Abscisic acid binding by pea lipid-transport proteins in vivo

Plant lipid transfer proteins (LTPs) belong to a family of small, widespread proteins characterized by the presence of a hydrophobic cavity and binding and transporting structural and signaling lipids, secondary metabolites, and phytohormones within cells, in the intercellular space, and through phloem and xylem vessels. The aim of this study was to establish the possibility of lipid transfer protein molecules binding to the phytohormone abscisic acid (ABA) in vivo. Pea seeds were used as the study object. Preliminary experiments using immunohistochemistry methods with specific antibodies to LTP revealed a coincidence in the localization of these proteins and the ABA hormone in the cell walls of the phloem in sections of pea roots during salinity stress. This coincidence in localization patterns indicated the possible binding of ABA by these proteins. The ability of plant LTPs to bind ABA in aqueous solution was confirmed in studies using 2-p-toluidinylnaphthalene-6-sulfonate (THS). However, in vitro LTP binding to ligands may not always accurately reflect their in vivo interaction. After ether extraction, ABA was detected in the precipitated complexes of lipid transfer proteins with specific polyclonal antibodies, demonstrating the ability of LTP proteins to bind this plant hormone in vivo. In the precipitated complexes of lipid-transporting proteins with specific polyclonal antibodies, ABA was extracted and identified using enzyme-linked immunosorbent assay, which confirmed the ability of LTP to bind this hormone not only in vitro but also in vivo.