Nitric Oxide is Involved in the Inhibition of Seed Germination by Paclobutrazol in Arabidopsis

Nitric oxide (NO) is a gaseous signaling molecule in plants. Paclobutrazol is a widely used plant growth retardant in agriculture and gibberellic acid (GA) biosynthesis inhibitor in research. Both of them involving in various biological processes. However, the crosstalk of paclobutrazol and NO was unclear. In this study, we explored the effect of paclobutrazol treatment on seed germination of Arabidopsis Col-0 and nia1nia2. The results showed that endogenous NO deficiency alleviated the inhibition effect of paclobutrazol on seed germination in nia1nia2. On the transcriptome level, NO and paclobutrazol commonly regulated the expression level of genes involving in oxidation–reduction process, phytohormone response, photosynthesis, light stimulus response, and abiotic stress response, etc. In the GA response pathways, NO deficiency reversed or offset the effect of paclobutrazol on the transcription of most of genes encoding GA metabolism enzymes and two DELLA proteins, RGA and RGL2. The global S-nitrosylated protein level was regulated not only by NO, but also paclobutrazol. Paclobutrazol enhanced the S-nitrosylated protein level in both of Col-0 and nia1nia2 seeds, but the level was constantly higher in Col-0 seeds. Our results suggest that NO may regulate the inhibition effect of paclobutrazol on seed germination in Arabidopsis, via S-nitrosylation of target proteins.