bluuebunny/crossref_metadata_2025 huggingface dataset:
Biofertilisers in action
Authors: Kennedy Ivan R.
Published: September 2002

This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000
Currently proposed means of entry of bacterial endophytes into roots of
field-grown crop plants, as well as niches available for their successful
colonization of living tissues, are evaluated from a plant biology perspective
and the following conclusions drawn. (1) Opportunities for passive
‘crack entry’ into healthy, undisturbed roots in the field may not
be as available as studies with laboratory-grown plants have suggested.
Consistent entry of endophytes into living root tissues in the field probably
requires bacterial capability to hydrolyse the hydrophobic incrustations of
the walls of epidermal, hypodermal, endodermal and other cortical cells. (2)
Xylem lumen apoplast is an unsuitable niche for endophytes, especially in the
grasses, because of the reduced fitness such colonization imposes on plants
subjected to field stresses. (3) The intercellular space apoplast is the most
suitable niche for endophytes. More data about the environment of this
apoplast are urgently needed so that plant varieties can be tailored to
provide an optimal environment in these spaces for particular endophytes. It
is suggested that many bacterial ‘endophytes’ may not have
colonized living tissues, but are living in protective niches in dead surface
tissues or closely adhering soil of rhizosheaths. Selection of strains of
beneficial bacteria adapted for colonizing these external niches may be
desirable.
Programmed cell death during flower senescence: isolation and characterization of cysteine proteinases from Sandersonia aurantiaca
Authors: Eason Jocelyn R. , Ryan Dacey J. , Pinkney Tatyana T. , O'Donoghue Erin M.
Published: September 2002

Cysteine protease inhibitors delayed the senescence of Sandersonia aurantiaca Hook. flowers. Tepal fading and wilting occurred later in the 2,2� -dipyridyl-treated flowers, and these flowers had a greater soluble protein content and less active endoproteases compared with control flowers that were held in water. Biochemical analysis revealed the presence of several protease-active bands in the soluble protein fraction of Sandersonia tepals. Activity of the polypeptides increased as flower senescence progressed. Western analysis with an antibody raised against the castor bean cysteine proteinase identified homologous proteins in Sandersonia flowers (ca 46, 41 and 31�kDa). Three cDNAs encoding cysteine proteinases were isolated from Sandersonia tepals (PRT5, PRT15 and PRT22). Expression of all three increased in tepals as senescence progressed. mRNAs for PRT5 were detected only in senescing flower tissue, whereas PRT15 and PRT22 were expressed in leaf, stem and root tissue. PRT5 has significant homology to C-terminus KDEL proteins, which have a role in the degradation of plant cell contents during programmed cell death. PRT15 is most similar to cysteine proteinases with a long C-terminal extension, whereas PRT22 is homologous to stress-induced cysteine proteinases.
Acclimation of Chlamydomonas to changing carbon availability
Authors: Spalding Martin H. , Van Kyujung , Wang Yingjun , Nakamura Yoshiko
Published: September 2002

Aquatic organisms, including Chlamydomonas reinhardtii,
are faced with a variable supply of dissolved inorganic carbon (Ci).
Accordingly, C. reinhardtii has the ability to acclimate
to the changing Ci supply through a variety of responses, including induction
of a CO2 concentrating mechanism (CCM) when Ci is
limiting. The CCM uses active Ci uptake to accumulate a high internal
concentration of bicarbonate, which is dehydrated by a specific thylakoid
carbonic anhydrase to supply CO2, the substrate used in
photosynthesis. In addition to the changes demonstrably related to the
function of the CCM, C. reinhardtii exhibits several
other acclimation responses to limiting Ci, such as changes in cellular
organization and induction or upregulation of several genes. A key area
currently under investigation is how C. reinhardtii
cells recognize the change in Ci or CO2 concentration,
and transduce that signal into needed gene expression changes. Mutational
analyses are proving very useful for learning more about the CCM and about the
acclimation response to changes in Ci availability. Cloning of the gene
disrupted in cia5, a mutant apparently unable to
acclimate to limiting Ci, has opened opportunities for more rapid progress in
understanding the signal transduction pathway. The Cia5
gene appears to encode a transcription factor that may control, either
directly or indirectly, much of the gene expression responses to limiting Ci
in C. reinhardtii. Several additional new mutants with
potential defects in the signal transduction pathway have been isolated,
including three new alleles of cia5.
Regulation of the expressions of HCO3- uptake and intracellular carbonic anhydrase in response to CO2 concentration in the marine diatom Phaeodactylum sp.
Authors: Matsuda Yusuke , Satoh Keiichi , Harada Hisashi , Satoh Dan , Hiraoka Yasutaka , Hara Takumi
Published: September 2002

The marine diatom, Phaeodactylum tricornutum Bohlin, is
probably one of the most extensively studied marine alga with respect to
carbon acquisition and assimilation mechanisms. However, quantitative analyses
of HCO3-utilization and the
detailed process of acclimation of cells from high CO2
to limited CO2 are yet to be done extensively. Suitable
molecular markers for this acclimation process are not established, either.
Recently, it became clear that the rate of CO2 formation
in artificial seawater is about eight times slower than that in freshwater,
and thatP. tricornutum cells utilize
HCO3- quite efficiently. Despite
their great capacity to take up
HCO3-, the signal controlling
photosynthetic affinity for dissolved inorganic carbon has been shown to be
CO2 in the medium. Furthermore, light seems to be
required for this process.
Internal carbonic anhydrase (CA) activity has been shown to be crucial for
high-affinity photosynthesis in a number of algae, including marine diatoms.
Internal β-type CA, which has been isolated in one strain of
P. tricornutum, was clearly shown to be a
low-CO2 inducible enzyme. This review paper additionally
includes data showing that this CA occurs generally in
P. tricornutum species.
Are crassulacean acid metabolism and C4 photosynthesis incompatible?
Authors: Sage Rowan F.
Published: September 2002

