bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Nitrate in the Osmotic and Nutritional Control of Plant Development
Authors: McIntyre G. I.
Published: August 2004

I postulate that certain of the effects of nitrate on plant development are
mediated by the combination of an osmotic effect on water uptake and a
nutritional effect on protein synthesis. This hypothesis is discussed with
reference to effects on seed germination, apical dominance, lateral root
initiation, flowering and leaf senescence. The postulated osmotic effect of
nitrate is consistent with the well-established role of both nitrate and
reduced forms of N as major osmotica in plant cells, and also with the
similarity and interaction between developmental effects of nitrate and water.
Evidence of the nutritional component of developmental effects of nitrate is
provided by a comparison of responses induced by nitrate and by other osmotica
of less nutritional significance. Carbohydrate has also been reported to
influence development by a combination of osmotic and nutritional effects. The
proposed hypothesis is a unifying concept which provides a similar
physiological explanation for a wide range of diverse developmental responses
that are usually attributed to the effect or interaction of different hormonal
factors.
Elicitor-induced Oxidative Burst and Phenylpropanoid Metabolism in Pinus radiata Cell Suspension Cultures
Authors: Hotter Grant S.
Published: August 2004

A cell wall elicitor preparation from the needle pathogen
Dothistroma pini was used to induce defence responses in
Pinus radiata cell suspension cultures. Addition of
elicitor to cell suspensions induced a rapid, transient burst in the
accumulation of H2O2, with maximal
response between 20 and 40 min post-elicitation. The protein kinase inhibitors
staurosporine and K252a inhibited
H2O2 accumulation showing that
protein phosphorylation is required in the signal transduction pathway leading
to the oxidative burst. Over a more extended time period elicitation of
suspension cells lead to the activation of phenylpropanoid biosynthesis. The
activity of phenylalanine ammonia-lyase (EC 4.3.1.5), the first enzyme in the
phenylpropanoid biosynthetic pathway, increased 8-fold following elicitation
with maximal activity 36 h post-elicitation. The activity of cinnamyl alcohol
dehydrogenase (EC 1.1.1.195), an enzyme involved in lignin biosynthesis,
increased 2.5-fold with maximal response 48–72 h post-elicitation.
Thioglycolic acid extractable material increased 2-fold with maximal response
48–72 h post-elicitation, and phloroglucinol–HCl-positive material
increased over the same time course. These data show that
P. radiata suspension cells are an excellent model
system for investigating the biochemistry and enzymology of pathogen defence
responses in P. radiata.
Chalcone Synthase Gene Expression in Transgenic Subterranean Clover Correlates with Localised Accumulation of Flavonoids
Authors: Djordjevic M.A. , Mathesius U. , Arioli T. , Weinman J. J. , Gärtner E.
Published: August 2004

Expression patterns of two clover chalcone synthase promoters
(TsCHS1 and TsCHS3) were examined
in transgenic Trifolium subterraneum plants to
investigate flavonoid gene regulation and to determine if there is
differential regulation of these promoters from the CHS
multigene family. The CHS1 and
CHS3 genes occur as part of a tightly linked cluster of
tandemly orientated genes in subterranean clover. The
CHS promoters were fused to the β-glucuronidase
(GUS) reporter gene and reintroduced into subterranean
clovers. Analysis of the expression of the reporter genes showed that
near-identical expression patterns occurred in the transgenic plants
containing either the CHS1:GUS or
the CHS3:GUS fusions. Both
promoters responded rapidly to wounding of the shoot. Distinct changes in the
expression patterns of both promoters occurred during the development of
leaves and flowers. In young shoots, expression occurred throughout the
tissues and was restricted to the cambium and xylem parenchyma in mature
tissue. Roots possessed the highest activity levels, which were primarily
located in the meristematic tissues of the tap root, lateral root and nodule.
Epifluorescent localisation of flavonoids using diphenylboric
acid-2-aminoethylester correlated with the site of GUS activity in most
tissues. These results indicate that histochemical detection of
CHS expression in various root meristems and flower
parts is correlated with localised flavonoid accumulation in these cells. Our
studies suggest a physiological role for flavonoids at those sites.
Studies of Cytokinin Action and Metabolism Using Tobacco Plants Expressing either the ipt or the GUS Gene Controlled by a Chalcone Synthase Promoter. I. Developmental Features of the Transgenic Plants
Authors: Wang Jian , Letham D. S. , Cornish Edwina , Stevenson K. R.
Published: August 2004

A chimaeric cytokinin biosynthetic gene was constructed by placing the coding
region of the bacterial ipt gene under the control of a
chalcone synthase (chs) promoter
(PCHS) from Antirrhinum majus. The
PCHS-ipt gene was transferred to
tobacco (Nicotiana tabacum L.). To provide control
plants for studies of the effect of expression of this gene on plant
development, a PCHS β-glucuronidase gene fusion was
also introduced into tobacco. Expression of the
PCHS-ipt gene caused release of
axillary buds, inhibition of root development, retardation of leaf senescence,
elevation of chlorophyll levels, delay in onset of flowering and retardation
of flower development. These effects, which were quantified in
PCHS- ipt plants, have previously
been associated with expression of ipt genes controlled
by heat shock or other promoters. Additional effects of ipt gene expression
characterised in PCHS-ipt plants
included growth of leafy shoots from the primary root, change in leaf shape
with the production of broader and larger leaves, induction of expansion of
excised leaf discs and development of leaves with an enlarged midrib and
enlarged veins. A particularly striking effect of the expression of the
PCHS-ipt gene was development of
thicker stems due mainly to increase of pith tissue caused by an enhancement
of both cell division and cell enlargement. Node number per primary stem was
also increased. Endogenous cytokinin and applied auxin interacted
antagonistically to affect both root and stem development in plants cultured
in vitro. The leaves of PCHS
-ipt transformed plants exhibited increased
transpiration rates and reduced diffusion resistance associated with increased
number of stomata and modified stomatal dimensions. The above changes, which
were associated with elevated endogenous cytokinin levels, are discussed in
relation to previous studies with ipt gene transformed
plants and to some aspects of normal plant development.
Comparison of sudden heat stress with gradual exposure to high temperature during grain filling in two wheat varieties differing in heat tolerance. II. Fractional protein accumulation
Authors: Stone P.J. , Nicolas M.E.
Published: August 2004

