Submitted to: Annals Of Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/12/2004
Publication Date: 5/1/2004
Citation: Volk G.M., L.J. Goss, V.R. Franceschi. 2004. Calcium channels are involved in calcium oxalate crystal formation in specialized cells of Pistia stratiotes L. Annals of Botany 93:741-753. Interpretive Summary: Pistia stratiotes, an aquatic plant, makes calcium oxalate crystals within idioblast cells within leaves. This project uses localization, microautoradiography, and inhibitors to demonstrate that calcium channels play a role in calcium accumulation within the endoplasmic reticulum of idioblast cells in Pistia.
Technical Abstract: Pistia stratiotes L. produces calcium (Ca) oxalate crystals in specialized cells called crystal idioblasts. Previous studies showing rapid crystal formation suggested Ca fluxes in idioblasts may involve Ca channels. The potential involvement of Ca channels in Ca oxalate crystal formation was investigated. Using protoplasts, radio-labeled Ca uptake was shown to be more than two orders of magnitude greater for crystal idioblast protoplasts compared to mesophyll protoplasts. Crystal idioblast number increased in plants when medium Ca was increased but crystal formation was inhibited by Ca channel blockers. Plants grown on media containing 1-50 micro Molar Ca channel blockers, isradipine, nifedipine or fluspirilene, showed almost complete inhibition of Ca oxalate crystal formation. When fresh tissue sections were treated with the fluorescent dihydropyridine-type Ca channel blocker DM-Bodipy-DHP, crystal idioblasts were intensely labeled compared to surrounding mesophyll, and the label appeared to be associated with both the plasma membrane and the endoplasmic reticulum, which is shown to be abundant in developing idioblasts. An antibody to a mammalian Ca channel alpha 1 subunit recognized a single protein band in total membrane protein fraction but not the soluble protein fraction on Western blots, and selectively and heavily labeled developing crystal idioblasts in tissue sections. The results demonstrate that Ca oxalate crystal idioblasts are enriched relative to mesophyll cells in dihydropyridine-type Ca channels and that the activity of these channels is critical to transport and accumulation of Ca required for crystal formation.