Fungus-feeding plant fends off herbivores
It's always good to hear of plants getting one over on their competitors. So, when a plant gets two over, that is cause for a double celebration. One such plant is the mycoheterotrophic ericaceous angiosperm Monotropsis odorata (pictured is Monotropastrum humile, a related mycoheterotroph). Not only has it done away with the need to photosynthesise (instead obtaining its sustenance from a fungal ‘partner’, organisms perhaps better known as plant pathogens), it seems that its dried bracts help to protect it from the attentions of would-be herbivores. A 2-year experimental study by Matthew Klooster and colleagues (American Journal of Botany 96: 2197–2205, 2009) discovered that the reflectance spectra of the bracts is similar to that of surrounding leaf litter, thereby helping to camouflage its edible flowers and stems from the attention of grazers. The dried bracts also appear to enhance fruit-set, helping to improve overall fitness, so that a member of the Plant Kingdom can profit from the hard work of a member of the Fungus Kingdom and avoid the undesirable attentions of members of the Animal Kingdom. Continuing with this theme of multi-Kingdom interactions …
Image: Wikimedia Commons.
Leaves, ants, fungus … and now N-fixing bugs, too
In the ‘who is the oldest gardener?’ stakes, Adam (of Holy Bible fame) may come to mind. Although he may be the first documented human gardener, he wouldn't even come close in the contest to find the first gardener. But, high on the list of corn-tenders for this accolade would probably be those ever industrious leaf-cutting ants beloved of cartoon film-makers. Incapable of digesting their leafy meals themselves, these highly social insects have been assumed to enjoy a cosy manger à trois: ants harvest the plant material, take it to their nests and subsequently dine on the fungus that uses the plant material as its food substrate. Compared to animal tissue, plant material is poor in nitrogen (a reason why herbivores have to eat so much more food than their carnivorous neighbours), yet these fungus farms sustain enormous numbers of ants: how? Work by Pinto-Tomás et al. (Science 326: 1120–1123, 2009) appears to provide the missing piece of the puzzle: nitrogen-fixing bacteria. Previously overlooked, bacteria, such as Klebsiella spp., could provide 45–60 % of the nitrogen in the ants' food. Any relevance of this discovery to the nitrogen economy of the wider ecosystem in which the ant nests reside remains to be studied and evaluated. Intriguing as this discovery is, the 4-kingdom mutually beneficial(?) symbiosis thus revealed is possibly even more amazing. Talking of food …
Image: Jarrod Scott, Science/AAAS.
A free launch
No, not a free lunch (they don't exist, as leaf-cutting ants would confirm), but the next best thing, a free facility recently launched by the international botanical journal, the Plant Cell. Entitled ‘Teaching Tools in Plant Biology’ it offers, well, tools for teaching plant biology. This online-only feature aims ‘to provide undergraduate-level overviews of plant-oriented topics, comprising PowerPoint presentations, lecture notes, and suggestions for further reading’. The Teaching Tools, which are published monthly and can be downloaded from www.plantcell.org/teachingtools/teaching.dtl, are peer-reviewed to ensure accuracy and their fitness-for-purpose. This feature will remain free for the first 6 months; thereafter it will only be available to the journal's subscribers. Already featured are items on leaf development (parts 1 and 2), and epigenetics; February's Teaching Tools topic is ‘The Small RNA World’. The first in this series – ‘Why Study Plants?’ – is designed for a general audience or first-year university students, and explores the theme of ‘what have plants ever done for us?’. Apart from the ‘obvious uses’ – providers of oxygen, food, fuel and fibre – the lecture also examines other reasons why plants are studied; e.g. to improve and secure the food supply for an increasing world population, and to identify new sources of bioactive compounds and medicines. Ever keen to encourage the development of the next generation of plant scientists, Plant Cuttings is happy to promote this resource. Maybe (and solely in the interests of balanced reporting you understand) we should mention that the Annals of Botany has made its Invited Reviews and Botanical Briefings (both of which are peer-reviewed) freely available for years? Always nice to know that where the Annals dares to tread others will follow … eventually!
