Atividade elicitora do ácido salicílico sobre o perfil de metabólitos primários e secundários com potencial antioxidante de Achillea millefolium L. cultivada a campo

Abstract

Elicitors are substances of natural or synthetic occurrence, which stimulate the synthesis of secondary metabolites in vegetables. The phenolic compound Salicylic Acid (SA) is a plant hormone the acts on the growth and development of plants and is also considered an abiotic elicitor. This study evaluated the effect of SA on biomass production and the synthesis of primary and secondary compounds in yarrow (Achillea millefolium L. - Asteraceae), a medicinal species commercially produced as raw material for the phytomedicines and beverages industries. The experiments were conducted under field conditions in two consecutive harvests in the years 2016 and 2017. The SA was applied by foliar spraying at two concentrations (0 and 1.0 mmol L-1) and at different phenological times of the crop. The effects of SA in yarrow were evaluated through biometric growth parameters, biochemical parameters and qualitative analysis of essential oil (GC/MS) and phenolic and flavonoid compounds (LC/MS). The exogenous application of SA resulted in increases of dry matter mass (leaves, roots and total), leaf area (total and specific), and leaf weight ratio. There was an increase in photosynthetic pigment contents in response to SA. The positive effects on the primary metabolism were evidenced by the higher concentrations of sugars, proteins and total soluble amino acids, as well as total reducing sugars contents, in both times of SA application and years of cultivation. Increases of total phenolic compounds and flavonoids (evidenced by the greater activity of the phenylalanine ammonia-lyase and chalcone synthase enzymes) were observed, as well as a higher content and yield of essential oil in both SA application times and years of culture. The antioxidant activity of the plant extract, evaluated by different in vitro tests, was higher in the plants treated with SA. The application of SA at different times of application and year of cultivation resulted in increases in the major compounds of the essential oil, such as chamazulene, caryophyllene, γ-terpinene, terpinen-4-ol and borneol. The identification of bioactive compounds revealed the presence of quercetin derivatives, apigenin, caffeoylquinic acid, quinic acid, caffeic acid and chlorogenic acid, amentoflavone, kaempferol and rutin. The results of this research lead us to affirm that SA exerted both the hormonal effect on biochemical and growth aspects, and also acted as elicitor in A. millefolium plants. There was a positive correlation between the higher contents of primary compounds and the higher levels of secondary compounds in plants treated with SA. It was concluded that the application of 1.0 mmol L-1 of SA in the pre-harvest (at 100 days after planting) results in higher productivity and a higher concentration of secondary compounds with antioxidant potential making it feasible to apply of this elicitor in the commercial crop of Achillea millefolium.