A mitochondrial signal system has been found in plant cells during temperature stresses. Interaction energetic and information systems of cells take part when this system is functioned. Changes in energetic activity of plant mitochondria under temperature fluctuations were shown. These changes are connected with reorganizations of composition of mitochondrial membrane lipids and it is caused signal about temperature stress. Energetic-state mitochondrial membranes is modified and formed stress-signal for change of expression of stress-genes which determine thermotolerance of cell.