Study on the laminar hydathodes of Ficus formosana (Moraceae) V.: Divergent evolution between stomata and water pores

Water pores and stomata play roles in water regulation through guttation and transpiration, respectively. On the Ficus formosana leaves, water pores are present in the hydathodes on the upper surface, whereas stomata are randomly distributed on the abaxial epidermis of non-vein regions. Here, we investigate the development and physiological functions of water pores and stomata from the same leaves and explore their evolutionary relationships. We compare their structures using optical and electron microscope, and establish their functions through physiological experiments. Ficus formosana Maxim. f. shimadae Hayata water pores are almost circular, whereas its stomata are elliptical. Water pores are clustered and occur at a higher density than stomata, with these latter being anomocytic. Our ultrastructural analysis shows that F. formosana f. shimadae water pores contain amyloplasts and have thickened walls around the pores, with many plasmodesmata observed during their development. The chloroplasts of the stomatal guard cells possess typical plant cell grana and thylakoids, and the inner walls around the stomatal space are thickened. The differentiation and developmental processes of water pores and stomata are similar. Stomatal apertures were regulated by light/dark, fusicoccin, ABA, or mannitol treatments, but water pores were not. Our findings indicate that water pores and stomata on the F. formosana f. shimadae leaves evolved divergently