All posts by Alun Salt

About Alun Salt

When he's not the web developer for AoB Blog, Alun Salt researches something that could be mistaken for the archaeology of science. His current research is about whether there's such a thing as scientific heritage and if there is how would you recognise it?

Where did your cells come from?

If you look at your cells under a microscope, you’ll see nearly all of them have a nucleus, mitochondria and other equipment inside them. Eukaryotic cells, cells with a nucleus, are the basis of all complex life fungi, plants and us. The change from prokaryotic cell to complex cell is profoundly important to evolution of life, but how did it happen?

The favoured explanation has been that an archaeon swallowed a bacterium. The two developed a symbiotic relationship and evolved into eukaryotes. This explanation bothers me slightly because it needs the pair to do a lot of work fast, but I suppose if archaea are eating bacteria millions upon millions of times each day, then they’re making a lot of attempts.

David Baum, a University of Wisconsin-Madison professor of botany and evolutionary biologist, has proposed a new model for eukaryote evolution. His model is inside out and, to a non-biologist like me, it looks plausible.

Baum and his cousin Buzz Baum at UCL, argue that archaea developed protrusions called blebs, little arms if you like. These enabled the cells to interact with their environment better. Along the way they encountered bacteria and started to develop ways to exploit the energy of bacteria, while the bacteria were still outside the cell. The cells that did this better survived more often and reproduced until they had engulfed the bacterium.

Inside-out model for the evolution of eukaryotic cell organization. Model showing the stepwise evolution of eukaryotic cell organization from (A) an eocyte ancestor with a single bounding membrane and a glycoprotein rich cell wall (S-layer) interacting with epibiotic α-proteobacteria (proto-mitochondria). (B) We envision the eocyte cell forming protrusions, aided by protein-membrane interactions at the protrusion neck. These protrusions facilitated material exchange with proto-mitochondria. (C) Selection for a greater area of contact between the symbionts would have led to bleb enlargement and the eventual loss of the S-layer from the protrusions. (D) Blebs would have then been further stabilized by the development of a symmetric nuclear pore outer ring complex (Figure 2) and through the establishment of LINC complexes that, following the gradual loss of the S-layer, physically connected the original cell body (the nascent nuclear compartment) to the inner bleb membranes. (E) With the expansion of blebs to enclose the proto-mitochondria, a process that would have facilitated the acquisition of bacterial lipid biosynthesis machinery by the host, the site of cell growth would have progressively shifted to the cytoplasm, facilitated by the development of regulated traffic through the nuclear pore. At the same time, the spaces between blebs would have enabled the gradual maturation of proteins secreted into the environment via the perinuclear space through glycosylation and proteolytic cleavage. (F) Finally, bleb fusion would have connected cytoplasmic compartments and driven the formation of an intact plasma membrane, perhaps through a process akin to phagocytosis whereby one bleb enveloped the whole. This simple topological transition would have isolated the endoplasmic reticulum from the outside world, driven the full development of a system of vesicular trafficking, and established strict vertical transmission of mitochondria, leading to a cell with modern eukaryotic cell organization. Baum and Baum BMC Biology 2014 12:76   doi:10.1186/s12915-014-0076-2

Inside-out model for the evolution of eukaryotic cell organization. Model showing the stepwise evolution of eukaryotic cell organization from
(A) an eocyte ancestor with a single bounding membrane and a glycoprotein rich cell wall (S-layer) interacting with epibiotic α-proteobacteria (proto-mitochondria).
(B) We envision the eocyte cell forming protrusions, aided by protein-membrane interactions at the protrusion neck. These protrusions facilitated material exchange with proto-mitochondria.
(C) Selection for a greater area of contact between the symbionts would have led to bleb enlargement and the eventual loss of the S-layer from the protrusions.
(D) Blebs would have then been further stabilized by the development of a symmetric nuclear pore outer ring complex (Figure 2) and through the establishment of LINC complexes that, following the gradual loss of the S-layer, physically connected the original cell body (the nascent nuclear compartment) to the inner bleb membranes.
(E) With the expansion of blebs to enclose the proto-mitochondria, a process that would have facilitated the acquisition of bacterial lipid biosynthesis machinery by the host, the site of cell growth would have progressively shifted to the cytoplasm, facilitated by the development of regulated traffic through the nuclear pore. At the same time, the spaces between blebs would have enabled the gradual maturation of proteins secreted into the environment via the perinuclear space through glycosylation and proteolytic cleavage.
(F) Finally, bleb fusion would have connected cytoplasmic compartments and driven the formation of an intact plasma membrane, perhaps through a process akin to phagocytosis whereby one bleb enveloped the whole. This simple topological transition would have isolated the endoplasmic reticulum from the outside world, driven the full development of a system of vesicular trafficking, and established strict vertical transmission of mitochondria, leading to a cell with modern eukaryotic cell organization.
Baum and Baum BMC Biology 2014 12:76 doi:10.1186/s12915-014-0076-2

