Abstract
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.
Highlights
Smoke derived from burning plant material stimulates germination of dormant and non-dormant caryopses of a number plant species from fire-prone and fire-free ecosystems (Thomas and Van Staden 1995; Van Staden et al 2000)
Inhibitors of gibberellin biosynthesis, ancymidol, paclobutrazol and flurprimidol inhibited the effect of KAR1
The results presented correspond to the mean ± standard deviation (SD) of the values obtained with five different extracts
Summary
Smoke derived from burning plant material stimulates germination of dormant and non-dormant caryopses of a number plant species from fire-prone and fire-free ecosystems (Thomas and Van Staden 1995; Van Staden et al 2000). Smoke can increase seed vigor of several crop plants (Light et al 2009). In 2003 was the active compound, a butenolide (3-methyl2H-furo[2,3-c]pyran-2-one, KAR1) responsible for the stimulatory action, isolated. It was isolated simultaneously from plant-derived smoke (Van Staden et al 2004) and from burned cellulose (Flematti et al 2004). KAR1 stimulate seed germination of many, but not all, plant species. Seeds which are sensitive to smoke responded positively to KAR1 (Light et al 2009) with more than 60 species reported as responsive to both smoke and to KAR1 (Chiwocha et al 2009). Later KAR2, KAR3 and KAR4 from smoke were identified (Nelson et al 2009) and different sensitivity to these compounds, depending on species, was noted (Chiwocha et al 2009)
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