Reproduction In Plants

(a) Asexual Reproduction: The formation of new individual from single parent without production of gametes is called asexual reproduction in plants the natural methods of reproduction are by spores, vegetables propagation and by Apomixis.

1. By Spores or Sporulation: Spores are asexual haploid cells formed by meiosis in plants the process of spores formation is called sporulation. In plants spores are formed during alternation of generation. In this process two generations saprophytes and gametophytes alternate with each other saprophytes forms the spores. Spores are unicellular cells they detach from parent plant during favourable condition. Spores formation occurs in bacteria, protozoan, algae, fungi, mosses and fern and in all plants.
2. Vegetative Propagation: It involves the separation of a part of the parent plant, which then develops into new plants. Any part of plant body like root, stem, leaf and bud breaks into pieces and each piece develops into new plant. In higher plants some specialised structure are formed for vegetative propagation. e.g. potato is a modified stem which is used for vegetative propagation. If potato is cut into pieces having eyes and burred into soil, each piece of potato will develop into a complete potato plant. In some plants, organs of vegetative propagation also act as parenting organs during unfavourable condition.
3. Apomixis: Apomixis is a process of asexual reproduction in which seeds are formed without fertilisation. In apomixis any cell of the ovule may develop into embryo and ovule changes into seeds. In ovule, egg, any cell of the nucleus, any antipodal cell or any other cell develops into embryo. Some plants only reproduce by apomixis. These are called obligate apomicty plants. Some plants reproduce both sexually and apologetically. They are called facilitative apomictic plants. e.g. apomixis occur in many plants like dandelion.
4. By Cutting: Many plants reproduce asexually by cutting. The plant fragments are called cutting. Cutting of shoots of stem are used. These cuttings are buried into moist soil. The cutting develops into new plant. Adventitious roots develop into two ways, if cutting has no node, the callus is formed at the cut end, which later forms adventitious roots. If cutting has node, then roots develop and callus is not formed. In bryophyllum a single leaf can be used for propagation. If potato is cut into many pieces, each with an eye, will develop into complete plant.

(b) Artificial method of Asexual Reproduction: 

1. Cloning: The production of duplicate copies of genetic material. Cells or complete organism is called cloning. The duplicate copies are called clones. In this process a piece of tissue or a single parenchyma cell is taken and is kept in the test tube containing nutrients and hormones. The cultured cells are divided and form undifferentiated callus. If there is balance of hormone, the callus forms shoots and roots with fully differentiated cells. Now this small plant is transferred to soil for further growth. A single plant can be cloned into thousand of copies by subdividing calluses as they grow. This method is used for the propagation of many plants like orchids and pines.
2. Genetic Engineering: Genetic engineering is also used in tissue culture in this case foreign genes are introduced into the genotype of other plants. Genes one plant are taken and are introduced into the tissue or into single cell of other plants. Now the piece of tissue, or cell is grown in the test tube. This gene works in this plant in the same way as they worked in original plant. In this way a plant is formed which contains two types of genes, their own gene and gene of other plant. e.g. The researches has transferred a gene for bean protein into cultured cells from a sun flower plant.
3. Portoplast Fusion: This technique is also used into tissue culture. By the use of this technique new variety of plants are developed. Protoplasts are plant cells whose cell will is removed. This protoplast may be subjected to mutation. Then these protoplasts can be cloned. In this way agricultural value of the plant is improved. It is also possible in some cases to fuse two protoplasts from different plant species. Now two protoplasts combine to form a single cell which will be developed by tissue culture and from a hybrid plant. This hybrid plant has the characteristics of two types of plants. e.g. A hybrid plant has been formed from potato and black night shade. The nightshade is resistant to herbicide, the hybrids are also resistant and they are not killed by herbicides.

(C) Sexual Reproduction: It is a kind of reproduction in which male and female gametes fuse to form zygote and it develops to form a new plant. Fusion of male and female gametes called fertilisation.

Types of Sexual Reproduction: There are different types of sexual reproduction.

1. Isogamy: The gametes, which are similar in shape, size and structures are called isogametes. The isogametes fuse to form zygote. This is called Isogamy.
2. Oogamy: In this case fusing gametes are dissimilar, both structurally and functionally. One gamete is similar and motile, it is called male gamete or sperm, the other gamete is larger and non-motile and contains food, it is called female gamete or egg. The fusion of egg and sperm to form zygote is called oogamy.
3. Hetero gamy: It occurs in bryophytes and is similar to oogamy. The male gamete is similar and motile while female gamete is larger, non-motile and contains food.