Characteristics

The plant growth regulators (PGRs) are small, simple molecules of diverse chemical composition. Chemically they may be:

• indole compounds — such as indole-3-acetic acid (IAA)
• adenine derivatives — such as N6-furfurylamino purine, or kinetin
• derivatives of carotenoids — such as abscisic acid (ABA)
• terpenes — such as gibberellic acid (GA3)
• gases — such as ethylene (C2H4)

In the literature these substances are variously described as plant growth substances, plant hormones or phytohormones.

Based on their functions in a living plant body, the PGRs can be broadly divided into two groups.

• One group is involved in growth-promoting activities such as cell division, cell enlargement, pattern formation, tropic growth, flowering, fruiting and seed formation. These are also called plant growth promoters; auxins, gibberellins and cytokinins belong here. …