Growth and development in plants-botany

Growth in plants:

Growth is irreversible and permenant increase in size of cell or tissue or organ or entire plant body.

It is always accompained by metabolic associated reactions.

Growth in plants is indeterminate and grows till death due to the activity of meristems in plants.

Growth can be measured by increase in protoplasmic content, fresh weight, dry weight, length, area, volume and number of cells.

 Phases of growth:

In plants growtg and development each cell undergoes three phases.

1.Meristematic phase:

      In this phase meristematic cells divides continuously. The cells are active and this phase is also called as Cell-division Phase.

2.Elongation phase:

       The cells which are formed in meristematic phase becomes enlarged in thier size and forms vacoules at the centre of the cell.

3.Maturation phase:

         The cells are matured and differentiated into tissues to perform special functions like transportation food, water, minerals, etc,..

Kinetics of growth:

   Sach in 1873 plotted growth rate, increased of growth per unit time and it obtained a sigmoid curve.

1.Lag phase:

        This is the first phase where the growtg is slow but steady.

2.Log phase:

        The plants shows rapid increase in its height and grows at an exponential rate.

3.Senescence phase:

       In this phase with limited nutrients the growth slows down and shows declinind growth activities.

Conditions required for growth:

Plants require mainly oxygen,carbondioxide, water, several nutrients and plant growth harmones.

Plant growth is also controlled by genetic factors as few genes are involved in protein synthesis and the other remain dormant.

The plants grow even in ansence of light such growth is called Etiolated. Gamma rays, x-rays, U.V.rays, etc., are highly injurious to plant growtg.

Minimum, optimum, and maximum temperature are usually 5°c, 20-30°c and 35°-40°c respectively required for plant growth.

Low PO4 supply decreased leaf growth.