bluuebunny/crossref_metadata_2025 huggingface dataset:
Coastal currents of northern Papua New Guinea, and the Sepik River outflow
Authors: Cresswell George R.
Published: September 2002

This paper reviews work on the currents of northern Papua New Guinea and then
examines recent observations with a research vessel, moored instruments,
simple drifters, and NOAA satellite AVHRR and RADARSAT synthetic aperture
radar (SAR) imagery. The dominant large scale features are: the strong New
Guinea Coastal Undercurrent that flows through Vitiaz Strait and then reaches
along the coast towards Irian Jaya; the New Guinea Coastal Current that
reverses with the monsoons; and a wind-driven upwelling plume from SW New
Britain during the SE monsoon that joins Solomon Sea waters to flow through
Vitiaz Str to bathe the offshore islands, as well as spreading along the PNG
coast. During the ship survey in the SE monsoon season the surface plume from
the Sepik River was only about 2 m thick and it moved offshore ~10 km at 1 m
s–1 before being turned to the NW by the
underlying currents. A coincident SAR scene provided a large-scale snapshot of
the plume. The plume switched to flow SE at the end of the several-day ship
survey. During the NW monsoon another SAR scene showed the plume streaming to
the SE. The waters down to several hundred metres in the Sepik study area were
comprised of stacks of many mixed layers, with enhanced loads of suspended
sediment at the bases of most of them. These subsurface sediment plumes became
depleted with increasing distance offshore. Although the tides in the region
are small, moored instruments showed semi-diurnal internal tidal currents to
have amplitudes up to 0.15 m s–1 and to be
associated with vertical oscillations of perhaps 40-50 m. The waters of
Goodenough Basin in eastern PNG were mixed from 500 m to the bottom at 1300 m,
with energetic subsurface flows at the sills.
Stock assessment of the blue grenadier Macruronus novaezelandiae resource off south-eastern Australia
Authors: Punt A. E. , Smith D. C. , Thomson R. B. , Haddon M. , He X. , Lyle J. M.
Published: September 2002

The fishery can be divided into two subfisheries (‘spawning’ and
‘non-spawning’). Commercial catch rates for the
‘non-spawning’ subfishery declined from the late 1980s to 1997,
whereas those for the ‘spawning’ subfishery exhibit no obvious
temporal trend. An ‘Integrated Analysis’ assessment, of the
feasibility of reconciling these differing trends, uses catch (landed and
discarded), catch rate, length-at-age, and catch-at-age data and estimates of
absolute abundance based on the egg-production method. It emphasizes
uncertainty due to model assumptions and the data included in the assessment.
Use of the discard data allows more precise estimation of the magnitude of
recent recruitments. Spawning biomass is estimated to have declined from a
peak in 1989–91 to 1999 although fishing mortality has consistently been
<6%for each subfishery. One main reason for the reduction in
population size is the weakness of year-classes spawned from 1988 to 1993.
Differences in catch rates between the two subfisheries can therefore be
explained by interactions between the components of the population harvested
by the two ‘subfisheries’, and the trends in year-class strength.
A risk analysis is used to evaluate the consequences of different future
levels of harvest for different assessment assumptions. Overall, the spawning
biomass is predicted to increase over the next five to ten years as a result
of the strong 1994 and 1995 year-classes, although the extent of this increase
remains uncertain.
Identifying resuspended sediment in an estuary using the 228Th/232Th activity ratio: the fate of lagoon sediment in the Bega River estuary, Australia
Authors: Hancock Gary J.
Published: September 2002

Thorium-series nuclides (228Th and
232Th) have been used to identify resuspended sediment
in the Bega River estuary, south-eastern Australia. A non-conservative
increase in concentration of suspended sediment of water in the vicinity of
mid-estuary back-flow lagoons was associated with a decrease in the
228Th/232Th activity ratio
(AR) of the suspended sediment. The lagoon sediment is characterized by a low
estuarine 228Th/232Th
signature, distinguishing it from freshwater suspended sediment recently
delivered to the estuary, and identifying it as the likely source of the
additional suspended sediment. Sediment-core 210Pb
profiles show that the lagoons are accumulating sediment, presumably during
high river-flow events. However this study indicates that during intervening
periods of low flow, 40% of sediment deposited in the lagoons is
subsequently resuspended and exported to the lower estuary, and possibly to
the ocean. The utility of the
228Th/232Th AR to quantify
sediment resuspension in estuaries is likely to be estuary-dependent, and is
controlled by the extent of scavenging of dissolved
228Th by suspended particles.
Water regimes, seedling recruitment and establishment in three wetland plant species
Authors: Nicol Jason M. , Ganf George G.
Published: September 2002

The regeneration niche of three wetland
species that co-occur at Bool Lagoon, South Australia, was investigated under
nine hydrologic conditions. Typha domingensis grown from
seed had the broadest niche requirements; seeds germinated and seedlings were
established in all 9 hydrologic regimes, and asexual reproduction occurred in
5 of the 9 regimes. Whether asexual reproduction occurred was dependent upon
an interaction between the rate of leaf elongation, the rate of drawdown and
whether the leaf was able to broach the water surface. The buoyant nature of
seeds and seedlings ofTriglochin procerum allowed it to
avoid unfavourable regeneration niches.
Melaleuca halmaturorum had a narrow regeneration niche
that was confined to wet mud flats. The results are consistent with the
changes in the floristic composition of the lagoon.
Fishers' description of changes in fishing gear and fishing practices in the Australian South East Trawl Fishery
Authors: Baelde Pascale
Published: September 2002

