الفهرس 
Title :Effect of drought stress and salicylic acid on active constituents of ammi visnaga L.
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Abstract
The present study was conducted to evaluate the impact of drought stress and foliar spraying of salicylic acid (SA) on the secondary metabolites, particularly the Þ-pyrones and total polyphenolic content in the different organs of Ammi visnaga L. plant.The following were measured: different growth parameters, Þ-pyrones and total phenolic content as well as the antioxidant activity and the cytotoxic activities of the methanolic extracts. from the results obtained, it was clear that drought stress had a negative impact on plant growth and yield of the fruits. The negative impact of drought stress was found to be partially tolerated by the salicylic acid foliar spray. In contrast, drought alone significantly (p < 0.001) increased the percentage of the two major Þ-pyrones: khellin and visnagin in most organs as well as increasing the total polyphenolic content and the radical scavenging activity. Application of SA on both drought stressed and normally irrigated plants showed a variable increase in the percentages of Þ-pyrones in the plant. The maximum amounts were observed in fruits sprayed with 2 mM SA combined with normal irrigation as well as the increase in the yield of fruits per plant. The highest polyphenolic content was recorded in the water stressed aerial parts sprayed with 2mM SA, where it increased to 78.28 ± 0.14 mg/gm dry weight expressed as gallic acid equivalen