Peer Review #2 of "Proanthocyanidins in seed coat tegmen and endospermic cap inhibit seed germination in Sapium sebiferum (v0.2)"

Abstract

Sapium sebiferum, an ornamental and bioenergetic plant, is propagated by seed. Its seed coat contains germination inhibitors and takes a long time to stratify for germination. In this study, we discovered that the S. sebiferum seed coat (especially the tegmen) and endospermic cap contained high levels of proanthocyanidins. Seed-coat and endospermic cap removal induced seed germination whereas exogenous application with seed-coat extract or proanthocyanidins significantly inhibited this process, suggesting that proanthocyanidins in the seed coat played a major role in regulating seed germination in S. sebiferum. We further investigated how seed-coat extract affected the expression of the seed-germination-related genes. The results showed that treatment with seed-coat extract upregulated the transcription level of the dormancy-related gene, gibberellins suppressing genes, abscisic acid biosynthesis and signalling genes. Seed-coat extract decreased the transcript levels of abscisic acid catabolic genes, gibberellins biosynthesis genes, reactive oxygen species genes and nitrates-signalling genes. Exogenous application of nordihydroguaiaretic acid, gibberellic acid, hydrogen peroxide and potassium nitrate recovered seed germination in seed-coat-extract supplemented medium. In this study, we highlighted the role of proanthocyanidins, and their interactions with the other germination regulators, in the regulation of seed dormancy in S. sebiferum.