What I like is that there are steps to bringing the bacterium inside the cell, instead of Pow! it’s there and everything has to develop now. That’s probably an unfair over-simplication of the standard model, but the inside-out model makes sense as each step along the way seems to either use material it already has, or confer a small advantage for survival by itself.

While the event happened unseen billions of years ago, Baum and Baum have some ideas of how they can test the idea. Genetic data could help indicate that an inside out model is more likely than the standard model. Their model predicts that some parts of the cell developed in the opposite order to the standard model, though I’ll admit I don’t understand the details of how “COPII-like coatomers are derived from structural components of the nuclear pore, rather than the reverse”. However, I can see a list of clear predictions that Baum and Baum are making that someone can test, even if it’s clearly not me.

Fossil data would be nice, but highly unlikely, but there is another prediction. If prokaryotes can gain an advantage by developing blebs to interact with bacteria, then it should be possible to see some prokaryotes in the wild that look like the first eukaryote before it engulfed its partner.

Best of all, it’s a very positive paper. Baum and Baum aren’t simply saying everyone else is wrong, they’re proposing new topics to research and new things to study, new ways to look at problems. Even if it turns out they’re wrong, they could be wrong in a really interesting and helpful way.

You can pick up the paper through Open Access from BMC Biology.

Baum D.A. & Baum B. (2014). An inside-out origin for the eukaryotic cell, BMC Biology, 12 (1) 76. DOI: http://dx.doi.org/10.1186/s12915-014-0076-2

Do changes in water levels in wetlands give plants a backbone?

The usual rule whenever a headline asks a silly question is that answer is no, and that’s the same here because plants don’t have backs. However research by Hamann and Puijalon does show that emergence due to falling water levels can cause a biomechanical response.

The stresses for aquatic and terrestrial plants differ, because aquatic plants have the support of water to give them buoyancy. Hamann and Puijalon point out, if a plant can float then the chief stress it will have is tension as it is dragged by the local current. What it needs is an anchor and flexibility to cope with the forces on it. A terrestrial plant in contrast feels gravity much more. It has to support its own weight. Wind can put a plant in tension, but the force of gravity can compress some tissues. So the mechanical needs of a plant out of water are different to those in water.

Diagram of forces on aquatic and terrestrial plants

Schematic overview of the main forces (thick arrows) and stresses (thin arrows) acting on plants in aquatic and terrestrial environments. In the aquatic environment, buoyant plants withstand the drag forces resulting from current flow through tension (σ +). In the terrestrial environment, in addition to the force of gravity, self-supportive plants withstand drag forces induced by wind through bending (a combination of tension σ + and compression σ −). Diagram by Elena Hamann and Sara Puijalon.

This is a problem for a plant that is happily sat in water, until there’s a drought. When the water goes the plants are faced with a major change in environment. Can they change their physical structure to cope? Hamann and Puijalon expected that plants could increase their cross-sectional area and the proportion of strengthening tissue in their stems to increase strength. They also expected the stems to become stiffer.

