Write a note on Avena curvature test.
Answers
The Avena geo-curvature test is a bioassay for auxin-type growth regulators. Etiolated oat coleoptiles are used and the test is conducted in special perspex trays under diffuse daylight. The coleoptiles, with the primary leaves intact, are arranged in grooves on the trays in 4 series of 6 coleoptiles each, and cut to a size of 10 mm. The test substance is applied on an agar strip covering only the lower halves of the apical cut surfaces of each series. After a 4-hour stay in the dark in moist Petri dishes the coleoptile cylinders are shadowgraphed on a 35-mm photographic film. The curvatures are measured from an enlarged projection (10 times natural size) of the shadowgraphs.The lowest IAA concentration which can be determined is around 30 to 60 μg/l, i.e. about 1 to 2 ng IAA. The concentration response curves follow a logarithmic course up to 1,000 μg/l. The standard error of the mean in a test series comprising 6 coleoptiles is on an average ± 7%. The simple and quick procedures make it possible for a worker to test 60 to 80 fractions a day.
NCERT based Answer for Class 11 Biology Students
Avena Curvature Test for Auxin:
Auxins are produced by root and shoot apices, from where they migrate to region of their action.
Charles Darwin and his son Francis Darwin observed that coleoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism).
A decapitated coleoptile did not respond to unilateral light.
Coleoptile tip covered by an opaque tin foil cap also could not respond to light.
When tip was removed but was put back with a block of gelatine, normal phototropic curvature formed.
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