Functional Plant Biology

The analysis of plant-pathogen interactions is a rapidly moving research field and one that is very important for productive agricultural systems. The focus of this review is on the evolution of plant defence responses and the coevolution of their pathogens, primarily from a molecular-genetic perspective. It explores the evolution of the major types of plant defence responses including pathogen associated molecular patterns and effector triggered immunity as well as the forces driving pathogen evolution, such as the mechanisms by which pathogen lineages and species evolve. Advances in our understanding of plant defence signalling, stomatal regulation, R gene-effector interactions and host specific toxins are used to highlight recent insights into the coevolutionary arms race between pathogens and plants. Finally, the review considers the intriguing question of how plants have evolved the ability to distinguish friends such as rhizobia and mycorrhiza from their many foes.

The outcome of infection of individual plants by pathogenic organisms is governed by complex interactions between the host and pathogen. These interactions are the result of long-term co-evolutionary processes involving selection and counterselection between plants and their pathogens. These processes are ongoing, and occur at many spatio-temporal scales, including genes and gene products, cellular interactions within host individuals, and the dynamics of host and pathogen populations. However, there are few systems in which host-pathogen interactions have been studied across these broad scales. In this review, we focus on research to elucidate the structure and function of plant resistance and pathogen virulence genes in the flax-flax rust interaction, and also highlight complementary co-evolutionary studies of a related wild plant-pathogen interaction. The confluence of these approaches is beginning to shed new light on host-pathogen molecular co-evolution in natural environments.

Plant organs may respond to gravity by vertical (orthogravitropic), oblique (plagiogravitropic) or horizontal (diagravitropic) growth. Primary roots of maize (Zea mays L.) provide a good system for studying such behaviours because they are reportedly capable of displaying all three responses. In current work using maize seedlings of the Silver Queen cultivar, stabilisation of growth at an oblique orientation was commonplace. Hypothetically, plagiogravitropism may be accomplished either by a process we call graded orthogravitropism or by hunting about a sensed non-vertical setpoint. In graded orthotropism primary bending is unidirectional and depends on facilitative stimuli that determine its extent. The hallmark of the setpoint mechanism is restorative curvature of either sign following a displacement; both diagravitropism and orthogravitropism are based on setpoints. Roots settled in a plagiogravitropic orientation were tested with various illumination and displacement protocols designed to distinguish between these two hypotheses. The tests refuted the setpoint hypothesis and supported that of graded orthotropism. No evidence of diagravitropism could be found, thus, earlier claims were likely based on inadequately controlled observations of graded orthotropism. We propose that orthotropism is graded by the sequential action of dual gravity receptors: induction of a vectorial gravitropic response requires gravitational induction of a separate facilitative response, whose decay in the absence of fresh stimuli can brake gravitropism at plagiotropic angles.

Gravitropism of vascular plants has been assumed to require a single gravity receptor mechanism. However, based on the evidence in Part I of this study, we propose that maize roots require two. The first mechanism is without a directional effect and, by itself, cannot give rise to tropism. Its role is quantitative facilitation of the second mechanism, which is directional like the gravitational force itself and provides the impetus for tropic curvature. How closely coupled the two mechanisms may be is, as yet, unclear. The evidence for dual receptors supports a general model for roots. When readiness for gravifacilitation, or gravifacilitation itself, is constitutive, orthogravitropic curvature can go to completion. If not constitutively enabled, gravifacilitation can be weak in the absence of light and water deficit or strong in the presence of light and water deficit. In either case, it can decay and permit roots to assume reproducible non-vertical orientations (plagiogravitropic or plagiotropic orientations) without using non-vertical setpoints. In this way roots are deployed in a large volume of soil. Gravitropic behaviours in shoots are more diverse than in roots, utilising oblique and horizontal as well as vertical setpoints. As a guide to future experiments, we assess how constitutive v. non-constitutive modes of gravifacilitation might contribute to behaviours based on each kind of setpoint.

Functional-structural models provide detailed representations of tree growth and their application to forestry seems full of prospects. However, owing to the complexity of tree architecture, parametric identification of such models remains a critical issue. We present the GreenLab approach for modelling tree growth. It simulates tree growth plasticity in response to changes of their internal level of trophic competition, especially topological development and cambial growth. The model includes a simplified representation of tree architecture, based on a species-specific description of branching patterns. We study whether those simplifications allow enough flexibility to reproduce with the same set of parameters the growth of two observed understorey beech trees (Fagus sylvatica L.) of different ages in different environmental conditions. The parametric identification of the model is global, i.e. all parameters are estimated simultaneously, potentially providing a better description of interactions between sub-processes. As a result, the source-sink dynamics throughout tree development is retrieved. Simulated and measured trees were compared for their trunk profiles (fresh masses and dimensions of every growth units, ring diameters at different heights) and compartment masses of their order 2 branches. Possible improvements of this method by including topological criteria are discussed.

Light interception is a major factor influencing plant development and biomass production. Several methods have been proposed to determine this variable, but its calculation remains difficult in artificial environments with heterogeneous light. We propose a method that uses 3D virtual plant modelling and directional light characterisation to estimate light interception in highly heterogeneous light environments such as growth chambers and glasshouses. Intercepted light was estimated by coupling an architectural model and a light model for different genotypes of the rosette species Arabidopsis thaliana (L.) Heynh and a sunflower crop. The model was applied to plants of contrasting architectures, cultivated in isolation or in canopy, in natural or artificial environments, and under contrasting light conditions. The model gave satisfactory results when compared with observed data and enabled calculation of light interception in situations where direct measurements or classical methods were inefficient, such as young crops, isolated plants or artificial conditions. Furthermore, the model revealed that A. thaliana increased its light interception efficiency when shaded. To conclude, the method can be used to calculate intercepted light at organ, plant and plot levels, in natural and artificial environments, and should be useful in the investigation of genotype-environment interactions for plant architecture and light interception efficiency. This paper originates from a presentation at the 5th International Workshop on Functional–Structural Plant Models, Napier, New Zealand, November 2007.

Protein elongation factors, EF-Tu and EF-1α, have been implicated in cell response to heat stress. We investigated the expression (accumulation) of EF-Tu and EF-1α in mature plants of spring wheat cultivars Kukri and Excalibur, and tested the hypothesis that cultivars with contrasting tolerance to heat stress differ in the accumulation of these elongation factors under prolonged exposure to high temperature (16 days at 36/30°C). In addition, we investigated the expression of EF-Tu and EF-1α in young plants experiencing a 24-h heat shock (43°C). Excalibur showed better tolerance to heat stress than Kukri. Heat stress induced accumulation of EF-Tu and EF-1α in mature plants of both cultivars, but to a greater extent in Excalibur. Young plants did not show appreciable accumulation of EF-Tu in response to heat shock. However, these plants showed increased accumulation of EF-1α and the accumulation appeared greater in Excalibur than in Kukri. The results support the hypothesis that EF-Tu plays a role in heat tolerance in spring wheat. The results also suggest that EF-1α may be of importance to wheat response to heat stress.

