bluuebunny/crossref_metadata_2025 huggingface dataset:
Genotypic Variation in Transpiration Efficiency, Carbon-Isotype Discrimination and Carbon Allocation During Early Growth in Sunflower
Authors: Virgona JM , Hubick KT , Rawson HM , Farquhar GD , Downes RW
Published: January 2006

Transpiration efficiency of dry matter production (W), carbon-isotope discrimination (�) and dry matter partitioning were measured on six sunflower (Helianthus annuus L.) genotypes grown for 32 days in a glasshouse. Two watering regimes, one well watered (HW) and the other delivering half the water used by the HW plants (LW), were imposed.
Four major results emerged from this study. (1) There was significant genotypic variation in W in sunflower and this was closely reflected in Δ for both watering treatments. (2) The low watering regime caused a decrease in Δ but no change in W; nonetheless the genotypic ranking for either Δ or W was not significantly altered by water stress. (3) A positive correlation between W and biomass accumulation occurred among genotypes of HW plants. (4) Q, the ratio of total plant carbon content to leaf area, was positively correlated with W and negatively correlated with Δ.
These results are discussed with reference to the connection between transpiration efficiency and plant growth. In short, Δ can be used to select for W among young vegetative sunflower plants. However, selection for W may be accompanied by changes in other important plant growth characteristics such as Q.
The Activation of Genes of Wheat and Barley by Fungal Phytopathogens
Authors: Scott KJ , Davidson AD , Jutidamrongphan W , Mackinnon G , Manners JM
Published: January 2006

The induction of six infection-related mRNAs (IRmRNAs) was studied in barley and wheat following infection by different pathogens. Barley was inoculated with the compatible pathogens, chlorostriate mosaic virus, barley stripe virus, Pseudomonas syringae, Pyrenophora teres, Bipolaris sorokiniana, Erysiphe graminis f. sp. hordei and the incompatible pathogens E. graminis f. sp. tritici, Puccinia graminis f. sp. tritici and Py. tritici-repentis. Wheat was inoculated with the compatible pathogens B. sorokiniana, Pu. Graminis f. sp. tritici and E. graminis f. sp. tritici and the incompatible pathogen E. graminis f. sp. hordei. Induction of the IRmRNAs was observed after inoculation with fungi but not by bacterial or viral infection. The results demonstrated that necrotrophic fungi will induce the mRNAs at very early stages of infection. The IRmRNAs are thus not specifically related to obligate parasites. A comparison of the extent and speed of mRNA induction following infection of both wheat and barley by closely related fungal species suggested a role for IRmRNAs 2, 5 and 6 in non-host resistance reactions. These studies indicate that cereals may resist fungal pathogens by the early activation of a series of defence genes.
The Genetic Control of Chromosome Pairing in Wheat
Authors: Ji LH , Langridge P
Published: January 2006

Bread wheat is an allohexaploid with three pairs of homoeologous chromosomes. This means that each chromosome pair is present in three related but not truly homologous chromosomes. In order to maintain the integrity of the three chromosome sets, pairing must be very tightly controlled at meiosis to allow homologous but not homoeologous chromosomes to pair and recombine. Several genes (termed Ph genes) are known to be involved in controlling chromosome pairing in wheat, but the strongest effect has been associated with a gene on the long arm of chromosome 5B, Phl. The manipulation of this gene can be used to induce recombination between chromosomes that will not normally pair at meiosis. This has application in the introduction of new genetic information into wheat.
Elucidation of the mechanism of action of the Ph genes has centred around genetic and cytogenetic studies with little attempt to investigate the molecular biology or biochemistry of these genes. Isolation of genes in meiosis in yeast and genes associated with the aerly stages of meiosis in lily have provided a potential entry point into the identification of the analogous genes in wheat.
Direct Gene Transfer to Protoplasts
Authors: Larkin PJ , Taylor BH , Gersmann M , Brettell RIS
Published: January 2006

Direct transfer of genes to protoplasts is considered, using electroporation and polyethylene-glycol-induced plasmid uptake. Both transient expression and stable transformation are discussed, with data and comparisons from the following protoplast systems: Nicotiana plumbaginifolia suspension culture, Nicotiana tabacum leaf, Medicago sativa leaf and Triticum monococcum suspension culture.
The Transfer of Cytoplasmic and Nuclear Genomes by Somatic Hybridisation
Authors: Rose RJ , Thomas MR , Fitter JT
Published: January 2006

