The Secret Life of Seeds

Most of us enjoy snapping pictures using the camera on our phones, and although the quality can be good, it could be better and that’s because the lens of the camera is made out of molded plastic rather than the optically superior glass. This is because, although glass was first made around 5000 years ago, no techniques have existed to mould glass in the same way that can for plastic. This makes manufacturing more costly. Traditionally glass is made out of sand - or silica - particles that are melted together at extremely high temperatures and then blown, ground, or etched into the right shapes. But now Frederik Kotz at the University of Freiburg has developed a technology to make glass mouldable, potentially solving the problem, as he told Eva Higginbotham...

Frederik - At the moment there are a lot of components which are made out of plastics, which we actually want to have made out of glasses. But at the moment, we don't have the possibility to shape these components in glasses at a compatible cost. We developed a novel method which now allows us to shape glass like classical plastic injection moulding.

Eva - What is injection moulding?

Frederik - You basically use a plastic - you melt it and you inject it into a mould. And the nice thing is that this process is extremely fast and can produce a lot of components at once.

Eva - How have you managed to make this new technology?

Frederik - We developed new materials, which we termed Glassomer - it's a mixed word of glass and polymer, which is something like a plastic. And these materials basically consist of a very high amount of glass powder within a plastic binder. You can still shape these materials like a classical plastic. After the shaping process, we put these components into an oven and convert them to real glass.

Eva - So is it like you have essentially a plastic goo that contains bits of sand?

Frederik - Exactly. It's basically like a plastic glue, which holds together this really high amount of sand glass particles.

Eva - The glass that you get out of it at the end, is it the same as just regular glass?

Frederik - Yeah. What you get in the end is a hundred percent class. It's really a pure glass, which you maybe know the glass fibres which we use for a high-speed internet. These types of glasses you can fabricate with this process.

Eva - What's the benefit here? Because we've designed all of these machines and we've designed various different products to use plastic. Why should we ever really want to use more glass?

Frederik - Glass has some very unique properties which are superior in many aspects. Optical transparency, thermal and chemical resistance - these glasses can be heated up to a few hundred degrees and nothing will happen. The mechanical stability is also higher. There's a reason why a car windshield is always made out of glass and not out of plastic because a plastic window would basically scratch over time.

Eva - And what about the environmental consequences of your technique? Is it better than normal glass?

Frederik - It is better. The huge advantage is that we don't melt the glass, we use a process which is called sintering, which is basically working at temperatures way below the melting temperature. So the temperature is really reduced. And we put a lot of effort also in designing this plastic binder that you can regain during this process - a really high amount of this material - and can reuse it multiple times.

Eva - Is this going to be much more expensive than making something out of plastic, like we've already organised the world to be able to do, or more expensive than making regular glass?

Frederik - In terms of making glass it's actually cheaper, especially if you look into more complex glass components. If you have multiple of these so-called etching processes then you need really big clean room facilities, high-tech etching machinery, and this makes the glass extremely expensive. Glass as itself is a super cheap material, it's even cheaper than many plastics which are out there.

Eva - What sorts of applications do you think this new material might have?

Frederik - So we see a lot of applications in different fields from optics, like camera modules, to data communication, coupling elements for glass fibres, to the pharmaceutical sector, vials for vaccines, which need to be stored at low temperatures where you need the thermal stability.

To the animal kingdom now and some interesting insights into why mountain gorillas do that thing they’re most famous for. Katie Haylor reports...

Katie - In the forests of Uganda, Rwanda and the Democratic Republic of Congo mountain gorillas beat their chests. But why? This could all be about saying, "Hey, look how big I am." According to a paper out this week in Nature Scientific Reports, by measuring the size of male mountain gorillas and recording the sounds of their chest beats, scientist Edward Wright and colleagues found ...

Edward - Larger males produce chest beats with lower frequencies than smaller males.

Katie - In other words, the larger gorillas emitted lower sounding chest beat and the smaller gorillas made a higher sounding chest beat. The team first had to measure how big the gorillas were, which can't be easy as for obvious reasons you can't really get that close.

Edward - So we use what we call the parallel laser technique. So we project two small green parallel lasers onto the gorilla, and they're separated by a known distance. And then we take a photograph with these two lasers in the photograph, which is then used as a scale to measure several different body parts of interest. And we also take care not to shine the lasers in their eyes. So we're usually taking photographs from behind the gorilla or from the side, but never from the front.

