Figure 2.

Characterization of mitochondria fractions isolated from either control or 3 d P_i-deprived A. thaliana cells. (A) To check purity and intactness of isolated mitochondria, succinate oxidation was followed by measuring O₂ consumption. On average, each purified fraction consumed ∼280 nmol O₂.min⁻¹.mg⁻¹ protein in the presence of succinate and ADP, and O₂ consumption was stimulated 2.4 times by addition of ADP. Therefore, fractions were considered to be highly enriched in functionally intact mitochondria. Cyanide resistant pathway was slightly enhanced in P_i-deprived conditions as expected according to Rébeillé et al. (1984). (B) Comparative Western blot analysis of mitochondrial (M) and total cell extract (Ce) using antibodies specific for mitochondrial proteins, HPPK, a matrix protein, NAD9, an inner membrane protein, and TOM20 and TOM40 outer membrane proteins. (C) Western blot analysis of mitochondrial (M), chloroplast (Chl), and total cell extract (Ce) of P_i-deprived cells and of chloroplast envelope (Env) prepared from Arabidopsis plants as in Awai et al. (2001) using antibodies specific for chloroplast membrane proteins, LHCII for thylakoid, E37 for inner envelope membrane, and OEP21 for outer envelope membrane.