For somatic hybridisation between two species to be successful, specific regenerability, compatibility and selection criteria must be met. The development of new methodologies has reduced the reliance on auxotrophic and albino mutants in selection strategies. Somatic hybridisation allows the transfer of chloroplast, mitochondrial or nuclear genomes in a single-step procedure and can extend the transfer boundaries defined by sexual hybridisation. Cytoplasmic genomes can be transferred over wider genetic distances than nuclear genomes. We consider the transfer of the three genomes but with particular emphasis on chloroplasts.
Strategies for chloroplast transfer are reviewed. When no selection strategies for a particular chloroplast are utilised the regenerated plant will have chloroplasts from either one of the parents, but not a mixture of both. The rapid sorting out can be explained by the changes in plastid numbers that occur in the first few divisions. Biased segregation can frequently be related to an unequal input of plastids but, in some cases, plastid-mitochondrial-nuclear incompatibilities are presumably involved and more studies of the callus stage are required to identify these phenomena. Chloroplast DNA recombination is rare, consistent with known inheritance patterns and the relative conservation of the chloroplast genome. Stable heteroplasmy of chloroplasts as a result of somatic hybridisation has not been reported, although chloroplast DNA heteroplasmy occurs naturally in some species.
Mitochondria can be transferred in a similar fashion to chloroplasts but, as their numbers are higher, their segregation is less likely to be complete in the regenerated plant. There are many reports of mitochondrial DNA recombination and cloned fragments containing sites of intergenomic recombination have been obtained. It appears that fusion between these organelles is common.
Interspecific somatic hybridisation within a genus can produce nuclear hybrid plants that can be part of a breeding program to provide novel sources of germplasm. Aneuploids rather than amphiploids may be produced as a result of chromosome loss during the culture phase. Nuclear hybrids from wider crosses are usually infertile. However asymmetric somatic hybridisation offers the possibility of incorporating nuclear genetic material from more diverse sources.
Somatic hybridisation has an important rc le in complementing conventional breeding in providing the gross genetic structure of chloroplast, mitochondrial and nuclear genomes. Specific gene transfer technologies can fine-tune the genomes thus provided.
Molecular Genetics and Biology of Self-Incompatibility in Nicotiana alata, an Ornamental Tobacco
Authors: Mcclure BA , Haring V , Ebert PR , Anderson MA , Bacic A , Clarke AE
Published: January 2006

Glycoproteins are present in the styles of several self-incompatible species within the Solanaceae which segregate with particular alleles of the S-(self-incompatibility) gene. The amino acid sequences of style glycoproteins corresponding to different S-alleles of N. alata are homologous in some regions and variable in others. Homologous regions include N-terminal sequences as well as most of the glycosylation sites and cysteine residues. The isolated style S-glycoproteins inhibit in vitro growth of pollen tubes of several S-genotypes, with some specificity in the interaction. The isolated S-glycoproteins have ribonuclease activity which may be involved in their action in arrest of growth of incompatible (self) pollen.
Development of Geminivirus-Based Gene Vectors for Dicotyledonous Plants
Authors: Coutts RHA , Buck KW , Hayes RJ
Published: January 2006

Geminiviruses are small icosahedral plant viruses that contain circular single-stranded DNA as their genome. In tomato golden mosaic virus (TGMV), a geminivirus that infects dicotyledonous hosts, several genes involved in replication, spread of virus or DNA in plants, and possibly insect transmission have been identified. Gene replacement experiments suggest that useful plant gene expression vectors can be constructed from TGMV. Following the integration of stable master copies of vectors based on TGMV DNA into plant chromosomal DNA, heritable gene amplification of a number of bacterial genes has been demonstrated, suggesting exciting possibilities for similar amplification of plant genes in the future.
Re-Evaluation of the Effects of Glucose-6-Phosphate and Malate on the Catalytic Properties of Phosphoenolpyruvate Carboxylase From Cynodon dactylon Under Physiological Assay Conditions
Authors: Stamatakis SK , Skaliora I , Gavalas NA , Manetas Y
Published: January 2006

Some catalytic and regulatory properties of the day- and night-form of phosphoenolpyruvate carboxylase (EC 4.1.1.31) from Cynodon dactylon (L.) Pers. leaves were re-evaluated in the presence of high concentrations of glycerol in the assay medium. This cosolute, known to be preferentially excluded from the hydration sphere of some proteins, apparently promotes aggregation, through an increase of the enzyme concentration in a fraction of the total volume. In the presence of this cosolute in the assay medium: (a) glucose-6-phosphate does not activate the enzyme, (b) inhibition of the Vmax by malate is increased, particularly with the night-form of phosphoenolpyruvate carboxylase, whereas the day-form is more responsive at the Km levels, (c) the light activation, detected as an increase in the apparent affinity of the substrate phosphoenolpyruvate is maintained under the new assay conditions.
Effects of Nitrogen Source and Water Limitation on Growth, Transpiration Efficiency and Carbon-Isotope Discrimination in Peanut Cultivars
Authors: Hubick KT
Published: January 2006

Effects on growth of nitrogen nutrition and its interactions with water availability were explored in two experiments using cultivars of peanut (Arachis hypogaea L.). In one experiment plants of the two cultivars, Tifton-8 and Chico, were given relatively high (high-N) or low (low-N) amounts of nitrogen, supplied as ammonium nitrate. The low-N plants accumulated less dry matter and used less water than the high-N plants. Transpiration efficiency, the ratio of dry matter produced to water used (W), was not significantly affected by the nitrogen treatment and neither was carbon-isotope discrimination (Δ). Isolated measurements showed leaf gas-exchange characteristics during pod filling were not affected in Tifton-8, but assimiliation rate was reduced in the low-N treatment, compared to the high-N treatment, in Chico. The ratio of intercellular CO2 pressure to ambient CO2 pressure, pi/pa, in the short term was consistent with Δ in leaves, a longer term measurement of pi/pa. The allocation of dry matter to roots was affected in Tifton-8 but not in Chico. The ratio of plant dry matter to leaf area was unaffected by nitrogen level. In another experiment, with four cultivars-Tifton-8, Chico, Robut 33-1 and TMV2-the nitrogen source was varied by giving plants ammonium nitrate or having them acquire nitrogen through nodules. Two levels of water availability were incorporated with the nitrogen treatments in a factorial design. Plants were either watered well or grown on water stored in the soil, in addition to having different nitrogen sources. In this experiment, the method of nitrogen acquisition caused different reductions in dry-matter accumulation among cultivars when plants were water-limited. Dry-matter accumulation in nodulated plants was less than in plants given ammonium nitrate, and nodulated plants had smaller values of W than plants which were given ammonium nitrate. Growing plants on stored soil water also affected dry-matter accumulation but there was no significant effect on W. The differences among cultivars in W were maintained over the two experiments so that the ranking of cultivars in W was conserved. Dry matter allocation among plant parts was affected by water limitation and by the nitrogen source. Water limitation had a greater effect on dry-matter accumulation of plants that were given ammonium nitrate than it did on dry matter of nodulated plants. Plants that were nodulated allocated more dry matter to the pods than did those that were not nodulated and this response varied among cultivars. Cultivars which accumulated the most dry matter had the greatest W but these cultivars did not necessarily allocate the most dry matter to pods. Irrespective of treatment, there was a strong negative correlation between W and Δ in both experiments. The small variations in the relationship between W and Δ among cultivars indicated that there may have been differences among cultivars in the carbon cost of nitrogen acquisition when the plants were nodulated.
Estimating Nitrogenase Activity of Faba Bean (Vicia faba) by Acetylene Reduction (Ar) Assay
Authors: Herdina  , Silsbury JH
Published: January 2006

