Plant Development and Meristems in Angiosperms

Tissues and Meristems during Plant Development (Angiosperms)

• Angiosperms' plant development follows patterns during embryo stage, distributing cells based on their position.
• Cells differentiate or specialize to take certain roles in the growing embryonic body (cell fate).
• Embryonic tissues, primarily meristems (Greek for division), are crucial for new cell formation.

Outline

• Cell Fate and Totipotency
• Embryogenesis
• Germination
• Morphogenesis
• Primary Growth
• Secondary Growth
• Plant Tissue Culture
• Asexual reproduction in plants

Cell Fate and Totipotency

• Meristems not only add new cells, but also maintain themselves as part of the plant's growth.
• Meristematic initials (initials) are cells that sustain the meristem's ongoing activity.
• Derivatives are products of initial cells, differentiating into other body cells.
• Totipotent cells possess the potential to form all cell types in a plant. Many cells in a mature plant retain this potential.

Embryogenesis

• The life cycle's sporophyte phase begins with the union of gametic products.
• A unicellular zygote develops into an embryo.
• Embryogenesis stages are similar in eudicots and monocots.
• Embryogenesis establishes two main patterns: apical-basal pattern along the main axis, and radial pattern for arranging concentrically tissues.
• Embryo development starts with divisions within the embryo sac of the ovule.
• The first division is transverse and asymmetrical, establishing the embryo's polarity.
• Upper pole gives rise to most of the embryo while the lower pole forms a suspensor for anchoring.
• Not all plant embryos come from the zygote.

Germination

• Mature embryo may become dormant, stopping growth until conditions are favorable for germination
• Germination is the resumption of embryo growth.
• A physical sign of germination is the elongation of the radicle and the break-through of the seed coat.

Morphogenesis (Shoot Formation)

• Apical meristem produces leaves, nodes, and internodes in a regular sequence.
• Axillary buds (from axils of leaves) develop into new shoots. This is not the case in palms.
• Young plants have stems with branches on the main one.

Morphogenesis (Root Formation)

• Apical meristem at the root tip of the hypocotyl forms the primary root.
• Primary root produces branch roots.
• Primary root formation continues from pericycle meristem.
• Mature primary root is the tap root (in dicots).
• Some roots develop from the stem (Monocots).

Primary Meristems

• Protoderm (precursor of epidermis).
• Ground meristem (precursor of cortex).
• Procambium (precursor of primary vascular system).

Primary Growth

• Primary growth is the plant's initial growth (length increase) from the apical meristems in roots and shoots.
• The primary plant body is formed by this initial growth, containing primary tissues.
• This process occurs in all plants and is complete in non-woody plants during the lifespan of the sporophyte.

Secondary Growth

• Secondary growth increases the girth in stems and roots of gymnosperms, and most woody dicots/some monocots.
• Vascular cambium (and phellogen) produce secondary tissues (xylem/phloem). The secondary growth forms the secondary plant body that replaces epidermis.

Plant Tissue Culture

• Tissue culture propagates plants from plant tissues other than the zygote,
• This technique starts with removing a tissue (tissue sample) from a plant & sterilizing the surfaces.
• Plant hormones (e.g., auxin and cytokinin) can induce callus formation, root, or shoot development.

Asexual Reproduction

• Asexual reproduction can happen without external chemical application
• Plant tissues can re-differentiate into meristematic tissues to create new roots and shoots for propagation.
• Asexual reproduction mechanisms include cuttings, runners, bulbs, tubers, and plantlets.