Detailed knowledge of the sodium distribution within the tissues of Australian native species that are highly salt tolerant could help in understanding the physiological adaptation to salt tolerance or sensitivity. 23Na NMR microimaging is presented as a tool to achieve this goal. Maps of the sodium distribution in stem tissue were obtained with an in-plane resolution of approximately 125 µm and a slice thickness of 4 mm. Simultaneously recorded high resolution 1H NMR images, showing water distribution in the same slice with 31 µm in-plane resolution and 1 mm slice thickness, were used as an anatomical reference together with optical micrographs which were taken immediately after the NMR experiments were completed. To quantify the sodium concentration reference capillaries with known NaCl concentration were located in the NMR probe together with the plant sample. Average concentration values calculated from signal intensities in the tissue and the capillaries were compared with concentration values obtained from atomic emission photometry, performed on digested stem sections harvested immediately after NMR experiments and with optical microscopy. This shows that 23Na NMR microimaging has great potential for physiological studies of salt stress at the macroscopic level and may become a unique tool for diagnosing salinity tolerance and sensitivity

We developed a double-digitising method combining a hand-held electromagnetic digitizer and a non-contact 3D laser scanner. The former was used to record the positions of all leaves in a tree and the orientation angles of their lamina. The latter served to obtain the morphology of the leaves sampled in the tree. As the scanner outputs a cloud of points, software was developed to reconstruct non-planar (NP) leaves composed of triangles, and to compute numerical shape parameters: midrib curvature, torsion and transversal curvature of the lamina. The combination of both methods allowed construction of 3D virtual trees with NP leaves. The method was applied to young beech trees (Fagus sylvatica L.) from different sunlight environments (from 1 to 100% incident light) in a forest in central France. Leaf morphology responded to light availability, with a more bent shape in well-lit leaves. Light interception at the leaf scale by NP leaves decreased from 4 to 10% for shaded and sunlit leaves compared with planar leaves. At the tree scale, light interception by trees made of NP leaves decreased by 1 to 3% for 100% to 1% light, respectively.

The ABA-deficient wilty pea (Pisum sativum L.) and its wild-type (WT) were grown at two levels of nitrogen supply (0.5 and 5.0 mM) for 5-6 weeks from sowing, to determine whether leaf ABA status altered the leaf growth response to N deprivation. Plants were grown at high relative humidity to prevent wilting of the wilty peas. Irrespective of N supply, expanding wilty leaflets had ca 50% less ABA than WT leaflets but similar ethylene evolution rates. Fully expanded wilty leaflets had lower relative water contents (RWC) and were 10-60% smaller in area (according to the node of measurement) than WT leaflets. However, there were no genotypic differences in plant relative leaf expansion rate (RLER). Growth of both genotypes at 0.5 mM N increased the RWC of fully expanded leaflets, but did not alter ethylene evolution or ABA concentration of expanding leaflets. Plants grown at 0.5 mM N showed a 20-30% reduction in RLER, which was similar in magnitude in both wilty and WT peas. Thus, leaf ABA status did not alter the leaf growth response to N deprivation.

The har1-1 mutant of Lotus japonicus B-129-S9 Gifu is characterized by two phenotypes: greater than normal nodulation (hypernodulation) and significantly inhibited root growth in the presence of its microsymbiont Mesorhizobium loti strain NZP2235. We demonstrate that the two traits co-segregate, suggesting a single genetic alteration involving developmental pleiotropy. A cross between the mutant and genotype Funakura (with wild-type root and nodule morphology) demonstrated Mendelian recessive segregation of both phenotypes (root and nodule) in 216 F2 individuals. Using DNA-amplification fingerprinting polymorphisms in Gifu har1-1 and Funakura, the mutant locus was positioned between two markers at about 7 and 13 cM distance. Reciprocal hypocotyl grafting of shoots and roots showed that the hypernodulation and reduced root phenotypes are both predominantly controlled by the shoot.

Dendrobium flower buds and flowers have an abscission zone at the base of the pedicel (flower stalk). Ethylene treatment of cv. Miss Teen inflorescences induced high rates of abscission in flower buds but did not affect abscission once the flowers had opened. It is not known if auxin is a regulator of the abscission of floral buds and open flowers. The hypotheses that auxin is such a regulator and is responsible for the decrease in ethylene sensitivity were tested. Severed inflorescences bearing 4¿8 floral buds and 4¿6 open flowers were used in all tests. The auxin antagonists 2,3,5-triiodobenzoic acid (TIBA, an inhibitor of auxin transport) or 2-(4-chlorophenoxy)-2-methyl propionic acid (CMPA, an inhibitor of auxin action) were applied to the stigma of open flowers. Both chemicals induced high flower abscission rates, even if the inflorescences were not treated with ethylene. The effects of these auxin antagonists virtually disappeared when the inflorescences were treated with 1-methylcyclopropene (1-MCP), indicating that the abscission induced by the auxin antagonists was due to ethylene. Removal of the open flowers at the distal end of the pedicel hastened the time to abscission of the remaining pedicel, and also resulted in an increase in ethylene sensitivity. Indole-3-acetic acid (IAA) in lanolin, placed on the cut surface of the pedicel, replaced the effect of the removed flower. Treatments that promoted abscission of open flowers up-regulated a gene encoding a ß-1,4-glucanase (Den-Cel1) in the abscission zone (AZ). The abundance of Den-Cel1 mRNA was highly correlated with ß-1,4-glucanase activity in the AZ. The results show that auxin is an endogenous regulator of floral bud and flower abscission and suggest that auxin might explain, at least partially, why pedicel abscission of Dendrobium cv. Miss Teen changes from very ethylene-sensitive to ethylene-insensitive

We studied the abscission of floral buds and open flowers in cut Dendrobium inflorescences. Abscission of floral buds was high and sensitive to ethylene in all cultivars studied. Many open flowers abscised in most cultivars, but cv. Willie exhibited only small amount of floral fall and cv. Miss Teen none. Applied ethylene (0.4 ¿L L¿1 for 24 h at 27°C) greatly hastened abscission of open flowers in most cultivars, but had only a small effect in cv. Willie and no effect in cv. Miss Teen. Flower fall, if it occurred, was completely inhibited by 1-methylcyclopropene (1-MCP), showing that it was regulated by endogenous ethylene. Ethylene production from the abscission zones was low in all cultivars studied. In cv. Miss Teen the abscission zone changed from highly ethylene sensitive to completely insensitive in ~30 h, coinciding with floral opening. Removal of the floral buds somewhat reduced abscission in open flowers, but the lack of open flower abscission in cv. Miss Teen could not be explained by higher bud fall. The ovary did not grow in the (unpollinated) flowers, showing that lack of abscission in cvv. Willie and Miss Teen was not due to parthenocarpy. Flower removal in cv. Miss Teen had no effect on ethylene sensitivity of the abscission of the remaining pedicel. However, removal of the distal 2 cm of the 3-cm-long pedicels dramatically increased ethylene sensitivity. This suggests that the pedicel is important for the low ethylene insensitivity of abscission, in this cultivar. It is concluded that the abscission zones in the cvv. Willie and Miss Teen, in contrast with the other cultivars investigated, became rapidly insensitive to ethylene at the time of flower opening. At least part of the ethylene sensitivity in Miss Teen seems to be due to a factor in the pedicel.