Methods of conducting acetylene reduction (AR) assay were appraised for estimating the nitrogenase activity of nodules of faba bean (Vicia faba L.). Factors considered were: (i) disturbance of plants when removing the rooting medium; (ii) assay temperature; (iii) the use of whole plants rather than detached, nodulated roots; (iv) diurnal variation in nodule activity; and (v) a decline in C2H4 production after exposure to C2H2. Plants growing in jars of 'oil dry' (calcined clay) had the same AR activity when assayed in situ in a closed system as when assayed after removal of the rooting medium. Assay temperatures of 12.5, 17.5 and 22.5°C influenced the specific rate of AR with the optimum at 17.5°C. Removal of the shoot resulted in a rapid decrease in AR activity in both vegetative and reproductive plants but the effect was much larger in the latter. AR and respiration by nodulated roots were closely linked and both varied markedly over a diurnal 12 h/12 h cycle. Since no fluctuation was found after nodules were detached, diurnal variation in the respiration of nodulated roots is attributed to change in nodule activity. Half of the dark respiration of nodulated roots was associated with respiration of the nodules and thus largely with N2 fixation. Since the AR assay provides no information on how electron flow in vivo is partitioned between reduction of N2 and reduction of protons, diurnal variation in hydrogen evolution (HE) in air and Ar/O2 in an open system was used to estimate this partitioning.
Diurnal variation in apparent N2 fixation estimated in this manner was examined at a 'low' PPFD (300 μmol m-2 s-1) and at 'high' (1300 μmol m-2 s-1) to explore whether variation could be attributed to change in carbohydrate supply. Although HE in air and in Ar/O2 were both closely linked with the respiration of the nodulated root, apparent N2 fixation showed only a slight diurnal variation at 'low' light and almost none at 'high'. Vegetative plants showed no C2H2-induced decline in activity with exposure to C2H2 but reproductive plants did. This difference appears to be an age effect rather than attributable to flowering per se, since a decline occurred even when plants were kept vegetative by disbudding. A closed system for AR assay appears satisfactory for vegetative faba bean but such an assay over a 40-min period during the reproductive stage would underestimate nitrogenase activity by about 20%.
A Comparison of the Respiratory Processes and Growth Rate of Selected Australian Alpine and Related Lowland Plant Species
Authors: Atkin OK , Day DA
Published: January 2006

Respiratory processes and growth rates of alpine and lowland species of three genera (Ranunculus, Plantago and Luzula) were compared. Relative growth rates were determined for the first 14 weeks of growth at two temperatures (7-10°C and 12-15°C). Generally, the relative growth rates of the alpine species were lower than those of their lowland relatives. Whole-plant respiration rates were measured and leaf slices from each species were used for a detailed analysis of respiratory pathways. Major differences were found between genera, particularly in their alternative oxidase activity, but respiratory patterns (both whole-plant respiration rates and the relative rates of cytochrome and alternative pathways in leaf slices) were maintained within a given genus, independent of the environmental or geographical origin of each species from that genus. The lack of correlation between growth rates and respiration rates suggests that the alpine plants used their respiratory products less efficiently than did the lowland species.
The Response to High Temperature Shock and Humidity Changes Prior to and During the Early Stages of Grain Development in Wheat
Authors: Tashiro T , Wardlaw IF
Published: January 2006

Transferring wheat (Triticum aestivum L. cv. Banks) from 21/16°C to high temperature (36/31°C) for intervals of 2 days in the period from head emergence to 10 days after anthesis resulted in grain sterility and specific forms of morphological and cellular damage depending on the stage of development of the grain at the time of transfer. Grain sterility was induced by high temperature 2-3 days prior to anthesis and this response was found to be considerably enhanced by high humidity. Parthenocarpic, abortive and shrunken grain were induced by high temperature between anthesis and 3 days after anthesis. High temperature from 6 to 10 days after anthesis resulted in notched, split and opaque grains.
Growth and Photosynthetic Responses of Spinach to Salinity: Implications of K+ Nutrition for Salt Tolerance
Authors: Chow WS , Ball MC , Anderson JM
Published: January 2006

