Cathie Martin - Purple tomatoes

Cathie Martin is using GM technology to make even healthier fruit and veg, including some striking purple tomatoes.
07 February 2015

Interview with 

Cathie Martin, John Innes Centre


Tomatoes on the vine


Kat - While I was in Norwich, I also caught up with Professor Cathie Martin at the John Innes Centre. She describes herself as a metabolic engineer, using GM technology to develop fruit and veg that are even more healthy- including her famous purple tomatoes. I started by asking what exactly is metabolic engineering?

Cathie - So, it's engineering metabolism and I'm very interested in engineering a group of compounds which are called polyphenols, and those are fairly recently recognised to have health promoting effects when you eat them.

Kat - So, this is basically making fruit and veg even more healthy than it was.

Cathie - That's right. I mean, I'm a bit fed up of all of the information that you get about food being things that are bad for you. It's got too much salt, it's got too much saturated fat, etc. So, I think we need to know whether there are any things that are good in foods for us. And all of the evidence suggests that eating fruit and vegetables is very good for you. There are specific compounds in fruit and vegetables than can really reduce the risk of what we call 'chronic disease' like certain cancers, cardiovascular and metabolic disease like type II diabetes.

Kat - In front of us on a table, we've got some beautiful tomatoes, but there's two red tomatoes that look like tomatoes and then there's two yellow tomatoes, and then these 4 black plum-coloured things. What have we got here? Tell me about these?

Cathie - Okay, so this is a control. So, this is a regular tomato, well-spotted, and then this is a tomato that has been metabolically engineered to produce compounds which are called flavonols.

Kat - That's the yellow one here.

Cathie - Yeah, it's the yellow one. And the reason it's yellowish or orangey yellow is because it has high levels of these pale yellow compounds. So, if I was to squash it, you'd see a pale yellow juice which would be more yellow than in this one. And so, it's not because it's got less of the red colour which is lycopene, but it's got more of a pale yellow compound.

Kat - So, it's an extra yellow rather than not red.

Cathie - An extra yellow, yeah and these are things like quercetin and campherol which are good for you. They're good anti-oxidants, but they're also shown to beneficial in the diet.

Kat - What about these purply ones? These are gorgeous.

Cathie - These ones have another compound. It's chemically related to the flavonols but these are anthocyanins. And so, there are pigments in plants. They're the sort of things that make delphinium blue.

Kat - That looks like blackberry colour. These are blackberry coloured tomatoes.

Cathie - Yes and that, it's the same compound that's present in blackberries and all of those super fruits that you've been hearing that are good for you. So now, we've done it in tomatoes. They also have this red lycopene, but you can't really see it because they've got so much anthocyanin and what will make you gasp...

Kat - Okay, we're cutting them open. Wow!

Cathie - Isn't it beautiful?

Kat - It's like a tomato but really beautiful rich, dark purple. Literally, like a tomato, but you're looking at it through a completely purple filter, almost black as night.

Cathie - They really are tomatoes, but they look completely different because they're very rich in these anthocyanins. Actually, this one is rich in both anthocyanins and the flavonols as well and it gives this rather beautiful royal purple. But we've shown experimentally in what we call pre-clinical studies that these can slow down the rate of progression in cancer in animal models of that disease. And also, that they can be protective against arteriosclerosis when they're eaten in their diet.

Kat - But I could get those benefits from eating loads and loads of blackberries.

Cathie - Absolutely, but probably, if you eat loads and loads of blackberries, enough that you'd get say, the equivalent of 2 of these tomatoes would be about 70 grams of blackberries.

Kat - That's a lot of blackberries.

Cathie - It's a lot of blackberries. You wouldn't get them all-year-round and you'd eat them with a lot of sugar which would be a bad thing. So these, you can eat without the sugar.

Kat - Am I allowed to taste one? These are laboratory specimens.

Cathie - I think we'll have to say that they're laboratory specimens. There's a problem if you eat the seeds because we haven't got a regulatory approval and it would be considered an inadvertent environmental release and I'd have to ask personal questions.

Kat - Okay. I don't want to inadvertently release anything into the environment. These tomatoes, they look beautiful, they've got useful compounds. What other kind of traits do you think you could engineer into our fruit and veg that would be beneficial?

Cathie - Well, we've already done some other polyphenols which you may have heard of, something called resveratrol that's present in grape juice and in red wine. We're looking to be able to regulate the production of this red compound here, lycopene. We haven't got  the tools yet to do it, but we're looking to make high lycopene tomatoes or even higher lycopene tomatoes.

Kat - Super tomatoes!

Cathie - Super tomatoes, because lycopene is quite healthy for you and protects against some cardiovascular disease. So, I think that the prospects, the potential is enormous, but we're just at the beginning at the moment.

Kat - How have you made these purple and yellow tomatoes? What's the process you go through to turn a red tomato into a purple tomato?

Cathie - Okay, so the genes that we use to do the engineering are essentially switches and they switch on the production of these compounds in a place where they're not normally made. So, the same compounds will be made by tomatoes in the leaves when they're stressed. And if you ever forget to water your tomato plants, you'll see these purple pigment forming at quite low levels in their leaves. What we've done is be able to switch them on by putting in a gene that serves as a molecular switch to turn on the pathway. So basically, we just moved where a metabolite, a compound is produced from the leaves to the fruit. There are actually some wild species of tomato that makes some anthocyanins in their skin of the fruit, but they don't make it on the inside so they don't have such high levels as these.

Kat - The examples of GM technology that we've talked about seem very beneficial, making our foods healthier and other types of technology, making foods more sustainable or growing with less chemicals and all these kind of things. But there are some people who say that we shouldn't be messing with our food in this way. Are there any risks of this kind of technology?

Cathie - I think that the procedure of genetic modification per se is an established neutral technology. So, that means that people have been using it in the pharmaceutical industry for the past 30, 40 years. Many of our medicines that we get now have been produced through genetic modification of microorganisms. And for modification of crops, the risks in terms of the safety of the food that you produce are only dependent on the trait that you engineer. I believe that it's possible to engineer something that's detrimental. I think that our tomatoes have proven health benefits. So, the technology is neutral. The trait itself has to be examined and regulated. I think that we have good evidence that this is a beneficial trait. For people that don't want GM products, that's okay. You don't have to buy them. But let everybody else have the choice.

Kat - Cathie Martin, from the John Innes Centre in Norwich.


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