The relative effects of soil N, water supply and elevated atmospheric CO2 on foliar delta-15N values were examined. Phalaris arundinacea L. (Holdfast) and Physalis peruviana L. (Cape Gooseberry) were grown for 80 d with three water availability treatments, two atmospheric CO2 concentrations and four N supply rates. Elevated CO2 increased total plant biomass and N for each treatment and decreased allocation to roots, leaf N concentrations and stomatal conductance. Leaves had less negative leaf delta-13C values under low water supply associated with decreased stomatal conductance and increased leaf N concentration, which decreased the ratio of intercellular to ambient CO2 concentration. The delta-15N value of the supplied nitrate (4.15‰) was similar to the value for Phalaris leaves (4.11‰), but Cape Gooseberry leaves were enriched (6.52‰). The effects of elevated CO2 on leaf delta-15N values were small, with Phalaris showing no significant change, while Cape Gooseberry showed a significant (P < 0.05) decline of 0.42 ‰. Variation in delta-15N values was unrelated to stomatal conductance, transpiration, differential use of N forms or denitrification. Plants with low foliar N concentrations tended to be depleted in 15N. We suggest that changes in N allocation alter foliar delta-15N values under different CO2 and water treatments.

Copyright: 2007 Csiro Publishing ASP53, a 53 kDa heat soluble protein, was identified as the most abundant protein in the mature seeds of Acacia erioloba E.Mey. Immunocytochemistry showed that ASP53 was present in the vacuoles and cell walls of the axes and cotyledons of mature seeds and disappeared coincident with loss of desiccation tolerance. The sequence of the ASP53 transcript was determined and found to be homologous to the double cupin domain-containing vicilin class of seed storage proteins. Mature seeds survived heating to 60°C and this may be facilitated by the presence of ASP53. Circular dichroism spectroscopy demonstrated that the protein displayed defined secondary structure, which was maintained even at high temperature. ASP53 was found to inhibit all three stages of protein thermal denaturation. ASP53 decreased the rate of loss of alcohol dehydrogenase activity at 55°C, decreased the rate of temperature-dependent loss of secondary structure of haemoglobin and completely inhibited the temperature-dependent aggregation of egg white protein.

Dendrobium flowers, pollinated with pollinia from individuals of the same cultivar or other cultivars, usually show rapid post-pollination effects such as. oral epinasty, a change in flower colour and early perianth senescence. However, pollination with the pollinia of cv. Karen or cv. Kenny flowers did not produce these effects. We compared these two cultivars with cvv. Pompadour, Willie and Sakura, and tested the hypotheses that the differences were related to levels of 1-aminocyclopropane-1-carboxylic acid (ACC) in the pollinia, ethylene production by the pollinated flower, pollen germination, or pollen tube growth. The pollinia of cvv. Karen and Kenny contained as much ACC as the pollinia of cv. Pompadour, but less than the pollinia of cvv. Willie and Sakura. Ethylene production after pollination with cvv. Karen and Kenny pollinia was much lower than after pollination with pollinia from the other cultivars tested. The pollen grains showed normal germination, but cvv. Karen and Kenny pollen grains exhibited much less tube growth than those of the other cultivars. Pollen tube growth in cv. Pompadour was positively affected by ethylene. Ethylene was required and sufficient for the induction of epinasty, rapid perianth colour changes and early perianth senescence, very similar to the changes after pollination. The absence of these effects after pollination with cvv. Kenny and Karen seems to be due to the low ethylene production induced by the pollinia of these cultivars. This low ethylene production could not be accounted for by the ACC content in the pollinia of cvv. Kenny and Karen.

The ratio of the capacities of ribulose-1,5-bisphosphate (RuBP) regeneration to RuBP carboxylation (J(max)/V-cmax) ( measured at a common temperature) increases in some species when they are grown at lower temperatures, but does not increase in other species. To investigate the mechanism of interspecific difference in the response of J(max) /V-cmax to growth temperature, we analysed the temperature dependence of V-cmax and Jmax in Polygonum cuspidatum and Fagus crenata with the Arrhenius function. P. cuspidatum had a higher ratio of J(max) /V-cmax in spring and autumn than in summer, while F. crenata did not show such change. The two species had a similar activation energy for V-cmax (E-aV) across seasons, but P. cuspidatum had a higher activation energy for J(max) (E-aJ) than F. crenata. Reconstruction of the temperature response curve of photosynthesis showed that plants with an inherently higher E-aJ /E-aV (P. cuspidatum) had photosynthetic rates that were limited by RuBP regeneration at low temperatures and limited by RuBP carboxylation at high temperatures, while plants with an inherently lower E-aJ / E-aV ( F. crenata) had photosynthetic rates that were limited solely by RuBP carboxylation over the range of temperatures. These results indicate that the increase in J(max) / V-cmax at low growth temperatures relieved the limitation of RuBP regeneration on the photosynthetic rate in P. cuspidatum, but that such change in J(max) / V-cmax would not improve the photosynthetic rate in F. crenata. We suggest that whether or not the J(max) / V-cmax ratio changes with growth temperature is attributable to interspecific differences in E-aJ / E-aV between species.

Transgenic sugarcane (Saccharum officinarum L. interspecific hybrids) line N3.2 engineered to express a vacuole-targeted sucrose isomerase was found to accumulate sucrose to twice the level of the background genotype Q117 in heterotrophic cell cultures, without adverse effects on cell growth. Isomaltulose levels declined over successive subcultures, but the enhanced sucrose accumulation was stable. Detailed physiological characterisation revealed multiple processes altered in line N3.2 in a direction consistent with enhanced sucrose accumulation. Striking differences from the Q117 control included reduced extracellular invertase activity, slower extracellular sucrose depletion, lower activities of symplastic sucrose-cleavage enzymes (particularly sucrose synthase breakage activity), and enhanced levels of symplastic hexose-6-phosphate and trehalose-6-phosphate (T6P) in advance of enhanced sucrose accumulation. Sucrose biosynthesis by sucrose phosphate synthase (SPS) and sucrose phosphate phosphatase (SPP) was substantially faster in assays conducted to reflect the elevation in key allosteric metabolite glucose-6-phosphate (G6P). Sucrose-non-fermenting-1-related protein kinase 1 (SnRK1, which typically activates sucrose synthase breakage activity while downregulating SPS in plants) was significantly lower in line N3.2 during the period of fastest sucrose accumulation. For the first time, T6P is also shown to be a negative regulator of SnRK1 activity from sugarcane sink cells, hinting at a control circuitry for parallel activation of key enzymes for enhanced sucrose accumulation in sugarcane.

Tissues of the Australian native plant species Hakea actities (Proteaceae) contain numerous metabolites and structural compounds that hinder the isolation of nucleic acids. Separate RNA and genomic DNA extraction procedures were developed to isolate high quality nucleic acids from H. actities. Total RNA was extracted from leaves, roots and cluster roots of H. actities grown in low nutrient levels. Cluster root formation in H. actities only occurs when the plants are grown in low nutrient concentrations. However, under these conditions, nucleic acid extraction becomes increasingly difficult. The new procedures are faster than many of the published nucleic acid extraction protocols, and avoid the use of hazardous chemicals. The RNA extraction method was used successfully on another Australian species and a crop species, suggesting that the procedure is useful for molecular studies of a broad range of plants.

The effects of elevated compared to current atmospheric CO2 concentration (720 and 365 L L -1 , respectively) on antioxidative enzymatic activities of two soybean (Glycine max (L.) Merr.) genotypes (R and S) grown in open-top field chambers were investigated. Enzymatic activities of leaves collected 40, 47, 54 and 61 d after planting were measured. Elevated CO2 significantly decreased activities of superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APOD, EC 1.11.1.7), glutathione peroxidase (GPOD, EC 1.11.1.9) and glutathione reductase (GR, EC 1.6.4.2) in both genotypes. The activities of dehydroascorbate reductase (DAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDAR, EC 1.1.5.4.) increased in genotype S, but decreased in genotype R under elevated CO2. Elevated CO2 decreased rubisco activity and rubisco, chlorophyll, carotenoids and total soluble protein contents in both genotypes. Results indicate that constitutive antioxidative enzymatic activities may decrease in a high-CO2 world. Significant CO2 x genotype interactions, however, suggest that there may be key genotypic differences in response patterns, potentially conferring differential resistance to biotic and abiotic stress.

