Effect of osmotic stress on Aspergillus chevalieri respiratory system

The osmotolerant fungus Aspergillus chevalieri tolerates up to 80% sucrose concentration in the growth medium. At 50% sucrose the growth rate is 1.5-fold higher than in control (3% sucrose), at 80% sucrose it drops to 30% of the control level. Total proteins and lipids in the mitochondrial fractions obtained from the mycelium rise with increasing sucrose concentration during growth (2.6 and 2.1 times at 80% sucrose). The rate of respiration by whole cells and mitochondrial fractions increases with increased sucrose level in the growth medium. The activity of respiratory enzymes, such as succinate dehydrogenase, cytochrome oxidase, NADH oxidase and succinate oxidase, were also higher in cells grown in the presence of elevated sucrose concentrations. The largest increase was observed with NADH dehydrogenase. A. chevalieri cells grown at high osmotic stress exhibited enlarged mitochondria. The mean mitochondrial diameter at 50 and 80% sucrose was approximately 2.9- and 2.6-fold larger than in the control, respectively. Agarose gel electrophoresis of nucleic acids revealed the presence of high-density bands of RNA in mitochondrial fractions from cells grown at elevated sucrose levels.