Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings

Abstract

The present study investigated whether the cold-sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35°C), mitochondrial membranes were characterized by a higher phosphatidylcholine:phosphatidylethanolamine ratio and a lower content in 18:3 fatty acid. After a reduction of temperature (from 25 to 18°C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35°C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18°C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35°C, but not at 18°C despite changes in lipid composition, in accordance with the cold-sensitive character of the plant.