Purple tomatoes!

As I write this, I munch on organic blue corn chips and homemade pico de gallo, made with purple peppers from Small Potatoes Farm (along with heirloom tomatoes and flat leaf Italian parsley and with a glass of local wine from Summerset Winery, yum!). Why choose blue and purple? Anthocyanins, of course. These natural plant compounds are nice to look at, and there is a lot of evidence that they have protecting health qualities for those who eat them, protecting us from diseases like cancer, diabetes, and obesity. So, what do we do to make sure that people can get recommended amounts of anthocyanins?

Anthocyanin-rich berries are delicious but expensive and only available during certain times of year. Most people do not seek out red cabbage or brightly colored heirloom varieties of veggies like carrots and cauliflower. In the US, the most frequently eaten vegetables are potatoes, lettuce, and tomatoes. Purple tomatoes exist, but heirloom tomatoes have issues like splitting and little time till spoilage. This is fine if you buy them at the farmer’s market and eat them the next day, but is not suitable for things like pasta sauce production (cans and bottles are where most people get their RDA of tomatoes, but it turns out they are healthier that way!). Varieties like Cherokee purple, while awesome, don’t produce anthocyanins throughout the fruit.

One option would be to develop tomatoes with high concentrations of anthocyanins. The trait could be bred into varieties that have more of the characteristics needed for processing into pastes and such (although I’m personally looking forward to purple cherry tomatoes, as in the photo). A collaboration of researchers in Europe has done it.

Could this GMO be accepted by people looking for healthier foods? It’s possible, but likely depends on marketing. Some people are simply afraid of anything new, from purple cauliflower (a heirloom variety) to Grapples (infused with grape juice in a dissapointingly boring way). Ah well. For the rest of us, though, purple tomatoes could be an interesting addition to our diets.

As Cathie Martin, the lead researcher, said: this is “certainly the first example of a GMO with a trait that really offers a potential benefit for all consumers.” The health benefits need to be verified in humans, but results look good so far. “In a pilot test, the lifespan of cancer-susceptible mice was significantly extended when their diet was supplemented with the purple tomatoes compared to supplementation with normal red tomatoes (SD).”

Will people be more willing to look into what GM really means when it has potential to benefit them directly? Will they even care how the tomatoes were made if benefits can be shown? This particular GMO transcends a lot of the issues associated with ones currently on the market.

Labeling isn’t as much of an issue when the trait is obvious, and these tomatoes will likely be proudly labeled due to their health benefits. Gene flow isn’t an issue because pollen spread in tomatoes doesn’t seem to be a problem, the trait can be eliminated from fields by sight, and will be of no advantage to wild relatives. The trait could be used with equal benefit in any farming strategy, organic or conventional, large or small, and will have no effect on natural ecosystems (except maybe preventing cancer in herbivores). The only issue left (please remind me if I’ve left any out!) is seed cost due to licensing. However, we must consider that all seed has a cost (simply Google purple tomato seeds to find prices – up to $4 for 20 seeds!), especially for hybrids.

I have to admit to surprise that this research was done in Europe – a collaboration of scientists from the UK, Italy, Germany, and the Netherlands. I’m happy that the research was able to bear fruit before anyone burnt down their lab.

Ok, back to the science.

First, the paper was really easy to read. I think a layperson wouldn’t have too hard of a time reading most it, given a glossary of genetics jargon. Of course, I could be totally wrong on that. Let me know what you think!

The results were achieved by expressing two interacting transcription factors from snapdragons (one of my favorite flowers) that in turn affect expression levels of genes in the anthocyanin pathway. I have to wonder why they ended up using snapdragon genes. You’d think there would be similar transcription factors in tomatoes.

The authors did thoroughly document an entire list of unsuccessful attempts at improving anthocyanins in tomatoes, both by themselves and other labs, including altering expression levels of transcription factors in related pathways and traditional breeding with wild tomatoes, so it seems unlikely that they would overlook a traditional breeding or cisgenic approach in favor of genetic engineering, if the other methods would accomplish their goals.

