Tag Archives: Plant Science

Plant parts doing unexpected things: Part 2 (or, Root research all up in the air)

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Our suitably erudite – albeit neophyte – botanical generation who knew about the functions of plant stems when quizzed previously (see Plant parts doing unexpected things: Part 1, posted previously) would probably do equally well when asked about the main roles of roots*. However, what they may be surprised to learn is that some roots photosynthesise (yes, like stems or leaves). We’re not talking about ‘typical’ soil-surrounded roots, but the so-called aerial roots of epiphytic plants perched high above the ground on trees – for example certain orchids. These photosynthetic roots dangle in the air that surrounds the epiphyte and its host plant. Whilst a photosynthetic capability is unusual for a root that is typically subterranean, you might expect that gain of this function might be at the expense of another, more typical root role, say absorption. But no, such roots still retain the capacity to absorb water from their surroundings. However, rather than rely on the assistance of root hairs as for their terrestrial, soil-rooted relatives, nature has equipped these aerial roots with an additional tissue, the velamen. The velamen is a remarkable multi-layered epidermis-like structure whose specially thickened cells not only absorb water from the humid air or rain water, but also help to reduce transpiration from the internal root tissues when the velamen cells are dried out. There is still much to uncover about the role of the velamen in the biology of epiphytes, but an interesting discovery has been made by Guillaume Chomicki et al., and one that relates not to the plant’s water relations but to the integrity of the root’s photosynthetic process. Recognising that levels of damaging ultraviolet B (UV-B) radiation are high in the epiphytes’ habitat, and knowing that UV-B screening compounds such as flavonoids help to protect leaves, the team wondered how similarly challenged, photosynthetic roots might be protected from UV-B harm. Using a nice combination of molecular and structural techniques – gene expression analyses, mass spectrometry, histochemistry and chlorophyll fluorescence – they demonstrated that UV-B exposure resulted in inducible production of two UV-B screening flavonoids within the living (i.e. young) velamen of Phalaenopsis × hybrida, but which compounds persist in the cell walls of the functional – dead – velamen tissue. Furthermore, and interestingly, this root mechanism of UV-B protection is apparently different from that employed by leaves. A case of same destination, different routes? Not bad for a dead tissue one could easily write-off as merely acting like a sponge!

* Which, for completeness, are generally assumed to be: anchorage of plant in soil, absorption of water/minerals from the soil, storage of reserve materials, and conduction of water/nutrients to/from the stem – Ed.

2015 International Year of…

 

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Ever since 1959/60 with ‘World Refugee Year’ we’ve seen all manner of ‘International Years of’ (IYO). These global ‘observances’ are endorsed by the United Nations, an international organisation established after the Second World War and whose noble and worthy objectives include maintaining international peace and security, promoting human rights, fostering social and economic development, protecting the environment, and providing humanitarian aid in cases of famine, natural disaster, and armed conflict. Developing the notion that global problems require global solutions and action – and few issues are more pressing and global than food security – 2015 is the IYO (or on…) Soils (or IYS at it is officially abbreviated). If you wonder what the connection between soils and food is, then the former is the rooting medium that supports (both literally and nutritionally) the great majority of human’s staple crops – whether cereal (e.g. ricewheatmaizesorghum), legumes (e.g. chickpeaslentilssoybean) or tubers (e.g. sweet potatocassavapotato). Quite simply, without soil we wouldn’t be able to grow the plants to feed Man or the animals he eats. But it has to be the right kind of soil, with sufficiency of the 17 nutrients essential for plant growth and development, minimal levels of harmful compounds such as heavy metals or salts, and with enough freshwater to help sustain plant life. In many areas of the world such suitable soils are diminishing resources as a result of phenomena such as desertification and salinisation (the latter ironically often a consequence of irrigation by human intervention). Recognising the central importance of soil to food security – and doing its bit to engender a Brown Revolution*, the Food and Agriculture Organization (FAO) of the United Nations has been nominated to implement IYS 2015, with the aims of increasing awareness and understanding of the importance of soil for food security and essential ecosystem functions. We wish them well in that worthy endeavour. But there’s more! For 2015 is also the IYO Light and Light-Based Technologies (IYL 2015). Although this IYO is much more about raising awareness of how optical technologies promote sustainable development and provide solutions to worldwide challenges in energy, education, agriculture, communications and health, amongst the thousands of words devoted to this ‘event’, but almost as an after-thought, it does dedicate 78 words to the most important light-related phenomenon of photosynthesis when it considers light in nature (alongside rainbows, sunsets and northern lights…). So, two IYOs with strong plant themes (even if the photosynthetic pre-eminence of light is somewhat ‘hidden under a bushel’).. But until we have an International Year of Plants, we’ll have to make the most of The Fascination of Plants Day 2015 on 18th May (2015)

 

* This is but one of a many-hued spectrum of agriculture-related revolutions (which includes the mid-20th century’s better known Green Revolution), but which is distinct from the other brown revolutions pertaining to leather or cocoa production in India.

