Considerable advances have been made, both in the technologies available to
study changes in intracellular cytosolic free Ca2+ ([Ca2+](i)), and in our
understanding of Ca2+ signalling cascades in plant cells, but how specific
ity can be generated from such a ubiquitous component as Ca2+ is questionab
le. Recently the concept of 'Ca2+ signatures' has been formulated; tight co
ntrol of the temporal and spatial characteristics of alterations in [Ca2+](
i) signals is thought to be responsible, at least in part, for the specific
ity of the response. However, the way in which Ca2+ signatures are decoded,
which depends on the nature and location of the targets of the Ca2+ signal
s, has received little attention. In a few key systems, progress is being m
ade on how diverse Ca2+ signatures might be transduced within cells in resp
onse to specific signals. Valuable pieces of the signal-specificity puzzle
are being put together and this is illustrated here using some key examples
; these emphasize the global importance of Ca2+-mediated signal-transductio
n cascades in the responses of plants to a wide diversity of extracellular
signals. However, the way in which signal specificity is encoded and transd
uced is still far from clear. (C) New Phytologist (2001) 151. 7-33.