Priming with salicylic acid, β-carotene and tryptophan modulates growth, phenolics and essential oil components of Ocimum basilicum L. grown under salinity

Abstract

Stress tolerance of the plant can be enhanced with the used of compounds that exhibit remarkable abilities to improve the growth without any side effects on plants and its environment. Many physiological and molecular activities in plants are controlled with those compounds. Of the medicinal and aromatic plants, sweet basil (Ocimum basilicum) possesses economic value due to their secondary metabolites such as essential oil and phenolic compounds. Along with the study, it was aimed to decrease the adverse impacts of the salinity stress from NaCl can be alleviated using priming with compounds. Herewith the study, salicylic acid, tryptophan and β-carotene were used for seed priming. Briefly, seeds of basil were soaked into 0.025 and 0.05 mM salicylic acid, 0.25 and 1 mM tryptophan and 0.1 and 0.2 mM β-carotene for 24 h. Following seed priming, when plants reached 5–6 leaf stage, the plants were exposed to salt stress (100 mM NaCl). In this context, plant growth parameters, photosynthetic pigments, essential oil components, total phenolic contents with their major fractions and DPPH activities of the plant leaves were screened. Results indicated that salinity decreased shoot and root length, root and leaf weight, leaf number, plant weight, and photosynthetic pigments of the plants. However, priming treatments partially alleviated the adverse effects of salinity on shoot and root length, root, leaf and plant weight, but had no significant effects on photosynthetic pigments in plants grown under saline conditions. Of the essential oil components, salinity reduced the percentage of linalool and eugenol but increased methyl eugenol percentage in non-primed plants. However, priming increased percentage of linalool and eugenol but decreased methyl eugenol percentage in plants grown under saline conditions. Regarding phenolics and individual fractions, salinity caused significant reductions in total phenolic, flavonoid contents, caffeic acid, chicoric acid, and rosmarinic acid content. Furthermore, DPPH activities of the extracts were also negatively affected by salinity. In addition, gas exchange parameters such as assimilation rate and stomatal conductance were affected negatively by salinity. Though, priming had a positive contribution to the gas exchange parameters under saline and non-saline conditions. As a result, it was observed that basil seedlings were negatively affected in terms of yield in 100 mM salt application, but especially 1 mM tryptophan priming could protect plants from the toxic effect of salt and increase the amount of individual phenolics under stress.