associated with starch hydrolysis and other ripening-related processes that commence near the endocarp.
Research note: Rapid isolation of total RNA and genomic DNA from Hakea actities
Authors: Mason Michael G. , Schmidt Susanne
Published: September 2002

Tissues of the Australian native plant species Hakea actities (Proteaceae) contain numerous metabolites and structural compounds that hinder the isolation of nucleic acids. Separate RNA and genomic DNA extraction procedures were developed to isolate high quality nucleic acids from H. actities. Total RNA was extracted from leaves, roots and cluster roots of H. actities grown in low nutrient levels. Cluster root formation in H. actities only occurs when the plants are grown in low nutrient concentrations. However, under these conditions, nucleic acid extraction becomes increasingly difficult. The new procedures are faster than many of the published nucleic acid extraction protocols, and avoid the use of hazardous chemicals. The RNA extraction method was used successfully on another Australian species and a crop species, suggesting that the procedure is useful for molecular studies of a broad range of plants.
Biolistic transformation of Eucalyptus grandis x E. urophylla callus
Authors: Sartoretto Laudete Maria , Cid Luis Pedro Barrueto , Brasileiro Ana Cristina Miranda
Published: September 2002

A procedure for genetic transformation of the hybrid Eucalyptus grandis × E. urophylla using particle bombardment is described. Cotyledon- and hypocotyl-derived calli growing on SP medium supplemented with 2�m�thidiazuron or on MS modified (MSM) medium supplemented with 10 m 2,4-dichlorophenoxyacetic acid (2,4-D) and 2.5�m�6-benzylaminopurine (BAP), were used as target material for bombardment assays. Multiple preincubation and bombardment conditions were tested. Tungsten particles were coated with the plasmid pBI426 harbouring a β-glucuronidase (gus) and neomycin phosphotransferase II (npt II) gene fusion controlled by a double 35S cauliflower mosaic virus (CaMV) promoter. Four days after bombardment, the transient transformation efficiency was determined by expression of the gus gene. Fully GUS-positive calli were then obtained after 105 d in MSM medium supplemented with 2,4-D, BAP, and the selective agent kanamycin at 200 mg L-1. The presence of the gus gene in these kanamycin-resistant calli was confirmed by polymerase chain reaction analysis. Extensive experiments were performed aiming to identify conditions for the regeneration of these GUS-expressing calli. However, they were unable to regenerate transgenic shoots, suggesting that conditions suitable for regeneration are unsuitable for transformation and vice versa.
The diversity of inorganic carbon acquisition mechanisms in eukaryotic microalgae
Authors: Colman Brian , Huertas I. Emma , Bhatti Shabana , Dason Jeffrey S.
Published: September 2002

Eukaryotic microalgae have developed CO2concentrating
mechanisms to maximise the concentration of CO2 at the
active site of Rubisco in response to the low CO2
concentrations in the external aquatic medium. In these organisms, the modes
of inorganic carbon (Ci) uptake are diverse, ranging from diffusive
CO2 uptake to the active transport of
HCO3 -and
CO2 and many have an external carbonic anhydrase to
facilitate HCO3- use. There is
unequivocal evidence for the mechanisms of Ci uptake in only about 25 species
of microalgae of the chlorophyte, haptophyte, rhodophyte, diatom, and
eustigmatophyte groups. Most of these species take up both
CO2 and
HCO3-, but the rates of uptake of
each of these substrates varies with the algal species. A few species take up
only one of the two forms of Ci, an adaptation that is not necessarily
correlated with their ecological distribution. Evidence is presented for the
active uptake of HCO3- and
CO2 in two marine
haptophytes,Isochrysis galbana Parke and
Dicrateria inornata Parke, and for active transport of
CO2 but lack of
HCO3- uptake in two marine
dinoflagellates, Amphidinium carteraeHulburt and
Heterocapsa oceanica Stein.
Freshwater angiosperm carbon concentrating mechanisms: processes and patterns
Authors: Maberly Stephen C. , Madsen Tom V.
Published: September 2002

Aquatic angiosperms are derived from terrestrial ancestors and appear to have
re-invaded water on many occasions. While removing problems of water supply
and reducing the need for supporting tissue, freshwaters have a potentially
low and fluctuating supply of CO2 for photosynthesis, as
well as generally low light. This paper reviews the structural, morphological,
physiological, and biochemical features of freshwater macrophytes in the
context of maximising net carbon uptake underwater, and discusses how
inorganic carbon may influence macrophyte ecology. Submerged leaves tend to
have a low photosynthetic capacity on an area basis, matching the low rates of
supply of CO2 and light. Morphological and structural
strategies to overcome potential carbon limitation include possession of
aerial or floating leaves, and lacunal connexions to high concentrations of
sedimentary CO2 via the roots. Physiological and
biochemical strategies include crassulacean acid metabolism,
C4-like metabolism in Hydrilla and
Egeria, and the ability to use
HCO3–. The activity of all
these can be regulated by environmental conditions to maximize growth rate.
Use of HCO3–. is the most
widespread carbon acquisition strategy, present in about half of the tested
submerged angiosperms. It is more common in lakes of high alkalinity and in
the elodeid growth form.
Use of the bleomycin resistance gene to generate tagged insertional mutants of Chlamydomonas reinhardtii that require elevated CO2 for optimal growth
Authors: Colombo Sergio L. , Pollock Steve V. , Eger Karla A. , Godfrey Ashley C. , Adams James E. , Mason Catherine B. , Moroney James V.
Published: September 2002

