Abstract: Through a combination of biophysical, molecular genetic and cell biological (approa-)(ches), it is compelling evidence that phytochrome signal transduction is spatially separated nonlinear chain of events. In particular, the discovery that different phytochrome species and their intermediates during Pr, Pfr phototransformation show multidimensional signal network, which lead to the suggestion that these intermediates are directly involved in these early signal transduction. Here, the primary photorseaction of phytochrome and the corresponding signalling mechanism will be discussed by reviewing some of recent progress in phytochrome phototransformation and its signal transduction in early stage.