Two varieties of wheat differing in heat tolerance (cvv. Egret and Oxley,
tolerant and sensitive, respectively) were exposed to either a sudden or
gradual (6°C h-1) increase from 20 to 40°C to
determine if the rate of temperature increase used in controlled-environment
studies (1) alters the accumulation of functionally
important proteins during grain-filling, and (2) affects
the ability to discriminate between heat tolerant and sensitive varieties of
wheat. After heat treatment, grain samples were taken throughout grain growth
and analysed for protein content and composition. Wheat proteins were
separated and quantified as albumin/globulin, monomer, SDS-soluble polymer
and SDS-insoluble polymer using size-exclusion high-performance liquid
chromatography.
The rate of temperature increase exerted a significant influence on the
accumulation of total wheat protein and its fractions, and protein fractions
differed in their responses to the suddenness of heat stress. The acclimation
to heat stress afforded by a gradual increase to high temperature can mitigate
the effects of heat stress on fractional protein accumulation, and
consequently grain protein composition at maturity. Furthermore, the ability
of wheat to acclimate to high temperature varies between genotypes, and this
needs to be taken into account when selecting for heat tolerance.
Phosphoenolpyruvate Carboxykinase in C4 Plants: Its Role and Regulation
Authors: Walker Robert P. , Acheson Richard M. , Técsi László I. , Leegood Richard C.
Published: August 2004

Some of the recent findings which revise our view of the role and regulation
of phosphoenolpyruvate carboxykinase (PEPCK) in
C4 plants are discussed. Evidence is presented that
PEPCK is present at appreciable activities in the bundle-sheath of some
NADP-malic enzyme-type C4 plants, such as maize, but it
was not detectable in NAD-malic enzyme-type C4 plants.
PEPCK is rapidly inactivated in crude extracts of leaves of the
C4 plant, Panicum maximum. This
inactivation could be prevented by high concentrations of dithiothreitol or by
the inclusion of ADP or ATP, suggesting the involvement of thiols at the
active site. PEPCK is also subject to rapid proteolysis in crude extracts of a
range of C4 plants, resulting in cleavage to a smaller
(62 kDa) form. This can be reduced by extraction at high pH and by the
inclusion of SDS, but it means that intact PEPCK has never been purified from
a C4 plant. The molecular mass of PEPCK varies
considerably in C4 plants, unlike
C3 and CAM plants in which it is usually 74 kDa. PEPCK
is phosphorylated during darkness (and reversed by light) in some
C4 plants with PEPCK of a larger molecular mass, such as
Panicum maximum (71 kDa), but it was not phosphorylated
in the PEPCK-type C4 plant,
Sporobolus pyramidalis (69 kDa). The known regulatory
properties of PEPCK are discussed in relation to its role in
C4 photosynthesis, in particular its sensitivity to
regulation by adenylates and by Mn2+.
myo-Inositol is the major sugar in Actinidia arguta during early fruit development
Authors: Klages Karin , Donnison Helen , Boldingh Helen , MacRae Elspeth
Published: August 2004

Actinidia arguta (Sieb. et Zucc.) Planch. ex Miq. is a
cold tolerant and heavy cropping species from the kiwifruit
[Actinidia deliciosa var.
deliciosa (A. Chev.) C.F. Liang et A.R.Ferguson]
family that has potential for commercialisation. As fruit developed, glucose
was the major sugar (74%) in A. deliciosa during
the first 40 days after anthesis, whereas myo-inositol
was the major sugar (60–65%) in
A. arguta.myo-Inositol accumulated
rapidly in A. arguta during the first 20–30 daa
then more slowly as fruit grew to reach a steady state level, between 15 and
50 mg fruit-1 for different selections. Peak levels were
55-60 mg g-1 dry wt. In contrast, maximum
myo-inositol concentrations in
A. deliciosa were only 18 mg g-1
dry wt. As fruit of A. arguta ripened, sucrose became
the dominant sugar. In contrast to the fruit,
myo-inositol concentrations were lower in leaves of
A. arguta(~5 mg g-1 dry wt;
~10% of major sugars) than in leaves of
A. deliciosa (15 mg g-1 dry wt;
~20% of major sugars). To ascertain whether
myo-inositol was transported from the leaves to the
fruit in the phloem stream, exudates were also analysed. In both species,
sucrose was the predominant sugar (>95%) in the phloem. Therefore we
suggest that an unusual accumulation of myo-inositol in
A. arguta during early stages of fruit development, may
be due to synthesis in the fruit.
Auxin control of photoassimilate transport to and within developing grains of wheat
Authors: Darussalam  , Cole Michael A. , Patrick John W.
Published: August 2004

