Ascorbic Acid Improves Tomato Salt Tolerance by Regulating Ion Homeostasis and Proline Synthesis

Area of Science:

• Plant Physiology
• Plant Stress Biology
• Biochemistry

Background:

• Salt stress significantly impacts crop yield and quality, particularly in economically important species like tomatoes (Solanum lycopersicum L.).
• Maintaining ion homeostasis, osmotic balance, and redox status is crucial for plant survival under abiotic stress conditions.
• Ascorbic acid (AsA) plays a vital role in plant defense mechanisms against various stresses.

Purpose of the Study:

• To investigate the role of endogenous ascorbic acid (AsA) levels in tomato seedlings subjected to salt stress.
• To elucidate the effects of exogenous AsA application on ion homeostasis, osmotic regulation, and redox status under NaCl-induced stress.
• To assess the potential of AsA as a tool for enhancing salt tolerance in processing tomatoes.

Main Methods:

• Hydroponic cultivation of tomato seedlings ('Ligeer 87-5') under 100 mM NaCl stress.
• Foliar application of ascorbic acid (AsA) and lycorine (LYC, an AsA synthesis inhibitor) to manipulate endogenous AsA levels.
• Measurement of enzyme activities and gene expression related to AsA synthesis, ion transport (SOS pathway), and proline metabolism (ProDH, P5CS, OAT).
• Analysis of ion content (K+, Ca2+, Mg2+) and proline accumulation in aerial parts.

Main Results:

• Exogenous AsA significantly increased AsA synthesis enzyme activity and gene expression, elevating cellular AsA content and maintaining its reduced state under salt stress.
• AsA application regulated ion transporters via the SOS pathway, enhancing selective uptake of K+, Ca2+, and Mg2+ to restore ion homeostasis.
• AsA increased proline dehydrogenase (ProDH) activity while decreasing P5CS and OAT activity, thereby reducing proline accumulation and alleviating osmotic stress.
• Lycorine treatment exacerbated salt stress impacts, which were reversed by AsA co-application.

Conclusions:

• Exogenous AsA application effectively increases endogenous AsA levels in tomato seedlings under salt stress.
• AsA reestablishes ion homeostasis and osmotic balance, crucial for mitigating salt stress damage.
• Ascorbic acid significantly enhances salt tolerance in tomato seedlings, offering a promising strategy for improving crop resilience.