To compare the effects of K+ under high and low salinity, spinach plants (Spinacia oleracea) were grown in nutrient solutions containing either 50 mM NaCl (low salinity) or 250 mM NaCl (high salinity), with a diurnal regime of 10 h light (~300 μmol photons m-2 s-1, 23°C) and 14 h dark (15°C). At each level of salinity, the nutrient KCl concentration was 0.01, 0.1, 1 or 10 mM.
The plant and shoot biomass was greater at low salinity than high salinity and increased with the logarithmic increase in nominal K+ concentrations supplied to the roots. Plant and shoot growth were related to the K+ uptake into the leaves, with leaves having a higher K+ content under low salinity than high salinity. Variation of the K+ content in the leaves, induced by the combinations of nutrient KCl concentrations with high or low salinity, were accompanied by changes in the photosynthetic capacity at light- and CO2-saturation per unit leaf area; there was a greater decrease in photosynthetic capacity with decreasing K+ supply to the roots under high salinity than under low salinity. The photosynthetic capacity was in turn highly correlated with the contents of cytochrome f and ATP synthase per unit leaf area. Under conditions of high salinity and low K+ supply, a reduction in the quantum yield of oxygen evolution also occurred, due to malfunction of photosystem II and, apparently, an increased proportion of light absorbed by non-photosynthetic tissue. The decreases in photosynthetic capacity and quantum yield partly account for the lower plant and shoot biomass at high salinity and low nutrient KCl concentrations.
Our results suggest strongly that there are higher K+ requirements for shoot growth under high than low salinity conditions, and that high concentrations of Na+ in the leaves may help to maintain turgor, but cannot substitute for adequate K+ levels in the leaves, presumably because K+ is specifically required for protein synthesis. Increasing the K+ supply at the roots can ameliorate reductions in plant and shoot biomass imposed by an increase in salinity.
Quantum Yields of Photosystem II Electron Transport and Carbon Dioxide Fixation in C4 Plants
Authors: Krall JP , Edwards GE
Published: January 2006

The quantum yields of non-cyclic electron transport from photosystem II (determined from chlorophyll a fluorescence) and carbon dioxide assimilation were measured in vivo in representative species of the three subgroups of C4 plants (NADP-malic enzyme, NAD-malic enzyme and PEP-carboxykinase) over a series of intercellular CO2 concentrations (CI) at both 21% and 2% O2. The CO2 assimilation rate was independent of O2 concentration over the entire range of Ci (up to 500 μbar) in all three C4 subgroups. The quantum yield of PS II electron transport was similar, or only slightly greater, in 21% v. 2% O2 at all Ci values. In contrast, in the C3 species wheat there was a large O2 dependent increase in PS II quantum yield at low CO2, which reflects a high level of photorespiration. In the C4 plants, the relationship of the quantum yield of PS II electron transport to the quantum yield of CO2 fixation is linear suggesting that photochemical use of energy absorbed by PS II is tightly linked to CO2 fixation in C4 plants. This relationship is nearly identical in all three subgroups and may allow estimates of photosynthetic rates of C4 plants based on measurements of PS II photochemical efficiency. The results suggest that in C4 plants both the photoreduction of O2 and photorespiration are low, even at very limiting CO2 concentrations.
Photoinhibition Causes Loss of Photochemical Activity Without Degradation of D1 Protein
Authors: Cleland RE , Ramage RT , Critchley C
Published: January 2006

Illumination of isolated thylakoids or intact leaves with excess light resulted in a decline in photosynthetic activity measured as primary charge separation in photosystem II (ΔA320), photosystem II- dependent electron transport, or leaf oxygen evolution. It is concluded that the primary damage causing photoinhibition involves inactivation of the reaction centre function, and that degradation of Dl may be a consequence of that event.
Route of Substrate Movement Into Wheat Endosperm. I. Carbohydrates
Authors: Ugalde TD , Jenner CF
Published: January 2006

Experiments were conducted to define the routes of soluble carbohydrate movement within developing wheat grains. Radioactive soluble carbohydrates originating from photosynthetic activity in the ear moved longitudinally in the tissues at the base of the crease, into the endosperm cavity, and radially across the endosperm in an outward direction. Surgical treatments were used to disrupt transport pathways. Their effects on delivery of carbohydrates to the endosperm were determined mainly by time-dependent profiles of radioactivity across the grain. Disruption to longitudinal movement within tissues at the base of the crease prevented any detectable transfer of radioactive carbohydrates to the grain's main vascular bundle, the endosperm cavity, and the endosperm distal to the site of the block. Disrupting movement in the stalk showed that soluble carbohydrates deriving from photosynthetic activity in the inner pericarp move to the endosperm also via the endosperm cavity. There was no evidence for a direct inward radial pathway from the inner pericarp. The nucellar epidermis and aleurone layer lie on the inside of the developing cuticular layers. Disrupting any circumferential movement of soluble carbohydrates around the grain in these or any other tissues had no noticeable effect on delivery of soluble carbohydrates to the endosperm. The results are discussed in relation to the anatomy of tissues that appear to have the potential for a transport function.
Route of Substrate Movement Into Wheat Endosperm. II. Amino Acids
Authors: Ugalde TD , Jenner CF
Published: January 2006

