Amorphous silica biomineralizations in rhizomes of Schoenoplectus californicus (C.A. Meyer) Soják (Cyperaceae)

ALTAMIRANO, STELLA MARIS; FERNÁNDEZ HONAINE, MARIANA; OSTERRIETH, MARGARITA

Rio de Janeiro

Congreso; 68º Congresso Nacional de Botânica e XXXVI Jornada Fluminense de Botânica.; 2017

Silicification of plants is a widespread process and involves a high amount of plant families. Amorphous silica biomineralizations in plant species (silicophytoliths) provide several benefits such as improvement of biomass production, antiherbivore defense, and amelioration of heavy metal toxicity. Cyperaceae is one of the main silica accumulator, along with Poaceae family. However, there are few studies of silicophytoliths in rhizomes of this family. In this study, we analyzed the content and distribution of silicophytoliths in rhizomes of Schoenoplectus californicus (C.A. Meyer) Soják from a freshwater shallow lake, Buenos Aires, Argentina. Rhizomes were placed in an ultrasound bath and washed with distilled water to remove possible mineral contaminants. Silicophytoliths were extracted through a calcination technique, they were counted and described under optical and scanning electron microscopes, and their composition was analyzed by energy dispersive spectroscopy. Silica content was measured as percentage of dry weight. In order to study the distribution of silicified cells, rhizomes were cross-sectioned by hand, cleared with 50% sodium hypochlorite, and stained with phenol. The mean silica content was of 2.29 ± 0.23% dry weight. Previous studies reported values that ranged between 1.05-3.5% dry weight for young culms and 5.38-12.65% for senescent culms. The main silicified tissues of rhizomes were epidermis, aerenchyma, parenchyma and, in lesser degree, xylem. In cross sections, cone-shaped amorphous silica bodies were observed in the epidermal cells. There were morphological differences between the cones in rhizomes and those found previously in aerial organs. Aerenchyma cells also differed between organs. Elongated and polyhedrical silicophytoliths were also observed and they may derived from epidermis and/or parenchyma. These results will be relevant not only for anatomical, but also paleobotanical/archeological studies, since the potential preservation of these structures in the soil could allow the identification of sedges in the fossil record. The important amount of silicophytoliths in rhizomes contributes to the silica biogeochemical cycle in wetlands. Finally, silicophytoliths in S. californicus could be involved in its capacity to accumulate heavy metals.