Tag Archives: Plant Science

Co-ordinated carbohydrate metabolism and hormone synthesis enables plants to survive unfavourable field conditions

Chrysolaena obovata

Chrysolaena obovata. Photo by Mauricio Mercadante.

Chrysolaena obovata, an aster of the Brazilian Cerrado, presents seasonal growth, marked by senescence of aerial organs in winter and subsequent regrowth at the end of this season. The underground reserve organs, the rhizophores, accumulate inulin-type fructans and confer tolerance to drought and low temperature. Fructans and fructan-metabolizing enzymes show a characteristic spatial and temporal distribution in the rhizophores during the developmental cycle. Previous studies have shown correlations between abscisic acid (ABA) or indole acetic acid (IAA), fructans, dormancy and tolerance to drought and cold, but the signalling mechanism for the beginning of dormancy and sprouting in this species is still unknown. A new paper in Annals of Botany examines the fructan metabolism in this species in response to environmental changes.

Plants were sampled from the field across phenological phases including dormancy, sprouting and vegetative growth. Endogenous concentrations of ABA and IAA were determined and measurements made of fructan content and composition, and enzyme activities. The relative expression of corresponding genes during dormancy and sprouting were also determined. Plants showed a high fructan 1-exohydrolase activity and expression during sprouting in proximal segments of the rhizophores, indicating mobilization of fructan reserves, when ABA concentrations were relatively low and precipitation and temperature were at their minimum values. Higher IAA concentrations were consistent with the role of this regulator in promoting cell elongation and plant growth. With high rates of precipitation and high temperatures in summer, the fructan-synthesizing enzyme sucrose:sucrose 1-fructosyltransferase showed higher activity and expression in distal segments of the rhizophores, which decreased over the course of the vegetative stage when ABA concentrations were higher, possibly signalling the entry into dormancy.

These results show that fructan metabolism correlates well with endogenous hormone concentrations and environmental changes, suggesting that the co-ordinated action of carbohydrate metabolism and hormone synthesis enables C. obovata to survive unfavourable field conditions. Endogenous hormone concentrations seem to be related to regulation of fructan metabolism and to the transition between phenophases, signalling for energy storage, reserve mobilization and accumulation of oligosaccharides as osmolytes.

 

Rigui,A., Gaspar,M., Oliveira, V., Purgatto, P. and Machado de Carvalho, M. Endogenous hormone concentrations correlate with fructan metabolism throughout the phenological cycle in Chrysolaena obovata. Annals of Botany 28 April 2015 doi: 10.1093/aob/mcv053

Reaction of Tibetan plants to climate change

Saussurea nigrescens Asymmetric warming is one of the distinguishing features of global climate change, in which winter and night-time temperatures are predicted to increase more than summer and diurnal temperatures. Winter warming weakens vernalization and hence decreases the potential to flower for some perennial herbs, and night warming can reduce carbohydrate concentrations in storage organs. A new paper in Annals Of Botany examines whether asymmetric warming acts to reduce flower number and nectar production per flower in a perennial herb, Saussurea nigrescens, a key nectar plant for pollinators in Tibetan alpine meadows.

A long-term (6 years) warming experiment was conducted using open-top chambers placed in a natural meadow and manipulated to achieve asymmetric increases in temperature during the growing and non-growing seasons. Measurements were taken of nectar volume and concentration (sucrose content) and leaf non-structural carbohydrate content and plant morphology. Six years of experimental warming resulted in reductions in nectar volume per floret, floret number per capitulum and capitulum number per plant, whereas nectar concentration remained unchanged. Depletion of leaf non-structural carbohydrates was significantly higher in the warmed than in the ambient condition. Overall plant density was also reduced by warming, which, when combined with reductions in flower development and nectar volumes, led to a reduction of ∼90 % in nectar production per unit area.

The negative effect of asymmetric warming on nectar yields in S. nigrescens may be explained by a depletion of leaf non-structural carbohydrates. The results highlights a novel aspect of how climate change might affect plant–pollinator interactions and plant reproduction via induction of allocation shifts for plants growing in communities subject to asymmetric warming.

