Adhesion of the mucilage envelope of Ocimum basilicum seeds probed by sum frequency generation spectroscopy

The attachment of seeds to natural surfaces is important for the reproductive success of plants. This study investigates the adhesion mechanisms of Ocimum basilicum seed mucilage to CaF₂ and polystyrene surfaces, using sum frequency generation (SFG) vibrational spectroscopy and pull-off force measurements. The results show that the adhesion is driven by the formation of crystalline cellulose at the interface. Initially, cellulose within the mucilage envelope is disordered due to strong cellulose-water interactions. As water evaporates, cellulose interactions with the substrate increase, leading to a more ordered molecular structure, with the degree of order varying between substrates. The CaF₂ surface promotes a more crystalline cellulose assembly, whereas polystyrene results in a less ordered structure. Despite the reduced order, adhesion strength is higher on the polystyrene surface, suggesting that molecular disorder enhances the ability of the mucilage to absorb mechanical stress, thereby improving adhesion. These findings highlight the significant role of substrate chemistry in seed adhesion.