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001.
Despite sharing a similar metabolism, crassulacean acid metabolism (CAM) and C4 photosynthesis are not known to occur in identical species, with the exception of Portulaca spp. In Portulaca, C4 and weak CAM photosynthesis occur in distinct regions of the leaf, rather than in the same cells. This is in marked contrast to the situation in most CAM species where C3 and CAM photosynthesis are active in the same cell over the course of a day and growing season. The lack of CAM and C4 photosynthesis in identical cells of a plant indicates these photosynthetic pathways are incompatible. Incompatibilities between CAM and C4 photosynthesis could have a number of biochemical, anatomical and evolutionary explanations. Biochemical incompatibilities could result from the requirement for spatial separation of C3 and C4 phases in C4 plants versus temporal separation in CAM plants. In C4 plants, regulatory systems coordinate mesophyll and bundle sheath metabolism, with light intensity being the major environmental signal. In CAM plants, a circadian oscillator coordinates day and night phases of CAM. The requirement for rapid intercellular transport in C4 plants may be incompatible with the intracellular transport and storage needs of CAM. For example, the large vacuole required for malate storage in CAM could impede metabolite diffusion between mesophyll and bundle sheath cells in C4 plants. Anatomical barriers could also exist because both CAM and the C4 pathway require distinct leaf anatomies for efficient function. Efficient function of the C4 pathway generally requires an outer layer of cells specialized for phosphoenolpyruvate (PEP) carboxylation and regeneration and an inner layer for CO2 accumulation and refixation, while CAM species require enlarged vacuoles and tight cell packing. In evolutionary terms, barriers preventing CAM and C4 photosynthesis in the same species may be the initial steps in the respective evolutionary pathways from C3 ancestors. The first steps in C4 photosynthesis are related to scavenging photorespiratory CO2 via localization of glycine decarboxylase in the bundle sheath cells. The initial steps in CAM evolution are associated with the scavenging of respiratory CO2 at night by PEP carboxylation. In each, simplified versions of the specialized anatomy may need to be present for the evolutionary sequence to begin. For C4 evolution, enhanced bundle sheath size may be required in C3 ancestors; for CAM evolution, succulence may be required. Thus, before CAM or C4 photosynthesis began to evolve, the outcome of the evolutionary experiment may have been predetermined.
Carbohydrate partitioning in crassulacean acid metabolism plants: reconciling potential conflicts of interest
Authors: Borland Anne M. , Dodd Antony N.
Published: September 2002

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001.
The construction of diel leaf carbon budgets, together with analyses of the δ13C composition of biochemical fractions, was used to examine how crassulacean acid metabolism (CAM) plants adjust carbohydrate partitioning in response to shifting sink demands. For Mesembryanthemum crystallinum L., net carbon budgets indicated clear shifts in assimilate partitioning and in the relative proportions of day : night export as CAM was induced. Different patterns of carbohydrate partitioning in primary and axillary leaves of this species may reflect the different sink priorities of determinate and indeterminate growth. In primary leaves, the high level of diel starch turnover may be a strategy for ensuring production of a critical mass of juvenile tissue that poises the plant for CAM induction. In axillary leaves, the high day-night flux through soluble sugars may ensure ready availability of assimilates for export to reproductive sinks. Carbon isotope ratios were measured for various organic fractions isolated from leaves and fruits of two species of Clusia that differ in CAM expression. Similar and C3-like isotopic signatures were obtained for the structural material isolated from fruits of Clusia minor L. and Clusia rosea Jacq. The data suggest that the partitioning of C4- and C3-derived assimilates into discrete storage and transport pools of soluble sugars will ensure reproductive output, regardless of the level of CAM that is induced in these species.
Metabolic control of photosynthetic electron transport in crassulacean acid metabolism-induced Mesembryanthemum crystallinum
Authors: Schöttler Mark Aurel , Kirchhoff Helmut , Weis Engelbert , Siebke Katharina
Published: September 2002

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001.
We investigated photosynthetic electron transport in leaves of the facultative crassulacean acid metabolism (CAM) plant Mesembryanthemum crystallinum L. After CAM induction, electron transport exhibited variable redox kinetics during the diurnal CAM cycle. In CAM Phase IV, most of PSI (P700) and chlorophyll a fluorescence relaxed with a halftime of 20 ms after a saturating light pulse. This time-constant may reflect the overall linear electron flux from PSII to PSI in saturating light. Comparable relaxation kinetics were also determined for C3 plants.
At the end of CAM Phase I and during Phase II, slow components (> 50% of signal amplitude) appeared in both P700 reduction and fluorescence relaxation. They displayed halftimes > 250 ms and > 1 s, suggesting a strong restriction of the linear electron flux from H2O to NADP. The appearance of the slow redox components was accompanied by a decrease in the Fv/Fm ratio of chlorophyll a fluorescence, suggesting a reversible detachment of light-harvesting complex (LHC) II from PSII. The slow redox fractions and the depression of Fv/Fm disappeared again in parallel to malate decarboxylation during CAM Phase III.

