Need me? Feed me!
One of the constant sources of amazement of marine biology to me is the realisation of how inter-dependent life forms are in ecological terms. Take for example cyanobacteria; only relatively recently has the major role of N(itrogen)-fixing cyanobacteria (which, as ‘blue-green algae’, are photosynthetic enough to be considered as honorary plants for this column) in the nitrogen economy of the oceans been appreciated. Without probing deeper it is easy to view it as a one-sided relationship: photoautotrophs and their eukaryotic dependents benefit from the selfless N-fixation of these prokaryotes. But it is not always as one-way as you might think. Work by Tripp and co-workers (Nature 464: 90–94, 2010) on the globally distributed, periodically abundant N-fixing marine cyanobacterium, UCYN-A has revealed that is has several biochemical deficiencies. For instance, although photosynthetic it lacks the associated oxygen-producing ability, but retains sufficient electron transport capacity to generate energy and reducing power from light. It lacks the trichloroacetic acid (Krebs') cycle, and the biosynthetic pathways for several amino acids and purines. All of which implies that it depends on other organisms, either in close association or in symbiosis, for critical nutrients, although so far there is no evidence of a symbiotic association with another microorganism. As the authors conclude, ‘UCYN-A is a paradox in evolution and adaptation to the marine environment’, but it ‘is an example of the tight metabolic coupling between microorganisms in oligotrophic oceanic microbial communities’. So, UCYN-A is probably currently more auxotroph than autotroph.
Image: Tripp et al. 2010. Nature 464: 90–94.
‘Big Brother’ welcomes Little Sister
As readers of this august publication will be aware, the Annals of Botany (the longest-continuously published journal of its type in the world) strives to publish papers of substantial and general botanical interest. But, as AoB's popularity has grown and competition for publication space has increased, many otherwise excellent but more specialised papers have had to seek an appropriate home elsewhere. Recognising this dilemma, the Annals of Botany Company has recently launched AoB PLANTS, a new journal that retains the promptness, courtesy and fairness of the Annals of Botany but which is more open to specialist papers in addition to those of wide potential interest (http://aobplants.oxfordjournals.org/). AoB PLANTS is published online-only by Oxford University Press, is internationally peer-reviewed and wholly open-access. It offers rigorous double-blind reviewing, a large and highly international editorial board, transparent minimum acceptance criteria and publication within a few days of final acceptance. Currently, there are no fees of any kind for authors. To find out more about this exciting new journal with all the advantages of open-access and state-of-the-art online provision, please see: http://www.oxfordjournals.org/our_journals/aobpla/message_from_the_editor.html. We at ‘The Annals’ welcome our little sister and wish her all the best as she also tries to spread the botanical word.
Bigging-up Brachypodium
Despite the fact that the approx. 10 000 species of grass all look very similar (as any 1st year undergraduate in a plant ID class would probably agree!), they represent a wide range of morphologies and physiological adaptations. So, as we rightly question any claims that Arabidopsis thaliana – the ‘model’ angiosperm – is a universal model for all the idiosyncrasies possessed by the >240 000 species of flowering plants, neither maize nor rice are likely to be good models that embrace the totality of grass diversity. To that end, it is fitting that the genome of the wild grass Brachypodium distachyon (Brachypodium) has recently been published by The International Brachypodium Initiative (Nature, 463: 763–768, 2010). As the first member of the economically important Pooideae subfamily (which includes nutritional staples wheat and barley) to be accorded this honour, Brachypodium can be rightly viewed as a model grass plant. These days, though, it is not enough just to have a high-quality genome sequence to qualify as a model organism. Fortunately, Brachypodium is not only small, it grows quickly, is easy to cultivate and to transform and manipulate in the laboratory, making it more than a match as a monocot equivalent of Arabidopsis. But now that its genome is sorted, this ‘thale cress for graminologists’ is poised to fulfil its potential as an important experimental system for developing new energy and food crops. For more Brachypodium information, visit http://www.brachypodium.org/
Image: Oregon State University.
