Evidence for opposing effects of calmodulin on cortical microtubules

Deborah D. Fisher, Simon Gilroy, Richard J. Cyr

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Microtubule integrity within the cortical array was visualized in detergent-lysed carrot (Daucus carota L.) protoplasts that were exposed to various exogenous levels of Ca2+ and calmodulin (CAM). CaM appears to help stabilize cortical microtubules against the destabilizing action of Ca2+/CaM complexes at low Ca2+ concentrations, but not at higher Ca2+ concentrations. The hypothesis that CaM interacts with microtubules at two different sites, determined by the concentration of Ca2+, is supported by the effects of the CaM antagonists N-(6-aminohexyl)-1-naphthalene- sulfonamide and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfanamide (20 μM) and by affinity chromatography. Two classes of proteins were identified that interact with tubulin and bind to CaM. One class required Ca2+ for CaM binding, whereas the second class bound only when Ca2+ concentrations were low (<320 nM). Thus, CaM's ability to have two opposing effects upon microtubules may be regulated by the concentration of intracellular Ca2+ and its differential interactions with microtubule-associated proteins. Experimental manipulation of intracellular Ca2+ concentrations, as monitored by Indo-1, revealed that the effect of Ca2+ is specific to the cortical microtubules and does not affect actin microfilaments in these cells.

Original languageEnglish (US)
Pages (from-to)1079-1087
Number of pages9
JournalPlant physiology
Issue number3
StatePublished - Nov 1996

All Science Journal Classification (ASJC) codes

  • Physiology
  • Genetics
  • Plant Science


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