The role of phytosterols in plant adaptation to temperature.

Membranes of composition approaching those found in "rafts" of plants, fungi and mammals were investigated by means of solidstate (2)H-NMR, using deuterated dipalmitoyl-phosphatidylcholine ((2)H-DPPC) as a reporter. The dynamics of such membranes was determined through measuring of membrane ordering or disordering properties. The presence of the liquid-ordered, lo, phase, as an indicator of rigid sterol-sphingolipid domains, was detected in all cases. Of great interest, the dynamics of mixtures mimicking rafts in plants showed the lesser temperature sensitivity to thermal shocks. The presence of an additional ethyl group branched on the alkyl chain of major plant sterols (sitosterol and stigmasterol) is proposed as reinforcing the membrane cohesion. The fine tuning of the sterol structure thus appears to be the evolution response for plant adaptation to large temperature variations.