bluuebunny/crossref_metadata_2025 huggingface dataset:
Photosynthetic Acclimation of Alocasia macrorrhiza (L.) G. Don
Authors: Chow WS , Qian L , Goodchild DJ , Anderson JM
Published: January 2006

The photosynthetic acclimation of Alocasia macrorrhiza (L.) G. Don, a species naturally occurring in deep shade in rainforests, has been studied in relation to a wide range of controlled irradiances during growth (~3-780 �mol photons m-2 s-1 of fluorescent or incandescent light, 10 h light/ 14 h dark). At the maximum growth irradiances, the light- and CO2-saturated rates of O2 evolution per unit leaf area were ~4 times as high as at low irradiance, and approached those of glasshouse-grown spinach. Growth at maximum irradiances reduced the quantum yield of O2 evolution only slightly.
Changes in the anatomy of leaf tissue, the ultrastructure of chloroplasts and the composition of chloroplast components accompanied the changes in photosynthetic functional characteristics. At low growth irradiance, palisade cell chloroplasts were preferentially located adjacent to the distal periclinal cell walls and had large granal stacks, and the destacked thylakoids had a very low surface charge density. In contrast, at higher growth irradiance, palisade cell chloroplasts were preferentially located adjacent to the anticlinal cell walls; they had small granal stacks, large stromal space, and a high surface charge density on the destacked thylakoids. The number of chloroplasts per unit section length increased with growth irradiance. Ribulosebisphosphate carboxylase activity per unit leaf area increased markedly with irradiance. Photosystem II, cytochrome f and latent ATPase activity per unit chlorophyll increased to a lesser extent. While the chlorophyll a/chlorophyll b ratio increased substantially with growth irradiance, the chlorophyll content per unit leaf area declined slightly.
Our results show that coordinated changes in the structure of leaf tissue, and the organisation and composition of chloroplast components are responsible for Alocasia being capable of acclimation to high as well as low irradiance.
Molecular Events of Photoinhibitory Inactivation in the Reaction Centre of Photosystem II
Authors: Cleland RE
Published: January 2006

The events of photoinhibition were examined at the molecular level. The evidence presented here suggests that the primary event of photoinhibition involves inactivation of photosystem II reaction centre function. Chlorophyll fluorescence emission and excitation spectra and fluorescence induction transients were suppressed after photoinhibitory treatment. Such fluorescence is directly dependent on photosystem II photochemistry. In addition, photoinhibition caused a decline in charge separation measured by the absorbance change at 320 nm arising from the light-induced reduction of the primary acceptor of photosystem II, QA. Inhibition of this parameter is indicative of damage to a component involved in primary photochemistry. That the effect of high light treatment could not be correlated with any loss of the D1 protein supports the suggestion that a cofactor involved in primary photochemistry is the initial site of photoinhibition. It is possible that D1 may eventually be lost as a result of such damage. The reaction centre chlorophyll of photosystem II, P680, is suggested to be the cofactor involved. Possible mechanisms of damage are discussed with reference to the prosthetic components of the reaction centre of photosynthetic bacteria.
Photosynthetic Utilisation of Lightflecks by Understory Plants
Authors: Pearcy RW
Published: January 2006

The light environment in forest understories is highly dynamic because the weak shade light is period- ically punctuated by lightflecks lasting from a second or less to tens of minutes. Although present for only a small fraction of the day, these lightflecks can contribute more than two-thirds of the photosynthetically active radiation. Several factots are of importance in determining the capacity of a leaf to utilise lightflecks. Following long low-light periods the induction state of the photosynthetic apparatus is limiting. During induction, 20-60 min may be required before maximum assimilation rates are reached due first to a light activation requirement. of ribulose-1,5-bisphosphate carboxylasel oxygenase and later to the light-induced stomatal opening. Continuous light is not required and induction occurring during a series of lightflecks results in higher carbon gain for later as compared to earlier lightflecks. Post-illumination CO2 fixation resulting from utilisation of metabolite pools built up during the lightfleck can significantly enhance carbon gain during short (5-20 s) lightflecks. The carbon gain of a leaf in response to a lightfleck is a consequence of the limitations imposed by induction state plus the enhancements due to post-illumination CO2 fixation. In the field, this will depend on the frequency and duration of the lightflecks and the duration of the intervening low-light periods.
Growth and Photosynthetic Response to Light and Nutrients of Flindersia brayleyana F. Muell., A Rainforest Tree With Broad Tolerance to Sun and Shade
Authors: Thompson WA , Stocker GC , Kriedemann PE
Published: January 2006

