β-Aminobutyric Acid Pretreatment Confers Salt Stress Tolerance in Brassica napus L. by Modulating Reactive Oxygen Species Metabolism and Methylglyoxal Detoxification

Salinity is a serious environmental hazard which limits world agricultural production by adversely affecting plant physiology and biochemistry. Hence, increased tolerance against salt stress is very important. In this study, we explored the function of β-aminobutyric acid (BABA) in enhancing salt stress tolerance in rapeseed (Brassica napus L.). After pretreatment with BABA, seedlings were exposed to NaCl (100 and 150 mM) for 2 days. Salt stress increased Na content and decreased K content in shoot and root. It disrupted the antioxidant defense system by producing reactive oxygen species (ROS; H₂O₂ and O₂^•-), methylglyoxal (MG) content and causing oxidative stress. It also reduced the growth and photosynthetic pigments of seedlings but increased proline (Pro) content. However, BABA pretreatment in salt-stressed seedlings increased ascorbate (AsA) and glutathione (GSH) contents; GSH/GSSG ratio; and the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT), glyoxalase I (Gly I), and glyoxalase II (Gly II) as well as the growth and photosynthetic pigments of plants. In addition, compared to salt stress alone, BABA increased Pro content, reduced the H₂O₂, MDA and MG contents, and decreased Na content in root and increased K content in shoot and root of rapeseed seedlings. Our findings suggest that BABA plays a double role in rapeseed seedlings by reducing Na uptake and enhancing stress tolerance through upregulating the antioxidant defense and glyoxalase systems.