Auxin is a class of plant growth regulators that are either indole-derivatives or acetic acid derivatives. They play an important role in several physiological activities in plants.
The bioassay for auxins includes the Avena coleoptile curvature test. The procedure is as follows:
1. 15 - 30 mm oats seedlings (Avena) were excised for 1 mm from the tips. Tips are the natural sources of auxin.
2. Tips were placed on agar-block for some hours. This ensured the diffusion of auxins from the tips to the agar layer.
3. Auxin containing agar blocks were placed on one side of the decapitated stumps of oats coleoptiles.
4. Auxin from agar blocks was allowed to diffuse to the coleoptiles along the sides to which blocks were placed.
5. It was observed the coleoptiles were bending to the opposite sides with respect to the side of the agar block.
Thus, from the step tip test, the presence of auxins in the solution can be detected.