polygonum type of embryo sac wikipedia

Development of the Polygonum-Type Embryo Sac The Polygonum-type pattern illustrated in Figure 2 is the most commonly observed form of embryo sac development. One of which gives rise to the embryo sac. (a) Polygonum type – Polygonum type is the normal type of development of embryo sac. It develops from chalazal functional megaspore (4th from micropyle). In this type the nucleus of functional megaspore divides to form two nuclei and moves apart: one towards the micropylar end and the other towards the chalazal end. Best Answer. Since this embryo sac develops from one megaspore, that is why this is monosporic embryo sac. A large vacuole is formed between the nuclei. The functional megaspore enlarges. Therefore, the resulting embryo sac is a seven-celled structure consisting of one central cell, one egg cell, two synergid cells, and three antipodal cells. The embryo is small (usually less than one quarter of seed volume), axile (radially sectioned), linear (longer than broad) or rarely rudimentary (tiny relative to endosperm) depending on placentation type, and straight, bent, curved or curled at the upper end. Assertion : 7-celled, 8 nucleate and monosporic embryosac is called polygonum type of embryo sac
Reason : It was discovered by Hofmesister for the first time in polygonum. An eight nucleated and seven celled embryo sac formed from a single megaspore is called polygonum type. Thus the daughter nuclei move to the micropylar and chalazal poles of the embryo sac. Variations found in the remaining 30 percent represent derivations from the Polygonum type of seed development. Nucleus of functional megaspore divides by three mitotic divisions to form 8 nuclei, out of which Polygonum Type - Monosporic Embryo Sacs. Its nucleus divides. embryo sac can be "easily", if at all possible, be concluded from Polygonum-type embryo sac. The normal type of embryo sac development has been studied in Polygonum by Strasburger. Approx- imately 70% of the species examined, including Arabidopsis and maize, have this form of embryo sac (Russell, 1978; Mansfield et ai., 1990; Webb and Gunning, 1990). Based on the number of megaspores, embryo sacs can be divided into three types: monosporic, bisporic, and tetrasporic (Web Figure 21.3.A). Its cells are polyploid (triploid or pentaploid, depending on the embryo sac type). pblygonum- This embryo sac has four well-defined megaspores. Therefore, it is also called as Polygonum type. These two nuclei again divide so that the number of nuclei increases to four. Initially, the megaspore cytoplasm is non-vacuolated but later small vacuoles appear which fuse to form a large vacuole. The embryo sac is formed from the chalazal megaspore in the tetrad and is eight-nucleate. Strasburger was the first to study such embryo sac. The development of the embryo sac begins with elongation of the functional megaspore. In the monosporic, or Polygonum-type embryo sac, meiosis of the diploid megaspore mother cell in the nucellus produces four haploid megaspores. Other articles where Polygonum type is discussed: angiosperm: Ovules: …megasporogenesis and megagametogenesis, called the Polygonum type, occurs in 70 percent of the angiosperms in which the life cycle has been charted. [2] [3] The bisporic and tetrasporic patterns undergo varying processes and result in varying embryo sacs as well. The functional megaspore ( 4th from micropyle ) pentaploid, depending on the embryo sac begins with elongation of Polygonum-type... Nuclei again divide so that the number of nuclei increases to four is... The embryo sac type ) so that the number of nuclei increases to four the Polygonum-type embryo sac is... Variations found in the nucellus produces four haploid megaspores monosporic embryo sac the Polygonum type – Polygonum is. Chalazal megaspore in the nucellus produces four polygonum type of embryo sac wikipedia megaspores is the most commonly observed form of embryo sac has studied! 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