The 1001st use of bamboo?

Image: David Raju, India Biodiversity Portal, http://indiabiodiversity.org. [http://indiabiodiversity.org/species/show/28371]

Image: David Raju, India Biodiversity Portal, http://indiabiodiversity.org. [http://indiabiodiversity.org/species/show/28371]

Bamboo, an extremely fast-growing, woody grass that is now established throughout the world, is so versatile that it allegedly has 1000 uses. Traditionally, such uses are numbered from the human perspective, including food (not limited to bamboo shoots, beloved of Giant Pandas – which iconic bears are so revered by humans that these endangered animals are shamelessly further exploited as the emblematic logo of the Worldwide Fund for Nature),  drink (e.g. bamboo beer),  medicine/therapy (e.g. ‘bamboo massage’),  construction (it makes a recyclable, light-weight alternative to the metal pipes and tubes commonly used as scaffolding outside of southeast Asia), paper (e.g. ‘ghost money’), textiles (not just ladies’ undergarments, such as bustles and ribs of corsets) and music (e.g. flutes). Added to that list – albeit from a non-human perspective – is the report by Kadaba Seshadri et al. that documents use of bamboo as a breeding base for Indian frogs. Chalazodes bubble-nest frog, Raorchestes chalazodes, and the Ochlandrae reed frog, R. ochlandrae, were observed to use the bamboos Ochlandra travancorica and O. setigera, respectively, in this novel reproductive behaviour in the Western Ghats (India). This unique life history involved adult frogs entering the hollow internodes of the bamboo through small openings (presumed to have been made by insects or rodents), depositing developing eggs within, and providing parental care. However, having now recognised their bamboo-dependence, a concern is that over-harvesting of the bamboo by humans outside of protected areas (for paper and pulp) threatens survival of the bamboo-nesting frog species, especially R. chalazodes, which is already known to be critically endangered in the wild. I don’t know – as if another dire warning of amphibian disease by the ‘chytrid fungus’ Batrachochytrium salamandrivorans wasn’t already enough to make these critters hopping mad!

 

[Ever-mischievous, P. Cuttings wonders if he’s found a 1002nd bamboo use – as biodegradable coffins for any frogs who ‘croak’ whilst engaged in babysitting duties within the bamboo… – Ed.]

Accurately measuring cavitation resistance to understand how plants cope with drought

Root resistance to cavitation Guest post by Danielle Marias, Oregon State University.

 

Plant water transport systems from roots to stems to leaves are under negative pressure due to tension on the water column. This is caused by water loss through stomata – small pores on leaves – and is driven by how dry the atmosphere is, as described by the cohesion-tension theory. This tension or negative pressure puts plants at risk for cavitation. Cavitation is the conversion of water from liquid to vapor and can result in a gas-filled (embolized) vessel or tracheid that no longer transports water. Therefore, cavitation resistance is crucial to coping with and surviving drought.

Methods to assess cavitation resistance have been highly debated. It has been suggested that the standard centrifuge method, the most common and efficient method for measuring cavitation resistance, may have methodological artifacts and is not appropriate for roots. To investigate this, Pratt et al. (2015) compared the standard centrifuge method to two other independent types of measurements of cavitation in roots. This compelling study suggested that the standard centrifuge method accurately measures cavitation resistance and is appropriate for measuring cavitation resistance in roots. Because roots are generally more vulnerable to cavitation and embolism than stems and leaves, studies accurately measuring root cavitation are vital to understanding plant responses to drought as the severity and frequency of drought may increase with changing climate. Drought resistance and related topics in tree hydraulic functioning will also be covered in the forthcoming Special Issue in Tree Physiology.

 

Pratt, R.B., MacKinnon, E.D., Venturas, M.D., Crous, C.J., & Jacobsen, A.L. (2015) Root resistance to cavitation is accurately measured using a centrifuge technique. Tree Physiology, 24 February 2015 doi: 10.1093/treephys/tpv003
Abstract
Plants transport water under negative pressure and this makes their xylem vulnerable to cavitation. Among plant organs, root xylem is often highly vulnerable to cavitation due to water stress. The use of centrifuge methods to study organs, such as roots, that have long vessels are hypothesized to produce erroneous estimates of cavitation resistance due to the presence of open vessels through measured samples. The assumption that roots have long vessels may be premature since data for root vessel length are sparse; moreover, recent studies have not supported the existence of a long-vessel artifact for stems when a standard centrifuge technique was used. We examined resistance to cavitation estimated using a standard centrifuge technique and compared these values with native embolism measurements for roots of seven woody species grown in a common garden. For one species we also measured vulnerability using single-vessel air injection. We found excellent agreement between root native embolism and the levels of embolism measured using a centrifuge technique, and with air-seeding estimates from single-vessel injection. Estimates of cavitation resistance measured from centrifuge curves were biologically meaningful and were correlated with field minimum water potentials, vessel diameter (VD), maximum xylem-specific conductivity (Ksmax) and vessel length. Roots did not have unusually long vessels compared with stems; moreover, root vessel length was not correlated to VD or to the vessel length of stems. These results suggest that root cavitation resistance can be accurately and efficiently measured using a standard centrifuge method and that roots are highly vulnerable to cavitation. The role of root cavitation resistance in determining drought tolerance of woody species deserves further study, particularly in the context of climate change

