Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2003
Publication Date: 5/1/2003
Citation: KOSTMAN, T.A., FRANCESCHI, V.R., NAKATA, P.A. ENDOPLASMIC RETICULUM SUB-COMPARTMENTS ARE INVOLVED IN CALCIUM SEQUESTRATION WITHIN RAPHIDE CRYSTAL IDIOBLASTS OF PISTIA STRATIOTES. PLANT SCIENCE. 2003. v. 165. p.205-212. Interpretive Summary: In this study, we studied water lettuce and in particular, examined the idioblasts, which are specialized cells that accumulate crystals of calcium oxalate. Within these cells, there was an abundance of endoplasmic reticulum (ER), which under a microscope look like tiny tubes or dumbbells. These cells can accumulate a great deal of calcium very quickly, so the calcium needs to have a special storage space. We theorized that these ER tubelike structures could be the storage places for all this calcium. We used dye to make stains that would highlight and identify these microscopic-sized elements and help us find the answer to our question. We determined that in fact, there was a lot of calcium in the ER. We localized the calcium to the balloon-like objects on the ends of the tubes, which would represent the weights on a pair of dumbbells. We are now interested in finding further ways to manipulate the calcium in plants, because much of it seems to be tied up in these storage places and therefore is not available nutritionally to human beings who eat such plants. Our goal, ultimately, is to free up the stored calcium to make it bioavailable.
Technical Abstract: To regulate tissue Ca2+ levels, many plants have evolved specialized Ca2+ accumulating cells called crystal idioblasts. Here we examine one of the structural modifications present in these cells that accommodate the large Ca2+ influxes that occur during crystal formation. Electron and confocal microscopy studies revealed that crystal idioblasts possess an extensive network of endoplasmic reticulum (ER) with specialized Ca2+ accumulating sub-domains. This is in stark contrast to surrounding mesophyll cells, which do not have an extensive ER network containing sub-domains. We suggest that the specialized sub-domains and extensive ER network found in crystal idioblasts cells function as the initial site of Ca2+ sequestration within this unique cell type.