Plant tolerance to heat stress proved to be entirely dependent on the signaling flow of information by which the plant can sense the changes in its surrounding environment and signal its genes to respond by producing special proteins to protect it-self. Any changes or manipulations in this signaling flow of information will presumably lead to a modification in the genetic expression inside the plant cells, consequently, changing plant performance. Understanding these signaling events in response to heat may help us to produce heat tolerant plants capable to stand high temperature stress. In the present investigation, the results showed that a heat activated MAP kinase cascade, involving heat activated MAP kinase (HAMK), played an essential role in heat shock gene expression in tobacco BY-2 cells. In order to determine if heat activation of HAMK involved additional pathways of signaling we studied the upstream regulation of HAMK, including membrane fluidization and reorganization of cytoskeleton. The activation of HAMK and accumulation of heat responsive HSFs, HSP70 and HSP27 proteins were used as end-point markers in these experiments.