Abscisic acid synthesis and metabolism in barley leaves and protoplasts

Abstract

Protoplasts isolated from barley ( Hordeum vulgare L. cv. Clipper) leaves contained abscisic acid (ABA). The ABA content of these protoplasts did not change when they were incubated for up to 6 h in media of decreasing osmotic potential. There was a substantial, but transient, increase in ABA in barley leaf segments during protoplast isolation. The magnitude of this increase was inversely dependent on the osmotic potential of the isolation medium. Maximum ABA content was recorded after 2 h of exposure to the sorbitol-containing medium. The subsequent decline was due to conversion of ABA to phaseic acid (PA) and to other metabolites. Barley mesophyll protoplasts were not able to metabolise ABA, PA or any of the other metabolites formed from ABA by intact leaf tissue.