Question

Match the growth regulators with the processes and choose the correct combination from the options.

List I	List II
a. Auxin	1. Colouring test in lemon
b. Gibberellin	2. Cell division test in plants
c. Cytokinin	3. Avena curvature test
d. Ethylene	4. Dwarf corn test

A) a-1, b-4, c-2, d-3
B) a-4, b-3, c-1, d-2
C) a-2, b-1, c-4, d-3
D) a-1, b-3, c-4, d-2
E) a-3, b-4, c-2, d-1

Answer 1

Hint: Plant growth regulators may be defined as small, simple molecules of different chemical composition which can regulate growth, differentiation, and development of a plant. Plant hormones are a type of growth regulator in plants. Gibberellin, auxin, indole acetic acid, cytokinin, ethylene are a few examples of plant hormones.

Complete answer:
a) Auxins have an unsaturated ring structure and are weakly acidic in nature. They have the ability to promote cell elongation, especially the elongation of the shoot. It can work at a very less concentration at about 10 ppm which acts as an inhibitor to roots. Auxin bioassay is a quantitative test and is used to measure auxin concentrations to produce the effect. Avena curvature test is an auxin assay. The test is conducted under diffuse sunlight and etiolated oat coleoptiles are used for the assay.
b) Gibberellins are involved in the cell elongation of intact plants and also increases the length of genetically dwarf plants. They have a gibbane ring and are weakly acidic in nature. Dwarf corn test is a bioassay of Gibberellin. This assay is based on the principle that gibberellins increase the length of the internodes of dwarf corn plants.
c) Cytokinin promotes cytokinesis or cell division and is mainly basic in nature. Hence, cell division in plants can be assayed with the help of cytokinin.
d) A transverse or isodiametric growth is stimulated by ethylene. It is a gaseous hormone and it retards longitudinal growth. Ethylene being a fruit ripening hormone is used for the assay of colouring in lemons. The test is based on the ripening nature of ethylene.
Thus, the correct answer is option E.

Note: Thus, a plant hormone is a chemical substance that can be translocated to another region for the regulation of growth when present in low concentrations. Plant growth regulators may either be plant growth promoters or plant growth inhibitors.