The impact of salinity stress on photosynthetic pigments, osmoprotectants, and antioxidant activity of three aromatic plants, Pelargonium graveolens L., Mentha longifolia L., and Chrysanthemum frutescens L.

Salinity represents one of the most critical hazards that cause significant crop losses, including those of aromatic and medicinal plants. These plants have medicinal uses that include anti-inflammatory, antiviral, antibacterial, and anticancer properties. According to our study, the three aromatic plants Pelargonium graveolens L., Mentha longifolia L., and Chrysanthemum frutescens L. exhibited distinct physiological responses to varying salinity levels (50, 75, and 100 mM NaCl). In M. longifolia L. and C. frutescens L., chlorophyll a and carotenoids increased significantly at 50 mM NaCl; in comparison, chlorophyll b reached the highest amount at 75 and 100 mM NaCl in P. graveolens L. and M. longifolia L., respectively. Osmoprotectant compounds (glucose, sucrose, and proline) increased in the three investigated plants in response to salinity. The malondialdehyde (MDA) and ascorbic acid (AsA) levels increased significantly at 75 and 100 mM NaCl in P. graveolens L. and M. longifolia L., respectively. The highest activity of superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO) and ascorbate peroxidase (APX) antioxidant enzymes was at 50 mM NaCl in P. graveolens L. Moreover, peroxidase (POX) enzyme activity was more pronounced at 75 mM NaCl in P. graveolens L., and C. frutescens L. According to our findings, the salinity levels enhanced the growth of C. frutescens L. and had no significant effect on P. graveolens L. plants, while the growth of M. longifolia L. plants was reduced significantly only at 100 mM NaCl. Therefore, these plants represent a recommended choice for irrigation with mild to moderate saline water.