Chlamydomonas reinhardtii Dangeard possesses a
CO2 concentrating mechanism (CCM) that enables it to
grow at very low CO2 concentrations. In previous
studies, insertional mutagenesis was successfully used to identify genes
required for growth at low CO2 in
C. reinhardtii. These earlier studies used the
C. reinhardtii genes, Nit1 and
Arg7 to complement
nit1– or
arg7– strains, thereby
randomly inserting a second copy of Nit1 or
Arg7 into the genome. Because these genes are already
present in the C. reinhardtii genome, it was often
difficult to identify the location of the inserted DNA and the gene disrupted
by the insertion. We have developed a transformation protocol using the
BleR gene, which confers
resistance to the antibiotic Zeocin. The insertion of this gene allows one to
use a variety of existing polymerase chain reaction (PCR) methodologies to
identify the disrupted gene. In this study the D66 strain
(nit2–,
cw15,
mt+) was transformed by
electroporation using a plasmid containing the
BleR gene. Primary transformants
(42 000) were obtained after growth in the dark on acetate plus Zeocin medium.
Colonies were then tested for their ability to grow photosynthetically on
elevated CO2 or low levels of CO2
(100 ppm). About 120 mutants were identified which grew on elevated
CO2 but were unable to grow well at low
CO2 concentrations. About 50% of these mutants
had low affinities for inorganic carbon as assessed by
K0.5(CO2),
indicating a potential defect in the CCM. The location of the inserted DNA is
being determined using inverse PCR (iPCR) and thermal asymmetric interlaced
(TAIL) PCR. Using these methods, one can rapidly locate the inserted DNA in
the genome and identify the gene that has been disrupted by the insertion.
In vivo evidence from an Agrostis stolonifera selection genotype that chloroplast small heat-shock proteins can protect photosystem II during heat stress
Authors: Heckathorn Scott A. , Ryan Samantha L. , Baylis Joanne A. , Wang Dongfang , Hamilton III E. William , Cundiff Lee , Luthe Dawn S.
Published: September 2002

Previous in vitro experiments indicated that chloroplast small heat-shock proteins (sHsp) could associate with thylakoids and protect PSII during heat and other stresses, possibly by stabilizing the O2-evolving complex (OEC). However, in vivo evidence of sHsp protection of PSII is equivocal at present. Using previously characterized selection genotypes of Agrostis stolonifera Huds. that differ in thermotolerance and production of chloroplast sHsps, we show that both genotypes contain thylakoid-associating sHsps, but the heat-tolerant genotype, which produces an additional sHsp isoform not made by the sensitive genotype, produces a greater quantity of chloroplast and thylakoid sHsp. Following a pre-heat stress to induce sHsps, in vivo PSII function decreased less at high temperatures in the tolerant genotype. Differences in PSII thermotolerance in vivo were associated with increased thermotolerance of the OEC proteins and O2-evolving function of PSII, and not with other PSII proteins or functions examined. In vivo cross-linking experiments indicated that a greater amount of sHsp associated with PSII proteins during heat stress in the tolerant genotype. PSII was the most thermosensitive component of photosynthetic electron transport, and no differences between genotypes in the thermotolerance of other electron transport components were observed. These results indicate that in vivo chloroplast sHsps can protect O2 evolution and the OEC proteins of PSII during heat stress.
Hypothesis: versatile function of ferredoxin-NADP+ reductase in cyanobacteria provides regulation for transient photosystem I-driven cyclic electron flow
Authors: Matthijs Hans C. P. , Jeanjean Robert , Yeremenko Nataliya , Huisman Jef , Joset Francoise , Hellingwerf Klaas J.
Published: September 2002

Pseudo-reversion of the high-CO2 requiring phenotype of
the NADH dehydrogenase type 1-impaired mutant of
Synechocystis PCC6803, strain M55, by salt stress
coincides with partial restoration of PSI-driven cyclic electron transfer. In
M55, the complete family of D proteins (D1–D6) that are needed for
electron transfer through the complex is lacking. Adaptation to salt stress
requires de novo synthesis of full-length 47-kDa
ferredoxin-NADP+ reductase (FNR). A mutant created
in the M55 background, which only expresses truncated chloroplast 37-kDa FNR
cannot adapt to salt stress and refrains from growth in low
CO2. A special feature of FNR in cyanobacteria is the
relatively high molecular mass of 44–48 kDa. A positively charged
extended N-terminal domain of the cyanobacterial enzyme
defines the extra mass. The extension likely plays a key role in the
salt-stress inducible enhancement of PSI-driven cyclic electron transfer, and
in the pseudo-reversion of the high-CO2 requiring
phenotype of M55. Data acquired with several other cyanobacteria and the
oxychlorobacterium Prochlorothrix hollandica contributed
to the present hypothesis. It proposes that FNR is involved in regulation of
inducible and transient PSI cyclic electron transfer in cyanobacteria via a
thylakoid surface charge and conditional-proteolysis steered mechanism.
Carboxysome genomics: a status report
Authors: Cannon Gordon C. , Heinhorst Sabine , Bradburne Christopher E. , Shively Jessup M.
Published: September 2002

