Mitochondria isolated from the gill tissues of the fishSarothredon mossambica were analysed for their macromolecular content, following transfer from freshwater to media of higher salinity. The results suggest a breakdown of mitochondria during the initial phases of the stress and a regeneration during continued exposure. Also all the synthetic machineries, in general, seem to be triggered in gill tissue during continuous exposure to hyperosmotic media.

The functional status of fish muscle mitochondria during exposure of the organism to salinity stress was studied. No alterations were observed in the substrate oxidation capacity. However, the mitochondria appear to be in an uncoupled state during the first few days of exposure and recover thereafter. This could be correlated to high endogenous Ca²⁺ levels in the mitochondria in the early period. A Na⁺-Ca²⁺ antiport in these mitochondria is shown. Evidence is also presented to show that the mitochondria isolated during the early stages of stress are in a swollen state and are unable to contract on addition of ATP and Mg²⁺ Continued exposure to the stress, however, reverses the situation.

Mitochondrial transcription has been studied as a function of mitochondriogenesis in yeast cells. Two systems have been used: synchronously growing cells and cells subjected to glucose repression followed by derepression. Maximal RNA synthesis has been found in the S phase of the cell cycle and during the ‘repressed’ phase in asynchronous cells. Activities of RNA polymerase, poly A polymerase and incorporation of [³²P]-into RNAin vitro are maximal at the same period. Gel analysis reveals the presence of some high molecular weight RNA species which are likely to be precursors. When chase experiments are carried out in the presence of excess glucose, the high molecular weight species remain unaffected, suggesting that RNA processing may be an important site of action of glucose repression