Katie - Using the parallel laser technique, the team managed to figure out the distance across the shoulders of 25 males. Then it's a question of recording the chest beats - which Edward says the gorillas don't do all that often, and you don't necessarily know when they're going to do it. So they ended up with recordings from six of the 25 gorillas.

Edward - Sometimes you can predict when they're going to do chest beats. Sometimes they hoot before they chest beat.

[gorilla hooting and then chest beating sfx]

Edward - We're not really sure what the function of the hooting is, but perhaps it inflates their lungs with air. And so when a gorilla starts to hoot, okay, maybe in the next few seconds or few minutes they may chest beat. Other times they just chest beat out of the blue. And so it's quite difficult to be at the right time at the right place.

So we put this together in a statistical model, controlling for several other variables like age. And then we found that larger individuals chest beated at lower frequencies than smaller individuals. And this was a robust, significant relationship.

Katie - Curiously, Edward isn't sure exactly why larger males have a lower chest beat.

Edward - It could be the volume of the lungs, hand size, and those two probably correlate with each other anyway. Gorillas also have laryngeal air sacs - big spaces inside the chest cavity. So we think that larger individuals may have larger laryngeal air sacs, which could also be influencing the frequency of the chest beat. But we're not exactly sure if it's a combination of those features or if it's just one.

Katie - Now it's not only males that do this chest beating, but it is more common in male adults than in females or younger ones.

Edward - The main goal I think is to advertise how strong they are. If you're another male and you hear a chest beat and you're able to determine or assess their competitive ability, that's really useful because then you might decide, "He's much bigger than me. I'm not going to pick a fight with him because I'm likely to lose." If you're a female and you hear a big strong male chest beat, "Ooh, that might be a good male for me to mate with." So I think it's definitely involved in male-male competition and female choice.

Katie - But what if you're a smaller male gorilla? Is it dangerous to lay your cards on the table and let others around you know how big or small you are?

Edward - One of the roles of chest beating is to maybe resolve conflicts before you get physical contact and aggression. Physical contact can be extremely fierce. And so it's very risky even for the larger male. The chest beat sort of acts as a, "Okay, you're bigger, I'm smaller. I'm going to let you have this one." But if you're bigger, you're going to say, "No, I'm going to take what I want. Because if we really did come to a fight, I'm very likely to win." So perhaps individuals only really fight when the size difference, so the fighting ability, is quite similar.

An extraordinary feature of seeds is that they can remain viable for long periods of time, which means they can wait until the time’s just right to emerge and grow. This also means that we can store them in facilities called “seed banks” to capture and preserve the genetic diversity that exists in nature. Noam Chayut manages just such a seed collection at the John Innes Centre in Norwich, and spoke with Chris Smith...

Noam - Our seed bank - or gene bank as we prefer to call it usually - is just a very big room, about 600 cubic metres of stable cold environment. It's only four degrees and very dry. So the main thing with preserving longevity of seeds is that dryness, we keep our seeds in envelopes made of paper so the air can flow through them and maintain the humidity very low, below 10% of relative humidity.

Chris - So a person walking through a seed bank would just see rows and rows basically of neat envelopes containing seeds of different species of plants?

Noam - Yes. So some gene banks would hold big freezers because you can also freeze seeds. Ours would just be a very big room of shelves with brown envelopes of seeds in fact, yes.

Chris - And how do you choose the seeds?

Noam - So we have in our custodianship over 45,000 different kinds of diversity of strategic UK crops, that's mainly wheat, barley, oats, peas, and some brassicas. And from each of them, we have many, many, many thousands of different kinds, different cultivars, different wild relatives of them that can be used in plant science and in breeding.

Chris - Have you got a sort of a database on each of the collections of seeds? So you can say, well, this one looks like this, and there's a photo of the plant and what its traits are, perhaps its DNA sequence to go with. Is that how you process them?

Noam - Yeah. So the other side of a gene bank is the databases. And it is just as important as the seeds, of course. Because we need to choose them for a project or for any purpose. So we have a database called Seed Store in our case that contains exactly that information, as you mentioned.