Seed from four species of rainforest trees with widely contrasting sunlight requirements for growth and development were sown within disturbance gaps amidst mature forest on the Herberton Range in North Queensland. Observations on seedling persistence plus comparative growth of young trees of Acacia aulacocarpa, Toona australis, Flindersia brayleyana and Darlingia darlingiana (species ranked according to adaptation from full sun to deep shade) confirmed a broad tolerance of Flindersia to sunlight under all conditions, from wide to narrow gaps (minimum 0.6% full sun equivalent).
Photosynthetic attributes which underlie such broad tolerance were subsequently inferred from single leaf gas exchange, plus foliar analyses of nitrogen, phosphorus and chlorophyll on tree seedlings held for 180 days under two nutrient × three irradiance levels adjusted to represent natural irradiance incident upon the forest floor (low), mid-canopy (medium) and emergent crowns (high irradiance treatment). Medium irradiance plus high nutrients proved optimal for leaf expansion, chlorophyll content and photosynthesis in air.
Growth under low irradiance was characterised by thinner leaf palisade tissue, lower rates of dark respiration, increased leaf chlorophyll per unit nitrogen and lower light compensation point for photosynthesis. Such leaves retained a relatively high photosynthetic capacity despite these other shade-leaf attributes.
High irradiance plus low nutrients proved supraoptimal for leaf expansion and expression of photosynthetic activity. Chronic photoinhibition appeared to prevail because apparent quantum yield was reduced, while photosynthetic processes on a nitrogen basis were substantially impaired. Nitrogen use efficiency, as inferred from leaf chlorophyll content, light saturated CO2 assimilation rate, electron transport rate and carboxylation rate on a nitrogen basis declined with increasing growth irradiance.
Some ecological implications for the establishment and growth of these rainforest tree species in disturbance gaps are discussed.
C4 Photosynthesis: Activities of Photosynthetic Enzymes in a Virescent Mutant of Maize Having a Low-Temperature Induced Chloroplast Ribosome Deficiency
Authors: Edwards GE , Jenkins CLD
Published: January 2006

A virescent mutant of maize (v16/v16), which has a low temperature induced deficiency in 70S ribosomes, was used to examine whether the enzymes of the C4 pathway and other photosynthetic enzymes are synthesised on chloroplast ribosomes. The mutant and control plants were grown at 20°C and 30°C and the rates of photosynthesis and enzyme activities were compared. There was no photosynthesis in v16/v16 grown at 20°C (pale yellow), while plants grown at 30°C (normal green) had rates equivalent to the wild type and normal enzyme activities. On a leaf area basis, with v16/v16 grown at 20°C, the activity of ribulose 1,5-bisphosphate (RuP2) carboxylase was only 2% that of the wild type grown at this temperature, while the activities of enzymes of the C4 cycle were much higher (as a percentage of the wild type activity: pyruvate,PI dikinase, 22%; NADP-malate dehydrogenase, 35%; NADP-malic enzyme, 47%; and phosphoenolpyruvate (PEP) carboxylase, 68%). In another experiment v16/v16 plants were grown initially at 30°C, then transferred to 20°C. After transfer to 20°C leaves previously formed under 30°C remained green and had normal rates of photosynthesis and enzyme activities, but newly formed leaves were pale yellow (only 11% as much Chl) and had low photosynthesis rates (2% of normal) and RuP2 carboxylase activity (5% of control). However, there was high activity of eight enzymes of the C4 cycle. The low activity of RuP2 carboxylase in the mutant grown at 20°C is consistent with the requirement of 70S ribosomes for its synthesis, while the high activities of enzymes of the C4 cycle, including those which are chloroplastic, suggest their synthesis is nuclear-encoded.
Submergence of Rice. I. Growth and Photosynthetic Response to CO2 Enrichment of Floodwater
Authors: Setter TL , Waters I , Wallace I , Bhekasut P , Greenway H
Published: January 2006

Growth and photosynthetic response of lowland rice following complete submergence is related to the concentration of CO2 dissolved in floodwater. Submergence of plants in stagnant solution at low CO2 concentration or solution gassed with air at 0.03 kPa CO2 (equilibrium of 0.01 mol m-3 dissolved CO2) decreased carbohydrates, and little or no growth occurred. Plants submerged in solutions gassed with 3-20 kPa CO2 in air (equilibrium of 0.9-6 mol m-3 CO2) showed at most small decreases in carbohydrates, and growth was up to 100% of the non-submerged plants.
At pH 7.5, there was little net photosynthetic O2 evolution by detached submerged leaves even at high HCO3- concentrations, which suggests that these rice leaves could utilise only CO2 and not HCO3-. At pH 6.5, O2 evolution in solutions in equilibrium with 7.4 kPa CO2 was 3-4 fold higher than in solutions in equilibrium with 0.6 kPa CO2. Photorespiration was indicated by a decrease in the rate of net O2 evolution with increasing external O2. In stagnant solutions this reduction of O2 evolution was pronounced; at a CO2 concentration of 0.25 mol m-3 net O2 evolution ceased when the O2 concentration in the water had reached only 0.125 mol m-3. The requirement of photosynthesis for a combination of high CO2 concentrations and low external O2 was presumably due to slow diffusion of these gases in the unstirred layer of solution around the leaves.
Growth, Photosynthesis and Distribution of Chloride, Sodium and Potassium Ions in Salt-Affected Quandong (Santalum acuminatum)
Authors: Walker RR
Published: January 2006

