Improving Phenolic Total Content and Monoterpene in Mentha x piperita by Using Salicylic Acid or Methyl Jasmonate Combined with Rhizobacteria Inoculation

Abstract

The effects of plant inoculation with plant growth-promoting rhizobacteria (PGPR) and those resulting from the exogenous application of salicylic acid (SA) or methyl jasmonte (MeJA) on total phenolic content (TPC) and monoterpenes in Mentha x piperita plants were investigated. Although the PGPR inoculation response has been studied for many plant species, the combination of PGPR and exogenous phytohormones has not been investigated in aromatic plant species. The exogenous application of SA produced an increase in TPC that, in general, was of a similar level when applied alone as when combined with PGPR. This increase in TPC was correlated with an increase in the activity of the enzyme phenylalanine ammonia lyase (PAL). Also, the application of MeJA at different concentrations in combination with inoculation with PGPR produced an increase in TPC, which was more relevant at 4 mM, with a synergism effect being observed. With respect to the main monoterpene concentrations present in peppermint essential oil (EO), it was observed that SA or MeJA application produced a significant increase similar to that of the combination with rhizobacteria. However, when plants were exposed to 2 mM MeJA and inoculated, an important increase was produced in the concentration on menthol, pulegone, linalool, limonene, and menthone concentrations. Rhizobacteria inoculation, the treatment with SA and MeJA, and the combination of both were found to affect the amount of the main monoterpenes present in the EO of M. piperita. For this reason, the expressions of genes related to the biosynthesis of monoterpene were evaluated, with this expression being positively affected by MeJA application and PGPR inoculation, but was not modified by SA application. Our results demonstrate that MeJA or SA application combined with inoculation with PGPR constitutes an advantageous management practice for improving the production of secondary metabolites from M. piperita.

Salicylic Acid Signalling in Plants

“…Exogenous SA increased the total phenol content in this plant, and depending on the concentration used, certain Rhizobacteria could improve this effect. The exogenous SA also modified the production of the main monoterpene compounds [27]. These results suggest that a combination of SA or other plant growth regulator with certain plant growth-promoting Rhizobacteria may improve the production of secondary metabolites in aromatic plants.…”

“…They include a "classical" demonstration of the importance of SA in biotic stress [23] and the importance of the use of various mutants related to SA signalling [24,25], as well as focus on the crosstalk with other stress-related compounds [25,26]. There are also works investigating the effects of environmental factors on the SA-related signalling [26,27], and on the role of different SA analogue compounds [28].…”

Nutraceutical Profiles of Two Hydroponically Grown Sweet Basil Cultivars as Affected by the Composition of the Nutrient Solution and the Inoculation With Azospirillum brasilense

“…Nonetheless, the effect produced by the rhizobacteria on the qualitative and quantitative profile of secondary metabolites has been observed to be strongly dependent both on the plant species/cultivar and on the microbial strain. This suggests the existence of specific microbe/host recognition and interaction mechanisms, thus inducing diverse effects at plant level (Cappellari et al, 2019a).…”

“…Several pieces of evidence have already addressed the positive role produced by PGPR inoculation on the quality of fruits like citrus, mulberry, apricot, sweet cherry, raspberry, and strawberry ( Esitken et al, 2002 , 2003 , 2005 , 2006 ; Orhan et al, 2006 ; Pii et al, 2018 ). More recently, PGPR as well as symbiotic arbuscular mycorrhizal fungi have been shown to have a promoting effect on the accumulation of secondary metabolites, like antioxidant molecules and essential oils, in aromatic herbs ( Banchio et al, 2009 ; Erika et al, 2010 ; Santoro et al, 2011 ; Heidari and Golpayegani, 2012 ; Cappellari et al, 2013 , 2019a , b ). Nonetheless, the effect produced by the rhizobacteria on the qualitative and quantitative profile of secondary metabolites has been observed to be strongly dependent both on the plant species/cultivar and on the microbial strain.…”

Structure Analysis and Study of Biological Activities of Condensed Tannins from Bruguiera gymnorhiza (L.) Lam and Their Effect on Fresh-Cut Lotus Roots

“…Total phenol content was determined according to the Folin-Ciocalteu method [ 39 ], with gallic acid used as the standard curve. A total of 0.2 mL of the standard/sample, 300 µL of ddH 2 O, 500 µL of Folin-Ciocalteu (FC) reagent and 2.5 mL of 20% Na 2 CO 3 were mixed and reacted for 50 min in a dark place.…”