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This paper reviews the results of several years' study by a multidisciplinary team comprising geneticists, physiologists, ecologists and statisticians of abiotic stress tolerance in barley. The strategy involves genetic fingerprinting of wild barley lines (Hordeum spontaneum C. Koch) from a range of habitats and testing these for responses to abiotic stresses under controlled conditions. Multiple regression analysis is used to identify genetic markers associated with experimentally determined stress responses. These data are related to site-of-origin ecogeographic data and used to identify areas of useful wild variation. Markers associated with traits of interest can be mapped in genetic mapping populations, revealing areas of the barley genome carrying genes controlling stress responses. This paper highlights our work on associations of amplied fragment length polymorphisms with salt tolerance and describes some initial results of the use of SSRs in studying drought tolerance in barley. [ABSTRACT FROM AUTHOR]

• This paper establishes relationships between two aspects of ribosomal DNA (rDNA) biology: epigenetic silencing of rDNA loci; and homogenization leading to concerted evolution. • Here, we examined rDNA inheritance and expression patterns in three natural Nicotiana allopolyploids (closest living descendants of diploid parents are given), N. rustica ( N. paniculata ×  N. undulata), N. tabacum ( N. sylvestris ×  N. tomentosiformis) and N. arentsii ( N. undulata ×  N. wigandioides), and synthetic F1 hybrids and allopolyploids. • The extent of interlocus rDNA homogenization decreased in the direction N. arentsii > N. tabacum >  N. rustica. The persistence of parental rDNA units in one of the subgenomes was associated with their transcription inactivity and likely heterochromatization. Of synthetic hybrids and polyploids only N. paniculata ×  N. undulata showed strong uniparental transcriptional silencing of rDNA triggered already in F1. • Epigenetic patterns of expression established early in allopolyploid nucleus formation may render units susceptible or resistant to homogenization over longer time-frames. We propose that nucleolus-associated transcription leaves rDNA units vulnerable to homogenization, while epigenetically inactivated units, well-separated from the nucleolus, remain unconverted. [ABSTRACT FROM AUTHOR]

This Virtual Issue "The biology of wood", highlights the central role of wood biology in basic plant science, as well as critical ecological, environmental, economic and societal issues. It seems as though the plastid and mitochondrial carbon metabolism pathway genes show a coordinated expression with their nuclear gene counterparts, and with specific stages of wood development. The functional characterization of a poplar Class I KNOX gene, I KNAT2/6b i , concluded that this gene is important for the regulation of cell differentiation, in part through its influence on the expression of NAC transcription factors (Zhao I et al i ., [14], in this issue of I New Phytologist i , pp. 1531-1543). Integration of these data showed an enrichment of specific epigenetic markers with genes expressed during wood formation, and together represent an important advancement in our global understanding of gene regulation during wood formation. [Extracted from the article]

Numerous authors have attempted to quantity the physical properties of leaves in relation to aspects of leaf ecology, including decomposition, sclerophylly, herbivory, and leaf function and longevity. This paper examines the relative merits of the punch-and-die, tearing and shearing tests for assessing leaf physical properties. We conducted a series of these three mechanical tests on leaves of Solanum laciniatum, and determined the effect of various test parameters on the measurement of fracture properties. For the punch-and-die test, the parameters considered were machine speed, clearance between the punch and the die, edge definition of the punch, and area of the punch. Aspects of the tearing test examined were notch length, and effects, and length-to width requirements of t est strips, and for shearing tests the effects of blade proximity, angle and sharpness were investigated. All the test parameters investigated were found significantly to affect the assessment of leaf-fracture properties. In addition, fracture properties were found to vary significantly within leaves. Some general principles for designing and implementing tests are outlined. This study suggests that while punching and shearing tests are useful means of quantifying leaf fracture properties, the value of the tearing test may be reduced as it is most constrained by the biological nature of the test material. [ABSTRACT FROM AUTHOR]

This paper reports general patterns of relative growth rate and related traits in response to elevated atmospheric CO2 in eight woody species ranging widely in life form, leaf habit, taxonomy and ecology. Young plants of these species, all of comparable ontogenetic phases, were grown simultaneously in large containers with favourable nutrient and water availability in transparent outdoor chambers at 350 and 700 μl l-1 CO2 for one growing season. We found the following consistent responses. (1) All species grew faster at elevated CO2, whereas the following leaf and allocation traits were consistently lower in CO2-enriched environments: specific leaf area (quotient of leaf area and leaf weight), leaf area ratio (quotient of total leaf area and plant weight), weight-based foliar N concentration and, to a smaller extent, leaf weight fraction (quotient of leaf weight and plant weight). (2) There was important interspecific variation in the magnitude of the response of relative growth rate to CO2. Specific leaf area at ambient CO2 explained 88% of the variation in relative growth rate to CO2 among the eight species. At ambient CO2, relative growth rate itself, was significantly correlated with the relative growth rate response to CO2 only if the leafless species Ulex gallii was excluded from analysis. (3) The four deciduous species had a significantly stronger relative growth rate response to CO2 than the four evergreens. This corresponded with their generally higher specific leaf area. (4) Specific leaf area and leaf habit might be useful for scaling up exercises, as easy-to-measure substitutes for growth responses of (woody) vegetation to elevated CO2. However, the usefulness of such traits in this context needs to be tested in realistic, longer-term manipulative experiments in real ecosystems. [ABSTRACT FROM AUTHOR]

