In some species, epicotyl dormancy break in seeds that have deep simple epicotyl morphophysiological dormancy requires a certain root length to be attained, but the mechanisms associated with this are unclear. Hao et al.study seeds of Tibetan peony (Paeonia ludlowii) and find that a root length of ≥6 cm is necessary before dormancy can be released by cold stratification. They determine that root length increases the ratio of GA3/ABA of the epicotyl in the seeds, with ABA accumulation decreasing with increasing root length. They conclude that the epicotyl becomes sensitive to cold stratification once a certain ratio is reached.
