If you soak seeds in water to soften them, and then cut them in half and stain them with iodine, most of the inside of the seed will change color, turning a purplish-black. What substance is the iodine reacting with to cause this color change?
Starch consists of amylopectin and amylose, and is found in plants. In the presence of iodine, amylose starch turns a dark purple or blue color, due to the absorption of different wavelengths of light than before.
