Growth and Development in Plant

Growth and Development in Plant
Definition
In higher plants, the entire plant body is not capable of growing but growth is limited to certain regions known as Growth Points.
Meristem
Definition
Growth points consists of groups of cells which are capable of division, these growing points are called Meristem.
Meristem Cell
Meristem consists of group of cells which are capable of division and giving rise to new cells. These dividing cells are called meristematic cell.
Location
These meristematic cells are located at the stem and root.
Types of Meristem
There are three type of meristem
i. Apical Meristem
ii. Intercalary Meristem
iii. Lateral Meristem
i. Apical Meristem
Definition
The meristem which is responsible for primary growth is called as Apical Meristem.
Location
The apical meristem are found at the tips of root and shoot.
Functions

• Due to their activity, primary structures are formed.
• They are responsible for the production of branches, leaves, flowers and root hairs.

ii. Intercalary Meristem
Definition
The meristem which is considered as a portion of apical meristem but separated by permanent tissues and it is of temporary nature called Intercalary Meristem.
Location
They are found at the base of internode, mint and also in other plants at the base of leaves.
Functions

• Increase in length also takes place by activity of intercalary meristem.
• It play important role in the production of leaves and flower.

iii. Lateral Meristem
Definition
The meristem which is responsible for the secondary growth is called Lateral Meristem.
Location
They are found in gymnosperms and dicot plants. These are composed of cambium and phalogen tssues. They are present in vascular bundle or between them and also beneath the epidermia.
Structure
Lateral meristem are cylindrical in structure.
Functions

• They increase the diameter of stem and roots.
• They formed secondary tissues.

Phases of Growth
Growth of multicellular plant is divided into three phases
1. The formative phase
2. Elongation phase
3. Maturation phase or differentiation phase
1. The Formation Phase

• It occurs at the tip of root and shoots.
• During this phase, cell constantly divides and thus increases their number by mitosis.
• In this phase cells are closely packed together.
• The cells having thin cellulose walls, dense cytoplasm and large nuclei in this phase.

2. Elongation Phase

• This phase occur immediately behind the formative phase.
• During elongation phase, the cells volume increases due to osmosis (uptake of water) and salt entrance.
• It increases the turgor pressure and their thin elastic wall is expanded.
• Synthesis of new cytoplasm and cell wall proceeds on.
• The cell enlarges and elongate until they reach their maximum size.
• In the root, the region of elongation extends over few millimeters and in stem over a few centimeters.

3. Cell Maturation Phase

• This lies behind the region of elongation.
• Thickening of cell wall takes place.
• The enlarged cell are modified into permanent tissues.
• The mature cells then start to perform their different functions.

Conditions for Growth (Factors)
There are different factors which influenced the rate of growth and development.
These factors are
1. External Factors
2. Internal Factors
1. External Factors
External factors which influenced growth are
i. Temperature
ii. Light
iii. Oxygen
iv. Carbondioxide
v. Nutrients
i. Temperature

• It is a very important factor.
• All hormone and enzymes work optimumly in between 25oC to 37oC.
• All metabolic functions of cell take place in between 0-35oC range of temperature.
• Normally, rate of growth increased with the increase of temperature but within limit.
• At very high temperature 35-40oC, the rate of growth stops and plant dies.

ii. Light

• Light is very important condition for the plant growth.
• It helps in photosynthesis e.g. manufacturing of plant’s food.
• Light affect the growth in three ways.

a. Light Intensity
b. Quality
c. Duration
a. Light Intensity

• It affects the synthesis of chlorophyll and other pigments.
• High light intensity destroys the chlorophyll.
• Photosynthesis is reduced due to high light intensity.

b. Light Quality

• Light quality also influence on growth rate.
• Red light increase cell growth, blue light enhanced cell division but ultraviolet light destroy the protoplasm and retards growth.

c. Light Duration

• Duration of light affects the growth of vegetative and reproductive structures.
• It induced or suppressed the flowering.

iii. Oxygen

• Oxygen influences the growth of roots.
• Process of respiration is carried out in the presence of oxygen.
• Without O2 no metabolic activity is possible and no growth takes place.
• High supply of O2 inhibits growth by photorespiration.

iv. Carbondioxide

• CO2 is necessary for photosynthesis i.e. food production.
• High concentration of CO2 retards growth.
• Low concentration slows the process of photosynthesis.

v. Nutrients

• Nutrients supply energy to growing plants.
• With the increase in nutrition, growth increases where as decrease in nutrition causes retardation of growth.

2. Internal Factors
Internal factors that effect growth are
i. Hormones
ii. Water
iii. Vitamin
iv. Genetic Constitution
i. Hormones

• In growth certain hormones play a very important role.
• Plant hormones that influence growth are auxin, gibberellin and cytokinin.
• Deficiency of hormone causes growth retardation.

ii. Genetic Constitution

• Genes influence growth.
• Change in gene may cause alternation in hormone production and certain process necessary for plant growth.

Growth Correlations
Definition

The growth of a plant organ is related with the growth of other organ which takes place in different directions, this reciprocal relationship is called as Growth Correlations.
Apical Dominance
Apical dominance is the most important correlation found in plant. It is observed that during growth of apical bud, growth of lower axillary bud is suppressed. When apical bud is removed the growth of axillary bud is initiated.
Role of Auxin
Auxin is responsible for apical dominance and also responsible for inhibiting the growth of lateral bud.
Inhibitory Effect
The inhibitory of growth of lateral bud is called inhibitory effect.
Compensatory Effect
The removal of apex releases the lateral buds from apical dominance is called Compensatory Effect.
Role of Cytokinin
Cytokinin also play important role in apical dominance and in many cases if cytokinin is applied directly on the inhibited but it allows lateral buds to be released from apical dominance. Those plants that have dense growth have very little apical dominance.