Exogenous epibrassinolide application improves essential oil biosynthesis and trichome development in peppermint via modulating growth and physicochemical processes

Abstract

Peppermint has gained a promising status due to the presence of a high proportion of bioactive compounds especially menthol. Due to its pharmacological efficacy, the demand for its plant-based bioactive compounds necessitates its cultivation worldwide. Brassinosteroids are polyhydroxylated sterol derivatives that regulate diverse processes and control many agronomic traits during plant growth and development. A factorial randomised pot experiment was performed in the net house to investigate the effect of 24-Epibrassinolide (EBL) on the growth, physiology, essential oil content, stomatal behaviour and trichome development of the three cultivars of peppermint. Four levels of foliage-applied EBL, viz. 0, 10− 5, 10− 6 and 10− 7 M were applied on the three cultivars of peppermint (Kukrail, Pranjal and Tushar). Among the different treatments of EBL on Kukrail, Tushar and Pranjal, the application of 10− 6 M increased shoot length by 38.84, 37.59 and 36.91%, root length by 36.73, 29.44 and 33.47%, respectively. Whereas chlorophyll content by 24.20, 22.48 and 23.32%, PN by 32.88, 32.61 and 33.61%, respectively. Further, EO content was enhanced by 32.72, 30.00 and 28.84%, EO yield per plant by 66.66, 77.77 and 73.33%, menthol yield per plant by 127.27, 110 and 118.18% compared with their respective control plants. The scanning electron microscopical analysis revealed increased trichome size and density whereas, the confocal laser scanning microscopical analysis revealed enhanced cellular viability in the treated plants as compared with the control. Moreover, the GC-MS analysis revealed the enhanced essential oil content particularly menthol in the treated plants over the control.