Question

Hormone involved in phototropism is
A. IAA
B. Gibberellin
C. Kintein
D. 2,4 - D

Answer 1

Hint: Movement of the plant part in response to the light is called phototropism.

Complete Answer:
A. IAA:
(i) Indole-\[3\] : Acetic acid (IIA) and other natural and synthetic compounds having certain growth regulating properties. They are generally produced by the growing apices of the stems and roots, from where they migrate to the regions of their action. IAA and Indole butyric acid (IBA) have been isolated from the plants and are natural aunins and extensively used in agricultural and horticultural practices.
(ii) IIA hormone is involved in phototropism
(iii) Charles Darwin and his son Francis Darwin when they observed that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source (phototropism).
(iv) After a series of experiments he concluded that the tip of the coleoptile was the site of transmittable influence that caused the bending of the entire coleoptile.
(v) Aumin was isolated by F.W. went from the tip of the coleoptile of oat seedlings.
(vi) The IAA is present in the tip of Coleoptile and hence it bends towards the source of light, its tip is cut and it will not bend towards light.

B. Gibberellin: This hormone has the ability to cause an increase in length of axis, it delays senescence, used up in the malting process. It promotes bolting in beet, cabbage with rosette habit.

C. Kinetin: (i) Cytokinins have specific effects on cytokinesis (i.e. cell division) and were discovered as Kinetin.
(ii) They help in cell division.
(iii) They overcome apical dominance.
(iv) They delay leaf senescence.

D. \[2,{\text{ }}4 - D - {\text{ }}2,{\text{ }}4 - D{\text{ }}\left( {2,{\text{ }}4 - dichlorophenony - acetic} \right)\] are synthetic auxins. They are used in agricultural and horticultural particles.

The correct option is (A), IAA.

Note: All above mentioned are plant hormones. They are involved in growth promoting activities, such as cell division, cell enlargement, tropic growth, flowering, fruiting and reed formation.