Tales from the crypt
Proof that you do – at least occasionally – have to update lecture notes comes from this cautionary tale. For many years I – like many plant biology lecturing colleagues I'm sure – have been happy to tell my students that the trichomatous, stomata-bearing crypts on the underside of leaves of xeromorphic species such as oleander (Nerium spp., transverse section of leaf pictured) help to reduce transpiration in those plants that live in arid environments. Work by Nebelsick et al. (Plant Physiology 151: 2018–2027, 2009), who examined transpiration of Banksia leaves using three-dimensional finite-element models generated using commercial computational fluid-dynamics software, suggests this may not be true. In their studies crypts only reduced transpiration by <15 % compared to non-encrypted superficially positioned stomata, and trichomes within the crypt had virtually no influence on transpiration. Thus, it appears unlikely that the primary function of crypts and their trichomes is to reduce transpiration. So, what on Earth are they for? The sooner we decode this encrypted message the better! In the meantime, what are we to tell our students? Perhaps the best we can do is direct them to the new ‘comparative omics database for plant trichomes’ – TrichOME – for inspiration (Plant Physiology 152: 44–54, 2010).
Image: John Curtis & Nels Lersten, Botanical Society of America Image Collection.
A-maizing money-making scheme(?)
Nobody ‘does’ science for the money: knowledge is after all supposed to be its own reward. But it is always nice to think that your hard work may receive more tangible recompense. To that end Nature magazine recently carried an advertisement seeking people who can ‘think outside of the box’ (https://gw.innocentive.com/ar/challenge/8836928?campaign=nature). Specifically it invited responses to an InnoCentive theoretical IP (Intellectual Property) transfer challenge to find novel approaches to protecting maize from damage caused by European corn-borer. Apparently, InnoCentive (http://www.innocentive.com/about-us-open-innovation.php) is the global innovation marketplace where creative minds solve some of the world's most important problems for cash awards (up to $1 million), although the reward for this particular challenge is a mere $20 000. That sum is not to be sneezed at, but to show how above all such tawdry concerns of pecuniary advantage this column is, we take some pleasure in advising that the closing date was … 31 January, 2010. Mind you, it seems that Nature has similar non-commercialisation ethics; the challenge was actually launched months before. No such qualms from InnoCentive, which has a strong commercial ethos – in exchange for the $20 000 prize the solver relinquishes all rights to the IP in the winning discovery.
Image: Köhler's Medicinal Plants, Wikimedia Commons.
Fruits with deadly ap-peal
As everybody knows, when you eat fruit, you throw away the peel, rind or whatever the outer coating is called. Now a team from Kingston University suggests that this could be the botanical equivalent of ‘throwing the baby out with the bathwater’. Work by Simon Gould et al. (BMC Complementary and Alternative Medicine, doi:10·1186/1472-6882-9-23, 2009) has demonstrated that extracts from the rind of pomegranate (Punica granatum, I assume, but nowhere was the scientific name of the main organism given in the Methods section of the paper!), imaginatively known as PRE (pomegranate rind extract) has anti-microbial activity. Significantly, PRE is active against MRSA (methicillin-resistant Staphylococcus aureus), a serious pathogen and scourge of hospital wards in the UK that can cause infections in humans and which is otherwise difficult to combat because it has developed a resistance to some antibiotics. Knowing how tedious it is to get the edible fleshy bits out of a pomegranate it comes as no comfort to realise that I've been eating the wrong bits all along! And, whilst we in northern Europe wait for spring to be sprung, it seems that even the common or garden snowdrop has potentially pharmacologically important secrets to reveal: three new alkaloids have been found in snowdrops – Galanthus spp. – which may be of benefit in treating malaria and Alzheimer's disease (http://www.alphagalileo.org/ViewItem.aspx?ItemId=64775&CultureCode=en). From ‘beauty’ to the ‘beast’ now …
Image: Wikimedia Commons.
