Maintenance of self-incompatibility in peripheral populations of a circumboreal woodland subshrub

A flowering individual of Linnaea borealis (twinflower) in Xinjiang, northwestern China, noting its clonal production by stolons.  Photo credit: Shuang-Quan Huang

A flowering individual of Linnaea borealis (twinflower) in Xinjiang, northwestern China, noting its clonal production by stolons. Photo credit: Shuang-Quan Huang

Compared with self-incompatible (SI) species, species that shift to self-compatibility (SC) are more likely to colonize a new habitat. Linnaea borealis, named after Carl Linnaeus and commonly known as twinflower, is an undershrub of woods with a circumpolar distribution in boreal forests. Twinflower is SC at the eastern edge of the species distribution in North America, and SI in populations from Canada through Britain to central Sweden. In a new study in AoB PLANTS, Zhang et al. observed that twinflower was strictly SI in northwestern China, the eastern margin of the species’ distribution in Eurasia. Generalist pollinators and clonal reproduction may help L. borealis to colonize in marginal areas without the shift from SI to SC, but with fruit-set failure resulting from self-plant pollination within clones.

Legume genomics and next-generation sequencing (Invited Review)

Legume genomics and next-generation sequencing (Invited Review)

Legume genomics and next-generation sequencing (Invited Review)

The legume family (Leguminosae) consists of approximately 17 000 species and those used as crops provide protein and carbohydrates for over 300 million people world-wide. O’Rourke et al. review how next-generation sequencing technologies and associated bioinformatic analyses have allowed individual researchers to assemble genomes, identify gene-coding regions and study gene expression patterns. To illustrate the power of next-generation sequencing in elucidating gene networks underlying biological processes, they present two example studies: an analysis of gene expression profiles in soybean oil seed development and an analysis of phosphate deficiency altering gene expression patterns to induce cluster root formation in white lupin.

Inflorescences take centre stage

Inflorescences issue cover Annals of Botany has a new special issue in Free Access: Inflorescences. It’s a useful reminder to me of another area of Botany I need to read more about.

For a start, I think I’ve said elsewhere that inflorescences are the structures where there are multiple flowers on a plant and not just a single flower. In a clumsy way this might be true but it also misses the point of an inflorescence. It’s not simply that there are multiple flowers, but also that those flowers work with each other as unit. They’re not just a collection of individuals.

If you approach inflorescences from this point of view, their structure becomes a bit of a puzzle. Why the diversity? But also, can you classify them sensibly and, if you can, what is the basis of that? Do different structures correspond with different functions?

Lawrence Harder and Przemyslaw Prusinkiewicz describe the interplay between inflorescence development and function as the crucible of architectural diversity. It highlights the importance of linking structures and function. In terms of tracing plant relationships, structure is useful but it’s also worth looking at what the structure does. A similar structure could have a very different result if the phenology, the timing of the flowering, changes.

Time is key factor that is highlighted by Harder and Prusinkiewicz. Looking at a display, it’s easy to think of it as an organisation in space, but they also make a point that inflorescences are dynamic. They change with time, and how they change with time has consequences for their function.

As far as plant reproduction goes, it’s easy to focus on the success of flowers, but Harder and Prusinkiewicz argue that what you have is part of a modular system, and that to understand it you have to look at the system as a whole, instead of modules in isolation. Most angiosperms use inflorescences so it’s clearly a powerful tool for a plant. Looking at them as a unit and not just parts can put plant reproduction into a new context.

Harder L.D. & Prusinkiewicz P. (2012). The interplay between inflorescence development and function as the crucible of architectural diversity, Annals of Botany, 112 (8) 1477-1493. DOI: http://dx.doi.org/10.1093/aob/mcs252

Asymmetric cell divisions in plant development

Asymmetric cell divisions in plant development

Asymmetric cell divisions in plant development

Asymmetric cell divisions define plant development. High-throughput genomic and modelling approaches can elucidate their regulation, which in turn could enable the engineering of plant traits such as stomatal density, lateral root development and wood formation. Asymmetric divisions are formative divisions that generate daughter cells of distinct identity. These divisions are coordinated by either extrinsic (‘niche-controlled’) or intrinsic regulatory mechanisms and are fundamentally important in plant development.

