National Geographic

Why supermarket tomatoes look great but taste bland

If you’ve ever bitten into a wild tomato, you’ll have enjoyed a sweet, intense explosion of flavour. The tomatoes that line most supermarket shelves are a world apart. They look great – a wall of even, ripe red – but they taste like cardboard. These two facts are related.

Ann Powell from the University of California, Davis has found that farmers have inadvertently ruined the taste of tomatoes by selecting for ones that ripen together and look good. That aesthetic appeal has been driven by a single change in a single gene, which also affects how the fruits taste.

Before they ripen, wild tomatoes are dark green near their stems, and lighter at the bottom. For the past 70 years, tomato breeders have preferred fruits that start off being uniformly light green. They ripen more evenly, which makes them more visually pleasing to consumers, and it’s easier to tell when they’re mature. This trait is governed by a cluster of genes called the “uniform ripening locus” or simply “u”. Powell showed that this region includes at least eight genes, including one called SIGLK2 that affects the tomato’s colour.

SIGLK2 controls the activity of hundreds of other genes. Around half of these are involved in the production of chloroplasts, the small structures in plant cells that allow them to harvest energy from the sun and produce their own food. They are the engines of photosynthesis. They also give plant tissues their colour because they contain the green pigment chlorophyll.

So, wherever SIGLK2 is active, tomatoes are a dark, intense green. In the wild fruits (denoted by a capital U), SIGLK2 is eight times more active near the stem than the bottom, while is why the top half is a darker shade of green.

In the evenly coloured fruits (denoted by a small u), SIGLK2 has picked up a single mutation – a difference in one DNA letter. This tiny change means that the gene encodes a stunted, broken protein. As a result, it doesn’t produce chloroplasts properly, it doesn’t increase levels of chlorophyll, and it doesn’t make the tomatoes any greener. This is why the u-fruits that are favoured by tomato breeders are light green, and evenly so.

But these changes also affect how the tomatoes taste. During photosynthesis, they convert carbon dioxide and water into sugar and oxygen. If you downplay the number of chloroplasts, you reduce the levels of photosynthesis, and you get a plant with less sugar in its tissues. And that’s why supermarket tomatoes aren’t going to hit your palate with the same sweet punch that their wild counterparts pack.

There’s a silver lining to all of this. If Powell stuck a working copy of SIGLK2 from a different plant into a u-tomato, she increased its sugar levels by around 40 per cent. She also boosted its levels of lycopene, the red pigment that affects the colour of ripe tomatoes. Perhaps by manipulating this gene, we can produce a tomato that is still easy to farm at a large scale, while restoring the wonderful tastes of ancestral varieties.

Reference: Powell, Nguyen, Hill, Cheng, Figueroa-Balderas, Aktas, Ashrafi, Pons, Fernandez-Munoz, Vicente, Lopez-Baltazer, Barry, Liu, Chetelat, Granell, Van Deynze, Giovannoni & Bennett. 2012. Uniform ripening Encodes a Golden 2-like Transcription Factor Regulating Tomato Fruit Chloroplast Development. Science http://dx.doi.org/10.1126/science.1222218

Image by Manjith Kainickara

There are 13 Comments. Add Yours.

  1. farmerbrown
    June 29, 2012

    Next, can we work out why Red delicious apples are not delicious? Like tomatoes, they also look nice, but taste like mealy cardboard.

  2. Robert S-R
    June 29, 2012

    And then watch as people label it “genetically modified” and ban it from their stores…

  3. Ron H.
    June 29, 2012

    Tomatoes are also harvested before ripening fully, if at all, to give them better shipping qualities and then exposed to ethylene to bring them to a ripened state. Unfortunately, green tomatoes lack the sugars and, presumably, the nutritional value of vine-ripened varieties. Our family doesn’t eat winter tomatoes anymore, but we can and freeze as many of our garden tomatoes as possible.

  4. Kaviani
    June 29, 2012

    @ farmerbrown – same song, different gene-verse. The average consumer is ridiculously hung up on appearance, so suppliers have accommodated. That’s why you find “irregular” produce priced way cheaper despite having the exact same nutritional value; also why we add pointless dyes to drinks and foods. People are trifling. HOWEVER…apples are notoriously disease prone, so I’m pretty sure resistance is a huge part of why RDs are cloned so readily.

    @ Robert S-R – you can watch me grow them myself. I don’t need your stinkin stores.

  5. ZL ‘Kai’ Burington
    June 29, 2012

    Robert, they should also ban every other domesticated crop. Because humans have been in the business of genetic modification since 10 thousand years ago, at least.

  6. riano
    June 29, 2012

    we must breeding again to reach good taste because this tomatoes we sale now only economic scale production.

  7. Dave
    June 30, 2012

    The second image is by Wikipedia user fir0002 — see page http://en.wikipedia.org/wiki/File:Bright_red_tomato_and_cross_section02.jpg for details on how this should have been acknowledged.

  8. Ed Yong
    June 30, 2012

    Oops! That’s not meant to be there! Unfortunate copy and paste error. Deleted it now!

  9. Monkey
    June 30, 2012

    So, the flip side to this is that there is less sugar in supermarket varieties, making them a healthier choice?!?
    :)

  10. Robert S-R
    July 1, 2012

    @Kaviani and @Kai: I’m with both of you, but I’m just being a cynic. : ) Homegrown for the win. And domestication is an amazing thing, when you look at the processes, lasting thousands of years, that can turn wolves into pup-like adult dogs and tiny cereal grains into juicy sweet corn.

  11. Candice
    July 2, 2012

    Before some of you guys kvetch about GMOs, perhaps you should do some research into Monsanto’s truly evil business of trademarking seeds and suing family farmers (conveniently putting them out of business) who can’t control what pollen drifts into their cornfields; engineers creating chemical-resistant strains which allow farmers to douse fields with increasing amounts of horrible pesticides; how GMO crops were marketed to Indian farmers, who paid exorbitant prices for failed crops, causing people to commit suicide over their losses. Furthermore, the widespread homogenization of crops gleefully invites a modern day blight that will be horrific in scale. Playing with genes in a lab, do you really know what you’re getting? Imagine losing 80-90% of America’s crops. That’s how much soy is GMO in America.

    Yes, humans have been breeding crops for thousands of years. But what’s going on nowadays is totally different. Get educated.

  12. Gopiballava
    July 7, 2012

    Candice: GMOs are not the cause of farmer suicides in India. You can find a number of pieces of research looking in to the causes. There are serious economic problems in Indian farming unrelated to GMOs.

    The courts looked at the Monsanto lawsuits I’ve read about and determined that the farmers were deliberately choosing the GMO containing versions of the seeds.

    Finally, I’m fairly sure you mean that they patent rather than trademark seeds. It’s a rather significant difference.

  13. Aaron
    August 23, 2012

    @Gopiballava: I’d look into what Monsanto gets up to, because many of their practices are totally unacceptable to anyone with any ethics. Terminator seeds for instance are a plight on the world and enslaves farmers to a brand, as well as colluding with 3rd world governments to ban seed collecting (a practice as old as farming) so they’re forced to buy brand seeds.

    Quite frankly I don’t trust GMO because I see what these companies get up to. There is a fairytale of big, tasty, disease resistant vegetables that will grow in harsh conditions. But the reality is James Bond villain esque companies who seem to be intentionally contaminating the food supply with their patented seeds. Suing whichever unlucky sucker’s field their patented products happened to infect, giving the impression they are trying to monopolise the worlds food supply for profit.

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