bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of respiratory metabolism correlates well with the response of Eucalyptus camaldulensis seedlings to NaCl and high pH
Authors: Marcar Nico E. , Criddle Richard S. , Guo Jianmin , Zohar Yale
Published: September 2002

Growth of sand-cultured Eucalyptus camaldulensis Dehnh. (river red gum) seedlings from six wide-ranging provenances was reduced in the presence of 150 mM NaCl, a high pH of 9.5, and combined NaCl and high pH, compared with no applied NaCl and neutral pH. Effects of these stress conditions on respiration rates and substrate carbon conversion efficiencies of rapidly-expanding leaf tissue were measured with calorespirometric techniques. Growth rates were calculated from respiration parameters. Respiration rate, measured as metabolic heat production rate (q), showed no consistent trend with either NaCl or high pH, whereas the rate measured as CO2 production rate (R
CO2) was generally lower with both treatments. The ratio of heat lost per mole of CO2 produced [q/(R
CO2)] was consistently increased by both stresses. Stress causes a larger fraction of metabolic energy produced by aerobic metabolism to be lost as heat, relative to non-stressed controls. Consequently, a larger fraction of photosynthetic product in stressed seedlings must be metabolized to CO2 per mole of C incorporated into biomass. Our results indicate that 0.42 mol substrate C is converted to CO2 per mole C incorporated into biomass for control plants, compared with 0.96 mol for plants treated with combined NaCl and high pH. Respiratory responses to treatment varied with provenance. Specific growth rates, calculated from repiratory parameters (q and RCO2) of stressed E. camaldulensis seedlings, generally paralleled experimentally-determined reduced growth (dry weight) of these seedlings. Thus, measurements of leaf respiration allow calculation of growth inhibition caused by NaCl and high pH stress. However, we could not discriminate among provenances in this experiment with only one level of NaCl and pH.
Characterization of the C-terminal extension of carboxysomal carbonic anhydrase from Synechocystis sp. PCC6803
Authors: So Anthony K.-C. , Cot Swan S.-W. , Espie George S.
Published: September 2002

Sequence analysis of the carboxysomal carbonic anhydrase (CcaA) from
Synechocystis PCC6803,
Synechococcus PCC7942 and Nostoc
ATCC29133, indicated high sequence identity to the β class of plant and
bacterial carbonic anhydrases (CA), and conservation of the active site
region. However, the cyanobacterial enzyme has a
C-terminal extension of about 75 amino acids (aa) not
found in the plant enzymes, and largely absent from other bacterial enzymes.
Using recombinant DNA technology, genes encoding
C-terminal truncation products of up to 127 aa were
overexpressed in E. coli, and partially purified lysates
were analysed for CA-mediated exchange of 18O between
13C18O2and
H216O. Recombinant CcaA proteins
with up to 60 aa removed (CcaAΔ60) were catalytically competent, but
beyond this there was an abrupt loss of activity. CcaAΔ0, along with
CcaAΔ40 and CcaAΔ60, also catalysed the hydrolysis of carbon
oxysulfide (COS; an isoelectronic structural analogue of
CO2), but CcaAΔ63 and CcaAΔ127 did not,
indicating that truncations greater than 62 aa resulted in a general loss of
catalytic competency. Analysis of protein-protein interaction using the yeast
two-hybrid system revealed that CcaA did not interact with the large or small
Rubisco subunits (RbcL and RbcS, respectively) of
Synechocystis, but there was strong CcaA-CcaA
interaction. This protein interaction also ceased with
C-terminal truncations in CcaA greater than 60 aa. The
correlation between loss of CcaA-CcaA interaction and CcaA catalytic activity
suggests that the proximal portion of the C-terminal extension is required for
oligomerization, and that this oligomerization is essential for catalysis by
the cyanobacterial enzyme. Thus, the C-terminal extension may play an
important role in the function of CA within cyanobacterial carboxysomes, which
is not required by the higher plant enzymes.
Ecological implications of microalgal and cyanobacterial CO2 concentrating mechanisms, and their regulation
Authors: Beardall John , Giordano Mario
Published: September 2002

The capacity of algae to express CO2 concentrating mechanisms (CCMs) is
regulated by environmental factors. Some of these factors, especially photon
flux, can influence the instantaneous activity of a CCM without necessarily
affecting gene expression or the capacity of the cell to transport inorganic
carbon. Other environmental parameters, especially those causing changes in
the availability of CO2 dissolved in the surrounding
medium, act at a transcriptional level. In this review, the complex
interactions between environmental factors in controlling CCM activity will be
discussed, as will the ecological consequences of CCMs as they relate to the
growth and ecological performance of algal cells in nature. We also consider
the consequences of global climate change for the performance of algae with
and without CCMs.
Acquisition of inorganic carbon by the marine diatom Thalassiosira weissflogii
Authors: Morel François M. M. , Cox Elizabeth H. , Kraepiel Anne M. L. , Lane Todd W. , Milligan Allen J. , Schaperdoth Irene , Reinfelder John R. , Tortell Philippe D.
Published: September 2002

