Abstract
Abscisic acid (ABA), known to regulate seed dormancy, stomata closure, and tolerance to environmental stresses of higher plants, has been shown to function in other groups of land plants including ferns, lycophytes and mosses. However, the role of ABA in liverworts, comprising the earliest diverging group of land plants has not been clearly understood. We examined molecular responses of ABA in liverworts, using the model organism Marchantia polymorpha. Exogenous ABA was found to inhibit growth of gemmae of M. polymorpha and increased desiccation and freezing tolerance. Assays using the GUS reporter gene fused to the ABA-inducible wheat Em promoter (Em-GUS) in both cultured cells and transgenic plants revealed that exogenous ABA increases Em-GUS expression. In contrast, lunularic acid, which had been suspected to be functioning as an ABA-like substance, had no effect on the Em-GUS expression. The ABA-induced Em-GUS expression was dependent on the conserved ABA-responsive element (ABRE) and RY sequences These results indicate that the liverworts possess a distinct molecular mechanism for ABA-induced gene expression, which is not affected by lunularic acid.