Rates of 14C-labelled photoassimilate and dry matter
import into developing grains of wheat
(Triticum turgidum cv. Franshawi) were enhanced by
indolyl-3-acetic acid (IAA) applied in an agar gel infused into the flag
internodal lacunae of intact plants or as an aqueous solution to detached,
aseptically-cultured ears. Enhancement of assimilate import occurred in the
absence of any changes in the net rates of flag leaf and ear photosynthesis
and the relative rates of 14C-labelled photoassimilate
export from the flag leaves. Sucrose concentrations and osmolalities of saps
collected from the rachis phloem and bulk maternal tissues of the grain crease
region also were unaffected. However, both the sucrose concentration and
osmolality of the endosperm cavity sap was elevated by IAA. The sucrose
concentration of the bulk filial sap increased without any detectable change
in sap osmolality. Auxin stimulated accumulation rates of
[14C]sucrose from the endosperm cavity of
detached intact grain and by filial tissue slices enriched in the cells of the
modified aleurone/subaleurone layers. Auxin-enhanced
[14C]sucrose accumulation was abolished by
para-chloromercuribenzenesulfonic acid and erythrosin B. We conclude that IAA
stimulates photoassimilate transport to and within developing wheat grains by
a primary action on the membrane exchange of solutes to and from the endosperm
cavity.
The changing peroxidase polymorphism in Lupinus albus during vegetative development
Authors: Jackson P. , Ricardo C. P. P.
Published: August 2004

Analyses of 14 samples representing organs in different stages of
skotomorphogenic and photomorphogenic development, and the iterative growth
from both root and shoot apical meristems, showed preliminary evidence for the
operation of at least six different peroxidase groups showing differential
patterns of activity during vegetative development. These included two acidic
forms, a neutral-basic form and three highly basic forms.
While no peroxidase group was organ specific or restricted to either the
skotomorphogenic or photomorphogenic developmental pathways, clear and similar
qualitative changes in peroxidase polymorphism occurred during the maturation
of several different organs. This suggested that a developmental program
regulating the changing isoperoxidase content in vegetative development was
common to several organs in Lupinus albus.
The subcellular locations, tissue specificity and spatial distribution of
individual peroxidase groups in etiolated hypocotyls were related to the
spatial location of active elongation and a marker of lignification, the
isoperoxidase A2. Individual isoperoxidases could be associated with the
developmental phases of either (a) pre-elongation,
(b) active elongation, (c)
restricted elongation and (d) active lignification. The
possible functions of these peroxidases are discussed, and we present our
selection of the peroxidase groups associated with the early phases of
vegetative development for further studies and purification. Those selected
include a highly soluble basic peroxidase (B5, pI 9.3) which appears to be
largely restricted to the apoplast of juvenile tissues prior to the onset of
active cellular elongation, and an ionically bound, basic peroxidase (B6, pI
9.7) of the epidermal apoplast which has a distribution strongly correlated to
the reduction in cellular elongation along the hypocotyl axis.
Is a Low Internal Conductance to CO2 Diffusion a Consequence of Succulence in Plants with Crassulacean Acid Metabolism?
Authors: Maxwell Kate , Caemmerer Susanne von , Evans John R.
Published: August 2004

Leaf internal conductance to CO2
(gi) from substomatal cavity to
the carboxylation sites of Rubisco was measured in the leaf succulent CAM
species, Kalanchoe daigremontiana Hamet et Perr.
Measurements were made during Rubisco-mediated atmospheric
C3 carboxylation in phase IV photosynthesis. Using
simultaneous gas exchange and chlorophyll fluorescence techniques, internal
conductance was calculated to be 0.05 mol m-2
s-1 bar-1 , when measured at both
saturating and limiting light. This is one of the lowest recorded values for
gi as compared to a range of
C3 species with comparable Rubisco content and indicates
a large diffusion limitation to atmospheric CO2 fixation
through the C3 pathway in
K. daigremontiana. In ambient air,
CO2 partial pressure at the carboxylation sites of
Rubisco was 109 µbar. Internal diffusion is limited by a thick leaf
consisting of densely packed, succulent mesophyll with a small portion of
airspace. We speculate that a low internal conductance to
CO2 diffusion results from the compromise between a
succulent mesophyll required for C4 acid storage and
access for CO2 diffusion to both PEPC in the cytoplasm
and Rubisco in the chloroplasts. Restricted diffusion of
CO2 within the leaf makes CO2
assimilation less efficient during the transient phases of crassulacean acid
metabolism.
The temporal correlation of changes in apoplast pH and growth rate in maize coleoptile segments
Authors: Peters W. S. , Lüthen H. , Böttger M. , Felle H.
Published: August 2004

Auxin induces extracellular acidification in growing shoot tissue. The causal
relationship between this process and auxin-mediated growth is debated, partly
because of contradicting previous reports on the temporal correlation of
auxin-induced apoplast pH-drops and growth bursts. We have simultaneously
measured both parameters on the background of spontaneously occurring
endogenous changes in growth rate and apoplast pH in maize coleoptile
segments. Our data demonstrate good temporal correlation, during both the
‘Spontaneous Growth Response’ and the response to exogenous auxin,
which is transient under the conditions chosen due to rapid auxin metabolism.
We suggest that cell wall pH and growth rate are co-regulated in this organ,
and that contradictions in the literature might be due to technical
difficulties.
T-DNA tagging of a flowering-time gene and improved gene transfer by in planta transformation of Arabidopsis
Authors: Richardson Kim , Fowler Sarah , Pullen Carly , Skelton Caryl , Morris Bret , Putterill Jo
Published: August 2004

