Evidence for surface perception of abscisic acid by rice suspension cells as assayed by Em gene expression
To determine if the initial perception of abscisic acid (ABA) occurs at the surface of plant cells, embryogenic rice (Oryza sativa L.) suspension cells have been treated with ABA covalently linked to bovine serum albumin (BSA). Although the ABA-BSA conjugate does not penetrate the plasma membrane, we demonstrate that the conjugate induces the accumulation of transcripts from the ABA-inducible Em gene. Protoplasts containing the Em promoter linked to the reporter gene β-glucuronidase (GUS) also respond to the ABA-BSA conjugate by increasing GUS activity in a dose-dependent manner. Data are presented which indicate that the ABA-BSA conjugate is not degraded during incubation with rice suspension cells. This suggests that release of ABA from the conjugate and its uptake into the cell as free ABA cannot account for the increased levels of Em mRNA. Furthermore, we demonstrate that at a neutral pH, where free ABA does not cross the plasma membrane, Em transcript levels increase in response to either ABA or the ABA-BSA conjugate. We conclude that ABA perception at the surface of rice suspension cells leads to internal signals which induce Em gene expression.
Schultz, TF; Quatrano, RS
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