Reproductive Biology Research Of Rare And Endangered Plant Ostrya Rehderiana Chun

Ostrya rehderiana Chun is an endemic species of China,also the only Ostrya plant in southeast China.There are only 5 wild plants of Ostrya rehderiana Chun left alive at present,which are scattered at the periphery of Tianmu Mountain National Nature Reserve in Lin'an.It's extremely rare and endangered,listed as a national first-level protected wild plant.All 5wild trees are mature plants with more than 100 years old.However,only 1 of them(Tree No.4)has the ability to reproduce,with the other 4 bearing almost no seeds.At present,the research on the endangered mechanism of Ostrya rehderiana has mainly focused on the ecology and habitat.No data have been established on the development of its flower and seed embryos,nor the related endangered mechanism.With the purpose to understand the relationship between development stages and fertility,we studied the reproductive biology of Ostrya rehderiana Chun,and firstly reported the complete reproductive stage and typical characteristics using histochemical staining and anatomical observation.We studied the fertility alteration by observing the anatomy of female and male inflorescence,and the development of male and female gametes between the fertile and sterile wild trees.For the first time,we predicted that female flower and embryo abortion might be the key factor for very low fertility of this species.We tried to illustrate the endangered mechanism of this species in order to provide a substantial theoretical basis for protection,regeneration and further utilization of Ostrya rehderiana Chun.The main results are as follows:1.The development process and related structure of male gametophyte of Ostrya rehderiana were clarified: the anther wall from the outside to the inside is divided into epidemics(suberized),inner wall of the endothecium,mid-level,tapetum(glandular type).Data showed that this species has the synchronous type of microspore mother cell meiosis;the tetrahedral type microspore tetrad;3-celled mature pollen grains and three germination pores.2.The development process and related structure of female gametophyte of Ostrya rehderiana were clarified.Our data showed that this species has anatropous ovule,single integument,thick nucellus,linear megaspore tetrad,and multipe embryo sacs with polygonum type.3.The development process and related structure of embryo and endosperm of Ostrya rehderiana were clarified.This species has double fertilization and nuclear-type endosperm,whose development is earlier than the embryo.The development of embryo experiences spherical stage,heart stage and torpedo stage.4.We showed that the different fertility between these mature individuals of Ostrya rehderiana is not related to the morphological structure and development process of male flowers,but very relevant to the female flowers.The cystic base of female flowers from high-fertility plants can normally develop and produce fruits,while the base of female flowers from low-fertility plants is shrivelled,the development of which is also interrupted and abortive.