Gene tagging with insertional mutagens greatly facilitates the isolation of
novel genes. A new collection of Arabidopsis T-DNA tag
insertion lines (n=2165) was generated by
in planta transformation. Whole plants were
vacuum-infiltrated in a suspension of Agrobacterium
carrying the pGKB5 tagging vector. The efficiency of transformation increased
with addition of the surfactant Silwet L-77 (0.005% v/v) to the
Agrobacterium suspension. Visual screens of the T-DNA
lines identified two mutants with floral defects. Allelism tests suggested
that a mutation in the GIGANTEA gene was responsible for
the late-flowering phenotype of one of the mutants. Linkage analysis indicated
that the GIGANTEA gene was tagged in this mutant.
In situ study of photoinhibition of photosynthesis and xanthophyll cycle activity in plants growing in natural gaps of the tropical forest
Authors: Thiele A. , Krause G.H. , Winter K.
Published: August 2004

Photoinhibition of photosynthesis was studied in situ in
leaves of several species of plants growing in natural treefall gaps of a
tropical lowland forest (Barro Colorado Island, Panama). Leaves showed several
features typical of sun-acclimation: relatively high pools of total
carotenoids and xanthophyll cycle pigments and high ratios of chlorophyll
a to b. During 1–2 h periods
of exposure to direct mid-day sun, all leaves experienced substantial
photoinhibition as indicated by a marked decline in the ratio of variable to
maximum chlorophyll a fluorescence emission,
FV/FM,
detected after 10 min of dark adaptation. After return to shade, these
‘dark-adapted’
FV/FM
ratios increased with biphasic kinetics, similar to previous findings under
controlled conditions in the laboratory. A phase lasting about 1 h accounted
for most of the recovery of
FV/FM
and was followed by a slow phase which proceeded until sunset. The decline in
FV/FM
during photoinhibition and the fast phase of recovery correlated closely with
the amounts of zeaxanthin in the leaves. Given the small portion of the second
recovery phase which has previously been attributed to turnover of the D1
protein in Photosystem II, high xanthophyll cycle activity in these gap leaves
is probably responsible for the major part of photoinhibition, providing an
efficient energy dissipation pathway during periods of high sunlight exposure.
Galactosidases in tomato fruit ontogeny: decreased galactosidase activities in antisense ACC synthase fruit during ripening and reversal with exogenous ethylene
Authors: Sozzi G.O. , Camperi S.A. , Cascone O. , Fraschina A.A.
Published: August 2004

α- and β-galactosidase (α- and β-Gal) activities, firmness
and pigment content were analysed in tomato
(Lycopersicon esculentum Mill.) pericarp during fruit
growth and ripening, comparing normal fruit with transgenic fruit containing
an ACC-synthase antisense transgene. Normal and transgenic immature green
fruit had similar temporal patterns of total α- and β-Gal activity.
Immature 21-day-old fruit displayed 93% and 134% higher α-
and β-Gal activity on a per gram fresh weight basis, respectively, than
mature-green fruit. During ripening, normal fruit presented increasing levels
of α- and β-Gal activity towards the red-ripe stage. β-Gal II
was detected in mature-green tomatoes; it rose rapidly and reached maximum
values at the red-ripe stage. In contrast, α- and β-Gal activity in
antisense fruit decreased after reaching the breaker stage, and a low
continuous level of activity was apparent between 54 and 108 days after
anthesis. 48- to 108-day-old transgenic fruit showed constant basal levels of
β-Gal II. There were no significant differences in enzyme activity between
antisense attached and detached fruit. An exogenous ethylene treatment
performed in transgenic tomatoes brought about a promotive effect on total
α- and β-Gal activity in general and on β-Gal II in particular,
thus suggesting a role for ethylene in de novo synthesis
or activation of these enzymes. Softening, chlorophyll breakdown and lycopene
biosynthesis were impaired in the antisense fruits, but the impairment was
only complete for lycopene synthesis and all were reversed by applied
ethylene. These results can be associated with the signal transduction
pathways proposed to be operational during tomato ripening.
Photosynthesis, quenching of chlorophyll fluorescence and thermal energy dissipation in iron-deficient sugar beet leaves
Authors: Morales Fermín , Abadía Anunciación , Abadía Javier
Published: August 2004

In sugar beet (Beta vulgaris L.) iron deficiency
decreased not only the photosynthetic rate but also the actual photosystem II
efficiency at steady-state photosynthesis. In moderate iron deficiency, the
decrease in actual photosystem II efficiency under illumination was related to
closure of photosystem II reaction centers, whereas in severe iron deficiency
it was associated to decreases of intrinsic photosystem II efficiency. The
O2 evolution, on an absorbed light basis, decreased more
than the actual photosystem II efficiency, suggesting the presence of a
significant fraction of electron transport to molecular oxygen or the
existence of some form of cyclic electron flow. Iron-deficient leaves reduced
the excess of light absorbed that cannot be used in photosynthesis not only by
decreasing absorptance, but also by dissipating a large part of the light
absorbed by the photosystem II antenna. This mechanism, that protects the
photosystem II reaction centers through the enhancement of energy dissipation,
was related to the de-epoxidation of violaxanthin (V) to antheraxanthin (A)
and zeaxanthin (Z) in iron-deficient leaves. These data provide additional
support for a role of Z+A in photoprotection under conditions of excess
photosynthetic light absorption.
The CO2/O2 specificity of single-subunit ribulose-bisphosphate carboxylase from the dinoflagellate, Amphidinium carterae
Authors: Whitney Spencer M. , Andrews T. John
Published: August 2004