The growth and photosynthetic responses to salinity of the partial root parasite, the quandong or native peach [Santalum acuminatum (R.Br.) A. DC.], were investigated under glasshouse conditions. Plants were established in a porous medium with strawberry clover (Trifolium fragiferum L.) as the host plant and subjected to salinities in the range 0.5-500 mol m-3 Cl- with accompanying cations Na+, Ca2+ and Mg2+ in the ratio 0.6 : 0.2 : 0.2 mequiv. L-1.
Growth of plants ceased during treatment with 500 mol m-3 Cl- and was markedly reduced by 300 mol m-3 Cl-. Treatment with 50, 100 or 200 mol m-3 Cl- had little effect on growth in the short term (up to 7 weeks), but treatment with 200 mol m-3 Cl- in the longer term (14 weeks) did reduce growth. Removal of the clover host plant from pots at the start of treatments had a detrimental effect on growth of both control and salt-treated plants and reduced total nitrogen concentration in leaves.
Photosynthetic rates per unit leaf area were reduced at salinities above 100 mol m-3 Cl- . Chlorophyll concentrations were also reduced, such that photosynthetic rates on a chlorophyll basis did not decrease despite leaf Cl- and Na+ concentrations (tissue water basis) of up to 490 and 404 mol mm-3, respectively. Water content (g H2O g-1 dry weight) of quandong leaves was increased by salinity, while water content and area of clover leaves decreased. There was a marked increase in Na- and reduction in K+ with resultant significant increases in Na : K ratio in mature leaves of salt-treated quandongs, but much smaller increases in Na : K ratio in stems and roots.
These data demonstrate the relatively high salt tolerance of the quandong, which can be classified as a salt-tolerant non-halophyte.
Leaf Gas Exchange and Water Relations of Lupins and Wheat. II. Root and Shoot Water Relations of Lupin During Drought-Induced Stomatal Closure
Authors: Jensen CR , Henson IE , Turner NC
Published: January 2006

Plants of Lupinus cosentinii Guss. cv. Eregulla were grown in a sandy soil in large containers in a glasshouse and exposed to drought by withholding water. Under these conditions stomatal closure had previously been shown to be initiated before a significant reduction in leaf water potential was detected. In the experiments reported here, no significant changes were found in water potential or turgor pressure of roots or leaves when a small reduction in soil water potential was induced which led to a 60% reduction in leaf conductance. The decrease in leaf conductance and root water uptake closely paralleled the fraction of roots in wet soil.
By applying observed data of soil water and root characteristics, and root water uptake for whole pots in a single-root model, the average water potential at the root surface was calculated. Potential differences for water transport in the soil-plant system, and the resistances to water flow were estimated using the 'Ohm's Law' analogy for water transport. Soil resistance was negligible or minor, whereas the root resistance accounted for 61-72% and the shoot resistance accounted for about 30% of the total resistance. The validity of the measurements and calculations is discussed and the possible role of root- to-shoot communication raised.
Modelling Stomatal Behaviour and and Photosynthesis of Eucalyptus grandis
Authors: Leuning R
Published: January 2006

Stomatal conductances, CO2 assimilation, transpiration and intercellular CO2 mol fractions of Eucalyptus grandis leaves were measured in the field using a portable, controlled environment cuvette. Test leaves were subjected to a range of temperatures, humidities, photon irradiances and external CO2 mol fractions. An empiral function, gsw = g0 + g1 Ahs/(cs-I'), was able to account for steady- state stomatal conductances g*sw, over a wide range of environmental conditions and leaf photosynthetic capacities. In this equation, termed the stomatal constraint function, A is CO2 assimilation rate, hs and cs are relative humidity and CO2 mol fraction at the leaf surface respectively, I' is the CO2 compensation point, g0 is conductance at A = 0 and gl is an empirical coefficient. Equations describing the supply of CO2 through stomata and demand for CO2 in photosynthesis were solved simultaneously with the constraint function to give a combined model of stomatal conductance, CO2 assimilation and intercellular CO2 mol fraction in terms of external environmental factors and several parameters describing C3 photosynthesis. The model provided a good description of experimental observations.
Current Applications of Tissue Culture in Plant Propagation and Improvement
Authors: Smith MK , Drew RA
Published: January 2006

Plant tissue culture involves the culture of all types of plant cells, tissues and organs under aseptic conditions. This definition also extends to the culture of excised embryos and to protoplast culture. An overview of tissue culture techniques and their applications in plant propagation and genetic improvement of plants is presented. The areas under review include: (1) embyro culture, (2) meristem culture, (3) micropropagation, (4) somatic embryogenesis, (5) somaclonal variation, (6) in vitro selection, (7) anther culture and (8) protoplast culture. Problems and limitations of each of the techniques are also discussed. Examples are given of work that has been undertaken or that is currently in progress on the application of these techniques to the improvement of Queensland's subtropical horticultural industries. Key examples are: (1) embryo culture to facilitate incorporation of genes conferring disease-resistance from wild Cucurbita species into cultivated varieties, (2) meristem culture for virus elimination in strawberries (Fragaria × ananassa) and sweet potato (Ipomoea batatas), (3) micropropagation for rapid increase in new varieties of ginger (Zingiber officinale) and pineapple (Ananas comosus) to enable more rapid field evaluation and early release, (4) micropropagation of disease-free, genetically uniform planting material of superior female papaya (Carica papaya) selections and banana (Musa spp.) selections and (5) the use of somaclonal variation and gamma-irradiation for the genetic improvement of banana. Finally, future opportunities for the utilisation of tissue culture in plant propagation and improvement in Queensland's horticultural industries are summarised.
The Regulation of Pea Seed Storage Protein Genes by Sulfur Stress
Authors: Spencer D , Rerie WG , Randall PJ , Higgins TJV
Published: January 2006

