🌻 Plant Growth and Development

1. Growth in Plants

Growth is a fundamental and conspicuous characteristic of a living being. In plants, growth is unique because plants retain the capacity for unlimited growth throughout their life due to the presence of meristems at certain locations.

Growth is measurable by various parameters: increase in fresh weight, dry weight, length, area, volume, and cell number.

2. Differentiation, Dedifferentiation and Redifferentiation

Definitions

Differentiation: Cells from meristems mature to perform specific functions (lose ability to divide).

Dedifferentiation: Living differentiated cells regain the capacity to divide under certain conditions (e.g., formation of cork cambium).

Redifferentiation: Dedifferentiated cells again lose the capacity to divide and mature to perform specific functions.

3. Plant Growth Regulators (PGRs)

Small, simple molecules of diverse chemical composition that control plant growth.

Types of PGRs

Growth Promoters:

Auxins: Induce apical dominance, root initiation, prevent premature fruit drop.
Gibberellins: Bolting (internode elongation), delay senescence, overcome seed dormancy.
Cytokinins: Promote cell division, help overcome apical dominance, delay leaf senescence.

Growth Inhibitors:

Abscisic Acid (ABA): Stress hormone, induces stomatal closure, promotes seed dormancy.
Ethylene: Gaseous hormone. Promotes fruit ripening, senescence, and abscission of leaves/flowers.

4. Photoperiodism and Vernalisation

Photoperiodism: The response of plants to periods of day/night. Divides plants into Long Day Plants (LDP), Short Day Plants (SDP), and Day Neutral Plants (DNP). Site of perception is the leaf.

Vernalisation: The qualitative or quantitative dependence of plants on exposure to low temperature to flower.