Some dinoflagellates have been shown recently to be unique among eukaryotes in
having a ribulose-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39)
composed of only one type of subunit, the 53-kDa large subunit [reviewed
by Palmer, J.D. (1996)
Plant Cell 8, 343–345].
Formerly, such homomeric Rubiscos had been found only in anaerobic bacteria
and are characterised by such poor abilities to discriminate against the
competitive alternate substrate, O2, that they would not
be able to support net carbon gain if exposed to the current atmospheric
CO2/O2 ratio. The capacity of
Rubiscos from aerobic organisms to discriminate more effectively against
O2 appeared to correlate with the presence of additional
12- to 18-kDa small subunits. Thus the
CO2/O2 specificity of the
homomeric dinoflagellate Rubisco is of considerable interest from the
structural, physiological and evolutionary viewpoints. However, for unknown
reasons, Rubiscos from dinoflagellates studied so far are so unstable after
extraction from the cells that kinetic characterisation has not been possible.
We redesigned two methods for measuring Rubisco’s
CO2/O2 specificity to adapt
them to rapid measurement at 10°C using unfractionated cell extracts. Both
methods revealed that the
CO2/O2 specificity of Rubisco
from the dinoflagellate, Amphidinium carterae Hulburt,
was approximately twice as great as that of other homomeric Rubiscos but
unlikely to be sufficient to support dinoflagellate photosynthesis without
assistance from an inorganic-carbon-concentrating mechanism.
An experimental and modeling study of responses in ecosystems carbon exchanges to increasing CO2 concentrations using a tropical rainforest mesocosm
Authors: Lin Guanghui , Marino Bruno D.V. , Wei Yongdan , Adams John , Tubiello Francesco , Berry Joseph A.
Published: August 2004

The ecosystem carbon exchanges in the enclosed rainforest of Biosphere 2, an
enclosed apparatus comprised of large synthetic ecosystems, were measured and
modeled during the winter of 1995–1996 under different atmospheric
CO2 concentrations. On eight separate days, this
mesocosm was exposed to various levels of CO2 ranging
from about 380 to 820 µmol mol-1 daily mean and
then sealed 24 hours for continuous measurements of ecosystem
CO2 fluxes. Our results indicated that net ecosystem
carbon exchange in the mesocosm was enhanced by increasing
CO2 over the short periods studied (2–7 weeks),
but, as expected from physiological studies, the response is not linear. The
main effect of short-term CO2 change was the enhancement
of canopy CO 2 assimilation, while soil respiration was not affected by the
atmospheric CO2 concentration. The whole ecosystem
radiation use efficiency was significantly higher under higher
CO2. The results of direct measurements were predicted
well by a simple canopy model (the ‘big-leaf’ model) that
incorporates current physiological understanding of the biochemistry of leaf
photosynthesis. Validation of this model with a range of
CO2 and light levels indicates that it can be used with
confidence to predict the responses of natural ecosystems to global climate
change. Response of ecosystem processes to elevated CO2
with relaxation time longer than a few weeks could not be resolved in this
study, but longer-term closure experiments are planned to examine these
processes.
Spatial distributions of inorganic ions and sugars contributing to osmotic adjustment in the elongating wheat leaf under saline soil conditions
Authors: Hu Yuncai , Schmidhalter Urs
Published: August 2004

In this study, we quantified the spatial distributions of inorganic ions and
sugars contributing to osmotic adjustment and their net deposition rates in
the elongating and mature zones of leaf 4 of the main stem of spring wheat
(Triticum aestivum L. cv. Lona) during its linear growth
phase under saline soil conditions. Plants were grown in growth chambers in
soil irrigated/treated with nutrient solution containing either no added
or 120 mM NaCl. The sampling was conducted on the 3rd day after emergence of
leaf 4 at 3 and 13 h into the 16 h photoperiod. The patterns of spatial
distributions of total osmoticum, cation, anion and sugar contents (mmol
kg-1 H2O) were distinct and were
affected by salinity. The total osmoticum content in the region between 0 and
60 mm above the leaf base differed between the two harvests at 120 mM NaCl.
Net deposition rates of total osmotica, cations, anions, and sugars (mmol
kg-1 H2O
h-1) in both treatments increased from the base of the
leaf to the most actively elongating location and then decreased near the end
of the elongation zone. Contributions of cations, anions, and sugars to
osmotic adjustment varied with distance from the leaf base, and were about
21–30, 15–21, and 13%, respectively, in the elongation
zone. We suggest that the accumulation of solutes under saline conditions
occurs both by increasing the net deposition rate of osmotica and by reducing
growth.
Carbon isotope discrimination in leaf and stem sugars, water-use efficiency and mesophyll conductance during different developmental stages in rice subjected to drought
Authors: Scartazza A. , Lauteri M. , Guido M.C. , Brugnoli E.
Published: August 2004

Carbon isotope discrimination (Δ), growth analysis, water-use efficiency
(WUE) and gas exchange characteristics were studied in rice plants
(Oryza sativa L.) subjected to drought during different
developmental stages. Drought caused major effects on growth, WUE, Δ and
photosynthetic CO2 assimilation. Substantial differences
in the Δ of the bulk biomass among different organs and in carbohydrates
extracted from leaves and stems were observed. Possible influences of chemical
composition, fractionation during translocation and seasonal changes in the
ratio of intercellular and atmospheric partial pressures of
CO2 on such differences in Δ are discussed. Stem
carbohydrate Δ was correlated with relative growth rate, and, during
early grain filling, was negatively correlated with WUE measured between
flowering and early grain filling. Δ in leaf sugars was used to estimate
mesophyll conductance (gm), the
conductance to CO2 diffusion inside leaves, from the
intercellular air spaces to the chloroplast. During ontogeny,
gm showed a marked progressive
decrease, evident in both droughted plants and fully irrigated controls. There
was a positive correlation between the rate of CO2
assimilation and gm. The analysis
of Δ in leaf and stem carbohydrates is proposed as a useful indicator of
growth, WUE and photosynthetic parameters relevant for yield of rice under
drought-prone conditions.
Photochemistry, energy dissipation and cold-hardening in Eucalyptus nitens and E. pauciflora
Authors: Hovenden Mark J. , Warren Charles R.
Published: August 2004

