Necessity of gibberellin for stimulatory effect of KAR₁ on germination of dormant Avena fatua L. caryopses

Avena fatua L. florets (caryopses enclosed by lemma and palea) were partially dormant at 10–20 °C and did not germinate at temperatures outside this range. After-ripening florets at 25 °C for 12 weeks completely removed dormancy. Caryopses (florets without lemma and palea) were able to germinate totally at 20 °C. Karrikinolide (KAR₁) and gibberellic acid (GA₃) applied at 10–25 °C partially or markedly induced germination of dormant florets and caryopses, respectively. Both florets and caryopses were more sensitive to KAR₁ than to GA₃. To obtain similar effects, 1,000 to 10,000 times lower concentrations of KAR₁ than GA₃ were required. After-ripening with time gradually increased sensitivity of caryopses to these regulators. Likewise, after-ripened, non-dormant caryopses were sensitive to KAR₁ and GA₃. Inhibitors of gibberellin biosynthesis, ancymidol, paclobutrazol and flurprimidol inhibited the effect of KAR₁. This inhibition was reversed by GA₃. Caryopses pre-incubated in water with ancymidol or paclobutrazol in the presence or absence of KAR₁ germinated completely but with different rates after transfer to GA₃. KAR₁ probably requires gibberellin biosynthesis to stimulate germination of dormant Avena fatua L. caryopses. Both KAR₁ and GA₃ increased α-amylase, β-amylase and dehydrogenases activities during imbibition before visible germination occurred.