Air spaces in the internodal regions of Ilippuris vulgaris L. are separated from each other by a single file of cells, a feature which permits a geometric description of their arrangement according to the number of adjacent air spaces. This number ranges from four to eight with an average of 6.04±0.29. Vertices between three adjacent air spaces are composed of either an hexagonal central cell from which three cells radiate outward, is called a cell vertex (CV) and has a frequency of o.453, or by three pentagonal cells with a common wall point, is called a wall vertex (WV) and has a frequency of 0.547. Air spaces arise from certain three-rayed vertices by wall separation and a subsequent series of unequal cell divisions in which the ends of cell plates only attach to walls bordering air spaces. A paper-pencil model was devised in order to identify the critical steps of this ontogenetic .sequence. One important ordering process in generating this pattern of air space arrangement is an alternating selection of vertices around cell and cell groupings which will become air spaces. A second ordering feature is the positioning of cell plates in order that they attach only to facets bordering air spaces. This model produces the features of spaces separated by a single row of cells and the ratio of the two types of vertices cited above but only approximates the number of cells around a space. It has been demonstrated here that walls of a cell can influence each other through some type. of inhibition, and as a morphogenetic mechanism in general, it may play an important role in other cases of tissue development. [ABSTRACT FROM AUTHOR]

The article introduces the February 1987 issue of the journal New Phytologist. This supplement is an annotated check-list of the distribution of mycorrhiza in the British flora by researchers J.L. Harley and E.L. Harley. Since its early days the journal has been a leading forum for the dissemination and discussion of matters mycorrhizal. Later the frequency of mycorrhizal papers increased. Although based on the British flora, the checklist which accompanies this issue has a far wider geographical and biological significance.

The standard method of measuring pollen limitation is to add pollen to a number of flowers, preferably to a whole plant, and to compare fruit and seed set with that of naturally pollinated flowers on other plants. In 25 yr of research, this method has yielded valuable data, but it is difficult to use in large plants. This has caused a bias in the available data towards smaller, herbaceous plants with relatively few flowers. I argue that, in order to widen our knowledge of how pollen limitation affects plants, we should go beyond whole-plant pollen addition and change our concept of how a flowering plant functions. The traditional method does not take into account the variation in and dynamics of resource allocation and pollen availability. The concept of integrated physiological units (IPUs) does, but, although it has been applied to pollination biology, it has not received the attention it deserves. I use this article to present its merits again, to propose a step-by-step methodology for studying pollen limitation, and to examine factors influencing possible plant strategies. [ABSTRACT FROM AUTHOR]

Summary: Late Paleozoic arborescent lycopsids have been thought to have grown from sporelings into large trees through the production of a periderm cylinder, particularly massive in the proximal portion of the trunk and tapering distally, with this rind of bark providing most of their structural support.Here, we argue that physiological limitations would have prohibited the production of thick periderm and test this hypothesis using multiple independent lines of evidence derived from anatomical permineralization and surface impression fossils that allow both direct and indirect measurement of periderm radial thickness.Across all six genera of Pennsylvanian arborescent lycopsids that were investigated, all evidence indicates limited periderm production: typically < 5 cm, always < 15 cm, even in trunks that would have reached 1 m or more in diameter.The large amount of arborescent lycopsid periderm in Middle Pennsylvanian coals represents taphonomic enrichment rather than a true anatomical signal, complicating interpretation of their biology including biomechanics and early ontogeny. [ABSTRACT FROM AUTHOR]

The article by professor A. D. Boney which opens this issue is both unusual and timely, unusual for this journal in that, rather than being scientific, it is an historical account, biographical in nature, timely because similar issues are at large today both within botanical teaching in particular and that of biology in general. By his compulsive and absorbing narrative, Boney's article, a product of his meticulous searching through the archives of the University of Glasgow, brings into sharp focus the events which followed a deliberately provocative paper on the teaching of elementary botany, published in 1917 in this journal "New Phytologist."

Plants are commonly exposed to abiotic and biotic stresses., We used 350 Arabidopsis thaliana accessions grown under controlled conditions. We employed genome-wide association analysis to investigate the genetic architecture and underlying loci involved in genetic variation in resistance to: two specialist insect herbivores, Pieris rapae and Plutella xylostella; and combinations of stresses, i.e. drought followed by P. rapae and infection by the fungal pathogen Botrytis cinerea followed by infestation by P. rapae., We found that genetic variation in resistance to combined stresses by drought plus P. rapae was limited compared with B. cinerea plus P. rapae or P. rapae alone. Resistance to the two caterpillars is controlled by different genetic components. There is limited overlap in the quantitative trait loci (QTLs) underlying resistance to combined stresses by drought plus P. rapae or B. cinerea plus P. rapae and P. rapae alone. Finally, several candidate genes involved in the biosynthesis of aliphatic glucosinolates and proteinase inhibitors were identified to be involved in resistance to P. rapae and P. xylostella, respectively., This study underlines the importance of investigating plant responses to combinations of stresses. The value of this approach for breeding plants for resistance to combinatorial stresses is discussed. [ABSTRACT FROM AUTHOR]

Abiotic filters have been found either to increase or reduce evolutionary relatedness in plant communities, making it difficult to generalize responses of this major feature of biodiversity to future environmental change. Here, we hypothesized that the responses of phylogenetic structure to environmental change ultimately depend on how species have evolved traits for tolerating the resulting abiotic changes., Working within ephemeral wetlands, we tested whether species were increasingly related as flooding duration intensified. We also identified the mechanisms underlying increased relatedness by measuring root aerenchyma volume ( RAV), a trait which promotes waterlogging tolerance., We found that species-specific responses to flooding explained most of the variation in occurrence for 63 vascular plant species across 5170 plots. For a subset of 22 species, we attributed these responses to variation in RAV. Large RAV specifically increased occurrence when flooding lasted for longer time periods, because large RAV reduced above-ground biomass loss. As large RAV was evolutionarily conserved within obligate wetland species, communities were more phylogenetically related as flooding increased., Our study shows how reconstructing the evolutionary history of traits that influence the responses of species to environmental change can help to predict future patterns in phylogenetic structure. [ABSTRACT FROM AUTHOR]

Introduces a series of articles on plant science and biology.

