Cold-induced cytosolic free calcium ion concentration changes in wheat

Relatively little is known about changes in the cytosolic free calcium ion concentration ([Ca2+]c) in monocotyledonous plants. Therefore, we produced transgenic winter wheat lines stably expressing the calcium-sensitive photoprotein aequorin constitutively in the cytosol. [Ca2+]c was detected in vivo by luminometry, and [Ca2+]c elevations were imaged at video rate. Experiments with the transgenic seedlings focused on potential changes in [Ca2+]c during cold exposure. Temperature-induced changes in [Ca2+]c were found to be more dependent on the change in temperature (dT dt−1) than on the absolute value of temperature. [Ca2+]c increased only at cooling rates higher than 8°C min−1, indicating that an overall cellular [Ca2+]c increase is of minor relevance as a signal for cold acclimation in wheat under ecological conditions. The results are discussed with regard to the so-called ‘calcium signature hypothesis’.