Water deficit stress changes in physiological, biochemical and antioxidant characteristics of anise (Pimpinella anisum L.)

This study was designed to evaluate the impact of water deficit stress on the seed yield and its components, physiological functions, fatty acid content and compositions, essential oil (EO) content and compositions, phenolic acids and flavonoids amounts, and antioxidant activities of anise seeds. Plants evaluations were performed under well-watered (WW), moderate water deficit stressed (MWDS), and severe water deficit stressed (SWDS). The results revealed that SWDS significantly reduced seed yield, branch number per plant, seed number, umbel number, and thousand seed weight. Water deficit stress also caused a decrease in chlorophyll content, relative water content, quantum efficiency of photosystem II, and cell membrane stability, while increasing leaf temperature. The analysis of fatty acid composition indicated that petroselinic acid was the main fatty acid and its percentage increased by 8.75% and 14.60% under MWDS and SWDS, respectively. Furthermore, MWDS increased the EO content by 1.48 times, while it decreased by 41.32% under SWDS. The chemotype of EO was altered from t-anethole/estragole in WW seeds to t-anethole/β-bisabolene in treated seeds. Higher levels of total phenolics were detected in stressed seeds. Water deficit stress increased the amount of the major class, naringin, by 1.40 and 1.26 times under MWDS and SWDS. The evaluation of antioxidant activity through reducing power, DPPH, and chelating ability assays indicated that stressed seeds exhibited the highest activity. The study's findings suggest that the application of drought stress before harvesting can regulate the production of bioactive compounds, which can affect the industrial and nutritional values of anise seeds.