Category Archives: Life

Revving up photosynthesis with nanotechnology – take that, greenhouse effect!

Carbon nanotube 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]

 

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Another bacterial trick to manipulate plant hormone-mediated responses

Another bacterial trick to manipulate host hormone-mediated response Pseudomonas syringae is a widespread bacterial pathogen that causes disease on a broad range of economically important plant species. In order to infect, P. syringae produces a number of toxins and uses a type III secretion system to deliver effector proteins into eukaryotic cells. This mechanism is essential for successful infection by both plant- and animal-associated bacteria as bacterial mutants are no longer pathogenic. However, the molecular function and host targets of the vast majority of effectors remain largely unknown.

Plant immunity relies on a complex network of small-molecule hormone signaling pathways (see: Wasternack, C. (2007) Jasmonates: an update on biosynthesis, signal transduction and action in plant stress response, growth and development. Annals of botany, 100(4), 681-697). Classically, salicylic acid (SA) signaling mediates resistance against biotrophic and hemi-biotrophic microbes such as P. syringae, whereas a combination of jasmonic acid (JA) and ethylene (ET) pathways activates resistance against necrotrophs such as the fungus Botrytis cinerea. SA and JA/ET defense pathways generally antagonize each other – elevated resistance against biotrophs is often correlated with increased susceptibility to necrotrophs and vice versa. The collective contribution of these two hormones during plant-pathogen interactions is crucial to the success of the interaction. Remarkably, some Pseudomonas strains have evolved a sophisticated strategy for manipulating hormonal balance by producing the toxin coronatine (COR), which mimics the plant hormone jasmonate-isoleucine (JA-Ile). The JA-Ile pathway plays a key role in plant immunity by activating defenses against fungal pathogens, while promoting bacterial growth by inhibiting the salicylic acid (SA)-dependent defenses required for Pseudomonas resistance.

A recent paper in PLOS Biology reports that the effector HopX1 from a Pseudomonas syringae strain that does not produce COR exploits an alternative evolutionary strategy to activate the JA-Ile pathway. HopX1 encodes a cysteine protease that interacts with and promotes the degradation of key JA pathway repressors, the JAZ proteins. Correspondingly, ectopically expressing HopX1 in the model plant Arabidopsis induces the expression of JA-dependent genes, and natural infection with Pseudomonas producing HopX1 promotes bacterial growth in a similar fashion to COR. These results highlight a novel example by which a bacterial effector directly manipulates core regulators of hormone signaling to facilitate infection:

Gimenez-Ibanez S, Boter M, Fernández-Barbero G, Chini A, Rathjen JP, et al. (2014) The Bacterial Effector HopX1 Targets JAZ Transcriptional Repressors to Activate Jasmonate Signaling and Promote Infection in Arabidopsis. PLoS Biol 12(2): e1001792. doi:10.1371/journal.pbio.1001792

 

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The March 2013 issue of Annals of Botany is now Free Access

Moss sporophytes

The sporophytes and calyptras of Funaria hygrometrica. The calpytra is the gametophytic tissue that covers the tip of the elongating sporophyte. A young sporophyte with an intact calyptra appears in the lower left corner, whilst other sporophytes are in the process of shedding their calyptras or have already shed them. The calyptra is proposed to function, in part, as a maternal constraint on capsule expansion, as an expression of parent-offspring conflict. Photo: Ron Oldfield, Macquarie University. See Haig 2013.

The March 2013 issue of Annals of Botany is now Free Access. The cover image is of two generations of moss, the younger sporophytes growing from the parent gametophyte. AJ Cann blogged about this paper last year.

If you get confused between sporophytes and gametophytes, then you’re not alone. Plants alternate generations between sporophytes and gametophytes. The children of oak trees aren’t acorns, they’re grandchildren. The ‘children’ of oaks would be pollen and the embryo sacs they pollinate. Contrary to popular belief pollen isn’t plant sperm.

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The Importance of Access

Three men, reading

Three men, before they read a paper on the dangers of tobacco. Photo: John Henry Harvey.

Kevin Folta has put up a thought-provoking post on his blog, Illumination. There’s been a flurry of news stories around a new research paper that shows a Round-Up, Monsanto’s herbicide, in rain. A closer look at the paper reveals that’s not quite the story.

What the research shows is there are chemicals in very low concentrations that are consistent with Round-Up. This might seem like pedantry, but it’s important pedantry because the same tests show a reduction in other chemicals associated with more harmful herbicides and pesticides between 1995 and 2007. It’s consistent with Round-Up and GM crops being ecologically safer.

There is room for debate. The fields were different crops in different places so it depends what standard of proof you want. What the paper does show is that chemicals are not-trivial additions to an environment and in some cases have a long-term presence.

Kevin’s post on the paper also shows access to papers is important. The original paper is here, but unless you’re at a university with a subscription, you might have trouble getting it. In a perfect world all papers would be Open Access, and for AoB, all papers in AoB Plants and this month Annals of Botany has three open access papers. Access to subscription papers is more difficult. In our case papers in Annals of Botany become free access after a year, but that’s a long time to wait.

