Recent advances in understanding plant hormonal signalling has resulted in
the identification of a variety of signalling components including receptor
kinases with homology to the bacterial two component system as well as ser
ine/threonine kinases and protein phosphatases. In addition, the existence
of MAP kinase pathways in plants indicates a similar role of these signalli
ng cascades in the relay of exogenous signals into the nucleus as has been
disclosed in animal cells. The emerging signalling pathways of the plant ho
rmone abscisic acid and ethylene are presented.