Response of 5-aminolevulinic acid to plant abiotic stress

Non-protein amino acid 5-aminolevulinic acid (ALA) is a precursor of tetrapyrrole compounds, which can be synthesized through the C4 and C5 pathways, involving in many physiological processes, such as photosynthesis, respiration, and nitrogen metabolism. Under normal physiological conditions, ALA maintains a low physiological level, while exogenous ALA application or under abiotic stress, its content can be increased to varying degrees, thereby regulating plant growth, development, and stress responses. ALA, as a potential signaling molecule, can enhance the activity of antioxidant system, increase photosynthetic efficiency, promote the accumulation of osmolytes, and regulate hormone signaling, thus improving the resistance of plants to abiotic stresses such as drought, salt, heavy metals, low temperature, and high temperature. However, till now, ALA-mediated plant stress resistance and possible physiological mechanism were not entirely clear. In this review, based on the current research progress on ALA, whose metabolism and response to plant abiotic stress were summarized. Also, the interaction between ALA and signaling molecules such as hydrogen sulfide (H2S) and nitric oxide (NO) were concluded. In addition, the future research directions were prospected.