In this review the role of sulfur in regulating the expression of genes for pea seed storage proteins in both peas and transgenic tobacco is discussed.
The levels of the sulfur-containing proteins, legumin and pea albumin 1 (PA1), are reduced in the seeds of peas grown under mild sulfur nutrient stress. In contrast, the levels of sulfur-poor proteins such as pea lectin and vicilin are either unaffected or increased slightly under the same conditions. The levels of all the proteins are a direct reflection of the levels of their respective mRNAs. The reduced levels of legumin and PA1 mRNAs under sulfur stress is known to be due largely to increased mRNA turnover rather than decreased transcription.
The advent of gene transfer procedures for plants has allowed re-examination of the mechanism of regulation of mRNA stability under conditions of sulfur stress. A pea albumin 1 gene was engineered for leaf expression and transferred to tobacco and the transgenic plants were grown on normal and low levels of sulfur. Sulfur stress reduces total leaf protein in tobacco by about 20% and there are minor qualitative changes in the total protein profile. In contrast, PA1 levels are reduced by over 90% compared with the controls when the transgenic tobaccos are grown under sulfur stress. Thus, it is clear that sequences responsible for recognising the sulfur status have been included in the transgene. A number of gene constructs have been designed to test where the sulfur-responsive sequences are located in the PA1 gene and some of the preliminary findings are reported.
The thylakoid membranes of cyanobacteria: structure, dynamics and function
Authors: Mullineaux Conrad W.
Published: January 2006

In recent years there has been remarkable progress in determining the
three-dimensional structures of photosynthetic complexes. A new challenge is
emerging: can we understand the organisation and interaction of those
complexes in the intact photosynthetic membrane? Intact membranes are complex,
dynamic systems. If we are to understand the function of the intact membrane,
we will need to understand the organisation of the complexes, how they can
diffuse and interact in the membrane, how they are assembled, repaired and
broken down, and how their function is regulated. Cyanobacteria have some
crucial advantages as model systems. The complete sequencing of the
Synechocystis 6803 genome, coupled with the ease of
genetic manipulation of Synechocystis (and certain other
cyanobacteria) have given us a unique tool for studying a photosynthetic
organism. Furthermore, some cyanobacteria have a very simple, regular
thylakoid membrane structure. The unique geometry of photosynthetic membranes
of these cyanobacteria will greatly facilitate biophysical studies of membrane
function. This review summarises recent progress in understanding the
structure, function and dynamics of cyanobacterial thylakoid membranes,
highlights the questions that remain to be answered and suggests some possible
approaches towards solving those questions.
Phytase and acid phosphatase activities in extracts from roots of temperate pasture grass and legume seedlings
Authors: Hayes Julie E. , Richardson Alan E. , Simpson Richard J.
Published: January 2006

Phytase and acid phosphatase activities were measured in extracts from roots
of 14- to 22- day old seedlings of a range of temperate pasture species that
were grown aseptically in sand culture. Phytase activity from roots of
phosphorus- (P-)-deficient Trifolium subterraneum L. was
characterised. Activity was enhanced by 40% when extracts were passed
through Sephadex G-25, and increased by a further 20–30% with the
addition of either 1 mМ EDTA or 5 mМ cysteine to assay solutions. The
optimum temperature for phytase activity was 50°C and the optimum pH was
5.3. When compared with phosphatase activity measured in the roots of
T. subterraneum, phytase activity exhibited narrower pH
and temperature optima, and was also more strongly inhibited by
Co2+, Zn2+ and
AsO42− ions. Significantly,
for the five pasture species examined, phytase activity was less than
5% of the total acid phosphatase activity in extracts of plant roots.
Measured phytase activity ranged between 0.13 and 1.7 nkat
g–1 root fresh wt and was enhanced under
P-deficient relative to P-sufficient growth conditions in all of the pasture
species with the exception of Trifolium repens L., for
which the Km constant for activity
was 50% lower in P-deficient plants. When expressed on a root fresh wt
basis, increases in phytase activity of ~1.25-fold were observed for
extracts from T. subterraneum and
Medicago polymorpha L., and of up to 3.3-fold for
Danthonia richardsonii A.B. Cashmore and
Phalaris aquatica L. Increases in acid phosphatase
activity with P deficiency were less evident. Between 3.1% and
4.3% only of the total phytase activity measured in root extracts was
eluted from intact roots into 0.1 М NaCl.
PEG-osmotic treatment in tomato seedlings induces salt-adaptation in adult plants
Authors: Balibrea María E. , Parra Margarita , Bolarín María C. , Pérez-Alfocea Francisco
Published: January 2006

Complete immersion of 5-day-old tomato seedlings
(Lycopersicon esculentum (L.) Mill.) for 12 h in low
osmotic potential PEG solutions (-0.5, -0.75 and -1 MPa) induced greater
vegetative growth of adult plants under 100 mМ NaCl conditions, as well as
adaptive physiological responses concerning ionic, nutritional and osmotic
regulation. After 6 weeks of salt-treatment the PEG-treated plants produced up
to 50% more biomass and accumulated 1.5- to 2-fold more
Na+ and Cl− and up to
25 mМ more K+ in the actively growing leaves
than did the non-treated control plants. Moreover, the most productive
PEG-treated plants also registered up to 40% lowered leaf osmotic
potential, twice as much proline, and 10% lower leaf water content than
the control plants cultivated under salinity. The viability of the method
used, the implication of the induced physiological responses on salt
adaptation and possible explanations are discussed.
A Gene Controlling Differences in Osmoregulation in Wheat
Authors: Morgan JM
Published: January 2006

