Effect of Exogenous Salicylic Acid on Some Physiological Parameters and Alleviation of Drought Stress in Nigella sativa Plant under Hydroponic Culture

To study the effect of salicylic acid on photosynthetic pigments (chlorophyll a, b, total chlorophyll, and carotenoids), polyphenol compounds, anthocyanin, flavonoids, phenylalanine ammonia-lyase activity, malondialdehyde, lipoxygenase activity, electrolyte leakage, relative water content, soluble sugar contents, and protein content of black cumin (Nigella sativa) under drought stress in hydroponic culture, an experiment was conducted as a completely randomised design in a factorial arrangement with three replicates. Experimental treatments included salicylic acid at three levels (0, 5, and 10 mu M) and drought stress (induced by polyethylene glycol 6000) at four levels (0, -0.2, -0.4, and -0.6 MPa). Results showed that salicylic acid application through the root medium increased drought tolerance of black cumin seedlings. Plants pre-treated with salicylic acid exhibited slight injury symptoms whereas those not pre-treated with salicylic acid had moderate damage and lost considerable portions of their foliage. In conclusion, salicylic acid could protect the Nigella plant against drought stress through increasing of all the mentioned traits, and 10 mu M salicylic acid was the most effective level under both conditions.