Recent data on the physiology of inorganic carbon acquisition by the model
marine diatom Thalassiosira weissflogii (Grunow)
demonstrate the importance of the catalytic equilibration of
HCO3-and
CO2by carbonic anhydrases located in the periplasm and
in the cytoplasm. These enzymes can use Zn, Co or Cd as their metal centre,
and their activity increases at low ambient CO2. The
silica frustule provides buffering for extracellular CA activity, The
transmembrane transport of CO2 may occur by passive
diffusion. Under CO2 limitation, the cytoplasmic
HCO3–is used to form malate
and oxaloacetic acid via phosphoenolpyruvate
carboxylase. It appears that subsequent decarboxylation of these compounds in
the chloroplast regenerates CO2 near the site of
Rubisco, and thus provides the organism with an effective unicellular
C4 photosynthetic pathway. These results, together with
other published data, bring up two major questions regarding inorganic carbon
acquisition in diatoms: What is the major species of inorganic carbon
(CO2 or
HCO3–) transported across
the membrane under natural conditions? And what is the form of carbon
(inorganic or organic) accumulated by the cells?
Mode of photosynthesis during different life stages of hemiepiphytic Clusia species
Authors: Wanek Wolfgang , Huber Werner , Arndt Stefan K. , Popp Marianne
Published: September 2002

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001.
Carbon isotope fractionation and nocturnal acid accumulation in Clusia osaensis Hammel-ined., C. �peninsulae Hammel-ined. and C. valerii Standl. were investigated during the seedling, epiphytic and hemiepiphytic phases in a lowland tropical forest in Costa Ricato study photosynthetic adaptations of different plant growth stages to their habitat. Foliar δ 13C values around -24 to -32‰ indicate predominant C3 fixation of CO2 and low crassulacean acid metabolism (CAM) activity in all three Clusia species. Only terrestrially rooted plants of C. osaensis showed increased CAM expression. However, all developmental stages exhibited significant CAM cycling as shown by significant day-night fluctuations of titratable protons and of malic and citric acid. In C. valerii and C. peninsulae, an increase in CAM expression with plant development was not observed, and CAM cycling in hemiepiphytic-stage plants was completely repressed during the high rainfall season. The expression of CAM in the three Clusia species is therefore not developmentally controlled but triggered by environmental factors such as water availability and light intensity. These factors remain relatively stable in this ecosystem and CAM is therefore not fully expressed. However, CAM cycling may be of ecophysiological significance in all life stages as it serves as a mechanism to improve carbon economy by reducing respiratory CO2 losses.
Regulation of Rubisco activity in crassulacean acid metabolism plants: better late than never
Authors: Maxwell Kate , Griffiths Howard , Helliker Brent , Roberts Andrew , Haslam Richard P. , Girnus Jan , Robe Wendy E. , Borland Anne M.
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 diurnal regulation of Rubisco was compared for a range of crassulacean acid metabolism (CAM) species in the context of high carboxylation and electron transport capacities, which may be an order of magnitude greater than rates of net CO2 uptake. Early in the light period, Rubisco activity and electron transport were limited when phosphoenolpyruvate carboxylase (PEPC) may have been operating, and maximal extractable activities and activation state for Rubisco were achieved at the end of Phase III, prior to the direct atmospheric uptake of CO2 during Phase IV. The delayed activation was associated with levels of Rubisco activase protein, which reached a maximum at midday, and may account for this pattern of Rubisco activation. This regulation may be modified by environmental conditions - processes that tend to restrict PEPC activity, such as drought stress or incubation of leaves overnight in an oxygen-free atmosphere, release Rubisco from inhibition early in the light period. The quantum yield of light use also tracks Rubisco carboxylation, being particularly low at dawn when PEPC is active. The plasticity in expression of the CAM cycle is therefore matched by the regulation of key carboxylases, with extractable Rubisco activity maximal when drawdown of atmospheric CO2 to cells in succulent CAM tissues is most likely to limit photon utilization shortly after midday, during Phase IV.
C4 mechanisms in aquatic angiosperms: comparisons with terrestrial C4 systems
Authors: Bowes George , Rao Srinath K. , Estavillo Gonzalo M. , Reiskind Julia B.
Published: September 2002

Aquatic C4 photosynthesis probably arose in response to
dissolved CO2 limitations, possibly before its advent in
terrestrial plants. Of over 7600 C4 species, only about
a dozen aquatic species are identified. Amphibious
Eleocharis species (sedges) have
C3–C4 photosynthesis and
Kranz anatomy in aerial, but not submersed, leaves. Aquatic grasses have
aerial and submersed leaves with C4 or
C3–C4 photosynthesis and
Kranz anatomy, but some lack Kranz anatomy in the submersed leaves. Two
freshwater submersed monocots, Hydrilla verticillata and
possibly Egeria densa, are C4
NADP-malic enzyme (NADP-ME) species. A marine macroalga,
Udotea flabellum (Chlorophyta), and possibly a diatom,
are C4, so it is not confined to angiosperms. Submersed
C4 species differ from terrestrial in that
β-carboxylation is cytosolic with chloroplastic decarboxylation and
Rubisco carboxylation, so the C4 and Calvin cycles
operate in the same cell without Kranz anatomy. Unlike terrestrial plants,
Hydrilla is a facultative C4 that
shifts from C3 to C4 in low
[CO2]. It is well documented, with
C4 gas exchange and pulse-chase characteristics, enzyme
kinetics and localization, high internal
[CO2], relative growth rate, and quantum yield
studies. It has multiple phosphoenolpyruvate carboxylase
isoforms with C3-like sequences.
Hvpepc4 appears to be the photosynthetic form induced in
C4 leaves, but it differs from terrestrial
C4 isoforms in lacking a C4
signature Serine. The molecular mass of NADP-ME (72 kDa) also resembles a
C3 isoform. Hydrilla belongs to the
ancient Hydrocharitaceae family, and gives insight to early
C4 development. Hydrilla is an
excellent ‘minimalist’ system to study C4 photosynthesis
regulation without anatomical complexities.
Sucrose transport across the vacuolar membrane of Ananas comosus
Authors: McRae Shelley R. , Christopher John T. , Smith J. Andrew C. , Holtum Joseph  A. M.
Published: September 2002

