离生心皮类植物中雌蕊外花粉管生长途径与生殖保障策略

Transition from apocarpy to syncarpy in angiosperms is thought traditionally to be a great evolution event, however, there are approximately one quarter of the apocarpy occurring from reversals based on phylogenetic analysis. Do apocarpous plants have disadvantages in floral resource allocation as well as offspring quantity and quality in comparision to the syncarpous group? The finding of extra-gynoecial pollen-tube growth (EGPG) may be a considerable impact to the traditional concept about the disadvantages of apocarpy. The apocarpous gynoecia are functionally similar to the syncarpous gynoecia due to the present of EGPG, which may fertilize the unpollinated carpels in the same gynoecium and could make the pollen tube competition from a single carpel expanding to the whole gynoecium. Based on our recent study, EGPG is phylogenetically widespread in apocarpous angiosperms, and they can be classified into three types: supra-/infra-/extra-stylar EGPG. Here, we want to know: 1) What is the relationship between EGPG and gynoecial structure? 2) Does pollen limitation do occure in apocarpous species? And what are the impacts of different types of EGPG on offspring quantity and quality in apocarpous species? 3) Why does EGPG distribute unsystematically on the phylogenetic tree? Do the gynoecial structure reversals from syncarpy to apocarpy have some relationships with the advantages by EGPG? In this project, we will focus on the adaptation of the evolution of gynoecial structures to the different pathway of pollen tube growth, as well as the reproductive assurance by extra-gynoecial pollen-tube growths in apocarpous angiosperms.

经典观点认为心皮从离生向合生演化是被子植物的一个重要变革，但系统发育分析表明约1/4的离生心皮来自"逆向转变"。离生心皮类是否一定在花部资源配置及子代产量与质量方面处于劣势？雌蕊外花粉管生长（EGPG）的发现对传统观念是一个极大冲击：EGPG使离生心皮在功能上类似于合生心皮，导致雌蕊群中未受粉雌蕊结实，并可能使花粉竞争从单个雌蕊扩展到整个雌蕊群。最近的研究发现，EGPG在离生心皮类群中较为普遍，且可被分为3种类型：supra-/infra-/extra-stylar EGPG。问题在于：1）EGPG与雌蕊群结构有何关系？2）离生心皮类植物有性生殖是否存在花粉限制？不同类型的EGPG对子代数量和质量有何影响？3）EGPG何以无序分布于系统树的不同分支上？合生心皮向离生心皮逆转是否与EGPG带来的利益有关？本项目将探讨被子植物心皮演化对花粉管生长途径的适应以及花粉管雌蕊外生长对生殖保障的意义。

为了探讨被子植物的心皮演化对花粉管生长的适应，以及花粉管雌蕊外生长对生殖保障的意义，进行了一系列研究，取得了如下成果：. 1）对野慈姑心皮发育过程的研究，揭示了慈姑属植物心皮折叠和边缘不完全融合的过程。这种心皮折叠和融合方式被认为是心皮间花粉管生长的结构基础。. 2）在前期发现花粉管生长途径不同而导致的同种花粉优势（CPA）的基础上，通过异种花粉提前或延迟授粉试验证明了上述途径对避免种间杂交所起的作用。. 3）在商陆和垂序商陆的雌蕊群中观察到各自的柱头乳突相似的中央乳突组织，认为心皮壁上乳突组织向中央延伸汇聚而成，有助于雌蕊外花粉管生长。同时发现心皮间花粉管生长途径存在于合生心皮雌蕊群中。. 4）采用番荔枝科和木通科中心皮分离而柱头粘合的植物为研究材料，研究柱头上的胞外分泌物对花粉管在雌蕊群中的分配以及结实率的提高所起的作用，取得初步结果。. 5）在八角茴香属植物假地枫皮中发现，当给离生心皮中的某一个心皮定量授粉时，在轮状着生的心皮中总是部分心皮间隔地发育为果实，这暗示着在离生心皮雌蕊群中也是优先保障子代质量。. 6）为了研究花粉管雌蕊外生长过程中的基因表达，以慈姑属植物为材料，对同一雌蕊群中已授粉和未授粉心皮进行转录组测序，取得大量数据。目前，正在对该结果进行整理和分析，以探寻与花粉管雌蕊外生长过程中相关基因。. 7）通过对黄水枝的心皮发育过程的扫描电镜观察揭示了其半开放式雌蕊的形成过程，并研究了不同大小的两个心皮在传粉和果实、种子形成过程中所起的作用。.