Plant – Growth and Development

Growth is seen in all living organisms, so in plants too. Although plants’ growth is visible, it is uncountable. However, in simple words, growth is the irreversible and permanent increase in the size of a particular organ or the entire plant. All the processes, from the development of the zygote to the maturing of the whole plant, everything occurs in a specific manner. The development of plants is the sum of two processes: growth and differentiation. Let’s understand it in this Plant-Growth and development study material. 

Plant Growth 

Plants contain meristematic cells on their tips. The meristematic cells can continuously divide, and as a result, the plant grows. There can be two meristematic cells: Apical meristems and lateral meristems. Apical meristems are present on the apices of stems and roots. However, lateral meristems are present on the sides of stems and roots. While Apical meristems cause the primary growth in the length of the plant, lateral meristems cause secondary growth by increasing stem girth and thickness. 

Some cells, after division, lose the ability to divide further. These types of cells are called permanent cells. 

Measurement of Plant Growth

The plant growth is measurable at the cellular level, i.e., the increase in the protoplasm level. However, it is difficult to determine the increase of protoplasm directly. Therefore, several other parameters are in use to determine plant growth. These parameters include increased fresh weight, dry weight, area, volume, length, and cell number. However, the pollen tube measurement of plants’ growth is in terms of its length. 

Phases of Plant Growth

There can be three phases of plant growth.

• Meristematic Phase– In the meristematic phase, the cells of plants have much protoplasm with large nuclei and thin cell walls. They keep dividing throughout the phase. 
• Elongation Phase– The elongation phase succeeds the meristematic phase. In the elongation phase, the cells enlarge with increased vacuole formation and new cell wall deposition. 
• Maturation Phase– The cells mature and attain their maximum size during the maturation phase. They attain maximum cell wall thickening and protoplasmic modifications. 

Growth Rate

The growth rate of plants is the increase in growth per unit time. They can either be arithmetic or geometric growth.

• Arithmetic Growth– In arithmetic growth, the growth rate is constant in a particular arithmetic progression. 

Lt = L0 + rt

Where Lt = length after time.

L0 = length at the beginning, and

r and t= growth rate and time, respectively. 

• Geometric Growth– In this, the growth is initially gradual but increases suddenly. This type of growth is usually common among unicellular organisms. 

 Factors that Affects Growth

• Water and nutrients– Water helps in keeping the cells turgid. Plants require water for several enzymatic activities. Macro and micronutrients are necessary for plants to synthesise protoplasm. It is also necessary as a source of energy. 

• Light– Light source is essential for the growth of plants. 

• Oxygen– Oxygen is responsible for releasing metabolic energy critical for growth activities.

• Temperature– Plants differ in a temperature range suitable for growth. Several plants prefer low temperatures to grow, while others require high temperatures. 

What are Differentiation, Dedifferentiation, and Redifferentiation?

• Differentiation– Differentiation refers to the state in which the root cells mature to perform specific functions in plant growth and development. The cells undergo significant structural changes in their cell walls and protoplasm during this process.

• Dedifferentiation– Dedifferentiation is the process when the cells, which had once lost their dividing capability, start dividing again.

• Redifferentiation– During dedifferentiation, some cells again lose their capacity to divide and start performing specific functions. This process is redifferentiation.

Plant Development

The development of a plant is controlled by various factors. It can be intrinsic (growth regulators) or extrinsic (temperature, light, oxygen, etc.) factors. The development of a plant refers to the complete cycle from germination up to its senescence.

The ability of plants to transform into different kinds of structures is ‘plasticity’. The best example of it is heterophylly in cotton.

Plant Growth Regulators

These regulators are naturally occurring, small and simple molecules with vast diversity in their chemical composition. The plant growth regulators are as follows:

• Auxin– Auxins are usually present in the apices of stems and roots of the plant and often migrate to the site of action. It causes cell enlargement and division, promoting its growth.

• Gibberellins– Gibberellins are present in about 100 different forms. It is also a growth promoter and causes cell elongation, early maturity and seed germination.

• Cytokinins– Cytokinins helps in cytokinesis. It has a significant role in cytoplasm division during cell division.

• Abscisic acid– Abscisic acid inhibits plant growth, promoting dormancy.

Photoperiodism 

Different flowering plants require a different duration of day/night. They have special proteins, i.e. phytochrome, to sense the changes. According to their need of duration of light, plants can be of the following types:

• Long day plants (LDP)
• Short day plants (SDP)
• Day neutral plants (DNP)

Vernalisation

It is the process of reducing the vegetative phase of plants to fasten the flowering procedures. The plants undergo a cold treatment process for vernalisation. The vernalisation process is common in temperate plants like rice and wheat. 

Conclusion 

A plant’s growth and development include all the stages, from seed germination to its senescence. There are three primary phases in the plant growth cycle: meristematic, elongation, and maturation. Plants produce certain chemical regulators to check the proper growth and development. The different plants require a different amount of time for the light/dark cycle. It is called photoperiodism.