Comparative study of gametophyte development in the some species of the genus Onobrychis: Systematic significance of gametophyte futures

Abstract

Male and female gametophytes have special characters that show a great variety in different taxa. In this study, gametophytes of four species belonging to three sections of the genus Onobrychis Mill. were studied with light microscopy. Results showed that the ovular primordium is tetra-zonate and gives rise to an anatropous ovule. The archesporium may consist of one or more archeosporial cells, but only one of them undergoes meiosis, forming a linear or T-shaped tetrad. Normally, only a single megaspore is functional which is located in the chalazal position while the others degenerate very soon. The young ovule is hemi-anatropous but the mature is anatropous, crassinucellar and bitegmic; integuments form a zig-zag micropyle. A 7-celled embryo-sac is formed corresponding to the Polygonum type. Based on our results, the ovular variable characters are the form and condition of ovary, presence or absence of ovary peduncle, the number and condition of ovule in ovary, length and width of ovule, length and width of embryo sac, number of layers in outer integument, condition of megaspore, alignment pattern of the integuments, asymmetrical initiation of the outer integument, shape of tetrad with the presence of one functional megaspore and so on. The separator characters in male gametophyte are including tri-cellular pollen grains and the number of tapetum nuclei. According to our study the female gametophyte characters are more variable than male gametophyte. The present study provides the first report on embryological description in the genus Onobrychis and also in section Heliobrychis.