Integrated Transcriptomic and Metabolomic Analyses Reveal the Positive Effects of 5-Aminolevulinic Acid (ALA) on Shading Stress in Peanut (Arachis hypogaea L.)

Shading stress is a major negative abiotic environmental factor seriously affecting peanut growth, development, and ultimately resulting in a yield decrease in peanut in peanut/maize intercropping systems. However, 5-aminolevulinic acid (ALA) is a potential plant growth regulator that can enhance its tolerance to various abiotic stresses. However, there is limited information on how ALA affects plant physiology and molecular mechanisms under shading stress. To address this, field experiments were designed involving two shading conditions (CK and AS0, no shading; S40 and AS40, 40% shading) and two ALA foliar sprayed levels (CK and S40, no ALA application; AS0 and AS40, 20 mg L⁻¹ (0.15 mM) ALA application) to investigate the effects of the exogenous application of ALA under shading stress via the evaluation of both transcriptome and metabolome. The research results suggested that the exogenous ALA application under normal light conditions significantly enhanced photosynthesis, while exogenous ALA application could improve the stability of the cell membrane structure and biological function in response to shading stress and thereby enhance shading tolerance of the plant. The results also implied that exogenous ALA regulates the adaptability of peanuts under different light conditions by affecting the concentration of endogenous ALA. This finding improves the understanding of ALA’s regulatory molecular mechanisms and the metabolic pathways of peanuts under shading stress. Our results extend the application of ALA in agricultural production and will provide a reference for crop cultivation, especially for peanut/maize intercropping systems.