 

Mu, J., Peng, Y., Xi, X., Wu, X., Li, G., Niklas, K.J. and Sun,S. Artificial asymmetric warming reduces nectar yield in a Tibetan alpine species of Asteraceae. Annals of Botany 28 April 2015 doi: 10.1093/aob/mcv042

Adventitious root formation in rice

Adventitious root formation in rice The root system is fundamentally important for plants to efficiently obtain nutrients and water. In contrast to the primary root system of plants, roots of monocot cereals consist almost entirely of a complex fibrous system and a mass of adventitious roots (ARs). AR formation is the process of root initiation from the stem base post-embryonically, which is tightly regulated to prevent the loss of valuable plant resources for non-essential root formation. A lack of stable and credible morphological data makes it difficult to study physiological and molecular mechanisms governing AR growth. However, comprehensive understanding of AR development should have important implications for manipulating root architecture, which contributes to both improving crop yield and optimizing agricultural land use.

Several plant hormones control AR formation, in which auxin plays a pivotal role. Indole-3-acetic acid (IAA) is the predominant form of active auxin in plants and it induces both AR and lateral root (LR) formation. Strigolactones (SLs) and their derivatives are plant hormones that have recently been identified as regulating root development. This study examines whether SLs play a role in mediating production of adventious roots (ARs) in rice (Oryza sativa), and also investigates possible interactions between SLs and auxin.

 

Sun, Huwei, Jinyuan Tao, Mengmeng Hou, Shuangjie Huang, Si Chen, Zhihao Liang, Tianning Xie et al. (2015) A strigolactone signal is required for adventitious root formation in rice. Annals of Botany doi: 10.1093/aob/mcv052
Strigolactones (SLs) and their derivatives are plant hormones that have recently been identified as regulating root development. This study examines whether SLs play a role in mediating production of adventious roots (ARs) in rice (Oryza sativa), and also investigates possible interactions between SLs and auxin. Wild-type (WT), SL-deficient (d10) and SL-insensitive (d3) rice mutants were used to investigate AR development in an auxin-distribution experiment that considered DR5::GUS activity, [3H] indole-3-acetic acid (IAA) transport, and associated expression of auxin transporter genes. The effects of exogenous application of GR24 (a synthetic SL analogue), NAA (α-naphthylacetic acid, exogenous auxin) and NPA (N-1-naphthylphalamic acid, a polar auxin transport inhibitor) on rice AR development in seedlings were investigated. The rice d mutants with impaired SL biosynthesis and signalling exhibited reduced AR production compared with the WT. Application of GR24 increased the number of ARs and average AR number per tiller in d10, but not in d3. These results indicate that rice AR production is positively regulated by SLs. Higher endogenous IAA concentration, stronger expression of DR5::GUS and higher [3H] IAA activity were found in the d mutants. Exogenous GR24 application decreased the expression of DR5::GUS, probably indicating that SLs modulate AR formation by inhibiting polar auxin transport. The WT and the d10 and d3 mutants had similar expression of DR5::GUS regardless of exogenous application of NAA or NPA; however, AR number was greater in the WT than in the d mutants. The results suggest that AR formation is positively regulated by SLs via the D3 response pathway. The positive effect of NAA application and the opposite effect of NPA application on AR number of WT plants also suggests the importance of auxin for AR formation, but the interaction between auxin and SLs is complex.

Stomatal density and aperture in non-vascular plants are non-responsive to above-ambient CO2 concentrations

Stomatal density Stomata are one of the crucial adaptations in the evolution of the land flora and the development of the terrestrial landscape and atmosphere on Earth. These microscopic pores on the plant epidermis first appeared in the fossil record more than 400 million years ago, some 50–60 million years after the first land plants. Today they are found on the sporophyte generations of all land plant groups with exceptions only in the liverworts, the earliest moss lineages and a few derived hornwort clades. Exposure to high atmospheric CO2 concentration ([CO2]) has been shown to consistently result in a reduction of stomatal density (number of stomata per mm2) and index (ratio of stomata to epidermal cells) in the newly developed leaves of many vascular plant species. The general consensus view is that stomatal morphology is conserved throughout land plants and that their primary function is related to the regulation of gas and water exchange, [CO2] being a key activator of stomatal frequency. However, a crucial missing piece in the jigsaw of stomatal evolution and function is the responsiveness of bryophyte stomata to [CO2]. In the only previous studies on the effects of [CO2] on stomata in non-vascular plants recorded larger apertures in the mosses Physcomitrella and Funaria grown in the absence of CO2.

