SALT EXPOSURE AND NITROGEN METABOLISM IN TOMATO (SOLANUM LYCOPERSICUM L.): IMPROVEMENT OF THE RESILIENCE TO ABIOTIC STRESS

Salt stress is a critical challenge to plant growth and global food security, necessitating an in-depth understanding of the mechanisms plants employ to adapt to saline environments. Nitrogen (N) metabolism plays a pivotal role in regulating plant responses to salinity, with complex interactions between salt stress and nitrogen availability influencing plant physiology and metabolism. This PhD research explored these interactions through three interconnected studies. The first study examined the physiological and biochemical responses of tomato plants (Solanum lycopersicum L.) to salt stress under varying nitrate (NO₃⁻) supplies. Salinity disrupted the Na⁺/K⁺ balance, reduced NO₃⁻ levels, and modulated N metabolism, as evidenced by changes in amino acids, proline, and GABA levels. The study highlighted the positive effects of higher NO₃⁻ availability, including increased accumulation of osmoprotectants and improved nutritional status, offering valuable parameters for developing salt-resistant cultivars. The second study investigated the differential effects of NaCl and CaCl₂ on tomato plants. While Na⁺ toxicity induced the synthesis of osmoprotectants like proline, trehalose, and GABA, Cl⁻ reduced the availability of key anions and carbon compounds, affecting biomass and Krebs cycle intermediates. These findings underscore the distinct impacts of specific ions on N and C metabolism under salt stress, advocating for tailored agronomic strategies. The third study focused on the potential of a combined NO₃⁻/NH₄⁺ regime to mitigate salt stress. The results revealed that partially replacing NO₃⁻ with NH₄⁺ in nutrient solutions enhanced N assimilation, improved ion balance, and promoted metabolic adjustments in roots and leaves. This dual nitrogen strategy alleviated salinity-induced reductions in growth and development by conserving energy for stress-responsive mechanisms. Overall, this research provides novel insights into the physiological and metabolic responses of tomato plants to salt stress, emphasizing the importance of nitrogen form and availability. These findings contribute to developing agronomic practices and molecular tools to enhance salt tolerance in crops, paving the way for sustainable agriculture in saline environments.