bluuebunny/crossref_metadata_2025 huggingface dataset:
The Fractionation of 2H and 18O in Leaf Water of Barley
Authors: Walker CD , Lance RCM
Published: January 2006

Small changes in the natural abundance of hydrogen and oxygen isotopes in water occur as a result of transpiration. We considered whether these may be sufficient to study the differences in water relations of barley cultivars having different water-use efficiency (W). A range of cultivars of varying W were grown in the glasshouse and in the field in breeders' plots. Foliage water samples were taken from a specific leaf stage over the course of a day. Certain field-grown cultivars had consistently higher 2H and 18O compositions in foliage water than others at almost all sampling times, resulting in a consistent ranking of the cultivars. Some evidence of a consistent ranking of isotopic compositions was also present in the glasshouse experiment.
Concurrent variations in 2H and 18O compositions of the stem and leaf water reflect the conditions under which transpiration is occurring. The composition of stem water remains steady over the course of such experiments. The slope of the line connecting the isotopic compositions of the stem water and leaf water varied with changes in leaf water composition. This variation in slope was more pronounced under the more humid conditions of the glasshouse experiment, as is predicted from theory.
The 2H and 18O compositions of water in the other plant parts, atmosphere and soil were also examined and porometry measurements were made. These indicated that daily variations in the contributions of soil and leaf water to the atmosphere occurred. This involves a maximum in the proportion of soil evaporation in the middle of the day, and a converse maximum in flag leaf evaporation early and late in the solar day.
High-Level, Seed-Specific Expression of Foreign Coding Sequences in Brassica napus
Authors: Stayton M , Harpster M , Brosio P , Dunsmuir P
Published: January 2006

The napin seed storage proteins of oilseed rape (Brassica napus) are encoded by a multigene family of at least 16 members. We have isolated five independent napin genes and five napin cDNAs from a rapid cycling line of B. napus (CrGC45). Two of the isolated genomic fragments, G1 and G2, were introduced into tobacco, and napin gene expression was analysed in the developing seeds. Both genes are expressed during the maturation phase of transformed tobacco seeds as judged by the accumulation of napin RNA in immature embryos. These genes appear to utilise the same transcription start site in tobacco as in Brassica, but are expressed at 20-50-fold lower levels in the heterologous host plant. The G1 and G2 promoter regions and 3' flanking regions were also fused to two foreign coding sequences: the chloramphenicol acetyl transferase (CAT) coding sequence and the pea seed 2S albumin (PSA) coding sequence, and these chimeric genes were introduced into B. napus and tobacco. Upon introduction into tobacco, only the PSA mRNA accumulated to a measurable extent. In transgenic rapeseed plants, PSA RNA accumulated to high levels, but CAT RNA was present only at low concentrations. The results demonstrate that high level expression of foreign coding sequences is possible in developing seeds of B. napus and that differential mRNA stability may contribute significantly to the level of foreign transcripts which can be observed in genetically engineered rapeseed.
Modification of Gene Expression in Ripening Fruit
Authors: Speirs J , Brady CJ
Published: January 2006

Fruit ripening is a coordinated series of biochemical changes that renders the fruit attractive to eat. The fruit may soften, develop colour, change starch or acid into sugar, become flavoursome, produce more ethylene, increase in sensitivity to ethylene, and respire more rapidly.
This syndrome is under contemporary genetic control as illustrated by mutants with fruit that develop normally but lack the ability to ripen, or are deficient or modified in an aspect of ripening. Molecular analysis has revealed changes in gene expression in ripening avocado, tomato, pear and apple fruits. Genes encoding β-1, 4-glucanase (avocado), polygalacturonase (tomato) and trypsin inhibitor (tomato) are among those whose expression increases through ripening.
To modify the softening of tomato fruits, antisense constructs with constitutive promoters have been used to reduce the apparent expression of the polygalacturonase gene. The experiments confirmed a role for polygalacturonase in fruit softening but a need for other inputs was also indicated. In experiments using chimaeric genes, the coding sequence of polygalacturonase linked to a fruit-specific and ethylene-sensitive promoter was introduced into the rin tomato genome. Rin plants have fruit which do not ripen or accumulate polygalacturonase. The transformed rin fruit accumulated polygalacturonase but did not ripen or soften. This experiment confirms conclusions drawn from the use of antisense constructs that polygalacturonase action is not the sole determinant of texture changes in ripening tomatoes.
Ethylene has a key role throughout ripening. The molecular biology of ethylene production and perception is gradually unfolding. A cDNA for ACC synthase for zucchini, a small gene family whose expression correlated with Ethylene Forming Enzyme (EFE) activity, and a consensus sequence in promoters that are ethylene sensitive have all been described. There is accumulating evidence that some of these sequences and the polygalacturonase sequence are conserved between species, and this will be useful in extending the presently available information.
Chloroplast Genes in Higher Plants
Authors: Scott NS , Timmis JN , Ayliffe MA
Published: January 2006

The role of chloroplast (cp) DNA in plastid and chloroplast function is discussed, particularly in relation to the interaction with nuclear DNA. The evolution of the chloroplast genome and the endosymbiont hypothesis are related to our results and those of others which show the occurrence of cpDNA sequences common to the nuclear and chloroplast genome.
Biological Control of Crown Gall Using Using
Agrobacterium Strains K84 and K1026
Authors: Ryder MH , Jones DA
Published: January 2006

