describe the structure of a 3 celled pollen grain and trace its development from sporogeneous tissue in an anther.
When the anther is developing, a group of compactly arranged similar types of cells called the sporogenous tissue is present at centre of each microsporangium.
As the anther starts to grow, the cells of the sporogenous tissue undergo meiotic divisions and form microspore tetrads. Each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is a potential pollen or microspore mother cell (MMC). The process of formation of microspores from a microspore mother cell through meiosis is called microsporogenesis. The microspores are arranged in a cluster of four cells called the microspore
tetrad. As the anthers mature the microspores separate from each other and develop into pollen grains. Inside each microsporangium many microspores or pollen grains are formed that are released when the anther opens .The cytoplasm of pollen grain is surrounded by a plasma membrane. When the pollen grain is mature it contains two cells, the vegetative cell and generative cell. The pollen grain germinates on the stigma to produce a pollen tube. Some plants shed pollen in two celled stage with a vegetative and a generative cell while some plant shed pollen in three celled stage where generative cell undergoes mitosis to produce two male gametes thus generating a three celled condition. Pollen grains which are shed at 3 celled stages contain one vegetative cell and two sperm cells (product of mitotic division in generative cell).
Stamen is the male reproductive part of the flowers. It consists of anther, filaments, and connective tissue. Each anther is bilobed. Each lobe contains two pollen sacs. So, there are four pollen sacs, in which pollen grains are produced. The two lobes of anther are joined together by a connective that contains the vascular bundle from the filaments that carries the nourishment. Each pollen sac contains several pollen grains. The anther wall is composed of four to five layers. The developing pollen grains consume the products of middle layer and tapetum, leaving behind the two layers namely the epidermis and endothecium . Each pollen sac is termed as microsporangium and is filled with number of specialised cells called sporogenous cells. The sporogenous cells may function directly as microspore mother cells MMC or microsporocytes. Alternatively, the cells of the sporogenous tissue may undergo mitotic divisions before entering meiosis. Each microspore mother cell is diploid. By a single meiotic divison, each MMC gives rise to for haploid microspores .Initially all the four spores remain enclosed in a common wall made of callose. This four cell organizations is called as tetrad. A mature microspore is called as pollen grain.
As the anther starts to grow, the cells of the sporogenous tissue undergo meiotic divisions and form microspore tetrads. Each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is a potential pollen or microspore mother cell (MMC). The process of formation of microspores from a microspore mother cell through meiosis is called microsporogenesis. The microspores are arranged in a cluster of four cells called the microspore
tetrad. As the anthers mature the microspores separate from each other and develop into pollen grains. Inside each microsporangium many microspores or pollen grains are formed that are released when the anther opens .The cytoplasm of pollen grain is surrounded by a plasma membrane. When the pollen grain is mature it contains two cells, the vegetative cell and generative cell. The pollen grain germinates on the stigma to produce a pollen tube. Some plants shed pollen in two celled stage with a vegetative and a generative cell while some plant shed pollen in three celled stage where generative cell undergoes mitosis to produce two male gametes thus generating a three celled condition. Pollen grains which are shed at 3 celled stages contain one vegetative cell and two sperm cells (product of mitotic division in generative cell).
Stamen is the male reproductive part of the flowers. It consists of anther, filaments, and connective tissue. Each anther is bilobed. Each lobe contains two pollen sacs. So, there are four pollen sacs, in which pollen grains are produced. The two lobes of anther are joined together by a connective that contains the vascular bundle from the filaments that carries the nourishment. Each pollen sac contains several pollen grains. The anther wall is composed of four to five layers. The developing pollen grains consume the products of middle layer and tapetum, leaving behind the two layers namely the epidermis and endothecium . Each pollen sac is termed as microsporangium and is filled with number of specialised cells called sporogenous cells. The sporogenous cells may function directly as microspore mother cells MMC or microsporocytes. Alternatively, the cells of the sporogenous tissue may undergo mitotic divisions before entering meiosis. Each microspore mother cell is diploid. By a single meiotic divison, each MMC gives rise to for haploid microspores .Initially all the four spores remain enclosed in a common wall made of callose. This four cell organizations is called as tetrad. A mature microspore is called as pollen grain.