They looked at a wide variety of species Berula erecta (Hudson) Coville, Hippuris vulgaris L., Juncus articulatus L., Lythrum salicaria L., Mentha aquatica L., Myosotis scorpioides L., Nuphar lutea L. and Sparganium emersum Rehmann. The plants were growing in wetlands along the Ain and the Rhône in eastern France. One set of plants was picked from submerged conditions and the other from close by in emergent conditions, to keep the population and growing conditions as similar as possible. They then tested the plants for strength and flexibility and examined them physically.
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Laughing gas no laughing matter for climate change

There’s an interesting article published in PLOS One that I like. It’s one of these things that’s very clever, but the basic idea is very simple.

Beech wood and leaves

The future of climate change might lie beneath the soil. Photo by Karl-Ludwig Poggemann / Flickr.

Temperatures are rising, and there’s plenty of research on how that might affect plants. In PLOS One this month Gschwendtner et al. investigate how rising temperatures affect the soil. In fact they look at the microbe community in it. Bacteria and archaea are part of the biological process of putting Nitrogen into usable form for plants. Knowing how they might react to climate change would be useful.

The experiment was very simple. At the Tuttlingen Research Station in southern Germany, Gschwendtner and her team took some beech seedlings, and the soil around them, growing on a northwest facing slope and replanted some of them on a southwest facing slope. They got more sunlight on the soil and so you effectively change the climate for those soil samples. Compare one with the other and you get to see what sort of changes warmer weather might have.

That sounds simple, but there are some obvious problems. If the geology of the new slope is radically different, maybe you’re just measuring the change in geology, not climate. So what they did was core the soil, to make sure the new sites were a close match for the old sites.

That’s fine, but there’s another problem. The moved seedlings will have moved. That might lead to stresses that the other seedlings didn’t have. If that’s the case you’re measuring stress not climate. So to get round that problem they also replanted the control sample in new locations on the northwest slope, so they had the same stresses too.

The target was to see how Nitrogen production in the soil was affected. Measuring the soil and sniffing for outgassing would be a pain, so they used a different technique. They tested the soil for specific genes. Sampling the soil and comparing the relative proportions and quantities of certain genes in the soil would give measure of the kind of activity going on. For example they looked for the genes nirK, nirS, cnor and nosZ as markers of denitrification. These are genes associated with microbes that take nitrates in the soil and convert them to gases. If there are more bacteria and archaea working on denitrification, then they will be more copies of these genes to find.

What they found is that these genes became much more common in soil samples from the seedlings moved to the sunnier position. They also followed up the experiment by simulating drought and flood. They found that the denitrifying microbes did better under those conditions.

This has a double blow for plants. The first is that the plants are competing with these microbes for nitrogen. We think of plants living off carbon dioxide and water, but building proteins needs nitrogen too. The second blow is that the nitrogen is lost from the soil when the microbes emit it as nitrous oxide N2O. It’s known as laughing gas, but it’s also a greenhouse gas, adding to the climate problems the plants are already facing.

I think what appeals to me about the paper is the clever way they’ve looked at denitrification. If I wanted to measure change of nitrogen in a soil, I’d try directly measuring the nitrogen. Looking for DNA markers is simpler, and it also gives an idea of what might be driving that change. I also like the simplicity of the idea let’s move seedlings from here to there, and the fact that the control was replanted too. With hindsight it’s easy to say that should be done, but I bet that wouldn’t have occurred to me until the experiment was near its end.

As it’s in PLOS One you can pick it up now as an Open Access paper.

Gschwendtner S., Tejedor J., Bimueller C., Dannenmann M., Kögel Knabner I. & Schloter M. (2014). Climate Change Induces Shifts in Abundance and Activity Pattern of Bacteria and Archaea Catalyzing Major Transformation Steps in Nitrogen Turnover in a Soil from a Mid-European Beech Forest, PLoS ONE, 9 (12) e114278. DOI: http://dx.doi.org/10.1371/journal.pone.0114278

Inflorescences take centre stage

Inflorescences issue cover Annals of Botany has a new special issue in Free Access: Inflorescences. It’s a useful reminder to me of another area of Botany I need to read more about.

For a start, I think I’ve said elsewhere that inflorescences are the structures where there are multiple flowers on a plant and not just a single flower. In a clumsy way this might be true but it also misses the point of an inflorescence. It’s not simply that there are multiple flowers, but also that those flowers work with each other as unit. They’re not just a collection of individuals.

