Here’s an embarrassing confession: when I was eight, the cartoon Attack of the Killer Tomatoes gave me nightmares. Seriously, what could be scarier than giant mutant tomatoes with teeth? (Don’t answer that.)
I’ve been thinking about these killer tomatoes a lot recently in the context of GMOs. Genetically modified organisms probably do seem about as unnatural and just as frightening (if less overt) as these tomatoes. It is scientists playing God. It is taking genes from one organism and sticking them into another. It is definitely unnatural.
But is it significantly more unnatural than other things we do to food plants?
I wanted to talk about some of the other weird s*** humans do to plants in this post, because I think there are a lot of misconceptions about how we develop crops. Unless you survive strictly off foraging, we all eat mutant plants every day. (That is, if you eat fruits and vegetables, which I hope you do.) Virtually all of our food plants are mutants, clones, or freaks, and about as far from their natural state as they can get through intense human meddling. Here are a handful of the ways we grow and eat mutants.
Plants don’t evolve to be edible. (Quite the opposite, generally.) Many, in their unmodified state, are toxic, unproductive, hard to get, or just plain unappetizing. If you take a look at the wild ancestors of things like corn or tomatoes, you will almost certainly come to the conclusion that our ancestors must have been damn hungry to eat that. Corn is a great example. It started off as a wild grass with 5-10 extremely hard kernels per spike. Now, we don’t know the whole story, but we guess that when our ancestors found a mutant plant with softer kernels, they saved them to grow more mutant corn plants, maybe bred them with each other. This particular mutation is bad for the plant (soft kernels = seeds are all eaten by predators), but good for humans. Lots of crosses and some more chance mutations later, we have corn. Mutations, which are the raw material of genetic diversity — and which result in novel proteins — still happen. So does cross-breeding. Kevin Folta, a plant geneticist at the University of Florida, estimates that between 10,000 and 300,000 genes are affected when we breed plants the traditional way. We definitely don’t eat what our ancestors ate, and in a lot of ways, that’s a good thing.
Making Mutants (MOARRR MUTANTS!)
Right. So mutation is the rough material of genetic diversity, but we can’t control where and what kind of mutations will occur in nature. If we’re trying to get a new a trait into a plant, we can a) damage its DNA through chemicals or radiation and hope that some of the resulting mutants will have good traits; b) insert the gene in through genetic engineering; or c) try to get it through traditional breeding. Believe it or not, we’ve been using the first (mutagenesis) for the past 80 years. Wiki notes that, between 1930-2007, more than 2540 mutagenic plant varieties have been released. These mutants are fairly common in our food supply and include varieties of grapefruit, pear, sweet potato, rice, peppermint, citrus, and yam. No label required. Yay for DNA damage!
Attack of the Clones
Not to take down a childhood hero or anything, but Johnny Appleseed probably left behind a lot of apple trees that produced gnarly inedible apples. Apples don’t breed true from seed (since they are not self-pollinated, a Golden Delicious tree will only pass on half its genetic data to its seeds), so in order to get an orchard growing, all the same type of apple, you need clones. Every Honeycrisp apple tree in the world is genetically identical.
One of the really weird things we do in order to clone trees is to take a branch, cut a slice in an existing, related plant, and bind them up until they grow together. This is an age old technique known as grafting. You can end up with at tree that bears several types of fruit! They’re called ‘fruit salad trees.‘ In the photo, you can still see where one tree started and the other left off, yet they’re part of the same tree. Sort of. These guys are the real frankentrees, in my opinion.
Would you be insulted if I called you a diploid? I’m one, too. So is your mother. So is my cat. It just means that we have two copies of each of our chromosomes (23 pairs in humans, for a total of 46 — get this, the adder’s tongue fern has 1440!). Some organisms have just one copy of each chromosome, like bacteria, where others can have four, six, or even more. When something has more than two copies of each chromosome, it’s a polyploid.
Humans have figured out how to induce polyploidy in plants by treating them with a certain chemical (colchicine). We’re not just adding a couple of genes — we’re adding a whole extra genome. (You’ll remember that even one extra copy of one chromosome in humans — 3 copies of chromosome 21 — causes Down syndrome.) And in fact, polyploidy is how we get things like seedless watermelon and seedless bananas. (I know, right? A seeded banana??) First we treat them to get tetraploid plants, which are crossed with regular diploid plants to produce sterile (seedless) offspring. Think about that the next time you eat a banana without spitting out seeds.
Bottom line: humans do lots of weird things to plants, most of which have the potential to result in harmful, toxic, or allergenic foods. We don’t have long term safety tests for most of the foods we eat, including things like hot dogs, goji berries, and root beer (one component, natural sassafras flavor, was found to be carcinogenic fairly recently). Given that almost all of these techniques (except cloning, of course), result in much greater genetic changes than genetic engineering, I think it makes sense to be, if anything, more worried about mutagenesis and polypoidy than genetic engineering.
…Or, if you’re lazy and have a family history of heart disease and cancer anyway, you could be like me and eat lots of fruits and veggies and not worry too much about the other stuff. Just an option.
On a side note, I’m back in school, and my brain is inundated — and I mean polyatomic ions are coming out my ears — with chemistry and biology at the moment. I’m hoping to pursue a graduate degree in botany or plant bio once I’ve beefed up my wussy language arts background. Having this blog has made me realize that it’s time to get out of my house and brain and start doing something about the many problems we face. It’s starting not to be enough for me to sit behind my computer and fret over the miniscule impact of forgetting to bring my reusable bulk bin bags. I want to be doing something. I’m not an activist — I don’t like ideology or emotions — so science it is. I hope you’ll wish me luck and forgive me my erratic postings in the months to come. Peace.