 

[So that you can be ready before the next IYO happens, here’s advance notice that 2016 is the IY of camelids (camels, llamas, alpacas, vicuñas, and guanacos), and pulses (the edible, dried seeds of members of the legume family, e.g. beans, lentils). And to whet your appetite for IYS 2015, five fascinating facts about soil can be found at the CropLife website – Ed.]

Plant parts doing unexpected things: Part 1 (or, Giving transpiration a little boost…)

Image: Wikimedia Commons.

Image: Wikimedia Commons.

All botanists (plant biologists/plant scientists/phytologists…) worthy of the name should be able to state the important roles played by various plant parts. Stems, for example, support the leaves(!), help to conduct water, photosynthates and other solutes to other plant parts, engage in some photosynthesis (primarily when young), and store such materials as starch. Well, so much for the commonplace quartet of functions. As botanists of an enquiring and sufficiently sceptical nature we probably also know that such a list is never complete, and plants can usually be found that defy convention and engage in practices additional to the received wisdom of general texts. So, welcome news that Or Sperling et al. have discovered the phenomenon of ‘transpirational-boosting’* in the date palm. Famously, the date palm (Phoenix dactylifera) grows in desert-like areas of northern Africa and the Middle East. Deserts are defined primarily in terms of low rainfall; consequently, water is a limiting resource to plant growth in that challenging environment. Yet palms are substantial arborescent monocots that can grow to 30 m tall and whose ecological dominance is sustained with uniquely high rates of transpiration. How is this possible in such water-limited regions? Recognising that the high transpiration rates cannot be sustained by soil water supply alone, Sperling et al. examined the reservoir of water within the palm’s stem. Using a combination of heat dissipation, gravimetric sampling and time domain reflectometry (you’ll need to read the open-access paper for the details of these techniques!), they determined that date palms substantially rely on the exploitation and recharge of the stem reservoir in their water budget; stem-located water contributes approximately 25 % of the daily transpiration rate. The date palm stem holds around 1 m3 of water and transpirational losses are recharged by more than 50 litres each night, which, the team argue, is sufficient to maintain daily reuse throughout the growing season. Although irrigated palms were specifically investigated, that still leaves 75 % of the water usage to be supplied externally. Whilst this column is not the place to engage in debate on contentious topics, such as globally growing demands (yes, unintentional pun noted…) on, and concerns over, future availability of fresh water, and not overlooking the issue of salinisation of soil that may accompany such anthropogenic irrigation practices, it is worth just raising the question of how long one can continue to engage in, or justify, human appropriation of water in this way. However, given the socio-economic importance, etc., of date palms – whose genome has been sequenced by Ibrahim S. Al-Mssallem et al. – perhaps there is a suitable case for ‘engineering’ of this magnificent monocot to enhance the contribution of transpirational-boosting**? Or, if we turn this discovery around, what about the rest of the approximately 351,999 other angiosperm species that haven’t been so examined? Might not more of them have evolved this T-B*** mechanism? And, if so, are estimates of future water demand by crops and other plants in need of revision? Botany, not afraid to tackle the big issues of the day (and tomorrow…)! Regardless, date palm is maybe another plant to add to the more conventional ones of cacti and euphorbs as examples of ‘stem succulents’.

* The ever-helpful Mr P Cuttings has kindly given this newly discovered phenomenon its suitably catchy name for the benefit of all plant science textbook writers (etc.) – Ed.

** No inverted commas this time – that must mean that this newly coined term is gaining acceptance by the community at large… – Ed.

*** And, having now been reduced to an initialism (as distinct from the frequently mis-applied term acronym), this phrase seems to be here to stay(?) – Ed.

Garlic and octopus battle tree disease

Image: From Tacuinum Sanitatis, ca. 1400.

Image: From Tacuinum Sanitatis, ca. 1400.