Crown gall has been successfully controlled on a commercial scale for over 15 years by the use of Agrobacterium radiobacter strain K84. The continued success of strain K84 has been jeoparised by the possibility of transfer of the agrocin plasmid, pAgK84, to pathogenic agrobacteria, making them resistant to control. The construction of a transfer-deficient deletion mutant of pAgK84 has resulted in a strain (K1026) from which the agrocin plasmid (pAgK1026) can no longer be transferred to other agrobacteria. Strain K1026 controls crown gall as effectively as strain K84 and may be used to ensure that the danger of breakdown of biological control is minimised.
Increased Carbonic Anhydrase Activity in Leaves of Sodium-Deficient C4 Plants
Authors: Brownell PF , Bielig LM , Grof CPL
Published: January 2006

The activitiy of carbonic anhydrase was determined in sodium-deficient and sodium-sufficient plants of Kochia childsii and Amaranthus tricolor. The enzyme extracted from leaves of sodium-deficient plants was found to be twice as active as that from leaves of control plants when expressed on a fresh weight or protein basis and three times as active on a chlorophyll basis. It was concluded that carbonic anhydrase activity was unlikely to limit the rate of photosynthesis in sodium-deficient C4 plants.
Modelling Stomatal Responses to Environment in Macadamia integrifolia
Authors: Lloyd J
Published: January 2006

Gas exchange measurements were made of photosynthetic and stomatal responses of Macadamia integrifolia under controlled conditions. Test leaves were subjected to a range of temperatures, humidities and photon irradiances. When stomatal responses to humidity were plotted as a function of vapour mol fraction difference (D) a similar curvilinear response was observed at all temperatures and at photon irradiances of 200 and 1500 μmol quanta m-2 s-1. By contrast, when expressed as a function of relative humidity, different slopes in the humidity response were observed, and at high photon irradiances, stomatal conductances (gs) appeared to have an optimum temperature below 15�C. Simple equations to quantify responses to leaf temperature (TI) and D were developed, the best of which was

gs = [1-k1(1-[Tl/Topt)]/k2√D,

where Topt is the leaf temperature at which maximal stomatal opening is observed and k1 and k2 are constants fitted by non-linear least squares regression analysis.
Calculation of the gain ratio of CO2 assimilation (A) to transpiration (E) (δA/δE) was complicated by effects of D on the relationship between A and leaf intercellular mol fraction of CO2 (CI). Calculation of δA/δE using A/CI relationships derived by varying external CO2 mol fraction at constant D showed the gain ratio to be virtually constant (1.5 mmol mol-1) across a range of leaf temperatures and vapour mol fraction differences but, when calculated directly from the relationship between A and gs, a decrease in δA/δE with D was observed. Macadamia leaves have heavily sclerified bundle sheath extensions and it is considered that this dependence was an artefact due to non-uniform stomatal closure in response to increasing D. It is shown that, at any given temperature, a stomatal response of the form gsD-1/2 gives rise to an approximately constant δA/δE.
Carbohydrate deposition and partitioning in elongating leaves of wheat under saline soil conditions
Authors: Hu Yuncai , Schnyder Hans , Schmidhalter Urs
Published: January 2006

The objective of this study was to
quantitatively evaluate the effect of salinity on the spatial distributionof
glucose, fructose, sucrose, fructan and total C contents, as well as on their
net deposition rates in the elongation and maturation zones of leaf 4 of the
main stem of spring wheat (Triticum aestivum L.) during
its linear growth phase. Plants were grown in growth chambers in 1.5-L pots
containing an illitic–chloritic silty loam treated with or without 120
mM NaCl. 3 d after emergence of leaf 4, sampling started at 3 and 13 h into
the 16 h photoperiod. The distribution of carbohydrates along the leaf axis
showed distinct patterns that were altered by salinity and time in the
photoperiod. Glucose and fructose concentrations were low at the base of the
elongation zone and increased sharply up to the end of the leaf elongation
zone in the two treatments. In contrast, sucrose concentration in the
elongation zone was high at the leaf base and decreased sharply with distance
from the base up to the end of the leaf elongation zone in both treatments.
The main effect of salinity on the water-soluble carbohydrates (WSC) was that
it significantly increased sucrose concentration in the elongation zone
throughout the day and accumulation in the photo-synthetically active zone
during the photoperiod. Net deposition rates of sucrose and fructan in the
elongation zone were enhanced by 120 mM NaCl. Salinity did not affect the
sucrose import rate (g C kg -1 H2O
h -1 ) in the sink (the elongation and secondary cell
wall deposition zone). However, the partitioning of imported sucrose to WSC
and structural C varied with salinity. In the basal part of the leaf (0-15 mm
above the leaf base), net deposition of sucrose in the control treatment
accounted for 7% of imported sucrose, compared with 17% at 120
mM NaCl. Eighty-seven percent of imported sucrose in the control treatment and
75% in the salinized treatment was used for synthesis of structural
biomass (estimated as total C minus WSC-C). Conversely, in the 15–30 mm
zone (i.e. in the distal part of the elongation zone and the secondary cell
wall deposition zone), a greater fraction of imported sucrose was partitioned
to synthesis of structural C under saline conditions. There was no significant
effect of salinity on sucrose use in the region 30–60 mm.
Xanthophyll cycle, light energy dissipation and electron transport in transgenic tobacco with reduced carbon assimilation capacity
Authors: Ruuska Sari A. , von Caemmerer Susanne , Badger Murray R. , Andrews T. John , Price G. Dean , Robinson Sharon A.
Published: January 2006