Better understanding of root system structure and function is critical to crop improvement in waterlimited environments. The aims of this study were to examine root system characteristics of two wheat genotypes contrasting in tolerance to water limitation and to assess the functional implications on adaptation to water-limited environments of any differences found. The drought tolerant barley variety, Mackay, was also included to allow inter-species comparison. Single plants were grown in large, soil-filled root-observation chambers. Root growth was monitored by digital imaging and water extraction was measured. Root architecture differed markedly among the genotypes. The drought-tolerant wheat (cv. SeriM82) had a compact root system, while roots of barley cv. Mackay occupied the largest soil volume. Relative to the standard wheat variety (Hartog), SeriM82 had a more uniform rooting pattern and greater root length at depth. Despite the more compact root architecture of SeriM82, total water extracted did not differ between wheat genotypes. To quantify the value of these adaptive traits, a simulation analysis was conducted with the cropping system model APSIM, for a wide range of environments in southern Queensland, Australia. The analysis indicated a mean relative yield benefit of 14.5% in water-deficit seasons. Each additional millimetre of water extracted during grain filling generated an extra 55 kg ha−1 of grain yield. The functional implications of root traits on temporal patterns and total amount of water capture, and their importance in crop adaptation to specific water-limited environments, are discussed.

Figs are rainforest keystone species. Non-strangler figs establish on the forest floor; strangler figs establish epiphytically, followed by a dramatic transition from epiphyte to free-standing tree that kills its hosts. Free-standing figs display vigorous growth and resource demand suggesting that epiphytic strangler figs require special adaptations to deal with resource limitations imposed by the epiphytic environment. We studied epiphytic and free-standing strangler figs, and non-strangler figs in tropical rainforest and in cultivation, as well as strangler figs in controlled conditions. We investigated whether the transition from epiphyte to free-standing tree is characterised by morphological and physiological plasticity. Epiphyte substrate had higher levels of plant-available ammonium and phosphate, and similar levels of nitrate compared with rainforest soil, suggesting that N and P are initially not limiting resources. A relationship was found between taxonomic groups and plant N physiology; strangler figs, all members of subgenus Urostigma, had mostly low foliar nitrate assimilation rates whereas non-strangler figs, in subgenera Pharmacocycea, Sycidium, Sycomorus or Synoecia, had moderate to high rates. Nitrate is an energetically expensive N source, and low nitrate use may be an adaptation of strangler figs for conserving energy during epiphytic growth. Interestingly, significant amounts of nitrate were stored in fleshy taproot tubers of epiphytic stranglers. Supporting the concept of plasticity, leaves of epiphytic Ficus benjamina L. had lower N and C content per unit leaf area, lower stomatal density and 80% greater specific leaf area than leaves of conspecific free-standing trees. Similarly, glasshouse-grown stranglers strongly increased biomass allocation to roots under water limitation. Epiphytic and free-standing F. benjamina had similar average foliar delta C-13, but epiphytes had more extreme values; this indicates that both groups of plants use the C-3 pathway of CO2 fixation but that water availability is highly variable for epiphytes. We hypothesise that epiphytic figs use fleshy stem tubers to avoid water stress, and that nitrate acts as an osmotic compound in tubers. We conclude that strangler figs are a unique experimental system for studying the transition from rainforest epiphyte to tree, and the genetic and environmental triggers involved.

The 2-fold difference in final length of leaf number three on the main stem between the fast-growing Aegilops tauschii L. and the slow-growing Aegilops caudata L. is correlated with a difference in leaf elongation rate (LER), and not in duration of leaf elongation. In this paper the cellular basis of inherent differences in LER between these species was investigated.The dynamics of abaxial epidermal cells along the growth zone of leaf number three on the main stem of both species was analysed by means of a kinematic analysis. The faster LER of Ae. tauschii compared with that of Ae. caudata was associated with (i) a larger leaf basal meristem and cell elongation-only zone, and (ii) a faster cell production rate owing to a larger number of dividing cells. Cell division rate, mature cell size and cell elongation rate did not differ between the two species. The lack of variation in cell expansion rate between the species was supported by a similar capacity of both species to extend their isolated cell walls upon acidification.These data suggest that differences in the number of dividing cells can bring about differences in the number of simultaneously elongating cells, and hence in LER.

Transgenic barley plants that over-express the gene encoding a phosphate transporter were generated and used to test the hypothesis that manipulation of transporters may lead to improved phosphate uptake by plant roots. Replicate T2 seedlings from a homozygous line with a single locus insertion were grown in dilute flow culture. The phosphate contents and uptake rates of these plants were compared with control transgenic and wild-type plants. When external phosphate concentration was maintained at 10 μM, all plants including the transgenic over-expressing line displayed low rates of phosphate uptake and contained high levels of phosphate in the shoot tissue. When external phosphate concentration was maintained at 2 μM, the uptake rates increased to a similar level in all plant lines. Three transgenic over-expressing lines were then grown in soil at a range of phosphate concentrations and the dry weights and total phosphorus contents of the shoots were measured and compared to a transgenic control line. The results showed that over-expression of the gene encoding a phosphate transporter did not improve the uptake of phosphate under any of the conditions tested. Transporter activity is likely to be influenced by post-transcriptional mechanisms and will require further investigation before this strategy can be applied to improving plant nutrition.

The recently released Affymetrix GeneChip Medicago Genome Array contains approximately 52 700 probe sets representing genes in both the model legume Medicago truncatula Gaertn. and the closely related crop species Medicago sativa L. (alfalfa). We evaluated the utility of the Medicago GeneChip for monitoring genome-wide expression of M. truncatula and alfalfa seedlings grown to the first trifoliate leaf stage. We found that approximately 40-54% of the Medicago probes were detected in leaf or root samples of alfalfa or M. truncatula. Approximately 45-59% of the detected Medicago probes were called 'present' in all replicate GeneChips of Medicago species, indicating a considerable overlap in the number and type of Medicago probes detected between root and leaf organs. Nevertheless, gene expression differences between roots and leaf organs accounted for approximately 17% of the total variation, regardless of the Medicago species from which the samples were harvested. The result shows that the Medicago GeneChip is applicable for transcript analysis for both alfalfa and M. truncatula.

Orthologous markers transferable between distantly related legume species allow for the rapid generation of genetic maps in species where there is little pre-existing genomic or EST information. We are using the model legume Medicago truncatula Gaertn. to develop such markers in legumes of importance to Australian agriculture. This will enable the construction of comparative genetic maps, help to determine patterns of chromosomal evolution in the legume family, and characterise syntenic relationships between M. truncatula and cultivated legumes. This information can then be used to identify markers that are tightly linked to the genes of interest, candidate gene(s) for a trait, and expedite the isolation of such genes. Among the Papilionoideae, we compared ESTs from the phylogenetically distant species, M. truncatula, Lupinus albus and Glycine max, to produce 500 intron-targeted amplified polymorphic markers (ITAPs). In addition to 126 M. truncatula cross-species markers from Department of Plant Pathology, University of California (USA), these markers were used to generate comparative genetic maps of lentil (Lens culinaris Medik.) and white lupin (Lupinus albus Linn.). Our results showed that 90% of the ITAPs markers amplified genomic DNA in M. truncatula, 80% in Lupinus albus, and 70% in Lens culinaris. The comparative map of Lens culinaris was constructed based on 79 ITAP markers. The Lupinus albus comparative map was developed from 105 gene-based markers together with 223 AFLP markers. Although a direct and simple syntenic relationship was observed between M. truncatula and Lens culinaris genomes, there is evidence of moderate chromosomal rearrangement. This may account for the different chromosome numbers in the two species. A more complicated pattern among homologous blocks was apparent between the Lupinus albus and M. truncatula genomes.

