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Fig tree fruit first then leaves
A cotyledon leaf is the embryonic leaf of a seedling.
Leaves that arise from a cotyledon are called "true leaves."
Other leaves are called "adventitious leaves."
"Adventitious" and "true" can be confused.
The two primary parts of a plant, stem and leaves, arise from the stem's cotyledons.
Totipotency is a unique aspect of embryonic development, which has no analog in post-embryonic development. While stem cells are multipotent (i.e., capable of forming any kind of plant tissue), the totipotent cells of the embryo are the source of all the tissues of the adult plant. These totipotent cells, which include all the stem cells, give rise to the embryonic axes, which later fuse to form the plant embryo.
The following hierarchy of embryonic axes indicates the sequence of steps during plant embryogenesis. The three lines of development (also known as embryogenesis lines) are cellular differentiation, asexual reproduction, and asexual reproduction via microsporogenesis. The plant embryogenesis lines are:
1) Tissue-formation: (cellular differentiation), 2) Tissue-formation via asexual reproduction (prophase I meiosis), and 3) Tissue-formation via microsporogenesis (prophase I meiosis and then megasporogenesis).
These three lines represent the embryonic axes in an embryo. At the end of embryogenesis, the axis is converted to a root, stem, leaves, and flowering reproductive parts.
The three-line model of embryogenesis was introduced by Landsberg and Ausubel (1984). They refer to the differentiation of tissue-forming cells into distinct types of tissue as the "cellular differentiation axis," which is a manifestation of the transition from the vegetative to the reproductive phase of the life cycle.
We have taken a new, computer-based approach in understanding embryogenesis. Our goal is to develop the most accurate computer simulation of embryogenesis. We plan to demonstrate the success of our simulation by demonstrating its ability to reconstruct the structures and sequences of cell differentiation (Landsberg, 1992, 1993).
Our first efforts toward a computer simulation of embryogenesis involved a mathematical simulation of plant cell differentiation. We discovered a developmental pathway that determines the developmental direction of plant cells. This pathway, called the "paradigm shift," establishes the cellular division pattern for a plant (Egusa, 1990, Egusa and Dusenbery, 1991, Egusa et al., 1993). The paradigm shift converts the first cell division into the first two cell divisions in the plant embryo.
The following are sample results from our simulation.
Both the red and green embryos have developed into a figure eight shape, with the stem at the center. The two end branches represent the leaf primordia. The two leaves of a green embryo are set above the apical meristem, and the leaf branches of the red embryo are beneath the apical meristem. The embryo thus has a figure eight configuration.
The figure eight pattern corresponds to the self-polarized neural pattern of the cortical axis (see Dekel and Havas, 1979). In the red embryo, there are two neural domains of opposite polarity that give rise to leaves above and below the apical meristem. The neural domains of the green embryo are not oppositely polarized. The red neural domains generate leaves that are always set above the apical meristem.
This green embryo does not have a figure eight pattern. The figure eight pattern is a consequence of the autonomous self-polarization