Physiological Responses of <Emphasis Type="Italic">Matricaria chamomilla</Emphasis> to Potassium Nitrate Supply and Foliar Application of Ethephon

The study is focused on changes in metabolism of Matricaria chamomilla, caused by potassium nitrate (KNO₃) supplement and foliar application of an ethylene releaser—ethephon (ET). ET-treated plants were irrigated with 0, 9, 18 or 27 mmol of KNO₃ during 1 week and simultaneously treated with ET. The same procedure was followed with ET non-treated plants, where an equal amount of distilled water was sprayed on leaves. Nitrogen addition into soil substrate caused considerable increment in dry matter content, nitrate accumulation and amino acids synthesis. After ET application, a positive correlation between KNO₃ supply and stress-related parameters, such as superoxide radical, hydrogen peroxide and malondialdehyde was found. Experimental conditions led to a sharp decrease in herniarin level, which was accompanied with increasing content of its glycosidic precursors in ET-treated plants. The observations indicated that higher doses of nitrate suppressed the stimulation effect of ET on the production of salicylic acid and umbelliferone, metabolites, which are involved in stress responses in plants. In the case of umbelliferone, ET strongly induced its accumulation in comparison with ET non-treated variants.