New John Innes No. 1
It's all change at the top of the UK's 100-year-old Norwich-based ‘fertiliser-to-plants-and-microbial-science-research-institution’, The John Innes Centre (JIC) (http://www.jic.ac.uk/corporate/media-and-public/current-releases/100302NewJICDirector.htm). From 1st September 2010 Prof. Dale Sanders (FRS) will take over as its Director and Chief Executive, succeeding Prof. Chris Lamb CBE, FRS who died in August 2009. Prof. Mike Bevan has been Acting Director in the intervening period and will continue to hold that post until this September. Funded in large part by the BBSRC (the UK's Biotechnology and Biological Sciences Research Council), the JIC conducts fundamental and strategic research across a range of bioscience disciplines that provide knowledge to address the major challenges of global food security, living with environmental change and healthy ageing. As a timely tie-in to these global ambitions the JIC has recently announced a £1·5 million, 3·5 year JIC-co-ordinated project to produce the perfect pea (http://www.alphagalileo.org/ViewItem.aspx?ItemId=69806&CultureCode=en), which aims to find new ways to develop improved pea varieties for the high-profit-margin food market, and to study the likely impact of greater uptake of legume farming on nitrogen fertiliser use. In another Norwich-based news item, an international team led by the Sainsbury Laboratory (a joint venture between the Gatsby Charitable Foundation, the John Innes Foundation, the University of East Anglia and the BBSRC, situated next to the JIC in Norwich, UK), has transferred broad spectrum resistance against some important plant diseases across different plant families (http://www.alphagalileo.org/ViewItem.aspx?ItemId=70379&CultureCode=en). Breeding programmes for resistance generally rely on single genes that recognise molecules specific to particular strains of pathogens. Unfortunately, this latter approach rarely confers the highly prized broad-spectrum resistance and is often rapidly overcome by the pathogen evolving to avoid recognition by the plant. The Sainsbury breakthrough therefore provides a new way to produce crops with sustainable resistance to economically important diseases. Finally, and aside from its impressive research credentials (but no doubt related thereto), the JIC has also supplied the two present Professors of Botany at the UK's University of Oxford, Nicholas Harberd (Sibthorpian Professor) and Liam Dolan (Sherardian Professor). What are they putting in the water in Norwich?
Shedding light on plant biology
When plants aren't using sunlight as an energy source, they are utilising it as a major environmental cue in a wide range of photomorphogenic processes. Major coloured photoreceptor modules that mediate that latter suite of responses are the phytochromes (the aptly – if unimaginatively – named ‘plant pigments’). But just because plants have phytochromes do they need them? Or, phrased a little more scientifically, can plants complete their cycle if light provides energy but no information about the environment? Such a question was asked by Barbara Strasser and colleagues (PNAS 107: 4776–4781, 2010). To solve this question involved the creation of a phytochrome-free plant – because all photosynthetically active wavelengths activate phytochromes – which was a quintuple phytochrome mutant of Arabidopsis thaliana. Their various researches led them to conclude that Arabidopsis development is stalled at several points in the life cycle in the presence of light that is suitable for photosynthesis but which provides no photomorphogenic signal. So, phytochromes are important (and are there for a reason… i.e. plants do need them)! In related light work Sander Hogewoning and colleagues (Journal of Experimental Botany 61:1267–1276, 2010) investigated growth differences between plants exposed to artificial and natural solar spectra. Such work is of enormous practical importance in any attempts to study plant growth under controlled conditions. However, they did not use natural daylight but an artificial solar spectrum (AS) which ‘closely resembles a sunlight spectrum’ but nevertheless demonstrated that AS-grown plants were taller and more massive than plants grown using fluorescent tubes or high-pressure sodium lamps. They – not unreasonably – conclude that this highlights the importance of a more natural spectrum if the aim is to produce plants representative of field conditions. I can't imagine anybody would argue with that conclusion.