Carboxysomes, microcompartments that enhance the fixation of carbon dioxide by
Rubisco, are found in several chemoautotrophs and in all cyanobacteria thus
far examined. The genes for Rubisco large (cbbL) and
small (cbbS) subunits (cbb for
Calvin-Benson-Bassham), along with the genes (csoS) for
the carboxysome shell peptides, are organized in a putative operon in
Halothiobacillus neapolitanus in the following order:
cbbL,cbbS,
csoS2, csoS3,
orfA, orfB,
csoS1C, csoS1A, and
csoS1B. DNA sequencing has revealed essentially the same
operon in three other thiobacilli,
Acidithiobacillus ferrooxidans,
Thiomonas intermedia, and
Thiobacillus denitrificans. The carboxysome genes are
also clustered inSynechococcus sp. and
Synechocystis sp., although in some cases certain genes
lie outside the cluster. The genes, labelled ccm for
CO2 concentrating mechanism, exist in
Synechococcus PCC7942 in the order
ccmK, ccmL,
ccmM, ccmN, and
ccmO, and are located upstream of the Rubisco genes.
ccmO is absent, and multiple copies of
ccmK exist in some species. The
ccmK/ccmO and ccmL genes are
homologues of csoS1CAB andorfAB,
respectively. The ccmM and ccmN
genes have no apparent counterpart in the thiobacilli. More recently, the
genome sequence of four additional cyanobacteria has become available. The
carboxysome genes in Nostoc punctiforme are clustered
like, and are similar to, the genes of the earlier mentioned cyanobacteria.
However, the three marine organisms
Prochlorococcus marinus MIT9313,
P. marinus MED4, and Synechococcus
WH8102, possess an operon nearly identical to that found in thiobacilli.
Furthermore, the genes exhibit surprising sequence identity to the carboxysome
genes of the thiobacilli.
Regulation of a carbon concentrating mechanism through CCM1 in Chlamydomonas reinhardtii
Authors: Miura Kenji , Kohinata Tsutomu , Yoshioka Satoshi , Ohyama Kanji , Fukuzawa Hideya
Published: September 2002

Aquatic photosynthetic organisms, including the green
alga, Chlamydomonas reinhardtii, induce a set of genes
for a carbon concentrating mechanism (CCM) through the
CO2-signalling system, to acclimate to
CO2-limiting stress conditions. We have described a
regulatory gene, Ccm1, which was shown to regulate CCM
induction in C. reinhardtii. In this review, we
summarize the current understanding of the regulatory process, which controls
the expression of genes for the CCM. In particular, CCM1-regulated genes and
possible functions of Ccm1 in the
CO2-signalling pathway are discussed, in relation to
findings in other green algae and cyanobacteria.
Antisense suppression of the rice transporter gene, OsSUT1, leads to impaired grain filling and germination but does not affect photosynthesis
Authors: Scofield Graham N. , Hirose Tatsuro , Gaudron Judy A. , Furbank Robert T. , Upadhyaya Narayana M. , Ohsugi Ryu
Published: September 2002

OsSUT1 encodes a rice sucrose transport protein that is highly expressed in developing grain, leaf sheath and stem after heading, and in germinating seedlings, but only at very low levels in source leaves. In this study, we have used antisense gene suppression to elucidate the in vivo function of OsSUT1. Rice was transformed with an antisense construct containing a portion of the 3′-coding and non-coding regions of OsSUT1 driven by the maize ubiquitin-1 promoter. Twenty-six independent stably transformed lines were obtained. T0 and selfed T1 progeny were analysed for suppression of OsSUT1 expression and function. Many of the plants showed a significant reduction in their ability to produce filled grain, and final grain weight was reduced. Severe phenotypes correlated with a reduction in OsSUT1 transcript level in filling grain. Unlike SUT1 antisense suppression in dicots, source supply of photosynthate was unaffected in these transformants. This provides the first direct evidence for the requirement of a sucrose transporter for grain filling in a cereal species. Furthermore, seed from some of the T0 population showed a reduction in the rate of germination and growth, supporting the hypothesis that OsSUT1 may also play a role in transporting sucrose remobilized from starch reserves in germinating seeds.
Variability of the pyrenoid-based CO2 concentrating mechanism in hornworts (Anthocerotophyta)
Authors: Hanson David , Andrews T. John , Badger Murray R.
Published: September 2002

