Comparative Proteomics Reveals the Mechanisms Underlying Variations in Seed Vigor Based on Maize (Zea mays L.) Ear Positions

Seed vigor is influenced by seed position in plant. However, current understanding of its underlying mechanism is limited. In this study, we used isobaric tags for relative and absolute quantitation technique to study the comparative proteomes between middle seeds (with higher vigor) and top seeds of maize (Zea mays L.) ears at 0 h, 24 h, and 48 h of imbibition. A total of 159 differentially accumulated proteins were identified. Among these, the largest number of proteins was from the functional categories of Disease/Defense and Metabolism. Compared with top seeds, most of the differentially accumulated proteins of Protein Synthesis and Energy showed higher accumulation in middle seeds at 0 h and 24 h of imbibition, but lower accumulation at 48 h of imbibition. Seed water absorption activates metabolic processes. The water content of middle seeds was significantly lower than that of top seeds at between 12 h and 30 h of imbibition, but energy production would be higher in the middle seeds at 24 h of imbibition. Meanwhile, tonoplast intrinsic proteins 3.1 and 3.2, which mediate water inflow into protein storage vacuoles, then activating enzymes involved in reserve mobilization, showed higher accumulation in middle seeds at 24 h of imbibition. In addition, our data also showed middle seeds may suffer less fungal damages. Our results contribute to understanding the mechanisms underlying the effects of growth position on seed vigor.