Detached spikelets of wheat were cultured on solutions containing [3H]glutamine and [14C]sucrose in a series of experiments designed to define the pathways of amino acid movement in developing wheat grains and endosperm. Some functions measured on the spikelets provide confidence that the system is valid for studies on transport. Microdissection was used to determine time-dependent distributional patterns of [3H]amino acids and [14C]soluble carbohydrates along a radial axis from the vascular bundle at the base of the crease to the inner pericarp on the dorsal surface. Surgical treatments were used to disrupt putative transport pathways. Amino acids moved along the grain in the tissues at the base of the crease, into the endosperm cavity, and radially across the endosperm in an outward direction. Any longitudinal movement within the endosperm was small. Amino acids moved also into tissues surrounding the endosperm, but there was no evidence for an inward radial route to the endosperm. Hence, amino acids destined for deposition in the endosperm move within the grain and endosperm along the same pathways as shown previously for movement of soluble carbohydrates. Gradients of protein deposition across wheat endosperm, increasing in an outward direction, are not due to proximity or direction of substrate supply. Solutes moving to the inner pericarp did not rely on a route involving the main vascular bundle of the grain, but they moved into the inner pericarp from a basal point.
Responses of Rhizobium-inoculated and nitrogen-supplied Phaseolus vulgaris and Vigna unguiculata plants to root volume restriction
Authors: Izaguirre-Mayoral María Luisa , Mallorca Margarita Sicardi de
Published: January 2006

Present investigation was undertaken to analyse the effect of root volume
restriction on the physiological performance of
Rhizobium-inoculated
(R+ ) and nitrogen-supplied
(N+) cowpea
(Vigna unguiculata (L.) Walp. var. Tuy.) and bean
(Phaseolus vulgaris L. var. Montalbán.) plants.
Restriction of root volume (RRV) was imposed via an 8-fold reduction in the
rooting space. Plants were grown under controlled conditions and an unlimited
availability of water and nutrients. For both plant species, RRV reduced the
dry weight of roots, shoots and nodules, retarded the rate of leaf initiation
and development, and increased the leaf chlorophyll concentration, regardless
of the source of nitrogen. In contrast, RRV did not alter the shoot/root,
leaf/root and nodule/root ratios, the concentration of total reducing
sugars in shoots, roots and nodules, the leaf relative water content or the
concentration of Rubisco in mature leaves of
R+ and
N+ bean and cowpea plants. Concentration of ureide
and α-amino-N in shoots and nodules of
R+ plants as well as of
α-amino-N in shoots of N+ plants were also
not affected by RRV, and abscission of trifoliolated leaves was not recorded
in any of the treatment combinations. We conclude that dwarfism of RRV plants
was not due to water stress, decreased rates of assimilation, increased
abscisic acid, sink/source alterations, or to a reduction on the
effectiveness of the symbiotic process or of nitrogen uptake in
R+ and
N+ plants, respectively.
Stomatal and non-stomatal limitations of photosynthesis under water stress in field-grown grapevines
Authors: Escalona J. M. , Flexas J. , Medrano H.
Published: January 2006

Long-term induced water stress in field-grown grapevine leads to a progressive
decline of stomatal conductance, accompanied by a decrease in CO
2 assimilation (40%). The apparent quantum yield
also decreases (59%), which may reflect a relative increase in
alternative processes for electron consumption. There is also a shift to
non-stomatal regulation, as judged from significant depletions (37%) in
maximum photosynthesis rate at saturating CO 2 related
to limited ribulose biphosphate (RuBP) regeneration, whereas small,
non-significant effects are observed on carboxylation efficiency. A high
correlation (87%) between photosynthesis and stomatal conductance is
observed for all experimental data and declines in intercellular CO
2 concentration parallel reductions in stomatal
conductance. The data show that field response of grapevines to increasing
soil water deficit involves stomatal and non-stomatal effects but, due to
gradually induced drought, regulation mechanisms able to adjust mesophyll
capacity to the average CO 2 supply. The non-stomatal
adjustment seems to be exerted mainly in metabolic pathways related with the
RuBP regeneration. Contrasting characteristics were observed for both
cultivars. Tempranillo exploited the non-stressful conditions successfully,
whereas Manto Negro, responding to its reputation as more drought resistant,
showed a higher intrinsic water use efficiency, particularly for low water
availability. This advantage seems to be due to lower non-stomatal
limitations.
Grana formation: entropy-assisted local order in chloroplasts?
Authors: Chow W. S.
Published: January 2006

Grana formation is a prominent feature of the ultrastructure of chlorophyll
b-containing chloroplasts, serving to fine-tune
photosynthetic efficiency. This paper examines the physical forces that
determine the state of minimum free energy of the chloroplast as manifested by
grana formation. In particular, it considers the interplay of van der Waals
attraction, electrostatic repulsion and short-range hydration repulsion
between thylakoid membranes. In addition to these interactions as determinants
of the free energy of the system, it is also proposed that ordering of
thylakoid membranes and of intramembrane protein complexes is driven by an
increase in the overall entropy of the system. This local order may partly
come about by an increase in entropy associated with a greater free volume for
diffusion of membrane and stromal components.
Cytoplasmic sucrolytic activity controls tomato fruit growth under salinity
Authors: Balibrea María E. , Parra Margarita , Bolarín María C. , Pérez-Alfocea Francisco
Published: January 2006