In this article the author discusses how plants response to salt in a soil salination. He is critical on how plants cope with excess salt in the environment and the effect of salt stress to plants. Also investigated is the integration of three disparate elements in plant stress biology including lipid signalling, mitogen-activated protein kinase (MAPK) signalling and the SOS1 salt tolerance mechanism.

Gene flow from diploid to polyploid species could have significant effects on the morphology and ecology of polyploids. The potential of such introgression for bringing about evolutionary change within polyploids has long been recognized, although there are few examples of the process in the wild. Here, we focus on introgression between the diploid species, Senecio squalidus, and the tetraploid, S. vulgaris, which resulted in the origin of a variant form of S. vulgaris that produces radiate rather than nonradiate flower heads. The radiate variant of S. vulgaris is more attractive to pollinators and has a higher outcrossing rate. We review recent work that has isolated and characterized two regulatory genes, RAY1 and RAY2, that control presence of ray florets in radiate flower heads, and which have been introgressed into S. vulgaris from S. squalidus in the recent past. We identify a copy of RAY2 in S. vulgaris ( RAY2b) homeologous to the copy ( RAY2a) previously isolated, thus providing further evidence that S. vulgaris is allotetraploid. We also show that the RAY2a-R allele, which is fixed in radiate S. vulgaris, occurs at intermediate frequency in S. squalidus. Thus, based on this result, it is not possible to distinguish whether radiate S. vulgaris originated once or multiple times following hybridization between nonradiate S. vulgaris and S. squalidus. [ABSTRACT FROM AUTHOR]

•Set out here is the first generic account of the cytological effects of dehydration and rehydration and exogenous abscisic acid on moss protonemata. •Protonemal cells were subjected to slow and fast drying regimes, with and without prior exposure to abscisic acid. The cytological changes associated with de- and rehydration were analysed by light, fluorescence and transmission electron microscopy, together with pharmacological studies. •Protonemata survive slow but not fast drying, unless pretreated with abscisic acid. Dehydration elicits profound cytological changes, namely vacuolar fragmentation, reorganization of the endomembrane domains, changes in the thickness of the cell wall and in the morphology of plastids and mitochondria, and the controlled dismantling of the cytoskeleton; these dynamic events are prevented by fast drying. In control cells, abscisic acid elicits changes that partially mimic those associated with slow drying, including controlled disassembly of cytoskeletal elements, thus enabling protonemal cells to survive normally lethal rates of water loss. •Our demonstration that moss protonemata are an ideal system for visualizing and manipulating the cytological events associated with vegetative desiccation tolerance in land plants now opens up the way for genomic dissection of the underlying mechanisms. [ABSTRACT FROM AUTHOR]

• Physiological changes with ontogeny are common in plants. Although ontogenetic changes are hypothesized to improve plant function, their adaptive significance has rarely been tested. • Here, we estimated phenotypic selection on ontogenetic change in photosynthesis ( A) and stomatal conductance ( gs) of Avena barbata. We tested whether ontogenetic changes in A and gs increased fitness in wet and dry soil environments. To determine whether evolution in response to this selection would be constrained, we estimated the heritability of ontogenetic change in physiology, as well as cross-environment genetic correlations. • Ontogenetic change in A, but not gs, was adaptive in the wet soil environment; plants that maintained or increased A from the prereproductive to the reproductive phase had higher fitness. In the dry soil environment, ontogenetic change in A and gs was adaptively neutral. We detected significant genetic variation for ontogenetic change in A and gs, but no cross-environment genetic correlations, suggesting that the evolution of these traits would not be genetically constrained. • We demonstrate that ontogenetic changes in physiological traits can increase fitness but the adaptive value of these changes varies among traits and environments. [ABSTRACT FROM AUTHOR]

Simultaneously growing sinks are thought to compete for plant resources. Negative correlations, for example between grain number and stem mass in cereals, indeed resemble competition; but is the notion of intra-plant competition evolutionarily justified? Here we review intra-plant competition in light of two aspects of evolutionary biology: (a) major transitions that led to the reorganization of evolutionary individuals (e.g. isolated DNA molecules and independent cells) into new units of adaptation (e.g. chromosomes and multicellular organisms) with associated constraints to intra-individual conflict; and (b) genomic conflicts within individual plants with implications for resource allocation. Against this background, we look at apparent competition among genetically identical plant parts, and conclude that plants might use competition-like mechanisms to allocate resources, but only to the extent that these proximate mechanisms enhance overall plant fitness. In dealing with apparent competition among genetically different plant structures, we emphasize developing seeds attached to the same maternal plant, and the determination of yield components in annual crops. We propose that competition-like mechanisms among genetically different plant parts have been strongly shaped by the evolution of genomic conflict between parent and offspring, between female and male parents, and among siblings. By defining the number and potential size of grain simultaneously and before fertilization, a strong maternal control of resource allocation is exerted that favours uniform offspring size and partially counteracts genomic conflict. [ABSTRACT FROM AUTHOR]

