Disruption of actin filaments inducesmitochondrial Ca²⁺ release to the cytoplasmand [Ca²⁺]c changes in Arabidopsis root hairs.

Background: Mitochondria are dynamic organelles that move along actin filaments, and serve as calcium stores in plant cells. The positioning and dynamics of mitochondria depend on membrane-cytoskeleton interactions, but it is not clear whether microfilament cytoskeleton has a direct effect on mitochondrial function and Ca²⁺ storage. Therefore, we designed a series of experiments to clarify the effects of actin filaments on mitochondrial Ca²⁺ storage, cytoplasmic Ca²⁺ concentration ([Ca²⁺]c), and the interaction between mitochondrial Ca²⁺and cytoplasmic Ca²⁺ in Arabidopsis root hairs. Results: In this study, we found that treatments with latrunculin B (Lat-B) and jasplakinolide (Jas), which depolymerize and polymerize actin filaments respectively, decreased membrane potential and Ca²⁺ stores in the mitochondria of Arabidopsis root hairs. Simultaneously, these treatments induced an instantaneous increase of cytoplasmic Ca²⁺, followed by a continuous decrease. All of these effects were inhibited by pretreatment with cyclosporin A (Cs A), a representative blocker of the mitochondrial permeability transition pore (mPTP). Moreover, we found there was a Ca²⁺ concentration gradient in mitochondria from the tip to the base of the root hair, and this gradient could be disrupted by actin-acting drugs. Conclusions: Based on these results, we concluded that the disruption of actin filaments caused by Lat-B or Jas promoted irreversible opening of the mPTP, resulting in mitochondrial Ca²⁺ release into the cytoplasm, and consequent changes in [Ca²⁺]c. We suggest that normal polymerization and depolymerization of actin filaments are essential for mitochondrial Ca²⁺ storage in root hairs. [ABSTRACT FROM AUTHOR]

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