Calcium phosphate in plant trichomes: the overlooked biomineral

Abstract

Calcium phosphate was unknown as a plant biomineral until recently reported in Neotropical Loasaceae. Here, we demonstrate its widespread occurrence in the trichomes of several plant families, including Brassicaceae. Calcium phosphate is the primary biomineral in, e.g., the bones and teeth of higher animals; in plants, it was only recently discovered in the stinging hairs and scabrid-glochidiate trichomes of South American Loasaceae (Ensikat et al. in Sci Rep UK 6:26073, 2016), where it appears to be deposited highly specifically, often replacing the common plant biomineral silica. We initiated a broader survey in a range of different plant orders to investigate a possibly wider distribution of calcium phosphate biomineralization in plants. Scanning electron microscopy with EDX element analysis and mapping was used for the detection of the biominerals: calcium phosphate, calcium carbonate, and silica in the trichomes of several common plant species of different orders. Results were authenticated with Raman spectroscopy. Calcium phosphate was found in the trichomes of several species in the orders Malpighiales, Rosales, Boraginales, and Brassicales. It occurred in trichome tips, replacing the more common silica, or together with silica and calcium carbonate at specific locations in the trichome cell walls. Most surprisingly, it was found in the trichomes of Arabidopsis thaliana, one of the most studied plant species-where it had been overlooked so far. The wide distribution of calcium phosphate as plant biomineral here demonstrated and the striking mineralization patterns with three different biominerals in the walls of single-celled trichomes underscore an unexpected complexity in plant biomineralization.

Trichome Biomineralization and Soil Chemistry in Brassicaceae from Mediterranean Ultramafic and Calcareous Soils

“…In Brassicaceae, amorphous calcium-phosphate has been recently documented in the trichome tips of the model organism Arabidopsis thaliana (L.) Heynh. [8]. The occurrence of amorphous calcium-phosphate in other lineages of Brassicaceae and particularly in Ni-hyperaccumulating species, however, is here demonstrated for the first time, underscoring that it is more widespread as a biomineral than previously documented.…”

“…Recent studies on a range of families, however, expanded our knowledge of plant biomineralization, demonstrating that calcium phosphate is also a widespread plant biomineral and that trichome biomineralization is both structurally and chemically much more complex than previously thought [4,7,8]. One of the plant groups shown to have trichomes mineralized with both calcium carbonate and calcium phosphate is Brassicaceae [8], a large and diverse family (ca. 328 genera and 3628 species; [9]) comprising numerous economically important representatives.…”

Phosphate Starvation Alters Abiotic-Stress-Induced Cytosolic Free Calcium Increases in Roots

“…Pi and Ca 2+ have a particularly interesting relationship, as they can form undissociated complexes (Cole et al, 1953;Verkhratsky and Parpura, 2014;Edel and Kudla, 2015). In animals, Ca 2+ -Pi complexes play significant structural roles (Plattner and Verkhratsky, 2015), but in plants, these have only recently been discovered in trichomes of a variety of plant species, including Arabidopsis (Ensikat et al, 2016;Mustafa et al, 2018;Weigend et al, 2018). Pi and Ca 2+ Figure 7.…”

Vibrational spectral fingerprinting for chemical recognition of biominerals

“…Because of their ability to readly accept substitution(s) and intercalation from a large variety of ions, apatites are relevant in the geophysics of pegmatite melts and, for the same reason, they are attractive for nuclear waste management and water remediation . Very recently, calcium orthophosphates have been recognized also in plant leaves, opening brand new scenarios on the role of carbonate biominerals in replacing the common plant biomineral silica …”