ABSTRACT
The interface between plants and the surrounding environment is formed by the modification of primary cell walls with the hydrophobic biopolymers cutin and suberin. These apoplastic barriers regulate plant–environment interactions occurring across leaf and root interfaces including water and solute transport and protection against pathogens. Major historic steps in cutin and suberin research mainly related to advances in microscopy, significantly advancing our knowledge of apoplastic barriers, are pointed out. Experimentally well-established results on biosynthesis and function of apoplastic barriers in plants are briefly summarised. Methodical aspects still restricting a detailed understanding of these barriers are given. Still existing limitations in experimental procedures and resolution of equipment are discussed. Biotechnological ideas for building synthetic, bio-inspired polymers using cutin and suberin polymers models are presented. Finally, several open and new research questions related to apoplastic barriers are raised. This includes not only the identification of the exact molecular structures of postulated polar paths of transport in cuticles but also the structure of the diffusional barrier build by cuticular waxes. Further aspects cover questions related to inverse transpiration (water uptake via cuticles) and biomechanical consideration for the potential formation and function of lignin in Casparian strips resisting the root pressure developing in the central cylinder.
