Embryological and cytological features of Gagea bohemica (Liliaceae)

Abstract

The present study describes the developmental features of the embryo sac and ovular structures, particularly the obturator, during development in Gagea bohemica (Zauschn.) Schult. & Schult. f. The nucellar epidermis is poorly developed and composed of 1-2 layers of cuboidal cells. The tissue at the chalazal end of the nucellus differentiates into a hypostase. The micropyle is formed by the inner integument and composed of 4-5 cell layers that include starch grains. The functional megaspore results in an 8-nucleated embryo sac and conforms to a tetrasporic, Fritillaria L. type. Cytoplasmic nucleoloids consisting of protein and RNA are obvious during megasporogenesis. The obturator attracts attention during embryo sac development. Cytochemical tests indicated that the cells of the obturator present a strong reaction in terms of insoluble polysaccharide, lipid, and protein. Obturator cells are coated by a smooth and thick surface layer that starts to accumulate partially and then merges. Ultrastructural studies reveal that obturator cells are rich in rough endoplasmic reticulum, polysomes, plastids with osmiophilic inclusions, dictyosomes with large vesicles, mitochondria, and osmiophilic secretory granules. After fertilisation, the vacuolisation in obturator cells increases by fusing small vacuoles to form larger ones. Some of the small vacuoles contain electron dense deposits. Afterwards, the obturator cells shrink and disappear.