Bizarre flowers, chloride ions and auxin, and the role of pectin in stomatal development – this week in Annals of Botany

Emmotum harleyi Floral structure of Emmotum (Icacinaceae sensu stricto or Emmotaceae), a phylogenetically isolated genus of lamiids with a unique pseudotrimerous gynoecium, bitegmic ovules and monosporangiate thecae
The Icacinaceae consist of a group of early branching lineages of lamiids whose relationships are not yet resolved and whose detailed floral morphology is poorly known. The most bizarre flowers occur in Emmotum: the gynoecium has three locules on one side and none on the other. It has been interpreted as consisting of three fertile and two sterile carpels or of one fertile carpel with two longitudinal septa and two sterile carpels. This study focuses on the outer and inner morphology of the gynoecium to resolve its disputed structure.

 

Molecular cloning of two novel peroxidases and their response to salt stress and salicylic acid in the living fossil Ginkgo biloba
Peroxidase isoenzymes play diverse roles in plant physiology, such as lignification and defence against pathogens. The actions and regulation of many peroxidases are not known with much accuracy. A number of studies have reported direct involvement of peroxidase isoenzymes in the oxidation of monolignols, which constitutes the last step in the lignin biosynthesis pathway. However, most of the available data concern only peroxidases and lignins from angiosperms. This study describes the molecular cloning of two novel peroxidases from the ‘living fossil’ Ginkgo biloba and their regulation by salt stress and salicylic acid.

 

Role of chloride ions in the promotion of auxin-induced growth of maize coleoptile segments
The mechanism of auxin action on ion transport in growing cells has not been determined in detail. In particular, little is known about the role of chloride in the auxin-induced growth of coleoptile cells. Moreover, the data that do exist in the literature are controversial. This study describes experiments carried out with maize, a classical model system for studies of plant cell elongation growth. These results suggest that chloride ions play a role in the IAA-induced growth of maize coleoptile segments.

 

Developmental changes in guard cell wall structure and pectin composition in the moss Funaria: implications for function and evolution of stomata
In seed plants, the ability of guard cell walls to move is imparted by pectins. Arabinan rhamnogalacturonan I (RG1) pectins confer flexibility while unesterified homogalacturonan (HG) pectins impart rigidity. Recognized as the first extant plants with stomata, mosses are key to understanding guard cell function and evolution. Moss stomata open and close for only a short period during capsule expansion. This study examines the ultrastructure and pectin composition of guard cell walls during development in Funaria hygrometrica and relates these features to the limited movement of stomata. This is the first study to demonstrate changes in pectin composition during stomatal development in any plant.

 

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Stevia hits the mainstream with ‘Life’

Last year Aurélien Azam blogged about Stevia in his post, Can we find all the tastes we like in the Wild? He mentions Stevia in it and if you don’t remember it, then Coca Cola will try to change that. Stevia is the plant behind the new Coke variety, Life.

Coca Cola Life and Death

The marketing department at Coca Cola are about to discover that if the green bottle is called ‘Life’ there’s an obvious name for the red bottle.

Stevia rebaudiana leaves are complicated sugar factories. Initially they import carbohydrates, but as leaf area increases photosynthesis means they start producing more sugars to supply the rest of the plant. The key chemicals are Steviol glycosides. These are, for the same concentration, around 300 times more sweet than sugar. The exciting feature is that human body cannot produce any calories from these sugars. For marketing, it’s the fact that it’s a plant that’s the chemical factory that’s news. If it’s made in a plant then you can label it: From Natural Sources.

But this is one of those situations where natural is probably not a synonym for good.

Stevia growing naturally in Paraguay. #156515950 / gettyimages.com

Abdel-Rahman et al. (2011) report on Stevia, among other natural products in Toxological Sciences, and note that in aqueous, crude or partially purified form Stevia can be bad news for rats. One side-effect can be reduced fertility in female rats. It’s always best to be wary from directly applying animal tests to humans, but they also note that the Guarani Indians of Paraguay would make something a bit like a tea from the Stevia leaves. They used it as an oral contraceptive.