If you approach inflorescences from this point of view, their structure becomes a bit of a puzzle. Why the diversity? But also, can you classify them sensibly and, if you can, what is the basis of that? Do different structures correspond with different functions?

Lawrence Harder and Przemyslaw Prusinkiewicz describe the interplay between inflorescence development and function as the crucible of architectural diversity. It highlights the importance of linking structures and function. In terms of tracing plant relationships, structure is useful but it’s also worth looking at what the structure does. A similar structure could have a very different result if the phenology, the timing of the flowering, changes.

Time is key factor that is highlighted by Harder and Prusinkiewicz. Looking at a display, it’s easy to think of it as an organisation in space, but they also make a point that inflorescences are dynamic. They change with time, and how they change with time has consequences for their function.

As far as plant reproduction goes, it’s easy to focus on the success of flowers, but Harder and Prusinkiewicz argue that what you have is part of a modular system, and that to understand it you have to look at the system as a whole, instead of modules in isolation. Most angiosperms use inflorescences so it’s clearly a powerful tool for a plant. Looking at them as a unit and not just parts can put plant reproduction into a new context.

Harder L.D. & Prusinkiewicz P. (2012). The interplay between inflorescence development and function as the crucible of architectural diversity, Annals of Botany, 112 (8) 1477-1493. DOI: http://dx.doi.org/10.1093/aob/mcs252

The Guardian tackles the ethics of rewilding

The Guardian posted an interesting article yesterday from Tori Herridge: Mammoths are a huge part of my life. But cloning them is wrong.

Mammoth

Mammoth of BC by Tyler Ingram / Flickr.

I’ll concede that a mammoth is not a plant, but part of what I found interesting is that Herridge points out that mammoths didn’t exist in isolation. She tackles the idea that mammoths could somehow be part of a plan to restore the arctic steppes, but she makes an important point:

There’s a reason the terms “de-extinction” and “rewilding” are so powerful and that’s because they imply a return to a time, a state of grace, a place that was somehow unspoiled. Cloning a mammoth offers us the hope of undoing the excesses of humanity, bringing back the creatures whose extinction we helped bring about.

I think the idea of turning back the clock, to a time when things are better, is a powerful image. However it isn’t practical. Herridge points out that the mammoth was part of a wider ecosystem of arctic steppe, and it’s not certain that the plants will naturally appear if you dump a load of mammoths in Siberia.

It’s not even purely about the plants. Looking this up I saw there was a lot about remediation in the Root Biology special issue of Annals of Botany (now free access). In particular, Interactions between exotic invasive plants and soil microbes in the rhizosphere suggest that ‘everything is not everywhere’ say Rout and Callaway. They’re talking about microbes in the context of invasive species, but I wonder what ten thousand years of change has done to the soil of the arctic.

We don’t have the plants, we may not have the right soils. We are going through a big extinction event. I’d love to see a mammoth, but sadly when you look at the social problems a mammoth would have, as well as the many conservation efforts competing for limited funding, I think Tori Herridge is right, and that she does a good job of explaining all the problems.

Microgravity and chromosome damage

The Karyological Observations of Krikorian and O’Connor look at plant material from flights STS-2 and STS-3 of the Space Shuttle.

STS-2, among other things, carried a payload of Helianthus annuus, sunflowers. STS-2 was cut short from five days to two when a fuel cell for producing electricity and processing water failed. Despite this the plants had some time to grow, in a couple of cases with roots protruding from the soil. Krikorian and O’Connor say: “The soil environment of the roots in the HEFLEX-type modules was not particularly well suited to recovery of roots tips for karyological examination.” In plain English it sounds like it was extremely difficult, and they go on in the paper to explain some of the problems they had.

The key result was that when they looked at the cells, they found only around 2% were in division. The same plant in a lab would be expected to be ten times more active. They also found some plants had aneuploidy. Usually chromosomes come in pairs, (though polyploidy is common in plants too). In this case one plant was missing a partner for chromosome 6. The same was true in another plant from the sample. Given these results, similar tests followed on the STS-3 material.

