Putative Spatiotemporal Changes in Inhibitor Activity during Cold Stratification of Sapium sebiferum Seeds

Sapium sebiferum is a tree with socioeconomic, environmental, and medicinal value. S. sebiferum seeds possess physiological dormancy, which is induced by endogenous inhibitors and can be broken by cold stratification. However, the putative spatiotemporal changes in inhibitor activity are currently unknown, which can hinder the propagation of S. sebiferum seeds. The objective of this study was to investigate the spatiotemporal dynamics of inhibitor activity and its effect on germination during the cold stratification of S. sebiferum seeds. An extractant consisting of 80% methanol was used to extract the inhibitory substance from the seed coat and endosperm at different stages of cold stratification. The extract was then applied to both the Chinese cabbage seeds and excised embryos of S. sebiferum. The germination percentage and germination index were used to assess the inhibitor activity of S. sebiferum seeds. The germination of non-stratified S. sebiferum seeds was completely inhibited (0% germination). As the stratification duration was extended, the germination percentage of S. sebiferum seeds gradually increased. However, dormancy persisted until the stratification duration reached 120 d: at this point, the mean germination was 81.3%. The germination test on Chinese cabbage seeds revealed a significant increase from 10.0% (stratified for 0 d) to 91.2% (stratified for 120 d) when treated with endosperm extracts. The germination indexes also increased from 0.0 to 40.3, indicating a decrease in the inhibitory activity of endosperm extracts. The seed coat extracting solution showed varying dynamic changes. The lowest germination was observed after 60 d of stratification, with no significant differences among the results of 0 d, 30 d, and 60 d. However, after stratification for 90 d, the germination percentage of Chinese cabbage seeds increased. The germination percentage of excised embryos exhibited similar changes to those of Chinese cabbage seeds. This study discovered that endogenous inhibitors were present in both the seed coat and endosperm of S. sebiferum seeds, and the inhibitor activity was higher in the endosperm. The spatiotemporal patterns of inhibitor activity suggest that the endogenous inhibitors move from the endosperm to the seed coat during early cold stratification stages, aiding in the physiological dormancy release of S. sebiferum seeds. These findings enhance our understanding of seed biology in S. sebiferum and will facilitate high-efficiency seed propagation.