Image: Wikimedia Commons.
Deadly blow for oceanic iron fertilisation?
Global concerns over atmospheric levels of CO2 cannot have escaped the notice of this journal's readers. One of the great advantages of photoautotrophs such as plants or algae is that they are often seen as part of the solution to reducing excess global CO2 burdens by removing it during photosynthesis. However, this is only an effective long-term ‘fix’ if the carbon is locked away and buried at depth in the oceans. To try and encourage such carbon drawdown fertilising the ocean with iron has been proposed, which hypothesises that photosynthesis in many areas of the world's oceans is limited by iron levels. Whilst there is evidence that addition of iron can enhance photosynthesis – and hence removal of CO2 from the atmosphere – the carbon is not always locked away long-term but is soon released back into the atmosphere. Another down side to this approach is revealed by Charles Tricka et al.'s study (PNAS 107: 5887–5892, 2010), which showed that populations of Pseudonitzschia increased in numbers in response to iron fertilisation in the sub-Arctic North Pacific Ocean. Although a photosynthetic diatom, Pseudonitzshia is also toxigenic, producing the potent neurotoxin that causes Amnesic Shellfish Poisoning. This could potentially cause human health risks if fish that feed on the algae, such as anchovies and sardines, were consumed; furthermore, marine mammals and seabirds that feed on these fish could also be harmed with knock-on effects to major marine ecosystems. It seems that there is no completely good news when it comes to strategies to deal with rising CO2 levels… but didn't Wikipedia (http://en.wikipedia.org/wiki/Iron_fertilisation) – that well-known barometer of opinion on global issues – warn us about such ocean enrichment and harmful algal blooms some time ago?
Image: Wikimedia Commons.
Biological warfare hots up
I doubt that there are many people who view terrorism or war as a good thing; it can be incredibly destructive and people get hurt and even killed. Better to solve disputes with negotiation and talking. However, when words are not enough, help is at hand with a weapon that doesn't kill, but merely incapacitates. That is the hope behind the recently announced deployment of ‘chilli grenades’ by the Indian Army (http://news.oneindia.in/2010/03/24/indian-army-to-use-chilli-grenades-to-fight-terror.html). The particular chilli concerned is bhut jolokia (also known as the ghost chilli), which, at >1 000 000 Scoville units, was officially declared the world's spiciest in 2007. After innumerable tests, the Indian military has decided to use the pungent spice in tear gas-like ‘chilli-nades’ to immobilise terror suspects. Trials are also under way to produce bhut jolokia-based aerosol sprays, which can be used by women to defend themselves against attackers and also by the police to disperse mobs. However, whether this should be considered biological or chemical warfare is likely to get politicians and military strategists hot under the collar for years to come. An interesting economic aside to this is that the chilli is grown in north-east India and could lead to a marked reduction in purchases of foreign weaponry, but may well push up the prices of curries in the Indian restaurants of the world as the ingredients for their vindaloos or phalls are diverted to military use. How will the curry-deprived angry mob be dealt with then? By chilli grenade? Thereby giving them their chilli fix for free…!? It's a funny old world…
Image: www.gigposters.com
Hanging around like a bad smell
Investigating emissions from forest and peatland plants in Scandinavia seems an enterprise unlikely to lead to the discovery of a botanical equivalent of Harry Potter's cloak of invisibility (http://en.wikipedia.org/wiki/Cloak_of_invisibility). And so it is, but Sari Himanen and co-workers' study of herbivore-repellant plant volatiles (New Phytologist doi: 10·1111/j.1469-8137·2010·03220.x) does have some similarities. The Scandinavian team discovered that Betula spp. effectively defended themselves from herbivore attack by coating their leaves with chemicals – more specifically, the ‘arthropod-repelling C15 semi-volatiles ledene, ledol and palustrol’ – adsorbed from neighbouring plants of Rhondodendron tomentosum. These adsorbed volatiles are then re-released by the birch plants, which may help to protect them from herbivore attack in the same way as they do the Rhododendron. In a remarkable bit of understatement, Himanen said, ‘Our results show that interactions between species through emissions are a good example of the ecological effects that need to be considered more from a plant community than from an individual plant point of view’. Which just goes to show that the more you look, the more you see, or can sniff out… And if the review by Josep Peñuelas and Michael Staudt (Trends in Plant Science 15: 133–144, 2010) is correct then there may be more of these biogenic volatile organic compounds (BVOCs) wafting about in future in response to climate change and global warming, with knock-on effects to existing plant–animal and plant–plant interactions.
