NO-mediated dormancy release of Avena fatua caryopses is associated with decrease in abscisic acid sensitivity, content and ABA/GAs ratios

Abstract

NO releases caryopsis dormancy in Avena fatua, the effect being dependent on the level of dormancy. The NO effect involves also the reduction of caryopsis sensitivity to ABA and to a decrease in the ABA to GA_s ratio due to a decrease in ABA levels and the lack of effect on GA_s levels before germination is completed. Nitric oxide (NO) from various donors (i.e. SNP, GSNO and acidified KNO₂), applied to dry caryopses or during initial germination, released primary dormancy in caryopses. Dormancy in caryopses was gradually lost during dry storage (after-ripening) at 25 °C, enabling germination at 20 °C in the dark. The after-ripening effect is associated with a decrease in NO required for germination. In addition, NO decreased the sensitivity of dormant caryopses to exogenous abscisic acid (ABA) and decreased the embryos' ABA content before germination was completed. However, NO did not affect the content of bioactive gibberellins (GA_s) from non-13-hydroxylation (GA₄, GA₇) and 13-hydroxylation (GA₁, GA₃, GA_6.) pathways. Paclobutrazol (PAC), commonly regarded as a GA_s biosynthesis inhibitor, counteracted the dormancy-releasing effect of NO and did not affect the GA_s level; however, it increased the ABA content in embryos before germination was completed. Ascorbic acid, sodium benzoate and tiron, scavengers of reactive oxygen species (ROS), reduced the stimulatory effect of NO on caryopsis germination. This work provides new insight on the participation of NO in releasing A. fatua caryopses dormancy and on the relationship of NO with endogenous ABA and GA_s.

Keywords: Abscisic acid; After ripening; Avena fatua; Dormancy; Gibberellins; Nitric oxide.

Fig.1

Effect of vapours released from SNP on germination of A. fatua caryopses. Dormant dry caryopses from the 2011 and 2015 harvests were incubated in the presence of vapours from SNP for 5 h (a) or 24 h (b). Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–f) are significantly different (P ˂ 0.05, n = 3)

Fig. 2

Effect of vapours released from GSNO on germination of A. fatua caryopses. Dormant dry caryopses from the 2011 harvest were treated for 24 h with vapours from GSNO or during initial 24 h of germination in water (a). Dormant dry caryopses from the 2011 and 2015 harvest were treated for 24 h with vapours from GSNO (b).Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–d) are significantly different (P ˂ 0.05; n = 3)

Fig. 3

Effect of vapours released from acidified KNO₂ on germination of A. fatua caryopses harvested in 2015 after various periods of after-ripening. Dry caryopses after various periods of after-ripening were treated, for 3 h, with vapours from 10^–3 and 2 × 10^–3 M KNO₂ acidified with H₂ SO₄. Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–e) are significantly different (P ˂ 0.05; n = 3)

Fig. 4

Effect of vapours released from acidified KNO₂ on germination of A. fatua caryopses in the presence of ABA. Dormant caryopses from the 2011 (a) and 2015 (b) harvests were treated during initial 3 h of germination in water or ABA solutions with vapours from KNO₂ solution acidified with HCl. Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–e) are significantly different (P ˂ 0.05, n = 3)

Fig. 5

Effect of vapours released from acidified KNO₂ on the ABA content in embryos of A. fatua caryopses after 18, 24 and 36 h of germination. Dormant caryopses from the 2015 harvest were treated for 3 h with vapours from KNO₂ solution acidified with HCl after 15, 21 and 33 h of germination. Changes in the ABA content in embryos from dormant caryopses during germination in water were described previously (Kępczyński et al. 2021). Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–d) are significantly different (P ˂ 0.05, n = 3)

Fig. 6

Effect of vapours released from acidified KNO₂ on germination of A. fatua caryopses in the presence of PAC. Dormant caryopses from the 2015 harvest were treated with vapours from KNO₂ solution acidified with HCl during the initial 24 h of germination in PAC solutions. Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–d) are significantly different (P ˂ 0.05, n = 3)

Fig. 7

Effect of vapours released from acidified KNO₂ on germination of A. fatua caryopses in the presence of ROS scavengers. Dormant caryopses from the 2015 harvest were treated for initial 3 h of germination in the presence of scavengers with vapours from KNO₂ solution acidified with H₂ SO₄. The scavengers were used at 10^–3 M concentration. The scavengers were used at 10^–3 M concentration. Vertical bars indicate ± SD. One-way ANOVA with Duncan’s post hoc test was used to test for significance of differences. Means denoted by different letters (a–e) are significantly different (P ˂ 0.05, n = 3)