The effects of reduced
CO2 assimilation capacity on the leaf pigment
composition and the dissipation of light energy were studied using transgenic
tobacco (Nicotiana tabacum L. cv. W38). Two plant types
were used: anti-SSu plants with reduced amounts of Rubisco and anti-GAPDH
plants with reduced activity of chloroplast glycer-aldehyde 3-phosphate
dehydrogenase. A moderate reduction in the photosynthetic capacity increased
the de-epoxidation state of the xanthophyll-cycle pigments. In contrast, there
was no large effect on the leaf pigment composition and the ratio of the
xanthophyll cycle pigments to chlorophyll, and total carotenoids increased
only in the most severe transgenic plants. The light induction of
photosynthesis, fluorescence quenching and de-epoxida ion of the xanthophyll
cycle pigments were also followed in wild-type and anti-SSu plants. Anti-SSu
plants maintained high nonphotochemical quenching and increased xanthophyll
de-epoxidation in the light but the reduction state of
QA remained high. For both wild-type and anti-SSu
plants, the electron transport rate estimated from chlorophyll a fluorescence
appeared to be much higher than that required to support the observed rate of
CO2 assimilation and photorespiration during the early
phase of photosynthetic induction. However, the two estimates converged with
the onset of steady-state photosynthesis.
Expression patterns of cytoplasmic pyruvate, orthophosphate dikinase of rice (C3) and maize (C4) in a C3 plant, rice
Authors: Nomura Mika , Sentoku Naoki , Tajima Shigeyuki , Matsuoka Makoto
Published: January 2006

Two types of mRNAs are transcribed from the
C4-type pyruvate, orthophosphate dikinase gene
(Pdk) with different sizes, which encode chloroplastic
and cytoplasmic forms of the enzyme. The two transcripts are pro duced by two
independent promoters and this unusual dual promoter system is also found in
the C4-like Pdk gene of the
C3 plant, rice. In order to elucidate the expression
pattern of the cytoplasmic transcript from the maize
C4-type and rice C4-like
Pdk genes, we have produced chimeric constructs with the
ß-glucuronidase (GUS) reporter gene under the control of the cytoplasmic
promoters and introduced the constructs into rice. Both cytoplasmic promoters
directed GUS expression in non-photosynthetic organs, such as endosperm and
roots, in transgenic rice plants, while expression was low in photosynthetic
organs. These results indicate that the organ-specific localization of the
cyto-plasmic enzyme is similar in C3 and
C4 plants. The results also suggest the possibility that
the cytoplasmic enzyme has a similar function(s) in non-photosynthetic organs
both in C3 and C4 plants.
Genotypic differences in growth and stomatal morphology of Southern Beech, Nothofagus cunninghamii, exposed to depleted CO2 concentrations
Authors: Hovenden Mark J. , Schimanski Lisa J.
Published: January 2006

Nothofagus cunninghamii
(Hook.) Oerst. clones of four different genotypes from Mt Field National Park,
Tasmania were grown at both current (~370 mol
mol–1 ) and depleted (~170 mol mol
–1 ) CO2. Growth was
significantly less in the lower [CO2]
treatment in all genotypes. The amount of growth reduction caused by low
[CO2] depended strongly upon genotype and
varied from less than 30% to greater than 75% reduction of whole
plant biomass when compared to growth at current
[CO2]. Specific leaf area was significantly
greater in all plants grown in reduced [CO2],
whereas individual leaf area was not significantly affected by
[CO2]. The direction and magnitude of the
response of stomatal index, stomatal density and epidermal cell density to
[CO2] was strongly dependent upon genotype.
[CO2] had a significant effect on the length
of the stomatal pore, but the magnitude of the effect (~3%) was trivial
compared to changes in stomatal density (up to 20%). There was a
significant (P < 0.01) and positive relationship between the response of
stomatal density and growth response of a genotype. Therefore, we propose that
the response of stomatal density to [CO2]
controls the relative growth response of N. cunninghamii
and that this response is highly dependent upon genotype.
Photosynthetic Response to Light and Nutrients in Sun-Tolerant and Shade-Tolerant Rainforest Trees. I. Growth, Leaf Anatomy and Nutrient Content.
Authors: Thompson WA , Kriedemann PE , Craig IE
Published: January 2006