For millennia, garlic, the ‘bulb’ of Allium sativum, has been used medicinally to help make humans better. Whilst many of these so-called ‘cures’ may be more fanciful than factually accurate, evidence-based medicine, there are studies that attest to the effectiveness of garlic or extracts thereof and therefrom against a range of human health-compromising bacteria and fungi (e.g. studies by Giles Elsom et al.Simon Woods-Panzaru et al. and Daniel Tagoe et al.). Indeed, so commonplace have such ideas become that garlic can be used as an educational tool investigating the anti-microbial effects of plant extracts. So much for humans: Is this relevant to looking after the health of, say, trees? Well, apparently so. In the battle against fungal diseases of trees, garlic has been mobilised with some success in Northamptonshire (a county in the east Midlands of the UK). Jonathan Cocking (Managing Director of Arboricultural & Ecological Consultants, JCA Ltd), whose company hold an ‘experimental government licence’ to engage in this work, use an allicin*-based solution administered directly to the base of trees. The solution is injected into an infected tree through eight pipes (the ‘octopus’ connection…) and transported throughout the tree via the transpiration stream. Apparently, ‘the moment the active agent starts to encounter the disease, it destroys it’, BBC Environment Correspondent Claire Marshall explains. Although details of the formula used are not forthcoming, it apparently uses organically-grown cloves from Wales, and somehow the allicin involved is stable for up to one year (rather than the usual 5–10 minutes’ lifespan of the molecule(!)). According to JCA’s website, their ‘Allicin/Conquer Project’ was started in 2009, and so far has had success against such fungus/oomycete infections as Bleeding Canker of Horse ChestnutSudden Oak Death,  Acute Oak Decline and Chalara dieback of ash. Although seemingly effective, widespread use of this treatment is considered impractical and expensive, and is unlikely to be used except to save trees of ‘historic or sentimental value’. It’s always reassuring to know that it’s still down to ‘value’(and that so-predictable human obsession with money/profit, etc…) as to which trees are allowed to die and which are worthy of being saved (in the UK, at least; I’m sure elsewhere in the world a much more enlightened attitude to saving trees prevails…). Anyway, let’s just hope the 10 finalists in England’s ‘Tree of the Year’ competition are in that ‘sufficiently worthy’ category should they succumb to some life-threatening infection, whether fungal or oomycete (or viral or bacterial or mycoplasmal or prionic, or …)!

* Allicin, ‘garlic’s defence mechanism against attacks by pests’.

[I expect it’s been considered (and ruled out), but, mindful of reports of viruses accompanying imported garlic and the fact that plants are attacked by a wide range of virus pathogens, one trusts that the Welsh allicin, as organic as it no doubt is, is sourced from virus-free garlic and doesn’t pose a virus-infection threat to the trees into which it is injected… – Ed.]

Prize-winning banana research

Image: Fir0002/Flagstaffotos, http://www.flagstaffotos.com.au.

Image: Fir0002/Flagstaffotos, http://www.flagstaffotos.com.au.

Readers of this blog will probably be aware of the high esteem/newsworthiness in which bananas (edible fruits, botanically a berry – a new snippet of information to me! – produced by several kinds of large herbaceous flowering plants in the genus Musa) are regarded. Well, in keeping with that musan leitmotif, here’s another banana-themed item. At the 24th First Annual Ig Nobel Prize ceremony in 2014, Kiyoshi Mabuchi et al. were suitably rewarded for their work investigating ‘why bananas are slippery’. Before this revelation elicits the anticipated “Eh? What?! They gave a prize for that??” reaction it should be pointed out that the Ig Nobel Prizes are awarded for achievements that make people laugh, but then think. In this case the Japanese tribologists’ work not only showed why banana skins are so hazardous (the comedic value of people slipping on discarded banana ‘skins’ has been known for generations), but also why apple and tangerine peel are not so ‘dangerous’. OK, so much for the ‘laugh’, what about the ‘thinking’? The team is interested in how friction and lubrication affect the movement of human limbs. The polysaccharide follicular gels that give banana skins their slippery properties are also found in the membranes in our own bodies where our bones meet and it is hoped that the botanical work will ultimately help in the development of a joint prosthesis. Banana research, going out on a limb?