Duplication is a prominent feature of plant genomic architecture. This has led many researchers to speculate that gene duplication may have played an important role in the evolution of phenotypic novelty within plants. Until recently, however, it was difficult to make this connection. We are now beginning to understand how duplication has contributed to adaptive evolution in plants. In this review we introduce the sources of gene duplication and predictions of the various fates of duplicates. We also highlight several recent and pertinent examples from the literature. These examples demonstrate the importance of the functional characteristics of genes and the source of duplication in influencing evolutionary outcome. [ABSTRACT FROM AUTHOR]

• Phenotypic and genetic clines have long been synonymous with adaptive evolution. However, other processes (for example, migration, range expansion, invasion) may generate clines in traits or loci across geographical and environmental gradients. It is therefore important to distinguish between clines that represent adaptive evolution and those that result from selectively neutral demographic or genetic processes. • We tested for the differentiation of phenotypic traits along environmental gradients using two species in the genus Silene, whilst statistically controlling for colonization history and founder effects. We sampled seed families from across the native and introduced ranges, genotyped individuals and estimated phenotypic differentiation in replicated common gardens. • The results suggest that post-glacial expansion of S. vulgaris and S. latifolia involved both neutral and adaptive genetic differentiation (clines) of life history traits along major axes of environmental variation in Europe and North America. Phenotypic clines generally persisted when tested against the neutral expectation, although some clines disappeared (and one cline emerged) when the effects of genetic ancestry were statistically removed. • Colonization history, estimated using genetic markers, is a useful null model for tests of adaptive trait divergence, especially during range expansion and invasion when selection and gene flow may not have reached equilibrium. [ABSTRACT FROM AUTHOR]

Contents Summary 513 I. Introduction 513 II. Continua in plant host–pathogen interactions 514 III. Mechanisms underlying continua in specificity and virulence 516 IV. Ecological consequences 519 V. Evolutionary patterns and processes 520 VI. Conclusions 524 Acknowledgements 525 References 525 Ecological, evolutionary and molecular models of interactions between plant hosts and microbial pathogens are largely based around a concept of tightly coupled interactions between species pairs. However, highly pathogenic and obligate associations between host and pathogen species represent only a fraction of the diversity encountered in natural and managed systems. Instead, many pathogens can infect a wide range of hosts, and most hosts are exposed to more than one pathogen species, often simultaneously. Furthermore, outcomes of pathogen infection vary widely because host plants vary in resistance and tolerance to infection, while pathogens are also variable in their ability to grow on or within hosts. Environmental heterogeneity further increases the potential for variation in plant host–pathogen interactions by influencing the degree and fitness consequences of infection. Here, we describe these continua of specificity and virulence inherent within plant host–pathogen interactions. Using this framework, we describe and contrast the genetic and environmental mechanisms that underlie this variation, outline consequences for epidemiology and community structure, explore likely ecological and evolutionary drivers, and highlight several key areas for future research. [ABSTRACT FROM AUTHOR]

• To better understand invasion dynamics, it is essential to determine the influence of genetics and ecology in species persistence in both native and nonnative habitats. One approach is to assess patterns of selection on floral and growth traits of individuals in both habitats. • Mimulus guttatus (Phrymaceae) has a mixed mating system and grows under variable water conditions across its native and nonnative range in North America. Field investigations of patterns of selection of floral and plant size traits were conducted in two native and two nonnative populations. Field-collected seed was grown and crossed in the glasshouse using a paternal half-sib design. The resulting offspring were grown in saturated and dry-down low-water conditions and the same traits were measured in both environments. • Patterns of selection varied across years in the native range. Nonnative populations exhibited selection for increased floral size, consistent with the hypothesis that selection favors larger size in nonnative habitats. In the glasshouse, we detected genetic variation for traits across population/treatment combinations. However, size hierarchy in the glasshouse was dependent on water conditions. • Our results suggest that both variable selection pressures and local adaptation probably influence the persistence of both native and nonnative populations. [ABSTRACT FROM AUTHOR]

• The repeated, independent evolution of phenotypic traits reflects adaptation to similar selective pressures. In some circumstances, parallel phenotypic evolution has a common genetic basis. Here, we investigate the types of genetic change responsible for the repeated evolution of red flowers among Ipomoea species. • We identified three independent transitions from cyanidin- (blue/purple) to pelargonidin-type (red) anthocyanin pigments among Ipomoea species. The genetic basis for these transitions was examined using transgenics and gene expression assays. Using a literature survey to estimate the expected spectrum of mutation types capable of producing red flowers, we evaluated whether the observed distribution of mutation types differed from expectation. • In these species, red floral pigmentation appears to be caused by the disruption of flux through the anthocyanin pathway at the same position. Results implicate tissue-specific regulatory changes in the same gene, which suggests the possibility that flower color evolved independently via the same genetic mechanism. • Although multiple molecular mechanisms are capable of producing red flowers, we found a deviation between the distributions of observed and expected mutation types responsible for these evolutionary transitions. Regulatory mutations thus appear to be preferentially targeted during evolutionary change between species. We discuss possible explanations for this apparent bias. [ABSTRACT FROM AUTHOR]

