Snacking helps Drosera’s appetite

A paper by Pavlovič et al. has caught my eye this week. Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis has moved into Free Access. I’m used to the idea that carnivorous plants trap insects to get Nitrogen, but it is a bit more complicated than that.

Drosera capensis

Drosera capensis

Pavlovič et al set up an experiment to follow the feeding cycle of D. capensis. D. capensis is a sundew, it eats insects by trapping them on sticky leaves, coiling round them and then secreting enzymes to digest the insect. Its home is South Africa, but it’s commonly cultivated around the world now.

Pavlovič et al. were testing a simple idea. What benefit does a plant get from feeding, and how can you measure it? Givnish et al. said feeding led to increased photosynthetic efficiency. So the experiment looked at gas exchange and chlorophyll a fluorescence. They also examined what enzymes get released by the sundew to see what it is that the plant is most eager to get. They also tried another experiment which worked, but didn’t get spectacular results.

D. capensis has another form. If you don’t want red tentacles on your plant you can now buy Drosera capensis alba, a plant with white tentacles. Pavlovič et al. wondered if red, found in the wild, was a signal to attract flies. The experiment they did to find out is the simplest. Get some fruitflies, put them into tanks with sundews with the two varieties and then see which plants catch most.

What they found was there was no significant difference. This doesn’t mean the experiment failed, instead it tells us that there is no preference and whatever reason there is for the red, it’s not to attract insects. It might sound dull, but it means something odd is happening. It’s not just sundews that are red. Various forms of Nepenthes and Sarracenia also grow red forms. Yet it doesn’t seem that these use red to attract insects either, so why are various carnivorous plants coming to the same colour?

As far as digestion goes, Pavlovič et al. found that all it takes for sundews to release enzymes is some mechanical stimulus, and they found this when they used polystyrene balls as well as flies. However, to really get digestion happening the plant seems to need more poking, like from a live insect and some chemical feedback. Obviously they weren’t getting this from the polystyrene balls.

When it came to seeing what the leaves were pulling out of the insect there was a mild surprise. Nitrogen and Phosphorus were obvious grabbed along with Potassium. They did not see absorption of Calcium or Magnesium, despite other people finding Mg take-up in other experiments. Pavlovič et al. think that their plants may have already had a relatively high Mg concentration.

The key input for Drosera was Phosphorus. Pavlovič et al. found their unfed plants were P-limited, meaning that it was a lack of Phosphorus that stopped them from growing as well as they could. Phosphorus is essential for making ATP, Adenosine triphosphate, which powers plant cells and is a key part of respiration. Without Phosphorus, plants would not be able to photosynthesise, so while it’s a small part of plant’s chemical make-up it is still very necessary.

The paper is good for what it finds, I like seeing how the nutrients are tracked so you can see the plant using them, but the referencing is important. This isn’t isolated research, it builds on other work and it’s contributing to a conversation. The authors don’t just include references to support them. The lack of Mg absorption by the sundew leaves is a puzzle, but Pavlovič et al. point to the papers that show this in order to put their own results in context. That is the best way of showing how new research can help expand the field more.

Pavlovic A., Krausko M., Libiakova M. & Adamec L. (2013). Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis, Annals of Botany, 113 (1) 69-78. DOI: http://dx.doi.org/10.1093/aob/mct254

Tensile properties of bamboo responsible for its mechanical performance

Tensile properties of bamboo responsible for its mechanical performance

Tensile properties of bamboo responsible for its mechanical performance

Bamboo is well known for its fast growth and excellent mechanical performance, but since it lacks secondary-thickening it cannot use adaptive growth in the same way as a tree would in order to cope with bending stresses. Wang et al. examine the mechanical properties of single fibres and tissue slices of stems of mature moso bamboo (Phyllostachys pubescens) and latewood of spruce (Picea abies) and find that the superior tensile properties of bamboo fibres and fibre bundles are mainly a result of amplified cell-wall formation leading to a densely packed tissue, rather than being based on specific cell-wall properties. The material optimization towards extremely compact fibres with a multi-lamellar cell wall in bamboo might be a result of a plant growth strategy that compensates for the lack of secondary thickening growth at the tissue level.

Provision of nitrogen as ammonium rather than nitrate increases silicon uptake in sugarcane

Sugarcane cultivated in the non-irrigated production areas of the South African sugar industry, where soils are frequently acid and low in plant-available silicon. Image credit: South African Sugarcane Research Institute.

Sugarcane cultivated in the non-irrigated production areas of the South African sugar industry, where soils are frequently acid and low in plant-available silicon. Image credit: South African Sugarcane Research Institute.

