Mitochondria Isolated from NaCl-Adapted Tobacco Cell Lines (Nicotiana tabacum/gossii) Maintain Their Phosphorylative Capacity in Highly Saline Media

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Abstract
The in vivo functioning of mitochondria isolated from two tobacco cell lines in suspension culture (Nicotiana tabacum/gossii), wild type, and NaCl-adapted (A190), has been compared in the face of rising external salinity. The O2 uptake of both state 3 and state 4 mitochondria was progressively inhibited with increasing external NaCl concentration in the case of both lines. Phosphorylation, however, was maintained at a higher level in the case of A190 mitochondria, as indicated both by stability of ADP:O ratio and rate of incorporation of 32Pi. The superior phosphorylation performance of A190 mitochondria also emerged when phosphorylation was calculated per reducing equivalent, but not per unit Δ̃μH+ (electrochemical potential gradient for protons). However, the overall Δ̃μH+ was maintained at a higher level in A190 mitochondria due to the fact that the depolarization accompanying increase in external NaCl concentration was compensated for in A190 mitochondria by an increase in the transmembrane pH gradient, but not in wild type mitochondria. Increased proton permeability of the inner membrane is among the probable causes suggested for the loss of phosphorylation ability in wild type mitochondria; in contrast, A190 mitochondria maintain better membrane integrity under saline stress.