濒危睡莲——热唇草睡莲的花生物学、胚珠及种子个体发育，热唇草睡莲有望成为基部被子植物的模式系统。
Floral biology and ovule and seed ontogeny of Nymphaea thermarum, a water lily at the brink of extinction with potential as a model system for basal angiosperms.
作者信息
Povilus Rebecca A, Losada Juan M, Friedman William E
机构信息
Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA
Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA.
出版信息
Ann Bot. 2015 Feb;115(2):211-26. doi: 10.1093/aob/mcu235. Epub 2014 Dec 14.
BACKGROUND AND AIMS
Nymphaea thermarum is a member of the Nymphaeales, of one of the most ancient lineages of flowering plants. This species was only recently described and then declared extinct in the wild, so little is known about its reproductive biology. In general, the complete ontogeny of ovules and seeds is not well documented among species of Nymphaea and has never been studied in the subgenus Brachyceras, the clade to which N. thermarum belongs.
METHODS
Flowers and fruits were processed for brightfield, epifluorescence and confocal microscopy. Flower morphology, with emphasis on the timing of male and female functions, was correlated with key developmental stages of the ovule and the female gametophyte. Development of the seed tissues and dynamics of polysaccharide reserves in the endosperm, perisperm and embryo were examined.
KEY RESULTS
Pollen release in N. thermarum starts before the flower opens. Cell walls of the micropylar nucellus show layering of callose and cellulose in a manner reminiscent of transfer cell wall patterning. Endosperm development is ab initio cellular, with micropylar and chalazal domains that embark on distinct developmental trajectories. The surrounding maternal perisperm occupies the majority of seed volume and accumulates starch centrifugally. In mature seeds, a minute but fully developed embryo is surrounded by a single, persistent layer of endosperm.
CONCLUSIONS
Early male and female function indicate that N. thermarum is predisposed towards self-pollination, a phenomenon that is likely to have evolved multiple times within Nymphaea. While formation of distinct micropylar and chalazal developmental domains in the endosperm, along with a copious perisperm, characterize the seeds of most members of the Nymphaeales, seed ontogenies vary between and among the constituent families. Floral biology, life history traits and small genome size make N. thermarum uniquely promising as an early-diverging angiosperm model system for genetic and molecular studies.
背景与目的
热唇睡莲是睡莲目植物的一员，睡莲目是开花植物中最古老的谱系之一。该物种直到最近才被描述，随后被宣布在野外灭绝，因此对其繁殖生物学知之甚少。一般来说，睡莲属物种中胚珠和种子的完整个体发育过程记录并不完善，且从未在热唇睡莲所属的短角睡莲亚属中进行过研究。
方法
对花朵和果实进行明场、落射荧光和共聚焦显微镜观察。重点研究花形态，尤其是雄花和雌花功能的时间，将其与胚珠和雌配子体的关键发育阶段进行关联。研究种子组织的发育以及胚乳、外胚乳和胚中多糖储备的动态变化。
主要结果
热唇睡莲在花朵开放前就开始释放花粉。珠孔珠心的细胞壁呈现出胼胝质和纤维素分层，类似于传递细胞壁的模式。胚乳发育从一开始就是细胞型的，珠孔和合点区域沿着不同的发育轨迹发展。周围的母体外胚乳占据种子体积的大部分，并离心积累淀粉。在成熟种子中，一个微小但发育完全的胚被一层单一的、持久的胚乳包围。
结论
早期的雄花和雌花功能表明热唇睡莲倾向于自花授粉，这种现象可能在睡莲属中多次进化。虽然胚乳中形成明显的珠孔和合点发育区域以及丰富的外胚乳是睡莲目大多数成员种子的特征，但种子个体发育在各组成科之间存在差异。花生物学、生活史特征和小基因组大小使热唇睡莲作为遗传和分子研究的早期分化被子植物模型系统具有独特的前景。
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