Hornworts (Anthocerotophyta) are the only group of land plants with
pyrenoid-containing chloroplasts. CO2 exchange and
carbon isotope discrimination values (Δ13C) values
have previously demonstrated the presence of a CO2
concentrating mechanism (CCM) in some pyrenoid-containing species. We have
examined hornwort CCM function by using a combined fluorometer/mass
spectrometer based technique to compare pyrenoid-containing
(PhaeocerosProsk. and Notothylas
Sull.) and pyrenoid-lacking (Megaceros Campbell)
hornworts, with the liverwort Marchantia polymorphaL.
that has standard C3 photosynthesis and a thalloid
growth form similar to hornworts. We found that
Notothylas has more CCM activity than
Phaeoceros, and that Megaceros has
the least CCM activity. Notothylas and
Phaeoceros had compensation points from 11–13 parts
per million (ppm) CO2, lower
K0.5(CO2)
than Marchantia, negligible photorespiration, and they
accumulate a pool of dissolved inorganic carbon (DIC) between 19–108
nmol mg–1 chlorophyll.
Megaceroshad an intermediate compensation point of 31
ppm CO2 (compared with 64 ppm CO2
in Marchantia), a lower
K0.5(CO2)
than Marchantia, and some photorespiration, but no DIC
pool. We also determined the catalytic rate of carboxylation per active site
of Rubisco for all four species (Marchantia, 2.6
s–1; Megaceros, 3.3
s–1; Phaeoceros, 4.2
s–1; Notothylas 4.3
s-1), and found that Rubisco content was 3% of
soluble protein for pyrenoid-containing species, 4% for
Megaceros and 8% for
Marchantia.
Increased seed cytokinin levels in transgenic tobacco influence embryo and seedling development
Authors: Ma Qing-Hu , Lin Zhan-Bing , Fu De-Zhi
Published: September 2002

Seed-specific expression of a heterologous vicilin-isopentenyl transferase (ipt) gene has been determined in transgenic tobacco lines 7 and 16. Genetic analysis of self-fertilized progeny showed that a single copy of the vicilin-ipt gene had been integrated, and T2 progeny had become homozygous for the transgene. Stable inheritance of the vicilin-ipt gene in T3 progeny was verified by polymerase chain reaction analysis. Seed cytokinin levels were 2-3-fold higher than control levels. Cytological analyses revealed a significant increase in the number of plerome cell layers and enlargement of diameter in transgenic embryos compared with controls. Dry weight of mature seeds and subsequent seedling growth was increased significantly. This correlated with the level of vicilin-ipt overexpression and increased cytokinin levels in transgenic tobacco seeds. The results suggest a crucial role for cytokinins in regulation of tobacco embryo development.
Evolution and diversity of CO2 concentrating mechanisms in cyanobacteria
Authors: Badger Murray R. , Hanson David , Price G. Dean
Published: September 2002

Cyanobacteria have developed an effective photosynthetic
CO2 concentrating mechanism (CCM) for improving the
efficiency of carboxylation by a relatively inefficient Rubisco. The
development of this CCM was presumably in response to the decline in
atmospheric CO2 levels and rising
O2, both of which were triggered by the development of
oxygenic photosynthesis by cyanobacteria themselves. In the past few years
there has been a rapid expansion in our understanding of the mechanism and
genes responsible for the CCM. In addition, there has been a recent expansion
in the availability of complete cyanobacterial genomes, thus increasing our
potential to examine questions regarding both the evolution and diversity of
components of the CCM across cyanobacteria. This paper considers various CCM
and photosynthesis gene components across eight cyanobacteria where
significant genomic information is available. Significant conclusions from our
analysis of the distribution of various genes indicated the following.
Firstly, cyanobacteria have developed with two types of carboxysomes, and this
is correlated with the form of Rubisco present. We have coined the terms
α-cyanobacteria to refer to cyanobacteria containing Form 1A Rubisco and
α-carboxysomes, and β-cyanobacteria having Form 1B Rubisco and
β-carboxysomes. Secondly, there are two NDH-1 CO2
uptake systems distributed variably,
withProchlorococcus marinus species appearing to lack
this CO2 uptake system. There are at least two
HCO3– transport systems
distributed variably, with some α-cyanobacteria having an absence of
systems identified in β-cyanobacteria. Finally, there are multiple forms
of carbonic anhydrases (CAs), but with only β-carboxysomal CA having a
clearly shown role at present. The α-cyanobacteria appear to lack a
clearly identifiable carboxysomal CA. A pathway for the evolution of
cyanobacterial CCMs is proposed. The acquisition of carboxysomes triggered by
the rapid decline of atmospheric CO2 in the Phanerozoic
is argued to be the initial step. This would then be followed by the
development of NDH-1 CO2-uptake systems, followed by the
development of low-and high-affinity
HCO3– transporters. An
intriguing question is, were carboxysomes developed first in cyanobacteria, or
did they originate by the lateral transfer of pre-existing proteobacterial
bacterial microcompartment genes? The potentially late evolution of the CCM
genes in cyanobacteria argues for a polyphyletic and separate evolution of
CCMs in cyanobacteria, algae, and higher plants.
Chiral macroaggregates of LHCII detected by circularly polarized luminescence in intact pea leaves are sensitive to drought stress
Authors: Gussakovsky Eugene E. , Salakhutdinov Bakhtiyar A. , Shahak Yosepha
Published: September 2002

Circularly polarized chlorophyll luminescence (CPL) was recently shown to be an effective tool for the study of chiral macroaggregate formation of the light-harvesting chlorophyll a/b pigment–protein complexes (LHCIIs) in isolated chloroplasts. The CPL measuring system was modified to study green leaves. Spectral and intensity features of pea leaf CPL signals suggested that CPL indeed detected chiral macroaggregates. The signals were found to depend on the excitation vs emission optical alignment, as well as on the side (adaxial or abaxial) of the leaf. Illumination of attached leaves with either low intensity or strong photoinhibitory light did not affect the chiral macroaggregation status. In contrast, the induction of drought stress in detached leaves led to full disruption of the chiral macroaggregates. The disruption developed gradually during slow dehydration, whereas under fast, heat-stimulated dehydration it was manifested in cooperative diminution of both CPL and photochemical capacity. Simultaneous exposure of the leaves to photoinhibitory illumination and fast dehydration resulted in negative CPL signals. The results demonstrate the potency of CPL as a non-destructive tool for structural studies of LHCII in intact leaves under varying environmental conditions.
H2O2 treatment induces glutathione accumulation and chilling tolerance in mung bean
Authors: Yu Chih-Wen , Murphy Terence M. , Sung Wei-Wen , Lin Chin-Ho
Published: September 2002

