Studies On The Megasporogenesis And Microsporogenesis And The Development Of Their Female And Male Gametophyte In Sesbania Grandiflora

Sesbania grandiflora(Linn.)Pers,also known as the Agati or Hummingbird tree,is a legume and butterfly pea subfamily small tree.Its flowers are large and beautiful,and the young pods are edible with high nutritional value.It also has high medicinal value,making it a highly potential woody vegetable economic tree species.However,due to the high rate of embryo degeneration in its pods,the development of the pods varies greatly in length,severely restricting its commercialization.The reasons for the variation in the development length of Sesbania grandiflora pods are not yet clear.Previous research on Sesbania grandiflora has mainly focused on physiological,biochemical,and genetic characteristics,with very little research on morphological anatomy and reproductive biology.Therefore,this study used methods such as paraffin sectioning and electron microscopy to conduct anatomical observations and analysis of the development of megaspores,microspores,and male and female gametophytes in Sesbania grandiflora for the first time.The study explored the relationship between the developmental characteristics of the flower bud and the development of megaspores,microspores,and male and female gametophytes,in order to provide guidance for improving the quality and yield of Sesbania grandiflora pods,and to provide an accurate morphological basis for future molecular mechanism studies on Sesbania grandiflora flower development.The main research results are as follows:1.Observation of the developmental characteristics of Sesbania grandiflora flowers.(1)Based on the analysis of the relevant features of Sesbania grandiflora inflorescence,single flower development process,and the development process of megaspores,microspores,and male and female gametophytes,the overall developmental stages of Sesbania grandiflora inflorescence can be divided into 12 periods,as follows:Visible bud stage,Bud stage,Sepal spreading stage Ⅰ,Sepal spreading stage Ⅱ,Sepal spreading stage Ⅲ,Pedicel emergence stage,Pedicel elongation stage Ⅰ,Pedicel elongation stage Ⅱ,Petal exposing stage,Initial flower stage,Peak bloom stage,Falling flower stage.The developmental process of a single Sesbania grandiflora flower can also be divided into 12 corresponding periods:bud thin stage,bud fat stage,calyx crack stage,calyx flat stage,calyx yellow stage,stalk showing stage,stalk length Ⅰ stage,stalk length Ⅱ stage,petal exposing stage,initial opening stage,full opening stage,petal withering stage.(2)The sesbania grandiflora is raceme inflorescence with 3-4 flowers on the same inflorescence axis.Each flower is connected to the inflorescence axis by a pedicel,and the small flowers on the same inflorescence axis are generally in the same developmental stage.Each flower bud has three sepals,which fall off early.The apex of the inflorescence grows upward in the early stages of development and faces downward when mature.On average,the time from the visible bud stage of the falling flower stage of the corolla of a single flower of the Sesbania grandiflora is approximately 39 days.2.Development of megaspores,microspores,and male and female gametophytes in Sesbania grandiflora.(1)The anther wall of Sesbania grandiflora consists of four layers of cells from the outside to the inside:epidermis,endothecium,middle layer,and tapetum.The developmental type belongs to the basic type,and the endothecium will appear fibrous thickening when the pollen matures.The cytoplasm of microsporocytes divides simultaneously,and the tetrad is tetrahedral.When the microsporocytes in the same locule undergo meiosis,they have synchronism,but occasionally there may be asynchrony with a difference of 0-1 period.(2)The tetrads formed by meiosis of the megasporocytes are linearly arranged along the funiculus,and the megaspore close to the chalaza end develops into the functional megaspore,while the three nuclei at the micropylar end degenerate and disappear.After continuous mitosis,the mature embryo sac with seven cells and eight nuclei develops with three-dimensional distribution in space.The development of the embryo sac belongs to the Polygonum type.(3)Sesbania grandiflora exhibits dioecious maturation during the development of the male and female reproductive organs.When the male stamen enters the tetrad stage,the female ovule begins to form megasporocytes.The embryo sac only develops to maturity when the anther is about to dehisce and release pollen.(4)The external morphology of Sesbania grandiflora flowers is closely related to the developmental stages of megaspores,microspores,and male and female gametophytes.The progress of megasporogenesis,microsporogenesis,and gametophyte development can be judged by the length,size,and external morphology of the flower buds during their development.3.Morphological and developmental characteristics of the male and female reproductive organs in Sesbania grandiflora.(1)The anthers of Sesbania grandiflora are cruciform in shape,spindle-shaped,yellow when mature,with four chambers,and four pollen sacs symmetrically distributed and longitudinally dehiscent.(2)The pollen of Sesbania grandiflora is nearly flattened spherical in shape,with a triangular appearance in polar view and near-circular or elliptical in equatorial view.It has three germinal pores that are spindle-shaped and concave,extending to the polar regions but not interconnected.The outer wall of the pollen grain has a mesh-like pattern composed of ridges and pores,with varying depths and sizes,Mainly distributed in the area between grooves and relatively less in the polar regions,and with shallow depths.The pollen morphology differs in different developmental stages.(3)The polar axis length of the pollen ranges from 19.66 to 37.98 μm,and the equatorial axis length ranges from 15.84 to 35.31 μm.(4)Sesbania grandiflora has diandrous stamens,with two types of filaments:free filaments and connate filaments,and the difference in longitudinal diameter between the two types is up to 25.38 mm.(5)The mature stigma of Sesbania grandiflora is hollow in the middle,with a serrated edge,closely arranged papillae cells,thicker at the top and thinner at the bottom.The top diameter is 9-11 μm,the middle diameter is 3-5 μm,the base is about 3 μm,and the height is about 45-50 μm.The surface of the papillae cells is covered with a layer of turbid,translucent wax.(6)During the development of the single flower of Sesbania grandiflora,the morphology of the stigma shows regular changes.In the bud stage,the stigma is flattened and round;in the bud fat stage to petal exposing stage,it is pointed and round,and bent;in the initial opening stage to full opening stage,it is spoon-shaped and oblique;in the petal withering stage,the middle part of the stigma collapses,and the whole stigma withers and bends.(7)The ovary of Sesbania grandiflora has one locule,with a marginal placenta and inverted ovules.During the bud thin stage to the petal exposing stage,the ovules are arranged in two rows,and the epidermis is wrinkled.During the stalk showing stage,square integument cells appear at the dorsal ridge position of the ovule outside the ovule,and the coverage area of the integument cells continues to expand with development.From the initial opening stage to the petal withering stage,the ovules are arranged in a single row,with larger gaps.