Structural Features of Root Cells of Nicotiana tabacum Grown in the Presence of Short Peptides AEDL and Its Methylated Analog AED(OMe)L

Peptides as signaling molecules play an important role in intercellular communication. Exogenous peptides AlaGluAspLeu (AEDL) and AlaGluAsp(OMe)Leu (AED(OMe)L) at a concentration of 10−7 M stimulate the growth and development of Nicotiana tabacum. A detailed study of Nicotiana tabacum root cells grown in the presence of exogenous peptides AEDL and AED(OMe)L using transmission electron microscopy revealed characteristic differences in the ultrastructure of some cytoplasmic organelles compared to control cells. Importantly, vacuoles and autophagosomes differing in size and content, as well as amyloplasts and proteinoplasts never previously described in the literature, were found in the cells of the outer and inner root cortex. Only lytic vacuoles were detected in the cytoplasm of control cells, whereas in the presence of peptides, predominantly protein-storing vacuoles were found in root cells. In the presence of the exogenous short peptide AEDL, tobacco root cells contained amyloplasts with numerous large starch granules in the stroma, which were not detected in control cells. In the presence of the modified short peptide AED(OMe)L, leukoplasts contained protein bodies. Moreover, in contrast to control cells and cells grown in the presence of the AEDL peptide, a megaphagic (pexophagic) variant of autophagosomes with peroxisomes was detected for the first time in tobacco cells treated with AED(OMe)L. Characteristic types of phagophores were identified, forming numerous small autophagosomes with cytoplasmic regions, multivesicular bodies or concentric membranes, and cytoskeletal elements. Data on the expression of the ATG, TOR, and FREE1 genes confirmed the pattern of the existence of a large number of small autophagosomes. Based on the obtained data, a scheme for the regulation of the formation of root architecture of Nicotiana tabacum in the presence of AEDL and AED(OMe)L was proposed.