Many plants are known to respond vigorously to changes in temperature. (A commonly cited example is the Rhododendron plant, which curls its leaves in response to low temperatures.)

Experiments have shown that the thermotropic effects are relative to previously 'recorded' ambient temperature, implying that there may be a plant 'thermometer' mechanism in operation. Various biophysical 'thermometers' have been proposed, but there is as yet no agreement on how such a system might operate.

Plants respond to ambient temperature changes over a series of timescales. Genetic and physiological studies over the last decades have revealed myriad thermally sensitive pathways in plants. A recent study provides a genetic and biochemical mechanistic description of how thermal changes can be transduced to influence gene expression. What remains to be revealed in this, and other thermally controlled responses, is a description of the primary temperature-sensing event."

Source : Ambient Thermometers in Plants: From Physiological Outputs towards Mechanisms of Thermal Sensing in Current Biology, 2010.