We discuss a reversible downregulation of linear electron flux during CAM Phases II and III, due to a reversible deprivation of cytochrome-b6f complexes (cyt-bfs) and PSI from the linear system. In parallel, a redistribution of some LHCIIs could also occur. This could be an adaptive response to a reduced metabolic demand for NADPH due to a limited carbon flux through the Calvin cycle, resulting from low Rubisco activation. Furthermore, the cyt-bfs and PSIs deprived of linear electron transport could support cyclic electron flux to cover an increased ATP demand during gluconeogenesis in CAM Phase III.
Effects of climate on growth traits of river red gum are determined by respiration parameters
Authors: Criddle Richard S. , Anekonda Thimmappa S. , Tong Sharon , Church John N. , Ledig F. Thomas , Hansen Lee D.
Published: September 2002

Temperature is the major uncontrollable
climate variable in plantation forestry. Matching plants to climate is
essential for optimizing growth. Matching is usually done with field trials
because of the lack of a predictive relation between laboratory measurements
of physiological responses and climatic factors affecting growth. This paper
evaluates the potential of using respiration parameters for selection of
appropriate drainage or seed sources within a drainage for superior growth in
a particular climate. The growth traits measured are tree height, stem
diameter and stem volume. The respiratory parameters measured are respiratory
heat rate, rate of CO2 production, and temperature
dependence of respiratory heat rate. Five open-pollinated families from each
of nine seed sources of river red gum
(Eucalyptus camaldulensis Dehnh.) were studied following
selection from a larger set of seed sources planted at three plantations in
California. The three plantations differ in climate, particularly in extreme
temperatures, diurnal temperature variability and total rainfall. Within each
plantation, growth and respiration parameters show high genetic variation
[overall coefficient of variation (CV) = 14–58%,
family CV = 11–33%], with at least one of these
traits showing significant (P < 0.10) difference due
to drainage, or source within drainage, or families within source. The
relationship of growth to respiration for each trait differs, depending on
testplantation, origin drainage, source or family, suggesting a unique pattern
for each trait. Correlation of drainage level averages between growth and
respiration were strongly negative and significant (P
= 0.10–0.01). Rankings for drainages between paired plantations
were strong and significant (P = 0.10–0.05)
only for respiration, but not for growth traits.
Regulation of growth and differential tissue dry mass accumulation by Citrus grandis, Poncirus trifoliata and their F1 under salinized and non-salinized environments
Authors: Tozlu Ilhami , Moore Gloria A. , Guy Charles L.
Published: September 2002

Salt stress responses of C. grandis L. (Osb.),
P. trifoliata (L.) Raf. and their F
1 were investi-gated. Growth, growth rates, as well as
leaf, stem, structural root (> 2 mm diameter), fine root (≤ 2mm
diameter) and whole plant dry masses were determined for the three genotypes
tested in 0, 40 and 80 mМ NaCl environments for 20 weeks.
P. trifoliata and C. grandis were
phenotypically distinct and their F1 had features that
were a combination of both parents. The different growth habits resulted in
significant differences between the net growth and growth ratios ([net
growth / initial growth] × 100) of the three genotypes and
between control and salinized plants within each genotype. The average growth
and dry weights of nearly all tissues were reduced in salinized plants
compared to those of control plants. The exceptions were the fine roots of
P. trifoliata at both salinities and of the
F1 plants at 40 mМ NaCl. The 40 mМ NaCl
treatment stimulated fine root production in
P. trifoliata plants, significantly increasing dry
weight by 30% compared to control plants. Average shoot dry weight
reduction was greatest in C. grandis and least in
P. trifoliata in the 40 mМ NaCl treatment. While
leaf tissues of P. trifoliata were the most sensitive to
salinity, root tissues were the most sensitive in
C. grandis. To avoid salt accumulation,
P trifoliata plants increased root dry mass production
while C. grandis plants increased leaf mass production.
These traits appeared to be heritable, since the F1
plants displayed responses intermediate to its parents leading to increased
salinity tolerance. We suggest that not only ion content of leaf tissues, but
ion content and mass production of all tissues should be considered when the
salinity tolerance of Citrus and related genera is
characterized.
Effects of increasing NaCl concentration on stem elongation, dry mass production, and macro- and micro-nutrient accumulation in Poncirus trifoliata
Authors: Tozlu Ilhami , Moore Gloria A. , Guy Charles L.
Published: September 2002

