Morpho-physiological Effects and Molecular Mode of Action of Mepiquat Chloride Application in Cotton: A Review

Mepiquat chloride (MC) (1,1-dimethylpiperidinum chloride) is a plant growth regulator, usually sprayed on cotton foliage at different growth stages as a practical tool for cotton management. MC foliar applications reduce plant height, leaf area, node distance, and plant canopy but increase light interception within the canopy that leads to increase yields. Application at squaring stage reduces the partitioning of photoassimilates towards main stem, branches, and growing points but increases partitioning to the reproductive organs. Furthermore, MC application increases the net photosynthesis rate in cotton leaves as compared with control and triggers carbohydrate formation by improved source-sink relationship. Disturbed carbohydrate metabolism could affect the activity of sucrose metabolic enzymes resulted in variable yield responses. More precisely, it retards the vegetative growth by inhibiting the activity of gibberellin involved in cell elongation, which inhibits the signaling pathways and disturbs gibberellin homeostasis by upregulation of site-specific genes that ultimately results in keeping the plant stature shorter. Besides this, it enhances the yield due to raised boll setting on the lower branches by manipulating a compact canopy. This review will focus on cotton morphology and yield responses to MC application that have been published in last decades. Various physiological mechanisms such as carbohydrate metabolism and sucrose-related enzymes as well as its molecular mode of action in cotton have also been discussed. Further research is needed to exploit the role of MC specifically in gibberellin inhibition and carbohydrate metabolism with its related enzymes.