Evidence is presented for a single gene controlling differences in osmoregulation in wheat in response to water stress, confirming earlier results. Analyses of osmoregulation were made on the flag leaves of wheat plants which were grown in pots in the glasshouse and stressed in a controlled environment chamber by withholding water after the flag leaf had fully emerged. Osmoregulation was derived from responses of osmotic potential to relative water content or from responses of relative water content and osmotic potential to water potential. Usable estimates of osmoregulation were obtained for 67 F2 lines derived from contrasting parents, to test for gene number, and for one substitution series with contrasting parents, to determine chromosomal location.
The F2 frequency response, which consisted of two overlapping distributions, was compatible with a single recessive gene, the estimated ratio being 2.79 : 1 (low: high osmoregulation). This confirmed previous measurements made on F1s and F4s Results for the substitution series were also compatible with these results in indicating a single chromosome, 7A, which had an identical response to the low osmoregulation parent, Red Egyptian. The effects of the gene were confined to solute accumulations at water potentials above, but not below, zero turgor.
Development and Optimisation of Microprojectile Systems for Plant Genetic Transformation
Authors: Birch RG , Franks T
Published: January 2006

The recently developed microprojectile method for gene transfer to intact cells has been successfully used to transform plant species including some which previously resisted attempts using Agrobacterium and protoplast mediated techniques. In addition, microprojectile bombardment has already proved uniquely suitable for other applications including direct transformation of organelle genomes and rapid assessment of transient expression of genetic constructs introduced into cells of intact tissues.
Here we describe various microprojectile acceleration devices and the steps necessary to develop an effective microprojectile mediated transformation system for any plant species. We ernphasise the need to optimise the delivery of DNA into cells, and to tailor strategies for generating stably transformed plants based on the nature of the target tissue, behaviour in tissue culture, and available marker genes.
Patterns of cotransformation and coexpression of introduced genes in stable nuclear transformants generated with microprojectiles are summarised, and other applications including organelle transformation are briefly described. We mention technical limitations to the application of microprojectile-mediated gene transfer which need to be overcome if the method is to achieve its full potential as a near-universal gene transfer technique with exciting applications in basic plant molecular biology and practical plant improvement.
Gene Transfer Into Intact Sugarcane Cells Using Microprojectile Bombardment
Authors: Franks T , Birch RG
Published: January 2006

A microprojectile accelerator has been constructed and used to bombard cultured sugarcane tissues with GUS reporter gene constructs. Design features useful to minimise target tissue damage and variation between shots are described. Transient expression of GUS occurred in pEmuGN-bombarded cells of nonregenerable suspension culture as well as in regenerable embryogenic callus of commercial sugarcane cultivar 463, and in suspension cultures capable of regeneration to plants. Parameters yielding transient GUS expression in up to 1055 cells per bombardment in homogeneous suspension cultures of sugarcane have been established with a mean of 206 expressing cells per bombardment over a series of 8 independent experiments. Approximately 4% of these transiently expressing cells continued to express GUS for extended periods, indicating probable stable transformation of intact cells of the commercial sugarcane cultivar. Microprojectile bombardment appears the most promising of the available gene transfer techniques for practical genetic transformation of sugarcane because most commercial cultivars readily form regenerable callus suitable for bombardment.
Expression of a Chicken Ovalbumin Gene in Three Lucerne Cultivars
Authors: Schroeder HE , Khan MRI , Knibb WR , Spencer D , Higgins TJV
Published: January 2006

Routine procedures have been developed for the transformation of lucerne (Medicago sativa cv. Rangelander) with foreign genes using the Agrobacterium tumefaciens binary vector system and for the regeneration of transgenic plants from tissue culture, via somatic embryogenesis.
Lucerne transformation was carried out with a gene encoding neomycin phosphotransferase (npt), which conferred resistance to the antibiotic kanamycin, together with a cDNA clone encoding chicken ovalbumin which was modified for expression in plant cells. The ovalbumin cDNA protein coding sequence was combined with the cauliflower mosaic virus 35S promoter and the nopaline synthase 3' flanking sequence to make a chimeric ovalbumin gene. A DNA construct containing both these genes was transferred to lucerne, and ovalbumin was detected in leaves of regenerated plants using protein immunoblots. Pulse-chase labelling experiments and analysis of leaves from the top to bottom of the transformed plants indicated that ovalbumin, once formed, was stable in the leaves of transgenic lucerne.
A wide variation in ovalbumin level was frequently observed in plants regenerated from multiple embryos on a single transformed callus. This variation correlated with changes in the restriction enzyme digestion pattern of the ovalbumin DNA from the transgenic plants. These results indicate that each transformed callus may have arisen from more than one transformation event. An alternative interpretation is that the callus may have arisen from a single transformed cell but during cell proliferation the DNA in some cells may have undergone rearrangement prior to embryogenesis.
Transformation and regeneration procedures were also developed for two Australian commercial cultivars of lucerne. Although the frequency of recovery of transformed plants was lower than with cv. Rangelander, these protocols open the way for a relatively rapid
Leaf Feeding of [15N]Urea for Labelling Wheat With Nitrogen
Authors: Palta JA , Fillery IR , Mathews EL , Turner NC
Published: January 2006

