Complex patterns of multiple biomineralization in single-celled plant trichomes of the Loasaceae.

Abstract

Plants of the family Loasaceae are characterized by a usually dense indument of various trichome types, including two basically different types of mineralized, unicellular trichomes (stinging hairs or setae and scabrid-glochidiate trichomes). Mineralized trichomes have long been known to have silicified or calcified walls, but recent studies demonstrated that trichomes of Loasaceae may also contain calcium phosphate. The current study investigates the distribution of different biominerals in the mineralized trichomes across several different taxa. Plants from cultivation were studied with scanning electron microscopy including energy dispersive x-ray analyses and element mapping. The vast majority of the 31 species investigated had at least two different biominerals in their trichomes, and 22 had three different biominerals in their trichomes. Thirty of the species had calcium phosphate in their trichomes. Loasa was mostly free of silica, but contained calcium phosphate in trichome tips and barbs, whereas calcium phosphate and silica were found in representatives of other genera of the family (Blumenbachia, Caiophora, Nasa). Biomineralization is remarkably diversified between species, different trichome types and parts of the same trichome. Individual genera largely had different patterns of biomineralization. The presence of three biominerals in the trichomes of the basally branching Eucnide urens indicates either an early evolution and subsequent loss or several independent origins of multiple biomineralization. Differential biomineralization of the parts of individual, unicellular trichomes clearly indicates an extraordinary degree of physiological control over this process.