Madagascar is the world’s fourth largest island, and is renowned for its species diversity and endemism. Due to the wide diversity of climatic and ecological conditions on the island, the native biota provides a fascinating context for the study of speciation and plant radiation. On Madagascar, the trees of the genus Adansonia (Bombacoideae, Malvaceae), the baobabs, are prominent in the dry deciduous forests and thickets of the western half of the island. Baobab trees may live for more than 1000 years and are characterized by outcrossing breeding systems with self-incompatibility.
Adansonia (Bombacoideae) comprises nine species, six of which are endemic to Madagascar and genetic relationships within these remain unresolved due to conflicting results between nuclear and plastid DNA variation. A recent paper in Annals of Botany analyses nuclear microsatellite variation using Bayesian clustering programs and find a clear interspecific differentiation. They identify early-generation hybrids in contact areas between the species showing overlapping flowering periods and sharing the same pollinators. The results reveal a new, stabilized differentiated entity originating from hybridization in the current absence of the parental species, suggesting a potential role of hybridization in the recent diversification history of the Malagasy baobabs.
Tsy, J. M. L. P., Lumaret, R., Flaven-Noguier, E., Sauve, M., Dubois, M. P., & Danthu, P. (2013) Nuclear microsatellite variation in Malagasy baobabs (Adansonia, Bombacoideae, Malvaceae) reveals past hybridization and introgression. Annals of botany, 112(9), 1759-1773
Epidemic models in complex networks are helping us better understand infectious disease outbreaks. A review by Pautasso and Jeger published in AoB PLANTS focuses on the application of new developments in network epidemiology to the study and management of plant diseases. The main aspects covered are: 1) surveys of social networks, 2) models and data about human mobility, 3) epidemic models in directed and hierarchical networks, 4) studies of dynamic networks, and 5) spatial epidemic simulations integrating network data. Because of the increasing amounts of traded plant commodities and the associated rise in introduced plant pests and pathogens, network theory has a great potential in plant science.
Plants are extremely flexible organisms adaptable to a range of diverse environments. Their intrinsic ability to simultaneously inhabit both above- and below-ground domains makes them unique among most other living organisms, which occupy a single habitat at a given time.
In response to diverse environmental signals, plants modify their development through the perception and integration of exogenous signals into the signalling pathways of plant hormones. Auxin is one of the most versatile plant hormones and plays essential roles in growth and development. The revelation of the existence of an auxin biosynthesis, signalling and transport apparatus in single-celled green algae is a clear indication that auxin has played an important evolutionary role during the adaptation of plants to diverse land environments.
In recent years, significant progress has been made towards understanding how this hormone regulates plant growth and development. However, less is known about the roles of auxin as a regulator of biotic and abiotic stress responses. In this free review article, interesting new insights into the role of auxin as an integrator of environmental signals are highlighted.
Kazan, K. (2013) Auxin and the integration of environmental signals into plant root development. Annals of botany, 112(9), 1655-1665
Background: Auxin is a versatile plant hormone with important roles in many essential physiological processes. In recent years, significant progress has been made towards understanding the roles of this hormone in plant growth and development. Recent evidence also points to a less well-known but equally important role for auxin as a mediator of environmental adaptation in plants.
Scope: This review briefly discusses recent findings on how plants utilize auxin signalling and transport to modify their root system architecture when responding to diverse biotic and abiotic rhizosphere signals, including macro- and micro-nutrient starvation, cold and water stress, soil acidity, pathogenic and beneficial microbes, nematodes and neighbouring plants. Stress-responsive transcription factors and microRNAs that modulate auxin- and environment-mediated root development are also briefly highlighted.
Conclusions: The auxin pathway constitutes an essential component of the plant’s biotic and abiotic stress tolerance mechanisms. Further understanding of the specific roles that auxin plays in environmental adaptation can ultimately lead to the development of crops better adapted to stressful environments.
Biosciences has a couple of free access papers out on Natural History. Natural History’s Place in Science and Society is a 17 author call for action by Tewksbury et al calling on some biologists to identify as Natural Historians.
Musée national d’Histoire naturelle. Photo: Trey Ratcliff / Flickr
The concept puzzled me slightly. I come from a History of Science background and I’m used to thinking of Natural History as the thing that’s not quite Science in the ancient world. Tewksbury et al have a better definition:
[N]atural history is the observation and description of the natural world, with the study of organisms and their linkages to the environment being central.
It’s the second half of the definition that makes the paper interesting and distinct from Biology. The paper gives a number of examples to explain why they think Natural History has a contribution to make in the 21st century, but at the heart of them all is the focus on organisms and their connection to the environment. The connectivity and inter-disciplinary character of Natural History should be part of the zeitgeist, but the authors show this is not the case.
Avoidance of interspecific pollen transfer in Pedicularis
Plants surrounded by individuals of other co-flowering species may attract more pollinators but can suffer a reproductive cost from interspecific pollen transfer. Yang et al. compare pollination and reproduction in Pedicularis densispica (lousewort) when occurring alone or together with co-flowering Astragalus pastorius. They find that mixed populations attract many more nectar-seeking bumble-bees, which move frequently between the species. However, differences in floral architecture mean that P. densispica is pollinated via the dorsum of the bees whilst A. pastorius receives pollen via the abdomen, thus avoiding interspecific transfer. The overall result is that co-flowering yields more seeds that are heavier and have higher germinability than in pure populations of P. densispica.