Aldose-6-phosphate reductase (A6PR), a key enzyme in sorbitol biosynthesis, has been purified to apparent homogeneity from fully developed apple (Malus domestica Borkh. cv. Gala) leaves. Inorganic phosphate inhibited A6PR by decreasing the maximum velocity of the enzyme and by increasing the Km for the substrate, glucose-6-phosphate (Glc6P). Divalent cations including Ca2+, Mg2+, Zn2+ and Cu2+ altered A6PR activity. Effects of Ca2+ and Mg2+ on A6PR activity were dependent upon both the metal ion concentration and the concentration of Glc6P. The activity of A6PR was increased by 0.5–5 mM Ca2+ or Mg2+ when Glc6P concentration was below 10 mM. However, these same metal ions decreased A6PR activity at greater Glc6P concentrations or in the presence of higher metal ion concentrations. A6PR displayed Michaelis–Menten kinetics either in the presence or absence of 2.5 mM MgCl2, but the apparent Km for Glc6P decreased from 11.3 mM for the control to 5.1 mM in the presence of 2.5 mM MgCl2 in the assay mixture. By contrast, Zn2+ and Cu2+ dramatically inactivated A6PR activity. A6PR activity was decreased approximately 50 and 70%, respectively, when the enzyme was pre-incubated with 2 mM Zn2+ or Cu2+ for 60 min at room temperature. This inactivation was partially reversed by dialysis or by chelation with 20 mM EDTA. NADPH and NADP+, which are substrates for A6PR in the oxidative and reductive directions, respectively, partially protected A6PR from inactivation by Zn2+. The above results suggest that both Mg2+ and Ca2+ were mixed-type, non-essential activators of A6PR that decreased the Km for sugar-phosphates but lowered the overall Vmax. The physiological significance of these findings is also discussed.

The allocation of biomass to different plant organs depends on species, ontogeny and on the environment experienced by the plant. In this paper we first discuss some methodological tools to describe and analyse the allocation of biomass. Rather than the use of shoot:root ratios, we plead strongly for a subdivision of biomass into at least three compartments: leaves, stems and roots. Attention is drawn to some of the disadvantages of allometry as a tool to correct for size differences between plants. Second, we tested the extent to which biomass allocation of plants follows the model of a 'functional equilibrium'. According to this model, plants respond to a decrease in above-ground resources with increased allocation to shoots (leaves), whereas they respond to a decrease in below- ground resources with increased allocation to roots. We carried out a meta-analysis of the literature, analysing the effect of various environmental variables on the fraction of total plant biomass allocated to leaves (leaf mass fraction), stem (stem mass fraction) and roots (root mass fraction). The responses to light, nutrients and water agreed with the (qualitative) prediction of the 'functional equilibrium' theory. The notable exception was atmospheric CO2, which did not affect allocation when the concentration was doubled. Third, we analysed the quantitative importance of the changes in allocation compared to changes in other growth parameters, such as unit leaf rate (the net difference between carbon gain and carbon losses per unit time and leaf area), and specific leaf area (leaf area: leaf biomass). The effects of light, CO2 and water on leaf mass fractions were small compared to their effects on relative growth rate. The effects of nutrients, however, were large, suggesting that only in the case of nutrients, biomass allocation is a major factor in the response of plants to limiting resource supply.

Adaptation to prolonged flooding was investigated using cuttings of two tree species from the Central Amazon white-water floodplain (Várzea). Morphological features and oxygen distribution patterns were correlated with metabolic changes under hypoxia, such as alterations in alcohol dehydrogenase (ADH) activity and adenylate energy charge (AEC) of root cells. Salix martiana (Leyb.) was able to react to hypoxic growth conditions with formation of adventitious roots rich in lysigenous aerenchyma, which facilitates root aeration by longitudinal oxygen transport and rhizosphere oxidation by radial oxygen loss (ROL). The oxygen concentration on the surface of adventitious roots of S. martiana reached 2-3 mg O2 L–1. The low resistance to gas exchange in Salix roots was reflected by low ADH activities, which ranged between 0.03-0.1 μmol NADH mg –1 min–1, and AEC values of 0.8-1 under hypoxic conditions. Adventitious roots were also formed by Tabernaemontana juruana ([Markgr.] Schumann ex. J.F. Macbride) during growth under low-oxygen conditions, although at a later stage. The gas-space continuum in roots of T. juruana was less pronounced, resulting in a 10-fold lower oxygen concentration in the root cortex under oxygen stress compared with adventitious roots of Salix. The lower oxygen content was reflected in 6-fold higher ADH activities and decreased AEC values. ROL occurred only at the non-suberized root tip, suggesting that the suberized hypodermis functions as a barrier against gas exchange between the root and the rhizosphere. These findings indicate that different strategies of adaptation to low oxygen levels are realized in the two species under investigation that occur naturally in the same ecosystem but inhabit different elevation sites

Although the impact of increasing atmospheric carbon dioxide concentration ([CO 2 ]) on production of common ragweed (Ambrosia artemisiifolia L.) pollen has been examined in both indoor and outdoor experiments, the relationship between allergen expression and [CO 2 ] is not known. An enzyme-linked immunosorbent assay (ELISA) was used to quantify Amb a 1, ragweed's major allergen, in protein extracted from pollen of A. artemisiifolia grown at different [CO 2 ] values in a previous experiment. The concentrations used approximated atmospheric pre-industrial conditions (i.e. at the end of the 19th century), current conditions, and the CO 2 concentration projected for the middle of the 21st century (280, 370 and 600 µmol mol −1 CO 2 , respectively). Although total pollen protein remained unchanged, significant increases in Amb a 1 allergen were observed between pre-industrial and projected future [CO 2 ] and between current and projected future [CO 2 ] (1.8 and 1.6 times, respectively). These data suggest that recent and projected increases in [CO 2 ] could directly increase the allergenicity of ragweed pollen and consequently the prevalence and / or severity of seasonal allergic disease. However, genetic and abiotic factors governing allergen expression will need to be better established to fully understand these data and their implications for public health.

Antarctic bryophyte communities presently tolerate physiological extremes in water availability, surviving both desiccation and submergence events. We investigated the relative ability of three Antarctic moss species to tolerate physiological extremes in water availability and identified physiological, morphological, and biochemical characteristics that assist species performance under such conditions. Tolerance of desiccation and submergence was investigated using chlorophyll fluorescence during a series of field- and laboratory-based water stress events. Turf water retention and degree of natural habitat submergence were determined from gametophyte shoot size and density, and delta C-13 signatures, respectively. Finally, compounds likely to assist membrane structure and function during desiccation events (fatty acids and soluble carbohydrates) were determined. The results of this study show significant differences in the performance of the three study species under contrasting water stress events. The results indicate that the three study species occupy distinctly different ecological niches with respect to water relations, and provide a physiological explanation for present species distributions. The poor tolerance of submergence seen in Ceratodon purpureus helps explain its restriction to drier sites and conversely, the low tolerance of desiccation and high tolerance of submergence displayed by the endemic Grimmia antarctici is consistent with its restriction to wet habitats. Finally the flexible response observed for Bryum pseudotriquetrum is consistent with its co-occurrence with the other two species across the bryophyte habitat spectrum. The likely effects of future climate change induced shifts in water availability are discussed with respect to future community dynamics.

