Abstract
Seagrasses are the only submerged marine higher plants, which can colonize the sea through sexual (via seeds) reproduction. The transition between seed dormancy and germination is an important ecological trait and a key stage in the life cycle of higher plants. According to our observations, the seeds of Zostera marina L. (eelgrass) in Swan Lake (SL) and Qingdao Bay (QB) in northern China have the same maturation time (summer) but different germination time. To investigate this phenomenon, we further carried out reciprocal transplantation experiment and transcriptome analysis. Results revealed that differences in the seed germination time between the two sites do exist and are determined by internal molecular mechanisms as opposed to environmental factors. Furthermore, we conducted comparative transcriptome analysis of seeds at the mature and early germination stages in both locations. The results that the number of genes related to energy, hormone and cell changes was higher in SL than in QB, could account for that the dormancy depth of seeds in SL was deeper than that in QB; consequently, the seeds in SL needed to mobilize more related genes to break dormancy and start germination. The results could have important practical implications for seagrass meadow restoration via seeds and provide in-depth and comprehensive data for understanding the molecular mechanisms related to seagrass seed germination.
Highlights
Seagrass meadows are key ecosystems, and they are among the most threatened habitats on the planet
Seeds collected from Qingdao Bay (QB) had a higher seed germination rate in autumn, regardless of whether they were planted in QB or Swan Lake (SL)
Seeds collected from SL had a very low seed germination rate in autumn, regardless of whether they were planted in QB or SL, with the germination rate close to 0; but the germination rate was relatively high in spring, with the germination rate 6.67 ± 1.33% and 36.00 ± 5.03% in QB and SL, respectively (Figure 2)
Summary
Seagrass meadows are key ecosystems, and they are among the most threatened habitats on the planet. While colonizing the sedimentary shorelines of the world’s oceans, seagrasses have experienced genomic losses and gains to achieve the structural and physiological adaptations required for its marine lifestyle, arguably the most severe habitat shift ever accomplished by flowering plants (Olsen et al, 2016). Seagrass species colonize the sea through both sexual (via seeds) and asexual (via clonal growth of rhizomes) reproduction (Phillips and Menez, 1988; Darnell et al, 2015; Zhang et al, 2020). Sexual reproduction plays an important role in colonizing new habitats and recolonizing severely declined seagrass meadows by dispersing seeds from parental meadows (Harwell and Orth, 1999; Jarvis and Moore, 2010; Kendrick et al, 2012)
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