Although, they did use a cauliflower mosaic virus terminator (stop signal – has nothing to do with the so-called “terminator gene”).  They used a fruit specific promoter, so why not just use the terminator from that gene?

I am very glad that they chose a fruit specific promoter, though. There is no reason to tax the plant’s resources by producing anthocyanins in the leaves and other non-edible parts, unless there is some advantage to expressing them in these parts, such as pest deterrence.

I’m not convinced that they couldn’t do achieve this result with an entirely cisgenic gene construct, but I’m  a particularly big fan of cisgenics. All in all, this seems like a beautiful use of genetic engineering to achieve a result that is important to consumers that could theoretically be achieved by decades of breeding (although it hasn’t yet!). I hope people are able to look past the scary GMO label.

Eugenio Butelli, Lucilla Titta, Marco Giorgio, Hans-Peter Mock, Andrea Matros, Silke Peterek, Elio G W M Schijlen, Robert D Hall, Arnaud G Bovy, Jie Luo, Cathie Martin (2008). Enrichment of tomato fruit with health-promoting anthocyanins by expression of select transcription factors Nature Biotechnology DOI: 10.1038/nbt.1506


  1. I was particularly impressed by the data from the mouse study showing cancer prone mice lived 30% longer with these tomatoes. For a human that could translate into a couple of decades.

    I don’t suppose you have any idea if the purple carrots or the purple cauliflower you mention contain similar levels of anthocyanins to these tomatoes?

  2. Are there p53-knockout humans? Maybe anthocyanins could indeed help those with inherited predispositions to certain cancers to live longer. But I’d also like to see the effect on the lifespan of normal (as far as that goes!) lab mice.

  3. Yeah the mice they tested the tomatoes on were prone to cancer, but what this certainly demonstrates are the cancer-protective effects of the anthocyanins in these tomatoes. But it could certainly translate into delaying the onset of cancer, the question is by how much, and how long would it take to know the answer to that question? Definitely a great piece of research, though.

  4. I’ll do some searching to see if I can find details on anthocyanin levels across different purple plant foods.

    Karl, I agree that the feeding study was nicely designed to test the effects of additional anthocyanins on lifespan and cancer. It looks like the researchers fed completely equivalent diets to both groups of mice except for one contained the genetically engineered tomato powder and the other contained powder from a near-isogenic line.

    One thing that frustrates me about the blogosphere or web-readers in general is that they don’t seem to understand that most people can’t all afford blueberries every day. These tomatoes could help decrease cancer rates in everyday people for zero additional cost to the consumer (depending on how the researchers decide to license their product). Considering that the cost to the environment is also zero, how could this possibly be a bad thing?

  5. Because GMOs are EEEEVIILLLL!

    I have noticed that a sizable contingent of people who are actively concerned with food, and I don’t mean getting enough food, I mean concerned with little details about their food, seem to have a good deal of disposable income. Some may not notice that privilege and how it affects what they say, while others who are more self-aware would simply argue that those without as much money should just spend much more of their money on food instead.

    I don’t know if it would be no additional cost to the consumer, at least at first. As a specialty item, it is bound to cost more than the average tomato. The question is by how much.

    You’re right that on the positive side, no changes are needed in other areas, such as growing, pest and disease issues, etc.

    Actually, here’s a thought. I’ll have to dig up the USDA links, but I wonder how tomatoes and blueberries compare in terms of pesticide and fertilizer use per acre and per pound of produce? Do blueberries give you more or less cancer-preventing antioxidants than these purple tomatoes for the land use and environmental impact? Hmm…

  6. Hello from an independent plant breeder that is indeed concerned about GMO technology, this is from my blog:

    Here are my thoughts on the subject (to be expanded upon shortly)

    I am currently and probably for the foreseeable future anti GMO. My reasoning is thus; too much power in too few hands with too few independent tests searching for actual specific side effects of gene splicing, an art I might add that is not present whatsoever in the record of natural agricultural history as opposed to spontaneous crosses and man made crosses.