Again with the oats, it was found that only a 2% of cells were in division, again about ten times less than anticipated from the lab. There was also chromosome damage. The mung beans too were found to have low counts for division, though less obvious signs of damage to the chromosomes.

It seems something was affecting the plants, but in their conclusions Krikorian and O’Connor were wary of saying exactly what. The obvious suspect is microgravity, but they also left open the possibility that it was the effect of launch and/or re-entry that was the problem. It’s this referring back to the control that marks out the value of the research on STS-3. It wasn’t simply that material was put into orbit, it was also that the same equipment was run on the ground to act as a control. If gravity is the variable you’re changing then it’s essential to get as much of the rest of the control experiment to run as closely to the orbital experiment as possible.

Like some of the other papers in this supplement, Karyological Observations has been cited this year in a paper Seed-to-Seed-to-Seed Growth and Development of Arabidopsis in Microgravity published October 2014 in Astrobiology. Link et al. also cite Kuang et al from 1996, Musgrave et al from 1998 and Kuang et al from 2000. In some ways it might be surprising that work from thirty years ago is still getting cited, but that’s how science works.

Currently NASA does plant science in orbit on the International Space Station, but this latest platform was built with the shuttle and the aging Russian Soyuz craft. In a similar way current plant research is built on the prior work of earlier scientists. Fortunately you don’t have to wait thirty years to see most research in Annals of Botany. If your library doesn’t have access to the journal, papers become free access a year after paper publication.

Space Shuttle landing

STS-3 lands at White Sands. Photo: NASA.

You can read more posts on papers from our spaceflight supplement by clicking the STS-3 tag.

Today’s Papers

Krikorian A.D. & O’Connor S.A. Karyological Observations, Annals of Botany, 54 (supp3) 49-63. DOI:

KUANG A. (1996). Cytochemical Localization of Reserves during Seed Development inArabidopsis thalianaunder Spaceflight Conditions, Annals of Botany, 78 (3) 343-351. DOI: http://dx.doi.org/10.1006/anbo.1996.0129

Kuang A. (2000). Influence of Microgravity on Ultrastructure and Storage Reserves in Seeds of Brassica rapa L., Annals of Botany, 85 (6) 851-859. DOI: http://dx.doi.org/10.1006/anbo.2000.1153

Link B.M. & Bratislav Stankovic (2014). Seed-to-Seed-to-Seed Growth and Development of Arabidopsis in Microgravity , Astrobiology, 14 (10) 866-875. DOI: http://dx.doi.org/10.1089/ast.2014.1184

MUSGRAVE M. (1998). Changes inArabidopsisLeaf Ultrastructure, Chlorophyll and Carbohydrate Content During Spaceflight Depend on Ventilation, Annals of Botany, 81 (4) 503-512. DOI: http://dx.doi.org/10.1006/anbo.1998.0585

Use it or lose it, for a plant’s sense of gravity?

Gravitropism is the ability of a plant to turn in response to gravity. Roots have gravitropism, bending to turn down and stems negative gravitropism to turn up. But what happens if you remove a plant’s ability to sense where down is?

In roots, plants feel where down is in the root cap. If you remove the root cap carefully, and then tip the plant on its side, the root will continue to grow without changing direction until the root cap regenerates. Once the root cap can signal to the root, cells on one side of the root elongate to bend the root downwards.

The flight of STS-3 posed a challenge to the plants on board. Once in orbit they would be in perpetual freefall and there’d be no sense of ‘up’. What effect would this have on the root cap? Slocum, Gaynor and Galston compared the responses of the oat and mung bean seedlings on board in their paper Cytological and Ultrastructural Studies on Root Tissues. Seedlings for both plants germinated either a few hours before launch or in orbit.

The oats were fine. Both the flight and ground-based oat seedlings had normal root structure. The same was almost true for the mung beans too. Most of the roots were normal, except for the root-cap in the flight sample. The root cap cells on the mung beans in space had had a very bad time. Most of the cells were degenerated. If you compare the control sample below (left) with the flight root (right) you can see one of them is not well.

