Bleckmann Andrea, Alter Svenja, Dresselhaus Thomas
Cell Biology and Plant Biochemistry, Biochemie-Zentrum Regensburg, University of Regensburg Regensburg, Germany.
Plant Breeding, Center of Life and Food Sciences Weihenstephan, Technische Universität München Freising, Germany.
Front Plant Sci. 2014 Sep 11;5:452. doi: 10.3389/fpls.2014.00452. eCollection 2014.
THE LAUNCH OF SEED DEVELOPMENT IN FLOWERING PLANTS (ANGIOSPERMS) IS INITIATED BY THE PROCESS OF DOUBLE FERTILIZATION: two male gametes (sperm cells) fuse with two female gametes (egg and central cell) to form the precursor cells of the two major seed components, the embryo and endosperm, respectively. The immobile sperm cells are delivered by the pollen tube toward the ovule harboring the female gametophyte by species-specific pollen tube guidance and attraction mechanisms. After pollen tube burst inside the female gametophyte, the two sperm cells fuse with the egg and central cell initiating seed development. The fertilized central cell forms the endosperm while the fertilized egg cell, the zygote, will form the actual embryo and suspensor. The latter structure connects the embryo with the sporophytic maternal tissues of the developing seed. The underlying mechanisms of double fertilization are tightly regulated to ensure delivery of functional sperm cells and the formation of both, a functional zygote and endosperm. In this review we will discuss the current state of knowledge about the processes of directed pollen tube growth and its communication with the synergid cells resulting in pollen tube burst, the interaction of the four gametes leading to cell fusion and finally discuss mechanisms how flowering plants prevent multiple sperm cell entry (polyspermy) to maximize their reproductive success.
开花植物（被子植物）种子发育的启动是由双受精过程引发的：两个雄配子（精子细胞）分别与两个雌配子（卵细胞和中央细胞）融合，形成种子两个主要组成部分——胚和胚乳的前体细胞。通过物种特异性的花粉管引导和吸引机制，不动的精子细胞由花粉管输送到含有雌配子体的胚珠。花粉管在雌配子体内破裂后，两个精子细胞与卵细胞和中央细胞融合，启动种子发育。受精的中央细胞形成胚乳，而受精的卵细胞（合子）将形成实际的胚和胚柄。后者结构将胚与发育中种子的孢子体母体组织相连。双受精的潜在机制受到严格调控，以确保功能性精子细胞的输送以及功能性合子和胚乳的形成。在这篇综述中，我们将讨论关于定向花粉管生长过程及其与助细胞通讯导致花粉管破裂的当前知识状态、四种配子相互作用导致细胞融合的情况，并最终讨论开花植物如何防止多个精子细胞进入（多精入卵）以最大化其繁殖成功率的机制。
