Ovule Ontogenesis and Megagametophyte Development in Onobrychis sintenissii Bormn. (Leguminosae-Papilionoideae)

Abstract

There have been few reports available on wild legume embryology and fewer studies have addressed the formation of Onobrychis sintenissii Bormn. The purpose of this research is to study the formation stages of a fl ower, microporogenesis and femel gametophyte development. In this research, the development of the ovule and the formation of the gametophyte on the coloured sections of O. sintenissii were studied using a light microscope. The primordial shows a tetra-zonate structural organization. The two integuments are initiated by perclinal divisions in the dermal layer (zone I), around the base of the archesporium. Subsequently, cells derived from the subdermal layer (zone II) start to push the dermal cells, so that they shift toward the micropylar region; the outer integument grows in a faster rate compared to the inner one. In ovule primordium, a laterally positioned subdermal cell (zone III & zone IV) grows and differentiates as an archesporial cell, containing a prominent nucleus and a dense cytoplasm, which differentiates directly into the megaspore mother cell, undergoes meiosis, and originates a linear tetrad of megaspores. The young ovule is hemi anatropous but the mature one is anatropous, crassinucellar and bitegmic integuments. The mature embryo sac mother cell is elongated, possessing a conspicuous central nucleus and a polygonum type of development. The embryological characters of O.sintenissii are compared with those of other texa within the leguminosae, such as the tetra-zonate ovule primordium, anatropous ovule type, dermal origin of the integuments, asymmetrical initiation of the outer integument, linear shaped tetrad with the presence of one functional megaspore, and having two young ovules and forming of two embryoes

Keywords

• Embryo sac, embryology, leguminosae, megaspore, Onobrychis, ovule