Silicon (Si) is important in mitigating abiotic and biotic plant stresses, yet many agricultural soils, such as those of the rainfed production areas of the South African sugar industry, are deficient in plant-available Si, making Si supplementation necessary. Means to maximise Si uptake via the roots from applied silicon sources and thereby enhance crop yields have not yet been fully explored. In a new study published in AoB PLANTS, Keeping et al. found that reduction of rhizosphere pH through provision of nitrogen fertilizer to sugarcane as ammonium rather than nitrate increased silicon uptake from a low-silicon soil amended with calcium silicate slag. They propose that ammoniacal fertilizers have potential for enhancing the solubilisation of silicate slags by acidifying the rhizosphere and increasing silicic acid solubility and availability for plant uptake.

Molecular phylogenetics of the orchid Himantoglossum

Molecular phylogenetics of the orchid <i>Himantoglossum</i>

Molecular phylogenetics of the orchid Himantoglossum

Lizard orchids (Himantoglossum) include several of Eurasia’s most spectacular and conservation-relevant species. Sramkó et al. provide the first comprehensive molecular phylogeny for these charismatic orchids by sampling all known taxa across the whole distribution area of the genus. By using sequences of two nuclear and four plastid DNA-regions, they reconstruct phylogenetic trees that collectively determined the order of branching of the early divergent taxa as H. comperianum > H. robertianum group > H. formosum > H. hircinum group. Molecular clock and ancestral area analyses indicate an origin of the group at approximately 9 million years ago in the Caucasus Mountains.

Timeless inner beauty…

Image: P. Cuttings’ personal archive.

Image: P. Cuttings’ personal archive.

When trying to appreciate something, it’s often remarked that it is the ‘inner beauty’ that’s important. In which case the plant cell biologists who probe the details within cells (and often illuminate them in all their glorious pin-point precision and fluorescent beauty with immunofluorescent techniques*) must not only, as scientists, be seekers of truth (for is it not writ, in scientia veritas?)  but also be true searchers after beauty. And if something’s really beautiful/true then it has a quality that transcends normal, mortal values and should be permanent. Is that correct? Well, the palaeopteridophytological work of Benjamin Bomfleur et al. may just be the definitive proof of that notion of transcendental permanence. Using language unusual for a serious, sober, scientific article, they describe the fossilised stem of a royal fern (family: Osmundaceae) in Lahar deposits (of putative Early Jurassic – Pliensbachian – date; 189.6–183 million years ago) from Korsaröd in Scania (southern Sweden) as having cellular details that are ‘exquisitely preserved’. Amongst the sub-cellular features discernible are parenchyma cells in the pith and cortex that show preserved membrane-bound cytoplasm, cytosol granules and putative amyloplasts (starch-bearing bodies). Furthermore, most cells contain interphase nuclei with conspicuous nucleoli! And – even more remarkably? – Supplementary Fig. S6 shows detail that is interpreted as signs of necrosis and programmed cell death(!). Whilst more importance is attached by the authors to the fact that the genome size of these reputed ‘living fossils’ has remained unchanged over at least 180 million years (and is understandably viewed as a ‘paramount example of evolutionary stasis’), the degree of internal preservation of cell contents is so good (see Figs S4 and S6 in the paper’s supplementary material!) I’m sure many extant workers could only hope to emulate such faithful preservation in their current work! So, not only is a thing of beauty a joy, it is a joy… forever (or 180 million years at least – long enough for you?). Somebody should write a poem about that!

* For a scientific haiku poem about this, may I humbly suggest the following? Page 15 at the Art Science Movement’s website.

 

[For an award-winning science journalist’s take on Bomfleur et al.’s Science paper, see Jennifer Frazer’s blog. Full-text of the paper – with supplementary pages – appears to be available in front of a paywall via the DiVA portal. And with apologies to our readers for the shameless self-advertisement by Mr P. Cuttings for his ‘poem’! – Ed.]

Tandem-repeat dynamics in a chromosomally variable plant group

Tandem-repeat dynamics in a chromosomally variable plant group

Tandem-repeat dynamics in a chromosomally variable plant group

Genomes of higher plants contain a spectrum of repetitive DNAs elements, and during genome restructuring these elements can be evolutionarily highly dynamic. Jang et al. examine the evolution of a novel satellite DNA, PaB6, in the chromosomally variable monocotyledonous genus Prospero. Although present in all three species, PaB6 has undergone differential amplification only in the P. autumnale complex, particularly in cytotypes that have experienced chromosomal fusions and genome size increases. The PaB6 copy numbers are among the highest for repetitive elements of any higher plant, and their changes are exceptionally dynamic in this group of closely related cytotypes within a single species.

Initial success of native grasses is contingent on multiple interactions among exotic grass competition, temporal priority, rainfall, and site effects

Kurt Vaughn and Steve Fick seeding the experimental plots at the Hopland site in November 2011. Photo by T. Young

Kurt Vaughn and Steve Fick seeding the experimental plots at the Hopland site in November 2011. Photo by T. Young

Throughout the western United States, native perennial grasses are being supplanted by aggressive non-native annuals. In a recent study published in AoB PLANTS, Young et al. show that giving native grasses just a two-week germination ‘head start’ over exotic invasive grasses shifts the competitive edge strongly in their favour. They also show that the strength of this advantage differs strikingly depending on the site at which the experiment is carried out, and the weather in the initial weeks of the experiment. These results a) give insight into the reasons for the competitive advantage that annuals usually demonstrate, and b) are an example of the likelihood that ecological experiments often produce results that are limited to a particular time and place, and less general than we might wish to believe.