Bad smells: double-whammy
Accepted views should always be challenged. One such view is that the foul smells of dung or rotting carrion associated with plants such as Rafflesia arnoldii (pictured) and Stapelia act as an attractant to their pollinating organisms. Sounds like a good idea. But when should you stop looking for answers? You could stop when you have a story that sounds plausible. Or you could go one step further and see if there is more to that tale (it's what scientists are supposed to do after all), which is what Simcha Lev-Yadun and colleagues did when considering such malodorous plants. In an interesting article (BioEssays 31: 84–88, 2009) they not only support the view that such odours act in that pollinator-attractant way, but also that those same volatile chemicals may deter herbivores from eating the plants at such a crucial stage in their life cycle. Citing examples of carrion odour as an indicator of the presence of pathogenic microbes and potential closeness of carnivores, and dung odour as a marker of faeces and consequently a site with a high risk of parasitism – all of which are bad news for a mammalian herbivore – the notion is highly plausible. Lev-Yadun et al. consequently propose two new types of ‘repulsive olfactory aposematic mimicry’: thanatosis – ‘olfactory feigning of carcass’ – and ‘olfactory mimicry of faeces’ (which seems not to have a fancy name). How do you follow that? Well …
Image: MA Suska, Wikimedia Commons.
Scatoethnophytopathology: hot on the trail of human pollution
Tourism advertising campaigns often encourage us to ‘leave nothing but footprints’. Yet these days footprints come in a wide variety of forms. Leaving aside carbon footprints, humans deposit a range of microfloral traces that betray their presence and activities. For example, and traditionally as a marker of pollution by human sewage, the numbers of intestine-dwelling bacteria such as Escherichia coli are used to indicate how safe the bathing is at beaches. Now a new silent witness – Pepper Mild Mottle Virus (PMMoV) – is poised to be exploited in a similar way, according to work in the USA by Karyna Rosario (Applied and Environmental Microbiology 75: 7261–7267, 2009). Although harmless to people, PMMoV can be a pathogen in hot, bell and ornamental peppers (Capsicum spp., pictured). Consequently, PMMoV finds its way into a wide variety of cuisines, and ultimately human sewage. Presence of the virus in water bodies can thus be used as an indicator of pollution by human waste and help to determine if beaches need to be closed to bathers. An advantage of the virus over bacteria as a proxy of human waste is its relative immediacy of detection compared to the 24 hours it takes to plate out and identify bacterial contamination. How well this new forensic tool will work in areas shunned by capsovores remains to be seen.
Image: Luc, Viatour, Wikimedia Commons.
Mind the gap!
It is widely known that there is an intimate relationship between plants and the soil in which most of them are rooted and from which they satisfy the majority of their water and nutrient requirements. For most of the time the connection between roots and surrounding soil is extremely close, but it has been assumed that the two partners separate as roots shrink during times of water deficit. For the first time, Andrea Carminati and co-workers (Vadose Zone Journal 8: 805–809, 2009) have actually ‘seen’ what happens at this important interface during droughting and subsequent re-watering of white lupin (Lupinus albus). Because it is not possible to view roots if completely surrounded by soil – and to uncover the roots so they can be seen rather defeats the aim of the study – the group used non-invasive soil-penetrating X-ray tomography to image the root/soil junction in situ. As expected, air gaps developed during dry periods – as roots shrank. However, although roots swelled following irrigation, the air gaps did not close up completely; the plant/soil interface was not re-established in older parts of the roots. This revelation raises important questions concerning the ability of plants to take up sufficient water and nutrients following droughts, and the knock-on effects for agricultural production during the drier summers that are predicted for north-east Germany where the work was undertaken. Proof indeed that out of sight should not mean out of mind! And talking of plants and soil …
Image: Ulrich Weller/Helmholtz Centre for Environmental Research (UFZ).