Mung bean (Vigna radiata L. cv. TN5, a chilling-sensitive cultivar) was employed to evaluate the importance of glutathione in hydrogen peroxide (H2O2)-induced chilling tolerance. Seeds germinated at 25°C for 7�d were subjected to different periods of chilling treatment, prior to analysis of the glutathione contents of their leaves. In a comparison of acclimation temperatures from 2-12°C, it was found that an 8°C acclimation for 36 h induced a 5.7-fold increase, the highest glutathione level among the temperatures tested. Seedlings acclimated at 8°C for 36 h showed 97% survival after a 36-h, 4°C chilling stress, compared with 33% survival of non-acclimated plants. Pretreatment with 200 mM H2O2 for 12 h before a 36-h, 4°C chilling treatment increased glutathione levels by 30% and reduced electrolyte leakage to 43%, relative to the untreated control. Treated seedlings also showed a survival rate of 71% after the same chilling treatment. Application of 1 mM buthionine sulfoximine, a specific inhibitor of glutathione synthesis, reversed the protection against chilling stress provided to seedlings either by acclimation at 8°C for 36 h or H2O2 pretreatment. The role of glutathione in chilling acclimation or H2O2-pretreatment-induced chilling tolerance is thus confirmed.
Is photosynthesis related to concentrations of nitrogen and Rubisco in leaves of Australian native plants?
Authors: Warren Charles R. , Adams Mark A. , Chen ZuLiang
Published: September 2002

The relationships among light-saturated
photosynthesis and concentrations of nitrogen and ribulose-1,5- bisphosphate
carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in Australian native plants
are poorly known, primarily due to the difficulty of extracting and analysing
Rubisco from such species. Rubisco may be rapidly quantified in crude extracts
of plant tissue by capillary electrophoresis (CE); however, the presence of
phenolic compounds in many Australian native plants limits the use of these
methods. The addition of insoluble polyvinylpolypyrrolidone (PVPP) during leaf
extractions effectively removed phenols permitting quantitation of Rubisco.
Relationships among maximum rates of photosynthesis and concentrations of
nitrogen and Rubisco were then investigated in ten species native to
Australia. Total nitrogen and the major pools of N in foliage varied greatly
between species. Equally, within species N-partitioning was highly plastic, as
affected by different concentrations and forms of N applied in sand culture
(0.5 or 8 mM, nitrate or ammonium). In Hakea prostrata,
for example, the proportion of total N present as soluble proteins varied
between 43 and 71%, while the proportion of total N present as Rubisco
N ranged between 9.4 and 30.0%, and the contribution of Rubisco to
soluble proteins varied between 21 and 42%. The measured concentration
of Rubisco varied between 40% and 600% of that estimated from
enzyme kinetics and measured rates of photosynthesis. Generally there was a
large ‘excess’ of Rubisco, and in only two cases was the measured
concentration of Rubisco significantly less than predicted. Total N, soluble
protein and Rubisco concentrations were poorly related to maximum rates of
photosynthesis, while the relationship between photosynthesis and Rubisco was
worse than that with N, primarily due to the plants’ variable
over-investment in Rubisco.
The significance of β-carotene, α-tocopherol and the xanthophyll cycle in droughted Melissa officinalis plants
Authors: Munné-Bosch Sergi , Alegre Leonor
Published: September 2002

Diurnal variations in pigment composition, α-tocopherol and
photosynthesis were measured during the summer drought and recovery after
autumn rainfalls in Melissa officinalis L. grown under
Mediterranean climate. Summer drought caused a drastic decrease in relative
water content and water potential of leaves to ca
35% and −3 MPa respectively, indicative of severe stress.
Chlorophyll levels decreased progressively in drought, associated with the
inability to increase total carotenoids, and especially ß-carotene. In
contrast, α-tocopherol increased by ca 60%
in response to drought and showed a significant decrease at midday in severely
stressed plants. The intrinsic efficiency of PSII photochemistry remained
unchanged at predawn throughout the experiment and decreased up to
ca 65% in plants exposed to the interaction of
high light and drought, associated with an enhanced de-epoxidation state of
the xanthophyll cycle. Although droughted M. officinalis
plants showed a significant decrease in the endogenous levels of
photosynthetic pigments, the antioxidant function of a-tocopherol and the
dissipation of excess excitation energy by the xanthophyll cycle may help to
avoid irreversible damage to the photosynthetic apparatus.
Acclimation to low temperature or high light mitigates sensitivity to photoinhibition: roles of the Calvin cycle and the Mehler reaction
Authors: Savitch Leonid V. , Massacci Angelo , Gray Gordon R. , Huner Norman P. A.
Published: September 2002