For this reason it’s a relief that the sweetener isn’t natural, but a highly processed form of Stevia. But how does it taste?

I set up a comparison taste test with Coca Cola Life (green bottle) and the Cola Cola from the red bottle – which for ease of labelling we’ll call Death. I also added Coke Zero as a third option. All bottles were chilled and the opened with ice added. I then ignored protests from the tasters that they weren’t that thirsty.

The taste test followed a predictable pattern.

After glass 1 Zero: “Hmm.”
After glass 2 Death: “That’s definitely the full-fat Coke and the first is Stevia.”
After glass 3 Life: “Euww! No, that’s Stevia isn’t it?”

Stevia has a distinctive taste, and one that’s unexpected in Coke. Success will depend on how much the public develop a taste for it.

If it does succeed, the payoff could be big. As well as the battle against obesity, Stevia-derived sweeteners promise other benefits including fighting diabetes, high-blood pressure and tooth decay. However for now if it’s a choice between liberty from health issues or Death, a good chunk of the public will opt for Death.

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The hidden cost of frankincense

A while back we covered a paper in Annals of Botany on tapping frankincense for resin. The mapping of the canals in the tree promised to improve the efficieny of tapping. Now in Tree Physiology Mengistu et al. have a paper Frankincense tapping reduces the carbohydrate storage of Boswellia trees, that’s recently become free access.

Boswellia Trees

Boswellia Trees in Ethiopia. Photo by Motuma Tolera.

Mengistu et al. show that tapping for resin reduces the trees’ stores of starches and sugars. They also show that stores deplete anyway, as the tree uses them itself. The resin is part of a store that tides the tree over the dry period, and get replenished during the wet period.

The paper ties in well with the Annals paper. In that Tolera et al. argued resin tapping could be done just as effectively with fewer cuts. Fewer cuts means less chance for disease to enter the tree. In the TreePhys paper Mengistu et al. argue that fewer cuts also means that trees have more of a chance to hold on to necessary stores of carbon, if they need them.

The evidence is that intensive tapping of Boswellia papyrifera is a problem and that the trees need some respite. However, there is also a religious imperative to tap them. Balancing supply and demand looks likely to remain a contentious problem.

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Intracellular ice and cell survival in seeds of Acer

Intracellular ice and cell survival in seeds of Acer

Intracellular ice and cell survival in seeds of Acer

Efforts to cryopreserve germplasm of recalcitrant-seeded species are hampered by potentially lethal intracellular freezing events. Wesley-Smith et al. study embryonic axes of silver maple, Acer saccharinum, subjected to various drying, cooling and warming treatments and find that intracellular ice formation is not necessarily lethal. In fully hydrated axes cooled at an intermediate rate, the interiors of many organelles are apparently ice-free and this may prevent the disruption of vital intracellular machinery. The findings challenge the accepted paradigm that intracellular ice formation is always lethal, as the results show that cells can survive intracellular ice if crystals are small and localized in the cytoplasm.

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Does Plant Science need a Sagan or Sheldon?

Here’s a slow reaction to a post at ASPB Plant Science Blog by Ian Street, Communicating Plant Science in the Digital Age. It’s taking me a while to respond, because I think it’s a good post – but I don’t quite agree with it. However, every time I think I’ve worked out why I don’t agree with it, I find I don’t agree with myself either.

In the original post, Ian Street holds up Neil deGrasse Tyson as an example of someone who is an excellent communicator and points out there’s no plant science equivalent. Here I start to feel a bit of a weasel. In terms of audience and fame he’s right. However, if you’re looking for people who can communicate plant science in an exciting way, there are plenty of researchers who could do a similar job to Tyson, given the opportunity. I think there are plenty of good communicators in botany, but they don’t have the audience.

I can see why not having a Plant Tyson is a problem, but I’ve not been sure that broadcasting is the answer. I don’t think astronomy is popular because Tyson is a good communicator. I think it’s the opposite way round. Tyson is such a good communicator because Astronomy is so popular. That might sound odd, but imagine if Tyson decided he’d had enough and was retiring to Tahiti, would Astronomy cease to be popular?