 

[Ig Nobel Prizes (administered by Improbable Research) should not be confused with the more prestigious Nobel Prizes, whose list of prize-winners for 2014 didn’t include any banana-related research (so far as one could tell!). It is, however, noteworthy that Ig Nobels are presented for work done relatively recently; work that earns a ‘proper Nobel’ often takes years for it to be recognised. We would be interested to hear of any Ig Nobel Prize-winners who have gone on to win a Nobel Prize for their ‘ignoble’ work. Who’d have the last laugh then? Something to think about! – Ed.]

Better together…

Image: pixabay.com.

Image: pixabay.com.

No, this is not a belated bit of biased support for the Scottish referendum on independence from England  (which was rejected by those who voted and thereby prevented the United Kingdom becoming the anagrammatically amusing Untied Kingdom…). Rather, it is recognition that – at least in nature – sometimes things do work better when two partners co-operate rather than work against each other. Take for example the reef-building corals – an intimate mutualistic symbiosis between a unicellular alga, a dinoflagellate and an animal, the coral polyp. Put very simply, the alga provides much of the polyp’s food requirements by dint of its photosynthesis, which ultimately allows it to make the massive coral reefs. Although warm-water coral reefs are the basis of extremely rich and biodiverse ecosystems, they are nutritionally poor. This ‘nutrient paradox’ – originally recognised by Charles Darwin (is there any branch of biology that doesn’t have a contribution from this venerable Victorian?) – has traditionally been presumed to be due to very tight cycling/recycling of nutrients within the ecosystem (and the abundance of mutualistic symbioses therein, amongst other factors…). However, a new twist to this nutrient tale has recently been proposed by Orr Shapiro et al. They have revealed that, far from being static structures dependent upon the vagaries of currents to bring nutrients to them and remove waste products, the coral polyp actively generates micro-currents and eddies that promote nutrient inflow and exchange of materials. Using externally located cilia, these miniature structures whip up ‘vortical flows’ immediately adjacent to the epidermal surface, which reduces the exchange-limiting boundary layer at that site thereby facilitating mass transport between coral and the ocean. And in the way of all good discoveries, there are potential spin-offs to other areas of study. In this instance the team posits that investigation of these surface-situated cilia could be used as an alternative to the study of more-inaccessible, internalized cilia, e.g. those in the airways of animals. Thus, there may be unpredictable benefits for biomedicine from this photosynthetically dependent marine mutualism (I know, plants lighting up the path for others to follow – again!!). I’ve oftentimes wondered what the polyp brought to this relationship – aside from providing a chalky castle for the enslaved, hard-working alga. Well, I guess we now know, and it’s reassuring to discover (finally…?) that this intriguing symbiosis is much more mutual than we might previously have imagined.

 

[A video of this phenomenon can be seen on YouTube. The irony of internalization of the dinoflagellate symbiont – which, as its name implies, usually has flagella (two in this case, like much bigger versions of cilia)  – within the coral polyp and its consequential loss of its flagella on the one hand, and the importance of the polyp’s cilia (pale imitations of flagella?) in and to this relationship on the other, is not lost on Mr P. Cuttings. And this item gives a whole new meaning to the phrase ‘on the lash’ because cilium is Latin for eye-lash… – Ed.]

Effect of light on anatomical and biochemical aspects of hybrid larch embryos

Larch embryos In conifers, mature somatic embryos and zygotic embryos appear to resemble one another physiologically and morphologically. However, phenotypes of cloned conifer embryos can be strongly influenced by a number of in vitro factors and in some instances clonal variation can exceed that found in nature. A recent study in Annals of Botany examines whether zygotic embryos that develop within light-opaque cones differ from somatic embryos developing in dark/light conditions in vitro. Embryogenesis in larch is well understood both in situ and in vitro and thus provides a suitable system for addressing this question.

In larch embryos, light has a negative effect on protein accumulation, but a positive effect on phenol accumulation. Light did not affect morphogenesis, e.g. cotyledon number. Somatic embryos produced different amounts of phenolics, such as quercetrin, depending on light conditions. The greatest difference was seen in the embryonal root cap in all embryo types and conditions.

Effect of light conditions on anatomical and biochemical aspects of somatic and zygotic embryos of hybrid larch (Larix × marschlinsii). Annals of Botany January 20 2015 doi: 10.1093/aob/mcu254

Growth responses of the mangrove Avicennia marina to salinity

Avicennia marina Halophytic plants are characterized by enhanced growth under saline conditions. A recent study in Annals of Botany combines physiological and anatomical analyses to identify processes underlying growth responses of the mangrove Avicennia marina to salinities ranging from fresh to seawater conditions.