The effects of salinization with 0, 30, 60, 90, and 120 mМ sodium chloride
(NaCl) on Poncirus trifoliata (L.) Raf. cv. Pomeroy were
studied by means of stem elongation patterns, whole plant and tissue mass
production, and mineral nutrient accumulation. The elements analyzed in leaf,
stem, structural root and fine root tissues included Na, Cl, P, K, Ca, Mg, Mn,
Fe, Cu, Al, and Zn. At the end of the 12-week experimental period, shoot
length was reduced 30–80% in the 30 to 120 mМ NaCl
treatments. The linear relationship found between stem elongation and salt
concentration, and different tissues and salt concentration suggests that a
40–60 mМ NaCl concentration is optimal to test
P. trifoliata or its progeny for salt stress. Root
production was found to be continuous and plants apparently used this process
as an avoidance mechanism to remove excess ions and delay onset of ion
accumulation in this tissue. This phenomenon, designated ‘Fine Root
Turnover’, is unique to P. trifoliata and may be
used as a genetic resource to improve Citrus for
salinity tolerance through intergeneric hybridization. Plants were able to
delay accumulation of Na ions in leaves but not Cl ions, resulting in high Cl
accumulation in leaves and accumulation of both ions in fine roots. The data
suggested that, while Cl ions were more toxic in leaf tissues, Na ions were at
least as toxic in fine root tissues. Among other nutrients, K was affected the
most in response to salinity, decreasing within root tissues and increasing in
leaf tissues with increased salin-ization. A similar phenomenon was observed
for P levels in salinized tissues. Changes in tissue and whole plant
accumulation patterns of the other tested elements as well as possible
mechanisms for how excess Na and Cl ions are removed from and/or
transported to less vulnerable tissues in
Poncirus trifoliata during salinization are discussed.
Whole-plant growth and N allocation in transgenic rice plants with decreased content of ribulose-1,5-bisphosphate carboxylase under different CO2 partial pressures
Authors: Makino Amane , Harada Masayo , Kaneko Kentaro , Mae Tadahiko , Shimada Takiko , Yamamoto Naoki
Published: September 2002

Growth of transgenic rice (Oryza sativa L.) with an
antisense gene to the small subunit of Rubisco was analysed under 36 and 100
Pa CO2 during a 14-h photoperiod (1000 mol quanta
m–2 s–1). Two lines of
the antisense plants were used; one with 65% wild-type Rubisco and the
other with 40% wild-type Rubisco. The plants were grown hydroponically
for 70 d. The final biomass of the antisense plants grown in 36 Pa
CO2 was much smaller than that of the wild-type plant.
However, several compen-sation phenomena were found in the antisense plants.
Increased biomass allocation to leaf blades and preferential N investment in
leaf blades were observed. Leaf senescence was also delayed. Elevated
CO2 levels up to 100 Pa caused the antisense plants to
achieve a size similar to that of the wild-type plant. However, although the
antisense plant with 65% wild-type Rubisco was selected as a plant with
optimal Rubisco content for CO2 -saturated
photosynthesis, its final biomass was not greater than that of the wild-type
plant. This may have been caused by a relatively strong Rubisco-antisense
effect during the early stage of growth (21–42 d). N-use efficiency for
growth after d 42 was greater in the selected antisense plant. Thus,
improvement of N-use efficiency at the level of a single leaf did not
necessarily lead to greater production of biomass at the whole-plant level.
Sucrose phosphate synthase and sucrose synthase activity during maturation of internodal tissue in sugarcane
Authors: Botha Frederik C. , Black Kevin G.
Published: September 2002

Sucrose accumulation rates, sucrose-phosphate synthase (SPS, EC 2.4.1.14) and
soluble sucrose synthase (SuSy, EC 2.4.1.13) activities were measured in
internodal tissue from a sugarcane (Saccharum species
hybrids) variety N19. The sucrose accumulation rate sharply increases between
internodes 3 to 11. In the older internodes SPS activity was at least three
times higher than the SuSy activity. A highly significant positive correlation
was found between SPS activity and sucrose content. In contrast, no
significant correlation was observed between SuSy and sucrose content. In
agreement, when radiolabelled glucose was fed to internodes with a high
sucrose accumulation rate, label was equally distributed in the hexose
moieties of sucrose. This clearly indicates that SPS is the major sucrose
synthesis activity in the culm of sugarcane. Different kinetic forms of SPS
apparently exist in the internodal tissue at different stages of development.
Growth responses to elevated CO2 in NADP-ME, NAD-ME and PCK C4 grasses and a C3 grass from South Africa
Authors: Wand Stephanie J. E. , Midgley Guy F. , Stock William D.
Published: September 2002

The potential use of C4 biochemical subtypes
[nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME),
nicotinamide adenine dinucleotide-malic enzyme (NAD-ME) and
phosphoenolpyruvate carboxykinase (PCK)] as
delimiters of plant functional types (PFTs) with distinct responses to rising
atmospheric CO2 concentrations was investigated in
South African grass species. Gas exchange and above-ground growth in ambient
and elevated CO2 (360 and 660 µmol mol–1 , respectively) were determined in three
NADP-ME species, two NAD-ME species, two PCK species and one C3 species, all excavated from the same field site.
Plants were grown in open-top chambers in a greenhouse for 178 d. Net CO2 assimilation rates were only significantly increased
in one NAD-ME species, but stomatal conductances decreased (in six out of
eight species, by a mean of 46%) and instantaneous leaf water-use
efficiency increased (in all species, by a mean of 89%) in elevated CO2. These responses did not differ between
photosynthetic pathways. Parameters derived from photosynthetic CO2 and light response curves were also not differentially
influenced by CO2 treatment between pathways. Gas
exchange responses were generally poorly related to CO2
responsiveness. Significant increases in leaf growth and canopy leaf area in
elevated CO2 were found in two NADP-ME species, whereas
increases in non-leaf above-ground growth were measured in three species
representing all three C4 subtypes. Growth responses in
elevated CO2 were apparently not simply correlated with
biochemical subtype characteristics, although the most significant responses
(particularly at the leaf level) were found for the NADP-ME pathway. This
result was more likely attributable to the significant positive correlation
found between CO2 responsiveness of leaf growth and
relative leaf regrowth potential of individual species, the latter being
higher in the two responsive NADP-ME species. Therefore, categorisation of
PFTs according to relative growth potential may be more appropriate for
predictions of CO2 responsiveness in C4 grasses.
Desiccation tolerance of three moss species from continental Antarctica
Authors: Robinson Sharon A. , Wasley Jane , Popp Marianne , Lovelock Catherine E.
Published: September 2002

