Hydrogen Sulfide Interacts with 5-Aminolevulinic Acid to Enhance the Antioxidant Capacity of Pepper (Capsicum annuum L.) Seedlings under Chilling Stress

5-Aminolevulinic acid (ALA) is the precursor of tetrapyrrole synthesis, and hydrogen sulfide (H2S) a gas signal molecule. Studies have shown that exogenous ALA H2S can alleviate abiotic stress. This study evaluated roles their interactions in regulating antioxidant activity pepper seedlings under chilling Chilling stress significantly inhibited growth increased amounts peroxide (H2O2), superoxide anion (O2•?), malondialdehyde (MDA). and/or activities dismutase (SOD), peroxidase (POD), catalase (CAT). Moreover, enhanced ascorbate (AsA)-glutathione (GSH) cycle by increasing contents AsA GSH, ratio to dehydroascorbic GSH glutathione disulfide increased, (APX), reductase (GR), dehydroascorbate (DHAR) monodehydroascorbate (MDHAR) also increased. At transcriptional level, upregulated expressions CaSOD, CaPOD, CaCAT, CaAPX, CaGR, CaDHAR, CaMDHAR reduced H2O2, O2•? MDA, eventually mitigating inhibitory effects on seedling growth. The combination had better effect than or alone. interact regulate oxidative response