Between the mid 1980s and early 1990s, the concurrence of three major events
significantly altered the structure and dynamics of the demersal trawl sector
in the Australian South-East Fishery (SEF). These events included marked
technological improvement, severe decline of major fish stocks and
introduction of an Individual Transferable Quota system. They have led to a
switch from maximizing catch volume to maximizing catch composition and
quotas, with important associated changes in fishing practices and catches. To
better understand these changes and their effect on stock assessment and
management, an industry survey asked SEF trawl fishers to describe their
fishing gear and fishing practices in detail. This paper is a qualitative
synthesis of current trends in fishing that most significantly affect the
single-species, logbook-dependent assessment and management of the fishery. It
demonstrates how effective collaboration between scientists and fishers can
benefit fisheries research and management, by helping scientists make more
informed analysis and interpretations of fisheries data.
Age, growth and spatial and interannual trends in age composition of jackass morwong, Nemadactylus macropterus, in Tasmania
Authors: Jordan Alan R.
Published: September 2002

Transverse sections of sagittae were examined. The first and second annual
increments were defined by examination of the progression of otolith radius
and length of the 0+ and 1+ cohorts. Growth in both sexes is rapid
until ~5 years old (32–35 cm), and then slows appreciably. There was a
broad range of lengths within individual age-classes, with a maximum of 12
age-classes present in a 1 cm length-class. Maximum ages of males and females
were 41 and 30 years, respectively, which is considerably higher than
previously estimated from whole otoliths. There was no significant difference
in the growth curves between males and females, although this is influenced by
the large number of juveniles and by the examination of relatively few large,
older fish. The sex-specific von Bertalanffy growth parameters are: L∞
38.4 cm FL, t0 –0.07 years,
K 0.36 year–1 for females
and L∞ 36.2 cm FL, t0 0.15
years, K 0.42 year–1 for
males. The age composition was dominated by 4–7 year olds but showed
evidence of considerable recruitment variability, particularly in the strong
1988 year-class. The relationship between the life-history strategy of
N. macropterus and recruitment variability is discussed.
Elevated chlorophyll a concentrations associated with a transient shelfbreak front in a western boundary current at Sydney, south-eastern Australia
Authors: Gibbs Mark T.
Published: September 2002

A mid-water phytoplankton bloom, measured by a
five-fold increase in chlorophyll a concentrations above
background levels, occurred in coastal waters off Sydney at depths of
80–100 m directly above the shelfbreak. The physical feature
underpinning the bloom was a transient shelfbreak front that developed in
response to the concurrent actions of an offshore-directed wind-forced bottom
boundary-layer flow over the shelf and an onshore-directed bottom
boundary-layer flow associated with a meso-scale oceanic eddy over the upper
slope. Never previously have these transient fronts been shown to result in
phytoplankton blooms on this shelf. The observations are significant because
processes leading to nutrient enrichment and enhanced pelagic primary
production over continental shelves on western boundaries are in many cases
not well understood.
Biogeochemistry, the watershed approach: some uses and limitations
Authors: Likens Gene E.
Published: September 2002

The watershed (catchment) approach provides a powerful conceptual model for
quantitatively evaluating the structure, function and change within a
landscape or region. The values and limitations of this approach are
considered in this paper, with particular reference to the Hubbard Brook
watershed–ecosystem model. The need for informed long-term (sustained)
research is stressed; a haphazard collection of data is rarely valuable.
Team-building efforts will be needed increasingly in the future to enhance the
success of multidisciplinary teams tackling large and complex environmental
problems.
Regulation and function of extracellular invertase from higher plants in relation to assimilate partitioning, stress responses and sugar signalling
Authors: Roitsch Thomas , Ehneß Rainer , Goetz Marc , Hause Bettina , Hofmann Markus , Sinha Alok Krishna
Published: September 2002

This paper originates from a presentation at the International Conference on Assimilate Transport and Partitioning, Newcastle, NSW, August 1999
Carbohydrates are synthesised in photosynthetically active source tissues and
exported, in most species in the form of sucrose, to photosynthetically less
active or inactive sink tissues. Sucrose hydrolysis at the site of utilisation
contributes to phloem unloading. This phenomenon links sink metabolism with
phloem transport to, and partitioning between, sinks. Invertases catalyse the
irreversible hydrolysis of sucrose and thus are expected to contribute to
carbohydrate partitioning. Different invertase isoenzymes may be distinguished
based on their intracellular location, their isoelectric points and pH optima.
Extracellular, cell-wall-bound invertase is uniquely positioned to supply
carbohydrates to sink tissues via an apoplasmic pathway, and links the
transport sugar sucrose to hexose transporters. A number of studies
demonstrate an essential function of this invertase isoenzyme for phloem
unloading, carbohydrate partitioning and growth of sink tissues. Extracellular
invertases were shown to be specifically expressed under conditions that
require a high carbohydrate supply to sink tissues. Further, their expression
is upregulated by a number of stimuli that affect source–sink relations.
Substrate and reaction products of invertases are not only nutri-ents, but
also signal molecules. Like hormones and in combination with hormones and
other stimuli, they can regu-late many aspects of plant development from gene
expression to long-distance nutrient allocation. Based on studies in
Chenopodium rubrum, tomato
(Lycopersicon esculentum) and tobacco
(Nicotiana tabacum), the regulation of extracellular
invertase and its function in assimilate partitioning, defence reactions and
sugar signal transduction pathways are discussed.
Sucrose transport-related genes are expressed in both maternal and filial tissues of developing wheat grains
Authors: Bagnall Neil , Wang Xin-Ding , Scofield Graham N. , Furbank Robert T. , Offler Christina E. , Patrick John W.
Published: September 2002

