BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.E. Yakubenko - 2011

VIII. FUNDAMENTALS OF PLANT MORPHOLOGY AND ANATOMY

Features of Reproduction in Angiosperms

Embryo Development. Amphimixis. Apomixis

Amphimixis

Amphimixis is The process of standard double Fertilization, As a result of which an embryo develops from the zygote in angiosperms. It begins with the elongation of the zygote Cell, which then divides via mitosis to form a two-celled proembryo. Subsequently, through multiple mitotic divisions, the inner cell develops into the embryo, while the outer cell forms the suspensor. The suspensor facilitates the nourishment of the embryo by supplying nutrients derived from the surrounding Cells of the maternal plant.

In most angiosperms, the embryo consists of a radicle, hypocotyl axis, cotyledons, leaves, and a plumule. The stem axis features the cotyledonary node (the attachment site of the cotyledons), the hypocotyl (the stem region located below the cotyledonary node), and the epicotyl (the stem portion situated between the cotyledons and the first leaves). At the apex of the stem lies the plumule, which subsequently develops into the primary SHOOT.

Apomixis

Many plants exhibit reproduction (seed formation) without fertilization, known as apomixis. Reproduction in apomicts occurs either vegetatively or through true seeds formed in the absence of fertilization.

During seed formation without fertilization, all cells of the embryo sac are diploid. This is achieved through a disruption of Meiosis, which prevents chromosome segregation. However, there are instances where meiosis proceeds normally, resulting in a haploid embryo sac. Such a sac rapidly degenerates and is replaced by one or more newly formed embryo sacs arising via mitosis from somatic diploid cells of the ovule.

The diploid egg cell of an unreduced female gametophyte can give rise to an embryo, a phenomenon known as parthenogenesis. The Development of an embryo from other diploid cells of the female gametophyte (synergids, antipodals) is termed apogamy, whereas the development of an embryo from other diploid cells of the ovule (integuments, nucellus, i.e., sporophytic tissue) is referred to as apospory.