Determination of antioxidant capacity, phenolic acid composition and antiproliferative effect associated with phenylalanine ammonia lyase (PAL) activity in some plants naturally growing under salt stress

Being a considerable abiotic stress factor particularly for arid and semi-arid regions, salt stress may significantly limit the plant growth and yield. Plant’s response to salt stress involves secondary metabolites and especially phenylpropanoids that significantly contribute to the antioxidant activity of plant tissues. In addition to their important role in the control of cancer, phenylpropanoid compounds act as quenchers of singlet oxygen formation, free radical scavengers and reducing agents. One of the important gateway enzymes in the secondary metabolic pathway leading to the synthesis of phenylpropanoids is phenylalanine ammonia lyase (PAL). The aim of this study is to determine the phenolic acid composition, antioxidant capacity and antiproliferative effect associated with PAL activity in some plants that grow naturally under salt stress. The PAL activities of Salsola nitraria, Salvia halophila and Cyathobasis fruticulosa were evaluated. The antioxidant content of the extracts was studied and they were evaluated for their antioxidant activity. MTT assay was used to determine the antiproliferative effects of the extracts on HT-29 cells. Also, phenolic acids in extracts, namely p-coumaric acid, vanillic acid, gallic acid, caffeic acid, chlorogenic acid and syringic acid were screened using LC-MS/MS. Considering all results, C. fruticulosa with its highest PAL activity (62.85 μmol.min−1.mg−1 protein) has become prominent among the three plants. C. fruticulosa extract exhibited the highest antioxidant content with total phenolic content (120.36 mg/g) as the major antioxidant component. It was also found to be the plant extract richest in p-coumaric acid, vanillic acid, gallic acid, caffeic acid, chlorogenic acid and syringic acid as phenolic acids. Besides its marked antiproliferative activity against HT-29 cells, C. fruticulosa extract had the highest antioxidant activity compared with other extracts. In conclusion, the antioxidant and anticancer properties of plants naturally growing under salt stress may partly arise from their high PAL activities. Therefore, compounds obtained through plants exhibiting high levels of PAL activities could be used in the development of new pharmaceuticals as an antioxidant and anticancer agent.