Regulation of 5-Aminolevunilic Acid and Its Application in Agroforestry

The review briefly introduces the natural occurrence, physicochemical properties, and biosynthesis of 5-aminolevuinic acid (ALA) and highlights a variety of applications in the planting industry and its possible mechanisms. It has been known that ALA can be used as biological pesticides, fungicides, and herbicides when the concentrations are higher than 838 mg L-1 (about 5 mmol L-1). When ALA concentrations are 100-300 mg L-1, it can be used to thin surplus flowers in the spring of orchards and promote fruit coloration before maturation. When the concentrations are lower than 100 mg L-1, especially not higher than 10 mg L-1, ALA can be used as a new plant growth regulator to promote seed germination, plant (including root and shoot) growth, enhance stress tolerance, increase crop yield, and improve product quality. In photosynthesis, ALA is involved in the regulation of the whole process. In stress tolerance, ALA induces plant preventive and protective systems through the NO/H2O2 signaling network. In secondary metabolism, ALA regulates many gene expressions encoding transcription factors or function proteins to promote anthocyanin and flavonol biosynthesis and accumulation. In general, ALA promotes plant health and robustness, reduces the use of chemical fertilizers and pesticides-which is conducive to improving the ecological environment, human production, and living conditions-and has a broad application prospect in agroforestry production. As a new plant growth regulator with multiple and powerful functions, the underlying regulatory mechanisms need more study.