Plant Growth Regulators (PGRs) are classified based on their chemical composition. Cytokinins (e.g., kinetin) are explicitly described as adenine derivatives (specifically N6-furfurylamino purine) . In contrast, Auxins are indole compounds (e.g., IAA), Abscisic acid (ABA) is a derivative of carotenoids, and Ethylene is a gaseous PGR .