Plant Growth Regulators: True Managers of Plant Life

摘要

Natural or synthetic compounds that can regulate developmental and metabolic processes in higher plants are designated plant growth regulators (PGRs) (Sabagh et al. 2021). The term 'PGRs' is more commonly used in reference to phytohormones and may also comprise inhibitors of phytohormone synthesis or translocation and blockers of their receptors (Rademacher 2015). Auxins, cytokinins (CKs), gibberellins, abscisic acid and ethylene constitute the 'classical' group of phytohormones, with salicylic acid, brassinosteroids (BRs) and jasmonates being the newly accepted members. The past decade has witnessed an increasing number of studies on karrikins (KARs)/yet-unknown endogenous KAR INSENSITIVE2 (KAI2) ligand and strigolactones (SLs) as two new promising classes of PGRs (Morffy et al. 2016, Antala et al. 2019). Melatonin is also considered an interesting candidate for use as a PGR due to its growth-promoting and anti-stress effects along with its ability to modulate the activities of various other phytohormones (Nawaz et al. 2020). The activities of PGRs are not only restricted to the longitudinal growth of plants, but they also affect a plethora of key processes including seed germination, defoliation, flowering, fruit formation and ripening and fruit drop, among others (Rademacher 2015). In addition, PGRs are frequently employed in agriculture, horticulture and viticulture for various benefits, such as improving morphological structure, increasing resistance and tolerance against biotic and abiotic stresses, and for qualitatively and quantitatively enhancing yields (Naeem and Aftab 2022).