In developing wheat grains (Triticum turgidum var.
durum cv. Fransawi), post-sieve element transport of
phloem-imported photoassimilates (sucrose) includes membrane transport, to and
from the grain apoplasm, between symplasmically-isolated maternal and filial
tissues. The cellular location and mechanism of these membrane transport steps
were explored during rapid grain fill. Genomic Southern analysis indicated the
presence of a multigene family of sucrose/H +
symporters (SUTs). One or more SUTs were highly expressed in developing
grains, as were P-type H + /ATPase(s) and a
sucrose binding protein (SBP). Transcripts of these genes were detected in
vascular parenchyma, nucellar projection and aleurone cells. Antibodies,
raised against a SUT, an H + /ATPase and a SBP,
were selectively bound to plasma membranes of vascular parenchyma cells,
nucellar projection transfer cells and modified aleurone/sub-aleurone
transfer cells. The nucellar projection transfer cells and modified
aleurone/sub-aleurone transfer cells exhibited strong proton pumping
activity. In contrast, SUT transport function was restricted to filial tissues
containing modified aleurone/sub-aleurone transfer cells. Based on these
findings, we conclude that SUTs expressed in maternal tissues do not function
as sucrose/H + symporters. Membrane exchange
from nucellar projection transfer cells to the endosperm cavity occurs by an
as yet unresolved mechanism. Sucrose uptake from the endosperm cavity into
filial tissues is mediated by a SUT localised to plasma membranes of the
modified aleurone/sub-aleurone transfer cells.
Water stress inhibits p-nitrophenyl phosphate hydrolysis activity of the plasma membrane H+-ATPase from soybean hypocotyls
Authors: Qiu Quan-Sheng , Zhang Nan
Published: September 2002

The influence of water stress on ATP and
p-nitrophenyl phosphate (PNPP) hydrolysis by plasma
mem-brane ATPases was investigated using plasma membrane vesicles purified
from soybean hypocotyls by the sucrose gradient centrifugation method. Results
showed that ATPase activity was reduced after 10% polyethylene glycol
(PEG) 6000 treatment for 12 h. Water stress also moved the optimal pH from 6.5
to 7.0. A significant decrease in PNPP hydrolysis was observed under PEG
treatment. The Km for PNPP hydrolysis was shifted from
2.3042 0.0009 to 2.5048 0.0346 mmol L –1 .
Moreover, PNPP hydrolysis was more sensitive to vanadate after PEG treatment,
while inhibition of ATP hydrolysis by hydroxylamine was not affected. Our
experimental results indicated that water stress changed the catalytic
mechanism of the plasma membrane H + -ATPase
through affecting the dephosphorylation process catalysed by its phosphatase
domain.
Contrasting adaptations to drought stress in field-grown Ziziphus mauritiana and Prunus persica trees: water relations, osmotic adjustment and carbon isotope composition
Authors: Arndt Stefan K. , Wanek Wolfgang , Clifford Sean C. , Popp Marianne
Published: September 2002

Drought resistance strategies of Ziziphus mauritiana
Lamk. and peach (Prunus persica L.) were studied,
focusing on changes in leaf water potential, carbon isotope composition, and
solute and stress metabolite contents during an annual cycle under natural
rainfed conditions at a field site in Zimbabwe. After a 100-d drought period,
leaf water potential (yleaf) of peach trees decreased to
–2.0 MPa, whereas yleaf of
Z. mauritiana remained constant at –0.7 MPa.
Values for the natural abundance of 13 C
(d13 C) of bulk peach leaves as well as of total
water-soluble compounds and soluble sugars of leaves increased gradually,
resulting in significantly higher values as drought stress developed,
indicative of increased water use efficiency (WUE). By the end of the dry
season, both leaves and roots of peach exhibited osmotic adjustment, with
significant accumulation of monosaccharide sugars, anions and cations in the
leaves. Sorbitol and oxalate accounted for the greatest proportion of solute
increases during drought, while foliar sucrose content decreased. In roots,
soluble sugars such as sorbitol, glucose and fructose all increased, whereas
root starch content decreased. For Z. mauritiana leaves,
neither d13 C values nor soluble sugar concentrations
changed markedly during the study period, and
Z. mauritiana plants showed no osmotic adjustment during
the dry season. Data indicate that the two species exhibited different
strategies for coping with soil moisture deficits under field conditions.
Although Z. mauritiana exhibited the capacity for
osmotic adjustment in glasshouse experiments, the trees avoided drought stress
in this investigation, which is an indication of a root system that has access
to deeper moist soil layers. In contrast, the increased WUE in peach is likely
due to stomatal control of water loss with onset of drought stress. The
observed active osmotic adjustment to maintain turgor is in contrast to
glasshouse studies, where no osmotic adjustment was found, and emphasizes the
importance of field studies where stress develops more slowly.
Metabolic engineering of invertase activities in different subcellular compartments affects sucrose accumulation in sugarcane cells
Authors: Ma Hongmei , Albert Henrik H. , Paull Robert , Moore Paul H.
Published: September 2002

