This experiment was carried out to provide a comprehensive insight into the protein activities involved in dormancy establishment in seeds of common cocklebur (Xanthium strumarium), an annual plant with two dimorphic seeds contained in one casing known as a burr. These consist of a smaller dormant seed and a larger non-dormant seed. The proteome profile was compared between developing dor- mant and non-dormant seeds of Xanthium strumarium at five consecutive stages including three, 10, 20, 30, and 45 days after burr emergence (stages 1 to 5). We identified 6524 proteins in total, and approximately 3.6% of these were differentially abundant proteins (DAPs) between the two seed types. Both seed types showed fun- damental changes in developmental programs during the examined stages. More than 38% of all DAPs were observed at the first stage, supporting the importance of the early developmental stage in seed fate determination. The detected DAPs at stage 1 were mainly associated with the cell division phase, which showed a delay in the dormant seeds. Over-representation of proteins responsible for cell wall biosynthesis, cytokinesis, and seed development were detected for non-dormant seeds at the first stage, while dormancy-associated proteins showed less abundance. Stage 3 was the critical stage for switching processes toward seed maturation and abscisic acid (ABA) signaling. Interestingly, higher abundance proteins in the mature non-dormant seed were mainly involved in the facilitation of seed germination. Taken together, the tem- poral pattern of the accumulated proteins in developing dormant seeds demonstrated a delay in the initiation of active cell division, enriched response to ABA, and defects in seed maturation. Moreover, stored proteins in the mature dormant seed delay ger- mination but not dormancy induction. Finally, our results suggest that dormancy may be established at a stage of seed development earlier than previously thought.

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