Tolerance of desiccation was examined in three
species of moss, Grimmia antarctici Card.,
Ceratodon purpureus (Hedw.) Brid. and
Bryum pseudotriquetrum (Hedw.) Gaertn., Meyer et Scherb.
collected from two sites of contrasting water availability in the Windmill
Islands, continental Antarctica. Physiological tolerance to desiccation was
measured using chlorophyll fluorescence in plugs of moss during natural drying
in the laboratory. Differences in relative water content, rate of drying and
the response of photosynthesis to desiccation were observed among the three
species and between sites. Of the three species studied,
G. antarctici showed the lowest capacity to sustain
photosynthetic processes during desiccation,
B. pseudotriquetrum had an intermediate response and
showed the greatest plasticity and C. purpureus showed
the greatest capacity to sustain photosynthesis during desiccation. These
results fit well with the known distribution of the three species with
G. antarctici being limited to relatively wet sites,
C. purpureus being common in the driest sites and
B. pseudotriquetrum showing a wide distribution between
these two extremes. Levels of soluble carbohydrates were also measured in
these samples following desiccation and these indicate the presence of
stachyose, an oligosaccharide known to be important in desiccation tolerance
in seeds, in B. pseudotriquetrum. Both gross morphology
and carbohydrate content are likely to contribute to differences in
desiccation tolerance of the moss species. These results indicate that if the
Casey region continues to dry out, as a result of local geological uplifting
or global climate change, we would expect to see not only reductions in the
moss community but also changes in community composition.
G. antarctici is likely to become more limited in
distribution as C. purpureus and
B. pseudotriquetrum expand into drying areas.
Nitrogen plays a major role in leaves when source-sink relations change: C and N metabolism in Lolium perenne growing under free air CO2 enrichment
Authors: Isopp Hubert , Frehner Marco , Almeida José P. F. , Blum Herbert , Daepp Markus , Hartwig Ueli A. , Lüscher Andreas , Suter Daniel , Nösberger Josef
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
Swards of Lolium perenne L. were grown in the field in a
long-term free air CO2 enrichment (FACE) facility. The
CO2 treatment was combined with two levels of N
fertilization and regular defoliation, which resulted in plants with a wide
range of source–sink relations. C and N metabolism were investigated to
assess the role of carbohydrate and nitrogenous compounds in leaves in
indicating source–sink relations. Sucrose exhibited the largest changes
in contents during the day–night cycle; therefore, it was identified as
the main short-term storage compound for night-time export. Fructan
accumulation indicated the degree of surplus C supply in the source compared
to C use in sinks. Nitrate content depended mainly on N fertilization, and was
reduced under elevated pCO2.
Nitrate appeared to indicate a current surplus of available N relative to the
need for growth. Amino acid content responded strongly to N fertilization but
decreased only slightly under elevated
pCO2. Protein content, however,
decreased significantly under elevated
pCO2. The patterns of diurnal
changes of C or N compounds did not differ between CO2
treatments. Down-regulation of photosynthesis appeared to occur when plants
were extremely N-limited as under elevated
pCO2, low N and at a late regrowth
stage.
A new method for rapid screening of xenobiotic phloem mobility in plants
Authors: Wang Ning , Lau Sze-Mei Cindy , Rogers Gregory , Ray Thomas
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
The deposition of hydrophobic polymers in the xylem of wheat grain floral axes
prevents water and solute movement into grains via the xylem (xylem
discontinuity). The only pathway for translocation of photosynthate or
externally applied xenobiotics into wheat grains is via the phloem. We have
developed a new method based on the xylem discontinuity for rapidly screening
phloem mobility of xenobiotics. By quantifying xenobiotic concentration in
grains and excised plants after the compounds were applied through the cut
stems, the phloem mobility can be estimated quantitatively. The phloem
mobility obtained with our new grain-based method was correlated to xenobiotic
chemical properties such as log
Kow,
pKa and electrical charge, and is
consistent with published literature. Phloem mobility values determined by the
grain-based assay were correlated to those from the direct phloem sap (aphid
stylet exudate) assay of excised and intact plants, indicating that the
grain-based assay is as reliable as the direct assay with aphid stylectomy.
The new grain-based method is simple, quick, and can be scaled up for rapid
screening of xenobiotic phloem mobility in plants. Similar seed (fruit)-based
assay could also be developed with wide ranges of plant species that use the
phloem as the only pathway for supplying water and nutrients into their seeds
or fruits.
Verapamil-induced kinetics of ion flux in oat seedlings
Authors: Babourina Olga , Shabala Sergey , Newman Ian
Published: September 2002

Verapamil application in ion transport studies on plant cells is widespread;
however, the mechanism of its action is still poorly understood. Net flux of
Ca 2+ , K + , Na
+ , H + and Cl
– were measured in solution around oat seedlings
using the non-invasive ion-selective microelectrode MIFE technique. The
verapamil effect on intact plant tissues was a distinct immediate influx of
monovalent cations, H + , K
+ or Na + .
Pre-treatment with tetraethyl-ammonium, Cs + , Ba
2+ or Ca 2+ did not
affect K + flux changes, whereas DMSO, Cd
2+ and vanadate increased verapamil-induced K
+ influx. Verapamil-induced K
+ flux increased with increased external KCl
concentration or pH. Verapamil concentration up to 1 mM failed to shift Ca
2+ flux to efflux. Pre-treatment with adrenaline
and dopamine agonists and antagonists led to changes in verapamil-induced ion
flux, especially for Ca 2+ . We suggest that a
transporter that allows entry of K + and Na
+ was the main system providing monovalent ion
influx after verapamil application.
Leaf water status controls day-time but not daily rates of leaf expansion in salt-treated barley.
Authors: Munns Rana , Guo Jianmin , Passioura John B. , Cramer Grant R.
Published: September 2002

