15. PLANT GROWTH AND DEVELOPMENT
Differentiation
- It is the process in which the cells in meristems (root apical & shoot-apical) and cambium differentiate and mature to perform specific functions.
- In this, cell walls & protoplasm undergo major structural changes. The capacity of cell division is lost.
- E.g. Loss of protoplasm to form a tracheary element. They also develop very strong, elastic, lignocellulosic secondary cell walls to carry water to long distances even under extreme tension.
Dedifferentiation
- Under certain conditions, living differentiated cells regain the capacity of division. This is called dedifferentiation.
- E.g. formation of meristems (interfascicular cambium & cork cambium) from differentiated parenchyma cells.
- The dedifferentiated cells can divide and produce cells that again lose the capacity to divide but mature to perform specific functions. It is called redifferentiation.
Final structure at maturity of cell/tissue is also determined by the location of the cell.
E.g. cells positioned away from root apical meristems differentiate as root-cap cells, while those pushed to the periphery mature as epidermis.
DEVELOPMENT
It is a process that includes all changes in the life cycle of an organism from seed germination to senescence.
It is the sum of growth and differentiation.
Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity. E.g.
- Heterophylly due to phases of life: E.g. In cotton, coriander and larkspur, the leaves of the juvenile plants and mature plants are different in shape.
- Heterophylly due to environment: E.g. Difference in shapes of leaves produced in air and water (e.g. buttercup).
- Intrinsic factors: Include intracellular (genetic) or intercellular factors (such as plant growth regulators).
- Extrinsic factors: Include light, temperature, water, oxygen, nutrition, etc.
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