Bioactive farina of Notholaena sulphurea (Pteridaceae): Morphology and histochemistry of glandular trichomes

The morphology and distribution of glandular trichomes in fronds at different developmental stages were investigated in Notholaena sulphurea, and the main components of the secreted material (farina) were identified. In addition antifungal and molluscicidal activities of farinose exudate were tested. Trichomes were examined using conventional light and scanning electron microscopy (SEM). The histochemical studies were conducted using the following tests on hand-sections: Toluidine Blue, Calcofluor White, Ruthenium Red, Phloroglucinol/HCl, NADI reagent, Sudan black B, Sudan IV, Nile Blue, Neutral Red, ferric chloride, Vainillin/H2SO4, Vainillin/HCl, alumimium chloride and Benedict reagent. Antifungal activity was evaluated by broth microdilution techniques and molluscicidal activity by Adenusi, 2008. One type of glandular trichomes was found in both the adaxial and the abaxial surfaces. Young fronds were densely covered with trichomes; however, the density decreased progressively with frond maturity. Secretions flowed by diffusion through cuticle micropores, and no rupturring mechanism to release secretions was observed. Histochemical reactions revealed that the main components of the materials secreted by trichomes include polysaccharides, lipids, terpenes, phenols and flavonoids. The farina showed antifungal and molluscicidal activity. Our results strongly support an ecological role of farina as herbivore deterrent and resistance to fungi. Since N. sulphurea is a xeric adapted fern, flavonoids present in farinous secretions may also function as stress protection against harsh environmental conditions.