For press releases we have a policy that if we put out a press release for a paper, we make the paper free access to anyone can compare the release to what is actually in the paper if they want. However, we can’t do this for every paper. We do have a limited marketing budget though. If there is interest in a paper and we see it get blogged in a couple of places we’ll do what we can to make it free access.

As always, if a blogger wants access to a paper behind a paywall then contact me and I’ll get a copy so you can write about more than just the abstract.

Or you can do what Kevin Folta, and no one else did, and contact the author.

Image

Three men sitting in deck chairs, smoking pipes and reading newspapers by John Henry Harvey. Courtesy of the State Library of Victoria, Asutralia.

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Where do olives come from?

Immature Green Olives Olives have a long and complex history. The origins of the Mediterranean cultivated olive (Olea europaea subsp. europaea) are hotly debated, but it is usually accepted that its domestication started in the Levant based on archaeological, historical and molecular evidence. Multiple local selections of cultivars has been suggested by genetic analyses, followed by secondary diversification of the crop followed the oleiculture diffusion over the whole Mediterranean basin. The contribution of western wild olives in this diversification process remains poorly understood.

A recent paper in Annals of Botany describes patterns of genetic differentiation in Mediterranean and Saharan olives, and tests for admixture between these taxa. Based on the results, the human-meditated diffusion of the oleiculture over the Mediterranean basin and the contribution of O. europaea subsp. laperrinei to the cultivated olive diversification are discussed. Although its genetic contribution is limited, it is clear from this work that Laperrine’s olive has been involved in the diversification of cultivated olives.

 

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Effects of water availability and pest pressures on tea (Camellia sinensis) growth and functional quality

Tea quality is notably impacted by climate variables such as the East Asian Monsoon. This images shows tea plants during the onset of the East Asian monsoon on southwestern China.  Photo credit: Selena Ahmed

Tea quality is notably impacted by climate variables such as the East Asian Monsoon. This images shows tea plants during the onset of the East Asian monsoon on southwestern China.
Photo credit: Selena Ahmed

Extreme shifts in water availability linked to global climate change are impacting crops worldwide. In a recent study published in AoB PLANTS, Ahmed et al. examine the effects of water availability and pest pressures on the growth and functional quality of tea, the world’s most consumed beverage after water. They show that higher water availability and pest pressures significantly increased the growth of new leaves while their effect on tea quality varied with individual secondary metabolites. Their findings point to the fascinating dynamics of climate change effects on tea plants with offsetting interactions between rainfall and pest pressures, and the need for future climate studies to examine interactive environmental effects.

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Central–marginal diversity in a Mediterranean endemic

Central–marginal diversity in a Mediterranean endemic

Central–marginal diversity in a Mediterranean endemic

Genetic diversity tends to decrease and genetic differentiation tends to increase towards the periphery of a species’ range, but this has rarely been tested for plants of azonal habitats such as rocky slopes or screes. Pouget et al. study a narrow endemic Mediterranean plant, Arenaria provincialis (Caryophyllaceae), across its geographic range and find that despite its narrow distribution it has a high level of molecular variation. As predicted by the central–marginal theory, the areas characterized by the highest genetic diversity are centrally located. The current range size and abundance patterns are not sufficient to predict the organization of genetic diversity, which can only be explained by phylogeographic analysis of the long-term history of migrations and persistence.

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Genetic variation among mainland and island populations of a native perennial grass used in restoration

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Photo of Santa Cruz Island (K Hufford)

Knowledge of species-level patterns of genetic diversity can inform and improve protocols when population reintroduction is a restoration objective. In a new study in AoB PLANTS, Hufford et al. describe the population genetic structure of a geographically widespread species, Elymus glaucus, which is now rare in temperate grasslands as a result of biological invasion and land conversion. They contrast data for mainland and Channel Island locations, and make recommendations for seed provenance selection in ecological restoration using genetic marker data and considering prior field studies of adaptive divergence.

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Celebrating basic plant science

Image: Alberto Salguero/Wikimedia Commons.

Image: Alberto Salguero/Wikimedia Commons.

In case you missed this, here’s news of a charming series that aims to present vignettes of current plant science research and researchers within a broader educational remit of promoting the importance of basic plant science. As such it could be useful for impressing upon those supposedly impressionable early-stage undergraduates the relevance of phytology, and might also have a role to play in wider outreach evangelising of the importance of plant biology. Anyway, this first – of many? – in the series showcases the work of Siobhan Braybrook, Career Development Fellow at the University of Cambridge’s Sainsbury Laboratory. Penned by Siobhan, it explains her fundamental work on aspects of plant development – including the important role of pectin in determining cell wall expansion – and discusses why such basic plant science is value for money. A little gem from GARNet (a sponsored network that supports arabidopsis researchers and the wider plant community).
[GARnet is in turn sponsored by the BBSRC (Biotechnology and Biological Sciences Research Council), a major UK government-funded sponsor of biological research. Another ‘importance of basic plant science’ item you might be interested in is the University of Cambridge’s Professor David Baulcombe’s keynote talk from the UK PlantSci 2013 meeting.

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