Apogamy (Definition)- Apogamy is a unique process of asexual reproduction in ferns, in which the development of haploid sporophyte(n) occurs from a haploid gametophyte(n) without the fusion of gametes. Heinrich Anton de Bary, termed this type of asexual reproduction in ferns as Apogamy, in the year 1878. In the year 1874, Farlow discovered the natural occurrence of apogamy in Pteris cretica. Dryopteris, Pteris, Osmunda, Adiantum are the ferns in which apogamy occurs naturally. Generally, the sporophyte which develops from gametophyte, when the fusion of gametes occurs are diploid (2n).
In the case of apogamy, since sporophyte develops from a gametophyte without the fusion of gametes, hence the sporophyte remains haploid(n). Therefore, The haploid sporophyte (n), which develops as a result of apogamy is generally infertile.
Apospory (Definition)- Apospory is the process of formation of the diploid gametophyte (2n) from the vegetative cells of the sporophyte (2n), without meiosis and formation of spores. It was first discovered in the year 1884 by Druery, in the plant Athyrium foemina var. clarissima jones. The aposporous gametophyte that has formed in this variety developed from its sporangium stalk and head. Pteris aquiline, Asplenium dimorphum, Osmunda javanica are the plants in which apospory occurs naturally.
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The major differences between apospory and apogamy are tabulated below.
Causes of Apogamy
The chances of occurrence of apogamy are high in those plants whose prothallus have aged.
When the gametophyte fails to produce gametes, there will be fewer chances for fusion. Hence, Apogamy will occur in such a situation where the failure of sex organ formation occurs.
Apogamy happens in those situations, when the plants fail to carry out normal fertilisation (sexual reproduction), either due to certain abnormal physiological conditions or environmental conditions.
If the prothallus of ferns or pteridophytes grows under high temperatures and bright light, their sexual organs cannot grow normally. Hence, apogamy occurs in that particular situation.
When there are water and nutrition deficiencies in the plant due to high temperature, under those conditions the plant carries out apogamy.
Apospory occurs in those pteridophytes who suffer from the deficiency of mineral nutrition due to the lack of minerals in the soil.
If the leaves of pteridophyte develop under dim light, chances of occurrence of apospory become high.
Asexual reproduction takes place during both apogamy and apospory.
Both of them take place in plants.
The gametophyte and sporophyte share the same ploidy level in both phenomena.
Both of them take place mainly in bryophytes.
The formation of gametes does not occur in apogamy and apospory.
Both of them participate in the alternation of generation (alteration of a sexual phase, i.e., gametophyte and an asexual phase, i.e., sporophyte) in the life cycle of an organism.
Apomixis is the process of formation of the plant from a seed without fertilisation or normal sexual reproduction. The word ‘Apomixis’ is derived from two Greek words- “Apo” means “without” and “mixis” means “the act of mixing”. It is a type of asexual reproduction, but it does not come entirely under the category of “normal asexual reproduction” which involves propagation from cuttings or leaves. Replacement of the flower by bulbis and replacement of the seed by a plantlet can be considered as types of apomixis. Apospory is the most common type of apomixis in higher plants.
Apospory and Apogamy can be induced artificially in a laboratory with the help of hormones. Lycopodium and equisetum are the plants in which apogamy can be induced artificially. The artificial induction of apospory was first reported in Pteridium. Ceratopteris richardii is a model fern that does not carry out asexual reproduction naturally. Still, apogamy and apospory can be induced in it, in the laboratory by using specific culture conditions.
1. What are sporophyte and gametophyte?
Sporophyte- When a haploid egg cell is fertilized by haploid sperm, it generates a zygote, which develops a multicellular diploid(2n) structure in the life cycle of plant or alga, called the sporophyte. The function of sporophyte is to produce spores through meiotic (reduction) division. A double set of chromosomes is present in each sporophyte cell, one chromosome set from each parent. While reproduction, specialized leaves called sporophylls are produced by the sporophyte.
Gametophyte- Gametophyte is the sexual phase in the life cycle of plants and certain algae and is a haploid multicellular organism. It develops from a haploid spore that has one set of chromosomes. The formation of the male gametophyte occurs in the anthers of the stamen and the female gametophyte is found in the ovules within the pistil.
2. What are haploid cells and diploid cells?
Haploid cells (Definition)- Haploid cells are those cells that have a single set of chromosomes. Examples of haploid cells are gametes that are produced as a result of meiosis. A parent cell divides twice, which results in two diploid cells after the first division and 4 haploid (n) daughter cells after the second division.
Diploid cells (Definition)- Diploid cells are those cells that contain the complete set of genetic material or chromosomes. They are produced by mitosis and they are identical to the parent cell from which they are produced. Skin cells and muscle cells are examples of diploid cells.