Sexual Reproduction in Ephedra and its Bearing on the Evolution of Double Fertilization and Endosperm

开花植物(被子植物)构成了地球上最多样化和最成功的植物类群，然而它们从更原始的种子植物进化而来的许多方面却鲜为人知。植物生物学家提出，被子植物的进化成功在很大程度上可以归因于它们不同寻常的高度衍生的有性繁殖模式。具体地说，这涉及双重受精过程，卵核与一个花粉携带的精子核融合，产生胚胎的受精卵，第二次受精事件涉及另一个花粉携带的细胞核。第二次受精的产物发育成一种高效的营养获取组织，称为胚乳，其功能是滋养种子内发育中的胚胎。到目前为止，很少有人致力于了解双受精这一独特的生殖过程是如何进化的。佐治亚大学的威廉·弗里德曼博士将研究麻黄属成员的有性繁殖模式，麻黄属被怀疑是种子裸子植物中亲缘关系最近的活着的群体。虽然麻黄属中受精的大部分方面还不是很清楚，但有迹象表明，类似被子植物双受精过程的事件可能在该属中发生。利用DNA测量和显微分析的现代技术和设备，弗里德曼博士将研究麻黄属几个代表性物种的生殖，分析配子形成、受精和胚胎早期发育的个体发育模式。相似性可能揭示导致被子植物双受精的中间步骤的线索，并有助于理解其适应意义。

Flowering plants (angiosperms) constitute the most diverse and successful group of plants living on earth, yet many aspects of their evolutionary origins from more primitive seed-bearing plants are poorly understood. Plant biologists have proposed that much of the evolutionary success of angiosperms can be attributed to their unusual and highly derived pattern of sexual reproduction. Specifically this involves a double fertilization process, the egg nucleus fusing with one pollen-borne sperm nucleus to produce the zygote of the embryo, and a second fertilization event involving another pollen-borne nucleus. The product of the second fertilization develops into a highly efficient nutrient-garnering tissue called endosperm, which functions to nourish the developing embryo inside the seed. Until now little effort has been devoted to understanding how the distinctive reproductive process of double fertilization might have evolved. Dr. William Friedman of the University of Georgia will examine patterns of sexual reproduction among members of the genus Ephedra, suspected of being the most closely related living group of seed-bearing gymnosperms. Although most aspects of fertilization in Ephedra are not well understood, there are indications that events similar to the process of double fertilization in angiosperms may occur in this genus. Using modern techniques and apparatus for DNA measurement and for microscopic analysis, Dr. Friedman will investigate reproduction in several representative species of Ephedra, analyzing the ontogenetic patterns of gamete-formation, fertilization, and early development of the embryo. Similarities may reveal clues about the intermediate steps leading to angiosperm double fertilization and help in understanding its adaptive significance.