Nitrogen Limitation Adaptation (NLA) modulates phosphorus and iron homeostasis during boron toxicity in Arabidopsis thaliana

Boron (B) toxicity is a major abiotic stress factor that impairs plant growth and disrupts nutrient homeostasis. The Nitrogen Limitation Adaptation (NLA) gene has been implicated in nutrient regulation; however, its role under B toxicity remains unclear. In this study, the physiological, biochemical, and nutrient responses of wild-type (Col-0) and nla mutant Arabidopsis thaliana were investigated under mild (1 mM H3 BO3 ; 1B) and severe (2 mM H3 BO3 ; 2B) B toxicity conditions. Excess B reduced fresh weight and photosynthetic pigment levels in both genotypes; however, nla mutants exhibited lower malondialdehyde accumulation under 1B, indicating a delayed oxidative stress response. B content increased dramatically in both genotypes, whereas Fe and Mn levels were differentially affected. Mutants of the nla gene maintained higher Fe concentrations under both stress levels and were less sensitive to Mn depletion. N remained stable under 1B but slightly decreased in nla mutants under 2B, whereas C content and the C/N ratio increased in both genotypes. Importantly, nla mutants retained significantly higher P concentrations under B stress, highlighting a potential role of NLA in P homeostasis. Other macronutrients (Ca, K, Mg, and S) declined similarly in both genotypes under B stress. These findings indicate that NLA deficiency modulates specific nutrient responses and oxidative stress under B toxicity, suggesting a regulatory role of NLA in maintaining Fe and P homeostasis and contributing to stress adaptation in A. thaliana.