Using the appearance of the coleorhiza and root emergence as indicators, germination was monitored over a 46-h period of the seedling development (Figure ). Caryopsis covering structures, i.e., seed coat and fruit coat, were disrupted at 6 h after imbibition (HAI) in most of the seeds (Figure A). In the majority of the seeds, the coleorhiza appeared at 8 HAI, while at 10 HAI, almost all of the seeds had a coleorhiza that was already visible.
The primary root emergence and coleoptile growth were the next steps in the Brachypodium seedling development. Primary roots appeared at 20 HAI (Figure A) in some seedlings, while at 24 HAI, almost all of the seedlings had visible roots. The measurements of the embryo length during germination and growth at various time points are presented in FigureB. The embryo size in dry seeds was estimated to be approx. 0.2 cm in length. During the first 16 h of imbibition, the size of the Brachypodium embryo increased only slightly. Intense embryo growth began at 18 HAI, and at 24 HAI, the Brachypodium embryos had doubled their length.
Brachypodium distachyon (Brachypodium) grains at key time points of imbibition (A) and the progress of Brachypodium embryo size growth during 46 h of imbibition (B), data are means ± SE. Abbreviations: Cr—coleorhiza, R—radicle, Cl—coleoptile. Scale bar represents 1 mm.