Transgenic sugarcane (Saccharum officinarum L.) lines
were created to express altered invertase isoform activity to elucidate the
role(s) of invertase in the sucrose accumulation process. A sugarcane soluble
acid invertase cDNA (SCINVm, AF062734) in the antisense
orientation was used to decrease invertase activity. The
Saccharomyces cerevisiae invertase gene
(SUC2), fused with appropriate targeting elements, was
used to increase invertase activity in the apoplast, cytoplasm and vacuole. A
callus/liquid culture system was established to evaluate change in
invertase activity and sugar concentration in the transgenic lines. Increased
invertase activity in the apoplast led to rapid hydrolysis of sucrose and
rapid increase of hexose in the medium. The cellular hexose content increased
dramatically and the sucrose level decreased. Cells with higher cytoplasmic
invertase activity did not show a significant change in the sugar composition
in the medium, but did significantly reduce the sucrose content in the cells.
Transformation with the sugarcane antisense acid invertase gene produced a
cell line with moderate inhibition of soluble acid invertase activity and a
2-fold increase in sucrose accumulation. Overall, intracellular and
extracellular sugar composition was very sensitive to the change in invertase
activities. Lowering acid invertase activity increased sucrose accumulation.
Rising CO2 and pollen production of common ragweed (Ambrosia artemisiifolia L.), a known allergy-inducing species: implications for public health.
Authors: Ziska Lewis H. , Caulfield Frances A.
Published: September 2002

Although environmental factors such as precipitation and temperature are
recognized as influencing pollen production, the impact of rising atmospheric
carbon dioxide concentration ([CO2]) on the
potential growth and pollen production of hay-fever-inducing plants is
unknown. Here we present measurements of growth and pollen production of
common ragweed (Ambrosia artemisiifolia L.) from
pre-industrial [CO2] (280 mol
mol–1) to current concentrations (370 mol
mol–1) to a projected 21st century concentration
(600 mol mol–1). We found that exposure to current
and elevated [CO2] increased ragweed pollen
production by 131 and 320%, respectively, compared to plants grown at
pre-industrial [CO2]. The observed
stimulations of pollen production from the pre-industrial
[CO2] were due to an increase in the number
(at 370 mol mol–1) and number and size (at 600 mol
mol–1) of floral spikes. Overall, floral weight as
a percentage of total plant weight decreased (from 21% to 13%),
while investment in pollen increased (from 3.6 to 6%) between 280 and
600 mol mol–1 CO2. Our
results suggest that the continuing increase in atmospheric
[CO2] could directly influence public health
by stimulating the growth and pollen production of allergy-inducing species
such as ragweed.
Hypergravity-induced increase in the apoplastic pH and its possible involvement in suppression of β-glucan breakdown in maize seedlings.
Authors: Soga Kouichi , Wakabayashi Kazuyuki , Hoson Takayuki , Kamisaka Seiichiro
Published: September 2002

Elongation growth of both coleoptiles and mesocotyls of maize
(Zea mays L. cv. Cross Bantam T51) seedlings was
inhibited under basipetal hypergravity (300 g)
conditions. Hypergravity increased the pH of the apoplastic fluid of
coleoptiles from 5.0 to 5.5 and mesocotyls from 5.2 to 5.7. When
β-1,3:1,4-D-glucanases (β-glucanases) extracted from cell walls of the
1-g control coleoptiles and mesocotyls were assayed at
pH 5.0 and 5.5 for coleoptiles, and at 5.2 and 5.7 for mesocotyls,
respectively, the activity in the increased pH conditions was significantly
lower than that in the control pH conditions. During the autolysis of the
enzymically active cell wall preparations obtained from
1-g control organs, a molecular mass downshift of
hemicellulosic polysaccharides occurred in cell walls. This downshift was
suppressed in the increased pH conditions as compared with the control pH
conditions. It was reported that hypergravity increased the molecular mass of
hemicellulosic polysaccharides by decreasing the β-glucanase activity, and
thereby decreased the mechanical extensibility of cell walls in maize
coleoptiles and mesocotyls. These results suggest that, in maize coleoptiles
and mesocotyls, hypergravity-induced increase in the pH in the apoplastic
fluid is involved in the reduction of the activity of β-glucanases which,
in turn, causes an increase in the molecular mass of hemicellulosic
polysaccharides and inhibits elongation growth.
Expression of a Bet v 1 homologue gene encoding a PR 10 protein in birch roots: induction by auxin and localization of the transcripts by in situ hybridization
Authors: Poupard Pascal , Brunel Nicole , Leduc Nathalie , Viémont Jean-Daniel , Strullu Désiré-Georges , Simoneau Philippe
Published: September 2002

In birch roots (Betula pendula Roth), two members of the
Bet v 1 gene family which encode PR 10 proteins have
previously been characterized. One of these members, named
Bet v 1-sc1, is significantly induced in response to
biotic or abiotic factors. We have analysed the expression of
Bet v 1-sc1 in birch roots treated either with 1 M
indole-3-acetic acid (IAA) or 1 M kinetin using reverse
transcription–polymerase chain reaction (RT–PCR), northern
blotting and competitive PCR. High accumulation of the
Bet v 1-sc1 transcripts was recorded only after auxin
application, while kinetin had no effect. By in situ
hybridization, we have investigated the localization of
Bet v 1-sc1 mRNA in birch roots after induction of the
gene by root treatment with 1 M IAA. Using root tip sections, we showed that
Bet v 1-sc1 is significantly expressed in the apical
meristem and the procambium. In sections taken in the zone producing lateral
roots, the presence of Bet v 1-sc1 was found at sites of
emerging secondary root primordia. This first report of localization of
Bet v 1-sc1 expression suggests that this gene could be
involved in the processes leading to lateral root initiation.
Ethylene production and post-pollination development in Dendrobium flowers treated with foreign pollen
Authors: Ketsa Saichol , Bunya-atichart Kanokporn , van Doorn Wouter G.
Published: September 2002