A recent paper in Annals of Botany challenges the widely accepted dogma that the responsiveness of stomata to [CO2] in terms of density and opening is conserved across the land plant phylogeny through careful experimentation and cytological observation and asks: (1) Are stomatal numbers on moss and hornwort sporophytes affected in the same way as those in angiosperms by elevated [CO2] representative of atmospheric concentrations in the Palaeozoic? (2) Do guard cell lengths and apertures in bryophytes change when subjected to representative Palaeozoic [CO2] throughout development?

 

Field, K. J., Duckett, J. G., Cameron, D. D., & Pressel, S. (2015) Stomatal density and aperture in non-vascular land plants are non-responsive to above-ambient atmospheric CO2 concentrations. Annals of Botany April 8, 2015 doi: 10.1093/aob/mcv021
Following the consensus view for unitary origin and conserved function of stomata across over 400 million years of land plant evolution, stomatal abundance has been widely used to reconstruct palaeo-atmospheric environments. However, the responsiveness of stomata in mosses and hornworts, the most basal stomate lineages of extant land plants, has received relatively little attention. This study aimed to redress this imbalance and provide the first direct evidence of bryophyte stomatal responsiveness to atmospheric CO2.
A selection of hornwort (Anthoceros punctatus, Phaeoceros laevis) and moss (Polytrichum juniperinum, Mnium hornum, Funaria hygrometrica) sporophytes with contrasting stomatal morphologies were grown under different atmospheric CO2 concentrations ([CO2]) representing both modern (440 p.p.m. CO2) and ancient (1500 p.p.m. CO2) atmospheres. Upon sporophyte maturation, stomata from each bryophyte species were imaged, measured and quantified. Densities and dimensions were unaffected by changes in [CO2], other than a slight increase in stomatal density in Funaria and abnormalities in Polytrichum stomata under elevated [CO2]. The changes to stomata in Funaria and Polytrichum are attributed to differential growth of the sporophytes rather than stomata-specific responses. The absence of responses to changes in [CO2] in bryophytes is in line with findings previously reported in other early lineages of vascular plants. These findings strengthen the hypothesis of an incremental acquisition of stomatal regulatory processes through land plant evolution and urge considerable caution in using stomatal densities as proxies for paleo-atmospheric CO2 concentrations.

Transcriptome and Genome of the Venus Flytrap

Venus Flytrap Dionaea muscipula Darwin was fascinated by the unusual adaptations of carnivorous plants during his often frustrating studies of the evolution of flowering plants, which he referred to as an ‘abominable mystery’. Darwin’s treatise on insectivorous plants noted that the Venus flytrap (Dionaea muscipula) was ‘one of the most wonderful of the world’. Studies of carnivorous plants have continued since Darwin’s time.

An understanding of the molecular adaptations to plant carnivory has also been sought via genome size estimates. Genome sizes vary more than 2,300-fold among angiosperms, from that of Paris japonica (~149 Gbp) to that of carnivorous Genlisea margaretae (~63 Mbp). The biological significance of this massive variation is puzzling.

A new paper in PLOS ONE examines the transcriptome and genome of the Venus flytrap, Dionaea muscipula. The transcriptome provides some insight into the molecular processes occurring in a Gb-sized carnivorous plant genome. Abundant representation of processes related to the expression of genes associated with catalytic, antioxidant and electron carrier activities was observed. Future uniform meta-analyses of short-read archives, including cDNA sequences from carnivorous Utricularia and Sarracenia species will aid studies of carnivorous plants and their ecology. This underlines the importance of further expansion of sequence repositories, especially for non-model organisms, for improved understanding of molecular physiology and evolution related to Darwin’s ‘abominable mystery’.

 

Jensen MK, Vogt JK, Bressendorff S, Seguin-Orlando A, Petersen M, et al. (2015) Transcriptome and Genome Size Analysis of the Venus Flytrap. PLoS ONE 10(4): e0123887. doi:10.1371/journal.pone.0123887
Abstract
The insectivorous Venus flytrap (Dionaea muscipula) is renowned from Darwin’s studies of plant carnivory and the origins of species. To provide tools to analyze the evolution and functional genomics of D. muscipula, we sequenced a normalized cDNA library synthesized from mRNA isolated from D. muscipula flowers and traps. Using the Oases transcriptome assembler 79,165,657 quality trimmed reads were assembled into 80,806 cDNA contigs, with an average length of 679 bp and an N50 length of 1,051 bp. A total of 17,047 unique proteins were identified, and assigned to Gene Ontology (GO) and classified into functional categories. A total of 15,547 full-length cDNA sequences were identified, from which open reading frames were detected in 10,941. Comparative GO analyses revealed that D. muscipula is highly represented in molecular functions related to catalytic, antioxidant, and electron carrier activities. Also, using a single copy sequence PCR-based method, we estimated that the genome size of D. muscipula is approx. 3 Gb. Our genome size estimate and transcriptome analyses will contribute to future research on this fascinating, monotypic species and its heterotrophic adaptations.