A recent review in Annals of Botany describes how asymmetric cell divisions are regulated during development and in different cell types in both the root and the shoot of plants. It further highlights ways in which omics and modelling approaches have been used to elucidate these regulatory mechanisms. For example, the regulation of embryonic asymmetric divisions is described, including the first divisions of the zygote, formative vascular divisions and divisions that give rise to the root stem cell niche. Asymmetric divisions of the root cortex endodermis initial, pericycle cells that give rise to the lateral root primordium, procambium, cambium and stomatal cells are also discussed. The authors provide a perspective on the role of other hormones or regulatory molecules in asymmetric divisions, the presence of segregated determinants and the usefulness of modelling approaches in understanding network dynamics within these very special cells.

 

Kajala, Kaisa, Priya Ramakrishna, Adam Fisher, Dominique C. Bergmann, Ive De Smet, Rosangela Sozzani, Dolf Weijers, and Siobhan M. Brady. Omics and modelling approaches for understanding regulation of asymmetric cell divisions in arabidopsis and other angiosperm plants. (2014) Annals of Botany 113(7): 1083-1105.
 

 

Zinc, meristem anatomy and seed germination – this week in Annals of Botany

Zinc concentration in young leaves In situ analysis of foliar zinc absorption and short-distance movement in fresh and hydrated leaves of tomato and citrus using synchrotron-based X-ray fluorescence microscopy
Globally, zinc deficiency is one of the most important nutritional factors limiting crop yield and quality. Despite widespread use of foliar-applied zinc fertilizers, much remains unknown regarding the movement of zinc from the foliar surface into the vascular structure for translocation into other tissues and the key factors affecting this diffusion. Using synchrotron-based X-ray fluorescence microscopy (µ-XRF), absorption of foliar-applied zinc nitrate or zinc hydroxide nitrate was examined in fresh leaves of tomato (Solanum lycopersicum) and citrus (Citrus reticulatus). The results advance our understanding of the factors that influence the efficacy of foliar zinc fertilizers and demonstrate the merits of an innovative methodology for studying foliar zinc translocation mechanisms.

 

How and why does the areole meristem move in Echinocereus (Cactaceae)?
In Cactaceae, the areole is the organ that forms the leaves, spines and buds. Apparently, the genus Echinocereus develops enclosed buds that break through the epidermis of the stem adjacent to the areole; this trait most likely represents a synapomorphy of Echinocereus. The development of the areole is investigated here in order to understand the anatomical modifications that lead to internal bud development and to supplement anatomical knowledge of plants that do not behave according to classical shoot theory. The enclosed areole meristem and internal bud development are understood to be an adaptation to protect the meristem and the bud from low temperatures.

 

Effects of germination time on seed morph ratio in a seed-dimorphic species and possible ecological significance
Diaspores of heteromorphic species may germinate at different times due to distinct dormancy-breaking and germination requirements, and this difference can influence life history traits. The primary aim of this study was to determine the effect of germination time of the two seed morphs of Suaeda corniculata subsp. mongolica on life history traits of the offspring. The flexible strategy of a species that produces different proportions of dimorphic seeds in response to variation in germination timing may favour the maintenance and regeneration of the population in its unpredictable environment.

 

The Guardian tackles the ethics of rewilding

The Guardian posted an interesting article yesterday from Tori Herridge: Mammoths are a huge part of my life. But cloning them is wrong.

Mammoth

Mammoth of BC by Tyler Ingram / Flickr.

I’ll concede that a mammoth is not a plant, but part of what I found interesting is that Herridge points out that mammoths didn’t exist in isolation. She tackles the idea that mammoths could somehow be part of a plan to restore the arctic steppes, but she makes an important point:

There’s a reason the terms “de-extinction” and “rewilding” are so powerful and that’s because they imply a return to a time, a state of grace, a place that was somehow unspoiled. Cloning a mammoth offers us the hope of undoing the excesses of humanity, bringing back the creatures whose extinction we helped bring about.

