Avena curvature test is a bioassay for examining the activity of

Bioassay is a testing of biological activity like growth response of a substance by employing plant part. Avena curvature test is a bioassay for examining the activity of auxins. It is based upon experiments of Went. $10^{\circ}$ curvature is produced by auxin concentration of $150 \mu \mathrm{g} /$ lit at $25^{\circ} \mathrm{C}$ and $90 \%$ relative humidity. It can measure auxin upto 300 $\mu \mathrm{g}$ /itre. Auxin from shoot tip or any other plant organ is allowed to diffuse in a standard size agar block. 15 - $30 \mathrm{~mm}$ long oat coleoptile grown in dark is held vertically over water. $1 \mathrm{~mm}$ tip of coleoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is carried out for $4 \mathrm{~mm}$ distance. Primary leaf is now pulled loose and agar block supported against it at the tip of decapitated coleoptile. After $90-110 \mathrm{~mm}$ the coleoptile is found to have bent. The curvature is measured.