Swelling of Tobacco Mitochondria

The swelling of mitochondria isolated from leaves, roots, and callus tissues of Nicotiana tabacum, L, var. White Gold, was measured by following changes in optical density at 520 mjt in buffered 025 M sucrose or 0.125 M KCI. Ozone induced rapid swelling of the isolated mitochondria and increased the permeability of mitochondrial membranes. The extent of mitochondrial swelling and the amount of soluble proteins and other substances absorbing at 260 and 280 m,u released from mitochondria into the suspending medium were positively correlated with the length of exposure to 03.. The correlation between the extent of mitochondrial swelling and the loss of intramitoohondrial materials was also highly significant. Protocatechuic acid, when initially present in the suspending medium, completely prevented 03-induced swelling. Reduced glutathione, asoorbate, and L-cys-teine partially prevented 03-induced swelling. But these reducing substances failed to reverse mitochondrial swelling when added after 03 treatment. Polyvinylpyrrolidone (PVP) and bovine serum albumin (BSA) induced contraction of tobacco mitochondria in the absence of 03, but did not reverse swelling of 03-treated mitochondria. PVP and BSA only stopped 03-induced swelling. Evidently 03-induced swelling was osmotically irreversible. Hypertonic solutions of sucrose neither induced contraction of tobacco mitochondria nor prevented 03-induced swelling. Contraction of tobacco mitochondria occurred rapidly at acid pH, but the contracting state affected by aoid pH did not protect mitochondria from 03-induced swelling. Although 0. induced greater swelling at acid pH, the 03-treated mitochondria were still responsive to acid-induced contraction. 3 No. 2