Barley plants were grown in pots that would fit inside a pressure chamber, so
that their shoots could be kept fully turgid by applying pressure in the
chamber to bring the xylem sap of the shoot to the point of bleeding.
Pressurisation increased the growth rate of NaCl-treated plants in the light
period but not in the dark. The promotive effect on growth was greatest in the
light period of the first day of pressurisation, but disappeared during the
first night. Pressurisation promoted growth the next day during the light
period, but on the second night the elongation rate was significantly lower
than that of unpressurised NaCl-treated plants. This pattern of high day-time
and low night-time growth then continued indefinitely. The lower night-time
growth counteracted the higher day-time growth, with the result that total
growth over 24 h was the same as in NaCl-treated plants that were not
pressurised. Levels of total reserve carbohydrates were unaffected by
pressurisation, indicating that the slower growth of the pres-surised plants
during the night was not due to depletion of assimilates. These results are
interpreted in the context of hormonal signals controlling growth on a 24-h
basis, such that any short-term stimulation of growth arising from unusually
high water status during the light period is counterbalanced by slower growth
during the night.
Water constraints on the photoinduction of weed seed germination during tillage
Authors: Botto Javier F. , Scopel Ana L. , Sánchez Rodolfo A.
Published: September 2002

Germination of light-requiring seeds may be
induced by very brief exposure to sunlight during soil disturbance through the
very-low fluence (VLF) mode of phytochrome action. We studied the effect of
soil water availability after cultivation on the photoinduction of seed
germination in two important weed species, Datura ferox
andChenopodium album. In daily-irrigated plots, seedling
density was 1- to 4-fold greater in plots cultivated during daytime than in
those tilled at night. In contrast, when plots were not irrigated soon after
tillage and rainfall was excluded, no significant differences were observed
between seed germination in daytime vs night-time cultivated plots, although
seedling emergence in night-time cultivated plots was higher than in
non-cultivated controls. The average critical value of soil water potential
required for the expression of VLF-induced germination was higher than
–0.5 MPa (at 3-cm depth during the 6 d following cultivation). Dark
germination was less sensitive to decreasing soil moisture than light-induced
seed germination. The promotive effect of the light signal perceived by the
seeds during daytime cultivation is maintained for several days
(ca 6) in drying soil, even though laboratory data
suggest that the far-red-light absorbing form of the phytochrome inducing the
VLF photoresponse is unstable, disappearing in less than 24 h. These results
reveal the complexity of interactions between the light signal and other
environmental factors that control seed germination under natural conditions.
Amino acid metabolism in senescing Sandersonia aurantiaca flowers: cloning and characterization of asparagine synthetase and glutamine synthetase cDNAs
Authors: Eason Jocelyn R. , Johnston Jason W. , de Vré Leigh , Sinclair Ben K. , King Graeme A.
Published: September 2002

We have studied nitrogen metabolism during
senescence of the ethylene-insensitive flower
Sandersonia aurantiaca Hook. We report here on the
isolation and characterization of two cDNAs from senescing sandersonia tepals.
SAND1 encodes asparagine synthetase (AS; EC 6.3.5.4) and SAND3 encodes
glutamine synthetase (GS; EC 6.3.1.2). The accumulation of SAND3 mRNAs was
consistently high throughout flower development and senescence and was not
associated with senescence per se. SAND1 mRNAs started
to accumulate in mature flowers just prior to visual signs of senescence.
Sucrose feeding of individual flowers delayed tepal senescence and altered
amino acid metabolism. The levels of Asn, Gln and Glu were higher and Asp
levels were lower in the sucrose-fed flowers. The senescence-associated peak
in Gln was delayed in sucrose-fed flowers compared to controls that were held
in water. Sucrose feeding had no effect on the initiation of SAND1
transcription at the onset of flower senescence; however, the later decline in
SAND1 mRNA abundance was delayed in sucrose-fed flowers. Elimination of GS
activity and the subsequent reduction in Gln levels caused by phosphinothricin
treat-ment was associated with a delay of SAND1 mRNA accumulation in senescing
flowers.
Rapid environmental changes that affect leaf water status induce transient surges or pauses in leaf expansion rate.
Authors: Passioura John B. , Munns Rana
Published: September 2002

