Histochemistry of simple hairs from the foliar cavities of Azolla filiculoides

Abstract

The foliar cavities of the water fern Azolla filiculoides have as many as 20 – 25 simple hairs (SH) protruding from the epidermal cells that delimit the cavity. These SH have a transfer-like ultrastructure normally associated with secretion of metabolites. The aim of this study was the chemical characterization of the compounds that accumulated in the SH of the zones F1-12 (from 1st to 12th leaves) and F13 (from 13th until the end of the sporophyte) throughout the seasons during a 1-year study. The histochemical tests show that the vacuoles of simple hairs contain a mixture of lipids, unsaturated lipids, polysaccharides, polyphenols (o-dihydroxyphenols, phenols with free ‒OH groups and tannins) and alkaloids or alkaloid-like compounds. These substances do not show seasonal variation, having been present throughout the one-year study. The histochemical analysis demonstrated that the SH always have a variety of metabolites. The function within the Azolla-Anabaena symbiosis is not known.

Key words:

• Alkaloids
• Azolla filiculoides
• histochemistry
• lipids
• polysaccharides
• tannins

Acknowledgements

This work was supported by FCT-MCES under POCTI and by FSE-IIIQCA, through the fellowship PRAXIS XXI/BD/21325/99 to A.L. Pereira. The authors thank I. Melo of Lisbon Botanical Garden (Faculty of Sciences, University of Lisbon) for A. filiculoides.