Tomato (Lycopersicon esculentum (L.) Mill cv.
Volgogradskij) crop yield reduction under salinity is mainly due to a decrease
in dry matter accumulation rate during the early fruit-growing period
(15–35 days after anthesis, DAA). However, partial restoration of growth
occurred during the late phase of fruit development (35–45 DAA). Salt
stress provoked sucrose accumulation in both apoplastic and symplastic spaces
of up to 15 mМ, as well as acidification and
Na+ accumulation in the apoplast and a transient
increase in starch content. According to the hypothesis stated, the decrease
in apoplastic pH imposed by salinity caused a loss of insoluble acid invertase
activity, which was associated with sucrose accumulation, and resulted in a
limiting step for fruit growth under moderate and high salinities. As a
consequence of sucrose accumulation in the symplast, cytoplasmic sucrolytic
activity (neutral invertase + sucrose synthase) was induced. It acted as
a metabolical adaptive response by regulating the sucrose homeostasis and
controlling the assimilate import, dry matter accumulation and fruit growth
under salt conditions. Although the compartmentation of the hexose excess into
starch could be considered as another adaptive response, the key enzyme
ADP-glucose pyrophosphorylase does not seem to be important in the control of
fruit growth under salinity conditions.
Calculation of the oxygen isotope discrimination factor for studying plant respiration
Authors: Henry Beverley K. , Atkin Owen K. , Farquhar Graham D. , Day David A. , Millar A. Harvey , Menz R. Ian
Published: January 2006

Measurement of discrimination against 18O during dark
respiration in plants is currently accepted as the only reliable method of
estimating the partitioning of electrons between the cytochrome and
alternative pathways. In this paper, we review the theory of the technique and
its application to a gas-phase system. We extend it to include sampling
effects and show that the isotope discrimination factor,
D, is calculated as –dln(1 +
δ)/dlnO*, where δ is isotopic
composition of the substrate oxygen and
O*=[O2]/[N2]
in a closed chamber containing tissue respiring in the dark. It is not
necessary to integrate the expression but, if the integrated form is used, the
resultant regression should not be constrained through the origin. This is
important since any error in D will have significant
effects on the estimation of the flux of electrons through the two pathways.
Chemiluminescence of Mn 2+-activated Rubisco: temperature and pH responses differ between L2 and L8S8 forms, and inhibitors provide no evidence for involvement of active oxygen species
Authors: Cox Sean D. , Andrews T. John , Lilley Ross McC.
Published: January 2006

Chemiluminescence associated with the oxygenase activity of Mn
2+ -activated D-ribulose-1,5- bisphosphate
carboxylase/oxygenase (Rubisco) was investigated using the L
8 S 8 enzymes from spinach and
Synechococcus PCC6301, and the L 2
enzyme from Rhodospirillum rubrum. Chemi-luminescence
was measured with a luminometer and oxygenase activity with an oxygen
electrode. The relative luminescence yield (light emitted per oxygenase
turnover) in the steady-state at pH 8.1 was highest with spinach Rubisco; the
enzymes from Synechococcus and
R. rubrum exhibited approximately one half and one
fifth, respectively, of the spinach value. The relative luminescence yield
from the L 8 S 8 enzymes was
unaffected by temperature (20–40°C) and pH (7.6–9.0). In
contrast, the luminescence yield of R. rubrum Rubisco
varied with temperature and pH, and its O 2 -consuming
activity exhibited a lower activation energy than that of the L
8 S 8 enzymes. The singlet O
2 -reactive compounds diazabi-cyclo[
2.2.2]octane and 10,10′-dimethyl-9,9′-biacridinium dinitrate
(lucigenin) had no effect on chemi-luminescence. Other compounds tested
inhibited chemiluminescence but also inhibited O 2
consumption. The inhibition of chemiluminescence of spinach Rubisco required
several seconds to exert its maximal effect, implying that the inhibitors had
access to the active site only at a particular stage of the catalytic cycle.
The data are consistent with the Mn 2+ ion at the
active site being the source of the luminescence.
Loss of chlorophyll with limited reduction of photosynthesis as an adaptive response of Syrian barley landraces to high-light and heat stress
Authors: Havaux Michel , Tardy Florence
Published: January 2006

The Syrian barley landrace Tadmor is adapted to semi-arid environments and
characterized by a reduced chlorophyll content (ca
−25% on a leaf area basis) compared to improved barley genotypes,
such as the European variety Plaisant. Tadmor leaves had reduced stomatal
conductance (gS ) compared to
Plaisant leaves both under well-watered conditions and during water stress.
Both Tadmor and Plaisant barley seedlings were progressively acclimated to
high temperature (39°C) and high photon flux density (1600 µmol
photons m −2 s −1 ).
During acclimation, the chlorophyll content of Tadmor leaves further decreased
whereas the carotenoid concentration remained virtually unchanged, leading to
a marked increase in the carotenoid:chlorophyll ratio. The chlorophyll content
of acclimated Tadmor leaves was reduced to approximately half of the
chlorophyll content of Plaisant leaves grown under the same conditions. Loss
of chlorophyll in Tadmor leaves was not observed when only one environmental
factor was increased (temperature or photon flux density). In the improved
variety, both chlorophylls and carotenoids accumulated during acclimation to
heat and strong light, leading to an almost constant carotenoid:chlorophyll
ratio. The loss of chlorophyll in the Syrian landrace was associated with
limited changes in the photosynthetic characteristics of the leaves (oxygen
evolution, electron transport quantum yield, chlorophyll antenna size of
photosystem II). Plaisant leaves, but not Tadmor leaves, exhibited symptoms of
oxidative damage during growth in strong light at high temperature. When the
stomata were closed, sudden exposure to bright light caused a smaller increase
in leaf temperature in Tadmor than in Plaisant. Taken together, our results
suggest that the ‘low chlorophyll’ feature of Syrian barley
landraces is related to their drought adaptation which is manifested by a low
g S : the very low chlorophyll content decreases leaf
absorbance which, in turn, reduces the potentially damaging heating effect of
high solar radiation in droughted plants whose stomata are closed.
Effects of growth temperature on the response of lupin stomata to drought and abscisic acid
Authors: Osório M. Leonor , Rodrigues M. Lucília , Chaves M. Manuela , Correia Maria João
Published: January 2006

