Question

Explain the role of meristems in plant development including in your answer: • The definition of a meristem. • The organisation of the two main plant meristems and key genetic components involved in their control (the CLV/WUS system). • An example of a plant secondary meristem and its function in plant development.

Answer 1

Answer. Meristematic cells refers to the cells that can continuously divide to form new cells. Meristematic cells organise to form the Meristematic tissues.

The regions in plants bearing such cells are known as the meri stems.

These cells have abundant cytoplasm, negligible intercellular spaces which helps them to divide continuously and helps forming new cells.

Basing upon the location in the plant, they can be:

1. Apical meristems: they are confined to the apex of root and the shoot region. They divide by mitotic divisions to increase the longitudinal growth of the plant. Growth occuring due to apical meri stems is known as the primary growth.
2. Intercalary meristems: are confined to the base of nodes and internodes. They divide too by mitotic divisions. Helps in bringing longitudinal or primary growth.
3. Lateral or secondary meristems: they are confined to the lateral regions of the stem and the roots. It includes vascular cambium and Cork cambium. They help in bringing the latitudinal growth or secondary growth in the plant. Because of these, diameter of plant increases.

Vascular cambium is present in the dicots between xylem and the phloem, whereas Cork cambium develops in the cortex to form cork on the outer side and secondary cortex on the inner side. The cell's formed due to secondary growth in the Cork cambium are known as the periderm. The tissues formed by the secondary growth in the vascular cambium forms secondary xylem and secondary phloem.

Mango plant which is an example of a dicots, shows secondary growth after an optimum primary growth. Because of which increase in diameter takes place on addition of secondary xylem and secondary phloem.

Tunica-corpus theory corresponds to the meristems in the plants. According to this, as we go from outer to inner side. There are three layers namely 1,2 and 3.layer 1 and layer 2 divides in the anticlinal fashion to increase the number of cells, whereas layer 3 divides in the irregular fashion to increase the number of cells.