Temperature sensing and cold acclimation

The fundamental question in cold acclimation is how do plants perceive the low but nonfreezing temperatures that activate cold acclimation responses. New findings in the past year suggest that changes in membrane fluidity, cy toskeleton rearrangement, and calcium influxes are among the earliest event s taking place in plants upon exposure to low nonfreezing temperatures. In the cyanobacterium Synechocystis PCC6803, temperature change is detected by at least two separate sensors. One of these measures membrane fluidity usi ng a classical two-component system involving histidine kinases and a respo nse regulator in a His-to-Asp phosphorelay. Although these Synechocystis re sults may not be directly relevant to cold acclimation, they can guide our thinking as we search for biological thermometers in higher plants.