Foliar Spraying of Salicylic Acid Alters Secondary Metabolites and Radical Scavenging Activity of Water Stressed Thymus vulgaris L.

Polyphenolic compounds are known to be one of the most valuable secondary metabolites produced in plants [1]. They have several medicinal and pharmacological importance [2]. They are known to play a physiological resistance mechanism in plants to help them face different types of stresses [3]. The present study aims to investigate the effect of different molar concentrations of the plant growth regulator; salicylic acid (SA), on some secondary metabolites of Thymus vulgaris L. exposed to decreasing amounts of irrigating water. The accumulation of flavonoids and polyphenols in the alcoholic extracts in different plant treatments was measured. The total flavonoid content in control plants was 6.135 ± 0.327 rutin equivalent/g dry weight and increased in drought plants (receiving 25% field capacity) sprayed with 3mM SA to reach 32.055 ± 0.095 mg rutin equivalent/g dry weight. Also, total phenolic content increased from 8.476 ± 0.344 to 68.510 ± 1.241 mg gallic acid equivalent/g dry weight in the same plant treatment. Radical scavenging activity on DPPH free radical was measured for the different plant treatments. IC50 for control plants was 74.36 ± 0.39 µg/ml and decreased to reach 36.55 ± 0.86 µg/ml in drought plants sprayed with 3mM SA. Comparison between the polyphenolic content in control plants and plants with highest total polyphenol content was carried out using LC/MS. Several flavonoids and polyphenolic compounds were identified.

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[3] Mazid M, Khan T, Mohammad F. Biology and Medicine 2011; 3: 232 – 249.