Pot plants: a breath of fresh air
When we think of phytoremediation – ‘contaminant removal by plants’ – we may have in mind exotic scenarios such as removal of heavy metals from soil or organic pollutants from water bodies, or even degradation of TNT. But work by Yang et al. (HortScience 44: 1377–1381, 2009) extends this role to the more mundane settings of the workplace and home ‘plantscape’. The group tested 28 plants, and identified five (including English ivy, Hedera helix, pictured, and Asparagus fern, Asparagus densiflorus) as ‘super ornamentals’– those with the highest rates of contaminant removal. To determine the plants' atmospheric clean-up ability they were exposed to a range of common household volatile organic compounds (VOCs), including aromatic hydrocarbons (benzene and toluene), an aliphatic hydrocarbon (octane), and a halogenated hydrocarbon (trichloroethylene). Perhaps surprisingly, these VOCs are widely present indoors and are derived from everyday items such as furnishings, carpets, plastics, cleaning products, paint, solvents and adhesives. The plants differed in their abilities to remove the VOCs and it is suggested that a mix of plants should be used in any air-purifying role, the exact composition tailored to the VOC signature of the intended location. So, pot plants are not simply decorative, they are functional, too. Now, if we could only get them to grow outdoors, they might be persuaded to soak up such problematic pollutants as carbon dioxide …
Image: Wikimedia Commons.
Phyto-fit: profile of a killer
If asked to name some carnivorous plants, most people would probably say Venus fly-trap (Dionaea muscipula), pitcher plant (Nepenthes spp.) or sundew (e.g. the pictured Drosera capensis). But, if we are to endorse the conclusion of the wide-ranging phylogenetic review by Mark Chase et al. (Botanical Journal of the Linnean Society 161: 329–356, 2009), we maybe now ought to number amongst their ranks the likes of petunias and potatoes. Promoting the term ‘proto-carnivore’, they suggest that those two latter solanaceous examples are contenders because their sticky hairs trap insects. Further blurring the distinction between carnivore and non-carnivore, they argue that certain accepted carnivorous plants have not been proven to digest their ‘prey’ or absorb the breakdown products. The thought-provoking, abundantly illustrated article makes for fascinating reading and is another tribute to the ground-breaking work of Charles Darwin whose various anniversaries were well celebrated throughout 2009. The article should also be remembered for its unusual concluding sentence: ‘We may be surrounded by many more murderous plants than we think’. You have been warned!
Image: Noah Elhardt, Wikimedia Commons.
Semantic enrichment – spreading the botanical word
The Annals of Botany is set to participate in a pilot project designed to explore ‘Semantic Enrichment of the Scientific Literature’ (SESL), run by the European Bioinformatics Institute (but funded by the Pistoia Alliance – http://pistoiaalliance.org/ – a ‘cross-pharma organisation’). The aim of the project is to establish whether content in various formats from disparate sources (e.g. literature from publishers and data from public databases) can be delivered to a central ‘knowledge brokering service’, which then makes the content machine-readable and allows key pieces of information to be extracted by data-mining approaches. These pieces of information can then be presented to consumers, generating leads for further reading and research and knowledge discovery. Although the information-flow model is analogous to Google's, much more information about concepts, entities and the nature of their relationships to each other are first embedded into the indexed content in a way that can be understood by specialist searching software. The main driver for the participating pharmaceutical companies is the admirably altruistic goal of finding machine-based ways of identifying literature/database content of relevance more quickly, which it anticipates will have wider benefits to the research community at large. Sadly, with increasing ‘digitalisation’ of information – and the electrification of the means to access and extract it – if research papers are not structured and coded in such a way as to be read automatically by intelligent machines, scouring a large volume of information beyond the capabilities of individual human researchers to digest, then it is likely that the research results and conclusions will be increasingly overlooked. But do remember that you probably read this in a hard copy journal first!