Abstract
Main conclusionThe induction of dormancy release and germination ofAvena fatuacaryopses by KAR1involves ABA degradation to phaseic acid. Both, KAR1and GA3, control the AsA–GSH cycle, DNA replication and accumulation of β-tubulin in embryos before caryopses germination.Avena fatua caryopses cannot germinate in darkness at 20 °C because of dormancy, but karrikinolide-1 (KAR1), a compound in plant-derived smoke, and gibberellic acid (GA3) induced an almost complete germination. The radicle protrusion through the coleorhiza was preceded by increased water uptake, rupture of coat, increased embryo size and coleorhiza length as well as coleorhiza protrusion through covering structures. The stimulatory effect of KAR1 was correlated with the reduced content of abscisic acid (ABA) and an increase in phaseic acid (PA) in embryos from caryopses before coleorhiza protrusion. Two non-enzymatic antioxidants, ascorbate (AsA) and reduced glutathione (GSH), did not affect the germination of dormant caryopses, but in the presence of KAR1 or GA3 they only slightly delayed the germination. The stimulatory effect of KAR1 or GA3 on the final germination percentage was markedly antagonized by lycorine, an AsA biosynthesis inhibitor. KAR1 and GA3 applied during caryopses imbibition resulted in increases of AsA, dehydroascorbate (DHA) and GSH, but reduced the embryos’ oxidized glutathione (GSSG) content. Furthermore, both KAR1 and GA3 induced an additional ascorbate peroxidase (APX) isoenzyme and increased the glutathione reductase (GR) activity. Both compounds stimulated β-tubulin accumulation in radicle+coleorhiza (RC) and plumule+coleoptile (PC), and enhanced the transition from G1 to S and also from S to G2 phases. The comparison of the effects produced by KAR1 and GA3 shows a similar action; thus the KAR1 effect may not be specific. The study provides new data regarding the mechanism with which KAR1, a representative of a novel class of plant growth regulators, regulates dormancy and germination of caryopses.
Highlights
Seed dormancy is induced during seed maturation and is defined as the inability of intact viable seeds to germinate under conditions favorable for the germination process (Bewley et al 2013)
Non-enzymatic antioxidants are represented by a-tocopherol, the reduced glutathione (GSH) and ascorbate (AsA); the enzymatic antioxidants involve superoxide dismutase (SOD) converting O2- to H2O2, catalase (CAT) converting H2O2 to water and oxygen, as well as the enzymes cooperating with the ascorbate–glutathione cycle: ascorbate peroxidase (APX), monodehydroascorbate reductase (MR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) (Noctor and Foyer 1998)
The increase in water uptake during this phase was associated with a progressive increase in the percentage of coleorhiza and radicle protrusion; after 48 h, ca 60 or 80 % germinated caryopses were observed in the KAR1 and GA3 treatment, respectively
Summary
Seed dormancy is induced during seed maturation and is defined as the inability of intact viable seeds to germinate under conditions favorable for the germination process (Bewley et al 2013). Non-enzymatic antioxidants are represented by a-tocopherol, the reduced glutathione (GSH) and ascorbate (AsA); the enzymatic antioxidants involve superoxide dismutase (SOD) converting O2- to H2O2, catalase (CAT) converting H2O2 to water and oxygen, as well as the enzymes cooperating with the ascorbate–glutathione cycle: ascorbate peroxidase (APX), monodehydroascorbate reductase (MR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) (Noctor and Foyer 1998)
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