This paper originates from a presentation at the IIIrd International Congress on Crassulacean Acid Metabolism, Cape Tribulation, Queensland, Australia, August 2001.
In Ananas comosus L. (Merr.) (pineapple), a widely cultivated bromeliad that exhibits crassulacean acid metabolism (CAM), much of the carbohydrate synthesized during the daytime appears to accumulate as soluble sugars in the vacuole. To investigate the mechanism of sugar transport into the vacuole, microsomal extracts were prepared from deacidifying leaves harvested during Phase III of the CAM cycle. The vesicle preparations exhibited features expected for a fraction highly enriched in vacuolar membranes (tonoplast), i.e. the ATPase activity of 16 ±�2�nkat mg-1 protein was inhibited 96% by 50 mm KNO3, an inhibitor of vacuolar ATPases, and was only 7% inhibited by 100μm NaN3 plus 100μm Na3VO4, inhibitors of mitochondrial and plasma membrane ATPases, respectively. Further, the microsomal ATPase activity showed a pH optimum between 7.0 and 8.0, typical of a vacuolar ATPase. When presented with Mg-ATP, vesicles established H+ gradients that could be maintained for at least 25 min. The vesicles were able to take up [14C]sucrose from an external medium. Sucrose uptake exhibited saturable kinetics with an apparent Km of 50 m sucrose and apparent Vmax of 171 ± 5 pkat mg-1 protein. Sucrose uptake was not dependent upon, nor stimulated by, Mg-ATP, suggesting that the mechanism of sucrose transport into the vacuole in A. comosus does not involve H+-coupled cotransport. However, the initial rates of sucrose uptake from the external medium were stimulated when vesicles were preloaded with sucrose. This trans-stimulation is consistent with characteristics expected for a sucrose uniporter capable of operating in an exchange mode. It is proposed that the accumulation of glucose and fructose in leaf vacuoles of Ananas during the light period involves at least two steps - transport of sucrose into the vacuole by a mechanism exhibiting characteristics of a sucrose uniporter, followed by cleavage of sucrose by a vacuolar acid invertase to form glucose and fructose.
Spatial and temporal regulation of a soybean (Glycine max) lectin promoter in transgenic cotton (Gossypium hirsutum)
Authors: Townsend Belinda J. , Llewellyn Danny J.
Published: September 2002

The activity of a soybean (Glycine max L. Merrill) lectin gene promoter was investigated in transgenic cotton plants (Gossypium hirsutum L.) with the view to using this promoter for the seed-specific alteration of gossypol, a secondary metabolite in cotton that has adverse effects on the nutritional value of cottonseed products like oil and protein-rich meal. Agrobacterium-mediated transformation generated stable transformants containing a construct with the lectin promoter fused to the β-glucuronidase reporter gene (pLeGUS). Fluorometric GUS assays and northern hybridization detected strong promoter activity during embryo development. GUS activity in developing embryos was detected as early as 10 d post-anthesis (dpa), peaking late in embryo maturation. Enzyme activity persisted in imbibed mature seed, and negligible activity remained detectable in the roots and cotyledons of 7-d-old seedlings. No GUS activity was detected in leaves and squares of mature plants. GUS transcripts increased during embryo development to peak about 35 dpa, declining to a low level in imbibed mature seed. No transcripts were detected in roots, cotyledons, leaves or squares. Histochemical GUS activity staining indicated promoter activity in all cells of the cotyledons, including the flattened cells of the gossypol glands, the presumed site of synthesis of gossypol. This study concluded that the soybean lectin gene promoter is a useful tool for the seed-specific expression of transgenes in cotton.
Mitochondrial protein expression in tomato fruit during on-vine ripening and cold storage
Authors: Holtzapffel Ruth C. , Finnegan Patrick M. , Millar A. Harvey , Badger Murray R. , Day David A.
Published: September 2002

We have investigated the activity and abundance of a number of respiratory chain components in ripening and cold-treated tomato fruits (Lycopersicon esculentum L. Mill cvv. Moneymaker and Sweetie). Expression of the alternative oxidase (AOX) protein increased dramatically in both situations. Levels of the plant uncoupling protein (UCP) initially fell, but increased substantially in the later stages of ripening. In contrast, ATP synthase subunits and the COXII subunit of cytochrome oxidase decreased during ripening and increased slightly in response to cold stress. Other proteins involved in electron transport, tricarboxylic acid cycle function, chaperonin function, and membrane transport were also studied. These showed varying degrees of enhanced and depressed expression patterns. There were modest changes in whole fruit respiratory activities, and electron transport capacity of isolated mitochondria in response to these stimuli. However, respiratory control by ADP in the isolated mitochondria decreased as AOX capacity and abundance increased, indicating that although total respiration rates changed little, flux between the coupled and uncoupled pathways altered. The changes observed in AOX and UCP accumulation in tomato fruit that were vine-ripened were significantly different from post-harvest ripening patterns previously reported. The altered protein profiles are discussed in the context of on- and off-vine ripening and the potentially different roles of uncoupled respiration in each situation.
Variation in nitrate nutrition leads to changes in the performance of the V-ATPase and immunological differences of proteolipid subunit c in tobacco (Nicotiana tabacum) leaves
Authors: Fischer-Schliebs Elke , Drobny Martina , Ball Erika , Ratajczak Rafael , Lüttge Ulrich
Published: September 2002