No. There’s a demand for astronomical talking heads. There’s someone almost as good who could do the job. The demand for popular astronomy means there’s almost certainly a pool of talented communicators that the media could draw upon. Tyson is at the top of a competitive field. There are plenty of talented plant science communicators, but lack of demand means we con’t see them so much.

I think a top plant science broadcaster lies at the end of the road to making botany more popular, it’s not part of the journey itself.

Sheldon Cooper

Is CBS’s Sheldon Cooper the face of Science in the 2010s?

That works as far as it goes, but elsewhere I think Ian Street proves me wrong and gives an example where broadcasting does work. He mentions The Big Bang Theory that, love it or hate it, humanises physicists.

In the UK it’s been credited with an increase in the number of physics students. For a similar effect see archaeology and Indiana Jones. You can’t learn physics from The Big Bang Theory any more than you can pass a course in archaeology with Indiana Jones – but the lack of facts hasn’t prevented them from changing how people value their respective sciences.

Street also points out the importance of using comedy to take the edge of hard science. I think he’s hit on a key point there. It’s not simply a matter of making plant sciences prestigious, you also need to make them likeable. Yesterday we had a post on a genetically engineered plant that might help fight Ebola. It’s a huge tragedy where plant science could make a major contribution to saving lives. But I’m also willing to bet that anti-vaxxers will decide it’s a secret Monsanto project.

In a perfect world Hollywood would solve the image problem for us, but that’s not a practical solution. So instead of aiming for mass audiences, it might be more reasonable to look to the small things people can do. Ian Street says that popularising science is a core part of scientists’ mission. This may be a culture difference, but in the UK it is emphatically not. The only things that matter are scientific publications. Departments make positive noises about outreach, but when it comes to assessments time spent doing Outreach can be viewed as Time Not Working.

If outreach success is all-or-nothing, then in this situation the vast majority of results are going to be nothing. If there were support for small victories, then hopes need not rest or a Sagan nor a Sheldon. Avoiding investing in a few personalities could have benefits. Not least, because it means scientists don’t have to just look like me, they can look like you and your neighbour too.

Quite how this is going to be put in place is difficult, but I think what Ian Street and the ASPB’s Digital Futures Initiative might well be a stepping stone to support for many plant scientists. Another event to cheer is Kevin Folta, who’ll be doing a Reddit AMA this afternoon.

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Life saving tobacco (with a mouse and virus assist)

Ebola virus currently has no licenced vaccine or cure, however several potential therapies are in development. Why does this merit mention on a blog about botany? For one good reason; scientists used plants in a bio-pharming approach to produce the potential Ebola treatment which was recently given to 3 patients infected with the virus. Bio-pharming uses genetic modification to introduce genes coding for pharmaceutical proteins (e.g. antibodies, or when produced in plants; ‘plantibodies’) into plants, the plant will then produce these proteins as if they were its own – essentially acting as a protein factory. The plants are harvested, the pharma-protein extracted and purified to a level comparable to any other medicinal protein.

Tobacco pharming might soon be good for your health. Photo: BigStockPhoto.

Tobacco pharming might soon be good for your health. Photo: BigStockPhoto.

Bio-pharming is currently in the news as ZMapp (Mapp Pharmaceuticals), an experimental antibody cocktail targeted against Ebola virus and produced in tobacco plants, was used in the treatment of two US aid workers and a priest infected with the virus. ZMapp is a combination of three antibodies which recognise different parts of Ebola glycoprotein; a protein present on the outside of the virus which allows the virus to attach to and enter into cells. The antibodies attach strongly to the Ebola glycoprotein thereby inactivating the virus, preventing it from entering cells and acting as a beacon to the patient’s immune system that the virus needs to be destroyed.
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Arabidopsis growth, shading and halophyte-based agriculture – new in Annals of Botany this week

