Morphology of lateral root development – free review article

Morphology of lateral root development

Morphology of lateral root development

The crucial role of roots in plant nutrition, and consequently in plant productivity, is a strong motivation to study the growth and functioning of various aspects of the root system. Numerous studies on lateral roots mostly focus on the physiological and molecular bases of developmental processes. Unfortunately, little attention is paid either to the morphological changes accompanying the formation of a lateral root or to morphological defects occurring in lateral root primordia. The latter are observed in some mutants and occasionally in wild-type plants, but may also result from application of external factors.

A recent free review article in Annals of Botany discusses morphological aspects of lateral branching in roots are analysed, examining studies that have looked at developmental changes in lateral root morphology in order to understand better the process of lateral root development.

Our knowledge of the molecular bases of lateral root initiation and development has increased rapidly within recent decades. Building on these advances, we may try to widen our knowledge of the probable relation between auxin and root system morphology, based in part on the auxin-related mutants whose root growth and development are altered in comparison with wild-type plants. Yet it is important to remember that, as a physical object, the lateral root (as well as other plant organs) also has characteristic physical properties. A change of form of such an object implies either a change in the distribution of mechanical stress or a change in mechanical properties. Direct measurement of both of these remains a challenge, mostly because of technical difficulties. However, the few reports examining the mechanical parameters of tissues of roots show that no challenge in science is so great that it is not taken up.

Szymanowska-Pułka, J. (2013). Form matters: morphological aspects of lateral root development. Annals of botany, 112(9), 1643-1654.

 

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Spatial and temporal functional changes in alpine summit vegetation are driven by increases in shrubs and graminoids

13080-TR1Classical approaches to investigating temporal and spatial changes in community composition offer only partial insight into the ecology that drives species distribution, community patterns and processes, whereas a functional approach can help to determine many of the underlying mechanisms that drive such patterns. In order to determine the mechanisms that drive changes in plant community composition across spatial and temporal scales, a new study published in AoB PLANTS by Venn et al. used plant functional traits to interpret the results of a repeat species survey across a gradient of five alpine summits in south-east Australia. Vegetation changes were strongly affected by the high and increasing proportion of tall shrubs and graminoids, especially at the lower elevation summits. Several significant relationships between the community trait-weighted mean of different traits and elevation suggest that processes such as competition are influencing vegetation preferentially across the elevation gradient, with shrubs and graminoids driving these patterns.

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Book Review – Pollination and Floral Ecology

Pollination and Floral Ecology

Pollination and Floral Ecology

Pat Willmer. 2011. Princeton University Press. £65. pp. 832.

Any text book that tries to assess and summarise the whole of a multidisciplinary research field such as pollination ecology and floral biology is required to be four things:  (1) comprehensive in its scope; (2) up to date in its coverage of the literature; (3) accurate in its assessment of the current state of the field; and (4) authoritative in the conclusions it presents.

This volume by Professor Pat Willmer of the University of St Andrews certainly ticks the first box.  It’s a huge book, and covers everything relating to the evolution of flower attraction and reward systems, ecological interactions with pollinators, biochemistry, physiology, agriculture and conservation; all in 29 chapters split into three sections, with 87 pages of references.  The literature extends to 2010, which is impressive for a book published in 2011 (though see my comments below about completeness of the literature).   Specialist terms are highlighted in bold to direct the reader to the glossary at the back, a useful device even if there are a few inaccuracies, which I’ll mention later.

So far so good, and the author is to be congratulated on putting together such a comprehensive, not to mention timely, single-author book.  It’s clearly the summation of a career devoted to studying pollinators and flowers, and the author’s passion for her subject is apparent throughout.

However when we come to points 3 and 4, things are less straightforward.  There are some issues with accuracy that are troubling in a book aimed at newcomers to the field as well as established researchers.  To give just a few examples:

- on p.18 we are told that asclepiads have “one stamen” (they have five); on p.169 and in the glossary that asclepiad pollinia are the pollen grains from one anther (they are the contents of half an anther); and on p.170 that the pollinaria are “glued” to pollinators (they actually clip on).

- in the glossary, tree ferns are referred to as “cycads”, an error that is repeated on p.89.

- on p.88 there is a statement suggesting that tree fern spores were dispersed by “animal fur” 300 million years ago, long before the evolution of mammals, and that this (and dispersal of spores of fungi and mosses) is the equivalent of pollination: it is not, it equates to seed dispersal.

These are troubling errors of basic botany that are forgivable in an early draft of the book (everyone makes mistakes) but not in the final published version, after it’s been read, reviewed, checked and edited.  If the book goes to a second edition I hope that these (and other) mistakes will be fixed.  But they do hint at a fundamental problem with a book (and a field) as large and complex as this: a single author is arguably unlikely to be able to do justice to all of the subject matter.

