PLANT PHYSIOLOGY , Vol 103, Issue 2 543-551, Copyright © 1993 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Calcium Levels Affect the Ability to Immunolocalize Calmodulin to Cortical Microtubules
D. D. Fisher and R. J. Cyr
Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802
Calcium affects the stability of cortical microtubules (MTs) in lysed
protoplasts. This calmodulin (CaM)-mediated interaction may provide a
mechanism that serves to integrate cellular behavior with MT function. To
test the hypothesis that CaM associates with these MTs, monoclonal
antibodies were produced against CaM, and one (designated mAb1D10) was
selected for its suitability as an immunocytochemical reagent. It is shown
that CaM associates with the cortical MTs of cultured carrot (Daucus carota
L.) and tobacco (Nicotiana tabacum L.) cells. Inasmuch as CaM interacts
with calcium and affects the behavior of these MTs, we hypothesized that
calcium would alter this association. To test this, protoplasts containing
taxol-stabilized MTs were lysed in the presence of various concentrations
of calcium and examined for the association of CaM with cortical MTs. At 1
[mu]M calcium, many protoplasts did not have CaM in association with the
cortical MTs, whereas at 3.6 [mu]M calcium, this association was completely
abolished. Control experiments were performed to eliminate alternate
explanations including differential antibody binding in the presence of
calcium and/or taxol, detergent-induced redistribution of antigen, and
epitope masking. The results are discussed in terms of a model in which CaM
associates with MTs via two types of interactions, one that occurs in the
presence of calcium and another that occurs only in its absence.
