Petka Yurukova-Grancharova

On the Reproductive Biology of Tribulus Terrestris L. (Zygophyllaceae): Embryological Features; Pollen and Seed Viability

ABSTRACT An embryological study of Tribulus terrestris from the Bulgarian flora was carried out. The anther is tetrasporangiate and its wall, the development of which follows the Dicotyledonous type, consists of epidermis, fibrous endothecium, two middle layers and glandular tapetum. Different types of microspore tetrads are formed after simultaneous microsporogenesis. The mature pollen grains are two-celled. The mature ovule is anatropous, bitegmic, crassinucellate with one-celled archesporium. The development of the embryo sac follows the Polygonum (monosporic) type. The formation of endothelium and hypostase were reported. The legitimate embryo and endosperm develop after double fertilization. Initially, the endosperm is nuclear. The embryogenesis runs according to the Solanad type. A high pollen and embryo viability was estimated.

Embryological features, pollen and seed viability of Arnica montana (Asteraceae) – a threatened endemic species in Europe

Abstract The embryological features, mode of reproduction and reproductive capacity (pollen and seed viability) on two naturalized populations of Arnica montana in Bulgaria were studied. The embryological study shows that A. montana is a facultative apomictic species in which sexual reproduction predominates. In this species, it was established that there is a comparatively high viability of the mature pollen and embryos, which enables the successful realization of its reproductive capacity. The results of the study on A. montana reveal that both sexual and asexual vegetative reproduction with rhizomes undoubtedly play more important roles than the apomixis (namely diplospory) for support and preservation of the populations.

Reproductive Features of Three Invasive Alien Species of Erigeron (Asteraceae) in Bulgaria

Embryological studies have been carried out on some established populations of three invasive alien species of the genus Erigeron in Bulgaria: E. bonariensis, E. canadensis and E. sumatrensis. The mode of reproduction and features of the reproductive system, especially these which facilitate the successful distribution and invasiveness of the species were established: a high amount of viable pollen; multicellular antipodal complex; antipodal and endosperm haustoria; simultaneous formation of mature embryos in the florets of the capitulum. All observed embryological features together with the enormous number of flower heads per individual and long flowering period, self-pollination, self-compatibility, autonomous production of achenes and their high dispersal capacity undoubtedly increase the invasive potential of the studied Erigeron species.

Pollen and Seed Morphology of Tribulus Terrestris L. (Zygophyllaceae)

ABSTRACT Light microscope (LM) and Scanning electron microscope (SEM) study of the pollen and seed morphology of Tribulus terrestris (Zygophyllaceae), especially in the native Bulgarian population from Thracian Lowland, was carried out. It was established that the pollen grains are oblate-spheroidal, radially symmetric, pantoporate. Exine ornamentation is reticulate. The seeds of Tribulus terrestris are flat, triangular-ovate. The seed sculpture corresponds to the Tubular-type, which is characterized with polygonal cells and straight arched anticlinal walls, whereas the periclinal ones are wavy with dense cuticular wax folds.