The Arabidopsis thaliana seed is a capsule composed of the embryo, endosperm, and seed coat. The seed coat covers the embryo and endosperm, contributing to seed dormancy and longevity. It consists of dead cells derived from the inner and outer integumental layers. The inner integuments contain tannins, a type of flavonoid. TT4 encodes the chalcone synthase, the enzyme responsible for the first committed step in flavonoid biosynthesis. Previous studies reported that tt4 loss-of-function seeds lack tannins at the inner integuments. However, histological staining of the tt4 seed sections revealed an unexpected signal at the outer integument 1 (oi1) cell layer. In this master project, I aimed to investigate the nature of the deposition leading to that unexpected signal and understanding why the absence of TT4 leads to its formation. Using histology and electron microscopy, I showed the presence of an excess of lignin and suberin depositions at oi1 cells of tt4. Reporter line analysis revealed the existence of the TT4 protein in oi1 cells during seed coat development. Finally, physiological assays in different genetic backgrounds provided evidence that excess lignin and suberin depositions in oi1 cell layer of tt4 contribute to increased longevity and impermeability. Overall, this work suggests that a compensatory mechanism exists, involving TT4 to promote the impermeability of the oi1 cell layer in the seed coat.