Abstract
Plant biominerals are not always well characterized, although this information is important for plant physiology and can be useful for taxonomic purposes. In this work, fresh plant material of seven wild neotropical species of genus Canna, C. ascendens, C. coccinea, C. indica, C. glauca, C. plurituberosa, C. variegatifolia and C. fuchsina sp. ined., taken from different habitats, were studied to characterize the biominerals in their internal tissues. For the first time, samples from primary and secondary veins of leaves were investigated by means of infrared spectroscopy, complemented with X-ray powder diffractometry and scanning electron microscopy. The spectroscopic results, supported by X-ray powder diffractometry, suggest that the calcium oxalate is present in the form of whewellite (CaC2O4 x H2O) in all the investigated samples. It is interesting to emphasize that all IR spectra obtained were strongly similar in all species studied, thus indicating an identical chemical composition in terms of the biominerals found. In this sense, the results suggest that the species of Canna show similar ability to produce biogenic silica and produce an identical type of calcium oxalate within their tissues. These results can be an additional trait to support the relationship among the families of Zingiberales.
Highlights
In the present work we have investigated the existence, characteristics and chemical nature of the biominerals present in the leaves of seven neotropical species of Canna growing in several different habitats, using infrared spectroscopy and complemented with X-ray powder diffractometry
Infrared spectra: Infrared spectroscopy is a powerful tool for the investigation of plant material (Baran 2005) and we have successfully applied this methodology in the investigation of biominerals of vegetal origin
The performed spectroscopic studies supported by some X-ray powder diffraction measurements as well as by the obtained scanning electron microscopy images, definitively confirm the presence of calcium oxalate in the form of whewellite, in all the investigated samples
Summary
The order is considered monophyletic (Tomlinson 1962, 1969, Dahlgren & Rassmusen 1983, Kress 1990, Chase et al 1993, Smith et al 1993, Kress 1995, Stevenson & Loconte 1995, Kress et al 2001) and the Cannaceae, Costaceae, Marantaceae and Zingiberaceae families would represent a unique clade, based on characters such as reduction of androecia to an only functional stamen, large and conspicuous staminodia, seeds with perisperm, absence of raphides in parenchymatic tissues and entire, firm and not torn leaves (Judd et al 2002). Up to 60cm long, with a central well-developed primary vein, referred to as foliar axis (Solereder & Meyer 1930). Transversal sections of this vein show external parenchymatic tissues with numerous vascular bundles, and central aerenchyma with diaphragms. Solereder & Meyer (1930), Tomlinson (1961, 1962, 1969) and Ciciarelli (1986) have described the morphology of the foliar axis and blades in species of Canna and their work contains so far the unique available information on the presence of biominerals in foliar cells. Calcium oxalate appears as crystalline sand in the epidermal cells, as large crystals or as amorphous aggregates in the cells of the hypodermis and as prismatic crystals in stellate cells of the diaphragms. Prychid & Rudall (1999) reported oxalate crystals for the Zingiberales, but they did not analyze their composition; later Prychid et al (2004) found silica in the form of opal
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