The allocation of absorbed photon energy to thermal energy dissipation and
photosynthetic electron transport was investigated as a function of
photosynthetic photon flux density (PPFD) and temperature in two species of
subalpine eucalypt, Eucalyptus nitens (Deane et Maiden)
Maiden and E. pauciflora Sieb. ex Spreng. The proportion
of absorbed light utilised in photosynthetic electron transport decreased with
increasing PPFD, and the decrease was more pronounced the lower the
temperature. The proportion diverted into dissipation processes increased with
increasing PPFD to a maximum where it reached a plateau. This maximum
increased with decreasing temperature. Exposure to a succession of cold
(4˚C) nights increased the photochemical quantum yield of photosystem II
and decreased the allocation of excitation energy to thermal dissipation
processes in conditions of excess light, particularly at low temperatures.
Consequently, the photosynthetic electron transport rate (ETR) was higher and
heat dissipation rate (HDR) was lower in hardened plants than in non-hardened
plants at low temperatures. At 20˚C, ETR was generally higher than HDR in
all plants, but as the temperature decreased, HDR became the dominant process.
The PPFD at which HDR exceeded ETR decreased with decreasing temperature, and
at low temperatures was always lower in non-hardened plants than hardened
plants, although quite similar between species.
Temperature effects on node appearance in sugarcane
Authors: Campbell James A. , Robertson Michael J. , Grof Christopher P. L.
Published: August 2004

Plants of the Australian commercial sugarcane varieties Q117 and Q138 were
grown to 6 months age in a controlled environment at temperatures of 14, 18,
22 and 26˚C. The rate of node appearance, which equates to the rate of
leaf appearance, was significantly correlated with temperature across the
temperature range examined. Analysis of the varietal rates of node deposition
as a function of time allowed determination of both base temperature for node
(hence leaf) appearance and phyllochron. The base temperatures for node
appearance were 7.8˚C for Q117 and 7.6˚C for Q138, significantly
lower than previously published base temperatures for leaf appearance in
sugarcane. During the developmental stages covered by this study, phyllochron
differed between the two varieties with Q117 requiring 108.7˚Cd per node,
whilst Q138 required 126.6˚Cd per node. This work reinforces the value of
controlled environment research as a way of elucidating basic functions of
plant growth and development.
Temperature-dependence of carbon acquisition and demand in relation to shoot growth of kiwifruit (Actinidia deliciosa) vines grown in controlled environments
Authors: Greer Dennis H. , Jeffares Daniel
Published: August 2004

Kiwifruit (Actinidia deliciosa (A. Chev) C.F. Liang et
A.R. Ferguson) vines were grown at day/night temperature regimes of
28/22 and 17/12˚C for 5 months starting from budbreak to measure
the relationship between shoot growth and carbon demand and to determine the
temperature-sensitivity of these processes. Leaf area, internode length,
photosynthesis and respiration were measured on the same leaves at regular
intervals in both growth temperatures. From daily net carbon acquisition of
the shoots and carbon accumulation in biomass, daily net carbon balance per
shoot was determined. High temperature-grown shoots had 100% more leaf
area and 20% longer stems than low temperature-grown shoots and,
although photosynthetic and respiration rates were only slightly affected by
temperature, shoots at 17/12˚C acquired a net gain of 35 g carbon and
182 g at 28/22˚C, of which 94% and 54%, respectively,
were used in shoot biomass growth. Net carbon balance was negative for
35–57 days after budbreak, but shoots at 17/12˚C had a total
surplus of 1.4 g over 5 months whereas shoots at 28/22˚C accumulated
46 g of carbon in this time. Results suggest potential for growth of fruit
from surplus carbon is likely to be highly dependent on temperatures in early
summer.
A paste method for estimating concentrations of ammonium, nitrate, and phosphate in soil solution
Authors: Smethurst P. J. , Herbert A. M. , Ballard L. M.
Published: August 2004

A paste method was evaluated for estimating the concentrations of
NH4, NO3, and
PO4 in soil solution. The method involves the addition
of enough water, e.g. 60 mL, to a fresh soil sample, e.g. 240 g, to prepare a
quasi-saturated paste. The paste is then equilibrated for 1 h at room
temperature before centrifugation and filtration. Solutes in the filtrate are
analysed by routine methods. Solute concentrations in the original soil
solution are estimated using a formula to account for the change in water
content and an appropriate solid{liquid partition coefficient
(Kd) of the soil for each
particular solute. The method was tested on 3 soils (clay loams derived from
basalt, sandstone, or siltstone), each with and without fertilisers applied in
field experiments. Dilution effects were evident with all soils for
NH4 and NO3, which were poorly
buffered, but not for PO4, which was well buffered.
Dilution effects for NO3 were adequately accounted for
by assuming no buffering, i.e. Kd
= 0, but for NH4 a
Kd value derived from a desorption
isotherm by using the paste method needed to be assumed. Based on theoretical
relationships, a guide is provided to the error associated with particular
combinations of dilution ratio and
Kd, when the latter is assumed.
Discrepencies that occurred between estimated concentrations using the paste
method and those collected using in situ soil solution
samplers soon after fertilisation were consistent with the expected
differences between the 2 methods in terms of the temporal and spatial
sampling of soil solution plus the possibility of microbial immobilisation of
extracted nutrients after in situ collection. We
conclude that the proposed paste method will be useful for estimating
concentrations of nutrients in soil solution.
Phosphorus movement down a toposequence from a landscape with texture contrast soils
Authors: Kirkby C. A. , Smythe L. J. , Cox J. W. , Chittleborough D. J.
Published: August 2004