Seedling trees of Argyrodendron sp., A. trifoliolaturn, Flindersia brayleyana and Toona australis
were grown for c. 180 days under one of three light regimes with either of two nutrient levels (6
treatments in all). Light regimes spanned the range of environmental conditions which these species
would normally experience in northern Queensland rainforest: deep shade (1.3 mol quanta m-2 day-1,
equivalent to forest floor), moderate light (5.6 mol quanta m-2 day-1, comparable to midcanopy), and
strong light (23 mol quanta m-2 day-1, matching daily irradiance of exposed crowns).
Long-term shade tolerance in Argyrodendron sp. and A. trifoliolaturn was associated with limited
responses in growth and leaf anatomy to low light and nutrients. Starch accumulation in leaves under
all treatments, and especially low nutrients, implied that supply of photoassimilate exceeded demand.
Such a conservative carbon economy, plus the accumulation of stem P reserves, even in a weak light
environment, is consistent with a protracted existence as part of a forest floor community. By contrast,
shade-intolerant Toona is an early successional species and lacks such adaptive features. Instead, light
and nutrients had a strong interactive effect on growth. Flindersia, with a broad tolerance to sun and
shade, was intermediate in growth response and leaf adjustment, which is consistent with its success
across a wide size range of forest gaps.
Photosynthetic Response to Light and Nutrients in Sun-Tolerant and Shade-Tolerant Rainforest Trees. II. Leaf Gas Exchange and Component Processes of Photosynthesis
Authors: Thompson WA , Huang LK , Kriedemann PE
Published: January 2006

Species with contrasting shade tolerance were grown under three light by two nutrient treatments.
Gas exchange by intact leaves, leaf disk O2 evolution and chlorophyll fluorescence were measured.
In shade-tolerant evergreen species (Argyrodendron sp., A. trifoliolatum and Flindersia brayleyana)
photosynthetic activity of seedlings in air at light saturation (A) was lower under weak (30 pmol quanta
m-2 day-1 ), compared with medium (130) or strong light (535). In Toona australis, a shade-intolerant
and deciduous tree, A was reduced 44% from strong to weak light treatment on high nutrients (71 mg
N L-1 nutrient solution). Nevertheless, nitrogen-use efficiency for leaf photosynthesis was highest in
Toona under all growing conditions and, with higher specific leaf area, probably contributes towards
fast occupancy of sites which underlies early succession in this species.
All species made photosynthetic and respiratory adjustments from strong to medium to weak light,
which resulted in a lower light compensation point (Q0). Such adjustments were accentuated by low
nutrient supply (1.0 mg N L-1 nutrient solution) and were especially pronounced for shade-intolerant
Toona. Reduced Q0 in Toona was accompanied by lower A and light saturation point (QA). Both
species of Argyrodendron showed no decrease in QA despite reduction in Q0 under weak light.Contrary to expectation, photosynthetic responses to light × nutrient treatments did not correlate
with degree of shade tolerance accorded each species by rainforest ecologists.
A Leaf Elongation Assay Detects an Unknown Growth Inhibitor in Xylem Sap From Wheat and Barley
Authors: Munns R
Published: January 2006

Recent research suggests that chemicals sent from roots in the transpiration stream could control leaf expansion, and that xylem sap from plants in dry or saline soil could contain increased amounts of a growth inhibitor, or decreased amounts of a growth promoter. In order to test these possibilities, a bioassay that could detect the presence of growth regulators in xylem sap was developed using whole shoots of wheat and barley seedlings. The bioassay showed that xylem sap collected from intact, transpiring plants in a drying soil contained a strong growth inhibitor. The inhibitory substance was not abscisic acid: while the concentration of abscisic acid in the sap rose as the soil dried, the highest concentration found, 4 × 10-8 M, was too low to inhibit leaf expansion. The identity of the new inhibitor is unknown.
Acid-Tolerant Species of Medicago Produce Root Exudates at Low pH Which Induce the Expression of Nodulation Genes in Rhizobium meliloti
Authors: Howieson JG , Robson AD , Abbott LK
Published: January 2006

An acid rhizosphere may interfere with the transcription of nodulation genes in Rhizobium spp. by modifying the production of legume root exudates, or the rhizobial response to them. Certain annual species of Medicago (M. murex, M. polymorpha) can nodulate better in acid soils and solutions than other species (M. truncatula, M. littoralis). The mechanisms of this acid tolerance in nodulation are poorly understood. Root exudates collected at pH 5.8 and pH 6.0 from acid-tolerant species of annual medics induced the expression of nodulation genes in Rhizobium meliloti as indicated from a lacZ gene fusion, whereas exudates from acid-sensitive species grown at these pH values displayed decreased induction activity. For the acid-sensitive host, M. truncatula, increasing the Ca concentration from 0.5 to 5.0 mM at pH 5.8 increased the nod-gene induction activity of its exudates, but there was no effect at higher pH. There was no effect of Ca or pH on the nod-gene induction activity of exudates collected from M. murex. These results indicate a likely mechanism underlying differences in ability to nodulate under acid stress among annual species of Medicago.
Seasonal Variation in Stomatal Responses of Two Cultivars of Lychee (Litchi chinenis Sonn)
Authors: Batten D , Lloyd J , Mcconchie C
Published: January 2006