Dendrobium ‘Pompadour’ flowers fade early
following pollination. This is associated with increased ethylene production
and early epinasty. These effects are also produced by application of
1-aminocyclopropane-1-carboxylic acid (ACC) on the stigma. Pollen (one anther
each) from Ruellia tuberosa L. (Acanthaceae) and
Caesalpinia pulcherrima (L.) Sw. (Fabaceae) also
increased ethylene production and caused early epinasty and fading. Pollen of
Hibiscus schizopetalus (Mast.) Hook.f. (Malvaceae), in
contrast, had no effect. R. tuberosa pollen increased
ACC concentration and ACC synthase activity of the orchid flowers.
Aminooxyacetic acid (AOA) pretreatment prior to
R. tuberosa pollination prevented early fading, epinasty
and the increase in ethylene production. It also prevented the increase in ACC
concentration, and ACC synthase activity. Ovary growth was stimulated by
Dendrobium ‘Pompadour’ pollinia, not by any
of the incompatible pollen. Applied ACC did not promote ovary growth. It is
concluded that incompatible pollen can hasten senescence and epinasty by
increasing ACC synthase activity and ethylene production. Ovary growth, in
contrast, is apparently not primarily regulated by ethylene.
Transgenic cotton (Gossypium hirsutum) over-expressing alcohol dehydrogenase shows increased ethanol fermentation but no increase in tolerance to oxygen deficiency
Authors: Ellis Marc H. , Millar Anthony A. , Llewellyn Danny J. , Peacock W. James , Dennis Elizabeth S.
Published: September 2002

Cotton (Gossypium hirsutumL.) was transformed with
constructs for the over-expression of two enzymes involved in ethanol
fermentation, alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC),
with the goal of increasing waterlogging tolerance. Four independent
transgenic lines transformed with the cotton Adh2 cDNA
driven by the CaMV 35S promoter showed ectopic expression of this isozyme in
leaves and up to 20-fold greater in vitro ADH activity
in roots. Under conditions of O2 deficiency, excised
roots from these transgenic plants showed up to 80% increase in ethanol
evolution compared to untransformed roots. Conversely, one line transformed
with a construct containing the Adh2 coding region in
the antisense orientation showed a 65% decrease in ADH activity and a
25% decrease in ethanol production from anaerobic roots relative to
untransformed cotton. Lines transformed with a rice Pdc1
cDNA driven by the CaMV 35S promoter showed high levels of expression of the
transgene-encoded protein in leaves, but only very low levels of protein and
no in vitro enzyme activity detectable in the roots of
these plants. Roots from plants transformed with the
35S-Pdc construct did not produce more ethanol than
roots from untransformed controls. We tested the ability of cotton roots to
withstand low O2 treatments under hydroponic conditions.
Neither the ‘ADH’ nor the ‘PDC’ transgenics showed
more tolerance than the wild-type on the basis of root growth under a mild
stress (5% O2), a strong stress (0%
O2 with or without a 5% O2
pretreatment), or in recovery growth following these treatments. Our results
show that over-expression of ADH can lead to ethanol over-production (even
though the activity of this enzyme by far exceeds that of PDC, its precursor
in the pathway), but this is not sufficient to increase waterlogging tolerance
in cotton.
Turgor and cell wall yielding in dicot leaf growth in response to changes in relative humidity
Authors: Serpe Marcelo D. , Matthews Mark A.
Published: September 2002

Epidermal cell turgor (P) and leaf growth in
Begonia argenteo-guttata L. were monitored
simultaneously following changes in air humidity in order to evaluate
P–growth relations. A decrease in air humidity
from 70 to 5% caused a decrease in P of 0.05 MPa.
This small decrease in P resulted in cessation of
growth. Subsequently, growth recovered partially at constant
P, indicating an increase in wall yielding to
P. Notwithstanding this increase in wall yielding, the
steady growth rates showed a marked dependence on P.
Decreases in P of 0.05 MPa caused a 30–40%
reduction in the steady rate of elongation. These results were reversible.
Upon a step increase in air humidity from 5 to 70%,
P and growth rate rapidly increased. Subsequently,
growth declined without a corresponding decrease in P,
although the rate of growth remained higher than at low humidity. The partial
self-stabilization of growth following P changes and the
positive relationship between steady growth rate and P
are consistent with the notion that wall yielding is controlled by
interactions between P and metabolism. Results are
discussed in relation to biophysical factors that control growth and to
present theories that accommodate variable wall yielding.
Histological and biochemical changes in Pinus spp. seeds during germination and post-germinative growth: triacylglycerol distribution and catalase activity
Authors: Jordy Marie-Noëlle , Danti Susanna , Favre Jean-Michel , Raccchi Milvia Luisa
Published: September 2002

