Cytological Studies And Genetic Analysis Of Male Sterile Mutants In Rice

Male sterility is the phenomenon that the plant can not produce normal pollen in sexual propagation.The effective utilization of heterosis and the increasing of yield are both based on the male sterility.Rice is the staple food for about a half of the world population.As the model species of monocotyledons,rice(Oryza sativa L.) is to become the ideal material for physiological-biochemical mechanism and functional genomics research.So the research on rice male sterility has dual significance on theory and application.The preliminary study of H₂S,Osfmds and Osmlp on which several cytological methods have been used,provide the basis for gene cloning and functional research.The main results are as follows:1 According to the genetic analysis results of hybrid populations,which derived from the cross of H₂S with several types of materials,H₂S,whose female organ is normal,is no-pollen male sterile mutant which is controlled by a recessive nuclear gene.There is no ubish bodies on the tapetal inner surface of H₂S,of which the anther is slim and the anther epidermis is smooth.Cytological studies show that the mutant anthers develop normally before the tetrad stage and pollen degeneration occurs shortly after release of the microspores from the tetrad,while the tapetum degenerates abnormally.The microspores and tapetum degenerate completely in the mutant while the normal microspores development into the late vacuolated stage,only remain tapetal remnants on the endothecium.It was presumed that the tapetal cell can not provide the nutrition and structural materials for the microspore because of its abnormal death,which result in the degeneration of microspore.2 Osfmds,which is screened from the T-DNA inserted mutant pool of zhong hua 11 (ZH11),is a female-and-male-double-sterile mutant.The result of genetic background analysis by ISSR molecular marker is that no different be detected between the mutant and ZH11,which demonstrates that the mutant's genetic background is identical to ZH11 but target character and the mutant comes from ZH11.Bar gene and the Basta resistance detection indicate that the mutant does not contain T-DNA fragement,so it is suggested that the mutant is derived from the tissue culture process.The result of genetic analysis inducates that Osfmds is controlled by a recessive nuclear gene.The mutant plant is dwarf whose anthers are thin and light yellow in color,but its gynoecium is normal on phenotype. By SEM observation,we discovered that the mature pollens of mutant present abnormal shape and adhere in pairs,the smaller operculum,the clear brim of the labrum,the normal tapetal and ubish bodies also can be discovered.Cytological studies show that the meiosis of meiocyte is abnormal;the chromosomes do not be arranged on the equatorial plate in meiotic metaphase stageâ… and separate asynchrony in meiotic anaphase stageâ… ,which result in the chromosome bridge and unequal tetrad.The formation of the embryo sac is inhibited because of the degeneration of the megaspore after the megasporocyte meiosis.It is presumed that the chromosome condensation and homologous chromosomes synapsis are inhibited in this mutant.3 Rice multi-pistil mutant Osmlp is also screened from the T-DNA inserted mutant pool of ZH11.The results of genetic background analysis and T-DNA detection by the same method as Osfmds show that the mutant has the same genetic background as ZH11 and segregating population of heterozygous strain progeny all contain T-DNA,but the results do not prove that if the Osmlp mutant character was induced by T-DNA insertion. The result of genetic analysis shows that Osmlp is controlled by a recessive nuclear gene. Homeologous transformation occurs in the floral organ,the stamen transformed into carpel and the lodicule transformed into glume-like structure.Cytological studies show that the ovule is replaced by parenchyma cells in the transformed ovary and the ovary wall looks like the anther wall,all of which indicate that the stamens transform into an intermediate form between ovary and pollen sac.The mutant is suggested to be class-B gene lost mutant.