Study On The Cytology Mechanism Of Flower Sexual Differentiation In Longan (Dimocarpus Iongan Lour.)

Longan(Dimocarpus longana Lour.)flower is miscellaneous.Male flowers,female flowers and hermaphroditic flowers appear on a tree.The development of these flowers is on the basis of the same gender primordium.Pistil aborts in the normal development of male flower,and stamen aborts in the normal development of female flowers because of selective differentiation and programmed cell death(PCD).The study on the mechanism of this phenomenon can help to take corresponding measures to reduce male flower,to increase female flower,to adjust the proportion of female/male flower in longan,to reduce the waste of nutrition in longan,and to improve the production of longan.We took 'red core' longan flower for the material,did our experiments using transmission electron microscopy,cytochemistry and high-performance liquid chromatography.Our study can help to explain the selective development mechanisms of longan flower from two aspects (the structure and physiology)through comparison of the changes in the shape and structure of pistil and stamen in the development of the male and female flowers in longan,and determination of the changes in the level of endogenous polyamines,and analysis of the changes in the distribution of calcium within cells.Main results are as follows:1.We observed the changes in the growth and decline of pistil and stamen of the male flowers and female flowers in the development of longan flowers.When the pistil and the stamen were the same high,stamen began to grow rapidly while pistils aborted and then gradually depauperated in the male flowers;Just the opposite,in the female flowers,the pistil's ovary began to expand rapidly and chapiter started to elongate,meanwhile the stamen was in the state of stopping growing, stamen's four anther sacs did not expand,anther stalk did not elongate.The whole process of differentiation had mainly finished before the crack of the sepal.2.We systematically observed the changes,on organization,cell and organelle level,of the apparatus and organization of pistil and stamen of male and female flowers which were in five different stages in longan using the microscope combined with thick slice technology and the transmission electron microscopy.â… .During the gender primordium period,the male and female flowers had no difference on the shape.â…¡.During the sporogenous period,they would all cause abnormal development of stamen in the female flowers that the abortion of some sporogenous cells of the stamen,the lack of starch deposition in the middle layer and the underdevelopment of vascular tissue.â…¢.During the tetrad period,pollen mother cell was part of abnormal cell meiosis and this would make the flower abort,the callose become black,the development of microspores became asynchronous.Tapetum's early disintegration would lead to microspores's malnutrition and make the microspores be unable to split normally,the middle and the endothecium cell wall completely disintegrate,the cell wall do not thicken,and the sporangium collapse.These results would all affect the normal development of microspores.â…£.During the development of microspores,the middle layer cell disintegrated too fast,the middle layer cell wall did not thicken and the exine of microspores was destroyed.These would all lead to some microspores's abortion. V.During the maturation of microspores,it would also lead to abortion that the internal structure was damaged.During the development of the pistil of the male flower,the nucellus cell could not develop normally,programmed cell death was triggered in nuclear cell.As a result,pistil stopped growing in early stage,then the ovary cell disintegrated,and the whole pistil was atrophic.3.We observed the changes in distribution of calcium precipitates in the stamen cell of male and female flowers using cytochemical technology,combined with transmission electron microscopy,of potassium antimonate to precipitate 'exchangeable cellular Ca^2+,.Our findings showed that:â… . During sporogenous period,it would make some sporogenous cell abort that calcium precipitates appeared largely on the sporogenous cell membrane and cytoplasm.And this was the reason why the stamen of female flowers stopped growing.At the same period,it would contribute to the normal development of the middle layer cell,and could promote the development of anther wall of male flowers that calcium precipitates appeared largely on the vacuole membrane and cell wall of the middle layer cell in stamen of the male flowers.â…¡.During the tetrad period,it would lead to abnormal development of microspores that calcium precipitates appeared largely on the tetrad cell in stamen of female flowers.And this was the reason why stamen of female flowers cannot develop normally.It would be propitious to the normal development of microspores that Calcium precipitates appeared largely on the endomembrane of ectexine and middle layer cell in stamen of the male flowers.â…¢.During the development period of microspores,it would be propitious to the normal development of microspores that calcium precipitates appeared largely on the microspores exine.Oppositely,it would lead to abort if calcium precipitates appeared largely in the microspores.â…£.During the maturation period of microspores,it would be propitious to keep the structure of microspores intact that calcium precipitates appeared little on the microspores exine.Oppositely,it would make the structure of microspores damaged if calcium precipitates appeared in the microspores.4,We determined the content of the putrescine and spermidine inside the pistil and stamen of the male and female flowers which was in different stages.â… .During the sporogenous cell period,high level of putrescine could promote the normal development of stamen.As a result,the stamen won the competition,the programmed cell death occurred in the pistil.â…¡.During the tetrad period,the high level of putrescine in stamen of male flowers was propitious to the normal development of tetrad cell.â…¢.During the development and maturation period of microspores,the low level of putrescine in stamen of male flowers could ensure the normal development and maturation of microspores.Spermidine played the same role of law in the gender primordium period,the sporogenous cell period and the tetrad cell period.However,it affected the development and maturation of microspores,which is in late period,of stamen in male flowers less than the putrescine.In the development of pistil,the low level putrescine of the early period was propitious to the development of the pistil.The reason was that the low level putrescine could not make the stamen win the competition,the pistil could seize the opportunity to develop.Putrescine affected little to the pistil of female flowers that were in the late period.But for abortion pistil in the male flowers, High level of putrescine would lead to pistil atrophy rapidly.When the stamen was aborted,the high level of spermidine was propitious to the normal development of pistil,especially in the megaspore mother cell period.The high level of spermidine was more conducive to the normal completion of the meiosis of the megaspore mother cell.