Teresita Montenegro

Insolubilization of potassium chloride crystals in Tradescantia pallida

Summary.Calcium oxalate crystals are by far the most prevalent and widely distributed mineral deposits in higher plants. In Tradescantia pallida, an evergreen perennial plant widely used as an ornamental plant, calcium oxalate crystals occur in the parenchymal tissues of stem, leaf, and root, as well as in flower organs, in the form of either raphides or tetragonal prismatic crystals or both. Energy-dispersive X-ray analysis revealed that C, O, and Ca were the main elements; and K, Cl, and Si, the minor elements. Infrared and X-ray analyses of crystals collected from these tissues detected the coexistence of two calcium oxalate chemical forms, i.e., whewellite and weddellite, as well as calcite, opal, and sylvite. Here, we show for the first time the occurrence of epitaxy in mineral crystals of plants. Epitaxy, which involves the oriented overgrowth of one crystal onto a second crystalline substrate, might explain how potassium chloride (sylvite) – one of the most water-soluble salts – stays insoluble in crystal form when coated with a calcium oxalate epilayer. The results indicate the potential role of crystals in regulating the ionic equilibrium of both calcium and potassium ions.

VARIABILIDAD EN LA UTILIZACIÓN DE PIGMENTOS EN ENTIERROS HUMANOS DEL HOLOCENO TARDÍO EN LA CUENCA SUPERIOR DEL RÍO SANTA CRUZ (PATAGONIA ARGENTINA)

El objetivo de este trabajo es analizar la existencia de cambios en la forma de utilizacion de pigmentos en dos sitios en los que se han realizado entierros multiples en la cuenca superior del rio Santa Cruz, a comienzos y finales del Holoceno Tardio. Se efectuaron analisis macroscopicos, con microscopio binocular y de difraccion de rayos X. Los resultados obtenidos sugieren la existencia de un cambio en la forma de aplicacion de pigmentos entre ca. 3600 y 430 anos AP, lo que se suma a las evidencias ya existentes referidas a variaciones en la seleccion de espacios para realizar las inhumaciones y a la utilizacion de termoalteracion sobre los restos humanos.

On the nature and origin of the oxalate package in Solanum sisymbriifolium anthers

SummaryThis is a detailed study carried out in Solanum sisymbriifolium Lam. on the development of the circular cell cluster (CCC) during crystal deposition, as well as the composition of the crystals. Light microscopy and scanning and transmission electron microscopy (TEM) were used to characterize tissue throughout anther development. Energy dispersive X-ray analysis (EDAX) allowed the determination of the elemental composition of crystals that form in the CCC region, and infrared and x-ray diffraction analysis were used to specify the crystal salt composition. TEM analysis revealed that the crystals originated simultaneously within the vacuoles in association with a paracrystalline protein. Prior to the appearance of protein within vacuoles, protein paracrystals were visible in both rough endoplasmic reticulum and vesicles with ribosomes on their membranes. In vacuoles, paracrystals constitute nucleation sites for druse crystals formation. EDAX revealed that C, O, and Ca were the main elements, and K, Cl, Mg, P, S, and Si, the minor elements. X-ray powder diffraction of crystals detected the predominant presence of calcium oxalate, but also vestiges of calcite, quartz, and sylvite. The calcium oxalate coexisted in the three chemical forms, that is, whewellite, weddellite, and caoxite. Infrared spectrophotometry identified bands that characterize O-C-O, H-O, C-H bonds, all of calcium oxalate, and Si-O-Si, of quartz. These results were compared with studies of anthers carried out in other Solanaceae genera.