Nature Podcast 25 October 2007

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Kerri Smith: This week: reasons to be cheerful and the brain areas that control them.

Elizabeth Phelps: People do not think that bad things are going to happen to them and if you did, lot of people may not get married. You may not take chances to have children assuming everything is going to work out okay, you know if you were a little bit optimistic that things are going to work out well for you.

Adam Rutherford: And rather less optimistically forthright views on climate change.

Gwyn Prins: It is time to ditch Kyoto, cut our losses, and to radically rethink climate policy.

Adam Rutherford: That is the opinion of this week's podium speaker.

Kerri Smith: Hello and welcome to the Nature Podcast, I am Kerri Smith.

Adam Rutherford: And I am Adam Rutherford. Coming up in just a moment, we will be digging around to find how auxin regulates root growth, but first we discover what happened when an ancient moon crashed into Saturn's outermost ring. Geoff Brumfiel reports.

Geoff Brumfiel: Saturn's rings may look imposing, but they are actually made almost entirely of tiny ice particles. I say almost entirely because last year the Cassini mission to Saturn discovered a few boulder-sized moonlets in Saturn's outermost ring. Just how the larger moonlets got there has been a mystery, but a paper in this week's Nature provides clues about their origins. I called author Miodrag Sremcevic at the University of Colorado at Boulder to learn more. Nature 449, 1019–1021 (25 October 2007)

Miodrag Sremcevic: Saturn rings, they are the largest of all rings in our Solar System. They are extremely thin, so you could, for instance, compare Saturn rings to a sheet of paper stretched over the football field. So, they are that thin and Saturn rings consist of mostly icy particles.

Geoff Brumfiel: I understand that as thin as these rings are, you managed to spot some rather large objects in one of Saturn's rings.

Miodrag Sremcevic: So, in the most outer Saturn ring, which is called A ring, we detected tiny moons or moonlets or on the other hand if you wish big boulders. So, they were discovered last yearend. That result was also reported in the Nature; however, at that time our colleagues had not had complete dataset as we had for this study and when we discovered these tiny moons first surprise came that they just exist in a narrow region of Saturn's ring.

Geoff Brumfiel: So, how narrow region and what are their implications?

Miodrag Sremcevic: So, the region is only 3000 kilometres wide, which compared to about 15,000 kilometres of the width of A ring and that is quite peculiar. So, based on the previous study, we were expecting to see these tiny moonlets everywhere in the rings and the surprise is that they are just there in that belt, as we call it. The very existence of the belt really is a big question now. How come that they are just in the belt and typically in science we have a discovery of something in this case a moonlet belt and then we start to line up the suspects and try to do detective work and this is a very constraining factor as most of the things that you would imagine of their origin or the reason why they are there just don't match with that belt appearance.

Geoff Brumfiel: How did they come to be there then?

Miodrag Sremcevic: If we imagine that those moonlets are there with the rings from the very ring origin, from the time when the rings were created that simply does not match, then how just belt, why not everywhere else or if we try to make a hypothesis that these moonlets originated in accretion or aggregation of smaller ring particles that again does not work. Simply, why again this belt? So, the only reason or hypothesis that we could put is that these moonlets originate from some ancient catastrophe. We put forward this idea that there was a big body, larger moon of at least 20 kilometres in size that got smashed by the meteoroids and what we see today are remnants of that old and unfortunate moon.

Geoff Brumfiel: Does that mean that all of Saturn's rings come from destroyed planetary bodies or do you think that this is something that was captured by Saturn's gravity, I mean, do you have any sense of how it got there?

Miodrag Sremcevic: Well, that is a big question that is still not answered. So, there is a bigger question how did rings got created? Perhaps, they were created together with all the other moons just from a disc of material around the Saturn or they were perhaps created in some old catastrophe of yet larger moon. But what appears now is that these tiny moonlets probably do not have the same origin as the rest of the rings.

Adam Rutherford: Miodrag Sremcevic ending that report from Geoff Brumfiel.

