Plant Physiol, February 2002, Vol. 128, pp. 707-713
Characterization of Calcium Oxalates Generated as Biominerals in
Cacti1
Paula V.
Monje and
Enrique J.
Baran*
Departamento de Biología, Bioquímica y Farmacia,
Universidad Nacional del Sur, San Juan 670, 8000-Bahía Blanca,
Argentina (P.V.M.); Centro de Química Inorgánica (Centro
de Química Inorgánica/Consejo Nacional de Investigaciones
Cientificas y Técnicas de la República Argentina,
Universidad Nacional de la Plata), Facultad de Ciencias Exactas,
Universidad Nacional de La Plata, C.Correo 962, 1900-La Plata,
Argentina (E.J.B.)
The chemical composition and morphology of solid material isolated
from various Cactaceae species have been analyzed. All of the tested
specimens deposited high-purity calcium oxalate crystals in their
succulent modified stems. These deposits occurred most frequently as
round-shaped druses that sometimes coexist with abundant crystal sand
in the tissue. The biominerals were identified either as
CaC2O4.2H2O (weddellite) or as
CaC2O4.H2O (whewellite). Seven
different species from the Opuntioideae subfamily showed the presence
of whewellite, and an equal number of species from the Cereoideae
subfamily showed the deposition of weddellite. The chemical nature of
these deposits was assessed by infrared spectroscopy. The crystal
morphology of the crystals was visualized by both conventional light
and scanning electron microscopy. Weddellite druses were made up of
tetragonal crystallites, whereas those from whewellite were most often
recognized by their acute points and general star-like shape. These
studies clearly demonstrated that members from the main traditional
subfamilies of the Cactaceae family could synthesize different chemical
forms of calcium oxalate, suggesting a definite but different genetic
control. The direct relationship established between a given Cactaceae
species and a definite calcium oxalate biomineral seems to be a useful
tool for plant identification and chemotaxonomy.
1
This research was supported by Consejo Nacional
de Investigaciones Cientificas y Técnicas de la República
Argentina and Agencia Nacional de Promoción Cientifica y
Tecnológica (PICT 06148). E.J.B. is a member of the
Research Career from CONICET and P.V.M. benefits from a fellowship from
the same organization.
*
Corresponding author; e-mail baran{at}quimica.unlp.edu.ar; fax
54-221-4259485.
© 2002 American Society of Plant Physiologists
