Question

Dr. F. Went noted that if coleoptile tips were removed and placed on agar for one hour, the agar would produce a bending when placed on one side of freshly cut coleoptile stumps. Of what significance is this experiment
(a) It is the basis of quantitative determination of small amounts of growth-promoting substances
(b) It supports the hypothesis that IAA is auxin
(c) It demonstrated the polar movement of auxins
(d) It made possible the isolation and exact identification of auxin

Answer 1

Hint: Agar is gel-like in consistency and thus chemicals can diffuse well into it from the coleoptile tips. Bending of freshly cut coleoptile stumps is due to a property of chemicals that diffuse from the tips and do not let the lateral buds to grow.

Complete step by step answer:
Dr. F. Went in 1928 collected the growth- stimulating substances in agar jelly. . He did so decapitating the coleoptile tips and placed them on the agar block for one hour so that the agar block absorbs the chemicals. The decapitated coleoptile tips along with the agar block were again placed over the freshly cut coleoptile stumps. This caused the bending of the freshly cut coleoptile stumps. He demonstrated the polar movement of auxins by discovering that the hormone traveled basipetal i.e from tip or apex to the base.
- Auxin is a weakly acidic growth- promoting hormone that is produced by the growing apices of the stems and the roots.
- It then migrates to the regions where they will perform their respective functions.
- They initiate rooting in stem cuttings and promote flowering as well as the abscission of older mature leaves and fruits.
- On the other hand, it prevents fruit and leaf drop at early stages and thus promotes their proper growth and development until it reaches maturity.
So, the correct answer is ‘(c) It demonstrated the polar movement of auxins.’

Note:
- Auxin exhibits a phenomenon of apical dominance wherein auxin production by the apical buds in a plant prevents the growth of lateral branches.
- This property is exploited by gardeners who remove apical buds to let lateral buds sprout. This leads to bushy growth for hedge making and tea plantations.