There are parts of the book where it is unclear (to me at least) what the author is actually saying.  For example, on p.96 there is a graph which, it is suggested, demonstrates that pollination by animals is “technically uncommon when assessed in terms of the numbers of broad taxonomic groups that use it”, though the legend to the figure claims that “most orders of plants have no families” that possess wind pollination.  This is confusing: what is to be concluded by someone new to the field?  Is animal pollination common or rare?  Likewise, on p.91 we are told that the “first angiosperms… would probably have had their pollen moved mainly by wind…”, but then on p.92 that “an element of insect pollination could be regarded as almost ancestral”.  Which is correct?

There are other aspects to the book that are simply out of date; for example the linear, rather deterministic schemes set out in Figures 4.6 and 4.8 showing that Cretaceous flowers were open and radially symmetrical, and only later evolved into complex, bilateral flowers in the Tertiary, ignores fossil discoveries showing that orchids evolved in the Cretaceous (Ramírez et al., 2007).  Likewise, discussion of “counterproductive” crypsis in flowers (p.124) neglects recent findings of cryptic, wasp-pollinated plants in South Africa (e.g. Shuttleworth & Johnson, 2009).

There is a theme emerging here: some of the botany that the book presents is inaccurate, confused or out-dated.  Fortunately the zoological aspects of the book are much better, as one might hope from a Professor of Zoology.

The final criterion, that the book should be “authoritative in the conclusions it presents”, is however, in my view, the main weakness of this volume.  The author is unhappy with recent developments in the field, particularly as they relate to community-scale assessments of plant–pollinator interactions, in terms of network analyses and predictive utility of pollination syndromes.  Clearly Professor Willmer is on a mission to rebalance what she perceives as failings within some of the current trends in studying pollination.  A book review is not the place for a technical dissection of the author’s arguments, which is best left to the peer-reviewed literature (though I would argue that that’s also the place to present some of the criticisms the author introduces, rather than into a text book such as this).  I could focus the whole of this review on these topics because: (a) they take up a large proportion of the book, about one-third of the text pages; and (b) they are highlighted on the cover as being one of the main contributions of the book; specifically, that the author provides a critique of previous work that does not distinguish between “casual visitors and true pollinators” that can in turn result in “misleading conclusions about flower evolution and animal-flower mutualism”. Unfortunately her targets are straw men, and one – I believe quite telling – example will suffice.

On p.447 there is a criticism of the use by Waser et al. (1996) of Charles Robertson’s historical data set, and specifically that the analyses they present “…did not distinguish visitors from pollinators even though Robertson’s database did include information on this”.  However Waser et al. clearly state (p.1045 of their paper) that only pollinators were included in the analyses, not all flower visitors, and that “visitation is not a synonym for pollination… non-pollinating visitors are excluded (as in Robertson 1928)” (p.1048).

Why should Professor Willmer make a statement to the contrary?  Evidently she wishes to impress upon her readers that (in her opinion) there are fundamental problems in current approaches to studying pollination at a community level.  But even if that were the case (and I don’t believe it is) misrepresenting previous studies to suit an argument is poor scholarship at best.

Regardless of whether some of her criticism is well founded, the author does not seem to appreciate that plant–flower visitor interaction networks are ecologically important regardless of whether or not a flower visitor acts as a pollinator.  More fundamentally, true pollination networks possess similar attributes to flower visitor networks, for example a nested pattern of interactions, and arguments about level of generalisation of species are a matter of scale, not category (Ollerton et al., 2003).

At the end of her Preface, Professor Willmer reveals to us quite a lot about her personal attitude to research when she states that some readers might find her approach “too traditional” in an “era where ecological modelers [might be claimed to] have more to tell us than old-style field workers”.  What the author fails to appreciate is that this is a grossly false dichotomy and that most of the pollination ecologists who have embraced new analytical methodologies for understanding plant–pollinator interactions are also “old-style field workers” with considerable experience of studying the ecology of flowers and their pollinators beyond the computer screen.

In summary this is a book that, for all its good qualities of comprehensiveness and (mostly) up to date coverage, should be read with caution: parts of it are neither as accurate nor as authorative as the field of pollination and floral ecology deserves.

 

Jeff Ollerton

Email jeff.ollerton@northampton.ac.uk

LITERATURE CITED

Ollerton J, Johnson SD, Cranmer L, Kellie, S. 2003. The pollination ecology of an assemblage of grassland asclepiads in South Africa. Annals of Botany 92: 807-834.

Ramírez SR, Gravendeel B, Singer RB, Marshall CR,  Pierce NE. 2007. Dating the origin of the Orchidaceae from a fossil orchid with its pollinator. Nature 448: 1042-1045.

Shuttleworth A, Johnson SD. 2009. The importance of scent and nectar filters in a specialized wasp-pollination system. Functional Ecology 23: 931-940.

Waser NM, Chittka L, Price MV, Williams N, Ollerton J. 1996. Generalization in pollination systems, and why it matters. Ecology 77: 1043-1060.

