Auxin can be bioassayed by
(b) lettuce hypocotyl elongation
(c) Avena coleoptile curvature
Ans : (c) Avena coleoptile curvature
Auxin bioassay is a quantitative test as it measures concentration of auxin to produce the effect and the amount of the effect. Avena Curvature is based upon experiments of Went (1928). 10° curvature is I produced by auxin concentration of 150 mg/litre at 25°C and 90% relative humidity. The test can measure 1 auxin upto 300 mg/litre. Auxin from a shoot tip or any other plant organ is allowed to diffuse in a standard size agar block (generally 2×2× mm). Auxin can ; also be dissolved directly in agar. 15- 30 mm long oat i coleoptile grown in dark is held vertically over water. 1 . mm tip of coleoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is j carried out for a distance of 4 mm. Primary leaf is now j pulled loose and agar block supported against it at the tip of decapitated coleoptile. After 90-110 minutes, the coleoptile is found to have bent. The curvature is measured. It can also be photographed and the curvature known from shadow graph.