The effect of cultivar and environment on the stomatal conductance and plant water relations of lychee (Litchi chinensis Sonn.) was investigated. Diurnal changes in stomatal conductance (gs) and leaf water potentials (Ψ1) were determined for leaves of irrigated trees of cv. 'Bengal' and cv. 'Kwai May Pink' between July and December 1990. Leaves of Bengal always had much higher gs than Kwai May Pink in winter, but as summer approached, this difference became less. Ψ1 values at midday for Bengal were always much lower than for Kwai May Pink. The linear model, E = G(Ψ1-Ψsoil), where E is transpiration rate and G is whole plant conductance, was found to be valid for nearly all the data sets collected. The values of G for Kwai May Pink were higher than for Bengal, especially in summer, and the average values of G (Bengal 4.1 and Kwai May Pink 6.3 mmol H2O m-2 s-1 Mpa-1) indicate that the lychee has a relatively efficient water transport system compared with other fruit tree species.
Laboratory measurements of the responses of these cultivars confirmed observed differences in gs in the field. The responses of each cultivar to irradiance (I), leaf temperature (Tl) and leaf-air water vapour pressure deficit (D) were obtained and used to model the orchard data. The equation (see pdf)
where Topt is the temperature for maximum gs, gdark is the basal gs in the dark at given T1 and D, and kI, kT and kD are constants fitted by non-linear least squares, provided an acceptable fit for both cultivars (R2 = 0.68 for Bengal and 0.55 for Kwai May Pink). The fit was not improved by including Ψ1 in the model. There was a significant difference between cultivars in kT, the temperature sensitivity coefficient. Possible implications of inter-cultivar differences in temperature sensitivity are discussed.
T-DNA Insertion Mutagenesis in Arabidopsis: Prospects and Perspectives
Authors: Forsthoefel NR , Wu YW , Schulz B , Bennett MJ , Feldmann KA
Published: January 2006

Approximately 13 000 independent transformants of Arabidopsis have been generated utilising the Agrobacterium-mediated seed infection/transformation procedure. The average number of functional independent T-DNA insertion events per transformed line is 1.5, thus constituting a population with 19 500 independent inserts. These transformed lines have been screened under two environmental regimes for visible alterations in phenotype. In one screen the lines were grown under greenhouse conditions and examined at weekly intervals. In the second, seeds from each line were plated under axenic conditions in vertically oriented square petri plates and examined 4 and 9 days after germination. The mutants observed were placed into 7 distinct phenotypic classes: seedling-lethal, size variant, reduced-fertility, pigment defect, embryo-defective, dramatic morphological, and physiological. The mutational spectrum of the first 8000 transformed lines has been reported earlier. The mutational spectrum for a further 5000 transformed lines is reported here and, with several notable exceptions, is similar to that observed previously.
Control of Flowering in Arabidopsis thaliana by Light, Vernalisation and Gibberellins
Authors: Bagnall DJ
Published: January 2006

The late flowering mutants of the Landsberg erecta race of Arabidopsis thaliana (L.) Heynh. were responsive to both vernalisation treatment and the ratio of red: far-red light (660 : 730 nm) with regard to time to flower and the numbers of leaves formed prior to flowering. The most vernalisation-sensitive mutants, fca, fve, fy and fpa, were also the most sensitive with regard to changes in the red:far-red light ratio. These responsive mutants flowered up to 40% earlier under lighting that included a greater proportion of far-red (730 nm) light from incandescent lamps compared with plants under light at the same photon flux density (PFD) with a greater proportion of energy from fluorescent lamps. Conversely, the mutants that were only slightly responsive to vernalisation (co, gi and fe) were also least responsive to changes in red:far-red ratio. The correlation between responsiveness to vernalisation and responsiveness to changes in red: far-red for the 11 mutants and Landsberg was highly significant (r2 = 0.88).
Time to flower and leaf number at flowering were also markedly affected by changes in PFD in the vernalisation-sensitive mutants. Halving the PFD approximately doubled time-to-flower and leaf number of fca, the most responsive of the late flowering mutants, whereas there were only slight changes in the flowering responses of the parent Landsberg. Thus, these single point late flowering mutants are responsive not only to vernalisation but also to changes in light quality and PFD. These responses imply that both daylength perception and photosynthesis have been affected by the mutations.
Gibberellins (GAS) induced earlier flowering not only in the late flowering mutant fca, but also in Landsberg, when that race was grown in short days. Dosages of 5 μg plant-1 of GA3, GA5 and GA9 were equaIly effective in promoting flowering of 15-day-old fca plants with subsequent flowering 9-13 days earlier with 4-6 fewer leaves.
Photoperiodic sensitivity to a single long day 15 days after sowing showed Landsberg flowering 6 days earlier and with 1.4 fewer leaves than plants continuously in short days.
Root Morphology Mutants in Arabidopsis thaliana
Authors: Baskin TI , Betzner AS , Hoggart R , Cork A , Williamson RE
Published: January 2006

We have begun a mutational analysis of root morphogenesis in Arabidopsis thaliana. We report here the initial genetic and physiological characterisation of six mutations that affect root growth and development. Three of them (rsw1, rsw2, rsw3) cause extensive radial swelling of the root apex. These mutations are recessive at different loci and show temperature-sensitive expression, such that the roots appear wild type when grown at 18�C but express the mutant phenotype when transferred to 31�C. Following transfer to the restrictive temperature, these three mutations have different kinetic and morphological patterns of radial swelling, and grow at different rates with continued time at high temperature. We believe that these mutations represent three different loci active in the wild type in regulating the shape of the root.
We have also characterised two mutations that affect only the root epidermis, causing many epidermal cells to bulge (reb1-1, reb1-2). The two mutations are recessive and are alleles. However, rebl-1 is constitutive whereas reb1-2 is temperature sensitive, only expressing at 33�C. Reb1-2 also causes a deviation from the normal straight growth of the root such that the affected roots grow with sharp bends or meanders. The final mutant reported here is a stunted plant (stp1), in which the root growth rate is approximately 25% of the wild type rate. Moreover, root growth steadily accelerates over 5 days following germination in the wild type but remains constant in stp1, which grows at a constant rate over the same interval.
Mutational Analysis of Root Gravitropism and Phototropism of Arabidopsis thaliana Seedlings
Authors: Okada K , Shimura Y
Published: January 2006