Growth rate distribution in the forming lateral root of arabidopsis Growth rate distribution in the forming lateral root of arabidopsis
Microscopic observations of lateral roots (LRs) in Arabidopsis thaliana reveal that the cross-sectional shape of the organ changes from its basal to its apical region. The founder cells for LRs are elongated along the parent root axis, and thus from the site of initiation the base of LRs resemble an ellipse. The circumference of the apical part of LRs is usually a circle. The objective of this study was to analyse the characteristics of changes in the growth field of LRs possessing various shapes in their basal regions. This is the first report of a description of growth of an asymmetric plant organ using the growth tensor method. The mathematical modelling adopted in the study provides new insights into plant organ formation and shape.

 

Contribution of above- and below-ground plant traits to the structure and function of grassland soil microbial communities
Abiotic properties of soil are known to be major drivers of the microbial community within it. Our understanding of how soil microbial properties are related to the functional structure and diversity of plant communities, however, is limited and largely restricted to above-ground plant traits, with the role of below-ground traits being poorly understood. This study investigates the relative contributions of soil abiotic properties and plant traits, both above-ground and below-ground, to variations in microbial processes involved in grassland nitrogen turnover.

 

Responses to shading of naturalized and non-naturalized exotic woody species
Recent studies have suggested that responses to shading gradients may play an important role in establishment success of exotic plants, but hitherto few studies have tested this. Therefore, a common-garden experiment was conducted using multiple Asian woody plant species that were introduced to Europe >100 years ago in order to test whether naturalized and non-naturalized species differ in their responses to shading. Specifically, a test was carried out to determine whether naturalized exotic woody species maintained better growth under shaded conditions, and whether they expressed greater (morphological and physiological) adaptive plasticity in response to shading, relative to non-naturalized species.

 

The development of halophyte-based agriculture: past and present
Freshwater comprises about a mere 2·5 % of total global water, of which approximately two-thirds is locked into glaciers at the polar ice caps and on mountains. In conjunction with this, in many instances irrigation with freshwater causes an increase in soil salinity due to overirrigation of agricultural land, inefficient water use and poor drainage of unsuitable soils. The problem of salinity was recognized a long time ago and, due to the importance of irrigated agriculture, numerous efforts have been devoted towards improving crop species for better utilization of saline soils and water. Irrigating plants with saline water is a challenge for practitioners and researchers throughout the world. This review critically analyses past and present halophyte-based production systems in the context of genetics, physiology, agrotechnical issues and product value. There are still difficulties that need to be overcome, such as direct germination in saline conditions or genotype selection. However, more and more research is being directed not only towards determining salt tolerance of halophytes, but also to the improvement of agricultural traits for long-term progress.

 

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It’s fruit Jim, but not as we know it

There’s an interesting paper we’ve just moved to free access: Gymnosperm B-sister genes may be involved in ovule/seed development and, in some species, in the growth of fleshy fruit-like structures by Lovisetto et al. The idea that seeds are associated with fruits should be no surprise. Animals eat the fruits and disperse the seeds, so the plant can spread its genes. Fruit from gymnosperms would be a surprise though, because you’d expect the fruit to grow from a flower and gymnosperms don’t have flowers, those are angiosperms.

However, the cover image for the August 2013 Annals of Botany shows ovules of Gingko biloba that grow a fleshy structure that attracts animals. What’s going on?

Ginkgo biloba

Ovules of the gymnosperm Ginkgo biloba. Image by Lovisetto et al. 2013

The answer seems to be in the genes. Both angiosperms and gymnosperms have B-sister genes that work to grow fruit. It looks like the foundation of growing fruit around a seed could pre-date the development of flowers.

You can read more free at Annals of Botany.

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One plus one does not always make two, when plants add up costs and benefits

Mutualism is a relatively simple concept in plant science. Plants will reward other organisms that perform services for them, so both the plant and partner are better off then they would be alone. But what happens when you add more than one species to an ecosystem? Non-additive benefit or cost? Disentangling the indirect effects that occur when plants bearing extrafloral nectaries and honeydew-producing insects share exotic ant mutualists by Amy Savage and Jennifer Rudgers shows it’s not always as simple as adding up costs and benefits to find out the net effect species interaction has.

