Suberin nanostructures of Malus domestica Borkh. (Rosaceae) pericarp

New data are presented on nanosized suberin structures that directly participate in the formation of suberin deposits into the cell walls of the Malus domestica outer pericarp zone. The nanostructures were spherical formations containing conglomerates of electron-dense nanoparticles (diameter 5-30 nm) in the center. It has been demonstrated for the first time that the site of synthesis of suberin monomers, along with the endoplasmic reticulum (ER), may be the chloroplasts of hypoderm cells. Several possibilities for the transport of suberin nanoparticles have been discovered: via ER cisterns and its subdomains, via Golgi apparatus microvesicles, and via plasma membrane invaginations. The membrane structures of these compartments are directly related to intracytosis, the intracellular movement of suberin monomers; they can carry suberin monomeric precursors of a lipid nature in the membranes themselves or in the tubule's lumen. Either way, fusion with the hydrophobic surface of the suberin plate releases monomers, and they become accessible to apoplastic enzymes that polymerize suberin. It cannot be ruled out that the extremely arid conditions of the steppe ecological zone where the M. domestica grew could have influenced the features of metabolic processes, in particular, activating all possible pathways for the formation of suberin monomers, which make up suberin nanostructures.