Image: Peñuelas & Staudt. 2010. Trends in Plant Science 15: 133–144.
Phoenixism and phytology
Of all the environmental ‘slings and arrows’ that vegetation has to contend with, fire is one of the most dramatic. Whether it is man-derived or natural from lightning strikes fire seems on the face of it to be nothing but bad news for botanics. Yet, for some plants this most destructive of abiotic factors is an essential part of their life cycles and they may not survive without it. Whether it is the heat that helps to release seeds from the constraints of tight-closed seed heads, or the life-giving nutritious soil fertilised by ashed plant remains, or removal of shading effects from competing plants, or chemicals in the smoke, nature has found many ingenious ways to make a virtue out of this calorific necessity. Studying the latter phenomenon, David Nelson and colleagues (PNAS, doi: 10·1073/pnas.0911635107) investigated the role of karrikins in Arabidopsis germination. Karrikins are a family of butenolide molecules recovered from smoke water fractions that are known to stimulate seed germination. Although not exactly known as a coloniser of the scorched earth that follows a vegetation fire, the Arabidopsis study reveals that karrikins affect light-dependent phenomena during germination and seedling establishment. For example, karrikins promoted germination at lower light intensity, and enhanced light perception in the stems of emerging seedlings compared to non-exposed plants. The study found similar effects in lettuce and wild turnip, too. How does this work on Arabidopsis (semi-naturalised denizen of high-tech growth cabinets) help us to understand the biology of, say, Banksias (indigenous to and survivors of bushfire-prone areas of Australia)? Maybe the karrikins help to prepare plants exposed to smoke naturally to sense fire-induced changes in sunlight at the soil surface, and are not therefore limited to a role in germination specifically. For the etymologically inclined, karrikins are named after ‘karrik’, the first recorded Aboriginal Nyungar word for smoke (Plant Physiology 149: 863–873, 2009).
Image: Moreira et al. 2010. Annals of Botany 105: 627–635.
Carnivores should eschew heavy me(t)als…
Heavy metals [elements that – amongst a plethora of definitions (Pure and Applied Chemistry 74: 793–807, 2002) – have a density >6 g cm−3] are notorious as potent poisoners of biological systems (in amounts that exceed the ranges of those deemed to be essential micronutrients, that is!). Accordingly, we are familiar with reports that document their various toxic effects. What is a little more unusual is the study by Christopher Moody and Iain Green (Environmental Science & Technology 44: 1610–1616, 2010) that has examined animal-derived heavy metal uptake by carnivorous plants. Living in nutrient-poor, quite fragile habitats, carnivorous plants are sensitive to a wide range of environmental outrages, including exposure to heavy metals such as copper and cadmium. The Bournemouth University (UK) team fed contaminated house-fly maggots to a group of endangered white-topped pitcher plants (Sarracenia leucophylla) and found that cadmium accumulated in the plants' stems in a way that can be toxic and disrupt growth. By contrast, copper intake was not associated with any sign of phytotoxicity. Whilst emphasising that not all heavy metals are the same, this work also highlights one of many factors that may be contributing to a worldwide decline in carnivorous plants. Suggestions that the maggots became dosed with copper and cadmium by feasting on heavy metal-loaded pitcher plants are mischievous and probably unfounded. For the record, they were fed on dog food(!).
Image: J.W. Buel. 1887. Land and Sea.