    Now don’t get me wrong, I understand there could be merits to this “fast food” version of plant breeding, I get that, but I also know that those who have the power to make such decisions very rarely have positive intentions in mind and instead have money regardless of consequence in mind. For example see any of the following, Monsanto, Big Pharma, Big Box Stores, Big Government.

    The problem I have with this particular “creation” is that there is
    A. No sport in what was done.

    By this I mean that it isn’t like other natural sources of Un-monopolized, anthocyanin producing crops don’t exist. See blueberries, purple carrots, purple flour, flint, and sweet corns, purple peas and so on, which brings me to part B.

    B. A traditionally bred alternative already in the pipeline

    In many ways I can see this hurting Jim Meyers research at OSU. I mean this guy has worked his butt off on the P-20 lines and here somebody just bypasses the work of one of the few remaining land grant schools doing actual plant breeding work without consideration for the novel and appreciable idea that Jim Meyers had. I’m sure the reason that so few land grant schools still exist with plant breeding and experimentation arms is due to the monopolization of agriculture by big business, most recently those dealing in GMO’s and and big PHarma. Couple this with the fact that this new blue tomato will probably be PVP’ed and you’ve just signed the death warrant for the OSU project.

    Now, the reason there is so much opposition by others to GMO’s?

    Probably because very little of any positive developments have come out of this technology since it was first implemented and most likely because they have been lied to so many times by the big companies of the world about what is “safe” and “unsafe” that there is no reason to any longer trust these folks. It’s the boy who cried wolf story if you will.

  7. Alan, you raise quite a few points in your comment that I’d like to respond to, but please bear with me, I am rather swamped at the moment. The first point that I was planning to look into was exactly how much anthocyanins are produced by typical purple crops, how likely people are to eat them, how much you can produce per acre and at what cost. Sort of a cost-benefit analysis, if you will, to decide if something like a purple tomato has a justifiable purpose for the consumer. I hope we can have some great educational discussions about this and other topics 🙂

  8. Someone posted this link on another site today http://www.bbc.co.uk/news/science-environment-25885756 The title is a bit misleading but it got me to dig around as I thought there were already purple tomato seeds on the market. I came here first and was disappointed to find a dead thread. Then I found a link to Oregon State U and info on their nonGM purple tomatoes. Isn’t it much more costly to do a GM version?
    Some of the comments on the other site were remarkable. One very anti-GM person seems to think that ALL GM products contain BT.
    “The prospect of genetically modified purple tomatoes reaching the shelves has come a step closer.
    Developed in Britain, large-scale production is now under way in Canada with the first 1,200 litres of purple tomato juice ready for shipping.
    Scientists say the new tomatoes could improve the nutritional value of everything from ketchup to pizza topping.
    The tomatoes were developed at the John Innes Centre in Norwich where Prof Cathie Martin hopes the first delivery of large quantities of juice will allow researchers to investigate its potential. ”
    Oregon State University has developed NONGMO purple tomatoes with increased anthocyanin, however. From their website:
    “Were genetic engineering techniques used to develop these lines?
    No, conventional crossing and selection techniques are being used. This is perhaps the most misunderstood aspect of this project, and we will say it again: These tomatoes are NOT GMO.”

  9. Yes, there are non-GMO true purple tomatoes available. However, these tomatoes really just turn purple in their skin and only where they are exposed to direct sunlight, and they don’t taste very good. I’ve grown them in my backyard! They’re called Indigo Rose. I have met the breeder who developed them, and we’re going to try to set up a dual interview and Q/A with his group and the group working on the GMO purple tomato to compare, contrast, and explore the possibilities of anthocyanin–producing tomatoes.

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