Plant beneficial rhizospheric microorganisms (PBRMs) mitigate deleterious effects of salinity in sesame (Sesamum indicum L.): Physio-biochemical properties, fatty acids composition and secondary metabolites content

Salinity is serious environmental stress that highly affects the quantity and quality of herbal products. In this study a pot experiment was carried out in greenhouse to investigate the interactive effects of Azospirillum lipoferum and Piriformospora indica on growth attributes and secondary metabolites production of sesame (Sesamum indicum L.) under saline condition. The applied microorganisms raised the ability of sesame in absorption of essential nutrients. The highest concentration of N (24.33 and 39.65 mg g−1 DW in shoot and root, respectively), K (23.13 and 18.74 mg g−1 DW in shoot and root, respectively) and P (11.08 and 13.70 mg g−1 DW in shoot and root, respectively) were observed in co-inoculated plants under non-stress condition. The results showed that increasing NaCl concentration in irrigation water (from 0 to 120 mM), significantly disordered the absorption and distribution of water and minerals. In addition, salt-induced reactive oxygen species lead to oxidative damage of sesame plants, consequently, 3.29 and 1.87 fold increases were observed in the amount of malondialdehyde (MDA) and electrolyte leakage (EL), respectively. During salt stress, activity of protective enzymes and amount of non-enzymatic antioxidants were dramatically raised. This study showed that inoculation of sesame with PBRMs can provide salt-tolerance by changing in physio-biochemical responses. Under saline condition, inoculation with Al and Pi resulted an enhancement of relative water content (up to 20%), maximum photochemical quantum yield of PSII (Fv/Fm) (up to 25%), antioxidant enzyme activity, nutrient absorption, proline (36–65%) and secondary metabolite contents, DPPH radical scavenging activity (18–22%) and linoleic acid. Conversely, the amount of MDA (up to 35%), EL (up to 23%), Na+ (up to 66 and 59% in shoot and root, respectively) as well as oleic/linoleic acids ratio were significantly decreased via microbial treatments. However, combined inoculation (Al + Pi) was generally more effective in alleviation of salinity deleterious effects than individual inoculation.