Root gravitropism and phototropism were analysed in young seedlings of Arabidopsis thaliana by a simple procedure using agar plates, by changing the position of plates or by covering the plates with black opaque sheet. Roots of A. thaliana seedlings growing on the surface of agar medium showed clear responses to gravity and light stimuli. A set of mutants with abnormal gravitropism or phototropism was isolated. Gravitropic mutants were separated into two types, reduced-response type and non-response type. The mutants were genetically divided into two complementation groups, aux1 and agr1. In both groups the reduced-response type mutants carried weaker genetic lesions, whereas the non-response type mutants carried heavier genetic lesions. Mutants with no phototropic response were classified into two complementation groups, rpt1 and rpt2. The root tropism mutants showed normal tropic responses in shoots, indicating that genetic regulation pathways are different in roots and shoots.
Mango Sapburn: Components of Fruit Sap and Their Role in Causing Skin Damage.
Authors: Loveys BR , Robinson SP , Brophy JJ , Chacko EK
Published: January 2006

Damage caused to the skin of mango fruit by contact with sap exuded from the cut or broken pedicel reduces consumer acceptance and storage life of the fruit. Mangoes of the Kensington cultivar are particularly susceptible to sapburn injury. On centrifugation, the fruit sap separated into two phases. Skin damage was caused predominantly by the upper non-aqueous phase. A major component of this phase was terpinolene which gave symptoms indistinguishable from sapburn injury when applied to the fruit surface. The same type of damage could be induced by the application of synthetic terpinolene when applied undiluted, diluted in hexane or as an aqueous emulsion. Non-volatile sap components separated by distillation were not damaging to mango skin. Sap exuded from the mango leaf petioles also contained terpinolene, but its concentration was less than 1% of the concentration in pedicel sap and this sap was not damaging to the fruit skin.
The Florida cultivar Irwin is less susceptible to sapburn injury and the predominant terpene in its sap was identified as car-3-ene. When applied to Kensington skin, car-3-ene caused significantly less damage than terpinolene. We conclude that the primary cause of mango sapburn is entry of volatile components of the sap such as terpinolene through the lenticels, resulting in tissue damage and subsequent enzymic browning.
Coupled Photosynthesis-Stomatal Conductance Model for Leaves of C4 Plants
Authors: Collatz GJ , Ribas-Carbo M , Berry JA
Published: January 2006

Leaf based models of net photosynthesis (An) and stomatal conductance (g) are often components of whole plant, canopy and regional models of net primary productivity and surface energy balance. Since C4 metabolism shows unique responses to environmental conditions and C4 species are important agriculturally and ecologically, a realistic and accurate leaf model specific to C4 plants is needed. In this paper we develop a simple model for predicting An and g from leaves of C4 plants that is easily parameterised and that predicts many of the important environmental responses.
We derive the leaf model from a simple biochemical-intercellular transport model of C4 photosynthesis that includes inorganic carbon fixation by PEP carboxylase, light dependent generation of PEP and RuBP, rubisco reaction kinetics, and the diffusion of inorganic carbon and O2 between the bundle sheath and mesophyll. We argue that under most conditions these processes can be described simply as three potentially limiting steps. The leaf photosynthesis model treats An as first order with respect to either light, CO2 or the amount of rubisco present and produces a continuous transition between limitations. The independent variables of the leaf photosynthesis model are leaf temperature (TI), intercellular CO2 levels and the absorbed quantum flux.
A simple linear model of g in terms of An and leaf surface CO2 level (ps) and relative humidity (hs) is combined with the photosynthesis model to give leaf photosynthesis as a function of absorbed quantum flux, T1 and ps and hs levels.
Gas exchange measurements from corn leaves exposed to varied light, CO2 and temperature levels are used to parameterise and test the models. Model parameters are determined by fitting the models to a set of 21 measurements. The behaviour of the models is compared with an independent set of 71 measurements, and the predictions are shown to be highly correlated with the data.
Under most conditions the leaf model can be parameterised simply by determining the level of rubisco in the leaves. The effects of light environment, nutritional status and water stress levels on An and g can be accounted for by appropriate adjustment of the capacity for rubisco to fix CO2. We estimate rubsico capacity from CO2 and light saturated photosynthesis although leaf nitrogen content or rubisco assays from leaf extracts could also be used for this purpose.
Adaptations to Drought in Five Woody Species Co-Occurring on Shallow-Soil Ridges
Authors: Mishio M
Published: January 2006

