We performed a starch-iodine test to see whether our seeds show α-amylases activity (eventually activated by gibberellic acid). For this seeds are placed on an agar plate containing starch so the α-amylases convert the starch into sugars (same as happens in the endosperm during germination). The seeds are kept on the agar plate for two days, then they are removed and the plate is immediately stained with iodine. Where starch is still present, the plate stains blue, where starch is converter into sugars no color is observed (transparent circles on the plate).
We performed this experiment with corn and banana seeds.
With corn, and as expected, colorless circles where the seeds were placed are immediately visible after the iodine application. With the banana seeds, however, the entire plate initially turned blue, but after 20 minutes, a colorless circles appear where the banana seeds was initially placed for two days and removed prior to the iodine application. We are looking for an explanations. Why do these colorless circles appear only after 20 minutes. Does it mean that during these 20 minutes (after removing the seed) the starch is broken down? For example are there chemical (biochemical reactions) reactions induced by removing the seeds?
a-amylases can partially convert starch (Takeshita, M., & Hehre, E. J. (1975). The capacity of α-amylases to catalyze the nonhydrolytic degradation of starch and glycogen with formation of novel glycosylation products. Archives of biochemistry and biophysics, 169(2), 627-637.) and it may cause staining for a short time only due to instability of the starch-iodine complex (Danilovas, P. P., Rutkaite, R., & Zemaitaitis, A. (2014). Thermal degradation and stability of cationic starches and their complexes with iodine. Carbohydrate polymers, 112, 721-728.)
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https://pdf.sciencedirectassets.com/778417/1-s2.0-S0021925818X50935/1-s2.0-S0021925818568113/main.pdf?X-Amz-Security-Token=IQoJb3JpZ2luX2VjEO7%2F%2F%2F%2F%2F%2F%2F%2F%2F%2FwEaCXVzLWVhc3QtMSJGMEQCIC%2B%2BjFeM1KGG%2FCZvbCav2q6uglgx%2FpapMNu9zpUW%2BrmfAiBK%2F7bZuVts5ZmlXDHMsPa7HnUVWCzgkBhJOHyk%2BKCXeCqDBAjm%2F%2F%2F%2F%2F%2F%2F%2F%2F%2F8BEAQaDDA1OTAwMzU0Njg2NSIMD4Q%2Fm1SxaR9im9YzKtcDzpuauW6X2aw48ixF7R2jKNSwTQZTdg2vaGWTwS5hPDtGbrQx93Pmg6ut6lF1LxfJ7W%2FGaHAL7VOVfs5FE3jM8SnAZIs2vP5Ju%2B8rvJCwOYfLDDiM7kMBmKKMp%2FLvU1dlP7Yha%2Br8VwYeZr76VrWPGj98nTNoJi92CIPG0y2a%2BVRhHrZaB0X7WJuYhopPj2Dif7xok3Ww4MKKYDPtHyW%2F9BVoTxntGqQrsmsDLX6lmfquchXp43iqqymRPuMivTCDugVRBLLDFZ43UfoRfTblG5si%2FVZQbfDA4NVlqCcRhDApkN0kQSj41De9t4N3blQtGuO%2BRcidCJkJDweKm3c1%2Bclgs%2FC70vT1ieq%2FQNW8SJllZisj9wXARMhYA2i%2BRiM7dNtGENe4o%2BDO9hHj3Cs%2B33OCTpg9Etnh1KzOlaUhAeIw68UR37wIkh7tx4PJDjCVHwRHGsTgdSb5KjMp09ewkE4jZ9JdVVwJxxKkiHXE3X42qbOM75McggiXvcD3A3TDrZC6XzppIzvYjiP%2BqsIWmTz3VP40LZUyzSD6wku6OlyIEbBrcEq4X6wtVJGQCKJOaSbph7a2iU%2FShzbXiwxXIfPYuKKb%2F%2B1bu%2B0wvqj5uznwCrybKBSfMKr%2BtI4GOqYB%2FcFwSorm%2F002E0D0t8TiIgWWRckVemXUiFi2ykSa8%2BjKcRPLG%2Bpb3Tiqq9EbGrg3oGY5hrgwLrsL3srpJP%2FtuYn1v0XffKqWng4o1q8MpXxUZUIBVklkyaPYTpEoCu6uku%2F6AUnwk5tc5L9RoXyOniIyAl4NWJlOwsK%2FarZG1ExcVZPREx8C9a7Lb5%2BC%2FvqB%2Bue7EkMFB%2B%2BTM0BEaecQ82QsCaiETQ%3D%3D&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20211230T062125Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTYRSLWF6UP%2F20211230%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=d001205f6d753de7c64de77561b9b24cfcede8a50b8b666b6811aeabf84e8608&hash=f06b1f8170e09ea44dfb4856c50d0569ef31ddbba6dddd19c1ce51986cbae286&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=S0021925818568113&tid=spdf-37c24a60-ed82-417c-bd7c-31762fadbd78&sid=07cb229d3d26324d14897734b9fcf641045cgxrqb&type=client
While staining the agar-starch-plate, possibly the remaining starch on the agar gel surface get distributed throughout due to the application of IKI- solution on the surface and hence initially all the surface appearing blue. Since, the area where seeds were kept had amylase that eventually degraded/hydrolyzed the starch again and become colorless. The latter can be observed or confirmed by repeating the same.
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