The spatio-temporal evolution of catalase (CAT) activity and triacylglycerol
distribution was investigated in seeds and seedlings from
Pinus pinaster Ait., P. pinea L.
and P. radiata D. Don during germination and
post-germination. The high amount of triacylglycerols contained in the whole
dehydrated embryo from the three species was progressively depleted, first, in
the radicle and then in hypocotyl and cotyledons during post-germinative
growth. In parallel, histological localisation of CAT activity and the
quantitative analysis confirmed the involvement of this enzyme in cell
detoxification from peroxide released during the intense lipid breakdown. Two
isozymes, CAT-1 and CAT-2, were identified during post-germinative growth.
Both were particularly active in the hypocotyl and radicle, while CAT-2 was
specifically active in the photosynthetic tissues. These results emphasise
that CAT activity is also independent from lipid metabolism in certain
tissues. The role of each isoenzyme is discussed in connection with the
metabolic changes occurring during seed germination and seedling growth.
Special attention is given to the role of the shoot apex in triacylglycerol
storage and breakdown. Central mother cells have been shown as a specific
lipid storage area of the shoot apical meristem, in contrast with the
peripheral zone in which lipid reserves were always reduced.
Research Note: Ozone induces a differential accumulation of phenyalanine ammonia-lyase, chalcone synthase and chalcone isomerase RNA transcripts in sensitive and resistant bean cultivars
Authors: Paolacci Anna Rita , D'Ovidio Renato , Marabottini Rosita , Nali Cristina , Lorenzini Giacomo , Abenavoli Maria Rosa , Badiani Maurizio
Published: September 2002

On exposure to a realistic ozone dose, an enhanced mRNA accumulation for
phenyalanine ammonia-lyase (EC 4.3.1.5), naringenin–chalcone synthase
[malonyl–CoA:4-coumaroyl–CoA malonyltransferase (cyclising);
EC 2.3.1.74] and chalcone isomerase [flavanone lyase (decyclising);
EC 5.5.1.6] genes, whose products are involved in the biosynthesis of
phenylpropanoid molecules, flavonoid pigments and isoflavonoid phytoalexins,
was observed in primary leaves of the bean
(Phaseolus vulgaris L.) cv. Pinto. This cultivar was
previously known to be ozone-sensitive on the basis of the appearance of
macroscopic foliar injury, but not in coeval leaves of the bean cv. Groffy,
known to be ozone-resistant on the basis of the aforementioned criterion.
Distinct time patterns were observed in Pinto leaves for the ozone-dependent
enhanced mRNA accumulation for the aforementioned genes, which in all cases
largely preceded the appearance of visible injury symptoms. These results lend
support to the view of ozone as an abiotic elicitor of plant defence
responses. By analogy with other case studies, it is also suggested that
proneness to develop visible ozone symptoms might rest on a sequence of
molecular events similar to that leading to the hypersensitive response during
plant–pathogen incompatible interactions.
Stem hydraulic properties and xylem vulnerability to embolism in three co-occurring Mediterranean shrubs at a natural CO2 spring
Authors: Tognetti Roberto , Longobucco Anna , Raschi Antonio , Jones Mike B.
Published: September 2002

Seasonal changes in hydraulic properties and vulnerability to xylem embolism
of Erica arborea L.,
Myrtus communis L. and
Juniperus communis L. were analysed by comparing plants
at two locations in a Mediterranean environment. A distinct atmospheric
CO2 concentration
([CO2]) gradient exists between the two sites
with higher [CO2] in the proximity of a
natural CO2 spring (700 mol
mol–1). Changes in native embolism in
E. arborea and M. communis
indicated rather clear seasonal segregation by species and by the growth
[CO2]. J. communis had
constantly lower percentage embolism than the other two species (the effect of
site being not consistent). Differences in summer embolism among species and
between sites were in accordance with vulnerability curves. Volumetric
fractions also showed seasonal and site-dependent changes. Mean specific
hydraulic conductivity was strongly affected by site in
E. arborea and M. communis (in
opposite directions). Hydraulic properties varied as a function of shoot
biomass and leaf area, and the latter increased with increasing sapwood area;
differences between sites were somewhat significant in
M. communis. Foliage biomass increased with stem
biomass; E. arborea had higher values of foliage biomass
at similar values of stem biomass at the control site. Altering branch biomass
allocation may influence or not (depending on the species) hydraulic
adjustment. Plant responses to resource imbalances caused by increasing
[CO2] tend to compensate for the imbalance by
changes in hydraulic properties and biomass allocation. However, the
plasticity or compensation ability of any particular species appears limited,
and effective compensation for large changes in resource balance caused by
environmental forcing factors may require changes in species composition.
Diurnal changes in carbohydrate metabolism in mature apple leaves
Authors: Zhou Rui , Sicher Richard , Quebedeaux Bruno
Published: September 2002

Net photosynthesis, individual carbohydrate concentrations, and the activities
of some enzymes involved in carbohydrate biosynthesis were monitored in mature
apple leaves at regular intervals throughout a natural day/night cycle.
Sorbitol was the major carbohydrate in mature apple leaves. Its concentration
increased gradually after dawn and reached its highest level of 18.0 mg g
–1 fresh weight, and then declined to its lowest
level of 9.6 mg g–1 at the end of the dark period.
Starch also showed a similar diurnal pattern with a lower maximum of 4.6 mg g
–1 fresh weight and a minimum of 1.8 mg g
–1 fresh weight. Aldose-6-phosphate reductase
(A6PR) activity showed significant diurnal fluctuations, whereas
sucrose-phosphate synthase (SPS) activity, under both saturating and limiting
substrate conditions, showed no variations. The highest A6PR activity under
natural light conditions appeared at 1000 h with 37.2 µmol h
–1 g ––1fresh
weight, which was about 30% higher than that in the night. The diurnal
alteration of A6PR activity was also found under controlled environmental
conditions in growth chambers. Treatments of 14/10 h light/dark
photoperiod, continuous light and continuous darkness, did not change the
pattern of diurnal variation in A6PR activity. Significant correlation between
A6PR activity, sorbitol concentration and photosynthetic rate suggested that
the processes of photosynthesis and carbohydrate biosynthesis are coordinated.
Xyloglucan endotransglycosylase: a role after growth cessation in harvested asparagus
Authors: O'Donoghue Erin M. , Somerfield Sheryl D. , Sinclair Ben K. , Coupe Simon A.
Published: September 2002