Following pre-exhaustion of cotyledonary reserves under optimal conditions (50% seawater), seedlings of A. marina were grown hydroponically in dilutions of seawater amended with nutrients. Whole-plant growth characteristics were analysed in relation to dry mass accumulation and its allocation to different plant parts. Gas exchange characteristics and stable carbon isotopic composition of leaves were measured to evaluate water use in relation to carbon gain. Stem and leaf hydraulic anatomy were measured in relation to plant water use and growth.

The results identified stem and leaf transport systems as central to understanding the integrated growth responses to variation in salinity from fresh to seawater conditions. Avicennia marina is revealed as an obligate halophyte, requiring saline conditions for development of the transport systems needed to sustain water use and carbon gain.

Growth responses of the mangrove Avicennia marina to salinity: development and function of shoot hydraulic systems require saline conditions. Annals of Botany January 19 2015 doi: 10.1093/aob/mcu257

Phytomonas: Trypanosomatids Adapted to Plant Environments

Phytomonas Over 100 years after trypanosomatids were first discovered in plant tissues, Phytomonas parasites have now been isolated across the globe from members of 24 different plant families. Most identified species have not been associated with any plant pathology and to date only two species are definitively known to cause plant disease. These diseases (wilt of palm and coffee phloem necrosis) are problematic in areas of South America where they threaten the economies of developing countries. In contrast to their mammalian infective relatives, our knowledge of the biology of Phytomonas parasites and how they interact with their plant hosts is limited. This review draws together a century of research into plant trypanosomatids, from the first isolations and experimental infections to the recent publication of the first Phytomonas genomes. The availability of genomic data for these plant parasites opens a new avenue for comparative investigations into trypanosomatid biology and provides fresh insight into how this important group of parasites have adapted to survive in a spectrum of hosts from crocodiles to coconuts.

Phytomonas: Trypanosomatids Adapted to Plant Environments. (2015) PLoS Pathog 11(1): e1004484. doi: 10.1371/journal.ppat.1004484

Thirsty? Then suck on a stone!

Golden gypsum crystals

Golden Gypsum Crystals from Winnipeg. Image: Rob Lavinsky/Wikimedia Commons

Whilst it is claimed that only the taxman can get blood out of a stone, it seems that some plants can abstract water from stone-like minerals.

Arguably, ahead of light, water is the most important abiotic factor that plants need and obtain from the environment. Although water is essential to plant life, it is not always available in sufficient amounts, and plants have evolved many adaptations that enable them to cope with water-limited environments – e.g. xerophytes in extremely arid areas, and halophytes in saline habitats. One strategy that was hitherto unrecognised is the extraordinary (I don’t think that’s too strong a word to use) ability of some plants to obtain large parts of their life-giving and -sustaining water from a mineral in the soil.

Analysing the isotopic composition of xylem sap in the rock rose Helianthemum squamatum, Sara Palacio et al. showed that it was similar to that of the water of crystallization in gypsum – CaSO4.2H2O, an inorganic mineral common in the plant’s environment. And, significantly, the composition of the water in the xylem differed from that of free water – i.e. that which is freely available within the soil (albeit in short supply!), the more usually assumed water source for plants. This therefore provided strong evidence that the plants were using the mineral as a water source – especially in the summer months when it accounted for 70–90% of the water used by these shallow-rooted plants.

Several other ‘coexisting shallow-rooted, sub-shrub species’ (the gypsum-specialist Lepidium subulatum – a gypsophyte – and the ‘non-specialists’ Linum suffruticosum and Helianthemum syriacum) behaved in an isotopically similar way to H. squamatum, suggesting that this phenomenon may be a widespread strategy of water-extraction by plants in this environment.

Although it is as yet unclear how the plants get hold of the water from this unusual source, it is suggested that high temperatures in the environment may cause the water to evaporate from the mineral when it can then be acquired by the plant.

Whilst this is a neat enough solution (pun recognised, but not intended!) for life on Earth, the authors conclude that ‘given the widespread occurrence of gypsum in dry lands throughout the Earth and in Mars, these results may have important implications for arid land reclamation and exobiology’. So, botanical research that may truly be ‘out of this world’!

[Intrigued by these intriguing gypsophytes? Then why not indulge your interest and read more of Sara Palacio et al.’s research in ‘Plants living on gypsum: beyond the specialist model’? – Ed.]