Living in a frozen desert, Antarctic mosses are characterised by the ability to survive desiccation and can tolerate multiple desiccation-rehydration events over the summer growing season. As a result of recent ozone depletion, such mosses may also be exposed to ultraviolet-B radiation whilst desiccated. The ultraviolet-B susceptibility of Antarctic moss species was examined in a laboratory experiment that tested whether desiccated or hydrated mosses accumulated more DNA damage under enhanced ultraviolet-B radiation. Accumulation of cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone dimers was measured in moss samples collected from the field and then exposed to ultraviolet-B radiation in either a desiccated or hydrated state. Two cosmopolitan species, Ceratodon purpureus (Hedw.) Brid. and Bryum pseudotriquetrum (Hedw.) Gaertn., B. Mey. & Scherb, were protected from DNA damage when desiccated, with accumulation of cyclobutane pyrimidine dimers reduced by at least 60% relative to hydrated moss. The endemic Schistidium antarctici (Cardot) L.I. Savicz & Smirnova accumulated more DNA damage than the other species and desiccation was not protective in this species. The cosmopolitan species remarkable ability to tolerate high ultraviolet-B exposure, especially in the desiccated state, suggests they may be better able to tolerate continued elevated ultraviolet-B radiation than the endemic species.

A fundamental component of most models of terrestrial carbon balance is an estimate of plant canopy photosynthetic uptake driven by radiation interception by the canopy. In this article, we review approaches used to model the conversion of radiation into photosynthate. As this process is well understood at the leaf-scale, the modelling problem is essentially one of up-scaling, to canopy, regional or global scale. Our review therefore focuses on issues of scaling, including model identification, parameterisation and validation at large scales. Four different approaches are commonly taken to modelling photosynthate production at large scales: the maximum productivity, resource-use efficiency, big-leaf, and sun-shade models. Models representing each of these approaches are discussed and model predictions compared with estimates of gross primary productivity derived from eddy covariance data measured above a Sitka spruce forest. The sun-shade model was found to perform best at all time scales considered. However, other models had significant advantages including simplicity of implementation and the ability to combine the model with remotely-sensed information on vegetation radiation interception. We conclude that all four approaches can be successfully used to model photosynthetic uptake and that the best approach in a given situation will depend on model objectives and data availability.

A fundamental component of most models of terrestrial carbon balance is an estimate of plant canopy photosynthetic uptake driven by radiation interception by the canopy. In this article, we review approaches used to model the conversion of radiation into photosynthate. As this process is well understood at the leaf-scale, the modelling problem is essentially one of up-scaling, to canopy, regional or global scale. Our review therefore focuses on issues of scaling, including model identification, parameterisation and validation at large scales. Four different approaches are commonly taken to modelling photosynthate production at large scales: the maximum productivity, resource-use efficiency, big-leaf, and sun-shade models. Models representing each of these approaches are discussed and model predictions compared with estimates of gross primary productivity derived from eddy covariance data measured above a Sitka spruce forest. The sun-shade model was found to perform best at all time scales considered. However, other models had significant advantages including simplicity of implementation and the ability to combine the model with remotely-sensed information on vegetation radiation interception. We conclude that all four approaches can be successfully used to model photosynthetic uptake and that the best approach in a given situation will depend on model objectives and data availability.

The arbuscular mycorrhizal (AM) association between terrestrial plants and soil fungi of the phylum Glomeromycota is the most widespread beneficial plant-microbe interaction on earth. In the course of the symbiosis, fungal hyphae colonise plant roots and supply limiting nutrients, in particular phosphorus, in exchange for carbon compounds. Owing to the obligate biotrophy of mycorrhizal fungi and the lack of genetic systems to study them, targeted molecular studies on AM symbioses proved to be difficult. With the emergence of plant genomics and the selection of suitable models, an application of untargeted expression pro. ling experiments became possible. In the model legume Medicago truncatula, high-throughput expressed sequence tag (EST)-sequencing in conjunction with in silico and experimental transcriptome pro. ling provided transcriptional snapshots that together defined the global genetic program activated during AM. Owing to an asynchronous development of the symbiosis, several hundred genes found to be activated during the symbiosis cannot be easily correlated with symbiotic structures, but the expression of selected genes has been extended to the cellular level to correlate gene expression with specific stages of AM development. These approaches identified marker genes for the AM symbiosis and provided the first insights into the molecular basis of gene expression regulation during AM.

The Asparagus officinalis L. asparagine (Asn) synthetase (AS) promoter was analysed for elements responding to carbohydrate and senescence signals. Transgenic Arabidopsis thaliana L. plants containing deletion constructs of the –1958 bp AS promoter linked to the β-glucuronidase (GUS) reporter gene (AS::GUS) were analysed by measuring GUS specific activity. Inclusion of sucrose (Suc), glucose (Glc) or fructose (Fru) in plant media repressed levels of GUS activity in –1958AS::GUS plants, regardless of the light environment, with increases in GUS found 1 d after incubation on Suc-lacking media. Hexokinase is likely to be involved in the signal pathway, as Suc, Glc, Fru, 2-deoxy-d-glucose and mannose were more effective repressors than 3-O-methylglucose, and the hexokinase inhibitor mannoheptulose reduced repression. Plants containing AS::GUS constructs with deletions that reduced the promoter to less than –405 bp did not show low sugar induction. AS::GUS activity was significantly higher in excised leaves induced to senesce by dark storage for 24 h, compared to fresh leaves, for lines containing at least –640 bp of the AS promoter but not those with –523 bp or smaller promoter fragments. Fusion of the –640 to –523 bp region to a –381AS::GUS construct generated a promoter that retained senescence induction but lacked low sugar induction. Alignment of this region to the 33-bp senescence-related sequence of the Arabidopsis and Brassica napus L. SAG12 promoters identified the sequence TTGCACG as being conserved in all the promoters, and which may be an important senescence-responsive element.

In asparagus (Asparagus officinalis L.), increased levels of asparagine (Asn) and Asn synthetase (AS) transcript are detected during foliar senescence and in harvested spears, possibly triggered by signals from a reduced supply of carbohydrate. To identify cis-elements mediating this regulation, the asparagus AS gene promoter was isolated and analysed by DNA sequencing, followed by expression of AS::GUS (beta-glucuronidase) reporter-gene constructs in transgenic tissue, and electrophoretic mobility shift assays (EMSA). The 1958-base pair ( bp) region of the AS promoter upstream of the translation initiation ATG(-1958 bp region) was sufficient to confer sucrose (Suc)-regulated expression on the GUS reporter gene in asparagus callus and protoplasts, which were transformed by particle bombardment and electroporation, respectively. Removal of Suc from callus or protoplast media resulted in the induction of GUS activity. Deletion analysis of this 1958-bp fragment identified elements in the -640 to -266 bp region as important for both high GUS levels and mediating the Suc response. This was supported by EMSA results, which showed the formation of three nuclear protein-DNA complexes with the -558 to -284 bp fragment of the promoter. A 20-bp oligonucleotide, designed to match the sequence from -423 to -404 bp, was able to out-compete formation of one of these protein-DNA complexes, suggesting a specific interaction with this sequence. This region of the promoter, overlapping with the 20-bp oligonucleotide sequence, contains a 10-bp stretch identical to a sequence previously shown to mediate low Suc induction of an Oryza sativa (rice) alpha-amylase gene, and may thus represent a conserved Suc-responsive element.