Little is known about the mode of xyloglucan endotransglycosylase (XET)
activity in cell walls once the turgor, which drives expansion, is reduced.
Such a situation exists when growing shoots are excised from the parent plant,
and is the case for many commercially valuable vegetable crops, e.g.
asparagus, Asparagus officinalis L. XET activity was
present in all zones of rapidly growing, immature asparagus spears, but with
highest levels at the spear base where elongation growth had ceased. Activity
increased in all parts of the spear for up to 72 h after harvest. Two members
of the XET-related gene family in asparagus (AoXET1 and AoXET2) were isolated
and mRNA corresponding to these clones accumulated at low levels, particularly
in the basal zone during spear growth. Transcript levels increased in all
parts of the asparagus spear after harvest, but this increase did not coincide
with the increase in XET activity. The harvest-related changes to xyloglucan
molecular weight were restricted to slight, segment-specific, up- or
down-shifts. However, this may hide strategic alterations to linkages leading
to a more rigid wall without major changes in overall molecular weight. The
initial postharvest surge in XET activity could be related to harvest stresses
such as water deficit, but we propose that the later induction of AoXET1 and
AoXET2 is linked to the development of lignified secondary cell walls.
Models for oscillations in plants
Authors: Gradmann Dietrich
Published: September 2002

Ionic relations of plant cells comprise enzymes such as channels, pumps and
co-transporters that catalyse the transition of ions through lipid membranes
and, therefore, affect the membrane voltage. Since the activity of most of
these enzymes is voltage dependent, these enzymes interact with each other via
voltage changes. The temporal patterns of these interactions include
oscillations. Models are presented here that simulate such oscillations based
on physical properties of the ion transporters. Three oscillating scenarios
are focussed on. Model A is adequate for short-term episodes. In model B, the
external concentration of the ions is constant. This model, which applies e.g.
to algae and single cells under experimental conditions, displays electric
oscillations, just as model A, but also osmotic oscillations in which the
internal ion concentrations play an essential role. Finally, model C applies
to parenchyma cells in planta, where ion fluxes across
the plasmalemma cause major concentration changes in the small apoplastic
volume. In this model, internal and external buffering of ions is accounted
for. For model C, it is assumed that the total quantities of substrates are
constant, and portions of them are redistributed between different
compartments. Oscillations of the model C are relatively rare. In most cases,
model C approaches a steady state where K+ is in
thermodynamic equilibrium.
Membranes and the electrophysiology of turgor regulation
Authors: Findlay Geoffrey P.
Published: September 2002

In many types of plant and algal cells, the turgor is regulated, either at a
constant level, or in some reproducible time-dependent way. This review
considers the electrophysiology of turgor control in marine algae, guard
cells, and motor cells of pulvini. There is a basic complement of
electrophysiological components in the plasma membranes of these cells. These
components are responsible for controlling the fluxes of potassium salts, the
major inorganic component of the osmoticum responsible for changing internal
osmotic pressure, and hence turgor, and consist essentially of inwardly and
outwardly rectifying K channels, Cl channels, H/Cl symporters, sucrose
transporters and the proton pump. There are also Ca channels in the plasma
membrane, allowing influx of Ca to the cytosol, that in turn acts, with other
second messengers, to co-ordinate the operation of the various ion channels,
the fluxes, and the turgor regulation. The review discusses the ways in which
these components work together in the various systems, and highlights various
areas where more information is required for an adequate description of turgor
regulation.
Diurnal and acclimatory responses of violaxanthin and lutein epoxide in the Australian mistletoe Amyema miquelii
Authors: Matsubara Shizue , Gilmore Adam M. , Osmond C. Barry
Published: September 2002

This study investigated the chloroplast pigment content of the Australian
mistletoe Amyema miquelii (Lehm. ex Miq.) Tiegh. over
diurnal periods in sun- and shade-acclimated leaves.
Amyema miquelii exhibited the typical higher plant
complement of neoxanthin, the xanthophyll cycle pigments, lutein, chlorophylls
a and b and β carotene.
Substantial levels of lutein epoxide were also present. Interestingly, diurnal
light exposure elicited a decrease in lutein epoxide that paralleled the
decrease in violaxanthin. Compared with shade-acclimated leaves, sun leaves
exhibited reduced lutein epoxide and violaxanthin levels and higher
chlorophyll a/b ratios. It is clear that the pools
of violaxanthin and lutein epoxide respond in parallel to both diurnal light
changes and sun–shade acclimation, although there seemed to be some
differences in the recovery characteristics. These results raise a question as
to whether lutein and lutein epoxide cycling may provide an auxiliary means of
energy dissipation for some species.
Mechanosensory ion channels in Chara: the influence of cell turgor pressure on touch-activated receptor potentials and action potentials
Authors: Shepherd Virginia A. , Shimmen Teruo , Beilby Mary J.
Published: September 2002