I think the idea of turning back the clock, to a time when things are better, is a powerful image. However it isn’t practical. Herridge points out that the mammoth was part of a wider ecosystem of arctic steppe, and it’s not certain that the plants will naturally appear if you dump a load of mammoths in Siberia.

It’s not even purely about the plants. Looking this up I saw there was a lot about remediation in the Root Biology special issue of Annals of Botany (now free access). In particular, Interactions between exotic invasive plants and soil microbes in the rhizosphere suggest that ‘everything is not everywhere’ say Rout and Callaway. They’re talking about microbes in the context of invasive species, but I wonder what ten thousand years of change has done to the soil of the arctic.

We don’t have the plants, we may not have the right soils. We are going through a big extinction event. I’d love to see a mammoth, but sadly when you look at the social problems a mammoth would have, as well as the many conservation efforts competing for limited funding, I think Tori Herridge is right, and that she does a good job of explaining all the problems.

More closely related plants have more distinct mycorrhizal communities

14090R1Neighbouring plants are known to vary from having similar to dissimilar arbuscular mycorrhizal fungal (AMF) communities. One possibility is that closely related plants have more similar AMF communities than more distantly related plants, an indication of phylogenetic host specificity. However, in a new study published in AoB PLANTS, Reinhart and Anacker observed that mycorrhizal communities were more divergent among closely related plant species than among distantly related plant species. This was counter to the observation that plant mutualists (e.g. pollinators, seed dispersers) are often shared among closely related host plant species. Since mycorrhizae may affect nutrient competition among neighbouring plants, closely related plant neighbours that associate with unique mycorrhizae may have greater functional complementarity and a greater capacity to coexist.

Pioneer root xylem development in Populus

Pioneer root xylem development in <i>Populus</i>

Pioneer root xylem development in Populus

Effective programmed xylogenesis is critical to the structural framework of the plant root system and its central role in the acquisition and long-distance transport of water and nutrients. Bagniewska-Zadworna et al. study the differentiation of tracheary elements (TEs) in pioneer roots of Populus trichocarpa grown in rhizotrons and find that the primary event is a burst of NO in thin-walled cells, followed by H2O2 synthesis and TUNEL-positive nuclei appearance. Subsequent events involve secondary cell wall formation and autophagy. Potential gene markers from the cinnamyl alcohol dehydrogenase (CAD) gene family that are related with secondary wall synthesis are associated with primary xylogenesis, showing clear expression in cells that undergo differentiation into TEs. The CAD genes appear to be involved in primary xylem differentiation and the formation of the cell walls in TEs before their functional maturity.

Phylogeny of OVATE family proteins in land plants

Phylogeny of OVATE family proteins in land plants

Phylogeny of OVATE family proteins in land plants

The OVATE gene encodes a nuclear-localized regulatory protein belonging to a distinct family of plant-specific proteins known as the OVATE family proteins (OFPs). Liu et al. identify 13 sequenced plant genomes in public databases that represent the major evolutionary lineages of land plants and conduct a phylogenetic analysis based on the alignment of the conserved OVATE domain. Genes for OFPs are found to be present in all the sampled land plant genomes, including the early-diverged lineages, mosses and lycophytes, and 11 subgroups of OFPs are defined in angiosperms. The results provide new insights into the evolution of the OVATE protein family and establish a solid base for future functional genomics studies on this important but poorly characterized regulatory protein family.

 

Effects of submergence and de-submergence on a clonal plant

Effects of submergence and de-submergence on a clonal plant

Effects of submergence and de-submergence on a clonal plant

Submergence and de-submergence are common phenomena encountered by riparian plants as water levels fluctuate, but little is known about the role of physiological integration in the adaptation of clonal plants to such conditions. Luo et al. study Alternanthera philoxeroides (alligator weed) after 30 days of submergence and find that connections between submerged and non-submerged ramets enhance the performance of the submerged ramets, but little effect remains once the ramets have then been de-submerged for 20 days. This is due to quick recovery of growth and photosynthesis, and this combines with the benefits of physiological integration in allowing riparian clonal plants to survive submergence and spread rapidly after de-submergence.