The tonoplast V-type H
+-ATPase (V-ATPase; EC 3.6.1.34) of higher plants
responds by its activity and molecular-subunit fine structure to environmental
parameters, such as temperature and salinity, or to the mode of photosynthesis
in C3–CAM intermediate plants. To test the
hypothesis that the enzyme is responding to varied mineral nutrition in
similar ways, tobacco plants were grown at low (2 mM) and high (40 mM) nitrate
supply, and a group of plants was also transferred from the low to the high
nitrate concentration for 48 h before analysis. Direct correlation of V-ATPase
properties with nitrate regimes and leaf nitrate content were not found, but
indirect effects related to nitrate-affected growth were obtained. Although
the ATP-hydrolysis of isolated tonoplast vesicles was similar under all three
conditions, H + -transport activity and hence the
apparent H + -transport activity/ATP-hydrolysis
coupling ratio of the V-ATPase in native tonoplast vesicles was high at low
growth-limiting nitrate supply and after growth acceleration following the
transfer of plants from low to high nitrate. Immunological differences of the
V-ATPase suggested that the membrane-integral proteolipid subunit
c showed structural differences related to nitrate
nutrition. These differences were revealed by differential cross-reactions
with two polyclonal antisera directed against the V-ATPase of
Kalanchoë daigremontiana, respectively. The
immunological differences could possibly be due to the expression of different
forms of subunit c correlated with actual growth rates
of leaves, which were high at 40 mM and after the transfer from 2 mM to 40 mM,
and low at 2 mM nitrate. These complex responses to variation in nitrogen
nutrition of plants are consistent with the notion in the literature that
nitrate is both a nutrient and a signal for plant growth.
Changes in grain weight as a consequence of de-graining treatments at pre- and post-anthesis in synthetic hexaploid lines of wheat (Triticum durum x T. tauschii)
Authors: Calderini Daniel F. , Reynolds Matthew P.
Published: September 2002

Grain weight is a trait which has hardly been
exploited for raising genetic yield potential of wheat. A clearer
understanding of physiological determinants of grain weight potential would be
useful in establishing the potential value of this trait in future breeding
programs. The objective of this study was to improve understanding of how
intra-spikelet competition for assimilates pre- and post-anthesis affect grain
weight potential, and to evaluate possible mechanisms determining final grain
weight in wheat. Two experiments were carried out under field con-ditions.
Proximal or distal grains from the two central spikelets of spikes of three
synthetic hexaploid lines were detached at heading or 7 d after anthesis.
Synthetic wheats were used since they represent a potential source of genetic
variability for grain weight potential. Carpel size at anthesis and grain
weight during the grain filling period were measured. The de-graining
treatment at heading significantly increased grain weight, especially in
distal posi-tions. On the contrary, the de-graining treatment carried out
after anthesis caused no increase in final grain weight. The largest response
to pre-anthesis de-graining occurred in grain positions with the lowest grain
mass. In addition, the effect of de-graining prior to anthesis was associated
hyperbolically with weight of carpels at anthesis within each grain position.
Therefore, carpel weight at anthesis could be partially associated with the
regulation of grain weight potential.
Light energy dissipation in Quercus ilex resprouts after fire
Authors: Fleck Isabel , Aranda Xavier , El Omari Bouchra , Permanyer Jon , Abadía Anunciación , Hogan Kevin P.
Published: September 2002

Holm oak (Quercus ilex) plants that have resprouted
after fire have higher photosynthetic capacity than control plants in intact
vegetation. In this study, branches detached from forest plants were fed with
dithiothreitol (DTT) in the laboratory to inhibit zeaxanthin production and
thus reduce the dissipation of light energy as heat. This allowed us to test
the hypothesis that plants with greater photosynthetic capacity, and therefore
greater photo-chemical sink strength, would suffer a lower reduction in
photochemical efficiency under stressful conditions. Greater rates of
photochemistry in resprouts, which exhibited increased photosynthesis
(A), leaf conductance (g), quantum
yield of PSII
(ΔF/Fm′)
and photochemical quenching (qP), were related to lower
non-radiative dissipation of excess energy as indicated by 1 –
(Fv′/Fm′).
However, the fraction of energy remaining of that used in photo-chemistry or
dissipated thermally in the PSII antennae was similar in resprouts and
controls and was not affected by DTT, especially under high irradiance
conditions. Zeaxanthin involvement in PSII protection operated in resprouts
and controls since DTT induced the same kind of response
(NPQ decrease) but was lower in resprouts. These
chloro-phyll fluorescence results suggest the participation of some additional
mechanism for energy dissipation. Light capture characteristics of the
photosynthetic apparatus did not differ between resprouts and controls, and
leaf age did not play a determining role in the differences observed.
Genotypic differences in seed growth rates of Phaseolus vulgaris L. I. General characteristics, seed coat factors and comparative roles of seed coats and cotyledons
Authors: Thomas Melinda , Hetherington Louise , Patrick John W.
Published: September 2002