Among carnivorous plants, Darwin was particularly fascinated by the speed and sensitivity of snap-traps in Dionaea and Aldrovanda. Recent molecular work confirms Darwin's conjecture that these monotypic taxa are sister to Drosera, meaning that snap-traps evolved from a ‘flypaper’ trap. Transitions include tentacles being modified into trigger hairs and marginal ‘teeth’, the loss of sticky tentacles, depressed digestive glands, and rapid leaf movement. Pre-adaptations are known for all these traits in Drosera yet snap-traps only evolved once. We hypothesize that selection to catch and retain large insects favored the evolution of elongate leaves and snap-tentacles in Drosera and snap-traps. Although sticky traps efficiently capture small prey, they allow larger prey to escape and may lose nutrients. Dionaea's snap-trap efficiently captures and processes larger prey providing higher, but variable, rewards. We develop a size-selective model and parametrize it with field data to demonstrate how selection to capture larger prey strongly favors snap-traps. As prey become larger, they also become rarer and gain the power to rip leaves, causing returns to larger snap-traps to plateau. We propose testing these hypotheses with specific field data and Darwin-like experiments. The complexity of snap-traps, competition with pitfall traps, and their association with ephemeral habitats all help to explain why this curious adaptation only evolved once. [ABSTRACT FROM AUTHOR]

• Local adaptation may be important for the preservation of genetic diversity and the promotion of speciation. However, local adaptation may also constrain establishment in different environments. The consequences of local adaptation depend strongly on the pleiotropic effects of the genes involved in adaptation. • Here, we investigated the pleiotropic effects of the genetic response to selection in outbred lines of Arabidopsis artificially selected to flower earlier under both winter- and spring-annual simulated conditions. The consequences of adaptation were evaluated by reciprocally transplanting selected and control lines between the two conditions. • Selected lines always flower earlier than their controls, independent of growing conditions. However, selected lines, growing in the same condition in which they were selected, flower earlier than plants selected in the alternative environment. Plants selected to flower earlier in spring produce more fruits than controls when growing in the spring, and less fruits when growing in the winter; indicating that local adaptation has negative pleiotropic effects in another environment. • Our results indicate that local adaptation can arise even when selection targets the same trait in the same direction. Furthermore, it suggests that adaptation under the two different environments can generate fitness trade-offs that can maintain genetic variation for flowering time. [ABSTRACT FROM AUTHOR]

Contents Summary 273 I. Introduction 274 II. A brief history of domestication in grasses 275 III. Domestication genes 278 IV. Models of the domestication process 280 V. Evolutionary consequences of domestication for grass genomes 281 VI. Mating systems and the evolutionary dynamics of domestication in grasses 284 VII. Conclusion 286 Acknowledgements 287 References 287 Crop grasses were among the first plants to be domesticated c. 12 000 yr ago, and they still represent the main staple crops for humans. During domestication, as did many other crops, grasses went through dramatic genetic and phenotypic changes. The recent massive increase in genomic data has provided new tools to investigate the genetic basis and consequences of domestication. Beyond the genetics of domestication, many aspects of grass biology, including their phylogeny and developmental biology, are also increasingly well studied, offering a unique opportunity to analyse the domestication process in a comparative way. Taking such a comparative point of view, we review the history of domesticated grasses and how domestication affected their phenotypic and genomic diversity. Considering recent theoretical developments and the accumulation of genetic data, we revisit more specifically the role of mating systems in the domestication process. We close by suggesting future directions for the study of domestication in grasses. [ABSTRACT FROM AUTHOR]

Contents Summary 22 I. Introduction 23 II. Evidence for the occurrence of MHB 23 III. Ecological and evolutionary implications of MHB 23 IV. The question of MHB specificity 27 V. Mechanisms of the MHB effect 28 VI. Role of MHB in mycorrhizal functions 31 VII. Conclusions and research priorities 32 References 33 In natural conditions, mycorrhizal fungi are surrounded by complex microbial communities, which modulate the mycorrhizal symbiosis. Here, the focus is on the so-called ‘mycorrhiza helper bacteria’ (MHB). This concept is revisited, and the distinction is made between the helper bacteria, which assist mycorrhiza formation, and those that interact positively with the functioning of the symbiosis. After considering some examples of MHB from the literature, the ecological and evolutionary implications of the relationships of MHB with mycorrhizal fungi are discussed. The question of the specificity of the MHB effect is addressed, and an assessment is made of progress in understanding the mechanisms of the MHB effect, which has been made possible through the development of genomics. Finally, clear evidence is presented suggesting that some MHB promote the functioning of the mycorrhizal symbiosis. This is illustrated for three critical functions of practical significance: nutrient mobilization from soil minerals, fixation of atmospheric nitrogen, and protection of plants against root pathogens. The review concludes with discussion of future research priorities regarding the potentially very fruitful concept of MHB. [ABSTRACT FROM AUTHOR]

