Abstract
BackgroundMitochondria 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.ResultsIn 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.ConclusionsBased 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.
Highlights
Mitochondria are dynamic organelles that move along actin filaments, and serve as calcium stores in plant cells
After root hairs were incubated in 10 μM Rhod-2, and [free Ca2+ concentration in mitochondria (Ca2+]m) was calculated based on the fluorescence density value of Rhod-2
In most of the mitochondria, [Ca2+]m varied from 230 nM to 800 nM, and in a small number, [Ca2+]m reached 1 μM. [Ca2+]m was unequal in different areas
Summary
Mitochondria are dynamic organelles that move along actin filaments, and serve as calcium stores in plant cells. 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. The actin cytoskeleton is a dynamic structure that participates in many cellular functions including the maintenance of cell polarity and morphology, intracellular trafficking of organelles, cell motility, and cell division [1,2,3,4]. Latrunculins (Lat) and jasplakinolide (Jas) were used often in recent years to disrupt or stabilize actin filaments, which change the structure of the actin cytoskeleton immediately [11,12]. Jas can disrupt actin filaments in vivo and induce the monomeric actin to polymerize into amorphous masses [13]
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