Developing seeds of four cultivars of Phaseolus vulgaris
L., raised under glasshouse conditions, exhib-ited a 4-fold range in rates of
storage product accumulation by their cotyledons. These growth rate
differences were established during seed expansion. Patterns of dry matter
distribution were consistent with absolute growth rates of cotyledons being an
inherent property of developing seeds and not limited by photoassimilate
supply. Seed surface areas and cotyledon volumes exhibited a 3.2-fold cultivar
difference and were the principal components contribut-ing to cultivar
variation in cotyledon absolute growth rates. The remaining cultivar variation
was attributable to a 1.3- fold difference in dry matter fluxes, expressed on
a seed surface area basis. Seed coats reflected these properties in terms of
fluxes of dry matter released for cotyledon storage and surface areas
supporting these fluxes. Seed coat surface areas correlated with estimates of
total plasma membrane areas of ground parenchyma cells that are respon-sible
for photoassimilate release. Cultivar differences in these membrane areas
largely arose from variation in cell size. Coat turgor pressures correlated
positively with dry matter fluxes imported into cotyledons. In contrast,
sucrose concentration in bulk saps extracted from seed coats was identical
across three cultivars but was positively related to growth rate in the
remaining cultivar. Overall, these data suggested that cultivar dry matter
fluxes were determined by variation in transport conductances for symplasmic
movement through the post-sieve element pathway and for release across the
plasma membranes of ground parenchyma cells. Comparable sucrose concentrations
were found in seed apoplasmic saps across cultivars, and cultivar differences
in absolute growth rates of in vitro cultured
coty-ledons were retained. Together, these observations support the conclusion
that cotyledons intrinsically express geno-typic variation in rates of dry
matter transport comparable to those set independently by seed coats.
The effect of low concentrations of sodium on potassium uptake and growth of wheat
Authors: Box Sally , Schachtman Daniel P.
Published: September 2002

Sodium is a beneficial mineral for some plant species when external
concentrations are low. The role of Na+ in
energising K+ acquisition in terrestrial plants has
recently been suggested because of evidence demonstrating that wheat root
cells express a high-affinity Na+-energised
K+ symporter. To determine whether low
concentrations of Na+ improve the
K+ nutrition and growth of wheat, long-term growth
and short-term tracer flux experiments were conducted. Long-term growth
experiments were conducted over a range of K+
concentrations, at acidic and alkaline pH, with and without 500 µM NaCl.
Plant biomass and tissue Na+ and
K+ content was measured. Short-term experi-ments
were conducted using tracers to determine whether low concentrations of
Na+ or K+ stimulate
Rb+ or Na+ uptake,
respectively. Sodium stimulated the growth of wheat only at low (20 µM)
external K+ in one of the long-term experiments,
but not in two other experiments. Na+ did not
stimulate Rb+ uptake, but
K+ stimulated Na+ uptake
in short-term tracer flux experiments. The results suggest that low
concentrations of Na+ do not increase
K+ uptake to a large extent, and only when light
levels are low does Na+ have a beneficial effect on
the growth of wheat.
Relationship between antioxidant defence systems and salt tolerance in Solanum tuberosum
Authors: Benavídes María P. , Marconi Patricia L. , Gallego Susana M. , Comba María E. , Tomaro María L.
Published: September 2002

A relationship between the antioxidant defence
system and salt tolerance in two clones of potato
(Solanum tuberosum L.) differing in salt sensitivity was
studied. The antioxidant defence system of the sensitive clone responded
differently to 100 and 150 mM NaCl. At 100 mM NaCl, growth, dehydroascorbate
reductase and catalase activities remained unaltered, but chlorophyll and
reduced glutathione content decreased (23% and 35%,
respectively), while ascorbate content and superoxide dismutase activity were
increased 34% and 63%, with respect to the control (0 mM NaCl).
The superoxide dismutase increment was higher under 150 mM NaCl treatment,
while a general decrease (except for dehydroascorbate reductase and catalase
activities) in all the antioxidant parameters studied was observed in the
sensitive clone. Reduced glutathione and ascorbate, the main antioxidant
soluble defences, and all antioxidant enzymes (except catalase) were
significantly elevated in the tolerant clone compared to the sensitive one
when both were grown in the absence of NaCl. Under 100 and 150 mM NaCl
treatments, no changes in the antioxidant stress parameters were detected in
the tolerant clone. These results suggest a relationship between salt
tolerance and the antioxidant defence system in the two clones.
Differential expression of soluble acid invertase genes in the shoots of high-sucrose and low-sucrose species of Saccharum and their hybrids
Authors: Zhu Yun J. , Albert Henrik H. , Moore Paul H.
Published: September 2002

