Histochemical and surface microstructural analyses of floral cuticles provide evidence for differential behaviors in scent volatiles emission in two tuberoses (Agave amica (Medik.) Theide and Govaerts) cultivars from Asparagaceae

Two popular cultivars of tuberose (Agave amica (Medik.) Theide and Govaerts syn. Polianthes tuberosa L.) from the family Asparagaceae, widely cultivated for floricultural purposes are ,'Calcutta Single' (CS) and 'Calcutta Double' (CD). It was evidenced that CS flowers emit intense scent volatiles as compared to CD flowers, while CD flowers retained higher contents of internal pool of scent volatiles than CS flowers. Such contrasting observations between the flowers of two cultivars suggest the role of possible barriers such as cuticles that prevent the emission of scent volatiles. The cuticular structure of both cultivars was studied using different histochemical approaches, including light and epi-fluorescence microscopies. Scanning electron microscopy (SEM) was used to understand the cuticular deposition in the cultivars. Our observations confirmed relatively higher cuticular thickness in CD flowers than in CS. SEM results showed the accumulation of wax crystalloids in CS flower and the formation of cuticular nanoridges in CD flowers over the surfaces of the tepals. In addition, accumulation of lipid droplets was also noticed on the tepal peels of the cultivars showing a denser deposition in CD. Our observations suggest that the presence of wax crystalloids in CS flowers enhances the emission of volatiles, while in CD flowers, the presence of thick cuticular nanoridges possibly deters the scent emission and accumulated as an internal pool in higher amounts. The stomatal behavior also indicates a proportional relationship between cuticular deposition and scent emission; low cuticular deposition corresponds to higher emission of floral volatiles emission and vice versa as observed in CS and CD flowers, respectively.