Ontogenesis of D-type stomata and cork-warts on the leaf epidermis of Camellia japonica (Theaceae) and functional assessment

Cork-warts are particular structures forming round areas by radially arranged concentric rows of suberized cells, and have been found in many flowering plant genera. The roles of large D-type stomata and cork-warts in plant blades remained unclear for many years. To distinguish the large D-type stomata from cork-warts and identify their possible functions, both the lower epidermis and cross-sections of leaves were studied in Camellia japonica L. Simultaneously, Fourier Transform Infrared Spectroscopy (FTIR) technology was used to assess whether the cork-warts were really the structures accumulating suberin. Furthermore, the gas exchange and water evaporation functions of D-type stomata and cork-warts were measured. The results showed that D-type stomata and cork-warts had the same origin but they developed into two separate functional structures at different developmental stages. FTIR spectroscopy revealed that the cork-warts accumulated more suberin with phenolic domains, and more cell wall polysaccharide than matured typical stomata and cork-wart protomeristem. It is proposed that the D-type stomata and cork-warts are responsible for air exchange and water evaporation and their presence might correlate with the adaptation of Camellia species to the more humid understory environment.