Sense about Science ? equipping people to make sense of science and evidence
The wheat experiment
We went to Rothamsted Research on Thursday 10th May armed with your questions on the development of the GM wheat and why it is being grown outside.
HJ: The glasshouse compartments contain the GM plant material. You can see in each of these rooms that there’s a different experiment going on, all GM linked, different genes for different research areas. These were the rooms where we grew our (E)-β-farnesene plants nine months ago, in order to obtain the seed for the field trial.
23. How do you look at this stage - you’re testing whether they are producing the pheromone?
HJ: The first thing is just to get the seed from these, so the original plants are in those little culture pots. We put them into the soil, grow them up and get seed from them, and do some basic testing to make sure that the gene has been incorporated into the plant: that it hasn’t been fragmented, that it’s intact. Then we gave some of those plants to Toby and his colleagues who took them into his lab, and it’s there that they do the testing for the smell, how much of the (E)-β-farnesene smell is being given off, and whether the aphids are changing their behaviour in response to that.
24. How do you check whether the gene has been incorporated?
HJ: We use a number of techniques. I don’t know whether you know the term PCR, the polymerase chain reaction or a technique called a Southern blot, named after the famous scientist Ed Southern?
3. That’s where you get the cells and mash them up, and use markers to the bits of DNA that you’re looking for to see whether it’s in the cells that you chose?
25. So you’re looking to see whether the plants are behaving as you want. Is that an easy thing? Do you get ten seeds from a whole row of plants, or do you get enough to sow a field?
HJ: So, one healthy wheat plant will make about 500 seeds. That’s normal, the wheat grows perfectly normally in here. And of course it self-pollinates, you don’t need to actively cross-pollinate wheat. Each flower on a wheat ear wants to pollinate itself. It’s very difficult in fact to stop it pollinating itself, and it’s very difficult to get wheat plants to cross-pollinate with another wheat plant. So just growing a wheat plant normally will allow it to set lots of seeds.
26. So when you did this, how much seed did you get from growing those plants out?
HJ: The first time, we might have got 60 or 70 individual plants that contained the genes, and we sent all of those to Toby’s lab to test. Once we had chosen the best two plants, one of them that just contained the (E)-β-farnesene synthase from peppermint and another one that had even more (E)-β-farnesene because it contained both genes, the gene from peppermint, and the animal form of the gene, we then planted lots of them and got six or seven kilos of seeds of those two types, enough to plant in the field.
27. That then got you into a position where you were ready to plant out, or did you plant another round of wheat in this lab?
HJ: Yes, to get our six kilos of seeds, we needed to grow in two large compartments. We needed to grow each of those two lines that we needed to plant in the field.
28. There’s a point that’s come in on twitter, that we need long term health/safety testing. Another question that’s come in from people writing about the attacks on your research is: what about the safety for human consumption? So people are asking why are you not looking at that, at this stage in the lab; because you’re not, are you?
HJ: No, we’re not, and it’s perfectly right that people ask these questions. If it was the case that a new GM variety was put on the market or sold commercially, then these things would be done as part of the regulatory processes of different countries; they are absolutely a requirement. But this is a research-scale field trial. It’s very small, it’s eight 6x6 metre squares, scattered around an 80 metre plot of other cereals, and all the material will be harvested and destroyed at the end, once we’ve got the data about how aphids respond to our plants.
HJ: It’s not for human consumption. And a couple of other points to note here are that this substance doesn’t have a toxic effect, it’s repellent against the insects, and also, it’s widely produced in nature already, so there are over 400 different species of plant which naturally produce this smell. It’s a common food ingredient, so it occurs in a lot of foods. It occurs in quite large amounts in beer, for example.
29. We have a question about the roundup gene modification, which is another genetically modified plant. The questioner says this is now failing and asks how do you know that what you’ve done here is stable and won’t change?
HJ: We know that our plants, our genes are stable for the three or four generations we’ve grown them under, and there’s no indication that that is going to change. Roundup is a herbicide and it’s true that other plants are grown commercially that have a roundup tolerance. The trait is perfectly stable, but it’s true to say that some of the weeds around them may be adapting so that they are killed less effectively by Roundup. That is part of the natural selection process. It’s nothing to do with the GM trait.
30. Is this the point at which, having got your seeds, you now move to outside plots?
HJ: Well, first of all they need to be tested for their efficacy in aphid behaviour, so they are taken by Toby and he does chemical analysis on the volatiles, what smells these plants are making, and then does tests on aphids.
