Wednesday, January 14, 2009

How does Development Take Place in Plants

The process of double fertilization results in the formation of zygote and an endosperm cell inside the embryo sac of ovule. The ovule is within the oyary. The zygote follows series of mitotic cell divisions and differentiates into a small plant later known as the embryo. The endosperm cell develops into the endosperm or the cotyledons. Ovules develop into the seed and the ovary forms the fruit.

The zygote within the embryo sac undergoes a number of repeated mitotic divisions to form a group of cells surrounded by the endosperm tissue, which is also under development. This structure is known as the proembryo. In the proembryo the cells are arranged in three layers:

# Protoderm, which forms the surface tissues such as the epidermis.
# Procambium, which forms the vascular tissues.
# Ground meristem, which gives rise to ground tissues.

At this stage, the embryo takes on the shape of an axis with meristems at both ends. These meristems are the apical shoot meristem and the apical root meristem, from which structures of the shoot system and root system will ultimately develop. In addition, two bumps appear near the anterior; these are the two cotyledons, characteristic of dicot embryos. The cotyledons rapidly elongate, and the embryo is divided into regions, with respect to the cotyledons. The region above the attachment of the cotyledons is the epicotyl, which contains the apical shoot meristem.

The region below the attachment of the cotyledons is the hypocotyl, which ends with the radicle, containing the apical root meristem. Typically, the embryonic axis will have to fold, to fit within the embryo sac. Endosperm may or may not be absorbed into the cotyledons. It may be consumed completely in the maturation of the embryo, or some may remain for germination. One of the main differences in the growth and development ?f plant systems from that of animal tissues is that in plants the growing ends or the meristems are very small but repeated many times above the ground as the terminal parts of shoot systems. These meristems are always active and never stop their embryonic nature. Because of this they continue to produce new tissues and cells throughout their life.

Tags: Bio Technology, Bio Genetics, Plant Development

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