Cool–Warm Temperature Stratification and Simulated Bird Digestion Optimize Removal of Dormancy in Rosa rugosa Seeds

Abstract

Rosa rugosa Thunb. has been explored multi-function in medicinal, edible, cosmetic, ornamental and ecological etc. However, R. rugosa natural populations have recently declined substantially in China, besides of global climate change, this species also has the defect of limiting the reproduction of itself such as the hard-to-release seed dormancy. In this study, only 30% of R. rugosa seeds were viable, and the others were incompletely developed or diseased seeds. Without stratification, morphologically complete viable seeds imbibed water but those seeds could not germinate even after seed husk removal under suitable condition to exhibit a physiological dormancy. After cold (4°C) and warm (18 ± 2°C) stratification, macromolecular substances containing carbon or nitrogen accumulated, and respiration, antioxidant enzyme activity, and gibberellin (GA3) /abscisic acid (ABA) and auxin (IAA)/ABA ratios increased significantly in seeds. Water absorption also increased as endocarps softened. Thus, physiological dormancy of seed was broken. Although warm and cold stratification increased separation between endocarp and embryo, the endocarp binding force was removed insufficiently, because only 10.20% of seeds germinated. Therefore, stratified seeds were treated with simulated bird digestion. Then, folds and cracks in loosened endocarps increased permeability, and water absorption rate increased to 64.43% compare to 21.14% in cold and warm stratification treatment. With simulated digestion, 24.20% of radicles broke through the endocarp with plumules and cambiums to develop into seedlings. Thus, the seed dormancy type of R. rugosa is physiological as seeds imbibed water and possessed fully developed embryos with a low growth potential in combination with a mechanical constraint from the endocarp. Cold stratification helped remove physiological dormancy, and additional warm stratification accelerated the process. The optimal stratification treatment was 4°C for 45 days followed by 18 ± 2°C for 15 days. After warm and cold stratification, simulated bird digestion broke the mechanical constraint from the seed covering layers. Based on this research, production of R. rugosa seedlings can be greatly increased to help protect the species from further declines.

Characterization and mechanism of seed dormancy in Symplocos paniculata

“…Lignification of the endocarp as a contributing factor to seed dormancy ( Gao et al., 2022 ). The resorcinol staining method was employed to investigate the alterations in lignin deposition within the endocarp of S. paniculata seeds during various developmental stages.…”

“…The failure of germination in seeds with high vitality and well-developed embryos under suitable conditions can be attributed to either the impermeability of the seed coat or hard endocarp, which acts as a mechanical restriction. The permeability of these structures plays a crucial role in determining successful germination by facilitating water absorption ( Manz et al., 2005 ; Farhana and Conor, 2013 ; Gao et al., 2022 ). In our study, the lignification of S. paniculata endocarp was observed to be severe, and water uptake in cracked seeds was significantly higher compared to intact seeds, thereby indicating that seed endocarp lignification causes impermeability and potentially contributes to the mechanical dormancy of S. paniculata seeds.…”

Gene-flow investigation between garden and wild roses planted in close distance

“…The germination rate in 2021 to 2022 was higher than 2020, although it was still low (Table 1). The low germination ratio may be due to the duration of vernalization; it was too short in 2020, and too long in 2021 and 2022 (Gao et al 2022). Although low germination ratio means less possibility of gene-flow to wild species, we cannot examine it without DNA from leaves.…”