Large lipid droplets of the guard cells are dynamic organelles of the functioning stomata of Fagraea ceilanica.

• Typical chloroplasts are present only in subsidiary cells of stomatal complexes. • Large lipid droplets are specific organelles of guard cells in Fagraea ceilanica. • The volume of lipid droplets can change in the stomata during stomatal movements. • When water supply to a leaf ceases, the stomatal conductance lowers slowly. • The formation of mucilage from wall components of spongy tissue cells takes place. Fagraea ceilanica is an evergreen epiphyte, a large shrub or a small tree. Its native range is tropical and subtropical Asia. Light, scanning and transmission electron microscopy were used to study the development and structure of its stomatal complexes. They are anisocytic or helicocytic. The absence of typical chloroplasts, the presence of complex-shaped mitochondria, the diurnal formation and destruction of large lipid droplets (LDs) are structural features of F. ceilanica guard cells. The plastids of these cells have few peripheral thylakoids and contain large starch grains. The plastids of subsidiary cells are typical chloroplasts with large grana. Stomata are functional. The data obtained indicate the relation between the filling of the guard cells with LDs and the opening of stomata. The measuring of stomatal conductance revealed its slow lowering in the cut-off leaves. The leaves of F. ceilanica are protected from rapid water loss by the formation of mucilage from wall components of spongy tissue cells. Their walls facing the substomatal chamber are covered with a mucilaginous layer. [ABSTRACT FROM AUTHOR]