Distinct hormonal and morphological control of dormancy and germination in Chenopodium album dimorphic seeds

Abstract

Dormancy and heteromorphism are innate seed properties that control germination timing through adaptation to the prevailing environment. The degree of variation in dormancy depth within a seed population differs considerably depending on the genotype and maternal environment. Dormancy is therefore a key trait of annual weeds to time seedling emergence across seasons. Seed heteromorphism, the production of distinct seed morphs (in color, mass or other morphological characteristics) on the same individual plant, is considered to be a bet-hedging strategy in unpredictable environments. Heteromorphic species evolved independently in several plant families and the distinct seed morphs provide an additional degree of variation. Here we conducted a comparative morphological and molecular analysis of the dimorphic seeds (black and brown) of the Amaranthaceae weed Chenopodium album. Freshly harvested black and brown seeds differed in their dormancy and germination responses to ambient temperature. The black seed morph of seedlot #1 was dormant and 2/3rd of the seed population had non-deep physiological dormancy which was released by after-ripening (AR) or gibberellin (GA) treatment. The deeper dormancy of the remaining 1/3rd non-germinating seeds required in addition ethylene and nitrate for its release. The black seeds of seedlot #2 and the brown seed morphs of both seedlots were non-dormant with 2/3rd of the seeds germinating in the fresh mature state. The dimorphic seeds and seedlots differed in testa (outer seed coat) thickness in that thick testas of black seeds of seedlot #1 conferred coat-imposed dormancy. The dimorphic seeds and seedlots differed in their abscisic acid (ABA) and GA contents in the dry state and during imbibition in that GA biosynthesis was highest in brown seeds and ABA degradation was faster in seedlot #2. Chenopodium genes for GA and ABA metabolism were identified and their distinct transcript expression patterns were quantified in dry and imbibed C. album seeds. Phylogenetic analyses of the Amaranthaceae sequences revealed a high proportion of expanded gene families within the Chenopodium genus. The identified hormonal, molecular and morphological mechanisms and dormancy variation of the dimorphic seeds of C. album and other Amaranthaceae are compared and discussed as adaptations to variable and stressful environments.

Environmental Regulation of Weed Seed Dormancy and Germination

“…The condition and location of seeds in the soil profile can determine the intensity and manner of the interaction of these factors. In summary, genotypes; environmental factors during seed development, maturation, and after-ripening; and seed morphology, such as size, shape, and colour, affect a seed's condition and dormancy state [68,[80][81][82].…”

Identification of Reference Genes for Precise Expression Analysis during Germination in Chenopodium quinoa Seeds under Salt Stress

“…In Beta vulgaris and Chenopodium album seeds (Amarantaceae), germination sensu stricto proceeds in a similar manner to C. quinoa, where testa breakage occurs before the ER [29,35]. In Poaceae species (Avena fatua, Brachypodium distachyon, and Hordeum vulgare), the coleorhiza, a tissue analogous to the endosperm, is broken after grain-covering layers do, and coleorhiza rupture has been established as the criterion for scoring seed germination.…”

“…Among the selected reference genes are Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), Monensin sensitivity 1 (MON1), and Polypyrimidine tract-binding protein (PTB) that have previously been reported as reference genes in quinoa [24,41,51,52]. Additionally, Actin-7 (ACT7), Ubiquitin-conjugating enzyme (UBC), and 18S ribosomal RNA (18S) were included in the selection due to their established use as reference genes in seeds of other plant species, such as Arabidopsis thaliana, Chenopodium album, Lepidium sativum, and Sisymbrium officinale [17,22,35]. EF1α (AUR62020767) has been previously reported as a reference gene in quinoa seedlings [41,52].…”

Pectin methylesterase 31 is transcriptionally repressed by ABI5 to negatively regulate ABA-mediated inhibition of seed germination

“…GA is essential for the release of dormancy and for the initiation of germination. They antagonistically modulate seed germination, which is at least in part regulated by the balance and sensitivity to ABA and GA (Shu et al, 2013;Loades et al, 2023). In adverse environmental conditions, such as drought, high salinity, and extreme temperatures, ABA dominates the dormant state.…”

“…ABA also represses cell division and regulates the ion transport of seeds in seed germination (Liu et al, 2022). Besides, ABA modulates gene expression and regulates the activity of enzymes, such as amylases and protein kinases, to control seed germination (Xue et al, 2021;Li et al, 2022;Loades et al, 2023).…”