Winter wheat
(Triticum aestivum L cv. Monopol) plants grown under
either control (20˚C, 250 PFD), low temperature (5˚C, 250 PFD) or
high light conditions (20˚C, 800 PFD) were compared in order to assess
the roles of the Calvin cycle and the Mehler reaction in the differential
sensitivity to chronic photoinhibition. Despite similar photosynthetic
responses to irradiance, the partial pressure of CO2
[p(CO2)] and photoinhibition, photosynthetic
acclimation to cold temperature appears to be quite distinct from acclimation
to high light. First, the lower ratio of Rubisco oxygenation/Rubisco
carboxylation and the reduced effects of p(CO2) on
number of electrons per mole of CO2 fixed in
cold-acclimated compared to high light-grown wheat indicate that
photorespiration is differentially suppressed in cold-acclimated Monopol.
Second, inhibition of the Calvin cycle by glyceraldehyde during
photo-inhibition indicated that the sensitivity of high light-acclimated
Monopol to photoinhibition was more dependent on Rubisco activity than the
sensitivity of cold-acclimated plants to photoinhibition. Third,
cold-acclimated Monopol exhibited higher electron transport rates in the
presence of either ambient CO2, 2 kPa
O2 or N2, 2 kPa
O2 (either 77% or 68%, respectively)
relative to controls compared to high light-acclimated plants exposed to
similar gaseous environments (either 57% or 38%, respectively).
Last, the activation state of NADP–malate dehydrogenase indicated that
the stroma is highly reduced during cold acclimation relative to either
controls or high light-grown Monopol. Thus, in cold-acclimated wheat, the
Mehler reaction appears to play an important role while photorespiration plays
a minimal role in mitigating the sensitivity to photoinhibition. In contrast,
both photorespiration and the Mehler reac-tion appear to mitigate the
sensitivity to photoinhibition in high light-grown Monopol. This is consistent
with the differential sensitivity to methylviologen and the differential SOD
activity observed between cold-acclimated and high light-grown Monopol.
Triticale grain growth and morphometry as affected by drought stress, late sowing and simulated drought stress
Authors: Royo Conxita , Abaza Mosbah , Blanco Ricardo , García del Moral Luis F.
Published: September 2002

The effects on grain filling and morphometry of natural drought, late sowing
and simulated drought by means of a chemical treatment with potassium iodide
(KI) were compared over 3 years of field trials in triticale ( ¥
Triticosecale Wittmack) cv. Trujillo and three
near-isogenic lines derived from it. Grain weight data fitted accurate to a
logistic curve. The maximum rate of grain filling was the curve coefficient
most sensitive to drought stress, and accounted for 7–50% of
grain yield variation. Chemical treatment with KI caused greater variation in
grain filling curve coefficients and grain morphometry than did a delay in the
sowing date, which in turn caused greater variation than natural drought. The
type and magnitude of the effects of the different kinds of stresses on grain
growth and morphometry could be related to the time that elapsed from
anthesis, at which time the effects were perceptible. KI reduced the maximum
rate of grain filling and final grain weight by 38 and 32%,
respectively, its effect being significant from 8 d after the treatment. The
volume of grain was reduced 11% by KI. The impact of delayed sowing
date and drought were significant 29 and 33 d after anthesis, respectively,
corresponding to the end of the linear phase of the grain filling curves. Both
treatments diminished grain filling duration (13% by delayed sowing,
and 6% by drought, respectively), final grain weight (16 and
12%, respectively), grain volume (15% and 8%,
respectively), and embryo area (8% in both cases), but neither altered
the maximum grain filling rate.
Anthocyanin regulatory gene expression in transgenic white clover can result in an altered pattern of pigmentation
Authors: de Majnik John , Weinman Jeremy J. , Djordjevic Michael A. , Rolfe Barry G. , Tanner Greg J. , Joseph Roslyn G. , Larkin Phil J.
Published: September 2002

This study presents the first evidence of
heterologous anthocyanin regulatory genes altering anthocyanin expression in
stably transformed leguminous plants. Two families of anthocyanin regulatory
genes, myc (delila,
B-Peru) and myb
(myb.Ph2, C1), are involved in the
activation of the phenylpropanoid pathway. White clover
(Trifolium repens cv. Haifa) plants were transformed
with dicotyledonous and monocotyledonous myb or
myc genes. Some of these transformed plants exhibited
enhanced anthocyanin accumulation in a range of tissues. One plant,
transformed with the B-Peru gene driven by the
Cauliflower Mosaic Virus 35S promoter, displayed a unique pattern of
anthocyanin accumulation in the leaf. The accumulation of anthocyanin in this
plant was closely associated with the crescent of leaves, which is normally
white. The red pigmentation declined in intensity in the oldest leaf stage.
The B-Peru message was detected in all leaf stages of
this white clover plant. This anthocyanin pattern was shown to be heritable.
Genotypic differences in seed growth rates of Phaseolus vulgaris L. II. Factors contributing to cotyledon sink activity and sink size
Authors: Tegeder Mechthild , Thomas Melinda , Hetherington Louise , Wang Xin-Ding , Offler Christina E. , Patrick John W.
Published: September 2002

