Disruption of actin filaments induces mitochondrial Ca ²⁺ release to the cytoplasm and [Ca ²⁺] _c changes in Arabidopsis root hairs

Abstract

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 Ca ²⁺ storage. Therefore, we designed a series of experiments to clarify the effects of actin filaments on mitochondrial Ca ²⁺ storage, cytoplasmic Ca ²⁺ concentration ([Ca ²⁺] _c), and the interaction between mitochondrial Ca ²⁺ and cytoplasmic Ca ²⁺ 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 Ca ²⁺ stores in the mitochondria of Arabidopsis root hairs. Simultaneously, these treatments induced an instantaneous increase of cytoplasmic Ca ²⁺, 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 Ca ²⁺ 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 Ca ²⁺ release into the cytoplasm, and consequent changes in [Ca ²⁺] _c. We suggest that normal polymerization and depolymerization of actin filaments are essential for mitochondrial Ca ²⁺ storage in root hairs.