Temperature sensing by plants: the primary characteristics of signal perception and calcium response

Cold elicits an immediate rise in the cytosolic free calcium concentration ([Ca2+](c)) of plant cells. We have studied the concerted action of the thr ee underlying mechanisms, namely sensing, sensitisation and desensitisation , which become important when plants in the field are subjected to changes in temperature. We applied different regimes of temperature changes with we ll-defined cooling rates to intact roots of Arabidopsis thaliana expressing the calcium-indicator, aequorin. Our results indicate that temperature sen sing is mainly dependent on the cooling rate, dT/dt, whereas the absolute t emperature T is of less importance. Arabidopsis roots were found to be sens itive to cooling rates of less than dT/dt = 0.01 degrees C/s. However, at c ooling rates below 0.003 degrees C/s (i.e, cooling 10 degrees C in 1 h) the re is no detectable [Ca2+](c) response at all. At low temperature, the sens itivity of the plant cold-detection system is increased. This in turn produ ces greater cooling-induced [Ca2+](c) elevations. Prolonged or repeated col d treatment attenuates the [Ca2+]c responses to subsequent episodes of cool ing.