The hydrolytic activity of soluble acid
invertase (SAI) is strongly correlated to sucrose accumulation in sugarcane
(Saccharum spp.). Plants exhibiting SAI activity above a
low threshold level do not accumulate high concentrations of sucrose. The
present work investigates the basis for the difference in SAI activity
observed between high- and low-sucrose-accumulating sugarcane lines.
SAI-encoding cDNAs were isolated from two high- and one low-sucrose lines. All
of these cDNAs were highly similar, with deduced proteins at least 98%
identical. Expression of SAI in the stem of sugarcane was developmentally
regulated, with relatively larger pools of SAI protein and mRNA in the apex
and young internodes, which declined rapidly in the maturing internodes where
sucroseaccumulation occurs. This developmental pattern, while qualitatively
similar, was quantitatively quite different between low- and high-sucrose
lines. SAI protein and mRNA pools started substantially higher, declined
later, and stabilized at a significantly higher level in a low-sucrose line
than in a high-sucrose line. These data indicate that differences in SAI
activity between high- and low-sucrose sugarcane lines are due, at least in
part, to differences inthe level of expression of essentially identical SAI
genes.
Dynamic transitions in the translocated phloem filament protein
Authors: Leineweber Kirsten , Schulz Alexander , Thompson Gary A.
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
Recent evidence suggests that the P-proteins of
Cucurbita maxima exist in at least two structural
states: large polymers that are immobilized in individual sieve elements and
small polymers or individual subunits that are translocated over long
distances. We investigated variation in the structure of the phloem filament
protein (phloem protein 1 or PP1) to determine the translocated form of the
protein and its relationship to the polymerized state. It was demonstrated
that the stability, folding state and assembly of the phloem filament protein
rely on distinct intramolecular disulfide bonds. Acid trapping experiments
combined with intergeneric grafts revealed that the phloem filament protein is
translocated as an 88 kDa globular protein. By altering the pH of the
collection buffer (pH 2–10), four individual conformational isoforms of
PP1 with molecular masses of 81, 83, 85 and 88 kDa were consistently observed.
The 81 kDa isoform represents the totally reduced phloem filament protein, the
83 and 85 kDa isoforms folding intermediates, and the 88 kDa its native
soluble translocated form. The 83 and 85 kDa folding intermediates are
susceptible to aggregation causing the gelation and formation of P-protein
filaments in oxidized phloem sap. In contrast to the 88 kDa globular transport
form, the 81, 83 and 85 kDa isoforms possibly exhibit lower stability, and
therefore a higher sensitivity to proteolytic digestion.
Phloem mobility of crop protection products
Authors: Lichtner Frank
Published: September 2002

Phloem mobility of a crop protectant is an
attribute that contributes positively to its efficacy. Herbicides,
insecticides and fungicides, generally organic molecules of small molecular
weight, are applied foliarly and often must move to remote plant parts (such
as meristems, emerging leaves, roots and fruits) via the phloem to achieve
economically useful activity. In addition, insecticides must move within the
phloem to be effective against piercing and sucking insects. Conversely,
phloem mobility of crop protectants and their metabolites can also contribute
to detectable residues in raw agricultural commodities. This is especially
true of compounds that are biologically stable and applied during fruit
development or seed set. Thus, the knowledge of phloem mobility allows an
understanding of potential benefits (efficacy) and potential risks (dietary
exposure) of a crop protection chemical. The customers for this knowledge
range from the discovery chemist and biologist (who participate in the design
of the chemical), through to the regulatory official (who grants permission to
sell) and the farmer, the ultimate beneficiary of the technology. One can
estimate or predict phloem mobility (based on physical/chemical properties
and molecular structure) using a number of models, or measure it directly (in
whole plants or explants) with a variety of techniques. In the future, crop
protection and crop production technology will increasingly rely on effective
transport of macro-molecules, such as protein toxins for insect control and
mRNA for signal initiation and coordination of growth and development
processes. Phloem mobility will be equally important for these macromolecules
and for the small molecules that currently control pests and influence plant
growth and development. Understanding the processes that control
macromolecular transport in the phloem will lay the foundation for effective
use of this technology in the decades to come.
Protein synthesis and phosphorylation by elongating 13 - 15-day-old cattle blastocysts
Authors: Morris D. G. , Diskin M. G. , Sreenan J. M.
Published: September 2002

Most early embryonic loss in cattle occurs during the period of blastocyst
formation and elongation. In this study de novo protein
synthesis and phosphorylation by 13–15-day-old cattle blastocysts was
determined. Blastocysts were classified by dimension into spherical, ovoid and
elongated stages and cultured under oil for 4 h in drops of KSOM medium
containing either 35S-methionine or
32P-orthophosphate. Protein content increased with shape
from spherical to ovoid to elongated. There were differences
(P<0.05) within and among days in the percentage of
radiolabel incorporated. Incorporation of 35S-methionine
increased with embryo protein content. However, incorporation of
35S-methionine into TCA-insoluble material, expressed
per g of protein, decreased with shape (P<0.001) with
more than a 10-fold difference between spherical and elongated 13-day-old
blastocysts. Incorporation of 32P-orthophosphate also
tended to decrease with shape, with a 3-fold difference between spherical and
elongated Day 13 blastocysts. It was concluded that, from Day 13, protein
synthesis and phosphorylation, when expressed per unit of protein, decreased
from a much higher level, which in the present study was around the time the
blastocysts began to elongate.
The viability of transferred sheep embryos after long-term cryopreservation
Authors: Fogarty N. M. , Maxwell W. M. C. , Eppleston J. , Evans G.
Published: September 2002