To assess how growth temperature affects stomatal responses to
xylem-transported abscisic acid (ABA), leaf conductance (g), the
concentrations of ABA and calcium ions, and the pH of the xylem sap were
measured in well-watered and water-stressed
Lupinus albus L. plants grown under two thermal regimes:
10/15°C and 20/25°C, night/day temperature. Moderate water
deficit was imposed, at the same thermal time, and induced a significant
reduction in g regardless of temperature. In the morning, g was higher in
plants grown at 20/25°C than in cooler conditions, and these
differences could not be explained by dissimilarities in shoot water status or
xylem ABA concentration. At midday, the apparent stomatal sensitivity to
xylem-carried ABA was increased and the effect of temperature on the
relationship between g and xylem ABA was no longer observed. A positive effect
of higher temperature on stomatal aperture was also evident when artificial
sap containing ABA was fed to leaves of well-watered plants. In response to
exogenous ABA, stomata closed to the same extent as observed in the morning in
water-stressed plants. However, exogenous ABA feeding could not mimic the
relationship between g and xylem ABA determined at midday in intact plants.
The pH and the concentration of calcium in xylem were not affected by
temperature. At midday, however, the calcium concentrations were higher in
water-stressed than in well-watered plants. These changes in the
concentrations of calcium or other xylem components, such as ABA conjugates,
together with possible changes in the ability of the leaves to degrade
and/or to compartmentalise ABA, may partly explain the midday increase in
the apparent stomatal sensitivity to xylem ABA.
The impact of elevated atmospheric CO2 and nitrate supply on growth, biomass allocation, nitrogen partitioning and N2 fixation of Acacia melanoxylon
Authors: Schortemeyer Marcus , Atkin Owen K. , McFarlane Nola , Evans John R.
Published: January 2006

The interactive effects of nitrate supply and atmospheric
CO2 concentration on growth, N2
fixation, dry matter and nitrogen partitioning in the leguminous tree
Acacia melanoxylon R.Br. were studied. Seedlings were
grown hydroponically in controlled-environment cabinets for 5 weeks at seven
15N-labelled nitrate levels, ranging from 3 to 6400 mmol
m–3. Plants were exposed to ambient (~350
µmol mol–1) or elevated (~700 µmol
mol–1) atmospheric CO2 for 6
weeks. Total plant dry mass increased strongly with nitrate supply. The
proportion of nitrogen derived from air decreased with increasing nitrate
supply. Plants grown under either ambient or elevated
CO2 fixed the same amount of nitrogen per unit nodule
dry mass (16.6 mmol N per g nodule dry mass) regardless of the nitrogen
treatment. CO2 concentration had no effect on the
relative contribution of N2 fixation to the nitrogen
yield of plants. Plants grown with ≥50 mmol m–3
N and elevated CO2 had approximately twice the dry mass
of those grown with ambient CO2 after 42 days. The rates
of net CO2 assimilation under growth conditions were
higher per unit leaf area for plants grown under elevated
CO2. Elevated CO2 also decreased
specific foliage area, due to an increase in foliage thickness and density.
Dry matter partitioning between plant organs was affected by ontogeny and
nitrogen status of the plants, but not by CO2
concentration. In contrast, plants grown under elevated
CO2 partitioned more of their nitrogen to roots. This
could be attributed to reduced nitrogen concentrations in foliage grown under
elevated CO2.
Nitrogen requirements for maximum growth and photosynthesis of rice, Oryza sativa L. cv. Jarrah grown at 36 And 70 Pa CO2
Authors: Aben Silvestre K. , Seneweera Saman P. , Ghannoum Oula , Conroy Jann P.
Published: January 2006

The hypothesis that growth of rice (Oryza sativa L. cv.
Jarrah) at elevated atmospheric CO2 partial pressure
alters leaf nitrogen (N) concentrations required to support maximum dry mass
production and photosynthetic rates during the period of rapid tiller
initiation was tested by growing plants for 30 days in unstirred
sand/hydroponic culture with N concentrations of 5, 20, 40, 60 and 100 mg
N L–1. Maximum growth and photosynthetic potential
was greater at 70 than 36 Pa CO2 at all N concentrations
in the solution. Elevated CO2 reduced leaf N
concentrations required to support 90% of maximum growth and
photosynthetic rates (critical concentration) from 40 to 27 g
kg–1 for growth and from 45 to 30 g
kg–1 for photosynthesis. Morphological changes at
elevated CO2 included increased tiller numbers and
reduced leaf area ratio. The latter could be explained by lower plant N
concentrations which occurred at high CO2 at each N
concentration in the solution, primarily due to lower leaf blade and root N
concentrations. Changes in tiller numbers at high CO2
were unrelated to leaf or plant N but were strongly correlated with leaf
soluble carbohydrate concentrations. We conclude that elevated
CO2 alters the nutritional physiology of rice during the
rapid tillering phase in a way that increases the efficiency of N utilisation
for growth and photosynthesis.
Role of LHCII-containing macrodomains in the structure, function and dynamics of grana
Authors: Garab G. , Mustárdy L.
Published: January 2006