A previous study [Thomas et al. (2000)
Aust. J. Plant Physiol. 27,
109–118] showed that genotypic dif-ferences in seed growth rates of
Phaseolus vulgaris L. cultivars was accounted for by
variation in dry matter flux and seed size. Bulk cotyledon saps contained
identical concentrations of sucrose across cultivars suggesting that
geno-typic variation in capacities for sucrose transport and metabolism are
equally matched. Cotyledon sucrose transport, monitored as
in vitro uptake of
[14C]sucrose, exhibited genotypic variation
and this was abolished by para-chloromercuribenzene-
sulfonate. Eadie–Hofstee transformations of concentration-dependent
[14C]sucrose uptake showed that genotypic
variation in sucrose flux resulted from differences in maximal transporter
activity. Maximal sucrose fluxes and levels of transcript and microsomal
protein for the sucrose/H+ symporter and
H+-ATPase were positively correlated. In contrast,
sucrose binding protein transcript and microsomal protein levels correlated
negatively with sucrose fluxes. In all cultivars, a
sucrose/H+ symporter and
H+-ATPase were co-localised to plasma membranes of
the dermal cell complexes. Total plasma membrane surface areas of the dermal
cell complexes and total volume of storage parenchyma cells correlated with
cultivar variation in seed growth rates. Differences in cell number and size
accounted for cultivar variation in total plasma membrane surface area of the
dermal cell complexes and total storage parenchyma cell volume.
Growth and carbon utilization in rice plants under conditions of physiologically low temperature and irradiance
Authors: Ohashi Keiko , Makino Amane , Mae Tadahiko
Published: September 2002

The effects of low temperature and irradiance on growth, N allocation, and the
diurnal turnover of carbo-hydrates in rice plants
(Oryza sativa L.) were examined. The plants were grown
hydroponically using two growth treatments, i.e. a day/night temperature
of 20/18°C under an irradiance of 350 µmol quanta
m−2 s−1 and a
day/night temperature of 25/20°C under an irradiance of 1000
µmol quanta m−2
s−1. The biomass production decreased remark-ably
under conditions of low temperature and low irradiance. This decreased biomass
was caused by an extreme decrease in the net assimilation rate. Several
adaptive phenomena were observed, similar to those observed in response to low
light environments such as the enlargement of leaf area relative to plant mass
and preferential N-investment in the leaf blades. In addition, although the
diurnal turnover of carbohydrates in the shoots per unit plant mass during the
night were greater in the low-temperature/irradiance-grown plants than in
the control plants, the amount of daily assimilated photosynthate which is
respired by the plant was almost the same during the night. These results
indicate that the efficiency with which photosynthates had been used for
growth during the night was also enhanced under such conditions. However, they
were insufficient to compensate for the decrease in photosynthesis caused by
the low temperature and irradiance. The results indicated that a decrease in
photosynthesis due to the com-bination of low temperature and low irradiance
directly suppresses the growth of the whole plant.
Biochemical aspects of assimilate transfers along the phloem path: N-solutes in lupins
Authors: Atkins Craig
Published: September 2002

Lupins
(Lupinus angustifolius L., L.
albus L.) are prolific ‘phloem bleeders’,
allowing collection of exu-dates en route to or at
phloem-fed sinks such as shoot apices, developing fruits and the root system,
as well as at or exiting the sources of phloem-borne solutes, leaves, petioles
and stems. Consequently, it has been possible to quan-tify the relative
contributions of xylem and phloem solutes to the nutrition of each developing
organ of a lupin plant. Studies that identify the sites and, especially for
solutes containing N, the nature of transfers between the two long distance
translocation channels are reviewed. These transfers are solute-specific and
can be accounted for largely by transfer of asparagine. In leaves, direct
transfer of asparagine from xylem to phloem in minor veins, such that
metabolism is precluded, is the most significant feature of N redistribution
in the shoot. Current research is aimed at identifying and isolating genes
encoding amino acid transporters expressed in strategically placed cells
(possibly transfer cells) at nodes, at the inner epidermis of the seed coat
and the epidermis of the developing cotyledons. Special emphasis is placed on
transporters for selective transfer of asparagine.
Can the stomatal changes caused by acute ozone exposure be predicted by changes occurring in the mesophyll? A simplification for models of vegetation response to the global increase in tropospheric elevated ozone episodes
Authors: Martin Marion J. , Farage Peter K. , Humphries Steve W. , Long Steve P.
Published: September 2002

