Reproduction

Reproduction
Definition
The process through which organisms produce young ones of their own kind to maintain their species are called as Reproduction.

Types of Reproduction
There are two types of reproduction.
1. Asexual Reproduction
2. Sexual Reproduction
1. Asexual Reproduction
The type of reproduction in which fusion of gamets does not take place and requires only a single parental organism and the offspring produced are exact copies of their parents. This type of reproduction is called Asexual Reproduction.
Asexual Reproduction of Plants
There are two methods of asexual reproduction in plants.
1. Natural Method of Asexual Reproduction
2. Artificial Method of Asexual Reproduction
1. Natural Method of Asexual Reproduction
In nature, plants reproduce asexually by following methods.
i. By Spores or Sporulation
ii. Vegetative Propagation
iii. Apomixis
i. By Spores or Sporulation
During alternation of generation plant produce haploid cell by meiosis called Spores. Each spore can develop into new organism without fertilization. The process of formation of unicellular spores is called Sporulation.
Example
Sporulation occurs in bacteria, protozoans, algae, fungi, mosses and fern as well as plants.
ii. Vegetative Propagation
The process which involves the separation of the part of the parent plant which then develop into new plant is called as Vegetative Propagation.

OR
When a new plant develops from tissue, organs of a plant or outgrowth of a plant. This type of reproduction is called Vegetative Propagation.

Process
In this process a plants part is separated which develops into new plant such as stem, leaves roots or buds may take part in the formation of new plant.
Methods of Vegetative Propagation
There are various method of propagation of plant by vegetative reproduction for improving crops, orchads and ornamental plants are as follows
i. By Cutting
ii. By Grafting
i. By Cutting
In this method stem or branch is cut from the plant. At the cut end of the shoot a mass of dividing undifferentiated cells called a callus forms and then adventitous roots develop form the callus. If the shoot fragment includes a node, then adventitous root forms without callus stage.
Example
Sugar cane, sweet potato and rose can be propagated by cutting. In raspberry and black berries root cutting are also used for artificial vegetative propagation.
ii. By Grafting
This is a technique whereby a branch from a desired variety of plant is joined to another plant with well established root system. The plant from which the branch is taken is called Scion and the plant to which it is joined is called Stock. The two plants involved are normally the different varieties of same species.
Example
Orange, lime and mango can be propagated by grafting.
iii. Apomixis
The modified form of asexual reproduction in which seeds are formed without fertilization is called Apomixis.
Mechanism
In apomixis, a diploid cell in the ovule gives rise to the embryo without any fertilization and the ovules mature into the seeds.
Example
In Dandelions and other plants seed formation take place without fertilization.
2. Artificial Method of Asexual Reproduction
In plant vegetative reproduction is performed by artificial method, which are as follows
i. Tissue Culture or Test Tube Cloning
ii. Protoplast Fusion Technique
i. Tissue Culture or Test Tube Cloning
Tissue culture or cloning is a special technique which is used to produce varieties of plants. By this technique, a group of genetically identical offspring produced by asexual method called Clones.
Procedure

• In this method, pieces of tissues are cut from the parent plant or from a single parenchymatous cell in a medium containing all the nutrients and hormones.
• The culture cells divide and form an undifferentiated Callus.
• The callus then produces root and shoot with fully differentiated cells.
• The test tube plant can be transferred to soil where they continue their growth.

Application
In plants tissue culture is also used in genetic engineering. To introduce new genes in plant body pieces of tissue or cells are used. By this technique, we produced a new variety of plant by introducing new DNA molecule.
Example
By cloning many thousand plants are produced from one plant. This method is used in Orchards and pinus trees to obtain wood.
Advantages of Tissue Culture
The main advantages of tissue culture are as follows
i. Development of Strong Plant: By this technique plants of Agriculture and horticulture are produced. These plants are strong than other plants produced by seeds.
ii. Development of Similar Plant: By this technique plants of similar character are developed.
iii. Development of Defence System in Plant: These plants have developed defence mechanism against any disease.
iv. Production of Useful Chemicals: By this technique, many useful chemicals are obtained such as shikonin (a dye used in silk and in the treatment of injuries caused by burning.
Disadvantages of Tissue Culture
There are also some disadvantages of tissue culture where are as follows
i. Production of Sterile Plant: The plant produced by this technique may be genetically sterile, do not reproduce by sexual method.
ii. Variation in Chromosome: This technique may cause change in the structure and number of chromosome.
ii. Protoplast Fusion Technique
Another technique known as protoplast fusion technique is developed to produce new varieties of plants.
Procedure
In this technique, outer cell wall is removed around the protoplast. After protoplast of one or more cells are fused together, then their protoplast are for culture. These protoplast produce a wall around them, then they are change into new plant. Protoplast of either same or different species may used for this technique.
Example
In potato and wild night shade plant this technique is used.
2. Sexual Reproduction
The type of reproduction in which fusion of gametes (sperm and ova) take place and two parents (male and female) are involved is termed as Sexual Reproduction.
Sexual Reproduction in Plant
In plants sexual reproduction takes place by three methods.
i. Isogamy
ii. Oogamy
iii. Heterogamy
i. Isogamy
The simplest type of sexual reproduction in which two morphologically similar gametes take part in fertilization to produced zygospore which then develop into new plant is called Isogamy.
It is also known as conjugation which means marriages of equals.
Example
This process occurs in algae and lower plants.
ii. Oogamy
The type of sexual reproduction in which a flagellated motile sperm fertilizes with non motile egg to produced a diploid zygote which then develop into new individual is called Oogamy.
Example
Some species of algae undergoes Oogamy.
iii. Heterogamy
The type of sexual reproduction in which two different structure gamets fused i.e. non flagellated large size female gamete fuses with small size flagellated male gamete to produced zygote which then develop into new plant is called Heterogamy.
It is also known as anisogamy.
Example
In higher plants such as bryophyte, heterogamy is present.