An increase in the speed of response, and sensitivity, of Avena fatua aleurone layers and protoplasts to gibberellin

Abstract

Summary In wild oat ( Avena fatua ) aleurone protoplasts and layers, α-amylase induction by gibberellin is very slow compared with other members of the Gramineae. Wild oat aleurone protoplasts for example do not secrete α-amylase until approximately 72 hours after treatment with gibberellin while in aleurone layers or protoplasts from wheat or barley this response takes between 8 and 24 hours. In this study, we demonstrate that the duration of the lag phase in A. fatua aleurone protoplasts can be reduced substantially by incubating the protoplasts in the absence of hormone for up to 4 days before treating with gibberellin. RNA gel blot analysis revealed substantial induction of α-amylase mRNA within 14 hours of gibberellin treatment in aged aleurone protoplasts. A reduction in the duration of the lag phase is also observed in intact wild oat aleurone layers that have been incubated in the absence of hormone for 4 days prior to gibberellin treatment. Interestingly, this effect is only observed in aleurones from which the endosperm has been removed. Dose response analysis revealed that the concentration of gibberellin required to induce a maximum response was approximately one order of magnitude lower in the 4 day-old tissue compared with freshly isolated material. These observations suggest that the long duration of the lag phase of freshly isolated aleurone layers and protoplasts of wild oat is due in part to gibberellin independent events.