Research On The Adaptive Significance And Mechanism Of Female Flower Of Euphorbia Fischeriana(Euphorbiaceae)

In hermaphroditic plants,any spatial separation between male and female organs has the problem of inaccurate pollination.Floral mechanisms through interactions of herkogamy and dichogamy may decrease the interference between pollen removal and pollen receipt,thus maintaining the pollination accuracy.Anther dehiscence and stigma maturation occur at different times,and the stamen and pistil occupy the same position in the flower successively.This movement pattern constitutes an effective flowering mechanism for understanding the hermaphrodite problem.Although movement herkogamy has been widely reported,less attention has been paid to the phenomena that the consecutive expression of two types of herkogamy in the same flower.In addition,the study of the significance of movement herkogamy adaptation needs to be combined with the specific pollination environment,so as to better understand the process of coevolution between these floral characteristics and pollinators.Based on Euphorbia fischeriana Steud as the experimental material,its cyathium similar to bisexual flower on the function.It has been reported that there is continuous movement of female flowers of E.fischeriana,which leads to changes in herkogamy type,our research also focuses on the effect of changes in herkogamy type on plant reproduction.In order to facilitate the description and discussion of herkogamy in cyathium,we extend several terms commonly applied to the reproductive biology of single flowers to apply to cyathium.In terms of research content,on the one hand,we observed that female flower curvature is caused by the curvature of the gynophore,and artificially control the bending state of the gynophore to change the type of herkogamy,study its influence on pollen deposition and pollen removal,as well as the influence of different types of artificial pollination on dynamic herkogamy,and explore how herkogamy and dichogamy cooperate with each other to achieve the optimization of sexual fitness,and the effect of different pollination environments on movement herkogamy;On the other hand,we observed that the gynophore bending rate was inconsistent between individuals.The stamens grew upright and the gynophore movement was from upright to curved.Therefore,we reasonably divided the growth stages of female flower movement according to the angle between the gynophore and stamen,and the first stage was the angle between the gynophore and stamen at flowering（female stage）was 0°.The 45°in the second stage（middle stage）,and the 90°in the third stage.Then,the cell morphology of both sides and the contents of IAA,CTK,GA₃and ABA in each stage were determined by paraffin section and enzyme-related immunosorbent method to explore the mechanism of gynophore bending in E.fischeriana.In order to provide a theoretical basis for understanding the effects of floral movement on plant reproduction and the evolutionary relationship between floral movement and pollination environment,the mechanism of gynophore bending was studied at the cell and hormone levels,providing a theoretical basis for the mechanism of gynophore movement.The main results show that:（1）There were movement herkogamy and dichogamy in E.fischeriana.The movement herkogamy was presented as vertical herkogamy in the female stage and lateral herkogamy in the male stage,and the types of herkogamy changed with the development of flowers.（2）In natural conditions,pollen removal,pollen deposition and seed set ratio of movement herkogamy were significantly higher than those of manual control of gynophore movement.At the same time,we observed it interesting that,while normally removing the sex organs might make them less attractive to pollinators,we removed the pistil and artificially bent the gynophore throughout the flowering process,which actually increased the frequency of pollinator visits.These results suggest that the movement herkogamy of E.fischeriana can improve the overall fitness of the plant while avoiding sexual interference.In addition,the change of herkogamy type may be the result of the trade-off between the frequency of visits and the precision of pollination.（3）The breeding system of E.fischeriana,showed that there was no pollen limitation,and pollination could significantly promote the curvature of the gynophore,leading to the change of the herkogamy type.This mechanism might be an adaptation strategy when pollinators were scarce.In addition,this study also provides sufficient evidence for the hypothesis that the variation of herkogamy type is caused by strong selection of pollination environment differences.（4）The outward curvature of the gynophore was caused by the difference of cell growth rate in the far and far axial sides of the gynophore.（5）Exogenous auxin（IAA）can promote the rate of gynophore bending,while naphthylphthalamic acid（NPA）can inhibit gynophore bending.The contents of endogenous IAA on both sides of the gynophore were consistent in the first stage,while the contents of endogenous IAA on both sides of the gynophore were inconsistent in the second and third stage,and the paraxial side was larger than the distal side.These results indicated that IAA regulated the periaxial lateral and distal curvature of the gynophore of E.fischeriana.In addition,the contents of IAA,CTK,GA₃and ABA were dynamically changed during the growth and development of gynophore.During the 2-3 stage,the contents of IAA,GA₃and CTK in the paraxial side of the gynophore were higher than those in the distal side,and the gynophore was curved from the paraxial side to the distal side.Therefore,we speculated that the curvature of the gynophore might be regulated by various hormones.In conclusion,the complex movement mechanism of the female flower leads to the separation of the two sex organs of E.fischeriana in time and space,and this separation method improves the overall fitness of the plant as well as the accuracy of pollination.In addition,the continuous movement of the gynophore was caused by the difference in cell growth rate on the far and near axial sides,and the inconsistent cell growth on both sides was caused by the asymmetric content of IAA on the far and near axial sides of the gynophore.GA₃and CTK may be involved in the regulation of the gynophore curvature together with IAA.