Pre-dawn leaf water potential and parameters controlling water flow through a plant of five co-occurring plant species, Dodonaea viscosa Jacquin (Sapindaceae), Wikstroemia pseudoretusa Koidzumi (Thymelaeaceae), Ligustrum micranthum Zucc. (Oleaceae), Distylium lepidotum Nakai (Hamamelidaceae) and Hibiscus glaber Matsumura (Malvaceae) were compared in late April, early June and early September 1989. These species are common members of the scrub community found on shallow-soil ridges in the Bonin Islands, Japan. Mean pre-dawn leaf water potential during the dry period of early September was lowest in Dod. Viscosa growing on microsites with shallower soil on a ridge. Deeper rooted species, Dis. Lepidotum and H. glaber, had higher values of pre-dawn leaf water potential than shallower rooted species, L. micranthum and W. pseudoretusa. Anatomical and morphological characteristics, and physiological characteristics such as water relations of leaves suggested that W. pseudoretusa and H. glaber are less tolerant to drought than L. micranthum and Dis. Lepidotum, and that W. pseudoretusa and H. glaber might avoid severe stress by temporal leaf fall and dense deeper root, respectively. Relationships between leaf conductance and hydraulic conductance suggested different water use patterns among the five species growing in close proximity on xeric shallow-soil ridges in the Bonin Islands.
Turgor and Cell Expansion: Beyond the Lockhart Equation
Authors: Passioura JB , Fry SC
Published: January 2006

The rheology of the expanding cell wall is often analysed in terms of the Lockhart equation, which equates the expansion rate of a cell to m(P - Y), where rn is the extensibility of the cell wall, P is the turgor pressure, and Y is a minimum value of P below which the cell will not grow. Many studies have shown that Y (and sometimes m) are variables which change in response to changes in P at a time scale of about 10 min. The result is that, apart from the transient responses, the expansion rate is often maintained at an approximately steady value despite changes in P. This paper describes a molecular model of the growing cell wall that accounts for how m and Y may vary to maintain a constant growth rate despite changes in turgor.
Evidence for the Consequences of a Barrier to Solute Diffusion Between the Apoplast and Vascular Bundles in Sugarcane Stalk Tissue
Authors: Welbaum GE , Meinzer FC , Grayson RL , Thornham KT
Published: January 2006

In a previous study we found that the apoplast of mature sugarcane stalk tissue contains up to 700 mM sucrose. In the current study, we found that xylem sap, exuded under root pressure from decapitated stalks, was virtually free of sucrose. This suggested that the apoplast of sugarcane stalk tissue contains at least two separate compartments: one within the free space of the vascular bundles, which is nearly free of sucrose, and another in the free space of the surrounding storage tissue. Anatomical observations indicated that these putative compartments were separated by the sclerenchymatous bundle sheath cell walls that were suberised and lignified early in development, constituting a barrier to the movement of relatively large molecular weight solutes but not water. It was hypothesised that this semipermeability would enable sucrose and other solutes in the apoplast of the storage tissue to provide a gradient for osmotic water flow from the xylem, generating a hydrostatic pressure in the apoplast. Additional lines of evidence were obtained to support this hypothesis: (i) apoplastic dyes were restricted to the xylem and did not accumulate in the apoplast of storage tissue when water-stressed plants were rehydrated, (ii) water potential measured with in situ psychrometers decreased when sections of intact stalks were cut, (iii) mature internode tissue of well-watered plants often cracks after maximum fresh and dry weight accumulation, and (iv) internode sections typically shrink in diameter immediately upon excision. The existence of a semipermeable barrier separating the vascular bundles from the storage parenchyma apoplast would require that phloem unloading involve a symplastic step in order to traverse the barrier. The presence of plasmodesmatal connections between companion, sclerenchyrna, and storage parenchyma cells supported this conclusion.
Ammonia Assimilation and Metabolite Transport in Isolated Chloroplasts. I. Kinetic Measurement of 2-Oxoglutarate and Malate Uptake Via the 2-Oxoglutarate Translocator in Oat and Spinach Chloroplasts
Authors: Yu JW , Woo KC
Published: January 2006

The stable double-layer silicone centrifugation system was used to determine the kinetic properties of the 2-oxoglutarate (2-OG) translocator in isolated oat and spinach chloroplasts. The uptake of [14C]2-OG and [14C]malate via the 2-OG translocator were measured in the presence of 20 mM glutamate in chloroplasts preloaded with unlabelled 2-OG. The characteristics of the general dicarboxylate (Dct) translocator were also determined using chloroplasts preloaded with glutamate. The Vmax values obtained for transport activity via the 2-OG translocator in oat and spinach chloroplasts exceeded 150 μmol mg-1 Chl h-1 and for the Dct translocator less than 100 μmol mg-1 Chl h-1. The K� (malate) values of the 2-OG and Dct translocators also showed large differences in the two species. In spinach chloroplasts they were 2.7 and 0.6 mM for the 2-OG and Dct translocators respectively whereas, in oat chloroplasts the corresponding values were 2.7 and 1.4 mM. This suggests that, in spinach, malate would be transported into the chloroplasts preferentially via the Dct translocator, thus providing a kinetic basis for the 'push and pull' mechanism proposed for dicarboxylate transport during photorespiratory NH3 recycling in the 2-translocator model.
Nodulation and Nodulin Gene Expression in an Interspecific Hybrid Between Glycine max and Glycine tomentella
Authors: Shen BH , Davis LC
Published: January 2006

