A gibberellin bioassay based on betacyanin production in Amaranthus caudatus seedlings.

Amaranthus caudatus L. seedlings produce less amaranthin in the presence of gibberellic acid A3 (GA3). This phenomenon has been tested as a bioassay for gibberellic acid and has been compared to the bioassay based on lettuce hypocotyl extension. The inhibition of pigment synthesis is much more sensitive to GA3 at concentrations from 1 to 0.01 μg/ml. Of the gibberellins tested GA1, GA3, GA4, and GA7 are the most active in the described bioassay.