Kerri Smith: Now, from planets to plants and from rings to roots, here is Sara Abdulla.

Sara Abdulla: How all plants grow has a lot to do with a hormone called auxin. Biologists have long wondered how auxin gets to plant roots and what it really does there. The answer is revealed in two papers in this week's Nature. I spoke to authors Stan Marée and Veronica Grieneisen from the University of Utrecht to find out how they had cracked this old conundrum. I started by asking Veronica to explain what auxin is. Nature 449, 1008–1013 (25 October 2007) ; Nature 449, 1053–1057 (25 October 2007)

Veronica Grieneisen: Auxin, it is a very small molecule. It is a hormone in fact and it has been known for quite a long time. So, even Darwin and his son were making experiments with plants where they were actually looking at the effect of auxin, but it had not been discovered fully yet and it is the hormone which gives lots of signals to the plant for it to develop, so where should it make a leaf, how should the root grow, where should flowers come out, so this is all somehow mediated through auxin.

Sara Abdulla: What did we know about the role of auxin in roots before your study?

Veronica Grieneisen: It had already startled people that they were the very significant pattern in the root if you would look at it. So, there was a very high concentration of auxin in the tip of the root and this was correlated with the stem niche. So, people knew that it had something to do with the stem niche maintenance; however, like through the growth of the Arabidopsis root you always see this maximum very clearly. So, the question was more how can you get it so stable through the whole process of development and what we were able to show that although one could think that you would have to have lots of mechanisms to keep it so stable like you would have to have control biosynthesis or control decay and breakdown, but just by taking into account how the layout of the cells in the root are distributed and with their internal sub-cellular properties we can explain this formation. So, we can now explain how what are the mechanisms that give rise to this very striking maximum.

Sara Abdulla: So, before you did your work we knew that auxin was in the root and we knew that it was at the tip.

Veronica Grieneisen: Yes.

Sara Abdulla: And your team have discovered how it gets there?

Veronica Grieneisen: How it gets there, how it is maintained, and we also show that besides this maximum we also observe a gradient, which is spanning through the whole root tissue and this gradient is also very well, it is significant to maintain the root tip as a meristematic zone, which means a zone which can always proliferate into more cells.

Sara Abdulla: What you are saying is the hormone is manufactured in the fingertips of the plant as it were and carried down to the toes, here it cycles around from cell to cell in a simple way that concentrates it in one spot and this spot drives how plant pushes down into the soil, is that right?

Veronica Grieneisen: Exactly, more over the interesting thing is this gradient, it is very dynamic, so it is stable, but at the same time there is a huge throughput going through the cells. So, although it is very misleading because if you just look at it biologically you think oh, well this is, you know, everything is just stuck here, it is concentrated at the root tip; however, we are able to show now that every single moment this auxin is just flowing through the cells like crazy, but because it is always being reshuffled it is always refluxing into the root tip it stabilizes gradient and then on slower timescales over days we start noticing that it is also moving, ever so slightly it is also moving. So, we are able to capture both these phenomena why it is stable, why you can see it coming up so fast, but also why over very long time periods it can actually move and this movement is also causing developmental changes in the root.

Sara Abdulla: We have heard that auxin travels to the roots of plants and moves constantly to maintain a high level there, Stan Marée talk us through how you used a combination of experiments and computer modelling to unpick this system?

Athanasius F. M. Marée: The beauty of it is i.e., it is a very close collaboration between the modelling and the experiments and it is highly intertwined in the sense that all the time we are looking at what kind of insights we can gain from the modelling and what kind of insights we get from the experiments and how they can be linked to one another and the interesting thing there is, is that our philosophy of modelling is that we want to describe only very well established facts, for example, we know that auxin diffuses and is transported over the membrane from the cell into the cell wall and starting from this well-established distribution of different transport facilitators, so-called PINs along the cells, we see what we get on a different level of organization. So, the details of the description are on the cellular level, on the sub-cellular level, but then we want to understand what is happening on the level of the whole tissue of the roots and that is something that is fairly hard to do directly with experiments, actually we really need the modelling to understand what are its consequences of these sub-cellular properties.