Two roots, the one on the right looking terrible.

Light micrographs of A, ground control and B, flight-grown mung bean roots, seen in near
median longitudinal section x 75.

It seems that the ability of plants to adapt to microgravity varies on the plant, so it’s not enough to extrapolate from one to all.

This is another paper that continues to get cited today. Most recently Simple sequence repeat markers reveal multiple loci governing grain-size variations in a japonica rice (Oryza sativa L.) mutant induced by cosmic radiation during space flight by Wang et al in Euphytica 2014. There’s also research on peas citing it like Ultrastructure and metabolic activity of pea mitochondria under clinorotation in Cytology and Genetics 2012.

If gravity is essential, then it might become something we have to fake in space. The usual idea is to gently rotate a space station to give a sense of centripetal force. Spin faster and it is possible to subject plants to hypergravity, as noted by Nigel Chaffey earlier this year. Perennial favourite Arabidopisis is the subject of a 300g (yes, three hundred times the force of gravity) in this paper from AnnBot. Subjecting humans to this level of gravity would be a Very Bad Idea.

You can read more posts on papers from our spaceflight supplement by clicking the STS-3 tag.

Today’s Papers

Slocum R.D., Gaynor J.J. & Galston A.W. (1984). Cytological and Ultrastructural Studies on Root Tissues, Annals of Botany, 54 (supp3) 65-76.

Brykov V.O. & I. P. Generozova (2012). Ultrastructure and metabolic activity of pea mitochondria under clinorotation, Cytology and Genetics, 46 (3) 144-149. DOI: http://dx.doi.org/10.3103/s0095452712030036

NAKABAYASHI I. (2006). Hypergravity Stimulus Enhances Primary Xylem Development and Decreases Mechanical Properties of Secondary Cell Walls in Inflorescence Stems of Arabidopsis thaliana, Annals of Botany, 97 (6) 1083-1090. DOI: http://dx.doi.org/10.1093/aob/mcl055

Wang J., Tianqing Zheng, Xiuqin Zhao, Jauhar Ali, Jianlong Xu & Zhikang Li (2013). Simple sequence repeat markers reveal multiple loci governing grain-size variations in a japonica rice (Oryza sativa L.) mutant induced by cosmic radiation during space flight, Euphytica, 196 (2) 225-236. DOI: http://dx.doi.org/10.1007/s10681-013-1026-8

Is there a downside for plants when they can’t sense ‘up’?

Looking at a tree, it can be hard to visualise the sheer volume of water being drawn up from the roots to the canopy. That volume of was is massive, and puts cells under a lot of pressure, so lignin, the substance plants use to strengthen cell walls, is an important product. But what happens to lignin if you take gravity away? Growth and Lignification in Seedlings Exposed to Eight Days of Microgravity by Cowles et al. is a study that aims to find out.

The experiment on STS-3 was growing pine seedlings with mung beans and oat seeds. There were a couple of targets. One was to examine how gravity affected the production of lignin. The other was to test the PGU, the plant growth unit, that would be used in following missions.

Plant Growth Unit

From Cowles et al.

To see the effect of gravity a PGU with similar plants was kept on Earth, so the development of the plants could be compared.

Germination of the orbiting plants was much like the 1g plants. However, Cowles et al. point out that the seeds have to be prepared before launch, which gave them twelve hours on Earth to germinate. They found that the flying plants grew less, and in the case of the seeds, roots were growing ‘up’ as well as ‘down’. Some of the plants that grew in orbit also contained less lignin.

There have been plenty of papers that went on to cite this research, most recently Expression of stress-related genes in zebrawood (Astronium fraxinifolium, Anacardiaceae) seedlings following germination in microgravity by Inglis et al. in Genetics and Molecular Biology from this year.

Recently in Annals of Botany there’s been Xylem Development and Cell Wall Changes of Soybean Seedlings Grown in Space and in the opposite directon Hypergravity Stimulus Enhances Primary Xylem Development and Decreases Mechanical Properties of Secondary Cell Walls in Inflorescence Stems of Arabidopsis thaliana by Nakabayashi et al.

