Endosperm development in Dyckia pseudococcinea (Pitcairnioideae - Bromeliaceae)

Abstract Dyckia pseudococcinea is a threatened species endemic to the restingas of the Atlantic Forest, an area under strong anthropic impact. From the perspective of conservation, plant embryology is interesting by the variety of approaches for in vitro culture of seedlings. With this in mind, the present study describes the endospermogenesis of D. pseudococcinea to provide data for conservation studies and indicate characters that may contribute to the systematics of Pitcairnioideae. Using anatomical analysis, samples of flowers and fruits at different developmental stages were analyzed. We observed the establishment of the primary endosperm nucleus and then the primary endosperm cell (PEC). Upon expansion of the central vacuole of PEC, nuclei migrate to the chalazal, peripheral, and micropylar domains. An early centripetal cellularization begins in the chalazal region, characterizing the endosperm as coenocytic/multicellular type. With cellularization, the endosperm enfolds the embryo. In addition, in the outermost layer of the endosperm, an aleurone layer is visible. These observations allowed some embryological characters to be identified, thus helping to clarify the systematic relationships of Pitcairnioideae and also the genus Dyckia, such as the presence of hypostasis, the persistence of the antipodals and synergids during the early stages of endospermogenesis and coenocytic/multicellular endospermogenesis. Having established the details of endospermogenesis, we then set forth guidelines for the development of in vitro culture protocols aimed at the conservation of D. pseudococcinea, an endangered Bromeliad species of the Atlantic Forest.

摘要 假球狄克凤梨（Dyckia pseudococcinea）为特有受胁物种，仅分布于大西洋森林的滨海砂质生境（restinga），该区域正遭受强烈的人为干扰。从物种保护的视角出发，植物胚胎学可依托多样的幼苗体外培养研究方法开展工作，因而具备重要的科研价值。本研究对假球狄克凤梨的胚乳发生过程进行了系统描述，旨在为保护生物学研究提供基础数据，并筛选可助力阐明皮特凤梨亚科（Pitcairnioideae）分类学关系的形态特征。研究采用解剖学分析手段，对不同发育阶段的花和果实样本进行观察。结果显示，初级胚乳核率先形成，随后发育为初级胚乳细胞（primary endosperm cell, PEC）；随着初级胚乳细胞中央液泡的扩张，胚乳核迁移至合点端、周缘区及珠孔端。合点区域率先启动向心式细胞化过程，使该胚乳兼具多核体/多细胞型特征。细胞化完成后，胚乳将胚胎完全包裹；此外，在胚乳的最外层可见糊粉层。上述观察明确了若干关键胚胎学特征，有助于阐明皮特凤梨亚科及狄克凤梨属的系统发育关系，例如承珠盘的存在、胚乳发生早期反足细胞与助细胞的持久性，以及多核体/多细胞型胚乳发生模式。在明确假球狄克凤梨的胚乳发生细节后，本研究进而为该濒危凤梨科物种的体外培养方案制定提供了指导方向，以助力大西洋森林生境中这一受胁物种的保护工作。