Kerri Smith: Stan Marée and before him Veronica Grieneisen talking to Sara Abdulla.

Adam Rutherford: Now it is time for The Podium. This week Gwyn Prins from the London School of Economics vents his spleen on the problems of Kyoto protocol.

Gwyn Prins: In December, the world's politicians, the climate policy community, activists, NGOs, and an army of attended media will converge on the Indonesian Island of Bali for the most important summit on climate change since Al Gore rescued the Kyoto protocol ten years ago. The Bali conference will decide the international climate policy for the years after 2012 when the protocol expires. The Bali agenda shows that unless something happens to stop it the plan is for a bigger and better Kyoto with more stringent targets, more ambitious timetables, more carbon trading, more countries inside the UN process. If that agenda is successfully achieved at Bali then ironically humanity will lose an important opportunity to start to make an impact on anthropogenic aspects of global climate change. Why? Because Kyoto has failed; it is time to ditch Kyoto, cut our losses, and to radically rethink climate policy. In this week's Nature, Steve Rayner and I outline the story of Kyoto's failure and also state a handful of key principles to underpin a radical and practical rethink. These should frame the Bali agenda. What failure? Kyoto's supporters may ask. Since coming into effect, Kyoto has produced no demonstrable reductions in emissions or even in anticipated emission's growth and it pays no more than token attention to the needs of societies to adapt to existing climate change, but the present moment is more precarious still. For Kyoto's continued policy failure is being spun by signatory governments, especially in Europe as a story of success. The danger is that while today there is strong public support for climate action, when the truth about the failure of Kyoto's admitted as circumstances will oblige, we may experience public withdrawal of trust and consent for action whatever form it takes. Kyoto's supporters often blame non signatory governments, especially the United States and Australia for its vows, but the Kyoto protocol was always the wrong tool for the nature of the job. Kyoto was constructed by quickly borrowing from past treaty regimes dealing with stratospheric ozone, acid rain from sulphur emissions, and nuclear bombs. Drawing on those plausible, but partial analogies Kyoto's architects assumed that climate change would be best attacked directly through global emissions controls, treating tons of carbon dioxide like stockpiles of nuclear weapons to be reduced via targets and timetables. Kyoto relied on firing a silver bullet. The top down creation of a global carbon market, but there is little sign of any stable global carbon price emerging for the next decade or so and certainly not with a price signal strong enough to drive innovation. In the final analysis, carbon's trade cannot deliver the escape velocity required to get investment in technological innovation into orbit in time. That calls as we do for putting investment in decarbonised energy technologies on a wartime footing. Otherwise, they will not be available in time to disrupt the impending cycle of new investment in carbon intensive infrastructure and present cause, we are all about to be hit by a tidal wave of coal, especially in China, but a new Apollo or Manhattan project is only one of the necessary principles. No single shot can work on a complex open system issue like this. What we need is not a silver bullet, but silver buckshot. What Bali needs is a portfolio of approaches to move us in the right direction of which decarbonising the energy cycle is only one.

Adam Rutherford: That was Gwyn Prins from the London School of Economics on The Podium. He and Oxford University's Steve Rayner elaborate on these opinions in this week's Nature. That article is available in our website along with all of the papers featured on every show.


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Kerri Smith: Now, we are often told to look on the bright side of life and now a team of researchers from New York University have pinpointed the regions of the brain that make us optimistic. Not only could this help us understand what makes humans predisposed to be optimistic about the future, but it could also have implications for depression, which is related to pessimism. I spoke to author Elizabeth Phelps and asked her about the so-called optimism bias. Nature advance online publication 24 October 2007

Elizabeth Phelps: There is perhaps good reason to be optimistic. If we think about the future it helps to imagine at least a little bit of positive future keeps in a better mood it is adaptive in a way. You should not be too optimistic because then you will not do preventative things that are important, but if you are not optimistic at all the truth is you know things can get kind of glum out there.

