Abstract Detail



Anatomy and Morphology

Paulina, Matias [1], Cote, Gary [2].

Isolation and Scanning Electron Microscopy of Calcium Oxalate Crystals from Tissues of Dieffenbachia seguine (Araceae).

Microscopic calcium oxalate crystals are found widely throughout the plant kingdom. They are generally assumed to discourage herbivores, although roles in calcium regulation, cell wall modification, and structural support have also been proposed.  Spherical aggregates called druses and long, double-pointed needles called raphides are the most common crystal forms.  We earlier reported a diversity of crystal forms and arrangements in all vegetative and floral tissues of the aroid Dieffenbachia seguine based on a survey by light microscopy (Coté, 2009, Am. J. Botany 96:1245-1254).  In follow-up work we have examined the ultrastructure of the crystals using scanning electron  microscopy (SEM).  Samples for SEM were prepared either by grinding tissues by hand and washing out the debris, or by pressing dried tissue between SEM stubs and then pulling the stubs apart to fracture the tissue parallel to the surface.  Using these methods, we were able to visualize all the crystals known from light microscopy, except very long thin raphides from the leaf edge, which perhaps were too fragile to survive these methods.  We have now developed a new isolation method in which cell walls are enzymatically digested, and the crystals are isolated by centrifugation and washing.  This procedure produces large numbers of crystals with little contamination by tissue debris.  We have used this procedure to recover the long raphides from leaves.   By isolating crystals separately from leaf edges and inner blades, we verified that crystals were more common at the edges.   In the crystal preparations from this method we have discovered very small (ca. 1 – 5 μm) crystal prisms in leaves.  These prisms are rare compared to raphides and druses.  We subsequently found evidence for them in cleared leaves by light microscopy, but they are hard to distinguish because of their small size.  They have the shape of two pyramids with square bases connected by a rectangular hexahedron of variable length, and resemble much larger crystals of similar geometry that were previously reported in pollen.  We are currently attempting to replicate the finding that all previously known crystals are calcium oxalate, and to test the chemical composition of the newly discovered tiny prisms.


1 - Radford University, Chemistry, P.O. Box 6949, Radford, VA, 24142, USA
2 - Radford University, Biology, P.O. Box 6931, Radford, VA, 24142, USA

Keywords:
calcium oxalate
crystals
scanning electron microscopy.

Presentation Type: Poster
Number: PAM012
Abstract ID:637
Candidate for Awards:None


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