TB: So, the first thing we need to check is whether they’re releasing the sort of smell we’re looking for. So we have to set up these ‘volatile collections’ to collect the smells and analyse them. You can see some of this over here: these small filters collect the smells of the plant, so there’s a system of pumps. It pushes in clean air, through this charcoal filter, the clean air passes into the container where the plants are, and then there’s another pump which pulls the air out through this special filter here, which traps the volatiles (the smell compounds).
TB: We leave that running for a day or two, then we take the small tube out and it goes to another part of the lab where we put half a millilitre of solvent into the tube, which just drips through. The smell compounds which have been trapped on that filter pass into the solvent, and then we can analyse that little sample on some of the machines we’ve got here in the lab, to see which chemicals are being made by the plant.
TB: To get the proper aphid alarm pheromone response, the purer this substance is, the better. We need just that compound on its own. That’s one of the reasons we’ve chosen to use wheat, because it’s not a naturally very smelly plant, so by engineering in this enzyme for making this one smell, then we get just like an aphid when it’s attacked, so it’s just that alarm signal that’s released and no other smell compounds.
31. From this you establish that you’re happy with the plants that are growing. Is that right?
TB: Yes, because even when the gene is expressed in the plant, you still need to verify that it is producing the right smell.
32. And how can you tell? Are you just taking it as read that the aphids will be repelled by that because that’s been established in previous work?
TB: No we’re not. We did a lot of very time-consuming experiments where we exposed aphids to the smell from these plants. We put them in a device called an olfactometer, where you have an aphid walking about, and you record the amount of time it spends in different parts of the device. We check to see whether they spend significantly less time in the area where there are the smells from this engineered plant.
33. We’ve got a lot of questions, that we’ll put to you as we go out to the plot, about the effect on other species as well. Have you looked at other species?
TB: Yes, we’ve looked at the aphids’ parasitic wasps. These are important natural enemies of the aphids, which reduce the populations of these aphids in the field. The ladybirds are better known, but in terms of actually reducing aphid populations, these little wasps are the really important ones. We’ve been looking at the amount of time that they spend on the normal wheat plants and on our new wheat plants which are releasing this smell. It is quite the opposite of what happens with a toxic pesticide where these poor creatures get killed. Our plants were actually more attractive to the natural enemy, and they spent about twice as long on the transformed plants as they do on the normal comparison plants.
34. You’re measuring the amount of time they spend on the plant?
TB: Yes, and in the field we’ll be looking at the numbers of parasitised aphids. It’s very easy to see when the aphids have been attacked by these wasps, because the aphid becomes swollen up and it gets a hard, white sphere-shaped case. We call it an aphid mummy. And we count the numbers of these as well as the numbers of live aphids, so by looking at these we can tell what percentage of the population has been parasitised by these predators.
35. So we’re out in the fields, looking at the wheat; but we’re still sitting in the car because it’s pouring with rain. So Toby, you come up here, in this kind of weather, to count aphids?
TB: That’s right. Once a week we need to come out here and count the numbers of aphids on the different field crops here, the different sorts of wheat; and compare the different treatments.
36. How do you count them?
TB: Looking at all the leaves and counting the numbers of insects. So in each plot there are nine sampling points. At each of those points we count eleven plants. So in each plots, there are 99 plants counted. Altogether there are sixteen plots - eight comparison normal wheat ones and eight with these GM transformed plants.
(Sense About Science and Pod Delusion run out of fingers and toes. It’s aphids x 9 x 11 x 16)
37. How big is the field we’re looking at?
TB: The field is quite big because we’ve got the area for next year’s experiment as well. But the actual plots themselves, they’re just eight 6 metre by 6 metre plots.
38. Why did you choose that size?
TB: Just for practical reasons really, if you have a much larger area it increases the cost of the experiment.
39. We’ve had a question in: you say it mimics farming conditions. How do you know that?
TB: It’s scaling up from what we have been doing in the lab so far, and obviously it’s a lot more realistic to be doing it under real conditions in the field. It’s not quite the same as having a huge area of it, but it’s moving a step closer to that, and we’re going to get a much better idea of what the performance of these plants is like in terms of reducing the insect pest under real field conditions.
40. Growing out here in Hertfordshire where it rains and it doesn’t get very warm, how are your results going to be able to tell you what the wheat does in other environments?
