Mixed-Oligosaccharides Promote Seedling Growth of Direct-Seeded Rice under Salt and Alkaline Stress

Rice direct seeding technology is an appealing alternative to traditional transplanting because it conserves labor and irrigation resources. Nevertheless, there are two main issues, salt stress and alkaline stress, which contribute to poor emergence and seedling growth, thereby preventing the widespread adoption and application of this technique in the Ningxia Region of China. Therefore, to determine whether germination can be promoted by mixed-oligosaccharide (KP) priming (in which seeds are soaked in a KP solution before sowing) under salt and alkaline stress, a proteomics study was performed. KP-priming significantly mitigated abiotic stress, such as salt and alkaline stress, by inhibiting root elongation, ultimately improving seedling establishment. By comparing the proteomics analyses, we found that energy metabolic pathway was a vital factor in KP-priming, which explains the alleviation of salt and alkaline stress. Key proteins involved in starch mobilization, pyruvate mobilization, and ATP synthesis, were up-regulated by KP-priming, significantly blocking salt and alkaline-triggered starch accumulation while enhancing pyruvate metabolism. KP-priming also up-regulated ATP synthase to improve energy efficiency, thereby improving ATP production. In addition, it enhanced antioxidant enzymatic activities and reduced the accumulation of reactive oxygen species. All of these factors contributed to a better understanding of the energy regulatory pathway enhanced by KP-priming, which mediated the promotion of growth under salt and alkaline conditions. Thus, this study demonstrated that KP-priming can improve rice seed germination under salt and alkaline stress by altering energy metabolism.