How tree species fill geographic and ecological space in North America

Distribution of forest plots Ecologists broadly accept that the number of species present within a region balances regional processes of immigration and speciation against competitive and other interactions between populations that limit distribution and constrain diversity. Although ecological theory has, for a long time, addressed the premise that ecological space can be filled to ‘capacity’ with species, only with the availability of time-calibrated phylogenies has it been possible to test the theory that diversification slows as the number of species in a region increases. Focusing on the deciduous trees of eastern North America, this study tested predictions from competition theory concerning the distribution and abundance of species.

Local assemblages of trees tabulated in a previous study published in 1950 were analysed. Assemblages were ordinated with respect to species composition by non-metric multidimensional scaling (NMS). Most of the variance in species abundance and distribution was concentrated among closely related (i.e. congeneric) species, indicating evolutionary lability. Species distribution and abundance were unrelated to the number of close relatives, suggesting that competitive effects are diffuse. Distances between pairs of species in NMS space did not differ significantly from distances between more distantly related species, in contrast to the predictions of both competitive habitat partitioning and ecological sorting of species.

Eastern deciduous forests of North America do not appear to be saturated with species. The distributions and abundances of individual species provide little evidence of being shaped by competition from related, ecologically similar, species. Diversification is constrained by interspecific competition.

Ricklefs, R.E. How tree species fill geographic and ecological space in eastern North America (2015) Annals of Botany, April 7, 2015. doi: 10.1093/aob/mcv029

The great botanical countdown

Image: Wikimedia Commons.

Image: Wikimedia Commons.

Always keen to promote sites that are planty, educational, informative and entertaining (especially those that are free-to-access!), we’re happy to give a belated mention of Oxford Plants 400. This botanical bonanza is offered as a gift to the world as the UK’s University of Oxford counts down towards the 25th July 2021, which date marks 400 years of botanical research and teaching by that world-renowned seat of higher learning. Sponsored by the University of Oxford Botanic Garden and the Harcourt Arboretum, together with the Oxford University Herbaria and that university’s Department of Plant Sciences, the site aims to highlight 400 plants that have scientific and cultural significance. Profiling one plant per week, it is illustrated with images from Oxford University’s living and preserved collections, and as I penned this piece it was showcasing plant No. 58, Monstera deliciosa, the Swiss cheese plant as it is commonly known in the UK. Previous plants displayed have included cinnamon, coffee, Norway spruce, giant redwood, sugarcane, sugar maple and ash. Additionally, it has included the liverwort, Marchantia, which is being exploited as a model plant at the UK’s University of Cambridge’s OpenPlant Laboratory for synthetic biology (so the listing is not limited to gymnosperms and angiosperms, but embraces so-called lower plants too), and the alga Chara (so it is not even constrained to members of the Plant Kingdom in the narrow sense*). I’ve not found a list that reveals all future plants, so it’s a nice surprise when each week’s new addition is revealed in my Twitter account direct from the project (@Plants400). This is a nice resource with much of plant-and-people relevance – ideal material for educators’ own botany lectures, talks, or their students’ essays, etc. Check it out!

* Although questioned by such workers as Sabina Wodniok et al., it is still widely held that a relative of modern-day Chara is the likely ancestor of the land flora, i.e. the members of the Plant Kingdom, which certainly justifies its inclusion as one of the chosen 400 ‘plants’.

