Surface Plant Opals of Setaria viridis Seeds Correlate with Seed Dormancy

Background and Objective: Plant opals, formed by the deposition of soluble silicic acid in plant cells, serve structural and defensive functions in leaves and stems. However, their role on seed surfaces remains unclear. This study investigates the structure and potential function of plant opals on the seeds of Setaria viridis, a species exhibiting seed dormancy. The objective was to determine whether these surface opals are associated with dormancy regulation. Materials and Methods: Seed surface morphology was analyzed using scanning electron microscopy. Comparative observations were made between S. viridis and S. italica (a non-dormant cultivated form). A standard cold and moist stratification treatment was applied to assess dormancy release. Observations focused on changes in seed coat structure, particularly the detachment or cracking of plant opals. No additional statistical tests were required for this morphological comparison. Results: A distinct parallel arrangement of plant opals was observed on the outer seed coat of S. viridis. These opals detached following dormancy-breaking treatment, initiating cracks in the seed coat. In contrast, S. italica exhibited pre-damaged or missing opal structures and lacked dormancy. These findings suggest a correlation between intact opal structures and seed dormancy, implying that opal detachment may facilitate water permeability and germination. Conclusion: The plant opals on the seed surface of S. viridis may contribute to seed dormancy by forming a physical barrier. Their structural disruption during dormancy-breaking treatments supports a role in regulating seed coat permeability. Further research is necessary to clarify the biochemical and mechanical processes involved.