Boavida Leonor C, Vieira Ana Maria, Becker Jörg D, Feijó José A
Centro de Biologia do Desenvolvimento, Instituto Gulbenkian de Ciência, Oeiras, Portugal.
Int J Dev Biol. 2005;49(5-6):615-32. doi: 10.1387/ijdb.052023lb.
The evolutionary success of higher plants relies on a very short gametophytic phase, which underlies the sexual reproduction cycle. Sexual plant reproduction takes place in special organs of the flower: pollen, the male gametophyte, is released from the anthers and then adheres, grows and interacts along various tissues of the female organs, collectively known as the pistil. Finally, it fertilizes the female gametophyte, the embryo sac. Pollen is released as bi or tricellular, highly de-hydrated and presumably containing all the biochemical components and transcripts to germinate. Upon hydration on the female tissues, it develops a cytoplasmic extension, the pollen tube, which is one of the fastest growing cells in nature. Pollen is completely "ready-to-go", but despite this seemingly simple reaction, very complex interactions take place with the female tissues. In higher animals, genetic mechanisms for sex determination establish striking developmental differences between males and females. In contrast, most higher plant species develop both male and female structures within the same flower, allowing self-fertilization. Outcrossing is ensured by self-incompatibility mechanisms, which evolved under precise genetic control, controlling self-recognition and cell-to-cell interaction. Equally important is pollen selection along the female tissues, where interactions between different cell types with inherent signalling properties correspond to check-points to ensure fertilization. Last but not least, pollen-pistil interaction occurs in a way that enables the correct targeting of the pollen tubes to the receptive ovules. In this review, we cover the basic mechanisms underlying sexual plant reproduction, from the structural and cellular determinants, to the most recent genetic advances.
高等植物的进化成功依赖于非常短暂的配子体阶段，这是有性生殖周期的基础。植物的有性生殖发生在花的特殊器官中：花粉，即雄配子体，从花药中释放出来，然后沿着雌蕊的各种组织附着、生长并相互作用，雌蕊是雌器官的统称。最后，它使雌配子体即胚囊受精。花粉以二细胞或三细胞形式释放，高度脱水，可能含有所有用于萌发的生化成分和转录本。在雌蕊组织上吸水后，它会形成一个细胞质延伸部分，即花粉管，这是自然界中生长最快的细胞之一。花粉完全“准备就绪”，但尽管这个反应看似简单，与雌蕊组织之间却发生了非常复杂的相互作用。在高等动物中，性别决定的遗传机制在雄性和雌性之间建立了显著的发育差异。相比之下，大多数高等植物物种在同一朵花中同时发育出雄性和雌性结构，允许自花受精。异花授粉通过自交不亲和机制来确保，该机制在精确的遗传控制下进化，控制着自我识别和细胞间相互作用。同样重要的是沿着雌蕊组织进行的花粉选择，不同具有内在信号特性的细胞类型之间的相互作用对应于确保受精的检查点。最后但同样重要的是，花粉与雌蕊的相互作用以一种能够使花粉管正确靶向可受精胚珠的方式发生。在这篇综述中，我们涵盖了植物有性生殖的基本机制，从结构和细胞决定因素到最新的遗传学进展。
