A natural feature of freshly harvested Avena fatua L. caryopses is primary dormancy which, however,was relieved partially by putrescine (Put) (10 -2 M) and completely by karrikinolide (KAR 1 ) (3 9 10 -9 M) or gibberellic acid (GA 3 ) (10 -5 M). The sensitivity of A. fatua caryopses to these stimulators was adversely affected by supraoptimal temperature (SOT) (30 °C). A reduced germinability of caryopses due to high temperature even after transferring them to lower temperatures (10 or 20 °C) indicated the induction of thermodormancy. The mainte-nance of relatively constant levels of abscisic acid (ABA) in embryos but not surrounding tissues during SOT treat-ment was observed. The application of Put either during the SOT treatment or afterwards counteracted the effects of high temperature but had no significant impact on ABA content. The action of exogenous Put in alleviating the loss of responsiveness to KAR 1 and GA 3 imposed by SOT treatment in A. fatua PD caryopses is discussed in reference to the interconnection between ABA and GA metabolism and signaling pathways.