The puroindoline proteins (PINA and PINB) of wheat (Triticum aestivum) are largely responsible for grain hardness (kernel texture), a property important in food technology and the wheat trade. PINs are small, basic, cysteine-rich proteins that possess antimicrobial properties, which make them very attractive for novel medical, pharmaceutical and food technology applications. Soft grain texture depends on the presence of both PIN proteins in their wild type form. To investigate grain texture and antimicrobial functions, interactions between PINA and PINB were investigated using Bimolecular Fluorescence Complementation (BiFC) in a plant system. The BiFC method is based on the complementation between fragments of enhanced Yellow Fluorescence Protein (YFP) that have been attached to target PIN proteins. Results based on the fluorescence intensity obtained for the various interaction combinations showed that PINA and PINB are able to interact in the cytoplasm and chloroplast. Additionally, PINB showed interaction with itself in the chloroplast. Western blot analysis using a monoclonal antibody was performed and confirmed the presence of recombinant PINA-PINB in oligomeric (~48KDa) forms. These results support the suggestion that the interactions between the PINA-PINB and PINB-PINB proteins are functionally important in affecting grain hardness.