Mnemonics are an Effective Tool for Adult Beginners Learning Plant Identification

Mnemonics are an Effective Tool The decline in interest in plants in biological education is an established phenomenon. Compared to animals, plants are under-represented in biology textbooks and other media. Biology teachers often avoid using plant examples in class due to their own lack of knowledge or interest, perpetuating the cycle. With botanical topics often relegated to single modules or lecture sets and limited opportunities for fieldwork, learning of species identification has inevitably suffered.

Species identification is a fundamental requirement for learning and understanding biodiversity, but it also plays a role in fostering concern for its preservation. Plant identification draws people’s attention to the wide variation in plant form, texture, colour, etc., increasing their interest in plants and their appreciation of biodiversity. Given the rapid rate of decline of plant species and consequences for wider ecosystems, there may be a greater need than ever to find ways to promote identification skills not only in the classroom but among the general public.

Most beginners are introduced to plant diversity through identification keys, which develop differentiation skills but not species memorisation. A paper in the Journal of Biological Education proposes that mnemonics, memorable ‘name clues’ linking a species name with morphological characters, are a complementary learning tool for promoting species memorisation.

In the first of two experiments, 64 adults in a group-learning environment were taught species identification using mnemonics, an educational card game and a text-based dichotomous key. In the second experiment, 43 adults in a self-directed learning environment were taught species identification using mnemonics and a pictorial dichotomous key. In both experiments, mnemonics produced the highest retention rates of species identification based on vegetative characters. The educational value of these findings is discussed for vegetative plant identification and broader applications. Participants in this study also enjoyed mnemonics more than a keying-out activity, suggesting that they could help to stimulate interest in botany.

Bethan C. Stagg and Maria E. Donkina. Mnemonics are an Effective Tool for Adult Beginners Learning Plant Identification. Journal of Biological Education 27 Feb 2015 doi: 10.1080/00219266.2014.1000360

Freezing-related CO2 bursts reduce winter embolism

Freezing-related CO2 bursts reduce winter embolism

Freezing-related CO2 bursts reduce winter embolism

Gases are not soluble in ice, so winter freezing of sap can lead to bubble formation in conducting vessels and hence to winter embolism when thawing occurs. Lintunen et al. measure CO2 efflux from stems of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) saplings and find that substantial freezing-related bursts of CO2 are released under both laboratory and field conditions. The results indicate that not all gases dissolved in the xylem sap are trapped within the ice in the stem during freezing, as has previously been assumed, and that release of gases can be important in avoiding winter embolism.

Live-cell imaging of Arabidopsis thaliana S-locus receptor kinase, the female specificity determinant of self-incompatibility

Live-cell imaging of Arabidopsis thaliana S-locus receptor kinase Live-cell imaging of ligand-activated receptor kinases that are tagged with a fluorescent protein can provide valuable information about the mechanism by which such a receptor transduces the signal it perceives at the cell surface into a cellular response. This approach has been used for analysis of several plant receptor-like kinases of the leucine-rich repeat class of receptors. However, it has not, as of yet, been applied successfully to the S-locus receptor kinase or any other member of the S-domain class of RLKs.

A recent paper in Annals of Botany describes the expression and live-cell imaging of functional FP-tagged versions of the A. lyrata SRKb variant in A. thaliana stigma epidermal cells. The successful FP tagging of SRK and its visualization in live stigma epidermal cells suggest new approaches for future analysis of the dynamics of SRK and SRK–SCR protein complexes. For example, it should be possible to visualize cYFP-tagged full-length SRK in conjunction with SCR proteins tagged with a different fluorescent label, and thus determine conclusively if SRK is indeed internalized subsequent to its interaction with its SCR ligand.

