Question 1

What are plant growth regulators?

Accepted Answer

Plant growth regulators are naturally synthesised organic compounds that influence physiological processes in plants at low concentrations. They are also called plant hormones. Auxins, gibberellins, and cytokinins are growth promoters, while ABA and ethylene are growth inhibitors.

Question 2

Where is auxin produced, and how does it affect a shoot?

Accepted Answer

Auxin is synthesised mainly at the shoot apical bud and in young leaves. It is transported downward and promotes cell elongation in shoots, maintains apical dominance by suppressing lateral buds, and helps initiate rooting in stem cuttings.

Question 3

How do gibberellins and cytokinins differ?

Accepted Answer

Gibberellins mainly promote internode elongation, bolting, fruit growth, and seed-dormancy breaking while delaying senescence. Cytokinins promote cell division and shoot-bud differentiation and delay leaf senescence.

Question 4

How does ABA help a plant during water stress?

Accepted Answer

ABA causes stomatal closure by reducing guard-cell turgor, which lowers water loss through transpiration. It also inhibits growth and induces or maintains dormancy in seeds and buds.

Question 5

What is the ethylene-induced triple response in seedlings?

Accepted Answer

The triple response consists of inhibition of stem elongation, swelling of the axis, and horizontal growth of the seedling. Ethylene is a gaseous plant growth regulator that also promotes fruit ripening, senescence, and abscission.

Plant Growth Regulators: Five Hormones, One Living Plant

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