Embryology of Onobrychis persica Sirj. and Rech.f. (Fabaceae) and its systematic implications

摘要

Developmental aspects of anther, pollen grains, ovule, embryo and seed has described in Onobrychis persica Sirj. and Rech.f. (Fabaceae) under bright field, polarizing and fluorescence microscopy. Anther development starts when the flowers are very small. The anther is tetrasporangiate, and its wall development follows the dicotyledonous type and consists of four layers: epidermis, endothecium, middle layer and a secretory tapetum. Cytokinesis is simultaneous and arrangement of microspores is tetrahedral and tetragonal. Fibrous thickenings are developed in the endothecium when shed. Ellipsoidal tricolpate pollen grains are two-celled when anthers dehisce. The young hemianatropous ovule changes to a anatropous, crassinucellar and bitegumic mature one with zigzag micropyle. Meiosis of megasporocytes results in a T-shaped tetrad. The chalazal megaspore develops into an eight-nucleate embryo sac with the pattern of Polygonum type. The polar nuclei remain separated before fertilization. After cellularization of endosperm, peripheral cells show dense lipid content. The axial embryo shows fleshy cotyledons, which accumulate lipid and starch. The inner integument differentiates into an endothelium and largely vanishes during development while the outer one produces several layers and establishes the typical seed coat structure: macrosclereid cells, osteosclereids and parenchyma cells. Different compounds, such as starch and lipid content were demonstrated with special staining in the tissues. The systematic significance of the embryological characters is discussed in O. persica.