Exogenous gibberellin can effectively and rapidly break intermediate physiological dormancy of Amsonia elliptica seeds

Fruit dehiscence mechanism and release of dimorphic seeds with different germination properties in Commelina erecta

Commelina erecta is a successful weed species. The aims of this study were to analyse the morpho-anatomy of the fruit and dimorphic seeds of the weed C. erecta, the dynamics and type of dormancy, and water entry. Flowers and fruits at different development stages were processed using standard anatomical techniques. Besides, experiments of imbibition, germinability and water entry were performed on both seed types. In the fruit of C. erecta, free and coated seeds are developed within dehiscent and indehiscent carpels, respectively. Dehiscent carpels open through a region of mechanical weakness in the dorsal vascular bundle. This region does not form in the indehiscent carpel. The main anatomical differences between the two seed types were observed in the testa and in the number of covering layers. Imbibition experiments showed that the covering of both seed types is water permeable, so these seeds lack physical dormancy and may exhibit physiological dormancy. Germinability experiments showed that the dormancy in free seeds is variable throughout the reproductive season, whereas, in coated seeds, it is high throughout the reproductive season. The embryotega is an area where the hardness of the seed coat is interrupted and facilitates water entry. Differences in the morpho-anatomy of carpels result in the formation of dimorphic seeds with different covering layers and different germination properties. These different properties allow some seeds germinate immediately after falling from the mother plant, and others to be incorporated into the seed bank. These results are useful for designing weed management strategies in agroecosystems.

Methods for Improving the Germination of Rhodotypos scandens (Thunb.) Makino Seeds through Endocarp Removal

Rhodotypos scandens (Thunb.) Makino is known to have a seed dispersal that is thick and stony (endocarp + seeds) and has potential as a landscaping tree seed. In several Rosaceae species, seeds are covered with a hard endocarp, making the internal seeds water-impermeable and germination difficult. Here, we analyzed the morphoanatomical traits and germination properties of R. scandens seeds. To identify ideal seed propagation conditions, we immersed R. scandens seeds in sulfuric acid for varying durations and subjected them to phytohormone (gibberellic acid A3 and fluridone) and a cold stratification (CS) (5 °C) treatment after endocarp removal (ER). The R. scandens stony seeds did not increase in mass by ≥25.0%. Following ER, the seed mass increased by ≥50.0% with water absorption when compared to the initial dry mass. Seed surfaces showed damage and cracks through scarification after 1 h of immersion in sulfuric acid, failing to germinate. A combination of ER, phytohormone treatment, and CS improved seed germination compared to ER alone (26.0 ± 5.3%). Overall, R. scandens seeds showed a dispersal with a hard endocarp from the parent plant, and a pre-treatment with ER, phytohormones, and CS was required for effective seed propagation.

Characterization and mechanism of seed dormancy in Symplocos paniculata

Symplocos paniculata is a highly desirable oil species for biodiesel and premium edible oil feedstock. While germplasm preservation and breeding are crucial, the severity of seed dormancy poses a challenge to successful germination. We employed S. paniculata seeds as experimental materials and conducted an investigation into the types and causes of seed dormancy by analyzing the morphology and developmental characteristics of its embryo, exploring the water permeability property of the endocarp, and examining the presence of endogenous inhibitors, aiming to establish a theoretical foundation for overcoming seed dormancy and maximizing germplasm resource utilization. The findings revealed that the seed embryo had matured into a fully developed embryo, and no dormancy in terms of embryo morphology was observed. Upon reaching maturity, the endocarp of seeds undergoes significant lignification, resulting in notable differences in water absorption between cracked and intact seeds. The impermeability of the endocarp is one of the factors contributing to mechanical restriction. The different phases of endosperm extraction exerted varying effects on the germination of Chinese cabbage seeds, with the methanol phase exhibiting the most potent inhibitory effect. The presence of endogenous inhibitors emerged as the primary factor contributing to physiological dormancy in seeds. GC-MS analysis and validation trials revealed that fatty acids and phenolics, including hexadecanoic acid, oxadecanoic acid, and m-cresol, constituted the main types of endogenous inhibitory compounds found within the endosperm. These findings suggest that the seed dormancy in S. paniculata seeds has endocarp mechanical restriction, and the presence of endogenous inhibitors causes physiological dormancy.

Dormancy-release and germination improvement of Korean bellflower (Campanula takesimana Nakai), a rare and endemic plant native to the Korean peninsula

Korean bellflower (Campanula takesimana Nakai) is a rare and perennial herb with medicinal and ornamental values, is endemic to the Ulleung Island of Korea. In this study, we investigated the dormancy-release and germination characteristics of C. takesimana (Campanulaceae) seeds by subjecting them to varying temperatures (5, 10, 15, 20, and 25°C and diurnal/nocturnal temperatures of 15/6, 20/10, and 25/15°C), cold stratification periods (0, 4, 8, or 12 weeks at 5°C), and gibberellic acid (GA3) concentrations (0, 10, 100, or 1,000 mg·L-1 at 15/6°C and 25/15°C) to identify the ideal seed propagation conditions. The seeds were stimulated to germinate (at 25°C, 12-h photoperiod with fluorescent lamps at 40 ± 10 μmol∙m-2∙s-1) after cold stratification. To examine the germination characteristics, the seeds were tested for water imbibition and found to readily absorb water. The seeds exhibited underdeveloped embryos during dispersal, showed final germination of 37.00% ± 4.43 at 25°C and were not influenced by temperature. The seeds subjected to 0, 4, 8, or 12 weeks of cold stratification germinated at a success rate of 22.00% ± 4.76, 87.00% ± 6.80, 79.00% ± 2.52, and 77.00% ± 1.91, respectively. Additionally, the germination characteristics, which were based on final germination, mean germination time, and germination velocity (Timson index), were significantly greater in the seeds pretreated with 1,000 mg·L-1 GA3 at 25/15°C than in seeds pretreated with 0 mg·L-1 GA3. Overall, the seeds broke dormancy with GA3 and short-term cold stratification. Therefore, we concluded that C. takesimana seeds have non-deep, simple, morphophysiological dormancy, and pretreatment with cold stratification and GA3 is required for effective seed propagation.