Calcium oxalate crystals in Geohintonia mexicana (Cactaceae: Cactoideae)

BORRELLI, N.; M. OSTERRIETH Y J. C. SORIA COLUNGA

Mar del Plata, Buenos Aires, Argentina

Congreso; 7th International Meeting on Phytolith Research-4th South American Meeting on Phytolith Research; 2008

Society for Phytolith Research-Grupo de Estudios Fitolíticos Aplicados del Cono Sur-Instituto de Geología de Costas y del Cuaternario

The Cactaceae family is native to the American continent, and the greatest diversity of species is distributed in arid and semiarid regions. The Chihuahuan Desert (north-central of Mexico to southwestern of EEUU) is one of the main center of cactus diversity and present high degrees of endemism, particularly in the southeastern region, where the state of Nuevo León is located. Calcium oxalate crystals are considered to be the most commonly biomineralizations in higher plants and the Cactaceae family is one of the major producers. Geohintonia mexicana Glass & Fitz Maurice (Cactaceae, Cactoideae, Cacteae) is endemic to a small area of southeastern Nuevo León in NE México. The soils where this species develops are Entisols with silt loam texture, high gypsum contents (59-78%), and consequently, high calcium (108-128 mmol/L) and sulfates (134-145mmol/L) contents in soil solution. The aim of this work is to describe the presence of calcium oxalate crystals and to determine their density in the stem and roots of G. mexicana. Stem and roots were washed with distilled water, some of the cross sections were cleared with 50% sodium hypochlorite, mounted on gelatin-glycerine and observed under optical and scanning electron microscope. To determine crystal density, all crystals within the following areas were counted: 0.132cm2 (stem) and 0.088cm2 (roots). In the stem a high density (53 crystals/cm2) of druses were observed. The crystals were distributed in the parenchyma, both in rectangular (palisade parenchyma) and isodiametric cells. Druses had an average size of 75x50µm, being smaller (40x25µm) those located below the epidermis. In the roots, a high density (79 crystals/cm2) of druses (average size: 37.5x35µm) were observed too, being distributed in the cortical parenchyma and in the radium zones. According with Monje y Baran (2002), these druses could be composed of weddellite (CaC2O4.2H2O) based on their external aspect. Because of the basal material of the soils is gypsum, it represents a large calcium source to the soil solution, so the high calcium oxalate crystal production could be related with the regulation of intracellular calcium ions and with a physiological mechanism to preserve water.