Contents Summary 7 I. Introduction 8 II. Cell expansion and plant growth 8 III. Cell wall responses to stress 11 IV. Pathogen attack and mechanical stimuli 11 V. Lessons from yeast 12 VI. Candidate sensors and receptors in plants 14 VII. Conclusions 17 Acknowledgements 17 References 17 The emerging view of the plant cell wall is of a dynamic and responsive structure that exists as part of a continuum with the plasma membrane and cytoskeleton. This continuum must be responsive and adaptable to normal processes of growth as well as to stresses such as wounding, attack from pathogens and mechanical stimuli. Cell expansion involving wall loosening, deposition of new materials, and subsequent rigidification must be tightly regulated to allow the maintenance of cell wall integrity and co-ordination of development. Similarly, sensing and feedback are necessary for the plant to respond to mechanical stress or pathogen attack. Currently, understanding of the sensing and feedback mechanisms utilized by plants to regulate these processes is limited, although we can learn from yeast, where the signalling pathways have been more clearly defined. Plant cell walls possess a unique and complicated structure, but it is the protein components of the wall that are likely to play a crucial role at the forefront of perception, and these are likely to include a variety of sensor and receptor systems. Recent plant research has yielded a number of interesting candidates for cell wall sensors and receptors, and we are beginning to understand the role that they may play in this crucial aspect of plant biology. [ABSTRACT FROM AUTHOR]

• The self-incompatibility (SI) status of 571 taxa from the Asteraceae was identified and the taxa were scored as having SI, partial SI or self-compatibility (SC) as their breeding system. A molecular phylogeny of the internal transcribed spacer (ITS) region was constructed for 211 of these taxa. • Macrophylogenetic methods were used to test hypotheses concerning the ancestral state of SI in the Asteraceae, the gain and loss of SI, the irreversibility of the loss of SI and the potential for partial SI or SC to be terminal states. • The ancestral breeding system in the family could not be resolved. Both maximum likelihood and parsimony analyses indicated that transitions among all breeding system states provide the best fit to the data and that neither partial SI nor SC is a terminal state. Furthermore, the data indicated that the loss of SI is not irreversible, although breeding system evolution has been more dynamic in some clades than in others. • These results are discussed within the context of evidence for the gain and loss of SI, the evolutionary role of partial SI and methodological assumptions of tests of breeding system evolution. [ABSTRACT FROM AUTHOR]

The article discusses the effects of precipitation change on ecosystems. Almost all terrestrial biomes is influenced by the availability of water influences ecosystem structure and function in almost all terrestrial biomes. Precipitation is the main input of this limiting resource, which drives both biotic and abiotic processes. The inherent variability in precipitation is one of the grand challenges associated with studies of precipitation change. An increasing number of experiments are focusing on the interaction of precipitation change with other potential abiotic or biotic driving variables becuase many global changes are occuring simultaneously.

• Although arbuscular mycorrhizal (AM) fungi are a major pathway in the global carbon cycle, their basic biology and, in particular, their respiratory response to temperature remain obscure. • A pulse label of the stable isotope 13C was applied to Plantago lanceolata, either uninoculated or inoculated with the AM fungus Glomus mosseae. The extra-radical mycelium (ERM) of the fungus was allowed to grow into a separate hyphal compartment excluding roots. We determined the carbon costs of the ERM and tested for a direct temperature effect on its respiration by measuring total carbon and the 13C:12C ratio of respired CO2. With a second pulse we tested for acclimation of ERM respiration after 2 wk of soil warming. • Root colonization remained unchanged between the two pulses but warming the hyphal compartment increased ERM length. δ13C signals peaked within the first 10 h and were higher in mycorrhizal treatments. The concentration of CO2 in the gas samples fluctuated diurnally and was highest in the mycorrhizal treatments but was unaffected by temperature. Heating increased ERM respiration only after the first pulse and reduced specific ERM respiration rates after the second pulse; however, both pulses strongly depended on radiation flux. • The results indicate a fast ERM acclimation to temperature, and that light is the key factor controlling carbon allocation to the fungus. [ABSTRACT FROM AUTHOR]

• The aim of the study was to assess the potential importance for Mediterranean plants of trade-offs in the response to irradiance and water availability at the regeneration stage. • Survival and growth patterns across an experimentally imposed irradiance gradient (1, 6, 20 and 100% sunlight) were studied in seedlings of eight Mediterranean woody species, together with the impact of a simulated summer drought. • We found evidence of some of the trade-offs previously reported for non-Mediterranean plant communities, such as between survival in the shade and relative growth rate (RGR) at high light, but no evidence for others, such as between shade and drought tolerances. The impact of drought on survival and RGR was stronger in high light than in deep shade. • The observed species-specific differences in performance provide a mechanistic basis for niche differentiation at the regeneration stage, contributing to possible explanations of species coexistence in Mediterranean ecosystems. [ABSTRACT FROM AUTHOR]

Contents Summary 453 I. Introducing plant metabolomics 453 II. The technologies for data acquisition 455 III. Mind the gap: data analysis, bioinformatics and statistics 458 IV. Potential and limitations 461 V. Applications 462 VI. Data integration, metabolic networks and systems biology 464 VII. Where do we go from here? Bright prospects for the future 465 Acknowledgements 465 References 465 In a short time, plant metabolomics has gone from being just an ambitious concept to being a rapidly growing, valuable technology applied in the stride to gain a more global picture of the molecular organization of multicellular organisms. The combination of improved analytical capabilities with newly designed, dedicated statistical, bioinformatics and data mining strategies, is beginning to broaden the horizons of our understanding of how plants are organized and how metabolism is both controlled but highly flexible. Metabolomics is predicted to play a significant, if not indispensable role in bridging the phenotype–genotype gap and thus in assisting us in our desire for full genome sequence annotation as part of the quest to link gene to function. Plants are a fabulously rich source of diverse functional biochemicals and metabolomics is also already proving valuable in an applied context. By creating unique opportunities for us to interrogate plant systems and characterize their biochemical composition, metabolomics will greatly assist in identifying and defining much of the still unexploited biodiversity available today. [ABSTRACT FROM AUTHOR]

