Cyclic AMP as a Second Messenger in Higher Plants (Status and Future Prospects)

Adenosine 3':5'-monophosphate, commonly known as cAMP, is a key second messenger in living organisms ranging from Dictyostelium to Homo sapiens. cAMP was first described as a regulator of glycogen breakdown in the liver and is now known to be a second messenger for a wide variety of cellular responses in animals. cAMP is produced from ATP by the action of adenylate cyclase and is hydrolyzed to AMP by the enzyme cAMP phosphodiesterase. The question of whether cAMP is an authentic second messenger in higher plants has engaged plant scientists for decades. This article will highlight aspects of the controversies surrounding cAMP and suggest steps toward their possible resolution. Literature citations are largely restricted to the last 5 years, since earlier work has been summarized in several reviews (Lin, 1974; Amrhein, 1977; Brown and Newton, 1981; Francko, 1983; Verhey and Lomax, 1993).