A leaf feeding technique that uses [15N]urea was examined to determine its suitability for labelling plant material in order to study the long-term storage and remobilisation of nitrogen in wheat. Leaves were fed continuously for intervals up to 4 days by dipping their cut tips into [15N]urea solutions (99 atom %) at tillering, stem elongation and flowering. The [15N]urea uptake closely followed the transpiration rate of the leaf being fed, with higher rates at midday when the transpiration rate averaged 4 mmol H2O m-2 s-1 and lower rates at early morning or late afternoon when the transpiration rate averaged 0.1 mmol H2O m-2 s-1. Uptake of [15N]urea was higher by mainstem leaves than by leaves on subtending tillers on the same plant. The simultaneous feeding of more than one leaf per shoot had little effect on the overall 15N uptake per plant. The overall uptake of 15N by mainstem leaves was reduced as soil water potentials (Ψsoil) decreased below -0.2 MPa. The necrotic area of the leaf that was fed increased as the concentration of the urea solution increased, and was critically burned when the solution concentration exceeded 2.5%. Two days after leaf feeding, 76% of the total 15N taken up was in the fed leaf and was continuously exported to the remainder of the plant throughout the period of measurements (up to 10 days after leaf feeding). The feeding of a mainstem leaf for 4 days at tillering using up to 1.5% [15N]urea solutions labelled the plant parts by about 2 stom % 15N excess. Such enrichments are required when labelling plant material to study the long-term storage and remobilisation of nitrogen.
Stomatal Responses and Whole-Tree Hydraulic Conductivity of Orchard Macadamia integrifolia Under Irrigated and Non-Irrigated Conditions
Authors: Lloyd J , Trochoulias T , Ensbey R
Published: January 2006

Diurnal patterns of stomatal conductance (gs) and leaf water potential (Ψ1) were determined for leaves on irrigated and non-irrigated 5-year-old Macadamia integrifolia trees over a 4-month period from September to December 1989. An empirical model for stomatal conductance was developed for irrigated trees using relationships to photon irradiance (I), leaf temperature (T1) and vapour mole fraction difference (D). This model accounted for 69% of the variance in gs, and was not improved by the inclusion of Ψ1 as an independent variable. Fitted parameters led to the effective prediction of gs for untried combinations of environmental variables. By using a simple expression to link leaf water potential to transpiration rate (E), the model was extended to prediction of Ψ1 from measurements of I, T1 and D.
Stornatal conductances were significantly lower on non-irrigated trees after a 2-month dry period. Lower stornatal conductances were not accompanied by more negative Ψ1 indicating that soil rather than leaf water status may control gs in macadamia trees under non-irrigated conditions.
Growth Analysis of the Effect of Phosphorus Nutrition on Seedings of Eucalyptus grandis
Authors: Kirschbaum MUF , Bellingham DW , Cromer RN
Published: January 2006

Eucalyptus grandis seedlings were grown in growth units in which plant roots were suspended in air while continuously being sprayed with nutrient solution (aeroponic system). Phosphorus was added to nutrient solutions in exponentially increasing amounts which determined plant growth. Phosphorus was added at five different relative addition rates.
The proportion of dry matter in stems increased with plant size, but was independent of plant internal phosphorus concentration. In contrast, the ratio of root to leaf dry weight decreased almost 2-fold with increasing phosphorus concentration but changed little with plant size, and specific leaf area more than doubled with increasing phosphorus concentration. Carbon fixation rate per unit plant dry weight increased about 5-fold with increasing nutrient addition rate over the range of addition rates used. That increase was due to a doubling in specific leaf area and a doubling in assimilation rate per unit leaf area, while leaf weight as a fraction of total plant dry weight increased by about 20%.
Osmotic Components and Properties Associated With Genotypic Differences in Osmoregulation in Wheat
Authors: Morgan JM
Published: January 2006

Solutes contributing to genotypic differences in osmoregulation in water-stressed wheat plants were investigated using samples of sap from expanded flag leaves of breeding lines with high and low osmoregulation. The sap samples were collected from leaves using a hand press after freezing and thawing. The leaves were sampled during a period of increasing stress created by withholding water from breeding lines growing in potting mix in the glasshouse. Measurements of potassium, free amino acids, proline, glucose, sucrose and fructose, as well as conductivity and refractive index, were made on the sap. The osmotic potential of the same sap samples was determined with a thermocouple psychrometer both before and after these measurements were made. Separate determinations of osmotic potential were also made on sections of frozen and thawed tissue from the same leaves used for sap samples, but without expressing the sap.
The level of osmoregulation was expressed as the solute accumulation between full and zero turgor. The lines showed either very low (0.18 MPa) or very high (1.35 MPa) levels of solute accumulation. These levels were similar to a single gene effect observed in other lines. High osmoregulation was largely (78%) due to potassium accumulation, with amino acids the only other important contributor (22%). No sugar accumulation was found. The osmotic potential due to the solutes potassium, amino acids and sugars accounted for, on average, 90% of the sap osmotic potential measured with a thermocouple psychrometer. The major components were potassium (42-53%) and amino acids (35-43%). In high lines, increases in the proportion of potassium with increased stress were associated with changes in the relationship between sap osmotic potential and either tissue osmotic potential or that derived from the component solutes. The various methods of measuring osmotic potential and effects on the calculation of solute accumulation are discussed.
Properties of Allantoinase From Whole Developing Fruits of French Bean, Phaseolus vulgaris L
Authors: Wells XE , Lees EM
Published: January 2006