This is interesting that it still gets cited because the results weren’t all significant. While the mung beans had less lignin, the oat and pine seedlings didn’t have significantly less and the experiment was relatively small. However, this flight wasn’t just about the results, it also worked to establish a method. By laying out the experimental technique used to analyse the plant Cowles et al laid down a baseline for other researchers to compare and improve their techniques.

The basic question they studied remains important. Understanding the processes that produce lignin could help with technology on Earth. For example, it would be helpful in producing biofuel if there were less lignin in it to start with. Launching plants and growing them in space would be a spectacularly inefficient way to do that. However for small samples, it can be a useful way to isolate one variable and help figure out the mechanics of lignin production.

You can read more posts on papers from our spaceflight supplement by clicking the STS-3 tag.

Today’s Papers

Cowles J.R., Scheld H.W., Lemay R. & Peterson C. (1984). Growth and Lignification in Seedlings Exposed to Eight Days of Microgravity , Annals of Botany, 54 (supp3) 33-48. DOI:

Chapple C. & Rick Meilan (2007). Loosening lignin’s grip on biofuel production, Nature Biotechnology, 25 (7) 746-748. DOI: http://dx.doi.org/10.1038/nbt0707-746

de Micco V., J.-P. Joseleau & K. Ruel (2008). Xylem Development and Cell Wall Changes of Soybean Seedlings Grown in Space, Annals of Botany, 101 (5) 661-669. DOI: http://dx.doi.org/10.1093/aob/mcn001

Inglis P.W., Ciampi A.Y., Salomão A.N., Costa T.D.S.A. & Azevedo V.C.R. (2013). Expression of stress-related genes in zebrawood (Astronium fraxinifolium, Anacardiaceae) seedlings following germination in microgravity., Genetics and molecular biology, PMID: http://www.ncbi.nlm.nih.gov/pubmed/24688295

NAKABAYASHI I. (2006). Hypergravity Stimulus Enhances Primary Xylem Development and Decreases Mechanical Properties of Secondary Cell Walls in Inflorescence Stems of Arabidopsis thaliana, Annals of Botany, 97 (6) 1083-1090. DOI: http://dx.doi.org/10.1093/aob/mcl055

Calibrating data in a weightless environment

A Test to Verify the Biocompatibility of a Method for Plant Culture in a Microgravity Environment by Brown and Chapman is an example of the basic science people needed to do with the shuttle.

If you’re going to run plant experiments, then the plants will need to perform basic function in order to live. One example is taking up water and this was a problem. Soviet experiments and theoretical work suggested the way plants reacted to soil moisture in orbit was very different to how they behaved on Earth. This would have a major effect on any experiment results because unusual behaviour could be due to whatever it was you were experimenting for, or it could just be the way it goes in microgravity.

STS-3 carried what NASA called ‘bio-engineering tests’ to see if botanical experiments with their systems were practical. The test has HEFLEX, the Helianthus Flight Experiment. The question HEFLEX was to look at was how sunflower nutation happened in orbit. This is the spinning effect of the stem in growing seedlings. You can see Arabidopsis doing this in the time-lapse video below.

There was a problem with STS-2 which meant that the experiments for that mission were cut short. STS-3 had the opposite problem, the mission was longer than HEFLEX would be, but it still allowed researchers to compare the effects of soil moisture.

Graph of results.

Comparison of shoot lengths of 8-9-day-old plants from STS-3 Mission (solid dot) and those from 1g control test (hollow dot). The same experiment hardware was used for both tests.

Tests showed plant responses seemed to be comparable, and additional post-landing inspection also show the effects of launch and re-entry were no big problem.

This research went on to be cited in a few papers, and you can pick up Circumnutations of Sunflower Hypocotyls in Satellite Orbit for free from Plant Physiology, which had Brown and Chapman among the authors. But the chain doesn’t stop there.

Nutation remains a puzzle in plant sciences. Circumnutation as an autonomous root movement in plants in AmJBot dates from 2012 (again free access). AoB PLANTS, the open access plant journal has a paper Petiole hyponasty: an ethylene-driven, adaptive response to changes in the environment by Polko et al. Both of these papers refer back to Brown et al’s PlanyPhys paper, despite being terrestrial papers. This first paper, specialising in how a lab on the space shuttle worked, is part of a chain of research. It shows launching seedlings away from the planet can bring us closer to understanding life upon it.

