Does plant growth temperature modulate the membrane composition and ATPase activities of tonoplast and plasma-membrane fractions from rye roots?

Abstract

The effect of plant growth temperature on the lipid composition and ATPase activity associated with tonoplast and plasma-membrane fractions from roots of rye ( Secale cereale cv. ‘Rheidol’) was investigated to try and explain the rapid (< 3 day), general increase in ion transport capacity observed when plants are acclimated to low root temperatures. Plants were grown at 8° (CG) or at 8° root: 20° shoot temperatures (DG) and compared with plants grown at 20° (WG). Growth temperature had little effect on plasma-membrane fatty acid composition. In contrast, the molar proportions of linoleic and linolenic acids were less, and the molar proportion of palmitic acid greater, in tonoplast fractions from CG and DG compared to WG roots. Growth temperature had no effect on the distribution of free sterol classes in either fraction, but the sterol/phospholipid ratio of both tonoplast and plasma-membrane fractions was greater in CG and DG than in WG roots. This increase in sterol/phospholipid ratio upon cooling was most marked in the tonoplast fraction from CG roots. Despite growth temperature-induced alterations in the lipid composition of subcellular membranes, the characteristic substrate affinity ( K m ), sensitivity to specific inhibitors (nitrate or vanadate), stimulation by KCI and activation energy ( E a ) of the plasma-membrane and tonoplast ATPases were unaffected. The only apparent difference between growth temperature pretreatments was an increase in the specific activity of the plasma-membrane ATPase, but not that of the tonoplast, after long term ( > 3 day) cooling of plant roots. It appears, therefore, that the enhancement of ion transport capacity which is evident upon cooling rye roots is not mediated by changes in activity or properties of the ATPases.