 

Rea, A.C., and Nasrallah, J.B. (2015) In vivo imaging of the S-locus receptor kinase, the female specificity determinant of self-incompatibility, in transgenic self-incompatible Arabidopsis thaliana. Annals of Botany, 24 February 2015 doi: 10.1093/aob/mcv008
The S-locus receptor kinase (SRK), which is expressed in stigma epidermal cells, is responsible for the recognition and inhibition of ‘self’ pollen in the self-incompatibility (SI) response of the Brassicaceae. The allele-specific interaction of SRK with its cognate pollen coat-localized ligand, the S-locus cysteine-rich (SCR) protein, is thought to trigger a signalling cascade within the stigma epidermal cell that leads to the arrest of ‘self’ pollen at the stigma surface. In addition to the full-length signalling SRK receptor, stigma epidermal cells express two other SRK protein species that lack the kinase domain and whose role in the SI response is not understood: a soluble version of the SRK ectodomain designated eSRK and a membrane-tethered form designated tSRK. The goal of this study was to describe the sub-cellular distribution of the various SRK protein species in stigma epidermal cells as a prelude to visualizing receptor dynamics in response to SCR binding.
The Arabidopsis lyrata SRKb variant was tagged with the Citrine variant of yellow fluorescent protein (cYFP) and expressed in A. thaliana plants of the C24 accession, which had been shown to exhibit a robust SI response upon transformation with the SRKb–SCRb gene pair. The transgenes used in this study were designed for differential production and visualization of the three SRK protein species in stigma epidermal cells. Transgenic stigmas were analysed by pollination assays and confocal microscopy.
Pollination assays demonstrated that the cYFP-tagged SRK proteins are functional and that the eSRK is not required for SI. Confocal microscopic analysis of cYFP-tagged SRK proteins in live stigma epidermal cells revealed the differential sub-cellular localization of the three SRK protein species but showed no evidence for redistribution of these proteins subsequent to incompatible pollination.

Flooding and floral variation in a clonal aquatic plant

Flooding and floral variation in a clonal aquatic plant

Flooding and floral variation in a clonal aquatic plant

Environmental conditions govern the balance between sexual and clonal reproduction. In clonal heterostylous species, deviations from equal morph ratios commonly occur in association with stochastic forces and limited sexual recruitment. Cunha et al. report variation in morph frequencies and floral traits in the tristylous clonal aquatic Eichhornia azurea in the Pantanal wetlands of Brazil. They demonstrate that although most populations are tristylous, biased morph ratios predominate and in some areas there is differentiation in floral traits, including smaller flowers and pollen. They find an unexpected lack of differences in morph evenness among flooding regimes, and propose that floral differentiation is associated with the breakdown of tristylous characters owing to the absence of specialized pollinators.

Revisiting spatial scale in the productivity-species richness relationship: fundamental issues and global change implications

14078S1R1The relationship between climate and biodiversity has been long debated. In a changing environment, there is new emphasis to resolve this debate for practical reasons: to manage conservation efforts we need to understand how diversity will change from both our own actions and natural global cycles. In a new study published in AoB PLANTS, McBride et al. show that the roles played by different ecological and evolutionary factors in shaping plant diversity change across the world’s ecoregions, and—critically—that these differences scale with ecoregion size. Ecoregions that are both large and productive are globally important biodiversity sources that shape the biota of the smaller regions around them.

Plants, grafty little critters…

Image: Richard Reames/Wikimedia Commons, www.arborsmith.com.

Image: Richard Reames/Wikimedia Commons, www.arborsmith.com.

When it comes to making new combinations of genes – which may help to generate new species  in the evolutionary process known as speciation – the most usual route in eukaryotes  is via sexual reproduction.  In this ancient process, and speaking rather generally, gametes, made via meiosis (in which the complement of genetic material is reduced), fuse with each other and thereby create a new individual with the full genetic complement of the adult. Generally, this mode of reproduction, whether leading to development of new species or not, is viewed as ‘good’. And sex is favoured during adaptation to new environments. But sex is also ‘expensive’,  and one might expect some organisms to have found a cheaper – better? – way. Although alternatives to sexual reproduction exist – so-called asexual reproduction –  they don’t generate the genetic variety that could give rise to creation [oops, controversial term… – Ed.] of new species.

But, guess what? Plants seem to have hit upon an asexual method that can give rise to new species, as work by Ignacia Fuentes et al., straightforwardly entitled ‘Horizontal genome transfer as an asexual path to the formation of new species’, suggests. Using grafting (a time-honoured, horticultural technique used to join parts from two or more plants so that they appear to grow as a single plant), the team demonstrated that entire nuclear genomes  could be transferred between plant cells of unlike species (and which you wouldn’t expect to be able to be able to reproduce sexually in nature…). Or, in the technical language of a scientific paper, the authors ‘provide direct evidence for this process resulting in speciation by creating a new allopolyploid  plant species from a herbaceous species (Nicotiana tabacum, ‘cigarette tobacco’) and a woody species (N. glauca, ‘tree tobacco’) in the nightshade family (Solanaceae).  The new species is fertile and produces fertile progeny’ (and has even been christened N. tabauca).