Approximately 10-15% of plant nuclear genes appear to encode mitochondrial proteins that are directed to mitochondria by specific targeting signals. Reports on the heterologous function of these targeting signals are generally limited to one or a few species, with an emphasis on model plants such as tobacco and Arabidopsis. Given their sequence diversity and their insufficient testing in commercially important crops (including monocotyledonous crops), the extent to which these signals can be relied on for biotechnological purposes across species remains to be established. This study provides the experimental verification of a mitochondrial signal that is functional across diverse crop species, including five monocots (sugarcane, wheat, corn, sorghum and onion) and seven dicots (cucumber, cauliflower, tomato, capsicum, pumpkin, coriander and sunflower). In all 12 crops, transient assays following microprojectile bombardment showed that the N-terminal mitochondrial presequence from F 1-ATPase β-subunit (ATPase-β) of Nicotiana plumbaginifolia Viv. targeted green fluorescent fusion protein to the mitochondria. The transient assay results in sugarcane were confirmed in stably transformed root cells. The ATPase-β signal should be a useful metabolic engineering tool for directing recombinant proteins to the mitochondrial matrix in diverse plant species of commercial interest.

Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha(-1) y(-1). The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated. We used N metabolite analysis, N-15 labelling and N-15 natural abundance (delta(15)N) techniques. Deposited guano-derived uric acid is hydrolysed to ammonium (NH4+) and gaseous ammonia (NH3). Ammonium undergoes nitrification, and nitrate (NO3-) and NH4+ were the main forms of soluble N in the soil. Plants from seabird rookeries have a high capacity to take up and assimilate NH4+, are able to metabolise uric acid, but have low rates of NO3- uptake and assimilation. We concluded that NH4+ is the principal source of N for plants growing at seabird rookeries, and that the presence of NH4+ in soil and gaseous NH3 in the atmosphere inhibits assimilation of NO3-, although NO3- is taken up and stored. Seabird guano, Pisonia forest soil and vegetation were similarly enriched in N-15 suggesting that the isotopic enrichment of guano (delta(15)N 9.9parts per thousand) carries through the forest ecosystem. Soil and plants from woodland and beach environments had lower delta(15)N (average 6.5parts per thousand) indicating a lower contribution of bird-derived N to the N nutrition of plants at these sites. The aquifer under the cay receives seabird-derived N leached from the cay and has high concentrations of N-15-enriched NO3- (delta(15)N 7.9parts per thousand). Macroalgae from reefs with and without seabirds had similar delta(15)N values of 2.0-3.9parts per thousand suggesting that reef macroalgae do not utilise N-15-enriched seabird-derived N as a main source of N. At a site beyond the Heron Reef Crest, macroalgae had elevated delta(15)N of 5.2parts per thousand, possibly indicating that there are locations where macroalgae access isotopically enriched aquifer-derived N. Nitrogen relations of Heron Island vegetation are compared with other reef islands and a conceptual model is presented.

Ecophysiological research in Australia has focussed, at different times, on the fundamental similarities in function between all plant species, and on the peculiarity of Australian species with respect to their survival in stressful environments. Early work on plant water relations emphasised the differences between species, and indicated that diverse structural and functional attributes occurred in species from the same water-limited environment. Most recent research has emphasised processes that optimise rates of carbon dioxide exchange, but the understanding of functioning in plants with different morphological arrangements is incomplete. Variation in functions between individual plants and geographic populations in wild species has been examined to a lesser extent. The great variety within and between populations of wild plant species warrants further study for both understanding and more effective management of this biological resource.

Net primary production links the biosphere and the climate system through the global cycling of carbon, water and nutrients. Accurate quantification of net primary productivity (NPP) is therefore critical in understanding the response of the world's ecosystems to global climate change, and how changes in ecosystems might themselves feed back to the climate system. Twelve model estimates of long-term annual NPP for the Australian continent were reviewed. These models varied considerably in the approaches adopted and the inputs required. The model estimates ranged 5-fold, from 0.67 to 3.31 GtCy -1. Within-continent variation was similarly large, with most of the discrepancies occurring in the arid zone of Australia, which comprises most of the continent. It is also within this zone that empirical NPP data are most lacking. Comparison with a recent global-scale analysis of six dynamic global vegetation models showed a similar level of variability in continental total NPP, 0.38 to 2.85 GtCy-1, and similar within-continent spatial variability. As a first tentative step towards model validation the twelve NPP estimates were compared with existing field measurements, although the ability to reach definitive conclusions was limited by insufficient data, and incompatibilities between the field-based observations and the model predictions. It was concluded that the current NPP-modelling capability falls short of the accuracy required for effective application in understanding the terrestrial biospheric implications of global atmospheric/climatic change. Potential methods that could be used in future work for improving modelled estimates of Australian continental NPP and their validation are discussed. These include increasing the spatial coverage of empirical NPP estimates within arid ecosystems, the use of existing high quality site data for more detailed model exploration, and a formal model inter-comparison using uniform driver datasets to investigate more intensively differences in model behaviour and assumptions.

Leaf trait data were compiled for 258 Australian plant species from several habitat types dominated by woody perennials. Specific leaf area (SLA), photosynthetic capacity, dark respiration rate and leaf nitrogen (N) and phosphorus (P) concentrations were positively correlated with one another and negatively correlated with average leaf lifespan. These trait relationships were consistent with previous results from global datasets. Together, these traits form a spectrum of variation running from species with cheap but frequently replaced leaves to those with strategies more attuned to a nutrient-conserving lifestyle. Australian species tended to have SLAs at the lower end of the spectrum, as expected in a dataset dominated by sclerophyllous species from low fertility or low rainfall sites. The existence of broad-scale, 'global' relationships does not imply that the same trait relationships will always be observed in small datasets. In particular, the probability of observing concordant patterns depends on the range of trait variation in a dataset, which, itself, may vary with sample size or species-sampling properties such as the range of growth forms, plant functional 'types', or taxa included in a particular study. The considerable scatter seen in these broad-scale trait relationships may be associated with climate, physiology and phylogeny.