The survival to term of 414 sheep embryos, thawed and transferred after
conventional cryopreservation and storage for 13 years, was evaluated. A
concurrent experiment involving the transfer of vitrified embryos to 91 ewes
and artificial insemination of 51 ewes with frozen–thawed semen from
sires of the long-term cryopreserved embryos provided forms of control
treatments. The donor ewes had a mean ovulation rate of 10.9, and 7.1 embryos
per ewe were cryopreserved. Each recipient ewe received two embryos and
pregnancy was assessed at Day 18, Day 54 and term. The pregnancy rate was
lower in the long-term embryo group than the artificial insemination group at
Day 18 (P<0.01) and Day 54
(P<0.05), although the difference at term (31%
v. 49%) was not significant, with the vitrified
embryo group being similar to the long-term group. Embryo survival to birth
was 21%, with the majority of loss (80%) occurring by Day 18.
The later stage of development and higher grade of transferred embryos and the
older age of donor ewes resulted in a significantly higher
(P<0.01) pregnancy rate at Day 54 and term, and
percentage of lambs born and weaned. Other effects of donor ewes (genotype,
superovulation treatment, number of ovulations and embryos cryopreserved) were
not significant. Implications for the design of genetic evaluation and
germplasm conservation programmes using embryo cryopreservation technology are
discussed.
Isolation of novel developmental genes from human germ cell, oocyte and embryo cDNA by differential display
Authors: Monk Marilyn , Holding Cathy , Goto Tetsuya
Published: September 2002

Due to the difficulties inherent in research on human embryos, almost nothing
is known about genes active in human early development. Although the human
genome project will provide resources that theoretically provide access to
every human gene, those genes specific to human early development may be
difficult to define. Also, by definition, genes specific to early development
will not be represented in cDNA databases derived from human somatic cells.
Yet these unknown human developmental genes are likely to be of key importance
for several areas of human health, including assisted reproduction and
contraception, embryo stem cell research and tissue trans-plantation, ageing
and cancer. In order to identify and isolate these human developmental genes,
we have prepared amplified cDNA from human primordial germ cells, oocytes and
embryos, and used differential display to compare patterns of gene expression
in these embryonic cells and in the cells of somatic tissues of a 10-week
human fetus. This paper reviews the highly sensitive procedures used to create
amplified cDNA representing expressed genes in a single cell and the use of
differential display to identify developmental genes. Several such genes have
been isolated, but their full-length sequences and function are yet to be
elucidated. Genes active in human early development are expected to play key
roles in the maintenance of the archetypal stem cell state, potential
immortality and the invasiveness of trophectoderm and primordial germ cells.
They represent candidate genes regulating these functions for targeting in
clinical research in human reproduction, stem cell differentiation and cancer.
Comparison of anterior-posterior development in the porcine versus chicken embryo, using goosecoid expression as a marker
Authors: van de Pavert Serge A. , Schipper Henk , de Wit Agnes A. C. , Soede Nicoline M. , van den Hurk Rob , Taverne Marcel A. M. , Boerjan Marleen L. , Stroband Henri W. J.
Published: September 2002

During early embryonic development, pig and chicken embryos share striking
morphological similarities. In the present study, the timing and location of
expression of mRNA for goosecoid
(gsc), a gene classically expressed in the nodal region
of developing embryos, was examined and compared in preprimitive streak and
gastrulating pig and chicken embryos. The expression of
gsc appeared first in the hypoblast and second in the
hypoblast of pig and chicken embryos. Because gsc
expression in these tissues was not symmetrical, gsc
appears to be a useful marker for the onset of embryonic polarity. During
gastrulation in both species, gsc expression became
confined to cells in and around the node, in the epiblast and mesoderm layers.
The only significant species-related difference in the distribution of
gsc expression at these stages of development was the
presence of gsc expression in the gut endoderm of
chicken but not pig embryos. Certainly, our results suggest that the molecular
mechanisms that control anterior–posterior development in different
classes of vertebrates are remarkably similar. In addition, we were able to
demonstrate that the pattern of gsc expression appears
to provide a more sensitive and accurate means of determining the
developmental stage of early porcine embryos than the more commonly used
trophoblast or embryoblast size. Using gsc expression
and accompanying embryo morphometric changes, we were able to develop a
four-point scale that may offer a more accurate means of quantifying early
embryo development in pigs.
Molecular mechanism of estrogen action in the male: insights from the estrogen receptor null mice
Authors: Couse John F. , Mahato Dipak , Eddy Edward M. , Korach Kenneth S.
Published: September 2002

Until recently, 17β-estradiol was thought to be of little importance
in male fertility. However, the descriptions of testicular dysfunction and
behavioral deficits leading to complete infertility in male mice lacking
estrogen receptor α (ERα) have indicated the importance of
estrogen action in fertility of the male rodent. In contrast, male mice
lacking the newly discovered estrogen receptor β (ERβ)
exhibit no compromised fertility. Recently, elaborate sperm transplantation
studies have shown that the altered sperm function characteristic of the
ERα knockout male are the result of the loss of ERα
actions in the supporting somatic cells of the testis and epididymis rather
than in the germ cell. This brief review will discuss the roles of estrogen
action in male reproduction as revealed by mice lacking both known forms of
the ER. A brief review of the estrogen signaling system is also included.
Alteration of goat sperm ecto-phosphoprotein phosphatase activity and its distribution on the sperm surface during epididymal maturation
Authors: Barua M. , Nath D. , Majumder G. C.
Published: September 2002

