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.

For they are jolly good fellows

The Royal Society/Wikimedia Commons.

The Royal Society/Wikimedia Commons.

We’d like to add our words of congratulations to two recently appointed plant-biological Fellows of the Royal Society (of London for Improving Natural Knowledge), Professor Liam Dolan FRS (Sherardian Professor of Botany, Department of Plant Sciences, University of Oxford, UK) and Professor David Beerling FRS (Professor of Palaeoclimatology, Department of Animal and Plant Sciences, University of Sheffield, UK). Fittingly, Dolan has been so honoured because his ‘pivotal discoveries illuminate our understanding of the interrelationships between the development of plants, their evolution and the Earth System’ (e.g. Victor Jones and Liam Dolan, 2012Timothy Lenton et al.,  2012). Beerling has received his accolade in view of how ‘his integration of ecosystem processes into a broad geosciences framework established the importance of the terrestrial biosphere in Earth’s climate history’ (e.g. Laura Llorens et al., 2009*; Beerling, 2012). In addition to their research activities both have also taken time out to help spread the botanical message and enthuse the next generation of plant biologists, Dolan in the highly regarded undergraduate textbook Plant Biology, and Beerling with The Emerald Planet. Dolan and Beerling join approximately 1600 other Fellows in the self-governing fellowship that is the Royal Society, and which includes ‘many of the world’s most distinguished scientists drawn from all areas of science, engineering, and medicine’. Well done to these most deserving botanists!

 

* It’s also rather gratifying to think that having their work published in the Annals of Botany will have helped both gentlemen attain fellowship!

[And congratulations, too, to those UK researchers working in plant sciences (including fungi…) who’ve been named in the global Top 1%. This listing of ‘Highly Cited Researchers 2014’ names more than 3000 people selected by having writing the greatest numbers of ‘reports officially designated by Essential Science IndicatorsSM as Highly Cited Papers’. I counted four female and 11 male notables from addresses – ‘primary affiliations’ – in north, central, west and south of England, but none from Scotland (or Wales or Northern Ireland). However, I am intrigued by included scientist ‘Philip J. White’, whose primary affiliation is shown as King Saud University, Saudi Arabia (KSU), because I found no mention of this notable person on KSU’s website. So, I wonder if this could actually be the Philip J. White currently at The James Hutton Institute (Invergowrie, Scotland, UK). That P. J. White has many other affiliations – Special Professor in Plant Ion Transport at the University of Nottingham (UK), Adjunct Professor at the University of Western Australia, Visiting Associate Professor at the Comenius University, Bratislava (Slovakia), Visiting Professor of the Brazilian Research Council, and an Honorary Lecturer at the University of Dundee (Scotland) – so maybe KSU was amongst those at the time the census was taken? Or perhaps there’s been a mistake? Or there’s another Philip J. White who is even more highly cited than James Hutton’s? So, will P. J. White please get in touch and put the record straight? – Ed.]

[Ed. – we are pleased to be able to report that the mystery has now been solved. The PJ White referred to is indeed Philip White of the James Hutton Institute who is also a Professor in Biology at the King Saud University. And we are more than happy to advise that the same PJ White is a co-author on one of the Annals of Botany’s most highly downloaded papers – White PJ and Broadley MR, Calcium in plants; Annals of Botany 92: 487-511, 2003.].

Early wound reactions of Japanese maple during winter dormancy: the effect of two contrasting temperature regimes

14082-TDuring winter dormancy, temperate trees are capable of only a restricted response to wounding. Depending on the ambient temperature during winter dormancy, wounded trees may start compartmentalization, e.g. by producing inhibitory compounds, but it is thought that processes involving cell proliferation, such as the formation of callus and wound xylem, are delayed until the next growing season. In a recent study published in AoB PLANTS, Copini et al. investigated the effect of wounding on Acer palmatum trees during winter-bud dormancy and found that in the cold (4 °C) treatment, wound reactions were virtually absent. In the warm (15 °C) treatment, however, trees reacted actively to wounding within a three-week period by, e.g., forming callus and local wound xylem. They conclude that temperature is an important factor in wound reactions during winter dormancy and may even induce the formation of callus and wound xylem within a three-week period.