• Arachnitis uniflora, a myco-heterotrophic plant species, has fleshy tuberous roots colonized by the arbuscular mycorrhizal fungal genus Glomus (Phylum Glomeromycota). These roots produce apical and lateral propagules, both reported here for the first time. The objective of the study was to characterize the ontogeny and structure of the propagules, and to determine their function. • Scanning electron microscopy, laser scanning confocal microscopy and light microscopy were used to study the ontogeny and structure of the propagules. • Propagules developed either from cortical parenchyma cells or from cells immediately beneath the root cap; they developed a shoot meristem and cells in the basal region which were colonized by various fungal structures including hyphae and vesicles. • These propagules may detach from the roots, establishing new plants. [ABSTRACT FROM AUTHOR]

• We conducted meta-analyses of 290 published field and glasshouse trials to determine the effects of various agricultural practices on mycorrhizal colonization in nonsterile soils, and the consequence of those effects on yield, biomass, and phosphorus (P) concentration. • Mycorrhizal colonization was increased most by inoculation (29% increase), followed by shortened fallow (20%) and reduced soil disturbance (7%). The effect of crop rotation depended on whether the crop was mycorrhizal. Increased colonization resulted in a yield increase in the field of 23% across all management practices. • Biomass at harvest and shoot P concentration in early season were increased by inoculation (57 and 33%, respectively) and shortened fallow (55 and 24%). Reduced disturbance increased shoot P concentration by 27%, but biomass was not significantly affected. Biomass was significantly reduced in 2% of all trials in which there was a significant increase in colonization. • Irrespective of management practice, an increased mycorrhizal colonization was less likely to increase biomass if either soil P or indigenous inoculum potential was high. [ABSTRACT FROM AUTHOR]

Based on empirical evidence from the literature we propose that, in nature, phenotypic plasticity in plants is usually expressed at a subindividual level. While reaction norms (i.e. the type and the degree of plant responses to environmental variation) are a property of genotypes, they are expressed at the level of modular subunits in most plants. We thus contend that phenotypic plasticity is not a whole-plant response, but a property of individual meristems, leaves, branches and roots, triggered by local environmental conditions. Communication and behavioural integration of interconnected modules can change the local responses in different ways: it may enhance or diminish local plastic effects, thereby increasing or decreasing the differences between integrated modules exposed to different conditions. Modular integration can also induce qualitatively different responses, which are not expressed if all modules experience the same conditions. We propose that the response of a plant to its environment is the sum of all modular responses to their local conditions plus all interaction effects that are due to integration. The local response rules to environmental variation, and the modular interaction rules may be seen as evolving traits targeted by natural selection. Following this notion, whole-plant reaction norms are an integrative by-product of modular plasticity, which has far-reaching methodological, ecological and evolutionary implications.New Phytologist(2005)doi: 10.1111/j.1469-8137.2004.01310.x© New Phytologist(2005) [ABSTRACT FROM AUTHOR]

Abrupt speciation through interspecific hybridisation is an important mechanism in angiosperm evolution. Flowering plants therefore offer excellent opportunities for studying genetic processes associated with hybrid speciation. Novel molecular approaches are now available to examine these processes at the level of both genome organization and gene expression– transcriptomics. Here, we present an overview of the molecular technologies currently used to study hybrid speciation and how they are providing new insights into this mode of speciation in flowering plants. We begin with an introduction to hybrid speciation in plants, followed by a review of techniques, such as isozymes and other markers, which have been used to study hybrid species in the past. We then review advances in molecular techniques that have the potential to be applied to studies of hybrid species, followed by an overview of the main genomic and transcriptomic changes suspected, or known, to occur in newly formed hybrids, together with commentary on the application of advanced molecular tools to studying these changes.New Phytologist(2004)doi: 10.1111/j.1469-8137.2004.01253.x© New Phytologist(2004) [ABSTRACT FROM AUTHOR]

Contents Summary 000 I. Introduction 000 II. Cyclic nucleotide monophosphates 000 III. cNMPs and their roles in cyanobacteria 000 IV. Molecular identification of components of the cNMP signalling pathway in cyanobacteria 000 V. Lessons from cAMP signalling in cyanobacteria for other organisms 000 Acknowledgements 000 References 000 The cyanobacteria are a diverse group of photosynthetic prokaryotes, of which many species synthesize cyclic nucleotide monophosphates. The role of cyclic nucleotide monophosphates in cyanobacterial biology has been studied through phenotypic, molecular, genetic, and computer-based analyses and here I review the history of the field. The study of cyclic nucleotide monophosphates in cyanobacteria has been informed by experiments performed in unrelated organisms but recent investigations have, however, demonstrated that scientific principles, applicable to a wide range of species, can be derived from the study of cyclic nucleotide biology in cyanobacteria and I detail some of this work. [ABSTRACT FROM AUTHOR]