Chara cells produce receptor potentials (RPDs) in
response to mechanical stimulation. We have used a mechanostimulatory device
to compare characteristics of touch-activated RPDs and action potentials (APs)
when cell turgor pressure was changed. The device delivered a series of
mechanical stimulations of increasing energy (F0.5, F1, F2, F3, F4, F5 and
F6). Cells were alternately stimulated in artificial pondwater (APW) and a
sorbitol series, in long-term experiments, involving up to six solution
changes. The calculated cell turgor pressures were about 0.6 MPa (APW), and
0.49 MPa, 0.37 MPa, 0.24 MPa and 0.12 MPa in 50, 100, 150 and 200 mM
sorbitol–APW, respectively. In other experiments, cells were
pre-conditioned in the sorbitol solutions, and then transferred to APW. All
cells were allowed long recovery periods (40–60 min) after APs or
solution transfers. Only small changes in cell conductance were observed in
I–V and
G–V analysis of unstimulated
cells after reducing turgor pressure from 0.59 MPa to 0.24 MPa. In APW, the
RPDs increased in amplitude and duration with increased stimulus energy until
the threshold RPD was reached, and an AP was triggered, usually between
stimulus F4 and F5. Cells with decreased turgor pressure became more sensitive
to stimulation, giving threshold RPDs or APs with smaller stimulus (e.g.
between F0.5 and F3). Conversely, an increase in cell turgor pressure (return
to APW) led to a decrease in sensitivity to stimulus. When turgor pressure was
greatly decreased (to 0.12 MPa), some cells became unresponsive or gave
unusual responses. However, only the mechanical part of the touch response was
affected by changing the cell turgor pressure. The mean amplitudes of the
subthreshold and threshold RPD (that triggers the AP), and of the
touch-activated APs, were independent of cell turgor pressure, although action
potentials had smaller amplitude when turgor was reduced to about 0.12 MPa.
The amplitude of the subthreshold RPD was close to 20 mV, and the amplitude of
the threshold RPD was close to 50 mV, in all cells. If tension of the cell
wall–plasma membrane–cytoskeleton complex decreased along with
decreased cell turgor pressure, a given stimulus could stretch the complex to
a greater extent, resulting in activation of more mechanosensory channels. The
effect on the RPD of changes in cell turgor pressure is discussed in relation
to the mechanical properties of the cell wall–plasma
membrane–cytoskeleton complex.
Involvement of receptor potentials and action potentials in mechano-perception in plants
Authors: Shimmen Teruo
Published: September 2002

The rapid turgor movements of Mimosa pudica and some
carnivorous plants have long stimulated the interest of botanists. In
addition, it is becoming evident that slower responses of plants to mechanical
stimuli, such as coiling of tendrils and thigmomorphogenesis, are common
phenomena. Electrophysiological studies on mechano-perception have been
carried out in M. pudica and carnivorous plants, and
have established that the response to mechanical stimulation is composed of
three steps: perception of the stimulus, transmission of the signal, and
induction of movement in motor cells. The first step is due to the receptor
potential, the second and third steps are mediated by the action potential. In
this article, the mechanisms of responses to mechanical stimuli of these
plants are considered. Since higher plants are composed of complex tissues,
detailed analysis of electrical phenomena is rather difficult, and so the
mechanism for generating the receptor potential had not yet been studied.
Characean cells have proved to be more amenable to the study of the
electrophysiology of plant membranes because of their large cell size and the
ease by which single cells can be isolated. Recent progress in studies of the
receptor potential in characean cells is also discussed.
Rhizobium plasmids are involved in the inhibition or stimulation of rice growth and development
Authors: Perrine Francine M. , Prayitno Joko , Weinman Jeremy J. , Dazzo Frank B. , Rolfe Barry G.
Published: September 2002

This paper originates from an address at the 8th International Symposium on
Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000
We examined growth responses of rice seedlings
(Oryza sativaL. cv. Pelde) to specific
Rhizobium strains and their mutants, to investigate the
molecular basis of colonization and the stimulation or inhibition of rice
growth and development by rhizobia. Inoculation experiments with rice
seedlings showed that specific Rhizobium isolates of
these rice-associated and legume-associated rhizobia could either promote,
inhibit, or have no influence on rice plant growth. There are genes on certain
plasmids of Rhizobium leguminosarum bv.
trifolii and R. leguminosarum bv.
viciae that affect the growth and development of rice
root morphology. Additionally, we found that bacteria can intimately associate
with, and enter into, rice seedling roots by alternative mechanisms to those
encoded by the symbiotic (pSym) and the tumour-inducing (Ti) plasmids.
Investigations suggest an involvement of the phytohormone auxin, and possibly
nitrate, in this complex rice–Rhizobium
interaction.
Arabidopsis thaliana: a model for studies of colonization by non-pathogenic and plant-growth-promoting rhizobacteria
Authors: O'Callaghan Kenneth J. , Dixon Richard A. , Cocking Edward C.
Published: September 2002

This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000
Arabidopsis thaliana L. has many features favoring its
use as a model in studies of plant-growth-promoting rhizobacteria (PGPR), such
as diazotrophs. Several niches are colonized in the root system of
Arabidopsis, including xylem, and intact colonized roots
can be observed microscopically without sectioning of tissues. Studies of
plant genes involved in colonization are facilitated by the ease with which
plants are transformed and by the availability of mutant lines and other
accessions obtainable from stock centers. Lines of
Arabidopsis carrying reporter gene fusions are helping
to reveal the pattern of expression of previously cloned plant genes induced
by rhizobacteria. Studies utilizing indole-3-acetic acid (IAA)-producing PGPR
and Arabidopsis that contain an auxin-responsive GUS
fusion suggest that plants perceive IAA released by bacteria in the
rhizosphere. The role of flavonoids in the colonization of non-legumes is
being assessed using transgenic Arabidopsis with altered
flavonoid metabolism and using tt mutants, which lack
functional versions of specific genes for flavonoid metabolism. Studies of
plant defence and of stress responses are producing molecular data on plant
genes induced by inoculation of Arabidopsis roots with
non-pathogens.