Nitric Oxide Pre-Treatment Advances Bulblet Dormancy Release by Mediating Metabolic Changes in Lilium

Abstract

The lily is a globally popular cut flower, and managing dormancy in lily bulblets is essential for continuous, year-round production. While nitric oxide (NO) has been shown to influence seed dormancy and germination, its role in dormancy release in lilies was previously unconfirmed. In this study, we investigated the effects of NO on dormancy release in lily bulblets using SNP and c-PTIO. Results showed that SNP treatment promoted dormancy release, while c-PTIO inhibited it. Measurement of endogenous NO levels in the bulbs, along with enzyme activities of NOS-like and NR and gene expression levels of LoNOS-IP and LoNR, confirmed that NO plays a role in promoting dormancy release in lilies. To further elucidate the physiological mechanisms involved, we analyzed H₂O₂ levels, antioxidant enzyme activities, endogenous hormone levels, and carbohydrate metabolism in the bulbs. Findings demonstrated that NO facilitated dormancy release by increasing H₂O₂, gibberellins (GAs), indole-3-acetic acid (IAA), zeatin riboside (ZR), reducing sugars, and by accelerating the metabolism of abscisic acid (ABA) and starch. This study provides a foundation for deeper investigation into the mechanisms underlying dormancy release in lily bulbs.

Keywords: Lilium; abscisic acid; dormancy; gibberellin; nitric oxide; sodium nitroprusside.

Figure 1

Lily bulblet dormancy release was affected by SNP and c-PTIO. (A) Phenotypes of bulblets treated with exogenous SNP (5 mM, 10 mM, and 20 mM) and c-PTIO (1 mM) for 3 h and grown at room temperature (4 °C) for 60 days. (B) Bulb length statistics. The data are shown as three independent biological replicates and three technical replicates (n = 3). ****—p ≤ 0.0001, ns—not significant.

Figure 2

Effects of SNP and c-PTIO on NO contents (A), no enzyme activity (B,C), and NO-related genes expression (D,E). Values are means ± SDs (n = 3). The data are shown as three independent biological replicates and three technical replicates (n = 3). Different lowercase letters indicate statistically significant differences at p ≤ 0.05.

Figure 3

Changes in antioxidant enzyme activity (B–D) and H₂O₂ contents (A) of lily bubs treated with 10 mM SNP, 1 mM c-PTIO or SNP with c-PTIO during dormancy release at room temperature (4 °C) for 60 days. The data are shown as three independent biological replicates and three technical replicates (n = 3).

Figure 4

Changes in endogenous phytohormone contents and related genes expression of lily bubs treated with 10 mM SNP, 1 mM c-PTIO or SNP with c-PTIO during dormancy release at room temperature (4 °C) for 60 days. (A) ABA contents; (B) GA contents; (C) IAA contents; (D) ZR contents; (E) relative expression of LoARR; (F) relative expression of LoCYP707A1; (G) relative expression of LoDELLA; (H) relative expression of LoGA20x; (I) relative expression of LoGH3.1; (J) relative expression of LoNCED1; (K) relative expression of LoVIL1; (L) relative expression of LoXERICO. The data are shown as three independent biological replicates and three technical replicates (n = 3). Different lowercase letters indicate statistically significant differences at p ≤ 0.05.

Figure 5

Changes in soluble sugar contents, starch contents, and related genes expression of lily bulbs treated with 10 mM SNP, 1 mM c-PTIO or SNP with c-PTIO during dormancy release at room temperature (4 °C) for 60 days. (A) Soluble sugar contents; (B) starch contents; (C) relative expression of LoAMY; (D) relative expression of LoBMY; (E) relative expression of LoSPS; (F) relative expression of LoSUS; (G) relative expression of LoSUT; (H) relative expression of LoTMT. The data are shown as three independent biological replicates and three technical replicates (n = 3). Different lowercase letters indicate statistically significant differences at p ≤ 0.05.

Figure 6

Model depicting how NO regulates bulblet dormancy release. Exogenous SNP treatment activates NOS-like or NR activity, which promotes NO production, while c-PTIO treatment has the opposite effect. NO promotes the contents of H₂O₂, GA, IAA, ZR for accelerating the progress of dormancy release. NO also promotes the catabolism of ABA and starch. The resulting decreased contents of ABA and starch ultimately lead to dormancy release.