Chris - And the nuts and bolts of actually getting the seed samples into the seed bank in the first place? Is that as laborious as it sounds, someone goes out with that envelope and just shakes a flower head and gets some seeds! And then what do they do with them?

Noam - So, yes many of the seeds sourced in expeditions around the world to collect wild diversity or traditional cultivars, some of our collections are very important because they were collected about a hundred years ago just before the industrial agriculture kicked in to generate more uniformed varieties that are grown today. And the diversity that is kept in this collection enabled a lot of the work that we are doing in the study of plant science and improving crops.

Chris - And how do you know, if you take some of those seeds from a hundred years ago, that A) they're viable and B) that we're not ending up changing them by storing them?

Noam - It's a very good question because evolution never stops. And it continues when we grow them in agriculture. And also when we grow them for gene banking purposes. We do regenerate them or rejuvenate the collection every two or three decades, or when they are depleted in term of stocks. We have ways to prolong their longevity, but we can't stop the deterioration. So in the end, the only way to check if a seed is viable is to put it in soil, water it and get the plant. But we have measures to protect it from gene flow from others. So we try to protect it as unique as it was.

Chris - You mean, so that when it's growing in the greenhouse, for example, there isn't the accidental pollination by a more modern species or another species that could introduce foreign DNA in there.

Noam - Exactly that. So we separate the flowers in some crops. In others we separate the whole plant. Exactly.

Chris - Can you get all of them to grow? Are there any that you end up storing and then you discover they just don't store and they won't grow?

Noam - So the science of conservation is relatively new. It's only half a century and there is not a lot of empiric information. We have a lot of theory that helps us to predict how long a seed would preserve themselves in certain conditions from different species of different kinds of seeds. But in the end, it's our responsibility as custodians of the collection to quality check them every so often, to make sure that they are viable and if not to rejuvenate them and maintain them viable for usage.

Chris - And while it's wonderful to have this, what are you actually going to do with it? What's its broader function in the long term?

Noam - So there is kind of a notion in the public about seed banks that they are there for a kind of a doomsday scenario to restore lost things. And that's a minor part of it. But we are - our bread and butter work - we are part of the chain that brings bread to the supermarkets and other crops to our shelves. We produce diversity, the raw material for plant breeders to improve crops and diversity that underpins plant science. And we do it daily. We send hundreds of samples yearly to end users.

Chris - Later on in the program, we're going to talk to somebody who has actually grown a date from a 2000-year-old preserved date stone. I bet you haven't got a seed as old as that!

Noam - No, no, our seeds are much younger and they date some decades back, as crops can do. But this is a famous and very exciting story in the field, absolutely.

Germination is when a seed wakes up and starts to grow, and when this happens is a life and death decision on the part of the plant: start growing in the middle of winter, and the frost could kill you; burst into life when it’s too dry and you’ll never make it either. As a result, seeds are constantly sensing their environments to figure out when it’s time to make their move. Shelley Lumba, from the University of Toronto in Canada, works on how they do this, and spoke with Chris Smith...

Shelley - Yeah, it's a great question Chris. As humans, we don't get to decide when to be born. We're fixed at 40 weeks of gestation, and we have to come out. Plants, on the other hand, have evolved this amazing seed; they're basically freeze dried embryos suspended in gelatin. And that means they can be preserved, or as you said, increase their longevity for a long period of time. And upon sensing the right conditions - like springtime - and their immediate environment, they can make this life and death decision - whether or not to start their life cycle. And the way they do that is they integrate all this information inside the seed, and they form what I think is a 'germination code' to determine - is this really the right time or not? When they start to wake up, the cellular processes start becoming active, and they make the committed step for the embryo or the seedling to come out of the seed coat and start to grow.

Chris - So are they almost like chemical detectors on a seed then, and thermal detectors, that it can use to work out, is it warm enough? Is it warm enough for long enough? Because obviously we have warm days in the middle of winter, don't they, and it would be awful if the seeds shot their bolt too soon. What are they actually doing in order to detect these messages coming in from the environment?

