Abstract
Salinity is a significant challenge for agriculture in semi-arid regions, affecting the growth and productivity of plants like Tropaeolum majus (nasturtium), which is valued for its ornamental, medicinal, and food uses. Salt stress disrupts the plant's biochemical, physiological, and anatomical processes, limiting its development. This study investigates the potential of proline as an osmoprotectant to mitigate the effects of salt stress on nasturtium's growth and physiology. A completely randomized factorial design was employed, testing five levels of electrical conductivity (0.0, 1.50, 3.00, 4.5, 6.5 dS m(-1)) and four proline concentrations (0.0, 5.00, 10.0, 15.0 mM) with six replicates. The results showed that proline application, particularly at 15.0 mM, enhanced growth parameters such as leaf number, stem diameter, and root length. At moderate salinity (3.0 dS m(-1)), proline significantly improved gas exchange, increasing net photosynthesis, transpiration, and stomatal conductance. Additionally, proline reduced the negative impact of salt stress on the fresh mass of leaves, stems, and roots, and increased both the mass and number of flowers. Proline also elevated the levels of total phenolic compounds and vitamin C while reducing soluble sugars, particularly under moderate salt stress (4.75 dS m(-1)). Overall, applying 15.0 mM proline shows promise for enhancing the biomass accumulation, flower production, and overall quality of nasturtium under saline conditions.