Phosphoprotein phosphatase (ecto-PPase) of goat epididymal sperm outer surface
showed a significant increase in its activity at the initial stage of
epididymal sperm maturation (up to the proximal corpus region) followed by a
sharp fall towards the terminal phase of the maturation event. PPase activity
showed nearly the same profile when estimated in intact cells as well as in
isolated sperm plasma membrane. The ecto-PPase was purified to apparent
homogeneity by using various biochemical fractionation procedures, such as
solubilization with Triton X-100, sephadex gel filtration chromatography,
concanavalin A–sepharose affinity chromatography and
diethylaminoethyl–cellulose ion-exchange chromatography. The isolated
PPase has a molecular mass of approximately 36 kDa and an isoelectric point of
5.95. Sperm surface topography of the enzyme was investigated using
fluorescein isothiocyanate-conjugated antibody of the purified PPase. The
immunofluorescent studies have demonstrated that the isolated PPase is
localized on the external surface of viable sperm. Immunocytochemical studies
also revealed a marked topographical alteration of ecto-PPase during
epididymal transit of the male gametes. Immunoreactivity was observed all over
the surface of caput sperm, but was restricted primarily to the anterior tip
of the head in the corpus sperm and to the posterior part of the head in cauda
sperm cells. The maturation-dependent decrease in PPase activity was also
confirmed by immunofluorescent studies. This remarkable maturation-dependent
modification of ecto-PPase activity, as well as its distribution on sperm
surface, suggest that the ecto enzyme may play an important role in sperm
function by regulating the phosphorylation states of the membrane-associated
and reproductive fluid phosphoprotein substrates.
The evolution of neuroendocrine mechanisms regulating sexual behaviour in female primates
Authors: Dixson Alan
Published: September 2002

The common marmoset is a small New World primate that lives in extended family
groups. Female marmosets show rhythmic changes in proceptivity during their
28-Day ovarian cycle, but fluctuations in sexual receptivity are relatively
subtle. Receptivity persists even after ovariectomy and adrenalectomy in the
female marmoset. In the intact female, increases in proceptivity at mid cycle
are due to the activational effects of oestradiol. Treatment of the
ovariectomized female with oestradiol-17β‚ stimulates proceptivity
and this effect is blocked by thermal or excitotoxic (neuronal cell body
specific) lesions in the anterior or medial hypothalamus. Implantation of
oestradiol into the anterior hypothalamus (via guide cannulae) also activates
proceptivity. Luteinizing hormone releasing hormone (LHRH) may also form part
of the neuroendocrine mechanism controlling proceptivity in the intact female,
given that exogenous LHRH stimulates proceptivity in ovariectomized,
oestrogen-primed marmosets. These effects of oestradiol (and LHRH) on
proceptive displays are much more pronounced than any effects involving sexual
receptivity. Conversely, treatment of the ovariectomized female with
progesterone, at doses sufficient to produce luteal phase concentrations of
circulating hormone, causes a marked suppression of proceptivity, but only
small decreases in sexual receptivity. These experiments on marmosets remain
some of the very few studies to define how hormones influence the brain and
sexual behaviour in female primates. They support the conclusion that sexual
receptivity is not under rigid neuroendocrine control in female anthropoids,
and that there is no peri-ovulatory period of oestrus, such as occurs in most
non-primate mammals.
Sex and season are major determinants of voluntary food intake in sheep
Authors: Clarke Iain J.
Published: September 2002

Seasonal changes in voluntary food intake (VFI) are seen in various species,
including sheep. This paper reviews recent work in this area, especially in
relation to alterations in the expression of appetite-regulating peptides in
the brain of the sheep. Work in the hamster is also reviewed because this is
another species in which VFI is regulated by photoperiod. In normally grazing
sheep, appetite is maximal in the late summer/early autumn and minimal in
spring. This appears to be owing to increased expression of the orexigenic
peptide, neuropeptide Y. Similar results are obtained in sheep that are
subjected to controlled photoperiod. The same does not appear to be true for
hamsters. Further work in sheep has shown that there is a seasonal pattern of
responsiveness to leptin that is more pronounced in females than in males. In
particular, the effect of leptin to reduce food intake is maximal in female
sheep in the spring; reasons for the sex difference are discussed.
Delayed ovulation and parturition in a viviparous alpine lizard (Niveoscincus microlepidotus): morphological data and plasma steroid concentrations
Authors: Girling J. E. , Jones S. M. , Swain R.
Published: September 2002

The southern snow skink, Niveoscincus microlepidotus,
exhibits an unusual biennial reproductive cycle with an extended gestation
period of approximately 1 year. Morphological data were gathered on a monthly
basis, providing a detailed picture of the reproductive cycle. Vitellogenesis
begins in spring, immediately after parturition. Maximum follicular diameter
is reached before the winter hibernation period and ovulation occurs the
following spring. Embryos are fully developed and reach maximum size by early
autumn. Yolk reserves are depleted before winter. Birth of between one and
four young occurs the following spring. Plasma progesterone concentrations are
low (2.7 ± 0.9 ng mL–1) in post-partum females,
begin to rise in autumn in vitellogenic females and peak (38.5 ± 7.9 ng
mL–1) in pre-ovulatory females after hibernation.
Concentrations are high (15.4 ± 5.9 ng mL–1) in
early pregnancy and decline to basal levels before winter and well before
birth in spring. Plasma oestradiol concentrations peak during vitellogenesis
(1.0 ± 0.3 ng mL–1) and decline to basal levels
during pregnancy (0.2 ± 0.03 ng mL–1). A second
oestradiol peak occurs before parturition (0.7 ± 0.2 ng
mL–1). Thus, functional completion of
vitellogenesis and gestation is achieved by autumn in successive years. The
mechanisms that defer ovulation and parturition by a further six months are
unknown.