Interaction of karrikinolide and ethylene in controlling germination of dormant Avena fatua L. caryopses

Caryopses of Avena fatua L. are dormant after harvest and germinate poorly at 20 °C. Dormancy was released by after-ripening the dry caryopses in the dark at 25 °C for 3 months. Karrikinolide (butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one, KAR1), in contrast to exogenous ethylene and the precursor of ethylene biosynthesis 1-aminocyclopropane-1-carboxylic acid (ACC), completely overcame dormancy. The effect of KAR1 was not affected by aminoethoxyvinylglycine (AVG), α-aminoisobutyric acid (AIB) and CoCl2, inhibitors of ACC synthase and oxidase, respectively. 2,5-Norbornadiene (NBD), a reversible inhibitor of ethylene binding to its receptor, counteracted the stimulatory effect of KAR1. Ethylene, ethephon and ACC counteracted and AVG reinforced inhibition caused by norbornadiene. Inhibition due to norbornadiene, applied during the first 3 days of imbibition in the presence of KAR1, disappeared after transfer to air or ethylene. The obtained results confirm that KAR1 breaks dormancy and indicate that ethylene alone plays no role in releasing dormancy of Avena fatua caryopses. KAR1 probably did not relieve dormancy via the stimulation of ethylene biosynthesis. Some level of endogenous ethylene is probably required for ethylene action, which might be required for releasing dormancy by KAR1 or for subsequent germination of caryopses after removing dormancy.