Carrots are certainly bred for flavor, including sweetness so that may be
part of the problem. Both types of starch, amylose and amylopectin
supposedly stain with iodine. Salisbury and Ross's Plant Physiology notes
that amylopectin stains less intensely and is purple to red. Amylose
stains more strongly and is purple or blue. The percentage of amylopectin
varies from 60 to 100% in the species examined.
Did you try grinding the carrot in a blender to be sure the amyloplasts
are ruptured?
Some plants use a fructose polymer, inulin, rather than starch as in
roots of dahlia, dandelion, and chicory and Jerusalem artichoke tubers. I
do not believe carrot roots store inulin, however.
The carrot storage root is often misinterpreted as having a lot of cortex.
In reality the carrot root has lost its cortex and epidermis to secondary
growth. Carrot storage root is mainly secondary phloem that has large
amounts of parenchyma.
*********************************************************************
David R. Hershey
Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1340
Adjunct Professor, Biology/Horticulture Dept.
Prince George's Community College, Largo, MD 20772-2199
Email: dh321 at pgstumail.pg.cc.md.us
*********************************************************************
On 18 Sep 1997, Douglas P. Jensen wrote:
> Hello all,
> I am prepping a lab on roots today, and I had wanted my students to
> stain carrots for starch using I2KI. I assumed there would be amyloplasts
> in the carrot, but the carrot did not stain. I tested it on a potato, which
> turned nearly black immediately, so I know the stain is fine.
> I'm wondering: (1) Is the starch possibly in a form in the carrot
> that iodine will not stain? (2) Are carrots harvested for the grocery store
> BEFORE the sugars are polymerized into starches? If so, is this something
> that carrots are selectivly bred for? Perhaps then if I find a queen anne's
> lace, I could stain its root with positive results. My students sure
> wouldn't mind a trek if the weather cooperates.
> I recall how every so often, I buy carrots and a few or event the
> whole bunch is nasty and woody. I always thought these were second-year
> carrots. Perhaps they are merely harvested too late.
>> Anyone have experience with this?
>> Doug
>> Douglas P. Jensen, Assistant Professor of Biology
> PO Box 9615
> Hollins College
> Roanoke, Virginia 24020
> (540)362-6549
>jensendp at diana.hollins.edu>>