In ureide-transporting legumes such as French bean, Phaseolus vulgaris L., allantoin is a major transport form of biologically fixed nitrogen. Allantoinase (allantoin amidohydrolase, EC 3.5.2.5) catalyses the conversion of allantoin to allantoate. In developing French bean fruits, seed coats contained the highest levels of soluble activity on a fresh weight basis, suggesting that this organ may be important in ureide metabolism. However, over 70% of the total allantoinase activity of the developing fruit was in the pods.
Allantoinase from whole developing French bean fruits was partially purified and characterised. Dithiothreitol inhibited activity, suggesting that disulfide bridges are necessary for activity. Mn2+ was found to relieve this inhibition to some extent; however, the presence of Mn2+ or EDTA in incubation mixtures did not affect activity. This suggests that, whilst allantoinase may not be a metalloenzyme, Mn2+ may have a role in maintaining the structure of the active enzyme. The Km for allantoin was determined to be 40.3 mM and the molecular mass of allantoinase was 50 000. Acid pretreatment of a crude extract reduced activity to 82% of control activity.
On the basis of sucrose density fractionation of French bean fruit extracts, allantoinase was determined to be associated with the microsomal fraction of the cell, probably the endoplasmic reticulum, as activity was coincident with NADPH-cytochrome c reductase.
Photosynthesis and the Accumulation of Proline in Response to Water Deficit
Authors: Joyce PA , Aspinall D , Paley LG
Published: January 2006

Light increases proline accumulation in water-stressed excised leaves of barley, and the response is linked to photosynthesis. The manner in which current photosynthesis contributes to proline accumulation and the role of soluble tissue carbohydrates has been examined. Increasing the CO2 content of the air surrounding stressed tissue had no effect on proline accumulation and reducing it to zero reduced proline accumulation only in leaves previously kept in darkness. The direct contribution of assimilated carbon to proline synthesis, assessed with labelled CO2, was small (< 10% of accumulated proline). The potential energy supply from photosynthesis during water stress was more than adequate for proline synthesis, but the potential energy supply from carbohydrate oxidation for segments stressed in darkness became limiting in leaves incubated in darkness for 48 h before stress. Energy provision from current photosynthesis may thus contribute to light stimulation of proline accumulation. Illumination modified the soluble carbohydrate content of the leaf segments and these variations were related to the rates of proline synthesis and oxidation. However, these effects were over-ridden by stress, and the mechanism of the response to light is not fully explained.
Control of Nitrate Reduction in Plants
Authors: Crawford NM , Wilkinson JQ , Labrie ST
Published: January 2006

The reduction of nitrate to nitrite is a critical step in the assimilation of nitrogen for most terrestrial plants. This reaction is catalysed by the enzyme nitrate reductase. Much has been learned about this enzyme over the past 40 years. Biochemical and molecular studies have provided insights into the structure of the enzyme and its prosthetic groups and molybdenum cofactor. Analysis of mutants that are defective in nitrate reduction has shed light on the nature and number of genes required for the synthesis of the nitrate reductase holoenzyme. Physiological studies have revealed an intricate and complex regulatory system that controls the expression of the nitrate reductase gene in response to environmental signals such as nitrate, light and carbon dioxide. In this paper we review what is known about the properties of nitrate reductase and its regulation in angiosperms with special emphasis on Arabidopsis thaliana.
Early-Flowering Mutants of Arabidopsis thaliana
Authors: Zagotta MT , Shannon S , Jacobs C , Meeks-Wagner DR
Published: January 2006

The transition from vegetative to reproductive growth represents a major change in angiosperm development. During the floral transition, shoot meristem activity progresses through the overlapping developmental phases: vegetative→inflorescence→floral. The transition to flowering is regulated by graft-transmissible substances, and the arrival of these substances at the shoot apex is correlated with the establishment of the inflorescence meristem. To identify the genes involved in regulating the floral transition, we have screened for mutants of Arabidopsis thaliana that display altered timing of flowering. We expect that such heterochronic mutants are defective either in the production or transport of floral signals, or in the response of the shoot meristem to these signals. We have isolated four early-flowering mutants: terminal flower 1 (tfl1) and early-flowering (elf) 1, 2 and 3. Three phenotypic classes are represented by these mutations: (I) early-flowering, photoperiod-sensitive, and displaying abnormal inflorescence development (tfl1); (II) early-flowering photoperiod-sensitive (elf1 and elf2); and (III) early-flowering, photoperiod-insensitive (elf3). This paper describes the initial phenotypic and genetic analysis of the mutants, and discusses how the genes represented by these mutations may fit into the signal/response pathway that leads to reproductive development.
The Nature of the Short-Term Inhibition of Stem Translocation Produced by Abrupt Stimuli
Authors: Pickard WF , Minchin PE
Published: January 2006

