Colchicine and Its Effect On Plant Growth

Polyploidy, in some crop plants occurs naturally but it has been induced by treating plants with chemicals, such as colchicine. 
Using ColchicineDO NOT SOAK THE SEEDS! When seeds are soaked in colchicine, most or all fail to reach maturity due to colchicine’s retarding property on root growth. Soaking seeds was what was done in the 1930’s, with little success. Colchicine use is increasing in scientific literature and I will cite specific studies in this post for readers to follow up on if interested. One thing recent studies have in common is that all applied colchicine on SEEDLINGS, not seeds. Soaking the seeds is like trying to reinvent the wheel. colchicine inhibits root growth, so what most people have done is applied it when seedlings are 4-6 days old.  The colchicine applied on the very tip of the plant (the apical meristem where growth is occurring), as far away from the roots as you can get. This can be done with an eye dropper or you can use a cotton swab. Experimentation is still going on (No one yet knows the best amount to use) so use the scientific method and give plants different amounts/concentrations. You can try mixing a 0.5mg tablet with 50ml, 100ml and 150ml of water. Of course you can try  weaker and stronger strengths. The important thing is to keep accurate records. In the few studies I read, they applied the colchicine at 12, 24 and 48 hrs but this also can be varied.   Even doing this, you will get a lot of mutated seedlings, but some will become polyploid. Also, temperature seemed to be important. Warmer temperatures lead to more mortality. In orchids, when young seedlings are treated in liquid culture with 50 mg/l colchicine, about 50% of the seedlings develop into tetraploids (polyploids with 4 copies of chromosomes). Moreover, when working with a maple tree, Liu et.al. (in Euphytica Volume 157, Issue 1-2 , pp 145-154) had better seedling polyploid production from soaking the seeds (40%), but all the seedlings died due to poor root growth formation.  Many studies just looked at polyploidy, they did not see if the plants could actually mature which is why people keep trying colchicine by soaking seeds.  Liu et al. also applied colchicine to the tips of growing seedlings and a few did become polyploid, and did survive to maturity. So, colchicine is not a magic bullet.
Why use Colchicine - Polyloid plants usually have increased growth, meaning they grow faster, yield more and have many improved or novel traits. (Click here to read more about what polyploid creation can do for plants)  We can look at orchids for examples. Orchids have been breed for a tremendous variety of flower colors, shapes and size. One way to get unique combinations of these characteristics is by creating polyploids. Soaking the seeds in colchicine has been done since the 1930’s. However, when the seeds are soaked many plants do not survive to maturity, many more of the plants are a chimera, meaning only parts are polyploid, some show aneuploidy and other parts have the normal cell number. It was not until the 1980’s when consistent ways to create polyploids were developed. If you are interested in reading the scientific literature check out, Plant Cell, Tissue and Organ Culture 1981, Volume 1, Issue 1, pp 103-107, and their citations.

Keep in mind, even if you do get polyploids, when you have plants with more than the normal number of chromosomes they are not guaranteed to be ‘better’. The benefit comes from having more genes (which are pieces of DNA located on the chromosomes) that make the plant grow well. For example, the normal number of chromosomes is two, one from dad and one from mom. Now, say gene A makes large flowers. If you have a triploid plant, it can have AAA or three copies of that gene. This means the plant will have 1/3 or larger flowers than a normal AA plant. However, it is also possible for the plant to have three genes that make small flowers. Again, the benefit from polyploidy is not in the number of chromosomes, but in the combination of genes, just like F1 hyrbrids usually show a hybrid vigor, this is what you get with polyploidy, (it is termed heterosis). If you have more chromosomes, and you START with two good parents genetically, you should be able to get a good combination of genes in the offspring. Polyploid offspring have more chromosomes so a greater chance of having more combinations of good genes.

A caveat, polyploid plants can result in difficulty breeding/getting offspring. Once you have a created a polyploid plant, you may need to clone the plant to get new plants. A polyploid plant will have many gametes that have the incorrect chromosome number. This abnormal chromosome number, from colchicine has been used to create "seedless" fruit, such as seedless watermelons (Citrullus lanatus). Seeds are babies if you will, so by creating sterile polyploids, they will produce fruit, but not seeds. If you want seeds from your polyploid, you will have to try many times and be lucky.

I have read that colchicine's is toxic, and regulated by the FDA, I don’t know how to get it, or if you should. I have also read it is used to treat gout in humans.  Breeders that use colchicine grow hundreds of plants, because many will be deformed and/or grow poorly if at all. I would not recommend it for the hobby enthusiasts, and I don’t like to use such powerful chemicals on plants I consume.  I will look into how long colchicine stays in plants and other long term effects of colchicine in later posts...

Good Growing,
Dr. E.R. Myers

1 comment:

Anonymous said...

Colchicine degrades in light so it has to be applied in darkness. After seedlings are exposed to light it will eventually breakdown into relatively nontoxic derivatives.