Being simple myself, the phrase ‘non-additive’ puzzled me, but there’s an excellent graph that explains what Savage and Rudgers mean. They think of a plant hosting two species. One is an ant. The ant tends to protect the plant from herbivores – except one. The second species is a sap-sucking insect that produces honeydew, a sugary substance that’s a bit like an insect’s version of nectar. What happens if you put the two species on a plant?

The Additive model simply adds up costs and benefits. So if ant protection boosts growth by two units, but the sap-suckers deplete it by one, then the net benefit is one unit to the positive. That’s the first graph below. But it might not be that simple.

Cost and Benefit models by Savage and Rudgers

Cost and Benefit models by Savage and Rudgers 2013.

Ants like honeydew, because of the complex sugars. But suppose ants REALLY like honeydew. So much that hosting the insects pulls a massive number of ants up to protect the leaf. Here is what is called a Non-additive benefit model. The next effect is far more positive than simply adding up the interactions of the two species with the plant. But this could go the other way too. Maybe the protection given by the ants really allows the sap-suckers the safety to plunder the plant. Then you have a Non-additive cost model – the third graph.

It turns out there hasn’t been much research on the combined effects of ants and honeydew producing insects (HPI) on plants. This is an issue because of another complex factor – what happens when one ant invades the territory of another?

Savage and Rudgers looked at ants on Savai’i, Samoa, in particular Anoplolepis gracilipes. A. gracilipes correlates with extra-floral nectaries on plants, and is more aggressive to other insects on its patch than other ants. The mutualism between A. gracilipes and plants could be aiding A. gracilipes kill off other insects in the area.

Samoa in the Pacific Ocean

Image from Google Maps.

The study was on the lava flows of Savai’i, colonised by Morinda citrifolia a plant with floral, extrafloral and post-floral nectaries. It produces nectar all year round. They picked a variety of sites, some with A. gracilipes and some with less invasive ants present.

To test the effects of the ecological interactions they could remove ants from plants, by circling the base of a plant with a pest barrier. They could reduce nectar production by bagging the nectary bodies. They could also reduce the presence of HPI by brushing them off the plants. They could then manipulate some of these factors together.

For A. gracilipes, they found the key was nectar. Reduce nectar and you reduce the number of ants on the plant. Reducing HPI only had a small effect, which suggests A. gracilipes aren’t so bothered about honeydew.

For the plants, the presence of the ants makes a big difference. They hardly grew without any A. gracilipes around, but grew 3000% with the ants around. HPI had little effect without A. gracilipes, but also promoted growth then there were ants there too. This supports a non-additive benefit model. For the less invasive ants the effect the effects were less than additive.

One of the interesting findings was that the A. gracilipes had an effect on HPI, turning them from a negative to a positive for plant growth. It’s something that you could not predict simply from observing just A. gracilipes or HPI. The paper certainly provides plenty to think about on the complexity of cost and benefit analysis. You can now pick it up for free from Annals of Botany.

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White-tailed deer are a biotic filter during community assembly, reducing species and phylogenetic diversity

13118S1R1

A photo of one of the exclosures and its adjacent control plot in 2009 (age then, 19 years).

White-tailed deer browsing has been implicated in the loss of species diversity from forests throughout eastern North America. In a new study published in AoB PLANTS, Begley-Miller et al. build on this previous research by examining how browsing also affects phylogenetic community structure in order to better understand the role of deer browsing in the community assembly process. In browsed plots, they found that reductions in phylogenetic diversity were much greater than reductions in species richness or diversity. Species persisting in browsed communities were also closely related. Their findings indicate that deer browsing acts as a biotic filter during the community assembly process. Their study also highlights the importance of utilizing new tools in assessing the influence of deer herbivory on plant communities, and should encourage future advances in our understanding of coexistence in communities.

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