兰科雄蕊发育多样性研究进展

Research progress on diversity of androecium development of Orchidaceae

关键词:  可育雄蕊, 退化雄蕊, 散粉单元, 花药发育, 系统学

Key words:  fertile stamen, staminode, pollen dispersal unit, anther development, systematics

摘要:

兰科是被子植物中多样性最丰富的家族,其雄蕊形态和功能分化在亚科间变化明显,是该物种多样性形成及适应性传粉生物学的研究重点。基于现有研究资料,该文初步归纳了兰科雄蕊发育多样性的主要研究内容及现状,为野生兰花资源的保护与利用提供科学依据。结果如下:(1)可育雄蕊数目的减少和花粉愈合程度的增加在兰科分子系统树上呈明显的平行演化趋势。(2)兰科雄蕊数目的减少和功能分化与早期花器官发生中存在大量的滞后和缺失、次生融合与分裂现象等密切相关。(3)花药开裂时的4类散粉单元的花粉超微形态特征在亚科、族、亚族、属和种间差异明显。(4)兰科花药散粉单元可以为单花粉粒,也可以通过花药发育过程中源自绒毡层的三类黏性物质而聚合成不同的散粉单元,包括花粉鞘、弹性黏素和其他黏性物质。(5)花药发育揭示了兰亚科的花粉小块结构主要有三类(红门兰型、树兰型和过渡型),树兰亚科的不同数目(2、4、8)和形态(全缘、浅裂、深裂、孔裂)的花粉团是由于花药原基分化出的不育隔膜组织的数目、朝向和位置而形成的。(6)兰科花药发育中,花药室数目、花药壁发育类型、绒毡层细胞核数目、不育隔膜组织分化、胞质分裂类型、小孢子四分体排列形式、花粉细胞核数目等在亚科和属间差异明显。然而,由于种类繁多,现有研究资料难以为理解兰科雄蕊发育提供清晰的线索,包括雄蕊的发育模式、散粉单元的形成机制、花药发育的胚胎学特征等。因此,有必要重视兰科雄蕊发育研究,包括扩大取样范围和利用多学科技术方法和修订兰科花形态常用术语等。

Abstract:

Orchidaceae is the most diverse family of angiosperms. The development of androecium varied greatly at the subfamily level, which has been a research focus of speciation and adatptive pollination biology. Progress on the development of androeceum in Orchidaceae was summarized according to a survey of literature. The results were as follows:(1)It was suggested that evolutionary trends on the decreasing number of fertile stamens was parallel with the increasing degree of coherence of pollens in the pollen dispersal units, which was present in the updated classification of Orchidaceae.(2)The reduced number of stamens and their functional differentiation would be related with the loss, delay, sub-fusion, sub-divsion of stamen primordia during the ontogeny of gynostemium in Orchidaceae.(3)Significant differences of the ultrastructural pollen existed in the four pollen dispersal units at the levels of taxonomic categories of Orchidaceae, including dry pollen, sticky pollen, sectile pollinium, and hard pollinium, which contains great implications of classifications.(4)Pollen may be dispersed in monads or grouped in pollen dispersal units by following three viscous substances(pollenkitt, elastoviscin, cohesion strands)derived from the tapetum.(5)Three main types of sectile pollinia in Orchidoideae were recognized based upon form and arrangement of massulae. Meanwhile, different numbers and varied morphology of pollinia in Epidendroideae were produced by the different numbers and orientations of sterile septum differentiated in the microsporangium during the early anther development based on anatomic evidence.(6)Some embryological features during anther development were diverse at the different categories, including the number of thecae, the type of anther wall development, the nuclei numbers of tapetum, the pattern of cytokinesis, the varied arrangements of microspore tetrads, and the nuclei number of pollens, which could provide a better understanding of taxonomy and evolution of Orchidaceae. However, considering the large number of orchid species, research data available seemed to be very limited. And then, it is necessary to clarify such fascinating questions as functional differentiation and developmental patterns of stamens and staminods, formation mechanisms for varied pollen dispersal units, and diverse embryological features of anther development. Therefore, much more efforts should be taken for the development of androecium in Orchidaceae, including expansive investigation of materials to be observed, using multidisciplinary technical methods, and rivising the common terminology of orchid floral morphology.