Apomixis is the process of formation of the plant from a seed without fertilization or normal sexual reproduction. The word ‘Apomixis’ is derived from two Greek words- “Apo” means “without” and “mixes” 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 bulbs 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.
What are Apogamy and Apospory?
Apogamy and apospory are two types of asexual reproduction that occur in the plant kingdom. In contrast, both sexual and asexual reproduction occur during fertilization. Apospory is a specific type of Apogamy in which new plants are formed without fertilization but using the diploid cells of an existing plant. This process does not create any new genetic variation in the species.
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.
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. Clarissa Jones. The prosperous gametophyte that has formed in this variety developed from its sporangium stalk and head. Pteris aquiline, Asplenium dimorphism, Osmunda javanica are the plants in which apospory occurs naturally.
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The Key Difference Between Apospory and Apogamy
The major differences between apospory and Apogamy are tabulated below.
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Apogamy |
Apospory |
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1. In Apogamy, the sporophyte in some ferns develops from the gametophyte. |
1. In apospory, gametophyte develops directly from the vegetative cells of the sporophyte. |
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2. The fusion of gametes does not occur, which means it happens without fertilization. |
2. Apospory occurs without the occurrence of meiosis or spore formation. |
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3. Apogamy occurs without syngamy. Therefore the haploid gametophyte (n) develops into a haploid sporophyte(n) instead of a diploid sporophyte (2n). |
3. Apospory occurs without sporadic meiosis; therefore, the diploid sporophyte (2n) develops into a diploid gametophyte(2n) instead of a haploid gametophyte(n). |
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4. It is commonly seen in Funaria. |
4. It is commonly seen in Anthoceros. |
Causes of Apogamy and Apospory
Causes of Apogamy
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The chances of occurrence of Apogamy are high in those plants whose prothallus have aged.
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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.
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Apogamy happens in those situations when the plants fail to carry out normal fertilization (sexual reproduction), either due to certain abnormal physiological conditions or environmental conditions.
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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.
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When there are water and nutrition deficiencies in the plant due to high temperature, under those conditions, the plant carries out Apogamy.
Causes of Apospory
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Apospory occurs in those pteridophytes who suffer from the deficiency of mineral nutrition due to the lack of minerals in the soil.
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If the leaves of pteridophyte develop under dim light, chances of occurrence of apospory become high.
Similarities Between Apogamy and Apospory
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Asexual reproduction takes place during both Apogamy and apospory.
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Both of them take place in plants.
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The gametophyte and sporophyte share the same ploidy level in both phenomena.
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Both of them take place mainly in bryophytes.
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The formation of gametes does not occur in Apogamy and apospory.
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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.
Did You Know?
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.