Moist Heat Overcomes Physical Dormancy at the Seed Coat Lens in Schizolobium parahyba var. amazonicum

ABSTRACT Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby (Fabaceae-Caesalpinoideae) is a tree of the Amazon region with pioneer characteristics and large seeds with physical dormancy. Using Accelerated Ageing (AA) methodology, seeds were exposed to Moist Heat (40 °C; >97% Relative Humidity; RH) or Dry Heat (40 °C; 22% RH). Furthermore, it was also investigated dormancy release and the primary site of water entrance into the seeds. Seeds tolerate these conditions for up to six days without any reduction in vigour, however, only Moist Heat could overcome seed dormancy, allowing germination. The lens is the water-gap for primary water entry (where the palisade layer is thinner), as seeds with blocked lens did not imbibe. An unusual multi-layered hypodermis of osteosclereids in the seed coat was observed. Our results suggest that the combination of high temperature with high RH is a key factor involved in overcoming dormancy in the natural habitat of this Amazonian species.

摘要：亚马逊裂叶黄檀（Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby，豆科-云实亚科）是亚马逊区域的先锋树种，其种子为带有物理休眠特性的大型种子。本研究采用加速老化试验（Accelerated Ageing, AA）方法，将种子分别置于湿热环境（40℃；相对湿度＞97%，RH）或干热环境（40℃；相对湿度22%，RH）中处理。此外，本研究还探究了该种子的休眠解除机制与水分初始进入位点。结果表明，种子可在上述条件下耐受长达6天而无活力下降，但仅湿热环境能够打破种子休眠，使其萌发。种皮上的水孔是水分初始进入的位点（该区域栅栏层较薄），当水孔被堵塞时，种子无法吸胀。本研究还观察到，该树种的种皮内存在一种特殊的多层骨状石细胞皮下组织。研究结果显示，高温高湿的组合是该亚马逊物种自然生境中打破种子休眠的关键因素。