Question

Which one of the plant growth regulators would you use if you are asked to
A) Induce rooting in a twig
B) Quickly ripen a fruit
C) Delay leaf senescence
D) Induce growth in axillary buds
E) Bolt a rosette plant
F) Induce immediate stomatal closure in leaves

Answer 1

Hint: Plant growth regulators which are also often called plant hormones, have several different functions which include increased branching, preventing the growth of excess fruit, increasing the bloom and hampering shoot growth.

Complete Answer:
A) In order to induce rooting in a twig, we would need to use any of the auxins like Indole acetoacetic acid or IAA. Auxins generally induce shooting, but in high concentrations they actually inhibit lateral bud formation.
B) To perform the action (B), the gas ethylene is used. This is what makes fruits ripen quicker when a ripe food is added
C) The plant hormone that delays leaf senescence is cytokine which is related in structure to nucleotide bases.
D) Inducing axillary bud growth is also done most efficiently by adding the regulator cytokinin. Cytokinins essentially promote cell division.
E) To perform action (E), gibberellins are used, but they can also be used to regulate dormancy.
F) And finally stomatal closure in leaves is induced by ABA or abscisic acid. This is the main hormone for regulating water loss, but it also controls seed dormancy.
It is therefore easy to see that plant growth regulators do not work completely in isolation, but have functions that overlap, over and beyond their main role in plant growth.

Note: Ethylene being in gaseous form, easily affects all fruits in the vicinity. That is why when a ripe fruit like a banana is added to a bowl, all the other fruits will start to ripen much quicker than if they were left on their own.