In Dendrobium and other orchids the ovule becomes mature long after pollination, whereas the ovary starts growing within two days of pollination. The signalling pathway that induces rapid ovary growth after pollination has remained elusive. We placed the auxin antagonist ¿-(p-chlorophenoxy) isobutyric acid (PCIB) or the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) on the stigma, before pollination. Both treatments nullified pollination-induced ovary growth. The ovaries also did not grow after similar stigma treatment with 1-methylcyclopropene (1-MCP), AgNO3 (both inhibitors of ethylene action), aminooxyacetic acid (AOA) or CoCl2 (which both inhibit ethylene synthesis), before pollination. Pollination could be replaced by placement of the auxin naphthylacetic acid (NAA) on the stigma. All mentioned inhibitors nullified the effect of NAA, indicating that if auxin is the initiator of ovary growth, it acts through ethylene. The results suggest that the pollination effect on ovary growth requires auxin (at least auxin transport and maybe also auxin signalling), and both ethylene synthesis and ethylene action

Limitations on maximum transpiration rates, which are commonly observed as midday stomatal closure, have been observed even under well-watered conditions. Such limitations may be caused by restricted hydraulic conductance in the plant or by limited supply of water to the plant from uptake by the roots. This behaviour would have the consequences of limiting photosynthetic rate, increasing transpiration efficiency, and conserving soil water. A key question is whether the conservation of water will be rewarded by sustained growth during seed fill and increased grain yield. This simulation analysis was undertaken to examine consequences on sorghum yield over several years when maximum transpiration rate was imposed in a model. Yields were simulated at four locations in the sorghum-growing area of Australia for 115 seasons at each location. Mean yield was increased slightly ( 5 - 7%) by setting maximum transpiration rate at 0.4 mm h(-1). However, the yield increase was mainly in the dry, low-yielding years in which growers may be more economically vulnerable. In years with yield less than similar to 450 g m(-2), the maximum transpiration rate trait resulted in yield increases of 9 - 13%. At higher yield levels, decreased yields were simulated. The yield responses to restricted maximum transpiration rate were associated with an increase in efficiency of water use. This arose because transpiration was reduced at times of the day when atmospheric demand was greatest. Depending on the risk attitude of growers, incorporation of a maximum transpiration rate trait in sorghum cultivars could be desirable to increase yields in dry years and improve water use efficiency and crop yield stability.

Sugarcane is an ideal candidate as a biofactory for the production of alternate higher value products. One way of achieving this is to direct useful proteins into the vacuoles within the sugarcane storage parenchyma tissue. By bioinformatic analysis of gene sequences from putative sugarcane vacuolar proteins a motif has been identified that displays high conservation across plant legumain homologues that are known to function within vacuolar compartments. This. ve amino acid motif, represented by the sequence IRLPS in sugarcane is shown to direct an otherwise secreted GFP fusion protein into a large acidic and proteolytic vacuole in sugarcane callus cells as well as in diverse plant species. In mature sugarcane transgenic plants, the stability of GFP appeared to be dependent on cell type, suggesting that the vacuolar environment can be hostile to introduced proteins. This targeting motif will be a valuable tool for engineering plants such as sugarcane for production of novel products.

Competition is a major determinant of plant community structure, and can influence the size and reproductive fitness of a species. Therefore, competitive responses may arise from alterations in gene expression and plant function when an individual is confronted with new competitors. This study explored competition at the level of gene expression by hybridising transcripts from Centaurea maculosa Lam., one of North America's most invasive exotic plant species, to an Arabidopsis thaliana (L.) Heynh microarray chip. Centaurea was grown in competition with Festuca idahoensis Elmer, a native species that generally has weak competitive effects against Centaurea; Gaillardia aristata Pursh, a native species that tends to be a much stronger competitor against Centaurea; and alone (control). Some transcripts were induced or repressed to a similar extent regardless of the plant neighbour grown with Centaurea. Other transcripts showed differential expression that was specific to the competitor species, possibly indicating a species-specific aspect of the competitive response of Centaurea. These results are the first to identify genes in an invasive plant that are induced or repressed by plant neighbours and provide a new avenue of insight into the molecular aspects of plant competitive ability.

Publicación ISI Email : frperez@uchile.cl Bud-break and the length and depth of endodormancy (ED) were studied in grapevine (Vitis Vinifera L.) cv. Thompson Seedless (Sultana) grown in the Elqui (warm winter) and in the Maipo (temperate winter) valleys of north and central Chile, respectively. High maximum daily winter temperatures, ordinarily occurring in the Elqui valley, reduced the depth without affecting the length of ED in comparison to buds grown in the Maipo valley. Furthermore, high winter temperatures during the ED period altered the oxidative metabolism of buds by increasing its mitochondrial respiratory capacity and increasing its levels of H2O2. Moreover, a reduced expression in alternative oxidase transcript was also observed at the end of the ED period in buds collected from the warmer Elqui valley in relation to those collected from the temperate Maipo valley. In controlled environments, the bud-break response of ecodormant (ECD) buds depended on the climatic zones from which buds were sampled (temperate or warm winter), and on whether growth chamber temperatures were held constant or fluctuated. Mitochondrial respiratory capacity of dormant grapevine buds was raised by warmer winter temperatures, and higher subsequent H2O2 levels at the ECD phase appeared to be related to the erratic breaking of latent buds in subtropical areas such as the Elqui valley.

Growing awareness of night-time leaf conductance (gnight) in many species, as well as genetic variation in gnight within several species, has raised questions about how genetic variation and environmental stress interact to influence the magnitude of gnight. The objective of this study was to investigate how genotype salt tolerance and salinity stress affect gnight for saltgrass [Distichlis spicata (L.) Greene]. Across genotypes and treatments, night-time water loss rates were 5-20% of daytime rates. Despite growth declining 37-87% in the high salinity treatments (300mm and 600mm NaCl), neither treatment had any effect on gnight in four of the six genotypes compared with the control treatment (7mm NaCl). Daytime leaf conductance (gday) also was not affected by salinity treatment in three of the six genotypes. There was no evidence that more salt tolerant genotypes (assessed as ability to maintain growth with increasing salinity) had a greater capacity to maintain gnight or gday at high salinity. In addition, gnight as a percentage of gday was unaffected by treatment in the three most salt tolerant genotypes. Although gnight in the 7mm treatment was always highest or not different compared with the 300mm and 600mm treatments, gday was generally highest in the 300mm treatment, indicating separate regulation of gnight and gday in response to an environmental stress. Thus, it is clear that genetics and environment both influence the magnitude of gnight for this species. Combined effects of genetic and environmental factors are likely to impact our interpretation of variation of gnight in natural populations.

Rising atmospheric carbon dioxide (CO₂) concentration and temperature will influence photosynthesis, growth and yield of agronomic crops. To investigate effects of elevated CO₂ and high temperature on leaf gas exchanges, activities of Rubisco and phosphoenolpyruvate carboxylase (PEPC) and growth of grain sorghum (Sorghum bicolor L. Moench), plants were grown in controlled environments at day-time maximum/night-time minimum temperatures of 30/20°C or 36/26°C at ambient (350μmolmol⁻¹) or elevated (700μmolmol⁻¹) CO₂. Gas-exchange rates, activities of Rubisco and PEPC and growth parameters (leaf, stem and total dry weights) were determined at different stages of leaf development. Between 6 and 25 days after leaf tip emergence, leaf carbon exchange rate (CER) of elevated CO₂ plants was greater at 30/20°C and 36/26°C than that of ambient CO₂ plants at the same temperatures. The positive response of CER to elevated CO₂ was greater in young leaves than in old leaves. In young leaves, elevated CO₂ enhanced Rubisco activity at 30/20°C and 36/26°C, whereas PEPC activity was not affected by elevated CO₂ at 30/20°C but was marginally enhanced at 36/26°C. At 30/20°C, growth parameters were not affected by elevated CO₂ until 50 days after sowing (DAS); at 36/26°C, they were progressively enhanced by elevated CO₂ to as high as 49 to 62% by 50 DAS. Leaf CER and Rubisco activity were enhanced by elevated CO₂ at early stages of leaf ontogeny for the C₄ grain sorghum. Such enhancement should have a significant role in dry matter production under elevated CO₂.