PLANT GROWTH STAGES

Plant growth And Development

By - Niranjana, Anna, Jeff and Miya Class - 11B

Phases of growth

Meristematic

elongation

maturation

3 phases: meristematic, elongation & maturation. 1. Meristematic phase: It occurs in the meristems at the root apex & the shoot apex. Here, cells have rich protoplasm and large nuclei. Cell walls are primary, thin & cellulosic with abundant plasmodesmata. 2.Elongation phase: It occurs in cells proximal (just next, away from the tip) to the meristematic zone. The cells have increased vacuolation, size and new cell wall deposition. 3.Maturation phase: It occurs in the cells further away from the apex, i.e., more proximal to the phase of elongation. The cells attain maximal size in terms of wall thickening and protoplasmic modifications.

growth rates

1. Arithmetic growth

In this, following mitotic division, only one daughter cell continues to divide while the other differentiates & matures. On plotting the length of the organ against time, a linear curve is obtained. Mathematically, it is expressed as Lt = LO + rt Lt = length at time 't' LO = length at time 'zero' r = growth rate / elongation per unit time.

growth rates

2. geometrical growth

Here, both daughter cells continue mitotic cell division.In most systems, the initial growth is slow (lag phase), then it increases rapidly (log or exponential phase). If nutrient supply is limited, the growth slows down leading to a stationary phase. On plotting the parameter of growth against time, we get a typical sigmoid (S) curve. A sigmoid curve is a characteristic of living organism growing in a natural environment. It is typical for all cells, tissues and organs of a plant.

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