What is Plant Growth Phase?
In growing plants, the meristematic growth phase is seen both in the root apex and the shoot apex of constantly dividing cells.
Meristematic growth phases may be divided into the following three categories:
1) Cell division
It is the first phase of meristematic growth. It has the following characteristics:
• In this region, cells possess large clear nuclei with dense protoplasm and small vacuole
• The cells are isodiametric and do not have intercellular spaces.
• Cells contain numerous plasmodesmata links in their thin cell walls, which are primary in nature and possess cellulose.
• These cells are highly active, the fast cell division results in the growth of the plant.
The phase of elongation is indicated by the cell situated proximal (near) to the meristematic region.
Elongation represents the second phase of meristematic growth which have the following features:
• Cells in this area comprise higher vacuolation, enlarged cells, and deposition of the new cell wall.
• During enlargement of the cell, a large vacuole appears at the center of the cell and the protoplasm occupies only the peripheral region of the cell.
Process of Elongation Growth Phase
• According to one view, the rich amount of solutes present within these cells causes absorption of water. As water diffuses into the cell certain solutes are absorbed.
• This further increases the growing cell osmotic pressure, which is essential for maintaining a high turgor pressure. The turgor pressure stretches out the walls of the growing cells.
• According to another view growth in the cell wall takes place by first incorporating new particles in the wall increasing the volume of the cell.
• An increase in the volume of the cell causes absorption of water and consequently, an increase in turgor pressure and turgor pressure stretches out the walls of the growing cells.
• Two explanations have been given for strengthening the cell wall during expansion.
• The first one says a new cell particle of cellulose is deposited between particles of the old wall. The process is known as intussusception.
• The second says that new cell particles are deposited on the inner surface of the old wall by the process known as apposition.
The portion of the axis near the phase of elongation and distant from the apex undergoes the maturation phase. After attaining maturity the cells in this phase differentiate in several sizes and shapes.
• The cells in this area show complete thickening and modification of protoplasm to attain the cell’s maximum size.