You can read more posts on papers from our spaceflight supplement by clicking the STS-3 tag.

Today’s Papers

Brown A.H. & Chapman D.K. (1984). A Test to Verify the Biocompatibility of a Method for Plant Culture in a Microgravity Environment, Annals of Botany, 54 (supp3) 19-31.

Brown A.H., Chapman D.K., Lewis R.F. & Venditti A.L. (1990). Circumnutations of Sunflower Hypocotyls in Satellite Orbit, Plant Physiology, 94 (1) 233-238. DOI: 10.​1104/​pp.​94.​1.​233

Migliaccio F. & A. Fortunati (2012). Circumnutation as an autonomous root movement in plants, American Journal of Botany, 100 (1) 4-13. DOI: 10.3732/ajb.1200314

Polko J.K., A. J. M. Peeters & R. Pierik (2011). Petiole hyponasty: an ethylene-driven, adaptive response to changes in the environment, AoB Plants, 2011 plr031-plr031. DOI: 10.1093/aobpla/plr031

30 years of Astrobotany in Annals of Botany

“In the newspapers I used to read about shuttles going up and down all the time, but it bothered me a little bit that I never saw in any scientific journal any results of anything that had ever come out of the experiments on the shuttle that were supposed to be so important.”

Richard Feynman – What Do You Care What Other People Think?

STS-3 Shuttle mission launching

STS-3 departs on its mission. Photo: NASA.

On 22 March 1982, at 11:00 local time, the STS-3 mission, manned by Lousma and Fullerton launched in the space shuttle Columbia. Over the next eight days the shuttle was a platform for a few plant science experiments. A year and a half later these experiments were the basis of most of an Annals of Botany supplement Experiments on Plants Grown in Space.

It’s not that surprising Richard Feynman hadn’t seen these results. It’s easy to forget what a difference electronic communications have made. This issue of Annals of Botany would not have been issued as a PDF. Anyone wanting to see the results would have to physically locate an issue at a local library, not just click – which made it difficult for the public to access. NASA would also be issuing paper releases, and the news was the next shuttle flight not the one several missions back. So some science of immense public interest was kept to a few specialists.

The supplement has been digitised, and with current papers Annals of Botany makes its papers free access a year after print publication. In this case the delay is around thirty years. Quite a few things have changed since then, so the first paper in the supplement is a useful primer. Status and Prospects by Halstead and Dutcher gives a sense of the state of play for botany in the early 1980s.

It’s easy to be accustomed to space flight, and most ISS launches are not inherently newsworthy. The space shuttle was the vehicle that started the West’s perception of space travel as a mundane event. Halstead and Dutcher looked forward to the prospect of regular and affordable spaceflight.

Hindsight comes from Paul et al. and their paper Fundamental Plant Biology Enabled by the Space Shuttle in AmJBot. They comment on how plant science changed on shuttle flights, eventually taking advantage of the long-term missions offered by the International Space Station. One of the features of their paper is they point out there’s more to botany in space than the effect of gravity. By eliminating gravity you can explore other tropisms. They give a couple of examples, you can test for phototropism obviously, by manipulating light. But they also point out that subtle effects like ionic gradients become visible, once you eliminate the effect of gravitropism.

Aside from plans to colonise Mars, basic science means that exploration of microgravity and extreme environments will continue to be growth areas in botany. Over this week, we’ll be looking at the papers in our Space Shuttle issue and the science that they inspired after publication. Posts will be going live daily.

Today’s Papers

Halstead T.W. & Dutcher F.R. (1984). Status and Prospects, Annals of Botany, 54 (supp3) 3-18.

Paul A.L., Wheeler R.M., Levine L.G. & Ferl R.J. (2013). Fundamental Plant Biology Enabled by The Space Shuttle, American Journal of Botany, 100 (1) 226-234. DOI: 10.3732/ajb.1200338