Salicylic Acid Sustains Flower Performance Under Salinity in Calendula officinalis L. Plants Associated with ABA Responses and Antioxidant Regulation

Floral development and reproductive performance are among the most stress-sensitive processes in plants. Importantly, salicylic acid (SA) has emerged as an important regulator of abiotic stress responses in vegetative organs, but its role in maintaining flowering under salinity remains poorly understood. Here, we investigated the effects of exogenous SA (0.25–2.00 mM) on physiological, biochemical, and hormonal responses of Calendula officinalis L. exposed to 100 mM NaCl. Salinity significantly reduced vegetative growth, flower production, flower diameter, relative water content, and photosynthetic pigments, while increasing lipid peroxidation, proline accumulation, antioxidant enzyme activities, and abscisic acid (ABA) levels. SA alleviated these effects but in a dose-dependent manner. Under salinity, 0.25–0.50 mM SA improved vegetative and floral performance, with plant height, leaf number, and flower number increasing by up to 30.5%, 59.6%, and 100%, respectively. These responses were accompanied by a modulation of chlorophyll, carotenoid and malondialdehyde contents, as well as enzyme activities. However, high SA concentrations did not confer additional benefits and occasionally induced mild phytotoxic effects. SA-treated plants also exhibited enhanced ABA accumulation under salinity, supporting the involvement of ABA-associated responses to salinity. Collectively, our findings indicate that salicylic acid mitigates the detrimental effects of salinity on flower production and quality through coordinated modulation of antioxidant responses and ABA-associated responses.