Ca2+-induced High Amplitude Swelling and Cytochrome c Release From Wheat (Triticum aestivum L.) Mitochondria Under Anoxic Stress

Abstract

Under stress conditions, mitochondria sense metabolic changes, e.g. in pH, cytoplasmic Ca(2+), energy status, and reactive oxygen species (ROS), and respond by induction of the permeability transition pore (PTP) and by releasing cytochrome c, thus initiating the programmed cell death (PCD) cascade in animal cells. In plant cells, the presence of all the components of the cascade has not yet been shown. In wheat (Triticum aestivum L.) root mitochondria, the onset of anoxia caused rapid dissipation of the inner membrane potential, initial shrinkage of the mitochondrial matrix and the release of previously accumulated Ca(2+). Ca(2+) uptake by mitochondria was dependent on the presence of inorganic phosphate. Treatment of mitochondria with high micromolar and millimolar Ca(2+) (but not Mg(2+)) concentrations induced high amplitude swelling, indicative of PTP opening. Alterations in mitochondrial volume were confirmed by transmission electron microscopy. Mitochondrial swelling was not sensitive to cyclosporin A (CsA)-an inhibitor of mammalian PTP. The release of cytochrome c was monitored under lack of oxygen. Anoxia alone failed to induce cytochrome c release from mitochondria. Oxygen deprivation and Ca(2+) ions together caused cytochrome c release in a CsA-insensitive manner. This process correlated positively with Ca(2+) concentration and required Ca(2+) localization in the mitochondrial matrix. Functional characteristics of wheat root mitochondria, such as membrane potential, Ca(2+) transport, swelling, and cytochrome c release under lack of oxygen are discussed in relation to PCD.

Endoplasmic reticulum stress-induced programmed cell death in soybean cells

“…Several reports also suggest the key role of mitochondria in plant PCD induced by various stimuli (Lam et al, 1999;Jones, 2000). Particularly, the requirement of Ca 2+ localization in the mitochondrial matrix seems to be important for the permeability transition pore opening and cytochrome c release (Virolainen et al, 2002). Cytochrome c leakage and activation of caspase-like proteases were detected in our study during CPA-induced PCD, suggesting the involvement of mitochondria in the death pathway.…”

Mitochondria in energy-limited states: mechanisms that blunt the signaling of cell death

“…In addition, a calcium-induced transition could not be found in mitochondria from the yeast Endomyces magnusii (Deryabina et al, 2004). Investigations of purified potato and wheat mitochondria show a calcium-sensitive permeability transition that is inhibited by cyclosporin A in the presence of dithiothreitol (Arpagaus et al, 2002;Virolainen et al, 2002 incubated in the presence of P i , but the amount of calcium required to induce the mitochondrial permeability transition was substantially higher than that needed for mitochondria from rat liver (Toninello et al, 2000). While data are not fully conclusive, a MPTP may exist in liver mitochondria from the Baltic lamprey Lampetra fluviatilis (Savina et al, 2006).…”

Binding of divalent cations is essential for the activity of the organellar peptidasome in Arabidopsis thaliana, AtPreP

“…In mammalian mitochondria free [Ca 2+ ] lies between 0.05 and 5 lM. However, it has been shown for plant mitochondria that at 100 lM [Ca 2+ ] there was no PTP (permeability transition pore) opening, swelling or cytochrome c release that was observed at 0.5-2.5 mM [Ca 2+ ] [27]. Thus, we conclude that complete activation of PreP by Ca 2+ occurs below concentrations that induce apoptosis.…”