Calcium‐Mediated Mitochondrial Permeability Transition Involved in Hydrogen Peroxide‐Induced Apoptosis in Tobacco Protoplasts

Abstract

AbstractIn the present study, we focused on whether intracellular free Ca2+ ([Ca2+]i) regulates the formation of mitochondrial permeability transition pore (MPTP) in H2O2‐induced apoptosis in tobacco protoplasts. It was shown that the decrease in mitochondrial membrane potential (ΔΨm) preceded the appearance of H2O2‐induced apoptosis; pretreatment with the specific MPTP inhibitor cyclosporine A, which also inhibits Ca2+ cycling by the mitochondria, effectively retarded apoptosis and the decrease in ΔΨm. Apoptosis and decreased ΔΨm were exacerbated by CaCl2, whereas the plasma membrane voltage‐dependent Ca2+ channel blocker lanthanum chloride (LaCl3) attentuated these responses. Chelation of extracellular Ca2+ with EGTA almost totally inhibited apoptosis and the decrease in ΔΨm induced by H2O2. The time‐course of changes in [Ca2+]i in apoptosis was detected using the Ca2+ probe Fluo‐3 AM. These studies showed that [Ca2+]i was increased at the very early stage of H2O2‐induced apoptosis. The EGTA evidently inhibited the increase in [Ca2+]i induced by H2O2, whereas it was only partially inhibited by LaCl3. The results suggest that H2O2 may elevate cytoplasmic free Ca2+ concentrations in tobacco protoplasts, which mainly results from the entry of extracellular Ca2+, to regulate mitochondrial permeability transition. The signaling pathway of [Ca2+]i‐mediated mitochondrial permeability transition was associated with H2O2‐induced apoptosis in tobacco protoplasts.(Managing editor: Ping He).