Definitions [8]
Define the term growth.
Growth is characterised as an essential process that results in permanent and irreversible changes to the shape, size, form, weight, and volume of a cell, organ, or entire organism, along with an increase in dry matter.
Re-differentiation is the process by which dedifferentiated cells regain specialised characteristics and functionality.
Differentiation is the process by which unspecialised cells become specialised and take on specific functions.
The living differentiated cells, that have lost the capacity to divide, can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation.
Define the term development.
In the life history of a cell, organ, or organism, development can be defined as a process that involves growth, differentiation, and maturation in a predictable sequence, such as seed germination, growth differentiation, flowering, seed production, and senescence.
Growth movements occurring in response to unidirectional external stimuli in a plant part are called tropic movements.
The direction of the response is related to the direction from which the stimulus comes. Such a response is known as tropism.
The term "tropic" comes from a Greek word "tropos" which means to "turn'.
Key Points
- Plant growth is seen in roots, stems, leaves, flowers, fruits, and seeds.
- Life stages: seed → seedling → plantlet → mature plant.
- Trees grow continuously, but leaves, flowers, and fruits have limited growth.
- Development includes growth and differentiation from a zygote.
- Germination starts growth in favourable conditions and depends on internal and external factors.
- Plant growth is indeterminate because it continues throughout life due to meristems.
- Meristematic cells keep dividing, and their daughter cells later differentiate to form plant parts.
- Continuous formation of new cells by meristems is called open growth.
- Apical meristems in roots and shoots cause primary growth (increase in length).
- Lateral meristems (in dicots and gymnosperms) cause secondary growth (increase in girth).
| Process | Description | Example |
|---|---|---|
| Differentiation | Cells mature permanently and lose capacity to divide. | Parenchyma develops schizogenous interspaces in hydrophytes. |
| Dedifferentiation | Mature cells regain capacity to divide as per need. | Interfascicular cambium & cork cambium from parenchyma. |
| Redifferentiation | Dedifferentiated cells again lose the capacity to divide and mature for specific function. | Secondary xylem & phloem from cambium. |
- PGRs (phytohormones) are classified into two groups - growth promoters (auxins, gibberellins, cytokinins) and growth inhibitors (abscisic acid, ethylene).
- Growth promoters help in cell division, enlargement, flowering, fruiting and seed formation; growth inhibitors respond to stress and control dormancy and abscission.
- Auxin - discovered by Charles & Francis Darwin (phototropism in coleoptiles), isolated by F.W. Went. Gibberellins - discovered from "bakanae" disease in rice by E. Kurosawa.
- Cytokinins - discovered by F. Skoog through tobacco stem callus, identified as kinetin. ABA - identified in the mid-1960s from inhibitors by independent researchers.
- Ethylene - discovered by H.H. Cousins, the only gaseous PGR
Concepts [10]
- Introduction of Plant Growth and Development
- Plant Growth Generally is Indeterminate
- Differentiation, De-differentiation, Re- Differentiation
- Concept of Development
- Characteristics of Growth Regulators
- Plant Growth Regulators
- Physiological Effects of Plant Growth Regulators
- Vernalisation
- Tropic Movements in Plants
- Plant Growth and Development (Questions)