TB: Well it won’t, it will just tell us how it gets on in this particular place, and it will give us some starting information; but if it has reduced the numbers of insects here, it’s quite likely that it will reduce it in other places as well. I mean, if we get hotter conditions the aphids will be growing faster, and they’ll actually be even more of a problem, so we’ll just have to see. But this experiment relies on natural infestation of insects in the field, so we are very much dependent on the weather.
41. I have a question here, which is: how can you be sure your results are down to your GM plant and not down to some other reason? Presumably they mean other reason such as low aphids in the area or something like that?
TB: Well what we’ve got out here is eight GM plots and eight comparison plots. These eight comparison plots are the untransformed plants, so by counting the number of aphids on those we’ll be able to get an idea of what it would be like with the normal plants.
42. We’ve got a question from Sheila from Derby. She’s raised this question on a discussion: by growing outside you’ve already put seeds into the environment. Effectively, people are saying, you’ve actually already released it into the wild here.
TB: It’s been done under very contained conditions, we’ve got as you can see, a fence round it, we’ve also got a 20-metre wide area with no plants on it, and then after that there’s a 10-metre strip of barley and a three metre strip of wheat, and this all prevents the pollen moving out from the experiment. It’s all been done with a very thorough risk assessment, and it’s a very small-scale trial.
43. So what do you do at the end of the experiment? Surely some seeds will be left?
TB: No, it will all be harvested, and it will all be destroyed at the end.
44. And you watch the plot, to see, just in case anything grows afterwards?
TB: Yes, some of the conditions of being able to do this experiment require that we come back and monitor how it is for the years afterwards as well, yes.
45. Is it just aphids you count? I’m asking because Pete from Hampshire has asked what about ladybirds, lacewings and wasps attracted to this crop and away from other farms that need them?
TB: We’re recording those insects as well. I think it’s a bit of a stretch of the imagination that they would be coming a long way from other farms, it’s more like localised movement of them, and we see this as a very positive part of this approach. We’re making the plants more attractive to the aphids’ natural enemies, and it’s not killing them like a conventional toxic pesticide, which is very broad spectrum and kills a lot of these natural enemies.
46. For people who don’t know the phrase ‘broad spectrum,’ you mean something that’s designed to kill aphids, but at the same time kills other things like ladybirds.
TB: Yes, exactly, normal pesticides, they’ll be killing the ladybirds, they’ll be killing the wasps, they’ll be killing everything.
47. A question here about the lifecycle. What will happen if you attract ladybirds and other creatures, and then there’s nothing for them to eat on the plant because the aphids have been encouraged away?
TB: I think there’ll still be a certain number of aphids there, it’s not going to be 100% effective in repelling them, so there will still be some that have been agitated, are still dropping down off the plant, and still walking around; so there will still be a certain number of aphids there on the plants. The other thing is that these natural enemies that have been attracted in are not trapped there permanently. They spend a longer period of time on these plants, but they don’t stay there forever, they fly away again, they will move off and they won’t starve.
48. What will the results look like? What will make you think this has been a success?
TB: If we get substantially lower aphid infestations in the plots that have got the GM plant, compared with the comparison plots, that will be a good result.
49. But if there are low aphids this year anyway, in your comparison plots, and it shows that there are low aphids, would you have to do this experiment again?
TB: Yes, that’s one reason why we’re doing this experiment for two years. We’re planning to do it again next year. The way things are with the weather at the moment, with it being so cold and wet, we haven’t actually got very many aphids. We hope that we will get more aphids later on in the season, if the experiment is allowed to continue and it doesn’t get trashed in the meantime. But that’s another difficulty that we face, we’re relying on natural aphid infestations, and if we don’t get enough of them it won’t be possible to compare the different treatments.
50. So what’s the period during which you expect aphids to be on the plants?
TB: They occur all through the season. They stop when the ears start to dry out, and when the grain hardens and the plant is too dry for them to feed, so that’s coming towards the end of June, beginning of July.
51. We have a question here, which doesn’t relate really to the trial, which is that there have been concerns that farmers would not be allowed to keep seeds from GM plants and regrow them. Is there anything in this particular plant that you’re growing that would stop farmers from regrowing it in future years, should it ever make it to a commercialised product?
TB: No. These plants can be grown on and seeds collected and another generation sown. There’s nothing to prevent the seeds being used again to grow more plants. In fact we’ve been rearing it through several generations in the lab, and it breeds true; this trait is stably incorporated into the wheat gene and it can be grown on.