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.]

The path to understanding water movement in leaves is not straightforward

Stable oxygen isotope analyses have various applications relevant to tracking water movement in ecosystems. The ratio of 16O to 18O (represented as δ18O) in leaf water provides information about the water vapor pressure deficit (VPD) in the air around the plant, the plant’s source of water and the physiological processes that govern leaf water loss, such as stomatal movements and transpiration. For example, as VPD increases (i.e. as environmental conditions become drier), more evaporation and thus evaporative enrichment in 18O occurs within the leaf water, since the lighter H216O evaporates more readily than the heavier H218O. This causes the remaining H2O at the sites of evaporation to become more enriched in 18O. Researchers have used this model, originally applied to oceans by Craig and Gordon (1965), to shed light on evaporative conditions and leaf physiology.

However, the Craig-Gordon model resulted in overestimates of leaf water H218O enrichment because it did not account for the less enriched water flowing from leaf veins to the sites of evaporation. This overestimation greatly impacts how we interpret δ18O as a proxy for evaporative conditions in which the plant grew, as well as leaf physiology. In response to this overestimation, Farquhar and Lloyd (1993) proposed the Péclet effect defined as: water flowing towards sites of evaporation by transpiration becomes enriched by the back diffusion of the enriched water at the sites of evaporation. In other words, the Péclet effect describes the mixing of water from both the xylem and evaporative sites. The Péclet effect is largely driven by changes in transpiration rate (E) and effective path length (L), where L describes the tortuous path that water travels from leaf veins to sites of evaporation.

The Péclet effect

The Péclet effect describes the mixing of water from the xylem and evaporative sites. Water flowing towards sites of evaporation by transpiration (A) becomes enriched by the back diffusion of the enriched water in H218O at the sites of evaporation (B). Figure adapted from Dr. Todd Dawson and Dr. Thorsten Grams.

To better inform interpretations of leaf water δ18O, the Craig Gordon-Péclet model is used to predict L. L is impossible to measure because it accounts for not only the distance that water travels, but also the tortuosity of the water movement pathway. However, the model requires assumptions about evaporative conditions that may or may not be true.

Previous work (Song et al. 2013) documented relationships between L and physiological parameters such as E and hydraulic conductance (k). However, few studies have estimated L under controlled environmental conditions. Loucos and colleagues did just that, and estimated L and k simultaneously on the same leaf to evaluate the findings of previous studies.

Loucos et al. (2015) found that estimates of L are strongly influenced by assumptions made when calculating 18O enrichment at the sites of evaporation. Contrary to previous studies, they found no support for the hypothesis that L is negatively related to both E and k within a single species. This negative correlation was expected because water movement was expected to follow a predominately small L pathway when E is high (i.e. E > 1 to 2 mmol m-2s-1), and when E is low (i.e. E < 1 to 2 mmol m-2s-1), there is a proportionally greater flux through a large L pathway (Song et al. 2013). As a result, the authors demonstrate that great caution must be taken when investigating and developing any relationships between L and environmental and physiological parameters. Clearly, the path to understanding L, the Péclet effect, and δ18O of leaf water is not straightforward.

References

Craig H. & Gordon L.I. (1965). Deuterium and oxygen-18 variations in the ocean and the marine atmosphere. In: Tongiorgi E (ed) Proceedings of a conference on stable isotopes in oceanographic studies and paleotemperatures, .Laboratory of Geology and Nuclear Science, Pisa, pp 9-130.

Farquhar G.D. & Lloyd J. (1993). Carbon and Oxygen Isotope Effects in the Exchange of Carbon Dioxide between Terrestrial Plants and the Atmosphere. In: Ehleringer J.R., Hall A.E., Farquhar G.D. (eds) Stable Isotopes and Plant Carbon-water Relations. Academic Press, San Diego. 47-70. DOI: http://dx.doi.org/10.1016/b978-0-08-091801-3.50011-8

Loucos K.E., Simonin K.A., Song X. & Barbour M.M. (2015). Observed relationships between leaf H218O Peclet effective length and leaf hydraulic conductance reflect assumptions in Craig-Gordon model calculations, Tree Physiology, DOI: http://dx.doi.org/10.1093/treephys/tpu110

Song X., Barbour M.M., Farquhar G.D., Vann D.R. & Helliker B.R. (2013). Transpiration rate relates to within- and across-species variations in effective path length in a leaf water model of oxygen isotope enrichment, Plant, Cell and Environment, 36 (7) 1338-1351. DOI: http://dx.doi.org/10.1111/pce.12063

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