All intriguing stuff. And which just goes to demonstrate – again, and if ’twere needed – how much more interesting (better?) plants are than animals! Finally, the authors suggest that this phenomenon could be exploited for the generation of novel allopolyploid crop species. But where will this all end? And isn’t this genetic engineering? Albeit of a kind that occurs naturally? And what should one make of the tree that’s been so multiply and repeatedly grafted that it’s a composite of dozens of different species? Or is it now just one species…? Discuss!

[Ed. – For more on plant grafting, why not check out Charles Melnyk and Elliot Meyerowitz’s ‘primer’ entitled “Plant grafting” in Current Biology 25(5): R184-R188, 2015 [doi:10.1016/j.cub.2015.01.029]? (Which may freely be available from: http://www.cell.com/current-biology/pdf/S0960-9822%2815%2900060-3.pdf). For more on the first author’s grafting ambitions in Arabidopsis and Zea mays, visit http://www.slcu.cam.ac.uk/directory/melnyk-charles, and http://www.slcu.cam.ac.uk/research/meyerowitz-group for ‘Distinguished Associate’ Elliot Meyerowitz]

Collaboration between grass seedlings and rhizobacteria to scavenge organic nitrogen in soils

Photo of annual bluegrass seedlings on agarose with 0.01% protein, showing dark brown H2O2 zones around roots of seedlings.

Photo of annual bluegrass seedlings on agarose with 0.01% protein, showing dark brown H2O2 zones around roots of seedlings.

Plants require nitrogen to make proteins, nucleic acids and other biological molecules. It is widely accepted that plants absorb inorganic forms of nitrogen to fill their needs. However, recently it has become clear that plants also have the capacity to absorb organic nitrogen from soils. In a new study published in AoB PLANTS, White et al. describe a new kind of symbiosis involving seed-vectored rhizobacteria and grasses that is targeted at enhancing acquisition of organic nitrogen from soils. The authors propose a diurnal process where during the day roots produce and release hydrogen peroxide that oxidizes microbial exoenzymes around roots; at night hydrogen peroxide production ceases, then roots and symbiotic rhizobacteria secrete proteases that degrade the oxidized proteins to form peptides that are absorbed by roots. The existence of a mechanism for organic nitrogen scavenging in grasses emphasizes the nutritional importance of non-pathogenic microbes that associate with roots. Future applications of this process could result in new methods for the cultivation of crop plants.

AmJBot explains Auxin to the perplexed

I’m delighted that there’s a review of Auxin in this month’s American Journal of Botany, Auxin activity: Past, present, and future by Enders and Strader. This might surprise a few of my friends as I’m not a fan of Auxin, Auxin is a difficult topic, and that’s why this review is so welcome.

Pink Perfection Camellia

Pink Perfection Camellia. Photo by Trish Hartmann. Construction by Auxin.

Auxins are hormones that are impossible to avoid if you’re studying botany. Sooner or later you’ll run into them. Recently in Annals of Botany they’ve been involved in inflorescence and floral organ development, adventitious rooting and xylogenesis, the growth of maize coleoptile segments and working with Arabinogalactan proteins in a paper with the best title I’ve seen in a while: Back to the future with the AGP–Ca2+ flux capacitor. AoB PLANTS is averaging a paper a month with an auxin influence this year to date (February).

What I find so confusing about Auxin is that it is everywhere, and it’s so well-known to botanists that it’s a necessary shorthand when writing a paper. This is great, but it makes papers featuring Auxin very difficult to read if you don’t already know about it. Enders and Strader cover a century of Auxin research for AmJBot and by placing Auxin research in a historical context, they help highlight how we know what we know about this very important hormone.

They start early with the quest to identify Auxin, but they highlight two key points in Auxin research in their review. One is the 1939 paper by Thimann and Schneider, The relative activities of different auxins. This pulled together what was known about Auxin, and helped clear some controversy. The other pivotal moment was adopting Arabidopsis as a model organism in the 1980s, and the associated advances of molecular biology that allowed experimentation with much greater resolution than before.

Like any good review there are plenty of links to other papers to read more, with major sections on metabolism, transport and signal transduction, but there’s also a helpful section at the end. Enders and Strader point to questions that are still open in Auxin research, like have all Auxins been discovered or are there still more to be found? There’s also an interview with Barbara Pickard on Kenneth Thimann which adds a human dimension to the research.

The impression I’ve had of Auxin research is that a lot of people have been finding out some really exciting stuff about the building blocks of plants. Reading one paper hasn’t turned me into an expert, but is has helped give me some idea about why people get so excited about Auxin.

You can pick up the paper free from AmJBot.