calcium oxalate crystals in Conyza canadensis (l.) cronq. and Conyza bonariensis (l.) cronq. (Asteraceae: Astereae)

Calcium oxalate crystals (CaOx) are found in most organs and tissues of many plant species. In this study the morphology and distribution of CaOx crystals in Conyza canadensis (L.) Cronq. and Conyza bonariensis (L.) Cronq. belonging to Asteraceae were investigated. CaOx crystals display a similar distribution in organs and tissues of C. canadensis and C. bonariensis. For the identification of CaOx crystals a histochemical technique (using silver nitrate and rubeanic acid) was applied to the cleared organs and tissues. Crystals in cleared organs and tissues were viewed using an Olympus photomicroscope fitted with polarizing filters. The sample tissues were also investigated with a scanning electron microscope. CaOx crystals were found in stems, leaves, petals, ovaries, and styles of two species, but no crystals were observed in filament or other tissues. Druses were observed in the stem epidermis and cortex cells and leaf epidermis cells and mesophyll layers in both species. They were also determined in corolla and style cells. The pith parenchyma cells of stem had needle-shaped and bipyramidal crystals. Styloid crystals were present in the ovary of both species. Raphides were not observed in both taxa. This study provides additional information about the presence of CaOx crystals in Asteraceae. Acta Biol Szeged 52(2):295-299 (2008) Key WordS Asteraceae calcium oxalate crystals Conyza canadensis Conyza bonariensis Accepted Nov 13, 2008 *Corresponding author. E-mail: [email protected] 295 The genus Conyza Less. belonging to tribe Astereae includes herbs, shrubs and trees and comprises over 60 species which are mainly distributed in tropical and subtropical areas. The Astereae tribe is the second largest tribe of Asteraceae, with over 170 genera and 3000 species worldwide (Bremer 1994). Most widespread two species of Conyza genus in Europe and Turkey are Conyza canadensis (L.) Cronq. and Conyza bonariensis (L.) Cronq. (Grierson 1975; Tutin et al. 1976). Conyza spp. contain alkaloids, saponins, tannins, glycosides, phenols, flavonoids, oil and sphingolipids (Kong et al. 2001; Mukhtar et al. 2002). Today no literature is found about the existence of calcium oxalate crystals in Conyza species. Calcium oxalate (CaOx) crystals are formed from environmentally derived calcium and biologically synthesized oxalate and they are common for most tissues and organs of plants (Franceschi and Horner 1980; Prychid and Rudall 1999; Nakata 2003). The shape and location of these crystals within a taxon are often very specific and they are used in classification of plants (Franceschi and Horner 1980; Lersten and Horner 2000). CaOx crystals occur in different plant tissues including leaves (Horner and Zindler-Frank 1982; Lersten and Horner 2000), stems (Franceschi and Horner 1980), roots (Horner et al. 2000), and seeds (Webb and Arnott 1982; Ilarslan et al. 1997, 2001). CaOx crystals also occur in floral organs including ovaries (Dormer 1961; Tilton and Horner 1980), anthers (Horner 1977; Horner and Wagner 1980; Meric and Dane 2004) and petals (Meric and Dane 2004). The only place where crystals have not been seen is the pollen (Tilton and Horner 1980). CaOx crystals are widely distributed in plant kingdom and found in over 215 families (Franceschi and Horner 1980; Molano-Flores 2001). However, their functional significance remains unclear, although various functions have been attributed to them. CaOx crystals give protection against foraging animals (Molano-Flores 2001), bind toxic oxalate (Borchert 1984) and are involved in in-plant Ca regulation (Franceschi 1989), salt stress and homeostasis (Hurkman and Tanaka 1996), light gathering (Franceschi and Horner 1980) and detoxification of heavy metals (Nakata 2003). Conyza Less. genus belongs to Asteraceae (about 15001600 genera and 23000 species) which is one of the greatest families of plant kingdom (Bremer 1994). Crystals in Asteraceae were shown by a few previous studies (Dormer 1961; Horner 1977; Meric and Dane 2004). The most comprehensive review of crystal types and distribution for a single family [Zindler-Frank 1987 (Leguminosae); Wu and Kuo-Huang 1997 (Moraceae)] lacks substantial documentation. The present study is a part of an ongoing project aiming to bring to light CaOx crystals in Asteraceae and this study aims to determine the CaOx crystals in C. canadensis and C. bonariensis. Thus additional research is needed to better determine CaOx crystals in other taxa belonging to Asteraceae.