Sporogenesis

Sporogenesis is the production of spores in

and form through cell fusion.we can also say this type of reproduction as single pollination

Reproduction via spores

Reproductive spores are generally the result of cell division, most commonly meiosis (e.g. in plant sporophytes). Sporic meiosis is needed to complete the sexual life cycle of the organisms using it.

In some cases, sporogenesis occurs via

ascomycetes, utilize both mitotic and meiotic spores. The red alga Polysiphonia

alternates between mitotic and meiotic sporogenesis and both processes are required to complete its complex reproductive life cycle.

In the case of dormant spores in eukaryotes, sporogenesis often occurs as a result of

fertilization or karyogamy forming a diploid spore equivalent to a zygote. Therefore, zygospores are the result of sexual reproduction

.

Reproduction via spores involves the spreading of the spores by water or air. Algae and some fungi (

anthers

.

Reproductive spores grow into multicellular haploid individuals or

homosporous

organisms, all spores look alike and grow into individuals carrying reproductive parts of both genders.

Formation of reproductive spores

Sporogenesis occurs in reproductive structures termed sporangia. The process involves sporogenous cells (sporocytes, also called spore mother cells) undergoing cell division to give rise to spores.

In meiotic sporogenesis, a diploid spore mother cell within the sporangium undergoes meiosis, producing a

heterosporous, two types of spores occur: Microsporangia produce male microspores, and megasporangia produce female

megaspores. In megasporogenesis, often three of the four spores degenerate after meiosis, whereas in microsporogenesis all four microspores survive.

In

pollen grains

(six nuclei in gymnosperms, three nuclei in flowering plants).

Megasporogenesis occurs in

embryo sac

in flowering plants).

Some algae, and fungi form resting spores made to survive unfavorable conditions. Typically, changes in the environment from favorable to unfavorable growing conditions will trigger a switch from asexual reproduction to sexual reproduction in these organisms. The resulting spores are protected through the formation of a thick cell wall and can withstand harsh conditions such as drought or extreme temperatures. Examples are chlamydospores, teliospores, zygospores, and myxospores. Similar survival structures produced in some bacteria are known as endospores.

Chlamydospore and teliospore formation

hyphae where the nuclei of the fused cells stay separate. These nuclei undergo karyogamy

and meiosis upon germination of the spore.

Zygospore, oospore and auxospore formation

conjugation between two hyphae (in zygomycota). Plasmogamy is followed by karyogamy, therefore zygospores are diploid (zygotes

). They will undergo zygotic meiosis upon germinating.

In oomycetes, the zygote forms through the fertilization of an egg cell with a sperm nucleus and enters a resting stage as a diploid, thick-walled oospore. The germinating oospore undergoes mitosis and gives rise to diploid hyphae which reproduce asexually via mitotic zoospores as long as conditions are favorable.

In diatoms, fertilization gives rise to a zygote termed auxospore. Besides sexual reproduction and as a resting stage, the function of an auxospore is the restoration of the original cell size, as diatoms get progressively smaller during mitotic cell division. Auxospores divide by mitosis.

Endospore formation

The term sporogenesis can also refer to endospore formation in bacteria, which allows the cells to survive unfavorable conditions. Endospores are not reproductive structures and their formation does not require cell fusion or division. Instead, they form through the production of an encapsulating spore coat within the spore-forming cell.

Parts of the spore

There are many parts of the spore 'plant'. The structure enclosing a group of spores is called a sporangium.^{[clarification needed]}

Bibliography

S.S. Mader (2007): Biology, 9th edition, McGraw Hill Companies, New York,
ISBN 978-0-07-246463-4

P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): Biology of Plants, 7th Edition, W.H. Freeman and Company Publishers, New York,
ISBN 0-7167-1007-2