GABA-mediated early iron deficiency responses in Medicago truncatula

Iron (Fe) is essential for plant growth, but its low availability in calcareous Mediterranean soils leads to chlorosis and reduced crop productivity, resulting in significant economic losses. Using a controlled hydroponic system as a mechanistic model inspired by the Fe limitation constraints characteristic of calcareous soils, this study investigated whether γ-aminobutyric acid (GABA) pretreatment influences Fe acquisition responses in Medicago truncatula . Plants were pretreated with 1.5 mM GABA for 72 hours and subsequently grown for seven days under Fe sufficient and deficient conditions. Under Fe-deficient conditions, known root responses were triggered earlier in pretreated plants, as evidenced by the acidification of the nutrient solution from the first day of Fe starvation, the induction of ferric-chelate reductase activity, and the accumulation of flavins in roots as early as 2 days after Fe-deprivation. In the same line, GABA-pretreated plants displayed earlier metabolic shifts, mainly in roots and to a lesser extent in shoots, with increases in Krebs cycle–related organic acids and amino acids, thereby stimulating both the Krebs cycle and the GABA shunt. These adjustments may contribute to an increased supply of energy and reducing power under Fe-deficient conditions. Hormonal analysis revealed that the most significant changes occurred in the roots under Fe deficiency. The pretreatment modified the profiles of indole-3-acetic acid, abscisic acid, and jasmonic acid, compared with both the Fe-sufficient and Fe-deficient untreated plants. Taken together, the physiological, biochemical and molecular responses indicate that GABA pretreatment promotes an earlier activation of Fe acquisition-related mechanisms under Fe-limited conditions.