Tuesday, September 22, 2009

Where seedless watermelons come from.


Autumn crocuses, Colchicum autumnale, are in bloom in several of the beds at Paulik Park. If you took biology in high school or university, Colchicum may ring a bell. This plant was the original source for colchicine, a compound used in cell biology to block spindle formation during cell division, which prevents the contracted chromosomes from segregating, a necessity for daughter cells to receive the correct number of chromosomes.

For this reason it has many medicinal applications, but watermelons are more interesting. If chromosome segregation is inhibited during meiosis, which usually results in four haploid gametes, two of the gametes will be diploid whereas the other two will contain no chromosomes. If two diploid gametes are combined, a tetraploid (twice the normal number of chromosomes) zygote will result. In animals this is usually fatal, but it can be a boon to plant growth and development. Then, if a tetraploid plant is crossed with a diploid plant, triploid offspring (thrice the normal number of chromosomes) will result, which are sterile, but if pollinated with pollen from a diploid plant can create seedless fruits.

Voila. Seedless watermelons.

4 comments:

Seabrooke said...

I always wondered how they made seedless fruits and veggies, though apparently never strongly enough to follow up on it by searching the internet - now you've saved me the trouble. :) It's funny that plants don't seem to mind the extra chromosomes. How come they can develop with additional sets just fine but most animals can't, I wonder? Questions (answers?) beget questions.

Garden Lily said...

Wow, I didn't know. But I remember as a kid that the seedless watermelons didn't have nearly the same taste as their seeded counterparts, and were much more expensive. Now I wish I could buy the old seeded varieties, they don't seem to be sold anymore, at least in the supermarkets where I shop. I bet the flavour would be awesome. And the seeds were not really so bad after all, it was fun spitting them out.

Hugh said...

Seabrooke,

Why polyploid plants are so robust, I dunno either. A question for Quirks & Quarks.

G Lily, Exactly. My children (oldest is 9) have never seen non-seedless watermelons. That's disturbing.

A more sinister side to the seedless trend is that only the agri-giants have seeds. You can't grow your own anymore, and farmers have to keep buying from the seed magnates.

Hugh said...

Seabrooke,

Why polyploid plants are so robust, I dunno either. A question for Quirks & Quarks.

G Lily, Exactly. My children (oldest is 9) have never seen non-seedless watermelons. That's disturbing.

A more sinister side to the seedless trend is that only the agri-giants have seeds. You can't grow your own anymore, and farmers have to keep buying from the seed magnates.