Physiological responses and secondary metabolite ingredients in sage plants induced by 24-epibrassinolide foliar application under different water deficit regimes

Water deficit stress is one of the most dramatic environmental agents, reduces the growth and efficiency of cultivated plants. Brassinostroids are ubiquitous steroidal compounds playing vital roles in the processes of growth and development, pharmaceutically important metabolite production, stress responses and adaptation in plants. Therefore, in the current study the impact of foliar application of 24-epibresinolide (0, 100 mg L⁻¹) under different water deficit stress [(100 % field capacity (FC), 60 % FC, and 30 % FC)] was assessed on field grown sage plants at two different locations of East Azarbaijan (Ahar and Kaleybar) in a factorial experiment arranged in randomized complete block design (RCBD). The results of combined ANOVA showed that triple interaction of locations, 24-epibrassinolide treatment and water deficit stress on total dry matter, chlorophyll b and proline contents were statistically significant. Water deficit had adverse effects on plant height, leaf relative water content (RWC), dry matter accumulation, and photosynthetic pigments in both cultivated sites, but spraying with 24-epibrassinolide led to an increase in these traits under water scarcity. The highest H₂O₂ content was found in plants subjected to water stress of 30 % FC without 24-epibrassinolide treatment cultivated in Ahar (a cold semi-arid) region compared to Kaleybar (a cold semi-humid) site. Mean comparison showed that brassinolide treatment and deficit irrigation of 60 % FC significantly increased (by 33 % and 42.5 %) the essential oil percentage of plants as compared to the respective control, respectively. Essential oil content was positively correlated with dry matter accumulation (r₀.₀₅ = 0.41) and proline (r₀.₀₁ = 0.66) content under the employed treatments. Based on the GC–MS analysis, about 28 volatile constituents were detected in the essential oil, which were mainly consisted of α-Terpinolene, α-Thujone, cis-Sabinene hydrate, γ-Terpinene, α-Thujene, Camphor, and β-Thujone. The highest content of cis-Sabinene hydrate was found in plants treated with 24-epibrassinolide at Ahar studied site, which was about 10.6-fold higher than that of Kaleybar.