Effects of exogenous γ-aminobutyric acid concentrations on growth and nutrient uptake in trifoliate orange (Poncirus trifoliata) seedlings under boron-deficient and -sufficient conditions.

Boron (B) deficiency is a major factor limiting plant growth and yield. Gamma-aminobutyric acid (GABA), a crucial non-protein amino acid in plants, plays vital roles in plant growth and stress responses. However, its specific regulatory role on nutrient homeostasis under B deficiency remains unclear. This study elucidated the regulatory effects of exogenous GABA on the growth and mineral element acquisition in trifoliate orange (Poncirus trifoliata) seedlings under both B-deficient and B-sufficient conditions. A completely randomized experiment with a two-way factorial design was conducted, where plants grown hydroponically were exposed to B-deficient or B-sufficient nutrient solutions, supplemented with five GABA concentrations (0.01, 0.05, 0.1, 0.5, and 1 mM). Our results showed that the effects of GABA are highly concentration-dependent. Under B deficiency, low concentrations of GABA significantly promoted plant growth, with the 0.1 mM treatment increasing plant biomass by 23.3% compared to the B-deficient control. These optimal treatments restored growth by improving root morphological traits and enhancing the accumulation of essential mineral elements (increasing specific nutrient accumulations by up to 27.6%). In contrast, high GABA concentrations exhibited toxic effects irrespective of B supply. Specifically, the 1 mM treatment decreased overall biomass by 8.9% and 19.2% under B-deficient and B-sufficient conditions, respectively. This study provides a physiological foundation for understanding GABA-mediated nutrient regulation, indicating its potential as a candidate for future nutrient management strategies under B-deficient conditions.