We subjected wheat and barley plants to rapid environmental changes, and
monitored leaf elongation rates for several hours thereafter. Changes in
light, humidity or salinity caused sudden rises (if the leaf water status
rose) or falls (if the leaf water status fell) in leaf elongation rate,
followed by a recovery phase that lasted 20–60 min. After a step change
in light or humidity, the growing leaf eventually resumed its original
elongation rate, although the shoot water status, as monitored by leaf
thickness, differed markedly. Salinity, on the other hand, produced a
persistent change in leaf elongation rate, which settled down to a lower
steady rate after the transient response was over. To determine whether the
sudden changes in leaf elongation rate were due to changes in leaf water
relations, we kept shoots fully hydrated through the environmental changes by
automatically pressurising the roots to maintain leaf xylem on the point of
bleeding. This annulled the environmental effects on leaf water status, and
thereby largely removed the changes in leaf elongation rate. The only
exception was at the dark:light transition, when the leaf elongation rate of
pressurised plants rose sharply (in contrast to that of unpressurised plants,
which fell), then underwent damped oscillations before settling at about its
initial value. The sudden excursions of leaf growth in unpressurised plants
accompanying the environmental changes were undoubtedly due to changes in leaf
water status. The subsequent, generally complete, return of the leaf
elongation rate to its initial value within an hour, despite the persistent
change in leaf water status, suggests that a control system is operating at a
time scale of tens of minutes that eventually overrides, partially or
completely, the rapid effects of changes in leaf water status.
Vasoactive intestinal peptide influences hatching of ovine blastocysts
Authors: Leoni G. , Bogliolo L. , Deledda F. , Ledda S. , Naitana S.
Published: September 2002

Expanded blastocysts collected from superovulated Sarda ewes were divided at
random into four groups for culture in a simple medium that does not support
blastocyst hatching (CZB) or a complex medium that is permissive to hatching
(TCM 199), with or without vasoactive intestinal peptide (VIP), a known embryo
mitogenic peptide. Plasminogen activator (PA) secretion after 24 h of culture,
and the number of cells, diameter of blastocysts and hatching rate after 48 h
of culture were compared. The results showed an increase in hatching rate
(78.6 v. 6.7%; P<0.01),
diameter and number of cells (220.89 v. 210.44 m,
P<0.01 and 246 v. 232,
P<0.01 respectively) and caseinolytic areas (1.33
v. 0.92 cm, P<0.01) of
blastocysts cultured in TCM 199 compared with those cultured in CZB.
Supplementation of the culture media with VIP increased these parameters in
CZB (P<0.01) and partially in TCM 199. In particular,
cell number, diameter and PA activity were significantly higher
(P<0.01) after culture with VIP in both media.
Immunoneutralization of exogenous VIP in culture with anti-VIP antibody caused
a decrease in the hatching rate (P<0.01) of embryos
cultured in medium with VIP, similar to the rate in unsupplemented CZB
(P<0.01). These results suggest a receptor-mediated
response. In immunohistochemical studies, VIP was shown to bind receptors in
hatched blastocysts demonstrating the VIP–receptor interaction, and VIP
receptors of approximately 150 kDa were revealed by electrophoretic studies.
In conclusion, ovine preimplantation embryos exhibit VIP receptors, providing
a basis for a receptor-mediated influence of VIP in the hatching of ovine
blastocysts.
In situ pH measurements of the Syrian hamster uterus during early pregnancy to determine the role of pH in zona pellucida loss in vivo
Authors: McDougall Kathryn , Hedrick Jerry L. , Bavister Barry D.
Published: September 2002

The mechanisms of zona pellucida (ZP) loss in peri-implantation hamster
embryos in vivo versus in vitro
are distinctly different. To investigate if ZP loss
in vivo is the result of transient uterine pH changes,
the luminal pH of the pregnant uterus was measured during the ZP loss period.
Prior to ZP loss, pH was 7.30 0.05 (mean SE; left uterine horn) and 7.35 0.03
(right horn). During ZP loss, pH was 7.26 0.07 (left) and 7.35 0.03 (right),
and after embryo attachment, 7.25 0.02 (left) and 7.27 0.02 (right). None of
these values are statistically different. The pseudopregnant uterine pH was
7.30 0.04 (left) and 7.31 0.04 (right), not statistically different from each
other or from pregnant uteri. Blastocyst ZP loss
in vitro (pH 3.0–8.5) occurred only at pH 3.0.
Loss of ZP occurred in uterine flushings from pregnant or pseudopregnant
hamsters, evidence that ZP loss is related to uterine factors. Complete ZP
loss occurred at pH 6.8, but was incomplete at pH 6.6, 7.0 and 7.2. No ZP loss
occurred in uterine flushings from non-mated females. In summary:
(i) a change in uterine pH does not cause ZP loss
in vivo in the Syrian hamster;
(ii) a pH-sensitive factor in pregnant and
pseudopregnant uterine fluid is responsible for ZP loss.
Embryo splitting: a role in infertility?
Authors: Wood Carl
Published: September 2002

Embryo splitting may be used to increase the potential fertility of couples
requiring IVF. Using cattle as a model, it is possible to increase pregnancy
rates from 70% per transfer of good
qualityin-vivo-produced embryos,
to 110% by transferring the two demi-embryos resulting from the
bisection of one embryo. The 30–40% greater chance of conception
would reduce costs for the government, health authorities and patients, and
reduce stress, time and complications for women having IVF treatment. Embryo
splitting may also provide donor embryos for infertile couples that cannot
conceive naturally or with IVF. The shortage of children for adoption and
donor embryos may be overcome by the production of demi-embryos.
Identification and regulation of the platelet-activating factor acetylhydrolase activity in the mouse uterus in early pregnancy
Authors: Chami O. , O'Neill C.
Published: September 2002

