Epicotyl Morphophysiological Dormancy in Seeds ofDaphniphyllum glaucescens, a Woody Member of the Saxifragales

Abstract

Available information on seed dormancy for various members of the Saxifragales and phylogenetic relationships within this order allowed us to accurately predict that Daphniphyllum glaucescens seeds have morphophysiological dormancy (MPD). However, our hypothesis that seeds had deep simple epicotyl MPD, i.e., nondeep physiological dormancy (PD) in root and deep PD in shoot, was not supported. Both the root and the shoot (cotyledons) of the underdeveloped embryo of D. glaucescens have nondeep PD. Exposure to moderate (15°/6°, 20°/10°C), rather than high (25°/15°C), temperatures for 10–12 wk broke the PD of the hypocotyl/root. After hypocotyl emergence, seeds with an attached developing root system did not require cold stratification to break the PD of the shoot. The PD of the shoot was broken by an additional 10–12 wk at moderate temperatures, during which time cotyledons slowly grew inside the seed. As cotyledons grew, all of the hypocotyl was pushed out of the seed, and the final cotyledon length was almost twice that of the seed; at this point, the folded cotyledons emerged. Since the level of PD in root and shoot may or may not be the same, we advocate stating the level of PD in both root and shoot when epicotyl MPD is described in a species. Thus, seeds of D. glaucescens have nondeep simple (root)–nondeep simple (epicotyl) MPD, which is written as C1bB(root)‐C1bB(shoot) in the formula system of Nikolaeva. This is the first report of this level of epicotyl MPD in the Saxifragales.