Abstract
Plant secondary metabolites (PSMs) provide taste, color, odor, and resistance to plants, and they are also used to treat cancer and cardiovascular diseases. Synthesis of PSMs in plants is stimulated in response to different forms of external stress. Use of ultrasonication (US) to clean or decontaminate fruits and vegetables leads to physical stress that finally results in the accumulation of PSMs. US can stimulate accumulation of taxol, ginsenoside saponins, shikonin, and resveratrol, e.g., up to 319-fold increase of resveratrol synthesis has been observed in grape due to US. US also increases carotenoids, total phenolics, and isoflavonoids accumulation. Furthermore, US shows synergistic effects in PSMs synthesis-when combined with ultraviolet (UV) irradiation, jasmonic acid (JA) or salicylic acid (SA). It has been observed that US stimulates the production of reactive oxygen species (ROS) which then upregulates expression of phenylalanine ammonia lyase (PAL), resulting in the synthesis of PSMs. In this review, we summarize the effects of US, as a physical stress, to maximize the accumulation of PSMs in crop produce and in cell cultures.
Highlights
Plant secondary metabolites (PSMs) impart taste, color, and odor as well as provide resistance to the plants against pathogens [1]
It is pertinent to say that US alone or in combination with ultraviolet ray (UV) has a great impact on the accumulation of different types of hydroxycinnamic acid in peanut kernels, and this might help in replacing red wine with roasted peanuts as a source of those phenolic compounds
Accumulation of PSMs depends on the incubation period after US or combined treatment procedures, as it might allow sufficient time to reach a threshold state for the activation of the required genes, which trigger such effects
Summary
Plant secondary metabolites (PSMs) impart taste, color, and odor as well as provide resistance to the plants against pathogens [1]. PSMs are classified into three major groups i.e., terpenes, alkaloids and phenolic compounds, based on their synthesis from different metabolic pathways [3]. Synthesis of PSMs in plants is affected by biotic and abiotic factors, including pathogens, light, UV radiation, wounding and nutrient deficiencies [12,13]. Dramatic rise (1.5–319 fold) in the accumulation of different PSMs including resveratrol, taxol, saponins, and shikonin has been reported after US treatment [14,18,19,20,21,22,23]. In light of the above reports, further investigations on the induction and accumulation of PSMs in response to the application of US, or its combinatorial use with other forms of synergistic stresses, is warranted. In this review, we summarize the past findings on PSMs accumulation by using US, or US in combination with SA and JA
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