EPICOTYL MORPHOPHYSIOLOGICAL DORMANCY IN SEEDS OF DAPHNIPHYLLUM GLAUCESCENS, A WOODY MEMBER OF THE SAXIFRAGALES

Available information on seed dormancy for various members of the Saxifragales and phylogenetic relationships within this order allowed us to accurately predict thatDaphniphyllumglaucescens seeds havemorphophysiological 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 underdevelopedembryo of D. glaucescens have nondeepPD. Exposure tomoderate (15/6, 20/10C), rather than high (25/15C), temperatures for 10–12 wk broke the PDof 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.针对虎耳草目（Saxifragales）各类群的种子休眠相关研究数据及该目内的系统发育关系，为我们精准预测粉叶虎皮楠（Daphniphyllum glaucescens）种子存在形态生理休眠（morphophysiological dormancy, MPD）提供了依据。然而我们提出的“该物种种子具有深度简单型上胚轴MPD，即胚根表现为非深度生理休眠（physiological dormancy, PD）而苗表现为深度PD”的假说并未得到验证。粉叶虎皮楠未发育完全的胚的胚根与苗（子叶）均表现为非深度PD。将种子置于适中温度（15/6、20/10℃）而非高温（25/15℃）下培养10~12周，可打破下胚轴/胚根的PD。当下胚轴萌发后，带有发育中胚根系统的种子无需经过低温层积即可打破苗的PD。苗的PD可通过在适中温度下继续培养10~12周得以打破，此阶段子叶会在种子内部缓慢生长。随着子叶生长，整个下胚轴会被推出种子，最终子叶长度可达种子本身的近两倍；此时折叠的子叶便会展开萌发。鉴于胚根与苗的PD程度可能相同也可能不同，我们建议在描述某一物种的上胚轴MPD时，需同时注明胚根与苗各自的PD程度。因此，粉叶虎皮楠种子的MPD类型为非深度简单型（胚根）-非深度简单型（上胚轴），在尼古拉耶娃（Nikolaeva）的休眠分类公式体系中可记为C1bB(root)-C1bB(shoot)。这是虎耳草目中首次报道该类型的上胚轴MPD。