Platelet-activating factor (PAF) is a product of the embryo and the
endometrium in early pregnancy. The actions of PAF may be regulated by its
degradation and this is largely achieved by the enzyme PAF acetylhydrolase
(PAF:ah; EC 3.1.1.47). The present study characterized the PAF:ah in the
endometrium and uterine fluid of mice during early pregnancy. The enzyme
activity from uterine endometrium and luminal fluids had the same biochemical
characteristics as the plasma form of the enzyme. The three sources of enzyme
activity (i) had an apparent native molecular mass
greater than 106 Da, but this was reduced after
detergent treatment and purification to 60–65 kDa;
(ii) bound to cholesterol hemisuccinate agarose matrix;
and (iii) were found in the high density
lipoprotein-enriched fraction after density gradient ultracentrifugation. In
castrate females, oestradiol-17β (E2) caused a
dose-dependent increase in the activity of the enzyme in endometrium and
luminal fluid. Progesterone (P4) inhibited the
E2-induced increase in PAF:ah in uterine tissue.
Treatment with E2 alone caused an increase in
endometrial PAF:ah activity within 24 h, which declined within 48 h. In
luminal fluid, the same treatment caused increased activity within 24 h,
peaking after 48 h of treatment and then declining. In
E2-treated castrate females, mRNA for an intracellular
(but not plasma) form of PAF:ah was detected, yet the intracellular form was
not detected biochemically. The results suggest that most of the enzyme
activity was not produced locally, but probably resulted from the influx of
the plasma form of the enzyme.
Selective estrogen receptor modulators: mechanism of action and clinical experience. Focus on raloxifene
Authors: Thiebaud Daniel , Secrest Roberta J.
Published: September 2002

Selective estrogen receptor modulators (SERMs) are a diverse group of
compounds that bind with specific, high-affinity binding to the estrogen
receptor (ER). Depending on the tissue, SERMs can act as either ER agonists or
antagonists. Recent advances in ER biology have provided insight into possible
mechanisms by which SERMs elicit these tissue-specific estrogen agonist and
estrogen antagonist activities. The estrogen response pathway has been shown
to differ among target tissues depending on various tissue and cellular
factors, such as the ER subtype, the structure of the bound
receptor–ligand complex, and the tissue-specific cellular
transcriptional machinery. Clinically available SERMs include clomiphene,
tamoxifen and toremifene, which are triphenylethylenes, and raloxifene, a
benzothiophene. Raloxifene has estrogen agonist effects on bone, serum lipids,
and arterial vasculature, and estrogen antagonist effects in breast and
uterus. Clinical trial data for raloxifene is used to illustrate some of the
mechanisms by which SERMs exert their tissue-specific estrogen agonist and
estrogen antagonist effects. The complex pharmacology surrounding the tissue
selectivity of SERMs is discussed.
Control of fertility in the red fox (Vulpes vulpes): effect of a single oral dose of cabergoline in early pregnancy
Authors: Marks Clive A. , Brzozowski Marian , Zurek Hieronim , Clark Malcolm
Published: September 2002

Single oral doses of 100 g kg–1 cabergoline (CAB)
were previously found to affect the reproductive success of silver fox
(Vulpes vulpes) vixens from Day 28 post insemination
(PI) onwards by causing abortions and postnatal mortality. The present trial
investigated the effect of a single oral dose of 100 g
kg–1 CAB given to farmed silver fox vixens at 7,
14, 21 or 28 days PI. Six vixens were dosed with CAB at each day PI and
abortions, total post-partum litter loss and the combined effects of both were
compared with a group of vixens that received a placebo and a control group of
vixens that received no treatment. No significant difference existed between
the placebo and control groups in the incidence of abortion, postnatal litter
loss and litter size at 3 weeks post partum. Overall, a significantly higher
frequency of abortions were detected in vixens dosed with CAB (6/24)
compared with the combined placebo and control (0/41) groups
(P<0.01). Cabergoline administration was
significantly associated with complete litter loss
(P<0.01) and the combined effects of abortion and
litter loss (P<0.001). Oral CAB significantly reduced
the reproductive success of vixens when given at Day 21 and Day 28 PI, but not
at Day 7 and Day 14 PI.
Protein coregulators that mediate estrogen receptor function
Authors: Ratajczak T.
Published: September 2002

The recent discovery of estrogen receptor β as a biological partner
with estrogen receptor β in mediating the estrogen response has come
at precisely the same time as intensive research is revealing the role played
by downstream coregulator proteins in linking nuclear hormone receptor
activity to general transcription machinery involved in gene transcriptional
activation. In what is a rapidly evolving area of research, findings to date
have led to a proposed model of hormonal action, in which a receptor activated
by estrogen or cell-membrane-derived phosphorylation-dependent signaling
pathways promotes recruitment of selected members of the multifunctional
steroid receptor coactivator family and the cointegrators, p300/CBP and
P/CAF. The intrinsic histone acetylase activity mediated by these
coactivator and cointegrator proteins, alters chromatin structure giving rise
to increased transcriptional efficiency. On the other hand, antiestrogen-bound
receptors favour the assembly of receptor-corepressor complexes containing the
sequence-related corepressors N-CoR (nuclear receptor corepressor) or SMRT
(silencing mediator of retinoid and thyroid hormone receptors), localizing
histone deacetylase activity to the promoter and leading to transcriptional
repression. The model predicts that a change in the balance between
corepressor and coactivator expression in favour of coactivators, might result
in antiestrogen resistance. Together with available crystal structure data for
estrogen- and antiestrogen-bound receptors, these studies have provided
valuable insights into events that occur subsequent to receptor interaction
with specific DNA sequences and have helped define the molecular basis of
estrogen and antiestrogen activity.