New insight into silica deposition in horsetail

Fluorescence microscopy has revealed ornate silica 'skeletons' of many of horsetail's anatomical structures and, in particular, the stomata are shown to be heavily silicified. The deposition of silica throughout horsetail was compared to the deposition of the carbohydrate callose in other plants including the related fern and it was shown to be identical. Silica deposition in horsetail was shown to mimic the known deposition of callose in other higher plants.

This suggested that callose might template silica deposition in horsetail and other biosilicifiers. To test this hypothesis we added a commercially available form of callose to solutions of silicic acid and determined if silica was formed using both fluorimetry and fluorescence microscopy.

Keele researchers found that callose initiated silica formation in undersaturated solutions of silicic acid and catalysed silica formation in saturated solutions of silicic acid. The former is the first example of any biomolecule which has been shown to be capable of inducing silica formation in an undersaturated solution of silicic acid.

Callose may be the 'missing link' in silica formation in horsetail and all other callose-forming biota including diatoms.