Adsorption of cell-penetrating peptide Tat₂ and polycation luviquat FC-370 to triticale microspore exine

Microspores are the pre-gametophyte stage of pollen, and have proven to be a successful tissue culture material for the production of doubled haploid plants. Microspore culture has also been used as a platform for the production of transgenic plants. The use of cell-penetrating peptides (CPPs) as transfection agents in microspores has been previously demonstrated, but at low efficiencies. Here, the pH dependent adsorption of the cationic CPP Tat₂ to the sporopollenin surface of the microspore (the exine) has been explored using electrophoretic light scattering (ELS). Furthermore the adsorption of a commercially available polycationic polymer; Luviquat FC-370 (polyquaternium D-16, PQ-D16) was similarly measured using ELS. It was found that a suspension media with a pH less than 7.0 showed an approximately ten fold decrease in the amount of Tat₂ that was required before apparent surface neutralization. This data suggests that a change in the surface chemistry of the microspore occurs in acidic pH conditions, that modulates the binding affinity of the CPP Tat₂ in a non-trivially complex manner.