在自然界里,，多數(shù)植物為雌雄同株,，植物具有紛繁復(fù)雜的機(jī)制以避免自交或促進(jìn)異交，雌雄異位就是其中一種機(jī)制,。柱高二態(tài)是被子植物中特殊的花內(nèi)雌雄異位的一種類型,，指的一個(gè)居群類存在兩種花型植株，它們的花柱高度顯著不同但花藥高度卻接近,。柱高二態(tài)現(xiàn)象并不普遍,，其中茜草科是被子植物中異型花柱最為集中的科，所包含的具異型花柱屬,、種數(shù)量超過其它所有科之和,。
中科院華南植物園植物系統(tǒng)與進(jìn)化生物學(xué)研究領(lǐng)域李愛民博士后與吳小琴博士，在對(duì)茜草科玉葉金花屬的玉葉金花（Mussaenda pubescens Ait. f.）繁育系統(tǒng)進(jìn)行研究時(shí)發(fā)現(xiàn),，該植物表型上符合柱高二態(tài)的特征,，但野外觀察發(fā)現(xiàn)其長柱植株開花時(shí)花藥萎縮，短柱植物不結(jié)實(shí),。進(jìn)一步對(duì)玉葉金花大小孢子及雌雄配子體發(fā)育觀察發(fā)現(xiàn),，其長柱花大孢子及雌配子體發(fā)育正常，最終形成可育胚囊,；由于花藥絨氈層提前解體,，導(dǎo)致長柱花小孢子及雄配子體發(fā)育不正常，不能形成可育的花粉,，即雄性不育,；而短柱花的大孢子及雌配子體發(fā)育的各個(gè)階段均出現(xiàn)退化現(xiàn)象，不能形成功能性大孢子或正常胚囊,，即雌性不育,。因此，玉葉金花是表型上的柱高二態(tài),，實(shí)際繁育系統(tǒng)為功能性雌雄異株,。
這個(gè)實(shí)例并不符合以往認(rèn)為的柱高二態(tài)是異型花柱進(jìn)化過程中不穩(wěn)定的中間階段這一論斷。對(duì)此,，作者首次提出了異型花柱并不是柱高二態(tài)進(jìn)化的唯一途徑,，柱高二態(tài)可以直接進(jìn)化為雌雄異株的新觀點(diǎn),。該項(xiàng)研究結(jié)果已發(fā)表在近期出版的國際著名學(xué)術(shù)期刊Annals of Botany上,。(生物谷Bioon.com)
生物谷推薦原文出處：
Annals of Botany, doi:10.1093/aob/mcq146
Cryptic dioecy in Mussaenda pubescens (Rubiaceae): a species with stigma-height dimorphism
Ai-Min Li1,2,, Xiao-Qin Wu1,, Dian-Xiang Zhang1,* and Spencer C. H. Barrett3
1 Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, The Chinese Academy of Sciences, Guangzhou 510650, China
2 Department of Life Sciences, Huaihua College, Huaihua 418008, China
3 Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
Background and Aims: Evolutionary transitions from heterostyly to dioecy have been proposed in several angiosperm families, particularly in Rubiaceae. These transitions involve the spread of male and female sterility mutations resulting in modifications to the gender of ancestral hermaphrodites. Despite sustained interest in the gender strategies of plants, the structural and developmental bases for transitions in sexual systems are poorly understood.
Methods: Here, floral morphology, patterns of fertility, pollen-tube growth and floral development are investigated in two populations of the scandent shrub Mussaenda pubescens (Rubiaceae), native to southern China, by means of experimental and open-pollinations, light microscopy, fluorescence microscopy and scanning electron microscopy combined with paraffin sectioning.
Key Results: Mussaenda pubescens has perfect (hermaphroditic) flowers and populations with two style-length morphs but only weak differentiation in anther position (stigma-height dimorphism). Experimental pollinations demonstrated that despite morphological hermaphroditism, the species is functionally dioecious. The long-styled (L) morph possesses sterile pollen and functions as a female, whereas the short-styled (S) morph is female sterile and functions as a male. Self- and intra-morph pollinations of the S-morph were consistent with those expected from dimorphic incompatibility. The two populations investigated were both S-morph (male) biased. Investigations of early stages of floral development indicated patterns typical of hermaphroditic flowers, with no significant differences in organ growth between the floral morphs. Meiosis of microspore mother cells was of the simultaneous type with tetrads isobilateral in shape. The tapetal cells in anther walls of the L-morph became vacuolized during meiosis I, ahead of the uninucleate microspore stage in the S-morph. In the L-morph, the microspore nucleus degenerated at the tetrad stage resulting in male sterility. Microsporogenesis and male gametophyte development was normal in the S-morph. Failure in the formation of megaspore mother cells and/or the development of megagametophytes resulted in female sterility in the S-morph, compared with normal megasporogenesis in the L-morph.
Conclusions: In M. pubescens, cryptic dioecy has evolved from stigma-height dimorphism as a result of morph-specific sterility mutations.