The treatment of wheat roots with 2,4-dichlorophenoxyacetic acid (2,4-D) led to the formation of tumour-like structures, para-nodules, which were readily colonized by cyanobacteria. The amount of cyanobacteria found on 2,4-D treated roots was 3.6 times higher than that found onuntreated roots. Cyanobacteria penetrated the para-nodules by migrating in between loosely arranged cells that covered their surfaces or by penetrating the space at the juction of root and para-nodule. In plants treated with 2,4-D and co-cultivated with cyanobacteria in medium without combined nitrogen, the rate of acetylene reducing was three times that seen in untreated but colonized roots. Addition of 2,4-D itself did not change the rate of acetylene reducing in free-living culture of Nostoc sp. strain 2S9B. In plants treated with 2,4-D and co-cultivated with Nostoc sp. strain 2S9B in medium without combined nitrogen the nitrogen content of roots but not shoots was significantly increased. [ABSTRACT FROM AUTHOR]

The interactive influences of elevated carbon dioxide, water stress, and ontogeny on carbon assimilation and biomass production were investigated in northern red oak, a species having episodic shoot growth characteristics. Seedlings were grown from acorns through three shoot-growth flushes (8-11 wk) in controlled-environment chambers at 400, 530 or 700 μmol mol-1 CO2 and under well watered or water-stressed soil-moisture regimes. Increasing CO2 growth concentration from 400 to 700 μmol mol-1 resulted in a 34% increase in net assimilation rate (A), a 31% decrease in stomatal conductance to water vapour (gs) and a 141% increase in water use efficiency (WUE) in well watered seedlings. In contrast, water-stressed seedlings grown at 700 μmol mol-1 CO2 demonstrated a 69 % increase in A, a 23% decrease in gs and a 104% increase in WUE. However, physiological responses to increased CO2and water stress strongly modified by ontogeny. During active third-flush shoot growth, A in first-flush and second-flush foliage of water-stressed seedlings increased relative to the quiescent phase following cessation of second-flush growth by an average of 115% ; gs increased by an average of 74%. In contrast, neither A nor gs in comparable foliage of well watered seedlings changed in response to active third-flush growth. Whereas seedlings growth was continuous through three flushes in well watered seedlings, growth of water-stressed seedlings was minimal following the leaf-expansion stage of the third flush. Through three growth flushes total seedling biomass and biomass allocation to root, shoot and foliage components were very similar in water-stressed seedlings grown at 700 μmol mol-1 CO2and well watered seedlings grown at 400 μmol mol-1 CO2. Enhancement effects of elevated CO2 on seedling carbon (C) assimilation and biomass production may offset the negative impact of moderate water stress and are likely to be determined by ontogeny and stress impact on carbon sink demand. [ABSTRACT FROM AUTHOR]

In the 'F' horizons of acid mor-humus soils of heathland ecosystems, mycorrhizal roots of the dominant ericaceous species form a large fraction of the soil biomass. Rapid turnover of these roots provides the potential for recycling of substantial amounts of nitrogen contained in their fungal and plant components. Here, we first determine the amount of N in the biomass of ericoid roots growing in heathland and show it to constitute a large proportion of total soil N. In order to assess the accessibility of this N to ericaceous plants, experiments were then conducted using aseptically produced shoot and root necromass of Vaccinium macrocarpon Ait., the roots being grown with or without mycorrhizal colonization. These materials were provided as sole nitrogenous substrates in growth experiments using the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan in pure culture and V. macrocarpon in the mycorrhizal (M) or non-mycorrhizal (NM) condition as test organisms. The experiments were designed to test the hypothesis that the N contained in these substrates can be mobilized by the mycorrhizal endophyte. The ability of the endophyte to utilize the substrates was determined by measuring fungal yields and by assessing the presence of its extra-cellular protease and chitinase enzymes. Transfer of N to the host by the endophyte was determined through measurements of plant yield and tissue N contents. H. ericae produced a significantly greater yield on shoot and mycorrhizal root necromass than on non-mycorrhizal root necromass. The extra-cellular enzymes protease and chitinase were produced by the fungus when grown on the M root necromass. The fungus also transferred N to the host plant, up to 76% of N contained in the substrate being found in M plants whereas less than 5% was present in their NM counterparts. [ABSTRACT FROM AUTHOR]

Three perennial grass species, Lolium perenne L., Agrostis capillaris L. and Festuca ovina L., were homogeneously labelled in phytotrons with 14CO2 at two CO2 concentrations (350 and 700 μl l-1). Plants were grown under two nitrogen regimes: one with a minor addition of 8 kg N ha-1, the other with an addition of 278 kg N ha-1. Carbon allocation over the different compartments of the plant/soil systems was measured: shoots, roots, rhizosphere soil (soil solution, microbial biomass and soil residue), and bulk soil. Elevated CO2 increased total net 14C recovery in all species by 14%, and significantly enhanced the below-ground 14C allocation by 26%, this enhancement was 24%, 39% and 21% for root, rhizosphere soil and bulk soil, respectively. Within the rhizosphere soil, the 14C amounts in the soil solution (+69%) and soil residue (+49%) increased significantly. Total microbial biomass-C in the rhizosphere soil was also increased (15%) by the elevated CO2 treatment, but only in proportion to the increased root mass. No interactions were observed between the elevated CO2 and N treatments. The N treatment increased total net 14C recovery by more than 300% and 14C was preferentially allocated to the shoots, leading to a significant increase in shoot-to-root ratio. However, N fertilization also increased (+111%) the absolute amount of 14C in soil. The three species behaved differently, but no interactions were observed between CO2 treatment and plant species. These results show that elevated CO2 induces an increased C input into soil for all three grass species at both N levels. However, the highest absolute amounts were found in the soils of the fastest growing species and at the highest N level. [ABSTRACT FROM AUTHOR]