I've been on quite a gardening kick lately, and one of the things I have been growing is tomatoes.  I am growing several different heirloom tomatoes, and none of them want to ripen on the vine.  Either that, or being ripe on the vine is what is attracting all the bunnies to eat them.  In any case, I have to pick them while they are still green.

Well, my last two batches of tomatoes decided that they didn't want to ripen up.  They just wanted to stay green.  Now, I know that Fried Green Tomatoes is a classic southern dish, but that just takes too much work and is too much of a mess.  So, I decided to try drying them.  I just sliced them up, stuck them on a rack with a little salt, and stuck them in the oven @ 225°F for a few hours.  They tasted delicious. There's only one problem - many people think that green tomatoes are poisonous.

This is because they are part of the Solanum genus (nightshades).  Solanums have a type of chemical in them called alkaloids, the most famous of which is probably Solanine.  This substance is neurotoxic to humans.  Many people say that green tomatoes shouldn't be eaten in medium or large quantities because of the large amounts of solanine in them (but ripe, red tomatoes are fine because the solanine gets catabolized during ripening).

So, curious as to whether I was creating a toxic hazard or an edible treat, I decided to do some digging.  What I found was that

1. Most reports of green tomatoes being toxic are entirely based on their being part of Solanum and therefore containing solanine, not on any real case reports of someone getting sick (nearly all examples of someone getting sick that I read about were from potatoes [not tomatoes] that had turned green)
   
2. Technically, in tomatoes, it isn't even solanine, but rather a related compound called tomatine, which is produced.
3. There has been no reports of tomatine causing illnesses, and some reports on tomatine's beneficial properties (including reducing cholesterol)
4. You may even be able to eat the leaves of tomato plants safely
5. Peruvians eat a variety of red tomatoe which has the same tomatine content as green tomatoes, without any apparent ill effects

So, I'm not as worried as I was about my dried green tomatoes, but I'm still not completely convinced they are safe.  If anyone knows anything more, please post in the comments.

But that's not the interesting part.

While I was investigating, I cam across this paper on tomato alkaloids.  On page 5759 (the 9th page of the PDF) it gives this amazingly interesting fact:

Until the recent discovery of dehydrotomatine, it was
thought that tomatoes contain only one glycoalkaloid, usually
called α-tomatine or tomatine. The question arises why each
of the major Solanum plants produced two glycoalkaloids
[potatoes, α-chaconine and α-solanine (106); eggplants, solamargine
and solasonine (115); tomatoes, dehydrotomatine and
α-tomatine].

So to my mind, this brings up several interesting questions:

1. Why are these glycoalkaloids in pairs?
2. More importantly, if we assume that these are from an original created kind, how did each one manage to get a different type of glycoalkaloid, and still get exactly two?
3. Is the usefulness or harmfulness of these substances an intentional part of creation or simply a byproduct of its diversification method?

So, for instance, many of these substances are used medicinally.  Is the wide variety of alkaloids there for the purpose of healing, or is that merely something that we've imposed on them?  Are the ones that are toxic there for the purpose of harming humans, or is that just a byproduct of how the plant's biochemistry evolved?

The wierd thing, which I think may be key to figuring at least some of this out, is that these alkaloids are evolving in pairs.  I think there must be some underlying mutational mechanism which is causing the coordination of the glycoalkaloids.  Thus, with a single mechanism, perhaps both compounds can be changed in a coordinated style, to maintain their synergistic reactions (whatever they are), but yet be modified in a way that is useful either to the plant or to others.  Perhaps the radiation of glycoalkaloids is stochastic - if it were purely stochastic, then this would possibly give weight to the idea that they were _designed_ for medicinal uses, since this would make sure that all (or nearly all) of the potential glycoalkaloids were available somewhere in creation.  If, instead, they were adaptive, then we would probably say that their use to humans is a byproduct and not their reason for existence.

In any case, if I had time, looking into these chemical structures, their gene sequences, and possible mutational mechanisms would make a fun project.  Of course, I may need to wait until the Tomato Genome Project is completed.

I had better stop now and get my last batch of dried green tomatoes out of the oven!

References:

• Friedman, M.  2002.  Tomato Glycoalkaloids: Role in the Plant and in the Diet.  Journal of Agricultural and Food Chemistry 50:5751-5780.
  
• Stimekova and Horsin.  2006.  Determination of Solanine in Tomato Cultivars.  Journal of Food Science 45(2):386-387. [note that I only read the abstract on this one] 
  
• McGee, H.  2009.  Accused, Yes, but Probably Not a Killer.  The New York Times (7/28/2009).