Pedological processes culminating in physical and chemical differences to the
soil profile down a toposequence also changed the migrating potential of
phosphorus (P) within the landscape. Considerable erosion had occurred
resulting in a large movement of soil from the upper to the lower slopes.
This, in turn, had led to a decrease in profile depths on the upper slopes and
an increase on the lower slopes. We found that in the upper parts of the
toposequence there was enhanced macropore or bypassing flow resulting in a
greater and deeper leaching of P compared with the lower slopes.
The P that moved was almost entirely in the dissolved form and clearly
originated from commercial phosphate fertiliser that had been added to the
soil surface immediately prior to the start of irrigation. We could find no
evidence to support the commonly held view that P often moves through soil in
association with very fine clay-sized particles.
When considering land management options for reducing phosphate movement in
catchment areas, our results suggest that the upper parts of the landscape
need to be given special consideration.
Transport of phosphorus through soil in an effluent-irrigated tree plantation
Authors: Falkiner R. A. , Polglase P. J.
Published: August 2004

A young plantation of Pinus radiata in south-eastern
Australia was irrigated with secondary-treated sewerage effluent for 48
months, when evapotranspiration exceeded rainfall. Concentrations of
phosphorus (P) in saturation pastes of soil were measured after 30, 37, 42,
and 48 months to monitor vertical transport of P, and results were compared
with depth of transport predicted from P sorption isotherms.
Standard laboratory isotherms greatly underestimated the capacity of soil to
retain P. Thirty months after plantation establishment, 165 kg/ha of P had
been applied in effluent, and P in soil solution was predicted from sorption
isotherms to be at a concentration of 5 · 7 mg/L to a depth of 0
· 29 m. In comparison, the concentration of P in saturation paste at
this time decreased exponentially from 3 · 5 mg/L at 0 · 025
m to 0 · 43 mg/L at 0 · 30 m. Similarly, 48 months after
plantation establishment, 318 kg/ha of P had been applied, and P was
predicted to be in equilibrium to a depth of 0 · 51 m. At this time,
concentration of P in saturation paste was 4 · 7 mg/L at 0 ·
25 m but decreased to a concentration of 0 · 11 mg/L at 0 ·
45 m. The concentration of P in saturation paste in the bore-water control was
low (<0 · 36 mg/L) thoughout the profile.
The discrepancy between predicted and observed results was found from
subsequent experiments to be due largely to the short (17 h) equilibration
time and to the wide solution : soil ratio (10 : 1) used during construction
of standard sorption isotherms. In the 0-0 · 1 m layer of soil,
P-retention capacity determined in saturation paste and after 21 days
incubation was about 9-fold greater than when the standard method was used.
Leaching of dissolved P is unlikely to threaten the sustainable life-time of
the effluent-irrigated plantation studied.
Water : soil ratio influences aqueous phase chemistry of indigenous copper and zinc in soils
Authors: Fotovat Amir , Naidu Ravendra , Sumner Malcolm E.
Published: August 2004

The effect of dilution on the composition of soil solutions of 8 contrasting
soils ranging in pH from 5·3 to 8·8 with reference to zinc (Zn)
and copper (Cu) was studied. Soil samples were equilibrated with water in
various water:soil ratios for 24 h. Equilibrium solutions were extracted and
analysed for dissolved organic carbon (DOC), and major and minor elements. The
separation of the soil solution at field capacity (FC) was carried out by a
drainage method. Although the concentration of ions decreased upon dilution,
the total quantity of sodium (Na), potassium (K), Zn, Cu, and DOC extracted
per unit of soil weight increased. In contrast, the total quantity of Ca and
Mg decreased in most soils. The ratio of Zn and Cu to Ca correlated to
dilution level, whereas the ratio of Zn to monovalent cations decreased in low
pH soils. The relationship between the quantity of Zn and Cu at different
levels of the water : soil ratio in the soils studied showed that the
concentration of these trace metals at FC soil moisture can be estimated from
the soil extract.
Increases in soil moisture content led to a marked change in the ion-pair,
free hydrated metal concentrations, and complexation. Log
Zn2+ was linearly related to solution pH. Zinc
solubility was not consistent with published solubilities of any common
minerals. Also, Zn solubility in alkaline soils tended to be higher than
reported values in the literature, indicating that soluble metal–organic
ligand complexation was underestimated in these soils. The relationship
between pH and log Zn2+ was affected by dilution in
several ways.
A scheme for evaluating the effectiveness of riparian zones in reducing overland flow to streams
Authors: Herron N. F. , Hairsine P. B.
Published: August 2004

