Exogenous 5-aminolevulinic acid alleviates low-temperature injury by regulating glutathione metabolism and β-alanine metabolism in tomato seedling roots

Food availability represents a major worldwide concern due to climate change and population growth. Low-temperature stress (LTS) severely restricts the growth of tomato seedlings. Exogenous 5-aminolevulinic acid (ALA) can alleviate the harm of abiotic stress including LTS; however, data on its protective mechanism on tomato seedling roots, the effects of organelle structure, and the regulation of metabolic pathways under LTS are lacking. In this study, we hope to fill the above gaps by exploring the effects of exogenous ALA on morphology, mitochondrial ultrastructure, reactive oxygen species (ROS) enrichment, physiological indicators, related gene expression, and metabolic pathway in tomato seedlings root under LTS. Results showed that ALA pretreatment could increase the activity of antioxidant enzymes and the content of antioxidant substances in tomato seedlings roots under LTS to scavenge the massively accumulated ROS, thereby protecting the mitochondrial structure of roots and promoting root development under LTS. Combined transcriptomic and metabolomic analysis showed that exogenous ALA pretreatment activated the glutathione metabolism and β-alanine metabolism of tomato seedling roots under LTS, further enhanced the scavenging ability of tomato seedling roots to ROS, and improved the low-temperature tolerance of tomato seedlings. The findings provide a new insight into the regulation of the low-temperature tolerance of tomato by exogenous ALA.