Exogenous application of 5-aminolevulinic acid alleviated damage to wheat chloroplast ultrastructure under drought stress by transcriptionally regulating genes correlated with photosynthesis and chlorophyll biosynthesis

5-Aminolevulinic acid (ALA), as a precursor of plant chlorophyll synthesis, can alleviate damage to photosynthesis and thus improve the drought resistance of plants, but the mechanism behind this is still obscure, especially its correlation with functional gene transcription and noncoding RNA regulation. The leaves were collected from Aikang-58 wheat seedlings subjected to drought stress and exogenous ALA application for ultrastructure observation and gene transcription analysis. The results indicated that drought stress attenuated the photosynthesis evidenced by the decrease of net photosynthetic rate (P-n) and stomatal conductance (g(s)), damaged the chloroplast ultrastructure by destroying the thylakoid matrix, degrading the chlorophyll, and leading to lipid peroxidation of the cells due to the toxicity of free radicals, causing lipids to dissociate and combine with osmium acid to form plastoglobuli. Under drought stress, exogenous ALA pretreatment can increase the transcript abundance of the chlorophyll synthesis-related genes. Moreover, exogenous ALA increased psb28 transcript abundance under drought stress, to alleviate the damage to the chloroplast ultrastructure and photosynthesis. Our data revealed the possible gene transcriptional regulation patterns in response to drought stress and exogenous ALA alleviation.