The transient inhibitions of phloem translocation which result when stem of Phaseolus vulgaris L. is (a) abruptly cooled by a few degrees Celsius, (b) vibrated vigorously at sonic frequencies, or (c) electrically shocked were examined. Fatigue of the inhibitory response was found to have the following properties: (i) a sequence of widely spaced stimuli often led to a shortened inhibitory period; (ii) for closely spaced stimuli, evidence of fatigue was found for neither temperature followed by vibration nor vibration followed by temperature; (iii) plants grown in strong oscillating wind gusts were fully vibration-sensitive even though two closely spaced vibrations applied to a normal plant led to fatigue; (iv) the vibration-induced inhibition was not sensitive to cytochalasin B. Experiments designed to examine the nature of the inhibition showed that: (i) an inhibitory stimulus essentially halted label import into the plant apex and label motion within the stimulated region but not leaf export, motion basal to the stimulated region, or motion apical to the stimulated region; (ii) the inhibition was affected by neither the callose synthesis blocker 2-deoxy-D-glucose nor the sulfhydryl-specific reagent p-chloromercuribenzenesulfonic acid; Cucumis melo L., whose sap does not gel in vitro, showed a normal inhibitory response. These data are consistent with the hypothesis that the inhibition of phloem translocation by a variety of different stimuli is the result of a local blockage of sieve elements in the region stimulated and that this blockage arises from the occlusion of sieve plate pores.
Ammonia Assimilation and Metabolite Transport in Isolated Chloroplasts. II. Malate Stimulates Ammonia Assimilation in Chloroplasts Isolated From Leaves of Dicotyledonous but Not Monocotyledonous Species
Authors: Yu JW , Woo KC
Published: January 2006

Malate stimulated NH3 assimilation, as determined by a (2-oxoglutarate, NH3)-dependent O2 evolution system, by up to 3-fold in chloroplasts isolated from leaves of dicot but not monocot species. This difference was apparently correlated with the endogenous metabolite pools present in these chloroplast preparations. During NH3 assimilation the glutamate and glutamine pools were large in spinach (dicot) but small in oat chloroplasts. The reverse was the case for the 2-oxoglutarate (2-OG) pool. The addition of malate substantially increased the glutamate, glutamine and 2-OG pools in spinach chloroplasts but had little effect in oat chloroplasts. This suggests that the supply of 2-OG was apparently limiting NH3 assimilation in spinach chloroplasts. Malate increased this supply and, consequently, stimulated NH3 assimilation. On the other hand, NH3 assimilation in oat chloroplasts seemed to be limited by the supply of glutamate and glutamine which could not be overcome by the addition of malate.
Chloroplasts were also isolated from oat seedlings watered with high nutrient solution. The rates of NH3 assimilation in these organelles exceeded those obtained in spinach chloroplasts. But the addition of malate had little effect on (2-OG, NH3)-dependent O2 evolution in these oat chloroplasts. Since malate did not inhibit this activity it is conceivable that it still might play a role, albeit a 'passive' role, in serving as a counter-ion for 2-OG uptake via the 2-OG translocator and glutamate export via the Dct translocator during NH3 assimilation.
Effects of Abscisic Acid on the Transfer of Sucrose From Host, Pelargonium zonale (L.) Aiton, to a Phanerogamic Parasite, Cuscuta reflexa Roxb
Authors: Bock FD , Fer A
Published: January 2006

Using isolated Pelargonium leaves parasitised by Cuscuta, we have established by means of autoradiographs that, in vivo, abscisic acid (ABA) is exported from the host leaf petiole to the attached parasite shoot. Experiments with simplified models (parasitised host stem slices, unparasitised host stem slices, isolated haustoria and parasitised host stem after removal of haustoria) showed that, in vitro, [2-14C]ABA is rapidly accumulated in haustorium tissues, and the internal/external ratio of ABA becomes greater than 1 within 45 min. The very fast ABA uptake, strongly dependent on the pH, may involve facilitated diffusion in addition to the diffusion of the undissociated acid. The high level of ABA concentration in Cuscuta, especially in haustoria, might be explained by ABA import from host tissues. In Cuscuta stem and haustoria, the hormone enhances the uptake and decreases the efflux of sucrose. In host tissues, ABA enhances phloem unloading of sucrose and decreases sucrose uptake.
Thus, ABA may have a central role in the host-parasite relationship by enhancing sucrose transfer.
Transient Depression of Photosynthesis in Bean Leaves During Rapid Water Loss
Authors: Modau H , Wong SC , Osmond CB
Published: January 2006

The response of the photosynthetic capacity of mesophyll to a rapid loss of water from the leaf was evaluated by measuring transpiration, net CO2 uptake and temperature in dwarf bean leaves exposed to saturating CO2 partial pressures in a leaf chamber before and after cutting the petiole in air. Some plants were pre-exposed to low or high photon flux density, or to water deficit before measurements. During 3-5 min after cutting, when the turgorpassive opening of the stomata accelerated the water loss from the leaf, the rate of CO2 uptake was depressed; the depression was more pronounced in young leaves, under higher CO2 partial pressure, and in leaves pre-exposed to low photon flux density or to slight water deficit. During subsequent closure of the stomata, the CO2 uptake rate accelerated, although the leaf water content and the internal CO2 partial pressure declined. The depression in CO2 uptake was poorly correlated with the water loss rate after cutting, but it was positively correlated with the increase in water loss rate relative to the transpiration rate before the cutting. It is speculated that sharp perturbation in leaf water regime may induce a transient leakage of cellular membranes and redistribution of metabolites between cell compartments, resulting in a depression of photosynthesis. Subsequent restoration of the concentrations of metabolites in compartments tends to restore the rate of photosynthesis, which then declines due to substantial stomatal closure.