It is generally believed that endophytic microorganisms are intercellular inhabitants present in either cultivable or non-cultivable form primarily as root colonizers. In a new study in AoB PLANTS, Thomas and Sekhar report extensive cytoplasmic colonization by endophytic bacteria in banana shoot-tissue which prima-facie displayed ‘Brownian movement’. Live cell imaging on tissue sections, callus, cell suspensions and protoplasts directly and after vital / SYTO-9 staining revealed two intracellular niches, namely cytoplasmic and periplasmic. Designated as ‘Cytobacts’ and ‘Peribacts’, these organisms were rarely amenable to cultivation and thus may have escaped the attention of biologists. This article, supported largely by live cell video-imaging, opens the way to studying these intracellular entities.
What happens when you insert single-walled carbon nanotubes into the leaves of Arabidopsis? The semiconducting nanotubes integrate themselves into the chloroplasts’ outer envelope and triple photosynthetic activity by enhancing electron transport.
So should we be making genetically modified plants containing carbon nanotubes? Well probably not – you have to believe that 3.5 billion years of evolution has optimised photosynthesis pretty well to achieve a nice balance. But that doen’t mean that this research is without applications, such as making living leaves that perform non-biological functions (for example, detecting pollutants or pesticides), or constructing artificial energy harvesting systems which don’t contribute to climate change.
Plant nanobionics approach to augment photosynthesis and biochemical sensing. (2014) Nature Materials 13, 400–408 doi:10.1038/nmat3890 [Subscription]
Abstract: The interface between plant organelles and non-biological nanostructures has the potential to impart organelles with new and enhanced functions. Here, we show that single-walled carbon nanotubes (SWNTs) passively transport and irreversibly localize within the lipid envelope of extracted plant chloroplasts, promote over three times higher photosynthetic activity than that of controls, and enhance maximum electron transport rates. The SWNT–chloroplast assemblies also enable higher rates of leaf electron transport in vivo through a mechanism consistent with augmented photoabsorption. Concentrations of reactive oxygen species inside extracted chloroplasts are significantly suppressed by delivering poly(acrylic acid)–nanoceria or SWNT–nanoceria complexes. Moreover, we show that SWNTs enable near-infrared fluorescence monitoring of nitric oxide both ex vivo and in vivo, thus demonstrating that a plant can be augmented to function as a photonic chemical sensor. Nanobionics engineering of plant function may contribute to the development of biomimetic materials for light-harvesting and biochemical detection with regenerative properties and enhanced efficiency.
Bioinspired materials: Boosting plant biology. Nature Materials News & Views (2014) 13, 329–331 doi:10.1038/nmat3926 [Subscription]
Hydrochoric gene flow in invasive riparian Impatiens
Riparian systems are prone to invasion by alien plant species, which may be facilitated by hydrochory, the transport of seeds by water. Love et al. study gene flow associated with hydrochoric dispersal of the invasive riparian plant Impatiens glandulifera (Himalayan balsam) in two contrasting river systems and find a significant increase in levels of genetic diversity downstream, consistent with the accumulation of propagules from upstream source populations. There is strong evidence for organisation of this diversity between different tributaries, reflecting the dendritic organisation of the river systems studied. The results indicate that hydrochory, rather than anthropogenic dispersal, is primarily responsible for the spread of I. glandulifera in these river systems.
Image: Marie Majaura/Wikimedia Commons.
Examples abound of ancient life forms trapped in suspended inanimation within amber (fossilised tree resin) and which give us clues about ancient – maybe even extinct – biota and their ecology (e.g. ‘The past is bright, the past is … amber’). A revelation concerning amber-encased plant material suggests that current sexual reproduction in angiosperms may have remained little changed in over 100 million years.
This insight comes from a new, albeit extinct, species named Micropetasos burmensis and work by George Poinar et al. with amber deposits from the mid-Cretaceous in Burma (Republic of the Union of Myanmar). Although given a binomial (with a formal description in English, as now permitted) and clearly a flowering plant, the team ‘prefer to leave the question of its exact familial relationships open at this time’. However, arguably the most interesting aspect of this discovery is the sight of pollen tubes growing out of two grains of pollen and penetrating the flower’s stigma (the receptive part of the female reproductive system). This precedes fertilisation of the egg, which would have begun the process of seed formation, had this act of plant coitus not been interrupted.
Curiously, this is not mentioned explicitly in the journal article, but was only discerned in the press release promoting it). Was that statement too outrageous or speculative for inclusion in the journal article? Surely not; legitimate commentary such as this ought to be encouraged, and only serves to make the discovery even more interesting. Come on, lads, don’t hide your light under a bush(-el)…
[OK, you can relax, I’ve saved you the trouble of finding that story about 165-million-year-old fossil insects caught during copulation. Text – and pictures – at the Smithsonian’s website. – Ed.]