Effect of Ozone on Swelling of Tobacco Mitochondria

Abstract

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 mmu in buffered 0.25 m sucrose or 0.125 m KCl. 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 mmu released from mitochondria into the suspending medium were positively correlated with the length of exposure to O(3). The correlation between the extent of mitochondrial swelling and the loss of intramitochondrial materials was also highly significant.Protocatechuic acid, when initially present in the suspending medium, completely prevented O(3)-induced swelling. Reduced glutathione, ascorbate, and l-cysteine partially prevented O(3)-induced swelling. But these reducing substances failed to reverse mitochondrial swelling when added after O(3) treatment.Polyvinylpyrrolidone (PVP) and bovine serum albumin (BSA) induced contraction of tobacco mitochondria in the absence of O(3), but did not reverse swelling of O(3)-treated mitochondria. PVP and BSA only stopped O(3)-induced swelling. Evidently O(3)-induced swelling was osmotically irreversible. Hypertonic solutions of sucrose neither induced contraction of tobacco mitochondria nor prevented O(3)-induced swelling.Contraction of tobacco mitochondria occurred rapidly at acid pH, but the contracting state affected by acid pH did not protect mitochondria from O(3)-induced swelling. Although O(3) induced greater swelling at acid pH, the O(3)-treated mitochondria were still responsive to acid-induced contraction.