When the genome of a wild species, Glycine tomentella, is combined with that of the cultivated soybean, Glycine max in a hybrid, nodulation specificity is altered. Two strains of Rhizobium fredii that nodulate the G. rnax parent fail to nodulate the hybrid, indicating the presence of a restriction gene, while three Bradyrhizobium japonicum strains that nodulate G. max are highly effective on the hybrid. Some strains of (Brady)rhizobium, originally isolated from wild Australian Glycine species, nodulate only one of the two parental species. One strain ineffective on G. max is effective on the hybrid. Two other strains, while effective on one parent, appear more effective on the hybrid. In three fully examined cases in which effective nodules are produced on the hybrid, the late nodulins leg-hemoglobin, glutamine synthetase, and xanthine dehydrogenase are expressed from both genomes. Thus, although a rhizobial strain may nodulate only one or the other of the parental types, if it successfully nodulates the hybrid, the nodulation process provides signals or internal conditions that lead to expression of late nodulins from both genomes.
Leaf Growth and Photosynthetic Response to Nitrogen and Phosphorus in Seedling Trees of Gmelina arborea
Authors: Cromer RN , Kriedemann PE , Sands PJ , Stewart LG
Published: January 2006

Plants were grown in sand cultures under controlled conditions using nutrient solutions which were adjusted with respect to either nitrogen (N) or phosphorus (P) concentrations (two separate experiments) with other elements non-limiting. Leaf expansion at successive nodes was measured non-destructively and analysed according to the Richard's function, revised to provide geometrically meaningful parameters that could be linked with the dynamics of leaf growth. The reparameterised form describes sigmoidal increase in area (W) over time (t) as follows:

W(t)= Wx(1+der(1+d)(to-t))-(1/d)

where W, (cm2) is the asymptotic value of W for large t, to (days) is the time at which W(t) undergoes its point of inflexion, r (days-1) is the relative rate of lamina expansion of W(t) at to, and d determines the shape of the curve W versus t, so that the inflexion point occurs further up the curve with larger d.
A comparison between N and P effects on leaf expansion parameters in plants showing similar net reduction in leaf mass and stem volume showed that Wx was more influenced by low N, whereas r was more sensitive to low P. A given reduction in canopy area due to nutrient deficiency was thus mainly attributable to smaller leaves on low N, but to fewer leaves on low P. Leaf photosynthesis (light-saturated in air) showed a curvilinear increase with tissue N and P, saturating above c. 2.5 mmol N (g dm)-1 and 100 μmol P (g dm)-1 in N and P experiments respectively. Leaf growth parameters Wx and r showed a similar dose response and highlight a potential use of those indices for analysis of growth response to N and P nutrition.
Changes in Carbon Isotope Discrimination in Grain Cereals From the North-Western Mediterranean Basin During the Past Seven Millenia
Authors: Araus JL , Buxo R
Published: January 2006

Carbon isotope discrimination (Δ) was determined for kernels of six-row barley and durum wheat cultivated in the north-western Mediterranean basin during the last seven millennia. Samples from the Neolithic, Bronze, Iron and Middle Ages came from different archaeological sites in Catalonia. Samples for the period 1910-20 and 1990 were also analysed. There was a slight decrease (P=0.10, carbonisation-corrected values) in Δ from the Neolithic to the Iron Age period and a much steeper decrease from the Middle Ages to 1910-20 (P<0.01). Since water-use efficiency and isotope discrimination are negatively correlated, from the pattern of change in Δ it is suggested that there has been a progressive increase in the water-use efficiency (WUE) of these cereals. Since the Middle Ages this has coincided with increases in atmospheric CO2 concentration. Thus, for a given relative humidity and air temperature, the estimated WUE (measured as the ratio of CO2 assimilation to transpiration) from the Neolithic to the Middle Ages samples ranged between 65-70% of present time WUE values, whereas WUE for 1910-20 was about 86% of present values.
Effects of Supplementary Ultraviolet-B Radiation on Rice and Pea Plants
Authors: He J , Huang LK , Chow WS , Whitecross MI , Anderson JM
Published: January 2006

To compare the effects of supplementary ultraviolet-B (UV-B) radiation on a tropical/subtropical and a temperate plant, two indica rice cultivars (Er Bai Ai and Lemont) and peas were exposed to supplementary UV-B radiation for 8 days (biologically effective irradiance of 0.68 W m-2, 12 h per day). Marked decreases occurred in the ratios of variable to maximum chlorophyll fluorescence yield and in the quantum yield of photosynthetic oxygen evolution over the 8 day treatment period. The greatest decline always occurred in pea leaves, while in rice, cv. Er Bai Ai was more susceptible to UV-B radiation than cv. Lemont. Compared with control plants, the content of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein decreased significantly after the UV-B treatment; the greatest decrease occurred in pea leaves, while the rate of decrease in rice was greater in cv. Er Bai Ai than cv. Lemont.
Over the 8 day UV-B treatment period, the increase of UV-B-absorbing compounds was greater in rice leaves than in pea leaves, and greater in cv. Er Bai Ai than in cv. Lemont, although cv. Lemont was more UV-B tolerant. We suggest that the increase in these compounds is not the only indicator of resistance to UV-B damage; other factors, yet to be identified, may also confer UV-B tolerance. While leaf orientation may be related to the severity of UV-B damage, naturally near-horizontal pea leaves were still much more susceptible to UV-B damage compared with rice leaves which were held horizontally over the 8 day treatment period. Brown spots appeared on the upper surface of leaves of cv. Er Bai Ai after 2 days of UV-B treatment and showed a cumulative increase with the duration of exposure. Our study confirms the multiplicity of photosynthetic responses and of different protective strategies that may account for the differential sensitivity of plants to supplementary UV-B radiation.