The prediction of complex interactive effects
of rising concentrations of ozone and CO2on vegetation
will require robust models based on mechanistic understanding of how these two
gases affect photosynthesis. This paper describes the development of a model
of acute ozone exposure effects on wheat leaf photosynthesis, based on the
mechanism of reactive oxygen scavenging processes. Based on experimental data,
the dose of ozone to the leaf above a threshold flux, here termed the
effective ozone dose, was found to be linearly related to the decline in the
in vivo maximum rate of carboxylation. The proposed
mechanism is that ozone damage to the photosynthetic ap paratus will only
occur above a critical rate of ozone delivery.
By combining the model of the response of ribulose-1,5-bisphosphate-saturated
and limited photosynthesis to ozone exposure with both a mechanistic
biochemical model of leaf photosynthesis and a phenomenological model of
stomatal conductance, it was possible to investigate the degree of dependency
of ozone-induced stomatal closure on changes in the mesophyll. The stomatal
conductance of the model simulation compared well with the magnitude of
measured stomatal closure. The results indicate that the stomatal changes
caused by acute ozone exposure can be predicted from changes in the mesophyll
rather than directly on the stomata.
The findings that the effects of ozone on photosynthesis can be predicted by
an effective ozone dose to the leaf, and that the resulting reduction in
CO2 assimilation rate can, in turn, predict stomatal
closure, greatly simplifies modelling the effects of elevated concentrations
of ozone and CO2 on wheat photosynthesis. Future work
should determine whether the model can be adapted to predict chronic ozone
exposure effects on photosynthesis, and whether it can be applied to other
species by adjusting the values of threshold flux, related to the maximum
scavenging capacity within the leaf, and the ozone slope coefficient,
representing the inherent sensitivity of the photosynthetic apparatus to
ozone.
Uptake, partitioning and utilization of carbon and nitrogen in the phloem bleeding tree, Tasmanian blue gum (Eucalyptus globulus)
Authors: Pate John S. , Arthur David J.
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
An empirical modelling procedure was employed to follow uptake, transport and
utilization of photo-assimilated carbon (C) and soil-derived nitrogen (N) over
a 19-d period (November 1998) in 2-year-old plantation-grown trees of
Eucalyptus globulus Labill. Models utilized data for
gains and losses of C and N in dry matter (DM) of tree parts,
CO2 exchanges and transpiration of foliage, respiratory
losses of stems and roots, C:N weight ratios of xylem and phloem sap collected
at different sites within the system, and phloem sap sugar concentration
gradients along trunks and branches to indicate directions of assimilate flow.
The model for C depicted the fate of exported fixed C from four levels of
branches on the shoot system, cycling of 16% of the C supplied from
shoot to root back to the shoot in xylem, major involvement of xylem-derived C
in nourishment of rapidly growing branches, and a net daily respiratory output
per tree equivalent to 39% of its net daytime photosynthetic gain in C
by foliage. The model for N showed that upper growing shoot parts gained more
N mobilized from lower branches than was being acquired from soil. It also
indicated high rates of cycling of N through mature foliage, effective
retention of xylem-derived N by growing branches and apices, and feedback of
substantial amounts of phloem-exported N from lower branches into xylem moving
further up the trunk. Transpiration loss per tree was equivalent to 272 mL
g–1 DM accumulated. Data are discussed in relation
to similarly executed C:N partitioning studies on herbaceous annual species.
Interaction between phloem proteins and viral movement proteins
Authors: Shalitin Dror , Wolf Shmuel
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
Recent studies support the concept that long-distance signals are involved in
the regulation of resource allocation among the various plant organs.
Following the finding that viral movement proteins (MPs) can exert an effect
on sugar metabolism and resource allocation at sites distant from their
expression, we suggested that the MPs interfere with an element(s) involved in
the plant’s endogenous long-distance signal network. To provide
experimental support for this hypothesis, several unique procedures were
employed to identify interactions between viral MPs and phloem sap proteins
(PSPs) collected from cut petioles of squash
(Cucurbita pepo L. subsp. pepo)
and melon (Cucumis melo L.) plants. Far-western
experiments with blotted PSPs, using both bacteria-overexpressed and
in vitro-translated CMV- and TMV-MPs, revealed that the
two virally encoded proteins react specifically with more than one PSP.
Moreover, isolation of the naturally folded phloem protein in an affinity
column containing a TMV-MP-maltose-binding protein indicated, once again, an
interaction between the viral protein and similar PSPs. Two melon PSPs with
molecular masses of 8 and 23 kDa were found to specifically interact with both
the CMV- and TMV-MPs. The possible effects of this interaction in terms of
altering the process of phloem transport and resource allocation are
discussed.
Dicotyledons lacking the multisubunit form of the herbicide-target enzyme acetyl coenzyme A carboxylase may be restricted to the family Geraniaceae
Authors: Christopher John T. , Holtum Joseph A. M.
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
The aryloxyphenoxypropionate herbicide haloxyfop is transported in the phloem
to the sink tissue where, in certain species, it disrupts the production of
lipids that are essential for the functioning of membranes and organelles
involved in the assimilation, partitioning and transport of carbon. Haloxyfop
inhibits a key regulatory enzyme of lipid synthesis, acetyl coenzyme A
carboxylase (ACCase), in species that lack a herbicide-insensitive
multisubunit (MS) form of ACCase found in most plants. The absence of
MS-ACCase, and sensitivity to haloxyfop, was considered to be restricted to
monocotyledons in the family Gramineae but has recently been demonstrated for
the dicotyledon Erodium moschatum (Geraniaceae). Species
related to E. moschatum were examined to determine how
widespread this phenomenon is among dicotyledons. In the two families most
closely related to the Geraniaceae, four species in the Oxalidaceae and one
species in the Tropaeolaceae respectively retained MS-ACCase. Within the
family Geraniaceae, certain species in the genera
Erodium and Pelargonium, but not
those in the genus Geranium, have lost MS-ACCase,
indicating that this phenomenon may be restricted to
Erodium and Pelargonium. When
treated with 104 g ai ha–1 haloxyfop-ethoxyethyl,
plants of all 15 species retaining MS-ACCase were resistant while 8 out of 13
species lacking MS-ACCase were susceptible. It is noteworthy that five species
lacking MS-ACCase were nonetheless resistant. The mechanism(s) of resistance
in such species remains to be determined.