In higher plants and green algae two types of thylakoids are distinguished,
granum (stacked) and stroma (unstacked) thylakoids. They form a
three-dimensional (3D) network with large lateral heterogeneity: photosystem
II (PSII) and the associated main chlorophyll
a/b light-harvesting complex
(LHCII) are found predominantly in the stacked region, while PSI and LHCI are
located mainly in the unstacked region of the membrane. This picture emerged
from the discovery of the physical separation of the two photosystems
(Boardman and Anderson 1964). Granal chloroplasts possess significant
flexibility, which is essential for optimizing the photosynthetic machinery
under various environmental conditions. However, our understanding concerning
the assembly, structural dynamics and regulatory functions of grana is far
from being complete. In this paper we overview the significance of the
three-dimensional structure of grana in the absorption properties, ionic
equilibrations, and in the diffusion of membrane components between the
stacked and unstacked regions. Further, we discuss the role of chiral
macrodomains in the grana. Lateral heterogeneity of thylakoid membranes is
proposed to be a consequence of the formation of macrodomains constituted of
LHCII and PSII; their long range order permits long distance migration of
excitation energy, which explains the energetic connectivity of PSII
particles. The ability of macrodomains to undergo light-induced reversible
structural changes lends structural flexibility to the granum. In purified
LHCII, which has also been shown to form stacked lamellar aggregates with long
range chiral order, excitation energy migrates for large distances; these
macroaggregates are also capable of undergoing light-induced reversible
structural changes and fluorescence quenching. Hence, some basic properties of
grana appear to originate from its main constituent, the LHCII.
Photoinhibitory printing on leaves, visualised by chlorophyll fluorescence imaging and confocal microscopy, is due to diminished fluorescence from grana
Authors: Osmond Barry , Schwartz Owen , Gunning Brian
Published: January 2006

By analogy with the starch printing technique, it was hypothesised that
photoinhibition could be used to print images on leaves that would be
invisible to the eye, but easily revealed by chlorophyll fluorescence imaging.
We first illustrate the process of chlorophyll fluorescence printing on leaves
of the shade plant, Cissus rhombifolia, using
photographs of artefacts from starch printing experiments in the laboratory of
Molisch. We then use portraits of current leaders in chlorophyll fluorescence
research to demonstrate the stability of these images in living tissues. Text
printing from microfilm of Ewart’s pioneering studies in photoinhibition
shows the resolution of the method with the fixed-focus, portable, imaging
system used here. The stability of images, as well as quenching analysis of
images and of leaves, suggests that localised photoinactivation, rather than
sustained photoprotection, is responsible for the detail displayed by
fluorescence printing. Electron micrograph positives of stained thylakoids can
be printed to create an illusion of what is imagined to be the source of
chlorophyll fluorescence at the membrane level. Individual chloroplasts in
adjacent cells under the grid pattern of granal stacks printed on leaves were
also examined using a confocal microscope. Compared with chloroplasts in the
shaded parts of the grid, those in the photoinactivated parts of the grid show
greatly reduced chlorophyll autofluorescence. Moreover, these chloroplasts
have lost the localised bright fluorescence from grana. Comparisons of
fluorescence yields show that relative chlorophyll autofluorescence from grana
observed in the confocal microscope parallels that determined in leaves. Our
experiments provide direct visual evidence that fluorescence from grana is
lost following photoinactivation of photosystem II
in vivo.
The effect of perturbations in temperature and photon flux density on the growth and photosynthetic responses of five pasture species to elevated CO2
Authors: Greer Dennis H. , Laing William A. , Campbell Bruce D. , Halligan Elizabeth A.
Published: January 2006

Five pasture grass species with known
differences in responses to elevated CO2 were grown at
18 and 28˚C, 350 and 700 mol mol –1
CO2 and a photon flux density of 700 mol m
–2 s –1 in controlled
conditions. After 2 (28˚C)–3 (18˚C) weeks growth, plants were
transferred to reciprocal temperature conditions and to 70% shade while
other plants were maintained as controls. The objective was to impose
environmental perturbations to evaluate how carbon supply and sink demand
affected CO2 responses in different species. Responses
were assessed by biomass accumulation and photosynthesis. Ranking of the
growth response to CO2 was similar between 18 and
28˚C. Lolium perenne and
Festuca arundinacea showed the lowest response to
elevated CO2 and Poa annua and
Trifolium repens the highest response. Response to
CO2was highest at 28˚C for all species and
significantly lower at 18˚C. When transferred to different conditions,
the growth response to CO2 of all species changed
markedly, and their relative ranking also changed. Photosynthetic responses to
CO2 were consistently higher for all species at 28 than
at 18˚C, but was enhanced by transfer to low temperature and suppressed
by transfer to high temperature. The photosynthetic response to
CO2, when multiplied by the leaf area of the plants, was
linearly related to the growth response to CO2 across
almost all treatments and species. This implies that there is an intrinsic
relationship between the responses of the two processes of photosynthesis and
growth when plants are exposed to elevated CO2.