N-source preference in plants (Viewpoint)
Plants can utilize two major forms of inorganic nitrogen, nitrate (NO3–) and ammonium (NH4+), with some species appearing to ‘prefer’ one form over another, under certain conditions. Soil-N speciation has been shown to be an important determinant of species distribution, but no ecophysiologically realistic, mathematically sound model has yet emerged to describe and predict this phenomenon.
In a viewpoint article in Annals of Botany, Britto and Kronzucker suggest that this is because assignment of such preferences is not straightforward, and must take into account a wide array of complex physiological and environmental features, which interact in ways that are still not well understood.
Britto D.T. & Kronzucker H.J. (2013). Ecological significance and complexity of N-source preference in plants, Annals of Botany, 112 (6) 957-963 DOI: 10.1093/aob/mct157
Highlight on diversity, ecology and evolution of extrafloral nectaries
Plants in over 100 families bear extrafloral nectaries (EFNs), which secrete a carbohydrate-rich food that attracts ants and other arthropods. By fostering ecologically important protective mutualisms, EFNs play a significant role in structuring both plant and animal communities. As an introduction to a Highlight collection of papers published in the June issue, Marazzi et al. provide an overview of recent research on EFN diversity, ecology and evolution, and conclude that our understanding of the roles EFNs play in plant biology is being revolutionized with the use of new tools from developmental biology and genomics, new modes of analysis allowing hypothesis-testing in large-scale phylogenetic frameworks, and new levels of inquiry extending to community-scale interaction networks. The authors highlight major gaps in our current knowledge, and outline directions for future research.
Mating system and adaptive potential for leaf morphology
Self-pollination is often regarded as an evolutionary dead end, yet many selfers seem capable of retaining high adaptive potential. Andersson and Ofori perform experimental crosses within an initially self-sterile population of Crepis tectorum to produce an outbred and inbred progeny population, and find that a shift to selfing promotes adaptive potential for leaf morphology by increasing the overall genetic variance and by exposing potentially advantageous recessive alleles to selection. The results point to a positive role for inbreeding in phenotypic evolution, at least during or immediately after a rapid shift in mating system.
Environmental and genetic effects on a cline in seed dormancy
Climate may determine changes in seed dormancy in the short and the long term, shaping plant responses to global change. Fernández-Pascual et al. investigate germination in Centaurium somedanum, a narrow endemic species, using seeds collected from different wild populations along a local altitudinal gradient and seeds of a subsequent generation produced in a common garden. They find a local dormancy cline that is related to climatic differences between sites and to population genetic composition. This cline is further affected by the weather conditions during seed maturation, which influence the receptiveness to dormancy-breaking factors. The presence of intraspecific variation at such a local scale highlights the great potential of physiological dormancy to adapt to environmental changes.
Apomixis in Paspalum (Review)
Apomixis, an asexual mode of reproduction by seeds, is desirable in agriculture because it guarantees the perpetuation of superior genotypes by self-seeding without loss of hybrid vigour. Ortiz et al. critically review more than half a century of research in Paspalum, a genus that provides an excellent model for studying apomixis in grasses (Poaceae). In particular they consider advances in cyto-embryology of apomixis, the development of detailed molecular maps of the trait, and the isolation of the first candidate genes. Strategies to validate the role of these genes in apomictic process are discussed, with special emphasis on plant transformation in natural apomictic species and the prospects for introgressing an apomixis system into crop plants.
Medieval iconography of watermelons
The watermelon, Citrullus lanatus (Cucurbitaceae), is an important fruit vegetable. In order to obtain an improved understanding of watermelon history in Mediterranean Europe, Paris et al. collect, examine and compare medieval drawings of watermelons from around 1300ad onwards. Drawings in herbal-type manuscripts depict watermelon foliage realistically, and the fruits are small, round and striped. Drawings in agriculture-based manuscripts show considerable variation in size, shape and coloration of fruits. Red-flesh and white-flesh watermelons are illustrated, corresponding to the typical sweet dessert watermelons common today and the insipid citron watermelons, respectively. Evidently, citron watermelons were more common in Mediterranean Europe in the past than they are presently.
Population structure and domestication events within Cynara
Globe artichoke and leafy cardoon are two crops belonging to the same species, Cynara cardunculus (Asteraceae). Gatto et al. analyse population structure and genetic relationships between var. scolymus (artichoke), var. altilis (leafy cardoon) and their wild progenitor, var. sylvestris, and suggest that two distinct domestication events took place. Artichoke probably originated in Sicily, and they find evidence in its history for a demographic bottleneck. The results suggest a possible new scenario for western wild cardoon having derived from leafy cardoon that escaped from cultivation.
Floral elaiophore structure in the Gomesa and Oncidium clades
Recent molecular approaches have resulted in the re-circumscription of Gomesa and Oncidium (Orchidaceae; Oncidiinae), together with their respective clades. Stpiczyńska et al. compare the anatomical organization of the floral elaiophore (oil gland) of a further four species of Oncidiinae (two species from each clade), and find that in terms of location, morphology, anatomy and ultrastructure, the floral elaiophores of both Gomesa and Oncidium species are very similar, and distinction between these genera is not possible based on these features alone. Furthermore, many of these elaiophore characters are shared with representatives of other clades of Oncidiinae, including the Ornithocephalus clade. Consequently, elaiophores are considered homoplasious and of limited value in investigating the phylogeny of this subtribe.
Threshing efficiency and domestication of emmer wheat
Harvesting method has long been recognized as an important factor in the emergence of domesticated cereal genotypes, but post-harvet processing has received little attention. Tzarfati et al. quantify the effects of spike brittleness and threshability (both major domestication traits) upon threshing time and efficiency in a diverse range of tetraploid wheat genotypes, including emmer wheat (Triticum turgidum ssp. dicoccoides) and modern cultivars of durum wheat (T. turgidum ssp. durum). They find that both non-brittleness and increased threshability are significant labour-saving traits that increase the efficiency of post-harvest processing, which could have been an incentive for rapid domestication of the Near Eastern cereals.
Floral longevity and autonomous selfing in Collinsia
Collinsia heterophylla, a protandrous, preferentially cross-pollinating hermaphrodite, undergoes delayed selfing facilitated by floral senescence. Jorgensen and Arathi find that under drought stress, cross-pollination early in the floral lifespan reduces floral longevity, but excess soil moisture does not extend longevity. Pollen receipt, a reliable cue for fecundity, accelerates flower drop, but similarly reduced longevity in unmanipulated flowers under water-stress generates a potential for exacerbating sexual conflict in this species. Reduction in longevity under drought suggests a strong environmental effect that could perhaps alter the preferred breeding mode; however, higher outcrossed seed production over that by autonomous selfing implies that inbreeding depression may limit the benefits of selfing.