 

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The ‘natural’ solution might not be best when your wildlife isn’t natural

Many ecosystems have been degraded or modified, and these are the sorts of systems you target for restoration. But when a system has been altered so much the original species might not be the best choice to bring it back to health. Therefore, says Thomas Jones, you need to look at alternative species.

The Dry Aral Sea

The Dry Aral Sea. Francois de Halleux / Flickr

A paper from BioScience has caught my eye. In Ecologically Appropriate Plant Materials for Restoration Applications Thomas Jones argues that restoration might go better sometimes if you bring in some novel species to a site. What I find interesting is that it tackles the question what does it mean to ‘restore’ an ecosystem? My initial reaction is put it back as it was, but the ecosystem that was there was the product of centuries of interactions. Perhaps putting the final ingredients into a place and expecting a working ecosystem is like expecting some eggs, sugar and flour to spontaneously become a cake.

Bringing in novel species might sound like giving up on restoration and replacing the ecosystem instead. Jones shows that it’s not the case. The abstract includes this section which explains:

Ecologically appropriate plant materials are those that exhibit ecological fitness for their intended site, display compatibility with other members of the plant community, and demonstrate no invasive tendencies. They may address specific environmental challenges, rejuvenate ecosystem function, and improve the delivery of ecosystem services. Furthermore, they may be improved over time, thereby serving to ameliorate the increasingly challenging environments that typify many restoration sites.

In the paper Jones says that, for some ecosystems, local has value rather than local is best. Following this way of thinking, you introduce novel plants so that you can support the local material. If you think of an ecosystem as a whole system, instead of a collection of parts, then this extra support is a success rather than an intrusion. It also helps acknowledge that ecosystems are rarely oases isolated from anywhere else. The restored system might well have novel neighbours. The new species could help make the restored system more robust to challenges from outside.

Another factor is ecosystems aren’t binary between natural and broken. They change with human activity. The longer they’ve been exposed to human activity the farther from natural they move. If the ecosystem you’re restoring isn’t strictly natural then how do you work out what natural is? Jones points out ecosystems are dynamic and not always in stasis.

If Jones is right then restoration is not the same as preservation.

This thought may be disturbing to preservationists, who may view anything less than entirely local plant material as an unwise exchange of restoration orthodoxy for a “slippery slope.” Nevertheless, one cannot continue to rely solely on local genotypes simply because they are local and theoretically best adapted if experience demonstrates otherwise.

It certainly bothers me. The question then becomes do you do what works, or what you wish would work? It’s a good paper and, as I write, free access so definitely worth a visit to read.

Image

The Dry Aral Sea by Francois de Halleux / Flickr. This image licensed under a Creative Commons by-nc-nd licence.

Reference

Jones T. (2013). Ecologically Appropriate Plant Materials for Restoration Applications, BioScience, 63 (3) 211-219. DOI:

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A positive plethora of plant papers!

Image: Ryan Kitko/Wikimedia Commons.

Image: Ryan Kitko/Wikimedia Commons.

Unusually for this column (why give the ‘competition’ a free bit of publicity, after all?), I here wish to promote The Scientist magazine. As a general science news item site it occasionally features plant-related items, but it has surpassed itself with its 1st January 2014 collection. Not only does it feature a wonderful image of the fruit of the lotus plant on its cover, but it also contains four big plant articles(!).

By way of introducing that compilation, Mary Aberlin observes in her editorial that, ‘the panoply of fictional plants offers a large and varied dose of the weird and wonderful. But there’s no need to resort to fiction to find truly unusual plant characteristics’… so, read on! Accordingly, the selection comprises an item by Abby Olena that considers halotropism, a newly identified tropism in roots. This showcases a study by Carlos Galvan-Ampudia et al. that demonstrates active growth of roots of several plant species away from sites of high salt content, and which is not gravitropism. This work begs the question of how many other tropisms might still await discovery in that understudied plant organ.

In ‘Green gold’ Tracy Vence reports on the discovery of gold bioaccumulation in eucalyptus leaves, which was covered on this very blog not so long ago. Megan Scudellari’s article begins by posing the question, ‘What do cells, genes, mutations, transposons, RNA silencing, and DNA recombination have in common?’: the answer – but, of course! – is that all were first discovered in plants; she then considers how plant DNA is challenging preconceptions about the evolution of life (including our own species). And Dan Cossins considers the question of whether plants ‘talk’ to each other. Reviewing a wide-ranging body of work, the conclusion is that plants do communicate and interact with each other, both above and below ground, in surprisingly subtle and sophisticated ways. And by way of demonstrating how the time is right for certain ideas, Kat McGowan has an item in Quanta Magazine on ‘The secret language of plants’.  Almost inevitably these sorts of articles raise the spectre of how intelligent plants are, and that issue is given a good airing in Michael Pollan’s New Yorker article. What a great botanical start to the New Year (which traditionally starts on 10th April…)!

[Visit YouTube for a documentary on plant intelligence, and also if you want to know what plants talk about  – Ed.]

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