Shelley - Yes, that's right. So they have to take into account long term cues about, for example, seasonality. Plants can sense that winter's occurred, and they do that through the right type of sensors. So they can sense, for example, light through photoreceptors; they can also sense temperature, although that mechanism isn't very well known; and they can figure out through light, proper day length, and temperature, that for example it's spring! It's time to start growing. And within short term cues, they also take into account their immediate environment, such as moisture and nutrients. And again, they have sensors around their seed coat to sense all of those particular environmental cues.

Chris - Because some seeds even 'know' when there's been a forest fire, don't they? Because they know, "now's the time to grow, all of the competition's been blitzed by the fire. If I grow now - lots of sunlight, and I'm going to succeed."

Shelley - That's right. There are these very unusual plant species, and there's definitely an alternative germination behaviour, and they're called 'fire chasing' or 'fire follower' species. And the way they start their life cycle is after a forest fire, and just as you said, because they want to take advantage of this extreme environment and start growing very quickly. And what they use as germination triggers are small molecules called karrikins, and karrikins are actually produced after the forest fire has burnt through the plant matter. So fire-chasing plants can sense the karrikin, and that's what they use to trigger their germination rather than the typical environmental cues that normal plants would generally use.

Chris - Do any seeds eavesdrop on what other seeds are doing? Because we know that plants talk to each other chemically, so they know for instance when their neighbours are being eaten by something, and they send out danger signals and that helps them to weaponise themselves with various repellents and so on. Do the seeds do this at all as well? So if they know, "right, everybody's germinating now, now's a good time to go," and then they follow the crowd?

Shelley - That's right. Unfortunately this is the adverse effect of these small molecules in soil. There's a very devastating parasitic plant which is called witchweed - its formal name is Striga hermonthica - and it's a terrible plant pest in Sub-Saharan Africa. It's a parasite, a plant parasite, that can attack crops like maize, sorghum, millet. And the way that they've evolved their lifestyle, to start their life cycle, is to sense a chemical that's actually being exuded by host crops in the soil. So they eavesdrop, and then that makes them realise that there's a host nearby, and that triggers their germination. And of course that means they start to grow towards the host crop, start to take the nutrients, water, and the assimilates from that host. And obviously that's not good in terms of the yield for the farmer. It's causing huge losses for subsistence farmers in Sub-Saharan Africa, and so it's obviously a huge problem. And the more we understand about the germination of the witchweed, the more we'll be able to develop strategies to decrease their infestations.

Chris - So that parasite physically wires itself into the host crop and steals what it's making?

Shelley - That's correct, Chris. Since they're also a plant, what they can actually do is connect through the vascular tissue to the host crop. And that's how they're able to suck all the water, and the nutrients, and the assimilates that it needs to start growing by itself. It's an obligate parasite, so they actually can't live without a host.

Chris - So can't you just wipe them out by just decimating a field with some really nasty weed killer for a season, and then leave the soil fallow, and then that'll be it?

Shelley - Unfortunately once they've gotten hold of a farmer's field, they've deposited millions of seeds into that field, and they're the size and colour of dust. So once they've actually come out of the soil, it's in some sense way too late because they've already done their damage.

Shelley - And so the way that people have been developing strategies, is to force them to germinate without a host nearby. This strategy is called suicide germination, because we know what compounds they use to trigger their own germination, what we've been working on, and other groups, are to develop compounds that they can sense, that also trigger their germination, but there's no host. So within five days, if they germinate without the host, you're going to die. So that's one of the strategies that we're actually trying to develop to try to mitigate striga infestations.

Chris - And are you using the same learning, not just to deal with witchweed, which sounds like a nightmare, but also with crops we do want to control and optimise germination for? Because presumably if you understand what these triggers are, how seeds integrate these signals and then kickstart the cells in the seed into life, can you take that same learning and use it to control things that we do want to grow, and when they grow?

Shelley - That's a great question, Chris. And that's definitely one of my missions in life. I want to be able to use the knowledge that we know about how seeds decide to make this life and death choice to germinate, and able to  positively affect agriculture. And one of the major issues for agriculture is to make sure that the seeds germinate at the same time, and pretty much when you actually want to start your growing season and the knowledge that we use, for example, from the small molecules, I think could have huge applications in making sure that the seeds germinate when we want them to, because obviously they can't germinate too early. That's also bad news and they have to germinate simultaneously so that they all grow uniformly. And it's much easier to grow them and harvest the crop.