A Stress Physiological Role for Abscisic Acid (ABA) in Lower Plants

Abstract

The role of the phytohormone abscisic acid (ABA) in cormophytes, especially its action as a stress hormone, and its function in seed germination and stomatal closure, has been well investigated in the last decades. In contrast, the existence of ABA in algae, bryophytes, and fungi has been ambiguous for a long time. Between 1960 and 1970 the detection of ABA in lower plants was limited by proper analytical methods of high sensitivity and lack of sufficient amounts of biological material for the analysis of microorganisms and tiny bryophytes. Nevertheless, by means of simple techniques, the presence of “ABA-like compounds” in at least a few algae appeared likely (Radley 1961; Moss 1965; Jennings 1969; Hussain and Boney 1973). When more precise and sophisticated analytical tools became available between 1970 and 1980, the existence of ABA in algae, bryophytes, and fungi was reinvestigated. First studies failed to demonstrate the presence of ABA in lower plants except mosses. It was concluded that ABA is entirely absent in algae, fungi, and liverworts (Pryce 1972; Bearder 1980; Niemann and Dorffling 1980; Addicott and Cams 1983) and that lunularic acid may replace ABA physiologically in protophytes and thallophytes (Pryce 1972). However, when analytical methods became more and more sensitive, and especially with the introduction of RIA — and ELISA — tests for ABA, the picomole range of sensitivity was reached and this hypothesis collapsed. It could be demonstrated convincingly that ABA does occur in algae (Kingsham and Moore 1982; Tietz and Kasprik 1986; Sabbatini et al. 1987; Boyer and Dougherty 1988; Tietz et al. 1989), fungi (Assante et al. 1977; Dahyia et al. 1988), and liverworts (Hartung et al. 1987).