[How one would have liked featured plant No. 1 to have been the larch (genus Larix), which includes trees that demonstrate that not all conifers are evergreen with the eponymously deciduous Larix decidua. Sadly, but understandably (and predictably?), that was probably never going to happen since that reference is to a comedy sketch from Monty Python’s Flying Circus, the majority of whose five-man acting cohort were alumni of the University of Cambridge, Oxford’s almost equally august competing seat of higher learning. However, Taxus baccata – the actual No. 1 –  is a conifer, which is not a million miles from Larix! In the interests of balance we’d like to point out that ‘other’ herbaria also exist, e.g. that associated with the Royal Botanic Gardens Edinburgh (Scotland, near England, UK), which is showcased in a short video presentation available on YouTube, and there’s also one at the University of Cambridge – Ed.]

Nature Plants: an appreciation [or, Now we are Three…*]

Image: Amédée Masclef, Atlas des Plantes de France, Paris: 1891.

Image: Amédée Masclef, Atlas des Plantes de France, Paris: 1891.

We don’t usually review science journals in this column (nor books come to that) [neither do we usually permit such long Cuttings pieces – Ed!], but occasionally we need to make an exception. So, exceptionally and on this occasion, one would like to say a few words by way of appraising Nature Plants (hereafter reduced to NP), the latest offering from the Nature Publishing Group (the publishers behind Nature, Nature Biotechnology, Nature Climate Change, NatureGeoscience, etc.). Launching its first issue in January 2015 [as exclusively revealed by Mr P. Cuttings? – Ed.], NP follows the layout familiar from several other companion journals in the Nature range.

Editorial and Commentary (and Books and Art…)

The journal greets the world with a timely [as such items should be! – Ed.] Editorial on ‘the compromise recently reached by the European Parliament over genetically modified crop legislation…’. Although non-attributed, one assumes this piece was either penned, or at least approved, by the journal’s Chief Editor, Chris Surridge. There follow two Comment pieces. The one from Professor Huw Jones (of the UK’s Rothamsted Research institution) deals with the topical topic of genome editing, a technique that allows modification of plants but which some argue falls outside of current legislative and regulatory strictures regarding GM (genetic modification) GE (an initialism here for genome editing, not genetic engineering…) is not considered to be genetic modification as such. The Comment piece by Pedro Sanchez (Director, Tropical Agriculture and the Rural Environment Program) of the Earth Institute (Columbia University, New York) is a rather upbeat, optimistic piece on agriculture productivity in Africa and dares to suggest that ‘sub-Saharan Africa could become one of the world’s breadbaskets by 2050’. On a cereal-related theme, the Books and Art (not something you’d expect in a serious botanical science journal…?) section contains a review of Renee Marton’s 2014 book, Rice: a global history; by University College London’s Professor of Archaeobotany Dorien Fuller (who certainly knows a thing or two about the book’s subject matter).

Research Highlights

The four short items in the Research Highlights section feature recent research from other journals (rather like Plant Cuttings’ items…? – Ed.), for example Peter van der Sleen et al.’s ‘No growth stimulation of tropical trees by 150 years of CO2 fertilization but water-use efficiency increased’. But it’s not all keep-it-in-the-family mutual appreciation/admiration of other Nature journals: this section also showcases Alison Bennett et al.’s ‘Plant lignin content altered by soil microbial community’,  Fangjun Li et al.’s ‘Modulation of RNA polymerase II phosphorylation downstream of pathogen perception orchestrates plant immunity’ and Yi Shang et al.’s ‘Biosynthesis, regulation, and domestication of bitterness in cucumber’. Sadly, all four articles so highlighted are behind paywalls. But, arguably, that is where Research Highlights come into their own, in providing a little more insight into the articles beyond their freely viewable abstracts. However, oftentimes the insight serves to reinforce the view that one wants to access the full article and can therefore be more frustrating than helpful…

 