Two time-independent equations are developed to assess the effectiveness of
riparian zones in reducing overland flow to streams for events in which the
time-scale of subsurface water redistribution exceeds that of the rainfall
event. In one equation, the effectiveness of the riparian area is limited by
the storage capacity of its soils, while in the other equation, the
infiltration rate determines the buffer’s effectiveness. Riparian zone
widths, expressed as a proportion of total hillslope length, are calculated
for a number of different climate, antecedent moisture, and management
scenarios for hillslopes of varying topographic convergence. A riparian zone
width not exceeding 20% of total hillslope length is proposed as a
practical management option in this paper. Riparian zone widths that fall
within these bounds are predicted for areas where both the hillslopes and
riparian areas are in good condition. Where conditions in either area are
degraded, disproportionately large riparian buffer widths are predicted. The
results suggest that land management initiatives need to be directed at the
catchment as a whole if riparian buffers of realistic widths are to be
effective.
Soil phosphorus tests and grain yield responsiveness of maize (Zea mays) on Ferrosols
Authors: Moody P. W. , Dickson T. , Aitken R. L.
Published: August 2004

The grain yield response of maize (Zea mays) to various
rates of applied phosphorus (P) was measured at each of 17 sites in the South
Burnett region of south-eastern Queensland. The soils at all sites were
Ferrosols. Relative grain yield of the nil applied P treatment [100
× (yield at nil applied P/maximum yield)] was related to
Colwell (0·5 M NaHCO3) extractable P
(PB), CaCl2-extractable P, and
equilibrium P concentration and P buffer capacity calculated from P sorption
curves. Of these P measurements, PB was most highly
correlated with relative grain yield
(R2 = 0·94 for a
linear response and plateau fit,
R2 = 0·92 for a
Mitscherlich fit), and the PB values at 90%
maximum grain yield were 20 mg/kg for the linear response and plateau
model and 32 mg/kg for the Mitscherlich equation.
Assessing the extent of decomposition of natural organic materials using solid-state 13C NMR spectroscopy
Authors: Baldock J. A. , Oades J. M. , Nelson P. N. , Skene T. M. , Golchin A. , Clarke P.
Published: August 2004

Solid-state 13C nuclear magnetic resonance (NMR)
spectroscopy has become an important tool for examining the chemical structure
of natural organic materials and the chemical changes associated with
decomposition. In this paper, solid-state 13C NMR data
pertaining to changes in the chemical composition of a diverse range of
natural organic materials, including wood, peat, composts, forest litter
layers, and organic materials in surface layers of mineral soils, were
reviewed with the objective of deriving an index of the extent of
decomposition of such organic materials based on changes in chemical
composition. Chemical changes associated with the decomposition of wood varied
considerably and were dependent on a strong interaction between the species of
wood examined and the species composition of the microbial decomposer
community, making the derivation of a single general index applicable to wood
decomposition unlikely. For the remaining forms of natural organic residues,
decomposition was almost always associated with an increased content of alkyl
C and a decreased content of O-alkyl C. The concomitant increase and decrease
in alkyl and O-alkyl C contents, respectively, suggested that the ratio of
alkyl to O-alkyl carbon (A/O-A ratio) may provide a sensitive index of the
extent of decomposition. Contrary to the traditional view that humic
substances with an aromatic core accumulate as decomposition proceeds, changes
in the aromatic region were variable and suggested a relationship with the
activity of lignin-degrading fungi. The A/O-A ratio did appear to provide
a sensitive index of extent of decomposition provided that its use was
restricted to situations where the organic materials were derived from a
common starting material. In addition, the potential for adsorption of highly
decomposable materials on mineral soil surfaces and the impacts which such an
adsorption may have on bioavailability required consideration when the
A/O-A ratio was used to assess the extent of decomposition of organic
materials found in mineral soils.
Nitrate and chloride leaching in Vertosols for different tillage and stubble practices in fallow - grain cropping
Authors: Turpin J. E. , Thompson J. P. , Waring S. A. , MacKenzie J.
Published: August 2004

Research conducted in the mid 1980s on a ‘long-term fallow management
trial’, located on a black Vertosol at the Hermitage Research Station,
indicated that leaching may have been the cause of low concentrations of
nitrate-N within the root-zone of zero-tillage stubble-retained treatments.
The ‘fallow management trial’ has 12 management treatments: a
factorial combination of zero or conventional tillage×stubble retention
or burning×3 nitrogen fertiliser rates (0, 23, and 69 kg N/ha). To
test the leaching hypothesis, all trial treatments were analysed for nitrate
and chloride concentrations to a depth of 5·4 m in order to assess the
relative rates of drainage, solute movement, and nitrate leaching between
treatments. Similar analyses were conducted on 2 cultivated sites and 2
permanently grassed sites on-farm, also on black Vertosols, to compare solute
movement rates under the continuous winter cereal rotation (trial site) with a
winter–summer cropping regime and permanent pasture.
Results from the Hermitage trial site showed zero tillage with stubble
retention had a chloride concentration peak 2 m deeper down the profile
(4·5 m) than all other management treatments, indicating that drainage
rates were greatest in zero tillage–stubble retained treatments. Nitrate
profiles, however, showed that movement of nitrate-N to below the root-zone
was greatest under zero tillage with stubble burning with 69 kg N/ha
applied (Z-B 69N), followed by zero tillage with stubble retention and 69 kg
N/ha. The large nitrate loss from the root-zone of Z-B 69N (about
30% of applied fertiliser) was considered to be a result of high
concentrations of nitrate-N in the top 1·5 m associated with stubble
burning and fertilisation.
The on-farm cultivated sites had very little nitrate-N throughout the whole
profile, suggesting that either the use of summer as well as winter crops
reduced residual or ‘spared’ nitrate-N (through control of
root-lesion nematodes) and/or mineralisation rates were lower on these
sites.