Study On The Morphological Structure And Development Of The Stamens Of Three Plants Of Menispermaceae

A typical flower is composed of calyx,corolla,androecia and gynoecia in the angiosperms.As the male reproductive organs,androecia are the places where pollen is produced and are essential for the reproduction of the angiosperms.The stamens show rich diversity in the number,the length,the fusion or the separation,and the appendage,some even reduced to staminodes,or become into nectaries.The changes of male reproductive organs in morphological structures are considered that may have important evolutionary significance for improving the rate and pollination efficiency.As a member of Ranunculales,Menispermaceae has unisexual flowers and dioecious.The number of floral organs are usually trimerous.The androecia are different in morphology and structure,in some groups(eg.Sinomenium et al.),the androecia are mostly trimerous and free in male flowers,and staminodes present in the female flowers.However,in other groups(eg.Stephania et al.),the filaments and anthers congregate as a synantherous stamen in male flowers.What are the development and differentiation characteristics of the different types of stamens in this family?In this study,paraffin sections,semi-thin sections,scanning electron microscopy,and transparent methods were used to study the developmental processes of Sinomenium acutum,Stephania japonica and Cyclea racemose,yet,the formation of anther wall,microsporogenesis and development of male gametophyte.The results are as follows:The development of the androecia:the 9 free stamens are initated in 3 whorls(3+3+3)in the male flowers of Sinomenium acutum,and 6 staminodes appear in the female flowers of Sinomenium acutum which initated in two whorls.In the early developmental stage,the staminode primordium are similar to fertile stamen in the male flowers.The shape of the staminode are relatively empty in the late stage.The synandrium stamen of Stephania japonica is initiated by the enlargement of the floral apex primordium.The microtomy and transparent results showed that the synandrium stamen is polymerized by 3 or 4 stamens in Stephania japonica,while 2 stamens in Cyclea racemose.The development of the anther wall:the development of the anther wall are the basic type in three species.At anthesis stage,the anther wall consists of epidermis and endothecium,however,middle layers of the Cyclea racemose are distinctly present in the stage of pollen maturation.The anther wall consists of about 5 to 7 layers of cells present in Sinomenium acutum and Stephania japonica,in which one to two layers of tapetum cells were both derived from the unequal division of the tapetum cells,on the other hand,the tapetum is single layer in Cyclea racemose.The tapetum cell have 2 to 3 nucleus in Sinomenium acutum and Stephania japonica,but 1 to 2 nucleus in Cyclea racemose.The tapetum are glandular in Sinomenium acutum and Cyclea racemose,which amoeboid in Stephania japonica.The endothecium is mostly monolayer,and begins to differentiate into two layers due to the mitosis of the cells(in partial regions)in Sinomenium acutum.Microsporogenesis and male gametophyte development:the microspore mother cell meiosis cytoplasm division are simultaneous type in three species.The microspore tetrads are mostly tetrahedral(approximately 90%),occasionally isobilateral(about 10%).The mature pollen grains are 2-celled.The mature pollen grains are extremely small in the Menispermaceae about 11?m-14?m,and are tircolporate in Sinomenium acutum and Cyclea racemose.The apertures are pori in Stephania japonica.The tectum of the pollen is perforate in Sinomenium acutum,yet reticulate in Cyclea racemose and Stephania japonica.The staminodes of Sinomenium acutum began to degenerate at the early developmental stage(the secondary sporogenous period)earlier than other groups of Ranunculales(Lardizabalaceae).According to the characteristics of anther wall development,the family of Menispermaceae,Berberidaceae and Papaveraceae are similar.The characteristics of microsporogenesis and male gametophyte development are similar to most of the taxa in Ranunculales,which provides evidence for further exploration of the development and evolution of the stamen in the Ranunculales.