Kerri Smith: So, there are evolutionary reasons then why we have this so-called optimism bias.

Elizabeth Phelps: It is hard to say. I do not really know why we have an optimism bias. It has been established for a number of years, however. Psychologists have known about this. It is really kind of interesting and surprising. When you ask, if you take a group of undergraduates for instance, I did this the other day in my introduction to psychology class. I said, how many of you think you will get divorced and we all know about 50% of the people get divorced assuming most people end up in a mirage-like relationship and you get maybe 3 or 4 out of 200. Now, that is just not the odds, right, but people do not think that bad things are going to happen to them.

Kerri Smith: Now, you have looked at the brain mechanisms mediating this optimism bias, what did you have your volunteers do so that you could study how optimistic or otherwise they were?

Elizabeth Phelps: We really were interested initially not necessarily an optimism per se, but we were interested in what happens in the brain when you are projecting and imagining your future. So, there have been a number of studies recently that have suggested that when we imagine the future really what we are doing is drawing on our memories from the past. So, the circuit of brain region that seems to be involved both in remembering the past and in imagining the future. So, we were not interested so much in optimism per se. We were interested in the idea that the emotion can influence your memories of the past, so how might emotion influence your ability to project into the future. One of the things that happened, however, when we started to pilot this study is that it was very hard to get people to imagine non-emotional or negative events into the future. We would take something like getting a haircut and instead of individual say well you know I went to the barber and I got a haircut and it cost me ten bucks and they imagine something like that, they would say I got this haircut, all my friends loved it, I then went out and I met great, they loved my hair and you know it became this highly emotional thing and so people tended to take even neutral events and make them positive events. So, we then had to change our events. So, we actually had more negative events than positive events just to get people to generate an equal number of negative and positive events and we also measured up with a standard scale how optimistic people are. So, when we did that we then were able to contrast what happens now when you are imagining in the future positive events and negative events versus say remembering positive events and negative events.

Kerri Smith: Now, the key areas that you have found are involved in this bias were the amygdala and the rostral anterior cingulate cortex, tell me a little bit about those regions.

Elizabeth Phelps: The amygdala is the region that we know is important in remembering emotional events from the past. So, it is not perhaps surprising it is also important in taking old memories and reconstructing them and projecting future emotional events. The rostral anterior cingulate, this is the only region of the brain that correlated with how optimistic you were across individuals. So, the more optimistic people showed more activity in the rostral anterior cingulate when imagining future events and they were more likely to say that future events were sort of, experienced as they imagine them and happen closer in time. This is the region that we know is important in a lot of functions that help you in regulating emotions in turning negative events into positive events. When you are in a positive mindset you will see more activity in this region. When you are trying to overcome a negative fear you will see more activity in this region. So, we think this is sort of a general regulatory region that may be mediating this tendency we have to think about things optimistically in the future. And what is particularly interesting about this region, both the rostral anterior cingulate and the amygdala is that both of these regions we know are regions that show differences in baseline activity and depression. Now, depression is something that you know, leads to a pessimism bias, like people who are depressed have either more, actually realistic based on the data are actually pessimistic views of the future. So, we do not really know, you know, how much this lack of an optimism bias may be linked to depression per se, but it is interesting it is the same brain regions that involved in depression are also those that seem to mediate this optimism bias.

Kerri Smith: New York University' Elizabeth Phelps. You can hear more on this and other neuroscience research in our special brain science podcast: Neuropod just go to to listen or subscribe for free.

Adam Rutherford: That is it for the Nature Podcast this week. Send us an email if you have got any feedback. The address is This week's sound of science is eight light minutes old. It is the sound of the sun i.e., solar oscillations translated into audio for earthlings as recorded by Alexander Kosovichev from Stanford University. Better set up the base for this one, I am Adam Rutherford.

Kerri Smith: And I am Kerri Smith. This is the Nature Podcast. Thanks for listening.[Sound of science]


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