News and Views

The penultimate section – News and Views (N&Vs) – is essentially the hors d’oeuvres for the main course, the ultimate Research section. N&Vs effectively showcase some of the Research articles in that issue and put them in context [rather like a hybrid of Annals of Botany’s Plant Cuttings and ContentSnapshots? – Ed.]. How items are selected to be so ‘bigged-up’ is not known to me, but it can’t do the authors of the featured paper any harm, and helps in putting research into context and explaining it for non-subject specialists [as Plant Cuttings aim to do – Ed.]. One of the Research articles given the N&V treatment that particularly caught my eye in this issue is Matthew Koski and Tia-Lynn Ashman’s ‘Floral pigmentation patterns provide an example of Gloger’s rule in plants’ by commentator – and wearer of two hats(!) –  Professor Innes Cuthill (University of Bristol, UK). The study is succinctly summarized thus: ‘a 180-year-old “law” in zoology has found its best support so far in a study of floral colour, which not only documents darker plants growing closer to the equator, but also supports the idea that the colour stems from ultraviolet protection’. Also ‘N&V’d’ is Andreas Bracher et al.’s study ‘Degradation of potent Rubisco inhibitor by selective sugar phosphatase’, commented on by Rebekka Wachter and Nathan Henderson (both at Arizona State University, USA). The study is summarised by the pair thus: ‘Rubisco catalyses the first step in photosynthetic carbon fixation, but it can be easily poisoned by side-products of its activity. Structural and functional analyses of a protein conserved across plants, algae and bacteria shows how one such blockage is both removed and recycled’.  Not knowing that this sort of ‘poisoning’ event took place, and in such a fundamental biochemical process [even Mr P. Cuttings can’t know everything – Ed.], it is always nice to read about ‘new’ phenomena and learn something (and share it with others)!

 

Research Articles

In this section, two Research articles that appealed to my quest for seeking out new botanical stuff – and neither of which was N&V’d (so how do they select those worthy of N&Ving…?) – are Chuanli Ju et al.’s ‘Conservation of ethylene as a plant hormone over 450 million years of evolution’ and Benjamin Jung et al.’s ‘Identification of the transporter responsible for sucrose accumulation in sugar beet taproots’. Although sugar beet (Beta vulgaris) satisfies approximately one third of global sugar (sucrose) demand – and sucrose (largely sequestered within vacuoles in the taproot) can be up to 18 % of the plant’s fresh weight – the identity of the transporter that leads to sucrose’s vacuolar accumulation has long been a mystery. Jung et al. have identified BvTST2.1 as a vacuole-sited sucrose-specific transporter, exploitation of which discovery it is hoped will help to increase sugar yields from sugar beet and other sugar-storing plants in future breeding programmes. Investigating the evolutionary development of higher plant’s ethylene (a plant hormone involved in such phenomena as fruit-ripening, leaf and flower senescence, and seed germination) signalling pathway, Chuanli Ju et al. have identified a homologous system in Spirogyra pratensis (a living representative of the putative charophyte green algal ancestors of land plants) that exhibits a cell-elongation response to ethylene. They infer from this discovery not only that the common aquatic ancestor of the Embryophyta possessed this pathway prior to the colonization of land and that cell elongation was possibly an ancestral ethylene response, but also that this finding highlights the importance of charophytes for investigating the origins of fundamental plant processes.

 

Finally, the verdict is…?

So, what does NP give to the botanical community? Well [deep breath! – Ed.], plant ecology, biochemistry, physiology, crop production, crop domesticationsexual reproduction, plant–environment interactions, book reviews, topical insights, and commentary on important and diverse botanical topics, for one. A great start to a new botanical journal! However, it’s not been a trouble-free launch. Errata have already been issued regarding supplementary material for two of the Research papers, but at least the errors have been spotted and rectified in a timely manner. Now to that all-important overall assessment from Mr P. Cuttings: Nature Plants, one to keep an eye on (not least because its format seems to be modelled on the Annals of Botany’s…). What’s that you say, emulation is the sincerest form of flattery? Cheers, NP!

 

* With apologies to AA Milne’s poem ‘Now we are Six’ (and unfortunately thereby demonstrating that Mr P. Cuttings is only half as good as the creator of Winnie the Pooh). Rather, the reference to ‘three’ is recognition that there is now a trio of premier botanical journals that embrace the full range of plant science – Annals of Botany, New PhytologistNature Plants.

[FYI, ‘All 18 open access journals owned by Nature Publishing Group … will use the Creative Commons Attribution license CC BY 4.0 as default from today…”. Which is good to know but, and despite extensive searching on your behalf, I’ve been unable to find out categorically if NP is open-access. Whilst I had no trouble getting full access to all items in the first issue, it seems that was a ‘loss-leader’ an example of ‘freebie marketing’ – i.e. a marketing gimmick – to engineer interest in the product since the only free-to-view item in issue 2 was the Editorial. Finally, it will be interesting to see what effect the ‘business arrangement’ recently announced between the publisher of Nature Plants and Springer will have on this fledgling botanical organ. In the spirit of appropriate botanical glossary imagery, let us hope it doesn’t turn out to be caducous (‘falling early’) – Ed.]

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.]