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.