Microspore

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microspore

[′mī·krə‚spȯr]
(botany)
The smaller spore of heterosporous plants; gives rise to the male gametophyte.

Microspore

 

a small spore of heterosporous Pteridophyta (Selaginella, Isoetes, Salvinia, and other water ferns) and seed plants. Microspores are usually formed in large numbers in special organs, the microsporangia, as a result of meiosis of arche-spores. Consequently, microspores are haploid. The microspore is covered with a thin inner membrane (inline) and a thicker outer membrane (exine). When the microspore of a pteridophyte sprouts (usually in the microsporangium), it forms a greatly reduced male prothallium with sex organs, the antheridia. The sprouted microspores (prothallia) are transported by water, wind, or other agents, to the female prothallia, where the spermatozoids, freed from the antheridia, penetrate the archegonia for fertilization.

In seed plants the pollen grain, which is homologous to the male prothallium, arises from the microspore in the microsporangium. In gymnosperms the pollen grain consists of several vegetative cells and one antheridial cell and forms the male gametes (in sago palms and ginkgoes there are flagellate spermatozoids; the rest of the gymnosperms have nonmotile spermatozoids). Angiosperms have the most reduced male prothallia, consisting of one vegetative and one generative cell. After the pollen falls on the stigma of the pistil, the vegetative cell becomes extended into the pollen tube and the generative cell divides, forming two spermatozoids, of which one merges with the egg cell and the other merges with the secondary nucleus of the embryo sac.

WORKS

Komarnitskii, N. A., L. V. Kudriashov, and A. A. Uranov. Sistematika rastenii. Moscow, 1962.

L. V. KUDRIASHOV

References in periodicals archive ?
The average size was obtained from 20 mega- or microspores per specimen.
Then the wall surrounding the each microspore cells dissolve and the microspores in the pollen sac are released.
There was a significant correlation between microspore mother cell divisions and anther's tapetum development that is coincides with other reports for dicotyledonous plants [7,10,6].
the plasmalemma of the microspores (reviewed by Wilson & Zhang, 2009).
5, 6); microspores mostly elliptic though some of them shrunken and distorted in shape, sparsely to moderately covered in short spines.
Microspores and pollen grains are produced from microspore mother cells (Microsporocytes), MMCs within loculus anthers (pollen sacs) of the flower.
Microspore size was determined in the same manner as for the megaspores except that microspores were hydrated in a wet mount and measured across the long axes of 51 elliptic-reniform microspores.
In contrast, the megaspores of most of the species from southern Brazil are usually less than 400 [micro]m in diameter, and the microspores always have smooth outer coatings.
In this route, a male-derived haploid plant is formed when microspores, typically at the vacuolate stage, or young pollen grains are experimentally deviated from their original gamete-producing pathway towards embryogenesis (Fig.
There are two major types of tapetum, the more primitive secretory type, considered to be the prevalent type in the majority of plants, and amoeboid type that extends to microspores in the anther locule [9].
Megaspores from plant A were fertilized adding microspores from plant A and the same procedure was followed for plant B using its own microspores.
Microspores of the 24 species of Isoetes that grow in southern