Characterization of calcium crystals in Abelia using x-ray diffraction and electron microscopes

Authors: BURCHI, GIANLUCA - National Research Council - Italy; Bauchan, Gary; Murphy, Charles; Roh, Mark

Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2013
Publication Date: 1/15/2014
Citation: Burchi, G., Bauchan, G.R., Murphy, C.A., Roh, M.S. 2014. Characterization of calcium crystals in Abelia using x-ray diffraction and electron microscopes. Journal of Horticultural Science and Biotechnology. 89:61-68.

Interpretive Summary: Calcium (Ca) is an essential plant nutrient, and performs critical functions in metabolism. Sequestering excess Ca in the form of Ca crystals such as Ca oxalate is quite common in many plant species. Crystal growth is a highly controlled intracellular process to prevent damage to the vacuolar membrane. The elemental composition of Ca crystals indicates that Ca oxalate, Ca sulfate, and Ca sulfate-magnesium crystals occur in almost all tissues. However, no information is available on the relationship between Ca concentration in leaves and stems with the Ca crystals in the cells. To our knowledge, there are no reports on the presence of Ca crystals in the genus Abelia (honeysuckle family). In this study, leaves and stems of Abelia mosanensis and A. ×grandiflora were collected for microanalysis, electron microscope observation, and foliar analyses of macro- and micro-elements. A larger quantity of crystals was observed in A. mosanensis than in A. ×grandiflora. Three morphologically distinguishable crystals were observed by VP-SEM, LT-SEM and TEM. These were prismatic crystals inside the chloroplast, large numbers of sand crystals in the cuticle, and druses (spherical and bladed aggregates) in the vacuoles. Microanalysis of elements indicated that the crystals are calcium oxalate with other elements, particularly magnesium in A. mosanensis and silicon in A. ×grandiflora. This is the first report, to our best knowledge, on the presence and possible expansion of crystals of different morphologies and chemical constituents in Abelia.

Technical Abstract: Localization, chemical composition, and morphology of calcium crystals in leaves and stems of Abelia mosanensis and A. ×grandiflora were analyzed with a variable pressure scanning electron microscope (VP-SEM) equipped with an X-ray diffraction system, low temperature SEM (LT-SEM) and a transmission electron microscope (TEM). Foliar analyses of macro- and micro-elements were performed on leaves and stems of A. mosanensis. A greater number of crystals was observed in A. mosanensis than in A. ×grandiflora. Three morphologically distinguishable crystals were observed: the prismatic crystals found inside the chloroplast and druses inside the vacuoles of the mesophyll cells and the sand crystals inside the cuticle. Semi-solid or solid crystals that may drip and accumulate to become a solid calcium crystal were observed by LT-SEM which indicated the expansion of druses of calcium crystals. Expansion of prismatic crystals and druses are evident through the formation of crystalline lamella or rings of facets. Microanalysis of elements indicated that the crystals are calcium oxalate containing magnesium in A. mosanensis and silicon in A. ×grandiflora. Low calcium concentrations in stems did not affect the formation of calcium crystals. This is the first report, to our best knowledge, on the presence and possible expansion of crystals of different morphologies and chemical constituents in Abelia.